Determination of the spin sublevel origin of radiative and non-radiative decay routes of phosphorescing benzene derived from precision lifetime measurements

The increase in the phosphorescence lifetime as temperature is lowered has been quantitatively determined in the 2–30 K range. Applying the Boltzmann population expression yields the information that virtually none of the radiative decay originates from the lowest spin sublevel (A_2g).     

Über Pterinchemie. Mitteilung. Die Kristallstruktur von 5,6,7-Trimethyl-5,6,7,8-tetrahydropterindihydrochlorid-monohydrat

The crystal structure of 5,6,7-trimethyl-5,6,7,8-tetrahydropterine-dihydrochloride-monohydrate The crystal structure of the title compound has been determined by X-ray analysis (direct methods) and refined with 947 structure amplitudes to R = 0.026. The crystal system is orthorhombic, space group Pna2₁, with unit cell dimensions a = 14.081, b = 14.623, c = 6.773 Å. The molecule is protonated at the N(1)- and N(5)-position. The tetrahydropyrazine ring exists in a conformation in which C(6) deviates markedly from the mean plane of the other five atoms. The CH₃-groups at N(5) and C(6) possess a trans configuration with a pseudoaxial and an axial conformation respectively. The CH₃-groups at C(6) and C(7) in return possess the cis configuration, whereby the CH₃-group at C(7) occupies an equatorial conformation.     

Random peptide synthesis using immobilized enzymes in high concentrations of organic solvents

Trypsin, leucine aminopeptidase, and carboxypeptidase B were separately immobilized on controlled pore glass and reacted with a dipeptide substrate in high concentrations of either acetone or 1-propanol. Hydrolytic activity was demonstrated and evidence for the possible synthesis of peptide polymer is presented. Directed synthesis using amino acids and blocked amino acids as substrates was not successful.     

Optically detected zero-field triplet state magnetic resonance in photosynthetic bacteria

Triplet state transitions of the photosynthetic bacteria Rhodospirillum Rubrum, Rhodopseudomonas Spheroides and Chromatium Vinosum in chemically reduced preparations have been observed by zero-field optical detection of magnetic resonance at 2 K. For each bacterial preparation two sharp, structureless, zero-field EPR transitions were observed as microwave-induced decreases in the fluorescence intensity of the frozen cellular preparations. The depopulating rate constants for the spin sublevels of the triplet states observed in R Rubrum and R Spheroides were also measured. The similarities of the triplet state frequencies, spectral features and intersystem crossing rates suggest a common structure for the reaction centers in the photosynthetic bacteria.     

SENSIBILISIERTE PHOTOOXYDATION DURCH METHYLENBLAU THIOPYRONIN UND PYRONIN-III. MITTEILUNG: ÜBER DEN MECHANISMUS DER PHOTOSENSIBILISIERTEN OXYDATION DES GUANOSINS DURCH THIOPYRONIN

Abstract— The thiopyronin-sensitized photooxidation of guanosine was investigated, using flash photolysis techniques. The reaction kinetics of three short-lived intermediates (the triplet state, the reduced radical, and the oxidized radical) were followed by spectroscopy. The influence of guanosine concentration on the reaction rate shows that only the oxidized radical (reaction 7) of thiopyronin is affected by guanosine. This suggests that the primary step in the photodynamic destruction of DNA is the oxidation of guanosine by the oxidized radical of thiopyronin (reaction 9). This mechanism is discussed in terms of the redox potentials of the donor and the acceptor for three different cases: (1) where the oxidation potential of the donor is more negative than that of the triplet state, the acceptor being the triplet state ( F^T ); (2) where the oxidation potential of the donor is between the potentials of the triplet state and the oxidized radical, the acceptor being the oxidized radical (F_ox); and (3) where the oxidation potential of the donor is more positive than the reduction potential of both the triplet state and the oxidized radical; in this case no electron exchange takes place. The thiopyronin-guanosine system is an example of the second case.     

Copolymerization of styrene. V. Copolymerization with α-cyanocinnamamide

Copolymers of styrene with α-cyanocinnamamide were prepared by free radical initiation in bulk and in DMF solution and also by thermal initiation in bulk. The copolymerization parameters were determined by the conventional scheme of copolymerization and by an improved scheme taking into account the penultimate unit. Different values of the copolymerization parameters were obtained at the above mentioned different polymerization conditions, indicating the existence of a solvent effect. The influence of the comonomer on some of the basic properties, like intrinsic viscosity, solubility, melting range, and glass transition temperature and on some mechanical and behavior properties of the copolymers was studied in comparison with homopolystyrene.     

Ring-chain tautomerism of substituted hydrazones

1-Hydrazino-2-propanol reacts with aliphatic carbonyl compounds to form the corresponding (2-hydroxypropyl)hydrazones. 1-(N-Alkylhydrazino)-2-propanols, on the other hand, give tautomeric mixtures of alkyl-substituted perhydro-1,3,4-oxadiazines and N-alkyl-N-(2-hydroxypropyl)hydrazones. As compared with derivatives of 2-(N-alkylhydrazino)ethanols, the position of the equilibrium in the investigated cases is shifted to favor the cyclic forms.See [1] for communication I.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 301–308, March, 1971.     

Gaussian expansions of orbital products for the evaluation of two-electron integrals

A method is described for evaluating multicenter integrals over contracted gaussian-type orbitals by the use of gaussian expansion of orbital products. The expansions are determined by the method of non-linear least squares with constraints. There is no restriction upon the symmetry of the orbital product and the method is applicable to all products arising from s, p and d-type orbitals. Results are given to indicate the accuracy of the method.     

Copolymerization characteristics of S-vinyl-O-tert-butylthiocarbonate

Poly-S-vinyl-O-tert-butylthiocarbonate is an excellent precursor to poly(vinyl mercaptan) because the tert-butyloxycarbonyl blocking group can be removed by either acid hydrolysis or thermolysis under conditions which minimize the oxidation of the liberated mercaptan to disulfide. Dilatometric studies of the homopolymerization of S-vinyl-O-tert-butylthiocarbonate demonstrated that the polymerization rate was directly proportional to the concentration of free-radical initiator; no thermal initiation was observed. The molecular weight of the homopolymers and copolymers ranged from 30,000 to 50,000 (GPC). Copolymerization of S-vinyl-O-tert-butylthiocarbonate (M₂) with styrene, (r₁ = 3.0, r₂ = 0.2), methyl methacrylate (r₁ = 1.40, r₂ = 0.17) and vinyl acetate (r₁ = 0.04, r₂ = 11.0) indicated that a sulfur atom adjacent to the vinyl group increases the resonance stability (Q₂ = 0.5) and the electron density (e₂ = ?1.4) of the double bond and the corresponding radical. Water-soluble copolymers could be prépared by incorporating either N-vinylpyrrolidone (r₁ = 0.12, r₂ = 3.94) or N-isopropylacrylamide (r₁ = 1.17, r₂ = 0.3) with M₂. The water solubility of the copolymers decreased markedly when the tert-butyloxycarbonyl group was removed. Copolymers of M₂ with N-vinyl-O-tert-butylcarbamate (r₁ = 0.13, r₂ = 5.10) were utilized to prepare crosslinked poly(vinyl amine–vinyl mercaptan); the crosslinking resulted from urea linkages formed during thermolysis of the copolymer.