分子印迹聚合物负载Fe(III)催化剂的底物识别性能

分别以o-, m-和p-硝基苯甲醇与FeCl₃的配合物为模板分子,丙烯酰胺为功能单体,二甲基丙烯酸乙二醇酯为交联剂,采用本体聚合法制备了三种Fe(III)含量相同的分子印迹聚合物(MIP)o-Fe(III)-MIP,m-Fe(III)-MIP和p-Fe(III)-MIP.并采用扫描电镜、N₂吸附-脱附及红外光谱等方法对催化剂结构进行了表征.在以水为溶剂,过氧化氢(30%)为氧化剂的苯甲醇衍生物氧化反应中,该类催化剂表现出优异的催化活性和独特的底物识别性能.当以p-Fe(III)-MIP为催化剂时,p-硝基苯甲醇的转化率达到80%,而在其他两个催化剂上均低于58%.这表明Fe(III)-MIP催化剂结构中具有与底物分子匹配的印迹空腔与识别位点,对底物分子表现出专一识别性,因而提高了催化剂对底物的选择性.     

Product bound structures of the soluble methane monooxygenase hydroxylase from Methylococcus capsulatus (Bath): protein motion in the alpha-subunit

The soluble methane monooxygenase hydroxylase (MMOH) alpha-subunit contains a series of cavities that delineate the route of substrate entrance to and product egress from the buried carboxylate-bridged diiron center. The presence of discrete cavities is a major structural difference between MMOH, which can hydroxylate methane, and toluene/o-xylene monooxygenase hydroxylase (ToMOH), which cannot. To understand better the functions of the cavities and to investigate how an enzyme designed for methane hydroxylation can also accommodate larger substrates such as octane, methylcubane, and trans-1-methyl-2-phenylcyclopropane, MMOH crystals were soaked with an assortment of different alcohols and their X-ray structures were solved to 1.8-2.4 A resolution. The product analogues localize to cavities 1-3 and delineate a path of product exit and/or substrate entrance from the active site to the surface of the protein. The binding of the alcohols to a position bridging the two iron atoms in cavity 1 extends and validates previous crystallographic, spectroscopic, and computational work indicating this site to be where substrates are hydroxylated and products form. The presence of these alcohols induces perturbations in the amino acid side-chain gates linking pairs of cavities, allowing for the formation of a channel similar to one observed in ToMOH. Upon binding of 6-bromohexan-1-ol, the pi helix formed by residues 202-211 in helix E of the alpha-subunit is extended through residue 216, changing the orientations of several amino acid residues in the active site cavity. This remarkable secondary structure rearrangement in the four-helix bundle has several mechanistic implications for substrate accommodation and the function of the effector protein, MMOB.     

Thin-layer chromatography of metal ions on bonded stationary phases

Summary The separation of iron, copper, nickel, and zinc by thin-layer chromatography was studied. Eight bonded-phase silica substrates and twenty-nine solvent systems were investigated. Solutions of 1% diphenylcarbazide in ethanol and 1% K₄Fe(CN)₆ in water were used to detect the metal ions. The best separation was obtained with an immobilized trifluoroacetylacetone substrate and 10% trifluoroacetylacetone in acetone mobile phase.     

Structural Determinants of the Specific Activities of an L-Amino Acid Oxidase from Pseudoalteromonas luteoviolacea CPMOR-1 with Broad Substrate Specificity

The Pseudoalteromonas luteoviolacea strain CPMOR-1 expresses a flavin adenine dinucleotide (FAD)-dependent L-amino acid oxidase (LAAO) with broad substrate specificity. Steady-state kinetic analysis of its reactivity towards the 20 proteinogenic amino acids showed some activity to all except proline. The relative specific activity for amino acid substrates was not correlated only with K_m or k_cat values, since the two parameters often varied independently of each other. Variation in K_m was attributed to the differential binding affinity. Variation in k_cat was attributed to differential positioning of the bound substrate relative to FAD that decreased the reaction rate. A structural model of this LAAO was compared with structures of other FAD-dependent LAAOs that have different substrate specificities: an LAAO from snake venom that prefers aromatic amino acid substrates and a fungal LAAO that is specific for lysine. While the amino acid sequences of these LAAOs are not very similar, their overall structures are comparable. The differential activity towards specific amino acids was correlated with specific residues in the active sites of these LAAOs. Residues in the active site that interact with the amino and carboxyl groups attached to the α-carbon of the substrate amino acid are conserved in all of the LAAOs. Residues that interact with the side chains of the amino acid substrates show variation. This provides insight into the structural determinants of the LAAOs that dictate their different substrate preferences. These results are of interest for harnessing these enzymes for possible applications in biotechnology, such as deracemization.     

