Study Of Internal Motions Research Articles

Study of internal motions and phase transitions in (NH4)2ZnCl4 and [(N(CH3)4)]2 ZnCl4 by proton magnetic resonance and relaxation

Proton second moment (M2) and spin-lattice relaxation time (T1 at 10 MHz have been measured in polycrystalline ammonium tetrachlorozincate (ATC-Zn) and tetramethyl ammonium tetrachlorozincate (TMATC-Zn) as a function of temperature, covering the phase transitions. In ATC-Zn, the motion of NH+4 ion is fast in all phases as seen by a small and temperature independent proton second moment. Two types of chemically inequivalent NH+4 ions have been identified from the observed double minima in proton T1. Proton T1 shows a discontinuous jump and change of slope at 319 K, probably due to a phase transition. In addition, T1 shows a maximum around the reported ferroelectric phase transition (270 K), indicating the presence of spin-rotation interaction. In TMATC-Zn, the lowest temperature transition seems to be related to the slowing down of CH3 groups as revealed by the proton second moment. In this system also, two kinds of [N(CH3)4] ions have been found to be present from the proton T1 studies. Proton T1 shows ch...

Motional behavior of "asperlin" in solution. A 13C spin-lattice relaxation study

l3C nuclear magnetic resonance spin-lattice relaxation times (T1) have been used to probe the motional behavior of 5-acetoxy-5,6-dihydro-6-(1,2-epoxypropyl)-2-pyrone ("asperlin") in dimethyl sulfoxide solution. This molecule offers structural features suited to a study of internal motions, i.e., epoxypropyl and methyl internal motions superimposed on an anisotropic overall reorientation. The rigidity of the pyrone ring and its semiplanar conformation result in an overall ellipsoidal shape, and hence the rotational dynamics of asperlin are adequately approximated by the diffusion of a prolate ellipsoid with the major axis passing through the C(2)—H(2) bond. The description of the internal motion of the epoxypropyl ring is strongly model dependent. Furthermore, the relaxation data for the oxirane ring carbons do not uniquely define a dynamic model. Due to similarities in the activation energies of the overall and internal motions, based on temperature-dependent measurements, it has not been feasible to interpret the relaxation data by a single type of motion. Internal rotation of the epoxymethyl substituent is rationalized by applying the stochastic diffusion model of multiple internal rotations

Study of internal motions through N.Q.R. in 6-Chloropyridin-2-ol

Chlorine-35 n.q.r, has been observed for the first time in 6-chloropyridin-2-ol and its temperature dependence has been studied from 77 K to room temperature. The torsional frequencies and their temperature dependences have been calculated by using Bayer's theory with and without Tatsuzaki's modification.

Dynamic light‐scattering studies of internal motions in DNA. I. Applicability of the rouse‐zimm model

AbstractThe intermediate scattering function G(K,t) for any polymer model obeying a linear separable Langevin equation can be expressed in terms of the eigenvalues and eigenvectors of its normal coordinate transformation. An algorithm for the extract numerical evaluation of G(K,t) for linear Rouse‐Zimm chains in the presence of hydrodynamic interaction has been developed. The computed G(K,t)2 were fit to C(t) = A exp(−t/τA) + B, and apparent diffusion coefficients calculated according to Dapp ≡ 1/(2τAK2). G(K,t)2 was surprisingly well‐fit by single‐exponential decays, especially at both small and large values of Kb, where K is the scattering vector and b the root‐mean‐squared subunit extension. Plots of Dapp vs K2 in‐variably showed a sigmoidal rise from D0 at K2 = O up to a constant plateau value at large K2b2.Analytical expression for G(K,t), exact in the limit of short times, were obtained for circular Rouse‐Zimm chains with and without hydrodynamic interaction, and also for free‐draining linear chains, and in addition for the independent‐segment‐mean‐force (ISMF) model. The predicted behaviors for G(K,t) at large Kb (or KRG) was found in all cases to be single‐exponential with 1/τ ∝ K2 at large Kb, in agreement with the computational results. A simple procedure for estamating all parameter of the Rouse‐Zimm model from a plot of Dapp vs K2 is proposed.Experimental data for both native and pH‐denatured calf‐thymus DNA in 1.0M Nacl with and without EDTA clearly plateau behavior of Dapp at large values of K, in harmony with the present Rouse‐Zimm and ISMF theories, and in sharp contrast to previous predictions based on the Rouse‐Zimm model.