Co-reporter:Massimo Boiocchi, Luigi Fabbrizzi, Nadia Fusco, Michele Invernici, Maurizio Licchelli, and Antonio Poggi
Inorganic Chemistry 2016 Volume 55(Issue 6) pp:2946-2959
Publication Date(Web):March 1, 2016
DOI:10.1021/acs.inorgchem.5b02826
The dinickel(II) complex of the face-to-face bicyclam ligand α,α′-bis(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecan-6-yl)-o-xylene (L∩L) in a dimethyl sulfoxide solution exists as a mixture of high- and low-spin forms and uptakes up to three halide and pseudohalide ions (X–), according to stepwise equilibria, whose constants were determined through spectrophotometric titration experiments. In the case of halides, the first anion goes into the intermetallic cavity, whereas pseudohalides first coordinate the metal center from outside. Comparison with equilibrium data for the complex with the macrocycle 5,7-dimethyl-6-benzyl-1,4,8,11-tetraazacyclotetradecane (L) shows that the dinuclear complex [NiII2(L∩L)]4+ displays an affinity for the first halide distinctly higher than the mononuclear complex [NiII(L)]2+, thus disclosing the existence of a bimacrocyclic effect for anion binding. Differential pulse voltammetry studies typically showed a three-peak profile: the most anodic pertaining to the [NiII2(L∩L)]4+ → NiIII2(L∩L)]6+ two-electron process, then one originating from the [NiII2(L∩L)X]3+ → NiIII2(L∩L)X]5+ two-electron process, and one deriving from the two two-electron half reactions [NiII2(L∩L)X2]2+ → NiIII2(L∩L)X2]4+ and [NiII2(L∩L)X3]+ → NiIII2(L∩L)X3]3+, taking place at nearly the same potential. The crystal structure of the [NiII2(L∩L)(μ-NCO)(NCO)2]ClO4·2.5H2O complex salt showed a caterpillar arrangement of the three metal-bound cyanate ions.
Co-reporter:Massimo Boiocchi; Carlo Ciarrocchi; Luigi Fabbrizzi; Maurizio Licchelli; Carlo Mangano; Antonio Poggi;Miguel Vázquez López
Inorganic Chemistry 2015 Volume 54(Issue 21) pp:10197-10207
Publication Date(Web):October 15, 2015
DOI:10.1021/acs.inorgchem.5b01273
The three nitrophenyl–cyclam derivatives (nitrocyclams): 1-(4-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (2), 1-(2-nitrophenyl)-1,4,8,11-tetraazacyclotetradecane (3), and 1-(2,4-dinitrophenyl)-1,4,8,11-tetraazacyclotetradecane (4), in an MeCN solution, specifically incorporate the CuII ion according to an irreversible process signaled by disappearance of the yellow color for a concentration c < 1 × 10–4 M and by a yellow-to-red color change for c ≥ 1 × 10–3, and must be considered efficient and specific dosimeters of copper(II) salts. When present in the ortho position of the nitrophenyl substituent, the −NO2 group coordinates the CuII according to a scorpionate mode, while the metallocyclam system exhibits a trans-I configuration. In an MeCN solution the red trans-I-[CuII(3)]2+ and trans-I-[CuII(4)]2+ scorpionate complexes slowly convert into the violet trans-III scorpionate complexes. Kinetic aspects of the trans-I-to-trans-III configurational rearrangement were investigated in detail for the [CuII(4)]2+ system. In particular, the conversion is spectacularly accelerated by catalytic amounts of Cl–, NCO–, and F–. While for Cl– and NCO– the effect can be associated with the capability of the anion to stabilize through coordination a possible dissociative intermediate, the amazingly powerful effect of F– must be related to the preliminary deprotonation of one N–H fragment of the macrocycle, driven by the formation of the HF2– ion. Most of the metal complex species studied in solution were isolated in a crystalline form, and their molecular structures were elucidated through X-ray diffraction studies. This study documents the first examples of effective metal coordination by the nitro group.
Co-reporter:Giuseppe Alibrandi, Valeria Amendola, Greta Bergamaschi, Luigi Fabbrizzi and Maurizio Licchelli
Organic & Biomolecular Chemistry 2015 vol. 13(Issue 12) pp:3510-3524
Publication Date(Web):20 Jan 2015
DOI:10.1039/C4OB02618G
Bistren cryptands can be easily synthesised through the Schiff base condensation of two molecules of tren and three molecules of a dialdehyde, followed by hydrogenation of the six CN double bonds to give octamine cages, whose ellipsoidal cavity can be varied at will, by choosing the appropriate dialdehyde, in order to include substrates of varying sizes and shapes. Bistrens can operate as effective anion receptors in two ways: (i) in their protonated form, providing six secondary ammonium groups capable of establishing hydrogen bonding interactions with the anion; (ii) as dicopper(II) cryptates, in which the two coordinatively unsaturated metal centres can be bridged by an ambidentate anion. Representative examples of the two approaches, as well as the design of an anion molecular dispenser, in which a dicopper(II) bistren cryptate acts as a bottle will be illustrated.
Co-reporter:Massimo Boiocchi and Luigi Fabbrizzi
Chemical Society Reviews 2014 vol. 43(Issue 6) pp:1835-1847
Publication Date(Web):17 Jan 2014
DOI:10.1039/C3CS60428D
In the presence of d10 metal ions, prone to tetrahedral coordination, ligands containing two bidentate subunits will give rise to double-stranded helical complexes (helicates). Upon electrochemical oxidation of CuI to CuII, the helicate complex tends to disassemble, thus giving rise to two mononuclear CuII complexes with tetragonal geometry. Upon subsequent CuII-to-CuI electrochemical reduction, two CuI complexes instantaneously re-assemble to give the helicate complex. A helicand containing a chiral subunit (e.g. 1,2-substituted cyclohexanediamine) contains a racemic mixture of the R,R and S,S enantiomers. The racemic helicand, reacting with CuI, forms dimetallic helicates, in which the two strands show the same chirality, whether R,R or S,S, thus obeying the principle of homochiral recognition.
Co-reporter:Dr. Valeria Amendola;Dr. Massimo Boiocchi; Luigi Fabbrizzi;Dr. Nadia Fusco;Dr. Elisa Valeri
Chemistry - A European Journal 2014 Volume 20( Issue 38) pp:11994-11998
Publication Date(Web):
DOI:10.1002/chem.201403969
Abstract
From an EtOH/H2O solution, 0.3 M each of Ni2+ and cyclic triamine tacn (2; tacn=1,4,7-triazacyclononane), after 10 min refluxing and cooling at room temperature, copious and comparable amounts of blue crystals (containing the complex [Ni(tacn)(H2O)3]2+) and pink crystals (containing in the same cell both [Ni(H2O)6]2+ and [Ni(tacn)2]2+) precipitated. This unusual behaviour is ascribed to the fact that at the refluxing temperature the three species are present at the equilibrium in similar concentrations, which are frozen on cooling, due to the inertness of the macrocyclic complexes [Ni(tacn)(H2O)3]2+ and [Ni(tacn)2]2+.
Co-reporter:Luigi Fabbrizzi and Antonio Poggi
Chemical Society Reviews 2013 vol. 42(Issue 4) pp:1681-1699
Publication Date(Web):02 Oct 2012
DOI:10.1039/C2CS35290G
Alfred Werner's complexes of formula [MIII(NH3)6−nXn]X3−n involved inert metal centres (M = Cr, Co), and anions X− ‘frozen’ in the coordination sphere, a circumstance which allowed the isolation of a variety of isomers. Amine complexes of labile transition metal ions, studied later, do not form isomers, yet they allow the investigation of the fast and reversible interaction of the anion X− with the metal–amine core. On these bases, anion receptors of varying degrees of sophistication have been synthesised, which consist of coordinatively unsaturated polyamine metal complexes and whose vacant coordination sites can be occupied by anion donor atoms. A thoughtful design of the polyamine framework may introduce geometrical selectivity, resulting from the matching between anion shape and size and the geometrical features of receptor's cavity. Compared to their purely organic counterparts, metal containing receptors display several advantages: (i) metal–anion interactions are strong enough to more than compensate anion dehydration energy, which allows recognition studies to be carried out in water; (ii) transition metal ions of different electronic configurations exhibit different geometrical preferences, which addresses anion binding and introduces a further element of selectivity. Chosen examples of polyamine metal complexes, including macrocycles and cages, displaying selective binding tendencies towards anions will be illustrated in this tutorial review.
