Isomerization of 1-pentene catalyzed by Wilkinson's catalyst coordinatively bound to silica

Hydrogen thermodesorption from Co–Ni/Al₂O₃ catalysts has been investigated. Hydrogen sorption on Co/Al₂O₃ catalyst has a strong temperature-activated character. The sorptive capacity of hydrogen, after its preliminary sorption at 900 K, is similar for all catalysts under study.

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Co–Ni/Al₂O₃. Co/Al₂O₃ . , 900 K, .

     

Distribution and accessibility of cyclodextrins covalently bound onto silica gel

Silica gel coated with a layer of β-cyclodextrins is a well investigated system. Earlier literature studies suggest that the coating changes the mesoporous structure of the silica gel and that the coating obtained might be heterogeneous. From surface area measurements it was found that the average pore diameter and accessible pore volume was reduced after grafting with 3-glycidyloxypropyltrimethoxysilane and β-cyclodextrin, but the change was reversible by simple pyrolysis of the organic compounds. To investigate the amount of accessible β-cyclodextrin on the silica particles, a Langmuir adsorption study was used. From the Langmuir binding isotherm it was found that the 8 Anilinonaphtalene-1-sulfonic acid ammonium (1,8 ANS) guest had a much larger stability constant with surface bound β-cyclodextrin compared to that found for free β-cyclodextrin. The accessible amount of β-cyclodextrin was found to be approximately 12% lower than the total amount of β-cyclodextrin indicating that some β-cyclodextrin is inaccessible for complex formation on the silica particles. The distribution of the cyclodextrin on the particle was investigated using the enhanced fluorescence of 1,8 ANS when complexed to β-cyclodextrin using confocal laser scanning microscopy. The confocal images of the particle show that the β-cyclodextrin was positioned on the outer layer of the particle, explained by the difficulty of diffusion of the β-cyclodextrin into the small pores. It was observed that smaller particles (>20 μm) has a more homogeneous distribution of β-CD compared to larger particles where a heterogeneous distribution was observed.     

Surface analysis by X-ray photoelectron spectroscopy of sol-gel silica modified with covalently bound peptides

Chemical surface characterization of biologically modified sol-gel derived silica is critical but somewhat limited. This work demonstrates the ability of x-ray photoelectron spectroscopy (XPS) to characterize the surface chemistry of peptide modified sol-gel thin films based on the example of four different free peptide-silanes, denoted RGD, NID, KDI ,and YIG. The N 1s and C 1s peaks were found to be good fingerprints of the peptides, whereas O 1s overlapped with the signal of substrate oxygen and, therefore, the O 1s peak was not informative in the case of the thin films. The C 1s peak was fitted and the contribution of the residual hydrocarbons was sorted out. The curve-fitting procedure of the C 1s peak accounted for the different chemical states of carbon atoms in the peptide structure. The curve-fitting procedure was validated by analyzing free peptides in the powder form and was then applied to the characterization of the peptide-modified thin films. The XPS measured ratio between nitrogen and carbon for the peptide thin film was similar to the corresponding value calculated from the peptide structures. Angle resolved XPS confirmed the surface nature of peptides in modified thin films. The coverage and thickness of the peptides on the thin film surface depended on the peptide sequence. The coverage was in the range of 10% of a monolayer, and the layer thickness varied from 10 to 30 A. We believe that the different thicknesses and surface coverage are due to the local structure of the peptides, with the RGD and NID peptides taking a globule conformation and the YIG and KDI peptides adopting a more linear structure.     

Linking photo- and redoxactive phthalocyanines covalently to graphene

"Green" graphene: For the first time, the covalent attachment of a light-harvesting and electron-donating phthalocyanine to the basal plane of few-layer graphene is reported. Physicochemical characterizations reveal an ultrafast charge separation from the photoexcited phthalocyanine to few-layer graphene followed by a slower charge recombination.     

