Showing papers on "Chemical binding published in 2001"

Steric Stabilization of a Cellulose Microcrystal Suspension by Poly(ethylene glycol) Grafting

Abstract: A sterically stabilized aqueous suspension of rodlike cellulose microcrystals was prepared by the combination of acid hydrolysis of native cellulose, oxidative carboxylation of microcrystals, and grafting of poly(ethylene glycol) having a terminal amino group on one end (PEG-NH2, MW = 1000) using water-soluble carbodiimide. Chemical binding of PEG to the microcrystals was confirmed by weight increase, diminishment of carboxyl groups, thermogravimetry, and infrared spectroscopy, resulting in consumption of 20−30% of the initially introduced carboxyl groups. The amount of bound PEG was 0.2−0.3 g/g of cellulose. The PEG-grafted cellulose microcrystals showed drastically enhanced dispersion stability, that is, resistance to addition of 2 M sodium chloride, and ability to redisperse into either water or chloroform from the freeze-dried state. The concentrated aqueous suspension of PEG-grafted microcrystals formed a chiral nematic mesophase through a phase separation similar to that of the ungrafted sample, but...

QSAR models using a large diverse set of estrogens

Abstract: Endocrine disruptors (EDs) have a variety of adverse effects in humans and animals. About 58,000 chemicals, most having little safety data, must be tested in a group of tiered assays. As assays will take years, it is important to develop rapid methods to help in priority setting. For application to large data sets, we have developed an integrated system that contains sequential four phases to predict the ability of chemicals to bind to the estrogen receptor (ER), a prevalent mechanism for estrogenic EDs. Here we report the results of evaluating two types of QSAR models for inclusion in phase III to quantitatively predict chemical binding to the ER. Our data set for the relative binding affinities (RBAs) to the ER consists of 130 chemicals covering a wide range of structural diversity and a 6 orders of magnitude spread of RBAs. CoMFA and HQSAR models were constructed and compared for performance. The CoMFA model had a r2 = 0.91 and a q2LOO = 0.66. HQSAR showed reduced performance compared to CoMFA with r2 = 0.76 and q2LOO = 0.59. A number of parameters were examined to improve the CoMFA model. Of these, a phenol indicator increased the q2LOO to 0.71. When up to 50% of the chemicals were left out in the leave-N-out cross-validation, the q2 remained significant. Finally, the models were tested by using two test sets; the q2pred for these were 0.71 and 0.62, a significant result which demonstrates the utility of the CoMFA model for predicting the RBAs of chemicals not included in the training set. If used in conjunction with phases I and II, which reduced the size of the data set dramatically by eliminating most inactive chemicals, the current CoMFA model (phase III) can be used to predict the RBA of chemicals with sufficient accuracy and to provide quantitative information for priority setting.

Solid-phase microextraction using fused-silica fibers coated with sol-gel-derived hydroxy-crown ether.

Abstract: A novel solid-phase microextraction (SPME) fiber containing hydroxydibenzo-14-crown-4 (OH-DB14C4)/hydroxy-terminated silicone oil (OH-TSO) was first prepared by a sol−gel method and investigated for the determination of phenols. The possible mechanism is discussed and confirmed by IR spectra. The coating has stable performance in high temperature (to 350 °C) and solvents (organic and inorganic) due to the chemical binding between the coating and the fiber surface. The addition of crown ether enhances the polarity of the coating compared with that of the sol−gel OH-terminated silicone oil fiber and, accordingly, provides higher extraction efficiency for polar phenolic compounds. On the other hand, OH-terminated silicone oil in the coating can not only increase the length of network but also help to spread the stationary phase on the silica surface uniformly. The fluorescence microscopy experiment suggests the benefit the more uniform surface of the sol−gel-derived OH-DB14C4/OH-TSO fiber in comparison with ...

Quantification and prediction of the detoxifying properties of humic substances related to their chemical binding to polycyclic aromatic hydrocarbons.

