L-asparaginase bound in a polyacrylamide gel

Summary The enzyme L-asparaginase fromE. coli has been included in polyacrylamide gel, and some of its properties have been investigated: stability, pH dependence, heat stability, K_m. It has been shown that the enzymegel obtained has a better stability then the native enzyme.Institute of Organic Synthesis, Academy of Sciences of the Latvian SSR, Riga. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 382–384, May–June, 1976.     

Gas-chromatographische Bestimmung von Mono-, Di- und Tri?thylenglykol in Wasser

Ohne Zusammenfassung

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Gas-chromatographie determination of ethylene glycol, diethylene glycol and triethylene glycol in water

     

Electrode processes in the oxidation of tetrahydroisoquinoline derivatives

The electrochemical oxidation of the alkaloid laudanosine (Ia) to O-methylflavinantine (II) has been studied in acetonitrile solvent. Using cyclic voltammetry, rotating disc voltammetry and preparative electrolyses on several alkaloids, simple aliphatic amines and aromatic compounds, some aspects of the mechanism of this coupling reaction are elucidated. The first anodic wave for laudanosine at platinum has E_p=0.55 V vs. Ag/Ag⁺. The electrode rapidly becomes partially passivated at potentials above 0.5 V. This is due to a film which “dissolves” below 0.5 V, at a rate independent of the potential. It is shown that the reaction (Ia)→(II) proceeds at 0.5 V by initial oxidation of the amine moiety. If acids such as sodium bicarbonate are added to the anolyte the amine is protonated causing the first wave to disappear. Oxidation at 1.1 V under these acidic conditions produces the same product, but more rapidly and in significantly higher yield because electrode filming and side reactions resulting from the amine oxidation are abrogated.     

Thermisches Verhalten von Cyclopropa[c]chromenen

The Cyclopropa[c]chromenes 14 , trans-and cis- 15 , trans-and cis- 16 and 17 rearrange on heating > 200° in N, N-diethylaniline to give 2-alkyl-2H-chromenes 7, 8, 21, 22. The rate determining step of this rearrangement is the ‘homoelectrocyclic’ ring opening of the cyclopro-pa[c]chromenes to give ω-allyl-quinomethanes of type 4. These intermediates show fast [1,5s] and [1,7a] H-shifts, followed by electrocyclic ring closure. Deuterium labelling experiments are in agreement with this mechanism. The remarkable dependence of the rates of rearrangement with respect to the stereochemistry of the cyclopropa[c]chromenes (cf. table 2) suggests that in the first step only one of the two possible disrotatory modes of ring opening is involved.     

The influence of ion pairing at the electrode/solution interface on the kinetics of heterogeneous electron transfer

A model is developed for the accelerating effect of non-reacting ions adsorbed on the inner Helmholtz plane on the kinetics of electron transfer to a reactant which is also situated on the same plane near the electrode. It is assumed that the charge density of non-reacting ions around the reacting ion can be described by a two dimensional distribution function analogous to that used by Fuoss to describe ion pairing in the bulk of the solution. Kinetic equations are presented in which the discreteness-of-charge terms are explicitly included and the magnitude of these terms is estimated on the basis of a simple model. The estimates show that the acceleration of hydrogen ion in the presence of adsorbed iodide ions can be attributed to the electrostatic effect of the surrounding ionic atmosphere.     

Comparison of the structural and chemical composition of giant T-even phage heads.

A study has been made of the structure of the capsids of T4D giant phage produced from mutants in gene 23 and temperature-sensitive mutants in gene 24, and T4D and T2L giant phage formed by the addition of L-canavanine followed by an Larginine chase in the growth medium. All the giant phage capsids have been shown to be built according to the same geometrical architecture. This consists of a near-hexagonal surface net, lattice constant 129.5 A, folded into a left-handed T = 13 prolate icosahedron elongated along one of its fivefold symmetry axes. Their only apparent difference from wild-type T-even phage capsids is their abnormally elongated tubular part. A comparison of the capsomere morphologies and protein compositions of the giant phage capsids showed that all T4D giants are identical but differ from T2L: The T4D capsomere has a complex (6 + 6 + 1)-type morphology, whereas the T2L has a simple 6-type. T2L phage, however, lack two capsid proteins, "soc" and "hoc", present in T4D. The difference in capsomere morphology can therefore be related to the difference in the protein compositions of these two phage. Possible differences between the initiation and means of length regulation of giant phage heads and the aberrant polyheads are discussed.     

Some difficulties in the application of the concept of density of states

The problem of defining N(E), the density of states, for molecular systems is discussed. It is shown that a numeric evaluation of N(E) is often only approximate, even for continuous data, and is not well defined for quantized systems. The application of the concept of density of states is discussed, particularly with regard to the RRKM theory of unimolecular reactions. The sum of states, W(E), and density of states curves are evaluated for several harmonic and anharmonic model systems and the results discussed in order to illustrate the foregoing considerations.     

The crystal structure of the NaNCS complex of nonactin

The NaNCS complex of the macrotetrolide antibiotic nonactin, which acts as an ionophore with biological and artificial membranes crystallizes in the space group C2/c, a = 15.55, b = 19.59, c = 15.31 Å, β = 90°. The X-ray crystal structure investigation shows that Na⁺ is coordinated by four carbonyl oxygen atoms (Na⁺ … O, 2.42 Å) and four ether oxygen atoms (Na⁺ … O, 2.77 Å). The cubic coordination by eight equidistant oxygen atoms observed in the K⁺ complex (K⁺ … O, 2.81 Å) is thus deformed. This, however, requires only very small changes in the ligand conformation.     

New method for the synthesis of macrocyclic compounds

A mixture of isomers corresponding to closing of the ring at the 3 and 4 positions of the thiophene ring is formed during intramolecular acylation of 12-(5-methyl-2-thienyl)-lauryl chloride in a homogeneous medium; the reaction proceeds primarily to favor the formation of the isomer with the larger ring (80%). A method for the synthesis of macrocyclic -alkylcycloalkanones by reductive desulfurization of the corresponding bicyclic ketones, which contain thiophene rings, was developed.See Izv. Akad. Nauk SSSR, Ser. Khim., 2228 (1970) for Communication XI.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1467–1472, November, 1970.