Co-reporter:Valeria Amendola ; Greta Bergamaschi ; Massimo Boiocchi ; Luigi Fabbrizzi ;Lorenzo Mosca
Journal of the American Chemical Society 2013 Volume 135(Issue 16) pp:6345-6355
Publication Date(Web):April 1, 2013
DOI:10.1021/ja4019786
The anion binding tendencies of the two fluorogenic ureas L1H and L2H, containing the 2-anthracenyl and 1-pyrenyl moieties as signaling units, respectively, have been investigated in MeCN and DMSO by absorption, emission, and 1H NMR spectroscopies. The formation of stable 1:1 receptor:anion H-bond complexes has been confirmed by structural studies on the crystalline [Bu4N][L1···Cl] and [Bu4N][L2H···CH3COO] salts. Complexation induces significant variations of the emission properties of L1H and L2H according to a multifaceted behavior, which depends upon the fluorogenic substituent, the solvent, and the basicity of the anion. Poorly basic anions (Cl–, Br–) cause a red shift of the emission band(s). Carboxylates (CH3COO–, C6H5COO–) induce fluorescence quenching due to the occurrence of an electron-transfer process taking place in the locally excited complex [*L-H···X]−. However, this excited complex may undergo an intracomplex proton transfer from one urea N–H fragment to the anion, to give the tautomeric excited complex [L···H–X]−*, which emits at higher wavelength. F– displays a unique behavior: It forms with L1H a stable [L–H···F]− complex which in the excited state undergoes intracomplex proton transfer, to give the poorly emissive excited tautomer [L···H–F]−*. With L2H, on moderate addition of F–, the 1:1 H-bond complex forms, and the blue fluorescence of pyrene is quenched. Large excess addition of F– promotes deprotonation of the ground-state complex, according to the equilibrium [L2H···F]− + F– ⇆ [L2]− + HF2–. The deprotonated receptor [L2]− is distinctly emissive (yellow fluorescence), which generates the fluorimetric response ON1–OFF–ON2 of receptor L2H with respect to F–.
Co-reporter:Giorgio Baggi, Massimo Boiocchi, Carlo Ciarrocchi, and Luigi Fabbrizzi
Inorganic Chemistry 2013 Volume 52(Issue 9) pp:5273-5283
Publication Date(Web):April 11, 2013
DOI:10.1021/ic400196a
Covalent linking of a Ru(terpy)22+ substituent improves recognition and sensing properties of the urea subunit toward anions. Urea’s anion affinity is enhanced by the electrostatic attraction exerted by the RuII cation and by the electron-withdrawing effect exerted by the entire polypyridine–metal complex. Such an enhancement of the anion affinity, which results from the combination of a through-space and a through-bond effect, is greater than that exerted by the classical neutral electron-withdrawing substituent nitrophenyl. Small yet significant modifications of π–π* and MLCT bands of the Ru(terpy)22+ chromophore, detected through UV–vis spectrophotometric titrations, allowed the determination of the constants for the formation of receptor–anion H-bond complexes in diluted MeCN solution. On 1H NMR titration experiments, carried out under more concentrated conditions, the interaction of a second Cl– ion was observed, taking place through an outer-sphere mechanism. The Ru(terpy)22+ substituent favors the deprotonation of a urea N–H fragment on addition of a second equivalent of fluoride, with formation of HF2–.
Co-reporter:Massimo Boiocchi, Valentina Brega, Carlo Ciarrocchi, Luigi Fabbrizzi, and Piersandro Pallavicini
Inorganic Chemistry 2013 Volume 52(Issue 18) pp:10643-10652
Publication Date(Web):September 4, 2013
DOI:10.1021/ic401684u
The bis-bidentate ligand, obtained from Schiff base condensation of RR-1,2-cyclohexanediamine and 8-naphthylmethoxyquinoline-2-carbaldehyde (L–L), forms with [CuI(MeCN)4]ClO4 a double strand helicate complex, made especially stable by the presence of four definite interstrand π–π interactions involving a quinoline subunit and a naphthylmethoxy substituent of the two strands. The [CuI2(L–L)2]2+ complex, which does not decompose even on excess addition of either L–L or CuI, undergoes a two electron oxidation in MeCN, through two one-electron fully reversible steps, separated by 260 mV, as shown by cyclic voltammetry (CV) studies. The high stability of the mixed valence complex [CuICuII(L–L)2]3+ with respect to disproportionation to [CuI2(L–L)2]2+ and [CuII2(L–L)2]4+ is essentially due to a favorable electrostatic term. CuII forms with L–L a stable species, with a 1:1 stoichiometric ratio, but, in the absence of crystallographic data, it was impossible to assess whether it is of mono- or dinuclear nature. However, CV studies on an MeCN solution containing equimolar amounts of CuII and L–L showed the presence in the reduction scan of two fully reversible waves, separated by about 250 mV, which indicated the presence in solution of a dicopper(II) double strand helicate complex, [CuII2(L–L)2]4+. This work demonstrates that additional interstrand π–π interactions can favor the formation of unusually stable dicopper(I) and dicopper(II) helicate complexes.
Co-reporter: Giuseppe Alibri;Dr. Valeria Amendola;Dr. Greta Bergamaschi;Dr. Riccardo Dollenz; Luigi Fabbrizzi; Maurizio Licchelli;Dr. Carmelo LoVecchio
Chemistry - A European Journal 2013 Volume 19( Issue 11) pp:3729-3734
Publication Date(Web):
DOI:10.1002/chem.201203933
Abstract
The combined activity of the 1.1.1-cryptand and of a dicopper(II) bistren cryptate complex including chloride makes the Cl− ion be continuously and slowly delivered to the solution, without any external intervention. The 1.1.1-cryptand slowly releases OH− ions, according to a defined kinetics, and each OH− ion displaces a Cl− ion from the cryptate. Chloride displacement induces a sharp colour change from bright yellow to aquamarine and can be conveniently monitored spectrophotometrically, even in diluted solutions. The 1.1.1-cryptand is the motor of a molecular dispenser (the dicopper(II) cryptate) delivering chloride ion automatically, from the inside of the solution.
Co-reporter:Valeria Amendola, Greta Bergamaschi, Massimo Boiocchi, Luigi Fabbrizzi and Nadia Fusco
Dalton Transactions 2011 vol. 40(Issue 33) pp:8367-8376
Publication Date(Web):19 Jul 2011
DOI:10.1039/C1DT10894H
The tris-benzimidazolium cage LH33+, in MeCN solution, in the presence of OH−, forms with CuI and AgI ions complexes of formula [MI(LH)]2+, in which each metal is linearly coordinated by two carbenes and one imidazolium N–H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [MI(LH)]2+ complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with CuI and AgI with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH+, was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of AgI are more stable than those of CuI. A significant cooperative effect has been observed with the formation of the [AgIQ2]+ complex.
Co-reporter:Valeria Amendola;Massimo Boiocchi;Nadia Fusco
European Journal of Organic Chemistry 2011 Volume 2011( Issue 32) pp:6434-6444
Publication Date(Web):
DOI:10.1002/ejoc.201100902
Abstract
The trisbenzimidazolium cyclophane receptor 23+ incorporates the F– anion in MeCN solution, which was inferred by spectrophotometric and 1H NMR titration experiments, with an association constant log K > 7. On the basis of geometric considerations, it is assumed that F– lies in the middle of the triangle 3C, whose vertices are the carbon atoms of the three imidazolium C–H fragments, and profits from three C–H···F H-bonds. No other anion is encapsulated by 23+ for reasons of size. The parent trisbenzimidazolium tripodal receptor 43+ does not exert size exclusion selectivity and forms 1:1 complexes not only with F–, but also with other mono- (Br–) and polyatomic anions (NO3–). X-ray diffraction studies on [4···Br]2+ and [4···NO3]2+ complexes indicated that, due to the steric restraints of the tripodal receptor, the anion is not positioned in the middle of the 3C triangle but stays below it, profiting from H-bonds. Cage effects are observed in the higher thermodynamic stability of the [2···F]2+ complex with respect to [4···F]2+ and in its resistance to excess F–. In fact, on addition of excess fluoride, the tripodal [4···F]2+ complex decomposes with deprotonation of a C–H fragment and formation of the very stable HF2– complex.
