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Covalent Bonding (covalent + bonding)
Selected AbstractsLayered Double Hydroxide Surface Modified with (3-aminopropyl)triethoxysilane by Covalent Bonding,ADVANCED MATERIALS, Issue 1 2005A.-Y. Park Interlayer surfaces of layered double hydroxide (LDH) have been functionalized with amine moieties by condensation between the hydroxyl groups and (3-aminopropyl)triethoxysilane (APS) molecules via the covalent oxane bonds M-O-Si (M=Zn and Cr) (see Figure). Since the galleries of the modified LDHs have a hydrophobic field, various functional molecules such as enzymes, catalysts, and organic molecules can be incorporated between the LDH layers. [source] Chiral separation of dansyl amino acids by ligand exchange capillary electrochromatography in a low molecular weight organogel,ELECTROPHORESIS, Issue 18 2008Shaul Mizrahi Abstract Chiral electroseparation is demonstrated, for the first time, by a low molecular weight organogel filled capillary. Five pairs of dansylated amino acids were separated by copper ligand exchange on a trans -(1S,2S)-1,2-bis-(dodecylamido) cyclohexane (1) gel in methanol. Low molecular weight organogels are emerging materials that form stable, fibrillar, thermoreversible and thixotropic gels without covalent bonding of their monomeric building blocks. The dependence of chiral resolution and complex formation stability on the pH*, the ratio between copper and the D -valine selector, as well as other parameters were investigated revealing trends that were unparalleled in previously reports on copper ligand exchange of dansylated amino acids. These observations were explained in view of a simple stacking model of (1) and the difference in axial ligation of the amide carbonyl backbone of the gel to the dansyl D - or L -amino acid:D -valine:copper ternary complexes. [source] Sorption of benzidine and 3,3,-dichlorobenzidine to lake sediments.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 20051. conceptualization, development of a multiparameter model Abstract Aromatic amines, such as benzidine and 3,3,-dichlorobenzidine (DCB), are part of the dyes and pigments manufacturing process. The prolonged use of these carcinogenic chemicals in the past generation has introduced a significant amount of contamination to the environment. Their persistency in several mediums has sparked a number of studies in an attempt to develop predictive tools of their fate and transport in the environment. In this study, benzidine and DCB batch isotherms were developed and evaluated. The sediment samples were variable in composition, ranging from sandy to silty-clay sediment samples. The batch isotherms were then analyzed using high-performance liquid chromatography. Subsequently, a multiparameter model (MPM) that accounted for partitioning, covalent bonding, and cation exchange was developed and tested in an effort to understand the various mechanisms. Results proved the proposed model to be effective in predicting sorption of aromatic amines to lake sediments. The findings suggest that the MPM can provide a better understanding of the sorption process of aromatic amines than more conventional models. [source] Synthetic bacterial lipopeptide analogs facilitate naive CD4+ T,cell differentiation and enhance antigen-specific HLA-II-restricted responsesEUROPEAN JOURNAL OF IMMUNOLOGY, Issue 8 2005Mascia Ghielmetti Abstract Synthetic di- and tri-palmitoylated bacterial lipopeptide analogs (BLpA) can enhance HLA-I-restricted immune responses. Here we show that BLpA indirectly promote antigen-driven differentiation of naive CD4+ T,lymphocytes in vitro, with mechanisms that require DC and are inhibited by CTLA-4/Ig. In mixed cultures of cord blood-derived PBMC and allogeneic DC, P3CSK4 lipopeptide facilitated the transition from CCR7+/CD45RA+/CD62L+ to CCR7,/CD45RA,/CD62Ldim T,cells with kinetics significantly exceeding those obtained with the unlipidated CSK4 analog. Moreover, P3CSK4 and P2CSK4, but neither the mono-palmitoylated PCSK4 analog nor the CSK4 peptide, increased the frequency of IFN-,-producing T,cells expanded under similar conditions. Along with this, P2CSK4 and P3CSK4, but not PCSK4, restored the in vitro antigenicity of MDP-OspA, a non-immunogenic analog of Borrelia burgdorferi major outer surface lipoprotein,A, and enhanced the frequency of in vitro expanded T,cells specific for the tetanus toxoid (TT) and hepatitis,B surface antigen (HBsAg) peptides TT947,967 and HBsAg19,33 and for TT. Altogether, BLpA bearing at least two ester-bonded palmitoyl side chains