Co-reporter:James Carsella;Igor Melnykov
JBIC Journal of Biological Inorganic Chemistry 2017 Volume 22( Issue 5) pp:751-763
Publication Date(Web):26 April 2017
DOI:10.1007/s00775-017-1457-0
Se is an environmental concern as it can be toxic if present in high concentrations even though it is a dietary requirement for all animals. Se levels are a special concern in the Fountain Creek Watershed located in southeastern Colorado whose geological source is the Se-rich Pierre Shale. Segments of Fountain Creek have Se water levels that exceed the current EPA limit of 5 µg/l. In the studies described here, the effects of river water containing selenium were examined on fish populations at different sites along the Fountain Creek Watershed. Based on the hypothesis that high levels of Se present in the Creek and resident bryophytes should be an indicator of diversity in the river fish we explored the possibility that the low toxicity of the selenium could be due to speciation. A speciation analysis was conducted to determine the selenium(IV) and selenium(VI). Our results show that sites with higher ratios of the more toxic Se(IV) relative to total selenium exhibit lower fish diversity and number of fish. Our results indicate that factors, other than total Se, such as Se speciation may be involved in controlling the bioavailability and toxicity of this element to aquatic organisms in Fountain Creek.
Co-reporter:Debbie C. Crans, Benjamin J. Peters, Xiao Wu, Craig C. McLauchlan
Coordination Chemistry Reviews 2017 Volume 344(Volume 344) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.ccr.2017.03.016
•Solid-state anion/cation organization can provide information for solution systems.•Microenvironments exist in Na+/decavanadate structures in chemistry and mineralogy.•Microenvironment bonding patterns in decavanadate solid-state materials vary.•Experimental and computational organization in nanoscale micellar water droplet.•Crystal structure data are used to convey structure in the nanoscale liquid(aq) phase.Bonding is commonly examined in the solid state and determined by placement of atoms and molecules. Bonding in solution is equally important but much less accessible because these systems are more fluid and thus difficult to characterize the exact bonding motifs. This paper gleans information from the bonding in solid-state structures including more complex mineral systems with varying microenvironments to the bonding within inhomogeneous solutions at the nanoscale. The analysis for the solid state uses structurally well-described anion systems combined with a range of cations and their association in the solid state of both synthetic and naturally-occurring materials, minerals. Detailed solid-state structural information is available on the >180 decavanadate structures reported, however, because the structures will be compared with aqueous nanodroplets of dissolved decavanadate captured within reverse micelles, the abundant Na+ cations stabilizing the reverse micellar interface formed with anionic surfactant focuses the current comparison to Na+-containing materials. As a result the structures observed for the Na+-containing decavanadate materials led to identification of the Na+-containing subclusters and the information is used to provide information on the decavanadate in nanosized water droplets found when a decavanadate anion associating with an Na+ interface in a bis-2-ethylhexyl-sulfosuccinate (AOT) reverse micelles.Download high-res image (97KB)Download full-size image
Co-reporter:Debbie C. Crans
Coordination Chemistry Reviews 2017 Volume 352(Volume 352) pp:
Publication Date(Web):1 December 2017
DOI:10.1016/j.ccr.2017.11.008
Co-reporter:James R. McKone, Debbie C. Crans, Cheryl Martin, John Turner, Anil R. Duggal, and Harry B. Gray
Inorganic Chemistry 2016 Volume 55(Issue 18) pp:9131-9143
Publication Date(Web):September 8, 2016
DOI:10.1021/acs.inorgchem.6b01097
A clear challenge for the coming decades is decreasing the carbon intensity of the global energy supply while simultaneously accommodating a rapid worldwide increase in power demand. Meeting this challenge of providing abundant, clean energy undoubtedly requires synergistic efforts between basic and applied researchers in the chemical sciences to develop and deploy new technologies. Among the available options, solar energy is one of the promising targets because of the high abundance of solar photons over much of the globe. Similarly, decarbonization of the global energy supply will require clean sources of hydrogen to use as reducing equivalents for fuel and chemical feedstocks. In this report, we discuss the importance of translational research—defined as work that explicitly targets basic discovery as well as technology development—in the context of photovoltaics and solar fuels. We focus on three representative research programs encompassing translational research in government, industry, and academia. We then discuss more broadly the benefits and challenges of translational research models and offer recommendations for research programs that address societal challenges in the energy sector and beyond.
