Ronald Breslow

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Name: Breslow, Ronald

Organization: Columbia University New York , USA

Department: Department of Chemistry

Title: Professor(PhD)

Chemicals
References

Aromaticity Decreases Single-Molecule Junction Conductance.

Co-reporter:Wenbo Chen, Haixing Li, Jonathan R. Widawsky, Chandrakumar Appayee, Latha Venkataraman, and Ronald Breslow

Journal of the American Chemical Society January 22, 2014 Volume 136(Issue 3) pp:918-920

Publication Date(Web):January 7, 2014

DOI:10.1021/ja411143s

We have measured the conductance of single-molecule junctions created with three different molecular wires using the scanning tunneling microscope-based break-junction technique. Each wire contains one of three different cyclic five-membered rings: cyclopentadiene, furan, or thiophene. We find that the single-molecule conductance of these three wires correlates negatively with the resonance energy of the five-membered ring; the nonaromatic cyclopentadiene derivative has the highest conductance, while the most aromatic of this series, thiophene, has the lowest. Furthermore, we show for another wire structure that the conductance of furan-based wires is consistently higher than for analogous thiophene systems, indicating that the negative correlation between conductance and aromaticity is robust. The best conductance would be for a quinoid structure that diminishes aromaticity. The energy penalty for partly adopting the quinoid structure is less with compounds having lower initial aromatic stabilization. An additional effect may reflect the lower HOMOs of aromatic compounds.

Physical Organic Chemistry, the Richest Chemical Science

Co-reporter:Ronald Breslow

Israel Journal of Chemistry 2016 Volume 56( Issue 1) pp:89-90

Publication Date(Web):

DOI:10.1002/ijch.201500029

No abstract is available for this article.

Single molecule conductance of aromatic, nonaromatic, and partially antiaromatic systems

Co-reporter:Adaickapillai Mahendran, Purushothaman Gopinath, Ronald Breslow

Tetrahedron Letters 2015 Volume 56(Issue 33) pp:4833-4835

Publication Date(Web):12 August 2015

DOI:10.1016/j.tetlet.2015.06.076

We describe the syntheses of thiophene, cyclopentadienone and dimethylketalcyclopentadienone derivatives and their single molecule electrical conductivities. The ketone had the lowest conductivity of the three, although it has some antiaromaticity. The carbonyl group is electron attracting and its ionization potential outweighs any conductivity increase that the antiaromaticity effect might bring.

Magnesium pyrophosphates in enzyme mimics of nucleotide synthases and kinases and in their prebiotic chemistry

Co-reporter:Purushothaman Gopinath;Vijayakumar Ramalingam

PNAS 2015 Volume 112 (Issue 39 ) pp:12011-12014

Publication Date(Web):2015-09-29

DOI:10.1073/pnas.1516239112

Derivatives of ribosyl pyrophosphate have been synthesized, and examined with magnesium salts in the coupling of the ribose unit to various nucleophiles, including pyrazole and 2-chloroimidazole. Only with the magnesium salt present did they generate the ribosyl cation by binding to the leaving group and then couple the ribose derivative with nucleophiles. The role of magnesium salts in phosphorylation of methanol by ATP was also examined. Here a remarkable effect was seen: phosphorylation by ATP was slowed with low concentrations of Mg2+ but accelerated by higher concentrations. Related effects were also seen in the effect of Mg2+ on phosphorylation by ADP. The likely mechanisms explain these effects.

Deuterium Studies Reveal a New Mechanism for the Formose Reaction Involving Hydride Shifts

Co-reporter:Chandrakumar Appayee

Journal of the American Chemical Society 2014 Volume 136(Issue 10) pp:3720-3723

Publication Date(Web):February 27, 2014

DOI:10.1021/ja410886c

In the formose reaction, formaldehyde is converted to glycolaldehyde, its dimer, under credible prebiotic conditions. Breslow proposed a mechanism for the process in 1959, but recent studies by Benner showed that it was wrong in detail. Our present studies clarify the mechanism, which involves the original Breslow intermediates but some different connecting steps.

