Kinetic compensation effect between the isothermal and non-isothermal decomposition of solids

A “true” kinetic compensation effect was established using the most appropriate kinetic functionF(α) for the non-isothermal decomposition of solids at various heating rates. It is likely that the correct kinetic mechanismF(α) is responsible for the “true” kinetic compensation effect, whereas an inappropriateF(α) would lead to “false” one. An establishment of such a “true” compensation effect between the isothermal and nonisothermal decompositions of a solid implies thatF(α) used is appropriate for both the isothermal and non-isothermal decompositions.     

Zur Definition von Selektivität,Spezifität und Empfindlichkeit von Analysenverfahren

The three metric, functional concepts named in the title can be defined without arbitrariness and their values may be calculated for any multicomponent-analytical procedure from the relation of the measurable physical quantities x _ito the contents c _kwhich are to be determined. This relation is mathematically a “mapping” (achieved by systems of functions). The system of “analytical functions” (x _i→ c _k) is the inverse of the system of “calibration functions” (c _k→ x _i) which alone can be directly gained by experiments. The ‘calibration matrix” (γik) whose elements γ_ik are the “partial sensitivities” \(\tfrac{{\partial x_i }}{{\partial c_k }}\) represents the system in first approximation but only locally, i.e. for the respective constitution of the sample. The “sensitivity” of the analytical procedure as a whole, is numerically given by the determinant of this matrix; the “selectivity” is derived from the condition that the inversion of the calibration system to the analytical system (of functions) shall be possible by an iteration process. “Specificity” is defined in analogy to selectivity. In the appendix it is explained why selectivity is the strongest means to reduce the expenditure for the complete calibration of multicomponent analyses to a realistic and tolerable degree.     

Documentation of bioactive principles of the exudate gel (EG) from the stem of Caralluma retrospiciens (Ehrenb) and in vitro antibacterial activity – Part A

Caralluma retrospiciens (Ehrenb) is a desert plant widely distributed in the hilly semi-desert regions of southern part of Saudi Arabia. The exudate gel (EG) from the stem of plant is occasionally used for wound healing by the people of the southern part of Saudi Arabia. This study investigated the phytochemical composition, FT-IR, GC–MS spectral analysis and in vitro antibacterial activity of the EG from the stem of C. retrospiciens (Ehrenb). The plant C. retrospiciens (Ehrenb.) was collected from the hills of Rijal Almaa, a heritage village of Saudi Arabia. The EG was isolated from the stem of C. retrospiciens (Ehrenb.). Physical parameters such as viscosity and zeta potential (ZP) were determined. Phytochemical analysis, FT-IR and GC–MS spectroscopy analysis were performed to determine the bio active constituents. The antibacterial activity of the isolated gel was performed by in vitro agar well diffusion technique. The study demonstrated that the viscosity and ZP of EG influenced the efficacy of antibacterial spectral properties. The FT-IR spectroscopy of the EG showed various functional groups at 3278.29, 2951.16, 2840.44, 2527.55, 2161.67, 1647.40, 1450.06, 1406.7, 1286, 1108.34, 5536.63 cm⁻¹. Various pharmaceutically important chemical compounds were identified using GC–MS analysis. The bioactive compounds are “Sorbic Acid”, “Rhodopsin”, “1-Heptatriacotanol”, “Oxiraneundecanoic acid, 3-pentyl-, methyl ester, trans”, “Cholestan-3-ol, 2-methylene-, (3á,5à)”, “Benzoic acid”, “3-pentyl-, methyl ester trans”, “Hexanoic acid, 2-ethyl-, oxybis (2,1-ethanediyloxy-2,1-ethanediyl) ester”, etc. The antibacterial effect of the EG showed a wide spectrum of activity against the screened human pathogenic bacteria. The results demonstrate the bioactive principles of EG from C. retrospiciens (Ehrenb.) exerts the antibacterial properties in vitro.     

Bioactive principles in exudate gel from the leaf of Aloe fleurentiniorum,traditionally used as folkloric medicine by local people of Aridah and Fayfa mountains,Saudi Arabia