Abstract: Effects of 27 different humic materials on the toxicity of polycyclic aromatic hydrocarbons (PAH) were studied for crustacean Daphnia magna. Sources included isolated humic acids, fulvic acids, and their combination from soil, peat, and freshwater. The PAH used were pyrene, fluoranthene, and anthracene. The observed reduction in toxicity of PAH in the presence of humic substances (HS) was shown to be a result of the detoxification effect caused by the chemical binding of PAH to HS and of the direct effect of HS on D. magna. An approach was developed to quantify the detoxifying impact of humic materials related to their chemical binding to PAH with a use of the "constant of detoxification" or "toxicological partition coefficient" K(oc)D. The latter was proposed to determine by fitting the experimental relationships of the detoxification effect versus concentration of HS. The obtained K(oc)D values were well tracked by the corresponding partition coefficients determined by the fluorescence quenching technique (K(oc)fq): K(oc)D=b x K(oc)fq, b (mean+/-Cl, n=26, P=95%)=2.6+/-0.3, 4.6+/-0.6, and 6.0+/-1.4 for pyrene, fluoranthene, and anthracene, respectively. The predictive relationships between the structure and detoxifying properties of humic materials in relation to PAH were developed. It was shown that the magnitude of the K(oc)D values correlated closely with the aromaticity of humic materials characterized with the 13C NMR descriptors (sigma(C)Ar, sigma(C)Ar/sigma(C)Alk) and atomic H/C ratio. The obtained relationships showed the highest detoxifying potential of the humic materials enriched with aromatics and allowed a conclusion on the chemical binding as the governing mechanism of the mitigating action of HS on the toxicity of PAH.

An XAFS investigation of the artefacts caused by sequential extraction analyses of Pb-contaminated soils.

Abstract: The chemical processes that occur during sequential extraction of a highly Pb-contaminated soil sample were investigated using XAFS spectroscopy for the identification of the Pb species in the solid residues after each step. The sequential extraction was performed following the procedure described by Salomons and Forstner [1]. It was found that during the sequential extraction serious alteration of the chemical binding forms of the Pb occurs. The most important processes underlying the chemical changes are the re-adsorption of solubilized Pb ions by soil matrix components and the precipitation of insoluble Pb species with anions from the extractant.

In vitro assessment of corrosive properties of titanium as a biomaterial.

Abstract: Titanium (Ti) is thought to be a highly biocompatible material, and its clinical applications are becoming increasingly frequent. However, there have recently been some clinical papers reporting hypersensitivity and allergic reactions to Ti. The purpose of this study was to assess the corrosive properties of Ti in the intra-oral environment in vitro. Cast pure Ti specimens were immersed in artificial saliva, physiological saline solution, and 128 mmol x L(-1) of lactic, formic and acetic acids for 3 weeks at 37 degrees C with shaking. The colour, weight, surface morphologies and chemical binding state of specimens were observed before and after immersion. Marked discoloration was recognized on the surface of specimens immersed in formic acid, and a significant difference was found between the immersion solutions. Weight changes also varied with solutions; a tendency to increase in formic acid and to decrease in lactic acid. A slight loss was observed in specimens immersed in lactic acid and artificial saliva. The oxide layer composed mainly of Ti-oxide on the surface of the immersed specimens was thinnest in lactic acid, and thickest in formic acid. The present study indicates that both hydrogen evolution type and oxygen diffusion type corrosion on Ti surfaces are possible in the living body. (Our results also confirm some clinical studies reporting Ti accumulation in surrounding tissues and Ti causing allergic reactions.)

QSAR Models Using a Large Diverse Set of Estrogens.

Abstract: Endocrine disruptors (EDs) have a variety of adverse effects in humans and animals. About 58,000 chemicals, most having little safety data, must be tested in a group of tiered assays. As assays will take years, it is important to develop rapid methods to help in priority setting. For application to large data sets, we have developed an integrated system that contains sequential four phases to predict the ability of chemicals to bind to the estrogen receptor (ER), a prevalent mechanism for estrogenic EDs. Here we report the results of evaluating two types of QSAR models for inclusion in phase III to quantitatively predict chemical binding to the ER. Our data set for the relative binding affinities (RBAs) to the ER consists of 130 chemicals covering a wide range of structural diversity and a 6 orders of magnitude spread of RBAs. CoMFA and HQSAR models were constructed and compared for performance. The CoMFA model had a r2 = 0.91 and a q2LOO = 0.66. HQSAR showed reduced performance compared to CoMFA with r2 = 0.76 and q2LOO = 0.59. A number of parameters were examined to improve the CoMFA model. Of these, a phenol indicator increased the q2LOO to 0.71. When up to 50% of the chemicals were left out in the leave-N-out cross-validation, the q2 remained significant. Finally, the models were tested by using two test sets; the q2pred for these were 0.71 and 0.62, a significant result which demonstrates the utility of the CoMFA model for predicting the RBAs of chemicals not included in the training set. If used in conjunction with phases I and II, which reduced the size of the data set dramatically by eliminating most inactive chemicals, the current CoMFA model (phase III) can be used to predict the RBA of chemicals with sufficient accuracy and to provide quantitative information for priority setting.

