A simple approach for determining a liquid structure using X-ray scattering data, in which a liquid structure is uniquely evaluated without construction of any plausible structure models, has been applied to liquid acetonitrile, acetone and cyclohexane. For a pair of molecules, a given point within a molecule is located at the origin with a given molecular orientation. The site of the given point of another molecule is defined by the polar coordinates and the molecular orientation is treated by three Eulerian angles. These parameters are optimized by a non-linear least-squares calculation applied to X-ray scattering data. The reliability of the method was examined by determining the liquid structure of polar acetonitrile and the obtained intermolecular interatomic distances are in good agreement with the previously reported values. The method was then successfully applied to the determination of the liquid structure of acetone and cyclohexane. Especially for nonpolar cyclohexane, the construction of a variety of plausible structural models is very difficult. It was revealed that acetone has an ordered liquid arrangement similar to that found in its crystal, although the intermolecular distances in liquid acetone are different from those in the crystal. On the other hand, the liquid structure of cyclohexane is disordered.
Quantitative structure-property relationship (QSPR) studies based on artificial neural network (ANN) and wavelet neural network (WNN) techniques were carried out for the prediction of solvent polarity. Experimental S′ values for 69 solvents were assembled. This set included saturated and unsaturated hydrocarbons, solvents containing halogen, cyano, nitro, amide, sulfide, mercapto, sulfone, phosphate, ester, ether, etc. Semi-empirical quantum chemical calculations at AM1 level were used to find the optimum 3D geometry of the studied molecules and different quantum-chemical descriptors were calculated by the HyperChem software. A stepwise MLR method was used to select the best descriptors and the selected descriptors were used as input neurons in neural network models. The results obtained by the two methods were compared and it was shown that in WNN, the convergence speed was faster and the root mean square error of prediction set was also smaller than ANN. The average relative error in WNN was 7.9 and 6.8% for calibration and prediction set, respectively, and the results showed the ability of the WNN developed here to predict solvent polarity.
Tryptophan (Trp), an aromatic amino acid, is a constituent of peptides/proteins and is also a precursor of serotonin, kynurenine derivatives, and nicotinamide adenine dinucleotides. There have been a number of reports on photochemical reactions involving peptides/proteins which contain Trp that showed significant photodegradation, dimerization, and photoionization. The photochemical properties of Trp have not been fully elucidated, and this would provide novel insight into the handling of Trp-containing peptides/proteins. Consequently, we have been trying to evaluate the photochemical properties of Trp, as well as other essential amino acids, focusing on their photosensitivity, photodegradation, and their ability to induce lipid peroxidation. Among all the essential amino acids tested, Trp exhibited the maximal level of superoxide anion generation under 18 h of light exposure (30000 lux). UV spectral analysis of Trp suggested the absorbability of UVA/B light, and exposure of Trp, in both solid and solution states, to UVA/B light resulted in significant photodegradation (t0.5: 18 h) and gradual color changes. In addition, photoirradiated Trp generated lipoperoxidant, a causative agent of photoirritation, and this might be associated with ROS generation.
A selective and sensitive fluorometric determination method for native fluorescent peptides has been developed. This method is based on intramolecular fluorescence resonance energy transfer (FRET) detection in a liquid chromatography (LC) system following precolumn derivatization of the amino groups of tryptophan (Trp)-containing peptides. In this detection process, we monitored the FRET from the native fluorescent Trp moieties (donor) to the derivatized fluorophore (acceptor). From a screening study involving 10 fluorescent reagents, we found that o-phthalaldehyde (OPA) generated FRET most effectively. The OPA derivatives of the native fluorescent peptides emitted OPA fluorescence (445 nm) through an intramolecular FRET process when they were excited at the excitation maximum wavelength of the Trp-containing peptides (280 nm). The generation of FRET was confirmed through comparison with the analysis of a non-fluorescent peptide (C-reactive protein fragment (77 - 82)) performed using LC and a three-dimensional fluorescence detection system. We were able to separate the OPA derivatives of the Trp-containing peptides when performing LC on a reversed-phase column. The detection limits (signal-to-noise ratio = 3) for the Trp-containing peptides, at a 20-µL injection volume, were 41 - 180 fmol. The sensitivity of the intramolecular FRET-forming derivatization method is higher than that of the system that takes advantage of the conventional detection of OPA derivatives. Moreover, native non-fluorescent amines and peptides in the sample monitored at FRET detection are weaker than those of conventional fluorescence detection.
