Investigation of asymmetric alcohol dehydrogenase (ADH) reduction of acetophenone derivatives: effect of charge density

In an effort to study the effect of substituent groups of the substrate on the alcohol dehydrogenase (ADH) reductions of aryl-alkyl ketones, several derivatives of acetophenone have been evaluated against ADHs from Lactobacillus brevis (LB) and Thermoanaerobacter sp. (T). Interestingly, ketones with non-demanding (neutral) para-substituents were reduced to secondary alcohols by these enzymes in enantiomerically pure form whereas those with demanding (ionizable) substituents could not be reduced. The effect of substrate size, their solubility in the reaction medium, electron donating and withdrawing properties of the ligand and also the electronic charge density distribution on the substrate molecules have been studied and discussed in detail. From the results, it is observed that the electronic charge distribution in the substrate molecules is influencing the orientation of the substrate in the active site of the enzyme and hence the ability to reduce the substrate.     

A designed synthetic analogue of 4-OT is specific for a non-natural substrate

The substrate specificity of 4-oxalocrotonate tautomerase (4-OT) is characterized by electrostatic interactions between positively charged arginine (Arg) side chains on the enzyme and the dianionic substrate, 4-oxalocrotonate. To generate specific hydrogen-bonding interactions with a monoanionic substrate analogue, we have introduced a urea functional group into the active site by replacing arginine side chains with isosteric citrulline (Cit) residues. This design was based on the complementarity between the urea functionality of citrulline and the uncharged amide function of the substrate, as opposed to the guanidinium-carboxylate electrostatic interaction between the wild-type enzyme and the natural substrate. Indeed, the synthetic (Arg39Cit)4-OT analogue catalyzed the tautomerization of the non-natural monoamide-monoacid substrate while it was a poor catalyst for the natural diacid substrate. The specificity of (Arg39Cit)4-OT for the monoamide-monoacid substrate relative to that of the diacid substrate was found to be 740-fold greater than that of the wild-type enzyme for tautomerization of the non-natural substrate as compared with the natural one. The role of electrostatic interactions in the tautomerization of the monoamide-monoacid substrate was probed in detail with several other Arg to Cit analogues of this enzyme. This study has demonstrated that chemical manipulation of the functional groups within the active site of an enzyme can modify its catalytic activity and substrate specificity in a predictable way, suggesting that the incorporation of noncoded amino acids into proteins has great promise for the development of new enzymatic mechanisms and new binding interactions.     

Modulation of the catalytic behavior of alpha-chymotrypsin at monolayer-protected nanoparticle surfaces

Amino-acid-functionalized gold clusters modulate the catalytic behavior of alpha-chymotrypsin (ChT) toward cationic, neutral, and anionic substrates. Kinetic studies reveal that the substrate specificity (k(cat)/K(M)) of ChT-nanoparticle complexes increases by approximately 3-fold for the cationic substrate but decreases by 95% for the anionic substrate as compared with that of free ChT, providing enhanced substrate selectivity. Concurrently, the catalytic constants (k(cat)) of ChT show slight augmentation for the cationic substrate and significant attenuation for the anionic substrate in the presence of amino-acid-functionalized nanoparticles. The amino acid monolayer on the nanoparticle is proposed to control both the capture of substrate by the active site and release of product through electrostatic interactions, leading to the observed substrate specificities and catalytic constants.     

计算机硬盘基片CMP中表面膜特性的分析研究

目前,普遍采用化学机械抛光(Chemical-mechanical polishing,CMP)技术对计算机硬盘基片(盘片)表面进行原子级平整。CMP加工中,盘片表面膜及其特性对CMP过程及CMP性能具有关键作用。本文分别采用俄歇能谱(AES)、X射线光电子能谱(XPS)、扫描电镜(SEM)、纳米硬度计、电化学极化法等分析手段对盘片表面物理、化学及机械特性进行了研究,发现盘片CMP后表面发生了氧化,氧化膜在盘片的表层,厚度在纳米量级,氧化产物为Ni(OH)₂;氧化膜为较软的、疏松的、粗糙的多孔结构;氧化膜的存在加快了盘片表面的腐蚀磨损。结合盘片CMP试验结果,推测盘片的CMP机理为盘片表面氧化生成机械强度较低的Ni(OH)₂氧化膜及随后氧化膜的机械和化学去除,二者的不断循环实现表面的全局平面化。     

