Determination of acetaminophen by square wave voltammetry at a gold electrode modified by 4-amino-2-mercaptopyrimidine self-assembled monolayers

A 4-Amino-2-mercaptopyrimidine self-assembled monolayer (AMP SAMs/Au) modified gold electrode was prepared. The electrochemical behavior of acetaminophen on the AMP SAMs/Au was studied in Britton-Robinson (BR) buffer solution. Compared to a bare gold electrode, the modified electrode exhibits a significant enhancement in the oxidation current response for acetaminophen. The modified electrode was used for the determination of acetaminophen by square wave voltammetry. The oxidation current increased linearly with the concentration of acetaminophen in the range of 2.0 × 10⁻⁶−4.0 × 10⁻³ M. The modified electrode made it possible to eliminate the interference of dopamine (DA), brucine, epinephrine (EP), and norepinephrine (NE). The practical analytical utility was illustrated by the determination of acetaminophen in a commercially available drug. The text was submitted by the authors in English.     

Visualisation of interlaboratory comparison results in PomPlots

In this work a novel graphical method is applied to the presentation of intercomparison results. This is demonstrated with the results of a recent intercomparison in measuring the ¹³⁷Cs, ⁴⁰K, and ⁹⁰Sr activity concentration in milk powder. The “PomPlot”, an intuitive graphical method, is used for producing a summary overview of the participants’ results of a common measurand. The “PomPlot” displays (relative) deviations of individual results from the reference value on the horizontal axis and (relative) uncertainties on the vertical axis.     

Host–Guest Complexation of <Emphasis Type="Italic">β</Emphasis>-, <Emphasis Type="Italic">γ</Emphasis>-Cyclodextrin with Alkyl Trimethyl Ammonium Bromides in Aqueous Solution

As a continuation of our previous investigation, interactions between cyclodextrin (β-CD), γ-cyclodextrin (γ-CD) and alkyl trimethylammonium bromides in aqueous solutions have been studied with titration calorimetry and ¹H NMR at 298.15 K. The results are discussed in terms of the amphiphilic interaction of CD with surfactants and the iceberg structure formed by water molecules existing around the hydrophobic tail of surfactant molecules. The stoichiometry of the β-CD–surfactant system is 1:1 whereas that of the γ-CD–surfactant system is 1:2. The corresponding formation enthalpy (negative) of the complexes of the two systems decreases with an increase in the number of carbon atoms (n) in hydrophobic chain of surfactant molecule, C _n H_2n+1, whereas the entropy increases with the enlargement of n.     

Polymorphism of paracetamol

The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG _sub²⁹⁸=60.0 kJ mol⁻¹; ΔH _sub²⁹⁸=117.9±0.7 kJ mol⁻¹; ΔS _sub²⁹⁸=190±2 J mol⁻¹ K⁻¹. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition enthalpy at 298 K, ΔH _tr²⁹⁸(I→II)=2.0±0.4 kJ mol⁻¹, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based on ΔH _tr²⁹⁸ (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification II were also estimated (ΔG _sub²⁹⁸=56.1 kJ mol⁻¹; ΔH _sub²⁹⁸=115.9±0.9 kJ mol⁻¹; ΔS _sub²⁹⁸=200±3 J mol⁻¹ K⁻¹). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported found by classical thermochemical methods.     

PROBING PHOTODYNAMIC DAMAGE IN NUCLEIC ACIDS WITH A DAMAGE-SPECIFIC DNA BINDING PROTEIN: A COMPARISON OF THE B and Z DNA CONFORMATIONS

—We have employed a damage-specific DNA binding protein from human cells as a probe for base damage in polymers irradiated with white light in the presence of methylene blue. Protein-recognizable damage is introduced only into guanine-containing polymers and quenching of damage introduction by H₂O and sodium azide suggest the involvement of a singlet oxygen mechanism. Using poly d(G-m⁵C), we have demonstrated that the left-handed double helical Z conformation is much less susceptible to guanine photooxidation than is the usual B conformation. We speculate that this difference in reactivity may reflect steric hindrance at the purine C-4 position and could provide some insight into the initial steps of the reaction between singlet oxygen and guanine in nucleic acid polymers.     