Co-reporter:Irma Sánchez-Lombardo, Bharat Baruah, Santiago Alvarez, Katarina R. Werst, Nicole A. Segaline, Nancy E. Levinger and Debbie C. Crans
New Journal of Chemistry 2016 vol. 40(Issue 2) pp:962-975
Publication Date(Web):30 Sep 2015
DOI:10.1039/C5NJ01788B
Polyoxometalates can serve as versatile catalysts in aqueous media. Solvation of these compounds is critical to their catalytic properties. In the studies reported here, we employ 51V NMR spectroscopy, dynamic light scattering and continuous shape measure analysis to probe the solvation of two polyoxometalates, decavanadate and monomolybdononavanadate, encapsulated in reverse micelles. The 51V NMR chemical shift reports on the protonation state of the oxometalate while its linewidth reveals the local environment sensed by the oxometalate in the reverse micelle. We have shown that placement of decavanadate in several protonation states in a microemulsion results in spectroscopic observation of the deprotonated [V10O28]6− (V10) molecule (Baruah, et al., J. Am. Chem. Soc., 2006, 128(39), 12758–12765). Previous studies have shown that the oxometalate requires at least 2–3 layers of water to stabilize it in the reverse micelles and present work shows that no differences are observed whether oxometalate has a charge of −5 or −6. The dynamic light scattering studies demonstrate that the size of the reverse micelles containing polyoxometalate does not change significantly upon loading. Finally, continuous shape measure (CShM) further describes the structural perturbation of V10 as one of the V-atoms is replaced with a heteroatom. CShM analysis shows minor structural perturbation of the oxovanadate core with heteroatom replacements even though the charge and thus overall polarity of the anion changes. Similarly, the continuous shape measure analysis of protonated forms of V10 show that the variation related to protonation of the V10 anion does not significantly change the shapes of the different classes of vanadium atoms within the compact oxoanion even though the charge and thus overall polarity of the anion changes. Thus, the change in shape and steric interactions are very minor because any change in geometry is counteracted by changes elsewhere in the structure. This study represents the first application of shape measures to oxometalates. Because size and shape could both be critical for interaction with interfaces, two differently charged oxometalates are placed in a nanosized water droplet to investigate how they are solvated. Because little change was observed in the 51VNMR spectra and smaller changes were found in the size, we conclude that the shape was most important for this interaction and that changes in charge appeared to have a smaller impact on the system.
Co-reporter:Kaitlin A. Doucette, Kelly N. Hassell, Debbie C. Crans
Journal of Inorganic Biochemistry 2016 Volume 165() pp:56-70
Publication Date(Web):December 2016
DOI:10.1016/j.jinorgbio.2016.09.013
•Drug efficacy can be approved by consideration of the metal ion.•Vanadium compounds serve as excellent model systems illustrating the importance of speciation.•The changes in speciation of cisplatin encapsulated by liposome improve efficacy: Lipoplatin.•Platinum(IV) compounds are inert and more stable changing speciation and improving efficacy.•Speciation chemistry should be a strategy included in development of new anticancer drugs.Improving efficacy and lowering resistance to metal-based drugs can be addressed by consideration of the coordination complex speciation and key reactions important to vanadium antidiabetic drugs or platinum anticancer drugs under biological conditions. The methods of analyses vary depending on the specific metal ion chemistry. The vanadium compounds interconvert readily, whereas the reactions of the platinum compounds are much slower and thus much easier to study. However, the vanadium species are readily differentiated due to vanadium complexes differing in color. For both vanadium and platinum systems, understanding the processes as the compounds, Lipoplatin and Satraplatin, enter cells is needed to better combat the disease; there are many cellular metabolites, which may affect processing and thus the efficacy of the drugs. Examples of two formulations of platinum compounds illustrate how changing the chemistry of the platinum will result in less toxic and better tolerated drugs. The consequence of the much lower toxicity of the drug, can be readily realized because cisplatin administration requires hospital stay whereas Lipoplatin can be done in an outpatient manner. Similarly, the properties of Satraplatin allow for development of an oral drug. These forms of platinum demonstrate that the direct consequence of more selective speciation is lower side effects and cheaper administration of the anticancer agent. Therefore we urge that as the community goes forward in development of new drugs, control of speciation chemistry will be considered as one of the key strategies in the future development of anticancer drugs.Metal-based drug efficacy can be improved by optimizing the coordination chemistry. Vanadium-based drugs illustrate the principles of speciation and these concepts are applied to platinum drugs. Speciation of cisplatin illustrates that more selective speciation reduces side effects and leads to cheaper health care. Future drug development should include speciation considerations.
