Showing papers in "Acta Chemica Scandinavica in 1997"
TL;DR: General properties of the radical enzymes are summarized from which it is concluded that their essential role in catalysis is to initiate substrate metabolism by hydrogen-atom abstraction.
Abstract: Enzymes that require a redox-active amino acid for catalysis or function have emerged as a distinct class of proteins. For the tyrosine-based radical enzymes, we show that the spin-density distribution in the radical follows an odd alternate pattern that is invariant to within 10% across the class. General properties of the radical enzymes are summarized from which we conclude that their essential role in catalysis is to initiate substrate metabolism by hydrogen-atom abstraction. These ideas are extended to the YZ and YD tyrosines in Photosystem II and a radical-based hydrogen-atom abstraction model for water oxidation is discussed. Differences in rates of oxidation of YZ and YD by the reaction-center chlorophyll, P680+, under various conditions, are considered and rationalized on the basis of changes in reorganization energy induced by the local protein structure and by the presence or absence of the (Mn)4 cluster that binds substrate water.
79 citations
TL;DR: In this paper, the structure of the space group Pmn2 was determined from three-dimensional single-crystal data and a final R-value of 0.0221 was obtained.
Abstract: The title compound (1) crystallites in the space group Pmn2(1) with a =
13.110 (3), b = 5.813(1) and c = 6.482(1) Angstrom. Its crystal
structure was redetermined from three-dimensional single-crystal data
to a final R-value of 0.0221. The Cd2+ ion is tetrahedrally coordinated
to two sulfur atoms from the tiourea ligand (Cd-S = 2.509 Angstrom) and
to two chloride ions at distances 2.545 and 2.518 Angstrom. When heated
in air or in an inert atmosphere 1 undergoes a complex degradation
process which was studied in situ by simultaneous TG/DTA as well as by
EGA-FTIR. The gaseous species evolved include NH3, HCl, H2NCN, HNCS and
CS2, which upon oxidation yield also HCN, SO2, COS and CO2. In the
solid residue, NH4CdCl3 and CdS were detected by X-ray diffraction,
Elemental and XPS analyses also indicated the presence of Cl and N as
well as some carbon residue. The results of the thermoanalytical study
are not directly applicable to the spray pyrolysis process because of
the different experimental conditions, but they nevertheless indicate
that it is extremely difficult to prepare impurity-free CdS. The
formation of HCN, not detected earlier, should also be taken into
account when designing the process parameters and safety measures.
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TL;DR: In this article, 5-ethyl-6-(1-naphthylmethyl)-2-thiouracil and 5-ethyl-6-1-methylamine-2-methyl (5-methyl-6)-methioxymethyl and methylthiomethyl uracil derivatives were alkylated with methyl bromoacetate.
Abstract: 5-Ethyl-6-(1-naphthylmethyl)uracil and 5-ethyl-6-(1-naphthylmethyl)-2-thiouracil were alkylated to give, respectively. N-1 and S2, ethoxymethyl and methylthiomethyl uracil derivatives. 5-Ethyl-6-(1-naphthylmethyl)-2-thiouracil was also S2 alkylated with methyl bromoacetate. The products showed activity against HIV-1, and the N-1 alkylated derivatives were indeed highly active.
33 citations
TL;DR: In this paper, 4-Toluenesulfonyloxymethylphenyl isothiocyanate was obtained from [F-18]fluoride and 4-toluene sulfonyloxide (4-TOLUEN) in 13-15% isolated, decay-corrected radiochemical yield within 40 min from the end of cyclotron bombardment.
Abstract: 4-([F-18] Fluoromethyl)phenyl isothiocyanate 8 was obtained from [F-18]fluoride and 4-(4-toluenesulfonyloxymethyl)phenyl isothiocyanate 5 in 13-15% isolated, decay-corrected radiochemical yield within 40 min from the end of cyclotron bombardment. The pre
TL;DR: Relationships between pK-values and different bulk properties and some microscopic parameters permit the interpretation of acid-base behaviour of these important antimicrobials in the widely used acetonitrile-water media.
Abstract: Quinolones are a family of antibacterial agents that are used extensively in both human and veterinary clinics. Their antibacterial activity is pH-dependent, and therefore an examination of protonation equilibria in quinolone solutions is essential. pK-Values of nine quinolone antibacterials in acetonitrile-water mixtures containing 0, 10, 30, 40, 50 and 70%(w/w) acetonitrile were determined according to the rules and procedures endorsed by IUPAC. In order to obtain quinolone pK-values in any acetonitrile-water mixture up to 70%(w/w) acetonitrile, relationships between pK-values and different bulk properties (such as dielectric constant) and some microscopic parameters (such as solvatochromic parameters alpha, beta and pi*) were established. These relationships and the application of the preferential solvation theory of electrolytes in acetonitrile-water mixtures permit the interpretation of acid-base behaviour of these important antimicrobials in the widely used acetonitrile-water media.
TL;DR: In this article, the authors describe the construction of three key intermediates 11, 15 and 23 for a projected total synthesis of the marine alkaloid zoanthamine, corresponding to the C-1-C-5, C-6 -C-10, and C-11-C -24 fragments of the target molecu
Abstract: This paper describes the construction of three key intermediates 11, 15 and 23 for a projected total synthesis of the marine alkaloid zoanthamine. These building blocks, corresponding to the C-1-C-5, C-6-C-10, and C-11-C-24 fragments of the target molecu
TL;DR: Fully optimised structures of Q-3 and Q-7 were obtained by performing semiempirical PM3 molecular orbital (MO) calculations for both neutral molecules and radical anions, neutral radicals and radical cations.
Abstract: Radical anions and cations of the biologically important coenzymes Q-6 and Q-10, which have 6 and 10 unsaturated isoprene units in their side chains, respectively, have been generated in various solvents, and the results compared with those obtained for Q-0, a ubiquinone with no isoprene units, and for decylubiquinone Q-2 which has a saturated side chain. Hyperfine splitting constants (hfsc) of methyl and methoxy protons of the substituents in the quinone ring, and beta and gamma protons of the side chain were measured by EPR and ENDOR spectroscopy for both the radical anions and cations of Q-0, Q-6 and Q-10, and for the radical anion of Q-2. The relative signs of the hfsc were determined by general TRIPLE resonance spectroscopy. TRIPLE induced EPR (TIE) spectra were used for identification of the primary and secondary radicals of Q-10. The temperature dependence of the hfsc of the beta protons of Q-2 was different from those of Q-6 and Q-10. Fully optimised structures of Q-3 and Q-7 were obtained by performing semiempirical PM3 molecular orbital (MO) calculations for both neutral molecules and radical anions, neutral radicals and radical cations. Partial optimisation of the molecules was carried out for the side chain in a planar conformation. The folded conformation always had the minimum energy. Folding was so complete in the Q-7 series that the end of the side chain came into contact with the quinone ring, and small hfsc were detected in the PM3 calculations.