Formation Constants for the Ternary Complexes of Vanadium(III), 2,2′-Bipyridine, and the Amino Acids Histidine, Cysteine, Aspartic and Glutamic Acids

In this study we report the stability constants and the speciation of the ternary vanadium(III) complexes with 2,2??-bipyridine (Bipy) and the amino acids histidine (HHis), cysteine (H₂Cys), aspartic acid (H₂Asp) and glutamic acid (H₂Glu) by means of potentiometric titrations employing 3.0 mol?dm^?3 KCl as the ionic medium at 25?°C. The potentiometric data were analyzed taking into account the hydrolysis of the vanadium(III) cation and the respective stability constants of the binary complexes and the acid?Cbase reactions of the ligands, which were kept fixed during the analysis. The complexes detected in the different systems are: in the vanadium(III)?CBipy?CHHis system, [V(HBipy)(HHis)]⁴⁺ and [V(HBipy)(H₂His)]⁵⁺; in the vanadium(III)?CBipy?CH₂Cys system, [V₂O(Bipy)(Cys)]²⁺; in the vanadium(III)?CBipy?CH₂Asp system, [V(Bipy) (Asp)]⁺, [V₂O(Bipy)(Asp)]²⁺, and V₂O(Bipy)₂(Asp)₂; and finally in the vanadium(III)?CBipy?CH₂Glu system, [V(Bipy)(H₂Glu)]³⁺ and [V(Bipy)(Glu)]⁺. The respective stability constants were determined and the specie distribution diagrams as a function of pH are briefly discussed.     

Polyenolates of Unsaturated Carboxylic Acids in Synthesis. Synthesis of Unsaturated α-Amino Acids and β-Hydrazing Acids

Regioselective reaction of lithium diene-and triene-diolates 1 and 2 with O-diphenylphosphinyl hydroxylamine affords unsaturated α-amino acids 3 and 4. Addition to DEAD leads selectively to γ-hydrazino unsaturated acids 5 and 6.     

Character of Enolization of the β-Dicarbonyl Fragment in α , γ-Dioxocarboxylic Acids. Crystal and Molecular Structure of Benzoyl- and Cinnamoylpyruvic Acids

Benzoyl- and cinnamoylpyruvic acids have been investigated by X-ray diffraction. In crystals these acids exist as 2-hydroxy-4-oxo-4-phenyl-3(Z)-butenic and 4-hydroxy-2-oxo-6-phenyl-3(Z),5(E)-hexadienic acids, respectively, stabilized by intramolecular hydrogen bonding.     

Intrinsically chiral aromaticity. Rules incorporating linking number, twist, and writhe for higher-twist Möbius annulenes

The geometries of coiled annulenes belonging to the chiral C2 and D(n) (n = 2,7) point groups are defined by two chiral indices, W(r) and T(w), respectively (writhe and twist), which sum to give an overall integer linking number, L(k) (the C?lug?reanu-White-Fuller theorem). While the value of L(k) can been equated with single-twist (L(k) = 1pi), double-twist (L(k) = 2), and higher-order (L(k) > 2) twisted (M?bius-Listing) annulenes, we suggest that the correct Huckel molecular-orbital treatment is to use T(w) specifically in the 2p(pi)-2p(pi) overlap correction first suggested by Heilbronner, rather than L(k). Quantitatively, because many of these systems project much of the finite value of T(w) into W(r), a simple mechanism exists to increase the pi-electron resonance stabilization beyond what simple Heilbronner theory predicts. Examples of a diverse set of such chiral annulenes are dissected into W(r) and T(w) contributions, which reveals that those with the minimum value of T(w) are associated with the greater delocalized stability.     

A Method for Preparing Phosphinic Acids from Hypophosphites: III. Synthesis of α-Hydroxy Phosphinic Acids

A one-pot method is proposed for preparing unsymmetrical -hydroxy phosphinic acids from ammonium hypophosphite. Bis(trimethylsilyl) phosphonites formed in situ on addition of bis(trimethylsilyl) hypophosphite to activated unsaturated compounds are brought without isolation into the Abramov reaction with an aldehyde or ketone. A series of new -hydroxy phosphinic acids are obtained.     

Synthesis and Properties of Phosphabetaine Structures: III. Phosphabetaines Derived from Tertiary Phosphines and α,β-Unsaturated Carboxylic Acids. Synthesis, Structure, and Chemical Properties

Methods of synthesis of acylate phosphabetaines by reactions of triphenylphosphine with methacrylic, cinnamic, and p-methoxycinnamic acids are developed. The phosphabetaine form is proposed to exist in equilibrium with the ⁵-oxaphospholane form. The features of methylation of the phosphabetaines are discussed.     

Advances in Electrochemical Science and Engineering,Alkire, R.C. and Kolb,D.M., Eds., Weinheim: Wiley–VCH, 1999, vol. 6, 344 pp.

Russian Journal of Electrochemistry -     

Heteropoly Acids as Heterogeneous and Reusable Catalyst for α-Thiocyanation of Ketones

Simple, efficient, and mild method for α-thiocyanation of ketones in presence of heteropolyacid has been developed. This methodology offered α-oxothiocyanates in good to excellent yields at room temperature in a highly selective manner. The catalyst could be efficiently recovered from the reaction and reused.