Metal ion binding to anticoagulation factor II from the venom of Agkistrodon acutus: stabilization of the structure and regulation of the binding affinity to activated coagulation factor X.

Anticoagulation factor II (ACF II) isolated from the venom of Agkistrodon acutus is an activated coagulation factor X (FXa)-binding protein with both anticoagulant and hypotensive activities. The thermodynamics of the binding of alkaline earth metal ions to ACF II and their effects on the stability of ACF II and the binding of ACF II to FXa were investigated by isothermal titration calorimetry, fluorescence, differential scanning calorimetry, and surface plasmon resonance. The binding of ACF II to FXa does not have an absolute requirement for Ca(2+). Mg(2+), Sr(2+), and Ba(2+) can induce the binding of ACF II to FXa. The radii of the cations bound in ACF II crucially affect the binding affinity of ACF II for cations and the structural stability of ACF II against guanidine hydrochloride and thermal denaturation, whereas the radii of cations bound in FXa markedly affect the binding affinity between ACF II and FXa. The binding affinities of ACF II for cations and the capacities of metal-induced stabilization of ACF II follow the same trend: Ca(2+) > Sr(2+) > Ba(2+). The metal-induced binding affinities of ACF II for FXa follow the trend Mg(2+) > Ca(2+) > Sr(2+) > Ba(2+). Although Mg(2+) shows significantly low binding affinity with ACF II, Mg(2+) is the most effective to induce the binding of ACF II with FXa. Our observations suggest that in blood the bindings of Ca(2+) in two sites of ACF II increase the structural stability of ACF II, but these bindings are not essential for the binding of ACF II with FXa, and that the binding of Mg(2+) and Ca(2+) to FXa may be essential for the recognition between FXa and ACF II. Like Ca(2+), the abundant Mg(2+) in blood also plays an important role in the anticoagulation of ACF II.

Determination of acetanilide herbicides in cereal crops using accelerated solvent extraction, solid-phase extraction and gas chromatography-electron capture detector.

A method was developed to determine eight acetanilide herbicides from cereal crops based on accelerated solvent extraction (ASE) and solid-phase extraction (SPE) followed by gas chromatography-electron capture detector (GC-ECD) analysis. During the ASE process, the effect of four parameters (temperature, static time, static cycles and solvent) on the extraction efficiency was considered and compared with shake-flask extraction method. After extraction with ASE, four SPE tubes (graphitic carbon black/primary secondary amine (GCB/PSA), GCB, Florisil and alumina-N) were assayed for comparison to obtain the best clean-up efficiency. The results show that GCB/PSA cartridge gave the best recoveries and cleanest chromatograms. The analytical process was validated by the analysis of spiked blank samples. Performance characteristics such as linearity, limit of detection (LOD), limit of quantitation (LOQ), precision and recovery were studied. At 0.05 mg/kg spiked level, recoveries and precision values for rice, wheat and maize were 82.3-115.8 and 1.1-13.6%, respectively. For all the herbicides, LOD and LOQ ranged from 0.8 to 1.7 µg/kg and from 2.4 to 5.3 µg/kg, respectively. The proposed analytical methodology was applied for the analysis of the targets in samples; only three herbicides, propyzamid, metolachlor and diflufenican, were detected in two samples.

Selective solid-phase extraction using molecularly imprinted polymer for analysis of methamidophos in water and soil samples.

An analytical methodology for the analysis of methamidophos in water and soil samples incorporating a molecularly imprinted solid-phase extraction process using methamidophos-imprinted polymer was developed. Binding study demonstrated that the polymer exhibited excellent affinity and high selectivity to the methamidophos. Evidence was also found by FT-IR analysis that hydrogen bonding between the CO(2)H in the polymer cavities and the NH(2) and P=O of the template was the origin of methamidophos recognition. The use of molecularly imprinted solid-phase extraction improved the accuracy and precision of the GC method and lowered the limit of detection. The recovery of methamidophos extracted from a 10.0 g soil sample at the 100 ng/g spike level was 95.4%. The limit of detection was 3.8 ng/g. The recovery of methamidophos extracted from 100 mL tap and river water at 1 ng/mL spike level was 96.1% and 95.8%, and the limits of detection were 10 and 13 ng/L respectively. These molecularly imprinted solid-phase extraction procedures enabled selective extraction of polar methamidophos successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.

