An in situ time-dependent study of the photodimerisation of chloro-derivatives of trans-cinnamic acid using infrared microspectroscopy with a synchrotron radiation source

The photodimerisation of single crystals of substituted cinnamic acid has been monitored continuously by infrared microscopy using a synchrotron source. The beta-form of 2,4-dichloro-trans-cinnamic acid dimerises under ultraviolet irradiation to form the corresponding beta-truxinic acid derivative in a reaction which follows strictly first order kinetics. By contrast the corresponding reactions in single crystals of beta-2-chloro-trans-cinnamic acid and beta-4-chloro-trans-cinnamic acid deviate somewhat from first order kinetics as a result of solid-state effects. In all three cases the reactions proceed smoothly from monomer to dimer with no hint of any reaction intermediate.

Higher oxides of chlorine: absorption cross-sections of Cl2O6 and Cl2O4, the decomposition of Cl2O6, and the reactions of OClO with O and O-3

The absorption cross-sections of Cl2O6 and Cl2O4 have been obtained using a fast flow reactor with a diode array spectrometer (DAS) detection system. The absorption cross-sections at the wavelengths of maximum absorption (lambda(max)) determined in this study are those of Cl2O6: (1.47 +/- 0.15) x 10(-17) cm(2) molecule(-1), at lambda(max) = 276 nm and T = 298 K; and Cl2O4: (9.0 +/- 2.0) x 10(-19) cm(2) molecule(-1), at lambda(max) = 234 nm and T = 298 K. Errors quoted are two standard deviations together with estimates of the systematic error. The shapes of the absorption spectra were obtained over the wavelength range 200-450 nm for Cl2O6 and 200-350 nm for Cl2O4, and were normalized to the absolute cross-sections obtained at lambda(max) for each oxide, and are presented at 1 nm intervals. These data are discussed in relation to previous measurements. The reaction of O with OCIO has been investigated with the objective of observing transient spectroscopic absorptions. A transient absorption was seen, and the possibility is explored of identifying the species with the elusive sym-ClO3 or ClO4, both of which have been characterized in matrices, but not in the gas-phase. The photolysis of OCIO was also re-examined, with emphasis being placed on the products of reaction. UV absorptions attributable to one of the isomers of the ClO dimer, chloryl chloride (ClClO2) were observed; some Cl2O4 was also found at long photolysis times, when much of the ClClO2 had itself been photolysed. We suggest that reports of Cl2O6 formation in previous studies could be a consequence of a mistaken identification. At low temperatures, the photolysis of OCIO leads to the formation of Cl2O3 as a result of the addition of the ClO primary product to OCIO. ClClO2 also appears to be one product of the reaction between O-3 and OCIO, especially when the reaction occurs under explosive conditions. We studied the kinetics of the non-explosive process using a stopped-flow technique, and suggest a value for the room-temperature rate coefficient of (4.6 +/- 0.9) x 10(-19) cm(3) molecule(-1) s(-1) (limit quoted is 2sigma random errors). The photochemical and thermal decomposition of Cl2O6 is described in this paper. For photolysis at k = 254 nm, the removal of Cl2O6 is not accompanied by the build up of any other strong absorber. The implications of the results are either that the photolysis of Cl2O6 produces Cl-2 directly, or that the initial photofragments are converted rapidly to Cl-2. In the thermal decomposition of Cl2O6, Cl2O4 was shown to be a product of reaction, although not necessarily the major one. The kinetics of decomposition were investigated using the stopped-flow technique. At relatively high [OCIO] present in the system, the decay kinetics obeyed a first-order law, with a limiting first-order rate coefficient of 0.002 s(-1). (C) 2004 Elsevier B.V. All rights reserved.

