Biomedical subjects

BM Fung

Publications and source records attributed to BM Fung.

3 recordsLinked to original sources

PubMed1999

13C NMR of liquid crystals with different proton homonuclear dipolar decoupling methods

The effect of several new homonuclear dipolar decoupling methods (frequency-switching Lee-Goldburg decoupling and two sequences based on z-rotational decoupling) on the 13C spectra of liquid crystals has been studied, and the results are compared with those obtained by using two well-established methods (MREV-8 and BLEW-48). For benzene dissolved in two liquid crystalline solvents, BLEW-48 gives the best spectral resolution. The BLEW-48 sequence has also been applied to the 2D method of proton-encoded local field (PELF) spectroscopy to study a bulk liquid crystal, 4-n-pentyl-4'-cyanobiphenyl (5CB). The results are compared with those obtained by using MREV-8, and it is suggested that the BLEW-48 sequence may be preferable to MREV-8 for application in the PELF method. Copyright 1999 Academic Press.

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PubMed1997

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.

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PubMed1996

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.

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