Darstellung, 19F-NMR-spektroskopischer Nachweis und Untersuchung zur Bildung der metallgemischten Clusteranionen [(Mo6−nWnCl)F]2−, n = 0−6

Preparation, ¹⁹F NMR Spectroscopic Evidence and Study of the Formation of Metal-Mixed Cluster Anions [(Mo_6?nW_nCl )F ]^2?, n = 0?6 The complete system of metal-mixed octahedral cluster ions [(Mo_6?nW_nCl)F]^2?, n = 0?6, is prepared by tempering Mo powder with WCl₆ at 600°C. A mixture containing inclusively the geometric isomers (n = 2, 3, 4) all ten possible species is transferred into the tetra-n-butylammonium salts (TBA)₂[(Mo_6?nW_nCl)F]. In the ¹⁹F nmr spectrum the 24 expected signals are observed, assigned on the basis of their chemical shifts, multiplicities and intensities, and confirmed by a 2D-¹⁹F-¹⁹F COSY spectrum. From the integrated intensities the distribution of the different components is derived revealing a non-statistical formation, in that isomers with Mo…?Mo or W…?W atoms in trans-positions in comparision to those with mixed Mo…?W axes are favoured, and that especially the homoleptic compounds Mo₆ and W₆ are present to an over-average extent. Evaluation of ¹⁹F chemical shifts reveals that F bound to W which is in antipodal position to Mo resonates at higher field compared to F bound to W in a W…?W arrangement, caused by an increased shielding, which is synonymous to a positive antipodal-effect by Mo. Vice versa F bound to Mo with an antipodal W resonates at lower field compared with F bound to Mo in an Mo…?Mo arrangement caused by an increased deshielding and synonymous a negative antipodal-effect by W. The chemical shifts, resulting from antipodal-effects, are different for the compounds within the [(Mo_6?nW_nCl)F]^2? - system. The difference of the antipodal effect of successive substitution products results in characteristic values designated as antipodal shift constants, depending on the kind of substituents, which is valid for other cluster systems, too.     

Re-Evaluation of the Activity Coefficients of Aqueous Hydrochloric Acid Solutions up to a Molality of 2.0 Using Two-Parameter Hückel and Pitzer Equations. Part II. Results from 0 to 95°C

Simple two-parameter Hückel and Pitzer equations were used for the calculation of the activity coefficients of aqueous hydrochloric acid at temperatures 0–60°C up to a molality of 2.0 mol-kg^–1. The data obtained by Harned and Ehlers^(2,3) on galvanic cells without a liquid junction were used in the parameter estimations of these equations. These data consist of sets of measurements at the temperature intervals of 5°C. It was observed that all estimated parameters follow very simple equations with respect to temperature. They are either constant or depend linearly on the temperature. The values for the activity coefficient parameters calculated by these simple equations are recommended here. The recommended parameter values were tested by predicting the data of Gupta, Hills, and Ives,⁽⁵⁾ consisting of cell measurements from 5 to 45°C and molalities up to 1.0 mol-kg^–1, and the data of Bates and Bower,⁽⁴⁾ which extend to 95°C but measurements were only made on molalities less than about 0.1 mol-kg^–1. The activity coefficients obtained by the new equations were also compared to those calculated by the Pitzer equations with the parameter values determined by Saluja, Pitzer, and Phutela⁽⁶⁾ from calorimetric data. The agreement observed was excellent up to a molality of 1.5 mol-kg^–1 at temperatures from 0 to 60°C.     

Novel evaluation method of biodegradabilities for oil-based polycaprolactone by naturally occurring radiocarbon-14 concentration using accelerator mass spectrometry based on ISO 14855-2 in controlled compost

The biodegradabilities of poly(?-caprolactone) (PCL) powders (av. size = 180.7 μm) in controlled compost at 58 °C have been studied using the microbial oxidative degradation analyzer (MODA) based on ISO 14855-2 entitled “Determination of the ultimate aerobic biodegradability of plastic materials under controlled composting conditions - Method by analysis of evolved carbon dioxide - Part 2: Gravimetric measurement of carbon dioxide evolved in a laboratory-scale test”. The biodegradability of the PCL powders was 101.4% in a 56-day test period by the ISO method. The biodegradabilities of PCL powders have been studied using percent modern carbon (pMC) measured by accelerated mass spectrometry (AMS). Trapped CO₂ was analyzed by AMS to determine the pMC (sample) using ¹⁴C radiocarbon concentration. By using the theory that the pMC (sample) was the sum of pMC (compost) (104.88%) and pMC (PCL) (0%) as the respective ratios in the determined period, CO₂ (respiration) was calculated only from one reaction vessel. The biodegradability of PCL powders was 79.9% in a 56-day test period by the AMS method. It was found that respiration activities in the sample vessel including PCL, compost and sea sand were the same as that in the blank vessel including compost and sea sand without PCL during the active biodegradation period (0-33 day) at 58 °C. It was confirmed that respiration activities in the sample vessel were slightly higher than that in the blank vessel after active biodegradation due to the propagation of microorganisms using energy and metabolites by PCL biodegradation during those periods.     

