Synthesis of four-armed poly(epsilon-caprolactone)-block-poly(ethylene oxide) by diethylzinc catalyst

Biodegradable, amphiphilic, four-armed poly(epsilon-caprolactone)-block-poly(ethylene oxide) (PCL-b-PEO) copolymers were synthesized by ring-opening polymerization of ethylene oxide in the presence of four-armed poly(epsilon-caprolactone) (PCL) with terminal OH groups with diethylzinc (ZnEt2) as a catalyst. The chemical structure of PCL-b-PEO copolymer was confirmed by H-1 NMR and C-13 NMR. The hydroxyl end groups of the four-armed PC L were successfully substituted by PEO blocks in the copolymer. The monomodal profile of molecular weight distribution by gel permeation chromatography provided further evidence for the four-armed architecture of the copolymer. Physicochemical properties of the four-armed block copolymers differed from their starting four-armed PCL precursor. The melting points were between those of PCL precursor and linear poly(ethylene glycol). The length of the outer PEO blocks exhibited an obvious effect on the crystallizability of the block copolymer. The degree of swelling of the four-armed block copolymer increased with PEO length and PEO content.

Heptaaquatetra-mu(3)-hydroxy-hexa-mu(2)-L-leucine-(L-leucine)tetraytterbium(III) tetrachlorozinc(II) trichlorohydroxyzinc(II) tetrachloride octahydrate

The title bimetallic compound, [Yb-4(mu(3)-OH)(4)(C6H13NO2)(7)-(H2O)(7)][ZnCl4][ZnCl3(OH)]Cl-4.8H(2)O, was synthesized at near physiological pH (6.0). The compound exhibits some novel structural features, including an asymmetric [Yb-4(mu(3)-OH)(4)(L-leucine)(7)(H2O)(7)](8+) complex cation in which four OH groups act as bridging ligands, linking four Yb3+ cations into a Yb4O4 structural unit. Each pair of adjacent Yb3+ ions is further bridged by one carboxy group from a leucine ligand. Water molecules and a monodentate leucine ligand also coordinate to Yb3+ ions, completing their eight-coordinate square-antiprismatic coordination. The Yb-4(mu(3)-OH)(4)(L-leucine)(7)(H2O)(7)](8+) cation, the [ZnCl4](2-), [ZnCl3OH](2-) and Cl- anions, and the lattice water molecules are linked via hydrogen bonds.

Study of the effect of hydrogen bonding on the phase behaviour of p-nitro azobenzene derivatives with hydrophilic tails

The infrared spect ra of N-n-(4-nitrophenyl)azophenyloxyalkyldiethanolamines (Cn) are examined in the range of 4000-400 cm(-1) at different temperatures and the assignment of the fundamental vibrations given. Based on (1) the localization of the broad absorption band at 3456 cm(-1), and (2) attribution of the associated OH bands centred at 1410-1390, 1100, and 650-634 cm(-1) to, respectively delta OH deformation, nu C-O stretching and gamma OH out-of-plane bending, intermolecular hydrogen bonding between OH groups in the crystalline, liquid crystalline and isotropic states is proposed. By considering the results of FTIR, WAXD and DSC measurements, the molecular arrangement of C10 in its smectic A phase as consisting of hydrogen bonding and strong interaction between dipolar groups (NO,) is proposed. This may explain the high stability and high orientational ordering property of Cn compounds in the liquid crystalline state compared with that of n-bromo-1-[4-(4-nitrophenyl)azophenyl]oxyalkanes (Bn).

