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1996[X]
121Author    R. C. Sharma, P. KumarRequires cookie*
 Title    Effect of Rotation on Thermal Instability in Rivlin-Ericksen Elastico-Viscous Fluid  
 Abstract    The thermal instability of a layer of Rivlin-Ericksen elastico-viscous fluid acted on by a uniform rotation is considered. For stationary convection, a Rivlin-Ericksen elastico-viscous fluid behaves like a Newtonian fluid. It is found that rotation has a stabilizing effect and introduces oscillatory modes in the system. The visco-elasticity also introduces oscillatory modes in the system. A suffi-cient condition for the non-existence of overstability is also obtained. 
  Reference    Z. Naturforsch. 51a, 821—824 (1996); received December 27 1995 
  Published    1996 
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 Identifier    ZNA-1996-51a-0821 
 Volume    51 
122Author    D. Ray, H. Anton, P. C. Schmidt, Al WeissRequires cookie*
 Title    A Theoretical Modeling of the Static and Dynamic Polarizability of O 2- in Large and Complex Oxides  
 Abstract    A time-dependent approach is employed in conjunction with a crystal potential model to study the environment-specific optical linear response of the O 2-ions in a number of cubic oxides with varying number of constituents, unit-cell dimension and degree of complexity. It is shown that the static polarizability of the anion may vary significantly depending on the position of the anion within the unit-cell. Due to neglect of overlap compression, our method has limited success in predicting the refractive indices of large crystals of complex structures. For small binary oxides the frequency-dependent polarizability of the 0 : ~ ion is found to exhibit the first poles close to the ultraviolet absorption edges ascribed to the lowest excitonic transitions in these crystals. 
  Reference    Z. Naturforsch. 51a, 825—830 (1996); received March 26 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0825.pdf 
 Identifier    ZNA-1996-51a-0825 
 Volume    51 
123Author    L. Lezama, T. Rojo, E. J. Baran, M. H. TorreRequires cookie*
 Title    ESR Spectrum and Magnetic Behavior of Copper(II) Sebacate  
 Abstract    The magnetic susceptibility of copper(II) sebacate, measured between 5 and 400 K, confirms the presence of strongly coupled Cu-Cu pairs. The ESR spectrum, obtained with a polycrystalline sample, shows an important rhombic anisotropy and supports a d xl _ yl ground-state. 
  Reference    Z. Naturforsch. 51a, 831—833 (1996); received February 14 1996 
  Published    1996 
  Keywords    Copper(II) sebacate, ESR spectrum, Magnetic behavior 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0831.pdf 
 Identifier    ZNA-1996-51a-0831 
 Volume    51 
124Author    S. Urban, B. Gestblom, H. Kresse, R. D^browskiRequires cookie*
 Title    Dielectric Relaxation Studies of 4-/i-Alkyloxy-4'-Cyanobiphenyls (/iOCB, /i = 5t8)  
 Abstract    The results of dielectric relaxation studies of series of four n-alkyloxy cyanobiphenyl (nOCB) compounds with n ranging from 5 to 8 are presented. The complex dielectric permittivity, e*(o)) — e'{oj) — i e"(co), was measured in the frequency range 1 kHz -3 GHz, with the use of an impedance analyzer and a time domain spectroscopy (TDS) set-up. The relaxation times: longitudi-nal ij| in the nematic and smectic A phase (80CB), transverse t ± in the nematic phase, and t is in the isotropic phase, were obtained as functions of the temperature. This allowed the calculation of activation barriers for different molecular relaxation processes occurring in particular phases. More-over, the retardation factors g^ and g ± and the nematic potential q according to two theoretical models were calculated. The analysis of q(T) and its relation to the order parameter S is done taking into account the results of NMR studies of the compounds under consideration. Finally, the dependencies of the obtained quantities on the number of carbon atoms in the alkyloxy chains are analyzed. 
