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1Author    H.-D Liidemann, H. Pladi, E. W. Esthof, L. B. TownsendRequires cookie*
 Title    Conformations of 3-Deazaadenosine, 3-Deaza-8-azaadenosine, and Benzimidazole-1-ß-D-riboside in Solution: H RNM R-, Proton-Relaxation-Time-, and Nuclear-Overhauser- Effect Studies  
 Abstract    The solution conformations of 3-deazaadenosine, 3-deaza-8-azaadenosine, and benzimidazole-l-/5-D-riboside have been determined by nuclear magnetic resonance methods in aqueous and ammonia solutions. The two-state S N model of Altona and Sundaralingam is used to analyse the ribose moiety. In order to characterize the orientation of the base relative to the ribose, longitudinal proton relaxation time and nuclear Overhauser enhancement measurements have been carried out. It is shown that 3-deazaadenosine and benzimidazole-l-/?-D-riboside exist preferentially in the S-syn-g+/t (70%) and the N-anti-g+/t (30%) conformation families. In the case of 3-deaza-8-aza-adenosine, some destabilization of the g+ rotamer occurs. In this case, the pulsed methods seem to indicate a preference of the base for the anti range. 
  Reference    Z. Naturforsch. 33c, 305 (1978); received February 17/March 30 1978 
  Published    1978 
  Keywords    Nucleosideanalogs, Conformations, NMR, NOE 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0305.pdf 
 Identifier    ZNC-1978-33c-0305 
 Volume    33 
2Author    G. Klimke, I. Cuno, H.-D Lüdem, R. Mengel, M. J. RobinsRequires cookie*
 Title    Arabinose Conformations of 9-ß -D-Arabinofuranosyladenine (ARA-A) Analogues Modified at the 2',3' or 5' Positions  
 Abstract    The solution conformations o f 9-/?-D-arabinofuranosyladenine analogues modified at the 2',3' or 5' positions are derived from the HRNMR spectra and the longitudinal relaxation rates o f the protons. The compounds studied are: 9-/?-D-arabinofuranosyladenine and its 2/-amino-2'-deoxy, 2'-chloro-2'-deoxy, 2'-azido-2'-deoxy, 3'-amino-3'-deoxy, 3'-bromo-3'-deoxy, 3'-chloro-3'-deoxy, 3'-fluoro-3'-deoxy, 3'-azido-3'-deoxy, 2',3'-diamino-2/,3'-dideoxy, 2',5'-diamino-2',5'-di-deoxy and 2',5'-diazido-2',5'-dideoxy analogues. It is derived from the data that the conforma­ tional equilibria o f the furanoside rings can be described by the two state N <*> S model of Altona and Sundaralingam. The emphasis in this work is to study systematically the influence o f the different chemical modifications upon the conformational equilibria o f the nucleosides. For the arabinosides it is found that substitution o f the hydroxyl groups at C2' or C3' by other atoms or groups always stabilizes the N conformation of the arabinose ring. The only exception is fluorine, where S is stabilized. The preference for the N state is correlated with an increasing population o f the g + rotamer of the exocyclic 5'-CH2OD group. From the relaxation study o f 2'-chloro-2'-deoxy-arabinofuranosyladenine the position of the syn <=> anti equilibrium o f the base was estimated to be predominantly anti. Thus a preference for the anti-N-g+ conformation was derived for the arabinosides excluding an intramolecular hydrogen bond between the 2' and 5' hydroxyl groups that was found in the solid state. The stabilization o f the N conformer in the modified compounds can be qualitatively explained by steric effects. 
  Reference    Z. Naturforsch. 35c, 853 (1980); received June 25 1980 
  Published    1980 
  Keywords    Arabinofuranosyladenine Analogues, Conformation, NMR 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0853.pdf 
 Identifier    ZNC-1980-35c-0853 
 Volume    35 
3Author    G. Klimke, I. Cuno, H.-D Lüdemann, R. Mengel, M. J. RobinsRequires cookie*
 Title    Xylose Conformations of 9-/?-D-Xylofuranosyladenine Analogues Modified at the 2'3' or 5'-Positions and Lyxose Conformations of 9-^-D-Lyxofuranosyladenine  
 Abstract    Proton magnetic resonance studies o f 9-/?-D-xylofuranosyladenine (xyloA), its 2'-amino-2'-deoxy, 2'-azido-2'-deoxy, 2'-bromo-2'-deoxy, 3'-thio-3'-deoxy, 3'-amino-3'-deoxy, 3'-azido-3'-deoxy, 3'-chloro-3'-deoxy, 3'-fluoro-3'-deoxy, 3'-0-methyl, 3',5'-diazido-3',5'-dideoxy analogues and 9-/?-D-lyxofuranosyladenine (lyxoA) have been carried out to study the effect o f chemical modifications at the sugar moiety on the solution conformational equilibria in these classes of nucleosides. Analogously to previous studies the xylose pucker can be described in the two-state N <=> 5 model o f Altona and Sundaralingam. For the xylosides, however, a somewhat different N state (C3'-endo-C4'-exo) has to be used than for the ribosides and arabinosides (C2'-exo-C3'-endo). The results o f the conformational analysis are that xyloA exists almost exclusively as an N conformer. The effect o f the substitutions in the modified compounds is to destabilize the N state. This decrease in the mole fraction o f N is accompanied by an increase in the population of the g + rotamer o f the exocylic 5'-CH2OD group. Thus for the xylosides a correlation N-t/g~ or S-g +, respectively, can be derived. Proton relaxation rate measurements on 2'-azido-2'-deoxyxylo-furanosyladenine indicate that in the xylosides the standard syn or anti ranges do not represent stable positions for the adenine base, but that a glycosyl torsion angle (* ~ 160°, T ~ 80°) be­ tween syn and anti is preferred. LyxoA behaves similar to the xylosides and also favours the N state o f the sugar pucker. In a summarizing discussion the conformational equilibria o f the different modified pentosides -ribose, arabinose, xylose and lyxose -are compared. It is shown that generally intramolecular hydrogen bonding does not yield an important contribution to the stabilization o f conformational equilibria in solution. It is also not possible to derive a quantitative relationship between such parameters as Van-der-Waals' radii or electronegativity o f the substituents and the mole fractions of the different conformers. It can, however, be seen that in all cases, where the hydroxyl groups at C2' or C3' are substituted by a more voluminous atom or group, steric effects become dominant and allow a qualitative explanation o f the changes of the conformational equilibria. Only for the smallest and most electronegative substituents, like fluorine, other interactions (e. g. electrostatic) may become important. It is thus suggested that the purine(/7)nucleoside conforma­ tion is essentially determined by steric interactions between the different parts o f the molecule. 
