W. E. Brittin

Bio: W. E. Brittin is an academic researcher. The author has contributed to research in topics: Silica gel & Phase (matter). The author has an hindex of 1, co-authored 1 publications receiving 785 citations.

Nuclear Magnetic Resonance Studies in Multiple Phase Systems: Lifetime of a Water Molecule in an Adsorbing Phase on Silica Gel

Abstract: Further evaluation studies of nuclear resonance relaxation phenomena of the hydrogen nuclei of HzO adsorbed on silica gel observed by means of radio frequency pulse techniques are described. A stochastic theory for multiphase systems sometimes encountered in relaxation phenomena is presented. Special emphasis is directed toward a theoretical understanding of two phase systems observed in the study of water vapor adsorbed on silica gel, Adsorption experiments are discussed which directly demonstrate, for a s ecific x / m value the simultaneous existence of (a) two phase behavior for transverse (T t ) relaxation measurements and (i) single hase behavior for longitudinal relaxation ( T I ) data. Finally, a close estimate is obtained of the life-time of a water molecuk in an adsorbing phase at low coverage on silica gel.

Hydration of Proteins and Polypeptides

Abstract: Publisher Summary This chapter describes many of the techniques employed to study water–macromolecules interactions, their general usefulness, points out areas of mutual support and contradiction. The chapter also presents hydration of other macromolecules and the hydration of small molecules. Four broadly based approaches to operational definitions of hydration include—(1) preferential hydration, (2) hydrodynamic hydration, (3) structural hydration, and (4) low temperature hydration. The use of high resolution X-ray and neutron diffraction data on protein crystals provides an independent approach for estimation of hydration. The chapter presents several proposals for predicting protein hydration based on the amino acid composition of the protein; however, the two main questions concerned include—whether ionic groups are more hydrated than other polar groups, and whether the amide and peptide functions are hydrated or not. Low pH, and to a much smaller degree, high pH should dehydrate proteins. Intermolecular association via ionic mechanisms should be strongly dehydrating; whereas hydrophobic interactions should not have much effect on hydration levels. Although, there is a presumption that both the enthalpy and the entropy are negative for the process of adding water molecules to isolated proteins, which are maintained in their native conformations, but there is no unequivocal evidence for this.

Heterogeneity at the glass transition: a review

Abstract: Theoretical concepts and experimental evidence of heterogeneity in glass-forming liquids and polymers are reviewed. The main purpose is to provide an introduction to theoretical developments and recent experiments which have led to rapidly increasing knowledge. Realizing that there is no consensus in regard to the various scenarios of the glass transition starting from rather different assumptions we try to give a balanced overview although we also compare and interrelate some of the approaches. The experimental part describes recent nuclear magnetic resonance, dielectric, and optical experiments from which dynamically distinguishable subensembles can be selected thus proving the existence of a well defined dynamical heterogeneity.

Polymer gel dosimetry

Abstract: Polymer gel dosimeters are fabricated from radiation sensitive chemicals which, upon irradiation, polymerize as a function of the absorbed radiation dose. These gel dosimeters, with the capacity to uniquely record the radiation dose distribution in three-dimensions (3D), have specific advantages when compared to one-dimensional dosimeters, such as ion chambers, and two-dimensional dosimeters, such as film. These advantages are particularly significant in dosimetry situations where steep dose gradients exist such as in intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery. Polymer gel dosimeters also have specific advantages for brachytherapy dosimetry. Potential dosimetry applications include those for low-energy x-rays, high-linear energy transfer (LET) and proton therapy, radionuclide and boron capture neutron therapy dosimetries. These 3D dosimeters are radiologically soft-tissue equivalent with properties that may be modified depending on the application. The 3D radiation dose distribution in polymer gel dosimeters may be imaged using magnetic resonance imaging (MRI), optical-computerized tomography (optical-CT), x-ray CT or ultrasound. The fundamental science underpinning polymer gel dosimetry is reviewed along with the various evaluation techniques. Clinical dosimetry applications of polymer gel dosimetry are also presented.

Structural and Dynamic Parameters Obtained from 17O NMR, EPR, and NMRD Studies of Monomeric and Dimeric Gd3+ Complexes of Interest in Magnetic Resonance Imaging: An Integrated and Theoretically Self-Consistent Approach1

Abstract: We present the results of new and previously published 17O NMR, EPR, and NMRD studies of aqueous solutions of the Gd3+ octaaqua ion and the commercial MRI contrast agents [Gd(DTPA)(H2O)]2- (MAGNEVIST, Schering AG, DTPA = 1,1,4,7,7-pentakis(carboxymethyl)-1,4,7-triazaheptane), [Gd(DTPA-BMA)(H2O)] (OMNISCAN, Sanofi Nycomed, DTPA-BMA = 1,7-bis[(N-methylcarbamoyl)methyl]-1,4,7-tris(carboxymethyl)-1,4,7-triazaheptane), and [Gd(DOTA)(H2O)]- (DOTAREM, Guerbet, DOTA = 1,4,7,10-tetrakis(carboxymethyl)-1,4,7,10-tetraazacyclododecane). High-field EPR measurements at different concentrations give evidence of an intermolecular dipole−dipole electronic relaxation mechanism that has not previously been described for Gd3+ complexes. For the first time, the experimental data from the three techniques for each complex have been treated using a self-consistent theoretical model in a simultaneous multiple parameter least-squares fitting procedure. The lower quality of the fits compared to separate fits of the data for each o...

Interpretation of magnetic resonance data from water nuclei in heterogeneous systems

Abstract: Nuclear magnetic resonance (NMR) data from water nuclei (1H, 2H, and 17O) can provide much information about the state of water in heterogeneous systems. In the present work, we present a theoretical framework for the interpretation of such data and discuss the implications of the theory. Due to the local anisotropy in heterogeneous systems, it is necessary to consider two components of water motion: a fast anisotropic reorientation superposed on a more extensive slow motion. On the basis of the experimentally verified assumption that these motions occur on different time scales, we develop a ’’two‐step’’ model of relaxation, showing that both motions may give important contributions to the relaxation. We derive a simple expression for the relevant correlation function, valid for isotropic systems. Anisotropic systems are also treated, making use of a new symmetry theorem for time correlation functions. The proof of this theorem is given in an Appendix. The magnitudes of the water 2H and 17O quadrupole coupling constants are estimated to 0.222 and 6.67 MHz, respectively. Results of ab initio quantum chemical calculations are presented, demonstrating the insensitivity of the water 17O field gradient to nearby ionic species. The possibilities and limitations of the NMR technique in answering the fundamental questions about water structure and dynamics in heterogeneous systems are discussed. We suggest a novel interpretation of the well‐known invariance of the ratio of 1H and 2H splittings. Furthermore, we argue that the available NMR data are consistent with a short‐ranged (≲2 molecular layers) perturbation of the water tumbling rate and anisotropy.