Aloe fleurentiniorum is a desert plant that is occasionally used to treat wounds by local people of Aridah and Fayfa mountains in Saudi Arabia. However, medicinal value of the plant has not been scientifically established. The purpose of this study was to determine the bioactive phytocomponents contained in the exudate gel (EG) from the leaves of Aloe fleurentiniorum using GC–MS and FT-IR studies, as well as antibacterial assays. Medicinally important bioactive compounds were identified using GC–MS analysis. The bioactive compounds are “pregn-5-ene-3α,20-diol”, “16α-methyl-pregnane-11,20-dione”, “3-hydroxy-(3α,5α)-, ursodeoxycholic acid”, “1-heptatriacotanol”, “allopregnane-7α,11α-diol-3,20-dione”, “D-arabino-hexopyranoside”, “2-octadecenoic acid methyl ester”, “D-ribo-hexose,2,6-dideoxy-3-O-methyl glucosamine”, “N-acetyl-N-benzoyl-alpha-D-glucopyranoside”, “nonyl 1-thio pregnenolone”, “5-cholestene-3-ol, 24-methyl-cholestanol”, and “D-allose hexadecanoic acid methyl ester”. Furthermore, specific groups and their respective chemical compounds were identified via FT-IR spectroscopy studies. The FT-IR spectroscopy of EG showed various functional groups at 3354, 2945, 2832, 2523, 2046, 1707, 1451, 1108, 1031, 880, 737 and 610 cm⁻¹. The FT-IR peaks revealed the likely presence of various compounds such as glycosides, flavonoids, steroids, saponins, flavonoids, amino sugars, cutin and isothiocyanate. Moreover, EG produced a wide range of antibacterial effects on some screened human pathogenic bacteria.     

Electronic,optical, and charge transport properties of A-π-A electron acceptors for organic solar cells: Impact of anti-aromatic π structures

Anti-aromatization and isomerization are found to be an effective way to tune the optoelectronic properties of A-π-A electron acceptors for organic photovoltaics.     

Plasma- and vacuum-ultraviolet (VUV) photo-polymerisation of N- and O-rich thin films

Nitrogen (N)- and oxygen (O)-rich organic thin films were deposited by vacuum-ultraviolet (VUV)-assisted photo-chemical polymerisation of flowing ethylene (C₂H₄)–ammonia (NH₃) and C₂H₄–nitrous oxide (N₂O) mixtures of varying ratios, R, respectively. The reaction mechanism of these binary gas mixtures was investigated as a function of the wavelength, λ, of two near-mono-chromatic VUV sources. Surface-near compositions of these “UV-PE:N” and “UV-PE:O” films were determined by X-ray photoelectron (XPS), and by Fourier transform (reflection–absorption) infrared (FTIR) spectroscopies. The two types of films were compared with plasma polymers deposited using low-pressure radio-frequency (r.f.) glow discharges in similar gas flow mixtures, “PPE:N” and “PPE:O”. VUV-photochemistry appears to be superior to plasma-chemistry in its capability to produce nearly “mono-functional” organic thin films, ones that are rich in primary amines, –NH₂, and in carboxylic acid groups, –COOH, respectively.     

Ion cyclotron resonance excitatio/de-excitation: A basis for Stochastic fourier transform ion cyclotron mass spectrometry

Previous mass spectrometers based on the ion cyclotron resonance principle have employed continuous excitation (single-pulse or frequency-sweep), With detection during (frequency-sweep) or after (single-pulse or frequency sweep) the excitation. The present paper introduces an experiment in which an ion is first excited to a Larger orbit by continuous excitation, and then “de-excited” back to its starting point. The effect is demonstrated for the C₉F₂₀N⁺ peak (m/z = 502) in the Fourier transform ion cyclotron mass spectrum of perfluorotributylamine. By choosing which ion m/z ratios are “de-excited”, it should be possible to generate mass “windows” within which ions experience no net excitation. Potential applications of the method include the generation of an excitation with sharply defined “windows” or “steps”, with major advantages for MS/MS or multiple-ion-monitoring experiments.     

Die horizontale Korrelation in π-Elektronensystemen und ihre Beschreibung durch Elektronenpaarfunktionen

Different types of pair functions (geminal products and their linear combinations) are tested with respect to their ability to describe the “horizontal correlation” of the π-electrons of butadiene. The validity of the π-electron approximation is not discussed and “full configuration interaction” within the limited LCAO basis is used as the standard to which the model calculations are referred. An APSG-function (APSG = antisymmetrized product of strongly orthogonal geminals) built up from equivalent (localized) geminals, which contains only one variational parameter is able to account for about 90% of the “horizontal correlation energy”. Both APSG and APIG functions constructed from delocalized geminals, are much less favorable. Criteria of the goodness of an approximate wave function are a) the energy b) comparison of its one- and two-particle density matrices with those obtained from “full CI”. The good results with the localized APSG function are related to the fact that electron correlation between electrons of opposite spin is (in this molecule) essential only within either of the “double bonds” of the “canonical structure”. The pertinent results are quite insensitive to different parametrization of the integrals.     