indirectly enhance antigen-driven CD4+ T,cell differentiation. BLpA adjuvanticity is independent of covalent bonding to Ag and Ag formulation. This information may be helpful to generate more potent recombinant vaccines. [source] Asymmmetric Diamino Functionalization of Nanotubes Assisted by BOC Protection and Their Epoxy NanocompositesADVANCED FUNCTIONAL MATERIALS, Issue 18 2010Yao Zhao Abstract Homogenous dispersion and strong interfacial bonding are prerequisites for taking full advantage of the mechanical properties of nanotubes in a composite. In order to simultaneously achieve both conditions, a highly efficient and mechanically non-destructive functionalization of nanotubes is developed. With fluoronanotubes as the precursor, asymmetric diamine molecules, N -BOC-1,6-diaminohexane, are used to replace fluorines on the wall of fluoronanotubes and construct covalent bonding to the surface of the nanotubes. A BOC de-protection reaction is conducted and the resulting exposed amino groups create strong covalent bonds with the matrix in the course of epoxy ring-opening etherification and curing chemical reactions. In comparison with the conventional functionalization based on symmetric diamine molecules, the functionalized nanotubes derived from the BOC-protected diamine molecule are more dispersed within the epoxy matrix. Dynamic mechanical analysis shows that the functionalized nanotubes have better crosslinking with the matrix. The composites reinforced by the nanotubes demonstrate improvement in various mechanical properties. The Young's Modulus, ultimate tensile strength, and storage modulus of composites loaded with 0.5 wt% functionalized nanotubes are enhanced by 30%, 25%, and 10%, respectively, compared with the neat epoxy. The increase of the glass transition temperature, as much as 10 °C, makes the composites suited for engineering applications under higher temperatures. The new functionalization method allows for an competitive enhancement in the composite performance in use of relatively low cost raw nanotubes at a small loading level. The reinforcement mechanism of the functionalized nanotubes in the epoxy resin is discussed. [source] Electrophosphorescent Polyfluorenes Containing Osmium Complexes in the Conjugated Backbone,ADVANCED FUNCTIONAL MATERIALS, Issue 9 2008Chen-Han Chien Abstract Electrophosphorescent copolymers have been synthesized by covalent bonding of a red-emitting osmium complex Os(bpftz), which contains two 3-trifluoromethyl-5-(4- tert -butyl-2-pyridyl)triazolate (bpftz) cyclometalated ligands, into the backbone of a bipolar polyfluorene (PF) copolymer. Employing these copolymers, a highly efficient red polymer light-emitting diode has been realised that has an external quantum efficiency of 18.0%, a maximum brightness of 38,000,cd,m,2, and an emission centered at 618,nm. In addition, after incorporating appropriate amounts of green-emitting benzothiadiazole (BT) and the aforementioned Os(bpftz) into the bipolar PF, an efficient white-light electroluminescent polymer is obtained that displays simultaneous blue, green, and red emissions. [source] Solution Processing of Chalcogenide Semiconductors via Dimensional ReductionADVANCED MATERIALS, Issue 31 2009David B. Mitzi Abstract The quest to develop thin-film solution processing approaches that offer low-cost and preferably low-temperature deposition, while simultaneously providing quality semiconductor characteristics, has become an important thrust within the materials community. While inorganic compounds offer the potential for outstanding electronic properties relative to organic systems, the very nature of these materials rendering them good electronic materials,namely strong covalent bonding,also leads to poor solubility. This review presents a "dimensional reduction" approach to improving the solubility of metal chalcogenide semiconductors, which generally involves breaking the extended framework up into discrete metal chalcogenide anions separated by small and volatile cationic species. The resulting soluble precursor may be solution-processed into thin-film form and thermally decomposed to yield the desired semiconductor. Several applications of this principle to the solution deposition of high-performance active layers for transistors (channel mobility >10,cm2 V,1 s,1), solar cells (power conversion efficiency of as high as 12%), and fundamental materials study will be presented using hydrazine as the deposition solvent. [source] Structure-Dependent Electrical Properties of Carbon Nanotube Fibers,ADVANCED MATERIALS, Issue 20 2007W. Li