Co-reporter:Craig C. McLauchlan, Benjamin J. Peters, Gail R. Willsky, Debbie C. Crans
Coordination Chemistry Reviews 2015 Volumes 301–302() pp:163-199
Publication Date(Web):15 October 2015
DOI:10.1016/j.ccr.2014.12.012
•Vanadate and vanadium compounds are potent inhibitors of phosphatases.•Five-coordinate vanadium covalently attached to the protein is most common.•Vanadium–protein complexes usually have vanadium in the trigonal bipyramidal geometry.•The potency of V inhibitors is not likely to change much as the ligand changes.Over the past two decades increasing information about the function and structural detail of phosphatases has become available detailing the interaction with vanadate or other vanadium compounds. Considering the importance of the phosphorylation reaction in signal transductions the structural details of the interaction of vanadate or other vanadium species with many phosphatases are used to provide information on the nature of successful inhibitors of these enzymes. Analysis shows that most of the available X-ray structures of vanadium–phosphatase complexes contain vanadium with five coordinating atoms in trigonal bipyramidal coordination geometries even though corresponding small molecule analog compounds may have square pyramidal geometries. This finding for the static structures in their solid state documents the fact that the variety of phosphatases all stabilize a vanadium geometry that is closer to the trigonal bipyramidal geometry than square pyramidal geometry. We also review the efficacy of vanadium-based inhibitors and examine both oxometalates and vanadium coordination complexes. The evaluation of the inhibitory efficacies of the oxometalates provides the opportunity to identify product-based inhibitors and transition-state-based inhibitors. Whether initial coordination geometry is important to inhibitor design geometry was examined. For vanadium–phosphatase complexes, regardless of what form was added to the protein crystal in all but one case vanadate was found bound in the phosphatase. Because of speciation considerations and prior hydrolysis of potential vanadium complexes, this result may be a consequence of the experimental conditions. With regard to inhibition we find that the coordination geometry of the starting complex does not need to be trigonal bipyramidal to result in a effective phosphatase inhibitor and that all reported phosphatase inhibitors span a range of only three orders of magnitude in Ki across all phosphatases examined.
Co-reporter:Debbie C. Crans, Andrew Ghio, Valeria Conte
Journal of Inorganic Biochemistry 2015 Volume 147() pp:1-3
Publication Date(Web):June 2015
DOI:10.1016/j.jinorgbio.2015.05.006
Co-reporter:Irma Sánchez-Lombardo, Santiago Alvarez, Craig C. McLauchlan, Debbie C. Crans
Journal of Inorganic Biochemistry 2015 Volume 147() pp:153-164
Publication Date(Web):June 2015
DOI:10.1016/j.jinorgbio.2015.04.005
•Shape analysis evaluated the geometry of V–phosphatase complexes vs. a trigonal bipyramid.•The shape analysis was superior to an analysis based on the t (tau)-value calculations.•5-Coordinate vanadium in protein complexes was trigonal bipyramidal and not square pyramidal.•The umbrella pathway distortions are observed during phosphoryl group transfer reactions.Shape analysis of coordination complexes is well-suited to evaluate the subtle distortions in the trigonal bipyramidal (TBPY-5) geometry of vanadium coordinated in the active site of phosphatases and characterized by X-ray crystallography. Recent studies using the tau (τ) analysis support the assertion that vanadium is best described as a trigonal bipyramid, because this geometry is the ideal transition state geometry of the phosphate ester substrate hydrolysis (C.C. McLauchlan, B.J. Peters, G.R. Willsky, D.C. Crans, Coord. Chem. Rev. http://dx.doi.org/10.1016/j.ccr.2014.12.012 ; D.C. Crans, M.L. Tarlton, C.C. McLauchlan, Eur. J. Inorg. Chem. 2014, 4450–4468). Here we use continuous shape measures (CShM) analysis to investigate the structural space of the five-coordinate vanadium–phosphatase complexes associated with mechanistic transformations between the tetrahedral geometry and the five-coordinate high energy TBPY-5 geometry was discussed focusing on the protein tyrosine phosphatase 1B (PTP1B) enzyme. No evidence for square pyramidal geometries was observed in any vanadium–protein complexes. The shape analysis positioned the metal ion and the ligands in the active site reflecting the mechanism of the cleavage of the organic phosphate in a phosphatase. We identified the umbrella distortions to be directly on the reaction path between tetrahedral phosphate and the TBPY-5-types of high-energy species. The umbrella distortions of the trigonal bipyramid are therefore identified as being the most relevant types of transition state structures for the phosphoryl group transfer reactions for phosphatases and this may be related to the possibility that vanadium is an inhibitor for enzymes that support both exploded and five-coordinate transition states.Shape analysis of coordination complexes was used to evaluate distortions in the trigonal bipyramidal geometry of vanadium coordinated in the X-ray crystallographically-characterized active sites of phosphatases. These studies identified the umbrella distortions to be directly on the reaction path between tetrahedral phosphate and the trigonal bipyramid transition state for the phosphoryl group transfer reactions.
