Ultraviolet resonance Raman spectroscopy of a β‐sheet peptide: a model for membrane protein folding

The partitioning of a hydrophobic hexapeptide, N‐acetyl‐tryptophan‐pentaleucine (AcWL5), into self‐associated β‐sheets within a vesicle membrane was studied as a model for integral membrane protein folding and insertion via vibrational and electronic spectroscopy. Ultraviolet resonance Raman spectroscopy allows selective examination of the structures of amino acid side chains and the peptide backbone and provides information about local environment and molecular conformation. The secondary structure of AcWL5 within a vesicle membrane was investigated using 207.5‐nm excitation and found to consist of β‐sheets, in agreement with previous studies. The β‐sheet peptide shows enhanced Raman scattering cross‐sections for all amide modes as well as extensive hydrogen‐bonding networks. Tryptophan vibrational structure was probed using 230‐nm excitation. Increases in Raman cross‐sections of tryptophan modes W1, W3, W7, W10, W16, W17, and W18 of membrane‐incorporated AcWL5 are primarily attributed to greater resonance enhancement with the B_b electronic transition. The W17 mode, however, undergoes a much greater enhancement than is expected for a simple resonance effect, and this observation is discussed in terms of hydrogen bonding of the indole ring in a hydrophobic environment. The observed tryptophan mode frequencies and intensities overall support a hydrophobic environment for the indole ring within a vesicle, and these results have implications for the location of tryptophan in membrane protein systems. Copyright © 2009 John Wiley & Sons, Ltd.     

The use of impregnated filters to collect traces of gases in the atmosphere : Part ii. collection of sulfur dioxide on membrane filters

HA and AA Millipore filters impregnated with 5% potassium bicarbonate and dried were found to be suitable for sampling concentrations of sulfur dioxide in air. The impregnation technique and filter loadings are described; flow rates are relatively unaffected by impregnation. The apparatus and procedures used for preparation and sampling known concentrations of sulfur dioxide in air are described. Comparisons of actual and theoretical concentrations in the 0.1 to 10 p.p.m. range showed that the concentrations prepared must be assayed.The collection efficiency of impregnated filters was evaluated for sodium tetrachloromercurate-(II) (less than 10% which is in contrast with the 100% efficiency found with TCM as a scrubbing solution) and potassium bicarbonate (greater than 95%). The capacity of the filters was such that sampling a 10 p.p.m. sample for at least 1 h is possible.     

Biomonitoring in the mercury-contaminated Wabigoon–English–Winnipeg river (Canada) system: selecting the best available bioindicator

Several organisms used for biomonitoring in the mercury-contaminated Wabigoon–English River System, Ontario, Canada (sport fish, forage fish, crayfish and others) were examined for their utility as bioindicators. Causes for spatial and temporal variability in mercury concentrations in biota are reviewed. The significance of intertrophic and intratrophic biotic relationships is evaluated on both a site-specific and intersite basis. Larger mature fish are the most effective integrators as these organisms are the most buffered from site-specific and seasonal variations in mercury concentrations and bioavailability. Where there are no physical barriers preventing movement of biota between contaminated and uncontaminated parts of the watercourse, younger, smaller organisms can better - ical zones of contamination because of their restricted range. Because many organisms can provide information on mercury contamination, the choice of the most suitable indicator depends upon the purpose of the study, the pharmacokinetics of mercury uptake by the organisms in question, and the chemodynamics of methyl and inorganic mercury species in the field.     

Field deployable tritium analysis system for ground and surface water measurements

Researchers from the Savannah River Technology Center, the Center for Applied Isotope Studies (CAIS) and Sampling Systems have developed a prototype Field Deployable Tritium Analysis System (FDTAS) for near-real-time measurements of environmental levels of tritium in ground and surface water. The device consists of a modified liquid scintillation counter coupled to an automatic sampler which incorporates on-line water purification. The FDTAS has been field tested at several Savannah River Site locations and has produced results comparable to laboratory analyses for low concentrations of tritium. Figures of merit obtained in the field include an average tritium background count rate of 1.5 counts per minute (cpm), tritium detection efficiency of ≈25%, and a detection limit of <10 Bq/l for a 100 minute count.     

Engineered biosynthesis of nonribosomal lipopeptides with modified fatty acid side chains

The biological properties of the calcium-dependent antibiotics (CDAs), daptomycin and related nonribosomal lipopeptides, depend to a large extent on the nature of the N-terminal fatty acid moiety. It is suggested that the chain length of the unusually short (C6) 2,3-epoxyhexanoyl fatty acid moiety of CDA is determined by the specificity of the KAS-II enzyme encoded by fabF3 in the CDA biosynthetic gene cluster. Indeed, deletion of the downstream gene hxcO results in three new lipopeptides, all of which possess hexanoyl side chains (hCDAs). This confirms that HxcO functions as a hexanoyl-CoA or -ACP oxidase. The absence of additional CDA products with longer fatty acid groups further suggests that the CDA lipid chain is biosynthesized on a single ACP and is then transferred directly from this ACP to the first CDA peptide synthetase (CdaPS1). Interestingly, the hexanoyl-containing CDAs retain antibiotic activity. To further modulate the biological properties of CDA by introducing alternative fatty acid groups, a mutasynthesis approach was developed. This involved mutating the key active site Ser residue of the CdaPS1, module 1 PCP domain to Ala, which prevents subsequent phosphopantetheinylation. In the absence of the natural module 1 PCP tethered intermediate, it is possible to effect incorporation of different N-acyl-L-serinyl N-acetylcysteamine (NAC) thioester analogues, leading to CDA products with pentanoyl as well as hexanoyl side chains.     