Programmed cell death in Laminaria japonica (Phaeophyta) tissues infected with alginic acid decomposing bacterium

TdT-mediated dUTP-biotin nick end labeling (TUNEL) is a sensitive and valid method for detecting DNA cleavage in programmed cell death (PCD). Using this method, DNA cleavage was observed in Laminaria japonica sporophytic tissues, which were infected with alginic acid decomposing bacterium. It was found that DNA cleavage occurred 5 min after the infection, the fragments with 3'-OH groups of cleaved nuclear DNA increased with time of infection and spread from the infection site. Although no typical DNA ladder (200 bp/ 180 bp) was detected by routine agarose gel electrophoresis, the cleavage of nuclear DNA fragments of 97 similar to 48.5 kb could be detected by pulsed field gel electrophoresis (PFGE). By using CaspGLOW(TM) fluorescein active caspase-3 staining method, caspase-3 activity has been detected in response to the infection of alginic acid decomposing bacterium. Our results are similar to the observations in hypersensitive response (HR) of higher plant, suggesting that the rapid cell death of L. japonica infected by alginic acid decomposing bacterium might be involved in PCD, and indicating that the occurrence of PCD is an active defense process against the pathogen's infection.

New route for light olefins production from chloromethane over HSAPO-34 molecular sieve

HSAPO-34 molecular sieve was employed in chloromethane conversion and showed high performance in activity and selectivity in production of light olefins. Our detailed IR investigation allowed the identification of the active sites and the adsorbed species and demonstrated that the conversion started from 350 degrees C with alkoxy group as the intermediate. The fixed-bed catalytic testing evidenced that in the range of 350-500 degrees C, 70-80% of chloromethane was transferred to ethylene, propylene and butenes. Increasing reaction temperature favors the conversion and enhances the yield of lighter olefins. A very important reversible phenomenon, the breaking of Al-O-P bonds upon adsorption of HCl, a main product of reaction to generate a large amount of P-OH groups and the recovery of Al-O-P upon removal of HCI was revealed. (c) 2005 Elsevier B.V. All rights reserved.

Soil differentiation using fingerprint Fourier transform infrared spectroscopy, chemometrics and genetic algorithm-based feature selection

Elliott, G. N., Worgan, H., Broadhurst, D. I., Draper, J. H., Scullion, J. (2007). Soil differentiation using fingerprint Fourier transform infrared spectroscopy, chemometrics and genetic algorithm-based feature selection. Soil Biology & Biochemistry, 39 (11), 2888-2896. Sponsorship: BBSRC / NERC RAE2008

Catalytic Water Formation on Platinum: A First-Principles Study

The study of catalytic behavior begins with one seemingly simple process, namely the hydrogenation of O to H2O on platinum. Despite the apparent simplicity its mechanism has been much debated. We have used density functional theory with,gradient corrections to examine microscopic reaction pathways for several elementary steps implicated in this fundamental catalytic process. We find that H2O formation from chemisorbed O and H atoms is a highly activated process. The largest barrier along this route, with a value of similar to1 eV, is the addition of the first H to O to produce OH. Once formed, however, OH groups are easily hydrogenated to H2O with a barrier of similar to0.2 eV. Disproportionation reactions with 1:1 and 2:1 stoichiometries of H2O and O have been examined as alternative routes for OH formation. Both stoichiometries of reaction produce OH groups with barriers that are much lower than that associated with the O + H reaction. H2O, therefore, acts as an autocatalyst in the overall H O formation process. Disproportionation with a 2:1 stoichiometry is thermodynamically and kinetically favored over disproportionation with a l:I stoichiometry. This highlights an additional (promotional) role of the second H2O molecule in this process. In support of our previous suggestion that the key intermediate in the low-temperature H2O formation reaction is a mixed OH and H2O overlayer we find that then is a very large barrier for the dissociation of the second H2O molecule in the 2:1 disproportionation process. We suggest that the proposed intermediate is then hydrogenated to H2O through a very facile proton transfer mechanism.

