Effect of Solvents on the Spectra of Some β-Diketones

Acetoacetanilide, benzoylacetanilide and their derivatives have been examined in ultraviolet region in a series of solvents covering a broad polarity range e. e. from chloroform (Z, 63.2) to methanol (Z .83.6). Transition energies and oscillator strengths have been calculated and transition energy (E_T) has been plotted against Z-values, a new empirical measurement of solvent polarity. A linear relationship was observed between the transition energy and Z-values for π → π* and n → π* transitions. These transitions are identified as charge transfer (c-t) transitions and with the solvents having carbonyl oxygen and sulphur atom a c-t complex formation has been suggested. Strong electron-donating substituents on phenyl group of the nitrogen atom also showed a weak to moderate n → π* transitions. These substituents have no influence on the position of the λ_max in the same solvent. Stabilization energy of the excited state of these ligands and hence the dipole moments of the excited states have been calculated in comparison with pyridinium iodide. Solvent sensitivities of these ligands have also been calculated.     

Synthesis,characterisation, mesomorphic investigation and temperature-dependent Raman study of a novel calamitic liquid crystal: methyl 4-(4′-n-alkoxybenzylideneamino)benzoate

A new series of Schiff base calamitic liquid crystal; methyl 4-(4′-n-alkoxybenzylideneamino)benzoate (MABAB), H_2n+1C _n OC₆H₄C(H)=NC₆H₄COOCH₃ (n = 6, 8, 10, 12, 14, 16) has been synthesised and characterised by elemental analyses, Fourier transform infrared spectroscopy (FT-IR), ¹H and ¹³C Nuclear Magnetic Resonance (NMR) spectroscopy. The mesomorphic properties of these compounds were studied by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All members of the series exhibit enantiotropic smectic A (SmA) mesophase. Temperature-dependent micro-Raman study of one of the members, MABAB-10 has been employed to identify phase transitions and the molecular rearrangement therein. Analysis of Raman marker bands; C–H in-plane bending, C–C stretching of phenyl rings and –C(H)=N– linking group of core confirms the transitions clearly as observed through DSC and POM. An in situ Raman measurement of C–H in-plane bending mode has also been performed to visualise the molecular changes more clearly. The Raman study gives an evidence of induced co-planarity of rings at Cr→SmA phase transition. The density functional theoretical (DFT) optimisation of monomer, dimer and rotational conformer of MABAB-10 also support the induced co-planarity at Cr→SmA phase transition.     

Zur Deutung des UV.-Spektrums von Pyridin-N-oxid

From measurements of the influence of an electric field on the absorption spectrum of pyridine-N-oxide it is concluded that the 330 nm band is polarized perpendicular to the dipole moment, while the 280 nm transition moment lies parallel. Furthermore from these experiments the dipole moments in both excited states have been determined (Table 1). PARISER -PARR -POPLE -calculations as well as CNDO-calculations admit an assignment of the 330 nm band to an A₁ → B₁, π → π* transition and of the 280 nm band to an A₁ → A₁, π → π* transition. Thereby energy, polarization, intensity of the transition, and the dipole moments of the excited states have been taken into consideration. This assignment does not exclude the possibility of a weak n-π* transition at approximately the same wavelength as the A₁ → B₁ transition.     

Some continuous geometry transitions and the consequences for a transition‐metal atom

By considering a transition‐metal ion in the field of some symmetrically placed ions, we illustrate the consequences of a continuous change of the structure of the ligands on the energies of the 3d electrons of the transition‐metal atom. Both a rigorous mathematical derivation and an analysis based on group theory are presented. For six ions surrounding the transition‐metal atom, a continuous D_∞h → D_3d → O_h→ D_3d→ D_6d transition is observed, whereas for four ions, a continuous D_{∞ h}→ D_2d→ T_d→ D_2d→ D_4d transition results. Although the two systems possess many similarities, interesting differences are found as well. Finally, we demonstrate that when including orbital interactions between the ligands and the transition‐metal atom, quantitative differences occur. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

