Determination and differentiation of nitrilotriacetic acid and ethylenediaminetetra-acetic acid

Ethylenediaminetetra-acetic acid (EDTA) and nitrilotri-acetic acid (NTA) can be differentiated and determined by titration with metal ions to visual metallochromic dye end-points. EDTA can be determined without interference from NTA, either by titrating with copper(II) at pH 5 using PAN indicator, or by titrating with iron(III) at pH 6 and 70 degrees using Tiron indicator. The total chelating power (EDTA + NTA) can be determined either by titrating with lead(II) at pH 4.4 using dithizone indicator, or by titrating with iron(III) at pH 3.5 using Tiron indicator ; NTA is determined by difference. The lowest concentration at which NTA can be determined in EDTA by titration to the iron(III)-Tiron end-point is about 1 wt.%. The apparent stability constants of the iron(III)-Tiron complexes under the conditions of the titration at pH 3.5 and pH 6 have been determined using the method of continuous variations.     

Biodegradability of Poly(ester‐ether) and Poly(ester) Obtained from a Radical Ring‐Opening Polymerization of Cyclic Ketene Acetals

2‐Methylene‐1,3,6‐trioxocane (MTC) and 2‐methylene‐1,3‐dioxepane (MD) were synthesized and polymerized via ring‐opening in the presence of a radical initiator. The obtained poly(ester‐ether) (PMTC) and poly(ester) (PMD) were found to be enzymatically degradable by total organic carbon (TOC) analysis using lipase. The enzymatic degradability of PMTC was higher than that of PMD. PMTC and PMD were also found to be biodegradable with a biological oxygen demand (BOD)‐tester using soil. The degradability of PMTC using soil was also higher than that of PMD. The higher degradability of PMTC by enzyme and soil are thought to be due to its higher hydrophilicity.     

Optical determination of Cr(VI) using regenerable, functionalized sol-gel monoliths

Transparent, pyridine-functionalized sol-gel monoliths have been formed and their use in Cr(VI) sensing applications is demonstrated. The monoliths were immersed in acidic Cr(VI)-containing solutions, and the Cr(VI) uptake was monitored using UV-vis and atomic absorption spectroscopies. At concentrations at the ppm level, the monoliths exhibit a yellow color change characteristic of Cr(VI) uptake, and this can be measured by monitoring the absorption change at about 350 nm using UV-vis spectroscopy. Concentrations at the ppb level are below the limit of detection using this wavelength of 350 nm for measurement. However, by adding a diphenylcarbazide solution to monoliths that have been previously immersed in ppb-level Cr(VI) solutions, a distinct color change takes place within the gels that can be measured at about 540 nm using UV-vis spectroscopy. Concentrations as low as 10 ppb Cr(VI) can be measured using this method. The monoliths can then be regenerated for subsequent sensing cycles by thorough washing with 6.0 M HCl. The factors affecting monolith uptake of Cr(VI) have been explored. In addition, the gels have been characterized using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) measurements.     

直观推导式演进特征投影法解析多环芳烃的重叠色谱峰

用高效液相色谱法(HPLC)测定多环芳烃时,因芴、苊和菲,茚(1,2,3-cd)芘和苯并(g,h,i)苝的色谱峰严重重叠而影响测定结果。本研究用高效液相色谱-二极管阵列检测器(DAD)和荧光检测器(FLD)测定多环芳烃,在激发波长λex=230nm,发射波长λem=300～500nm范围内采集重叠峰的HPLC-FLD二维色谱数据,再用直观推导式演进特征投影法(HELP)解析它们的重叠色谱峰,分辨结果令人满意。该方法对重叠组分的分辨下限为0.02mg/L。结果表明,用二维色谱荧光数据解析色谱重叠峰,灵敏度更高,可用于环境样品中多环芳烃的测定。     

Surface characterization of poly(lactic acid) and polycaprolactone by inverse gas chromatography

Inverse gas chromatography (IGC) has been used to characterise the surface properties of polycaprolactone (PCL) and poly(lactic acid) (PLA). The dispersive component of the surface free energy (gamma(S)(D)) was found to be very small for both of them--values close to 30 mJ/m(2) in the case of the PLA and ca. 40 mJ/m(2) for the PCL. The retention times of the n-alkanes, necessary to calculate the dispersive component of the surface energy, were obtained from the maximum, the centre at half height and the centre of mass of the chromatographic peak. While the values obtained using the first two parameters appear not to be affected by the peak asymmetry, in spite of having been obtained above the glass transition temperature of the polymer, the values obtained using the latter have been found to be not reliable. The drawbacks of using n-alkanes with a very small retention time have also been discussed, estimating the error it can introduce in the final results. Finally, the acid-base properties of the two biopolymers were determined using the approaches suggested by Schultz et al. and by St. Flour and Papirer. Although both methods describe the surfaces of PLA and PCL as neutral ones, differences between the values of the parameters K(A), K(D) and S(C) were obtained.     