A new route to furanoeremophilane sesquiterpenoids. Synthesis of Senecio metabolites (+/-)-6-hydroxyeuryopsin, (+/-)-1,10-epoxy-6-hydroxyeuryopsin, (+/-)-toluccanolide A and (+/-)-toluccanolide C

A new strategy for the synthesis of sesquiterpenoids of the furanoeremophilane family was developed in which the tricyclic nucleus was assembled in an A + C -> A - C -> A - B - C sequence. The A - C connection was made via coupling of a cyclohexenylmethyl bromide with a stannylfuran under "ligandless" Stille conditions, and the key cyclization which closed ring B was accomplished with complete stereocontrol by intramolecular formylation of a 2-silylfuran in the presence of trimethylsilyl triflate. This route was used to complete the first total syntheses of the furanoeremophilane 6-hydroxyeuryopsin and the eremophilenolides toluccanolide A and toluccanolide C, as well as a formal synthesis of 1,10-epoxy-6-hydroxyeuryopsin.

Oxovanadium(V) complexes of bis(phenolate) ligands with acetylacetone as co-ligand: synthesis, crystal structure, electrochemical and kinetics studies on the oxidation of ascorbic acid

Two vanadium(V) complexes, [VO(L-1)]acac)] (1) and [VO(L-2)(acac)] (2), where H2L1 = N,N-bis(2-hydroxy-3-5-di-tert-butyl-benzyl)propylamine and H2L2 = 2,2'-selenobis(4,6-di-tert-butylphenol), have been synthesized and characterized by elemental analyses, IR, V-51 NMR, both in the solid and in solution, and cyclic voltammetric studies. Single crystal X-ray studies reveal that in complex 1 the vanadium atom is octahedrally coordinated with an O5N donor environment, where the oxygen atom of the V-V=O moiety and the N atom of the ONO ligand occupy the axial sites while two oxygen atoms (O1 and O2) from the bisphenolate ligand and two oxygen atoms (O3 and O4) from the acac ligand occupy the equatorial plane. A similar bonding pattern has also been encountered for 2 with the exception that a Se atom instead of N is involved in weak bonding to the metal center. Both complexes showed reversible cyclic voltammeric responses and E-1/2 appears at -0.18 and 0.10 V versus NHE for complexes 1 and 2, respectively. The kinetics of oxidation of ascorbic acid by complex 1 were carried out in 50% MeCN-50% HO (v/v) at 25 degrees C. The high formation constant value, Q = 63 +/- 7 M-1, reveals that the reaction proceeds through the rapid formation of a H-bonded intermediate. The low k(2)Q(2)/k(1)Q(1) ratio (13.4) for 1 points out that there is extensive H-bonding between the oxygen atom of the V-V=O group and the OH group of ascorbic acid. (c) 2007 Published by Elsevier Ltd.

Facile strategies for the synthesis and crystallization of linear trinuclear nickel(II)-Schiff base, complexes with carboxylate bridges: Tuning of coordination geometry and magnetic properties

Three new linear trinuclear nickel(II) complexes, [Ni-3(salpen)(2)(OAc)(2)(H2O)(2)]center dot 4H(2)O (1) (OAc = acetate, CH3COO-), [Ni-3(salpen)(2)(OBz)(2)] (2) (OBz=benzoate, PhCOO-) and [Ni-3(salpen)(2)(OCn)(2)(CH3CN)(2)] (4) (OCn = cinnamate, PhCH=CHCOO-), H(2)salpen = tetradentate ligand, N,N'-bis(salicylidene)-1,3-pentanediamine have been synthesized and characterized structurally and magnetically. The choice of solvent for growing single crystal was made by inspecting the morphology of the initially obtained solids with the help of SEM study. The magnetic properties of a closely related complex, [Ni-3(salpen)(2)(OPh)(2)(EtOH)] (3) (OPh = phenyl acetate, PhCH2COO-) whose structure and solution properties have been reported recently, has also been studied here. The structural analyses reveal that both phenoxo and carboxylate bridging are present in all the complexes and the three Ni(II) atoms remain in linear disposition. Although the Schiff base ligand and the syn-syn bridging bidentate mode of the carboxylate group remain the same in complexes 1-4, the change of alkyl/aryl group of the carboxylates brings about systematic variations between six- and five-coordination in the geometry of the terminal Ni(II) centres of the trinuclear units. The steric demand as well as hydrophobic nature of the alkyl/aryl group of the carboxylate is found to play a crucial role in the tuning of the geometry. Variable-temperature (2-300 K) magnetic susceptibility measurements show that complexes 1-4 are antiferromagnetically coupled (J = -3.2(1), -4.6(1). -3.2(1) and -2.8(1) cm(-1) in 1-4, respectively). Calculations of the zero-field splitting parameter indicate that the values of D for complexes 1-4 are in the high range (D = +9.1(2), +14.2(2), +9.8(2) and +8.6(1) cm(-1) for 1-4, respectively). The highest D value of +14.2(2) and +9.8(2) cm(-1) for complexes 2 and 3, respectively, are consistent with the pentacoordinated geometry of the two terminal nickel(II) ions in 2 and one terminal nickel(II) ion in 3. (C) 2009 Elsevier Ltd. All rights reserved.

