Abnormal difference between the mobilities of left- and right-twisted conformations of C6H12N2 roto-symmetrical molecules at very low temperatures.

We report an abnormal difference of low-temperature mobility of left-twisted and right-twisted conformations of roto symmetric molecules C6H12N2 (dabco) located in the same positions in crystal Zn2(C8H4O4)2⋅C6H12N2. The difference between (1)H NMR (Nuclear Magnetic Resonance) spin-relaxation data for left-twisted and right-twisted molecules reaches ∼3 × 10(3) times at 8 K and tends to grow at lower temperatures. We argue that taking into account four-component relativistic Dirac wave functions in the vicinity of the nodal plane of dabco molecules and vacuum fluctuations due to virtual particle-antiparticle pairs can explain the changes which C6H12N2 conformations undergo at low temperatures.

NMR study of localization and mobility of 1-phenylethanol enantiomers in homochiral metal-organic sorbent Zn2(bdc)(S-lac)(dmf).

Structural features of localization of chiral isomers of 1-phenylethanol (R-PhEtOH and S-PhEtOH) and their mobility activation in homochiral metal-organic [Zn2 (bdc)(S-lac)(dmf)] sorbent were studied with (1)H and (13)C NMR methods. (13)C NMR chemical shifts do not show obvious advantage of selective interaction of molecule guests. But activation molecular mobility of S-PhEtOH and R-PhEtOH clearly indicates that stabilization of [Zn2(bdc)(S-lac)(dmf)]·S-PhEtOH structure is more preferable than stabilization of [Zn2 (bdc)(S-lac)(dmf)]·R-PhEtOH structure.

Chirality-related interactions and a mirror symmetry violation in handed nano structures.

Hindering of inversion transitions and a violation of mirror symmetry of the right- and left-handed configurations of diazabizyclooctane (dabco, N2C6H12) enantiomers has been studied with low-temperature adiabatic calorimetry. The dabco molecules were sandwiched in a high-porous layered structure of a metal organic framework (MOF) compound. We show from the data of low-temperature adiabatic calorimetry and (1)H NMR spin relaxation method that hindering of inversion transitions of dabco molecules cannot be associated with the influence of the intracrystalline self-consistent molecular field as a continuously monitoring environment within the quantum Zeno effect. In addition, lack of another manifestation of this effect associated with the collisional suppression of the inversion transitions in MOF samples impregnated by helium has been shown. These results lead to the conclusion that chiral polarization is related to the fundamental effect of parity nonconservation.

Electronic Switch in the Carbon-Centered [Re(12)CS(17)(CN)(6)] Nanocluster.

An abrupt change in internuclear Re-Re distances between {Re(6)} subunits in the carbon-centered [Re(12)mu(6)-CS(17)(CN)(6)](n-) complexes caused by the change of the oxidation state (n = 6, 8) is first theoretically shown to be possibly controlled by an external electric field. (13)C NMR signal is shown to change over ~400 ppm (~37G) for mu(6)-C atom together with n. Thereby, the metal cluster [Re(12)mu(6)-CS(17)(CN)(6)](n-) can be considered as a perspective model of a molecular switch.

[Collagen structure and the disordering of the water subsystem in fibrillar polypeptides according to 2H-NMR data].

2H NMR spectra of native collagen of rat tail tendon doped by 2H2O were studied. It was shown that the fine structure of 2H NMR multicomponent spectra is related to the diffusion mobility of constituent water molecules and their partial ordering. A bimodality of the distribution of the H2O ordering parameter was revealed, which corresponds to the alternation of dense and loose regions in the supramolecular structure of collagen-type polypeptides. The lower values of the ordering parameter correspond to loose regions of the structure characterized by the cooperative dynamics of polypeptide chains and water molecules.

125Te NMR tomography of [Re6] cluster in Re6Te15 and related cluster compounds.

The static and magic angle spinning NMR solid-state spectra of Re6Te15 and a series of Re(6)-Te cluster compounds demonstrate the positive and negative 125Te NMR chemical shifts indicating that the [Re6] cluster distorts strongly magnetic field at the neighboring Te sites. The local magnetic field is decreased at the facial tellurium sites (Teface) and enhanced at the apexial tellurium sites (Teapex). The facial and sagittal sections of the Re(6)-Te clusters were reconstructed from analysis of Teface and Teapex NMR spectra, respectively.

207Pb NMR of minium, Pb3O4: evidence for the [Pb2]4+ ion and possible relativistic effects in the Pb-Pb bond.

