Prediction of solvents extraction-the organochlorine pesticides in soil using solubility parameter

Prediction of the optimal extraction solvent based on the solubility parameter to extract the typical organochlorine pesticides from Jiangxi red soil was reported in this paper. Hildebrand solubility parameters, including dispersion coefficient (δ_d), polarity (δ_p) and hydrogen bonding (δ_h), of extraction solvents (including hexane, dichloromethane, hexane/methanol (4:1, v/v), hexane/acetone (1:1, v/v), hexane/dichloromethane (1:1, v/v) and organochlorine pesticides were calculated using group contribution method. The solvents, such as hexane/methanol (4:1, v/v) and hexane/acetone (1:1, v/v) were selected as ideal extraction solvents to extract o,p′-DDT o,p′-DDE and o,p′-DDD with high recoveries (>82%), furthermore, these solvents can be used to extract α-endosulfan, Endrin and HCB with the reliable recoveries (>75%). The estimated finding by solubility parameters was supported by the results of soxhlet extraction.     

Investigations of radiative lifetimes in the 3p5p configuration of neutral silicon

Lifetimes for the³ S ₁,³ P _{0, 1, 2} and³ D _{1, 2, 3} states in the 3s ²3p5p configuration of silicon have been determined using stepwise dye laser excitation and time resolved detection. A comparison is made with theoretical values, calculated using multi-configuration Hartree-Fock wavefunctions. Laser-evaporation was used to produce free silicon atoms by focusing a Nd: YAG laser on a rotating silicon target.     

Spectkophotometric determination of the dissociation constants of n,n'-bis(3-hydroxypropyl)dithiooxamide and n,n'-bis(2-hydroxypropyl)dithiooxamide

The dissociation constants of N,N'-bis(3-hydroxypropyl)dithiooxamide and N,N'-bis(2-hydroxypropyl)dithiooxamide were determined by a spectrophotometric method using a weighted least squares technique for the calculations. For N,N'-bis(3-hydroxypropyl) dithiooxamide a thermodynamic constant pK₁^T of 11.37 was found. At ionic strength μ = 1, pK₁ = 11.27 and pK₂ = 14.29. For N,N'-bis-(2-hydroxypropyl) dithiooxamide, these values were respectively: pK₁^T = 11.11; pK₁ = 10.99 and pK₂ = 13.75.     

Photochimie d'heterocycles azotes—V : Reactions de photosubstitution en serie heterocyclique: cas des p-nitrophenyl-1 pyrazoles et imidazoles

The photosubstitution reactions of eight 1-p-nitrophenylpyrazoles and two 1-p-nitrophenylimidazoles bearing different substituents in the heterocyclic ring have been studied. In the case of pyrazole derivatives, among the different nucleophiles utilized, only the acetate, cyanate and cyanide ions gave identifiable products. The two first ones lead to the 4-formyl derivative of the starting material. With the cyanide ion the reaction is more complicated, not only the 4-cyano derivative is formed but also the 4-carboxamido and several reduced products: p-amino, p-formamido, p-acetamido, p-carbamate and p-azoxypheny 1-1 pyrazoles. In the case of 1-p-nitrophenylimidazoles, the only interesting results have been obtained with the cyanide ion: formation of cyano- and hydroxymethylene-imidazoles.     

Selective electrochemical molecular recognition of benzenediol isomers using molecularly imprinted TiO2 film electrodes

In this paper, selective recognition of benzenediol isomers was studied using molecularly imprinted TiO₂ film formed on a graphitic electrode. The imprinting process was investigated in detail using IR. The electrode process for p-hydroquinone follows a E_rC_r mechanism. The cavities formed by p-phthalic acid have good selectivity toward p-hydroquinone among the isomers. The complex ratio between p-hydroquinone and binding sites was estimated to be 1:2 with an apparent equilibrium constant of 2.98×10⁶ l² mol⁻². For o-hydroquinone and m-benzenediol, the ratio decreased to 1:1 with an apparent equilibrium constant of 1.20×10³ and 1.35×10³ l mol⁻¹. The apparent complexing ratio and equilibrium constants could shed some insight on the nature of isomeric selectivity of the recognition sites with respect to different isomers of benzenediol. The cavities designed by o-phthalic acid present good selectivity toward o-hydroquinone.     