  Reference    Z. Naturforsch. 51a, 834—842 (1996); received February 17 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0834.pdf 
 Identifier    ZNA-1996-51a-0834 
 Volume    51 
125Author    Ewa Mykowska, Danuta BaumanRequires cookie*
 Title    Perylene-like Dyes in Liquid Crystalline Media  
 Abstract    The spectral and electrooptical properties of some dichroic fluorescent dyes (derivatives of 3.4,9,10-perylenetetracorboxylic acid and of 3,4,9-perylenetricarboxylic acid) in isotropic solvents and nematic liquid crystals have been studied. The order parameter of the dyes in the anisotropic matrices has been determined by means of optical spectroscopy methods. Moreover, the influence of the dye addition on the nematic-isotropic phase transition temperature of the pure host has been investigated. It was found that some of the dyes studied can be utilized in guest-host liquid crystal display devices. 
  Reference    Z. Naturforsch. 51a, 843—850 (1996); received February 13 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0843.pdf 
 Identifier    ZNA-1996-51a-0843 
 Volume    51 
126Author    OttoL. StiefvaterRequires cookie*
 Title    Analysis of the FTIR Bands v u and v 8 of 1,1-difluoroethylene with Rotational Background Information on Excited States  
 Abstract    Much earlier work on the analysis of the fundamental infrared bands v u and v 8 of 1,1-difluo-roethylene has been resumed and extended. The Q-branch of the C-type band v n ~ 802 cm -1 has been analysed, and sextic distortion constants have been obtained for v 8 = 1 at ~ 1301 cm -1 . The rotational constants of the two states are found to differ noticeably (20-100 standard deviations) from values reported earlier. The discrepancies are believed to result in part from the availability of purely rotational data on v n and v 8 in the present study, but to originate primarily from the adoption of rather poor values of the ground state constants of 1,1-difluoroethylene in the earlier work on these two fundamentals. 
  Reference    Z. Naturforsch. 51a, 851—858 (1996); received March 7 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0851.pdf 
 Identifier    ZNA-1996-51a-0851 
 Volume    51 
127Author    Imre Bakó, Tamás Radnai, Gábor PálinkásRequires cookie*
 Title    Investigation of the Structure of Liquid Pyridine: a Molecular Dynamics Simulation, an RISM, and an X-ray Diffraction Study  
 Abstract    The structure of liquid pyridine is investigated by molecular dynamics simulation and the RISM integral equation methods. The calculated total radial distribution functions (RDF) are compared with the experimental RDF's, obtained by X-ray diffraction measurement. It is shown that the local structure of liquid pyridine is mainly determined by the dipole-dipole interaction between the molecules. The local order is characterized by the pair distribution functions, angular correlation functions and orientational distributions. Dynamical properties (self-diffusion coefficients, rota-tional correlation times and reorientational correlation times) calculated on the basis of MD results are in good agreement with experimental data. 
  Reference    Z. Naturforsch. 51a, 859—866 (1996); received October 20 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0859.pdf 
 Identifier    ZNA-1996-51a-0859 
 Volume    51 
128Author    T. A. Mirnaya, Y. V. Bereznitski, S. V. VolkovRequires cookie*
 Title    Liquid Crystals and Glasses in Binary Systems from Sodium and Alkali-Earth Metal Butyrates  
 Abstract    The temperature and composition ranges of liquid crystal and glass formation have been estab-lished for the binary mixtures of mesogenic sodium butyrate with non-mesogenic magnesium, calcium and strontium butyrates by means of differential thermal analysis and hot stage polarization microscopy. The formation of a vitreous optically anisotropic mesophase has been found for binaries of sodium butyrate with calcium and strontium butyrates. 