Co-reporter:Debbie C. Crans
The Journal of Organic Chemistry 2015 Volume 80(Issue 24) pp:11899-11915
Publication Date(Web):November 6, 2015
DOI:10.1021/acs.joc.5b02229
Studies of antidiabetic vanadium compounds, specifically the organic vanadate esters, are reviewed with regard to their chemistry and biological properties. The compounds are described from the perspective of how the fundamental chemistry and properties of organic vanadate esters impact their effects as inhibitors for phosphatases based on the structural information obtained from vanadium–phosphatase complexes. Vanadium compounds have been reported to have antidiabetic properties for more than a century. The structures and properties of organic vanadate complexes are reviewed, and the potency of such vanadium coordination complexes as antidiabetic agents is described. Because such compounds form spontaneously in aqueous environments, the reactions with most components in any assay or cellular environment has potential to be important and should be considered. Generally, the active form of vanadium remains elusive, although studies have been reported of a number of promising vanadium compounds. The description of the antidiabetic properties of vanadium compounds is described here in the context of recent characterization of vanadate–phosphatase protein structures by data mining. Organic vanadate ester compounds are generally four coordinate or five coordinate with the former being substrate analogues and the latter being transition-state analogue inhibitors. These studies demonstrated a framework for characterization of five-coordinate trigonal bipyramidal vanadium inhibitors by comparison with the reported vanadium−protein phosphatase complexes. The binding of the vanadium to the phosphatases is either as a five-coordinate exploded transition-state analogue or as a high energy intermediate, respectively. Even if potency as an inhibitor requires trigonal bipyramidal geometry of the vanadium when bound to the protein, such geometry can be achieved upon binding from compounds with other geometries. Desirable properties of ligands are identified and analyzed. Ligand interactions, as reported in one peptidic substrate, are favorable so that complementarity between phosphatase and coordinating ligand to the vanadium can be established resulting in a dramatic enhancement of the inhibitory potency. These considerations point to a frameshift in ligand design for vanadium complexes as phosphatase inhibitors and are consistent with other small molecule having much lower affinities. Combined, these studies do suggest that if effective delivery of potentially active antidiabetic compound such a the organic vanadate peptidic substrate was possible the toxicity problems currently reported for the salts and some of the complexes may be alleviated and dramatic enhancement of antidiabetic vanadium compounds may result.
Co-reporter:Debbie C. Crans;Michael L. Tarlton;Craig C. McLauchlan
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 27) pp:4450-4468
Publication Date(Web):
DOI:10.1002/ejic.201402306
Abstract
The five-coordinate geometry is an important factor in phosphoryl group transfer, particularly for phosphate ester hydrolysis. In the following review we analyze the five-coordinate geometries for a range of VO4X coordination spheres with regard to their structure from the point of view of square pyramidal or trigonal bipyramidal geometries. The actual differences for the coordination environment of the reported small molecule structures are compared to the coordination environment of vanadate complexed to a protein tyrosine phosphatase (PTP) with four coordinating O atoms and one S atom. These considerations demonstrate that actual differences between the coordination environments are very small and presumably less critical than generally anticipated. This analysis suggests that it is a combination of structural and electronic properties leading to the perfect combination of reactivity and stability for the potent protein phosphatase inhibitor complex, thus confirming the fact that some other geometries have been reported.
Co-reporter:Debbie C. Crans;Ebbe Nordler
European Journal of Inorganic Chemistry 2014 Volume 2014( Issue 27) pp:4413-4416
Publication Date(Web):
DOI:10.1002/ejic.201402826
Abstract
An overview of the papers in this cluster issue is presented. “It is more than 100 years ago that Alfred Werner developed the research that led to the birth of coordination chemistry as we know it today. The consequences of this seminal work continue to evolve, documenting that not only structural and electronic effects but also perhaps, most importantly, the application of coordination chemistry remain as timely and current now as it was back then.”
