Biochemie und Chemie
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The current definitions of isosterism are incomplete if excited species are considered; here any reasonable definition must include the specification of the valence state too. Implications of this are discussed. A criterion for the selection of consistent valence state energies is developed.
In systems containing singlet-oxygen and aromatic fluorescers energy transfer from singletoxygen dimers to the dye should be observable by emission of the fluorescer. In order to prove this hypothesis, externally generated singlet-oxygen (1Δg) was bubbled through the solutions of dyes (chlorophyll a, eosin y, rhodamine b, luminol, rubrene and acridine orange) in organic solvents.
Luminescence could be observed and its spectral distribution analyzed by sharp cut-off filters and interference filters (rubrene) . Spectra, rates of oxidation, addition of quenchers and the long lasting time dependence of the reported reactions lead to the conclusion that the observed afterglow is due to chemical oxidation mechanisms producing a chemiluminescence. Therefore an excitation of the substances investigated in these experiments by simple physical energy transfer seems not to be predominant.
The effect of NNMG on the template activities of different polynucleotides (polyuridylic acid, polycytidylic acid, polyadenylic acid and copolymer of adenylic and guanylic acid 5,5:1) and t-RNS was studied. The maximum inhibition of the messenger activity was found for poly-C, followed by poly-Α and poly-U. The acceptor activity of t-RNA was found to be inhibited by NNMG: maximum for proline, followed by serine, leucine, phenylalanine and lysine. The mechanism of these inhibitions was studied using NNMG radioactively labelled on the methyl group. Different amounts of radioactivity were found in the various polynucleotides and t-RNS.
The preparation of (CH3)3SnSPSFC2H5, Pb(SPSFCH3)2, Pb(SPSFC2H5)2 and CH3HgSPSFCH3 is described. On the basis of NMR the structure was formulated as ... All the complexes are colourless and monomeric in solution. The magnetic and reflectance spectra of Cr(S2PFCH3)3, Mn(S2PFC2H5)2, Co(S2PFCH3)2, Ni(S2PFCH3)2 and Ni(S2PFC2H5)2 are reported and interpreted.
The near and far UV spectra of the aminoboranes (Me2N)n B X3-n, n = 1, 2, 3, Me=CH3, X= H, Me, F, Cl, Br are presented. In most of the monoamino boranes the π→π * transitions dominate. In the di- and triamino boranes there were additionally found a Rydberg series and some single Rydberg transitions, partly preceding the π→π * band. The Rydberg assignments were settled particularly by comparing the band positions of the compounds relatively to their ionization energies.
Substituted amides react with tridiloromethanesulfenyl chloride in the presence of triethylamine to following compounds: S=PCl2NCH3SCCl3, S=PFCl2NCH3SCCl3, S =PFClNCH3SCCl3, S=PF2NCH3SCCl3, O = PCl2NCH3SCCl3, O= PFClNCH3SCCl3, O = PF2NCH3SCCl3, FSO2NCH3SCCl3 and CF3SO2-NCH3SCCl3. The properties of these substances are described. They were characteriszed by elemental analyses, IR- and mass spectra. 19F-, 1H- and 31P-NMR spectra are reported and discussed.
Two routes for the preparation of (CH3)2SnS2N2 are given, which are kinetically controlled reactions. The molecule (CH3)2SnS2N2 was characterized by X-ray analysis. It is an interesting starting material for the preparation of S2N2CO and S3N2O. The latter reacts with iminosulfur oxides and isocyanates under the formation of S3N3SO2F and S3N3SO2CF3. The structure of S3N3SO2F was established by X-ray analysis. The bonding properties are discussed.
The cleavage of thin-nitrogen derivatives with S3N2Cl2 yields also five membered sulfurnitrogen rings. The structure and properties of P3N3F5NS3N2 and C3N3F2NS3N2 are reported. Six, eight and ten membered rings are formed by the reactions of (CH3)3Si–N = S = N–Si (CH3)3 with FSO2–N=S=O, these are S4N4O2 and S5N5+S3N3O4, respectively. The cation S5N5+ is a planar molecule, while the oxygen containing species are puckered. In S4N4O2 the oxygens are attached to one sulfur atom, which has a tetrahedral configuration.
The structure of the silicon containing cyclic and bicyclic rings (CH3)2Si(NSN)2Si(CH3)2 and CH3Si(NSN)3SiCH3 were determined.
By reacting S = PX2NHCH3 or O = PX2NHCH3 (X = F and/or Cl) with S = PF2Br in the presence of triethylamine the following compounds are prepared: S = PCl2NCH3F2P = S, S = PFClNCH3F2P = S, O = PCl2NCH3F2P = S and O = PFClNCH3F2P = S. Also, the infrared, proton NMR, fluorine NMR, phosphorus NMR, and mass spectral data of these compounds are presented and discussed.
R-P(Se)F2- (R = CH3, C2H5, C3H11, C6H5, N(CH3)2, N(C2H5)2, NHSi(CH3)3) and R-P(Se)FCl-compounds (R = CH3, C2H5) can be prepared by reaction of R-P(Se)Cl2-derivatives with antimony(III)fluoride under reduced pressure. In some cases the oxidation of fluorophophines with elemental selenium is successful. The isolated compounds are colourless volatile liquids which are sensitive to air and moisture. The chemical properties are described.
