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21Author    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 
22Author    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 
23Author    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 
24Author    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 
25Author    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 
26Author    J. Wąsicki, Z. Pająk, A. KozakRequires cookie*
 Title    Cation and Anion Reorientation at Phase Transition in Pyridinium Tetrafluoroborate  
 Abstract    Temperature dependences of and 19 F second moment and spin-lattice relaxation times for polycrystalline pyridinium tetrafluoroborate were measured. A phase transition was discovered at 202 K. A model of cation reorientation between inequivalent (low-temperature phase) and equiva-lent (high-temperature phase) equilibrium positions is proposed. Whether the anion reorients isotropically or about a symmetry axis cannot be decided. An analysis of cross-relaxation effects yielded activation parameters for cation and anion reorientation. The rotational correlation times for both ions converge just at the phase transition reaching the value of 10~ 10 s. 
  Reference    Z. Naturforsch. 45a, 33—36 (1990); received August 5 1989 
  Published    1990 
  Keywords    NMR, cross-relaxation, molecular motions, phase transitions 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0033.pdf 
 Identifier    ZNA-1990-45a-0033 
 Volume    45 
27Author    W. W. Warren, R. E. WalstedtRequires cookie*
 Title    NQR and NMR Studies of Spin Dynamics in High T c Superconducting Cuprates  
 Abstract    Recent NQR and NMR studies of Cu spin dynamics in metallic YBa 2 Cu 3 0 6+JC are reviewed. The Cu nuclear relaxation rates are shown to be inconsistent with weak correlation (band) theory and the Korringa relation, but the Cu spins retain important characteristics of itinerancy. These include pairing of the Cu d-spins in the superconducting state and strong sensitivity of the Cu spin dynamics to changes in carrier concentration associated with variation of the oxygen content. Samples of reduced oxygen content (T c = 60 K) are found to contain a high concentration of Cu + Cu(l) sites associated with "full chain-empty chain" vacancy ordering. These samples also exhibit remarkable precursive suppression of planar Cu(2) nuclear relaxation above T c . 
  Reference    Z. Naturforsch. 45a, 385—392 (1990); received October 25 1989 
  Published    1990 
  Keywords    NMR, NQR, Nuclear relaxation, Spin fluctuations, Superconductivity 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0385.pdf 
 Identifier    ZNA-1990-45a-0385 
 Volume    45 
28Author    H. Nishihara, K. Hayashi, M. Naito, T. Butz, A. Lerf, S. SaibeneRequires cookie*
 Title    NQR and Low-Field NMR of 181 Ta in the Low-Temperature CDW State of 2 H-TaS 2  
 Abstract    NQR and low-field NMR spectra of 18I Ta are reported to probe the electronic environment of inequivalent tantalum sites in the low-temperature CDW state of a layered compound 2 H-TaS 2 . The overall features are found to be consistent with the structure consisting of nine-atom snowflake clusters in a locally commensurate CDW state. 
  Reference    Z. Naturforsch. 45a, 412—414 (1990); received August 23 1989 
  Published    1990 
  Keywords    NQR, NMR, 181 Ta, CDW, TaS 2 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0412.pdf 
 Identifier    ZNA-1990-45a-0412 
 Volume    45 
29Author    Z. Szafrańska, A. Pająk, KozakRequires cookie*
 Abstract    Proton and fluorine NMR second moments and spin-lattice relaxation times for polycrystalline tetrabutylammonium tetrafluoroborate have been measured over a wide range of temperatures at several Larmor frequencies. An analysis of cross-relaxation effects results in a determination of activation parameters for anion and cation reorientations. Three solid phases characterized by different ion dynamics are evidenced. M o le c u la r M o tio n in S o lid T e tra b u ty la m m o n iu m T e tr a f lu o r o b o r a te 
  Reference    Z. Naturforsch. 46a, 545—550 (1991); received March 14 1991 
  Published    1991 
  Keywords    NMR, Cross-relaxation, Molecular motions, Phase transitions 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0545.pdf 
 Identifier    ZNA-1991-46a-0545 
 Volume    46 
30Author    Silvia Wigand, Tetsuo Asaji, Ryuichi Ikeda, Daiyu NakamuraRequires cookie*
 Title    Reorientational Motion of Trihalogenomethyl Groups in Organic Compounds as Studied by 35 C1 NQR and 19 F NMR Spectroscopy  
 Abstract    Trihalogenomethyl derivatives of 4-chloroacetanilide, 4-ClC6HfNHCOCCl3,4-ClC6H4NHCOCF2Cl, and 4-ClC6H4NHCOCF3 were prepared. The 35 C1 NQR and 79 F NMR spin-lattice relaxation times T1Q and T1F, respectively, of these compounds were measured at various temperatures. On heating, T1Q of the CC13 and CF2C1 groups decreased rapidly above ca. 110 and 150 K, respectively, showing the onset of reorientation of the trihalogenomethyl group about the pseudo-triad axis. The activa-tion energies were determined to be 27 and 13kJmol _1 for the CC13 and CF2C1 reorientation, respectively. The temperature dependences of the 19 F NMR T1F of the CF2C1 and CF3 groups lead to activation energies of 13 and 4.3 kJ mol~ 1 , respectively, for the same reorientations. T1F of the CF3 group observed above ca. 200 K was attributed to the spin-rotational interaction. The TIQ 1 of ring-chlorine in 4-ClC6H4NHCOCCl3 and 4-ClC6H4NHCOCF3 can be interpreted by the T" law with « = 2.2 and 1.1, respectively, whereas that of 4-ClC6H4NHCOCF2Cl by the sum of two contributions: T" law (n = 2.0) and the modulation mechanism due to the CF2C1 reorientation. 
