Near-infrared laser desorption/ionization aerosol mass spectrometry for investigating primary and secondary organic aerosols under low loading conditions.

A new method, near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS), is described for the real time analysis of organic aerosols at atmospherically relevant mass loadings. Use of a single NIR laser pulse to vaporize and ionize particle components deposited on an aluminum probe results in minimal fragmentation to produce exclusively intact pseudomolecular anions at [M-H](-). Limits of detection (total particulate mass sampled) for oxidized compounds of relevance to atmospheric primary and secondary organic aerosol range from 89 fg for pinic acid to 8.8 pg for cholesterol. NIR-LDI-AMS was used in conjunction with the University of Vermont Environmental Chamber to study secondary organic aerosol (SOA) formation from ozonolysis of limonene at total aerosol mass loadings ranging from 3.2 to 25.0 µg m(-3) and with a time resolution of several minutes. NIR-LDI-AMS permitted direct delineation between gas-phase, homogeneous SOA formation and subsequent heterogeneous aerosol processing by ozone.

Access to a pair of ambiphilic phosphine-borane regioisomers by rhodium-catalyzed hydroboration.

Lewis basic substrates, such as vinylphosphines and enamines, can be problematic for transition-metal catalysed hydrofunctionalization reactions due to their propensity to ligate and deactivate transition-metal catalysts as well as form direct Lewis adducts with reaction partners. While exploring rhodium-catalyzed hydroboration of diphenylvinylphosphine with pinacolborane, we found that a high degree of regiocontrol could be achieved without the need to diminish the Lewis basicity of the phosphine by oxidation or prior-protection. At slightly elevated temperature, a high yield of the previously unreported branched regioisomer, 1-pinacolatoborono-1-diphenylphosphinoethane, was achieved with regioselectivity greater than 10 : 1 using [Rh(COD)Cl]2 as the catalyst and AgOTf as a catalytic additive. Inversion of regioselectivity occurred at low temperature and high yield of the linear regioisomer was observed. Subsequent functionalization of the new branched phosphine-boronic ester and its coordination to rhodium were also investigated.

Folate synthesis in plants: purification, kinetic properties, and inhibition of aminodeoxychorismate synthase.

pABA (p-aminobenzoate) is a precursor of folates and, besides esterification to glucose, has no other known metabolic fate in plants. It is synthesized in two steps from chorismate and glutamine, the first step being their conversion into glutamate and ADC (4-aminodeoxychorismate). In Escherichia coli, two proteins forming a heterodimeric complex are required for this reaction, but, in plants and lower eukaryotes, a single protein is involved. The Arabidopsis enzyme was expressed in E. coli and was purified to homogeneity. The monomeric enzyme (95 kDa) catalyses two reactions: release of NH3 from glutamine (glutaminase activity) and substitution of NH3 for the hydroxy group at position 4 of chorismate (ADC synthase activity). The kinetic parameters of the plant enzyme are broadly similar to those of the bacterial complex, with K(m) values for glutamine and chorismate of 600 and 1.5 microM respectively. As with the bacterial enzyme, externally added NH3 was a very poor substrate for the plant enzyme, suggesting that NH3 released from glutamine is preferentially channelled to chorismate. The glutaminase activity could operate alone, but the presence of chorismate increased the efficiency of the reaction 10-fold, showing the interdependency of the two domains. The plant enzyme was inhibited by dihydrofolate and its analogue methotrexate, a feature never reported for the prokaryotic system. These molecules were inhibitors of the glutaminase reaction, competitive with respect to glutamine (K(i) values of 10 and 1 microM for dihydrofolate and methotrexate respectively). These findings support the view that the monomeric ADC synthase is a potential target for antifolate drugs.

Vitamin B3 confers resistance to sulfa drugs in Saccharomyces cerevisiae.

