Efficiency studies in nonaqueous capillary electrophoresis

Nonaqueous capillary electrophoresis (NACE) is a relatively new area with several advantages that include enhanced efficiency and improved detection sensitivity. The goal of this study was to investigate the influence of NACE compared to aqueous CE on the separation efficiency of oligosaccharides. The applied voltage and buffer concentration were optimized for the aqueous and nonaqueous buffer media to minimize the band broadening effects of Joule heating and electrophoretic dispersion. At the optimized conditions a 1.5-fold enhancement in efficiency was obtained with the nonaqueous buffer medium.     

The crystal structure of a Di(tetramethylammonium)-bis[R,R-tartrato(2-)]-cis-dioxomolybdate(VI), (NMe4)2[MoO2(C4H4O6)2] · EtOH · 1.5 H2O,with comments on tartrate coordination

Summary In the salt (NMe₄[MoO₂(H₂tart)₂] · EtOH · 1.5 H₂O (H₄tart = R,R-(+)-tartaric acid) the tartrato-ligands are linked to molybdenum through a carboxyl oxygen and the vicinal deprotonated hydroxyl oxygen atom, with carboxyl oxygentrans to terminal oxygen of the MoO₂ cis-dioxo core. The configuration about Mo is A. The C-C-C-C torsion angles of the ligands are almost 180°. This enables inter-ligand H-bonding from the uncoordinated hydroxyl groups. The five skeletal atoms from the uncoordinated section of a ligand are nearly co-planar. The probable strong preference fortrans coordination of carboxyl must limit the range of dissolved molybdenum(VI)-tartrate species.     

Effect of crown-ether surfactants on flame atomic absorption and flame emission signals of some monovalent cations

Two surface-active and one surface-inactive 18-crown-6 derivatives were synthesized and evaluated for their abilities to enhance flame atomic absorption and flame emission signals of monovalent cations. Enhancement of potassium signals were noted for the surface-active compounds but not for the surface-inactive compound. The critical micelle concentration was determined and compared to the degree of enhancement. Surfactant-induced signal enhancements are not due to the slight or moderate decrease in the size of the aerosol first produced in the nebulizing chamber. Additional mechanistic considerations are discussed.     

CIS 1,2-functionalization of cyclohexane using selenium intermediates

The trans 1,2-phenylseleno acetate, acetamide, alcohol and nitrile of cyclohexane may be oxidized at selenium by halogens and the phenylseleno moiety displaced by halide to give high yields of 1,2 halide-containing products with cis geometry.     

The convergent syntheses of pyrazinyl and quinoxalinyl phenylmethanones from 2-lithio pyrazines and quinoxalines

Pyrazines and quinoxalines bearing 2-substituents that direct ortho metalation reacted with lithium 2,2,6,6-tetramethylpiperidide to produce 2-substituted-3-lithiopyrazines and quinoxalines. These lithio reagents reacted with N-methoxy-N-methylbenzamide to give good to moderate yields of 3-substituted pyrazinyl or quinoxalinylphenylmethanones. The 3-methylthio substituents of some ketone products were oxidized to methylsulfonyl groups that were susceptible to nucleophilic displacement.     

The preparation of dimolybdenum(V,V) complexes from molybdenum quadruply bonded metal-metal dimers

Oxidation of quadruply bonded metal-metal dimers in the presence of good π-accepting ligands results in the formation of Mo^V---Mo^V compounds of the type [MO₂(μ-X)₂(Y)(Y′)]²⁺ (X = O or S; Y,Y′ = O,O; S,S; O,S). Reaction of MO₂(O₂CCH₃)₄ with oxygen in the presence of Na₂mnt (mnt = 1,2-dicyanoethylene-2,2-dithiolate) gives [MO₂(μ-S)₂(O)(S)(mnt)₂]²⁻ (1). The compound crystallizes in the monoclinic space group P2₁/c, with cell dimensions a = 19.547(4), b = 15.210(4), c = 18.754(6) Å, β = 101.69(2)°, V= 5460(2) ų, and Z = 4. Similarly, oxidation of o-dichlorobenzene solutions of Mo₂Cl₄(CH₃CN)₄ and 4,4′-dimethyl-2,2′-dipyridyl (dmpby) or, more directly, the reaction of Mo₂Cl₄(dmbpy)₂ with oxygen leads to the formation of a red solid, which was characterized by X-ray crystallography to be Mo₂(μ-O)₂(O)₂(Cl)₂(dmbpy)₂ (2). Red diamond crystals, prepared by slow evaporation of CH₃CN solutions of 2, are trigonal and in the space group P3₁21 with cell dimensions a = 16.135(4), b = 16.135(4), c = 10.709(3) Å, V = 2414.4(13) ų and Z = 3. In both structures, the geometry about each of the molybdenum atoms is a distorted square pyramid with terminal oxygen or sulphur atoms at the apices and in a syn conformation. The molybdenum-molybdenum bond distances of 2.858(1) Å and 2.562(2) Å in structures of 1 and 2, respectively, are typical of other Mo^V---Mo^V dimers and indicative of a single Mo---Mo bond.     