DMF竞争性抑制大豆脂氧酶好氧催化及其松弛底物抑制的综合作用

在大豆脂氧酶催化亚油酸的氧化反应中加入溶剂二甲基甲酰胺DMF(lgP为-1.01)可将底物亚油酸浓度提升到232 mmol/L而不产生底物抑制作用, 并使平衡产率从38.93%提高到66.09%. 在有底物存在时, 质量分数为5%的DMF基本不影响酶活; 此时体系具有最大的Kss与Ki值, 表明5%DMF对底物抑制作用的松弛效应最强, 而对酶的抑制作用最小.     

Detection of the local structural changes in the dimer interface of BamHI initiated by DNA binding and dissociation using a solvatochromic fluorophore

To detect the local structural change in an interface between proteins induced by the substrate binding and dissociation, a solvatochromic fluorescent N(beta)-L-alanyl-5-(N,N-dimethylamino)-naphthalene-1-sulfonamide (DanAla) was introduced into 132 position of the dimer interface in BamHI. Before addition of the substrate, the fluorescence from the normal planer excited state of DanAla moiety was observed as a main emission, and thereby the DanAla in the dimer interface is located in the hydrophobic microenvironment. The incubation with the substrate for 20 min induced the gradual increase in fluorescence intensity around 430 nm. The fact reflects that the polarity is reduced by the slight structural change initiated by the formation of the complex with the substrate. Furthermore, the incubation for more than 20 min caused the slight decrease in fluorescence around 430 nm and an appearance of fluorescence (560 nm) due to twisted intramolecular charge transfer (TICT) excited state. Therefore, the DanAla is exposed to comparative polar environment after the dissociation of the substrate. The fluorescence lifetime as a minor component, which is attributed to the TICT excited state, was reduced by addition of the substrate. The results provide that the hydrophobicity in the dimer interface is increased by the substrate binding. Interestingly, we found that the structure of an initial form is different from that of a refolded form after the dissociation of the substrate using a spectral subtraction technique. We have achieved detection of the changing structure induced by the substrate binding and dissociation using a steady-state and time-resolved fluorescence.     

The effect of surface roughness on the adhesion of solid surfaces for systems with and without liquid lubricant

We present molecular dynamics results for the interaction between two solid elastic walls during pull-off for systems with and without octane (C(8)H(18)) lubricant. We used two types of substrate--flat and corrugated--and varied the lubricant coverage from approximately 1/8 to approximately 4 ML (monolayers) of octane. For the flat substrate without lubricant the maximum adhesion was found to be approximately three times larger than for the system with the corrugated substrate. As a function of the octane coverage (for the corrugated substrate) the pull-off force first increases as the coverage increases from 0 to approximately 1 ML, and then decreases as the coverage is increased beyond monolayer coverage. It is shown that at low octane coverage, the octane molecules located in the substrate corrugation wells during squeezing are pulled out of the wells during pull-off, forming a network of nanocapillary bridges around the substrate nanoasperities, thus increasing the adhesion between two surfaces. For greater lubricant coverages a single capillary bridge is formed. The adhesion force saturates for lubricant coverages greater than 3 ML. For the flat substrate, during pull-off we observe discontinuous, thermally activated changes in the number n of lubricant layers (n-1-->n layering transitions), whereas for the corrugated substrate these transitions are "averaged" by the substrate surface roughness.     