  Reference    Z. Naturforsch. 47a, 265—273 (1992); received July 19 1991 
  Published    1992 
  Keywords    Spin-lattice relaxation, NQR, NMR, Reorientational motion 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0265.pdf 
 Identifier    ZNA-1992-47a-0265 
 Volume    47 
31Author    B.V S Murthy, K. P. Ramesh, J. RamakrishnaRequires cookie*
 Title    Molecular Dynamics in Tetramethyl Ammonium Hexabromo Selenate [N(CH 3 ) 4 ] 2 SeBr 6 . A Proton NMR Study  
 Abstract    spin-lattice relaxation time Ti and second moment M 2 have been studied as a function of tem-perature over the temperature range 445 to 77 K. A discontinuous change in Ti at 365 K, in-dicates the presence of a phase transition, while the slope change at 152 K, is attributed to a change in the TMA ion dynamics from tumbling to torsion. The 7i results could be explained in terms of inequivalent TMA ions and their small angle torsional oscillations. A second moment (M 2) transition occurs around 160 K and is ascribed to the freezing of TMA tumbling and CH 3 reorientation. 
  Reference    Z. Naturforsch. 48a, 868—870 (1993); received February 22 1993 
  Published    1993 
  Keywords    Molecular dynamics, Second moment, NMR, Spin-lattice relaxation time 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0868.pdf 
 Identifier    ZNA-1993-48a-0868 
 Volume    48 
32Author    Ho Sung, ChohRequires cookie*
 Title    Magnetic Resonances of 5l V, 209 Bi, Mn 2 + , and Fe 3 + in BiV0 4 Single Crystals  
 Abstract    Nuclear magnetic resonance (NMR) of 51 V and 209 Bi, and electron paramagnetic resonance (EPR) of Mn 2 and Fe 3+ impurities in ferroelastic BiV0 4 single crystals are reviewed. The nuclear quadrupole parameters and principal axes of the two host nuclei, 51 V and 209 Bi, and the second-or-der zero field splitting tensor of the isoelectronic 3d 5 ions, Mn 2 + and Fe 3 + , in Bi V0 4 are determined for the first time. Temperature dependence studies on 51 V NMR and Mn 2+ EPR confirmed that this crystal undergoes a second order phase transition. The substitutional sites of Mn 2+ and Fe 3 + in BiV0 4 are Bi 3 and V 5 + , respectively. 
  Reference    Z. Naturforsch. 51a, 591—602 (1996); received February 3 1996 
  Published    1996 
  Keywords    NMR, EPR, Quadrupole parameters Zero field splittings, Substitutional sites 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0591.pdf 
 Identifier    ZNA-1996-51a-0591 
 Volume    51 
33Author    T. A. Babushkina, YuV. Goltyapin, S. I. GushchinRequires cookie*
 Title    I NQR Spectra of Iodobenzoic Acid and Iodophenol Derivatives. H-Bonds and C-I Characteristic Bonds of These Substances  
 Abstract    This is a review of investigations on iodo-benzoic acid, iodohippuric acid, and iodophenol derivatives by NQR, NMR, and emission Mössbauer spectroscopy. The influence of intermolecular, intramolecular, and bifurcated O-H- • I and O-H- • O bonds on the properties of iodine-carbon bonds is demonstrated. Ionized and non-ionized forms of tyrosine differ by the probability of H-bond formation. The simultaneous use of 127 1 NQR and emission Mössbauer 12 T spectroscopy open the possibility to determine the types of tellurium-organic substances formed in the process 
  Reference    Z. Naturforsch. 51a, 651—656 (1996); received October 20 1995 
  Published    1996 
  Keywords    NQR, NMR, iodobenzoic acid, iodohippuric acid, iodophenol 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0651.pdf 
 Identifier    ZNA-1996-51a-0651 
 Volume    51 
34Author    Takahiro Ueda, Nobuo NakamuraRequires cookie*
 Title    Sb NMR and SCF-MS-Xa Studies of Quadrupole Interaction and The Electronic Structure of Mixed-Valence Compound, Cs 2 SbCl 6  