The kernel of DWBA transition amplitude in atom–diatom reactive scattering

The kernel of the distorted-wave Born approximation (DWBA ) transition amplitude will be explored with attention to the atom–diatomic molecule reactive scattering process of A + BC → AB + C. Our study of the kernel reveals valuable intrinsic properties regarding the state-to-state reactive scattering process. In particular, such a study will help us to better understand (i) the favored geometric configuration during collision, (ii) the spatial domain of contribution to the differential and total cross sections, and (iii) the structural dependence of the kernel distribution on the mass ratio of the reactant molecule BC and the departing atom C, particularly in the case of colinear rearrangement collisions. In this study we choose the FH₂ system as an illustration.     

Reaction of excited iodine atoms with methyl iodide: Rate constant determinations

The rate constant for the reaction I(²P_1/2) + CH₃I → I₂ + CH₃ has been reevaluated taking into account both collisional deactivation of excited iodine atoms and loss of I₂ by I₂ + CH₃ → I + CH₃I. The reevaluation is based upon data obtained (R. T. Meyer), J. Chem. Phys., 46 , 4146 (1967) from the flash photolysis of CH₃I using time-resolved mass spectrometry to measure the rate of I₂ formation. Computer simulations of the complete kinetic system and a closed-form solution of a simplified set of the differential equations yielded a value of 6(± 4) × 10⁶ 1./mole-sec for the excited iodine atom reaction in the temperature region of 316 to 447 K. A slight temperature dependence was observed, but an activation energy could not be evaluated quantitatively due to the small temperature range studied. An upper limit for the collisional deactivation of I(²P_1/2) with CH₃I was also determined (2.4 × 10⁷ 1./mole-sec).     

Electro-optical properties of a new series of fluorinated antiferroelectric orthoconic liquid crystalline esters

The electro-optical properties of orthoconic antiferroelectric liquid crystals of some analogues of (S)?MHPOBC ((S)?4?(1?methylheptyloxy)carbonylphenyl 4'-octyloxy-4-biphenylcarboxylate) have been investigated and discussed in terms of the structure property correlations of liquid crystalline molecules. Polarisation field reversal technique has been used for their characterisation. In this study the occurrence of such a high value of spontaneous polarisation (P_s) for the investigated compound is especially noteworthy as they comprise a bulky chiral unit, zigzag ester linkage and polar fluorinated terminal. Lengthening of oligomethylene spacer in the terminal chain and placement of fluorine atom in the molecular core structure leads to reduction in the value of P_s. The P_s data suggest that the nature of the chiral smectic C (SmC*) to smectic A (SmA) phase transition is of second order and the critical exponent β is in the range 0.19–0.34. The ‘V-shaped’ mode or thresholdless switching in such high-polarisation ferroelectric liquid crystals has also been discussed.     

The simultaneous UPLC–MS/MS determination of emerging drug combination; candesartan and chlorthalidone in human plasma and its application

A novel, precise, sensitive and accurate ultra‐performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) method has been developed for the simultaneous determination of a novel drug combination, candesartan (CAN) and chlorthalidone (CHL), in human plasma. Chromatographic separation was achieved on Waters Acquity UPLC BEH C₁₈ (50 × 2.1 mm, 1.7 μm). Mobile phase consisting of 1 mm ammonium acetate in water–acetonitrile (20:80 v /v) was used. The total chromatographic runtime was 1.9 min with retention times for CAN and CHL at 0.7 and 1.1 min respectively. Ionization and detection of analytes and internal standards was performed on a triple quadrupole mass spectrometer, operating in the multiple reaction monitoring and negative ionization mode. Quantitation was done to monitor protonated precursor → product ion transition of m /z 439.2 → 309.0 for CAN, 337.0 → 189.8 for CHL and 443.2 → 312.1 for candesartan D4 and 341.0 → 189.8 for chlorthalidone D4. The method was validated over a wide dynamic concentration range of 2.0–540.0 ng/mL for candesartan and 1.0–180.0 ng/mL for chlorthalidone. The validated method was successfully applied for the assay of CAN and CHL in healthy volunteers.     

