Prospects for ultracold carbon via charge exchange reactions and laser cooled carbides

Strategies to produce an ultracold sample of carbon atoms are explored and assessed with the help of quantum chemistry. After a brief discussion of the experimental difficulties using conventional methods, two strategies are investigated. The first attempts to exploit charge exchange reactions between ultracold metal atoms and sympathetically cooled C+ ions. Ab initio calculations including electron correlation have been conducted on the molecular ions [LiC]+ and [BeC]+ to determine whether alkali or alkaline earth metals are a suitable buffer gas for the formation of C atoms but strong spontaneous radiative charge exchange ensure they are not ideal. The second technique involves the stimulated production of ultracold C atoms from a gas of laser cooled carbides. Calculations on LiC suggest that the alkali carbides are not suitable but the CH radical is a possible laser cooling candidate thanks to very favourable Frank-Condon factors. A scheme based on a four pulse STIRAP excitation pathway to a Feshbach resonance is outlined for the production of atomic fragments with near zero centre of mass velocity.

Second-order NMR spectra at high field of common organic functional groups

The proton NMR spectra of aryl n-propyl sulfides gave rise to what may appear to be first-order proton NMR spectra. Upon oxidation to the corresponding sulfone, the spectra changed appearance dramatically and were clearly second-order. A detailed analysis of these second-order spectra, in the sulfone series, provided vicinal coupling constants which indicated that these compounds had a moderate preference for the anti-conformer, reflecting the much greater size of the sulfone over the sulfide. It also emerged, from this study, that the criterion for observing large second-order effects in the proton NMR spectra of 1,2-disubstituted ethanes was that the difference in vicinal coupling constants must be large and the difference in geminal coupling constants must be small. n-Propyl triphenylphosphonium bromide and 2-trimethylsilylethanesulfonyl chloride, and derivatives thereof, also exhibited second-order spectra, again due to the bulky substituents. Since these spectra are second-order due to magnetic nonequivalence of the nuclei in question, not chemical shifts, the proton spectra are perpetually second-order and can never be rendered first-order by using higher field NMR spectrometers.

Dioxygenase-catalysed cis-dihydroxylation of meta-substituted phenols to yield cyclohexenone cis-diol and derived enantiopure cis-triol metabolites

cis-Dihydroxylation of meta-substituted phenol (m-phenol) substrates, to yield the corresponding cyclohexenone cis-diol metabolites, was catalysed by arene dioxygenases present in mutant and recombinant bacterial strains. The presence of cyclohexenone cis-diol metabolites and several of their cyclohexene and cyclohexane cis-triol derivatives was detected by LC-TOFMS analysis and confirmed by NMR spectroscopy. Structural and stereochemical analyses of chiral ketodiol bioproducts, was carried out using NMR and CD spectroscopy and stereochemical correlation methods. The formation of enantiopure cyclohexenone cis-diol metabolites is discussed in the context of postulated binding interactions of the m-phenol substrates at the active site of toluene dioxygenase (TDO).

Rapid synthesis of nucleotide pyrophosphate linkages in a ball mill

Using a ball mill, rapid, atom-economic coupling between adenosine-5'-phosphoromorpholidate and phosphorylated ribose derivatives as their sodium or barium salts was achieved. Facile purification by reversed-phase HPLC enabled product isolation within hours.

Surface-Enhanced Raman Evidence of Protonation, Reorientation, and Ag+ Complexation of Deoxyadenosine and Deoxyadenosine-5 '-Monophosphate (dAMP) on Ag and Au Surfaces

Surface-enhanced Raman (SERS) spectra of deoxyadenosine and 5'-dAMP on Ag and Au surfaces showed the protonation of both compounds in the N1 position, their orientation geometry on metal surfaces, and the formation of Ag+ complexes at alkaline pH on hydroxylamine-reduced Ag colloids. Interestingly, substitution at the N9 position caused dramatic changes in the relative band intensities within the spectra of both deoxyadenosine and 5'-dAMP compared to that of simple adenine, although they continued to be dominated by adenine vibrations. Concentration-dependent spectra of 5'-dAMP were observed, which matched that of adenine at high concentrations and that of deoxyadenosine at lower concentration (

Examination of the Silver Colloid Binding Behavior of Disulfide-Tethered Bipyridine Ligands and Their fac-Tricarbonylrhenium(I) Complexes

