Efficient Photoswitching of Aryloxy‐Substituted Naphthacenequinones

Two-State Conformations in the Hyaluronan-Binding Domain Regulate CD44 Adhesiveness under Flow Condition

14] Biochemical and NMR studies of RNA conformation with an emphasis on RNA pseudoknots

Nuclear magnetic resonance and electron paramagnetic resonance ( and respectively) are powerful experimental probes of the atomic-scale structure of glass. This chapter provides a practical introduction to the current state of the art of these methods in glass research, and is intended to provide researchers with the basic knowledge needed to apply and interpret the results of these methods. Topics covered include the basic physics of spin resonance experiments, necessary instrumentation and sample considerations, representative experimental results, and methods of interpretation.

Human hemoglobin has a molecular weight of 64,500 and is composed of four subunits, two each of two types, a and F. Each subunit consists of an aor fpolypeptide chain and one protoheme IX group. In the biologically active state, each heme group contains one iron (II) ion which binds molecular oxygen in its first coordination sphere. The entire hemoglobin molecule, a232, thus contains four heme groups and binds four oxygen molecules in the fully oxygenated state. It has been fournd that the oxygen affinity is closely related to the structure of hemoglobins.' In the present paper we give a preliminary account of proton nuclear magnetic resonance (NMR) studies of human cyanomethemoglobin. From the NAMR data, electron spin densities at various positions in the heme group are derived. We indicate how this kind of N1\IR experiment can give new information about some aspects of the relations between structure and function in hemoglobin. In the NA/MR spectra of proteins, essentially all the proton resonances are observed in a narrow range which extends from the internal standard DSS (2,2dimethyl-2-silapentane-5-sulfonate) downfield to ca. -10 ppm (parts per million relative to DSS). The larger the protein molecule, the more the resoniances of the protons of the individual amino acid side chains overlap. Therefore most NMR studies are done with relatively small proteins with molecular weights less than 20,000. In paramagnetic heme proteins, local magnetic fields arising both from aromatic ring currents2' I and from the unpaired electron spins have been shown to shift certain proton resonances out of the range between DSS and -10 ppm.4-6 For these reasons the NMR spectrum of cyanomethemoglobin contains a considerable number of resolved resonances despite its high molecular weight. Experimental.-Human hemoglobin solutions were prepared from the freshly drawn blood of one of us (K. W.) by the following method. The erythrocytes were separated from the plasma by centrifugation within 15 min. after the addition of the anticoagulant (sodium oxalate), then washed four times with 1 vol of 1% NaCl. After hemolysis, the solution was subjected to 105,000 g centrifugation for 21/2 hr. The upper two thirds of the supernatant, free of any flocculus precipitate, was separated off and then further centrifuged. This procedure was repeated twice. The hemoglobin solution was dialyzed overnight at 4?C against 0.1 M phosphate buffer. Some hemoglobin solutions were also prepared by the widely used toluene method.7 The NMR spectra of cyanomethemoglobin solutions prepared by these two different methods were found not to differ noticeably. Methemoglobin was prepared by addition of a sixfold excess of K3Fe(CN)6 to the hemoglobin solution that was thenl dialyzed extensively against 0.1 M phosphate buffer. Methemoglobin was purified on the cation exchange resin Bio-Rex 70 (Bio-Rad) and concentrated by vacuum dialysis. Sodium phosphate buffer, pH 6.42, total ionic strength of 0.304, was used for the elution of methemoglobin.8 The homogeneity of isolated hemoglobin fractions was checked by starch gel electrophoresis9 with the discontinuous buffer system.10 Methemoglobin A1 was then converted to cyanomethemoglobin by the addition of a freshly prepared solution of KCN in phosphate buffer.

12-P-12 - NMR studies on the pyrrole adsorption over Na+, Li+ exchanged zeolites of type FAU

Phase transitions and incommensurate phases in layered thallium sulfide semiconductor - An NMR study

The lecture presents examples of Nuclear Magnetic Resonance (NMR) and Nuclear Quadrupole Resonance (NQR) studies performed in compounds of the Y-Ba-Cu-O family in order to show the kind of information these microscopic techniques can provide with respect to structural and electronic properties. Topics which are addressed are the following: calculation of electric field gradients; valences and bonding and temperature and pressure effects; oxygen distribution; doping with cations; Knight shifts and relaxation times and their relations to hole concentration, one-component susceptibilities, coupling of planes, spin-gap and BCS orbital-pairing.