In this paper, we develop a new method for evaluating chromatographic fingerprints of traditional Chinese medicine (TCM) by the average involution similarity and the quantitative involution similarity. To validate this novel approach, we studied the chromatographic fingerprints of Ginkgo biloba extract by the new similarity parameters. The results were compared with those of the cosine of vectorial angle (SF), the correlative coefficient (r) and some other quantitative parameters, such as the apparent quantitative similarity of fingerprint R% and the average mass percentage M%. The approach represented in this paper was proved to well reflect the similarity alteration of each batch of Ginkgo biloba extract and the quantitative differences of the extracted constituents. The Sgxq and Sgxsq are the best qualitive and quantitative similarity parameters of all those mentioned in this paper; they can be profitably used for the qualitative and quantitative assessments of TCM chromatographic fingerprints. Through this study, the quality evaluation of TCM can be simplified by using only one parameter of with the qualitive and quantitative functions proposed in this paper.
A novel capillary electrophoretic (CE) method, based on in-capillary complexation with [PW11O39]7-, was developed for the determination of cadmium(II) in natural water samples. When a sample solution is injected into a capillary containing 0.20 mM [PW11O39]7- and 0.10 M malonate buffer (pH 3.0), the ternary Keggin-type complex, [P(CdIIW11)O39]5-, which possesses high molar absorbtivities in the UV region, is formed in the capillary, and its migration toward the anode gives a well-defined migration peak in the electropherogram. An advantage of this method is that many divalent metal ions do not interfere. The proposed method was successfully applied to the determination of Cd(II) in environmental samples. The detection limits were 1 × 10-7 and 5 × 10-7 M for river-water and seawater samples, respectively (signal-to-noise ratio = 3).
A liquid-crystalline benzocrown ether, 4′-[(4″-1,1,2,2-tetrahydroperfluorooctyloxy)biphenyloxycarbonyl]benzo-15-crown-5, was used as a neutral carrier of ion-selective electrodes (ISEs) to elucidate the effect of highly ordered assembling of the neutral carrier on the sensor properties through fluorophilic interactions. The properties for the membrane and the resulting ISEs based on a benzocrown ether bearing a perfluoroalkyl chain were compared with those based on the corresponding crown ether bearing an alkyl chain. Atomic force microscopy and fluorescence measurements suggested that the neutral carrier bearing a perfluoroalkyl chain formed highly aggregational states in the membranes of ISEs.
A conducting polymer modified electrode based on the incorporation of 4,5-dihydroxy-3-(p-sulfophenylazo)-2,7-naphthalene disulfonic acid, SPADNS, as an anionic complexing ligand into polypyrrole film during electropolymerization was prepared. The electroanalysis of copper(II) in this modified electrode was achieved by medium exchange and differential pulse voltammetry. Copper ions were accumulated from ammonia buffer on the electrode surface by the formation of a chemical complex at open circuit. The resulting electrode with complexed Cu2+ was then transferred to an acetate buffer and subjected to anodic stripping voltammetry. The analytical performance was evaluated and, finally, linear calibration graphs were obtained in the concentration range of 2 - 250 ng ml-1 for Cu(II). The detection limit was found to be 1.1 ng ml-1 and RSD was obtained at 3.1 and 1.9% for two different concentrations. Many coexisting metal ions had little or no effect on the determination of copper. The developed method was applied to Cu(II) determination in natural water and human hair samples. Also, the rapid and convenient regeneration of electrode allows the use of a single modified electrode in multiple analyses.