On the “third decay channel” and vibrational redistribution problems in benzene derivatives

Fluorescence lifetimes and yields have been measured for toluene, aniline-h₇ and aniline-d₅ vapors in the spectral range corresponding to a rapid increase of the non-radiative rates. Non-exponential decays and discrepancies between lifetime and yield dependence on ν_exc are observed. Results are discussed on the ground of a model assuming: (a) strong anharmonic coupling of “active” and “non-active” modes, (b) specific “third channel” threshold for each vibrational progression and (c) absence of rapid vibrational redistribution.     

Steric diversion—I : Addition of halogens and pseudo-halogens to isolongifolene

Addition of halogens (Cl₂, Br₂) and pseudo-halogens (ICl, halogen azides, NOCl) to solongifolene does not yield any “normal” addition products due to severe steric hindrance to the approach of counter ion at C-7. Initially formed halogenonium ions undergo elimination or rearrangement to give “abnormal” products. The term Steric Diversion is suggested to describe this switch over from the “normal” route.     

Molecular aspect of the even-odd effect in cyanobiphenyls (n-CB): Theoretical studies of the molecular geometrical conformation and optical anisotropy. II. n ⪢ 6

The optical anisotropy γ² and the average molecular length 〈ΔR〉 in a series of n-alkyl-cyanobiphenyl compounds (n ⪢ 6) have been determined by means of “dipole—induced-dipole” method and “molecular mechanics”. These theoretical results compared to the half-width at half height of the Rayleigh scattered light spectrum suggest the hypothesis that the alkyl chain undergoes a perturbation due to the environment inducing a folding-back effect (“scorpion effect”) on its geometrical conformation.     

Sintering kinetic study of the nano-crystalline 3-mol% yttria-samaria codoped tetragonal zirconia polycrystal ceramics

Dilatometric shrinkage data was utilized to study the sintering kinetics of the in-house synthesized nano-crystalline 3-mol% yttria-samaria codoped tetragonal zirconia polycrystal (TZP) ceramics. The objective was to determine activation energy (Q) of sintering and the sintering mechanism (n) relevant to the initial stage of sintering. The product of activation energy and sintering parameter, i.e., “nQ” was calculated from the shrinkage data acquired from the constant rate of heating experiment. The apparent activation energy of sintering (Q) was calculated using modified-“Dorn” method. Modified Johnson’s equation was used to determine value of “n” using the activation energy obtained from the Dorn method. Stepwise isothermal dilatometry technique was utilized as an independent method to determine the “n” value. The activation energy of sintering was in the range of 400–525 kJ mol^?1 and found to be dependent on the dopant concentration. The value of “n” was found to be ~0.33 for both 3 mol% yttria-doped (3Y-TZP) and yttria-samaria codoped (3(Y,S)-TZP) TZP, whereas for 3 mol% samaria-doped tetragonal zirconia (3S-TZP), the value of “n” was ~0.40. From the obtained “n” values, it may be concluded that grain boundary diffusion (GBD) was the dominant sintering mechanism in 3Y-TZP and 3(Y,S)-TZP, whereas an intermediate of GBD and volume diffusion influences the initial sintering stage in the 3S-TZP.     

General methods of analysing molecular vibrations

An acute need may arise to develop for the complete analysis of molecular vibrations practically convenient general methods based on coordinates other than “chemical coordinates”. One reason is the proven proposition: Among independent internal coordinates corresponding to a molecule, there cannot be one which describes a small displacement of a chemical group as a whole relative to a certain molecular plane, provided this group contains more than two linearly or three non-linearly arranged atoms. Two methods are presented in some detail. The first is based on the use of X⁰_δ coordinates which are components of “bond vectors” in the “sown” (for each “bond”) Cartesian coordinate system. The second method utilizes X⁰ coordinates, i.e. the components of atomic displacements in the “down” (for each atom) Cartesian coordinate system. Computation of the torsional vibration of transdichloroethane is given as an example illustrating the first method. The Mayants treatment of the symmetry of a molecule, proceeding from elementary considerations which do not use the group theory explicitly and are valid for any coordinates, is expounded in a somewhat improved version. The peculiarities arising when considering the mean-square amplitude matrix, Σ, in X⁰_δ and X⁰ coordinates are also discussed.     

