Trace enrichment of phenylcarboxylic acids from a model biological fluid and serum of human blood.

The study was focused on the development of a solid-phase extraction protocol for seven phenylcarboxylic acids from albumin solutions by using unmodified hyper-cross-linked polystyrene restricted access materials with crosslinking degrees varying from 100 to 400% (four of the acids are known to be markers of sepsis). The breakthrough volume of the most hydrophilic 3,4-dihydroxybenzoic acid rises as the sorbent bridging extent grows. Inversely, the breakthrough volume of the most hydrophobic 3-phenylpropionic acid was found to decrease considerably when the degree of crosslinking exceeds 200%.

Hypercrosslinked polymeric restricted access materials for analysis of biological fluids.

New restricted access materials based on microporous hypercrosslinked polystyrene have been developed. The materials are aimed to use as packings for solid-phase extraction cartridges to isolate low-molecular-weight analytes from biological fluids (for instance, blood plasma or serum). Two features distinguish these polymers from all known restricted access materials.

The role of substrate strain in the mechanism of the carbon-carbon lyases.

The carbon-carbon lyases, tryptophan indole lyase (TIL) and tyrosine phenol-lyase (TPL) are bacterial enzymes which catalyze the reversible elimination of indole and phenol from l-tryptophan and l-tyrosine, respectively. These PLP-dependent enzymes show high sequence homology (∼40% identity) and both form homotetrameric structures. Steady state kinetic studies with both enzymes show that an active site base is essential for activity, and α-deuterated substrates exhibit modest primary isotope effects on kcat and kcat/Km, suggesting that substrate deprotonation is partially rate-limiting.

Physicochemical and adsorption properties of hypercross-linked polystyrene with ultimate cross-linking density.

The paper describes unexpected properties of hypercross-linked polystyrenes with ultimate cross-linking degrees of 300, 400, and 500%, where three, four, or five methylene links, respectively, could bind each polystyrene phenyl ring to its spacious neighbors. The polymers exhibit a strong electron spin resonance signal, unusual spectra in IR, UV, and visible ranges, and they are not typical dielectrics. The nonfunctionalized hypercross-linked polymers absorb significant amounts of inorganic acids, salts, and bases due to interactions of protons or other cations with electron-donating fragments of the aromatic network with the high extent of mutual connectivity and also due to dispersion interactions of anions with the polymer matrix.

Paradoxes of thermodynamics of swelling equilibria of polymers in liquids and vapors.

An automatic registration of the changing size of a single spherical microbead of a cross-linked polymer was applied for studying the swelling process of the bead by the sorption of vapors and/or liquids. Many representatives of all three basic types of polymeric networks, gel-type, hypercrosslinked, and macroporous, were examined. Only the first two display large volume changes and prove suitable for following the kinetics and extent of swelling by the above dilatometric technique.

Mechanism-guided development of VO(salen)X complexes as catalysts for the asymmetric synthesis of cyanohydrin trimethylsilyl ethers.

Catalyze this! Detailed study of the mechanism of asymmetric cyanohydrin synthesis catalyzed by VO(salen)X complexes (see figure) led to the development of VO(salen)NCS, as the most active vanadium-based catalyst yet developed for this reaction.The mechanism by which oxovanadium(V)(salen) complexes(1) VO(salen)X catalyze the asymmetric addition of trimethylsilyl cyanide to benzaldehyde has been studied. The reaction kinetics indicated that the structure of the counterion (X) had a significant influence on the rate, but not on the enantioselectivity of the reaction.

VO(salen)(X) catalysed asymmetric cyanohydrin synthesis: an unexpected influence of the nature of anion X on the catalytic activity.

The nature of the anionic ligand X (X = EtOSO3, BF4, Cl, Br, OSO2CF3, F or CN) in vanadium(V)salen complexes [V+ O(salen) X-] was found to have a significant influence on the catalytic activity of the complexes, but not on their enantioselectivities; with the complexes in which X = Cl or F being most active and the complex with X = OSO2CF3 being totally inactive.

Cyanide ion cocatalysis in Ti(salen) catalysed asymmetric cyanohydrin carbonate synthesis.

In the presence of potassium cyanide or the potassium cyanide/18-crown-6 complex as a cocatalyst, 1-2 mol% of titanium(salen) complex catalyses the asymmetric addition of achiral cyanoformates to aldehydes, giving cyanohydrin carbonates with high enantiomeric excesses; and catalyses the diastereoselective addition of chiral cyanoformates derived from alpha-methylbenzyl alcohol to aldehydes, a reaction which exhibits double asymmetric induction.

Catalytic, asymmetric synthesis of cyanohydrin ethyl carbonates.

[reaction: see text] The bimetallic titanium complex [(salen)TiO](2), where salen is the ligand derived from (R,R)-cyclohexanediamine and 3,5-di-tert-butyl-salicylaldehyde, has been shown to catalyze the asymmetric addition of ethyl cyanoformate to aldehydes leading to cyanohydrin carbonates with high enantiomeric excesses.

Synthesis of alpha-amino acids via asymmetric phase transfer-catalyzed alkylation of achiral nickel(II) complexes of glycine-derived Schiff bases.