[Spectroscopy study of binding mechanisms and molecular recognition of methamidophos-specific moleculary imprinted polymer].

A new methamidophos-specific molecularly imprinted polymer (MIP) was synthesized based on non-covalent interaction. The complexes formed between MAP and MAA were evaluated by 1H NMR, FTIR and UV spectrometry. The MAP-MAA complexes of 1 : 2 mole ratio were obtained by cooperative hydrogen bonding and the complexes possessed better stabilization (K = 2.894 x 10(6) L2 x mol(-2). The Infrared spectrometry differences of the MIPs before and after saturated with MAP further indicated that there were carboxyl functional groups in the MIP, which could interact with the template by cooperative hydrogen bonding specifically.

Enantiomeric analysis of anatabine, nornicotine and anabasine in commercial tobacco by multi-dimensional gas chromatography and mass spectrometry.

A fully automated multi-dimensional gas chromatography (MDGC) system with a megabore precolumn and cyclodextrin-based analytical column was developed to analyze the enantiomeric compositions of anatabine, nornicotine and anabasine in commercial tobacco. The enantiomer abundances of anatabine and nornicotine varied among different tobacco. S-(-)-anatabine, as a proportion of total anatabine, was 86.6% for flue-cured, 86.0% for burley and 77.5% for oriental tobacco. S-(-)-nornicotine, as a proportion of total nornicotine, was 90.8% in oriental tobacco and higher than in burley (69.4%) and flue-cured (58.7%) tobacco. S-(-)-anabasine, as a proportion of total anabasine, was relatively constant for flue-cured (60.1%), burley (65.1%) and oriental (61.7%) tobacco. A simple solvent extraction with dichloromethane followed by derivatisation with trifluoroacetic anhydride gave relative standard deviations of less than 1.5% for the determination of the S-(-)-isomers of all three alkaloids. The study also indicated that, a higher proportion of S-(-)-nornicotine is related to the more active nicotine demethylation in the leaf.

[Determination of cadmium in tobacco using thermospray-chemical vapor generation-AAS system].

A new and sensitive method for the determination of cadmium was developed using thermospray chemical vapor generation AAS system. The sample and KBH4 solutions were introduced into two separate thermospray tubes by peristaltic pumps and then thermosprayed into a reaction tube. The aerosol of the sample and KBH4 were mixed and reacted in the reaction tube, and after gas-liquid separation in a cyclonic spray chamber, the water vapor was removed by a desolvating unit, while the analyte was transferred into the quartz T-cell and determined by AAS. This design improved the stability and sensitivity by thermospray chemical vapor sample introducing technique. The effect of several experimental parameters of the proposed system was optimized. Under the optimized experimental conditions, the detection limits of 18 ng x L(-1) with RSD of 2.1% was obtained for cadmium determination. This method has been successfully applied to the determination of cadmium in tobacco with the recoveries of 94%-103%.

Photoacoustic and luminescence spectra study on the effects of chlorine substituent on the energy transfer of Eu(III)-chlorobenzoic acid.

The photoacoustic (PA) amplitude spectra of three complexes of Eu(III) combined with chlorobenzoic acid (Eu(o-ClC6H4CO2)3.H2O, Eu(m-ClC6H4CO2)3.H2O and Eu(p-ClC6H4CO2)3.H2O) have been measured, and the PA phase of the different complexes have been calculated. Both the PA amplitude spectra and the luminescence spectra reflect the variation of the luminescent properties, and the PA phase is directly relative to the relaxation time. Since the relaxation is the process of the intramolecular energy transfer between the ligands and the central ion, the molecular structure of ligand is the important factor to decide the energy gap between the lowest triplet state of ligand and the resonance level of central ion. The effects of chlorine substituent on the molecular structure and energy gap of the complexes have been studied by PA phase and luminescence spectra.

