The determination of small amounts of long-chain tertiary alkylamines and quarternary ammonium salts

Bromocresol green has been investigated as an alternative to ammonium erdmannate for the absorptiometric determination of small amounts of long-chain alkylamines and quaternary ammonium salts in aqueous solution in a solvent extraction procedure. The molecular absorption coefficient of the reagent at 615 nm is about 3 times that of the erdmannate ion at 353 nm; visual methods of comparison are simplified by the blue colour of the bromocresol green anion The sensitivity of both the bromocresol green and the erdmannate method may be increased by stripping the coloured reagents into a small volume of aqueous solution. Both methods are free of interference from iron, but the present procedure has the disadvantage of a blank which depends both on the pH and on the concentration of excess reagent.     

The Cytotoxic Effect of α-Synuclein Aggregates

Parkinson's disease is a neurodegenerative disorder involving a functional protein, α-synuclein, whose primary function is related to vesicle trafficking. However, α-synuclein is prone to form aggregates, and these inclusions, known as Lewy bodies, are the hallmark of Parkinson's disease. α-synuclein can alter its conformation and acquire aggregating capacity, forming aggregates containing β-sheets. This protein's pathogenic importance is based on its ability to form oligomers that impair synaptic transmission and neuronal function by increasing membrane permeability and altering homeostasis, generating a deleterious effect over cells. First, we establish that oligomers interfere with the mechanical properties of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) membrane, as demonstrated by nanoindentation curves. In contrast, nanoindentation revealed that the α-synuclein monomer's presence leads to a much more resistant lipid bilayer. Moreover, the oligomers’ interaction with cell membranes can promote lactate dehydrogenase (LDH) release, suggesting the activation of cytotoxic events.     

Formation and structure of a novel enediyne-RNA base covalent adduct

The structure of an unusual covalent adduct formed by thiol-activated neocarzinostatin chromophore (NCS-chrom) and a RNA-DNA hybrid having an overhang of four unpaired residues at the 3'-end of the RNA strand has been elucidated by MS and NMR spectroscopic analyses. Unlike previously characterized adducts formed by NCS-chrom on the sugar residue of the DNA target, this adduct has been found to be on one of the uracil bases in the RNA overhang. Covalent linkage is between C-6 of the post-activated NCS-chrom and C-5 of the uracil. A novel mechanism involving adduction of the NCS-chrom C-6 radical, generated by 2-mercaptoethanol activation, to C-5 of the uracil at the U9 position of the RNA 11-mer, oxidation by dioxygen, reduction by the thiol, and subsequent dehydration is proposed for adduct formation.     

Heat capacities of concentrated multicomponent aqueous electrolyte solutions at various temperatures

The specific heat capacities of the aqueous multicomponent system NaCl +KCl+MgCl₂+CaCl₂ with ionic strength between 8.3 and 9.6 (resembling Dead Sea waters) were measured between 15°C and 45°C. The obtained data were fitted to an empirical equation as a function of concentration and temperature. The thermodynamic functions of the studied multicomponent system were found to be strongly influenced by changes in MgCl₂ concentrations. The application of Young's rule to such concentrated systems was checked at 25°C. The calculated (by Young's rule) specific heat capacitiesC _p and apparent molar heat capacities C_p, of these multicomponent electrolyte solutions were in reasonable agreement with the measured values (–0.008 J-g^–1-K^–1 and –2.6 J-mol^–1-K^–1, respectively).     

Coloured liquid anion-exchangers

Of the several stable and coloured uninegative ions examined, trans-bis(dimethylglyoximato) dinitritocobaltate(III) ([Co(C₄H₇O₂)₂(NO₂)₂]^-, termed goldenate ion, G^-) can advantageously replace the erdmannate ion in the formation of a more photochemically stable coloured anion-exchanger derived from Aliquat-336 chloride. Quantitative spectrophotometric measurements of its displacement by chloride, bromide and perchlorate ions were made and are discussed together with literature data to examine the effect of parameters such as the nature of the cation and of the anion and change in the organic solvent on the relative and absolute values of extraction constants.