Improved electron transport along a carbon nanotube (CNT) fiber when it is spun from an array of longer nanotubes is reported. The effect of chemical post-treatments is also demonstrated. For example, the covalent bonding of gold nanoparticles to the CNT fibers remarkably improves conductivity (see figure), whereas annealing CNT fibers in a hydrogen-containing atmosphere leads to a dramatic decrease in conductivity. [source] Broken symmetry approach and chemical susceptibility of carbon nanotubesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 8 2010Elena F. Sheka Abstract Constituting a part of odd electrons that are excluded from the covalent bonding, effectively unpaired electrons are posed by the singlet instability of the single-determinant broken spin-symmetry unrestricted Hartree,Fock (UBS HF) SCF solution. The correct determination of the total number of effectively unpaired electrons ND and its fraction on each NDÀ atom is well provided by the UBS HF solution. The NDÀ value is offered to be a quantifier of atomic chemical susceptibility (or equivalently, reactivity) thus highlighting targets that are the most favorable for addition reactions of any type. The approach is illustrated for two families involving fragments of arm-chair (n,n) and zigzag (m,0) single-walled nanotubes different by the length and end structure. Short and long tubes as well as tubes with capped end and open end, in the latter case, both hydrogen terminated and empty, are considered. Algorithms of the quantitative description of any length tubes are suggested. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Chemical susceptibility of fullerenes in view of Hartree,Fock approachINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 14 2007Elena F. Sheka Abstract Constituting a part of fullerenes odd electrons which are removed from the covalent bonding (Int J Quantum Chem, 2004, 100, 375), effectively unpaired electrons are posed by the singlet instability of the unrestricted Hartree,Fock SCF solution. The feature occurs to be of a particular importance leading to a quantitative description of atomically matched chemical susceptibility of the odd-electron molecular species via the relevant electron density on atoms. A correct determination of the total number of effectively unpaired electrons ND and its partial density NDA is well provided by the UHF solution. The calculation procedure and the obtained results reliability are justified for a set of diatomic molecules and ethylene. Practically full identity of the distribution of both NDA values and independently calculated free valence over atoms of X60 (X = C, Si) and C70 molecules makes it possible to consider the NDA maps as chemical portraits of the fullerenes. The NDA value is offered to be a quantitative pointer of the atom chemical activity thus highlighting targets, which are the most favorable for addition reactions of any type. Basic grounds for a NDA -based computational synthesis of the fullerene derivatives are illustrated for initial steps of C60 fluorination. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007 [source] Highly Active and Recyclable Heterogeneous Iridium Pincer Catalysts for Transfer Dehydrogenation of AlkanesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 1-2 2009Zheng Huang Abstract Pincer-ligated iridium complexes have proven to be highly effective catalysts for the dehydrogenation and transfer-dehydrogenation of alkanes. Immobilization onto a solid support offers significant potential advantages in the application of such catalysts particularly with respect to catalyst separation and recycling. We describe three approaches toward such immobilization: (i) covalent attachment to a Merrifield resin, (ii) covalent bonding to silica via a pendant alkoxysilane group, and (iii) adsorption on ,-alumina (,-Al2O3), through basic functional groups on the para- position of the pincer ligand. The simplest of these approaches, adsorption on ,-Al2O3, is also found to be the most effective, yielding catalysts that are robust, recyclable, and comparable to or even more active than the corresponding species in solution. Spectroscopic evidence (NMR, IR) and studies of catalytic activity support the hypothesis that binding occurs at the para- substituent and that this has only a relatively subtle and indirect influence on catalytic behavior. [source] Novel bioactive scaffolds with fibronectin recognition nanosites based on molecular imprinting technologyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 6 2010Elisabetta Rosellini Abstract Biomimetic