Chemisorption of the dipeptide Arg-Cys on a gold surface and the selectivity of G-protein adsorption

Abstract: Arginine-l-cysteine dipeptide adsorbates are used in this study as a model system for G-protein-coupled receptors (GPCRs). An arginine-containing model molecule is chosen because the GPCR α2A has been shown to include an arginine-rich region in the G-protein-binding part of the third intracellular loop, and the role of arginines by means of recognition is believed to exceed their positive charge. The dipeptide Arg-Cys is adsorbed to gold surfaces and the peptide monolayers are characterized. These peptide monolayers are then used for G-protein adsorption experiments to study the molecular interaction and binding. The molecular adsorption, orientation, and chemical binding of the peptide to the surface are studied by X-ray photoelectron spectroscopy and infrared reflection−absorption spectroscopy. A chemical shift in the S(2p) core level spectrum of the peptide adsorbate on gold shows that there is a strong molecular surface interaction consistent with a chemical binding of the peptide to the surface throu...

How is the chemical bonding of W-Si-N sputtered coatings?

Abstract: Thin films of W–Si–N, deposited by reactive magnetron sputtering, were investigated using X-ray photoelectron spectroscopy (XPS). The objective of this research work was to study the chemical binding state of these coatings. During the sputtering process, the established atomic bonds may possibly not agree to the elemental bonding preview using the values of chemical affinity, which decrease for SiN, SiW to WN bonds. XPS data show that in W-based films which have simultaneous additions of Si and N, a SiN type is the preferential bond established. This behaviour is confirmed either by the evolution of the Si/W atomic ratio of the as-deposited coatings, which increase with the N content, or the variation of the lattice parameters of the b.c.c. α-W phase for W–N, W–Si and W–Si–N systems. However, since no compound of silicon nitride was detected, it was concluded that this phase, formed by specific contents of Si and N must have been present in the W–Si–N films in the amorphous state.

Estrogen receptor-α and C-ERBB-4 expression in breast carcinomas

Abstract: The presence of estrogen receptors (ERs) in breast carcinomas is important for clinical response to endocrine therapy. However, the cellular mechanisms following ER activation are not fully understood. It has been indicated that expression of the ER is associated with the expression of c-erbB-4. To address this question, 103 breast carcinoma samples were studied using reverse transcriptase polymerase chain reaction (RT-PCR) analysis after application of a microselection method for RNA isolation. Total RNA for RT-PCR was isolated from 20-µm-thick frozen sections, which were made from microselected areas. Paraffin blocks from 98 of these 103 tumors were also immunohistochemically examined. Significant associations between ER-α and c-erbB-4 mRNA and protein expressions were found in the present study with both methods. One-fourth of the tumors did not express ER-α (22%, 24%, and 26% with chemical binding, immunohistochemistry, and RT-PCR, respectively). About one-half of the ER-α negative tumors did not express c-erbB-4 on both mRNA and protein levels (48% with RT-PCR and 46% with immunohistochemistry, P=0.001 for both methods). The endocrine therapy responsive breast cancer cell lines MCF-7 and T47-D were positive for both ER-α and c-erbB-4 expression, while the endocrine therapy non-responsive breast cancer cell lines MDA-MD-231 and SK-BR-3 were not. Thus, we confirm the association between the expression of ER-α and c-erbB-4 mRNA and protein in breast carcinomas, indicating a role for c-erbB-4 in estrogen signal transduction.

Disproportionation of a model chromium(V) complex causes extensive chromium(III)-DNA binding in vitro.

Abstract: The first direct evidence for the role of Cr(V) complexes in the formation of potentially mutagenic Cr(III)-DNA adducts has been obtained. A model complex for the stabilized Cr(V) species formed in Cr(VI)-treated cells, [Cr(V)O(ehba)(2)]-[ehba = 2-ethyl-2-hydroxybutanoato(2-)], rapidly disproportionates in HEPES buffers at pH 7.4 [3 Cr(V) --> 2 Cr(VI) + Cr(III)], and the formed Cr(III) species undergo efficient ionic binding to DNA, followed by slower covalent binding. The extent of Cr(III)-DNA binding significantly exceeds that caused by [Cr(III)(OH(2))(6)](3+) or by the Cr(III) products of Cr(VI) reductions under similar conditions. The Cr(III)-DNA binding can be dramatically reduced by the ability of the reaction medium (e.g., phosphate buffer) to form complexes with Cr(III) during and after the disproportionation reaction. A mechanism of Cr(III)-DNA binding caused by Cr(V) disproportionation has been proposed on the basis of stoichiometric and kinetic studies.