Sulfa drugs are ubiquitous antibiotics used to treat bacterial infections and diseases caused by eukaryotes, such as Pneumocystis carinii, the leading cause of pneumonia (PCP) in HIV patients. A daily regimen of sulfonamides and multivitamins including vitamin B3 is also recommended for persons with HIV. We show that exogenous vitamin B3 (nicotinate) confers resistance to sulfa drugs in Saccharomyces cerevisiae, a model for P. carinii. We propose a model of metabolic rerouting in which increased nicotinate leads to increased intracellular concentration of p-aminobenzoate, thus leading to sulfonamide resistance.

Amblyopia treatment outcomes.

PURPOSE: To determine the effectiveness and side effects of full-time occlusion for the treatment of amblyopia. METHODS: Patients with unilateral amblyopia secondary to strabismus, anisometropia, or a combination of the two were retrospective reviewed. All patients had full-time occlusion encompassing 24 hours per day or all waking hours, followed to a defined endpoint. Success was defined as 20/30 or better or equal visual acuity by fixation pattern between the two eyes. The ultimate goal was equal visual acuity. RESULTS: Six hundred patients fit the inclusion criteria. Mean follow-up after the cessation of full-time patching was 7.2 years. Eighty-nine percent were followed for more than 1 year. Mean age at last follow-up visit was 10.82 years. Ninety-six percent of patients attained a successful visual result. Sixty percent attained equal visual acuity. Younger patients required less occlusion time to endpoint and had a better visual outcome ( P < 0.0001). Initial visual acuity was significantly related to best visual acuity attained ( P < 0.0001). The incidence of occlusion amblyopia was 25.8%. CONCLUSIONS: Full-time occlusion produces excellent visual acuity results. It was shown to be effective with no long-term complications if patients proceed as directed.

Acute uncomplicated UTI and E. coli resistance: implications for first-line empirical antibiotic therapy.

BACKGROUND: Uncomplicated urinary tract infection (uUTI) typically affects immunocompetent, anatomically normal women. Escherichia coli (E. coli) accounts for approximately 80% of cases. Given increased E. coli-trimethoprimsulfamethoxazole (TMP-SMX) resistance, practice guidelines advocate first-line alternatives based on local resistance rates above 10%. This paper provides a model incorporating use of a new extended-release formulation of ciprofloxacin, used once daily, to facilitate revision of uUTI treatment policies by managed care organizations (MCOs) and practitioners. METHODS: A cost-minimization model was designed from the MCO perspective, assuming an initial office visit with a urinalysis and empiric, 3-day treatment (TMP-SMX 800/160 mg twice daily or ciprofloxacin XR 500 mg once daily). Persistent infections were assumed to require a second visit. Costs were provided by a major employee health and benefit plan provider; clinical data were based on published information. Five case scenarios were used to compare average treatment costs based on varying E. coli resistance rates to therapy and to identify rates of TMP-SMX resistance where total treatment costs are equal. RESULTS: Using national surveillance resistance data, Case 1 demonstrated average cost savings of 9.59 dollars to 10.21 dollars with ciprofloxacin XR. In Case 2, treatment costs (49.19 dollars) were equal at an E. coli resistance rate of 4.3% for TMP-SMX and 1.0% for ciprofloxacin. Case 3 assumed empiric telephone prescribing, demonstrating that, at 4.3% TMP-SMX resistance, costs are equal for both treatments (4.19 dollars). Case 4 used real-world data on therapy duration, demonstrating that, at 2.8% TMP-SMX resistance, costs are equal for both treatments (54.87 dollars). Case 5 assumed 10% ciprofloxacin-E. coli resistance; at 13.3% TMP-SMX resistance, treatment costs were equal (57.50 dollars). Results from all cases demonstrate that while the per-dose cost of ciprofloxacin XR far exceeds TMP-SMX, average total treatment costs are lower for ciprofloxacin XR at expected local levels of E. coli resistance to TMP-SMX. CONCLUSIONS: The results suggest that in areas where local TMP-SMX E. coli resistance exceeds 10% and resistance to ciprofloxacin remains low, (0.5% to 6%) ciprofloxacin XR is an appropriate alternative to standard empiric treatment. The data provide evidence to MCOs that switching to a more expensive per-dose alternative will not necessarily increase total costs when guideline recommendations are followed. Responsible use of antibiotics for uUTI requires selection and administration of the right dosage of the most suitable antibiotic for an appropriate time period to eliminate pathogens quickly and successfully. The decision to use an alternative first-line therapy for uUTI should be driven by local resistance and susceptibility data--not simply per-dose drug acquisition costs.

