Growth control of homogeneous pulsed electrodeposited Co thin films on n-doped Si(1 1 1) substrates

Cobalt thin films were deposited by pulsed electrodeposition on n-doped silicon substrates. We show that the morphology and the magnetic properties of the samples can be controlled by a careful choice of the deposition conditions. Atomic force microscopy measurements reveal a granular growth with grain size and homogeneity strongly dependent on the total deposition time and pulse frequency of the applied signal. Magnetic force microscopy and magnetization measurements indicate the formation of magnetically correlated grain systems with a maximum magnetic correlation and homogeneity for samples with grain diameters of about 40 nm.     

A theoretical study of five nitrates: Electronic structure and bond dissociation energies

Three density-functional methods (B3P86, B3PW91, and B3LYP) are employed to investigate the O–NO₂ bond lengths, frontier orbital energies, and O–NO₂ bond dissociation energies (BDEs) of n-propyl nitrate (NPN), isopropyl nitrate (IPN), 2-ethylhexyl nitrate (EHN), triethylene glycol dinitrate (Tri-EGDN), and tetraethylene glycol dinitrate (Tetra-EGDN). It is found that the O–NO₂ bond lengthens (destabilizes) in the order of IPN, NPN, EHN, Tetra-EGDN, and Tri-EGDN. From the data of frontier orbital energies (E_HOMO, E_LUMO), and energy gaps (ΔE), we estimate the relative thermal stability ordering of five nitrates and their corresponding radicals. The predicted BDEs of O–NO₂ bond in NPN, IPN, EHN, Tri-EGDN, and Tetra-EGDN, are 176.6, 174.5, 168.1, 156.1, and 159.3 kJ mol⁻¹, respectively. Based on the finding that the present results of BDEs are well coincident with the experimental results of apparent activation energies from the literature, we can draw a conclusion that the experimental thermolysis of five nitrates is only unimolecular homolytical cleavage of the O–NO₂ bonds.     

The first asymmetric addition of organogallium to aldehydes catalyzed by chiral titanium catalysts

The addition of organogallium to aldehydes was realized with titanium tetrachloride as a Lewis acid catalyst. For the first time, the catalytic asymmetric addition of organogallium to aldehydes was investigated with chiral titanium complexes, which were formed from titanium tetrachloride and salan ligands, with mediocre to good chemical yields and enantioselectivities.     

Highly efficient NMR enantiodiscrimination of 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane,a chiral degradation product of sevoflurane,by heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin

The molecular basis of the efficient enantiodiscrimination of 1,1,1,3,3-pentafluoro-2-(fluoromethoxy)-3-methoxypropane, a chiral degradation product of the inhalation anaesthetic sevoflurane, using heptakis(2,3-di-O-acetyl-6-O-tert-butyldimethylsilyl)-β-cyclodextrin as chiral selector, has been investigated by NMR spectroscopy. An interaction mechanism is proposed, which highlights the role of the functional groups on the β-cyclodextrin rims in addition to a partial molecular inclusion.     

Total synthesis of (+)-(S)-angustureine and the determination of the absolute configuration of the natural product angustureine

Angustureine, isolated from the bark of Galipea officinalis Hancock, is a novel quinoline alkaloid with a n-pentyl side chain at the 2-position. The total synthesis of (+)-(S)-angustureine and a determination of the absolute configuration of the natural product angustureine were achieved using ring-closing metathesis (RCM) and the Mitsunobu reaction as key steps.     

An X-ray photoelectron spectroscopic study of some copper(II) tetraaza complexes

A selected series of copper(II) tetraaza complexes, involving open-chain and macrocyclic ligands, has been studied by X-ray photoelectron spectroscopy. The binding energy data obtained are interpreted in terms of the structures of these complexes with particular reference to the existence of π-electron delocalisation over metal and ligand, peripheral ring substituents, cation-anion interaction and hydration water. It is apparent that the degree of cation-anion interaction and photoreduction is a function of the existing experimental conditions.     

Determination of the relative quantum yields of the conformational species of autoassociating polypeptide gramicidin A in organic solvent using combined fluorescence spectroscopy and high performance liquid chromatography

A simple, novel method is proposed for the accurate determination of the relative quantum yields of each of the interconverting conformational species of the autoassociating polypeptide gramicidin A in organic solution. The method is based on fitting the experimental results obtained independently from fluorescence emission spectroscopy and high performance liquid chromatography. The fluorescence parameters obtained are discussed in terms of the structural features of the individual conformational species. The advantages of this approach and its possible application to other different organic solvents or to other autoassociating polypeptides are also considered.     

Observation by neutron incoherent inelastic spectroscopy of split higher harmonics of the ammonium ion librational mode in the cubic phase of NH4Br

This paper deals with high-resolution neutron scattering studies of the librational mode v₆ (0 → 1) and its higher overtones for NH⁺₄ in the ordered cubic phase of ammonium bromide, NH₄Br. Experiments were conducted on the time-focused crystal analyser (TFXA) spectrometer of the UK spallation neutron source, ISIS. v₆ (0 → 2) and v₆ (0 → 3) show distinct splittings of ≈ 5 meV, the results are compared with optical data and a theoretical model.     

Solvent effect in an “isolated” solvated molecule in a free jet: Intramolecular charge-transfer state of solvated 9,9'-bianthryl

The fluorescence spectra of bare and solvated 9,9'-bianthryl were recorded in a free Jet. In the case of bare bianthryl, only the fluorescence from the locally excited (LE) state was observed, even on excitation to a high vibronic state. In contrast, the excitation of the 0-0 band of 9,9'-bianthryl solvated by acetone gave fluorescence from the charge-transfer (CT) state. The ratio of the intensity of the CT fluorescence to that of the LE fluorescence increases with increasing degree of solvation. Solvation by cyclohexane did not give CT fluorescence.     

Analysis of thermal reactions of photochromic species in glassy matrices based on the concept of dispersive processes

Thermal decoloration reactions of photochromic spiroindolinonaphthoxazine in glassy polymer matrices have been studied. The non-exponential kinetic behaviour in these systems was analyzed using the phenomenological equation with an exp(-t^α) dependency describing dispersive processes in glassy solids. The dispersive parameter α represents the molecular environmental characteristics of matrix polymers.