Co-reporter:Dr. Audra G. Sostarecz;Dr. Ernestas Gaidamauskas ;Steve Distin; Sra J. Bonetti ; Nancy E. Levinger; Debbie C. Crans
Chemistry - A European Journal 2014 Volume 20( Issue 17) pp:5149-5159
Publication Date(Web):
DOI:10.1002/chem.201201803
Abstract
We explore the interactions of VIII-, VIV-, and VV-2,6-pyridinedicarboxylic acid (dipic) complexes with model membrane systems and whether these interactions correlate with the blood-glucose-lowering effects of these compounds on STZ-induced diabetic rats. Two model systems, dipalmitoylphosphatidylcholine (DPPC) Langmuir monolayers and AOT (sodium bis(2-ethylhexyl)sulfosuccinate) reverse micelles present controlled environments for the systematic study of these vanadium complexes interacting with self-assembled lipids. Results from the Langmuir monolayer studies show that vanadium complexes in all three oxidation states interact with the DPPC monolayer; the VIII–phospholipid interactions result in a slight decrease in DPPC molecular area, whereas VIV and VV–phospholipid interactions appear to increase the DPPC molecular area, an observation consistent with penetration into the interface of this complex. Investigations also examined the interactions of VIII- and VIV-dipic complexes with polar interfaces in AOT reverse micelles. Electron paramagnetic resonance spectroscopic studies of VIV complexes in reverse micelles indicate that the neutral and smaller 1:1 VIV-dipic complex penetrates the interface, whereas the larger 1:2 VIV complex does not. UV/Vis spectroscopy studies of the anionic VIII-dipic complex show only minor interactions. These results are in contrast to behavior of the VV-dipic complex, [VO2(dipic)]−, which penetrates the AOT/isooctane reverse micellar interface. These model membrane studies indicate that VIII-, VIV-, and VV-dipic complexes interact with and penetrate the lipid interfaces differently, an effect that agrees with the compounds’ efficacy at lowering elevated blood glucose levels in diabetic rats.
Co-reporter:Debbie C. Crans ; Kellie A. Woll ; Kestutis Prusinskas ; Michael D. Johnson ;Eugenijus Norkus
Inorganic Chemistry 2013 Volume 52(Issue 21) pp:12262-12275
Publication Date(Web):September 16, 2013
DOI:10.1021/ic4007873
The influence of metals in biology has become more and more apparent within the past century. Metal ions perform essential roles as critical scaffolds for structure and as catalysts in reactions. Speciation is a key concept that assists researchers in investigating processes that involve metal ions. However, translation of the essential area across scientific fields has been plagued by language discrepancies. To rectify this, the IUPAC Commission provided a framework in which speciation is defined as the distribution of species. Despite these attempts, contributions from inorganic chemists to the area of speciation have not fully materialized in part because the past decade’s contributions focused on technological advances, which are not yet to the stage of measuring speciation distribution in biological solutions. In the following, we describe how speciation influences the area of metals in medicine and how speciation distribution has been characterized so far. We provide two case studies as an illustration, namely, vanadium and iron. Vanadium both has therapeutic importance and is known as a cofactor for metalloenzymes. In addition to being a cation, vanadium(V) has analogy with phosphorus and as such is a potent inhibitor for phosphorylases. Because speciation can change the metal’s existence in cationic or anionic forms, speciation has profound effects on biological systems. We also highlight how speciation impacts iron metabolism, focusing on the rather low abundance of biologically relevant iron cation that actually exists in biological fluids. fluids. Furthermore, we point to recent investigations into the mechanism of Fenton chemistry, and that the emerging results show pH dependence. The studies suggest formation of FeIV-intermediates and that the generally accepted mechanism may only apply at low pH. With broader recognition toward biological speciation, we are confident that future investigations on metal-based systems will progress faster and with significant results. Studying metal complexes to explore the properties of a potential “active species” and further uncovering the details associated with their specific composition and geometry are likely to be important to the action.
Co-reporter:Debbie C. Crans ;Thomas J. Meade
Inorganic Chemistry 2013 Volume 52(Issue 21) pp:12181-12183
Publication Date(Web):November 4, 2013
DOI:10.1021/ic402341n
Co-reporter:Craig C. McLauchlan and Debbie C. Crans
Dalton Transactions 2013 vol. 42(Issue 33) pp:11744-11748
Publication Date(Web):18 Jul 2013
DOI:10.1039/C3DT90107F
A graphical abstract is available for this content
Co-reporter:Abeer Al-Qatati, Fabio L. Fontes, B. George Barisas, Dongmei Zhang, Deborah A. Roess and Debbie C. Crans
Dalton Transactions 2013 vol. 42(Issue 33) pp:11912-11920
Publication Date(Web):16 Jul 2013
DOI:10.1039/C3DT50398D
Vanadium oxides (VOs) have been identified as low molecular weight sensitizing agents associated with occupational asthma and compromised pulmonary immunocompetence. Symptoms of adult onset asthma result, in part, from increased signal transduction by Type I Fcε receptors (FcεRI) leading to release of vasoactive compounds including histamine from mast cells. Exposure to (VOs) typically occurs in the form of particles which are insoluble. Upon contact with water or biological fluids, (VOs) form a series of soluble oxoanions, one of which is decavanadate, V10O286− abbreviated V10, which is structurally related to a common vanadium oxide, that is vanadium pentoxide, V2O5. Here we investigate whether V10 may be initiating plasma membrane events associated with activation of FcεRI signal transduction. We show that exposure of RBL-2H3 cells to V10 causes a concentration-dependent increase in degranulation of RBL-2H3 and, in addition, an increase in plasma membrane lipid packing as measured by the fluorescent probe, di-4-ANEPPDHQ. V10 also increases FcεRI accumulation in low-density membrane fragments, i.e., lipid rafts, which may facilitate FcεRI signaling. To determine whether V10 effects on plasma membrane lipid packing were similarly observed in Langmuir monolayers formed from dipalmitoylphosphatidylcholine (DPPC), the extent of lipid packing in the presence and absence of V10 and vanadate was compared. V10 increased the surface area of DPPC Langmuir monolayers by 6% and vanadate decreased the surface area by 4%. These results are consistent with V10 interacting with this class of membrane lipids and altering DPPC packing.
