Monolayers from synthetic glycolipids

Summary Synthetic glycolipids have been prepared by coupling of (a) aliphatic amines with lactone derivatives, or (b) fatty acids with amino derivatives of mono- and disaccharides via amide linkage. The aliphatic chain was varied with respect to the chain length and to its chemical composition (fluorination, functional end group). The influence of the glycolipid structure on the monolayer properties was investigated. Stable films are obtained with most of the products mainly due to strong interactions by hydrogen bonds in the subphase. Polymeric films may be produced by polycondensation in the subphase using particular crosslinking agents for the carbohydrate head group.     

Binding of organic anions by synthetic supramolecular metallopores with internal Mg2+-aspartate complexes

We report that cation-selective transmembrane pores formed by synthetic p-octiphenyl beta barrels with internal aspartate residues can be transformed into anion-permeable metallopores with internal Mg(2+)-aspartate complexes. These metallopores are shown to be useful for fluorimetric sensing of a broad variety of organic anions of biological relevance such as phytate, heparin, thiamine phosphates, and adenosine triphosphate. The negligible flippase activity measurable for Mg(2+)-free pores indicates that transmembrane p-octiphenyl beta barrels do not disturb the lipid bilayer suprastructure, in other words, they form barrel-stave rather than toroidal pores.     

Development of a structural model for the cytoplasmic domain of an integrin

The cytoplasmic tails of integrin heterodimers play central roles in controlling the activation states of integrins and in transmitting intracellular signals. Despite their short length, no structure of any integrin cytoplasmic domain has been determined. Therefore, molecular models for the cytoplasmic domain of alpha(IIb)beta3, the major platelet integrin, were generated, including models for the individual cytoplasmic tails, the binary alphaIIb-calcium complex, and the ternary alphaIIb-beta3-calcium complex. Structural analysis of circular dichroism spectra were compiled with data obtained from short homologous sequences within crystallized proteins, and with secondary structural predictions to develop starting models for each subunit. These models were subjected to a series of energy minimization and molecular dynamic simulations to generate final models. AlphaIIb was predicted to be ordered at its N-terminus and its C-terminus could accommodate a cation in a multicoordinated complex. The structure of beta3 was dominated by a beta-turn at its NPXY motif (beta3 744-747). In docking of alphaIIb to different sites within beta3, the conformation of the beta3 juxta-transmembrane (beta3 716-721) was greatly altered. This region was confirmed to be a conformational 'hot- spot' by circular dichroism. The conformational flexibility of this juxta-transmembrane region, which is highly conserved amongst integrins, is ideally located to regulate signaling.      

Hydraulic behavior of synthetic non-woven filter fabrics

The filtration performance of non-woven thick synthetic membranes used as filter fabrics is predicted from a proposed analytical method. The morphological analysis of many commercial fabrics has been utilized to identify internal structure parameters responsible for their hydraulic properties and also to predict the water permeability and the retention of particles in these fabrics. Experimental filtration tests were performed to gather data on the water permeability used in predicting clogging level. Also fibres' density and pore size histograms of fabrics were measured with an Image Analyser and a relationship was developed between the water permeability and the fibres' density. Finally it was found that the pore size histogram of non-woven fabrics of thickness greater than 1.5 mm could be calculated simply by measuring its water permeability and using an empirical correlation.     

Synthesis and application of CDA‐beta‐CD in controlling release of drug

To chemically attach beta‐cyclodextrin (beta‐CD) molecules to cellulose diacetate (CDA), an isocyanate containing preformed polymer was synthesized by prepolymerization of CDA and toluene‐2,4‐diisocyanate (TDI), which was then grafted with beta‐CD. Effects of reaction temperature, time, and mixture ratio on reactions were observed. The structure of CDA‐beta‐CD was characterized by ¹H‐ and ¹³C‐NMR spectra; the release of CDA‐beta‐CD with medicament naproxen by dynamic dialysis in the artificial simulated intestinal fluid (pH = 7.4) was studied in vitro. Results indicated that the release time could reach more than 8 h at a graft ratio of 68.7%, which showed a good controlled‐release drug effect. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Low-temperature synthetic route for boron carbide