Spectral,electrochemical and computational investigations on the host–guest interaction of Coumarin-460 with <Emphasis Type="Italic">p</Emphasis>-sulfonatocalix[4]arene

The supramolecular host–guest investigation of Coumarin 460 (C460), a salient coumarin family dye molecule is studied with a noteworthy host molecule, p-sulfonatocalix[4]arene (p-SC4). The investigation is carried out by both experimental and theoretical approach. The binding affinity of C460 with p-SC4 is experimentally studied using absorption, emission, excited state lifetime and Cyclic Voltammetry methods. The binding constant is around 10³ M^??1, which shows potent binding. The binding stoichiometry is 1:1. The binding orientations and binding energies are studied using computational simulations. The mode of binding is also established using NMR spectral techniques.     

Structural Characteristics,Antioxidant and Hypoglycemic Activities of Polysaccharide from Siraitia grosvenorii

The structural characterization, the in vitro antioxidant activity, and the hypoglycemic activity of a polysaccharide (SGP-1-1) isolated from Siraitia grosvenorii (SG) were studied in this paper. SGP-1-1, whose molecular weight is 19.037 kDa, consisted of Gal:Man:Glc in the molar ratio of 1:2.56:4.90. According to the results of methylation analysis, GC–MS, and NMR, HSQC was interpreted as a glucomannan with a backbone composed of 4)-β-D-Glcp-(1→4)-, α-D-Glcp-(1→4)-, and 4)-Manp-(1 residues. α-1,6 linked an α-D-Galp branch, and α-1,6 linked an α-D-Glcp branch. The study indirectly showed that SGP-1-1 has good in vitro hypoglycemic and antioxidant activities and that these activities may be related to the fact that the SGP-1-1’s monosaccharide composition (a higher proportion of Gal and Man) is the glycosidic-bond type (α- and β-glycosidic bonds). SGP-1-1 could be used as a potential antioxidant and hypoglycemic candidate for functional and nutritional food applications.     

Two-photon ionization of an inner shell electron of the Cl atom

We have calculated, using second order perturbation theory, the two photon ionization cross section of a K-shell electron of chlorine forE=1.6 keV incident photons. Two classes of intermediate states must be considered, those in which a 1s electron moves to an emptyp-orbital, and those in which an electron from an occupiedp-orbital moves into the continuum. The first class of intermediate states is followed by the ejection of ap-electron into the continuum. The second class of intermediate states is followed by the transfer of a 1s electron into an emptyp-state. The largest contribution comes from 3p →d-continuum followed by 1s → 3p transition. Our result is σ⁽²⁾/I=2.06×10⁴¹ cm⁴/W where σ⁽²⁾ is the two photon ionization cross-section andI is the light intensity.     

Facile synthesis of pseudo-C-glycosyl p-amino-dl-phenylalanine building blocks via Amadori rearrangement

We studied the synthesis of pseudo-C-glycosyl amino acid via an Amadori rearrangement in aqueous solution using unprotected d-lactose and a tyrosine analogue: the p-amino-dl-phenylalanine. Two steps were necessary. In the first step, the N-glycosylation of d-lactose was carried out in aqueous conditions. The synthesized N-glycosylamine was stabilized in a second step by the formation of Amadori compound, the N-[β-d-galactosyl-1-4-(1-deoxyfructos-1-yl)]-p-amino-dl-phenylalanine. Products were purified and characterized by mass spectrometry and by ¹H and ¹³C NMR. The influence of the temperature, the pH, the nature of acid and the concentration of the acid on the synthesis yield was examined in order to determine the optimum conditions of Amadori rearrangement. In the best conditions, 35% of p-amino-dl-phenylalanine was converted into N-[β-d-galactosyl-1-4-(1-deoxyfructos-1-yl)]-p-amino-dl-phenylalanine. For the N-glycosylation, a specific base catalysis took place in the media whereas a general acid catalysis was observed for the Amadori rearrangement using weak acids and with a temperature close to 75 °C. The Amadori compound from glucose [N-(1-deoxyfructopyranos-1-yl)-p-amino-dl-phenylalanine] was also synthesized and characterized by mass spectrometry and by ¹H and ¹³C NMR.     