Nuclear Magnetic Resonance of Less Common Quadrupolar Nuclei

Myocardial proton spin-lattice relaxation times in vitro: Effect of elapsed time after excision

The erosion of effective patent life—An international comparison

NMR Spectroscopy of Biofluids

Summary Recent nuclear magnetic resonance (NMR) studies in water-saturated porous media showed that magnetic resonance relaxation of 1H nuclei is a powerful tool for studying the interplay between geometry and fluid transport. Proper combinations of spin-lattice relaxation lifetime, T1, and porosity allow permeability to be predicted. T1, as defined here, provides a bridge between structural and transport properties because it can be viewed as a dynamically weighted (by diffusion) version of the specific surface. In this paper, we probe this role of T1 for a suite of clean sandstone samples in which, besides permeability and porosity, specific surface by mercury porosimetry and the formation resistivity factor (FRF) also have been measured. We studied the correlations among these properties and found that the ability of T1 to estimate permeability is a result of its linear dependence on the PV-to-surface ratio, Vp/S. For clean sandstone rocks, one may view the reciprocal electrical resistivity formation factor, 1/F, as representing the transport properties and the factor T12 as representing the distance scale, giving k∝T12/F. A suitable analysis of the spin-lattice relaxation curve can yield an estimate of an appropriate specific surface pertinent to permeability because it indirectly accounts for the connectivity of the pore space. This NMR approach constitutes a useful technique for a better reservoir characterization and for studying some elusive properties of natural porous media in a nondestructive manner. Theoretical and phenomenological correlations among permeability, porosity, FRF, and PV-to-surface ratio can be established.

Intracellular metabolism of 3′-azido-3′-deoxythymidine (AZT): A nuclear magnetic resonance study on T-lymphoblastoid cell lines with different resistance to AZT

The frequency-dependent dielectric relaxation in barium–aluminium–niobate,BaAl1/2Nb1/2O3 (BAN), at low temperatures (103–443 K) is investigated by alternating-current impedancespectroscopy in the framework of conductivity and electric modulus formalisms. TheHavriliak–Negami expression is used to analyse the electric modulus data. The scalingbehaviour of the imaginary part of the electric modulus suggests that the relaxationdescribes the same mechanism at various temperatures. The frequency-dependentconductivity spectra follow the power law. The electronic structure of BAN is studiedusing x-ray photoemission spectroscopy (XPS). The XPS data are analysed bythe first-principles full potential linearized augmented-plane-wave method usingdensity functional theory under the generalized gradient approximation. Theelectronic structure calculation reveals that the electrical properties of BAN aredominated by the interaction between niobium d-states and oxygen p-states. The27Al and 93Nb nuclear magnetic resonance (NMR) studies of the sample are performed at 78and 73 MHz, respectively, in the temperature range 4–295 K to understandthe transport properties of charge carriers in terms of their dynamics on amicroscopic level. The description of the NMR lineshape is given on the basis ofanalytical formulae. The NMR investigation confirms the chemical ordering of 1:1Al/Nb in BAN.

This paper presents results of laboratory studies of nuclear magnetic resonance (NMR) relaxometry for NMR log calibration aimed at enhancing petrophysical measurements in oil wells. Relationships between NMR longitudinal relaxation parameters and the Hydraulic Units (HU) concept for predicting petrophysical properties from wireline logs have been established previously. However, modern NMR logging tools measure the transverse relaxation parameters. Hence in this paper, we show that measurements of the transverse component of the NMR signal can provide the same information as the longitudinal. Laboratory NMR transverse relaxation characteristics of water in rock samples were measured with CoreSpec-1000. The NMR data were used to validate models for predicting permeability and producible fluid in clastic rocks. The predictive model for permeability includes the rock surface area to grain volume (Sgv) the tortuosity of the flow paths (), the shape factor (Fs), the transverse relaxation time (T2), relaxivity (), and porosity (). The models were used to develop the required NMR log calibration. The transverse relaxation parameters were used with core analysis data of permeability, porosity, and mercury injection capillary pressures to sort the rock samples into hydraulic (flow) units. Protocol for the use of laboratory NMR core spectrometry and core analysis data for NMR log calibration is presented. Relationships between T1 and T2, and between flow zone indicators (FZI) and relaxivity () were established. It was observed that T2 cut-off (T2c) is related to T1 cut-off (T1c) in the same way that T2 is related to T1. Relaxation time cutoffs are used for determining producible fluid (free fluid porosity or free fluid index, FFI). The results show that reliable prediction of permeability and producible fluid from NMR logging tools requires calibration of the tools with laboratory NMR measurements on representative rock samples. We demonstrate the use of T2c for determining FFI from T2 distributions. The methodology for identification and characterization of HU within geological facies based on NMR T2 was validated. Introduction The (HU) concept has successfully been integrated with laboratory core NMR measurements for evaluating petrophysical properties from wireline logs (Ohen et al.). The HU and NMR techniques were linked through the FZI and NMR relaxation parameters, because both the FZI and the relaxation parameters are related to the rock surface phenomenon which controls the microscopic attributes of the rock. Ohen et al. measured the longitudinal (spin-lattice) relaxation time (T1) on a number of reservoir rock samples at a Larmor frequency of 1 MHz with the CoreSpec-1000. P. 329