A disk-shaped microfluidic device (lab-on-a-Disk) was developed to allow the evaluation of mental stress. As a standard sample, secretory immunoglobulin A (sIgA), which is a candidate marker of mental stress, was measured by a heterogeneous enzyme immunoassay (EIA) on the lab-on-a-Disk. Centrifugal force provided a microfluidic control on the lab-on-a-Disk. We examined the relationship between the rotational speed, the channel profile, and the position of the microfluidic chambers from the center of rotation to manipulate sample solutions into each reaction reservoir through microchannels sequentially, i.e., retain in a reservoir or flow into a subsequent reservoir. A single glass bead with immobilized sIgA on its surface was injected into a reservoir for a competitive antigen-antibody reaction, and applied to a specific surface in a heterogeneous assay. It is expected that the lab-on-a-Disk would be suitable for miniaturization and automation of the processes in EIA compared with a conventional EIA using a titer plate.
A novel palladium-polyphenosafranine nano-composite (PPS-Pd) was synthesized by electrochemical co-deposition at a glassy carbon electrode (GCE) for fabrication of a nitrite sensor, PPS-Pd/GCE. This PPS-Pd film was characterized by X-ray photoelectron spectroscopy (XPS) and field emission scanning electron microanalysis (SEM). It was found that the PPS-Pd nano-composite consisted of Pd nanoparticles smaller than 10 nm in diameter which stick together due to the polymer, forming a Pd-embedded PPS layer structure. The sensing ability was investigated by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and differential pulse amperometry (DPA). The PPS-Pd/GCE had excellent catalytic activity toward the oxidation of nitrite: high current sensitivity of 0.365 A/M cm-2, good reproducibility, good stability and fast response. In neutral solutions, a linear concentration range of 1.0 × 10-6 to 1.1 × 10-3 M (R2 = 0.999) with the detection limit (s/n = 3) of 3 × 10-7 M nitrite was obtained for DPV determination.
This research attempts to establish a method to measure 11 kinds of oxygenated volatile organic compound (OVOC) in ambient air by using the canister collection-gas chromatography/mass spectrometry (GC/MS) method. Since several compounds such as acetone exhibited high blank concentrations due to their laboratory use, stringent quality control was conducted for the VOC-free added water and the VOC-free nitrogen gas. In order to prevent the decline of recovery rates due to lack of sufficient relative humidity, it is necessary to add VOC-free water when pressurizing and diluting the air samples. Thus, all the target compounds in ambient air were obtained from the canisters at high recovery rates without significant contamination. Furthermore, the canister collection-GC/MS method makes it possible to apply simultaneous air monitoring of OVOCs as well as volatile hazardous air pollutants without additional sampling.
A rapid and sensitive method has been proposed for the determination of chromium and cobalt in seafood samples by flame atomic absorption spectrometry combined with a dynamic ultrasound-assisted acid extraction and an on-line minicolumn preconcentration. The use of diluted nitric acid as extractant in a continuous mode at a flow rate of 3.5 mL min-1 and room temperature was sufficient for quantitative extraction of these trace metals from seafoods. A minicolumn containing a chelating resin was an excellent device for the quantitative preconcentration of chromium and cobalt prior to their detection. A flow-injection manifold was used as interface for coupling all analytical steps, which allowed the automation of the whole analytical process. A Plackett-Burman experimental design was used as a multivariate strategy for the optimization of both sample preparation and preconcentration steps. The method was successfully applied to the determination of chromium and cobalt in seafood samples.