The syntheses of 2,2'-bipyridin-5-ylmethyl-5-(1,2-dithiolan-3-yl)pentanoate (L1) and N-(2,2'-bipyridin-5-ylmethyl)-5-(1,2-dithiolan-3-yl)pentanamide (L2) and their neutral fac carbonylrhenium(I) complexes [Re(L1)(CO)(3)Br] and [Re(L2)(CO)(3)Br] are reported. The. electronic absorption and emission spectra of the complexes are similar to the spectrum of the reference compound [Re(bipy)(CO)(3)Br] and correlate well with the density functional theory calculations undertaken. The surface-enhanced Raman spectroscopy (SERS) spectra (excited at both 532 and 785 nm) of the ligands and complexes were examined and compared to the spectrum of ethyl 5-(1,2-dithiolan-3-yl)pentanoate (L3), revealing that there is very little contribution to the spectra of these species from the dithiolated alkyl chains. The spectra are dominated by the characteristic peaks of a metalated 2,2'-bipyridyl group,arising from the silver colloid/ion complexation, and the rhenium center. The rhenium complexes show weak SERS bands related to the CO stretches and a broad band at 510 cm(-1) assigned to Re-CO stretching. Concentration dependent studies, measured by the relative intensity of several assigned peaks, indicate that, as the surface coverage increases, the bipyridine moiety lifts off the surface In the case of L1 and L2, this gives rise to complexes with silver at low concentration, enhancing the signals observed, while for the tricarbonylbromorhenium complexes of these ligands, the presence of the disulfide tether allows an enhancement in the limits of detection of these surface-borne species of 20 times in the case of [ReL2(CO)(3)Br] over [Re(bipy)(CO)(3)Br].

Characterizing capacity loss of lithium oxygen batteries by impedance spectroscopy

Polymer based carbon aerogels were prepared by synthesis of a resorcinol formaldehyde gel followed by pyrolysis at 1073K under Ar and activation of the resultant carbon under CO2 at different temperatures. The prepared carbon aerogels were used as active materials in the preparation of cathode electrodes for lithium oxygen cells and the electrochemical performance of the cells was evaluated by galvanostatic charge/discharge cycling and electrochemical impedance measurements. It was shown that the storage capacity and discharge voltage of a Li/O2 cell strongly depend on the porous structure of the carbon used in cathode. EIS results also showed that the shape and value of the resistance in the impedance spectrum of a Li/O2 cell are strongly affected by the porosity of carbon used in the cathode. Porosity changes due to the build up of discharge products hinder the oxygen and lithium ion transfer into the electrode, resulting in a gradual increase in the cell impedance with cycling. The discharge capacity and cycle life of the battery decrease significantly as its internal resistance increases with charge/discharge cycling.

The effects of temperature on the performance of electrochemical double layer capacitors

An electrochemical double layer capacitor test cell containing activated carbon xerogel electrodes and ionic liquid electrolyte was tested at 15, 25 and 40 OC to examine the effect of temperature on electrolyte resistance (RS) and equivalent series resistance (ESR) measured using impedance spectroscopy and capacitance using charge/discharge cycling. A commercial 10F capacitor was used as a comparison. Viscosity, ionic self-diffusion coefficients and differential scanning calorimetry measurements were used to provide an insight into the behaviour of the 1,2-dimethyl-3-propylimdazolium electrolyte. Both RS and ESR decreased with increasing temperature for both capacitors. Increasing the temperature also increased the capacitance for both the test cell and the commercial capacitor but proportionally more for the test cell. An increase in temperature decreased the ionic liquid electrolyte viscosity and increased the self diffusion coefficients of both the anion and the cation indicating an increase in dissociation and increase in ionic mobility.

Resonance Raman and surface-enhanced resonance Raman studies of polymer-modified electrodes which mimic heme enzymes

Iron-5,10,15,20-tetraphenylporphyrin (FeTPP) has been incorporated into films of a coordinating hydrogel polymer support medium, poly(gamma-ethyl-L-glutamate) (PEG) functionalised with imidazole pendant arms (PEG-Im), and studied in situ on silver electrodes using a combination of both resonance Raman (RR) and surface-enhanced resonance Raman (SERR) spectroscopy. The SERR spectra give information on the portion of the film close to the electrode surface while RR spectra probe the

The Potential of Antimicrobial Peptides as Biocides

Antimicrobial peptides constitute a diverse class of naturally occurring antimicrobial molecules which have activity against a wide range of pathogenic microorganisms. Antimicrobial peptides are exciting leads in the development of novel biocidal agents at a time when classical antibiotics are under intense pressure from emerging resistance, and the global industry in antibiotic research and development stagnates. This review will examine the potential of antimicrobial peptides, both natural and synthetic, as novel biocidal agents in the battle against multi-drug resistant pathogen infections.

Electrochemistry of Hg(II) Salts in Room-Temperature Ionic Liquids

The electrochemistry of HgCl(2) and [Hg(NTf(2))(2)] ([NTf(2)](-) = bis-{(trifluoromethyl)sulfonyl}imide) has been studied in room temperature ionic liquids. It has been found that the cyclic voltammetry of Hg(II) is strongly dependent on a number of factors (e.g., concentration, anions present in the mixture, and nature of the working electrode) and differs from that found in other media. Depending on conditions, the cyclic voltammetry of Hg(II) can give rise to one, two, or four reduction peaks, whereas the reverse oxidative scans show two to four peaks. Diffuse reflectance UV-vis spectroscopy and X-ray powder diffraction have been used to aid the assignment of the voltammetric waves.

