Acidification of reverse micellar nanodroplets by atmospheric pressure CO2

Water absorption of atmospheric carbon dioxide lowers the solution pH due to carbonic acid formation. Bulk water acidification by CO(2) 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 CO(2)-buffering in cellular systems, surprisingly little information exists about the absorption of CO(2) by nanosized water droplets. The fundamental interactions of CO(2) 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 CO(2) 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 CO(2) introduction. Collectively, the pH-dependent vanadium probes show CO(2) dissolves in the nanowater droplets, causing the reverse micelle acidity to increase.     

Switching off electron transfer reactions in confined media: reduction of [Co(dipic)2]- and [Co(edta)]- by hexacyanoferrate(II)

The kinetics of reduction of two cobalt(III) complexes with similar redox potentials by hexacyanoferrate(II) were investigated in water and in reverse micelle (RM) microemulsions. The RMs were composed of water, surfactant [(sodium(bis(2-ethylhexylsulfosuccinate)), NaAOT], and isooctane. Compared to the reaction in water, the reduction rates of (ethylenediaminetetraacetato)cobaltate(III) by hexacyanoferrate(II) were dramatically suppressed in RM microemulsions whereas a slight rate increase was observed for reduction of bis-(2,6-dipicolinato)cobaltate(III). For example, the ferrocyanide reduction of [Co(dipic)(2)](-) increased from 55 M(-1) s(-1)in aqueous media to 85 M(-1) s(-1) in a w(o) = 20 RM. The one-dimensional (1-D) and two-dimensional (2-D) (1)H NMR and FT-IR studies are consistent with the reduction rate constants of these two complexes being affected by their location within the RM. Since reduction of [Co(edta)](-) is switched off, in contrast to [Co(dipic)(2)](-), these observations are attributed to the penetration of the [Co(edta)](-) into the interfacial region of the RM whereas [Co(dipic)(2)](-) is in a region highly accessible to the water pool and thus hexacyanoferrate(II). These results demonstrated that compartmentalization completely turns off a redox reaction in a dynamic microemulsion system by either reactant separation or alteration of the redox potentials of the reactants.     

The anti-diabetic bis(maltolato)oxovanadium(IV) decreases lipid order while increasing insulin receptor localization in membrane microdomains

The effects of treatment with bis(maltolato)oxovanadium(IV) (BMOV) on protein localization in membrane microdomains were investigated by comparing the effects of insulin and treatment with BMOV on the lateral motions and compartmentalization of individual insulin receptors (IR). In addition, effects of insulin and BMOV on the association of IR, phosphorylated IR (pIR) and phosphorylated insulin receptor substrate-1 (pIRS-1) with chemically-isolated plasma membrane microdomains on rat basophilic leukemia (RBL-2H3) cells were evaluated. Single particle tracking experiments indicate that individual quantum dot-labeled IR on RBL-2H3 cells exhibit relatively unrestricted lateral diffusion of approximately 1 × 10(-10) cm(2) s(-1) and are confined in approximately 475 nm diameter cell-surface membrane compartments. After treating of RBL-2H3 cells with 10 μM BMOV, IR lateral diffusion and the size of IR-containing membrane compartments is significantly reduced to 6 × 10(-11) cm(2) s(-1) and approximately 400 nm, respectively. BMOV treatment also increases the association of IR with low-density, detergent-resistant membrane fragments isolated using isopycnic sucrose-gradient centrifugation from 2.4% for untreated cells to 25.8% for cells treated with 10 μM BMOV. Additionally, confocal fluorescence microscopic imaging of live RBL-2H3 cells labeled with the phase sensitive aminonaphthylethenylpyridinium-based dye, Di-4-ANEPPDHQ, indicates that BMOV treatment, but not insulin treatment, decreases cell-surface plasma membrane lipid order while fluorescence correlation spectroscopy measurements suggest that BMOV treatment does not affect IR surface-density or insulin binding affinity. Finally, model studies using microemulsions of cetyltrimethylammonium bromide (CTAB) micelles and (1)H NMR spectroscopy show that an oxidized form of BMOV readily localizes near the CTAB head-groups at the lipid-water interface. These observations were supported by IR spectroscopic studies using microemulsions of CTAB reverse micelles showing that both BMOV and oxidized BMOV are associated with the water pool. This conclusion is based on changes in (1)H NMR chemical shifts observed for the complex, oxidized BMOV. Moreover, these shifts appeared to be informative about the location of the complex. No differences were observed in the OD absorption peak positions for the CTAB reverse micelles prepared in the presence and absence of BMOV, oxidized BMOV or maltol. Combined, these results suggest that activation of IR signaling by both insulin and BMOV treatment involves increased association of IR with specialized, nanoscale membrane microdomains. The observed insulin-like activity of BMOV or decomposition products of BMOV may be due to changes in cell-surface membrane lipid order rather than due to direct interactions with IR.     