Cooperative stabilisation of 14-3-3σ protein–protein interactions via covalent protein modification

14-3-3 proteins are an important family of hub proteins that play important roles in many cellular processes via a large network of interactions with partner proteins. Many of these protein–protein interactions (PPI) are implicated in human diseases such as cancer and neurodegeneration. The stabilisation of selected 14-3-3 PPIs using drug-like ‘molecular glues’ is a novel therapeutic strategy with high potential. However, the examples reported to date have a number of drawbacks in terms of selectivity and potency. Here, we report that WR-1065, the active species of the approved drug amifostine, covalently modifies 14-3-3σ at an isoform-unique cysteine residue, Cys38. This modification leads to isoform-specific stabilisation of two 14-3-3σ PPIs in a manner that is cooperative with a well characterised molecular glue, fusicoccin A. Our findings reveal a novel stabilisation mechanism for 14-3-3σ, an isoform with particular involvement in cancer pathways. This mechanism can be exploited to harness the enhanced potency conveyed by covalent drug molecules and dual ligand cooperativity. This is demonstrated in two cancer cell lines whereby the cooperative behaviour of fusicoccin A and WR-1065 leads to enhanced efficacy for inducing cell death and attenuating cell growth.

The aminothiol WR-1065 covalently modifies 14-3-3σ to stabilse its interactions with p53 and ERα. It enhances the effect of fusicoccin A via a cooperative mechanism that leads to 14-3-3 partner-protein specific activty against cancer cells.      

Synergistic effect of nanoionic destabilization and partial dehydrogenation for enhanced ionic conductivity in MBH4-C60 (M = Li+, Na+) nanocomposites

Journal of Solid State Electrochemistry - In this work, we evaluate the electrochemical properties of MBH4-C60 (M = Li+, Na+) nanocomposites for potential use as a solid-state electrolyte in...     

Backbonding in Thorium(IV) and Uranium(IV) Diarsenido Complexes with tBuNC and CO

The coordination of tBuNC and CO with the diarsenido complexes (C₅Me₅)₂An(η²-As₂Mes₂), An=Th, U, has been investigated. For the first time, a comparison between isostructural complexes of Th^IV and U^IV has been possible with CO; density functional calculations indicated an appreciable amount of π backbonding that originates from charge transfer from an actinide-arsenic sigma bond. The calculated CO stretching frequencies in the Th^IV and U^IV diarsenido complexes are consistent with the experimental measurements, both show large shifts to lower frequency. We demonstrate that the π backbonding is crucial to explaining the red shifts of CO frequency upon An^IV complex formation. Interestingly, this interaction essentially correlates to the parallel orientation of π*(C−O) orbitals relative to the An−As bond.     

SPECTRAL PERTURBATIONS OF THE AEQUOREA GREEN-FLUORESCENT PROTEIN

Abstract— In the jellyfish Aequorea, the green-fluorescent protein (GFP) functions as the in vivo bio-luminescence emitter via energy transfer from the photoprotein aequorin. Accumulated evidence has indicated that the Aequorea GFP is a relatively inflexible protein. Present evidence, however, indicates that the chromophore environment is readily accessible to a variety of external perturbants. Native Aequorea GFP has an absorbance maximum at 395 nm and a shoulder at 470 nm. In low ionic strength buffer at neutral pH and room temperature the 395/470 nm absorbance ratio is about 2.0. We show that this ratio is highly variable depending upon temperature, ionic strength, protein concentration, and pH. A maximum ratio of 6.5 (at a protein concentration of 18.6 mg/m/) and minimum of 0.42 (at a pH of 12.2) have been measured. In the latter case, the resulting absorption and excitation spectra resemble those of Renilla GFP in spectral shape (but not wavelength maximum). In all cases as the perturbant is varied the resulting spectra pass through a sharp isosbestic point, suggesting a relatively simple two-state mechanism. These spectral perturbations are fully reversible. On the basis of these results, we suggest that the chromophore binding site is conformationally flexible. pH-Dependent changes in the near-UV and visible circular dichroism spectra plus spectrophotometric titration of tyrosine residues lend additional support to this hypothesis.