Photometric titrations with indicators

Various types of photometric titration curves are discussed. If a metal M is titrated conipleximetrically using a metal indicator and the absorbance is plotted vs. the titrant consumed, the inflection point appears at a pM value defined by the equation 3 pM_infl = pM_trans + 2 pM_eqThis expression is valid when M combines in a 1 : 1 ratio with the complexing agent and the indicator and when the indicator concentration is small compared to the total metal concentration.The difference between the pM values at the inflection and equivalence points can be calculated from the equation ΔpM = pM_infl — pM_eq = $\text{1}\text{3}$(pM_trans — pM_eq) = $\text{1}\text{6}$log(C_MK²_MI/K_MY)If the inflection point is taken as the equivalence point, the error arising can be calculated from ΔpM, or more simply, read from a diagram.If transmittance, instead of absorbancc, is plotted as a function of the titrant volume, the inflection point depends on the added amount of indicator. However, at high transmittance values, i.e., at low indicator concentrations, the inflection point of a transmittance curve occurs practically at the same volume of added titrant as the inflection point of an absorbance curve. Rules are given for applying an indicator correction for the amount of metal bound to the indicator at the end-point.The derived equations and discussions can also be applied to acid-base titrations.     

Calculating the acidity constants of homologues and isomers of organic acids by means of recurrence relations

It is noted that the pK _a values of organic acids can be calculated using the unique recurrence relation pK _a(n + 1) = apK _a(n) + b from the pK _a values of other (usually the simplest and, consequently, better characterized) homologues of the same series. It is shown that this relation is valid within two taxonomic groups: insertion homologues of the ω-substituted acids X(CH₂) _n CO₂H (n ≥ 1) and isomers that differ in the position of substituents X in their alkyl fragments, k-X(C _n H_2n )CO₂H (n ≥ 1, 1 ≤ k ≤ n + 1). It is concluded that this algorithm is a consequence of the unique mathematical properties of recurrence relations.     

Generation of harmonic radiation by helium atoms in intense laser pulses

Measurements of natural radiative lifetimes in atomic tellurium in the 5p ³7p configuration are reported. Two-step laser excitation was applied on tellurium vapour in a cell that was differentially heated and pumped through a capillary. The decay of the fluorescence signal was recorded at different vapour pressures. The following four radiative lifetime values were obtained: 7p ⁵ P ₁: 128(11) ns, 7p ⁵ P ₂: 99(8) ns, 7p ³ P ₁: 82(10) ns and 7p ³ P ₂: 124(8) ns.     

Host-Guest Complexation of Oxaliplatin and Para-Sulfonatocalix[n]Arenes for Potential Use in Cancer Therapy

