Artificial lotus leaf by nanocasting.
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Journal Article↗
Biomedical subjects
Yong Chen
Publications and source records attributed to Yong Chen.
Calibration of solid-phase micro-extraction for quantitative analysis by gas chromatography.
Calibration of SPME by the injection of liquid standard solution is a common method for SPME quantitative analysis by gas chromatography. The feasibility of this calibration method relies on the assumption that sample transfer efficiencies are the same for both the liquid injection and the SPME fiber injection. Sample transfer efficiencies for liquid injection and SPME fiber injection were studied in this paper. The results showed that the sample transfer efficiency for liquid injection was affected by several factors, such as the dimensions of the liner, the presence of the wool, and the temperature of the injector. The sample transfer efficiency for SPME fiber injection was affected by the cross-sectional area of the space between the column and the liner, the carrier gas flow rate, and the length of the column inside the liner. An equation was proposed to estimate the sample loss rate for SPME injection. It was found that the use of a direct injection (DI) liner and program temperature vaporizing provides high sample transfer efficiencies, for both liquid injection and SPME fiber injection. When a common SPME straight liner is used, large outer diameter (o.d.) pre-column will help to achieve high sample transfer efficiency.
Acenaphthenes↗
Synthesis and in vitro pharmacological studies of new C(2) modified salvinorin A analogues.
Salvinorin A is the most potent naturally occurring opioid agonist yet discovered with high selectivity and affinity for kappa-opioid receptor. To explore its structure and activity relationships, a series of salvinorin A derivatives modified at the C2 position were prepared and studied. These salvinorin A derivatives were screened for binding and functional activities at the human kappa-opioid receptor. Compound 4, containing a methoxymethyl group at the 2-position, was a full kappa-agonist with an EC50 value at 0.6 nM, which is about 7 times more potent than salvinorin A.
Diterpenes↗
Implicit solvent simulations of DPC micelle formation.
The formation of micelles by dodecylphosphocholine (DPC) is modeled by treating the surfactants in atomic detail and the solvent implicitly, in the spirit of the EEF1 solvation model for proteins. The solvation parameters of the DPC atoms are carried over from those of similar atoms in proteins. A slight adjustment of the parameters for the headgroup was found necessary for obtaining an aggregation number consistent with experiment. Molecular dynamics simulations of 960 DPC molecules at different concentrations are used to obtain the aggregation number, the micelle size distribution, and the CMC. At 20 mM concentration we obtain an aggregation number of 53-56 and a CMC of 1.25 mM, values close to the experimental ones. At 100 mM the aggregation number increases to 90. Simulations of individual micelles of varying size show that the effective energy per surfactant molecule is initially a decreasing function of aggregation number but stabilizes at about 60 molecules. The van der Waals term and the desolvation of nonpolar groups contribute to micellization, whereas the desolvation of polar groups opposes it. From the difference between the effective energy and the free energy (calculated from the CMC), the translational and rotational entropy contributions to the free energy are estimated at about 7 kcal/mol per monomer. The micelles obtained here are more irregular than those obtained in explicit water simulations. This modeling approach allows the study of larger surfactant aggregates for longer times and the extraction of thermodynamic in addition to structural information.
Computer Simulation↗
Sensitive and specific liquid chromatographic-tandem mass spectrometric assay for atropine and its eleven metabolites in rat urine.
A sensitive and specific method is described for the simultaneous determination of atropine and its metabolites in rat urine by combining liquid chromatography and tandem mass spectrometry (LC-MS(n)). Various extraction techniques (free fraction, acid hydrolyses and enzyme hydrolyses) and their comparison were carried out for investigation of the metabolism of atropine. After extraction procedure the pretreated samples were separated on a reversed-phase C18 column using a mobile phase of methanol/ammonium acetate (2 mM, adjusted to pH 3.5 with formic acid) (70: 30,v/v) and detected by an on-line LC-MS(n) system. Identification and structural elucidation of the metabolites were performed by comparing their changes in molecular masses (DeltaM), retention-times and full scan MS(n) spectra with those of the parent drug. The results revealed that at least eleven metabolites (N-demethyltropine, tropine, N-demethylatropine, p-hydroxyatropine, p-hydroxyatropine N-oxide, glucuronide conjugates and sulfate conjugates of N-demethylatropine, p-hydroxyatropine and the parent drug) and the parent drug existed in rat urine after ingesting 25 mg/kg atropine. p-Hydroxyatropine and the parent drug were detected in rat urine for up 106 h after ingestion of atropine.
Acetates↗
Thio[2-(benzoylamino)ethylamino]-beta-CD fragment modified gold nanoparticles as recycling extractors for [60]fullerene.