Co-reporter:Pabitra B. Chatterjee
Inorganic Chemistry 2012 Volume 51(Issue 17) pp:9144-9146
Publication Date(Web):August 10, 2012
DOI:10.1021/ic301026b
Visible light facilitates a solid-to-solid photochemical aerobic oxidation of a hunter-green microcrystalline oxidovanadium(IV) compound (1) to form a black powder of cis-dioxidovanadium(V) (2) at ambient temperature. The siderophore ligand pyridine-2,6-bis(thiocarboxylic acid), H2L, is secreted by a microorganism from the Pseudomonas genus. This irreversible transformation of a metal monooxo to a metal dioxo complex in the solid state in the absence of solvent is unprecedented. It serves as a proof-of-concept reaction for green chemistry occurring in solid matrixes.
Co-reporter:Nancy E. Levinger ; Lauren C. Rubenstrunk ; Bharat Baruah
Journal of the American Chemical Society 2011 Volume 133(Issue 18) pp:7205-7214
Publication Date(Web):April 20, 2011
DOI:10.1021/ja2011737
Water absorption of atmospheric carbon dioxide lowers the solution pH due to carbonic acid formation. Bulk water acidification by CO2 is well documented, but significantly less is known about its effect on water in confined spaces. Considering its prominence as a greenhouse gas, the importance of aerosols in acid rain, and CO2-buffering in cellular systems, surprisingly little information exists about the absorption of CO2 by nanosized water droplets. The fundamental interactions of CO2 with water, particularly in nanosized structures, may influence a wide range of processes in our technological society. Here results from experiments investigating the uptake of gaseous CO2 by water pools in reverse micelles are presented. Despite the small number of water molecules in each droplet, changes in vanadium probes within the water pools, measured using vanadium-51 NMR spectroscopy, indicate a significant drop in pH after CO2 introduction. Collectively, the pH-dependent vanadium probes show CO2 dissolves in the nanowater droplets, causing the reverse micelle acidity to increase.
Co-reporter:Myles A. Sedgwick, Alejandro M. Trujillo, Noah Hendricks, Nancy E. Levinger, and Debbie C. Crans
Langmuir 2011 Volume 27(Issue 3) pp:948-954
Publication Date(Web):December 28, 2010
DOI:10.1021/la103875w
Dynamic light scattering and NMR spectroscopic experimental evidence suggest the coexistence of two compositionally different self-assembled particles in solution. The self-assembled particles form in solutions containing water, Aerosol OT (AOT, sodium bis(2-ethylhexyl) sulfosuccinate) surfactant, and cholesterol in cyclohexane. In a similar series of studies carried out in 1-octanol only one aggregate type, that is, reverse micelles, is observed. Dynamic light scattering measurements reveal the presence of two different types of aggregates in the microemulsions formed in cyclohexane, demonstrating the coexistence of two compositionally distinct structures with very similar Gibbs energies. One particle type consists of standard AOT reverse micelles while the second type of particle consists of submicellar aggregates including cholesterol as well as small amounts of AOT and water. In microemulsions employing 1-octanol as the continuous medium, AOT reverse micelles form in a dispersed solution of cholesterol in 1-octanol. Although the size distribution of self-assembled particles is well-known for many different systems, evidence for simultaneous formation of two distinctly sized particles in solution that are chemically different is unprecedented. The ability to form microemulsion solutions that contain coexisting particles may have important applications in drug formulation and administration, particularly as applied to drug delivery using cholesterol as a targeting agent.