P-sulfonatocalix[n]arenes have demonstrated a great potential for encapsulation of therapeutic drugs via host-guest complexation to improve solubility, stability, and bioavailability of encapsulated drugs. In this work, guest-host complexes of a third-generation anticancer drug (oxaliplatin) and p-4-sulfocalix[n]arenes (n = 4 and 6; p-SC4 and p-SC6, respectively) were prepared and investigated, using ¹H NMR, UV, Job’s plot analysis, and DFT calculations, for use as cancer therapeutics. The peak amplitude of the prepared host-guest complexes was linearly proportional to the concentration of oxaliplatin in the range of 1.0 × 10⁻⁵ M⁻¹ to 2.1 × 10⁻⁴ M⁻¹. The reaction stoichiometry between either p-SC4 or p-SC6 and oxaliplatin in the formed complexes was 1:1. The stability constants for the complexes were 5.07 × 10⁴ M⁻¹ and 6.3 × 10⁴ M⁻¹. These correspond to complexation free energy of −6.39 and −6.52 kcal/mol for p-SC4 and p-SC6, respectively. Complexation between oxaliplatin and p-SC4 or p-SC6 was found to involve hydrogen bonds. Both complexes exhibited enhanced biological and high cytotoxic activities against HT-29 colorectal cells and MCF-7 breast adenocarcinoma compared to free oxaliplatin, which warrants further investigation for cancer therapy.     

Evaluation of expanded graphite as on-line solid-phase extraction sorbent for high performance liquid chromatographic determination of trace levels of DDTs in water samples

Dichlorodiphenyltrichloroethane (DDT) and its metabolites are a typical kind of persistent organic pollutants (POPs). Development of a simple, cost-effective and sensitive methodology to monitor DDTs concentrations in water environment is of particular significance for understanding the fate and behavior of these pollutants. In this paper, a method on the basis of solid-phase extraction (SPE) using expanded graphite (EG) as sorbent coupled on-line with high performance liquid chromatography (HPLC) was developed for the determination of trace levels of p,p′-DDD (2,2-bis(4-chlorophenyl)-1,1-dichloroethane), p,p′-DDT, o,p′-DDT and p,p′-DDE (2,2-bis(4-chlorophenyl)-1,1-dichloroethene) in water. The analytes in water were preconcentrated onto the SPE column packed with expanded graphite, and subsequently eluted with methanol-water (90:10) mixed solvent. HPLC with a photodiode array detector was used for their separation and detection. The developed on-line solid-phase extraction protocol for HPLC permits the current HPLC separation and the next preconcentration proceeded in parallel, and thus allows one determination within 8 min. The precision (R.S.D.) for 10 replicate injections of a mixture of 1 μg l⁻¹ of each analyte was 3.2-6.2% for the peak area measurement. The detection limits (S/N = 3) for preconcentrating 50 ml of sample solution ranged from 10 to 25 ng l⁻¹ at a sample throughput of 7.5 samples h⁻¹. The enhancement factors were about 700. The method was applied to the determination of trace p,p′-DDD, p,p′-DDT, o,p′-DDT and p,p′-DDE in local lake, river and tap water samples.     

The effect of vinyl esters on the enantioselectivity of the lipase-catalysed transesterification of alcohols

The enantioselectivity of the lipase from Pseudomonas cepacia (PCL) in the transesterification of 2-phenyl-1-propanol 1 was studied using a series of vinyl 3-arylpropanoates as acyl donors. The most enantioselective transesterification reaction of the alcohol was attained by using vinyl 3-(p-iodophenyl)- or 3-(p-trifluoromethylphenyl)propanoates, with enantiomer ratios, E, of 116 and 138, respectively. Vinyl 3-phenylpropanoate was also effective for the resolution of 1 mediated by lipases from P. fluorescens and porcine pancreas and for the PCL-catalysed transesterification of several 2-phenyl-1-alkanols. The enantiomeric resolution of 1 was practically carried out by the first enantioselective transesterification using PCL and vinyl 3-(p-iodophenyl)propanoate to afford (R)-1 and then the enantioselective hydrolysis of the resultant ester to afford (S)-1.     

Kinetic amperometric determination of hydrolase activity

Alkaline phosphatase is determined by using o-hydroxyphenyl or p-aminophenyl phosphate as substrate; for β-glucosidase, p-aminophenol β-D-glucoside is used. The products, p-aminophenol and catechol, are monitored amperometrically. The limit of determination for the hydrolase is about 2.5 × 10^-3 units ml^-1. The apparent Michaelis constants are given.     

