Capillary electrophoresis as a method for ozone determination in atmospheres

Capillary electrophoresis (CE) is used to quantify nitrate and nitrite extracted from nitrite-impregnated glass fiber filters (IGFF) that are used to monitor ozone in atmospheres. The amount of nitrate produced from conversion of nitrite in the filters is directly related to the amount of ozone passed over the filter. The limit of detection for ozone using the CE method is 1.17 ppml and the method is linear over two orders of magnitude. The effect of the excess nitrite in the IGFF on the limits of detection is discussed. Results from CE analyses of both active and passive filters are presented. The active filter results are compared to ion chromatographic analyses.     

The burden borne by urease

At the active site of urease, urea undergoes nucleophilic attack by water, whereas urea decomposes in solution by elimination of ammonia so that its rate of spontaneous hydrolysis is unknown. Quantum mechanical simulations have been interpreted as indicating that urea hydrolysis is extremely slow, compared with other biological reactions proceeding spontaneously, and that urease surpasses all other enzymes in its power to enhance the rate of a reaction. We tested that possibility experimentally by examining the hydrolysis of 1,1,3,3-tetramethylurea, from which elimination cannot occur. In neutral solution at 25 degrees C, the rate constant for the uncatalyzed hydrolysis of tetramethylurea is 4.2 x 10-12 s-1, which does not differ greatly from the rate constants observed for the uncatalyzed hydrolysis of acetamide (5.1 x 10-11 s-1) or N,N-dimethylacetamide (1.8 x 10-11 s-1) under the same conditions. We estimate that the proficiency of urease as a catalyst, (kcat/Km)/knon, is 8 x 1017 M-1, slightly higher than the values for other metalloenzymes (carboxypeptidase b and cytidine deaminase) that catalyze the hydrolysis of similar bonds.     

IR-UV double resonance spectroscopy of xanthine

We present resonant two-photon ionization (R2PI), UV-UV, and IR-UV double resonance spectra of xanthine seeded in a supersonic jet by laser desorption. We show that there is only one tautomer of xanthine which absorbs in the wavelength range of 36 700 to 37 700 cm(-1). The IR-UV double resonance spectrum shows three strong bands at 3444, 3485, and 3501 cm(-1), all of which we assign as N-H stretching vibrations. Comparison of the IR-UV double resonance spectrum with frequencies and intensities obtained from density functional theory (DFT) and second order M?ller Plesset (MP2) calculations suggests that the observed xanthine is the diketo N(7)H tautomer.     

NMR Studies of Hindered Rotation. The Diels-Alder Adduct of Phencyclone with Maleic Anhydride: Restricted Motion of Bridgehead Phenyls

¹H NMR studies at 300 MHz have been performed for the Diels-Alder adduct of phencyclone and maleic anhydride in CDCl₃ at ambient temperatures. The 1D spectrum shows four equal (2H) intensity doublets in the aryl region (in addition to other absorptions) which is fully consistent with a slow exchange limit (SEL) spectrum of a system in which the unsubstituted bridgehead phenyls exhibit hindered rotation around the C(sp²)-C (sp³) bond on the NMR timescale. These protons are assigned to H-1,8 and H-4,5 of the phenanthrene moiety and to H-2′ and H-6′ of the phenvls based on the two-dimensional (2D) homonuclear chemical shift correlation spectrum (COSY) together with arguments regarding carbonyl and aromatic ring anisotropy. Full proton assignments are given.     

Studies on coordination compounds : Formation constants of some metal salts of the nitrosonaphthols

Formation constants of various metal derivatives of I-nitroso-2-naphthol and 2-nitroso-1-naphthol have been measured in 50 and 75 volume per cent dioxan. The anomalies of the nickel and cobalt compounds are considered and explanations offered.     

IR-UV double resonance spectroscopy of guanine-H2O clusters

We present the IR-UV double resonance spectrum of guanine monohydrate in the region 3100 cm(-1) to 3800 cm(-1) along with the energies and frequencies of these structures calculated at the non-empirical correlated ab initio RI-MP2/cc-pVDZ level. We assign the structures of guanine-water clusters by comparing the experimental spectra with the ab initio calculations and with the IR spectra of the bare guanine monomer. We find two clusters with guanine in the enol-amino tautomeric form and one structure with guanine in the keto-amino form.     

Quadrupole ion trap studies of the structure and reactivity of transition metal ion pair complexes

Ion pairs are common species observed in the electrospray mass spectra of transition metal coordination complexes. To understand the nature of these ion pairs, a systematic study of the gas-phase chemistry of these species using ion-molecule reactions and collision-induced dissociation (CID) was carried out. Ion pair complexes of the type MLnX+ (where M is Mn(II), Fe(II), Co(II), Ni(II), Cu(II) or Zn(II), L is 1,10-phenanthroline, 2,2'-bipyridine, ethylenediamine, diethylenetriamine or 1,4,8,11-tetraazacyclotetradecane and X is Cl-, NO3-, acetylacetonate, ClO4-, acetate or SCN-) were studied. Ion-molecule reactions can distinguish whether the counterion in an ion pair is an inner- or outer-sphere ligand and can determine the coordination mode of the counterion. In addition, CID and ion-molecule reactions reveal some interesting chemistry of these complexes and unique coordination modes for some of the anions studied here were inferred from the ion-molecule reactions. For example, the thiocyanate ion is found to coordinate in a bidentate fashion in Zn(II) and Ni(II) complexes, contrasting behavior typically observed in solution. Also, certain Co(II) and Fe(II) ion pair complexes undergo oxidation reactions in which species such as dioxygen and nitric oxide from the counterions ClO4- and NO3- are transferred to the Co(II) and Fe(II) complexes, showing the inherent affinity of these metals for these molecules. These complexes were also studied by ion-molecule reactions and CID. Dioxygen in complexes formed by CID is demonstrated to be bidentate, suggesting the formation of a peroxo ligand with concurrent oxidation of the metal.