materials for application in the field of tissue engineering are usually obtained through covalent bonding between the polymer backbone and the bioactive molecules. A totally new approach, proposed for the first time by our research group, for the creation of advanced synthetic support structures for cell adhesion and proliferation is represented by molecular imprinting (MI) technology. In this article, we describe the synthesis and characterization of molecularly imprinted polymers with recognition properties toward a fibronectin peptide sequence and their application as functionalization structures. Polymers, in the form of densely fused microgel particles, were obtained by precipitation polymerization. The imprinted particles showed good performance in terms of recognition capacity and quantitative rebinding; moreover, the epitope effect was observed, with the particles able to recognize and rebind not only the specific peptide sequence but also a larger fibronectin fragment. The cytotoxicity tests showed normal vitality in C2C12 myoblasts cultured in a medium that was put in contact with the imprinted particles. Therefore, imprinted particles were used to functionalize synthetic polymeric films by deposition on their surface. The deposition of the imprinted particles did not alter their specific recognition and rebinding behavior. The most remarkable result was obtained by the biological characterization: in fact, the functionalized materials appeared able to promote cell adhesion and proliferation. These results are very promising and suggest that MI can be used as an innovative functionalization technique to prepare bioactive scaffolds with an effective capacity for improving tissue regeneration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 [source] Why does electron sharing lead to covalent bonding?JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2007A variational analysis No abstract is available for this article. [source] Synthesis of PEGylated single wall carbon nanotubes by a photoinitiated graft from polymerizationAICHE JOURNAL, Issue 6 2010Pu Zhang Abstract A considerable amount of research has been devoted to carbon nanotubes because of their unique electrical, mechanical, optical, and chemical properties. Here, in this report, we introduce a novel, simple ultraviolet initiated "graft from" polymerization method to synthesize PEGylated carbon nanotubes. This grafting procedure significantly enhanced nanotube aqueous dispersibility and long term stability in solution. Mass of grafted polymer chains was easily modulated by adjusting polymerization reaction time, and nanomaterials containing up to 80% polymer by weight were synthesized. Nanotube morphology was characterized by SEM, TEM before and after the functionalization. In addition, the covalent bonding of polymer chains to the nanotubes structure was elucidated by Raman, ATR-FTIR, and XPS spectroscopy. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Raman and surface-enhanced Raman spectroscopic studies of the 15-mer DNA thrombin-binding aptamerJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2010Cynthia V. Pagba Abstract Aptamers are single-stranded oligonucleotides that selectively bind to their target molecules owing to their ability to form secondary structures and shapes. The 15-mer (5,-GGTTGGTGTGGTTGG-3,) DNA thrombin-binding aptamer (TBA) binds to thrombin following the formation of a quadruplex structure via the Hoogsten-type G,G interactions. In the present study, Raman and SERS spectra of TBA and thiolated TBA (used to facilitate covalent bonding to metal nanoparticle) in different conditions are investigated. The spectra of the two analogs exhibit vibrations, such as the C8N7H2 deformation band at ,1480 cm,1 of the guanine tetrad, that are characteristic of the quadruplex structure in the presence of K+ ions or at low temperature. Interestingly, SERS spectra of the two analogs differ markedly from their respective normal Raman spectra, possibly due to changes in the conformation of the aptamer upon binding, as well as to the specific interaction of individual vibrational modes with the metal surface. In addition, the SERS spectra of the thiolated aptamer show significant changes with different concentrations, which may be due to different orientation of the molecule with respect to the metal surface. This study provides useful information for the development of label-free aptamer-based SERS sensors and assays. Copyright © 2009 John Wiley & Sons, Ltd. [source] Density functional study of graphene overlayers on SiCPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 7 2008Alexander Mattausch Abstract Despite the ongoing "graphene boom" of the last three years our understanding of epitaxial graphene grown on SiC substrate is only beginning to emerge. Along with experimental methods such as low energy electron diffraction (LEED), scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy (ARPES), ab initio calculations help to uncover the geometric and electronic structure of the graphene/SiC interface. In this chapter we describe the density-functional calculations we performed for single and double graphene layers on Si- and C-terminated 6H-SiC surfaces. Experimental data reveal a pronounced difference between the two surface terminations. On a Si-terminated surface the interface adopts a 6,3 × 6,3 unit cell whereas the C-face supports misoriented (turbostratic) graphene layers. It has been recently realized that, on the Si-face, the large commensurate cell is subdivided into patches of coherently matching to the substrate carbon atoms. In our calculations we assumed the "coherent match" geometry for the whole interface plane. This reduces the periodic unit to the ,3 × ,3R 30° cell but requires a substantial stretching of the graphene sheet. Although simplified, the model provides a qualitative picture of the bonding and of the interface electron energy spectrum. We find that the covalent bonding between the carbon layer and the substrate destroys the massless "relativistic" electron energy spectrum, the hallmark of a freestanding graphene. Hence the first carbon layer cannot be responsible for the graphene-type electron spectrum observed by ARPES and rather plays a role of a buffer between the substrate and the subsequent carbon sheets. The "true" graphene spectrum appears with the second carbon layer which exhibits a weak van der Waals bonding to the underlying structure. For Si-terminated substrate, we find that the Fermi level is pinned by the interface state at 0.45 eV above the graphene Dirac point, in agreement with experimental data. This renders the interface metallic. On the contrary, for a C-face the "coherent match" model predicts the Fermi level exactly at the Dirac point. However, this does not necessarily apply to the turbostratic graphene layers that normally grow on the C-terminated substrate. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Covalent addition of diethyltoluenediamines onto carbon nanotubes for composite applicationPOLYMER COMPOSITES, Issue 8 2009Shiren Wang Diethyltoluenediamines (DETDA) was grafted to single-walled carbon nanotubes (SWNTs) through diazonium-based addition for improving dispersion and interfacial bonding in SWNT/epoxy nanocomposites. Characterization results of Fourier Transformed Infrared spectroscopy and Raman spectroscopy validated covalent bonding between DETDA and carbon nanotubes. The degree of functionalization was about 4% based on thermo-gravimetric analysis. Interfacial bonding strength was computed in the presence of chemical bonding and the computation results indicated that the interfacial shear strength in the presence of functionalized carbon nanotubes was significantly enhanced. The experimental test revealed that the tensile strength of nanocomposites was enhanced about 23% and Young's modulus about 25%, with 0.5 wt% loading of functionalized-nanotubes. These considerable improvements further verified the load-transfer enhancement in the functionalized-SWNTs/epoxy nanocomposites. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers [source] Biodegradable polyester layered silicate nanocomposites based on poly(,-caprolactone)POLYMER ENGINEERING & SCIENCE, Issue 9 2002Nadège Pantoustier Nanocomposites based on biodegradable poly(,-caprolactone) (PCL) and layered silicates (montmorillonite, MMT) were prepared either by melt interaction with PCL or by in situ ring-opening polymerization of ,-caprolactone as promoted by the so-called coordination-insertion mechanism. Both non-modified clays (Na+ -MMT) and silicates modified by various alkylammonium cations were studied. Mechanical and thermal properties were examined by tensile testing and thermogravimetric analysis. Even at a filler content as low as 3 wt% of inorganic layered silicate, the PCL-layered silicate nanocomposites exhibited improved mechanical properties (higher Young's modulus) and increased thermal stability as well as enhanced flame retardant characteristics as a result of a charring effect. It was shown that the formation of PCL-based nanocomposites depended not only on the nature of the ammonium