Selective Palladium-Catalysed Aerobic Oxidation of Alcohols

Palladium has a significant track record as a catalyst for a range of oxidation reactions and it has been explored for the selective oxidation of alcohols for many years. This chapter focuses on the two main types of aerobic Pd catalysts: heterogeneous and ligand-modulated systems. In the case of heterogeneous systems, the mechanistic understanding of these systems and the use of in situ and operando techniques to obtain this knowledge are discussed. The current state-of-the-art is also summarized in terms of catalytic performance and substrate scope for heterogeneous Pd-based catalysts. In terms of ligand-modulated systems, leading examples of molecular Pd(ii) catalysts which undergo direct O2 coupled turnover are highlighted. The catalyst performance for such catalysts is exemplified and mechanistic understanding for these molecular systems is discussed.

A Highly Efficient Palladium(II)/Polyoxometalate Catalyst System for Aerobic Oxidation of Alcohols

A simple catalyst system composed of Pd(OAc)2, phosphomolybdic acid and tetrabutylammonium acetate oxidises a range of alcohols efficiently, with turnover numbers (TONs) of up to 10 000.

Reduction of the temperature sensitivity of Halomonas hydrothermalis by iron starvation combined with microaerobic conditions

The limits to biological processes on Earth are determined by physicochemical parameters, such as extremes of temperature and low water availability. Research into microbial extremophiles has enhanced our understanding of the biophysical boundaries which define the biosphere. However, there remains a paucity of information on the degree to which rates of microbial multiplication within extreme environments are determined by the availability of specific chemical elements. Here, we show that iron availability and composition of the gaseous phase (aerobic vs. microaerobic) determine susceptibility of a marine bacterium, Halomonas hydrothermalis, to sub-optimal and elevated temperature and salinity by impacting rates of cell division (but not viability). In particular, iron starvation combined with microaerobic conditions (5 % v/v of O2, 10 % v/v of CO2, reduced pH) reduced sensitivity to temperature across the 13 °C range tested. These data demonstrate that nutrient limitation interacts with physicochemical parameters to determine biological permissiveness for extreme environments. The interplay between resource availability and stress tolerance, therefore, may shape the distribution and ecology of microorganisms within Earth's biosphere.

Systemic oxidative-nitrosative-inflammatory stress during acute exercise in hypoxia; implications for microvascular oxygenation and aerobic capacity

New Findings

What is the central question of this study?Exercise performance is limited during hypoxia by a critical reduction in cerebral and skeletal tissue oxygenation. To what extent an elevation in systemic free radical accumulation contributes to microvascular deoxygenation and the corresponding reduction in maximal aerobic capacity remains unknown.What is the main finding and its importance?We show that altered free radical metabolism is not a limiting factor for exercise performance in hypoxia, providing important insight into the fundamental mechanisms involved in the control of vascular oxygen transport.

Exercise performance in hypoxia may be limited by a critical reduction in cerebral and skeletal tissue oxygenation, although the underlying mechanisms remain unclear. We examined whether increased systemic free radical accumulation during hypoxia would be associated with elevated microvascular deoxygenation and reduced maximal aerobic capacity (). Eleven healthy men were randomly assigned single-blind to an incremental semi-recumbent cycling test to determine  in both normoxia (21% O_{2) and hypoxia (12% O2) separated by a week. Continuous-wave near-infrared spectroscopy was employed to monitor concentration changes in oxy- and deoxyhaemoglobin in the left vastus lateralis muscle and frontal cerebral cortex. Antecubital venous blood samples were obtained at rest and at  to determine oxidative (ascorbate radical by electron paramagnetic resonance spectroscopy), nitrosative (nitric oxide metabolites by ozone-based chemiluminescence and 3-nitrotyrosine by enzyme-linked immunosorbent assay) and inflammatory stress biomarkers (soluble intercellular/vascular cell adhesion 1 molecules by enzyme-linked immunosorbent assay). Hypoxia was associated with increased cerebral and muscle tissue deoxygenation and lower  (P < 0.05 versus normoxia). Despite an exercise-induced increase in oxidative–nitrosative–inflammatory stress, hypoxia per se did not have an additive effect (P > 0.05 versus normoxia). Consequently, we failed to observe correlations between any metabolic, haemodynamic and cardiorespiratory parameters (P > 0.05). Collectively, these findings suggest that altered free radical metabolism cannot explain the elevated microvascular deoxygenation and corresponding lower  in hypoxia. Further research is required to determine whether free radicals when present in excess do indeed contribute to the premature termination of exercise in hypoxia.}