Monooxygen transfer potential of the transannular ozonide of 9-tert-butyl-10-methylanthracene

The efficiency of oxygen transfer from the transannular ozonide 1 to several organic substrates was investigated. The efficiency was estimated to be as high as 90% in the case of Ph₃P as the substrate.     

Engineered Substrate‐Specific Delta PKC Antagonists to Enhance Cardiac Therapeutics

Most protein kinases phosphorylate multiple substrates, each of which induces different and sometimes opposing functions. Determining the role of phosphorylation of each substrate following a specific stimulus is challenging but is essential to elucidate the role of that substrate in the signaling event. Here we describe a rational approach to identify inhibitors of delta protein kinase C (δPKC), each inhibiting the phosphorylation of only one of δPKC′s substrates. δPKC regulates many signaling events and we hypothesized that a docking inhibitor of a given substrate to δPKC should selectively abrogate the phosphorylation of only that substrate, without affecting the phosphorylation of the other δPKC substrates. Here we report the development of selective inhibitors of three δPKC substrates (in vitro K_d≈3 nm ); two greatly reduced ischemia‐induced cardiac injury with an IC₅₀ of ≈200 nm and the third had no effect, indicating that its respective substrate phosphorylation by δPKC has no role in the response to cardiac ischemia and reperfusion. The three inhibitors are highly specific; even at 1 μm , the phosphorylation of other δPKC protein substrates was unaffected. The rationale we describe is likely applicable for the development of other substrate‐specific inhibitors as well.     

Structure-Reactivity correlations in the addition of water to aromatic substrates

The addition of water to 1-(4-Z-2,6-dinitrophenyl)-3-methylimidazolium chloride (Z = CN, NO₂, and CF₃) is catalyzed by carboxylate bases. There is a decrease in ρ with increasing basicity of the catalyst with ?ρ/?pK_BH = ?0.090. The results indicate that the mechanism of the reaction involves the addition of water to the aromatic substrates catalyzed by general bases. The changes in the structure-reactivity parameters with changing pK of the catalysts or Z in the substrate are rationalized in terms of changing bond lengths in the transition state. The activation parameters and the kinetic solvent isotopic effect were determined for the water, acetate, and OH^? catalyzed reactions and are consistent with the proposed mechanism.     

Molecular Recognition of Immobilized Supramolecular Complex of Ironporphyrin and β-CD Polymer as an Analogue for Peroxidase

The immobilized supramolecular inclusion complex of FeTPPS4 and -CD polymer was applied as a mimesis of peroxidase, and its molecular recognition for twenty substrates was studied. As the space structure;CD interior cavities, high selectivity was obtained by immobilized mimetic enzyme. p-Chlorophenic acid was identified as an optimal substrate in the system tested.     

The Effect of Varying Organosolv Pretreatment Chemicals on the Physicochemical Properties and Cellulolytic Hydrolysis of Mountain Pine Beetle-Killed Lodgepole Pine

Mountain pine beetle-killed lodgepole pine (Pinus contorta) chips were pretreated using the organosolv process, and their ease of subsequent enzymatic hydrolysis was assessed. The effect of varying pretreatment chemicals and solvents on the substrate’s physicochemical characteristics was also investigated. The chemicals employed were MgCl₂, H₂SO₄, SO₂, and NaOH, and the solvents were ethanol and butanol. It was apparent that the different pretreatments resulted in variations in both the chemical composition of the solid and liquid fractions as well in the extent of cellulolytic hydrolysis (ranging from 21% to 82% hydrolysis after 12 h). Pretreatment under acidic conditions resulted in substrates that were readily hydrolyzed despite the apparent contradiction that pretreatment under alkaline conditions resulted in increased delignification (approximately 7% and 10% residual lignin for alkaline conditions versus 17% to 19% for acidic conditions). Acidic pretreatments also resulted in lower cellulose degree of polymerization, shorter fiber lengths, and increased substrate porosity. The substrates generated when butanol/water mixtures were used as the pretreatment solvent were also hydrolyzed more readily than those generated with ethanol/water. This was likely due to the limited miscibility of the solvents resulting in an increased concentration of pretreatment chemicals in the aqueous layer and thus a higher pretreatment severity.     

