A simple and very sensitive spectrophotometric method for the direct determination of copper ions

A sensitive spectrophotometric method for the direct determination of copper in aqueous samples without a preconcentration step has been developed. It is based on the formation of a yellow complex with the chromogenic reagent di-2-pyridyl ketone benzoylhydrazone (dPKBH) in an alkaline medium. The complex stoichiometry was 1:2 (Cu:dPKBH) and presents maximum absorbance at 370 nm. The influence of chemical variables affecting the behaviour of the system such as pH, concentration of dPKBH, buffer solution and ethanol, order of addition of the reagents and stability of the complex, were evaluated. The molar absorptivity (epsilon) was 3.92x10(4) L mol(-1) cm(-1), and Beer's law was obeyed up to 3 mg L(-1) of copper. The relative standard deviation was 0.46% (n=11) for a sample containing 1 mg L(-1) Cu(II). The limit of detection was 2.5 micro g L(-1) and was therefore more sensitive than the direct methods reported previously. Finally, the method was successfully validated by analysing several real samples with different matrices, such as tap water, natural water or copper alloys, with an average relative error of 2.46%.     

Biomimetic alcohol oxidations by an iron(III) porphyrin complex: relevance to cytochrome P-450 catalytic oxidation and involvement of the two-state radical rebound mechanism

The systematic oxidation reactions of a wide range of alcohols have been carried out by using an iron porphyrin complex in order to understand their relation to cytochrome P-450 enzymes and to have a practical application to organic synthesis. The iron porphyrin complex catalyzed efficiently alcohol oxidation to the respective carbonyl compound via a high-valent iron-oxo porphyrin intermediate ((Porp)Fe=O+). Several mechanistic studies such as isotope 18O labeling, deuterium isotope effect, linear free energy relationship, and ring-opening of radical clock substrate, have suggested that the alcohol is oxidized by a sequence of reactions involving an alpha-hydroxyalkyl radical intermediate and oxygen rebound to form the gem-diol, dehydration of which yields the carbonyl compounds. Moreover, it has been proposed that a two-state reactivity mechanism can also be adopted for alcohol oxidation reactions in iron porphyrin model systems as exhibited by P-450 enzymes.     

Redetermination of (6R,7S,9S,11S)‐(–)‐sparteinium monoperchlorate

The structure of the title compound, C₁₅H₂₇N₂⁺·ClO₄^?, consists of a monoprotonated sparteinium cation and a perchlorate anion. The two tertiary N atoms of the cation, one perchlorate O atom and a H atom form a bifurcated hydrogen bond, the four hydrogen‐bonding atoms being nearly in the same plane.     

Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.     

An improved scheme for the identification of antigens recognized by specific antibodies in two-dimensional gel electrophoresis and immunoblotting

This paper describes an improved scheme for the identification of antigens in crude extracts recognized by specific antibodies when analyzed by a combination of two-dimensional gel electrophoresis and immunoblotting. First, protein components in gels are electrophoretically transferred to a polyvinylidene difluoride membrane which does not shrink or change dimensions in organic solvents. The efficiency of transfer and the localization of sample proteins on the membrane are checked and recorded by staining the blotting membrane with Fast Green FCF and recording the profile on a transparency. After blocking and the immunoassay, the results are recorded by photography. The sites of immune reaction are marked and the same membrane is restained briefly with Coomassie Brilliant Blue R-250 for the protein profile. Thus antigens in complex mixtures, recognized by antibodies of interest, can easily be identified from the restained membrane. If the whole protein profile is not well demonstrated, when used in combination with the profile recorded on the transparency, spots appearing on the restained membrane can still be used as useful landmarks in the final unequivocal antigenic identification. This improved scheme circumvents problems arising from membrane shrinkage and difficulties in accurately matching immunoreactive spots by conventional procedures and thus provides an accurate, simple and fast approach in the identification of antigens after immunoblotting.     

