A model for establishing the ultimate enhancements (A∞) in the low to high magnetic field transfer dynamic nuclear polarization experiment

In a preliminary report, we have demonstrated transfer of a flowing bolus enhanced in low magnetic fields (e.g., 0.33 T) with dynamic nuclear polarization (DNP), but monitored in a high magnetic field (4.7 T). The advantages of the high magnetic field monitoring approach include: 1) greater chemical shift dispersion, and 2) improved signal strength in comparison with static low field DNP experiments. In the present study, a model is developed to predict ultimate DNP enhancements (A_∞) in this experiment for flow liquid/liquid intermolecular transfer (L²IT). L²IT¹H and¹³C data is obtained for benzene and chloroform in order to test the validity of the model. The ultimate¹H and¹³C DNP enhancements obtained for benzene/TEMPO are ?150 and ?220, respectively. For a chloroform/TEMPO (L²IT) sample, the ultimate enhancements are close to the¹H dipolar (?330) and the¹³C scalar (+2660) limit, respectively. In the latter case, the observed¹³C DNP enhancement exceeds the thermal Boltzmann magnetization at 4.7 T by a factor of 21. For a 1-chlorobutane/TEMPO sample selective enhancements were observed at different sites in the molecule. For example, the C-1 carbon exhibits a large scalar enhancement, whereas, the other carbons exhibit dipolar enhancements. Data illustrating the importance of three-spin effects in¹³C DNP studies is also presented. Alternative methods of sample transfer from the low to high magnetic field are also discussed.     

Ionization Behavior and Ionization-Dependent Conformation of Raclopride,a Dopamine D2 Receptor Antagonist

Raclopride, an antipsychotic 6-methoxysalicylamide (= 2-hydroxy-6-methoxybenzamide) derivative, was shown by titrimetry and UV-pholometry to exist in zwitterionic form at physiological pH. Calculations revealed that the neutral and zwitterionic forms differ considerably in their conformational behavior, the latter form being energetically favored by an intramolecular phenolate–ammonium ionic bond. These findings indicate that raciopride and other halogenated 6-melhoxysalicylamides with a highly acidic phenolic group may not resemble other ortho-methoxybenzamides in their stereoelectronic structure and mode of binding to the dopamine D₂ receptor.     

The thermoelectric power of the metallic glass Ca0.8Al0.2

We report the first measurement of the thermoelectric power Q, of a metallic glass that contains only normal metals. The thermoelectric power of amorphous Ca_0.8Al_0.2 has been measured as a function of temperature from 10 K to 420 K. It is found that Q is positive, varies linearly with temperature and has a small slope. This is similar to the thermoelectric power found for other metallic glasses containing large concentrations of transition metal atoms.     

Two particle rapidity correlation in proton-emulsion nucleus interactions at 400 GeV

We present a study of two-particle correlations in proton-emulsion nucleus reactions at 400 GeV. In particular the correlations at different nuclear excitations and different rapidity regions are treated. Positive correlations, depending on nuclear excitation, are observed in the rapidity region η<1.5.     

Interstitial site of Cu in Ca

Fluorescence EXAFS was used to study the siting of a dilute solution of Cu in Ca. The Cu is interstitial in Ca, and no more than .4Å away from the center of the octahedral site. No lattice dilation was seen about the Cu atom, even though Cu is “too big” to fit into the interstitial site.     

Marangoni convection in weld pools with a free surface

A steady-state two-dimensional model of heat transfer and fluid flow was developed to describe Marangoni convection in the weld pool. Both the pool surface and the fusion boundary were calculated. The validity of the model was verified against an asymptotic solution for Marangoni-convection-induced free surface geometry. Two different cases were studied, i.e. a negative surface tension temperature coefficient ?γ/?T a positive one, and the resultant shapes of the weld pool surface were compared.     

Polyarylates (I): Investigation of the interfacial polycondensation reaction by UV

The interfacial polycondensation of bisphenol A with isophthaloyl chloride and terephthaloyl chloride in dichloromethane with triethylbenzylammonium chloride as the catalyst was described. A well-defined two-phase system had been observed, so the concentration of bisphenolate in the aqueous phase could be determined by UV spectrometer. The conversion was found to increase rapidly with reaction time, but the rate of increase in molecular weight was slow. At the initial stage with conversion up to 95%, the reaction proceeded similarly to that of solution polycon-densation because the synthesized polyarylate could be dissolved in dichloromethane, and a polymer with a low molecular weight resulted. At the final stage of the reaction, the molecular weight was increased to a very high value due to the local concentration effect. The mole ratio of bisphenol A to diacid chlorides was found to affect the molecular weight very much. In the case of a mole ratio less than 1, the reaction remained in the initial stage mostly, and the molecular weight was low. However, for a mole ratio greater than 1, polyarylate with a very high molecular weight could be obtained because the local concentration effect was much more significant owing to the high concentration of bisphenolate that remained in the aqueous phase at the final stage.