Co-reporter:Dr. R. Dario Falcone;Dr. Bharat Baruah;Dr. Ernestas Gaidamauskas;Dr. Christopher D. Rithner;Dr. N. Mariano Correa; Juana J. Silber; Debbie C. Crans; Nancy E. Levinger
Chemistry - A European Journal 2011 Volume 17( Issue 24) pp:6837-6846
Publication Date(Web):
DOI:10.1002/chem.201002182
Abstract
Microemulsions form in mixtures of polar, nonpolar, and amphiphilic molecules. Typical microemulsions employ water as the polar phase. However, microemulsions can form with a polar phase other than water, which hold promise to diversify the range of properties, and hence utility, of microemulsions. Here microemulsions formed by using a room-temperature ionic liquid (RTIL) as the polar phase were created and characterized by using multinuclear NMR spectroscopy. 1H, 11B, and 19F NMR spectroscopy was applied to explore differences between microemulsions formed by using 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]) as the polar phase with a cationic surfactant, benzylhexadecyldimethylammonium chloride (BHDC), and a nonionic surfactant, Triton X-100 (TX-100). NMR spectroscopy showed distinct differences in the behavior of the RTIL as the charge of the surfactant head group varies in the different microemulsion environments. Minor changes in the chemical shifts were observed for [bmim]+ and [BF4]− in the presence of TX-100 suggesting that the surfactant and the ionic liquid are separated in the microemulsion. The large changes in spectroscopic parameters observed are consistent with microstructure formation with layering of [bmim]+ and [BF4]− and migration of Cl− within the BHDC microemulsions. Comparisons with NMR results for related ionic compounds in organic and aqueous environments as well as literature studies assisted the development of a simple organizational model for these microstructures.
Co-reporter:M. A. Sedgwick, D. C. Crans and N. E. Levinger
Langmuir 2009 Volume 25(Issue 10) pp:5496-5503
Publication Date(Web):April 23, 2009
DOI:10.1021/la8035067
The interiors of reverse micelles formed using nonionic surfactants to sequester water droplets in a nonpolar environment have been investigated using the decavanadate molecule as a probe. Chemical shifts and line widths of the three characteristic signals in the 51V NMR spectrum of decavanadate, corresponding to vanadium atoms in equatorial peripheral, equatorial interior, and axial locations, measure the local proton concentration and characteristics of the reverse micellar interior near the decavandate probe. All samples investigated indicate deprotonation of the vanadate probe in the reverse micelle environment. However, the relative mobility of the decavanadate molecule depends on the reverse micellar components. Specifically, the 51V NMR signals of the decavandate in reverse micelles formed using only the Igepal CO-520 surfactant display sharp signals indicating that the decavandate molecule tumbles relatively freely while reverse micelles formed from a mixture of Igepal CO-610 and -430 present a more viscous environment for the decavanadate molecule; the nature of the interior of the nonionic reverse water pool varies significantly depending on the specific Igepal. The 51V NMR spectra also indicate that the interior core water pool of the reverse micelles is less acidic than the bulk aqueous solution from which the samples were created. Together, these data provide a description that allows for a comparison of the water pools in these different nonionic reverse micelles.
Co-reporter:Debbie C. Crans, Bharat Baruah, Ernestas Gaidamauskas, Brant G. Lemons, Bret B. Lorenz, Michael D. Johnson
Journal of Inorganic Biochemistry 2008 Volume 102(5–6) pp:1334-1347
Publication Date(Web):May 2008
DOI:10.1016/j.jinorgbio.2008.01.015
The anti-oxidant properties of l-ascorbic acid were investigated in the confined medium produced by a sodium bis(2-ethylhexyl)sulfosuccinate (aerosol-OT, AOT) self-assembled reverse micelle. Using 1H–1H NOESY (proton-proton 2D nuclear overhauser enhancement correlation spectroscopy) NMR spectroscopy, the location of ascorbic acid was investigated and found to be at the AOT-interface in contrast to earlier studies where the ascorbate was assumed to be in the water pool in these microemulsions. The reaction of ascorbic acid with oxygen was investigated using EPR spectroscopy. A delocalized monoanionic ascorbate radical was observed in microemulsions prepared from pH 5.6 stock solutions. This is in contrast to studies carried out in aqueous media where no radical formation was observed. The oxidation of ascorbic acid by aqueous V(V) was investigated in reverse micelles. Modest changes in the kinetic parameters were observed for this system compared to that in water. Details of these reactions were examined and can be summarized as the microemulsion solvating and stabilizing reactive intermediates via rate inhibition or enhancement. The inhibition of the oxidation is due to solvation stabilization of ascorbic acid in microemulsion media. Since ascorbate is a valuable marker of oxidative stress, our results suggest that compartmentization can modify the stabilization of the ascorbate radical and the changes in properties could be important in biological systems.
