Raman spectra of p-cresol, a model compound for tyrosine, were measured in solutions of various solvents, paying special attention to the effects of hydrogen bonding on the Raman bands in the 1300-1150 cm-' region. The frequency of the v,,,. (C-O stretch) band was found to be sensitive to the state of hydrogen bonding at the phenolic hydroxyl group. It occurs at 1275-1265 cm-' in protondonating states, 1240-1230 cm-' in proton-accepting states and around 1255 cm-' in weakly or non-hydrogen-bonding states. This relationship between the v7,,. frequency and hydrogen bonding was verified in the Raman spectra of L-tyrosine and its derivatives in the crystalline state. Analysis of the crystal Raman spectra further suggested that the v7,, (C-C stretch) frequency also serves as a marker, though less sensitive, of hydrogen bonding and the v9,, (C-H bend) frequency reflects the displacement of the OH hydrogen atom from the plane of benzene ring, which may be induced by hydrogen bonding. These Raman bands are strong with UV excitation and are expected to be useful in characterizing tyrosine side-chains in peptides and proteins by UV resonance Raman spectroscopy.

URL: http://www.umin.ac.jp/ctr/index/htm/ Unique identifier: UMIN000007109.

No abstract

A survey of oligotrophic Lake Rara, the biggest lake in Nepal, was carried out from 1982 till 1984. Mean depth is 100 m, and maximum depth is 167 m. The surface area covers 9.8 km2, and the lake contains 0.98 km3 volume of water.Transparency was about 16 m, photoquantum yield decreased exponentially with depth below 5 m, and the extinction coefficient was 8.3 x 10m2. The concentration of Chl.-a was in the range of 0.06-0.46 mg me3, and total nitrogen was 18-30 pg 1-l. The whole water column was well oxygenated. Primary productivity was extremely low. It has more than 30 inflowing brooks and one outlet. The water quality of the brooks changes drastically with their location. The pH, electrical conductivity, and EDTA hardness in the waters from a landslide area were high. In the waters from a rich pine forest they were extremely low.The zooplankton consisted of two species of protozoa, five species of rotifers, two species of Cladocera, and two species of Copepoda. The zooplankton density range was 6200-16200 individuals mv3. The minimum was on November llth, 1983 and the maximum on August 19th, 1983.