Carbene‐Stabilized Phosphenium Oxides and Sulfides

Carbene→chalcogenophosphenium adducts, which correspond to an intermolecular stabilization mode of the so far elusive, free oxo‐ and thiooxophosphenium species [R₂P⁺ = X] (X=O, S) by imidazolylidene (NHC) and diaminocyclopropenylidene (BAC) donors, have been isolated and fully characterized. The dative character of the R₂C:→P⁺(X)Ph₂ bond was confirmed experimentally by nucleophilic displacement of the carbene donor with a chloride ion and by an exchange reaction of the NHC ligand of the NHC:→P⁺(O)Ph₂ adduct with an independently prepared BAC ligand, thereby giving the BAC:→P⁺(O)Ph₂ adduct. This dative character was further characterized by the DFT‐calculated preference of carbene→chalcogenophosphenium systems for a heterolytic dissociation mode over a homolytic one.     

Diminished electron density in the Vaska‐type rhodium(I) complex trans‐[Rh(NCBH3)(CO)(PPh3)2]

Vaska‐type complexes, i.e. trans‐[RhX(CO)(PPh₃)₂] (X is a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the Rh^I atom in these complexes plays an important role in their reactivity. Many cyanotrihydridoborate (BH₃CN⁻) complexes of Group 6–8 transition metals have been synthesized and structurally characterized, an exception being the rhodium(I) complex. Carbonyl(cyanotrihydridoborato‐κN)bis(triphenylphosphine‐κP)rhodium(I), [Rh(NCBH₃)(CO)(C₁₈H₁₅P)₂], was prepared by the metathesis reaction of sodium cyanotrihydridoborate with trans‐[RhCl(CO)(PPh₃)₂], and was characterized by single‐crystal X‐ray diffraction analysis and IR, ¹H, ¹³C and ¹¹B NMR spectroscopy. The X‐ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the Rh^I atom through the N atom in a trans position with respect to the carbonyl ligand; this was also confirmed by the IR and NMR data. The carbonyl stretching frequency ν(CO) and the carbonyl carbon ¹J_C–Rh and ¹J_C–P coupling constants of the C_ipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central Rh^I atom compared to the parent trans‐[RhCl(CO)(PPh₃)₂] complex.     

Collaborative control of branching ratio in the O + HO2 → OH + O2 reaction via vibrational and rotational excitation

To understand the effect of different vibrational and rotational modes of reactant to enhance the reactivity of the O + HO₂ → OH + O₂ reaction, we revisited this important atmospheric reaction. We report here a quasi-classical trajectory (QCT) study of the reaction dynamics on a recently developed full-dimensional potential energy surface (PES). Our previous work has indicated that this reaction has two pathways, the H abstraction (HA) channel and the O abstraction (OA) channel, which lead to totally different product energy distribution. In this work, we identified that the vibrational excitation of the OH stretching (v₁) mode of HO₂ is the switch of the HA channel at low collision energy; meanwhile, the rotational excitation can also greatly change the branching ratio of the two pathways. With the excitation of v₁ mode, the original negligible HA channel controlled by the tight transition state becomes quite important. This work presents an approach to control the branching ratio via collaboration between vibrational and rotational excitation and will enrich the knowledge of the O + HO₂ reaction in atmospheric chemistry and physics.     