The thermal transformations of bicyclopropylidene and methylenespiropentane revisited

The overall and the individual rate constants of the unimolecular thermal isomerization of methylenespiropentane (4) to 1,2- and 1,3-dimethylenecyclobutanes (7 and 8) have been determined to be lg (k(-4)/s(-1)) = (13.78 +/- 0.06) - (49.7 +/- 0.2) kcal mol(-1)/RT.ln 10, lg(k(7)/s(-1)) = (13.03 +/- 0.19) - (48.0 +/- 0.6) kcal mol(-1)/RT.ln 10 and lg(k(8)/s(-1)) = (14.15 +/- 0.19) - (52.4 +/- 0.5) kcal mol(-1)/RT.ln 10, respectively. The activation energies are significantly lower than that for the rearrangement of the parent spiropentane. ((c) Wiley-VCH Verlag GmbH & Co.

Wheat glutenin proteins assemble into a nanostructure with unusual structural features

The proteins of wheat have a known propensity to aggregate into a variety of forms. We report here a novel nanostructure from wheat proteins, derived from a crude extract of high molecular weight glutenins. The structure was characterised by a significant thioflavin T (ThT) fluorescence and a fibrillar morphology by transmission electron microscopy (TEM). The ThT fluorescence and TEM data are suggestive of an amyloid structure, but the X-ray fibre diffraction data show a reflection pattern (4.02, 4.2-4.3, 4.6, 12.9,19.3 and 38.7 angstrom) inconsistent with both the classic amyloid form and the previously described beta-helix structure. The 4.6 angstrom reflection is consistent with that predicted for the amyloid inter-beta-strand, and the absence of the inter-beta-sheet distance at approximate to 10-11 angstrom is not unprecedented in amyloid-like structures. However, our observed X-ray reflection pattern has not been previously reported and suggests a novel wheat glutenin nanostructure. (C) 2008 Elsevier Ltd. All rights reserved.

Comparative analysis of four beta-galactosidases from Bifidobacterium bifidum NCIMB41171: purification and biochemical characterisation

Four different beta-galactosidases (previously named BbgI, BbgII, BbgIII and BbgIV) from Bifidobacterium bifidum NCIMB41171 were overexpressed in Escherichia coli, purified to homogeneity and their biochemical properties and substrate preferences comparatively analysed. BbgI was forming a hexameric protein complex of 875 kDa, whereas BbgII, BbgIII and BbgIV were dimers with native molecular masses of 178, 351 and 248 kDa, respectively. BbgII was the only enzyme that preferred acidic conditions for optimal activity (pH 5.4-5.8), whereas the other three exhibited optima in more neutral pH ranges (pH 6.4-6.8). Na+ and/or K+ ions were prerequisite for BbgI and BbgIV activity in Bis-Tris-buffered solutions, whereas Mg++ was strongly activating them in phosphate-buffered solutions. BbgII and BbgIII were slightly influenced from the presence or absence of cations, with Mg++, Mn++ and Ca++ ions exerting the most positive effect. Determination of the specificity constants (k(cat)/K-m) clearly indicated that BbgI (6.11 x 10(4) s(-1) M-1), BbgIII (2.36 x 10(4) s(-1) M-1) and especially BbgIV (4.01 x 10(5) s(-1) M-1) are highly specialised in the hydrolysis of lactose, whereas BbgII is more specific for beta-D-(1 -> 6) galactobiose (5.59 x 10(4) s(-1) M-1) than lactose (1.48 x 10(3) s(-1) M-1). Activity measurements towards other substrates (e. g. beta-D-(1 -> 6) galactobiose, beta-D-(1 -> 4) galactobiose, beta-D-(1 -> 4) galactosyllactose, N-acetyllactosamine, etc.) indicated that the beta-galactosidases were complementary to each other by hydrolysing different substrates and thus contributing in a different way to the bacterial physiology.

