AN IMPROVED MODEL FOR COMPUTING SOLUTION DYNAMICS OF NATURAL PRODUCTS WITH ^(13)C NUCLEAR MAGNETIC RELAXATION

The fully anisotropic molecular overall tumbling model with methyl conformation jumps internal rotation among three equivalent sites is proposed,the overall tumbling rotation rates and the methyl internal rotation rates of ponicidin are computed with this model from ~C relaxation parameters.

COMPATIBILITY IN POLYMER BLENDS OF POLY (VINYL ACETATE) AND POLY (METHYL METHACRYLATE)STUDIED BY NMR

Compatibility of poly (vinyl acetate) (PVAc) with poly (methyl methacrylate) (PMMA) mixtures has been studied by using nuclear magnetic relaxation, differential scanning calorimeter and small-angle X-ray scattering techniques. The nuclear magnetic relaxation time T_1's were measured as a function of composition in blends of PMMA and PVAc prepared from chloroform solution. The results show that the system is miscible for casting from chloroform solution.

Water Efflux in Red Blood Cells of Sickle Cell Patients under Spontaneous Deoxygenation

The water transport through Red Blood Cells (RBC) membrane has been previously studied in Sickle Cell Disease (SCD) using oxygenated RBC or under complete deoxygenation. In this work, the water efflux in RBC of sickle cell patients was studied under spontaneous deoxygenation conditions. With that purpose, a magnetic resonance method was used to evaluate the water exchange time (τe) and the permeability through the erythrocyte membrane (P) measuring the spin-spin relaxation time (T2) in doped and non-doped RBC. Carr-Purcell-Meiboon-Gill (CPMG) pulse sequence was used to measure T2 in a magnetic resonance console coupled to one homogeneous magnet system (0.095 T). An increase of the water transport in RBC from sickle cell patients was observed and characterized with a τe value of 15.2 ± 0.8 ms. The abnormal activation of the Psickle, Gardos, and potassium chloride cotransporter channels starting from deoxygenation, as well as, the possible appearance of new pores due to the increase of the hemoglobin-membrane interaction, are suggested to explain this abnormal transport phenotype. The change of the water volume to surface ratio (V/S) in the sickle cells is also suggested to be considered in P calculation under deoxygenation. The results obtained in this work increase the fundamental knowledge about molecular mechanism involved in SCD and could be useful in the development of new methods for diagnostic and treatment evaluation.

Influence of nanosized magnesia on the hydration of borehole-sealing cements prepared using different methods

Gas drainage is an efective technology for gas control in coal mines.A high borehole-sealing quality is the fundamental precondition for efcient gas drainage.The expansibilities of cement pastes used in borehole-sealing processes are critical for the borehole-sealing efect.Nanosized magnesia expansive agents are used to improve the expansibilities of cement pastes and improve the borehole-sealing efect.Nuclear magnetic resonance spectrometry and scanning electron microscopy were adopted to study the efects of nanosized magnesia on the hydration of borehole-sealing cements used with diferent preparation methods.The results showed that an increase in the mass fraction of the nanosized magnesia promoted cement hydration,and the mass fraction was positively correlated with the promotion efect.The use of diferent preparation methods did not change the water-phase distribution in the cement.When using the wet-mixing preparation method,nanosized magnesia promoted the induction,acceleration,and deceleration periods of hydration;when using the dry-mixing preparation method,the nanosized magnesia promoted the induction period of cement hydration,and the promotion efect was less obvious than that seen when using the wet-mixing method.When using the wet-mixing preparation method,the nanosized magnesia was uniformly dispersed,thus enlarging the surface area of the reaction,which provided more nucleation sites for the hydration products of the cement and therefore accelerated the hydration reaction.When using the dry-mixing preparation method,the nanosized magnesia powders were dispersed nonuniformly and aggregated.Under these conditions,only a few nanosized magnesia particles on the surfaces of the aggregated clusters took part in hydration,so only a small number of nucleation sites were provided for the hydration products of cement.This led to inconsistent hydration of cement pastes prepared using the dry-mixing method.The surface porosity of the cement prepared with the wet-mixing preparation method frst decreased and then increased with increases in the mass fraction of the nanosized magnesia.The cement surface exhibited compact hydration products and few pores,and the surface was relatively smooth.In comparison,the surface porosity of the cement prepared using the dry-mixing method fuctuated with increasing mass fraction of the nanosized magnesia,resulting in a rough cement surface and microfractures on some surfaces.The two preparation methods both reduced the surface porosity of the cement.The wet-mixing preparation was more efective and consistent in improving the compactness of the cement than the dry-mixing preparation.These results provide important guidance on the addition of nanosized magnesia in borehole-sealing engineering and the selection of cement preparation methods,and they also lay a solid foundation for realizing safe and efcient gas drainage.