化学镀镍诱发过程的研究 I:金属催化活性的鉴别和反应机理

Electroless plating is known to be an autocatalytic process. For the reaction to start, the substrate metall should be either catalytic or activated by a suitable catalyst. For example, steel and nickel can be plated directly, but in the case of copper or brass, catalytic metal inducing is need. In this paper, the catalytic activity of different metals and their inducing effects were in vestigated by measuring stationary potentials nd stationary potential-time curves. Experimental results showed: (1) The stationary potential of metal provides a simple parameter to estimate the catalytic activity of metals in electroless nickeling. When 1-hydroxyethylidenediphosphonic acid (HEDP) aelectroless nickeling bath containing NaH2PO2 as reducing agent is used, electrolessnickeling may proceed spontaneously, if the stationary potential of metal is more nagative than -0.60V, no matter whether nickel (autocatalytic active) or other metals(non-autocatalytic active) is used as substrate. (2)When an autocatalytic meta is in contact with the substrate metal in the bath, a sudden decrease of stationary potential is observed. The whole inducing process could be finished within 0.5-2 sec. (3) The stationary potential of electroless nickeling coating in HEDP bath at 80`C is-0.72V, consequently nickel coating itself is a catalytic active metal. Once an electroless nickeling coating is deposited on a substrate metal, electroless nickeling reaction can then proceed continuously. (4) The sufficient conditions of electroless nickeling in HEDP bath containing NaH2PO2 are that the stationary potential of substrate metal must be more nagative than -0.60V and that the temperature of electroless nickeling bath should be higher than 50`C. (5) Inducing mechanism of electroless nickeling can be explained with chemical cell consisting of substrate metal and catalytic metal. Electrons from catalytic metal would suddenly decrease the stationary potential of substrate metal, H+ and Ni2+ complex ion would be reduced on the substrate me     

Photocontrolled Multidirectional Differentiation of Mesenchymal Stem Cells on an Upconversion Substrate

The effective guidance of mesenchymal stem cell (MSC) differentiation on a substrate by near‐infrared (NIR) light is particularly attractive for tissue engineering and regenerative medicine. However, most of current substrates cannot control multidirectional differentiation of MSCs like natural tissues. Herein, a photocontrolled upconversion‐based substrate was designed and constructed for guiding multidirectional differentiation of MSCs. The substrate enables MSCs to maintain their stem‐cell characteristics due to the anti‐adhesive effect of 4‐(hydroxymethyl)‐3‐nitrobenzoic acid modified poly(ethylene glycol) (P1) attached on the upconversion substrate. Upon NIR irradiation, the P1 is released from the substrate by photocleavage. The detachment of P1 can change cell–matrix interactions dynamically. Moreover, MSCs cultured on the upconversion substrate can be specifically induced to differentiate to adipocytes or osteoblasts by adjusting the NIR laser. Our work provides a new way of using NIR‐based upconversion substrate to modulate the multidirectional differentiation of MSCs.     

Control of surface anchoring properties of liquid crystal by thermo-transfer printing of siloxane oligomers

We presented the results for the surface anchoring properties of a nematic liquid crystal (LC) in a wide range of the substrate wettability through thermo-transfer printing of siloxane oligomers. For the modification of the surface energy, poly(dimethylsiloxane) (PDMS) oligomers were directly transferred onto a glass substrate from a bulk PDMS plate by contact printing at elevated temperatures. The hydrophobicity of the PDMS-modified surface was found to increase with the temperature of the substrate during transfer printing. The LC alignment on the PDMS-modified substrate exhibited continuous variations of the pretilt angle from nearly 0° to 90° and the polar anchoring strength according to the surface energy.     

HRTEM-EELS cross-sectional structural analyses of glassy carbon substrate irradiated by platinum ions using a coaxial arc plasma gun

A glassy carbon (GC) substrate was irradiated by Pt ions using a coaxial arc plasma gun in vacuum. The structure of the substrate was studied in the atomic scale using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) with a thin foil specimen prepared by cross-sectioning using focused ion beam milling. HRTEM combined with the EELS measurements of the cross-sectioned sample indicated a disordering of the GC substrate surface and the detection of phenol-type species, carbon atoms in aliphatic chain molecules, and carboxyl groups, which are considered to have been formed by chemical reaction between the carbon atoms of the GC substrate surface and hydrogen or oxygen atoms. Penetrated Pt atoms were observed inside the GC substrate, and the surface position of the GC substrate was located from the depth profiles of the EELS spectra. STEM-EELS analyses of a pristine GC substrate without Pt ion irradiation were also conducted for reference.     