  Reference    Z. Naturforsch. 51a, 867—870 (1996); received March 11 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0867.pdf 
 Identifier    ZNA-1996-51a-0867 
 Volume    51 
129Author    Roman Strauss, Sigmar Braun, Shi-Qi Dou, Hartmut Fuess, Alarich WeissRequires cookie*
 Title    Phase Diagram of the Orientationally Order-disorder Binary System 2,2-dimethyl-1,3-propanediol / 2,2-dimethyl-l,3-diaminopropane, [(CH 3 ) 2 C(CH 2 OH) 2 L [(CH 3 ) 2 C(CH 2 NH 2 ) 2 ] 1 A Thermodynamic, X-ray, and ^-NMR study  
 Abstract    The phase diagram of the binary system [2,2-dimethyl-1,3-propanediol]. v (1) / [2,2-dimethyl-1,3-diaminopropane]i_x (2) was studied by X-ray diffraction and DTA/DSC, for (2) also by 1 H-NMR. The system is miscible over the whole concentration range 0 < .v < 1 in the liquid state and in the plastic solid state, phase I, just below the melting point. At lower temperatures the system is demixing, and at room temperature two plastic mixed crystals coexist. The plastic phases of (1), (2), and (l). v (2)i_. v crystallize face centered cubic, Fm3m, Z = 4, the lattice constants decreasing linearely with increasing x, and the lattice constants are: (1) a (327K) = 880.3 pm , (2) a (243K) = 905.6 pm. By single crystal X-ray diffraction the structure of the ordered phase II of (1) was refined at room temperature, monoclinic, P2i/n, Z = 4, a = 596.9 pm, b = 1090.2 pm, c = 1011.0 pm, ß = 99.74°. The results are in good agreement with the literature. The phase transition temperatures (in Kelvin) are T,_", = 399.2, T M ~i = 399.7, T n _, = 316.2, T,_n = 308.2 for (1); = 300.2, = 301.7, Tii_i = 228.7, T]_n = 194.2 for (2). Strong hysteresis is observed for the transition Ti^n in (2). In the mixed systems (l). v (2)i_ x , 0 < x < 1, the disordered phases do not order even by quenching to liquid nitrogen temperature. High resolution 1 H-NMR measurements are reported for phase I of (2) as a function of temper-ature. The "liquid" 'H-NMR spectrum is present far below the thermodynamic phase transition temperature 7H_I, overlapping the wide line unresolved powder spectrum of phase II. 
  Reference    Z. Naturforsch. 51a, 871—881 (1996); received February 23 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0871 
 Volume    51 
130Author    Igor NovakRequires cookie*
 Title    Quantification of Symmetry  
 Abstract    A new mathematical criterion is suggested for symmetry ranking, i.e. determination of an "absolute symmetry scale" for discrete, finite groups. The criterion is based on both, the periods (orders) of each group element and the order of the group itself. This is different from the current criteria which consider only the orders of the groups themselves. The sym-metry ranking, based on the new criterion, is applied to the symmetry point groups. 
  Reference    Z. Naturforsch. 51a, 882—883 (1996); received February 8 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0882_n 
 Volume    51 
131Author    S. Hansen, B. D. Mosel, W. Müller-Warmuth, P. E. FieldingRequires cookie*
 Title    EPR Studies of Tb 4+ in Single Crystals of Zircon and Scheelite Structure Silicates and Germanates  
 Abstract    In memoriam Professor Gerhard Lehmann Electron paramagnetic resonance spectra of tetravalent terbium ions have been observed in host crystals of ZrSi0 4 , HfSi0 4 , ThSi0 4 , ThGe0 4 (zircon structure) and ZrGe0 4 , HfGe0 4 (scheelite structure) at X band and Q band and various temperatures. The spin Hamiltonian parameters have been determined from the rotational diagrams; the zero field splittings turned out to be extremely large, so that complex spectra far from the strong magnetic field limit had to be analyzed. In all the compounds Tb 4+ substitutes for the tetragonal metal lattice sites. The incorporation of terbium, the origin of the large second-order parameters and comparisons with the spectra of trivalent gadolin-ium in similar systems are discussed. 
