Local order in the Ni-Ta system

Short-range order in the Ni -Ta system is studied both experimentally (by diffuse scattering of x rays) and theoretically (by the pseudopotential method). The existence of local order is found in the alloy Ni-7 at. % Ta. The short-range order parameter calculated by the pseudopotential method, using Animalu form factors, coincided in sign with that observed experimentally.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 21–25, December, 1976.In conclusion the authors thank Prof. A. A. Katsnel'son for valuable advice and discussions of the results.     

Thermal equilibrium of high- and low-spin forms of cytochrome P450 BM-3: repositioning of the substrate?

We demonstrate that cytochrome P450 BM-3 in complex with N-palmitoylglycine undergoes a spin state change between room temperature, where optimal activity is seen, and low temperatures, where X-ray diffraction characterization has been carried out. On the basis of NMR measurements of the full-length protein, this spin state change is likely to be accompanied by a general structural rearrangement in the enzyme pocket. The substrate remains bound at all temperatures. We propose that the substrate may "slide" from a position directly atop the heme (thus displacing the ligating water) to the more distant position (thus restoring the ligating water) as the temperature is lowered. This proposal is evaluated on the basis of computational modeling of the protein-ligand complex, using a novel induced fit methodology. We thereby generate a structure with the ligand in close contact with the heme, similar in energy to the experimental structure. With this combination of theory and experiment we provide a specific proposal of how ligands may be positioned for chemistry for this enzyme.     

DNA REPAIR IN V-79 CELLS TREATED WITH COMBINATIONS OF PHYSICAL AND CHEMICAL CARCINOGENS*

Excision repair of DNA damage was measured by the photolysis of bromodeoxyuridine incorporated into parental DNA during repair in Chinese hamster V-79 cells treated with 254 nm of ultraviolet radiation (UV), 7,12-dimethylbenz[a]anthracene 5,6-oxide (DMBA-epoxide), N-acetoxy-2-acetylaminofluorene (AAAF), 4-nitroquinoline 1-oxide (4NQO), 2-methoxy-6-chloro-9-[3(ethyl-2-chloroethyl)-aminopropylamino]acridine dihydrochloride (ICR-170), X-rays, ethylmethanesulfonate (EMS), methyl methanesulfonate (MMS) and combinations of these agents. Compared to normal human cells V-79 were defective in repair of UV lesions and the lesions induced by the UV-mimetic chemicals. The extent of the defects varied from 10 to 50% and was similar to those in Xeroderma pigmentosum group C cells (XP C). V-79 cells repaired X-ray damage and damage from the alkylating agents EMS and MMS to the same extent as human cells. Repair was additive after a combination of UV plus MMS indicating, as expected, that there are different rate-limiting steps for removal of the damages from these agents. Repair was less than additive in cells treated with UV plus ICR-170, AAAF plus ICR-170, AAAF plus 4NQO, and 4NQO plus ICR-170 and approximately equal to that observed for the higher of the two agents separately, indicating that there may be similar rate-limiting steps for removal of lesions. Although the results on repair after combinations of UV plus 4NQO, UV plus DMBA-epoxide or X-rays plus MMS were difficult to interpret, there was not any inhibition of repair in these combinations.     

Differential pulse polarographic determination of lead in complex materials after adsorption of its N-methylethylxanthocarbamate complex on microcrystalline naphthalene or on N-methylethylxanthocarbamate-benzyldimethyltetradecylammonium-naphthalene adsorbent

Lead is quantitatively adsorbed as the lead N-methylethylxanthocarbamate (MEXC)-benzyldimethyltetradecylammonium (BDTA) ion pair complex on microcrystalline naphthalene in the pH range 4.0-11.0. The metal is desorbed with HCI and determined by differential pulse polarography. Alternatively lead can be quantitatively adsorbed on the adsorbent (MEXC-BDTA-naphthalene) packed in a column at a flow rate of 1-2 mL/min and determined similarly. Dissolved oxygen is removed by adding a few milliliters of 4% NaBH4 solution. The detection limit is 0.12 microg/mL at the minimum instrumental settings (signal-to-noise ratio, 2). Linearity was obtained over the concentration range 0.3-20.0 microg/mL with a correlation factor of 0.9998 and a relative standard deviation of +/- 0.98%. Various parameters, such as the effect of pH, volume of aqueous phase, flow rate, and the interference of a large number of metal ions and anions, were studied in detail to optimize the conditions for the trace determination of lead in various standard alloys, standard biological materials, and environmental samples.     

Benzimidazole condensed ring systems,VI: Organic azides in heterocyclic synthesis,X: Synthesis of some substituted pyrimido[1,6-a]-benzimidazoles as potential antimicrobial agents

Summary The syntheses of 3-chloro derivatives of 2-alkyl-pyrimido[1,6-a]benzimidazol-1(2H)-ones2a, b as well as of 4,4-dichloro and 4,4-dibromo derivatives of 2-alkylpyrimido[1,6-a]benzimidazole-1,3(2H,4H)-diones3 a, b and4 are reported. Methods for converting some of the chloro compounds to azido (5, 6), amino (8), morpholino (9 a,10,11), piperidino (9 b), cyano (12), and methoxy (13) derivatives of the adopted tricyclic system are also described.

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Kondensierte Ringsysteme des Benzimidazols, 6. Mitt.: Organische Azide in der Heterocyclen-Synthese, 10. Mitt.: Synthese von substituierten Pyrimido[1,6-a]benzimidazolen als mögliche antimikrobielle Wirkstoffe

Zusammenfassung Die Synthese von 3-Chlor-2-alkyl-pyrimido[1,6-a]benzimidazol-1(2H)-onen (2 a, b) und von 4,4-Dichlor- und 4,4-dibrom-pyrimido[1,6-a]benzimidazol-1,3(2H,4H)-dionen (3 a, b, 4) wird beschrieben. Diese Verbindungen lassen sich zu den entsprechenden Azido- (5, 6), Amino- (8), Morpholino- (9 a, 10, 11), Piperidino- (9 b), Cyano- (12) und Methoxy- (13) Derivaten umwandeln.

     

Benzimidazole condensed ring systems,III . Synthesis of some substituted 2,3-dihydrocyclopenta-1H-[4′,5′: 2,3]pyrido[1,2-a]benzimidazole-11-carbonitriles

Summary The synthesis of compound3 by condensing 1H-benzimidazole-2-acetonitrile (1) with ethyl cyclopentanone-2-carboxylate (2) in the presence of ammonium acetate is described. Methylation of3 with trimethyl phosphate yielded the N-methyl derivative4. Methods for converting3 to some of its related derivatives in which the carbonyl function was replaced by Cl, N₃ and amines are also reported.

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Kondensierte Ringsysteme des Benzimidazols, 3. Mitt.. Synthese von substituierten 2,3-Dihydrocyclopenta[4,5:2,3]pyrido[1,2-a]benzimidazol-11-carbonitrilen

Zusammenfassung Die Synthese der tetracyclischen Verbindung3 durch Kondensation von 1H-Benzimidazol-2-acetonitril (1) mit Cyclopentanon-2-carbonsäureester (2) in Gegenwart von Ammonacetat wird beschrieben. Die Methylierung von3 mit Trimethylphosphat liefert das N-Methylderivat4. Die Sauerstoffunktion in3 kann durch Chlor, Azid und Aminogruppen ersetzt werden.