Co-reporter:Dr. Giorgio Baggi;Dr. Massimo Boiocchi; Luigi Fabbrizzi;Dr. Lorenzo Mosca
Chemistry - A European Journal 2011 Volume 17( Issue 34) pp:9423-9439
Publication Date(Web):
DOI:10.1002/chem.201100490
Abstract
The study of the interactions of the three urea-based receptors AH, BH+ and CH2+ with a variety of anions, in MeCN, has made it possible to verify the current view that hydrogen bonding is frozen proton transfer from the donor (the urea NH fragment in this case) to the acceptor (the anion X−). The poorly acidic, neutral receptor AH establishes two equivalent hydrogen bonds NH⋅⋅⋅X−, with all anions, including CH3COO− and F−, in which moderate proton transfer from NH to the anion takes place. The strongly acidic, dicationic receptor CH2+ forms, with most anions, complexes in which two inequivalent hydrogen bonds are present: one involving moderate proton transfer (NH⋅⋅⋅X−) and one in which advanced proton transfer has taken place, described as N−⋅⋅⋅HX. The degree of proton advancement is directly related to the basic tendencies of the anion. The cationic receptor BH+ of intermediate acidic properties only forms complexes with two inequivalent hydrogen bonds (moderate+advanced proton transfer) with CH3COO− and F−, and complexes with two equivalent hydrogen bonds (moderate proton transfer) with all the other anions. Moreover, [B⋅⋅⋅HF] and [C⋅⋅⋅HF]+, on addition of a second F− ion, lose the bound HF molecule to give HF2−. Release of CH3COOH, with the formation of [CH3COOH⋅⋅⋅CH3COO]−, also takes place with the [B⋅⋅⋅CH3COOH] complex in the presence of a large excess of anion.
Co-reporter:Valeria Amendola, Luigi Fabbrizzi and Lorenzo Mosca
Chemical Society Reviews 2010 vol. 39(Issue 10) pp:3889-3915
Publication Date(Web):01 Sep 2010
DOI:10.1039/B822552B
Since 1992 a variety of urea-based anion receptors have been synthesised, of varying complexity and sophistication. This critical review will focus on some distinctive aspects of anion recognition by urea derivatives, with a special reference to: (i) design and synthesis, (ii) methodologies for the investigation of the receptor–anion interaction in solution, (iii) the interpretation of the solution behaviour on the basis of the structural interplay between the receptor and the anion. It will be shown that the efficiency of urea as a receptor subunit depends on the presence of two proximate polarised N–H fragments, capable (i) of chelating a spherical anion or (ii) of donating two parallel H-bonds to the oxygen atoms of a carboxylate or of an inorganic oxoanion, a property which is shared with other diamides, e.g. squaramide. The wide use of urea in the design of neutral anion receptors seems to depends on the ease of its synthesis, in particular through the reaction of a primary amine group with an isocyanate, which allows the high-yield preparation of symmetrically and unsymmetrically substituted derivatives (83 references).
Co-reporter:Luigi Fabbrizzi, Maurizio Licchelli, Lorenzo Mosca, Antonio Poggi
Coordination Chemistry Reviews 2010 Volume 254(15–16) pp:1628-1636
Publication Date(Web):August 2010
DOI:10.1016/j.ccr.2009.12.002
Nickel(II) and copper(II) azacyclam complexes can be obtained through a metal template procedure involving the pertinent open-chain tetramine, formaldehyde and a primary amide (either carboxy- or sulfonamide) as a locking fragment. Azacyclam complexes, which display the same properties and solution behavior of the corresponding cyclam analogues, can be obtained with any desired side-chain appended to the ligand's framework, by choosing the appropriate amide derivative, through a convenient one-pot synthesis. This opens the way to the design of multi centered redox systems, redox switches of fluorescence, and anion receptors of unusually high Brønsted acidity.
Co-reporter:Valeria Amendola ; Massimo Boiocchi ; Valentina Brega ; Luigi Fabbrizzi ;Lorenzo Mosca
Inorganic Chemistry 2010 Volume 49(Issue 3) pp:997-1007
Publication Date(Web):December 23, 2009
DOI:10.1021/ic9019684
The racemic form of 5 (RR5 + SS5) gives dinuclear complexes of 2:2 stoichiometry both with CuII, acting as a bis-terdentate ligand, and with CuI, acting as a bis-bidentate ligand. Single crystal X-ray diffraction studies have shown that the CuII complex exists as double-strand homochiral helicate molecules: P,P-[Cu2II(RR5)2]4+ and M,M-[Cu2II(SS5)2]4+; in which the two trans-1,2-cyclohexanediamine subunits have the same chirality for of the two strands. Each CuII metal center is six-coordinated according to a cis-octahedral geometry and interacts with a NNO donor subunit of each strand. The CuI complex, when crystallized from THF in the presence of rac5, gives a double-strand homochiral helicate complex and in the solid state forms a racemic mixture of the homochiral metal complexes M,M-[Cu2I(RR5)2]2+ and P,P-[Cu2I(SS5)2]2+. When crystallizing from a MeCN solution, CuI and rac5 give rise to the heterochiral nonhelicate dimeric complex [Cu2I(RR5)(SS5)]2+, in which the two strands of the dimer have inverse configuration of the trans-1,2-cyclohexanediamine subunits and are assembled side-by-side. In both structural architectures, the CuI centers are four-coordinated by two nitrogen atoms from each strand, according to a distorted tetrahedral geometry. In MeCN solution, the dinuclear CuII complex disassembles to give the mononuclear species, which, on reduction at a platinum electrode in a cyclic voltammetry experiment, gives two CuI mononuclear complexes that quickly assemble to give the dinuclear CuI complex. This complex undergoes two consecutive one-electron oxidation processes, but the dinuclear CuII species that forms decomposes in less than 1 s. On the contrary, the [Cu2I(rac5)2]2+ complex is stable in MeCN solution and undergoes two one-electron oxidation processes to give a form of dinuclear CuII complex that lasts in solution for more than 20 s.
Co-reporter:Valeria Amendola Dr.;Greta Bergamaschi Dr.;Massimo Boiocchi Dr. ;Michele Milani Dr.
Chemistry - A European Journal 2010 Volume 16( Issue 14) pp:4368-4380
Publication Date(Web):
DOI:10.1002/chem.200903190
Abstract
The interaction of a neutral squaramide-based receptor, equipped with two 4-nitrophenyl substituents (Rsq), with halides and oxoanions has been studied in MeCN. UV/Vis and 1H NMR spectroscopy titration experiments clearly indicated the formation of 1:1 hydrogen bonding [Rsq⋅⋅⋅X]+ complexes with all the investigated anions. X-ray diffraction studies on the chloride and bromide complex salts confirmed the 1:1 stoichiometry and indicated the establishment of bifurcated hydrogen-bond interactions between the squaramide-based receptor and the halide anion that involved both 1) amide NH and 2) aryl proximate CH fragments, for a total of four bonds. Probably due to the contribution of CH fragments, complexes of Rsq with halides are 1 to 2 orders of magnitude more stable than the corresponding ones with the analogous urea-based receptor that contains two 4-nitrophenyl substituents (Rur). In the case of oxoanions, Rsq forms complexes, the stability of which decreases with the decreasing basicity of the anion (H2PO4−>NO2−≈HSO4−>NO3−), and is comparable to that of complexes of the urea-based receptor Rur. Such a behaviour is ascribed to the predominance of different contributions: electrostatic interaction for halides, acid-to-base ‘frozen’ proton transfer for oxoanions. Finally, with the strongly basic anions F− and CH3COO−, Rsq first gives genuine hydrogen-bond complexes of 1:1 stoichiometry; then, upon addition of a second anion equivalent, it undergoes deprotonation of one NH fragment, with the simultaneous formation of the dianion hydrogen-bond complexes, [HF2]− and [CH3COOH⋅⋅⋅CH3COO]−, respectively. In the case of the urea-based derivative Rur, deprotonation takes place with fluoride but not with acetate. The apparently higher Brønsted acidity of Rsq with respect to Rur reflects the capability of the squaramide receptor to delocalise the negative charge formed on NH deprotonation over the cyclobutene-1,2-dione ring and the entire molecular framework.