Gold particles are modified with surface-attached bis(beta-cyclodextrin)s bearing S-S bridges to give water-soluble cyclodextrin-modified gold nanoparticles, which are successfully used as recycling extractors for [60]fullerene.
Cell Surface Extensions↗
YKT6 is a core constituent of membrane fusion machineries at the Arabidopsis trans-Golgi network.
SNARE complex formation is essential for membrane fusion in exocytotic and vacuolar trafficking pathways. Vesicle-associated (v-) SNARE associates with a target membrane (t-) SNARE to form a SNARE complex bridging two membranes, which may facilitate membrane fusion. The Arabidopsis genome encodes a large number of predicted SNARE proteins that might function primarily as fusogens for vesicle transport in endomembrane systems. The SNAREs SYP41, SYP61 and VTI12 reside in the trans-Golgi network and have been proposed to function together in vesicle fusion with this organelle. Here, we use a liposome fusion assay to demonstrate that VTI12 and either SYP41 or SYP61, but not both, are required for membrane fusion. This indicates that SYP41 and SYP61 are likely to function in independent vesicle fusion reactions in Arabidopsis. In addition, we have identified two new functionally interchangeable components, YKT61 and YKT62, that show sequence similarity to the multifunctional yeast SNARE YKT6. Both YKT61 and YKT62 interact with SYP41 and are essential for membrane fusion mediated by either SYP41 or SYP61. These results therefore define the core constituents required for membrane fusion at the Arabidopsis trans-Golgi network.
Arabidopsis↗
Cyclodextrins as carriers for cinchona alkaloids: a pH-responsive selective binding system.
A series of cyclodextrin-cinchona alkaloid inclusion complexes were prepared from beta-cyclodextrin, heptakis(2,6-di-O-methyl)-beta-cyclodextrin and heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin and four cinchona alkaloids in ca. 90% yields, and their inclusion complexation behavior was investigated at pH 7.2 and 1.5 by means of fluorescence, UV/Vis and 2D NMR spectroscopy. The results showed that the cinchona alkaloids can be efficiently encapsulated in the cyclodextrin cavity in an acidic environment and sufficiently released in a neutral environment, which makes these cyclodextrin derivatives the potential carriers for cinchona alkaloids. The binding ability and molecular selectivity of cyclodextrins toward cinchona alkaloids were discussed from the viewpoint of the size-fit concept and multiple recognition mechanism between host and guest.
Binding Sites↗
Synthesis and in vitro pharmacological evaluation of salvinorin A analogues modified at C(2).
Salvinorin A is the only known non-nitrogenous and specific kappa-opioid agonist. A series of salvinorin A derivatives were prepared and tested for in vitro activity at the kappa-opioid receptor. Unsubstituted carbamate 9 was a potent kappa-agonist (EC(50) = 6.2 nM) and should be more stable than salvinorin A toward metabolic transformations. Compound 10, containing an N-methyl carbamate at C(2), showed partial agonist activity with 81% efficacy when compared with the full agonist U50,488H. No antagonist ligands were observed.
Animals↗
Spectrophotometric study on the controlling factor of molecular selective binding of dyes by bridged bis(beta-cyclodextrin)s with diselenobis(benzoyl) linkers.
A series of beta-cyclodextrin (beta-CD) dimers with 4,4'-diselenobis(benzoyl) linkers, that is, 6,6'-[4,4'-diselenobis(benzoyloxyl)]-bridged bis(beta-CD) (1a), 6,6'-[4,4'-diselenobis[2-(benzoylamino)ethyleneamino]]-bridged bis(beta-CD) (2a), and 6,6'-[4,4'-diselenobis[2-(benzoylamino)-3,6-diazaoctylamino]]-bridged bis(beta-CD) (3a), were synthesized in moderate yields by the reaction of 4,4'-diselenobis(benzoic acid) with beta-CD or oligo(ethylenediamino)-6-deoxy-beta-CD. Their binding behaviors with some structure-related substrates, such as acridine red (AR), neutral red (NR), rhodamine B (RhB), ammonium 8-anilino-1-naphthalenesulfonate (ANS), and 6-p-toluidino-2-naphthalenesulfonic acid (TNS), were investigated in aqueous phosphate buffer solution (pH 7.20) at 298.15 K by means of fluorescence, NMR, as well as circular dichroism spectroscopy and compared with those of their 2,2'-diselenobis(benzoyl)-linked analogues, that is, 6,6'-[2,2'-diselenobis(benzoyloxyl)]-bridged bis(beta-CD) (1b), 6,6'-[2,3'-diselenobis[2-(benzoylamino)ethyleneamino]]-bridged bis(beta-CD) (2b), and 6,6'-[2,2'-diselenobis[2-(benzoylamino)-3,6-diazaoctylamino]]-bridged bis(beta-CD) (3b). The results showed that bis(beta-CD)s 1a-3a, whose Se-Se bonds were located at the para position of the carboxyl group, gave stronger binding abilities toward nonlinear guests (RhB and ANS) than their analogues 1b-3b, whose Se-Se bonds were located at the ortho position relative to the carboxyl group. The molecular binding ability and selectivity of model substrates by these ditopic hosts were sufficiently discussed to reveal not only the cooperative contributions of the linker group and CD cavities upon inclusion complexation with dye guest molecules but also the controlling factors for the molecular selective binding.