Calculations of the Gibbs Energy of Formation of Cavities in Water

The Gibbs energy Δ_cav G of formation of cavities in water was calculated by thermodynamic integration. The cavities corresponded to organic molecules of various volumes and shapes with characteristic radii of 3–7 Å and spheres of radii 3–6 Å. Statistical integrals were calculated by the Monte Carlo simulation of an ensemble of water molecules with periodic boundary conditions at 25°C and pressure 1 atm. Interaction between water molecules was described by the TIP4P four-point nonpolarizable model. It was found that the proportionality of Δ_cav G to cavity volume V obtained earlier for spheres with radii not exceeding 5 Å remained valid for cavities corresponding to organic molecules of different volumes and shapes, including cavities with the characteristic radii exceeding 5 Å. A possible explanation of the retention of the Δ_cav G ∞ V dependence at large characteristic radii was suggested in terms of the two-peak binomial model of the cavitation effect. The conclusion was drawn that the Δ_cav G = αV dependence could be used for calculating the nonpolar part of the Gibbs energy of solvation in implicit water models.     

Effect of substrate on phase formation and surface morphology of sol-gel lead-free KNbO3, NaNbO3, and K0.5Na0.5NbO3 thin films

Environmentally acceptable lead-free ferroelectric KNbO₃ (KN) or NaNbO₃ (NN) and K_0.5Na_0.5NbO₃ (KNN) thin films were prepared using a modified sol-gel method by mixing potassium acetate or sodium acetate or both with the Nb-tartrate complex, deposited on the Pt/Al₂O₃ and Pt/SiO₂/Si substrates by a spin-coating method and sintered at 650°C. X-ray diffraction (XRD) analysis indicated that the NN and KNN films on the Pt/SiO₂/Si substrate possessed a single perovskite phase, while NN and KNN films on the Pt/Al₂O₃ substrate contained a small amount of secondary pyrochlore phase, as did KN films on both substrates. Scanning electron microscopic (SEM) and atomic force microscopic (AFM) analyses confirmed that roughness R _q of the thin KNN/Pt/SiO₂/Si film (?? 7.4 nm) was significantly lower than that of the KNN/Pt/Al₂O₃ film (?? 15 nm). The heterogeneous microstructure composed of small spherical and larger needle-like or cuboidal particles were observed in the KN and NN films on both substrates. The homogeneous microstructure of the KNN thin film on the Pt/SiO₂/Si substrate was smoother and contained finer spherical particles (?? 50 nm) than on Pt/Al₂O₃ substrates (?? 100 nm). The effect of different substrates on the surface morphology of thin films was confirmed.     

Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

Spectrophotometric and Polarographic Studies on 9,10-Anthradione-2-Sodium Sulfonate

The effect of solvent structure on the rates of redox reactions in alcohol+water mixture was discussed by some authors. The rate of photoreduction of 9,10-anthraquinone-2-sulfonate was decreased by addition of H₂SO₄ but was unchanged by increase of ionic strengh with (NH₄)₂SO₄. The magnitude of the decrease in presence of acid was greater with ethanol or isopropanol than with N-ethylacetamide as substrate. The formation of semiquinone and carbonate radical anions was observed⁽⁴⁾ during the direct photoreaction. The electron transfer from the carbonate anion to sulfoanthraquinone in the first excited triplet state was the controlling step of this process. Therefore, anthraquinone β-sodium sulfonate is efficient sensitizers of the photooxidation of organic substrates in aqueous media.     

Supramolecularly Regulated Ligands for Asymmetric Hydroformylations and Hydrogenations

Herein we report the use of polyether binders as regulation agents (RAs) to enhance the enantioselectivity of rhodium‐catalyzed transformations. For reactions of diverse substrates mediated by rhodium complexes of the α,ω‐bisphosphite‐polyether ligands 1 – 5 , a – d , the enantiomeric excess (ee) of hydroformylations was increased by up to 82 % (substrate: vinyl benzoate, 96 % ee), and the ee value of hydrogenations was increased by up to 5 % (substrate: N‐(1‐(naphthalene‐1‐yl)vinyl)acetamide, 78 % ee). The ligand design enabled the regulation of enantioselectivity by generation of an array of catalysts that simultaneously preserve the advantages of a privileged structure in asymmetric catalysis and offer geometrically close catalytic sites. The highest enantioselectivities in the hydroformylation of vinyl acetate with ligand 4 b were achieved by using the Rb[B(3,5‐(CF₃)₂C₆H₃)₄] (RbBArF) as the RA. The enantioselective hydrogenation of the substrates 10 required the rhodium catalysts derived from bisphosphites 3 a or 4 a , either alone or in combination with different RAs (sodium, cesium, or (R,R)‐bis(1‐phenylethyl)ammonium salts). This design approach was supported by results from computational studies.     