Identifying an O-2 supply pathway in CO oxidation on Au/TiO2(110): A density functional theory study on the intrinsic role of water

Au catalysis has been one of the hottest topics in chemistry in the last 10 years or so. How O-2 is supplied and what role water plays in CO oxidation are the two challenging issues in the field at the moment. In this study, using density functional theory we show that these two issues are in fact related to each other. The following observations are revealed: (i) water that can dissociate readily into OH groups can facilitate O-2 adsorption on TiO2; (ii) the effect of OH group on the O-2 adsorption is surprisingly long-ranged; and (iii) O-2 can also diffuse along the channel of Ti (5c) atoms on TiO2(1 10), and this may well be the rate-limiting step for the CO oxidation. We provide direct evidence that O-2 is supplied by O-2 adsorption on TiO2 in the presence of OH and can diffuse to the interface of Au/TiO2 to participate in CO oxidation. Furthermore, the physical origin of the water effects on Au catalysis has been identified by electronic structure analyses: There is a charge transfer from TiO2 in the presence of OH to O-2, and the O-2 adsorption energy depends linearly on the 02 charge. These results are of importance to understand water effects in general in heterogeneous catalysis.

A density functional theory study of hydroxyl and the intermediate in the water formation reaction on Pt

Density functional theory has been used to study the adsorption of hydroxyl at low and high coverages and also to investigate the nature of the intermediate in the H2O formation reaction on Pt(111). At low coverages [1/9 of a monolayer (ML) to 1/3 ML] OH binds preferentially at bridge and top sites with a chemisorption energy of similar to2.25 eV. At high coverages (1/2 ML to 1 ML) H bonding between adjacent hydroxyls causes: (i) an enhancement in OH chemisorption energy by about 15%; (ii) a strong preference for OH adsorption at top sites; and (iii) the formation of OH networks. The activation energy for the diffusion of isolated OH groups along close packed rows of Pt atoms is 0.1 eV. This low barrier coupled with H bonding between neighboring OH groups indicates that hydroxyls are susceptible to island formation at low coverages. Pure OH as well as coadsorbed OH and H can be ruled out as the observed low temperature intermediate in the water formation reaction. Instead we suggest that the intermediate consists of a mixed OH+H2O overlayer with a macroscopic surface coverage of 3/4 ML in a 2:1 ratio of OH and H2O. (C) 2001 American Institute of Physics.

