Spectral investigations of the tautomeric equilibria of thioacyl derivatives of 2-aminothiazole and 2-aminobenzothiazole

The positions of the tautomeric equilibria for a number of thioacyl derivatives of 2-aminothiazole and 2-aminobenzothiazole were determined by UV and IR spectroscopy with the use of model compounds. Quantum-chemical calculations by the CNDO/2 method were made for some of the acyl and thioacyl derivatives of 2-aminothiazole and 2-iminothiazole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 24, No. 3, pp. 410–417, March, 1988.     

Double asymmetric induction in benchrotrene derivatives

Attachment of a Cr(CO)₃ moiety to one of the aromatic rings in rigid diaryl ketones of very low prochirality followed by addition of a chiral and optically pure reagent leads to satisfactory asymmetric induction ~40%. Asymmetric induction is smaller in the case of acyclic systems.     

Manganese Complexes with Octaphenyltetraazaporphine: Acid–Base Interactions and Kinetic Stability in Proton-Donor Solvents

Complexes of manganese(III) and manganese(V) with octaphenyltetraazaporphine (H₂OPTAP) were synthesized. Acid–base interactions of these complexes in the CH₂Cl₂–CF₃COOH system and kinetics of their dissociation in concentrated sulfuric acid, as well as kinetics of octaphenyltetraazaporphine destruction in sulfuric acid solutions were studied by spectrophotometric methods. Acid–base interactions in CH₂Cl₂–CF₃COOH were shown to involve two macrocyclic meso-nitrogen atoms in succession. Concentration stability constants of the acid forms obtained pK ₁ = 0.29 ± 0.01 and pK ₂ = –0.62 ± 0.08 for (chlorine)manganese(III)octaphenyltetraazaporphine ((Cl)MnOPTAP); pK ₁ = 0.99 ± 0.02 and pK ₂ = – 0.70 ± 0.03 for (nitrido)manganese(V)octaphenyltetraazaporphine ((N)MnOPTAP). The rate of dissociation of the complexes in 94–98% H₂SO₄ does not depend on the acid concentration. The manganese(V) complex is three times as stable as the manganese(III) complex.     

An investigation of the component composition of the essential oil of Monarda fistulosa

The composition of the essential oil of wild bergamot bee balm introduced into the Krasnodarsk Krai has been analyzed by chromatomass spectrometry. The essential oil contains 34 components of which the main ones are -pinene (3.5%), -pinene (2.9%), -terpinene (1.7%), p-cymene (32.5), an aliphatic aldehyde (6.3%), sabinene hydrate (1.9%), -caryophyllene (1.1%), the methyl ether of carvacrol (5.5%), citronellyl acetate (1.6%), thymol (12.6%), and carvacrol (24.0%). The compounds were identified on the basis of their mass-spectrometric characteristics and arithmetical retention indices.A. N. Severtsov Institute of Animal Evolutionary Morphology and Ecology, Academy of Sciences of the USSR, Moscow. All-Union Scientific-Research Institute of Drugs, Moscow. Translated from Khimiya Prirodnykh Soedinenii, Vol. 5, pp. 646–649, September–October, 1989.     

Experimental (NMR) and Computational (MD) Studies on the Inclusion Complexes of 1-Bromoadamantane with alpha-, beta-, and gamma-Cyclodextrin

The inclusion complexes between the most commonly used cyclodextrins (alpha-, beta-, and gamma-CD) and 1-bromoadamantane were prepared and studied experimentally by NMR methods and by molecular dynamics simulations (AMBER force field) with solvation. The NMR results suggest host/guest ratios of 2:1, 1:1, and 1:1 for the complexes with alpha-, beta-, and gamma-cyclodextrin, respectively, as well as defined geometries for the complexes. Averaged geometrical data from the molecular dynamics simulations agree with the complexation geometries deduced experimentally.     

Synthesis of enantiomerically enriched allenes by (-)-sparteine-mediated lithiation of alkynyl carbamates

[reaction: see text]. The alpha-deprotonation of alkynyl carbamates 3 with the chiral base (-)-sparteine (4)/n-butyllithium, transmetalation with ClTi(O(i)()Pr)3, and subsequent substitution with an aldehyde results in the formation of enantioenriched 4-hydroxyallenyl carbamates 11. Stereoselection is determined by dynamic resolution of the lithium/(-)-sparteine complexes by selective crystallization.     

Unique structural properties of the Mg-Al hydrotalcite solid base catalyst: an in situ study using Mg and Al K-edge XAFS during calcination and rehydration

The changes in the layered structure of Mg-Al hydrotalcite (Mg/ Al = 2) during heat treatment have been investigated by using in situ XAFS simultaneously at the Mg and Al K-edges. The development of unique in situ instrumentation allowed the coordination environments at both the Mg and Al centers to be monitored as a function of the temperature and heat treatment. The results of this study show that the hydrotalcite structure is highly flexible, and should lead to the further development of hydrotalcites as new solid basic catalysts. Moreover, the Mg and Al cations in the cation layers show different behavior as a function of temperature. The coordination of some octahedral Al ions decreases already at a temperature of 425 K, whereas the coordination about Mg does not show any modification at this temperature. However, hydrotalcite treated at 425 K, followed by cooling down to room temperature resulted in a complete reversal to the original octahedral Al coordination. It is proposed that Al-OH bond breakage occurs at 425 K, without the evolution of H2O. This bond is restored after cooling to room temperature. The actual dehydroxylation of hydrotalcite commences between 425 and 475 K, as indicated by a change in coordination of both the Mg and Al centers. This is accompanied by the evolution of H2O molecules and the changes are hence irreversible without the presence of excess water. Heat treatment at 725 K leads to the development of an MgO-like phase (octahedral Mg) and a mixed octahedral/tetrahedral Al phase. A subsequent rehydration at room temperature entirely restores the original coordination about the Al and Mg centers of hydrotalcite to a distance of 15 A, to which XAFS spectroscopy is sensitive.     

Predicting discotic mesomorphism from molecular parameters for discogenic structures

Molecular parameters (M_m, M_r, K_p, K, K_c, and K_s) are calculated for polysubstituted cycloveratrilenes and cyclophanes as a continuation of our series of papers on prediction of discotic mesomorphism (DM). Histograms showing the distribution of 57 mesogenic and 28 nonmesogenic structures according to the first three parameters are constructed. Prediction probabilities are estimated at more than 50% for M_m and M_r. This approach is used to analyze 150 hypothetical structures of polysubstituted cycloveratrilenes and cyclophanes to examine the occurrence of a discophase. Several structures with predictable DM are selected for further research. Ivanovo State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 39, No. 3, pp. 473–477, May–June, 1998.     

Type I and type II sensitizers based on Rose Bengal onium salts

Abstract— New Rose Bengal oniurn salts containing one or two iodonium, sulfonium, phosphonium, and pyrylium ions have been prepared as part of a program to develop sensitizers which can function as Type I radical photoinitiators and Type II energy transfer donors depending on experimental conditions. The absorption spectra of the onium salts in different solvents indicate an equilibrium between tight and loose ion pairs which depends on the solvent polarity, the cation and concentration. Typical Rose Bengal photochemistry requires the structure be that of the loose ion pair in the solvent of choice. Similar factors also influence bleaching behavior, and bleaching is the result of electron transfer processes. The quantum yields of singlet oxygen production from the onium salts in polar solvents are similar to that of the parent, Rose Bengal disodium salt.