Achiral, diamagnetic Ni(II) complexes 1 and 3 have been synthesized from Ni(II) salts and the Schiff bases, generated from glycine and PBP (7) and PBA (11), respectively, in MeONa/MeOH solutions. The requisite carbonyl-derivatizing agents pyridine-2-carboxylic acid(2-benzoyl-phenyl)-amide 7 (PBP) and pyridine-2-carboxylic acid(2-formyl-phenyl)-amide 11 (PBA) were readily prepared from picolinic acid and o-aminobenzophenone or picolinic acid and methyl o-anthranilate, respectively. The structure of 1 was established by X-ray crystallography.

Synthesis and properties of stereoregular cyclic polysilanols: cis-[PhSi(O)OH](4), cis-[PhSi(O)OH](6), and tris-cis-tris-trans-[PhSi(O)OH](12).

New stereoregular cyclic polysilanols of the general formula [PhSi(O)OH]n (n = 6 and 12) have been selectively obtained in high yields by the reaction of cagelike oligophenylmetallasiloxanes with dilute solutions of hydrochloric acid at low temperatures. An alternative method was used to prepare cis-[PhSi(O)OH](4) from sodium phenylsiloxanolate, cis-[(Na(+))(4)[PhSi(O)O(-)](4)].(1-butanol)(x).

Catalytic asymmetric synthesis of O-acetyl cyanohydrins from KCN, Ac2O and aldehydes.

A (salen)titanium catalyst has been found to induce the asymmetric addition of potassium cyanide and acetic anhydride to aldehydes, giving enantiomerically enriched cyanohydrin esters with up to 92% enantiomeric excess using just 1 mol% of the catalyst. This is the first report of the asymmetric synthesis of cyanohydrin derivatives using a cyanide source which is non-volatile and inexpensive.

Interaction of tyrosine phenol-lyase with phosphoroorganic analogues of substrate amino acids.

The phosphinic analogues of tyrosine and pyruvate were first demonstrated to be substrates in the reactions of elimination and synthesis catalyzed by tyrosine phenol-lyase. Kinetic parameters of the enzymatic process were determined, and the first enzymic synthesis of an aminophosphinic acid was carried out. Replacement of the planar HOOC-group by the tetrahedral (HO)(O)PH-group in the substrate slightly affected its affinity for the enzyme but substantially diminished the conversion rate.

Asymmetric PTC C-alkylation catalyzed by chiral derivatives of tartaric acid and aminophenols. Synthesis Of (R)- and (S)-alpha-methyl amino acids.

A new type of efficient chiral catalyst has been elaborated for asymmetric C-alkylation of CH acids under PTC conditions. Sodium alkoxides formed from chiral derivatives of tartaric acid and aminophenols (TADDOL's 2a-e and NOBIN's 3a-h) can be used as chiral catalysts in the enantioselective alkylation, as exemplified by the reaction of Schiff's bases 1a-e derived from alanine esters and benzaldehydes with active alkyl halides. Acid-catalyzed hydrolysis of the products formed in the reaction afforded (R)-alpha-methylphenylalanine, (R)-alpha-naphthylmethylalanine, and (R)-alpha-allylalanine in 61-93% yields and with ee 69-93%.

Ion-exchange high-performance liquid chromatography of nucleotides and polypeptides on new types of ion-exchange sorbents, based on polystyrene-coated silicas.

A novel type of ion exchanger was prepared by multipoint covalent binding of polystyrene chains onto the surface of porous silica followed by polymer-analogous modification of the bonded layer. Both anion and cation exchangers were synthesized and examined in the separation of nucleotides and proteins. Rapid and efficient separation of basic polypeptides on strong anion exchangers and that of acidic polypeptides on strong cation exchangers could be achieved.

Tyrosine phenol-lyase from Citrobacter intermedius. Factors controlling substrate specificity.

L-Amino acids are competitive inhibitors of tyrosine phenol-lyase from Citrobacter intermedius. For non-branched amino acids the correlation exists between -RTlnKi and side-chain hydrophobicity. Aspartic and glutamic acids are anomalously potent inhibitors taking into account low hydrophobicity of their side chains.

Structure of protein solutions. Part 2. Solutions of total protein of yeast Saccharomyces cerevisiae.

Water systems formed by total protein of yeast Saccharomyces cerevisiae and model systems on the basis of unfractionated casein were studied by viscosimetry and electron microscopy. Methodologically, both methods offered a possibility of distinguishing several quantitatively different concentration intervals in protein solutions under different conditions. Viscosimetry gave the most informative results at the concentration intervals where the solutions approached the true ones, while electron microscopy did so when supermolecular formations prevailed.

Kinetic description of proteolysis. Part 4. Hydrolysis kinetics of partial protein hydrolysates.

This report presents experimental data on kinetics of casein hydrolysate hydrolysis. The experiments were interpreted in the framework of a theory reported, which is guided by an experimentally measurable value--a total molar concentration of all peptides and amino acids (total amino nitrogen). The total amino nitrogen N was determined by photometry of N-trinitrophenyl (N-TNP) derivatives obtained by means of trinitrobenzenesulfonic acid (TNBS).