Hydrodynamic and conformational properties of cellulose myristate molecules in solution

Cellulose myristate samples with a degree of substitution of 230–250 have been studied by the methods of molecular hydrodynamics (viscometry, analytical ultracentrifugation (flotation), and isothermal translational diffusion) in chloroform in the range M = (56–652) × 10³. The experimental evidence has been interpreted within the framework of the generalized wormlike Yamakawa-Fuji model with the following parameters: the persistence length a = 115 × 10^?8 cm, the chain diameter d = 45 × 10^?8 cm, and the molecular mass per unit chain length M _L = 270 × 10⁸ cm^?1. It has been inferred that the polymer dissolves in chloroform in the form of dimers.     

Fragmental analysis of energies of electronic transition in monosubstituted benzene derivatives. I. A single configuration approximation

Conclusions The analysis of EET in the SC-approximation that has been carried out on the example of MSB showed that the use of the FO basis instead of the AO basis gives additional information on the relationship between the energies of transitions of the chromophoric (benzene) molecule and its substituted derivatives.In the FO basis the decomposition of the EET into the fragmental and interfragmental components becomes natural. The value of the fragmental components is determined by the LN of the transition MO in the separate fragments, while that of the one-electronic energies and the coulombic and exchange integrals of the fragment (the chromophore) are approximately transferable parameters.Since the LN are dependent on the degree of mixing of the FO of the fragments the study of the relationship between the transition energies of the SC-transitions in the chromophoric molecule and the fragmental components in the substituted molecule is reduced to the study of formation the LCFO MO. Moreover, the LCFO MO makes it possible to find a relationship between the SC-transitions even when the LCAO MO of the two molecules are not commensurable. This makes it possible to carry out a classification of the SC-transitions in MSB according to the SC-transitions of benzene.We wish to express our gratitude to A. L. Gineitite for useful comments made during the preparation of the article.Institute of Biochemistry, Lithuanian Academy of Sciences. Institute of Theoretical Physics and Astronomy, Lithuanian Academy of Sciences. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 6, pp. 45–56, November–December, 1992.     

Methane Hydroxylation by Methane Monooxygenase: On the Problem of the Process Dynamics

Published data on the kinetic isotope effects of the hydroxylation of deuterium-substituted methane molecules (CHD₃, CH₂D₂, and CH₃D) by methane monooxygenase are examined in the framework of the two-step nonradical mechanism through the intermediate formation of a complex containing pentacoordinate carbon. The kinetic schemes with the first step involving one, two, and three hydrogen atoms of the oxidized substrate are considered. Contrary to the widely accepted oxygen rebound mechanism, the experimental results obtained for the oxidation of various substrates by methane monooxygenase and cytochrome P450 can be explained from the viewpoint of the dynamics of a general nonradical mechanism.     

Meldrum's acid and its analogs

2-Substituted or 2,2-disubstituted 4,6-dioxo-1,3-dioxanes, which are analogs of Meldrum's acid and were obtained by reaction of malonic acid with acetic anhydride and the appropriate carbonyl compound in the presence of sulfuric acid, exist in solution preferably in a single form according to the PMR and ¹³C NMR spectral data. Fluctuation of the CH₂ group is not observed. The mass spectra are characteristic and are distinguished by splitting out of the carbonyl compound from the molecular ion or successive splitting out of CO₂ and ketene molecules. The Meldrum acid analogs do not affect plant growth but have a depressive effect on the central nervous system of animals and low toxicity.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1482–1486, November, 1975.