Sodium interacting with amorphous water films at 10 and 100 k

In the present study, we compare the adsorption of Na on amorphous D(2)O ice films, held at 10 and 100 K. OH, D(2)O, and Na are easily distinguished by their characteristic signatures in metastable impact electron spectroscopy (MIES). It is found that at 10 K substrate temperature the donation of 3sNa charge to the ice film, which is regarded as a precursor for water deprotonation, is significantly reduced relative to 100 K. This observation is discussed on the basis of recent theoretical work, suggesting that a rearrangement of the water molecules at the outermost water surface is the prerequisite for hydration/solvation of the 3sNa electron in the water ice bulk. The MIES spectra, showing spectral features from both OH and D(2)O, can be interpreted as reflecting the composition of the Na-water complexes in the near surface region. The relative intensity of the OH and D(2)O features is the same for 10 and 100 K. This finding suggests that two different sites for Na adsorption exist, one on the perfect water network and the other at OH dangling bond sites whereby, at 10 K, only the latter one leads to deprotonation of D(2)O. Finally, charge exchange phenomena observed when applying electron spectroscopies to ice films are discussed.     

Hydrophobic hydration of alkanes: its implication for the property of amorphous solid water

We measured the incorporation of adsorbed alkanes in and their desorption from the amorphous solid water (ASW) by means of secondary ion mass spectroscopy and temperature programmed desorption. The heavier alkanes such as butane and hexane are incorporated completely in the bulk of the nonporous ASW layer below 100 K probably due to the preferential formation of ice structures around the solute molecules. The self-diffusion of water molecules occurs above the glass transition temperature (136 K). The liquid water emerges above 165 K, as evidenced by simultaneous occurrence of the dehydration of alkanes and the morphological change of the water layer induced by the surface tension.     

Roles of deeply supercooled ethanol in crystallization and solvation of LiI

The mechanisms of glass-liquid transition and crystallization of amorphous solid ethanol were investigated through detailed analyses of the interaction with LiI using time-of-flight secondary ion mass spectrometry and reflection absorption infrared spectroscopy. The LiI species adsorbed on the surface are incorporated into the bulk of ethanol at temperatures higher than 100 K, concomitantly with the reorganization of the ethanol molecules at the surface. This behavior is explicable by self-diffusion of the ethanol molecules as a consequence of the glass-liquid transition. The resulting liquid is a distinct phase, as revealed from the similarity of the IR absorption band to that of amorphous solid ethanol rather than liquid ethanol. The liquid-liquid phase transition occurs at 130 K, and a supercooled liquid ethanol is formed, as evidenced by formation of a metastable LiI solution when ethanol is deposited on the LiI film. The supercooled liquid ethanol is unstable, so that it crystallizes immediately at 130 K on the Ni(111) substrate. The film morphology changes continuously, even after crystallization, and the film abruptly becomes smoother before film evaporation. This behavior implies that crystallization is not completed and that a liquidlike phase coexists.     

Glass-liquid transition of vapor-deposited hexane studied using TOF-SIMS

Thermodynamic connection between liquid and glass is not obvious for poor glass formers. In this study, microscopic molecular diffusivity and macroscopic fluidity of vapor-deposited thin films of n-hexane were investigated using TOF-SIMS to elucidate the mechanism of the glass-liquid transition. The C 6H 14 film deposited at 15 K is characterized by a porous structure, as inferred from the intermixing with adsorbed C 6D 14 and D 2O molecules, as well as the formation of D 2O nanoclusters on the surface. The hexane molecules are reoriented at temperatures higher than 60-70 K, resulting in smoothing of the surface and densification of the film. Self-diffusion of the hexane molecules commences at 110 K; then, the film dewets the Ni(111) substrate after some aging time. Results indicate that ultraviscous liquid formed at the glass transition temperature of 110 K transforms into fluidized liquid immediately before crystallization. The D 2O molecules adsorbed onto the surface play a role as a surfactant, as evidenced by quenching the film dewetting. The ultraviscous liquid is likely to be a distinct phase, which might explain the absence of calorimetric glass transition for poor glass formers like hexane.     

A scalable approach to combinatorial library design for drug discovery

In this paper, we propose an algorithm for the design of lead generation libraries required in combinatorial drug discovery. This algorithm addresses simultaneously the two key criteria of diversity and representativeness of compounds in the resulting library and is computationally efficient when applied to a large class of lead generation design problems. At the same time, additional constraints on experimental resources are also incorporated in the framework presented in this paper. A computationally efficient scalable algorithm is developed, where the ability of the deterministic annealing algorithm to identify clusters is exploited to truncate computations over the entire data set to computations over individual clusters. An analysis of this algorithm quantifies the tradeoff between the error due to truncation and computational effort. Results applied on test data sets corroborate the analysis and show improvement by factors as large as 10 or more, depending on the data sets.     