Novel Aromatic and Antiaromatic Systems

Co-reporter:Ronald Breslow

The Chemical Record 2014 Volume 14( Issue 6) pp:1174-1182

Publication Date(Web):

DOI:10.1002/tcr.201402070

Deoxypolypeptides bind and cleave RNA

Co-reporter:Liang Cheng;Adaickapillai Mahendran;Ruben L. Gonzalez, Jr.

PNAS 2014 Volume 111 (Issue 22 ) pp:7920-7924

Publication Date(Web):2014-06-03

DOI:10.1073/pnas.1407295111

We have prepared L- and D-deoxypolypeptides (DOPPs) by selective reduction of appropriately protected polyhistidines with borane, reducing the carbonyl groups to methylenes. The result is a chiral polyamine, not amide, with a mainly protonated backbone and chirally mounted imidazolylmethylene side chains that are mostly unprotonated at neutrality because of the nearby polycationic backbone. We found that, in contrast with the D-octahistidine DOPP, the L-octahistidine DOPP is able to cooperatively bind to a D-polyuridylic acid RNA; this is consistent with results of previous studies showing that, relative to d-histidine, l-histidine is able to more strongly bind to RNA. The l-DOPP was also a better catalyst for cleaving the RNA than the d-DOPP, consistent with evidence that the l-DOPP uses its imidazole groups for catalysis, in addition to the backbone cations, but the d-DOPP does not use the imidazoles. The l-DOPP bifunctional process probably forms a phosphorane intermediate. This is a mechanism we have proposed for models of ribonuclease cleavage and for the ribonuclease A enzyme itself, based on our studies of the cleavage and isomerization of UpU catalyzed by imidazole buffers as well as other relevant studies. This mechanism contrasts with earlier, generally accepted ribonuclease cleavage mechanisms where the proton donor coordinates with the oxygen of the leaving group as the 2-hydroxyl of ribose attacks the unprotonated phosphate.

Transketolase reaction under credible prebiotic conditions

Co-reporter:Chandrakumar Appayee

PNAS 2013 Volume 110 (Issue 11 ) pp:4184-4187

Publication Date(Web):2013-03-12

DOI:10.1073/pnas.1301522110

A transketolase reaction was catalyzed by cyanide ion under prebiotic conditions instead of its modern catalyst, thiamine pyrophosphate (TPP). Cyanide ion converted fructose plus glyceraldehyde to erythrose plus xylulose, the same products as are formed in modern biochemistry (but without the phosphate groups on the sugars). Cyanide was actually a better catalyst than was TPP in simple solution, where there is a negligible concentration of the C-2 anion of TPP, but of course not with an enzyme in modern biology. The cyanide ion was probably not toxic on prebiotic earth, but only when the oxygen atmosphere developed and iron porphyrin species were needed, which cyanide poisons. Thus, catalyses by TPP that are so important in modern biochemistry in the Calvin cycle for photosynthesis and the gluconic acid pathway for glucose oxidation, among other processes, were probably initially performed instead by cyanide ion until its toxicity with metalloproteins became a problem and primitive enzymes were present to work with TPP, or most likely its primitive precursors.

Catalysis of Glyceraldehyde Synthesis by Primary or Secondary Amino Acids Under Prebiotic Conditions as a Function of pH

Co-reporter:Ronald Breslow;Vijayakumar Ramalingam

Origins of Life and Evolution of Biospheres 2013 Volume 43( Issue 4-5) pp:323-329

Publication Date(Web):2013 October

DOI:10.1007/s11084-013-9347-0

The synthesis of an excess of D-glyceraldehyde by coupling glycolaldehyde with formaldehyde under prebiotic conditions is catalyzed by L amino acids having primary amino groups at acidic pH’s, but at neutral or higher pH’s they preferentially form L-glyceraldehyde. L Amino acids having secondary amino groups, such as proline, have the reverse preferences, affording excess L-glyceraldehyde at low pH but excess D-glyceraldehyde at higher pHs. Detailed mechanistic proposals make these preferences understandable. The relevance of these findings to the origin of D sugars on prebiotic Earth is described.