Force constants and bond polarizabilities of thiocyanate ion adsorbed on the silver electrode as interpreted from the surface enhanced Raman scattering

The surface enhanced Raman spectra of the thiocyanate ion is studied in two ways. First, normal mode analysis is employed to determine the force constants of the adsorbed thiocyanate ion. The result shows that the force constant for the CN bond becomes larger while that for the SC bond smaller in the adsorbed state. The adatom model with an effective silver mass of 0.1 m_Ag (m_Ag being the mass of the silver atom) is adequate for the analysis. This implies that the silver adatom is bound to the bulk electrode surface. The adsorption is also shown to be physical. Second, the SER intensifies are analyzed to obtain the molecular polarizability derivatives. The result shows that the polarizability derivative of the CN stretching motion is most responsive to the applied voltage. The polarizability derivative of the SC stretching motion is much smaller than that of the CN bond as compared in the solution. This conclusion is attributed to the adsorption center at the sulfur atom. In general, molecular polarizability derivatives are functions of the frequencies of the exciting lasers and the applied voltages on the electrode.     

Release of Formic Acid from Copper Formate: Hydride,Proton-Coupled Electron and Hydrogen Atom Transfer All Play their Role

Although the mechanism for the transformation of carbon dioxide to formate with copper hydride is well understood, it is not clear how formic acid is ultimately released. Herein, we show how formic acid is formed in the decomposition of the copper formate clusters Cu(II)(HCOO)₃⁻ and Cu(II)₂(HCOO)₅⁻. Infrared irradiation resonant with the antisymmetric C−O stretching mode activates the cluster, resulting in the release of formic acid and carbon dioxide. For the binary cluster, electronic structure calculations indicate that CO₂ is eliminated first, through hydride transfer from formate to copper. Formic acid is released via proton-coupled electron transfer (PCET) to a second formate ligand, evidenced by close to zero partial charge and spin density at the hydrogen atom in the transition state. Concomitantly, the two copper centers are reduced from Cu(II) to Cu(I). Depending on the detailed situation, either PCET or hydrogen atom transfer (HAT) takes place.     

Monoclinic‐to‐orthorhombic phase transition of the hexamethylenetetramine–2‐methylbenzoic acid (1/2) cocrystal with temperature‐dependent dynamic molecular disorder

As a function of temperature, the hexamethylenetetramine–2‐methylbenzoic acid (1/2) cocrystal, C₆H₁₂N₄·2C₈H₈O₂, undergoes a reversible structural phase transition. The orthorhombic high‐temperature phase in the space group Pccn has been studied in the temperature range between 165 and 300 K. At 164 K, a t₂ phase transition to the monoclinic subgroup P2₁/c space group occurs; the resulting twinned low‐temperature phase was investigated in the temperature range between 164 and 100 K. The domains in the pseudomerohedral twin are related by a twofold rotation corresponding to the matrix (100/00/00). Systematic absence violations represent a sensitive criterium for the decision about the correct space‐group assignment at each temperature. The fractional volume contributions of the minor twin domain in the low‐temperature phase increases in the order 0.259 (2) → 0.318 (2) → 0.336 (2) → 0.341 (3) as the temperature increases in the order 150 → 160 → 163 → 164 K. The transformation occurs between the nonpolar point group mmm and the nonpolar point group 2/m, and corresponds to a ferroelastic transition or to a t₂ structural phase transition. The asymmetric unit of the low‐temperature phase consists of two hexamethylenetetramine molecules and four molecules of 2‐methylbenzoic acid; it is smaller by a factor of 2 in the high‐temperature phase and contains two half molecules of hexamethylenetetramine, which sit across twofold axes, and two molecules of the organic acid. In both phases, the hexamethylenetetramine residue and two benzoic acid molecules form a three‐molecule aggregate; the low‐temperature phase contains two of these aggregates in general positions, whereas they are situated on a crystallographic twofold axis in the high‐temperature phase. In both phases, one of these three‐molecule aggregates is disordered. For this disordered unit, the ratio between the major and minor conformer increases upon cooling from 0.567 (7):0.433 (7) at 170 K via 0.674 (6):0.326 (6) and 0.808 (5):0.192 (5) at 160 K to 0.803 (6):0.197 (6) and 0.900 (4):0.100 (4) at 150 K, indicating temperature‐dependent dynamic molecular disorder. Even upon further cooling to 100 K, the disorder is retained in principle, albeit with very low site occupancies for the minor conformer.     