The production, purification and characterisation of two novel alpha-D-mannosidases from Aspergillus phoenicis

1,6-alpha-D-Mannosidase from Aspergillits phoenicis was purified by anion-exchange chromatography, chromatofocussing and size-exclusion chromatography. The apparent molecular weight was 74 kDa by SDS-PAGE and 81 kDa by native-PAGE. The isoelectric point was 4.6. 1,6-alpha-D-Mannosidase had a temperature optimum of 60 degrees C, a pH optimum of 4.0-4.5. a K-m of 14 mM with alpha-D-Manp-(1 -> 6)-D-Manp as substrate. It was strongly inhibited by Mn2+ and did not need Ca2+ or any other metal cofactor of those tested. The enzyme cleaves specifically (1 -> 6)-linked mannobiose and has no activity towards any other linkages, p-nitrophenyl-alpha-D-mannopyranoside or baker's yeast mannan. 1,3(1,6)-alpha-D-Mannosidase from A. phoenicis was purified by anion-exchange chromatography, chromatofocus sing and size-exclusion chromatography. The apparent molecular weight was 97 kDa by SDS-PAGE and 110 kDa by native-PAGE. The 1,3(1,6)-alpha-D-mannosidase enzyme existed as two charge isomers or isoforms. The isoelectric points of these were 4.3 and 4.8 by isoelectric focussing. It cleaves alpha-D-Manp-(1 -> 3)-D-Manp 10 times faster than alpha-D-Manp-(1 -> 6)-D-Manp, has very low activity towards p-nitrophenyl-alpha-D-mannopyranoside and baker's yeast mannan, and no activity towards alpha-D-Manp-(1 -> 2)-D-Manp. The activity towards (1 -> 3)-linked mannobiose is strongly activated by 1 mM Ca2+ and inhibited by 10 mM EDTA, while (1 -> 6)-activity is unaffected, indicating that the two activities may be associated with different polypeptides. It is also possible that one polypeptide may have two active sites catalysing distinct activities. (c) 2005 Elsevier Ltd. All rights reserved.

A question of identity - wiring in the human

This paper discusses the RFID implants for identification via a sensor network. Brain-computer implants linked in to a wireless network. Biometric identification via body sensors is also discussed. The use of a network as a means for remote and distance monitoring of humans opens up a range of potential uses. Where implanted identification is concerned this immediately offers high security access to specific areas by means of only an RFID device. If a neural implant is employed then clearly the information exchanged with a network can take on a much richer form, allowing for identification and response to an individual's needs based on the signals apparent on their nervous system.

Communicating neurons: a connectionist spiking neuron implementation of stochastic diffusion search

An information processing paradigm in the brain is proposed, instantiated in an artificial neural network using biologically motivated temporal encoding. The network will locate within the external world stimulus, the target memory, defined by a specific pattern of micro-features. The proposed network is robust and efficient. Akin in operation to the swarm intelligence paradigm, stochastic diffusion search, it will find the best-fit to the memory with linear time complexity. information multiplexing enables neurons to process knowledge as 'tokens' rather than 'types'. The network illustrates possible emergence of cognitive processing from low level interactions such as memory retrieval based on partial matching. (C) 2007 Elsevier B.V. All rights reserved.

