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.     

Ion-chromatographic study of the possible absorption of copper and zinc by the skin of Rana pipiens

Frogs are known to obtain some of their nutrients (e.g., glucose and sodium) through their skin. However, no studies have been made of the possible absorption of transition metals, which exist in most river water at low-ppb (w/w) levels. Therefore, this research was undertaken to evaluate the use of ion chromatography for such an investigation. Solutions of copper and zinc (20 ppb in each) were chosen for use in a small-scale screening study. Ten live frogs were each placed in individual baths for approximately 50 h. Of interest were the net changes in the concentrations of the metals. These differences were the result of any absorption and/or excretion processes that took place. A Dionex IonPac CS5 column was used to analyze this simulated river water, both before and after frogs had been placed in the solution. Included in this paper are: (1) methodology and calculation formulas; (2) precautions needed to ensure sample integrity; (3) statistical analyses, which indicated that ion chromatography is an accurate, precise technique for quantifying Cu and Zn in these samples; and (4) screening-study results, which were used to test the null hypothesis that frogs do not absorb copper and zinc either onto or through their skin.     

An immobiline DryStrip application method enabling high-capacity two-dimensional gel electrophoresis

In the field of proteomics the need to detect low-abundance cellular components, such as regulatory proteins, is of critical importance. Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is one of the most commonly used separation tools for these biological investigations. In this paper we report an alternative micropreparative 2-D PAGE sample application method, called the "paper bridge loading" method. This method makes it possible to apply a larger sample volume to commercially available immobilized pH gradient (IPG) strips. The Vh products required for focusing are only marginally longer than those used in analytical experiments. The method was compared to traditional cup loading and in-gel rehydration. With 18 cm long narrow-range Immobiline DryStrip pH 4.5-5.5, the "paper bridge" method allowed the application of 10 mg human plasma proteins compared to 3 mg with traditional loading methods. The corresponding figures using Escherichia coli sample was found to be 6 mg and less than 2 mg, respectively. The paper bridge method also showed the best results in terms of spot resolution and separation of high molecular weight proteins.     

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.