Folate synthesis in plants: the last step of the p-aminobenzoate branch is catalyzed by a plastidial aminodeoxychorismate lyase.

In plants, the last step in the synthesis of p-aminobenzoate (PABA) moiety of folate remains to be elucidated. In Escherichia coli, this step is catalyzed by the PabC protein, a beta-lyase that converts 4-amino-4-deoxychorismate (ADC)--the reaction product of the PabA and PabB enzymes--to PABA and pyruvate. So far, the only known plant enzyme involved in PABA synthesis is ADC synthase, which has fused domains homologous to E. coli PabA and PabB and is located in plastids. ADC synthase has no lyase activity, implying that plants have a separate ADC lyase. No such lyase is known in any eukaryote. Genomic and phylogenetic approaches identified Arabidopsis and tomato cDNAs encoding PabC homologs with putative chloroplast-targeting peptides. These cDNAs were shown to encode functional enzymes by complementation of an E. coli pabC mutant, and by demonstrating that the partially purified recombinant proteins convert ADC to PABA. Plant ADC lyase is active as dimer and is not feedback inhibited by physiologic concentrations of PABA, its glucose ester, or folates. The full-length Arabidopsis ADC lyase polypeptide was translocated into isolated pea chloroplasts and, when fused to green fluorescent protein, directed the passenger protein to Arabidopsis chloroplasts in transient expression experiments. These data indicate that ADC lyase, like ADC synthase, is present in plastids. As shown previously for the ADC synthase transcript, the level of ADC lyase mRNA in the pericarp of tomato fruit falls sharply as ripening advances, suggesting that the expression of these two enzymes is coregulated.

Folate synthesis in plants: the p-aminobenzoate branch is initiated by a bifunctional PabA-PabB protein that is targeted to plastids.

It is not known how plants synthesize the p-aminobenzoate (PABA) moiety of folates. In Escherichia coli, PABA is made from chorismate in two steps. First, the PabA and PabB proteins interact to catalyze transfer of the amide nitrogen of glutamine to chorismate, forming 4-amino-4-deoxychorismate (ADC). The PabC protein then mediates elimination of pyruvate and aromatization to give PABA. Fungi, actinomycetes, and Plasmodium spp. also synthesize PABA but have proteins comprising fused domains homologous to PabA and PabB. These bipartite proteins are commonly called "PABA synthases," although it is unclear whether they produce PABA or ADC. Genomic approaches identified Arabidopsis and tomato cDNAs encoding bipartite proteins containing fused PabA and PabB domains, plus a putative chloroplast targeting peptide. These cDNAs encode functional enzymes, as demonstrated by complementation of an E. coli pabA pabB double mutant and a yeast PABA-synthase deletant. The partially purified recombinant Arabidopsis protein did not produce PABA unless the E. coli PabC enzyme was added, indicating that it forms ADC, not PABA. The enzyme behaved as a monomer in size-exclusion chromatography and was not inhibited by physiological concentrations of PABA, its glucose ester, or folates. When the putative targeting peptide was fused to GFP and expressed in protoplasts, the fusion protein appeared only in chloroplasts, indicating that PABA synthesis is plastidial. In the pericarp of tomato fruit, the PabA-PabB mRNA level fell drastically as ripening advanced, but there was no fall in total PABA content, which stayed between 0.7 and 2.3 nmol.g(-1) fresh weight.