Effect of replicated polymeric substrate with lotus surface structure on adipose-derived stem cell behaviors

We fabricated polystyrene substrates with lotus leaf surface structure (LLSS) and investigated cell behaviors, including attachment, morphology, proliferation, and differentiation of adipose-derived stem cells (ASCs) on them. Compared to the flat substrate, the LLSS substrate induced higher cell attachment rate, but did not significantly change the cell proliferation rate. In addition, ASCs on the LLSS substrate exhibited relatively narrower spreading morphology and less organized cytoskeleton, there by resulting in smaller sizes of cells than those on the flat substrate. According to histochemical staining and RT-PCR analysis, the LLSS substrate induced higher adipogenic differentiation of ASCs than the flat substrate, while chondrogenic and osteogenic differentiation were decreased.     

SERS: A new method for the study of electronic structure in ultrasmall particles

Earlier work suggested that surface enhanced Raman scattering arises from off-diagonal coupling of excitations in the molecule and substrate. Using a free-electron model for a metallic substrate, large enhancements are confirmed, and insight gained about the effects of (1) substrate size, (2) molecular location, (3) density of states, and (4) excitation wavelength. Structured SERS and anti-enhancements occur under suitable conditions.     

衬底温度对Fe3N薄膜生长和磁性的影响

采用直流磁控溅射方法, 以Si(100) 单晶片为衬底, 在衬底温度为150～450 ℃的范围内得到了ε-Fe3N薄膜样品. 利用 XRD, SEM和VSM等表征手段, 研究了衬底温度对ε-Fe3N薄膜的生长和磁性的影响. 实验结果表明, 随着衬底温度的升高, 薄膜的生长速率、晶粒尺寸和单位质量磁化强度均增大, 而矫顽力呈现先增加后减小的变化趋势, 当衬底温度为350 ℃时, 矫顽力达到最大值18.72 kA/m, 可以认为此时薄膜样品的晶粒尺寸接近于交换作用长度.     

Asymmetric hydrogenations one by one: differentiation of up to three beta-ketocarboxylic acid derivatives based on Ruthenium(II)-binap catalysis

Noyori-type reductions of pairs of beta-ketoamides and beta-ketoesters with elemental hydrogen (4 bar) proceeded substrate by substrate. When Et(2)NH(2) (+)[{RuCl(S)-binap}(2)](mu-Cl)(3)(-) was employed as a catalyst in a methanol or ethanol solution, the substrates were reduced at room temperature in the order beta-ketopyrrolidide > or = beta-ketopiperidide > or = beta-keto(N,N-diethylamide) > beta-keto(alkyl esters) > beta-keto(oligofluoroalkyl esters). This is the first time that beta-ketoamides have been reduced asymmetrically (91 to >98 % ee) under such mild conditions. Monitoring the concentrations of these beta-ketocarboxyl acid derivatives and their respective hydrogenation products over the course of time showed that the most electron-rich substrate is captured by the catalyst preferentially and exothermically; whether this occurs reversibly or irreversibly remains to be determined. The hydrogenation product is subsequently formed. The last transformation includes the rate-determining step. The combination of these events explains why starting from appropriate mixtures of substrates a "first-choice substrate" reacted from early on while the "second-choice substrate" stayed virtually untouched over an extended period of time and reacted no earlier than after the "first-choice substrate" had disappeared. From then onward, however, the "second-choice substrate" also reacted relatively rapidly.     

Effect of argon plasma treatment on surface-enhanced Raman spectroscopy of polypyrrole deposited on electrochemically roughened gold substrates

In this work, polypyrrole (PPy) films were electrodeposited on electrochemically roughened gold substrates modified by argon plasma treatment. First, a gold substrate was roughened by a triangular-wave oxidation-reduction cycle (ORC) in an aqueous solution containing 0.1 N HCl. Then the roughened gold substrate was further treated by argon plasma. Encouragingly, the surface-enhanced Raman scattering (SERS) spectroscopy of polypyrrole electrodeposited on this roughened gold substrate modified by argon plasma treatment exhibits a higher intensity by 8-fold, as compared with the SERS of PPy electrodeposited on an unmodified roughened gold substrate. Meanwhile, the electropolymerization for pyrrole monomers occurring on the modified roughened gold substrate is easier. Also, the nucleation and growth of electropolymerization of pyrrole monomers on the modified and unmodified gold substrates are different.     

