Possible interactions of cyclobutadiene with by-products in inert matrix isolation studies

The dimer and the molecular associations of cyclobutadlene with carbon monoxide, carbon dioxide, hydrogen cyanide, benzene, and phthalan have been studied theoretically by means of a 1/R expansion.     

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.     

Theoretical studies of peptidic structures. Environmental effects

Summary The peptide Asp-Glu-Arg-Ser has been studied using the software package maPSI, with simulation of the pH conditions and the influence of the solvent. It is concluded, in agreement with the experimental observation, that in solution DERS is distorted from a true -turn conformation, without H-bond but stabilized by a weak salt-bridge between the side chains of the Glu and Arg residues.Dedicated to Professor Alberte Pullman     

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.     

Studies on the electronic structure of conjugated systems

A comprehensive study of the electronic structure of conjugated systems, within the approximation and using a CI SCF procedure, has been undertaken. In this work the common features (method and approximations, semiempirical parameters, details of the program, etc.) are examined and the general characteristics of the results are discussed.

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Zusammenfassung Eine ausführliche Untersuchung der Elektronenstruktur konjugierter Systeme wurde mit Hilfe eines CI SCF Verfahrens innerhalb der normalen -Annäherung durchgeführt. In der vorliegenden Arbeit werden die Grundzüge (wie Methode und Näherungsverfahren, halbempirische Parameter, Einzelheiten des Programms, usw.) besprochen.

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Résumé On a entrepris une étude comprehensive de la structure électronique des systèmes conjugués, dans le cadre de l'approximation et en utilissant la méthode de champ auto-cohérent avec interaction de configurations. Dans le présent travail on examine les charactéristiques générales (méthode et approximations, paramètres sémiempiriques, détails du programme, etc.).

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This work has been supported in part by the National Research Council of Canada.

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Temporary address while on sabbatical leave:Instituto de Quimica Fisica, C.S.I.C., Serrano 119, Madrid 6, Spain.     

Non-relativistic self-consistent-field theory. III

An exact self-consistent-field formalism, which obviates the need of evaluating interelectronic repulsion integrals, is developed. This formulation claims general applicability and can lead either to Hartree-Fock functions or to the exact solutions of a non-relativistic Hamiltonian, depending on the trial functions used.

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Zusammenfassung Es wird ein exakter seIf-consistent-field-Formalismus entwickelt, der die Berechnung von Elektronenwechselwirkungsintegralen unnötig macht. Diese Formulierung beansprucht allgemeine Anwendbarkeit und kann, je nach Art der verwendeten Funktionen, entweder zu Hartree-Fock-Funktionen oder zu exakten Lösungen eines nichtrelativistischen Hamiltonoperators führen.

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Résumé On a développé un formalisme exact de champ «gauto-cohérent», où il n'y en a pas besoin de calculer les intégrales concernant la répulsion interélectronique. Ce formalisme est complètement général et il peut Être employé pour déterminer bien des fonctions de Hartree-Fock ou les fonctions propres d'un hamiltonien non-relativistique, dépendant des caractéristiques des fonctions employées.

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This work has been supported in part by the National Research Council of Canada.     

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.     

Rotational spectrum of the dimethyl ether-acetylene complex: evidence for an effective C2v geometry

The rotational spectra for five isotopomers of the 1:1 weakly bound complex formed between dimethyl ether (DME) and acetylene (HCCH) have been measured by Fourier transform microwave spectroscopy. The experimental rotational constants, planar moments, and dipole moment components are consistent with a floppy complex possessing an effective C2v structure in which the hydrogen atom of acetylene is hydrogen bonded to the oxygen atom of dimethyl ether with an intermolecular H...O separation of 2.08(3) A. Experimental rotational constants for the normal isotopic species are A = 10382.5(17) MHz, B = 1535.7187(18) MHz, and C = 1328.3990(17) MHz and the dipole moment components are mua= mutotal = 1.91(10) D. Ab initio calculations at the MP2/6-311++G(2d,2p) level indicate that the energy barrier for motion of the HCCH subunit between the lone pairs of the DME, via a C2v intermediate structure, is very low (approximately 0.29 kJ mol(-1)). Inclusion of basis set superposition error and zero point energy corrections to the energies of four stationary points located on the potential energy surface shows that the relative stabilities are particularly sensitive to these corrections. The ab initio optimizations give rotational constants for the C2v structure of A = 10066 MHz, B = 1496 MHz, and C = 1324 MHz, and a dipole moment of mua= mu(total) = 2.12 D, in reasonable agreement with the experimentally determined values. The structural parameters and energetics of the DME-HCCH complex will be discussed and compared to similar complexes such as H2O-HCCH.     

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

Available Hartree-Fock functions have been used to evaluate the magnetic hyperfine structure constants for various neutral atoms and positive and negative ions with configurations involving equivalentp- andd-electrons. The necessary formulation is presented; in particular, theJ-dependence of the hyperfine structure constant is tabulated for the mentioned configurations.

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Zusammenfassung Mittels vorhandener Hartree-Fock-Funktionen werden die magnetischen Hyperfeinstrukturkonstanten für neutrale Atome sowie positive und negative Ionen mit Konfigurationen von äquivalentenp- undd-Elektronen berechnet; der dazu notwendige Formelapparat wird zusammengestellt. Die für die erwähnten Konfigurationen berechneten Werte und ihreJ-Abhängigkeit werden in Tabellenform angegeben.

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Résumé On a employé des fonctions de Hartree-Fock pour le calcul des constantes de structure hyperfine magnétique pour quelques atomes neutres et ions positifs et négatifs, qui possèdent des configurations électroniques avec des électronsp oud équivalents. Les formules nécessaires sont présentées. On donne la dépendance deJ de la constante de structure hyperfine.

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This work has been supported in part by the National Research Council of Canada.