拟静态循环法测定稀溶液气液平衡的研究

根据沸点计误差公式,ε≡x_0-x/x=K-1/1+r(r+a)(1)研究设计了能够在r=0的拟静态循环态操作三种新型沸点仪。在稀浓度区,从不同角度进行检证,以期使方法和仪器得以完善。拟静态循环法的原理静态法和双循环法在浓度分布上的差别在于,后者有汽相回流(r>0)从而产生三个浓度区间,使配制浓度x_0代替平衡浓度x有(1)式所示的误差。仅当循环控制在r=0的状态,与静态法等价,称之为拟静态循环态,此时的误差为     

Adsorption enthalpy and desorption enthalpy during displacement of adsorbate to solvent in a liquid-solid system

The adsorption heat of the stoichiometric displacement process for the adsorption of a solute in a liquid-solid system was investigated. On the basis of the SDM-A and the rule of the additivity of energy, an expression which describes the dependence of the adsorption enthalpy on the nature and concentration of the solute, and on the solvent and adsorbent, was derived. The adsorption heat determined for the solute with the traditional method can be divided into two independent fractions, relating to the adsorption of the solute and to the desorption of the solvent. Experimental data on both isotherms from the literatures and precise calorimetry were used to test the adsorption heat and its fractions computed quantitatively via the equations presented in this study, and a satisfactory degree of conformity between them was obtained. Supported by the Natural Science Foundation of Shaanxi Province in China.     

Ligand influence on the electrochemical behavior of some copper(II) thiosemicarbazone complexes

The redox properties of the title mono- and binuclear copper(II) chelates have been investigated by cyclic voltammetry in DMF at a working platinum electrode. The cathodic reduction and anodic oxidation of the investigated chelates produced the corresponding electrochemical Cu^I and Cu^IIIspecies stable only in the voltammetric time scale, The effects of substituents on E_1/2, redox properties and stability towards oxidation of the complexes were related to the electron-withdrawing or releasing ability of the substituents on the C=N¹[H, CH₃ or C₆H₅] and/or N⁴H [H, C₂H₅, C₆H₅ or pClC₆H₄] groups, The electron attracting substituents stabilize the Cu(II) complexes while electron-donating groups favor oxidation to Cu(III). Changes in the E_1/2 for the complexes due to remote substituent effects could be related to changes in basicity of N⁴H.Thus, variation in N⁴1-J has more influence on E_1/2 than changes in C=N¹. The correlation between E_1/2 of the complexes and pK_a of the ligands has been attributed to the spherical potential generated by the electron density of the donor atoms at the antibonding d orbitals.     

Accurate ionization potentials for UO and UO2: a rigorous test of relativistic quantum chemistry calculations

Accurate ionization potential (IP) measurements provide essential thermodynamic information and benchmark data that can be used to evaluate the validity of electronic structure models. Calculations of the first IP of UO2 using relativistic methods consistently predict values that are approximately 0.7 eV higher than the accepted experimental value. The present measurements validate the theoretical calculations and show that the previous determinations corresponded to the ionization of thermally excited molecules. Similarly, new measurements of the IP for UO show that the currently accepted value is too low by 0.4 eV.     

Photolysis of NSAIDs. I. photodegradation products of carprofen determined by LC-ESI-MS

A solution of carprofen in methanol at a concentration of 2.74 x 10(-2) mg/mL is subjected to photoirradiation using a Hanovia 200-W high-pressure Hg lamp for 9 h. In total, seven photodegradation products are separated, and their quasimolecular ions are subsequently determined online using a liquid chromatography (LC)-electrospray ionization (ESI)-mass spectrometry (MS) method. The high-performance LC consists of an Inertsil 5 ODS-80A (2.1- x 150-mm) column. The mobile phase is initially CH(3)CN. NH(4)OAc (20mM in de-ionized H(2)O) is 43:57 (v/v), and after 14 min it is CH(3)CN. NH(4)OAc (20mM in de-ionized H2O) is 54: 46 (v/v). The UV detector was set at 260 nm. The parameters of LC-MS for mass determination involves an atmospheric pressure ionization electron spray interface with a negative mode of polarity (ESI(-)). The chemical structures of the degradants are elucidated based on the mass-to-charge ratio of the quasimolecular ions and the molecular weight changes by comparison with the parent drug (carprofen). The degradation proceeds via an initial dechlorination. A dechlorination or esterification reaction is competed with decarboxylation. This finding is in accordance with our previously reported result of first order photodecomposition kinetics for carprofen.