Dynamic ultrasound-assisted extraction of catechins and caffeine in some tea samples.

A novel dynamic ultrasound-assisted extraction (DUAE) device has been constructed for extraction of five catechins and caffeine in solid sample. The accurate, simple, reproducible and sensitive method for the determination of five catechins and caffeine has been developed and validated. A comparison has been made of the efficiencies by employing DUAE and conventionally static ultrasound-assisted extraction (UAE). The proposed method can not only improve extraction efficiency but also decrease time and solvent consumption. The commercial Chinese tea samples, involving green and black teas, are rapidly analyzed by the proposed DUAE method. The linearity, range, selectivity, precision, accuracy, and robustness also showed acceptable values.

Determination of pesticide residues in soil by modified matrix solid-phase dispersion and gas chromatography.

Modified matrix solid-phase dispersion (MMSPD) and gas chromatography have been developed for quantitative analysis of various classes of pesticides (pirimicarb, metalaxyl, metolachlor, isopropalin and pendimethalin) in soil. MMSPD used Florisil as dispersant and acetone as solvent. Determination was carried out by gas chromatography with nitrogen-phosphorus detection (GC-NPD). The effect of the residence time of pesticides in soil on the recoveries was studied. MMSPD was compared with continuous liquid-solid extraction (LSE). MMSPD had good extraction efficiency and cleanup efficiency and the extract obtained could be directly subjected to GC analysis without further purification. The method gave recoveries ranging from 93% to 100% with relative standard deviations (RSDs) lower than 10%. The limits of detection (LODs) ranged from 0.2 to 2.0 ng g(-1).

[Study of thermal diffusivity by piezoelectric photoacoustic phase].

Piezoelectric photoacoustic phase information can be applied to determine the thermal diffusivity of sample. In actual experiments, the results of phase versus modulation frequency deviate from the theory heavily because of the disturbance of instrumental contribution from the whole detecting system. Considering that the instrumental contribution of phase from PA cell can be ignored reasonably, there will be no additional phase contribution after the piezoelectric PA cell has been replaced by microphone PA cell while the other experimental conditions have been kept invariable. Based on this hypothesis, the conventional photoacoustic cell with microphone is employed to determine the instrumental contribution of whole detecting system by studying the PA phase of solid rare earth complexes. The instrumental contribution of phase was considered to be constant for that the same detecting system was used in both the microphone PA method and piezoelectric PA method. This method has been proved by detecting the thermal diffusivity of aluminium sample. The corrected results of experiments match the theory well, showing that the method of subtracting the instrumental contribution from the original experimental phase can be applied reasonably in relevant chopping frequency region. While in lower chopping frequency region, there will be a little deviation from the theoretical results. The method has been also employed to the photoacoustic detection of leaf, and the thermal diffusivity of leaf can be acquired by studying the piezoelectric photoacoustic phase.

[Spectroscopy and XPS studies on molecular recognition of a molecularly imprinted cotinine-specific polymer].

In the present study, molecular imprinting technique was used to develop a method based on noncovalent interaction for the systhesis of a cotinine-specific polymer. The molecular recognition characteristics of the template polymer were evaluated by UV, IR, XPS and 1H NMR. The results indicated that the interactions should be cooperative hydrogen bonds produced by self-assembling of the template and the monomer. The stoichiometric mole ratio of COT-MAA complex is 1 : 2. Furthermore, nitrogen atom of the pyridine ring and oxygen atom of the lactam group in cotinine molecular are hydrogen-bond acceptors, being the predominant binding sites interacting with the functional monomer.

Films coated with molecular imprinted polymers for the selective stir bar sorption extraction of monocrotophos.