Preparation of new materials by heterogeneous modification of cellulose

O presente trabalho teve como principal objectivo estudar a modificação química heterogénea controlada de fibras de celulose com diferentes reagentes de modo a alterar as suas propriedades de superfície, em especial em termos da criação de um carácter hidrofóbico e lipofóbico, preservando, sempre que possível, as suas propriedades mecânicas e, consequentemente, abrindo novas perspectivas de aplicação. O desenvolvimento do trabalho envolveu três abordagens principais, envolvendo, em cada caso, o estudo de diferentes condições reaccionais. Na primeira abordagem foram utilizados como reagentes de modificação compostos perfluorados, nomeadamente o anidrido trifluoroacético (TFAA), o cloreto de 2,3,4,5,6-pentafluorobenzoílo (PFBz) e o cloreto de 3,3,3- trifluoropropanoílo (TFP), para promover a acilação heterogénea da superfície das fibras. A segunda estratégia usada consistiu na preparação de híbridos de celulose do tipo orgânico-inorgânico classe-II, através da modificação das fibras de celulose com o (3-isocianatopropil)trietoxissilano (ICPTEOS), um reagente organossilano bifuncional. A ligação às fibras de celulose foi efectuada através das funções isocianato e, posteriormente, os grupos etoxissilano foram sujeitos a tratamentos de hidrólise ácida, como tal ou na presença de outros siloxanos, nomeadamente o tetraetoxissilano (TEOS) e o 1H,1H,2H,2Hperfluorodeciltrietoxissilano (PFDTEOS). Finalmente, a última abordagem foi baseada na modificação das fibras com triclorometilssilano (TCMS), através de uma reacção gás-sólido, que dispensou assim o uso de solventes orgânicos. A ocorrência de modificação química foi em cada caso confirmada por Espectroscopia de Infravermelho com Transformada de Fourier e Reflectância Total Atenuada (FTIR-ATR), Análise Elementar (EA) e determinação de ângulos de contacto. Adicionalmente, e dependendo de cada caso específico, diversas outras técnicas foram empregues na caracterização aprofundada dos materiais preparados, nomeadamente Ressonância Magnética Nuclear CPMAS no Estado Sólido (RMN), Espectroscopia de Difracção de Raios-X (XRD), Análise Termogravimétrica (TGA), Espectrometria de Massa de Iões Secundários com Análise de Tempo de Vôo (ToF-SIMS), Espectroscopia Fotoelectrónica de Raios-X (XPS) e Microscopia Electrónica de Varrimento (SEM). Relativamente à acilação das fibras de celulose com reagentes perfluorados, o sucesso da reacção foi comprovado por FTIR-ATR, EA, XPS e ToF-SIMS. Neste contexto, obtiveram-se fibras modificadas possuindo graus de substituição (DS) compreendidos entre 0.006 e 0.39. Verificou-se por XRD que, em geral, mesmo para os valores de DS mais elevados, a cristalinidade das fibras não foi afectada, indicando que a modificação foi limitada às camadas mais superficiais das mesmas ou a regiões amorfas das suas camadas mais internas. Adicionalmente, observou-se por ToF-SIMS que a distribuição dos grupos perfluorados à superfície das fibras foi, de facto, bastante heterogénea. Todos os derivados de celulose perfluorados apresentaram elevada hidrofobicidade e lipofobicidade, tendo-se atingido ângulos de contacto com água e diiodometano de 126º e 104º, respectivamente. Um aspecto interessante relativo a estes materiais é que a elevada omnifobicidade foi observada mesmo para valores de DS muito reduzidos, não se mostrando significativamente afectada pelo aumento dos mesmos. Em consonância, verificou-se por XPS que a cobertura da superfície das fibras de celulose com grupos perfluorados aumentou apenas ligeiramente com o aumento do DS, apontando para a esterificação de camadas mais internas das fibras, associada, neste caso, predominantemente aos seus domínios amorfos. No que diz respeito à estabilidade hidrolítica destes derivados, obtiveram-se dois tipos distintos de comportamento. Por um lado, as fibras de celulose trifluoroacetiladas são facilmente hidrolisáveis em meio neutro, e, por outro, as fibras pentafluorobenzoiladas e trifluoropropanoiladas mostram-se bastante resistentes face a condições de hidrólise em meio neutro e ácido (pH 4), podendo, contudo, ser