Interactions between soil, toxicant, and a lux-marked bacterium during solid phase-contact toxicity testing

Bioluminescence-based, solid-contact toxicity assays allow test bacterium and toxicant to interact at the solid-solution interface. A lux- marked bacterium, Burkholderia sp. RASC, and 2,4-dichlorophenol (2,4-DCP) were used to characterize these interactions. In the basic bioassay, cells were added to soil slurries containing 2,4-DCP (0-120 μg ml^-1). After 15 min, soil was removed by centrifugation, and bioluminescence in the supernatant was determined. Investigation of 2,4-DCP adsorption to soil revealed that sorption was linear and not significantly (p > 0.1) affected by the presence of Burkholderia cells. The numbers of culturable Burkholderia cells in the assay supernatant were 48.2 to 64.8% of the inoculum and independent of the soil weight. The effect of soil on 2,4-DCP toxicity was investigated by comparing soil aqueous extract and contact assays. The percentage bioluminescence for the contact assay was consistently higher than the extract assay at all test concentrations, and counts of viable Burkholderia cells were enhanced by the presence of 2,4-DCP in the contact assay. Expressing results as specific bioluminescence decreased the variability in response and the discrepancy in results between the two protocols. We suggest that solid-contact assays need improvement to ensure defined contact between cells and solid phase, and that the reporting of specific activity should be emphasized.

Toxicity of chlorobenzenes to a lux-marked terrestrial bacterium, Pseudomonas fluorescens

Insertion of lux genes, encoding for bioluminescence in naturally bioluminescent marine bacteria, into the genome of Pseudomonas fluorescens resulted in a bioluminescent strain of this terrestrial bacterium. The lux- marked bacterium was used to toxicity test the chlorobenzene series. By correlating chlorobenzenes 50% effective concentration (EC50) values against physiochemical parameters, the physiochemical properties of chlorobenzenes that elicit toxic responses were investigated. The results showed that the more chlorinated the compounds, the more toxic they were to lux-marked P. fluorescens. Furthermore, it was shown that the more symmetrical the compound, the greater its toxicity to P. fluorescens. In general, the toxicity of a chlorobenzene was inversely proportional to its solubility (S) and directly proportional to its lipophilicity (K(ow). By correlating lux- marked P. fluorescens EC50 values, determined for chlorobenzenes, with toxicity values determined using Pimephales promelas (fathead minnow), Cyclotella meneghiniana (diatom), and Vibrio fischeri (marine bacterium), it was apparent that lux-marked P. fluorescens correlated well with freshwater species such as the diatoms and fathead minnow but not with the bioluminescent marine bacterium V. fischeri. The implications of these findings are that a terrestrial bacterium such as P. fluorescens should be used for toxicity testing of soils and freshwaters rather than the marine bacterium V. fischeri.

The common vaginal commensal bacterium Ureaplasma parvum is associated with chorioamnionitis in extreme preterm labour

OBJECTIVE: To assess the association of vaginal commensal and low grade pathogenic bacteria including Ureaplasma parvum, Ureaplasma urealyticum, Mycoplasma hominis, Mycoplasma genitalium, Group B Streptococcus (GBS), and Gardnerella vaginalis, in women who delivered preterm at less than 37 weeks gestation in the presence or absence of inflammation of the chorioamnionitic membranes.

METHODS: A case control study involving women who delivered before 37 weeks gestation with and without inflammation of chorioamnionitic membranes. A total of 57 placental samples were histologically examined for polymorphonuclear leukocyte infiltration of placental tissue for evidence of chorioamnionitis, and by type-specific nucleic acid amplification for evidence of infection with one or more of the target bacteria. Demographic data was collected for each mother.

RESULTS: Amongst the 57 placental samples, 42.1% had chorioamnionitis and 24.6% delivered in the second trimester of pregnancy; U. parvum, U. urealyticum, G. vaginalis and GBS were all detected in the study with respective prevalence of 19.3%, 3.5%, 17.5% and 15.8%; M.genitalium and M. hominis were not detected. U. parvum was significantly associated with chorioamnionitis (p value = 0.02; OR 5.0; (95% CI 1.2-21.5) and was more common in women who delivered in the second (35.7%) compared to the third trimester of pregnancy (13.9%). None of the other bacteria were associated with chorioamnionitis or earlier delivery and all G.vaginalis positive women delivered in the third trimester of pregnancy (p value 0.04).

CONCLUSIONS: The detection of U. parvum in placental tissue was significantly associated with acute chorioamnionitis in women presenting in extreme preterm labour.

