Photophysics of Zinc (II) Phthalocyanine Polymer and Gel Formulation

The photophysical properties of lipophilic phthalocyanines encapsulated into a polymer and two different gels were studied in order to predict their photosensitizing efficacy in vivo. Photophysical techniques for solid phase were adapted for light dispersing samples. Gel formulation of two tetrasubstituted phthalocyanines, tetra-t-butylphthalocyaninato zinc(II) ( 1 ), tetrakis(1,1-dimethyl-2-phthalimido)ethylphtalocyaninatozinc(II) ( 2 ) and two octasubstituted phthalocyanines, 2,3,9,10,16,17,23,24-octakis(decyloxy)phthalocyaninatozinc(II) ( 3 ) and 2,3,9,10,16,17,23,24-octakis[(N,N-dimethylamino)ethylsulfanyl]phthalocyaninatozinc(II) ( 4 ) were investigated for their possible use in photodynamic therapy for topical purposes. Supporting the fact that gel formulation improves the photophysical properties of phthalocyanines, singlet molecular oxygen quantum yield (Φ_Δ) values for 1 – 4 zinc(II) phthalocyaninates in Lutrol^® F 127-Cremophor^® RH 40 were 0.60, 0.60, 0.20 and 0.26, respectively. Permeation studies showed that no release of phthalocyanines occurs, thus indicating there should be no risk of generalized skin photosensitivity in areas other than the dye-deposition site.     

On interpolating discrete varieties for weighted spaces of entire functions

We study interpolating discrete varieties for weighted spaces Ap(Cn) of entire functions such that sup_zC ⁿ|f(z)|exp(-B p(z))< for some B>0. We give a necessary and sufficient condition for a finite union of interpolating discrete varieties to be itself interpolating. Then we use L² techniques for &#8706; to give a sufficient geometric interpolating condition.     

Imperfect and Nonideal Clutters: A Common Approach

We prove three theorems. First, Lovászs theorem about minimal imperfect clutters, including also Padbergs corollaries. Second, Lehmans result on minimal nonideal clutters. Third, a common generalization of these two. The endeavor of working out a common denominator for Lovászs and Lehmans theorems leads, besides the common generalization, to a better understanding and simple polyhedral proofs of both.* Visiting of the French Ministry of Research and Technology, laboratoire LEIBNIZ, Grenoble, November 1995—April 1996.     

2-Aminopyrimidine directed self-assembly of zinc porphyrins containing bulky 3,5-di-tert-butylphenyl groups

The 2-aminopyrimidin-5-yl ligand is revealed to be a promising candidate for the construction of supramolecular porphyrin arrays with broad absorption bands for efficient light-harvesting. 10-Mono- and 10,20-di(2-aminopyrimidin-5-yl) derivatives of 5,15-bis(3,5-di-tert-butylphenyl)porphyrin have been synthesized in high yield. Their Zn(II) salts show variable concentration and temperature-dependent UV/vis spectra in solution, consistent with supramolecular aggregation. Whereas the FAB mass spectra of the monosubsituted derivative in toluene suggest the formation of a tetramer at high concentrations and low temperatures (estimated association free enthalpy Delta H = 220 +/- 10 kJ/mol), the larger splitting of the Sorret band (ca. 40 nm) in the variable temperature UV/vis spectra of the disubstituted bis(3,5-di-tert-butylphenyl)porphyrin is indicative of yet higher aggregates involving both 2-aminopyrimidin-5-yl groups. The tetrameric nature of the monosubsituted derivative is confirmed by X-ray analysis, which reveals that two of the 2-aminopyrimidin-5-yl groups are encapsulated by the aggregate and consequently are prevented from undergoing hydrogen bonding. NMR studies show there is no exchange of the 2-aminopyrimidin-5-yl groups, so the tetramer is rigid, which is confirmed by molecular modeling calculations. The tetramer formation is governed by pi-pi interactions, metal coordination, and hydrogen bonding. The di(2-aminopyrimidin-5-yl) derivative forms strongly scattering solutions, which upon standing form green flocculate precipitates, reminiscent of shaken suspensions of bacteriochlorophyll c.     

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.     

Transesterifications mediated by t-BuNH2

A mild protocol for transesterification of simple esters is described. The method is based on the use of t-BuNH₂/ROH (R = Me, Et, i-Pr, t-Bu) with or without LiBr. The scope of the procedure was explored for aliphatic and aromatic esters. The protocol is particularly useful when going from higher to lower hindered esters and harsh reaction conditions are needed for the reversal process. A rationalization of the mechanism is presented. The scope and limitation of this transformation are also described.     

Syntheses of the tedanolides and myriaporones

This review covers the synthetic contributions leading to the syntheses of the polyketides tedanolide, 13-deoxytedanolide and the structurally related myriaporones. Fragment syntheses that lead to valuable insight into the subtle synthetic problems of the tedanolides are also presented.     

Optical performance of carbon-nanotube electron sources

The figure of merit for the electron optical performance of carbon-nanotube (CNT) electron sources is presented. This figure is given by the relation between the reduced brightness and the energy spread in the region of stable emission. It is shown experimentally that a CNT electron source exhibits a highly stable emission process that follows the Fowler-Nordheim theory for field emission, fixing the relationship among the energy spread, the current, and the radius. The performance of the CNT emitter under realistic operating conditions is compared with state-of-the-art electron point sources. It is demonstrated that the reduced brightness is a function of the tunneling parameter, a measure of the energy spread at low temperatures, only, independent of the geometry of the emitter.