A theoretical evaluation of the synergetic capto-dative stabilisation of free radicals

$\text{Ab initio}$ molecular orbital calculations on the model capto-dative radicals, BH₂- CHNH₂^· and H₂NCHCN^·, demonstrate that simultaneous stabilisation by pi-donor and pi-acceptor substituents is significantly greater than the additive substituent stabilisation energies of the individual groups.     

A unified analysis for a class of long-step primal-dual path-following interior-point algorithms for semidefinite programming

We present a unified analysis for a class of long-step primal-dual path-following algorithms for semidefinite programming whose search directions are obtained through linearization of the symmetrized equation of the central pathH _P (XS) [PXSP ^–1 + (PXSP ^–1) ^T ]/2 = I, introduced by Zhang. At an iterate (X,S), we choose a scaling matrixP from the class of nonsingular matricesP such thatPXSP ^–1 is symmetric. This class of matrices includes the three well-known choices, namely:P = S ^1/2 andP = X ^–1/2 proposed by Monteiro, and the matrixP corresponding to the Nesterov—Todd direction. We show that within the class of algorithms studied in this paper, the one based on the Nesterov—Todd direction has the lowest possible iteration-complexity bound that can provably be derived from our analysis. More specifically, its iteration-complexity bound is of the same order as that of the corresponding long-step primal-dual path-following algorithm for linear programming introduced by Kojima, Mizuno and Yoshise. © 1998 The Mathematical Programming Society, Inc. Published by Elsevier Science B.V.Corresponding author.This author's research is supported in part by the National Science Foundation under grants INT-9600343 and CCR-9700448 and the Office of Naval Research under grant N00014-94-1-0340.This author's research was supported in part by DOE DE-FG02-93ER25171-A001.     

Do probe molecules influence water in confinement?

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.     

Probing of ferrocenylanilines on model micelle/reverse micelle membrane and their enhanced reactivity for reactive oxidants

Reactive oxygen species are formed in the human body but can be removed by suitable antioxidants. In this study we synthesized and characterized three ferrocene derivatives, 4‐ferrocenylaniline (pFA), 3‐ferrocenylaniline (mFA) and 3‐methyl‐4‐ferrocenylaniline (MeFA), having significant potential to be used as antioxidants. The synthesized compounds are insoluble in water, with the solubility of these compounds increasing in micelle solution. The micelle and reverse micelle solutions were considered as model membranes. The synthesized compounds were probed on the model membranes, made by sodium dioctylsulfosuccinate reverse micelle and tetradecyltrimethylammonium bromide micelle, using ¹H NMR spectroscopy. The ¹H NMR results indicated that these compounds are present in the polar region of the model membrane interface. Quantitative measurements showed that mFA has the greatest ability to penetrate into the micelle membrane among these compounds, and pFA is least penetrating in this respect. Solubilization of these compounds in aqueous micelle solution facilitates crystallization (of mFA) and enhances the antioxidant potential of these compounds. X‐ray crystal structure analysis revealed that mFA captures water molecules during crystallization in micelle solution. Their ability to act as antioxidants was evaluated, in dimethylsulfoxide (DMSO) and in micelle solution, using standard 1,1‐ diphenyl‐2‐picrylhydrazyl (DPPH) assay. It was found that their antioxidant potential is good in DMSO and that potential increases on the interface of the model membrane. The highest increase (by 19.6%) in the antioxidant potential, on the model membrane interface, was observed for mFA.     