Binding and biomimetic cleavage of the RNA poly(U) by synthetic polyimidazoles

Co-reporter:Liang Cheng;K.G. Abhilash;

Proceedings of the National Academy of Sciences 2012 109(32) pp:

Publication Date(Web):July 23, 2012

DOI:10.1073/pnas.1210846109

Four polyimidazoles were used in the binding and cleavage studies with poly(U). The two polydisperse polyvinylimidazoles were previously described by others, while the other two new polymers of polyethyleneimines were prepared by cationic polymerization of oxazolines. The latter had imidazole units attached to each nitrogen of the polymers. They were characterized by gel permeation chromatography and had very low polydispersities. When they were partially protonated they bound to the poly(U) and catalyzed its cleavage by a process analogous to that used by the enzyme ribonuclease A. The kinetics of the cleavage were followed by an assay we had previously described using phosphodiesterase I from Crotalus venom after the cleavage processes. Cleavage of poly(U) with Zn²⁺ was also examined, with and without the polymers. A scheme is described in which these cleavages could be made sequence selective with various RNAs, particularly with important targets, such as viral RNAs.

Single-Molecule Conductance through Multiple π−π-Stacked Benzene Rings Determined with Direct Electrode-to-Benzene Ring Connections

Co-reporter:Severin T. Schneebeli ; Maria Kamenetska ; Zhanling Cheng ; Rachid Skouta ; Richard A. Friesner ; Latha Venkataraman

Journal of the American Chemical Society 2011 Volume 133(Issue 7) pp:2136-2139

Publication Date(Web):January 25, 2011

DOI:10.1021/ja111320n

Understanding electron transport across π−π-stacked systems will help to answer fundamental questions about biochemical redox processes and benefit the design of new materials and molecular devices. Herein we employed the STM break-junction technique to measure the single-molecule conductance of multiple π−π-stacked aromatic rings. We studied electron transport through up to four stacked benzene rings held together in an eclipsed fashion via a paracyclophane scaffold. We found that the strained hydrocarbons studied herein couple directly to gold electrodes during the measurements; hence, we did not require any heteroatom binding groups as electrical contacts. Density functional theory-based calculations suggest that the gold atoms of the electrodes bind to two neighboring carbon atoms of the outermost cyclophane benzene rings in η2 fashion. Our measurements show an exponential decay of the conductance with an increasing number of stacked benzene rings, indicating a nonresonant tunneling mechanism. Furthermore, STM tip−substrate displacement data provide additional evidence that the electrodes bind to the outermost benzene rings of the π−π-stacked molecular wires.

Highly Conducting π-Conjugated Molecular Junctions Covalently Bonded to Gold Electrodes

Co-reporter:Wenbo Chen ; Jonathan R. Widawsky ; Héctor Vázquez ; Severin T. Schneebeli ; Mark S. Hybertsen ; Ronald Breslow ;Latha Venkataraman

Journal of the American Chemical Society 2011 Volume 133(Issue 43) pp:17160-17163

Publication Date(Web):September 22, 2011

DOI:10.1021/ja208020j

We measure electronic conductance through single conjugated molecules bonded to Au metal electrodes with direct Au–C covalent bonds using the scanning tunneling microscope based break-junction technique. We start with molecules terminated with trimethyltin end groups that cleave off in situ, resulting in formation of a direct covalent σ bond between the carbon backbone and the gold metal electrodes. The molecular carbon backbone used in this study consist of a conjugated π system that has one terminal methylene group on each end, which bonds to the electrodes, achieving large electronic coupling of the electrodes to the π system. The junctions formed with the prototypical example of 1,4-dimethylenebenzene show a conductance approaching one conductance quantum (G0 = 2e2/h). Junctions formed with methylene-terminated oligophenyls with two to four phenyl units show a 100-fold increase in conductance compared with junctions formed with amine-linked oligophenyls. The conduction mechanism for these longer oligophenyls is tunneling, as they exhibit an exponential dependence of conductance on oligomer length. In addition, density functional theory based calculations for the Au–xylylene–Au junction show near-resonant transmission, with a crossover to tunneling for the longer oligomers.

A likely possible origin of homochirality in amino acids and sugars on prebiotic earth

Co-reporter:Ronald Breslow

Tetrahedron Letters 2011 Volume 52(Issue 17) pp:2028-2032

Publication Date(Web):27 April 2011

DOI:10.1016/j.tetlet.2010.08.094

For life to start on earth and elsewhere, it is critical that the building blocks—amino acids and sugars—be in predominant homochiral form. Over the past century, the origin of terrestrial prebiotic homochirality has been the subject of many speculations. In this Letter I summarize the experimental evidence for ways in which some meteoritic components could have led to the dominance of l amino acids and d sugars on earth, and the most likely way in which the original chiral excesses in the meteorites were formed.