  Reference    Z. Naturforsch. 35c, 865—877 (1980); received June 251980 
  Published    1980 
  Keywords    Adenosine Analogues, Conformation, NMR 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0865.pdf 
 Identifier    ZNC-1980-35c-0865 
 Volume    35 
4Author    H. Janzen, E. Matuszak, E. V. Goldammer, AnnenBundesrepublik Deutschland, H. R. WenzelRequires cookie*
 Title    Thermodynamic and Magnetic Resonance Studies on the Hydration of Polymers: II. Protein-Water Interactions in Powdered Ribonuclease  
 Abstract    ESR studies on spin-labeled amorphous RNase A as a function of varying concentrations of sorbed H 2 0 and D 2 0 will be presented. A relaxation analysis of saturation transfer (ST-)ESR spectra of l4 N('H) nitroxide spin-label molecules essentially fixed at amino acid residue His-105 will be given. A characteristic correlation has been observed between the microdynamic behavior — express-ed by the rotational correlation times of the paramagnetic label — and the macroscopic thermo-dynamic entropy for the sorption process of H 2 0 and D 2 0 at RNase. This correlation is particu-larly pronounced at low water concentrations, viz., n H20 /n protein < 100. A significant difference in this concentration range exists between the two systems "RNase-H 2 0" and "RNase-D 2 0", which is manifested not only by the thermodynamic data but also by the microdynamic behavior ex-tracted from the corresponding non-linear ESR absorption line shapes. 
  Reference    Z. Naturforsch. 43c, 285—293 (1988); received December 18 1987 
  Published    1988 
  Keywords    Protein, Structure, Hydration, NMR, Thermodynamic 
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 TEI-XML for    default:Reihe_C/43/ZNC-1988-43c-0285.pdf 
 Identifier    ZNC-1988-43c-0285 
 Volume    43 
5Author    Rainer Bieganowski, Wilhelm FriedrichRequires cookie*
 Title    Über die Eisenanaloga von Cobalamin und Cobyrsäure* About the Iron Analogues of Cobalamin and Cobyric Acid  
  Reference    Z. Naturforsch. 36c, 9 (1981); eingegangen am 15. Septem ber 1980 
  Published    1981 
  Keywords    Vitamin B12, Cobyric Acid, Fe(III)Cobalam in, Fe(III)Cobyric Acid, Iron-B12-Analogues, UV/VIS-, NMR-, ESR-Spectra 
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 TEI-XML for    default:Reihe_C/36/ZNC-1981-36c-0009.pdf 
 Identifier    ZNC-1981-36c-0009 
 Volume    36 
6Author    Sa-Ouk Kang, Helmut Sapper, Wolfgang LohmannRequires cookie*
 Title    The Oxidative Degradation of L-Ascorbic Acid via an a-Ketoaldehyde  
 Abstract    Dehydro-L-ascorbic acid, the oxidation product of L-ascorbic acid, is unstable in aqueous solution and decomposed by a hydrolytic disruption of its ring structure to 2,3-diketo-L-gulonic acid. It is shown by means of UV, 'H-, and 13C-NMR spectroscopy that after decarboxylation 3,4,5-trihydroxy-2-keto-L-valeraldehyde, an a-ketoaldehyde, is formed. This substance is oxidized further to L-erythroascorbic acid, coupled with a reduction of 2,3-diketo-L-gulonic acid to L-ascorbic acid. 
  Reference    Z. Naturforsch. 37c, 1064—1069 (1982); received August 24 1982 
  Published    1982 
  Keywords    L-Ascorbic Acid, Dehydro-L-Ascorbic Acid, a-Ketoaldehyde, L-Erythroascorbic Acid, NMR 
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 TEI-XML for    default:Reihe_C/37/ZNC-1982-37c-1064.pdf 
 Identifier    ZNC-1982-37c-1064 
 Volume    37