Atomic force microscopy and solid state photolyses: phase rebuilding

Atomic force microscopy (AFM) was used for the study of the mechanism of phase rebuilding in photodimerizations in crystals and of photoreactions on polymer surfaces. The AFM features that are found upon photochemical reactions in the surface regions indicate far-reaching (up to 100 nm) molecular transport which are well directed in space and depend on the crystal face. Thus, not only proximity considerations (topochemistry) but more importantly phase-rebuilding mechanisms are crucial for solid state photoreactivity and this depends on the bulk crystal structure. 2-benzylidenecyclopentanone (d=4.123 Å) and trans-stilbene (d=5.720 Å) are not reactive, because no phase-rebuilding mechanism is available, while anthracene (d=6.038 Å) does form a photodimer. The phase-rebuilding mechanisms on two natural faces of antharacene are analysed and interpreted on the molecular level. The formation of three different photoproducts from 2,5-dibenzylidenecyclopentanone shows two different phase-rebulding mechanisms on the morphologically dominant face and there are extraordinarily wide molecular rotations of the highly skewed (46°, 131°) reactants in the crystal. Photolyses of polymeric foils of styrene-isopropyl-acrylate copolymer and polystyrene give rise to very nanostructures in the surface region that can be imaged by AFM.     

Fluorine absorption spectra and some fluorides in condensed state

The absorption spectra of liquid F₂, NF₃, N₂F₄, CF₄, BF₃, NF₃, SF₆ have been obtained at diminished temperatures in the near ultra-violet region of the spectrum. It is shown that the absorption spectrum does not differ from the spectra in the gaseous phase, therefore the elementary absorption act is characterized by the cross section of photon absorption by an individual molecule. The absorption cross sections of the above mentioned molecules are represented in the liquid phase, which do not differ strongly from absorption cross sections of these molecules in the gaseous phase. The dependence of the absorption cross sections of liquid fluorine on its concentrations in solutions with N₂, Ar, NF₃, O₂ at - 196°C has been studied. The cross sections of photon absorption by the fluoride molecule in different liquid media with small fluorine concentrations have been obtained.     

Influence of wilt infection on the gossypol pigments of seeds and roots of a cotton plant of the variety Tashkent-1

A study has been made of the gossypol pigments of the seeds and roots of a cotton plant of the variety Tashkent-1 infected with wilt in comparison with a healthy plant. The amount of gossypol in the infected plant was lower than in the healthy plant. In the diseased plant, gossypurpurin was concentrated in the roots, and in the healthy plant it was concentrated in the seeds. Gossypol possessing optical activity was detected in the seeds and roots of both the healthy and the diseased plants.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 63–66, January–February, 1989.     

Reaction of 2-substituted 4,4-dimethyl-5-methylene-1,3-dioxolanes with dichlorocarbene and certain transformations of adducts obtained

A series of derivatives of 4,4-dimethyl-5-methylene-1,3-dioxolane has been synthesized, and their reaction with dichlorocarbene, obtained under interphase catalysis conditions, has been studied. The adducts obtained undergo thermal isomerization into dichloroethylidene derivatives.     

Reactions of heterocyclic cations with nitrogen-containing nucleophiles. 10. Synthesis of 3,5,7-triaryl-1,2-oxazepinium perchlorates by the reaction of 2,4,6-triarylpyrylium salts with nitrones and substituted hydroxylamines

2-Substituted 3,5,7-triaryl-1,2-oxazepinium perchlorates were obtained by the reaction of 2,4,6-triarylpyrylium salts in dimethylformamide with nitrones and N-arylhydroxylamines. The products are the first representatives of seven-membered cations with eight electrons.See [1] for Communication 9.Deceased.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 457–460, April, 1982.     

Autocatalytic condensation of 1,2-orthoesters of sugars with 2,3-dihydroxy-1,4-naphthoquinone (isonaphthazarin)

The autocatalytic glycosylation of isonaphthazarine and its derivatives with 1,2-orthoesters of D-glucose and maltose in chlorobenzene has been studied. It has been established that the ratio of mono- and bisglycoside forms depends on the acidity of the glycosylated hydroxy group and its steric accessibility. Free monoglycosides of 2,3-dihydroxy-1,4-naphthoquinone have been synthesized by deacetylation with sodium methoxide in methanol.Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 477–482, July–August, 1989.     

On the thermal expansion of nanohole free volume in perfluoropolyethers

To determine the free volume in polymers, positron annihilation lifetime spectroscopy data are transformed into nanohole volumes by modeling the cavities as spheres or, more generally, using geometries assuming an isotropic thermal expansion. However, this guess could be unrealistic owing to the irregular shape of nanoholes and constrained movements of the macromolecules. In this work, it is shown that a comparison of hole-lattice theory with positron and dilatometric data for a homologous series of perfluoropolyethers supplies information on the anisotropic expansion of nanoholes; the relation between volume and typical unconstrained size of the cavities can be expressed by a power law with noninteger exponents.     

Mannich Condensation of exo-2,exo-6-Tricyclo[5.2.1.02,6]decan-8-one

Mannich condensation of exo-2,exo-6-tricyclo[5.2.1.02,6]decan-8-one with paraformaldehyde and dimethylamine hydrochloride results in the addition of dimethylaminomethyl fragment at the C⁹ atom to give the exo-9-isomer. The reaction of exo-9-dimethylaminomethyl-exo-2,exo-6-tricyclo[5.2.1.02,6]decan-8-one with hydroxylamine hydrochloride in alcoholic alkali yields the corresponding Z-oxime which undergoes selective rearrangement into exo-10-dimethylaminomethyl-9-aza-exo-2,exo-6-tricyclo[5.3.1.02,6]undecan-8-one by the action of sulfuric acid in acetonitrile.     

Z/E PHOTOISOMERIZATION OF UROCANIC ACID*

The E ? Z photoisomerization of the title compound (UA) (a naturally occurring sunscreen) has been studied in aqueous solution. At a UA concentration of 6mM and using 313nm excitation, φ_E→z= 0.52, φ_Z→E= 0.47 and the photostationary state is 34% E. Under these conditions, loss of UA is minimal. Low energy triplet quenchers fail to impede the isomerization, but the reaction can be induced by several triplet sensitizers. The E_T for UA is estimated to be approximately 55 kcal/mol.     

Low frequency vibrational spectra of some amino acids

Far-IR absorption and reflection spectra, as well as laser Mandelshtam–Brillouin and Raman scattering spectra of -glycine, β-alanine, -histidine, -tryptophane single crystals in the 0.2–400 cm⁻¹ range were investigated. It was revealed that the far-IR and Raman spectra of the amino acids under study contain more bands than predicted by factor-group analysis, thus indicating a possible contribution of low-energy intramolecular vibrations and overtones, as well as an emergence of forbidden vibrations. Some of the low-frequency bands have never, to our knowledge, been detected previously.