Catalytic Potential of Pyrazolone Based Dioxidomolybdenum(VI) Complexes for Multicomponent Biginelli Reactions,Epoxidation of Olefins and Oxidative Bromination of Phenol Derivatives

Three different types of dioxidomolybdenum(VI) complexes of 4-acetyl-3-methyl-1-phenyl-5-pyrazolone (Hmp, I )), 3-methyl-1-phenyl-4-propionyl-5-pyrazolone (Hpp, II ), 4-butyryl-3-methyl-1-phenyl-5-pyrazolone (Hbutp, III ), and 4-isobutyryl-3-methyl-1-phenyl-5-pyrazolone (isobutp, IV ) have been isolated and characterized by various spectroscopic (FT-IR, UV/Vis, ¹H and ¹³C NMR) techniques, thermal analysis and single crystal X-ray analysis. These complexes adopt a distorted six-coordinate octahedral geometry where ligands act as bidentate, coordinating through the two O atoms. These complexes have been used as catalysts to explore a single pot multicomponent (benzaldehyde or its derivatives, urea/thiourea and ethyl acetoacetate/phenyl acetoacatate) Biginelli reaction producing biologically active 3,4-dihydropyrimidin-2-(1H)-one and 3,4-dihydropyrimidin-2-(1H)-thione based biomolecules under solvent-free conditions. Presence of H₂O₂ improves the yield of dihydropyrimidin-2-(1H)-one but it acts as poison for the later molecule. Epoxidation of internal and terminal alkenes mainly resulted in the formation of the corresponding epoxide. The catalytic oxidative bromination of thymol, a reaction facilitated by vanadium dependent haloperoxidases, resulted in the formation of three product namely 2-bromothymol, 4-bromothymol and 2,4-bromothymol. Other phenol derivatives have also been brominated effectively.     

Transport properties of nanocrystalline silicon and silicon–germanium

We report on the minority carrier lifetime, diffusion length and mobility in nanocrystalline Si and (Si,Ge) p⁺nn⁺ devices. The devices were fabricated on stainless steel using VHF plasma deposition techniques. Minority carrier lifetime was measured using junction reverse recovery techniques. The minority carrier lifetime was found to be well correlated with the inverse of defect density and increased with increasing measurement temperature. Simultaneous measurement of diffusion length and lifetime yielded values for hole mobility.     

Study of sodium diuranate concentrate refining using H2O2

Journal of Radioanalytical and Nuclear Chemistry - An alternate route for refining Sodium diuranate concentrate to nuclear grade product following uranium peroxide precipitation using Hydrogen...     

Proton hyperpolarisation preserved in long-lived states

The polarisation of abundant protons, rather than dilute nuclei with low gyromagnetic ratios, can be enhanced in less than 10 min using dissolution DNP and converted into a long-lived state delocalised over an ensemble of three coupled protons. The process is more straightforward than the hyperpolarisation of heteronuclei followed by magnetisation transfer to protons.     

Selective Aromatic Hydroxylation with Dioxygen and Simple Copper Imine Complexes

The formation of a bis(μ‐oxido)dicopper complex with the ligand 2‐(diethylaminoethyl)‐6‐phenylpyridine (PPN) and its subsequent hydroxylation of the pendant phenyl group (studied earlier by Holland et al., Angew. Chem. Int. Ed.­ 1999 , 38, 1139–1142) has been reinvestigated to gain a better understanding of such systems in view of the development of new synthetic applications. To this end, we prepared a simple copper imine complex system that also affords selective o‐hydroxylation of aromatic aldehydes by using dioxygen as the oxidant: Applying the ligand N′‐benzylidene‐N,N‐diethylethylenediamine (BDED), salicylaldehyde was prepared in good yields and we show that this reaction also occurs through an intermediate bis‐μ‐oxido copper complex. The underlying reaction mechanism for the PPN‐supported complex was studied at the BLYP‐D/TZVP level of density functional theory and the results for representative stationary points along reaction paths of the BDED‐supported complex reveal a closely related mechanistic scenario. The results demonstrate a new facile synthetic way to introduce OH groups into aromatic aldehydes.