PubMed · 5284975
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M Weiselberg, F L Harris. Root canal medication.. https://pubmed.ncbi.nlm.nih.gov/5284975/
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The generalised H-point standard addition method (GHPSAM) was applied to quantify phenol and o-cresol in waters and compared with other analytical approaches. The method is based on spectroscopic and kinetic measurement of the formation of derivatives with p-aminophenol and KIO(4) in presence of NaOH. First, pseudo-first order kinetic behaviour of the reaction products was demonstrated. The unbiased formation rate constants of phenol and o-cresol derivatives were calculated. The analytical figures of merit were determined using the GHPSAM as calibration method. Detection limits achieved were 0.2 microg L(-1) of phenol and 0.2 microg L(-1) of o-cresol using a preconcentration factor of 10. Styrene-divinyl benzene cartridges were used in the preconcentration step. Repeatability values were 3.7% for phenol and 2.0% for o-cresol; reproducibility values were 6.9% and 3.5%, respectively. Accurate and precise results were obtained when the method was applied to real samples of natural water.
Experimental observations of sustained oscillations of both shear stress and first normal stress differences are reported in flowing liquid crystalline polymers in a limited range of shear rates. The results can be described by considering the response of a rigid-rod model. Depending on the initial conditions, the frequency spectrum of the stress signal contains either one or two characteristic frequencies. This can be explained by the occurrence of either pure "wagging" or the coexistence of wagging and "log-rolling" behavior of the director.
Ultraviolet resonance Raman (UVRR) studies designed to test the utility of fluorinated tyrosines as spectroscopic probes of the local environment are presented. Specifically, resonance Raman spectra of 2-fluoro-L-tyrosine and 3-fluoro-L-tyrosine (3-Y(f)) obtained with 229 nm excitation are reported. In contrast to the modest environmental dependence of the tyrosine resonance Raman spectrum, the spectrum of 3-Y(f) is found to be extremely dependent on the hydrogen bonding strength of the surrounding environment. Preliminary ab initio studies suggest that this behavior is due to normal modes having dominant contributions from the C-OH and C-F internal coordinates. Hydrogen bonding to the solvent perturbs the internal coordinate energetics and/or couplings, thereby altering the character of the normal modes and the corresponding transition frequencies and/or intensities. In addition to the solvent studies, 3-Y(f) is site specifically incorporated into the influenza hemagglutinin (HA) 100-107 peptide which binds to the Fv fragment of the 17/9 anti-HA(98-108) peptide antibody. These studies demonstrate that the spectrum of 3-Y(f) can be monitored in the presence of native tyrosine. In summary, the studies presented here demonstrate that 3-Y(f) holds exceptional promise as a probe of the protein environment.