Draft Genome Sequence of Staphylococcus succinus Strain CSM-77, a Moderately Halophilic Bacterium Isolated from a Triassic Salt Mine.

Here, we report the draft genome sequence of Staphylococcus succinus strain CSM-77. This moderately halophilic bacterium was isolated from the surface of a halite sample obtained from a Triassic salt mine.

Enantiocomplementary preparation of (S)- and (R)-1-pyridylalkanols via ketone reduction and alkane hydroxylation using whole cells of Pseudomonas putida UV4

A previously unreported alcohol dehydrogenase enzyme in the mutant soil bacterium Pseudomonas putida UV4 catalyses the reduction of 2-, 3- and 4-acylpyridines to afford the corresponding (S)-1-pyridyl alkanols, with moderate to high e.e., whilst under the same conditions 2,6-diacetylpyridine is readily converted to the corresponding enantiopure C2-symmetric (S,S)-diol in one step. In contrast, the toluene dioxygenase enzyme in the same organism catalyses the hydroxylation of 2- and 3-alkylpyridines to (R)-1-(2-pyridyl) and (R)-1-(3-pyridyl)alkanols. This combination of oxidative and reductive biotransformations thus provides a method for preparing both enantiomers of chiral 1-pyridyl alkanols using one biocatalyst.

Biotransformation of Substituted Pyridines with Dioxygenase-containing Microorganisms.

A series of 2-, 3- and 4-substituted pyridines was metabolised using the mutant soil bacterium Pseudomonas putida UV4 which contains a toluene dioxygenase (TDO) enzyme. The regioselectivity of the biotransformation in each case was determined by the position of the substituent. 4-Alkylpyridines were hydroxylated exclusively on the ring to give the corresponding 4-substituted 3-hydroxypyridines, while 3-alkylpyridines were hydroxylated stereoselectively on C-1 of the alkyl group with no evidence of ring hydroxylation. 2-Alkylpyridines gave both ring and side-chain hydroxylation products. Choro- and bromo-substituted pyridines, and pyridine itself, while being poor substrates for P. putida UV4, were converted to some extent to the corresponding 3-hydroxypyridines. These unoptimised biotransformations are rare examples of the direct enzyme-catalysed oxidation of pyridine rings and provide a novel synthetic method for the preparation of substituted pyridinols. Evidence for the involvement of the same TDO enzyme in both ring and side-chain hydroxylation pathways was obtained using a recombinant strain of Escherichia coli (pKST11) containing a cloned gene for TDO. The observed stereoselectivity of the side-chain hydroxylation process in P. putida UV4 was complicated by the action of an alcohol dehydrogenase enzyme in the organism which slowly leads to epimerisation of the initial (R)-alcohol bioproducts by dehydrogenation to the corresponding ketones followed by stereoselective reduction to the (S)-alcohols.

Detection of Anaerobic Bacteria in High Numbers in Sputum from Patients with Cystic Fibrosis

Rationale: Pulmonary infection in cystic ?brosis (CF) is polymicrobial and it is possible that anaerobic bacteria, not detected by routine aerobic culture methods, reside within infected anaerobic airway
mucus.
Objectives: To determine whether anaerobic bacteria are present in the sputum of patients with CF.
Methods: Sputum samples were collected from clinically stable adults with CF and bronchoalveolar lavage ?uid (BALF) samples from children with CF. Induced sputum samples were collected from healthy volunteers who did not have CF. All samples were processed using anaerobic bacteriologic techniques and bacteria within the samples were quanti?ed and identi?ed.
Measurements and Main Results: Anaerobic species primarily within the genera Prevotella,Veillonella, Propionibacterium, andActinomyces were isolated in high numbers from 42 of 66 (64%) sputum samples from adult patients with CF. Colonization with Pseudomonas aeruginosa signi?cantly increased the likelihood that anaerobic bacteria would be present in the sputum. Similar anaerobic species were identi?ed in BALF from pediatric patients with CF. Although anaerobes were detected in induced sputum samples from 16 of 20 volunteers, they were present in much lower numbers and were
generally different species compared with those detected in CF sputum. Species-dependent differences in the susceptibility of the anaerobes to antibiotics with known activity against anaerobes were apparent with all isolates susceptible to meropenem.
Conclusions: A range of anaerobic species are present in large numbers in the lungs of patients with CF. If these anaerobic bacteria are contributing signi?cantly to infection and in?ammation in the CF
lung, informed alterations to antibiotic treatment to target anaerobes, in addition to the primary infecting pathogens, may improve management.