Electrocatalytic oxidation of L-tyrosine by a nitroxide

The electrochemistry of L-tyrosine was studied by cyclic voltammetry at a glassy carbon electrode. Although L-tyrosine itself showed very poor electrochemical response, the response could be greatly enhanced by using 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-1-oxy (HO-TEMPO) as a mediator that enables a sensitive determination of the substrate. An electrocatalytic EC' mechanism with the oxoammonium ion of HO-TEMPO as the active oxidant is proposed. The catalytic rate constant was determined to be 2.0 x 10(4) M(-1) s(-1) by using chronoamperometry.     

Characterization of poly(ethylene glycol)-b-poly(ε-caprolactone) by liquid chromatography under critical conditions: Influence of catalysts and reaction conditions on product composition

Amphiphilic block copolymers were synthesised by ring opening polymerization of ε-caprolactone with polyethylene glycol monomethyl ether (PEG-MME) using different catalysts (boron trifluoride, sodium hydride, and tin octoate) in a one pot procedure. The products obtained were characterized with respect to their molar mass distribution and content of homopolymers using size exclusion chromatography (SEC), Liquid chromatography under critical conditions (LCCC) and MALDI-TOF-MS. The homopolymers of caprolactone could be separated from the block copolymer by LCCC on a reversed phase column in tetrahydrofurane-water mobile phases with evaporative light scattering detection (ELSD). Residual monomer could be determined under the same conditions using density detection, a separation of the copolymer from residual initiator could be achieved on a normal phase column in acetone-water mobile phases.     

Evaluation of the extraction efficiency of thermally labile bioactive compounds in Gastrodia elata Blume by pressurized hot water extraction and microwave-assisted extraction

Our earlier work showed that the stability of the bioactive compounds gastrodin (GA) and vanillyl alcohol (VA) in Gastrodia elata Blume behaved differently with varying compositions of water-ethanol using pressurized liquid extraction (PLE) at room temperature. To have a better understanding of the extraction process of these thermally labile compounds under elevated temperature conditions, pressurized hot water extraction (PHWE) and microwave-assisted extraction (MAE) methods were proposed. PHWE and MAE showed that GA and VA could be extracted using pure water under optimized conditions of temperature and extraction time. The extraction efficiency of GA and VA by the proposed methods was found to be higher or comparable to heating under reflux using water. The marker compounds present in the plant extracts were determined by RP-HPLC. The optimized conditions were found to be different for the two proposed methods on extraction of GA and VA. The method precision (RSD, n=6) was found to vary from 0.92% to 3.36% for the two proposed methods on different days. Hence, PHWE and MAE methods were shown to be feasible alternatives for the extraction of thermally labile marker compounds present in medicinal plants.     

Extending reversed-flow chromatographic methods for the measurement of diffusion coefficients to higher temperatures

A reversed-flow gas-chromatography (RF-GC) apparatus for the measurement of binary diffusion coefficients is described and utilized to measure the binary diffusion coefficients for several systems at temperatures from (300 to 723)K. Hydrocarbons are detected using flame ionization detection, and inert species can be detected by thermal conductivity. The present apparatus has been utilized to measure diffusion coefficients at substantially higher temperatures than previous RF-GC work. Characterization of the new apparatus was accomplished by comparing measured binary diffusion coefficients of dilute argon in helium to established reference values. Further diffusion coefficient measurements for dilute helium in argon and dilute nitrogen in helium (using thermal conductivity detection) and dilute methane in helium (using flame ionization detection) were performed and found to be in excellent agreement with literature values. The measurement of these well-established diffusion coefficients has shown that specific experimental conditions are required for accurate diffusion measurements using this technique, particularly at higher temperatures. Numerical simulations of the diffusion experiments are presented to demonstrate that artifacts of the analysis procedure must be specifically identified to ensure accuracy, particularly at higher temperatures.     

An efficient and highly selective deprotecting method for beta-(trimethylsilyl)ethoxymethyl ethers

A series of beta-(trimethylsilyl)ethoxymethyl ethers were hydrolyzed to their corresponding alcohols in high yields by using a catalytic amount of CBr4 (15%) in MeOH under refluxing reaction conditions. The chemoselective deprotection between trialkylsilyl and beta-(trimethylsilyl)ethoxymethyl-protected alcohols can be achieved by using an alcohol with steric hindrance such as iPrOH. The selectivity also can be achieved in the CBr4/MeOH reaction mixture under ultrasonic reaction conditions.     

