Charge transfer complex formation between TX-100/CCl4 reverse micelle and a series of π-electron acceptors: determination of cmc and aggregation number

Electron donor–acceptor interaction of the reverse micelle (RM) of TX-100 in CCl₄ medium with a number of π-acceptors has been established by analysing the charge transfer (CT) absorption bands in the light of Mulliken's theory. Aggregation number (n) and operational critical micellisation concentration of the RM and formation constants of the RM–p-chloranil and RM-o-chloranil complexes have been determined by UV-visible spectrophotometry. Values of n thus obtained (20–30) are close to that of TX-100/cyclohexane dry reverse micelles determined by other methods and also to a theoretically calculated value of n for AOT/CCl₄ dry RM.     

Measurement of wedge angle of a transparent parallel plate using quasi-monochromatic light source and phase shifting interferometry

A new technique (to our knowledge), for the measurement of residual wedge angle (RWA) of high optical quality transparent nearly parallel plate (PP), using a quasi-monochromatic light source, is presented. Advantages and drawbacks of the technique and the results obtained for a PP, using a filtered white light source, is discussed. A slightly modified optical setup for accurate determination of RWA, using phase shifting interferometry (PSI), has been described. Results obtained, applying PSI, for a validation experiment and for the determination of RWA of a quasi-PP is presented. The PSI based technique does not suffer from any measurement ambiguities due to limitation in effective beam aperture. Hence the technique is suitable for high accuracy measurement of RWA of PP. In both the optical setups, presented in this paper, the respective interfering beams travel the same optical circuit and are thus subject to same perturbation in optical path, due to external mechanical vibration, which finally cancels out. Thus the measurements are much less affected by external vibrations. Since the respective interfering beams undergo identical reflections and transmissions, the visibility or contrast of the interference fringes is very good.     

The biological buffer bicarbonate/CO2 potentiates H2O2-mediated inactivation of protein tyrosine phosphatases

Hydrogen peroxide is a cell signaling agent that inactivates protein tyrosine phosphatases (PTPs) via oxidation of their catalytic cysteine residue. PTPs are inactivated rapidly during H(2)O(2)-mediated cellular signal transduction processes, but, paradoxically, hydrogen peroxide is a rather sluggish PTP inactivator in vitro. Here we present evidence that the biological buffer bicarbonate/CO(2) potentiates the ability of H(2)O(2) to inactivate PTPs. The results of biochemical experiments and high-resolution crystallographic analysis are consistent with a mechanism involving oxidation of the catalytic cysteine residue by peroxymonocarbonate generated via the reaction of H(2)O(2) with HCO(3)(-)/CO(2).     

Revisiting the reactivity of different carbon bases: A theoretical study

Quantum chemical calculations are performed on different carbon bases to understand the origin of their reactivity. Both carbon(0) and carbon(II) bases may show very high values of second proton affinity as well as bond dissociation energies for gem‐dimetallation. Thus, their distinction becomes blurred when subjected to electrophilic attack. However, unlike carbon(0) bases, carbon(II) bases are ambiphilic in nature owing to the presence of a σ symmetric lone pair and a vacant π orbital concentrated on the central carbon atom. Thus, they may show different reactivity when subjected to nucleophilic attack. This reactivity difference may be considered as another distinction between these two classes of compounds. © 2013 Wiley Periodicals, Inc.     

Oximato bridged RhIII2MII and RhIIIMI species (MII = Mn, Co, Ni; MI = Cu, Ag)

The reaction of [RhCl₂(HPhL)(PhL)] with M^II(ClO₄)₂·6H₂O in presence of alkali has furnished trinuclear [RhCl₂(PhL)₂]₂M(H₂O)₂·H₂O (HPhL is phenylazobenzaldoxime; M = Mn, Co, Ni). A similar reaction with M^I(PPh₃)₂NO₃ yielded binuclear [RhCl₂(PhL)₂]M(PPh₃)₂ (M = Cu, Ag). In these molecules the oximato group acts as a bridge between Rh^III (bonded at N) and M^II or M^I (bonded at O). In structurally characterized [Rh^IIICl₂(PhL)₂]₂Mn(H₂O)₂.H₂O the centrosymmetric distorted octahedral MnO₆ coordination sphere is spanned by four oximato oxygen atoms and two water molecules lying in trans position. In the lattice the neighbouring molecules are held together by H₂O⋯H₂O⋯H₂O hydrogen bonds generating infinite zigzag chains. The manganese atoms lie parallel to the C-axis, the shortest Mn...Mn distance being 7.992 ?. Magnetic exchange interactions if any are small as seen in room temperature magnetic moments. The manganese system displays a strong EPR signal near g = 2.00. In the complex [RhCl₂(PhL)₂]Cu(PPh₃)₂ the copper atom is coordinated to two oximato oxygen atoms and the two phosphorus atoms in a distorted tetrahedral geometry. The softness of the phosphine ligand is believed to sustain the stable coordination of hard oximato oxygen to soft Cu^I. The coordination sphere of the RhIII atom in both the complexes is uniformly trans-RhN₄Cl₂.     