Sequence and phosphorylation level determination of two donkey β‐caseins by mass spectrometry

Two coeluting components, with experimentally measured M_r values of 25529 and 24606 Da, were identified by reversed‐phase high‐performance liquid chromatography (RP‐HPLC) and mass spectrometric analysis in the dephosphorylated casein fraction of a milk sample collected from an individual donkey belonging to the Ragusano breed of the east of Sicily. By coupling enzymatic digestions, matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) and RP‐HPLC/nano‐electrospray ionization tandem mass spectrometry (nESI‐MS/MS) analysis, the two proteins were identified as donkey β‐CNs and their sequences characterized completely, using the two known β‐CNs from mare as references. The two donkey β‐CNs, showing a mass difference of 923 Da, differ by the presence of the domain E²⁷SITHINK³⁴ in the full‐length component (M_r 25529 Da). In comparison with the mare's β‐CNs used as reference, they present nine amino acid substitutions: L→S³⁷, R→H⁵², S→N⁸¹, P→V⁸⁴, L→V⁹¹, R→Q²⁰³, P→L/I²⁰⁶, L→F²¹⁰ and A→P²¹⁹. Together, these substitutions account for the increase of 18 Da in the M_r of the donkey β‐CNs with respect to the counterparts from the mare. The molecular mass determination by ESI‐MS for the phosphorylated proteins showed that the full‐length component was composed of highly multi‐phosphorylated isoforms with five to seven phosphate groups. By analogy with the homologous mare's β‐CNs, the full‐length (226 amino acids) β‐CN was termed variant A, whereas the shorter (218 amino acids) β‐CN was termed variant A^Δ5. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical studies on the reaction mechanism of CH2CH radical with HNCO

The reaction mechanism of CH₂CH radical with HNCO has been investigated systematically by density functional theory (DFT). The geometries and harmonic frequencies of reactants, intermediates, transition states, and products have been optimized with the B3LYP at different levels. At the same time, AIM is performed to calculate the charge density of some bonding critical points and the charges of some atoms. Nine feasible reaction pathways have been investigated. The results indicated that the main pathway is CH₂CH + HNCO → IMA1 → TSA1 → CH₂CH₂ + NCO, which is characterized by hydrogen atom transferring. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Simultaneous determination of epalrestat and puerarin in rat plasma by UHPLC–MS/MS: Application to their pharmacokinetic interaction study

In the present study, a simple, rapid and reliable ultrahigh‐performance liquid chromatography–tandem mass spectrometric (UHPLC–MS/MS) method was developed and validated to determine simultaneously epalrestat (EPA) and puerarin (PUE) in rat plasma for evaluation of the pharmacokinetic interaction of these two drugs. Both the analytes and glipizide (internal standard, IS) were extracted using a protein precipitation method. The separation was performed on a C18 reversed phase column using acetonitrile and 5 mmol/L ammonium acetate in water as the mobile phase with a gradient elution program. The analytes, including IS, were quantified with multiple reaction monitoring under negative ionization mode. The optimized mass transition ion pairs (m /z ) were 318.1 → 274.0 for EPA, 415.1 → 266.9 for PUE and 444.2 → 166.9 for IS. The linear calibration curves for EPA and PUE were obtained in the concentration ranges of 10–4167 and 20–8333 ng/mL, respectively (r > 0.99). The current method was successfully applied for the pharmacokinetic interaction study in rats following administration of EPA and PUE alone or co‐administration (EPA 15 mg/kg, oral; PUE 30 mg/kg, intravenous). The results showed that the combination of EPA and PUE could increase t _1/2 of EPA and reduce T _max of EPA. These changes indicated that EPA and PUE might cause drug–drug interactions when co‐administrated.     