The origin of homochirality in amino acids and sugars on prebiotic earth

Co-reporter:Ronald Breslow

Tetrahedron Letters 2011 Volume 52(Issue 32) pp:4228-4232

Publication Date(Web):10 August 2011

DOI:10.1016/j.tetlet.2011.06.002

For life to start on earth and elsewhere, it is critical that the building blocks—amino acids and sugars—be in predominant homochiral form. Over the past century the origin of terrestrial prebiotic homochirality has been the subject of many speculations. In this Letter I summarize the experimental evidence for ways in which some meteoritic components could have led to the dominance of l amino acids and d sugars on earth, and the most likely way in which the original chiral excesses in the meteorites were formed.Figure optionsDownload full-size imageDownload as PowerPoint slide

Erratum to “The origin of homochirality in amino acids and sugars on prebiotic Earth” [Tetrahedron Letters 52 (2011) 2028-2032]

Co-reporter:Ronald Breslow

Tetrahedron Letters 2011 Volume 52(Issue 32) pp:4227

Publication Date(Web):10 August 2011

DOI:10.1016/j.tetlet.2011.06.001

Formation of L Amino Acids and D Sugars, and Amplification of their Enantioexcesses in Aqueous Solutions, Under Simulated Prebiotic Conditions

Co-reporter:Ronald Breslow

Israel Journal of Chemistry 2011 Volume 51( Issue 10) pp:990-996

Publication Date(Web):

DOI:10.1002/ijch.201100019

Abstract

The Murchison meteorite delivered five α-methyl amino acids to Earth with small excesses of the L enantiomer; later, additional examples were found and such compounds were also found in other meteorites. I describe our work using them under prebiotic conditions to form normal proteinogenic amino acids with an excess of the L enantiomers, and to amplify such excesses to dominant concentration in solution. I also extend this work to show how D sugars, such as D-ribose, can have been formed and amplified in solution. I also show the high concentration amplifications of D-nucleosides that can be obtained under credible prebiotic conditions. The simple theory of such amplifications, and corrections resulting from solvation effects, are described along with modern ideas of the source of such α-methyl amino acids in meteorites.

Structure–property relationships in molecular wires

Co-reporter:Ronald Breslow, Severin T. Schneebeli

Tetrahedron 2011 67(52) pp: 10171-10178

Publication Date(Web):

DOI:10.1016/j.tet.2011.08.008

Artificial enzymes, cancer chemotherapy, conjugation and nanoelectronics, and prebiotic chemistry

Co-reporter:Ronald Breslow

Science China Chemistry 2011 Volume 54( Issue 12) pp:1803-1814

Publication Date(Web):2011 December

DOI:10.1007/s11426-011-4375-y

This is a summary, with extensive references, of several areas of chemistry in which the Breslow lab has been involved, leading to work still underway in several of them. The principal conclusions are described, but it will be necessary to consult the references for details of the work involved.

The Electrical Properties of Biphenylenes

Co-reporter:Severin Schneebeli, Maria Kamenetska, Frank Foss, Hector Vazquez, Rachid Skouta, Mark Hybertsen, Latha Venkataraman, and Ronald Breslow

Organic Letters 2010 Volume 12(Issue 18) pp:4114-4117

Publication Date(Web):August 19, 2010

DOI:10.1021/ol1017036

The effect of the partial antiaromaticity of biphenylene on its substitution chemistry, its oxidation potential, and its single-molecule conductance is explored. Biphenylene and fluorene molecules with linkers of two amino groups or two cyclic thioether groups were synthesized and their conduction properties were investigated using scanning tunneling microscopy (STM) break-junction techniques and DFT calculations. Despite the partial antiaromaticity of biphenylene, which causes the biphenylenes to be much more easily oxidizable, no significant increase in molecular conductance was found.