Co-reporter:Valeria Amendola ; Greta Bergamaschi ; Armando Buttafava ; Luigi Fabbrizzi ;Enrico Monzani
Journal of the American Chemical Society 2009 Volume 132(Issue 1) pp:147-156
Publication Date(Web):December 3, 2009
DOI:10.1021/ja9046262
The dimetallic cryptate [Cu2II(1)]4+ selectively recognizes guanosine monophosphate with respect to other nucleoside monophospates (NMPs) in a MeOH/water solution at pH 7. Recognition is efficiently signaled through the displacement of the indicator 6-carboxyfluorescein bound to the receptor, monitoring its yellow fluorescent emission. Titration experiments evidenced the occurrence of several simultaneous equilibria involving 1:1 and 2:1 receptor/NMP and receptor/indicator complexes. It was demonstrated that the added NMP displaces the indicator from the 2:1 receptor/indicator complex, forming the 1:1 receptor/analyte inclusion complex. Recognition selectivity is thus ascribed to the nature of nucleotide donor atoms involved in the coordination and their ability to encompass the CuII−CuII distance within the cryptate.
Co-reporter:Valeria Amendola and Luigi Fabbrizzi
Chemical Communications 2009 (Issue 5) pp:513-531
Publication Date(Web):03 Dec 2008
DOI:10.1039/B808264M
Transition metals can be used as structural elements to build up anion receptors, enhancing H-bond donor tendencies, favouring the assembling of the molecular framework, inducing the formation of a cage. The versatile spectroscopic and electrochemical properties of the metal ion can provide a convenient signalling mechanism to communicate the occurrence of anion recognition.
Co-reporter:Massimo Boiocchi Dr. ;Mauro Garolfi Dr.;Maurizio Licchelli ;Lorenzo Mosca Dr.;Cristina Zanini Dr.
Chemistry - A European Journal 2009 Volume 15( Issue 42) pp:11288-11297
Publication Date(Web):
DOI:10.1002/chem.200901364
Abstract
Copper(II) azacyclam complexes 32+ and 42+ were obtained through a metal-templated procedure involving the pertinent open-chain tetramine, formaldehyde and a phenylurea derivative as a locking fragment. Both metal complexes can establish interactions with anions through the metal centre and the amide NH group. Equilibrium studies in DMSO by a spectrophotometric titration technique were carried out to assess the affinity of 32+ and 42+ towards anions. While the NH group of an amide model compound and the metal centre of the plain CuII(azacyclam)2+ complex do not interact at all with anions, 32+ and 42+ establish strong interactions with oxo anions, profiting from a pronounced cooperative effect. In particular, 1) they form stable 1:1 and 1:2 complexes with H2PO4− ions in a stepwise mode with both hydrogen-bonding and metal–ligand interactions, and 2) in the presence of CH3COO−, they undergo deprotonation of the amido NH group and thus profit from axial coordination of the partially negatively charged carbonyl oxygen atom in a scorpionate binding mode.
Co-reporter:Valeria Amendola ; Massimo Boiocchi ; Benoît Colasson ; Luigi Fabbrizzi ; Enrico Monzani ; Maria Jesús Douton-Rodriguez ;Cristina Spadini
Inorganic Chemistry 2008 Volume 47(Issue 11) pp:4808-4816
Publication Date(Web):April 4, 2008
DOI:10.1021/ic800099j
The tripodal system [1]3+ forms a 1:1 complex with CoII in which the metal is octahedrally coordinated by three bpy fragments. The [CoII(1)]5+ complex provides a cavity suitable for solvent or anion inclusion. X-ray diffraction studies on the crystalline complex salt of formula [CoII(1)···H2O]Cl(PF6)4·2MeCN have shown that a water molecule is included in the cavity and the water oxygen atom receives six H-bonds from the C−H fragments of the three imidazolium subunits and of the three proximate pyridine rings, according to a slightly distorted trigonal prismatic geometry. Anion inclusion in an aqueous MeCN solution induces a distinct cathodic shift of the potential of the CoIII/CoII couple, whose magnitude decreases along the series: Cl− > Br− ∼ NCO− > I− ∼ NCS−, which reflects anion tendencies to receive H-bonds from the receptor. The variation of the water content in the MeCN solution (from 0 to 20%) induces a gradual change of the voltammetric response to anion titration: from two well distinguished peaks at a fixed potential to a single peak progressively shifted to a more cathodic potential. Such a behavior parallels the gradual decrease of the equilibrium constant for anion inclusion into the [CoII(1)]5+ receptor.
Co-reporter:Valeria Amendola, Greta Bergamaschi, Massimo Boiocchi, Luigi Fabbrizzi, Antonio Poggi, Michele Zema
Inorganica Chimica Acta 2008 Volume 361(14–15) pp:4038-4046
Publication Date(Web):1 October 2008
DOI:10.1016/j.ica.2008.03.049
The inclusion of halide ions into a dicopper(II) bistren cryptate complex containing 2,5-dimethylfuran spacers has been investigated through spectrophotometric titration experiments in MeCN solution. X-ray diffraction studies on the 1:1 chloride inclusion complex have shown that the encapsulated halide ion and the furan oxygen atoms lie at an interacting distance. Such an interaction perturbs the energy of the halide-to-copper(II) charge transfer transition, which is shifted to the visible region. As a consequence, an intense yellow colour develops on halide inclusion. Such a colour change is not observed on chloride or bromide inclusion into the dicopper(II) bistren cryptate containing spacers which are not capable to interact with the encapsulated halide and do not perturb the charge transfer transition, e.g. 1,3-xylyl fragments.The inclusion of chloride and bromide ions into a dicopper(II) bistren cryptate complex containing 2,5-dimethylfuran spacers is signalled by the development of an intense yellow colour. The drastic colour change results from a halide-to-metal charge transfer transition, which has been shifted to the visible region through the interaction of the encapsulated halide with the oxygen atoms of the furan spacer.
Co-reporter:Valeria Amendola Dr.;Massimo Boiocchi Dr. ;Lorenzo Mosca Dr.
Chemistry - A European Journal 2008 Volume 14( Issue 31) pp:9683-9696
Publication Date(Web):
DOI:10.1002/chem.200800801
Abstract
The terdentate ligand 3 (LH, 2-formylpyridine 4-thiosemicarbazone) forms with FeII and NiII 2:1 complexes of octahedral geometry of formula [MII(LH)2]2+. X-ray diffraction studies have shown that in both complexes the thiourea moieties of the coordinated thiosemicarbazones are exposed to the outside and are prone to establish hydrogen-bonding bifurcate interactions with oxoanions. However, spectrophotometric studies in CHCl3 solution have shown that only the poorly basic NO3− ion is able to form authentic hydrogen-bond complexes with thiourea subunits, whereas all the other investigated anions (CH3COO−, NO2−, F−) induce deprotonation of the N-H fragment. The extreme enhancement of the thiourea acidity is based on the coordinative interaction of the sulphur atom with the metal, which stabilises the thiolate form, and it is much higher than that exerted by any other covalently linked electron-withdrawing substituent, for example, NO2.