Boron carbide is one of the hardest materials with diamond-like mechanical properties, and is already used for a variety of applications including armor plating, blasting nozzles, and mechanical seal faces, as well as for grinding and cutting tools. It is produced on an industrial scale by classical carbothermal reduction of boric oxides at high temperatures, but the formation of pure boron carbide in processed forms, such as films and fibers, is difficult. As an alternative to high-temperature powder techniques, there is recently great interest in the development of polymer precursors to produce ceramic materials. The aim of the present work is to develop a cost effective and low-temperature manufacturing process to synthesize boron carbide from cheap and easily available raw materials. The initial objective of our research is the design and synthesis of a new type of boron–carbon polymer, which would serve as precursor for boron carbide. The polymeric precursor is synthesized by the reaction of boric acid and polyvinyl alcohol that after pyrolysis at 400 °C and 800 °C gives boron carbide. The polymeric precursor and its pyrolyzed products are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). X-ray diffraction shows that boron carbide (B₄C) obtained from this method has an orthorhombic crystal structure. It is a unique low-temperature (∼400 °C) synthetic route for boron carbide.     

Effect of heat treatment on synthetic carbon precursors

Carbonaceous materials obtained from polyethyleneterephthalate (PET), a potential precursor for polymer-based carbon, were studied after heat treatment at 750, 900 and 1200 °C in an inert atmosphere. The carbon content increases to more than 95% (w/w) already at the lowest temperature applied. The surface area decreases from 242 to 14.7 m²/g between 750 and 1200 °C, causing also a reduced pore volume and the conversion of open to closed pores. The pore structure exhibits a gate effect. The carbon matrix contains both amorphous and semicrystalline regions. The spatial extent of the latter can be described by a Maxwellian distribution with a maximum of 12 Å at the lowest and 17 Å at the highest temperature values. Increasing the temperature from 900 to 1200 °C does not increase the size of these domains but yields a more ordered carbon skeleton. In the WAXS spectrum a flat diffuse peak about 3.5-4.0 Å corroborates that the graphitic domains are of colloidal size. The immersional wetting enthalpies determined in water, methanol and benzene indicate that the surface has an amphoteric character and that the carbon structure and surface chemistry are strongly affected by the heat treatment processes.     

Fabrication of interpenetrating polymer network to enhance the biological activity of synthetic hydrogels

A three dimensional porous hydrogel with suitable biological and mechanical properties are required for bone tissue engineering. Hydrogels of poly(lactic-ethylene oxide fumarate) (PLEOF), crosslinked with poly(ethylene glycol)-diacrylate (PEG-da) have desirable mechanical properties, however, their application for bone regeneration is limited due to the lack of cell motif sites within their structure. The aim of this study was to incorporate a naturally derived polymer such as gelatin into PLEOF hydrogels to promote their biological properties. Interpenetrating polymer network (IPN) was used as an efficient technique to acquire uniform mixture of these two polymers. Additionally gas foaming agents were used to create pores with average diameter of 250 μm in these IPN hydrogels. The concentrations of PEG-da and gelatin were optimized to tune the mechanical strength and degradation properties of these hydrogels. A compression modulus of 500 kPa was achieved for hydrogel fabricated with 400 mg/ml PLEOF, 200 mg/ml PEG-da and 150 mg/ml gelatin. The addition of gelatin to PLEOF elevated the compression modulus by two-fold and decreased the energy loss by 40%. The result of protein analysis demonstrated that IPN substantially enhanced the retention of physically crosslinked gelatin in the 3D structure of hydrogel. More than 50% of gelatin was retained in IPN hydrogel after two weeks of incubation in simulated physiological environment. Preserving gelatin in the hydrogel structure provides cell motif sites for a longer period of time, which is desirable for uniform cell proliferation. In vitro studies showed that primary human osteoblast cells adhered and proliferated in PLEOF-gelatin hydrogel. These results demonstrated the potential of using this IPN hydrogel for bone tissue engineering.     