Cell and molecular biology of chemical allergy

Abstract: Objective The objective of this review is to provide current approaches to gain increased understanding of the molecular basis of chemical allergenicity. Chemical allergy refers to an allergic reaction to a low molecular weight agent (ie, Data Sources Data were obtained from published clinical reports and from the Documentation of Threshold Limit Values (1998) published by the American Congress of Governmental Industrial Hygienists. Results In vitro studies indicate the stoichiometric reaction of some chemical allergens with glutathione and the subsequent transfer of the allergen from glutathione to other nucleophiles. Computer-generated structure-activity relationship models have been developed for chemicals that induce respiratory allergy. The models, based on physicochemical properties of the agents, have high sensitivity and specificity. Conclusions The structure-activity relationship model suggests that chemical binding is the essential feature of chemical allergens. Their in vivo reactions with thiols may result in glutathione deficiency with consequent alteration in cellular reduction-oxidation (redox) status, release of cytokines, and promotion of the T helper cell 2 phenotype. Prevention of permanent disease is dependent on periodic medical surveillance of affected workers. When detected early, the disease can frequently be reversed.

Local reactivity of fullerenes and nano-device applications

Abstract: A conceptual framework to understand the chemical reactivity of fullerenes is developed as a design tool for nano-scale device applications. The internal and external chemical reactivity of fullerenes is found to depend strongly on the curvature and local atomic structure. As examples, we study C36, C60 and graphite, and use a hydrogen atom to probe chemical reactivity as a function of local atomic structure. The analysis shows that the balance of strain energy and chemical binding energy determines the local reactivity. This understanding provides an insight into the use of chemically doped endo-fullerenes as suitable target material for a recently proposed design of a solid-state quantum computer.

Chitosan–Oligo(silsesquioxane) Blend Membranes: Preparation, Morphology, and Diffusion Permeability

Abstract: Preparation of the blend chitosan (CHI) membranes containing polyhedral oligomeric silsesquioxane (POSS) derivatives was investigated. POSS derivatives such as (3-aminopropyl)isobutyl-POSS (amino-POSS), [2-(3,4-epoxycyclohexyl)ethyl]isobutyl-POSS (epoxy-POSS), and octa(tetramethylammonium)-POSS were used. The blend CHI–amino-POSS membranes were predicted to be the most porous due to having the weakest interactions between the components in the blends. The CHI–epoxy-POSS blend membranes were assumed to be more dense owing to chemical binding of the chitosan amino groups with the epoxy groups of POSS. Studies of membrane morphology and diffusion permeability support these predictions.

Interaction between Metallic p Orbitals and the π Orbitals of Organic Molecules: The Binding between Ethylene and Aluminum

Abstract: A set of first principles calculations has been performed to characterize the interaction of a π bonded organic molecule with a simple s−p metal surface. The structures of the Al(C2H4) and [Al(C2H4)]+ complex molecules, and of the adsorption of an isolated ethylene molecule onto Al(100) were calculated. We find a C2H4π →Al3p interaction to be the most significant in Al(C2H4) and [Al(C2H4)]+ with additional Al 3p → C2H4π* back-donation in Al(C2H4). In complete contrast, no chemical binding of ethylene to Al(100) is observed, but physisorption is predicted. These calculations show how the binding between a π bond and the π orbitals of a simple metal atom cannot be extended to describing the binding with a p band of a solid. Our conclusions may be extended to other systems where this interaction could be significant.

Method for immobilising probes, in particular for producing biochips

Abstract: The invention concerns a solid support comprising sites designed to immobilise oligonucleotide probes or proteins or biological cells provided with ligands, the sites being provided with species bound to the support by a chemical binding function. The species exhibit a diol group bound to the support by an alkyl chain. The invention is applicable to biochips.

Specific surface association of avidin with N-biotinylphosphatidylethanolamine membrane assemblies: effect on lipid phase behavior and acyl-chain dynamics.

Abstract: The interaction of avidin with aqueous dispersions of N-biotinylphosphatidylethanolamines, of acyl chain lengths C(14:0), C(16:0), and C(18:0), was studied by using spin-label electron spin resonance (ESR) spectroscopy, 31P nuclear magnetic resonance (31P NMR) spectroscopy, differential scanning calorimetry, and chemical binding assays. In neutral buffer containing 1 M NaCl, binding of avidin is due to specific interaction with the biotinyl lipid headgroup because avidin presaturated with biotin does not bind. Saturation binding of the protein corresponds to a ratio of 50 lipid molecules per tetrameric avidin. Phospholipid probes spin-labeled at various positions between C-4 and C-14 in the sn-2 chain were used to characterize the effects of avidin binding on the lipid chain dynamics. In the fluid phase, protein binding results in a decrease of chain mobility at all positions of labeling while the flexibility gradient characteristic of a liquid-crystalline lipid phase is maintained. There is no evidence f...