1H-, 19F-, 31P-NMR-, IR- and Raman-spectroscopic data are given. Main stretching frequencies are discussed by comparison with similar oxygen- and sulphur-compounds.
The preparations of the following compounds are described: O = PF2N = PCl2N = PCl3, O = PF2N = PCl2N = PCl2N (CH3) 2, O = PF2N=PCl2N = PCl2N (C2H5) 2, O = PF2N = PCl2N (CH3) 2, O = PF2N = PCl2N (C2H5)2, O = PF2N = PCl2N (CH3) Si (CH3)3, O = PF2N = PCl2NCS, O = PFClN = PCl2N (CH3)2, O = PFClN = PCl2N (C2H5)2, O = PFClN = PCl [N (C2H5)2]2 and O =P (C6H5) FN = PCl3. They were characterized by 1H-, 19F- and 31P-nmr spectroscopy. Analytical, ir and mass spectral data are reported. The properties of these substances are compared with the corresponding thiophosphorylderivatives.
Following treatment with the β-galactosidase inducer [methyl-3H] -thiogalactoside, an induceracceptor-complex was isolated from extracts of E. coli K 12 using DEAE cellulose chromatography. Enzymatic digestion with trypsin suggested that the inducer was bound to a protein component.
Specific radioactive peaks demonstrated acceptor activity in the inducible strains E. coli K 12 and ML 3, but different results were obtained using the non-inducible mutants ML 35, ML 308 and ML 309.
The potent inhibitor of TMG-induction, o-nitrophenylfucoside, reduced the radioactive acceptor peak and caused a similar inhibition of β-galactosidase synthesis, p-nitrophenylfucoside was ineffective.
Further evidence is presented for the in vitro formation of an inducer-acceptor-complex in cell free extracts of E. coli K 12.
Tetraphenylbutatriene is reduced under aprotic conditions to its ESR/ENDOR-spectroscopically characterized radical anion and to its dianion, with both electron transfers quasireversible according to cyclovoltammetric measurements. The alkali cation salts, the red contact ion pair [(H5C6)4C4·⊖][Na⊕ (H3COCH2CH2OCH3)3] and the dark violet contact ion triple [(H5C6)4C4⊖⊖][Li⊕(H3COCH2CH2OCH3)3]2 can be prepared by single electron reduction at a sodium metal mirror or by twofold de-protonation of 1,1,4,4-tetraphenylbutyne-2 using lithium-n-butyl. Their single crystal structures as well as that of the parent acetylene have been determined at low temperatures. The essential structural changes observed are the twisting of both molecular halves (H5C6)2CC relative to each other with increasing negative charge. The simultaneously resulting bond alternancy >C = C = C = C< → >C⊖ - C ≡ C⊖ - C < within the cumulene chain is discussed based on MNDO calculations for the structures determined.
The two-electron reduction of tetraphenyl-p-quinodimethane M via its radical anion M⊖ to its dianion M⊖⊖ is explored both by cyclovoltammetry and ESR/ENDOR spectroscopy. Contact of the diglyme solution with added 15-crown-5 under aprotic conditions with a sodium metal mirror yields black crystals of a solvent-separated contact ion triple [M⊖⊖][Na⊕(OCH2CH2)5(H3CO(CH2CH2O)2CH3)]2. The two-electron-insertion into the pquinodimethane derivative R2C⊖=C(HC=CH)2C=CR2 changes its structure drastically to that of a twofold carbanion substituted benzene, R2C⊖ -(C6H4)- ⊖CR2. MNDO calculations provide a rationale for both the tremendous solvation of a Na⊕ center coordinated to seven oxygen centers of 15-crown-5 and of one diglyme molecule and the structural changes as well as the charge distribution in the unique Tetraphenyl-p-quinodimethane dianion (H5C6)2C⊖-(C6H4)- ⊖C(C6H5)2, in which the two negative charges are largely localized at the carbanion center of the benzene -substituents.
The photoelectron (PE) spectra of dicyano methane and of its dimethyl derivative are tentatively assigned on the basis of a simple MO model. The interactions defined therein between the two cyano groups as well as with the R2C-framework can be parametrized using the PE data. Thus the hyperconjugation πCN/πCR₂ is estimated to amount to 1.7 eV in both compounds. Hyperconjugative effects in methane derivatives H3CX and H2CX2 with X = Br, Cl and CN are compared.
The cis-trans-isomerism of the WITTIG hydrocarbon was investigated in solid state and solution by means of fluorescence spectroscopy. The fluorescence behavior of both isomers in 2-methyltetrahydrofurane was determined as a function of concentration, temperature, and wavelength of exciting radiation. Furthermore, irradiation experiments were undertaken with light of various wavelengths.
The results obtained are in agreement with the assumption that the WITTIG hydrocarbon behaves with regard to the cis-trans-isomerism like a 1,3-butadien derivative, i.e. a thermal but no photochemical cis-trans-isomerisation can be detected. The enthalpy difference between the two isomers was estimated to ΔΗ = 250 ± 50 cal/mole. It could be shown that the fluorescence of the cis-isomer is quenched by the trans-isomer. This quenching occurs probably according to the resonance energy transfer mechanism.