Phase state and molecular mobility of segmented polyurethanes

Spin-lattice and spin-spin NMR relaxation was studied in a series of segmented polyurethanes based on poly(diethylene glycol adipate), 2,4-tolylene diamine, and 2,4-toluene diisocyanate. It was concluded that NMR relaxation is determined by physical interactions between rigid blocks and also between rigid and flexible blocks. The dependence of the degree of segregation on the molecular weights of rigid and flexible blocks was determined. A quite high degree of segregation in the investigated systems and the related manifestations of individual features of flexible blocks allowed us to follow the dynamics of the molecular chain with fixed end and study variation of the glass transition temperature and the activation energy of the segmental motion of this chain as a function of its molecular weight

Phase state and molecular mobility of segmented polyurethanes

Spin-lattice and spin-spin NMR relaxation was studied in a series of segmented polyurethanes based on poly(diethylene glycol adipate), 2,4-tolylene diamine, and 2,4-toluene diisocyanate. It was concluded that NMR relaxation is determined by physical interactions between rigid blocks and also between rigid and flexible blocks. The dependence of the degree of segregation on the molecular weights of rigid and flexible blocks was determined. A quite high degree of segregation in the investigated systems and the related manifestations of individual features of flexible blocks enabled to follow the dynamics of the molecular chain with fixed end and study variation of the glass transition temperature and the activation energy of the segmental motion of this chain as a function of its molecular weight

System of active regulation of the temperature and temperature gradient in nuclear magnetic resonance sensors

An active system of temperature regulation and temperature gradient in a sample on the example NMR sensor is described in this work. By supporting the given average temperature, the system of temperature-stabilization allows one to set and supervise the size and direction of the temperature gradient along a sample. The temperature of a sample is maintained with on accuracy of about ±0.1°C in a temperature interval of-150 to +200°C with a longitudinal temperature gradient no more than ±0.2°C. The value of the temperature gradient is established in the range of 0° to 10°C/cm in both directions. © 1998 MAHK Hayka/Interperiodica Publishing

Pulsed 1H NMR study of the effects of the rigid block content on the phase state of segmented polyurethanes

The effect of the content of rigid blocks on the phase state and structure of rigid domains in segmented polyurethane based on polyethylenebutyleneglycol adipate, 1,4-butandiol, and 4,4′-diphenylmethane diisocyanate is studied with the aid of pulsed 1H NMR. It is shown from an analysis of free induction decays and using the Goldman-Shen technique that in the specimen having the minimum rigid block length a microphase is formed whose domains have sharp boundaries without intermediate regions. With increase in rigid block length, a second type of domain appears together with the first, consisting of a central part and an intermediate region of high molecular mobility. The ratio of the number of domains of different types depends on the temperature. The dimensions of the domains and intermediate regions are evaluated, and possible structural models are considered. © 1989

Manipulating Biopolymer Dynamics by Anisotropic Nanoconfinement

How the geometry of nano-sized confinement affects dynamics of biomaterials is interesting yet poorly understood. An elucidation of structural details upon nano-sized confinement may benefit manufacturing pharmaceuticals in biomaterial sciences and medicine. The behavior of biopolymers in nano-sized confinement is investigated using coarse-grained models and molecular simulations. Particularly, we address the effects of shapes of a confinement on protein folding dynamics by measuring folding rates and dissecting structural properties of the transition states in nano-sized spheres and ellipsoids. We find that when the form of a confinement resembles the geometrical properties of the transition states, the rates of folding kinetics are most enhanced. This knowledge of shape selectivity in identifying optimal conditions for reactions will have a broad impact in nanotechnology and pharmaceutical sciences.Comment: to appear in Nano Letter

fMRI scanner noise interaction with affective neural processes

The purpose of the present study was the investigation of interaction effects between functional MRI scanner noise and affective neural processes. Stimuli comprised of psychoacoustically balanced musical pieces, expressing three different emotions (fear, neutral, joy). Participants (N=34, 19 female) were split into two groups, one subjected to continuous scanning and another subjected to sparse temporal scanning that features decreased scanner noise. Tests for interaction effects between scanning group (sparse/quieter vs continuous/noisier) and emotion (fear, neutral, joy) were performed. Results revealed interactions between the affective expression of stimuli and scanning group localized in bilateral auditory cortex, insula and visual cortex (calcarine sulcus). Post-hoc comparisons revealed that during sparse scanning, but not during continuous scanning, BOLD signals were significantly stronger for joy than for fear, as well as stronger for fear than for neutral in bilateral auditory cortex. During continuous scanning, but not during sparse scanning, BOLD signals were significantly stronger for joy than for neutral in the left auditory cortex and for joy than for fear in the calcarine sulcus. To the authors' knowledge, this is the first study to show a statistical interaction effect between scanner noise and affective processes and extends evidence suggesting scanner noise to be an important factor in functional MRI research that can affect and distort affective brain processes