Regioselective Beckmann rearrangements of furanoside and pyranoside-derived oximes

The Beckmann rearrangement is a useful reaction employed to provide access to amides from oxime substrates. Applied to cyclic structures, the Beckmann rearrangement leads to ring expansion and allows access to cyclic lactams. Our investigations focused upon the synthesis of glycoside-derived lactams from oxime precursors. In probing a range of conditions, we observed that 2,4,6-trichloro[1,3,5]triazine (TCT) was an effective and mild promoter of the rearrangement affording pyrano- and heptanoside lactam products with excellent regioselectivities.

Thermal decomposition of potassium hexanitronickelate(II) hydrate

The thermal decomposition of the complex K-4[Ni(NO2)6]center dot H2O has been investigated over the temperature range 25-600 degrees C by a combination of infrared spectroscopy, powder X-ray diffraction, FAB-mass spectrometry and elemental analysis. The first stage of reaction is loss of water and isomerisation of one of the coordinated nitro groups to form the complex K-4 [Ni(NO2)(4) (ONO)]center dot NO2. At temperatures around 200 degrees C the remaining nitro groups within the complex isomerise to the chelating nitrite form and this process acts as a precursor to the loss of NO2 gas at temperatures above 270 degrees C. The product, which is stable up to 600 degrees C, is the complex K-4[Ni(ONO)(4)]center dot NO2, where the nickel atom is formally in the +1 oxidation state. (c) 2005 Elsevier B.V. All rights reserved.

Water adsorption on O-covered Ru{0001}: coverage-dependent change from dissociation to molecular adsorption

When water is coadsorbed with oxygen at coverages above 0.25ML an intact water species is observed in high resolution X-ray photoelectron spectroscopy up to 220 K, which is significantly more stable than intact water on the clean surface. The presence of this species causes a shift in the O 1s binding energy of the pre-adsorbed oxygen, which indicates the formation of hydrogen bonds between the two adsorbates. Low coverages of oxygen induce partial dissociation and recombinative desorption in the same temperature range, which illustrates that desorption temperatures alone cannot be used to determine whether water is molecularly intact or not.

Dimetallic complexes of macrocycles with two rigid dibenzofuran units as receptors for detection of anionic substrates

The hexaazamacrocycles [28](DBF)2N6 {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminoethyleneiminoethylene]} and [32](DBF)2N6 {cyclo[bis(4,6-dimethyldibenzo[b,d]furaniminopropyleneiminopropylene]} form stable dinuclear copper(II) complexes suitable to behave as receptors for several anionic substrates. These two receptors were used to study the binding interactions with several substrates, such as imidazole (Him) and some carboxylates [benzoate (bz−), oxalate (ox2−), malonate (mal2−), phthalate (ph2−), isophthalate (iph2−), and terephthalate (tph2−)] by spectrophotometric titrations and EPR spectroscopy in MeOH (or H2O):DMSO (1:1 v/v) solution. The largest association constant was found for ox2− with Cu2[32](DBF)2N64+, whereas for the aromatic dicarboxylate anions the binding constants follow the trend ph2− > iph2− > tph2−, i.e. decrease with the increase of the distance of the two binding sites of the substrate. On the other hand, the large blue shift of 68 nm observed by addition of Him to Cu2[32](DBF)2N64+ points out for the formation of the bridged CuimCu cascade complex, indicating this receptor as a potential sensor for the detection and determination of imidazole in solution. The X-band EPR spectra of the Cu2[28](DBF)2N64+ and Cu2[32](DBF)2N6]4+ complexes and the cascade complexes with the substrates, performed in H2O:DMSO (1:1 v/v) at 5 to 15 K, showed that the CuCu distance is slightly larger than the one found in crystal state and that this distance increases when the substrate is accommodated between the two copper centres. The crystal structure of [Cu2[28](DBF)2N6(ph)2]·CH3OH was determined by X-ray diffraction and revealed the two copper centres bridged by two ph2− anions at a Cu···Cu distance of 5.419(1) Å. Each copper centre is surrounded by three carboxylate oxygen atoms from two phthalate anions and three contiguous nitrogen atoms of the macrocycle in a pseudo octahedral coordination environment.