facilmente hidrolisadas em meio alcalino (pH 9 e 12, para derivados do PFBz e do TFP, respectivamente). Na segunda abordagem verificou-se a ocorrência de reacção por FTIR-ATR e EA. Em geral, a modificação química com ICPTEOS ocorre predominantemente nas zonas mais superficiais das fibras de celulose ou em regiões amorfas. Contudo, em condições reaccionais mais severas (maior quantidade de reagente e tempo de reacção), esta atingiu também regiões cristalinas, afectando, consequentemente, a estrutura cristalina das fibras, como verificado por XRD. Por RMN de 29Si observou-se que após reacção com o ICPTEOS já existiam indícios de alguma hidrólise dos grupos etoxissilano, e que a sua subsequente condensação parcial tinha levado à formação de uma película inorgânica em redor das fibras (verificado por SEM), constituída maioritariamente por estruturas lineares, com uma contribuição mais modesta de estruturas “diméricas” e outras mais ramificadas. Consequentemente, este revestimento inorgânico transformou as fibras de celulose em materiais híbridos com elevada hidrofobicidade (ângulos de contacto com água entre 103-129º). A hidrólise ácida dos restantes grupos etoxissilano, como tal ou na presença de TEOS, originou híbridos de celulose com elevada hidrofilicidade, sendo impossível medirem-se os ângulos de contacto com água dos produtos finais, devido à presença maioritária de grupos silanol (Si-OH) e ligações Si-O-Si à superfície, os quais contribuíram para o consequente aumento de energia de superfície. No entanto, quando a hidrólise foi realizada na presença de PFDTEOS, obtiveram-se materiais híbridos com elevada hidrofobicidade e lipofobicidade (ângulos de contacto com água e diiodometano de 140º e 134º, respectivamente), devido à combinação da presença de grupos perfluorados e micro- e nano-rugosidades na superfície das fibras de celulose, conforme confirmado por SEM. Finalmente, a última abordagem permitiu preparar materiais derivados de celulose altamente hidrofóbicos e lipofóbicos (ângulos de contacto com água e diiodometano de 136º e 109º, respectivamente) por um processo simples, envolvendo tempos de tratamento tão curtos como 0.5 min. Este comportamento omnifóbico foi gerado pelo efeito sinergético entre a diminuição de energia de superfície das fibras, devido à presença de grupos metilo dos resíduos de TCMS ligados a estas, e a condensação dos resíduos de TCMS na forma de micro- e nano-partículas inorgânicas, que levou à criação de um revestimento rugoso à superfície das fibras, conforme observado por RMN de 29Si e SEM, respectivamente. A pré-humidificação das fibras de celulose demonstrou desempenhar um importante papel de “acelerador” dos processos de hidrólise e condensação das moléculas de TCMS. Nestas condições, o tempo de tratamento foi um dos parâmetros mais relevantes, pois para tempos de tratamento muito curtos (0.5 min) os materiais resultantes não apresentaram quaisquer diferenças a nível de propriedades físico-químicas em relação ao substrato de partida (a humidade em excesso consumiu todo o TCMS antes que este conseguisse reagir com os grupos hidroxilo das fibras de celulose), possuindo, por exemplo, valores de ângulos de contacto com água idênticos. Para tempos de tratamento mais longos, como 30 min, os materiais finais apresentaram a maior quantidade de componentes inorgânicos, tal como verificado por EA e TGA. Assim, o controlo da humidade das fibras é imperativo para se poder moldar as propriedades finais dos produtos. Esta última abordagem é particularmente promissora uma vez que tem como base um sistema simples e “verde” que pode ser facilmente implementado. Em conclusão, este trabalho permitiu demonstrar que a modificação química heterogénea controlada das fibras de celulose representa uma iniciativa promissora para a preparação de novos materiais obtidos a partir de recursos renováveis, com propriedades interessantes e passíveis de ser potencialmente aplicados em diferentes áreas. Para além do mais, as estratégias de modificação estudadas podem também ser precursoras de novos estudos que possam vir a ser desenvolvidos dentro do mesmo âmbito.

