New heterocyclic structures. [1,3]Thiazino[3,2-a]purine and [1,2,3]triazolo[4,5-d][1,3]thiazino[3,2-a]pyrimidine

Derivatives of two new molecular structures, namely, [1,3]thiazino[3,2-a]purine and [1,2,3]triazolo[4,5-d]-[1,3]thiazino[3,2-a]pyrimidine, were synthesized together with other heterocyclic compounds. Retrosynthetic analysis of their molecular skeletons suggested a simple way of obtaining 3,4-dihydro-7,8-diamino-2H,6H-pyrimido[2,1-b][1,3]thiazin-6-one, which is a useful intermediate for their synthesis. This intermediate and the thiazole homologue were obtained directly by reaction of 5,6-diamino-2,3-dihydro-2-thioxo-4(lH)-pyrimidi-none with 1,3- or 1,2-dibromoalkane, respectively.     

One-step synthesis and characterization of difunctionalized N-confused tetraphenylporphyrins

Three disubstituted N-confused porphyrins (2-4) were prepared in ca. 4% yield using a one-pot synthesis. These porphyrins bear 3,5-di-tert-butylphenyl groups substituted at the C(5) and C(20) meso positions and para-substituted (Br, NO(2), ethynyl) phenyl groups at the C(10) and C(15) meso positions. The specific orientation of the aryl rings around the macrocycle in porphyrin 2 was definitively determined using a combination of 1D ((1)H and (13)C) and 2D (gHMQC and gHMBC) NMR spectroscopy. The absorption spectra of 2-4 in CH(2)Cl(2) and dimethylacetamide are similar to those of N-confused tetraphenylporphyrin in the same solvents but have Soret and Q-bands that are shifted to lower energies. Steady-state fluorescence measurements revealed Q(x)(0,0) and Q(x)(0,1) bands similar in energy to the unsubstituted NCPs 1i and 1e. The fluorescence quantum yield results for two of these NCPs (2, 4) are atypical of porphyrin behavior and are being further investigated by time-resolved spectroscopy.     

Analyse de population dans les calculs LCAO: charges et moments atomiques

Résumé Les auteurs montrent que le moment dipolaire d'une molécule peut, avec une bonne approximation, se réduire à la somme vectorielle des moments atomiques et d'un moment de charges ponctuelles centrées sur les atomes. Les charges ainsi définies sont indépendantes du système d'axes de coordonnées.

---

Population analysis by LCAO calculations: Charges and atomic moments

The authors show that the dipole moment of a molecule can be reduced to the vector sum of the atomic moments and of a moment due to point charges centred on atoms with a good accuracy. The so defined charges are independent of the coordinate system.

---

Zusammenfassung Die Autoren zeigen, daß das Dipolmoment von Molekülen als Vektorsumme der Atommomente und eines Moments, das von Punktladungen an den Atomen herrührt, dargestellt werden kann. Die dabei definierten Ladungen sind unabhängig vom Koordinatensystem.

---

---

Equipe de Recherche Associée au C.N.R.S. n 22.

---

Remerciements. Ce travail a été en partie présenté au 2ème Colloque International des Chimistes Théoriciens d'expression latine (Paris, septembre 1970).Les auteurs remercient les participants à ce Colloque et en particulier Madame A. Pullman et Monsieur P. Claverie pour leurs remarques et leurs suggestions. Leur gratitude va également au Centre National de la Recherche Scientifique pour l'aide matérielle qu'il apporte à ces recherches.     

Automorphisms of (B)-geometries

(B)-Geometries are incidence structures arising from permutation sets. The present paper studies the automorphism groups of (B)-Geometries. In certain cases these automorphisms yield examples of inversive planes and of subplanes which are embedded in Minkowski planes (chapter 2). In chapter 3 we describe the automorphism groups of the (B)-Geometries arising from the groups PL(2, pⁿ) and AL(1, pⁿ) in their natural representations on the points of the projective and affine line.Dedicated to Prof.Dr. Walter Benz on his 60th birthdayWork done within the activity of G.N.S.A.G.A. of C.N.R. and supported by the 40% grants of M.U.R.S.T.     

The Electronic Nature of the 1,4‐β‐Glycosidic Bond and Its Chemical Environment: DFT Insights into Cellulose Chemistry

The molecular understanding of the chemistry of 1,4‐β‐glucans is essential for designing new approaches to the conversion of cellulose into platform chemicals and biofuels. In this endeavor, much attention has been paid to the role of hydrogen bonding occurring in the cellulose structure. So far, however, there has been little discussion about the implications of the electronic nature of the 1,4‐β‐glycosidic bond and its chemical environment for the activation of 1,4‐β‐glucans toward acid‐catalyzed hydrolysis. This report sheds light on these central issues and addresses their influence on the acid hydrolysis of cellobiose and, by analogy, cellulose. The electronic structure of cellobiose was explored by DFT at the BB1 K/6‐31++G(d,p) level. Natural bond orbital (NBO) analysis was performed to grasp the key bonding concepts. Conformations, protonation sites, and hydrolysis mechanisms were examined. The results for cellobiose indicate that cellulose is protected against hydrolysis not only by its supramolecular structure, as currently accepted, but also by its electronic structure, in which the anomeric effect plays a key role.     

Zn[aminoacid]2 hybrid materials applied as heterogeneous catalysts in the synthesis of β-enaminones

Hybrid materials have seized attention from scientific community mainly as heterogenic catalysts in organic reactions on a large scale succeeding in some organic compounds with high yields. One of the most important classes of hybrid materials used for this purpose involves the complexation of Zn and aminoacids. Herein, we introduced Zn[Pro]₂ and Zn[Gly]₂ in the synthesis of several β-enaminones via solvent free protocol and using an ultrasound device.