A novel method of online microcolumn separation and preconcentration coupled to inductively coupled plasma atomic emission spectrometry (ICP-AES) with the use of acetylacetone-modified silica gel as packing material was developed for the determination of trace rare earth elements (REEs) in environmental and food samples. The main parameters affecting online separation/preconcentration, including pH, sample flow rate, sample volume, elution and interfering ions, have been investigated in detail. Under the optimized operating conditions, the adsorption capacity values for Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu were 25.65, 23.23, 24.01, 19.40, 22.89, 23.77, 24.40, 23.96, 25.58, 25.15, 24.86, 22.75, 16.05, 24.13, 26.51 and 27.93 mg g-1, respectively. Detection limits (3σ) based on three times standard deviations of the blanks by 8 replicates were in the range from 48 pg mL-1 for Lu to 1003 pg mL-1 for Sm. With 90 s preconcentration time and 10 s elution time, the enrichment factor was 10 and the sample frequency was 28 h-1. The precisions (RSDs) obtained by determination of a 250 ng mL-1 (n = 8) REEs standard solution were in the range from 1.7% for Y to 4.4% for Sm. The proposed method was successfully applied to the determination of trace REEs in pig liver, agaric and mushroom. To validate the proposed method, we analyzed three certified reference materials (GBW07401 soil, GBW07301a sediment, and GBW07605 tea leaves). The determined values were in a good agreement with the certified values. The method is rapid, selective, sensitive and applicable to the determination of trace REEs in biological and environmental samples with complicated matrix effects.
The ion-pair formation constant (KMLA0 in mol-1 dm3) for Li(B15C5)+ with a picrate ion (Pic-) in water was determined by potentiometry with a K+-selective electrode at 25°C and an ionic strength of 0, where B15C5 denotes benzo-15-crown-5 ether. Using the concentration equilibrium constants, KMLA, estimated from this value, the extraction constants (mol-2 dm6 unit) of about ten diluents were re-calculated from previously reported extraction data. Also, the distribution constants of an ion-pair complex, Li(B15C5)Pic, between water and the diluents were re-estimated. A disagreement in the determined KMLA value between a solvent-extraction method and potentiometry was explained in terms of the Scatchard-Hildebrand equation; it came from the fact that the hydration of Li(I) in Li(B15C5)Pic was larger than that of free B15C5 in water. Then, the previously determined value by the former method was re-estimated using the potentiometric KMLA value.
A method using fullerene for adjusting the NMR spectral resolution for multiple quantum magic angle spinning (MQMAS) experiments is proposed. To observe its 13C MAS signal, it is not necessary to apply 1H decoupling, unavailable with single-resonance MQMAS probes. Although 13C T1 of fullerene is rather long, a recycle time of 5 s in shimming yields its signal with sufficiently high sensitivity if setting the appropriate Ernst angles corresponding to magnetic fields. It is demonstrated that so-adjusted high resolution is reflected in the 87Rb MQMAS spectra of RbNO3.
Bidentate and tridentate heterocyclic azo compounds with and without a long alkyl chain were prepared and examined for cation exchange chromatography of manganese, zinc, and cadmium; these ions could not be separated by reversed phase HPLC following precolumn derivatization with heterocyclic azo compounds owing to the dissociation of the complexes. The newly prepared azo compounds having a long alkyl chain favorably orientate in the reversed-phase stationary phase such that the coordinating parts of the ligand may make contact with metal ions in the mobile phase. Bidentate ligands showed sharp peaks but almost no resolution of manganese and cadmium. A tridentate ligand strongly retained all the three metal ions, which could be separated within 10 min by a competing ligand and by optimizing the pH.
A sensitive liquid chromatography-electrospray ionization-tandem mass spectrometric (LC-ESI-MS/MS) method for the determination of the rat brain 5α-androstane-3α,17β-diol (3α,5α-Adiol) has been developed and validated. The brain extract was purified using solid-phase extraction cartridges, derivatized with isonicotinoyl azide, and subjected to LC-MS/MS. The method was accurate and reproducible, and the limit of quantitation was 0.1 ng/g tissue when a 100-mg tissue sample was used. The change in the brain 3α,5α-Adiol level by immobilization stress was also analyzed using the developed method.
Yttrium hydroxide quantitatively coprecipitated Be(II), Ti(IV), Cr(III), Mn(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II), and Pb(II) at pH 9.6 - 10.0 for seawater and pH 10.5 - 11.4 for a table-salt solution. The coprecipitated elements could be determined by inductively coupled plasma atomic emission spectrometry; yttrium was used as an internal standard element. The detection limits ranged from 0.0016 µg (Mn(II)) to 0.22 µg (Zn(II)) in 100 mL of sample solutions. The operation time required to separate 11 elements was approximately 30 min.