Control of calcium carbonate polymorphism and morphology through biomimetic mineralization by means of nanotechnology

In vitro biomimetic mineralization by means of nanotechnology allows the formation of calcium carbonate polymorphs at low temperatures (<25 degrees C) under a CO(2) atmosphere of 500-1500 ppm. A two-dimensional zinc-ion ordered array (zinc array), which acts as an active-site mimic of carbonic anhydrase, has been prepared by immersing the self-organized monolayer of 3-(2-imidazolin-1-y)propyltriethosilane on mica (ImSi substrate) into aqueous zinc solution. The zinc array mounted on the ImSi substrate catalyzed the conversion from CO(2) to HCO(3) (-), and accelerated the formation of calcium carbonate. In situ X-ray diffraction data of the formed calcium carbonate on the poly(L-aspartate)-coated chitin substrate (pAsp substrate), with calcium ion-recognition sites, demonstrated that the interaction between the zinc array and pAsp substrates formed both vaterite and calcite at low temperature (15 degrees C) and mainly vaterite at 25 degrees C; this interaction also controlled the morphology of calcium carbonate formed on pAsp substrate.     

One-armed artificial receptors for the binding of polar tetrapeptides in water: probing the substrate selectivity of a combinatorial receptor library

We have recently developed a new class of one-armed artificial receptors 1 for the binding of the polar tetrapeptide N-Ac-D-Glu-L-Lys-D-Ala-D-Ala-OH (EKAA) 2 in water using a combined combinatorial and statistical approach. We have now further probed the substrate selectivity of this receptor library 1 by screening a second tetrapeptide substrate (3) with the inverse sequence N-Ac-D-Ala-D-Ala-L-Lys-D-Glu-OH (AAKE). This "inverse" substrate is also efficiently bound by our receptors, with K(ass) approximately 6000 M(-1) for the best receptors, as determined both by a quantitative on-bead binding assay and by UV and fluorescence titration studies in free solution. Hence, the inverse tetrapeptide 3 is in general bound two to three times less efficiently than the "normal" peptide 2 (K(ass) approximately 17,000 M(-1)), even though the complexation mainly involves long-range electrostatic interactions and both the receptor and substrate are rather flexible. Molecular modeling and ab initio calculations have been used to rationalize the observed substrate selectivity and to analyze the various binding interactions within the complex.     

Transportation and mixing of droplets by surface acoustic wave

Unit operations for complicated biochemical analysis cannot usually be integrated into one substrate. A possible solution to solve this problem is to integrate multi-unit operations into two or more substrates. In this case, transporting droplets from one substrate to another is essential. In this work, a new method to transport droplets from a hydrophobic glass substrate to a piezoelectric substrate is proposed. An interdigitated transducer (IDT) and reflectors were fabricated on an optic grade 128° YX-cut lithium niobate (LiNbO₃) substrate, and its working surface between the IDT and a reflector was modified to be hydrophobic. Droplets to be transported were first pipetted onto a glass substrate. Adjust the glass substrate so that the droplets could contact the working surface of the piezoelectric substrate, and then was moved down. These droplets could be successfully transported from the glass surface to the piezoelectric substrate because of their “adhesion work” difference. By using this mechanism, water and red dye droplets were successfully transported from glass substrate to piezoelectric substrate. As an application, droplets mixing process was demonstrated in the piezoelectric substrate by using surface acoustic wave after they have been transported from the glass substrate.     

Morphology of ultrathin polymer films based on poly(ethylene oxide) blends

The structure of ultrathin (15–200 nm) films of two types prepared from polymer blends based on PEO (the crystallizable component), namely, PEO-poly(arylene sulfone oxide) (the amorphous component) and PEO-PB (the amorphous component), has been studied by atomic force microscopy. The content of PEO in both blends is 76 wt %. Ultrathin blend films have been applied on a Si substrate via substrate dipping into dilute solutions of polymer blends in chloroform at room temperature. The rate of the substrate lift has been varied from 0.1 to 1 mm/min. The amorphous-amorphous separation takes place during formation of ultrathin films of the above blends in the course of the substrate lift at the stage of gelation. The crystallization of PEO and dewetting in the resulting two-phase blend gels depend on the rate of the substrate lift and the rigidity of macromolecules of the amorphous component. Moreover, the predominant interaction of the substrate with one of the components plays a significant role in structure formation of ultrathin films of both polymer blends.