Journal Article↗
Transplantation of human hepatocytes cultured with deleted variant of hepatocyte growth factor prolongs the survival of mice with acute liver failure.
BACKGROUND: Considering the scarcity of donor livers, it is extremely important to establish a functional culture method for isolated hepatocytes. As a tool for maintaining hepatocyte functions in vitro, dHGF, a variant of HGF (hepatocyte growth factor) with a deletion of five amino acids, attracted our attention because it is less cytotoxic compared with HGF. METHODS: We evaluated growth, albumin production, metabolizing abilities of ammonia, lidocaine, and diazepam of human hepatocytes in the presence of dHGF (10-1000 ng/ml). The gene expression of liver markers was comparatively analyzed. The effect of intrasplenic transplantation of dHGF-treated human hepatocytes into severe combined immunodeficient (SCID) mice was evaluated in an acute liver failure (ALF) model induced by D-galactosamine (D-gal). RESULTS: When 100 ng/ml of dHGF was utilized, metabolism rates of ammonia, lidocaine, and diazepam and albumin production per unit cell significantly increased. The gene expression analysis demonstrated the enhanced expression of albumin, HNF-4alpha, and C/EBPalpha in the hepatocytes treated with 100 ng/ml of dHGF. Transplantation of such hepatocytes prolonged the survival of the SCID mice with ALF induced by D-gal. CONCLUSIONS: The present work clearly demonstrates the usefulness of dHGF (100 ng/ml) for maintaining the differentiated functions of human hepatocytes in tissue culture.
Albumins↗
Inclusion complexes of azadirachtin with native and methylated cyclodextrins: solubilization and binding ability.
The inclusion complexation behavior of azadirachtin with several cyclodextrins and their methylated derivatives has been investigated in both solution and the solid state by means of XRD, TG-DTA, DSC, NMR, and UV-vis spectroscopy. The results show that the water solubility of azadirachtin was obviously increased after resulting inclusion complex with cyclodextrins. Typically, beta-cyclodextrin (beta-CD), dimethyl-beta-cyclodextrin (DMbetaCD), permethyl-beta-cyclodextrin (TMbetaCD), and hydroxypropyl-beta-cyclodextrin (HPbetaCD) are found to be able to solubilize azadirachtin to high levels up to 2.7, 1.3, 3.5, and 1.6 mg/mL (calculated as azadirachtin), respectively. This satisfactory water solubility and high thermal stability of the cyclodextrin-azadirachtin complexes, will be potentially useful for their application as herbal medicine or healthcare products.
Cyclodextrins↗
Equilibrium in-fibre standardisation technique for solid-phase microextraction.
This note describes a fundamental investigation into solid-phase microextraction (SPME) using a standard loaded into the fibre coating as a means of internal standardisation for the analysis of samples contained in vials. The loading of reproducible amounts of standards into a non-porous SPME fiber was investigated. It was found that spiking low milligram quantities of standards such as benzene, toluene, ethylbenzene, xylenes (BTEX) and/or naphthalene into a few grams of pump oil sealed in a 20 mL vial provided an excellent standard generator. A single solution allowed over a hundred standard loadings with a reproducibility of <4% R.S.D. When a fiber, loaded with the standard(s) was introduced into a sample vial, extraction of analytes into the fiber and desorption of the standard(s) into the sample matrix occur simultaneously. Quantification was then based on the equilibrium distribution of the standards and the analytes between the fibre coating and the sample matrix in the vial. A comparison of equilibration profiles obtained using traditional internal standardisation and the in-fibre approach generally showed the same equilibration behaviour. The developed method was successfully used to correct for matrix effects in the BTEX analysis of a wine sample.
Automation↗
PDMS microfludic device for optical detection of protein immunoassay using gold nanoparticles.
A simple but highly specific immunoassay system for goat anti-human IgG has been developed using gold nanoparticles and microfluidic techniques. The assay is based on the deposition of gold nanoparticles that are coated with protein antigens in the presence of their corresponding antibodies to microfluidic channel surface. The effects of time accumulation, the flow velocity, and the concentration of antibodies to the red light absorption percentage (RAP) of deposition were investigated with an ordinary optical microscope. By controlling the reaction time and flow velocity, a dynamic range of 3 orders of magnitude and a detection sensitivity of 10 ng ml(-1) of goat anti-human IgG were achieved. Because of its simplicity and flexibility, this new technique should be useful for fast, highthroughput screening of antibodies in clinical diagnostic applications.