Binding modes of diketo-acid inhibitors of HIV-1 integrase: A comparative molecular dynamics simulation study

HIV-1 integrase (IN) has become an attractive target since drug resistance against HIV-1 reverse transcriptase (RT) and protease (PR) has appeared. Diketo acid (DKA) inhibitors are potent and selective inhibitors of HIV-1 IN: however the action mechanism is not well understood. Here, to study the inhibition mechanism of DKAs we performed 10 ns comparative molecular dynamics simulations on HIV-1 IN bound with three most representative DMA inhibitors: Shionogi inhibitor, S-1360 and two Merck inhibitors L-731,988 and L-708,906. Our simulations show that the acidic part of S-1360 formed salt bridge and cation-pi interactions with Lys159. In addition, the catalytic Glu152 in S-1360 was pushed away from the active site to form an ion-pair interaction with Arg199. The Merck inhibitors can maintain either one or both of these ion-pair interaction features. The difference in potencies of the DMA inhibitors is thus attributed to the different binding modes at the catalytic site. Such structural information at atomic level, not only demonstrates the action modes of DMA inhibitors but also provides a novel starting point for structural-based design of HIV-1 IN inhibitors.

Alkynyl-Bridged Ruthenium(II) 4 '-Diferroceny1-2,2 ':6 ',2 ''-terpyridine Electron Transfer Complexes: Synthesis, Structures, and Electrochemical and Spectroscopic Studiese

The novel ligand 4'-diferrocenylallcyne-2,2':6',2 ''-terpyridine (7; Fc-C C-Fc-tpy; tpy = terpyridyl; Fc = ferrocenyl) and its Ru2+ complexes 8-10 have been synthesized and characterized by single-crystal X-ray diffraction, cyclic voltammetry, and UV-vis and luminescence spectroscopy. Electrochemical data and UV absorption and emission spectra indicate that the insertion of an ethynyl group causes delocalization of electrons in the extended pi* orbitals. Cyclic voltammetric measurements of 7 show two successive reversible one-electron-oxidation processes with half-wave potentials of 0.53 and 0.78 V. The small variations of the E-1/2 values for the Fe2+/Fe3+ redox couples after the coordination of the Ru2+ ion suggest a weak interaction between the Ru2+ and Fe2+ centers. After insertion of an ethynyl group, UV-vis absorption spectra show a red shift of the absorption peak of the (1)[(d(pi)(Fe))(6)]->(1)[(d(pi)(Fe))(5)(pi*(Ru)(tpy))(1)] MMLCT of the Ru2+ complexes. The Ru2+ complex 8 exhibits the strongest luminescence intensity (lambda(em)(max) 712 nm, Phi(em) = 2.63 x 10(-4), tau = 323 ns) relative to analogous ferrocene-based terpyridine Ru(II) complexes in H2O/CH3CN (4/1 v/v) solution.

On the self-aggregation and fluorescence quenching aptitude of surfactant ionic liquids

The aggregation behavior in aqueous solution of a number of ionic liquids was investigated at ambient conditions by using three techniques: fluorescence, interfacial tension, and H-1 NMR spectroscopy. For the first time, the fluorescence quenching effect has been used for the determination of critical micelle concentrations. This study focuses on the following ionic liquids: [C(n)mpy]Cl (1-alkyl-3-methylpyridinium chlorides) with different linear alkyl chain lengths (n = 4, 10, 12, 14, 16, or 18), [C(12)mpip]Br (1-dodecyl-1-methylpiperidinium bromide), [C(12)mpy]Br (1-dodecyl-3-methylpyridinium bromide), and [C(12)mpyrr]Br (1-dodecyl-1-methylpyrrolidinium bromide). Both the influence of the alkyl side-chain length and the type of ring in the cation (head) on the CMC were investigated. A comparison of the self-aggregation behavior of ionic liquids based on 1-alkyl-3-methylpyridinium and 1-alkyl-3-methylpyridinium cations is provided. It was observed that 1-alkyl-3-methylpyridinium ionic liquids could be used as quenchers for some fluorescence probes (fluorophores). As a consequence, a simple and convenient method to probe early evidence of aggregate formation was established.

Protic ionic liquids based on the dimeric and oligomeric anions: [(AcO)(x)Hx-1](-)

We describe a fluidity and conductivity study as a function of composition in N-methylpyrrolidine-acetic acid mixtures. The simple 1 : 1 acid-base mixture appears to form an ionic liquid, but its degree of ionicity is quite low and such liquids are better thought of as poorly dissociated mixtures of acid and base. The composition consisting of 3 moles acetic acid and 1 mole N-methylpyrrolidine is shown to form the highest ionicity mixture in this binary due to the presence of oligomeric anionic species [(AcO)(x)Hx-1](-) stabilised by hydrogen bonds. These oligomeric species, being weaker bases than the acetate anion, shift the proton transfer equilibrium towards formation of ionic species, thus generating a higher degree of ionicity than is present at the 1 : 1 composition. A Walden plot analysis, thermogravimetric behaviour and proton NMR data, as well as ab initio calculations of the oligomeric species, all support this conclusion.