What is the enthalpy of formation of acrylonitrile?

Acrylonitrile is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious. There is a 12 kJ mol⁻¹ range of values reported for the gas phase quantity: 173–185 kJ mol⁻¹. Quantum chemical calculations, using current methodologies and defining reactions, suggest values between 185 and 191 kJ mol⁻¹: the recommended value, an average, is 188 ± 7 kJ mol⁻¹.     

Single step preparation and conformational analysis of novel thiophosphorylated ligands based on calix[4]resorcinol matrix

We have synthesized novel calix[4]resorcinols with four 2-thioxo-1,3,2-dioxaphospholane groups introduced in aromatic substituents in the methylidene bridges of macromolecules by the condensation of new thiophosphorylated benzaldehyde with resorcinol and its derivatives in acidic media with high yields. The formation of only one rctt isomer with corresponding chair conformation is observed, which was determined by 2D NMR-experiments.     

Development and validation according to European Union Decision 2002/657/EC of an HPLC‐DAD method for milk multi‐residue analysis of penicillins and amphenicols based on dispersive extraction by QuEChERS in MSPD format

A precise and reliable method for milk residue analysis regarding five penicillins and three amphenicols by HPLC‐diode array detection has been developed herein. The chromatographic separation was performed using a mobile phase of CH₃COONH₄ (0.05 M) and ACN delivered by gradient program on a Kinetex^?‐C₁₈ core‐shell, 2.6 μm column, starting at a volume ratio of 95:5 and ending at 60:40 after 17 min, remaining stable for 3 more min. A modified matrix solid phase dispersion procedure was applied for the extraction and clean‐up procedure of antibiotics using a mixture of Strata by Phenomenex and QuEChERS as a sorbent. The method was validated at the respective 0.5× MRL, MRL and 1.5 ×MRL level for each compound. Results were quantitated against the internal standard paracetamol (2 ng/μL) according to the matrix‐matched approach. The method was validated in line with the EC guidelines as cited in the Decision 2002/657/EC. The within‐laboratory reproducibility, expressed as a RSD, never exceeded 16%. All decision limit (CCα) values lay in the range between 35.2 and 56.3 μg/kg and the corresponding results for detection capability (CCβ) were 39.9 and 61.9 μg/kg. Ruggedness was estimated according to the Youden approach.     

Photophysics and Photochemical Studies of the Vitamin B6 Group and Related Derivatives

The photophysics and photochemical properties of vitamin B6 constituents and analogs were studied as function of pH and solvent. The p K of the phenolic oxygen and the pyridine ring nitrogen depends on the electron donor-acceptor ability of the 4-substituent, and agrees with the calculated proton affinity. For all studied compounds, the fluorescence properties showed that the phenolic oxygen is 8 units more acidic in the lowest singlet excited state than in the ground state. The pyridine N-atom is slightly more basic in the excited state. At pH of biological significance, pH 6–8, pyridoxamine and 4-pyridoxic acid are the more efficient chromophores with higher fluorescence yield and longer lifetime. Spectroscopic studies showed that the tautomeric equilibrium depends on the nature of the 4-substituent. The quenching of the singlet excited state of pyridoxamine and 4-pyridoxic acid by amino acids, free or in a peptide, and DNA bases at pH 7 was studied by time-resolved fluorescence techniques. The quenching rate constants are well correlated with the redox properties of the pyridoxinic compound and amino acids, and are related to the free energy change in the electron transfer process. Guanosine and pyrimidine bases also are efficient quenchers, involving an electron transfer reaction.     

Complexation of trivalent lanthanoid ions with 4-benzoyl-3-phenyl-5-isoxazolone and p-tert-butylcalix[4]arene fitted with phosphinoyl pendant arms in solution during synergistic solvent extraction and structural study of solid complexes by IR and NMR

The liquid extraction of 14 lanthanoids with a 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) alone in CHCl₃ as a diluent from perchlorate medium at constant ionic strength μ = 0.1 is investigated. The synergistic solvent extraction of five selected lanthanoid ions (La³⁺, Nd³⁺, Eu³⁺, Ho³⁺ and Lu³⁺) with 4-benzoyl-3-phenyl-5-isoxazolone (HPBI) and 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis-(dimethylphosphinoylmethoxy)calix[4]arene, (S) in CHCl₃ has been studied too. The stoichiometry of the extracted species was characterised by a classical log–log plot analysis. It was found that the composition of the extracted species with HPBI are Ln(PBI)₃ and in the presence of the phosphorus-containing calix[4]arene the lanthanoid ions have been extracted as [Ln(PBI)₃S₂]. The values of the equilibrium constants and the separation factors have been calculated. The influence of the synergistic agent on the extraction process has been discussed.     

Interaction of polyhedral boron hydride anions [B10H10] and [B12H12] with cyclic copper and silver 3,5-bis(trifluoromethyl)pyrazolate complexes

The interactions of cyclic trinuclear copper {[3,5-(CF₃)₂Pz]Cu}₃ and silver {[3,5-(CF₃)₂Pz]Ag}₃ complexes with polyhedral borate anions [B₁₀H₁₀]²⁻ and [B₁₂H₁₂]²⁻ in solvents of low-polarity were studied using IR spectroscopy (190-290 K). Two types of complexes were found in solution: {[((3,5-CF₃)₂PzM)₃][B_nH_n]}²⁻ and {[((3,5-CF₃)₂PzM)₃]₂[B_nH_n]}²⁻ (M = Ag, Cu; n = 10, 12). The stability constants of these complexes were determined from IR-spectra.