A mimic of the pyruvate dehydrogenase complex

Co-reporter:Huanyu Zhao, Ronald Breslow

Bioorganic & Medicinal Chemistry Letters 2010 Volume 20(Issue 20) pp:5973-5975

Publication Date(Web):15 October 2010

DOI:10.1016/j.bmcl.2010.08.077

Pyruvic acid undergo decarboxylation catalyzed by a hydrophobic thiazolium salt and reacts with a hydrophobic analog of lipoic acid to form a hydrophobic acylthioester that reacts with aniline to form acetanilide in water, but only in the presence of a hydrophobically modified polyaziridine that acts to gather the reactants just as the enzyme complex does.

L-amino acids catalyze the formation of an excess of D-glyceraldehyde, and thus of other D sugars, under credible prebiotic conditions

Co-reporter:Ronald Breslow;Zhan-Ling Cheng

PNAS 2010 Volume 107 (Issue 13 ) pp:5723-5725

Publication Date(Web):2010-03-30

DOI:10.1073/pnas.1001639107

Previous work by us, and others, has shown that the formation of amino acids on prebiotic earth with the geometric arrangement called the L configuration can be understood. Some meteorites of the carbonaceous chondritic type deliver unusual amino acids, with alpha-methyl groups, which have an excess of the L isomers. We previously showed that in decarboxylative transamination reactions under credible prebiotic conditions they produce normal amino acids that also have a preference for the L isomer, as is found in our proteins. We, and others, showed that as little as a 1% excess of the L isomers could be amplified up to a 95/5 ratio of L over D on simple evaporation of a solution, so life could start with such a solution in which the dominant L isomers would be selectively chosen. We now find that the geometry of sugars referred to D, as in D-ribose or D-glucose, is not an independent mystery. D-glyceraldehyde, the simplest sugar with a D center, is the basic unit on which other sugars are built. We find that the synthesis of glyceraldehyde by reaction of formaldehyde with glycolaldehyde is catalyzed under prebiotic conditions to D/L ratios greater than 1, to as much as 60/40, by a representative group of L-amino acids (with the exception of L-proline). The D/L glyceraldehyde ratio in water solution is amplified to 92/8 using simple selective solubilities of the D and the DL forms. This D center would then be carried into the prebiotic syntheses of larger sugars.

Imitating Prebiotic Homochirality on Earth

Co-reporter:Ronald Breslow;Mindy Levine

Origins of Life and Evolution of Biospheres 2010 Volume 40( Issue 1) pp:

Publication Date(Web):2010 February

DOI:10.1007/s11084-009-9179-0

We show how the amino acids needed on prebiotic earth in their homochiral L form can be produced by a reaction of L-alpha-methyl amino acids—that have been identified in the Murchison meteorite—with alpha-keto acids under credible prebiotic conditions. When they are simply heated together they perform a process of decarboxylative transamination but with almost no chiral transfer, and that in the wrong direction, producing D-amino acids from the L-alpha-methyl amino acids. With copper ion a square planar complex with two of the reaction intermediates is formed, and now there is the desired L to L transformation, producing small enantioexcesses of the normal L-amino acids. We also show how these can be amplified, not by making more of the L form but by increasing its concentration in water solution. The process can start with a miniscule excess and in one step generate water solutions with L/D ratios in the over 90% region. Kinetic processes can exceed the results from equilibria. We have also examined such amplifications with ribonucleosides, and have shown that initial modest excesses of the D-nucleosides can be amplified to afford water solutions with D to L ratios in the high 90’s. We have shown that the homochiral compound has two effects on the solubility of the racemate. On one hand it decreases the solubility of the racemate by its role in the solubility product, as a theoretical equation predicts. On the other hand, it increases the solubility of the racemate by changing the nature of the solvent, acting as a cosolvent with the water. This explains why the amplification, while large, is not as large as the simple theoretical equation predicts. Thus when credible examples are produced where small enantioexcesses of D-ribose are created under credible prebiotic conditions, the prerequisites for the RNA world will have been exemplified.