Self-assembled reverse micelles in supercritical CO2 entrap protein in native state

Molecular dynamics simulations of random quaternary mixtures of protein-water-CO2-fluorosurfactants show the self-assembly of reverse micelles in supercritical carbon dioxide where the protein becomes entrapped inside the aqueous pool. Analyses show that the protein native state remains intact in the water pool. This is because of the bulk nature of the enclosed water that provides a suitable environment for the extracted protein. Results from ab initio calculations imply that the existing fluorosurfactants can be made more effective in stabilizing water-in-CO2 microemulsions by a partial hydrogenation in their tails. A Lewis acid-Lewis base interaction among CO2 and the surfactant tails enhances the stability of the aqueous droplets substantially. The study can help accelerate the search for surfactant process for environmentally benign applications in dense CO2.     

A rare unsupported iridium(II) dimer, [IrCl2(CO)2]2

Oxidative additions of dichloromethanes to a diiridium(i) core, bridged by 2-ferrocenyl-1,8-naphthyridines (NP-Fc), provide an iridium(II) dimer, [IrCl2(CO)2(eta 1-NP-Fc)]2, featuring an unsupported Ir-Ir single bond (2.7121(8) A).     

Use of fluorescence probes for studying Kamlet-Taft solvatochromic parameters of micellar system formed by binary mixture of sodium dodecyl sulfate and Triton-X 100

Fluorescence probes have been used to estimate Kamlet-Taft solvatochromic parameters alpha and pi* representing hydrogen-bond donation ability and dipolarity/polarizability, respectively, of sodium dodecyl sulfate (SDS)-Triton X 100 (TX100) mixed aggregates with varying compositions. The hydrogen-bond donation ability of the mixed aggregate has been found to increase with SDS composition, whereas the dipolarity/polarizability parameter decreases. The relative contribution of electrostatic and steric effect toward the total free energy of micellization have been calculated for the mixture. The solvatochromic parameters alpha and pi* depend linearly on the total free energy of micellization, indicating a correlation between aggregational and solvatochromic properties.     

Role of axial donors in the ligand isomerization processes of quadruply bonded dimolybdenum(II) compounds

Quadruply bonded dimolybdenum(II) complexes with NP-R (2-(2-R)-1,8-naphthyridine; R = thiazolyl (NP-tz), furyl (NP-fu), thienyl (NP-th)) and 2,3-dimethyl-1,8-naphthyridine (NP-Me 2) have been synthesized by reactions of cis-[Mo2(OAc)2(CH3CN)6][BF4]2 with the corresponding ligands. The products cis-[Mo2(NP-tz)2(OAc)2][BF4]2 (1), trans-[Mo2(NP-fu)2(OAc)2][BF4]2 (2), trans-[Mo2(NP-th)2(OAc)2][BF4]2 (3), and trans-[Mo2(NP-Me2)2(OAc)2][BF4]2 (4) were isolated and characterized. The NP-R ligands with stronger R = pyridyl and thiazolyl donors result in cis isomers whereas the weaker furyl and thienyl appendages lead to compounds having a trans orientation of the ligands. The use of NP-Me2 leads to a trans structure with a tetrafluoroborate anion occupying one of the axial sites. Complete replacement of two acetate groups by acetonitrile in 1 and 2 resulted in the cis isomers [Mo2(NP-tz)2(CH3CN)4][OTf]4 (5) and [Mo2(NP-fu)2(CH3CN)4][OTf]4 (6) respectively. The combination of one acetate and two acetonitriles as ancillary ligands, however, yields trans-[Mo2(NP-tz)2(OAc)(CH3CN)2][BF4]3 (7) in the solid state as determined by X-ray crystallography. (1)H NMR spectra of the products are diagnostic of the cis and trans dispositions of the ligands. Solution studies reveal that the ligand arrangements observed in the solid state are mostly retained in the acetonitrile medium. The only exception is 7, for which a mixture of cis and trans isomers are detected on the NMR time scale. The isolation of trans compounds 2- 4 from the cis precursor [Mo2(OAc)2(CH3CN)6][BF4]2 indicates that an isomerization process occurs during the reactions. The mechanism involving acetate migration through axial coordination has been invoked to rationalize the product formation. Compounds 1- 7 were structurally characterized by single-crystal X-ray methods.