Co-reporter:Valeria Amendola Dr.;Benoît Colasson Dr. ;Maria-Jesús Rodriguez Douton Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 17) pp:
Publication Date(Web):15 MAR 2007
DOI:10.1002/chem.200601865
Dicationic ligands incorporating two 2,2′-bipyridine units and two imidazolium moieties, [1]2+ and [2]2+, form stable chelate complexes with CuII and CuI in acetonitrile solution. Each CuII complex binds two X− ions according to two stepwise equilibria, the first involving the CuII centre and the second involving the bis-imidazolium compartment. CuI complexes are able to host only one NO3− ion in the bis-imidazolium cavity, while other anions induce demetallation. Thus, in the presence of one equivalent of NO3−, the CuII/CuI redox change makes the anion translocate quickly and reversibly from one binding site to the other within the [CuII,I(1)]4+/3+ system, as demonstrated by cyclic voltammetry and controlled-potential electrolysis experiments.
Co-reporter:Michela Allevi Dr.;Marco Bonizzoni Dr.
Chemistry - A European Journal 2007 Volume 13(Issue 13) pp:
Publication Date(Web):24 JAN 2007
DOI:10.1002/chem.200601682
The tripodal system 4, in which urea fragments are appended to the three terminal amine nitrogen atoms of a tris(2-aminoethyl)amine (tren) subunit, includes a CuII ion and two anions X−, according to a cascade mechanism through three well defined stepwise equilibria in a DMSO solution. The first anion X− (halide, N3−, NCS−, NO2−, H2PO4−) seeks the CuII centre coordinated by the tren moiety; the second anion X− interacts with the trisurea cavity, but this occurs only if the stronger H-bond acceptors, such as N3− and H2PO4−, are used. Binding of the second X− ion is favoured by the preorganising effect exerted by the metal and disfavoured by the steric and electrostatic repulsions between the anions. Under the appropriate conditions, heterodinuclear complexes of formula [CuII(4)(Cl)(H2PO4)] can be obtained in solution, in which Cl− is bound to the metal centre and H2PO4− interacts with the trisurea compartment.
Co-reporter:Marco Bonizzoni;Angelo Taglietti;Federico Tiengo
European Journal of Organic Chemistry 2006 Volume 2006(Issue 16) pp:
Publication Date(Web):13 JUL 2006
DOI:10.1002/ejoc.200600388
A family of neutral N-(R1-substituted-benzylideneamino)-N′-(R2-substituted-phenyl)thioureas (LH) were designed as anion receptors, and their interactions with anions in MeCN solution were investigated through spectrophotometric and 1H NMR titration experiments. While oxo anions (e.g., CH3COO–, H2PO4–) form genuine H-bond complexes based on complementary N–H···O interactions with LH receptors, the fluoride ion undergoes a two-step interaction, involving (i) formation of the [LH···F]– complex, and (ii) release of an HF molecule to give [HF2]– and the deprotonated form of the receptor (L–). Deprotonation takes place at the N–H fragment closer to the R2-substituted phenyl ring, as indicated by 1H NMR spectroscopy. The log K values for the formation of the [LH···CH3COO]– H-bond complexes vary over the 3.1–3.8 range and are scarcely affected by the natures of the R1 and R2 substituents. The investigated systems may be of interest in the design of molecular devices in which the optical properties of different and distant substituents are modulated through the interaction of a chosen anion at the thiourea site.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)
Co-reporter:Marco Bonizzoni;Angelo Taglietti;Federico Tiengo
European Journal of Organic Chemistry 2006 Volume 2006(Issue 16) pp:
Publication Date(Web):2 AUG 2006
DOI:10.1002/ejoc.200690032
The cover picture shows the behavior of a family of neutral N-R1-substituted-benzylideneamine)-N′-(R2-substituted-phenyl)thioureas (LH) as anion receptors. Spectrophotometric and 1H NMR titration experiments in MeCN solution have shown that oxo anions (e. g. CH3COO–, H2PO4–) form genuine H-bond complexes with LH receptors through complementary N–H···O– interactions. The use of fluoride ions gives a two-step interaction, which involves (i) the formation of the [LH···F]– complex, (ii) the release of an HF molecule to give [HF2]– and the deprotonated form of the receptor, L–. Direct deprotonation of LH is obtained on reaction with 1 equiv. of OH–. The occurrence of the different processes can be visually perceived through definite color changes. The colors shown in the picture refer to the receptor with R1 = NO2 and R2 = OCH3. Details are discussed in the article by L. Fabbrizzi et al. on pp. 3567 ff.
Co-reporter:Valeria Amendola Dr.;Massimo Boiocchi Dr.;Benoît Colasson Dr. ;Maria-Jesús Rodriguez Douton Dr.;Franco Ugozzoli
Angewandte Chemie 2006 Volume 118(Issue 41) pp:
Publication Date(Web):20 SEP 2006
DOI:10.1002/ange.200602598
Dach überm Kopf: Ein Trisimidazolium-Käfig mit überdachender {FeII(bpy)3}2+-Einheit (bpy=2,2′-Bypyridyl) wirkt als Rezeptor für kleine Anionen. Stabförmige „Pseudohalogenide“ (N3−, NCO−, NCS−) und sphärische Halogenide (Cl−, Br−, I−) binden über Wasserstoffbrücken an die C-H-Fragmente im Hohlraum des Rezeptors. Das N3−-Ion bildet die stärkste Einschlussverbindung (siehe Struktur; Fe rot, C hellblau, H weiß, N dunkelblau).
Co-reporter:Valeria Amendola Dr.;Massimo Boiocchi Dr.;Benoît Colasson Dr. ;Maria-Jesús Rodriguez Douton Dr.;Franco Ugozzoli
Angewandte Chemie International Edition 2006 Volume 45(Issue 41) pp:
Publication Date(Web):20 SEP 2006
DOI:10.1002/anie.200602598
Sheltering under the roof: A trisimidazolium cage is capped with a {FeII(bpy)3}2+ subunit to produce a receptor that can bind small anions (bpy=2,2′-bipyridine). Rodlike “pseudohalide” (N3−, NCO−, and NCS−) and spherical halide (Cl−, Br−, and I−) anions accept hydrogen bonds from CH fragments in the receptor cavity. The N3− ion forms the most stable inclusion compound (see structure; Fe red, C light blue, H white, N dark blue).
Co-reporter:David Esteban-Gómez, Luigi Fabbrizzi, Maurizio Licchelli and Donatella Sacchi
Journal of Materials Chemistry A 2005 vol. 15(Issue 27-28) pp:2670-2675
Publication Date(Web):04 May 2005
DOI:10.1039/B502869H
A neutral receptor, in which a urea fragment has been equipped with two naphthaleneimide subunits, on interaction with acetate, in a DMSO solution, undergoes deprotonation of one of the N–H fragments; an event which is signalled by a yellow-to-red colour change and by the quenching of the blue fluorescence of the naphthalneimide subunit, with no competition by a number of anions (phosphate, nitrate, sulfate, chloride or bromide). This procedure can be employed for the visual and spectroscopic detection of cholic acid, even in presence of the other competing bile acids, such as glycocholic and taurocholic.
Co-reporter:David Esteban Gómez, Luigi Fabbrizzi, Maurizio Licchelli and Enrico Monzani
Organic & Biomolecular Chemistry 2005 vol. 3(Issue 8) pp:1495-1500
Publication Date(Web):10 Mar 2005
DOI:10.1039/B500123D
Neutral anion receptors (LH) form stable 1 : 1 H-bond [LH⋯X]− complexes with carboxylates, halides and phosphate (X−). Some of the [LH⋯X]− complexes, in presence of an excess of X−, release an HX fragment, with formation of [HX2]− and the deprotonated receptor L−. The tendency towards deprotonation increases with the acidity of the receptor and with the stability of the [HX2]− self-complex. Thus, the more acidic thiourea containing receptor deprotonates in the presence all the investigated anions except chloride, whereas the less acidic urea containing receptor undergoes deprotonation only in the presence of fluoride, due to the high stability of [HF2]−.