Composition of gas hydrates of CHClF2, CCl2F2 and SF6

Gas hydrates are forms of ice stabilized by the presence of molecules of gas occupying cavities in the solid water lattice. There are two common forms: structure I and structure II. The mean free diameters of the two types of cavities in structure I are about 5.0 and 5.8 angstroms. Very small gas molecules such as Xe or H₂S can occupy both. In the past it has been considered that gas molecules of larger diameter than 5.0 angstroms could not occupy the smaller cavities. It has now been shown through measurement of hydration numbers of CHClF₂ (diameter about 5.4 angstroms) under various pressures at 0°, that some of the small cavities are filled. This state of affairs also exists for CH₃Br. In structure II, the mean diameters of the two types of cavities are about 5.0 and 6.6 angstroms. Hydration numbers of SF₆ (diameter about 5.8 angstroms) and CCl₂F₂ (about 6.2 angstromsm) show that nearly all of the large cavities but essentially none of the small cavities are occupied.     

SERS from two-tier sphere segment void substrates

Sphere segment void, or inverse opal, films prepared from a variety of coinage metals have shown promise as reliable and reproducible substrates for surface enhanced Raman spectroscopy (SERS). Sphere segment void substrates are prepared from colloidal templates consisting of one or more layers of polystyrene spheres. In this paper, we investigate the reflection spectra and SERS for a gold film consisting of two-tiers of spherical cavities, and show that the best SERS enhancements are obtained from substrates consisting of just a single layer of sphere segment voids.     

Comments on the wetting behavior of non-porous substrates for ceramic coated-conductor applications

This work gives an overview of the possibilities to improve the wetting behavior of precursors for coated conductors on non-porous substrates. Within this work, all coatings were performed on a metallic Ni–W/La₂Zr₂O₇/CeO₂ substrate using water-based Y, Ba, Cu containing precursors. The results described in this paper can be used for different technologies of chemical solution deposition, as there are ink jet printing, dip coating, spin coating etc. Starting from the forces involved during wetting, a separation between solid and liquid modifications was made. This study revealed that if a good cleaning procedure of the substrate, whether or not combined with a targeted modification of the precursor is applied, water-based solutions can be used without restriction towards their wetting behaviour leading to a sustainable technology within the coating industry. Within this work, special attention is given to (1) fast determination of the substrate cleaning procedure quality by the creation of wetting envelopes and (2) the use of a screening design of experiment to study the effects of intrinsic solution factors, such as precursor formulation, influencing the coating behavior. All modification discussed are expandable to all kinds of precursors and substrates.     

Brønsted Acid Catalyzed Tandem Defunctionalization of Biorenewable Ferulic acid and Derivates into Bio-Catechol

An efficient conversion of biorenewable ferulic acid into bio-catechol has been developed. The transformation comprises two consecutive defunctionalizations of the substrate, that is, C−O (demethylation) and C−C (de-2-carboxyvinylation) bond cleavage, occurring in one step. The process only requires heating of ferulic acid with HCl (or H₂SO₄) as catalyst in pressurized hot water (250 °C, 50 bar N₂). The versatility is shown on a variety of other (biorenewable) substrates yielding up to 84 % di- (catechol, resorcinol, hydroquinone) and trihydroxybenzenes (pyrogallol, hydroxyquinol), in most cases just requiring simple extraction as work-up.     

Characterization and application of silylated substrates for the preconcentration of cations

Chelating functional groups immobilized on silica and controlled pore glass beads are used to preconcentrate cations from aqueous solution in the concentration region of ng ml^?1. The functional groups are chemically bonded to the substrates by silylation reagents which may be employed as received or further modified. For example, commercially available 1,2-diamines may be used or converted to the dithiocarbamate after immobilization. This report includes studies of ionic strength and sodium chloride effects on the recovery of transition metal ions. Batch extraction of transition metal ions is accomplished with silica as the substrate for solutions containing transition metal ions at μg ml^?1 concentrations. Column extraction of solutions pumped at 50 ml min^?1 is accomplished at concentrations of 25 ng ml^?1. Recovery is good in both cases. The cations were determined directly on pelletized substrates by x-ray fluorescence. However, the ions may be eluted from the substrate and determined by other methods. Examples of determinations of several cations in lake water and high-purity industrial water are given.     

Studies on substrates for the spectrophotometric determination of hydrogen peroxide based on the catalytic effects of peroxidase-like metalloporphyrins

Summary The effects have been studied of ten phenol derivatives as chromogenic substrates for the hydrogen peroxide oxidation of 4-aminoantipyrine, catalysed by horse radish peroxidase or peroxidase-like metalloporphyrins. Sodium 2-hydroxy-3,5-dichlorobenzene-sulfonate was found to be the most suitable substrate for the determination of H₂O₂.