Reversed-phase liquid chromatography and argentation chromatography of the minor capsaicinoids

An investigation of the liquid chromatography of the minor capsaicinoids in a commercial capsaicinoid mixture is reported. Twelve stationary phases including C₈, C₁₈, C₃₀, phenyl, and cation-exchange chemistries were examined in combination with isocratic aqueous methanol and aqueous acetonitrile mobile phases. A phenyl stationary phase and aqueous acetonitrile mobile phase baseline-resolved 7 of 11 capsaicinoids, and selected ion chromatograms (LC–ESI-MS) demonstrated this was the most effective reversed-phase separation. Argentation chromatography with an alkyl or phenyl column and aqueous silver nitrate–methanol mobile phase revealed the presence of the 6-ene-8-methyl and 6-ene-9-methyl homocapsaicin isomers and the absence of 7-ene-9-methyl homocapsaicin. A mixed phenyl–cation-exchange stationary phase (charged with silver ion) enabled unique and useful separations of the capsaicinoids.     

Transition-Metal Complexes with Nano-Sized Phosphine and Pyridine Ligands-Catalysis,Fluxional Behavior and Molecular Recognition

Nano-sized phosphine and pyridine ligands having tetraphenylphenyl-, m-terphenyl-, poly(benzylether) moieties were synthesized. These ligands showed a remarkable effect on homogeneous transition metal catalyzed reactions. Pd(II) complexes with tetraphenylphenyl substituted pyridine ligands show high catalytic activities for oxidation of ketones suppressing Pd black formation and maintains the catalytic activity for a long time. Rh(I) complex catalysts with m-terphenyl substituted phosphine ligands showed remarkable rate acceleration in the hydrosilylation of ketones. In addition, several phosphinocalixarene ligands were synthesized and their coordination studies with Pd(II), Pt(II), Ru(II), Ir(I), and Rh(I) metals were documented. Ir(I) and Rh(I) cationic complexes with a 1,3,5-triphosphinocalix[6]arene ligand showed dynamic behavior with size-selective molecular recognition.     

Oxidation of α-methylstyrene on an MCM-22 encapsulated (<Emphasis Type="Italic">R,R</Emphasis>)-(−)-<Emphasis Type="Italic">N,N′</Emphasis>-bis(3,5-di-<Emphasis Type="Italic">tert</Emphasis>-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) catalyst

(R, R)-(−)-N, N′-bis(3,5-di-tert-butylsalicylidene)-1,2-cyclohexanediaminocobalt(II) was encapsulated into MCM-22 using the zeolite synthesis method. The encapsulated catalyst proved to be active in the oxidation of α-methylstyrene with NaOCl with higher specific activity than the homogeneous catalyst. At the same time, this encapsulated catalyst was completely inactive in the hydrolytic kinetic resolution of racemic styrene oxide. This observation is in a good correlation with the assumption of the cooperative bimetallic mechanism proposed by Annis and Jacobsen.     

Thermogravimetry as a screening tool for the estimation of the vapor pressures of pure compounds

A simplified approach was developed to estimate the vapor pressure of pure compounds from experimental data obtained by isothermal thermogravimetric (TG) analysis. A numerical procedure was developed to estimate the Antoine parameters of the substance by the analysis of isothermal TG data. The results of the experimental validations carried out evidenced that at least a preliminary estimation of vapour pressures of pure substances by the analysis of TG data is possible. The limited time and the reduced amounts of sample required for the experimental runs make the technique attractive with respect to the conventional and more accurate techniques for vapor pressure assessment.     

Hydroformylation of Olefins Catalyzed by Rhodium Trichloride Anchored on Ti-HMS

Rhodium trichloride supported on Ti-hexagonal mesoporous silica (Ti-HMS), via a bipyridyl group, is an efficient catalyst for the hydroformylation of olefins at 120 °C and 40.8 atm of CO/H₂ (CO/H₂=2/1). The catalyst is selective leading to high ratios of linear or branched aldehydes from functionalized olefins, and high activity in the case of propene which gave a turnover frequency of 6209 mol/mol(Rh)/h.