Co-reporter:Giovanni Cacchione, Luigi Fabbrizzi, Francesco Foti and Angelo Taglietti
Dalton Transactions 2005 (Issue 16) pp:2672-2674
Publication Date(Web):15 Jul 2005
DOI:10.1039/B507169K
In the decomposition in acidic solution of the octahedral high-spin nickel(II) complex with the hexamine sen, a thermodynamically unstable, kinetically controlled, square-planar low-spin species forms, with a lifetime of 5 s.
Co-reporter:Valeria Amendola Dr.;Massimo Boiocchi Dr. ;Arianna Palchetti
Chemistry - A European Journal 2005 Volume 11(Issue 1) pp:
Publication Date(Web):10 NOV 2004
DOI:10.1002/chem.200400592
When the amide-containing receptor 1+ is in a solution of dimethyl sulfoxide (DMSO) in the presence of basic anions (CH3COO−, F−, H2PO4−), it undergoes deprotonation of the -NH fragment to give the corresponding zwitterion, which can be isolated as a crystalline solid. In the presence of less basic anions (Cl−, Br−, NO3−), 1+ establishes true hydrogen-bond interactions of decreasing intensity. The less acidic receptor 2+ undergoes neat proton transfer with only the more basic anions CH3COO− and F−, and establishes hydrogen-bond interactions with H2PO4−. An empirical criterion for discerning neutralisation and hydrogen bonding, based on UV/Vis and 1H NMR spectra, is proposed.
Co-reporter:Valeria Amendola Dr.;Massimo Boiocchi Dr. ;Arianna Palchetti Dr.
Chemistry - A European Journal 2005 Volume 11(Issue 19) pp:
Publication Date(Web):15 JUL 2005
DOI:10.1002/chem.200500351
The trifurcate receptor 13+ forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1H NMR experiments, and selectively recognizes chloride (lg Kass>7) in the presence of fluoride and bromide. The high stability reflects the receptor's ability to donate up to six hydrogen bonds (from three pyrrole NH and three CH fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F− and CH3COO−) induces stepwise deprotonation of the NH groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO3− and a capsule consisting of two interconnected trifurcate subunits, one of which includes an H-bound Br− ion, while the other is doubly deprotonated and includes an H-bound water molecule. Finally, evidence is given for the formation in solution of an authentic complex of OH−, in which H-bound hydroxide is included within the cavity of 13+.
Co-reporter:Massimo Boiocchi Dr.;Laura Del Boca;David Esteban-Gómez Dr. ;Maurizio Licchelli ;Enrico Monzani Dr.
Chemistry - A European Journal 2005 Volume 11(Issue 10) pp:
Publication Date(Web):15 MAR 2005
DOI:10.1002/chem.200401049
The urea-based receptor 1 (1-(7-nitrobenzo[1,2,5]oxadiazol-4-yl)-3-(4-nitrophenyl)urea, LH), interacts with X− ions in MeCN, according to two consecutive steps: 1) formation of a hydrogen-bond complex [LH⋅⋅⋅X]−; 2) deprotonation of LH to give L− and [HX2]−, as shown by spectrophotometric and 1H NMR titration experiments. Step 2) takes place with more basic anions (fluoride, carboxylates, dihydrogenphosphate), while less basic anions (Cl−, NO2−, NO3−) do not induce proton transfer. On crystallisation from a solution containing LH and excess Bu4NF, the tetrabutylammonium salt of the deprotonated urea derivative (Bu4N[L]) was isolated and its crystal and molecular structure determined.
Co-reporter:Massimo Boiocchi, Luigi Fabbrizzi, Francesco Foti and Miguel Vázquez
Dalton Transactions 2004 (Issue 17) pp:2616-2620
Publication Date(Web):30 Jul 2004
DOI:10.1039/B408085H
The spin interconversion equilibrium involving the [NiII(cyclam)]2+ complex has been investigated in a variety of polar solvents, at varying temperatures. The greater the donor tendencies of the solvent, the higher the endothermicity of the high-to-low-spin conversion. In particular, a positive linear relationship exists between ΔH° and Gutmann's Donor Number (DN). In the same way, higher donor tendencies of the solvent favour the occurrence of the NiII-to-NiIII oxidation process and negative linear relationship has been found between the E1/2(NiIII/NiII) and DN. General behaviour is related to the intensity of the metal–solvent axial bonds in the octahedrally elongated cyclam complexes (of both NiII and NiIII).
Co-reporter:Massimo Boiocchi, Marco Bonizzoni, Luigi Fabbrizzi, Francesco Foti, Maurizio Licchelli, Angelo Taglietti and Michele Zema
Dalton Transactions 2004 (Issue 4) pp:653-658
Publication Date(Web):21 Jan 2004
DOI:10.1039/B312980B
The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a ‘salting out’ effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation is increased).
Co-reporter:Massimo Boiocchi Dr.;Marco Bonizzoni Dr. ;Giulio Piovani;Angelo Taglietti Dr.
Angewandte Chemie 2004 Volume 116(Issue 29) pp:
Publication Date(Web):12 JUL 2004
DOI:10.1002/ange.200460036
Passt wie angegossen! Der Dikupfer(II)-Komplex 1 eines Bistren-Käfigs mit Ditolyl-Abstandshaltern bindet Dicarboxylat-Ionen in wässriger Lösung. Die Wechselwirkung reagiert hoch selektiv auf den Abstand zwischen den COO−-Gruppen. So wird beispielsweise Terephthalat (siehe Bild) von Isophthalat und Phthalat unterschieden.
Co-reporter:Luigi Fabbrizzi ;Francesco Foti Dr.;Stefano Patroni Dr.;Piersro Pallavicini Dr. and;Angelo Taglietti Dr.
Angewandte Chemie 2004 Volume 116(Issue 38) pp:
Publication Date(Web):22 SEP 2004
DOI:10.1002/ange.200460568
Eine pH-abhängige doppelte Translokation von Cu2+-Ionen tritt innerhalb eines heteroditopen Makrocyclus auf. Sie öffnet und schließt das System und steuert so dessen Funktion als Rezeptor für zweizähnige Anionen. Wird die gepufferte Lösung mit Imidazol versetzt, kann die Öffnung des Systems und die Substratbindung durch das Substrat selbst induziert werden. Daraus resultiert ein scharfer Farbwechsel (siehe Bild).
Co-reporter:Luigi Fabbrizzi ;Francesco Foti Dr.;Stefano Patroni Dr.;Piersro Pallavicini Dr. and;Angelo Taglietti Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 38) pp:
Publication Date(Web):22 SEP 2004
DOI:10.1002/anie.200460568
pH-driven double Cu2+ion translocation occurs inside an heteroditopic macrocycle. The movement opens and closes the system allowing or preventing it to function as receptor for bidentate anions. When imidazole is added to a solution buffered at an appropriate pH value, opening of the system and substrate binding can be induced by the substrate itself, which results in a sharp color change (see picture).
Co-reporter:Massimo Boiocchi Dr.;Marco Bonizzoni Dr. ;Giulio Piovani;Angelo Taglietti Dr.
Angewandte Chemie International Edition 2004 Volume 43(Issue 29) pp:
Publication Date(Web):12 JUL 2004
DOI:10.1002/anie.200460036
Fits like a glove! The dicopper(II) complex 1 of a bistren cage containing ditolyl spacers binds dicarboxylate anions in aqueous solutions. The inclusion is highly selective on the basis of the distance between the COO− groups. For example, terephthalate (see picture) is discriminated from isophthalate and phthalate.
Co-reporter:Valeria Amendola Dr. ;Enrico Monzani Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 1) pp:
Publication Date(Web):19 DEC 2003
DOI:10.1002/chem.200305338
The ligand 2, in which three fluorogenic 6-methoxy-1-methylquinolinium fragments are appended to a mesityl platform, in MeCN forms 1:1 adducts with halides and other inorganic anions. 1H NMR studies and molecular modelling indicate that 2 provides a cavity for anion inclusion and establishes electrostatic interactions with the guest. Anion inclusion induces quenching of the fluorogenic fragments with an efficiency decreasing along the series Br−≫I−>NCS−≫Cl−>NO3−>HSO4−. The fluorimetric response of 2 to anions is orders of magnitude more sensitive than that of just 6-methoxy-1-methylquinolinium, ligand 1.
