Recognition of amino acids in solution

The basic solvation shells of all the amino acids, of use in the study of their recognition in aqueous solutions, are determined by means of a method based on the use of 1/R expansions parameterized on the basis of the results from accurate SCF calculations. The accuracy of the calculations is tested in a more extensive study of the solvation of glycine, for which the results of Monte Carlo calculations are reproduced.     

Micro Assay for Malondialdehyde in Human Serum by Extraction-Spectrophotometry Using an Internal Standard

Malondialdehyde (MDA) is a widely accepted biomarker of lipid peroxidation. Thus, the measurement of MDA in clinical samples is useful in the evaluation of oxidative stress. In this study, a micro-extraction-spectrophotometric assay was developed, based on the formation of MDA–thiobarbituric acid (TBA) adduct. To enhance the analytical performance, Erioglaucine A was used as an internal standard (IS), and the first derivative spectra were obtained. The volume of serum sample was 20µL and the total volume of aqueous phase 420µL (200µL of 0.6% TBA in acetic acid, pH 2.5 and 200µL of 6.25·10^–4% IS). The extraction of adduct and IS was carried out with 300µL of aliquat 336 (0.06%) in ethyl acetate. The analytical signal S was defined as the ratio between the first derivative absorbances measured at 543.1nm (adduct) and 644.4nm (IS). In the calibration range up to 10µmolL^–1 MDA, the linear regression coefficient was 0.9998. The quantification limit was 0.19µmolL^–1 and the CV values for 2µmolL^–1 and 5µmolL^–1 MDA, respectively, were 0.8% and 0.7%. The procedure was applied to the analysis of diabetic sera and the results compared with those obtained by HPLC (derivatization with 2,4-dinitrophenylhydrazine). Lower HPLC results (about 15%) indicated that interferences from other TBA reactive substances had not been completely eliminated by the extraction procedure and derivatization of spectral data. On the other hand, the micro-procedure presents important advantages: it is simple, precise and environmentally friendly (small amounts of reagents), which makes it readily adaptable to the analysis of large sample series. The feasibility of micro-assay in the evaluation of lipid peroxidation status was demonstrated in the analysis of 156 serum samples from diabetic patients divided into three groups according to the stage of development of typical complications.     

Self-consistent-field theory for positive ions

Investigation of the stability characteristics of Hartree-Fock functions leads to conclusions of interest in relation to the functions of positive ions. These considerations, in conjunction with an existing modified SCF formalism, make it possible to reformulate the SCF method in order to adapt it to the determination of Hartree-Fock functions for positive ions.

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Zusammenfassung Die Untersuchung der Stabilitätseigenschaften von Hartree-Fock-Funktionen führt zu Schlußfolgerungen, die von Interesse sind im Zusammenhang mit Funktionen für positive Ionen. Diese Betrachtungen, in Verbindung mit einem veränderten SCF-Formalismus, machen es möglich, die SCF-Methode umzuformulieren, um sie der Bestimmung von Hartree-Fock-Funktionen für positive Ionen anzupassen.

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Résumé L'étude de la stabilité des fonctions de Hartree-Fock mène à des conclusions présentant un intérêt par rapport aux fonctions des ions positifs. Ces considérations, liées à un formalisme SCF modifié, permettent de reformuler la méthode SCF en l'adaptant à la déterminantion des fonctions de Hartree-Fock des ions positifs.

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This work has been supported in part by the National Research Council of Canada and presented in part at the 3rd Gordon Research Conference on Theoretical Chemistry, Andover, N. H., June 26–July 1, 1966.     

Synthesis and Crystal Structure of [(1‐(Phenyltriazenido)‐2‐(phenyltriazeno)benzene)(nitrato)mercury(II)], {Hg[PhN3C6H4N3(H)Ph](NO3)}, a Complex with Weak Metal‐Arene π‐Interactions

The reaction of PhN₃(H)C₆H₄N₃(H)Ph with Hg(NO₃)₂ in THF in the presence of triethylamine yields {Hg[PhN₃C₆H₄N₃(H)Ph](NO₃)} as a yellow powder that can be recrystallized from THF/acetone. The crystals belong to the monoclinic system, space group P2₁ with the cell dimensions a = 9.639(2), b = 5.412(1), c = 19.675(4) Å, β= 97.47(3)°, V = 1017.7 (4) ų, Z = 2. The crystal structure determination (2668 unique reflections with [I>2σ(I)], 262 parameters, R₁ = 0.0393) shows that the structure consists of mononuclear complexes. Hg atoms are linearly coordinated by one N_α atom of the triazenide unit of the planar ligand [Hg‐N(1) = 2.101(8) Å] and an O atom of the NO₃^— ion [Hg‐O(1) = 2.11(1) Å]. Additional weak Hg‐N contacts [Hg‐N(4) = 2.662(9) and Hg‐N(3) = 2.851(9) Å] and an intramolecular hydrogen bond between the triazenide hydrogen and an O atom of the nitrate group are observed [N(6)‐H(6)···O(2) = 2.92(2) Å]. The complexes are stacked to infinite chains by metal‐arene π‐interactions. Each Hg atom is coordinated by the terminal phenyl rings of two neighboring complexes [Hg‐C from 3.40(1) to 4.10(1) Å] in a η² fashion.     