 Abstract    Cs 2 SbCl 6 is known as a typical mixed-valence compound. It crystallizes into a tetragonal space group I4 1 /amd and contains two different complex anions, Sb(III)Cl| _ and Sb(V)Clg . The dark blue color of this compound has been considered to originate from a charge transfer between the above two anions. In order to study the electronic structure of these complex anions and the existence of charge transfer between them we measured the 121 Sb NMR spectrum and carried out molecular orbital calculations on the electronic states of these anions. The 121 Sb NMR spectrum consists of two peaks at 0 and 30 kHz which can be assigned to the central transition of l21 Sb in Sb(V)Cl<~ and Sb(III)Cl| _ , respectively. The line shape analyses of the spectra led to nuclear quadrupole coupling constants of nearly zero for Sb(V)Cl7 and 4.9 ±0.5 MHz for Sb(III)Cl| at room temperature. The quadrupole coupling constant of 1 Sb(III) decreases steadily on heating. The calculations of the electronic ground state energies of both anions were calculated by the MS-Xa molecular orbital method. The calculated charge-transfer band from the A lg state of Sb(III)Clg" to the A lg state of Sb(V)Cl6 appears at 610 nm and can account for the experimental electronic spectrum, the calculated quadrupole coupling constant in Sb(III)Clg" however is far larger than the experimental one. The contribution of the charge-transferred state to the ground state is negligible and so the temperature dependence of the quadrupole coupling constant of 121 Sb(III) is attributed to an anisotropic thermal expansion of the compound. 
  Reference    Z. Naturforsch. 51a, 672—676 (1996); received October 10 1995 
  Published    1996 
  Keywords    NMR, Quadrupole interaction, Molecular orbital, Mixed valence 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0672.pdf 
 Identifier    ZNA-1996-51a-0672 
 Volume    51 
35Author    K. Ishida, H. Mukuda, Y. Kitaoka, K. Asayama, Y. OnukiRequires cookie*
 Title    Ru NMR and NQR Studies in CeRu 2  
 Abstract    We have carried out Ru NMR and NQR measurements in superconductor CeRu 2 having T c = 6.1 K in the temperature range of 1.3-30 K. From the 9y Ru NMR in 10.2 T above H c2 , T{T-const was found in the measured-T range, and the value of T,TK 2 is almost the same as that in the uncorrelated Korringa relation, suggesting that there does not exist the strong spin fluctuation of Ru d-spins. The property of the superconducting state was investigated by using Ru NQR. We observed the Hebel-Slichter peak just below T c and the exponential decrease in 1 /T,, indicating that this superconductivity has an ordinary s-wave character. The effect of Al substitution for Ru was also studied by NMR and NQR. 
  Reference    Z. Naturforsch. 51a, 793—796 (1996); received February 1 1996 
  Published    1996 
  Keywords    Superconductor CeRu 2, NMR, NQR, T, Knight shift 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0793.pdf 
 Identifier    ZNA-1996-51a-0793 
 Volume    51 
36Author    M. Grottel, A. Kozak, Z. PająkRequires cookie*
 Title    *H and 19 F NMR Study of Cation and Anion Motions in Guanidinium Hexafluorozirconate  
 Abstract    Proton and fluorine NMR second moments and spin-lattice relaxation times of polycrystalline guanidinium hexafluorozirconate and its deuterated analogue were studied in laboratory (60 MHz) and rotating (H, = 20 G) frames over a wide range of temperature. An analysis of the experimental results enabled us to reveal a dynamical inequivalence of two crystallographically independent cations and an unexpected high mobility of nonspherical anion dimers. A comparison of the ions dynamics in 2:1 complex studied with the guanidinium 1:1 and 3:1 complexes has shown a significant contribution of the hydrogen bonds to the potential barriers hindering the anion reorien-tations. At low temperatures a proton motion in the hydrogen bond and at 400 K a solid-solid phase transition have been discerned. 
  Reference    Z. Naturforsch. 51a, 991—996 (1996); received May 14 1996 
  Published    1996 
  Keywords    NMR, Ion Motions, Hydrogen Bonds, Phase Transitions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0991.pdf 
 Identifier    ZNA-1996-51a-0991 
 Volume    51 
37Author    Zoran Marković, Stanimir Konstantinović, Ivan GutmanRequires cookie*
 Title    The Dependence of Vicinal Proton-Proton Coupling Constants of Norbomenes on Molecular Structure  
 Abstract    A modification of the Karplus equation, containing four mutually independent structural terms and five adjustable parameters, is put forward. The new structural factor, intro-duced into this modification is sin {6 1 -I-6 2)/2. The new equa-tion reproduces experimental NMR vicinal coupling con-stants of norbornenes with a standard deviation of about 0.45 Hz. 