Co-reporter:Miguel Vázquez Dr. ;Angelo Taglietti Dr.;Rosa M. Pedrido Dr.;Ana M. González-Noya Dr.;Manuel R. Bermejo
Angewandte Chemie 2004 Volume 116(Issue 15) pp:
Publication Date(Web):30 MAR 2004
DOI:10.1002/ange.200353148
Ein farbloser neutraler Rezeptor ohne charakteristische chromogene Substituenten erkennt selektiv Fluorid-Ionen (siehe Schema). Der Rezeptor trägt zwei äquivalente Molekülarme, die jeweils mit einer Thioharnstoff-Gruppe ausgerüstet sind. Die gelbe Farbe des Rezeptor-Anion-Komplexes stammt von einer ausgeprägten π-Elektronen-Delokalisierung, induziert durch die starken Wasserstoffbrücken zwischen den F−-Ionen und den inneren NH-Gruppen der Thioharnstoff-Einheiten.
Co-reporter:Massimo Boiocchi Dr.;Marco Bonizzoni Dr. ;Francesco Foti Dr.;Maurizio Licchelli ;Antonio Poggi ;Angelo Taglietti Dr.;Michele Zema Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 13) pp:
Publication Date(Web):29 APR 2004
DOI:10.1002/chem.200305717
The demetallation in acidic solution of the CuII complexes with open-chain and cyclic tetramines containing a piperazine unit (2 and 3) has been investigated in terms of its kinetic aspects and compared with the behaviour of unsubstituted counterparts (tetramines 1 and 4). The presence of the piperazine fragment slows demetallation of the open-chain-ligand complex owing to the activation barrier associated with the conformational change from boat-to-half-boat; however, it does not affect the demetallation of the macrocyclic complex, which involves the spontaneous boat-to-twist conformational change. Thus, lateral reinforcement of a cyclam-like ligand does not add any further contribution to the typical inertness in demetallation of macrocyclic complexes.
Co-reporter:Miguel Vázquez Dr. ;Angelo Taglietti Dr.;Rosa M. Pedrido Dr.;Ana M. González-Noya Dr.;Manuel R. Bermejo
Angewandte Chemie International Edition 2004 Volume 43(Issue 15) pp:
Publication Date(Web):30 MAR 2004
DOI:10.1002/anie.200353148
A colorless neutral receptor with no particular chromogenic substituents selectively recognizes fluoride ions with a concomitant development of a yellow color (see scheme). The receptor contains two equivalent arms, each equipped with a thiourea fragment. Color originates from the extended π delocalization induced by the strong hydrogen-bonding interaction of the F− ion with the internal NH groups of thiourea moieties.
Co-reporter:Massimo Boiocchi, Luigi Fabbrizzi, Maurizio Licchelli, Donatella Sacchi, Miguel Vázquez and Cristina Zampa
Chemical Communications 2003 (Issue 15) pp:1812-1813
Publication Date(Web):27 Jun 2003
DOI:10.1039/B305456J
A cyclam-like macrocycle with an integrated push-pull chromophore selectively detects Cu2+ inclusion through both orange-to-yellow colour change and quenching of the green fluorescence.
Co-reporter:Valeria Amendola, Luigi Fabbrizzi, Etienne Mundum and Piersandro Pallavicini
Dalton Transactions 2003 (Issue 5) pp:773-774
Publication Date(Web):03 Feb 2003
DOI:10.1039/B212321E
Reaction of the monomeric polyamine complex [CuII(1)]2+ with OH− and O2 gives the dimeric double-helix complex [Cu2I(2)2]2+, in which the –CH2–NH– amine groups have been dehydrogenated to –CHN– functions.
Co-reporter:Luigi Fabbrizzi, Maurizio Licchelli and Angelo Taglietti
Dalton Transactions 2003 (Issue 18) pp:3471-3479
Publication Date(Web):27 Jun 2003
DOI:10.1039/B304172G
Fluorescent sensors are molecular systems consisting of a receptor moiety and of a fluorogenic fragment, which are capable of recognising a given analyte and signalling recognition through a variation of the emission intensity. The fluorogenic fragment responsible of the signal can be associated to the receptor either covalently or non-covalently, giving rise to two well distinct classes of fluorosensors and sensing paradigms. The design of fluorescent sensors is described, with a special attention to the sensing of anionic groups (including those of amino acids). In any case, it seems convenient that the receptor moiety contains one or more metal centres, which establish strong coordinative interactions with the envisaged anionic substrate. Selectivity is related to the energy of the metal–analyte interaction and can be achieved by taking profit of the concepts developed in more than one hundred years of coordination chemistry. As an example, recognition and sensing of the amino acid histidine is considered in detail, which is based on the attitude of the imidazole residue to deprotonate and bridge two MII ions prepositioned at the right distance, within a defined coordinative framework (M = Cu, Zn).
Co-reporter:Irene Bruseghini, Luigi Fabbrizzi, Maurizio Licchelli and Angelo Taglietti
Chemical Communications 2002 (Issue 13) pp:1348-1349
Publication Date(Web):23 May 2002
DOI:10.1039/B202815H
An intramolecular photoinduced electron transfer which takes place in a ZnII polyamine complex can be interrupted through coordination of a bulky carboxylate anion, acting as a curtain.
Co-reporter:Valeria Amendola Dr. ;Carlo Mangano Dr.;Hamish Miller Dr.;Piersro Pallavicini Dr.;Angelo Perotti ;Angelo Taglietti Dr.
Angewandte Chemie 2002 Volume 114(Issue 14) pp:
Publication Date(Web):15 JUL 2002
DOI:10.1002/1521-3757(20020715)114:14<2665::AID-ANGE2665>3.0.CO;2-C
pH-abhängige Metalltranslokation: Die Fluoreszenz von Cumarin 343 wird „ausgeschaltet“, wenn es (in deprotonierter Form) an ein CuII-Ion, komplexiert in der Bindungsstelle B des gezeigten Liganden, bindet. Nach Erhöhung des pH-Werts von 7 auf ≥11 und zweifacher Deprotonierung der anderen Bindungsstelle (AH2A) wandert das CuII-Ion dorthin. Hier ist es quadratisch-planar koordiniert; infolgedessen dissoziiert das Cumarin-343-Anion, wodurch seine Fluoreszenz wieder „eingeschaltet“ wird. Dieser Vorgang ist reversibel und lässt sich mehrfach wiederholen.
Co-reporter:Luigi Fabbrizzi ;Nathalie Marcotte Dr.;Floriana Stomeo Dr.;Angelo Taglietti Dr.
Angewandte Chemie International Edition 2002 Volume 41(Issue 20) pp:
Publication Date(Web):18 OCT 2002
DOI:10.1002/1521-3773(20021018)41:20<3811::AID-ANIE3811>3.0.CO;2-W
Displacement of the previously bound, and quenched, fluorescent indicator (I) by coordination of the pyrophosphate ion to the two CuII centers of the receptor R results in the generation of the natural fluorescence of the indicator, and thus signals pyrophosphate recognition (see scheme). Discrimination from interfering anions (HPO42−, SO42−, NO3−, Cl−, NCO−, N3−, acetate, benzoate) can be achieved by tuning the indicator affinity towards the receptor.
Co-reporter:Valeria Amendola Dr. ;Carlo Mangano Dr.;Hamish Miller Dr.;Piersro Pallavicini Dr.;Angelo Perotti ;Angelo Taglietti Dr.
Angewandte Chemie International Edition 2002 Volume 41(Issue 14) pp:
Publication Date(Web):15 JUL 2002
DOI:10.1002/1521-3773(20020715)41:14<2553::AID-ANIE2553>3.0.CO;2-U
Shedding light on the environment: An auxillary light-emitting fragment (coumarin-343) binds to a CuII ion in the right-hand compartment (B) of the ligand shown and its fluorescence is “switched off”. If the pH value is raised from 7 to ≥11 the metal moves to the left compartment (A), which imposes a square stereochemistry and forces dissociation of the indicator, thus “switching on” the fluorescence. The pH-driven metal translocation is reversible and can be carried out for many cycles.