The flexibility and simplicity of stir bar sorption extraction (SBSE) have been combined with the selectivity of molecularly imprinted polymers (MIP). Stir bars were coated reproducible with a 180 microm film formed from a formic acid solution of nylon-6 polymer either nonimprinted or imprinted with monocrotophos. Time sorption profiles were measured for the extraction of monocrotophos from dichloromethane at the concentration of 10-200 micromol/L levels with both types of films in order to compare extraction characteristics. The results indicated that the MIP coated layer showed remarkable high affinity toward monocrotophos and equilibrium adsorption was attained rapidly (60 min) in contrast to free standing molecularly imprinted polymer in which equilibrium adsorption was normally attained after several hours. The stir bars coated with MIP films were capable of extracting four structural analogues of monocrotophos from dichloromethane solution, which suggests that both the amino group and PO part of these molecules is responsible for interaction with the imprinted polymer. Evidence was also presented by FT-IR analysis that the amide-hydrogen-bonding interaction between the MIP-coated films and monocrotophos was originated for monocrotophos recognition. To achieve selective extraction of monocrotophos from sample, stir bars coated with MIP films were washed with 10% (v/v) acetic acid/methanol and methanol. Clean extracts and yields of 95% were obtained, demonstrating the suitability of stir bar coated with MIP films for the analysis of environmental and biological samples. Compared with traditional MIP and SBSE, the MIP-coated film showed not only the high selectivity but also the rapid equilibrium adsorption.

Photoacoustic phase study on the frequency dependence of phase angle and triplet state lifetime of Nd(III)-acetylacetonate.

The amplitude and phase of the photoacoustic (PA) signal generated in the rare earth complex powder of Nd(III)-acetylacetonate (Nd(AA)3) were examined. By using the reasonably simplified formula about phase angle at the wavelengths assigned to pi-pi* transition of ligand and f-f transitions of Nd3+, the instrumental contribution to phase angle at different chopping frequency was calculated. The frequency dependence of sample phase angle, the relative phase angle shift caused by instrumental factors and the calculation of triplet state lifetime of sample under study were also discussed. Being independent of sample, the instrumental contribution to phase angle was regarded as a parameter representing the situations of instruments and measurement and it became an approach to calculate the relaxation time of ligand in rare earth complex.

Two-step simultaneous distillation and solvent extraction for isolation both free and bound aroma in tobacco.

In this investigation, a novel two-step simultaneous distillation and solvent extraction (two-step SDE) method was developed to isolate both free and bound aroma in tobacco. Firstly, free aroma were extracted into dichloromethane by SDE for 4 h with SDE sample solution at pH 5.5. Then the SDE sample solution was adjusted to pH 2.5, bound aroma were hydrolyzed, and released as free aroma extracted by fresh dichloromethane. Following, both the free and bound aroma were analyzed by gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS). The whole isolation procedure of both free and bound aroma was carried out in one SDE apparatus and using one same sample. Especially, the procedure of isolation of bound aroma was greatly simplified. To apply and validate the proposed two-step SDE method, a traditional method were also used to isolate the bound aroma. The total bound aroma obtained by the proposed two-step SDE method and the traditional method were 119.83 mg kg(-1) and 88.9 mg kg(-1), respectively. For isolation of bound aroma, the proposed two-step SDE method was of better extraction recovery, less labourious, solvent and time consuming than the traditional method.

[Spectroscopy study of molecular recognition of a molecular imprinted monocrotophos-specific polymer].

In the present study, molecular imprinting was used to develop a method based on noncovalent interaction for the synthesis of a monocrotophos-specific polymer. The selective binding characteristics of the template polymer were evaluated by 1H NMR and ultraviolet spectrometry. The polymer obtained was found to interact specifically with monocrotophos by cooperative hydrogen bonding. The infrared spectrometry of the polymer further indicated that there were some functional groups in the moleculary imprinted polymer which could interact on the template.

[Spectroscopic characterization of structure of cerium incorporated MCM-48 mesoporous molecular sieve].

Cerium incorporated MCM-48 molecular sieves have been hydrothermally synthesized using a mixed template and pH adjusting route. The samples were characterized by various physicochemical methods, including X-ray diffraction, diffuse reflectance UV-Vis spectroscopy, FTIR spectroscopy, XRF spectroscopy, and nitrogen adsorption. These results reveal that cerium is incorporated in MCM-48 and it is in the form of well-dispersed tetra-coodinated cerium ion. The proper concentration of cerium and adjusting pH can keep Ce-MCM-48 with higher specific surface area , larger unit-cell parameter, narrower pore-size distribution, and thicker pore wall than those of MCM-48. These deduce higher activity, and better selectivity, thermal stability and hydrothermal stability than those of MCM-48. The concentration of Ce incorporated in MCM-48 affects the vibration of the framewoke Si of molecular sieves.

