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

Dipole-Echo Formation in Three-Pulse-Sequence NMR Experiments on Polymer Systems

Data from three-pulse NMR experiments, namely, the Goldman-Shen pulse sequence and the stimulated-echo sequence, on partially crystallized poly(ethylene glycol) and tetrafunctional dimethylsiloxane networks are presented. A dipole echo has been observed after a third radiofrequency pulse. Quantum mechanical calculations of the response of the spin system to the three-pulse sequences have been performed, considering only thez-zcomponent of the dipole-dipole spin coupling. The resulting expression suggests dipole-echo formation and is in agreement with experimental data. © 1995

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

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

Specifics of the physicochemical properties of tetramethylurea

The rotational and translational mobility of tetramethylurea molecules over the temperature range 15-60°C was studied using the NMR relaxation and proton spin-echo methods. The activation energies for these motions were calculated. The density, viscosity, isothermal compressibility, and cubic expansivity were determined. A thermogravimetric analysis of the substance was performed. The physicochemical properties of tetramethylurea were compared to those of urea, its other methyl-substituted derivatives, and dimethylformamide. Copyright © 2005 by Pleiades Publishing, Inc

Conformational Flexibility and Self-Association of Fibrinogen in Concentrated Solutions

© 2017 American Chemical Society. We studied the hydrodynamic behavior of fibrinogen, a blood plasma protein involved in blood clotting, in a broad 0.3-60 mg/mL range of concentration and 5-42 °C temperature using pulsed-field gradient 1 H NMR-diffusometry. Arrhenius plots revealed the activation energy for fibrinogen diffusion E d = 21.3 kJ/mol at 1.4 mg/mL and 28.4 kJ/mol at 38 mg/mL. We found a dramatic slowdown in fibrinogen self-diffusion with concentration beginning at 1.7-3.4 mg/mL, which deviated from the standard hard-particle behavior, suggesting a remarkable intermolecular entanglement. This concentration dependence was observed regardless of the absence or presence of the GPRP peptide (inhibitor of fibrin polymerization), and also in samples free of fibrin oligomers. By contrast, diffusivity of fibrinogen variant I-9 with truncated C-terminal portions of the Aα chains was much less concentration-dependent, indicating the importance of intermolecular linkages formed by the αC regions. Theoretical models combined with all-atom molecular dynamics simulations revealed partially bent fibrinogen solution conformations that interpolate between a flexible chain and a rigid rod observed in the crystal. The results obtained illuminate the important role of the αC regions in modulating the fibrinogen molecular shape through formation of weak intermolecular linkages that control the bulk properties of fibrinogen solutions

Structure and properties of aqueous dispersions of sodium dodecyl sulfate with carbon nanotubes

© 2016, Springer Science+Business Media New York.The dispersing action of the surfactant (sodium dodecyl sulfate, SDS) on the carbon nanotubes (CNT) in aqueous medium has been studied. Electron microscopy, molecular docking, NMR and IR spectroscopies were applied to determine the physical-chemical properties of CNT dispersions in SDS—water solutions. It was established that micellar adsorption of the surfactant on the surface of carbon material and solubilization of SDS in aqueous medium contribute to improving CNT dispersing in water solutions. It was shown that the non-polar hydrocarbon radicals of a single surfactant molecule form the highest possible number of contacts with the graphene surface. Upon increase of the SDS in solution these radicals form micelles connected with the surface of the nanotubes. At the sufficiently high SDS concentration the nanotube surface becomes covered with an adsorbed layer of surfactant micelles. Water molecules and sodium cations are concentrated in spaces between micelles. The observed pattern of micellar adsorption is somewhat similar to a loose bilayer of surfactant molecules

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