cation and related functionality but also on the selected synthetic route, melt intercalation vs. in situ intercalative polymerization. Interestingly enough, when the intercalative polymerization of ,-caprolactone was carried out in the presence of MMT organo-modified with ammonium cations bearing hydroxyl functions, nanocomposites with much improved mechanical properties were recovered. Those hybrid polyester layered silicate nanocomposites were characterized by a covalent bonding between the polyester chains and the clay organo-surface as a result of the polymerization mechanism, which was actually initiated from the surface hydroxyl functions adequately activated by selected tin (II) or tin (IV) catalysts. [source] Polyoxometalate/polymer hybrid materials: fabrication and propertiesPOLYMER INTERNATIONAL, Issue 11 2009Wei Qi Abstract In this article we provide an overview of the fabrication and properties of polyoxometalate/polymer hybrid materials. Physical blending, electrostatic adsorption, covalent bonding and supramolecular modification are the main strategies to incorporate polyoxometalates into organic or inorganic (taking silica as an example) polymer matrices. The polyoxometalate/polymer hybrid materials obtained concurrently possess the unique optical, electrical or catalytic properties of polyoxometalates and the favorable processability and stability of polymer matrices. Polyoxometalate/polymer hybrid materials may have potential applications in optics, electronics, biology, medicine and catalysis. Copyright © 2009 Society of Chemical Industry [source] Plasma polymerization and deposition of glycidyl methacrylate on Si(100) surface for adhesion improvement with polyimidePOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 10 2001X. P. Zou Abstract Thin polymer films were deposited on Si(100) surfaces by plasma polymerization of glycidyl methacrylate (GMA) under different glow discharge conditions. The FT-IR, X-ray photoelectron spectroscopy (XPS), and amine treatment results suggested that the epoxide functional groups of the deposited films had been preserved to various extents, depending on the plasma deposition conditions. The use of a low radio frequency power (, 5 W) and a relatively high system pressure (100,400 Pa) readily resulted in the deposition of thin films having nearly the same composition of the epoxide functional groups as that of the GMA homopolymer. The plasma-polymerized GMA (PP-GMA) thin films deposited on the Ar plasma-pretreated Si(100) surfaces were retained to a large extent after acetone extraction, suggesting the presence of covalent bonding between the PP-GMA layer and the Si surface. Thermal imidization of the poly(amic acid) precursor of polyimide on the GMA plasma-polymerized Si(100) surface resulted in a strongly adhered polyimide film. The adhesion results further suggested that the GMA polymer had been grafted on the Si(100) surface and the epoxide functional groups had undergone reactive interaction (curing) with the carboxylic and amine groups of the poly(amic acid) during thermal imidization. Copyright © 2001 John Wiley & Sons, Ltd. [source] Acid-Base Interactions in Energetic Materials: I. The Hard and Soft Acids and Bases (HSAB) Principle,Insights to Reactivity and Sensitivity of Energetic MaterialsPROPELLANTS, EXPLOSIVES, PYROTECHNICS, Issue 1 2005Ernst-Christian Koch Abstract The chemistry of energetic materials can be described applying acid-base reaction formalism. Addressing the HSAB concept, the number of electrons transferred, ,N, in an acid-base reaction, allows for description and prediction of properties of composite and homogeneous materials. At first ,N helps in estimating the rate of reaction of binary systems with either given fuel or oxidizer. Nevertheless ,N is only a relative number thus the range of comparability remains narrow. At second ,N can be used as a measure for the sensitivity of homogeneous explosives. The increased reactivity of hypothetical fragments to recombine in a reaction such as R3C.