Implementation of the MARSSIM philosophy to evaluate the remedial status of a radioactive waste disposal site at the Idaho National Engineering and Environmental Laboratory. Multi-Agency Radiation Survey and Site Investigation Manual.

Implementation of the MARSSIM remedial-verification protocol at a radioactive waste disposal site is described in some detail to provide a record of the utility of this process. The selected site was the Stationary Low-Power Reactor No. 1 burial ground at the Idaho National Engineering and Environmental Laboratory. Evaluation was restricted to 137Cs in the uppermost 10 cm of potentially contaminated soils. According to the MARSSIM, this site warranted a "Class 1" designation based on previous remedial activities within the burial ground, its status as a radioactive disposal facility, and the anticipated presence of discrete radioactive particles. Nine survey units within the confines of the burial ground were selected, based primarily on the presence of physical boundaries and disparate histories. Surface scans with 100% coverage were performed using a hand-held plastic scintillator and rate meter with audible output. In situ gamma-ray spectrometry was not used for the individual stationary measurements due to the limited area and proximity of engineered barriers. Instead, individual soil samples were obtained using a standard hand-held coring device. The number of soil samples taken from the background reference area and each survey unit were determined with the MARSSIM protocol, which resulted in a total of 160 (including quality-control samples). Two of the nine regions exhibited elevated radiation levels and the null hypothesis could not be rejected in one survey unit, thereby indicating the need for additional remediation. The MARSSIM process proved to be flexible, scientifically rigorous, and cost effective in this field application. Several modifications to the procedure are discussed and offered as recommendations for enhancement of the MARSSIM.

Time-resolved fluorescence anisotropy of HIV-1 protease inhibitor complexes correlates with inhibitory activity.

The tryptophan time-resolved fluorescence intensity and anisotropy of the HIV-1 protease dimer is shown to be a quick and efficient method for the conformational characterization of protease inhibitor complexes. Four fluorescence lifetimes were needed to adequately describe the fluorescence decay of the two tryptophan residues, W6 and W42, per protease monomer. As a result of the wavelength dependence of the respective amplitudes, the 2.06 ns and the 4.46 ns decay constants were suggested to be the intrinsic fluorescence lifetimes of the more solvent-exposed W6 and the less exposed W42 residues, respectively. Analysis of the fluorescence anisotropy decay yielded a short correlation time of 250 ps corresponding to local chromophore motions, and a long correlation time of 12.96 ns resulting from overall rotation of the protease enzyme. Fluorescence lifetimes and rotational correlation times changed when inhibitors of the HIV-1 protease were added. The effects of 11 different inhibitors including statine-derived, hydroxyethylamine-derived, and 2 symmetrical inhibitors on the protease fluorescence dynamics were investigated. Inhibitor binding is shown to induce an increase of the mean fluorescence lifetime taumean, an increase of the short rotational correlation time phi1, as well as a decrease of the long rotational correlation time phi2. The mean rotational correlation time phimean was identified as the global dynamic parameter for a given molecular complex, which correlates with the inhibitor dissociation constant Ki, and therefore with the activity of the inhibitor.

Characterization of human immunodeficiency virus-1 (HIV-1) rev by (time-resolved) fluorescence spectroscopy.

Fluorescence spectroscopy has been applied to the single tryptophan-containing regulatory protein Rev of human immunodeficiency virus (HIV-1). The fluorescence emission was found to have a maximum at 336 nm which refers to a surrounding of the chromophore of intermediate polarity. Fluorescence transients recorded at the maximum of fluorescence were found to decay nonexponentially. A bimodal lifetime distribution is obtained from exponential series analysis (ESM) with centers at 1.7 and 4.5 ns. Two microenvironments for tryptophan are suggested to be responsible for the two lifetime distributions. No innerfilter effect occurred in a Rev solution up to a concentration of 40 µM. A data quality study of ESM analysis as function of collected counts in the peak channel maximum (CIM) showed that, for reliable reconvolution, at least 15,000 CIM are necessary. The widths of the two distributions are shown to be temperature dependent. The broadening of the lifetime distributions when the temperature is raised to 50°C is interpreted as extension of the number of conformational substates which do not interconvert on the fluorescence time scale. The thermal deactivation (temperature quenching) is reflected in a constant decrease in the center of the short-lived lifetime distribution.