High Rates and Substrate Selectivities in Water by Polyvinylimidazoles as Transaminase Enzyme Mimics with Hydrophobically Bound Pyridoxamine Derivatives as Coenzyme Mimics

Co-reporter:Rachid Skouta ; Sujun Wei

Journal of the American Chemical Society 2009 Volume 131(Issue 43) pp:15604-15605

Publication Date(Web):October 13, 2009

DOI:10.1021/ja9072589

Free-radical polymers of 4-vinylimidazole and copolymers with 1-dodecyl-4-vinylimidazole were used as enzyme mimics to transaminate pyruvic acid to alanine, phenylpyruvic acid to phenylalanine, and indole-3-pyruvic acid to tryptophan in water at pH 7.5 and 20 °C using pyridoxamines carrying hydrophobic side chains as coenzyme mimics. The best enzyme mimic accelerated the transamination of indole-3-pyruvic acid by a factor of 4 million relative to the rate without the polymer, a higher rate ratio than we had previously achieved with a polyaziridine-based enzyme mimic. The properties of various polyvinylimidazoles were compared, including those prepared with the RAFT modification of the polymerization process.

Dendrimers in solution can have their remote catalytic groups folded back into the core: Enantioselective transaminations by dendritic enzyme mimics-II

Co-reporter:Sujun Wei, Jianing Wang, Scott Venhuizen, Rachid Skouta, Ronald Breslow

Bioorganic & Medicinal Chemistry Letters 2009 Volume 19(Issue 19) pp:5543-5546

Publication Date(Web):1 October 2009

DOI:10.1016/j.bmcl.2009.08.061

PAMAM dendrimers with double thioether arms have been synthesized with a pyridoxamine core and terminal chiral amino groups. Transamination to afford natural isomers of phenylalanine and alanine induced enantioselectivity by the peripheral chiral caps, supporting a computer model that indicates folding of dendrimer chains back into the core.PAMAM dendrimers, which have double thioether arms, have been synthesized with a pyridoxamine core and chirally terminal amino groups. Transamination to afford natural isomers of phenylalanine and alanine induced enantioselectivity by the peripheral chiral caps, supporting a computer model that indicates folding of dendrimer chains back into the core.

Reply to Bada: The relevance of meteoritic alpha-methyl amino acids to prebiotic homochirality

Co-reporter:Ronald Breslow

PNAS 2009 Volume 106 (Issue 32 ) pp:E86

Publication Date(Web):2009-08-11

DOI:10.1073/pnas.0907800106

On the origin of terrestrial homochirality for nucleosides and amino acids

Co-reporter:Ronald Breslow;Zhan-Ling Cheng

PNAS 2009 Volume 106 (Issue 23 ) pp:9144-9146

Publication Date(Web):2009-06-09

DOI:10.1073/pnas.0904350106

Before life could start on earth, it was important that the amino acid building blocks be present in a predominant handedness called the L configuration and that the ribose of RNA be predominantly in the D configuration. Because ordinary chemical processes would produce them in equal L and D amounts, it has long been a puzzle how the needed selectivities could have arisen. Carbonaceous chondrites such as the Murchison meteorite, which landed in Australia in 1969, brought some unusual amino acids with a methyl group replacing their α hydrogen. They cannot racemize and have a small but real excess of those with the L configuration. We have shown that they can partake in a synthesis of normal L amino acids under credible prebiotic conditions. We and others showed that small preferences can be amplified into solutions with very high dominance of the L amino acids because of the higher solubility of the pure L form than of the more stable DL racemic compound crystal. Here, we show that such solubility-based amplification of small excesses of three D nucleosides, uridine, adenosine, and cytidine, can also occur to form solutions with very high D dominance under credible prebiotic conditions. Guanosine crystallizes as a conglomerate and does not amplify in this way. However, under prebiotic conditions it could have been formed from homochiral D ribose from the hydrolysis of amplified adenosine or cytidine.

The hydrophobic effect in reaction mechanism studies and in catalysis by artificial enzymes

Co-reporter:Ronald Breslow

Journal of Physical Organic Chemistry 2006 Volume 19(Issue 12) pp:813-822

Publication Date(Web):29 NOV 2006

DOI:10.1002/poc.1037

Water is an environmentally benign solvent, easily cleaned and with a harmless vapor, so there is great interest in using water in chemical manufacturing. However, water also has important special properties as a solvent, with the hydrophobic effect promoting rapid and selective reactions in addition reactions, atom transfer reactions, and substitutions. The presence of the hydrophobic effect can be determined with the addition of prohydrophobic and antihydrophobic materials to the water solution. Using such materials, it is possible to determine the detailed geometry of transition states for a number of classical reactions, including alkylation of phenoxide ions on oxygen and carbon. The factors involved, particularly the effect of antihydrophobic agents such as ethanol in lowering the free energy of non-polar reactants, have not been taken into account in previous well-known mechanistic studies. Copyright © 2006 John Wiley & Sons, Ltd.