Foldamer structuring by covalently bound macromolecules

We used fluorescence and electronic absorption spectroscopy to study the molecular weight dependence of macromolecule-induced folding in a chain-centered meta-phenylene ethynylene (mPE) oligomer. Analogous to the ability of intrinsically unstructured proteins (IUPs) to induce folding of globular proteins in cellular environments, we show that macromolecules attached to both ends of an mPE dodecamer induce the foldamer to collapse into a presumed helical conformation. The collapse is especially prominent once the macromolecule segments become larger than ca. 50 kDa. For sufficiently large macromolecules, the conformational structuring occurs even in solvents that normally denature the foldamer. Based on these findings, chain-centered foldamers might find use as models to investigate the fundamental macromolecular physics of IUPs.     

Oxidation of thiols with molecular oxygen catalyzed by cobalt(II) phthalocyanines in ionic liquid

An efficient procedure for catalyst solubility, recycling and easy product isolation in oxidation of thiols to disulfides with molecular oxygen catalyzed by cobalt(II) phthalocyanines dissolved in ionic liquid at room temperature is reported.     

Preparation and time-gated luminescence bioimaging application of ruthenium complex covalently bound silica nanoparticles

Luminescent ruthenium(II) complex covalently bound silica nanoparticles have been prepared and used as a probe for time-gated luminescence bioimaging. The new nanoparticles were prepared by copolymerization of a luminescent Ru(II) complex tris(5-amino-1,10-phenanthroline)ruthenium(II) conjugated with 3-aminopropyl(triethoxy)silane (APS-Ru conjugate), free (3-aminopropyl)triethoxysilane (APS) and tetraethyl orthosilicate (TEOS) in a water-in-oil reverse microemulsion consisting of Triton X-100, n-octanol, cyclohexane and water in the presence of aqueous ammonia. Characterization by transmission electron microscopy indicates that the nanoparticles are monodisperse, spherical and uniform in size, 64 ± 4 nm in diameter. Compared with the dye-doping nanoparticles, dye leakage of the new nanoparticles was remarkably decreased. In addition, it was found that the Ru(II) complex luminescence could be effectively enhanced with a longer luminescence lifetime (∼2.3 μs) after forming the nanoparticles, which enables the nanoparticles to be suitable as a bioprobe for time-gated luminescence bioimaging applications. The nanoparticle-labeled streptavidin was prepared and successfully used for time-gated luminescence imaging detection of an environmental pathogen, Giardia lamblia, with high specificity and sensitivity.     

A nanometer-ZnO catalyst to enhance the ozonation of 2,4,6-trichlorophenol in water

Removal of 2,4,6-trichlorophenol (TCP) from water has been accomplished through zinc oxide (ZnO) catalytic ozonation. In the presence of ZnO catalyst, aqueous ozone (O₃) can be described by a two-stage behavior, first involving a short-term rapid decomposition followed by a second slow decomposition. The low reaction rate (k_d2) of second stage for O₃-ZnO systems suggested that most of O₃ was transferred into OH radical by ZnO catalyst and was rapidly consumed during the first stage. The combined use of O₃ and ZnO catalyst leads to a conspicuous 99.8% of TCP conversion in 30 min which compares favorably to the hardly 75% reached in the absence of the catalyst. The high reactivity of hydroxyl radicals that were generated by O₃-ZnO during the oxidation process effectively degraded TCP. Without regard to the O₃ dose, the catalytic–oxidation kinetics of the process depends on the concentration of ZnO catalyst and size of ZnO particles. At the same concentration of three different ZnO size in batch tests, TCP degradation rates were in the order of nanometer > submicrometer > micrometer. The effect of pore diffusion on the rate of TCP–ZnO reactions was determined by examination of the effectiveness factor using different particle sizes of ZnO. Calculations show that the rate of TCP decomposition by nano-size ZnO was strongly controlled by surface reaction with little influence of pore diffusion, as indicated by the high effectiveness factors.     