Co-reporter:Luigi Fabbrizzi ;Francesco Foti Dr.;Maurizio Licchelli ;Paola M. Maccarini Dr.;Donatella Sacchi Dr.;Michele Zema Dr.
Chemistry - A European Journal 2002 Volume 8(Issue 21) pp:
Publication Date(Web):28 OCT 2002
DOI:10.1002/1521-3765(20021104)8:21<4965::AID-CHEM4965>3.0.CO;2-X
A cyclam-like macrocycle has been synthesized with a pendant arm containing a dansylamide group. In the corresponding nickel(II) complex, binding of the pendant arm to the metal is pH controlled. In particular, at pH 4.3, the sulfonamide group deprotonates and coordinates the NiII center, giving rise to a complex of trigonal bipyramidal stereochemistry, as shown by X-ray diffraction studies performed on the crystalline complex salt. At pH 7.5, an OH− ion binds the metal and a six-coordinate species forms. The binding-detachment of the pendant arm to/from the NiII center is signaled by changes in the emission properties of the dansyl subunit in the side chain; the fluorescence of this side chain is high when the pendant arm is not coordinated and low when the sulfonamide group is bound to the metal. The system investigated represents the prototype of a light-emitting molecular machine, driven by a pH change.
Co-reporter:Valeria Amendola, Luigi Fabbrizzi and Lorenzo Mosca
Chemical Society Reviews 2010 - vol. 39(Issue 10) pp:NaN3915-3915
Publication Date(Web):2010/09/01
DOI:10.1039/B822552B
Since 1992 a variety of urea-based anion receptors have been synthesised, of varying complexity and sophistication. This critical review will focus on some distinctive aspects of anion recognition by urea derivatives, with a special reference to: (i) design and synthesis, (ii) methodologies for the investigation of the receptor–anion interaction in solution, (iii) the interpretation of the solution behaviour on the basis of the structural interplay between the receptor and the anion. It will be shown that the efficiency of urea as a receptor subunit depends on the presence of two proximate polarised N–H fragments, capable (i) of chelating a spherical anion or (ii) of donating two parallel H-bonds to the oxygen atoms of a carboxylate or of an inorganic oxoanion, a property which is shared with other diamides, e.g. squaramide. The wide use of urea in the design of neutral anion receptors seems to depends on the ease of its synthesis, in particular through the reaction of a primary amine group with an isocyanate, which allows the high-yield preparation of symmetrically and unsymmetrically substituted derivatives (83 references).
Co-reporter:Luigi Fabbrizzi and Antonio Poggi
Chemical Society Reviews 2013 - vol. 42(Issue 4) pp:NaN1699-1699
Publication Date(Web):2012/10/02
DOI:10.1039/C2CS35290G
Alfred Werner's complexes of formula [MIII(NH3)6−nXn]X3−n involved inert metal centres (M = Cr, Co), and anions X− ‘frozen’ in the coordination sphere, a circumstance which allowed the isolation of a variety of isomers. Amine complexes of labile transition metal ions, studied later, do not form isomers, yet they allow the investigation of the fast and reversible interaction of the anion X− with the metal–amine core. On these bases, anion receptors of varying degrees of sophistication have been synthesised, which consist of coordinatively unsaturated polyamine metal complexes and whose vacant coordination sites can be occupied by anion donor atoms. A thoughtful design of the polyamine framework may introduce geometrical selectivity, resulting from the matching between anion shape and size and the geometrical features of receptor's cavity. Compared to their purely organic counterparts, metal containing receptors display several advantages: (i) metal–anion interactions are strong enough to more than compensate anion dehydration energy, which allows recognition studies to be carried out in water; (ii) transition metal ions of different electronic configurations exhibit different geometrical preferences, which addresses anion binding and introduces a further element of selectivity. Chosen examples of polyamine metal complexes, including macrocycles and cages, displaying selective binding tendencies towards anions will be illustrated in this tutorial review.
Co-reporter:Valeria Amendola and Luigi Fabbrizzi
Chemical Communications 2009(Issue 5) pp:NaN531-531
Publication Date(Web):2008/12/03
DOI:10.1039/B808264M
Transition metals can be used as structural elements to build up anion receptors, enhancing H-bond donor tendencies, favouring the assembling of the molecular framework, inducing the formation of a cage. The versatile spectroscopic and electrochemical properties of the metal ion can provide a convenient signalling mechanism to communicate the occurrence of anion recognition.
Co-reporter:Valeria Amendola, Greta Bergamaschi, Massimo Boiocchi, Luigi Fabbrizzi and Nadia Fusco
Dalton Transactions 2011 - vol. 40(Issue 33) pp:NaN8376-8376
Publication Date(Web):2011/07/19
DOI:10.1039/C1DT10894H
The tris-benzimidazolium cage LH33+, in MeCN solution, in the presence of OH−, forms with CuI and AgI ions complexes of formula [MI(LH)]2+, in which each metal is linearly coordinated by two carbenes and one imidazolium N–H fragment remains intact. To achieve two-coordination, the two N-heterocyclic moieties of the cage make a saloon-door type motion, with a conformationally costless rotation of ca. 30° each. The two [MI(LH)]2+ complexes show high thermodynamic stability and are inert with respect to metal substitution, due to the mechanical constraints imposed by the ligating framework. Complexation with CuI and AgI with the reference unidentate carbene ligand Q, derived from the benzimidazolium precursor QH+, was studied for comparison. Both metals in MeCN form 1:1 and 1:2 complexes with the carbene ligand Q according to two stepwise equilibria. Q complexes of both metals are labile with respect to metal substitution and those of AgI are more stable than those of CuI. A significant cooperative effect has been observed with the formation of the [AgIQ2]+ complex.
Co-reporter:Massimo Boiocchi and Luigi Fabbrizzi
Chemical Society Reviews 2014 - vol. 43(Issue 6) pp:NaN1847-1847
Publication Date(Web):2014/01/17
DOI:10.1039/C3CS60428D
In the presence of d10 metal ions, prone to tetrahedral coordination, ligands containing two bidentate subunits will give rise to double-stranded helical complexes (helicates). Upon electrochemical oxidation of CuI to CuII, the helicate complex tends to disassemble, thus giving rise to two mononuclear CuII complexes with tetragonal geometry. Upon subsequent CuII-to-CuI electrochemical reduction, two CuI complexes instantaneously re-assemble to give the helicate complex. A helicand containing a chiral subunit (e.g. 1,2-substituted cyclohexanediamine) contains a racemic mixture of the R,R and S,S enantiomers. The racemic helicand, reacting with CuI, forms dimetallic helicates, in which the two strands show the same chirality, whether R,R or S,S, thus obeying the principle of homochiral recognition.
Co-reporter:Giuseppe Alibrandi, Valeria Amendola, Greta Bergamaschi, Luigi Fabbrizzi and Maurizio Licchelli
Organic & Biomolecular Chemistry 2015 - vol. 13(Issue 12) pp:NaN3524-3524
Publication Date(Web):2015/01/20
DOI:10.1039/C4OB02618G
Bistren cryptands can be easily synthesised through the Schiff base condensation of two molecules of tren and three molecules of a dialdehyde, followed by hydrogenation of the six CN double bonds to give octamine cages, whose ellipsoidal cavity can be varied at will, by choosing the appropriate dialdehyde, in order to include substrates of varying sizes and shapes. Bistrens can operate as effective anion receptors in two ways: (i) in their protonated form, providing six secondary ammonium groups capable of establishing hydrogen bonding interactions with the anion; (ii) as dicopper(II) cryptates, in which the two coordinatively unsaturated metal centres can be bridged by an ambidentate anion. Representative examples of the two approaches, as well as the design of an anion molecular dispenser, in which a dicopper(II) bistren cryptate acts as a bottle will be illustrated.