+.NO2=R3C,NO2 given by ,N correlates very well with experimentally determined reduced impact sensitivity of 1,3,5-trinitrobenzene compounds. On the contrary the rising impact sensitivity of metal azides correlates with rising values of ,N of Mn+/N3, reaction because increased reactivity, that is increased electron transfer from the azide anion to the metal cation triggers formation of the azide radical (.N3). The latter then decomposes rapidly to give dinitrogen. This increased reactivity/sensitivity of metral azides coincides with covalent bonding whereas ionic azides are relatively insensitive. [source] Applications of silver nanoparticles capped with different functional groups as the matrix and affinity probes in surface-assisted laser desorption/ionization time-of-flight and atmospheric pressure matrix-assisted laser desorption/ionization ion trap mass spectrometry for rapid analysis of sulfur drugs and biothiols in human urineRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 18 2008Kamlesh Shrivas A strategy is presented for the analysis of sulfur drugs and biothiols using silver nanoparticles (AgNPs) capped with different functional groups as the matrix and affinity probes in surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOF MS) and atmospheric pressure-matrix assisted laser desorption/ionization ion trap mass spectrometry (AP-MALDI-ITMS). Biothiols adsorbed on the surface of AgNPs through covalent bonding were subjected to ultraviolet (UV) radiation that enabled desorption and ionization due to the excellent photochemical property of NPs. The proposed method has been successfully applied for the determination of cysteine and homocysteine in human urine samples using an internal standard. The limit of detection (LOD) and limit of quantification (LOQ) for cysteine and homocysteine in urine sample are 7 and 22,nM, respectively, with a relative standard deviation (RSD) of <10%. The advantages of the present method compared with the methods reported in the literature for biothiol analysis are simplicity, rapidity and sensitivity without the need for time-consuming separation and tedious preconcentration processes. Additionally, we also found that the bare AgNPs can be directly used as the matrix in MALDI-TOF MS for the analysis of sulfur drugs without the addition of an extra proton source. Copyright © 2008 John Wiley & Sons, Ltd. [source] Differential effects of redox-cycling and arylating quinones on trans-plasma membrane electron transportBIOFACTORS, Issue 3 2008An S. Tan Abstract Cytotoxicity of quinones has been attributed to free radical generation and to arylation of cellular nucleophiles. For redox-cycling quinones, cell injury is associated with mitochondrial permeability transition, whereas arylating quinones directly depolarise the mitochondrial membrane and deplete ATP. Like mitochondrial electron transport, plasma membrane electron transport (PMET), plays a multifaceted role in cellular redox homeostasis but the effects of quinones on PMET are unknown. Here we investigate the effects of redox-cycling 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), arylating 1,4-benzoquinone (BQ) and mixed mechanism 2-methyl-1,4-naphthoquinone (MNQ) on PMET, viability and growth of P815 mouse mastocytoma cells. BQ and MNQ rapidly and extensively inhibited PMET as determined by WST-1 /mPMS reduction (IC50 3.5-5 ,Mat 30 min) whereas the effects of DMNQ were less pronounced. In contrast, MTT reduction (cytosolic NADH dehydrogenase activity over 30 min) was weakly inhibited by BQ (IC50 20 ,M) but not by MNQ or DMNQ and cell viability was unaffected. Inhibition of WST-1/mPMS reduction by BQ and MNQ but not DMNQ was fully reversed by NAC. Treatment with DMNQ, MNQ and to a lesser extent BQ inhibited cell proliferation as determined by MTT reduction at 48 h. The effects of BQ and MNQ were reversed by NAC through covalent bonding to BQ and MNQ, but not DMNQ. These results show that arylating quinones are more potent inhibitors of PMET than pure redox-cycling quinones, but that redox-cycling quinones are more cytotoxic. [source] Co-application of hydroxyalkyl dyes and polyphosphonic acids to cotton to achieve dye,fibre covalent bondingCOLORATION TECHNOLOGY, Issue 6 2001Estelle L Gillingham The dyeing of cotton to a high standard of wet-fastness with hydroxyalkyl dyes and a polyphosphonatecrosslinker system has been investigated. Dyes containing hydroxyalkyl groups were prepared, by the reaction of commercial reactive dyes with ethanolamine, and applied to cotton fabric in the presence of polyphosphonic acid crosslinking agents using cyanamide as a catalyst. The application was carried out using a pad-thermosol method. The effects of cyanamide concentration, the nature of the crosslinker and the type of hydroxyalkyl dye were studied in detail. It was concluded that multifunctional polyphosphonates are capable of producing dyeings on cellulosic fibres exhibiting a high degree of covalent bonding (fixation). The efficiency of dye fixation at ca. 2% pure dye (owf), obtained from this method, was greater than 90%. [source] | |||||||||||||||||||||||||||||||