Autoxidation of synthetic isomers of triacylglycerol containing eicosapentaenoic acid

Several triacylglycerols (TAG) that contained eicosapentaenoic acid (EPA) were chemically synthesized and stored at 25°C to assess the influence of TAG structure on oxidative stability and formation of oxidation products. Oxidative stability was evaluated by oxygen consumption during storage of the TAG. Autoxidation products of TAG were analyzed by high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). Results showed that a 2:1 (mole/mole) mixture of trieicosapentaenoylglycerol (EEE) and tripalmitoylglycerol (PPP) was most susceptible to autoxidation. The oxidative stability of TAG that contained EPA and palmitic acid was negatively correlated with the moles of EPA in a single TAG molecule. When TAG with one EPA and two other fatty acids were oxidized, chainlength of constituent fatty acids hardly affected the oxidative stability of EPA-containing TAG molecules, except for stearic acid. HPLC and LC-MS analyses showed that monohydroperoxides were major oxidation products regardless of type of TAG. Bis- and tris-hydroperoxides were formed during autoxidation of EEE and dieicos-apentaenoylpalmitoylglycerol. Monohydroperoxy epidioxides were found in all autoxidized TAG. These observations suggested that TAG structure affected the oxidation of TAG with highly unsaturated fatty acids.     

Transalkylation of Multi-secbutylbenzenes with Benzene over Hierarchical Beta Zeolite

A hierarchical beta zeolite synthesized by quasi-solid phase conversion method was characterized by BET, scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (X...     

CCl4低温氯化人造金红石制备TiCl4

为了开发低温钛氯化工艺及解决工业副产物CCl₄的再利用问题,在固定床和流化床反应器中考察了自贡法人造金红石原料与CCl₄低温氯化制备TiCl₄的反应过程,利用SEM、XRD、XPS等手段表征了人造金红石原料在反应前后的变化。结果显示,在450～500℃下,自贡法人造金红石能与CCl₄快速反应生成TiCl₄产品。少量Fe元素的掺杂是金红石相具备较高反应速率的关键原因。人造金红石原料制备过程中的弱氧化焙烧处理在颗粒表面形成的惰性金红石壳层,导致TiCl₄收率极限为90%,但该壳层能在酸解过程以及低温CCl₄氯化过程中维持颗粒粒度,使该原料能用于流化床操作。此过程具有显著的环保价值和工业应用前景。     

Analyses of structures for a synthetic leather made of polyurethane and microfiber

A gradient extraction method was developed and used for a synthetic leather made of polyurethane (PU) and microfiber polycaprolactam (PA‐6), by which the two components were separated using DMF and formic acid as solvents, respectively. Their chemical structure was confirmed by FTIR spectra, and the result showed that the PU is a kind of polyester polyurethane with phenylene rings in the molecule. The condensed phase structure was analyzed using X‐ray diffraction (XRD). The crystallinity of the PA‐6 is about 65.6%, and for the PU, there was not distinct crystalline character shown in the XRD pattern but a phase separation structure of hard block‐soft block with the hard domains content about 58.7%. SEM images showed that the PA‐6 microfibers transfixing the PU matrix form a net bundle structure, and there are two kinds of porous structures in the synthetic leather, with one type of pore sized 5–80 μm between the components of PU and PA‐6, and the other in PU matrix with a size of 0.1–2 μm. The multipores run through the synthetic leather as three‐dimensional channels, benefit for transportation of air, water, dyes, and so on. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 903–908, 2007     

Kinetic analysis of crystallization of zeolite beta synthesized by direct heating

To quantitatively investigate the initial crystallization of zeolite beta synthesized by direct heating, the extent of the reaction was precisely evaluated by X-ray diffraction measurements and Rietveld structural refinement, and a kinetic analysis of crystallization was performed using the Avrami-Erofe'ev equation. The activation energy for crystallization was lower than that for hydrothermal synthesis. Reaction and synthesis time curves revealed that the initial zeolite beta crystallization consisted of three stages. The first was an induction period with nucleation by the generation of building units and the formation of an initial coordinated structure. The second stage was crystal growth by a diffusion-controlled reaction, and the third stage involved slowing down of crystallization by the limitation of dehydrocondensation. These stages could be analyzed by calculation of the rate constant and Avrami exponent for each stage.     