Ultra‐high‐performance liquid chromatography–tandem mass spectrometry for pharmacokinetics of bakuchiol in rats

Psoralea Corylifolia L. is a traditional Chinese medicine with many beneficial effects in medical therapies. Bakuchiol was the main active ingredient of Psoralea Corylifolia L., used for the treatment of various diseases and also as a natural food additive. A specific and reliable ultra‐high performance liquid chromatography–tandem mass spectrometry has been developed and fully validated for the quantification of bakuchiol in rat plasma. Chromatographic separation of bakuchiol and an internal standard, daidzein, was achieved on a Hypersil Gold C₁₈ column with gradient elution that consisted of methanol and water at a flow rate of 0.2 mL/min. The compounds were detected at negative ionization mode using mass transition m/z 255.2 → 172.0 and 252.9 → 132.0 for bakuchiol and daidzein, respectively. Good linearity was obtained over the range of 2–1000 ng/mL and the lower limit of quantification was 2 ng/mL. The intra‐ and inter‐day accuracies ranged from 91.1 to 105.7% and precisions (relative standard deviations) were within 9.3%. Bakuchiol was found to be stable under three freeze–thaw cycles, short‐term temperature, post‐preparative and long‐term temperature conditions. The method was applied to a pharmacokinetic study of bakuchiol intravenously administered to rats at a dose of 5 mg/kg. Copyright © 2013 John Wiley & Sons, Ltd.     

Liquid chromatography tandem mass spectrometry method for determination of bisoprolol in human plasma using d5‐bisoprolol as the internal standard

A simple, reliable and sensitive liquid chromatography tandem mass spectrometry (LC‐MS/MS) protocol was developed and validated for quantification of bisoprolol in human plasma. The sample was pretreated with a simple procedure of protein precipitation and an isotope‐labeled d5‐bisoprolol was used as internal standard. The chromatographic separation was performed on a Capcell Pak C₁₈ MG III column (100 mm × 2.0 mm, 5 µm). The protonated ion of the analyte was detected in positive ionization by multiple reaction monitoring mode. The mass transition pairs of m/z 326.3 → 116.3 and m/z 331.3 → 121.3 were used to detect bisoprolol and the internal standard, respectively. Linearity, accuracy, precision, recovery, matrix effect, dilution test and stability were evaluated during method validation over the range of 0.5–100 ng/mL. The validated method was successfully applied to analyze human plasma samples in a bisoprolol bioavailability study. Copyright © 2009 John Wiley & Sons, Ltd.     

Analysis of saikosaponins in rat plasma by anionic adducts-based liquid chromatography tandem mass spectrometry method

Saikosaponins (SSs) are a class of triterpene saponins with a wide spectrum of bioactivities. A sensitive liquid chromatography tandem mass spectrometry (LC‐MS/MS) method was developed for simultaneous determination of saikosaponin a, saikosaponin c, saikosaponin d and saikosaponin b₂ in rat plasma. Plasma samples were prepared by liquid–liquid extraction. The analytes and the internal standard (IS) digoxin were well separated on an octadecyl column using gradient elution and analyzed by monitoring the fragmentation transition pair of anionic adducts to deprotonated molecules in negative‐mode electrospray. By neutral loss of HCOOH, the transition pairs of m/z 825 → 779 for SSa, SSd, SSb₂ and the IS, and m/z 971 → 925 for SSc were sensitive for MS/MS detection with the lower limits of quantification in the range of 0.20–0.40 ng/mL. Method validation experiments were performed, including selectivity, precision, accuracy, linearity, matrix effect, recovery and stability. The validated method was further applied to determine the pharmacokinetics parameters of SSa, c and d in rats following a single oral administration of the extract of chaihu (the dried roots of Bupleurum chinense DC). Copyright © 2011 John Wiley & Sons, Ltd.