  Reference    Z. Naturforsch. 51a, 1042—1044 (1996); received April 27 1996 
  Published    1996 
  Keywords    Norbornenes, Coupling Constants, Molecular Mechanics, Karplus Equation, NMR 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-1042_n.pdf 
 Identifier    ZNA-1996-51a-1042_n 
 Volume    51 
38Author    Roman GocRequires cookie*
 Title    Calculation of the NMR Second Moment for Solid Benzene with Rotation and Diffusion of Molecules -Numerical Approach  
 Abstract    Numerical calculations of the NMR second moment in case of rotation and diffusion of molecules were performed. As an example computer simulations of molecular reorientation and self-diffusion in solid benzene have been performed. For each model and rate of motion the Van Vleck's second moment of the proton NMR absorption spectrum was calculated, and these values were compared with experimental data. It is concluded that restricted self-diffusion must be implied in order to obtain better agreement between calculated and experimental NMR second moments. The temperature at which self-diffusion was detected through NMR line-width narrowing was found to be about 120 K, nearly 80 K less than the temperature at which the self-diffusion was detected by T lp relaxation measurements. 
  Reference    Z. Naturforsch. 52a, 477—184 (1997); received March 29 1997 
  Published    1997 
  Keywords    NMR, molecular rotation, self-diffusion, numerical approach 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0477.pdf 
 Identifier    ZNA-1997-52a-0477 
 Volume    52 
39Author    Roman Goc, JanW. WąsickiRequires cookie*
 Title    Computer Simulation of the Order-Disorder Transition in Ammonium Chloride  
 Abstract    The phase transition at T c = 243 K in ammonium chloride is well established to be of the order-disorder type. The ammonium chloride has a CsCl-type cubic structure with hydrogen atoms pointing toward four of the eight chloride ions at the corners of the unit cell. This means that there are two possible orientations of ammonium tetrahedron; a and b. In the ordered phase below the T c temperature all ammonium ions have the same, let it be a, orientation. Above the T c temperature ions are randomly distributed among the two possible orientations a and b. An attempt was made to correlate such structural transition with the second moment of the proton NMR absorption line. This approach was chosen because the second moment is the parameter of the NMR line for which the exact theoretical formula exist, and which is mainly a function of the structure and the reorien-tational state of the studied material. It was found that the NMR second moments calculated for the described above model of the structural transition properly reflect the changes of the experimental NMR second moments measured at temperatures below and above this transition. 
  Reference    Z. Naturforsch. 52a, 609—613 (1997); received June 18 1997 
  Published    1997 
  Keywords    NMR, Ammonium chloride, Phase transition, Simulation 
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 TEI-XML for    default:Reihe_A/52/ZNA-1997-52a-0609.pdf 
 Identifier    ZNA-1997-52a-0609 
 Volume    52 
40Author    Tetsuo Asaji, Keizo Horiuchi, Takehiko Chiba, Takashige Shimizu, Ryuichi IkedaRequires cookie*
 Title    NMR * NQR and DTA * DSC Studies of Phase Transitions in Pyridinium Tetrachloropalladate(II) and Pyridinium Tetrachloroplatinate(II)  
 Abstract    From the measurements of DTA • DSC and the temperature dependences of 35 C1 NQR frequen-cies, phase transitions were detected at 150 K, 168 K, and 172 K for (pyH) 2 [PtCl 4 ], and at 241 K for (P yH) 2 [PdCl 4 ], In order to elucidate the motional state of the constituent ions in the crystals in connec-tion with the structural phase transitions, the 35 C1 NQR and 'H NMR spin-lattice relaxation times and the second moment of the 'H NMR line were measured as functions of temperature. For both com-pounds, the potential wells for the cationic reorientation are suggested to be highly nonequivalent at low temperatures. Above 168 K, the pyridinium ions in (pyH) 2 [PtCl 4 ] are expected to reorient between almost equivalent potential wells. As for (pyH) 2 [PdCl 4 j, it is expected that the orientational order of the cation still remains even above the second order transition at 241 K. A change of the potential curve from two-unequal to three-unequal wells is proposed as a possible mechanism of the second order tran-sition. The activation energies for the cationic motion in the respective model potential are derived for both compounds at high and low temperatures. 
  Reference    Z. Naturforsch. 53a, 419—426 (1998); received December 30 1997 
  Published    1998 
  Keywords    Phase transition, NQR, NMR, Spin-lattice relaxation, DSC 
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 TEI-XML for    default:Reihe_A/53/ZNA-1998-53a-0419.pdf 
 Identifier    ZNA-1998-53a-0419 
 Volume    53