Cobalt impurities in synthetic diamond

High-quality single crystals of diamond were grown by the temperature-gradient method using cobalt-containing metals as the solvent-catalyst. Cobalt and nickel impurities in the crystals were measured by X-ray fluorescence using synchrotron radiation. Their distributions were imaged by a mapping technique. Their concentrations were also measured at a number of points of the crystals. X-ray absorption near edge structure (XANES) spectroscopic measurements were carried out to investigate the bonding nature of the impurities. It was confirmed that the cobalt impurity distributes preferentially in the {111} sectors like nickel. We found that the concentration of cobalt is in proportional correlation with that of nickel in crystals grown from alloys containing both cobalt and nickel, and that cobalt is more difficult to incorporate than nickel. The XANES measurements revealed that the cobalt impurity occupies tetrahedral sites like nickel.     

Increasing the synthetic performance of penicillin acylase PAS2 by structure-inspired semi-random mutagenesis

A semi-random mutagenesis approach was followed to increase the performance of penicillin acylase PAS2 in the kinetically controlled synthesis of ampicillin from 6-aminopenicillanic acid (6-APA) and activated D-phenylglycine derivatives. We directed changes in amino acid residues to positions close to the active site that are expected to affect the catalytic performance of penicillin acylase: alpha R160, alpha F161 and beta F24. From the resulting triple mutant gene bank, six improved PAS2 mutants were recovered by screening only 700 active mutants with an HPLC-based screening method. A detailed kinetic analysis of the three most promising mutants, T23, TM33 and TM38, is presented. These mutants allowed the accumulation of ampicillin at 4-5 times higher concentrations than the wild-type enzyme, using D-phenylglycine methyl ester as the acyl donor. At the same time, the loss of activated acyl donor due to the competitive hydrolytic side reactions could be reduced to <20% with the mutant enzymes compared >80% wild-type PAS2. Although catalytic activity dropped by a factor of 5-10, the enhanced synthetic performance of the recovered penicillin acylase variants makes them interesting biocatalysts for the production of beta-lactam antibiotics.     

Adsorption of pharmaceuticals from aqueous solutions on synthetic zeolites

The objectives of this study were to measure the sorption capacity of a dilute solution of drugs in water on hydrophobic zeolites and to quantify aspects of their adsorption mechanisms for potential use in wastewater remediation. The removal of three drugs, erythromycin (ERY), carbamazepine (CBZ) and levofloxacin (FLX) from water using three organophilic zeolites (Y, mordenite (MOR), ZSM-5) was investigated. Adsorption isotherms show that these three drugs are adsorbed in remarkable amounts by Y. These data were confirmed by thermogravimetric analysis. The presence of these drugs inside the Y cage was revealed by unit cell parameter variations and structural deformations obtained by X-ray structure analyses carried out using the Rietveld method on zeolite after adsorption. Our results indicate that the adsorption properties of zeolitic materials do not only depend on micropore size and that zeolite shape selectivity also depends on structural features which are difficult to determine “a priori”. In order to test the ability of organophilic zeolites in removing drugs from wastewater, the adsorption of ERY, FLX and CBZ on zeolite Y from water samples collected at the outlet of a wastewater treatment plant located in Northern Italy was determined. These drugs were almost completely adsorbed by Y zeolite, confirming that this material is suitable for removing drugs from wastewater.     

