Microwave spectra and molecular structures of (Z)-pent-2-en-4-ynenitrile and maleonitrile.

Accurate equilibrium structures have been determined for (Z)-pent-2-en-4-ynenitrile (8) and maleonitrile (9) by combining microwave spectroscopy data and ab initio quantum chemistry calculations. The microwave spectra of 10 isotopomers of 8 and 5 isotopomers of 9 were obtained using a pulsed nozzle Fourier transform microwave spectrometer. The ground-state rotational constants were adjusted for vibration-rotation interaction effects calculated from force fields obtained from ab initio calculations. The resultant equilibrium rotational constants were used to determine structures that are in very good agreement with those obtained from high-level ab initio calculations (CCSD(T)/cc-pVTZ). The geometric parameters in 8 and 9 are very similar; they also do not differ significantly from the all-carbon analogue, (Z)-hex-3-ene-1,5-diyne (7), the parent molecule for the Bergman cyclization. A small deviation from linearity about the alkyne and cyano linkages is observed for 7-9 and several related species where accurate equilibrium parameters are available. The data on 7-9 should be of interest to radioastronomy and may provide insights on the formation and interstellar chemistry of unsaturated species such as the cyanopolyynes.     

Efficient nanocoax‐based solar cells

The power conversion efficiency of most thin film solar cells is compromised by competing optical and electronic constraints, wherein a cell must be thick enough to collect light yet thin enough to efficiently extract current. Here, we introduce a nanoscale solar architecture inspired by a well‐known radio technology concept, the coaxial cable, that naturally resolves this “thick–thin” conundrum. Optically thick and elec‐ tronically thin amorphous silicon “nanocoax” cells are in the range of 8% efficiency, higher than any nanostructured thin film solar cell to date. Moreover, the thin nature of the cells reduces the Staebler–Wronski light‐induced degradation effect, a major problem with conventional solar cells of this type. This nanocoax represents a new platform for low cost, high efficiency solar power. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Selective detection of the reduced form of glutathione (GSH) over the oxidized (GSSG) form using a combination of glutathione reductase and a Tb(III)-cyclen maleimide based lanthanide luminescent 'switch on' assay

The synthesis of a novel Tb(III) luminescent probe for the detection of thiols is presented. The probe 1.Tb, possessing a maleimide moiety, as its sulfhydryl acceptor, was poorly emitting in aqueous pH 7 solution in the absence of a thiol. However, upon addition of thiols such as glutathione (GSH), large enhancements were observed, particularly within the physiological pH range. In contrast no enhancements were observed in the presence of the oxidized form of glutathione (GSSG), except in the presence of the enzyme glutathione reductase and NADPH which enabled 1.Tb to be used to observe the enzymatic reduction of GSSG to GSH in real time.     

The role of continuous and discrete water structures in protein function

Proteins have evolved to perform numerous roles as specific catalysts and nano-machines. Some of the mechanisms exploited by evolution are clear. Hydrophobicity drives the stabilization energy of folding, charges mediate long-range interactions and facilitate catalysis, and specific geometries and hydrogen bonding patterns facilitate molecular recognition and catalysis. In this work, we examine the energy landscape of protein dynamics in terms of the continuous and discrete water structures that control protein dynamics. We observe that the internal structures at the active site of proteins are constantly shaped by strong interactions with hydration shell and bulk water motions. By describing the energy landscape of proteins in terms of its three component motions; conformational, hydration and protonation, and electronic structure, it is possible to systematically understand protein function.     

Organic Semiconductors: Impact of Disorder at Different Timescales

The charge transport in organic materials, from molecular crystals to polymers, is determined by their degree of disorder. The dynamic disorder in ideal molecular crystals at room temperature and the static disorder in disordered polymers are just two limiting cases of the timescale of the fluctuations in the electronic Hamiltonian caused by nuclear motions. In fact, a very large number of important materials (e.g. liquid crystalline semiconductors) are actually in an intermediate regime where the disorder is neither purely static nor purely dynamic. This Minireview discusses the recent contribution of computational chemistry (molecular dynamics and quantum chemistry) to the characterization of these transport regimes and outlines the theoretical methods that can be used to relate the system characteristics to the measurable mobility.     

The first synthesis of an epidiselenodiketopiperazine

Epidithiodiketopiperazines (ETPs) are natural products (e.g., gliotoxin) with varied and important biological activity, which often is attributed to the redox properties of the disulfide moiety. As such, analogs with altered redox properties and similar structural characteristics would be of value to biological investigations. The use of an ETP as the point of departure in the first synthesis of an epidiselenodiketopiperazine (ESeP) and its activity against Mycobacterium tuberculosis (MTB) is reported.     