Co-reporter:Michelle L. Stahla, Bharat Baruah, Dustin M. James, Michael D. Johnson, Nancy E. Levinger and Debbie C. Crans
Langmuir 2008 Volume 24(Issue 12) pp:6027-6035
Publication Date(Web):May 17, 2008
DOI:10.1021/la8002965
Simple procedures and characterization of a series of well-defined precursors are described for preparation of a unique microenvironment in nanoreactors, reverse micelles. The Na+, K+, Rb+, Cs+, and Mg2+ surfactants were prepared using liquid–liquid ion exchange using chloride and nitrate salts. The surfactants were characterized using 1H NMR spectroscopy and a variety of other techniques. 1H NMR spectroscopy was found to be a sensitive probe for characterization of the size of the nanoreactor as well as its water content. 1H NMR spectra can be used for detailed characterization of reactions in confined environments when counterion effects are likely to be important. 1H NMR spectroscopy revealed two separate peaks corresponding to water in Mg(AOT)2 samples; one peak arises from water coordinated to the Mg2+ ion while the other peak arises from bulk water. The two water signals arise directly from the slow exchange of the water coordinated to Mg2+ in these microemulsions with water in the water pool, and provide an opportunity to study hydration of Mg2+. This work thus extends the potential use of MAOT microemulsions for applications such as in green chemistry.
Co-reporter:Bharat Baruah, Laura A. Swafford, Debbie C. Crans and Nancy E. Levinger
The Journal of Physical Chemistry B 2008 Volume 112(Issue 33) pp:10158-10164
Publication Date(Web):July 24, 2008
DOI:10.1021/jp800390t
The water inside reverse micelles can differ dramatically from bulk water. Some changes in properties can be attributed to the interaction of water molecules with the micellar interface, forming a layer of shell water inside the reverse micelle. The work reported here monitors changes in intramicellar water through chemical shifts and signal line widths in 51V NMR spectra of a large polyoxometalate probe, decavanadate, and from infrared spectroscopy of isotopically labeled water, to obtain information on the water in the water pool in AOT reverse micelles formed in isooctane. The studies reveal several things about the reverse micellar water pool. First, in agreement with our previous measurements, the proton equilibrium of the decavanadate solubilized within the reverse micelles differs from that in bulk aqueous solution, indicating a more basic environment compared to the starting stock solutions from which the reverse micelles were formed. Below a certain size, reverse micelles do not form when the polyoxometalate is present; this indicates that the polyanionic probe requires a layer of water to solvate it in addition to the water that solvates the surfactant headgroups. Finally, the polyoxometalate probe appears to perturb the water hydrogen-bonding network in a fashion similar to that in the interior surface of the reverse micelles. These measurements demonstrate the dramatic differences possible for water environments in confined spaces.
Co-reporter:Craig C. McLauchlan and Debbie C. Crans
Dalton Transactions 2013 - vol. 42(Issue 33) pp:NaN11748-11748
Publication Date(Web):2013/07/18
DOI:10.1039/C3DT90107F
A graphical abstract is available for this content
Co-reporter:Abeer Al-Qatati, Fabio L. Fontes, B. George Barisas, Dongmei Zhang, Deborah A. Roess and Debbie C. Crans
Dalton Transactions 2013 - vol. 42(Issue 33) pp:NaN11920-11920
Publication Date(Web):2013/07/16
DOI:10.1039/C3DT50398D
Vanadium oxides (VOs) have been identified as low molecular weight sensitizing agents associated with occupational asthma and compromised pulmonary immunocompetence. Symptoms of adult onset asthma result, in part, from increased signal transduction by Type I Fcε receptors (FcεRI) leading to release of vasoactive compounds including histamine from mast cells. Exposure to (VOs) typically occurs in the form of particles which are insoluble. Upon contact with water or biological fluids, (VOs) form a series of soluble oxoanions, one of which is decavanadate, V10O286− abbreviated V10, which is structurally related to a common vanadium oxide, that is vanadium pentoxide, V2O5. Here we investigate whether V10 may be initiating plasma membrane events associated with activation of FcεRI signal transduction. We show that exposure of RBL-2H3 cells to V10 causes a concentration-dependent increase in degranulation of RBL-2H3 and, in addition, an increase in plasma membrane lipid packing as measured by the fluorescent probe, di-4-ANEPPDHQ. V10 also increases FcεRI accumulation in low-density membrane fragments, i.e., lipid rafts, which may facilitate FcεRI signaling. To determine whether V10 effects on plasma membrane lipid packing were similarly observed in Langmuir monolayers formed from dipalmitoylphosphatidylcholine (DPPC), the extent of lipid packing in the presence and absence of V10 and vanadate was compared. V10 increased the surface area of DPPC Langmuir monolayers by 6% and vanadate decreased the surface area by 4%. These results are consistent with V10 interacting with this class of membrane lipids and altering DPPC packing.
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