阿那曲唑的合成工艺改进研究

以3,5-二溴甲苯为原料,经插羰、甲基化、氯代、氰代、溴代、N-烷基化6步反应合成标题化合物,考察了不同催化剂、反应时间、反应温度等因素对反应结果的影响,选择了氢化钠作为合成目标产物的缚酸剂,避免了同分异构体的产生。确定最佳工艺条件为:以PdCl2(PPh3)2作催化剂,Et3N做碱,90℃,9.12×106Pa为反应条件,获得了较好结果,总收率55.2%。产物结构经1HNMR和MS确证,改进后的合成方法简便,适合工业化生产。     

Helical tubuland diols: a synthetic and crystal engineering quest

Despite many advances in recent years, crystal engineering remains a risky venture. A successful outcome requires manipulation of the noncovalent bonding and properties such as size, shape, repulsion, attraction, polarity, and chirality. In this Account, we describe the interplay of crystal engineering and synthetic organic chemistry required to develop the family of helical tubuland diol hosts, the members of which exhibit a wide range of tube dimensions and inclusion properties. Certain alicyclic dialcohols crystallize with a hydrogen-bonded network structure, termed the helical tubuland lattice, in space group P3(1)21 (or its enantiomorph P3(2)21). Double helices of diol molecules surround parallel tubes that contain guest molecules, which are included on the basis of size and shape rather than functional group. The crystal structure of (diol)(3).(chloroacetic acid)(1.2) is illustrative. These chiral helical tubulate lattice inclusion compounds are formed when the racemic host diol is allowed to crystallize from solution. Complete enantiomer separation occurs during this process, producing a 1:1 mixture of pure (+)- and pure (-)-crystals (a conglomerate). The challenge of creating this family of compounds required the development of much synthetic chemistry, in particular new pathways to alicyclic ring systems with specific substitution patterns. It was also necessary to understand and control the supramolecular properties of the diol molecules. What makes the original compound tick, and why did it behave in this remarkable manner, when most of its structural neighbors crystallize totally differently? The synthesis of new helical tubuland diols requires not just preparation of a new molecular structure but also a transplant of the original unchanged hydrogen-bonding supramolecular synthon. Synthesis of the specific crystal space group is necessary. This was achieved by defining structural characteristics, termed molecular determinants, which are essential for the helical tubuland structure to occur. If these requirements were met, then the target molecule had a high probability of success. This investigation has close conceptual parallels with the search for pharmacophore properties of bioactive molecules. In both situations, parts of a molecule with little or no chemical reactivity may actually play vital supramolecular roles. The review illustrates how crystal engineering is based on specific supramolecular properties that can be uncovered and then exploited by synthetic chemists.     

Direct observation of amyloid fibril growth, propagation, and adaptation

Amyloid fibrils form through nucleation and growth. To clarify the mechanism involved, direct observations of both processes are important. First, seed-dependent fibril growth of beta2-microglobulin (beta2-m) and amyloid beta peptide was visualized in real time at the single fibril level using total internal reflection fluorescence microscopy combined with the binding of thioflavin T, an amyloid-specific fluorescence dye. Second, using atomic force microscopy, ultrasonication-induced formation of beta2-m fibrils was shown, indicating that ultrasonication is useful to accelerate the nucleation process. Third, with the proteolytic fragment of beta2-m, propagation and a transformation of fibril morphology was demonstrated. These direct observations indicate that template-dependent growth and structural diversity are key factors determining the structure and function of amyloid fibrils.     

A new family of synthetic diterpenes that regulates cytokine synthesis by inhibiting IkappaBalpha phosphorylation

The synthesis and the biological evaluation of a new family diterpenes are presented. The synthetic studies were inspired by the structural framework of acanthoic acid (1) and yielded a family of compounds that were evaluated as anti-inflammatory agents. Among them, compounds 2, 10, 12, and 16 exhibited a very low nonspecific cytotoxicity and inhibited the synthesis of TNF-alpha with greater than 65 % efficacy at low micromolar concentrations. Cytokine-specificity studies revealed that these compounds also inhibited the synthesis of the proinflammatory cytokines IL-1beta and IL-6, while inhibition of IL-1ra and IL-8 synthesis was marginal and only occurred at high concentrations. Further studies, through EMSA and Western blot analyses, indicated that these compounds decreased the extent of phosphorylation of IkappaBalpha; this suggests that they exert their anti-inflammatory profile by inhibiting NF-kappaB-mediated cytokine synthesis. These findings imply that these diterpenes represent promising leads for the development of novel anti-inflammatory agents.