An efficient broadband decoupling sequence for liquid crystals

A new and efficient broadband decoupling sequence is presented. It is based on the phase cycling of two pulses with small phase angles. The pulse width is 180 degrees +/- 30 degrees, and the phase angle is +/-10 degrees-12 degrees. The sequence contains 16 elements, and is called SPARC-16 as an abbreviation for small phase angle rapid cycling. The application of this sequence to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl (5CB), is reported. The signal-to-noise ratios and the linewidths of the 13C peaks of 5CB with SPARC-16 decoupling and with other decoupling methods are compared. The results show that the broadband decoupling efficiency of SPARC-16 is considerably better than those of other methods.

A Study of the Adsorption of Acrylic Acid and Maleic Acid from Aqueous Solutions onto Alumina

The adsorption of acrylic acid and maleic acid on alumina was studied, and it has been found that the adsorption obeys the Langmuir isotherm. The adsorption of the acids is dependent on the pH of the solutions. For acrylic acid, the optimal pH is 4.5; for maleic acid, the optimal pH is 1.1-1.6. These pH values are close to the pKa for acrylic acid and pKa 1 for maleic acid, respectively. The maximum amount of each acid adsorbed at its optimal pH was obtained by fitting the adsorption data to the Langmuir isotherm, and the values are 727 &mgr;mol/g for acrylic acid and 525 &mgr;mol/g for maleic acid. These values are consistent with monolayer adsorption. Solid state 13 C NMR was used to investigate the nature of the adsorption. It is suggested that the adsorbed carboxylic acids are present in the undissociated form.

Line Narrowing in Solid-State Proton NMR with Acquisition Delay

Organic solids have extensive proton-proton dipolar interactions, and their 1H NMR linewidths are very large even with magic-angle spinning at moderate speeds. Recently it has been shown that substantial narrowing of the proton linewidths of organic solids can be achieved by using single-pulse excitation with acquisition delay or spin echo [S. Ding and C. A. McDowell, J. Magn. Reson. A 111, 212 (1994); 115, 141 (1995); 117, 171 (1995)]. This interesting line-narrowing phenomenon has been further examined through the study of several amino acids, their deuterated analogs, and some aromatic compounds. The results confirm that narrow proton peaks are observed with long acquisition delay, and the peaks appear in the appropriate chemical-shift ranges for organic protons (0-10 ppm with respect to tetramethylsilane). However, except for some special cases, the observed peaks cannot be assigned to individual types of protons based on chemical-shift considerations only. To explore the reason for the line narrowing, the effect of acquisition delay on the 19F linewidth of CaF2 was also studied and compared with that on the 1H linewidths of organic solids. It is suggested that the broad proton peak in an organic solid is a superposition of numerous transitions. These transitions have different linewidths, and the narrow peaks in the spectrum remain observable with long acquisition delays.

Thrombolysis using liposomal-encapsulated streptokinase: an in vitro study

The clot-lysing ability of streptokinase (SK) was examined using membrane-bound thrombi. Encapsulation of SK in large unilamellar phospholipid vesicles (liposomes) resulted in entrapping approximately 30% of its original activity. Measurements of streptokinase activity for liposomal-encapsulated streptokinase (LESK) indicated little loss of activity or leakage in Tris-buffered saline over a 24-hr period at temperatures of 4 and 23 degrees C. However, incubation of free SK and LESK in platelet-poor plasma (PPP) at 37 degrees C resulted in a decrease of SK activity. The retention of SK activity in LESK was considerably higher than that of unentrapped SK. Clot-dissolving time (CDT) was measured by monitoring the pressure drop during slow filtration in plasma through membrane-bound thrombi. The results indicated that both LESK and free SK were able to activate the fibrinolytic system. Without prior incubation in PPP at 37 degrees C, the CDT of a SK and PPP mixture (SK/PPP) was 10.7 +/- 1.9 min (n = 12), while that of a LESK and PPP mixture (LESK/PPP) was 12.4 +/- 1.7 min (n = 12). The CDT-detected clot-lysing abilities of both SK and LESK were diminished by incubation in PPP, but to different extents. After 15- and 30-min incubations, the CDT of SK/PPP increased significantly to 15.5 +/- 1.5 and 24.1 +/- 2.4 min (n = 5, P less than 0.05), respectively. In contrast, the CDT of LESK/PPP increased to 13.3 +/- 0.8 min (n = 5) after 15 min of incubation and to 16.0 +/- 1.1 min (n = 5, P less than 0.05) after a 30-min incubation. These results suggest that entrapment of SK in liposomes preserves the thrombolytic potential of the plasminogen activator by limiting its exposure to the components of the plasma.

Dynamic evaluation of clotting phenomena in vitro and perfluorochemical oxygen transport across a membrane-bound thrombus model

Citrated platelet-rich plasma was used to occlude 3-microns and 10-microns poresize Nuclepore membranes after recalcification as a thrombus model. Morphologic studies, using both light microscopy and scanning electron microscopy, indicated that over 90 percent of the number of pores available for filtration in hydrophilic and hydrophobic membranes were occluded either partially or completely. Results of transient and steady state pressure drop measurements supported the morphologic studies. It was found that the percentage of oxygen transported across the occluded membranes was greater for filtration of red blood cell suspensions diluted with a perfluorochemical emulsion than that of those diluted with Ringers. The findings in this study suggested that perfluorochemical emulsions might transport oxygen across a thrombus to maintain tissue viability during acute ischemic events.

Interaction between erythrocytes and a perfluorochemical blood substitute

Perfluorochemicals (PFCs) are being widely developed for use as erythrocyte substitutes to carry oxygen to tissue in acute crises. Oxypherol, a commercially available PFC preparation commonly used for animal tests, reduces erythrocyte deformability in the presence of plasma. This undesirable effect further complicates oxygen delivery by erythrocytes. Our experiments indicate that one or more plasma proteins must be present to observe Oxypherol-induced reduction in erythrocyte deformability, but the latter is not protein specific. Neither platelet activation nor enhanced protein adsorption could account for the mechanism of altered erythrocyte flexibility. Using fluorine-19 NMR, it was found that a small amount of Oxypherol droplets is adsorbed on the surface of the erythrocytes. The amount of adsorbed droplets increases when Oxypherol is incubated with the erythrocytes in the presence of plasma, in parallel with a decrease in erythrocyte deformability. Therefore, it seems likely that the loss of deformability of the erythrocytes is caused by the adsorption of small Oxypherol droplets on the erythrocytes.

Plasma-mediated alterations of erythrocyte deformability by perfluorochemical blood substitutes

The effect of perfluorochemical blood substitutes (eg, Oxypherol or Fluosol-DA) on red cell deformability was investigated because these emulsions are in direct contact with red cells when they are used as temporary circulatory aids. Erythrocyte deformability was assessed by a constant volumetric flow rate filtration method. The results of in vitro incubation experiments indicate that perfluorotributylamine causes the deformability of human red cells to decrease significantly in the presence of plasma. However, there is no obvious loss in the deformability when washed cells are used. Neither mean cell volume nor white cells appear to be responsible for the observed effects of perfluorotributylamine. Perfluorodecalin and perfluorotripropylamine, two perfluorochemical compounds that are widely applied clinically, do not induce significant changes in red cell deformability with or without plasma. These results indicate the need for in vitro testing in the development of perfluorochemicals as blood substitutes.