Isomerization of the protonated acetone dimer in the gas phase.

Mass spectrometry-based methods have been employed in order to study the reactions of non- (h(6)/h(6)), half (d(6)/h(6)), and fully (d(6)/d(6)) deuterium labeled protonated dimers of acetone in the gas phase. Neither kinetic nor thermodynamic isotope effects were found. From MIKES experiments (both spontaneous and collision-induced dissociations), it was found that the relative ion yield (m/z 65 vs m/z 59) from the dissociation reaction of half deuterium labeled (d(6)/h(6)) protonated dimer of acetone is dependent on the internal energy. A relative ion yield (m/z 65 vs m/z 59) close to unity is observed for cold, nonactivated, metastable ions, whereas the ion yield is observed to increase (favoring m/z 65) when the pressure of the collision gas is increased. This is in striking contrast to what would be expected if a kinetic isotope effect were present. A combined study of the kinetics and the thermodynamics of the association reaction between acetone and protonated acetone implicates the presence of at least two isomeric adducts. We have employed G3(MP2) theory to map the potential energy surface leading from the reactants, acetone and protonated acetone, to the various isomeric adducts. The proton-bound dimer of acetone was found to be the lowest-energy isomer, and protonated diacetone alcohol the next lowest-energy isomer. Protonated diacetone alcohol, even though it is an isomer hidden behind many barriers, can possibly account for the observed relative ion yield and its dependence on the mode of activation.

Quantification of grafted poly(ethylene glycol)-silanes on silicon by time-of-flight secondary ion mass spectrometry.

Silicon grafted monodisperse poly(ethylene glycol) (PEG) silanes with various PEG chain lengths and mixtures of these were systematically analyzed with static time-of-flight secondary ion mass spectrometry (TOF-SIMS). The mass spectra show differences in the various relative signal intensities, an observation that was used to elucidate important aspects of the grafting process. The relationship between PEG-silane fragment ion abundances and Si(+) ion abundances were used to (i) qualitatively describe layer thicknesses of grafted mixtures of PEG-silanes on silicon, (ii) construct a calibration curve from which PEG chain length (or molecular mass) can be determined and (iii) quantitatively determine surface mixture compositions of grafted monodisperse PEG-silanes of different chain lengths (3, 7 and 11 PEG units). The results suggest that discrimination does take place in the adsorption process. The PEG-silane with the shorter PEG chain is discriminated for mixtures containing PEG3-silane, whereas the PEG-silane with the longer PEG chain is discriminated in PEG7/PEG11-silane mixtures. The origin of this difference in adsorption behavior is not well understood. Aspects of the grafting process and the TOF-SIMS analyses are discussed.

Shuttle vector plasmid propagation in human peripheral blood lymphocytes facilitated by liposome-mediated transfection.

Transfection of human peripheral blood lymphocytes facilitated by a positively charged liposome preparation (Lipofectin, BRL) is 100-fold more efficient than the DEAE dextran technique for the uptake and replication of shuttle vector plasmid DNA. The yield of progeny plasmids obtained from 10 ml of blood was high enough for mutational analysis. A marked increase in the mutation frequency of the shuttle vector marker gene was noted in response to the induction of psoralen adducts in the vector. By using normal human lymphocytes, this method will permit shuttle vector analysis of DNA repair and mutagenesis in a large number of individuals. This method could also prove useful for studies of human lymphotropic viruses.

Methenamine-hippurate and bacteriuria in the geriatric patient with a catheter.

Oral treatment with methenamine-hippurate (MH) in patients with an indwelling catheter has been found to reduce the need of frequent catheter exchange and the number of symptomatic infections. Bacteriuria, however, persists during MH treatment. The hypothesis that the therapeutic effect is due to a reduction in the number of bacteria, or a change in the pattern of strains was tested in a crossover study (2 x 6 weeks). MH treatment, 1 g twice daily, was compared to control periods in 52 patients. The majority of quantitative and qualitative bacterial cultures at 2-week intervals yielded 2--4 strains. Of the bacterial isolates, 50% were found on 4--6 occasions out of 6 possible. MH treatment had no significant influence on the pattern of various strains. A 30% decrease in the mean total bacterial count during MH treatment did not reach statistical significance (p approximately 0.07). It is suggested that prevention of catheter complications during MH treatment may be due to a physiochemical action on salt formation rather than a direct antibacterial effect.

Treatment with methenamine hippurate in the patient with a catheter.

Methenamine hippurate, 1 g twice daily, was given for four months to twenty-two elderly female subjects with an indwelling catheter. The incidence of catheter blockage was significantly reduced when compared with the control period of similar duration, although bacteriuria persisted throughout treatment. The incidence of symptomatic urinary tract infection also decreased during treatment with methenamine hippurate.