Solid Pb3O4 has been studied with 207Pb nuclear magnetic resonance (NMR) spectroscopy. The 207Pb NMR chemical-shift tensor of the Pb2+ site has principal values of delta11 = 1980 +/- 5 ppm, delta22 = 1540 +/- 5 ppm, and delta33 = -1108 +/- 10 ppm; delta(iso) = 804 +/- 10 ppm. The chemical-shift tensor of the Pb4+ site is axial, with principal values delta(parallel) = -1009 +/- 3 ppm and delta(perpendicular) = 1132 +/- 3 ppm; delta(iso) = -1091 +/- 3 ppm. The Pb4+-Pb2+ scalar coupling constant J(Pb-Pb) = 2.3 +/- 0.1 kHz. The main contribution to the Pb2- chemical-shift anisotropy is proposed to arise from an exchange interaction in the Pb2+-Pb2+ pairs, conventionally regarded as molecular [Pb2]4+ ions.

[Molecular mobility and electrical properties of keratin]. / Molekuliarnaia podvizhnost' i élektretnye svoistva keratina.

The samples made from the horn of Saiga tatarica were investigated by PMR method. It was shown that an increase of mobility of adsorbed molecules correlated with the appearance of the peaks of thermally stimulated currents of depolarization in the region of 370 K-390 K. The activation energies of molecular mobility in keratin were found.

[Fractionation of carbon isotopes in human atherosclerotic tissues]. / Fraktsionirovanie izotopov ugleroda v tkaniiakh cheloveka pri ateroskleroze.

A decrease in heavy carbon isotope 13C content has been detected in atherosclerotically-altered aortic tissues. An extent of the isotope shift is increased with the intensification of sclerotic process in different regions of the aorta and depends on the patient's age. To explain the observed effect of isotope 13C content decrease in the altered aortic tissues it was suggested that the rates of biochemical conversions become considerably higher in sclerotically-altered tissues.

[Molecular mobility of soluble collagen]. / Molekuliarnaia podvizhnost' rastvorimogo kollagena.

Conformation structure of soluble collagen in anhydrous form, films and gels was studied by broad line NMR. An analysis of spectra points to partial ordering of polymer chains in the films and possible formation of secondary structure of collagen molecules by alpha-helix type. Distinction of gel spectra from those of films is explained by unordered rotation movements of the chain fragments at the expense of "superspiralization" of collagen molecules.

[Interaction of collagen with sodium ions]. / Vzaimodeistvie kollagena s ionami natriia.

A change was found in the correlation between donor and acceptor adsorptive sites on the collagen surface in NaCl solution treatment. The number of binding sites was estimated by the value of spin-spin interaction constant (alpha) of native and treated by 3% NaCl solution; it accounts for 12,5 sites per 100 amino acid residues. A non-specific effect of water freezing after Na+ and K+ ions penetration was noticed.

[Temperature relationship of the NMR 1H spectrum of hydrated collagen]. / Temperaturnaia zavisimost' spektra IaMR 1H gidratirovannogo kollagena.

It is shown from temperature relationship analysis of spin-spin interaction constant (alpha) that at temperature below 265K the donor and acceptor adsorptive sites probability occupation in collagen surface accounts for P(S+) less than or equal to 1/10, P(S-) = 0, but at temperature 265-283K it is P(S+) less than or equal to 1/30, P(S-) = 0. If the temperature is above 283K, fine structure NMR 1H spectrum diminishes which may be explained by the clathrate--like structure collapse of protein hydrate shell.

[Discovery of age effect in molecular structure of collagen]. / Obnaruzhenie vozrastnykh izmenenii v molekuliarnoi strukture kollagena.

The temperature dependences of the NMR-broad line spectra of collagen from Achilles tendon have been investigated. It is found that the narrow doublet splitting collapsed at certain temperature Tx determined by age of collagen sample. The Tx varied from approx. +35 degrees C for 8 years sample to -2 degrees C for 82 years. The interpretation of results obtained is based on the theory of NMR spectra of diffusing water molecules.

[Phase transition in natural collagen]. / Fazovyi perekhod v nativnom kollagene

The state of water protons and peptide chains in natural collagen was investigated by the method of nuclear magnetic resonance. The study of orientation and temperature dependence of collagen PMR spectra allows us to mage a conclusion about the considerable disorder of mutual orientation in the polypeptide chains at the temperature above -4 degrees C. Under these conditions it was observed that natural collagen was near to the liquid-crystal. The phasic transition at -4 degrees C was discovered, the latter was followed by an abrupt change of the character of water proton mobility and by the change of orientation of collagen fibres order. The thermal effect of transition was measured, the latter presents 18k/gr of the whole specimen.