Consecutive Fragmentation Mechanisms of Protonated Ferulic Acid Probed by Infrared Multiple Photon Dissociation Spectroscopy and Electronic Structure Calculations

Protonated ferulic acid and its principle fragment ion have been characterized using infrared multiple photon dissociation spectroscopy and electronic structure calculations at the B3LYP/6-311?+?G(d,p) level of theory. Due to its extensively conjugated structure, protonated ferulic acid is observed to yield three stable fragment ions in IRMPD experiments. It is proposed that two parallel fragmentation pathways of protonated ferulic acid are being observed. The first pathway involves proton transfer, resulting in the loss of water and subsequently carbon monoxide, producing fragment ions m/z 177 and 149, respectively. Optimization of m/z 177 yields a species containing an acylium group, which is supported by a diagnostic peak in the IRMPD spectrum at 2168?cm^?1. The second pathway involves an alternate proton transfer leading to loss of methanol and rearrangement to a five-membered ring.     

Neural mechanisms underlying the facilitation of naming in aphasia using a semantic task: an fMRI study

Background

In the fruit fly, Drosophila melanogaster, serotonin functions both as a neurotransmitter to regulate larval feeding, and in the development of the stomatogastric feeding circuit. There is an inverse relationship between neuronal serotonin levels during late embryogenesis and the complexity of the serotonergic fibers projecting from the larval brain to the foregut, which correlate with perturbations in feeding, the functional output of the circuit. Dopamine does not modulate larval feeding, and dopaminergic fibers do not innervate the larval foregut. Since dopamine can function in central nervous system development, separate from its role as a neurotransmitter, the role of neuronal dopamine was assessed on the development, and mature function, of the 5-HT larval feeding circuit.

Results

Both decreased and increased neuronal dopamine levels in late embryogenesis during development of this circuit result in depressed levels of larval feeding. Perturbations in neuronal dopamine during this developmental period also result in greater branch complexity of the serotonergic fibers innervating the gut, as well as increased size and number of the serotonin-containing vesicles along the neurite length. This neurotrophic action for dopamine is modulated by the D₂ dopamine receptor expressed during late embryogenesis in central 5-HT neurons. Animals carrying transgenic RNAi constructs to knock down both dopamine and serotonin synthesis in the central nervous system display normal feeding and fiber architecture. However, disparate levels of neuronal dopamine and serotonin during development of the circuit result in abnormal gut fiber architecture and feeding behavior.

Conclusions

These results suggest that dopamine can exert a direct trophic influence on the development of a specific neural circuit, and that dopamine and serotonin may interact with each other to generate the neural architecture necessary for normal function of the circuit.     

Gas phase SN2 reactions of halide ions with trifluoromethyl halides: front- and back-side attack vs. complex formation

Density functional theory computations and pulsed-ionization high-pressure mass spectrometry experiments have been used to explore the potential energy surfaces for gas-phase S(N)2 reactions between halide ions and trifluoromethyl halides, X(-) + CF(3)Y --> Y(-) + CF(3)X. Structures of neutrals, ion-molecule complexes, and transition states show the possibility of two mechanisms: back- and front-side attack. From pulsed-ionization high-pressure mass spectrometry, enthalpy and entropy changes for the equilibrium clustering reactions for the formation of Cl(-)(BrCF(3)) (-16.5 +/- 0.2 kcal mol(-1) and -24.5 +/- 1 cal mol(-1) K(-1)), Cl(-)(ICF(3)) (-23.6 +/- 0.2 kcal mol(-1)), and Br(-)(BrCF(3)) (-13.9 +/- 0.2 kcal mol(-1) and -22.2 +/- 1 cal mol(-1) K(-1)) have been determined. These are in good to excellent agreement with computations at the B3LYP/6-311+G(3df)//B3LYP/6-311+G(d) level of theory. It is shown that complex formation takes place by a front-side attack complex, while the lowest energy S(N)2 reaction proceeds through a back-side attack transition state. This latter mechanism involves a potential energy profile which closely resembles a condensed phase S(N)2 reaction energy profile. It is also shown that the Cl(-) + CF(3)Br --> Br(-) + CF(3)Cl S(N)2 reaction can be interpreted using Marcus theory, in which case the reaction is described as being initiated by electron transfer. A potential energy surface at the B3LYP/6-311+G(d) level of theory confirms that the F(-) + CF(3)Br --> Br(-) + CF(4) S(N)2 reaction proceeds through a Walden inversion transition state.