Immobilization of Pd nanocatalysts on magnetic rattles and their catalytic property

Here we report a magnetic composite nanocatalyst (MP@NiSiO/Pd) with a rattle type nanostructure. The nickel silicate shell encapsulated magnetic core (MP@NiSiO) rattle particles were synthesized by using a facile templating method and the Pd nanocrystals with different sizes can be directly immobilized onto the MP@NiSiO rattles without using any surfactant or capping reagents. X-Ray powder Diffraction (XRD) and Transmission Electron Microscopy (TEM) are employed to characterize the rattle type particles. The MP@NiSiO/Pd composites show catalytic activity on the Heck and Suzuki reactions. They can be separated from the reaction system by using a magnet and the catalyst can be cycled at least for 5 times.     

A light scattering study of concentrated dispersions in nonaqueous media

Interparticle interactions between colloidal poly(methylmethacrylate) particles stabilised by poly(12-hydroxystearic acid) in non-aqueous media have been investigated using time-average light scattering. The problem of multiple scattering was avoided by using a binary mixture of solvents such that the colloidal particles were optically matched. This enabled the static structure factor to be measured and from the small scattering vector expansion the osmotic pressure to be determined. The softness of the pairwise interaction potential has been exposed using the Chandler-Weeks-Anderson perturbation theory. However, it is concluded that dispersions of the type studied can be reasonably well approximated by a hard sphere fluid model.     

Detection and quantitative estimation of metalloporphyrins in vivo

Spectrofluorometry, radioisotope (RI) labelling and high performance liquid chromatography (HPLC) can be used to estimate photosensitizer concentrations. The biodistribution of porphyrins and metalloporphyrins containing the bifunctional chelating agent diethylenetriamine pentaacetic acid (DTPA) was examined in tumour-bearing mice by nitrogen-pulsed laser spectrofluorometry (PLS) and RI labelling. The biodistribution of metalloporphyrin amino acid derivatives containing alkoxyl groups was also examined by PLS and HPLC analysis using an acetone powder extraction method. Spectrofluorometry is useful for estimating the biodistribution of porphyrins in tumour, lung, kidney and serum, but not in liver. However, spectrofluorometry cannot be used to evaluate the concentration of certain metalloporphyrins such as manganese complexes. The concentrations of porphyrins in liver measured by PLS and two other methods showed remarkable differences. RI labelling and HPLC analysis are obviously tedious methods. Therefore it seems practical to screen for a number of compounds using the spectrofluorometric method (PLS). Subsequently, the porphyrins which give good results with PLS should be measured using RI labelling and HPLC.     

Peptide synthesis using pentafluorophenyl diphenylphosphate (FDP) as coupling reagent

Comparison of the reaction speed and yield with its analogues and some conventional peptide coupling reagents, pentafluorophenyl diphenylphosphate (FDP) was shown to be a more preferable "active ester" type reagent for the peptide synthesis. The synthesis of oligopeptides using FDP was achieved with high yields. The influences of several reaction parameters such as solvent, base, additive and temperature on the coupling reaction were studied using HPLC method. The degree of racemization with FDP determined by HPLC or Young test was shown to be lower than that of DCCI. Octapeptide Gly-Cys(Bzl)-Ser-Gly-Lys-Leu-Ile-Cys(Bzl)-OH, corresponding to the amino acid sequence of gp41 of HIV-1, was successfully synthesized by 5+3 approach using FDP with high yield.     

Transmission surface-plasmon resonance (T-SPR) measurements for monitoring adsorption on ultrathin gold island films

Evaporation of ultrathin (1.3-10 nm nominal thickness) gold films onto quartz or mica leads to the formation of a layer of rather uniform gold islands on the transparent support. The morphology of ultrathin gold island films of various thicknesses was studied by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging. The surface plasmon (SP) absorption characteristic of such films is highly sensitive to the surrounding medium, with the plasmon band changing in intensity and wavelength upon binding of various molecules to the surface. The binding process can be monitored quantitatively by measuring the changes in the gold SP absorption, by using transmission UV/Vis spectroscopy. The method, termed transmission surface plasmon resonance (T-SPR) spectroscopy, is shown to be applicable to both chemically and physically adsorbed molecules, in liquid or gas phase, with measurements carried out either ex situ or in situ (real-time measurements) using a variety of molecular probes. Binding to a preformed molecular layer on the Au surface produces a similar response, suggesting the possible use of T-SPR for selective sensing. The sensitivity of T-SPR spectroscopy in detecting molecular binding to the gold depends strongly on the film preparation conditions, and may be comparable to that obtained in surface plasmon resonance (SPR) sensing.     