Water Exclusion and Enantioselectivity in Catalysis

Co-reporter:Ronald Breslow Dr.;Subhajit Byopadhyay Dr.;Mindy Levine;Wenjun Zhou

ChemBioChem 2006 Volume 7(Issue 10) pp:

Publication Date(Web):15 SEP 2006

DOI:10.1002/cbic.200600120

High and dry. Enzymes perform catalyses in the interior of the protein, which is not aqueous in character. Polyethylenimine enzyme mimics with a hydrophobic core also achieve high rates by excluding water. Two different approaches to the synthesis of such artificial enzymes with chirally attached side chains are described, as well as the use of these enzymes in performing biomimetic transaminations with chiral selectivity

Transamination by Polymeric Enzyme Mimics

Co-reporter:Wenjun Zhou;Lei Liu

Helvetica Chimica Acta 2003 Volume 86(Issue 11) pp:3560-3567

Publication Date(Web):24 NOV 2003

DOI:10.1002/hlca.200390300

Pyridoxamine was linked to a series of polyethylenimines (PEIs) with M_n=600, 1800, 10,000, and 60,000, both simply permethylated and with additional attached dodecyl chains. They were examined in the transamination of pyruvic acid and of phenylpyruvic acid, and showed MichaelisMenten behavior. The values of k₂ and of K_M determined showed only small variations with polymer size. Thus, the previously reported strong advantage of pyridoxamines attached to the M_n=60,000 PEI, relative to simple pyridoxamine alone, is seen to almost the same extent with the smaller PEIs.

The hydroxylation and amidation of equilenin acetate catalyzed by chloro[5,10,15,20-tetrakis(pentafluorophenyl)porphyrinato]manganese(III)

Co-reporter:Jerry Yang, Richard Weinberg and Ronald Breslow

Chemical Communications 2000 (Issue 7) pp:531-532

Publication Date(Web):13 Mar 2000

DOI:10.1039/B000463O

The aromatic steroid equilenin acetate undergoes regioselective and stereoselective hydroxylation and amidation catalyzed by a manganese porphyrin using iodosobenzene (PhIO) and N-tosyliminophenyliodinane (PhINTs) as the oxygen and nitrogen donor, respectively.

Selective disruption of protein aggregation by cyclodextrin dimers

Co-reporter:Zhiwei Yang;David K. Leung

PNAS 2000 Volume 97 (Issue 10 ) pp:5050-5053

Publication Date(Web):2000-05-09

DOI:10.1073/pnas.97.10.5050

β-Cyclodextrin (CD) dimers (n = 11) were synthesized and tested against eight enzymes, seven of which were dimeric or tetrameric, for inhibitor activity. Initial screening showed that only l-lactate dehydrogenase and citrate synthase were inhibited but only by two specific CD dimers in which two β-CDs were linked on the secondary face by a pyridine-2,6-dicarboxylic group. Further investigation suggested that these CD dimers inhibit the activity of l-lactate dehydrogenase and citrate synthase at least in part by disruption of protein–protein aggregation.

Selective Hydroxylation of a Steroid at C-9 by an Artificial Cytochrome P-450

Co-reporter:Jerry Yang Dr.

Angewandte Chemie 2000 Volume 112(Issue 15) pp:

Publication Date(Web):2 AUG 2000

DOI:10.1002/1521-3757(20000804)112:15<2804::AID-ANGE2804>3.0.CO;2-U

Aromaticity Decreases Single-Molecule Junction Conductance.

Co-reporter:Wenbo Chen ; Haixing Li ; Jonathan R. Widawsky ; Chandrakumar Appayee ; Latha Venkataraman

Journal of the American Chemical Society () pp:

Publication Date(Web):January 7, 2014

DOI:10.1021/ja411143s