Enhanced photodegradation of 2,4,6-trichlorophenol over palladium phthalocyaninesulfonate modified organobentonite

This article explores a supported photocatalyst of palladium(II) phthalocyaninesulfonate (PdPcS) onto organoclay for removal of 2,4,6-trichlorophenol (TCP) from water under visible light (lambda > or = 450 nm) irradiation. The composite clay was not only a good sorbent for uptake of TCP from water, but it also exhibited notable activity for TCP oxidation via singlet molecular oxygen, generated in situ from PdPcS photosensitization. Complete dechlorination of TCP could be achieved after TCP was totally oxidized. The initial rate of TCP degradation was observed to increase with the initial amount of TCP sorption, the kinetics following well the Langmuir-Hinshelwood equation. The resulting rate constant of TCP oxidation was found to increase with the alkyl chain length of the intercalated surfactant from dodecyltrimethylammonium to cetyltrimethylammonium and to octadecyltrimethylammonium. Such the trend in photoactivity was in agreement with the catalyst capacity for TCP sorption from aqueous medium. The result showed that enrichment of toxic TCP on the catalyst was indeed an efficient way for enhancement of the photosensitized degradation of target pollutant. However, PdPcS loading led to a notable decrease in TCP sorption, because of partial blocking of the sorptive sites. The optimal loading of PdPcS was about 1.0 wt %. The catalyst was characterized by nitrogen adsorption, X-ray diffraction, visible diffuse reflectance spectroscopy, and TCP sorption, which revealed that the incorporated PdPcS, mainly in the form of photoactive monomer, coexisted with the intercalated surfactant in the bentonite interlayers. Seven repeated experiments demonstrated that the composite clay was relatively stable and could be repeatedly used for sorption and degradation of TCP pollutant via molecular oxygen and visible light.     

In situ synthesis of polysulfides covalently bonded to silica

Silanol groups, triple bond SiOH, on the surface of silica were esterified with unsaturated alcohols and long-chain alcohols bearing thiol groups. The modified silicas obtained were used as substrates for a vulcanization-analogous reaction with sulfur catalyzed by zinc dimethyldithiocarbamate. Surface-esterified thiols could be smoothly converted to bridged polysulfides bonded to the silica surface, whereas the use of surface-esterified unsaturated alcohols led to removal of the surface-esterified alcohol from the silica surface. The materials were characterized by solid-state NMR and thermal and microanalytical analysis. The linking of surface-esterified alkenols and thiols by sulfide bridges was investigated by a numerical model for a flat surface. This showed that for a typical density of 3-4 micromol/m(2) surface groups, a statistical maximum of 70-75% of groups could be linked by S(n) bridges (n=2-4).     

Examination of covalently bound polymeric stationary phases by luminescence spectroscopy

Luminescnce spectroscopy is used to prove silica-gel surfaces derivatized with [3-(3-pyrenyl)propyl]methyldichlorisilane. Evidence of solution pre-polymerizatiln and subsequent derivatization to acceisibl surface silanols is presented. Conformatonal changes of the bound ligands in polar and non-polar solvents indicate a dynamic surface which minimized its surface area in hostile solvents.     

Surface mixed adsorption films of 2,4,6- trimethylphenol–2,4,6-trichlorophenol at aqueous solution/air interface

 The results of experimental studies of the adsorption at the solution/air interface from an aqueous mixture: 2,4,6-trimethylphenol–2,4,6-trichlorophenol are presented. The surface properties of the above-mentioned mixture were studied by surface potential and surface tension measurements. These measurements were carried out as a function of the concentration of 2,4,6-trimethylphenol aqueous solution at a constant concentration of 2,4,6-trichlorophenol. Using the results obtained and based on the Gibbs equation, Helmholtz formula and Motomura’s method the relative surface excesses of adsorbed substances, effective dipole moments, surface molar fractions of solutes and miscibility of adsorbed films were determined. Received: 7 November 1997 Accepted: 26 February 1998     

Comparative Baeyer-Villiger oxidation of cyclohexanone on Fe-pillared clays and iron tetrasulfophthalocyanine covalently supported on silica

The Baeyer-Villiger oxidation of cyclohexanone to caprolactone has been investigated at room temperature over AlFe-pillared clays, using oxygen as oxidant in the presence of benzaldehyde. A nearly complete conversion is observed with a selectivity into caprolactone above 80%. The observation of an induction period in the kinetics, of high activity of the non-pillared clay, and the detection of Fe traces in the reaction medium, suggest a process involving homogenous catalysis. The reaction is indeed catalysed in homogeneous phase by a few ppm of Fe. By contrast, iron phthalocyanine covalently supported on silica appears as a true heterogeneous catalyst, giving a selectivity above 95% to caprolactone at 61% conversion.     