  Reference    Z. Naturforsch. 51a, 885—894 (1996); received May 14 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0885.pdf 
 Identifier    ZNA-1996-51a-0885 
 Volume    51 
132Author    D.Mehmet Zengin, Mehmet Birey, Huseyin Aktas, Ahmet Hancer, AtillaM. MurathanRequires cookie*
 Title    ESR of Gamma Irradiation Damage Centers in Single Crystals of Some Glutamic Acid Derivatives  
 Abstract    We have observed four radicals in the ESR spectra of y-irradiated single crystals of some glutamic acid derivatives. These radicals, produced by gamma-irradiation, in single crystals of N-Acetyl-L-Glutamic acid, L-Glutamic acid and DL-Glutamic acid hydrochloride were identified as CH3CONH, —C 3 H 5 , -CH. and —NH 2 radicals respectively. 
  Reference    Z. Naturforsch. 51a, 895—897 (1996); received January 24 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0895 
 Volume    51 
133Author    AxelH. Saleck, Thomas Klaus, SergeiP. Belov, Gisbert WinnewisserRequires cookie*
 Title    THz Rotational Spectra of HBr Isotopomers in their v = 0,1 States  
 Abstract    We have observed the pure rotational spectra of HBr isotopomers in their v = 0 and v = 1 states between 0.97 and 1.02 THz. i. e. the HBr .7 = 2—1 and the DBr .7 =4 — 3 transitions, respectively. In the analysis, all presently available rotational transitions of all isotopomers have been fitted to a Dunham-type Hamiltonian to obtain the isotopically invariant parameters, including vibrational and rotational expansion coefficients for the hyperfine constants. In the analysis, the vibrational expansion coefficients of the nuclear quadrupole interaction are determined up to second order, and up to first order for the nuclear spin-rotation interaction. 
  Reference    Z. Naturforsch. 51a, 898—904 (1996); received April 18 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0898 
 Volume    51 
134Author    A. Kawski, G. Piszczek, A. KubickiRequires cookie*
 Title    Fluorescence Properties of p-Quaterphenyl and /7-Quinquephenyl Derivatives in Liquid Solvents  
 Abstract    Absorption, fluorescence and emission anisotropy spectra, as well as quantum yields and fluores-cence decay times of p-quaterphenyl (PQP), 4,4"'-bis-(2-butyloctyloxy)-p-quaterphenyl (BBQ), 2,5,2"",5""-tetramethyl-p-quinquephenyl (TMI) and 3,5,3"",5""-tetra-f-butyl-p-quinquephenyl (QUI) were investigated in several nonpolar and polar solvents. It was found that high quantum yield is accompanied by a short (not exceeding 1 ns) lifetime and considerable emission anisotropy in low viscosity solvents. For TMI and QUI, which incorporate as many as 5 phenyl groups, the quantum yield in dioxane is 0.98 and 0.97, respectively. In the case of molecules with 4 phenyl groups, the quantum yield is slightly lower, amounting to 0.91. Rotational motions of terminal phenyl groups cause a lower deactivation of the excitation energy of the singlet state S p the longer the linear molecule. 
  Reference    Z. Naturforsch. 51a, 905—909 (1996); received May 14 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0905 
 Volume    51 
135Author    T. Ueda, K. Shimizu, H. Ohki, T. OkudaRequires cookie*
 Title    C CP/MAS NMR Study of the Layered Compounds [C 6 H 5 CH 2 CH 2 NH3] 2 [CH 3 NH 3 ] fI _ 1 Pb n l3 n+1 (n = 1, 2)  
 Abstract    19, 1996 13 C CP/MAS NMR spectra were measured on the layered compounds [C 6 H 5 CH 2 CH 2 NH 3 ] 2 [CH 3 NH 3 ] n _ 1 Pb"I 3n + j (w = 1, 2). The linewidth of the resonance peak corresponding to the phenyl carbons changed with temperature. The maximum broadening took place at 363 K for both com-pounds. The activation energy £ a for the reorientation of the phenyl group was determined to be 25 kJ mol" 1 for n — 1 and 26 kJ mol" 1 for n = 2. The frequency factor t 0 was evaluated from the linewidth at 363 K. The value of the second moment, estimated from the maximum linewidth, was interpreted by assuming a 180° flip of the phenyl group around its two-fold axis. The similarity of the activation energies for the reorientation of the phenyl group suggested that the local structure and the molecular motion of the organic cations is little affected by the difference in the sub-structure of the inorganic layer in those compounds. 