Ultraviolet resonance Raman spectroscopy of folded and unfolded states of an integral membrane protein

The vibrational structure of native anchoring tryptophan (Trp) and tyrosine residues in an integral membrane protein, bacterial outer membrane protein A (OmpA), have been investigated using UV resonance Raman (UVRR) spectroscopy for the first time. Spectra of native OmpA, a single-Trp mutant, and a Trp-less mutant were recorded in folded and unfolded states, and reveal significant changes in tryptophan structure and local environment. Salient alterations upon folding include loss of hydrogen-bonding character of indole N1H, evidenced by a shift in W17 frequency from 874 and 878 cm(-1), and growth in hydrophobicity of the local tryptophan environment, supported by increase in the ratio I1361/I1340. In addition to these site-specific changes in a single tryptophan residue, modification of the vibrational structure of the remaining native tryptophan and tyrosine amino acids is also evident. Finally, the UVRR data presented here indicate that the structures of OmpA folded in vesicle and folded in detergent may differ, and provide important foundations for ongoing studies of membrane protein folding.     

Fe3O4@organic@Au: core-shell nanocomposites with high saturation magnetisation as magnetoplasmonic MRI contrast agents

The synthesis and characterization of core-shell Fe(3)O(4)@organic@Au nanoparticles displaying plasmonic behavior, high magnetism, and high relaxivity is presented. The incorporation of a thin organic layer between the two metals is crucial in maintaining the saturation magnetisation of the superparamagnetic core.     

A Precision Ethylene‐Styrene Copolymer with High Styrene Content from Ring‐Opening Metathesis Polymerization of 4‐Phenylcyclopentene

Ring‐opening metathesis polymerization of 4‐phenylcyclopentene is investigated for the first time under various conditions. Thermodynamic analysis reveals a polymerization enthalpy and entropy sufficient for high molar mass and conversions at lower temperatures. In one example, neat polymerization using Hoveyda–Grubbs second generation catalyst at −15 °C yields 81% conversion to poly(4‐phenylcyclopentene) (P4PCP) with a number average molar mass of 151 kg mol⁻¹ and dispersity of 1.77. Quantitative homogeneous hydrogenation of P4PCP results in a precision ethylene‐styrene copolymer (H₂‐P4PCP) with a phenyl branch at every fifth carbon along the backbone. This equates to a perfectly alternating trimethylene‐styrene sequence with 71.2% w/w styrene content that is inaccessible through molecular catalyst copolymerization strategies. Differential scanning calorimetry confirms P4PCP and H₂‐P4PCP are amorphous materials with similar glass transition temperatures (T_g) of 17 ± 2 °C. Both materials present well‐defined styrenic analogs for application in specialty materials or composites where lower softening temperatures may be desired.

     

A new synthesis of biologically active pyrroles: Formal synthesis of pentabromopseudilin,bimetopyrol, and several antitubercular agents

Although pyrroles have been synthesized from azido dienes, the corresponding reactions of structurally similar nitrodienes had not been investigated until it became the main focus of this study. This article describes the synthesis of several biologically active pyrroles and mechanistically intriguing results in connection with our new approach using nitrodienes in the presence of Ph₃P and a Mo catalyst, bis (acetylaceto)dioxomolybdenum (VI). The final precursor of pentabromopseudilin (PBP), pseudilin, was synthesized in four steps from o-hydroxycinnamaldehyde. An alternate pathway to PBP proceeded through o-methylpseudilin, prepared in two steps from o-methoxycinnamaldehyde. Both starting materials are commercially available. Similarly, bimetopyrol (2-methyl-4,5-bis(p-methoxyphenyl)pyrrole), a potent anti-inflammatory, was prepared using the new methodology. The remarkable conversion of nitrodienes 14 and 15 to bimetopyrol highlights the formation of a nitroso or nitrene intermediate. We also established that 14 and 15 interconvert in the presence of ambient light and each converts to bimetopyrol when reacted separately. The wide application of our synthetic methodology includes preparation of several antitubercular and Herpes Simplex 2 (HSV2) agents.     

Thiadiazolidine 1-oxide systems for phosphine-free palladium-mediated catalysis

We herein report several highly active catalyst systems with thiadiazolidine 1-oxides as ligands for palladium in the Mizoroki-Heck reaction. Excellent yields of stilbenes derived from aryl iodides and bromides have been achieved using as little as 0.00002 mol % catalyst. The ligand/palladium system can be stored as a stock solution open to air at room temperature with no observable loss of activity for a period of several months.