Atomic radical—molecule reactions F + CH<Subscript>3</Subscript>C≡CH: mechanistic study

The reaction of atomic radical F with propyne has been studied theoretically using ab initio quantum chemistry methods and transition state theory. The potential energy surface was calculated at the CCSD(T)/aug-cc-pVDZ (single-point) level using the UMP2/6-311++G(d,p) optimized structures. Two reaction mechanisms including the addition–isomerization–elimination reaction mechanism and the directed hydrogen abstraction reaction mechanism are considered. For the hydrogen abstraction reactions, i.e., the most probable evolution pathway in the title reaction, the HF formation occurs via direct abstraction mechanism dominantly and the H atom picked up by the atomic radical F should come mostly from the methyl group of normal propyne. On the other hand, for the addition–isomerization–elimination mechanism, the most feasible pathway should be the atomic radical F attacking on the C≡C triple bond in propyne (CH₃C≡CH) to form a weakly-bound adduct A1 with no barrier, followed by F addition to the C≡C triple bond to form the low-lying intermediate isomer 5. Subsequently, isomer 5 directly dissociates to P3 H₂CCCHF + H via transition state TS₅/P3. The other reaction pathways on the doublet PES are less competitive due to thermodynamical or kinetic factors. Furthermore, based on the analysis of the kinetics of all channels through which the addition and abstraction reaction proceed, we expect that the competitive power of reaction channels may vary with experimental conditions for the title reaction. The present work will provide useful information for understanding the processes of atomic radical F reaction with other unsaturated hydrocarbons. This material is available from author via E-mail.     

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.     

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.     

Resonant Raman spectra and first molecular hyperpolarizabilities of strongly charge-transfer molecules

The effect of vibrational structure on the frequency dependence of the first molecular hyperpolarizability of two thiophene-based charge-transfer chromophores is investigated. A time domain formulation is used to express the polarizability. The new expression includes the solvent-induced inhomogeneous distribution of electronic transition frequencies as well as the effect of the motion of solvent molecules that modulates the vibrational and electronic transition frequencies of the nonlinear optical molecule on which the first molecular hyperpolarizability depends. Resonance Raman scattering and one-photon absorption spectra of the chromophores are measured. By simultaneously fitting the experimental one-photon absorption spectrum and Raman cross sections of vibrational lines derived from resonance Raman scattering to a theoretical model, important parameters needed for the calculation of the first molecular hyperpolarizability are obtained. The first molecular hyperpolarizability is calculated as a function of frequency covering both nonresonance and two-photon resonance regions. The calculated result is compared with the measured hyperpolarizability as a function of frequency of the excitation laser. The resonance Raman-based analysis is shown to account reasonably well for the dispersion of the hyperpolarizability of the two charge transfer chromophores.     

MECHANISM OF OXYGEN DETOXIFICATION IN NEONATAL RAT LUNG TISSUE

Abstract— Pulmonary macrophages obtained from neonatal rats contain approximately four times the activity of cyanide resistant superoxide dismutase and catalase compared with the cells from adult animals. The activity is highest immediately after birth and diminishes with age until the minimum level is reached at approximately 3 weeks of age. Superimposed upon this change in basal activity is the capability of neonatal cells to synthesize additional cyanide resistant superoxide dismutase and catalase when either the animals or isolated pulmonary macrophages are exposed to 95–100% oxygen. The inductive effect begins at 2–3 days after birth, peaks at 10 days, and disappears at approximately 15 days after birth. In contrast to adult rats, neonatal rats are extremely resistant to the toxic effects of oxygen. If, however, the oxygen mediated increase in both enzymes is prevented or the maximum effective pulmonary macrophage number is diminished in test animals, these animals become vulnerable to toxic effects of oxygen exposure, observed by gross and histologic examination of lung tissue, in a manner similar to adult animals. These data indicate that both cyanide-resistant superoxide dismutase and catalase may be part of the endogenous defense mechanisms which provide neonatal rats with an exceptional resistance to oxygen toxicity.     

Molecules organiques coordinees a un metal. : Nouveaux complexes olefiniques d'α-enones par le fer(0)

Heterodienetricarbonyliron complexes react with ligands ( L = PMe₂Ph, P(OMe)₃ or P(OPh)₃) to give the adducts (enone)Fe(CO)₃L with the ethylenic double bond coordinated only to the iron(0). Electron-releasing and low-steric effects of L make the reaction which is specific for enones easier compared to that for dienes. PMe₂Ph allows enone exchange and P(OPh)₃ promotes carbonyl elimination. Ligand influence is shown by infrared spectroscopy and by the shielding of ethylenic protons in NMR spectroscopy.     

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.