Modified mesoporous MCM-41 as hosts for photochromic spirobenzopyrans

The influence of the chemical composition and silylation of mesoporous MCM-41 materials on the photochromic behaviour of adsorbed spiropyran (BIPS) and 6-nitrospiropyran was studied. Upon incorporation, the spiropyrans underwent ring opening to form either zwitterionic merocyanine or its corresponding O-protonated form. In all silica MCM-41 or in the MCM-41 containing aluminium, the O-protonated merocyanine was predominantly formed. In the case of MCM-41 modified by silylation of the OH groups, a mixture of zwitterionic merocyanine and spiropyran was present. The photochromic response was studied by means of steady-state irradiation and by laser flash photolysis. Steady-state irradiation (λ > 450 nm) of the solid samples gives rise in all cases to an intensity decrease of the absorption bands corresponding to either the protonated or the unprotonated merocyanine form (reverse photochromism). In contrast, laser flash photolysis at 308 nm of spiropyrans supported on silylated MCM-41 allows observation of the photochemical ring opening of residual spiropyran to the corresponding zwitterionic form (normal photochromism).

A study of co-precipitated bimetallic gold catalysts for water-gas shift reaction

Synthesis, testing and characterisation of bimetallic gold, Au-M on ceria as catalysts were carried out for low temperature water-gas shift reaction (WGS). Amongst the entire screened catalysts 3 wt% (AU-Pt)/CeO2 displayed the best WGS activity than the monometallic promotors, giving the light-off curve at the lowest temperature in the range 100-300 degrees C. (Au-Pd)/CeO2 also achieved the same activity but at a higher temperature. It was also found that WGS activity was strongly correlated with the surface reducibility which in turn depended on the modified local electronic band structure of promoted ceria. These results clearly suggest that the key role of bimetallic promoter may involve in facilitating the creation of defective reduced surface by exerting its local electronic effect on ceria to form the surface germinal -OH groups in water which act as active sites for enhanced WGS activity. (C) 2008 Elsevier B.V. All rights reserved.

Aerogel-coated metal nanoparticle colloids as novel entities for the synthesis of defined supported metal catalysts

Nanometer metal particles of tailored size (3-5 nm) and composition prepared via inverse microemulsion were encapsulated by ultrathin coatings (<2.5 nm) of inorganic porous aerogels covered with surface -OH groups. These composite materials formed metastable colloids in solvent(s), and the organic surfactant molecules were subsequently removed without leading to aggregation (the ethanolic colloid solution was shown to be stable against flocculation for at least weeks). We demonstrate that the totally inorganic-based composite colloids, after the removal of surfactant, can be anchored to conventional solid supports (gamma-alumina, carbons) upon mixing. Application of a high temperature resulted in the formation of strong covalent linkages between the colloids and the support because of the condensation of surface groups at the interface. Detailed characterizations (X-ray diffraction (XRD), pore analysis, transmission electron microscopy (TEM), CO chemisorption) and catalytic testing (butane combustion) showed that there was no significant metal aggregation from the fine metal particles individually coated with porous aerogel oxide. Most of these metal sites on the coated nanoparticles with and without support are fully accessible by small molecules hence giving extremely active metal catalysts. Thus, the product and technology described may be suitable to synthesize these precursor entities of defined metal sizes (as inks) for wash coat/impregnation applications in catalysis. The advantages of developing inorganic nanocomposite chemical precursors are also discussed.

Three-centre hydrogen bonds in triphenylphosphine oxide-hydroquinone (1/1)

The title cocrystal, C18H15OP center dot C6H6O2, belongs to a series of molecular systems based on triphenylphosphine P-oxide. The O atom of the oxide group acts as an acceptor for hydrogen bonds from OH groups of two hydroquinone molecules which lie on inversion centres [O center dot center dot center dot O = 2.7451 (17) and 2.681 (2) A S]. The crystal structure is stabilized by weak C-H center dot center dot center dot O hydrogen bonds, forming a C-2(1)(8) chain which runs parallel to the [100] direction.

Global and local expression of chirality in serine on the Cu{110} surface

Establishing a molecular-level understanding of enantioselectivity and chiral resolution at the organic−inorganic interfaces is a key challenge in the field of heterogeneous catalysis. As a model system, we investigate the adsorption geometry of serine on Cu{110} using a combination of low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. The chirality of enantiopure chemisorbed layers, where serine is in its deprotonated (anionic) state, is expressed at three levels: (i) the molecules form dimers whose orientation with respect to the substrate depends on the molecular chirality, (ii) dimers of l- and d-enantiomers aggregate into superstructures with chiral (−1 2; 4 0) lattices, respectively, which are mirror images of each other, and (iii) small islands have elongated shapes with the dominant direction depending on the chirality of the molecules. Dimer and superlattice formation can be explained in terms of intra- and interdimer bonds involving carboxylate, amino, and β−OH groups. The stability of the layers increases with the size of ordered islands. In racemic mixtures, we observe chiral resolution into small ordered enantiopure islands, which appears to be driven by the formation of homochiral dimer subunits and the directionality of interdimer hydrogen bonds. These islands show the same enantiospecific elongated shapes those as in low-coverage enantiopure layers.