Microwave spectrum, dipole moment, and internal dynamics of the methyl fluoride-carbonyl sulfide weakly bound complex

Rotational spectra for the normal and four isotopically substituted species of the 1:1 complex between methyl fluoride (H3CF) and carbonyl sulfide (OCS) have been measured using Fourier-transform microwave spectroscopy in the 5-16 GHz frequency region. The observed spectra fit well to a semirigid Watson Hamiltonian, and an analysis of the rotational constants has allowed a structure to be determined for this complex. The dipole moment vectors of the H3CF and OCS monomers are aligned approximately antiparallel with a C...C separation of 3.75(3) A and with an ab plane of symmetry. The values of the Pcc planar moments were found to be considerably different from the expected rigid values for all isotopologues. An estimate of approximately 14.5(50) cm-1 for the internal rotation barrier of the CH3 group with respect to the framework of the complex has been made using the Pcc values for the H3CF-OCS and D3CF-OCS isotopic species. Two structures, very close in energy and approximately related by a 60 degrees rotation about the C3 axis of the methyl fluoride, were identified by ab initio calculations at the MP2/6-311++G(2d,2p) level and provide reasonable agreement with the experimental rotational constants and dipole moment components.     

Role of the ubiquitin proteasome system in Parkinson's disease

Parkinson's disease (PD) is the most common neurodegenerative movement disorder. Although a subject of intense research, the etiology of PD remains poorly understood. Recently, several lines of evidence have implicated an intimate link between aberrations in the ubiquitin proteasome system (UPS) and PD pathogenesis. Derangements of the UPS, which normally functions as a type of protein degradation machinery, lead to alterations in protein homeostasis that could conceivably promote the toxic accumulation of proteins detrimental to neuronal survival. Not surprisingly, various cellular and animal models of PD that are based on direct disruption of UPS function reproduce the most prominent features of PD. Although persuasive, new developments in the past few years have in fact raised serious questions about the link between the UPS and PD. Here I review current thoughts and controversies about their relationship and discuss whether strategies aimed at mitigating UPS dysfunction could represent rational ways to intervene in the disease. Publication history: Republished from Current BioData's Targeted Proteins database (TPdb; http://www.targetedproteinsdb.com).     

Efficiency of superoxide anions in the inactivation of selected dehydrogenases

The most ubiquitous of the primary reactive oxygen species, formed in all aerobes, is the superoxide free radical. It is believed that the superoxide anion radical shows low reactivity and in oxidative stress it is regarded mainly as an initiator of more reactive species such as OH and ONOO^‐.In this paper, the effectiveness of inactivation of selected enzymes by radiation-generated superoxide radicals in comparison with the effectiveness of the other products of water radiolysis is examined. We investigate three enzymes: glyceraldehyde-3-phosphate dehydrogenase (GAPDH), alcohol dehydrogenase (ADH) and lactate dehydrogenase (LDH).We show that the direct contribution of the superoxide anion radical to GAPDH and ADH inactivation is significant. The effectiveness of the superoxide anion in the inactivation of GAPDH and ADG was only 2.4 and 2.8 times smaller, respectively, in comparison with hydroxyl radical. LDH was practically not inactivated by the superoxide anion.Despite the fact that the studied dehydrogenases belong to the same class of enzymes (oxidoreductases), all have a similar molecular weight and are tetramers, their susceptibility to free-radical damage varies. The differences in the radiosensitivity of the enzymes are not determined by the basic structural parameters analyzed. A significant role in inactivation susceptibility is played by the type of amino acid residues and their localization within enzyme molecules.     

Functionalized nanodiamonds: triamantane and [121]tetramantane

The selective functionalizations of the fundamental hydrogen-terminated nanodiamonds triamantane 1, as well as the most symmetrical representative of the tetramantanes (C(2h)-[121]tetramantane 2) were elaborated. Electrophilic reagents (Br2, HNO3) predominantly attack the medial C-H positions of the cages; bromination of 2 gave the medial 2-bromo derivative almost exclusively. Highly selective apical substitution in 1 and 2 is possible either under single-electron-transfer oxidations via hydrocarbon radical cations or through photoacetylation with diacetyl. The mono- and the bis-acetyl derivatives of 1 and 2 were converted through Bayer-Villiger oxidation and subsequent hydrolysis to the respective apical mono- and dihydroxy derivatives. This exceptional synthetic specificity facilitates the transformation of 2, and perhaps larger nanodiamond molecules, into functionalized building blocks needed for a wide range of applications such as nanotechnology.     

Ion plated indium oxide : infrared and optical study

The high optical transparency of ion plated indium oxide combined with their mechanical hardness and good environmental stability have opened up numerous applications in the line of sophisticated optoelectronic devices. Indium is evaporated at a low oxygen pressure on to an ordinary glass substrate mounted under the cathode and biased by a r.f. generator at 13,6 M Hz. Infrared spectra are recorded in the range 5000–200 cm^?1 by A.T.R. and reflexion-absorption spectroscopy, and show between 800 and 200 cm^?1 bands due to stretching and bending modes predicted by a factor group analysis. A tentative assignment is made of the highest frequency. Last U.V. and visible spectra are discussed.     

Physical properties of many-electron atomic systems evaluated from analytical Hartree-Fock functions

Two types of approximate functions have been tested through the evaluation of various physical properties: for ground states, double-, SCF functions have been used, while for excited states the calculations have been carried out using the expectation values obtained from the Hartree-Fock functions for the corresponding lowest configuration. The agreement with the Hartree-Fock values or the experimental results, respectively, can be considered to be very satisfactory.This work has been supported in part by the National Research Council of Canada.