The formation of cation-ligand complexes of tributylammonium cation with diethyl carbonate,ethylene carbonate,propylene carbonate, 4-butyrolactone,ethyl acetate,and cyclopentanone ino-dichlorobenzene at 25°C

The effects of adding millimolar quantities of a series of compounds containing the carbonyl function on the conductances of solutions (0.2 mM) of tri-n-butylammonium picrate ino-dichlorobenzene solvent at 25°C have been measured. Values of the complex formation constants K ₁ ⁺ for 1:1 cation-ligand complexes are derived from these data. The corresponding values of –G ₁ ⁰ at 25°C are (in kcal-mole ^–1 ): 4-butyrolactone, 4.29; propylene carbonate, 3.87; ethylene carbonate, 3.59; cyclopentanone, 3.42; ethyl acetate, 2.84; and diethyl carbonate, 2.78. These results together with earlier results from this laboratory are discussed in terms of the effects of structure on cation-ligand affinity.     

Surface chemical analysis of raw cotton fibres and associated materials

The surface chemical composition of raw unscoured cotton was successfully investigated by the surface analytical techniques X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The presence of non-cellulosic material at the fibre surface was established and determined to be a complex mixture of fatty acids, alcohols, alkanes, esters and glycerides. The effect of scouring and bleaching was to reduce the surface concentration of these materials but even after aqueous processing some non-cellulosic material residue was still detected at the fibre surface.     

Identification of 4-amino-4-deoxychorismate synthase as the molecular target for the antimicrobial action of (6s)-6-fluoroshikimate

(6S)-6-Fluoroshikimate has antimicrobial activity. The molecular basis of this effect had not been identified, but there was speculation that (6S)-6-fluoroshikimate is first converted in vivo into 2-fluorochorismate, which then could inhibit 4-amino-4-deoxychorismate synthase (ADCS). 2-Fluorochorismate was prepared from E-fluorophosphoenolpyruvate and erythose-4-phosphate by the sequential reactions of DAHP synthase, dehydroquinate synthase, dehydroquinase, shikimate dehydrogenase, EPSP synthase, and chorismate synthase. Inhibition studies on ADCS showed that it was inhibited rapidly and irreversibly by 2-fluorochorismate. Electrospray mass spectrometry of the inactivated enzyme showed an additional mass of 198 +/- 10 Da. A novel peptide of 1087.6 Da was identified in the HPLC trace for the tryptic digest of 2-fluorochorismate-inactivated ADCS. Sequencing of this peptide by MS/MS showed that the peptide corresponded to residues 272-279 with a modification of 206.1 Da on Lys-274. This observation is particularly exciting in the context of a recent proposal for the catalytic mechanism of ADCS.     

An investigation of catalytic activity in mixed metal oxide nanophase materials

We present preliminary evidence for catalytic activity by unsupported mixed metal oxide nanocrystalline materials. The results of this study show that a nanophase form of Li-MgO has begun to exhibit catalytic activity by 300 °C. This is at least 200 degrees below the temperature at which conventional Li-MgO catalysts exhibit comparable activity. Furthermore, at higher temperatures, the same nanophase composition shows enhanced activities and somewhat improved hydrocarbon selectivities over conventional Li-MgO catalysts.     

Gas-phase structures and mass spectra of binary pentafluorides

Most known non-radioactive pentafluorides have been examined by molecular-beam mass spectrometry and by the deflection of molecular beams in inhomogeneous electric fields. Extensive association of the vapors occurs for all but the lighter pentafluorides and the interhalogens. The interhalogen pentafluorides are strongly polar, consistent with the accepted C_4v symmetry. The transition-metal and Group V pentafluorides are all non-polar, except VF₅ and CrF₅ for which temperature-dependent polarity is observed. However, uncertainty exists as to whether these observations are applicable to monomeric pentafluorides in all cases. Mass-spectral cracking patterns are presented for all species.     

ESR spectra of AsF2−6 and SbF2−6

ESR spectra observed in γ-irradiated CsAsF₆ and CsSbF₆ matrices have been assigned to the free radicals AsF^2?₆ and SbF^2?₆ respectively. The large, isotropic central-atom hyperfine interactions and isotropic g-values of these species suggest that they possess ²A_tg ground-states in O_h symmetry. The contribution to the semi-occupied orbital of the central-atom valence s atomic orbital is ≈ 0.6, greater than in the halogen hexafluorides (≈0.4) and the chalcogen hexafluoride anions (≈ 0.5). Variation of the central-atom hyperfine interaction with temperature is interpreted in terms of a second-order Jahn-Teller effect involving a low-lying ²T_1u excited state.     

Synthesis and pharmacological analysis of high affinity melatonin receptor ligands

We report the synthesis and radioligand binding analysis of a series of naphthalenic melatonin receptor ligands, N-[2-(7-alkoxy-2-methoxy-1-naphthyl)ethyl]propionamide. This series of ligands exhibits subpicomolar binding affinity to both MT1 and MT2 melatonin receptors expressed in chinese hamster ovary (CHO) cells.     

Some biological transformations involving unsaturated linkages: the importance of charge separation and charge neutralization in enzyme catalysis

Current status of knowledge on the biological reduction of CC and CO is briefly reviewed. It is Argued that the crucial event in the reduction of CC is the addition of a proton to the more electron-rich terminal of the double bond to produce an electron-deficient species which is then neutralized through hydride transfer from NADPH. The activation for the reduction of a CO group may also be achieved by a related process in which the carbonyl oxygen is polarized by H-bonding to an acidic group on the enzyme, prior to hydride transfer from NAD(P)H.Thus with both these systems an early event in catalysis is the protonation of the substrate for which, normally, strong adds win be required. Since the groups available at the active-met of enzymes are weak acids, a mechanism through which powerful proton donating species could be transiently generated from them is proposed. The salient features of this mechanism may be enuinciatcd as follows: Let us consider the enzyme-substrate complex (A) in which an imidazolium group is about to play a role as a proton donating species. It is argued that rearrngement of initial complex(A)to the catalytic-complex(B), in which the negatively chared counter ion is removed away from the imidazolium cation, would transiently convert the latter group into a powerful proton danating species. the rearrangement (A)→(B) could occur through a protein conformational change or via a charge-relay system or a combination of both processes.