Selective solid-phase extraction using molecularly imprinted polymer for the analysis of polar organophosphorus pesticides in water and soil samples.

An analytical methodology for the analysis of four polar organophophorus pesticides (monocrotophos, mevinphos, phosphamidon, omethoate) in water and soil samples incorporating a molecularly imprinted solid-phase extraction (MISPE) process using a monocrotophos-imprinted polymer was developed. Binding study demonstrated that the polymer showed excellent affinity and high selectivity to monocrotophos. The MISPE procedure including the clean-up step to remove any interferences was optimized. The accuracy and selectivity of the MISPE process developed were verified using a non-imprinted (blank) polymer and a classical ENVI-18 cartridge as the SPE matrix during control experiments. The use of MISPE improved the accuracy and precision of the GC method and lowered the limit of detection. The recoveries of four polar organophosphorus pesticides (OPPs) extracted from 1 L of river water at a 100 ng/L spike level were in the range of 77.5-99.1%. The recoveries of organophosphorus pesticides extracted from a 5-g soil sample at the 100 microg/kg level were in the range of 79.3-93.5%. The limit of detection varied from 10 to 32 ng/L in water and from 12 to 34 microg/kg in soil samples. The molecularly imprinted polymer (MIP) enabled the selective extraction of four organophosphorus pesticides successfully from water and soil samples, demonstrating the potential of molecularly imprinted solid-phase extraction for rapid, selective, and cost-effective sample pretreatment.

Determination of glucosamine in impure chitin samples by high-performance liquid chromatography.

A simple, rapid, selective, and specific high-performance liquid chromatography (HPLC) method was developed to quantitate glucosamine, and its application for estimating purity of chitin was investigated. The chromatographic separation was achieved using a reversed-phase C8 column, pre-column derivatization with 9-fluorenylmethoxycarbonyl chloride (Fmoc-Cl) and ultraviolet detection (lambda=254 nm). The mobile phase consisted of CH3CN and H2O. The optimum conditions of acid hydrolysis of chitin (concentration of HCl, temperature, and heating time) was obtained by performing the orthogonal array design (OAD) procedure and the released glucosamine was determined by the above HPLC method. The accuracy of the method was checked by the standard addition technique. The method was found to be specific with good linearity, accuracy, precision, and well suited for quantitation of glucosamine and determination of the purity of chitin in biological materials and food products.

Simultaneous wavelength selection and outlier detection in multivariate regression of near-infrared spectra.

Near-infrared (NIR) spectrometry will present a more promising tool for quantitative measurement if the robustness and predictive ability of the partial least square (PLS) model are improved. In order to achieve the purpose, we present a new algorithm for simultaneous wavelength selection and outlier detection; at the same time, the problems of background and noise in multivariate calibration are also solved. The strategy is a combination of continuous wavelet transform (CWT) and modified iterative predictors and objects weighting PLS (mIPOW-PLS). CWT is performed as a pretreatment tool for eliminating background and noise synchronously; then, mIPOW-PLS is proposed to remove both the useless wavelengths and the multiple outliers in CWT domain. After pretreatment with CWT-mIPOW-PLS, a PLS model is built finally for prediction. The results indicate that the combination of CWT and mIPOW-PLS produces robust and parsimonious regression models with very few wavelengths.

Multivariate calibration analysis for metal porphyrin mixtures by an ant colony algorithm.

A new biomimetic algorithm, Chemical Ant Colony Algorithm, has been developed, which has the characteristics of intelligent search, global optimization, robustness, distributed computation and easy combination with other heuristic. The proposed method has been successfully applied to the spectroscopy analysis of the Zn2+, Cd2+, Pb(2+)-porphyin tribasic color system with supramolecular properties; the errors are within +/-8.0%.