Inelastic neutron scattering on three mixed-valence dodecanuclear polyoxovanadate clusters

The magnetic exchange interactions in the mixed-valence dodecanuclear polyoxovanadate compounds Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].23H(2)O, Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(D(2)O)].16.5D(2)O, and (NHEt(3))(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].H(2)O were investigated by an inelastic neutron scattering (INS) study using cold neutrons. In addition, the synthesis procedures and the single-crystal X-ray structures of these compounds have been investigated together with the temperature dependence of their magnetic susceptibilities. The magnetic properties below 100 K can be described by simply taking into account an antiferromagnetically exchange coupled tetramer, consisting of four vanadium(IV) ions. Up to four magnetic transitions between the cluster S = 0 ground state and excited states could be observed by INS. The transition energies and the relative INS intensities could be modeled on the basis of the following exchange Hamiltonian: H(ex) = -2J(12)(xy)[S(1x)S(2x)+ S(3x)S(4x)+ S(1y)S(2y)+ S(3y)S(4y)] - 2J(12)(z)[(S(1z)S(2z)+ S(3z)S(4z)] - 2J(23)(xy)[(S(2x)S(3x)+ S(1x)S(4x)+ S(2y)S(3y)+ S(1y)S(4y)] - 2J(23)(z)[(S(2z)S(3z)+ S(1z)S(4z)]. The following sets of parameters were derived: for Na(4)[V(12)As(8)O(40)(H(2)O)].23H(2)O, J(12)(xy)() = J(12)(z)= -0.80 meV, J(23)(xy) = J(23)(z) = -0.72 meV; for Na(4)[V(12)As(8)O(40)(D(2)O)].16.5D(2)O, J(12)(xy) = J(12)(z) = J(23)(xy) = J(23)(z = -0.78 meV; for (NHEt(3))(4)[V(12)As(8)O(40)(H(2)O)].H(2)O, J(12)(xy) = -0.80 meV, J(12)(z) = -0.82 meV, J(23)(xy)() = -0.67 meV, J(23)(z) = -0.69 meV. This study of the same [V(12)As(8)]-type cluster in three different crystal environments allows us to draw some conclusions concerning the applicability on INS in the area of nondeuterated molecular spin clusters. In addition, the effects of using nondeuterated samples and different sample container shapes for INS were evaluated.     

NMR, CD and MCD studies of vanadate-nucleoside complexes

Complex formation between tetraoxovanadate(V) and each of the nucleosides adenosine, guanosine, cytidine and uridine has been studied in a constant salt medium at pH 7. 13C- and 51V NMR studies show that only complexes with the formula V2L2 (V = vanadate, L = nucleoside) are formed, and their formation constants have been determined. They have 51V NMR resonances around -523 ppm relative to VOCl3 and they exhibit no CD in the spectral region of the charge-transfer transitions. MCD spectra were also measured, and all experiments are in accord with a molecular structure composed by two edge-sharing VO6 octahedra forming an O4V(mu-O)2VO4 skeleton with each of the nucleoside ligands bridging the two vanadium centres through the ribose 2',3'-oxygens, which are the oxygens outside the V2O6 plane. Admixture of imidazole-HCl buffer at pH 7 gives rise to additional complexes of 1:1 stoichiometry. They have been characterized by 51V NMR and CD, and their formation constants are reported. Vanadate(V) and the deoxynucleosides deoxyadenosine, deoxyguanosine, deoxycytidine and thymidine form very weak complexes which cannot be detected by 51V NMR or CD under conditions for which vanadate and the nucleosides form complexes.