Animals↗
Spatial prisoner's dilemma game with volunteering in Newman-Watts small-world networks.
A modified spatial prisoner's dilemma game with voluntary participation in Newman-Watts small-world networks is studied. Some reasonable ingredients are introduced to the game evolutionary dynamics: each agent in the network is a pure strategist and can only take one of three strategies (cooperator, defector, and loner); its strategical transformation is associated with both the number of strategical states and the magnitude of average profits, which are adopted and acquired by its coplayers in the previous round of play; a stochastic strategy mutation is applied when it gets into the trouble of local commons that the agent and its neighbors are in the same state and get the same average payoffs. In the case of very low temptation to defect, it is found that agents are willing to participate in the game in typical small-world region and intensive collective oscillations arise in more random region.
Journal Article↗
Molecular recognition thermodynamics of bile salts by beta-cyclodextrin dimers: Factors governing the cooperative binding of cyclodextrin dimers.
The complex stability constants (K(S)), standard molar enthalpy (DeltaH degrees), and entropy changes (DeltaS degrees) for the inclusion complexation of two families of beta-cyclodextrin (beta-CD) dimers, i.e. beta-CD dimers Se1-Se4 bearing 2,2'-diselenobis(benzoyl) tether (Se-dimers) and beta-CD dimers Py1-Py4 bearing 2,2'-bipyridine-4,4'-dicarboxy tether (Py-dimers), with four bile salt guests, i.e. sodium cholate (CA), sodium deoxycholate (DCA), sodium glycocholate (GCA), and sodium taurocholate (TCA), were determined at 25 degrees C in Tris buffer solution (pH 7.4) at 298.15 K by means of isothermal titration microcalorimetry. The thermodynamic parameters obtained, together with the ROESY spectra of interactions between beta-CD dimers and bile salts, consistently suggest that the length, flexibility, and structure of spacers linking the two beta-CD cavities not only determine the binding modes but also significantly alter the molecular selectivity of beta-CD dimers.
Calorimetry↗
Efficient fluorescent sensors of oligopeptides by dithiobis(2-benzoylamide)-bridged bis(beta-cyclodextrin)s: structure in solution, binding behavior, and thermodynamic origin.
Two 6,6'-bis(beta-cyclodextrin)s linked by 2,2'-dithiobis[2-(benzoylamino)ethyleneamino] and 2,2'-dithiobis[2-(benzoylamino)diethylenetriamino] bridges (1 and 2) have been synthesized as cooperative multipoint recognition receptor models for non-aromatic oligopeptides. Their structures in solution and inclusion complexation mechanism are comprehensively investigated by means of circular dichroism, 2D NMR spectra and temperature-dependent fluorescence titrations. The results show that the cooperative 'host-linker-guest' binding mode and the extensive desolvation effect jointly contribute to the guest-induced fluorescence enhancement of bis(beta-cyclodextrin)s. Further examinations on the binding behavior of hosts 1-2 with a series of di- and tri-peptides demonstrate that bis(beta-cyclodextrin) 1 can recognize not only the size/shape of oligopeptides but also the dipeptide sequence, giving an exciting residue selectivity up to 37.5 for Gly-Gly-Gly/Glu-Glu pair and a high sequence selectivity up to 5.0 for Gly-Leu/Leu-Gly pair. These fairly good selectivities are discussed from the viewpoint of cooperative binding, multiple recognition and induced-fit interactions between host and guest.
Fluorescent Dyes↗
Vapor-phase self-assembled monolayer for improved mold release in nanoimprint lithography.
Resist adhesion to the mold is one of the challenges for nanoimprint lithography. The main approach to overcoming it is to apply a self-assembled monolayer of an organosilane release agent to the mold surface, either in the solution phase or vapor phase. We compared the atomic force microscopy, ellipsometry, reflection-absorption infrared spectroscopy, and contact angle results collected from substrates treated by two different application processes and found that the vapor-phase process was superior. The vapor-treated substrates had fewer aggregates of the silane molecules on the surface, because the lower density of the agent in the vapor phase was not conducive to aggregation formation, and received a superior coating of the releasing agent, because the vapor was more effective than the solution in penetrating into the nanoscale gaps of the mold. A pattern transfer of 20 parallel nanowires with a line width of 40 nm at 100 nm pitch-size was performed faithfully with the vapor-treated mold without any resist adhesion.
Letter↗