Quantum-Chemical Calculation of the Electronic Structure and Ionic Conductivity of Lead Hexaferrite with a Magnetoplumbite Structure

Abstract: The ab initio linear muffin-tin orbital method in a tight binding approximation (LMTO-TB) and semiempirical extended Huckel theory (EHT) were used to study the electronic structure, chemical binding, and ion conductivity of hexaferrite PbFe12O19. The analysis of chemical bonds showed that Fe–O interactions play the dominant role in the chemical bonding in hexagonal ferrites, the covalent component of the Pb–O bond being insignificant. The metallic Fe–Fe bonds have been found. The predicted increased mobility of Pb2+ ions in the structure of magnetoplumbite agrees well with the experimental parameters of lead diffusion and ion–electron conductivity in PbFe12O19. The mechanism of migration of lead ions in the structure of the hexaferrite is discussed.

Binding Capability of Chloride Ions in Mortar and Paste with Ground Granulated Blast Furnace Slag

Abstract: The chloride binding capability of mortar and paste blended with 70% ground granulated blast furnace slag (GGBS) is greatly increased, especially the chemical binding capability. The binding capability is greatly weakened when blended with some sulphate. The reason is that the added sulphate weakens the chemical binding capability. Alkalinity also weakens the chloride binding capability. Admixture can influence the physical binding capability.

A Transport Model with Coupled Ternary Exchange and Chemisorption Retention for Hydrazinium Cations

Abstract: A numerical model was developed to describe the fate and transport of hydrazinium (N2H5+) and competing Ca2+ and H+ cations applied in acidic solutions to columns of Ca2+/H+-saturated sandy soil during steady saturated flow conditions. Instantaneous ternary H+-Ca2+-N2H5+ cation exchange using the Gaines-Thomas approach was combined with second-order, irreversible, kinetic chemisorption of exchange-phase N2H5+ ions as major retention mechanisms for N2H5+. Exchange-mediated chemisorption is assumed to occur as chemical binding of N2H5+ ions located on carboxyl-group exchange sites to nearby carbonyl groups, consequently decreasing the effective soil cation exchange capacity (CEC). Comparison of simulated and observed breakthrough curves (BTCs) for concentrations of N2H5+ and Ca2+ ions in column effluent was used in model evaluation. The cation transport model with cation exchange coupled with exchange-mediated chemisorption provided a valid first approximation for N2H5+ transport.

Preparation and characterisation of biocompatible vitroceramic-metal systems for applications in medicine

Abstract: Vitroceramic coatings from the oxide system SiO2–CaO–Na2O–B2O3
50;TiO2 were obtained on metallic supports (titanium and austenitic steels with high Cr and Ni contents). The coating technology was classical enamelling. The metallic support is coated by either immersion or painting with a slurry layer resulting from a mixture of a frit (having the best oxide composition for each metallic support) with a liquid, fired at the enamelling temperature and then subjected to a thermal treatment for crystallisation. Good adherence between the two different materials is achieved when their thermal expansion coefficients are close to each other. The vitroceramic coating–metallic support system was characterised by optical microscopy, SEM, and X-ray diffraction. The adherence of the vitroceramic layer to the metallic supports was determined using microhardness tests carried out at the interface. Evidence of the processes occurring at the interface (gas bubbles, micropores, chemical binding, etc.) was also f...

Interfacial Adhesion of Cu to Self-Assembled Monolayers on SiO2

Abstract: As the critical feature size in microelectronic devices continues to decrease below 100 nm, new barrier materials of > 5 nm thickness are required. Recently we have shown that self-assembled monolayers (SAMs) are attractive candidates that inhibit Cu diffusion into SiO2. For SAMs to be used as barriers in real applications, however, they must also promote adhesion at the Cu/dielectric interfaces. Here, we report preliminary quantitative measurements of interfacial adhesion energy and chemical binding energy of Cu/SiO2 interfaces treated with nitrogen-terminated SAMs. Amine-containing SAMs show a ~10% higher adhesion energy with Cu, while interfaces with Cu-pyridine bonds actually show degraded adhesion, when compared with that of the reference Cu/SiN interface. However, X-ray photoelectron spectroscopy (XPS) measurements show that Cu-pyridine and Cu-amine interactions have a factor-of-four higher binding energy than that of Cu-N bonds at Cu/SiN interfaces. The lack of correlation between adhesion and chemical binding energies is most likely due to incomplete coverage of SAMs.