  Reference    Z. Naturforsch. 51a, 910—914 (1996); received March 
  Published    1996 
  Keywords    13 C CP/MAS NMR, Molecular motion, Layered compounds Activation parameters, Local structure 
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 Identifier    ZNA-1996-51a-0910 
 Volume    51 
136Author    Giorgio Concas, Francesco Congiu, Anna Corrias, Carlo Muntoni, Giorgio Paschina, Daniela ZeddaRequires cookie*
 Title    Investigation of the Reaction between Fe 2 0 3 and Si Activated by Ball Milling  
 Abstract    The path of the reaction between Fe 2 0 3 and Si, activated by high energy ball milling, has been investigated by X-ray diffraction and Mössbauer spectroscopy. Hematite reduction involves oxygen transfer from Fe to Si with the formation of intermediate phases containing Fe(II), which are then reduced to Fe(0). A steady state is reached in the milling process where the reduction of stoichiomet-ric amounts of Fe 2 0 3 and Si is not complete and an amount of Fe(II) in an amorphous matrix still remains. The same intermediate compounds are also observed in the milling process of mixtures with higher Fe 2 0 3 /Si molar ratio. 
  Reference    Z. Naturforsch. 51a, 915—922 (1996); received April 1 1996 
  Published    1996 
  Keywords    Mechanosynthesis, Nanocomposite, Reduction reaction, Mössbauer spectroscopy, X-ray diffraction 
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 Identifier    ZNA-1996-51a-0915 
 Volume    51 
137Author    H. Hartwig, H. DreizlerRequires cookie*
 Title    The Microwave Spectrum of trans-2,3-E>imethyloxirane in Torsional Excited States  
 Abstract    The microwave spectrum of trans-2,3-dimethyloxirane (CH 3 CHOCHCH 3) in the excited tor-sional states u 17 = 1 and v i3 — 1 has been measured in the range from 8 to 26 GHz and assigned. An analysis of internal rotation splittings of the observed rotational transitions was performed using the internal axis method (or "combined axis method") with a newly developed program accounting for the top-top coupling. The threefold hindering potential V 3 and the direction cosines /. g of the internal rotation axes i with respect to the principal inertia axes g are in a good agreement with the ground state values. Additionally, the sixfold hindering parameter V t was found to be — 0.2600(12) kJ/mol. The value of the parameter V[ 2 describing the top-top coupling in the potential function (via V[ 2 sin3r! sin3i 2), was determined to —0.4240(6) kJ/mol. 
  Reference    Z. Naturforsch. 51a, 923—932 (1996); received May 2 1996 
  Published    1996 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0923.pdf 
 Identifier    ZNA-1996-51a-0923 
 Volume    51 
138Author    J. Jadżyn, C. Legrand, P. Kędziora, B. Żywucki, G. Czechowski, D. BaumanRequires cookie*
 Title    Dielectric Behaviour of l-(4-Isothiocyanatophenyl)-2-(4-hexyl- bicyc!o[2,2,2]octane-l)ethane in Nematic and Isotropic Phases  
 Abstract    Static and dynamic investigations of the dielectric properties of the liquid crystal l-(4-isothio-cyanatophenyl)-2-(4-hexyl-bicyclo[2,2,2]octane-l)ethane in the nematic and isotropic phases have been carried out in the frequency region from 1 kHz to 1 GHz. Two relaxation processes, described by the Debye functions, have been observed not only in the isotropic but also in the nematic phase, when the measurements of the electric permittivity vs. frequency have been made parallel to the orientation axis of liquid crystal. These processes are related to the rotation of the permanent dipole moment around two main molecular axes. The height of the potential barrier which hinders the rotation of the liquid crystal molecule around the short axis in the ordered nematic phase and the order parameter of the liquid crystal investigated have been estimated on the basis of the relaxation time values in the nematic and isotropic phases. 