Evaluation of the Coulomb energy in relativistic self-consistent-field theory

 Computational schemes are presented with which to evaluate the electrostatic Coulomb energy in relativistic molecular electronic structure calculations using a basis of four-component Dirac spinor amplitudes. We demonstrate that algorithms may be constructed and implemented which differ only in minor details from those in common use in nonrelativistic quantum chemistry, and that the four-component formalism is neither as complicated nor as expensive as has been suggested recently in the literature. Spherically symmetrical atomic basis sets are presented which indicate that accurate representations of the Coulomb energy may be obtained using modest expansions of the electronic density in a scalar auxiliary basis set of spherical harmonic Gaussian-type functions. Received: 15 April 2002 / Accepted: 15 May 2002 / Published online: 29 July 2002     

Chemical, sensory and microbiological changes of gamma irradiated coconut cream powder

A study was carried out to determine optimum decontamination dose for a locally manufactured coconut cream powder. Samples were gamma irradiated (0–15 kGy) and ageing process was achieved using GEER oven at 60 °C for 7 days, which is equivalent to one-year storage at room temperature. Iodine value (IV), ranging from 4.8 to 6.4, was not affected by radiation doses and storage, however peroxide value and thiobarbituric acid (TBA) generally increased with radiation doses. In most samples, peroxide value (meq/kg) reduced after storage, whilst the TBA (mg malonaldehyde/kg), indicator for product quality, slightly increased. The sensory evaluation conducted using 25 taste panellists indicated that scores on odour, creamy taste and overall acceptance for all irradiated samples at more than 5 kGy were significantly lower (P<0.05) than the control. However, the panellists could not detect any significant differences among the irradiation doses (P>0.05). All stored products were significantly different in colour, creamy taste, odour and overall acceptance (P<0.05) when compared to the non-stored non-irradiated control. Microbiological count of the samples prior to irradiation was in the range of 1×10²–1.7×10³ cfu/g with no detection of Salmonella sp. and Escherichia coli. No microbial colonies were detected after irradiation. Based on the TBA and overall sensory acceptance, gamma irradiation of 5 kGy was found to be the optimum dose and lower doses can be considered to decontaminate coconut cream powder.     

Advanced statistical evaluation of the complex formation constants from electrophoretic data II: Diastereomeric ion-pairs of (R,S)-N-(3,5-dinitrobenzoyl)leucine and tert-butylcarbamoylquinine

Intermolecular association and ion-pair formation, respectively, between a cationic chiral selector, viz. o-9-(tert-butylcarbamoyl) quinine (CQN), and the both enantiomers of anionic N-(3,5-dinitrobenzoyl)leucine, (R)-DNB-Leu and (S)-DNB-Leu, were investigated by affinity capillary electrophoresis (ACE). Thus, binding constants of the both diastereomeric ion-pairs, (R) and (S)-DNB-Leu/CQN associates, were determined by different experimental setups and correction of nonlinear effects. A reciprocal setup was employed for the high-affinity (S)-enantiomer, and the experimental mobility data obtained for CQN at variable (S)-DNB-Leu concentrations in the background electrolyte were linearized and evaluated by advanced statistical model. A binding constant of K_S=125.1 l mol⁻¹ was afforded. The constant for the (R)-enantiomer, which is outside the range suitable for direct affinity CE, was obtained from indirect affinity CE utilizing the separation of the DNB-Leu racemate at a single appropriate CQN concentration in the BGE (resolution method) taking advantage of the known constant for the (S)-enantiomer yielding a binding constant of K_R=2.51 l mol⁻¹. Thereby, the so-called “constant time method” was adopted for the required precise measurement of the effective mobilities of the both enantiomers. A combined approach of reciprocal affinity CE with racemic DNB-Leu as additive and the resolution method confirmed the results. The resulting constants evidence excellent enantioselectivity of the tert-butylcarbamoyl derivative of the cinchona alkaloid quinine as chiral selector for N-(3,5-dinitrobenzoyl) derivatives of amino acids.     

A study for quality evaluation of Taxilli Herba from different hosts based on fingerprint-activity relationship modeling and multivariate statistical analysis

In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH.     

Error Levels of Different Methods of Evaluation of TG Measurements

It follows from an analysis of the error levels of TG evaluation methods that it is a conceptual error to disregard the analogies of mass, energy and momentum streams of subordinate partial processes. This error is bypassed by means of the introduced method of dimensionless analysis and by determining the characteristic, constants-like data of thermal processes by using the measured data directly. These methods are very suitable for increasing the consistency of the calculated results by seeking for similarity, even in comparisons of measurements made under very different conditions and for emphasizing the differences too, quantitatively. With this new interpretation of TG processes, the idea of the kinetic compensation effect becomes only a consequence of the discussed conceptual error. This revised version was published online in August 2006 with corrections to the Cover Date.     

Qualitative evaluation of aromatic herbs by direct headspace GC analysis. Applications of the method and comparison with the traditional analysis of essential oils

GC headspace analyses of various aromatizing herbs have been compared with those relating to the essential oils, obtained by steam distillation, of the same plants. In this way it was possible to establish the most significant differences between the composition of a herb flavor and that of its essential oil. In particular, we observed some very volatile compounds in the headspace samples which were absent from the essential oil; these components may make an important contribution to the herb flavor. The identification of these substances is still in progress.