Determination of Lanthanide (III) Ions by Using a Flotation - Spectrophotometric Method

Abstract

This paper reports our attempt at determining Ln (III) ions by using a flotation-spectrophotometric method and our findings. When a ternary ion-association complex of Ln (III) coordinated by thiocyanate (SCN^?) and diantipyryl methane (DA[Mdot]) is separated by a mixed solvent containing benzene and chloroform at pH 3.1 – 4.2, a third phase is observed between the aqueous and organic phases. The solid ternary complex can be dissolved in acetone that contains thenoyltrifluoroacetone (TTA). The individual Ln (III) ion can be determined by using the 4th derivative spectra directly. The equilibrium constant of the ternary composition ratio of Ln(II1) to ligand is estimated by the equilibrium shift method. The mole ratio of Ln(II1) to DAM and to SCN^? is 1:3 each. The composition of the tcrnary complex seems to be Ln(III):DAM:SCN^?=1:3:3.     

Two-dimensional homonuclear chemical shift correlation established by the cross-relaxation driven spin diffusion in solids

A new type of spin diffusion, cross-relaxation driven spin diffusion (CRDSD), is investigated using (15)N NMR on a N-acetyl-L-valyl-L-leucine (NAVL) single crystal under stationary condition. A two-dimensional (2D) pulse sequence that correlates the chemical shifts of (15)N nuclei, with a radio-frequency spin lock on the (15)N channel during the mixing time, is used to observe CRDSD. Experimental results obtained using CRDSD, rf-driven spin diffusion, and proton driven spin diffusion approaches on the NAVL single crystal are compared. Our experimental results suggest that the (15)N spin diffusion rate can be enhanced by about 1000 times using CRDSD than by the normal proton driven spin diffusion. Interestingly, the required spin-locking rf field strength for CRDSD is much lower than that used for the rf-driven spin diffusion experiments. The cross-peak patterns observed in 2D (15)N-(15)N correlation spectra using CRDSD and RFDSD are very different as they arise from different spin-spin interactions. A detailed theory describing CRDSD and RFDSD processes is also presented using a thermodynamic model. The speedy spin diffusion process rendered by the CRDSD approach will be useful to assign resonances from a uniformly (15)N or (13)C labeled proteins and peptides, particularly in aligned samples.     

A Simplified Extraction for Mexiletine from Serum and Analysis by High Performance Liquid Chromatography

Abstract

The analysis of mexiletine by High Performance Liquid Chromatography (HPLC) requires organic extraction followed by evaporation of the organic solvent. Calibration curves must be prepared using standards in drug-free serum. This procedure has been simplified by using a back extraction of the mexiletine from serum. Calibration curves can then be more quickly prepared since good agreement can be obtained using standards in hydrochloric acid (HCl) instead of having to prepare standards in serum with the time-consuming necessity of having to extract these standards.     

Reactions and polymerization of 1-trityl-4-vinylimidazole

1-Trityl-4-vinylimidazole was prepared by direct tritylation of 4(5)-vinylimidazole and polymerized using a free radical initiator. Poly(1-trityl-4-vinylimidazole) was hydrolyzed using aqueous acetic acid to give poly[4(5)-vinylimidazole]. The poly[4(5)-vinylimidazole], which was obtained from the hydrolysis of poly(1-trityl-4-vinylimidazole), was compared with poly[4(5)-vinylimidazole] prepared directly from 4(5)-vinylimidazole for differences in stereochemistry. The stereochemistry of both polymers was found to be similar by high-resolution NMR. Thus, the trityl does not influence the stereochemistry of poly[4(5)-vinylimidazole]. The reaction of 1-trityl-4-vinylimidazole with n-butyllithium gave 2-lithio-1-trityl-4-vinylimidazole. This intermediate was used to prepare 2-substituted 4(5)-vinylimidazoles, which are new monomers that can be polymerized using free radical initiators.     

In situ generation of HCN for mass spectrometric studies

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me(3)SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F(-)(HCN), Cl(-)(HCN), CN(-)(HCN), PhNO(2)(.-)(HCN), Me(3)SiO(-)(HCN),and PhSiF(4)(-)(HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN(-)(HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0.87 +/- 0.07 eV.