Direct characterization of iodine covalently bound to fulvic acids by electrospray mass spectrometry.

Numerous studies have demonstrated that humic substances (HS) react with iodine to form iodo derivatives and thereby can control the bioavailability of radioisotopes. Unfortunately, none of these studies have provided detailed insights into product compounds and so far, to our knowledge, the direct analysis of these species by electrospray ionization (ESI) mass spectrometry has not been explored. The reactivity of iodine with fulvic acids (FA) present in HS was investigated by means of ESI coupled with a quadrupole time-of-flight (Q-TOF) mass spectrometer. ESI spectra of solutions, that were indicated by MS/MS analysis to have formed iodinated species, apparently displayed singly charged ions corresponding in m/z to hypothesized species, viz., [RI - H](-), R = (substituted FA compound). MS/MS analysis based on the diagnostic fragment ions for FA compounds and their iodo derivatives suggests that FA undergo aromatic substitutions. Furthermore, significant differences in mass profiles are observed that presumably result from extended redox reactions. The ESI-MS technique opens up new opportunities to understand the scavenging properties of HS towards radionuclides and heavy metals for environmental studies.     

Oxidation of primary alcohols to aldehydes catalyzed by ruthenium compounds

The RuCl₃ and RuO₂·nH₂O catalyzed oxidation of alkanes, aromatic fatty acids, alcohols, citronellol, and hydroxycitronellol by NaOCl was studied in the diphase system CCl₄-aqueous NaOCl at pH 13–13.5. At 60–65°C, using 1–2 mole % of catalyst and a 1.5-fold molar excess of NaOCl, primary alkanols (hexanol-1, 2-ethylhexanol-1, decanol-1, hexadecanol-1) benzyl and 3-phenyl-propyl alcohols, and hydroxycitronellol are converted to the corresponding aldehydes with a selectivity of 70–90% and a yield of over 75%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 115–121, January, 1991.     

Attractive mode manipulation of covalently bound molecules

We have investigated the manipulation of C₆₀ molecules on Si(1 0 0)-2×1 using the tip of a scanning tunnelling microscope. An attractive mode of manipulation has been identified in which molecules hop across the Si(1 0 0)-2×1 surface in steps of two lattice constants. An abrupt transition to repulsive manipulation occurs as the tip is lowered towards the surface. The attractive interaction is attributed to chemical forces between the tip and molecule.     

Unsupervised guided docking of covalently bound ligands

Summary An approach for docking covalently bound ligands in protein enzymes or receptors was implemented in MacDOCK, a similarity-driven docking program based on DOCK 4.0. This approach was tested with a small number of covalent ligand–protein structures, using both native and non-native protein structures. In all cases, MacDOCK was able to generate orientations consistent with the known covalent binding mode of these complexes, with a performance similar to that of other docking programs. This method was also applied to search for known covalent thrombin inhibitors in a medium-sized molecular database (ca. 11,000 compounds). Detection of functional groups suitable for covalent docking was carried out automatically. A significant enrichment in known active molecules in the first 5% of the database was obtained, showing that MacDOCK can be used efficiently for the virtual screening of covalently bound ligands.     

Phase-transfer reactions catalyzed by phosphonium salts bound to macroporous polystyrene supports

The rate of reaction of alkyl halides with aqueous sodium acetate or cyanide catalyzed by phosphonium salts supported on insoluble polystyrene resins, and rates of ion-exchange of the chloride ion in the catalysts against the acetate ion, were studied as a function of catalyst particle size, the percentage of ring substitution, the morphology of polymer support, and distance between active site and polymer backbone. Rates of 1-bromooctane or benzyl chloride with macroporous, 7–25% ring-substituted catalysts increased with increasing ring substitution. Rates with macroporous catalysts increased as a heptamethylene spacer was introduced between the active site and the polymer backbone. Rates of ion-exchange with macroporous catalysts were facilitated with increasing ring substitution or by the introduction of the spacer chain. A relation between the catalytic activity of macroporous or microporous catalysts and ion-exchange rates under triphase conditions was discussed.