Equilibrium structure and harmonic force field of the known PH3 and the unknown PH5

The equilibrium geometries and harmonic force fields of PH₃ and PH₅ are calculated in an ab initio way including electron correlation. The results for PH₃ are in very good agreement with experimental values, whereas those for PH₅ have to be regarded as predictions. We find for PH₅ in its equilibrium D _3h structure r _ax = 1.47 Å, r _eq = 1.42 Å and the harmonic vibration frequencies in Table 7 given under the heading “CEPA”. The barrier for Berry inversion is 2 kcal/mol. The ab initio calculation of phosphoranes such as PH₅ not only requires the inclusion of polarization functions (d on P and p on H) but is also very sensitive to the choice of these polarization functions. This problem is taken care of by a detailed comparison of various basis sets. It is confirmed that a (10/6) basis for P in “double zeta contraction” is better balanced than a (12/9) basis in “double zeta contraction” and that the total energy is not a good criterion for the quality of a basis.     

Electron correlation and the compton profile of atomic neon

The radial momentum distribution I_o(p) and the Compton profile J_o(q) are determined for atomic neon from several restrictid Hartree-Fock (RHF) wavefunctions and two configuration interaction (CI) wavefunctions. The CI functions are the well correlated (full“second-order”) function of Viers, Schaeffer and Harris, and the Ahlrichs-Hinze multi-configuration Hartree-Fock (MCHF) function which includes only L-shell correlation. It is found for this completely closed shell system that the effects of electron correlation are quite small. This contrasts with the results for systems such as Be(²S) and B(²P) where the semi-internal and internal correlation effects were responsible for significant discrepancies between the RHF and CI results. These results indicate that a wavefunction which carefully includes the semi-internal, orbital polarization, and internal correlations beyond the RHF wavefunction (i.e., a “first-order” or “charge-density” function), should account for the principal correlation effects on the Compton profiles and momentum distributions.     

Simulation of EPR spectra of ThBr8:Pa4+ in the incommensurable phase

At T = 95 K β-ThBr₄ undergoes a phase transition from a “high-temperature” phase with space group I_41/amd to a structure with an incommensurable distortion wave along the crystallographic c axis. The modulation can be thought to consist of a combination of a “rotation” and a “twist” of the Br atoms in the plane perpendicular to the c axis. The EPR spectra at 4.2 K show the characteristic “edge singularities” of the incommensurable structure. A model is presented for the simulation of these spectra. It is based on the “twist” component of the modulation only.     

Accurate thermochemistry from quantum chemical calculations?

The answer to the title question is definitely “yes” – at least for fairly small molecules. Computational procedures, namely the Weizmann (Wn) and Gaussian-3 (G3) family of methods, the complete basis set extrapolation scheme (CBS-x), the “high accuracy extrapolated ab initio thermochemistry” (HEAT) as well as the “correlation consistent composite approach” (ccCA), aimed at energies with chemical accuracy or even better (sub kJ?mol^?1) are described and several applications illustrating the level of accuracy that can be achieved are presented.     

Na*(3p)-Formation under grazing scattering of Na+-ions at an Al(111) surface

Excited Na*(3p)-atoms are observed in grazing surface-collision experiments with Na⁺-beams. Such atoms can be formed beyond a certain threshold velocity via resonant electron transfer between atomic and metallic conduction band levels due to motion of the atom relative to the surface of the metal (“kinematic resonance”). This mechanism is studied here theoretically employing two different techniques: the nonperturbative “Coupled Angular Mode” (CAM) method and the approximate “Transfer Hamiltonian” (TH) method. The calculated Na*(3p)-populations agree well with recent experimental results. Moreover, the complete density matrix of the Na*(3p)-subspace has been computed with the TH-method for ion-energies between 10 and 300 keV.     

A compact fluorescence/circular dichroism dual-modality probe for detection,differentiation, and detoxification of multiple heavy metal ions via bond-cleavage cascade reactions

Selective detection of multiple analytes in a compact design with dual-modality and theranostic features presents great challenges. Herein, we wish to report a coumarin-thiazolidine masked d-penicillamine based dual-modality fluorescent probe COU-DPA-1 for selective detection, differentiation, and detoxification of multiple heavy metal ions (Ag⁺, Hg²⁺, Cu²⁺). The probe shows divergent fluorescence (FL) /circular dichroism (CD) responses via divergent bond-cleavage cascade reactions (metal ion promoted C-S cleavage and hydrolysis at two distinctive cleavage sites): FL “turn-off” and CD “turn-on” for Ag⁺ (no hydrolysis), FL “turn-on” and CD “turn-off” for Hg²⁺ (imine hydrolysis), and FL “self-threshold ratiometric” and CD “turn-off” for excess Cu²⁺ (lactone and imine hydrolysis), providing the first example of a fluorescence/CD dual-modality probe for multiple species with complimentary responses. Moreover, the bond-cleavage cascade reactions also lead to the formation of d-penicillamine heavy metal ion complexes for potential detoxification treatments.