Positron-hydrogen scattering at intermediate energies using CCA

Positron-hydrogen scattering has been studied using close coupling approximation (CCA) in the energy range 19.584–200 eV. The coupling scheme: H(1s), H(2s), H(2p), H(3d), Ps(1s) is used to study elastic, 1s–2s excitation and ground state capture cross sections. The effect of capture channel is found to influence the scattering parameters.     

Gamma-ray irradiation and characterization of synthesized bidentate and tetradentate Schiff base ligands and their complexes with some transition metal ions

Salen ligands are essential for coordinating a diverse group of metals in their respective oxidation states. This creates significant complexes of salen metals that are used in different fields. Condensation of ehylenediamine (en) with p-methoxybenzaldehyde (L¹) or o-hydroxyacetophenone (L²) with a ratio 1: 2 (en: p-methoxybenzaldehyde or o-hydroxyacetophenone) or by the interaction of o-phenylenediamine (phen) with o-hydroxybenzaldehyde (L³) or p-hydroxybenzaldehyde (L⁴) with a ratio 1: 2 (phen: o-hydroxybenzaldehyde or p-hydroxybenzaldehyde) has been used to prepare four symmetrical Schiff bases (L¹-L⁴). The UV–vis spectroscopy has been used to investigate the diverse electronic transitions associated with the Schiff bases molecules as well as how these transitions are impacted by diverse polarities of solvents. Elemental analysis, FT-IR, UV–vis spectra, molar conductivity, and ¹H NMR have been used to characterise all the compounds obtained in this process. The continuous variation applied alongside molar ratio spectral methods showed the formation of different complexes arising from the reaction of the ligand (L^1-L⁴) with the metal ions Mn(II), Fe(III) and Cu(II) is 1: 1 and/ or 1: 2 (M: L). A series of universal buffer solutions (20 % ethanol v/v) with varying pH values were used in spectrophotometry to determine the acid dissociation constants of the L² and L⁴ ligands. Gamma radiation was applied to examine the compounds’ irradiation stability. Additionally, the absorptions of the main functional groups were screened using FT-IR spectra before and after Gamma irradiation. The results show that all the compounds are stable after irradiation process; therefore, it could be used as enhancing agents in cancer therapy.     

Ionization of some derivatives of benzamide, oxamide and malonamide in DMF-water mixture

The ionization of six compounds of bis-phenolic amides was studied spectrophotochemically in DMF-water mixture. The compounds showed two pK_a values in the range of 5.97-7.32 for pK_a1 and 7.61-8.44 for pK_a2. The obtained values of K_a were normalized using the distribution diagrams of the different species and found to be in the range of 5.81-7.42 for pK_a1 and 7.48-8.27 for pK_a2.     

Determination of Organochlorine Pesticides and Polychlorinated Biphenyls Residues in Municipal Solid Waste Compost by Gas Chromatography with Electron−Capture Detection

A simple and efficient method for the simultaneous gas chromatographic determination of ten organochlorine pesticides (α-HCH, β-HCH, γ-HCH, p,p’-DDT, o,p’-DDT, p,p’-DDD, p,p’-DDE, aldrin, endrin, and dieldrin) and six congeners of PCBs (PCB 28, 52, 118, 138, 153, and 180) in municipal solid waste compost is described. The procedure involves a solid-phase dispersion matrix using celite as dispersant sorbent, alumina as clean up sorbent and hexane-dichloromethane (7:3, v/v) mixture as eluting solvent. An additional purification step with copper was necessary to eliminate sulphur. Analysis of the sample was performed by GC-ECD. The method was validated with fortified samples at two concentration levels (0.025 and 0.05 mg kg^?1). Average recovery ranged from 77 to 121% with relative standard deviation between 1 and 18%. The detection limits, which ranged from 0.003 to 0.01 mg kg^?1, were lower than those established by the Baden–Württemberg directive (0.033 mg kg^?1).