Reaction kinetics and pathway of hydrothermal decomposition of aspartic acid

The kinetics and pathway of hydrothermal decomposition of aspartic acid were studied using a continuous‐flow tubular reactor. The reaction was carried out in the temperature range of 200–260°C and at a pressure of 20 MPa. Deamination was the primary reaction, indicated by the presence of significant amount of ammonia, fumaric acid, or maleic acid in the products. Other reaction products were pyruvic acid, malic acid, and traces of succinic and lactic acid. Traces of alanine were also detected, showing the possibility of decomposing high‐molecular weight amino acids to obtain simple amino acids such as glycine or alanine. Results on the effect of reaction parameters demonstrated that decomposition of aspartic acid is highly temperature dependent under hydrothermal conditions. For a slight temperature difference of 60°C (from 200 to 260°C), the first‐order reaction rate constants of 0.003 significantly increased to 0.231 s^?1. The activation energy was 144 kJ/mol, as calculated by the Arrhenius equation. No significant effect was exhibited by other reaction parameters such as pH and pressure. The results are useful in controlling the hydrolysis of proteinaceous materials toward high yield of aspartic acid under hydrothermal conditions. © 2007 Wiley Periodicals, Inc. 39: 175–180, 2007     

Evaluation of atomic fluorescence, absorption and emission techniques for the determination of mercury

Summary Atomic fluorescence (AFS), absorption (AAS) and emission (AES) systems were evaluated for the determination of inorganic mercury. Identical vapour generation and amalgamation procedures were used to permit direct comparison of the performance of a commercial long-path AAS instrument to laboratory constructed non-dispersive AFS as well as He-MIP based AES instruments. Instrumental noise-limited detection limits (LOD) were 0.94, 2.4, 2.8 pg for AAS, AES and AFS techniques, respectively. Methodological LOD's were found to be blank controlled and similar for all three instruments, viz. 9, 25 and 16 pg for AAS, AFS and AES, respectively. All three systems produced accurate results at the low ng/l concentration, as verified by the analysis of a certified river water reference material (NRCC ORMS-1).     

n-sigma charge-transfer interaction and molecular and electronic structural properties in the hydrogen-bonding systems consisting of p-quinone dianions and methyl alcohol

Molecular and electronic structural properties of the hydrogen-bonded complexes of p-quinone dianions (PQ(2)(-)) were investigated by electrochemistry and spectroelectrochemistry of PQ in MeCN combined with ab initio MO calculations. Hydrogen bonding between PQ(2)(-) and MeOH was measured as the continuous positive shift of the apparent second half-wave reduction potentials with increasing concentrations of MeOH. Detailed analyses of the behavior reveal that PQ(2)(-) forms the 1:2 hydrogen-bonded complexes at low concentrations of MeOH and the 1:4 complexes at high concentrations, yielding the formation constants. Temperature dependence of the formation constants allows us to yield the formation energy as 76.6 and 118.9 kJ mol(-)(1) for the 1:2 and 1:4 complex formation of the 1,4-benzoquinone dianion (BQ(2)(-)) with MeOH, respectively. These results show that the pi-dianions involving the quinone carbonyl groups exhibit very strong hydrogen-accepting ability. The longest wavelength band of the spectra of BQ(2)(-) and the chloranil dianion (CL(2)(-)) is assigned to the (1)B(3u) <-- (1)A(g) band mainly contributed from an intramolecular charge-transfer (CT) configuration. Hydrogen bonding allows the band of BQ(2)(-) and CL(2)(-) to be blue-shifted, depending on the strength of the hydrogen bonds. CNDO/S-CI calculations reveal that the blue shift is ascribed to stabilization of the ground state by the hydrogen bonding involving strong n-sigma-type CT interaction. The HF/6-31G(d) calculation results show that the structure of PQ(2)(-) is characterized by a lengthening of the C=O bonds and a benzenoid ring. The geometrical properties of the hydrogen-bonded complexes of PQ(2)(-) are a slight lengthening of the C=O bonds and a short distance of the hydrogen bonds. It is demonstrated that this situation is due to the strong n-sigma CT interaction in the hydrogen bonds. The results suggest that the differing functions and properties of biological quinones are conferred by the n-sigma CT interaction through hydrogen bonding of the dianions with their protein environment.     

Difference in electrophoretic mobility and plasmic digestion profile between four recombinant fibrinogens, gamma 308K, gamma 308I, gamma 308A, and wild type (gamma 308N)

We have produced recombinant gamma-chain variant fibrinogens, gamma308K, gamma308I, and gamma308A simultaneously with wild-type fibrinogen, gamma-308N, by genetic protein engineering using Chinese hamster ovary cells. Although all three variant fibrinogens are a result of a single amino acid substitution, the aberrant gamma-chains of gamma308K and gamma308I fibrinogens migrated faster than gamma308N. Furthermore, plasmic digestion profiles were examined in the presence of 5 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) or 1 mM CaCl2. In the presence of EGTA, the three variant fibrinogens were digested into D1 and D2 fragments slightly faster than wild type. In addition, the D2 fragment derived from gamma308K was further digested into D3 by plasmin much faster than that from gamma308N. These data suggest that cleavage of gamma356Lys-gamma357Ala bond by plasmin in gamma308K, gamma308I, and gamma308A is slightly accelerated and the gamma302Lys-gamma303Phe bond is cleaved by plasmin rapidly in only the gamma308K variant. Furthermore, the substitution of Lys for gamma308Asn results in the generation of a new plasmin cleavage site between gamma308Lys and gamma309Gly in the presence of EGTA. In conclusion, a substitution at residue gamma308Asn may cause a conformational change in the gammachain of fragment D affecting polymerization and plasmin cleavage.     

Tosylation of endocrine-disruptive alkylphenolic compounds in a solid-phase reaction system consisting of C18-modified silica gel and aqueous buffer solution

The tosylation reaction of endocrine-disruptive alkylphenolic compounds in a solid-phase aqueous system was investigated with the aim of developing an environment-friendly and efficient derivatization method for HPLC analyses of environmental samples. The phenols were rapidly and efficiently converted to the tosyl derivatives on a commercially available ODS solid-phase cartridge by passing an aqueous buffer solution through it. The solid-phase aqueous tosylation system has been incorporated into a preconcentration step performed by solid-phase extraction from environmental water.