  Reference    Z. Naturforsch. 51a, 933—938 (1996); received April 3 1996 
  Published    1996 
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 Identifier    ZNA-1996-51a-0933 
 Volume    51 
139Author    Ch Frommen, M. Mangold, J. PeblerRequires cookie*
 Title    Magnetic Solitons in the 1-D Antiferromagnetic Chains of Li 2 Mn 0 98 Fe 0 02 F 5 and Na 2 Mn 0 98 Fe 0 0 2 F 5  
 Abstract    Measurements of the 57 Fe Mössbauer effect and magnetic susceptibility have been performed on 57 Fe-doped quasi-l-d antiferromagnetic chains of Li 2 MnF 5 and Na 2 MnFg as a function of temper-ature. The Mössbauer spectra, fitted by the Blume-Tjon model, show definite relaxation effects near the Neel temperature, which are attributed to short-range order with temperature-dependent relax-ation times. The soliton model of non-linear excitations was applied. Experimental data confirm the predicted exponential temperature dependence of the thermal excitation of moving domain walls. From the activation energies E 2 Jk 2 as a function of 1-d exchange energies J/k the local anisotropy energy D/k of —3.7(2) K was derived on the basis of sine-Gordon theory. This result is in fair agreement with —3.5(1) K previously derived from magnetic susceptibility measurements. In the light of our results there is some evidence that at low bridging angle ß % 102(5)° a phase-transition from antiferromagnetic to ferromagnetic ordering occurs. 
  Reference    Z. Naturforsch. 51a, 939—949 (1996); received February 1 1996 
  Published    1996 
  Keywords    Magnetization Exchange and Anisotropy Energy, Relaxation, Solitons 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0939.pdf 
 Identifier    ZNA-1996-51a-0939 
 Volume    51 
140Author    C. Margheritis, C. SinistriRequires cookie*
 Title    /?-cyclodextrine and Water: Semiempirical Calculations  
 Abstract    AMI and PM3 calculations were carried out on ß-cyclodextrine (ß-CD) undecahydrate in the experimental conformation at 120 K. The calculated /TCD/water interaction energies are very small and indicative for each water molecule of an unfavorable condition in respect to that of pure water. The conformationally optimized system was also studied: ß-CD appears highly symmetrical with negligible dipole moment, mainly because of the circular arrangement of the single vectors. Primary hydroxyls can easily rotate, while the secondary ones are stabilized by heteroannular hydrogen bonds and homoannular electrostatic interactions due to the consequent increase of the atomic charges. The ß-CD/water interaction energies in the optimized hydrated system are not significantly different from the experimental ones. This almost hydrophobic character is also shown by MM equilibrated solutions: all water molecules are rejected beyond 2.4 A; between 2.4 and 2.9 A highly structured water is present. From a purely enthalpic standpoint the molecule hydration appears highly improbable, thus the formation of ß-CD 11 H 2 0 must involve a compensation mechanism. 
  Reference    Z. Naturforsch. 51a, 950—956 (1996); received May 13 1996 
  Published    1996 
  Keywords    ß-cyclodextrine hydrate, Semiempirical calculations, Water interactions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0950.pdf 
 Identifier    ZNA-1996-51a-0950 
 Volume    51 
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