The Antiepileptic Lamotrigine and Its Analogues: Comparative Theoretical Electronic Properties

Electronic properties of lamotrigine (LTG) and two analogues (A1 and A2) are compared through MOPAC-AM1 calculations. Two stable conformers of LTG are calculated to exist in agreement with X-ray crystallography. In the three compounds and the two conformers for each of them, the more favorable protonation sites are N₂ and N₄; these should then be the sites appropriate for interaction with a receptor, and group valence reinforces the supposition. The molecular electrostatic potentials show that a region between the two chlorine atoms in LTG could be the site for an electrostatic interaction with a corresponding site in the receptor. The fluorine atom in A1 would play an equivalent role. A simple model for LTG-receptor interaction is proposed.     

Quelques considérations sur la structure électronique du naphtalène

Theπ electronic structure of naphtalene is studied, using a semi-empirical approximation for coulombic and resonance integrals; forH andS (H, hamiltonian;S, overlap) the complete matrices are adopted, together withKohlrausch's nuclear effective charges. A non uniform charge distribution is obtained, with charge accumulation at the tertiary carbons. Bond orders between non neighboring atoms indicate contributions to the fundamental state from other structures besides the classical ones. A comparative study of the obtained interatomic distances is carried. It is shown that [H, S]=0 is not a sufficient condition for the identity of the bond orders for the fundamental state calculated with and without overlap.     

About counterintuitive orbital mixing and bond populations

It is shown that negative bond and orbital populations may be avoided by the introduction of a weight factor in a bond index definition, together with a suitable parameterization. The negative bond populations found for first-row metal complexes need not be ascribed to counterintuitive orbital mixing but rather, essentially, to the equipartition of the charge distribution. Different definitions of the bond population are compared for ferrocene and the effects of some parameterizations are discussed.     

Graphical linking of a MO multicenter bond index to VB structures

The multicenter bond index proposed within the MO framework depends on the order of the centers for which it is calculated, outside from the 3-c case. For the 6-c case, the eventually different values are 60. A graphical approach links the MO values to VB structures. Benzene, chosen as our paradigm for the 6-c case, illustrates our proposition.     

An analysis of the polarizabilities in some conjugated molecules

Atom-atom, atom-bond and bond-bond polarizabilities are calculated with a previously used LCAO approximation. Some properties of naphtalene, assumed as general for alternant hydrocarbons, seem to depend on the approximation employed. Atom-atom polarizabilities in azines are related to other theoretical and experimental quantities. In all the molecules studied, the part played by formal bonds is highly stressed.

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Zusammenfassung Atom-Atom-, Atom-Bindungs- und Bindungs-Bindungs-Polarisierbarkeiten werden mit einem schon früher benutzten LCAO-Verfahren berechnet. Einige Eigenschaften von Naphthalin, die für alternierende Kohlenwasserstoffe als charakteristisch angesehen werden, scheinen von der benutzten Näherung abzuhängen. Atom-Atom-Polarisierbarkeiten in Azinen werden auf andere theoretische und experimentelle Größen zurückgeführt. In allen betrachteten Molekülen spielen formale Bindungen eine bedeutende Rolle.

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Résumé Calcul des polarisabilités atome-atome, atome-liaison et liaison-liaison dans une approximation LCAO utilisée auparavant. Certaines propriétés du naphtalène, supposées générales pour les hydrocarbures alternants, semblent dépendre de l'approximation employée. Les polarisabilités atome-atome des azines sont reliées à d'autres grandeurs théoriques et expérimentales. Dans toutes les molécules étudiées, le rôle joué par les liaisons formelles est mis en relief.

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With a fellowship from the Consejo Nacional de Investigaciones Científicas y Técnicas, Argentina.

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With a fellowship from the Centro Latino Amerioano de Física.

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The authors gratefully acknowledge the helpful discussions with Dr. J. Brieux and Lic. H. C. González, who has besides collaborated in part of the calculations.     

Hydrogen bonding and charge transfer in some interactions involving methyl glyoxal and formamide

Summary The possibility of hydrogen bonding between the nucleic-acid bases and methyl glyoxal or formamide is studied through an IEH calculation; the charge transfer and hydrogen bond indices support this hypothesis. The CH...Y indices are similar to those of usual hydrogen bonds. In six of the nine configurations previously proposed by other authors in order to analyse the H₂S-formamide interactions, formamide is predicted to be an electron acceptor.

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Riassunto In un calcolo IEH, si studia la possibilità del legame a idrogeno fra le basi costituenti gli acidi nucleici ed il metilgliossale o la formamide, il trasferimento di carica e gl'indici del legame a idrogeno sembrano confermare l'ipotesi. Gl'indici CH...Y sono simili a quelli dei legami a idrogeno usuali. In sei delle nove configurazioni, proposte da altri autori per analizzare l'interazione fra il solfuro d'idrogeno e la formamide, questa risulta essere un accettore di elettroni.

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Резюме Используя вычисления IEH, исследуется возможность водородной связи между основаниями нуклеиновых кислот и глиоксалом метила или формамидом. Перенос заряда и индексы водородной связи подтверждают зту гипотезу. Индексы CH...Y являются аналогичными для обычных водородных связей. В шести из девяти конфигураций, ранее предложенных другими авторами для анализа взаимодействий ?H₂S-формамид?, предсказывается, что формамид является акцептором злектронов.

     

Comparative borazarobenzenes calculations following different methods

Borazarobenzenes are studied with different approaches, some treating only electrons and others including all valence electrons. The importance of the total net electronic density for interpreting the chemical behaviour of the molecules is stressed. All methods agree in assigning fairly high values to dipole moments. Disagreeing conclusions about other properties in the different methods are analyzed.

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Zusammenfassung Die Borazarobenzol-Isomeren werden mit verschiedenen Methoden untersucht, die entweder nur die -Elektronen oder alle Valenzelektronen behandeln. Die Wichtigkeit der Gesamt-Elektronen-dichte für die Erklärung des chemischen Verhaltens der Moleküle wird hervorgehoben. Alle Methoden stimmen in dem Ergebnis recht hoher Werte für die Dipolmomente überein. Unterschiedliche Ergebnisse bei der Anwendung der verschiedenen Methoden werden analysiert.

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Résumé On étude les borazarobenzènes suivant de diverses méthodes; les unes traitent seulement les électrons et les autres impliquent tous les électrons de valence. On souligne l'importance des charges nettes totales pour interpréter le comportement chimique des molécules. Toutes les méthodes s'accordent en attribuer des valeurs assez hautes au moment dipolaire. On analyse des conclusions discordantes sur d'autres propriétés prévues par les différents méthodes.

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One of us (M. G.) wishes to thank the Consiglio Nazionale delle Ricerche for making possible his stay in Italy.     

Definition of a multicenter bond index

The tensor character of the first-order density matrix leads to the definition of an MO multicenter bond index for closed-shell systems. It is here applied to three-center bonds. Satisfactory results are obtained for compounds involving secondary bonds, strong and normal hydrogen bonds; the index for the peptide bond is found to be similar to that of strong hydrogen bonds.On leave of absence from Inst. de Física, UFBA, 40000 Salvador, BA, Brasil.     

Finite interaction from an evanescent coupling

We compute the first-order vertex radiative corrections in a theory in which the only interactions is an evanescent one of the form {γ₅, γ_μ}. An effective finite γ₅ interaction is obtained.     

Die Bildung von Liesegang'schen Ringen durch Azotobakter bei O2-Hemmung

Ohne Zusammenfassung