“Model-free” kinetic analysis?

All kinetic analyses aim to determine a sufficient number of kinetic parameters, usually at least an apparent Arrhenius activation energy and pre-exponential factor, and a conversion function or kinetic model (making up a ‘kinetic triplet’), so that accurate extrapolations of kinetic behaviour can be made. “Model-free” methods of kinetic analysis postpone the problem of identifying a suitable kinetic model until an estimate of the activation energy has been made. A major reason for doing this is that misidentification of the kinetic model has a marked effect on the values obtained for the Arrhenius parameters in both isothermal and non-isothermal kinetic analyses. Some aspects of this problem are discussed.

The non-parametric kinetics (NPK) method [1 and 2] is a “model-free” method of kinetic analysis that does not seem to have received the attention that it deserves. This is probably because of its mathematical sophistication and the fact that the matrix and non-linear regression calculations involved are not readily automated. The principle of the method appears to be that of “forcing” a set of non-isothermal data into the set which should have been obtained if the experiments had been carried out isothermally. The method deserves wider testing and also raises some interesting aspects of the philosophy behind non-isothermal kinetic analysis.     

The “Facilitated Transition” hypothesis as an explanation for the gemdialkyl effect

A new technique of searching the conformational space of transition states was used to explore the cause of the rate acceleration in the gem-dialkyl effect in intramolecular cyclization reactions. Several previous hypotheses were discarded and a new hypothesis was advanced based on this new data. This hypothesis, the “Facilitated Transition” hypothesis, states that increased steric hindrance reduces the overall activation energy by facilitating rotation through the transition state. The older “Reactive Rotamer” hypothesis was eliminated by generating all conformations of the starting materials using the and computer programs and demonstrating that no relationship is found between rate increase and a change in the concentration of “reactive rotamers”.     

Syntheses of heparin - like pentamers containing “opened” uronic acid moieties

The syntheses of four analogues of pentasaccharide Ia, which corresponds to the minimal AT III binding region of heparin, are presented and the biological activities of these analogues will be discussed. Three of these analogues (i.e. compounds II, III and IV) contain an R-glyceric acid oxymethylene residue (i.e. B in fig.3) instead of -L-iduronic acid and in the other analogue (i.e. compound V) the β-D-glucuronic acid unit has been replaced by an s-glyceric acid oxymethylene residue (i.e. A in fig3). The R and S-glyceric acid oxymethylene residues represent an “opened” iduronic acid unit and an “opened” glucuronic acid unit, respectively, containing the essential carboxylate function in the appropriate configuration. The crucial step in the syntheses of these “opened” uronic acid pentamer analogues, was the preparation of the required glyceric acid oxymethylene residues 8a, 8b and 8c.

Analogues II and III, containing an “opened” iduronic acid moiety, display a significant AT III mediated Xa activity. Compound III contains two extra sulphate groups at unit 2. Removal of the contributing O-sulphate groups at position 3 and 6 of unit 6 of compound II (i.e. compound IV) results in a seven-fold drop in Xa activity. Replacement of the β-D-glucuronic acid unit by an S-glyceric acid oxymethylene residue (i.e. compound V) leads to almost a complete loss of Xa activity, notwithstanding the fact that all the essential and contributing charged groups are present in the molecule.     

Vapor liquid equilibrium modeling of alkane systems with Equations of State: “Simplicity versus complexity”

Two types of Equations of State (EoS), which are characterized here as “simple” and “complex” EoS, are evaluated in this study. The “simple” type involves two versions of the Peng–Robinson (PR) EoS: the traditional one that utilizes the experimental critical properties and the acentric factor and the other, referred to as PR-fitted (PR-f), where these parameters are determined by fitting pure compound vapor pressure and saturated liquid volume data. As “complex” EoS in this study are characterized the EoS derived from statistical mechanics considerations and involve the Sanchez–Lacombe (SL) EoS and two versions of the Statistical Associating Fluid Theory (SAFT) EoS, the original and the Perturbed-Chain SAFT (PC-SAFT).

The evaluation of these two types of EoS is carried out with respect to their performance in the prediction and correlation of vapor liquid equilibria in binary and multicomponent mixtures of methane or ethane with alkanes of various degree of asymmetry. It is concluded that for this kind of systems complexity offers no significant advantages over simplicity. Furthermore, the results obtained with the PR-f EoS, especially those for multicomponent systems that are encountered in practice, even with the use of zero binary interaction parameters, indicate that this EoS may become a powerful tool for reservoir fluid phase equilibria modeling.     

Consumer attitudes to radiation and irradiated potatoes at “radiation fair” in Osaka, Japan

“Radiation Fair” has been held in summer vacation season in August for more than 10 years in Osaka, the largest city of western Japan, for the purpose of public education and information transfer of radiation and radiation-related technology. We distributed questionnaires to the visitors for recent 3 years to inquire their status toward radiation and irradiated products including irradiated potatoes as well as impression toward the displays. According to the survey results, more than 60% of the kids visitors were satisfied with this exhibition as informative, more than half of the older visitors (16 years old and upward) indicated that they recognized the word of “radiation” when they were at elementary school and the most significant sources of this information were school lessons and the mass media. Consumer's image toward radiation seems to shift to more “positive” when correct knowledge about radiation is given. More than half of consumers did not know “irradiated potatoes” but the percentage indicating that irradiated potatoes was definitely hazardous was less than 10%.     

Can triorganoboroxins exist in a “monomeric” R---B=O form? MNDO calculations and ebulliometric molecular weight determination

MNDO calculations were made for triethylboroxin (EtBO)₃ and triphenylboroxin (PhBO)₃ using both X-ray determined and optimized geometry of these molecules. The results were compared with hypothetical “monomeric” molecules R---B=O. Calculated energies of trimerization are about −200 kJ mol⁻¹ for both compounds and confirm the much higher stability of the “trimer”. Ebulliometric determination of molecular weight of triphenylboroxin in 2-pentanone confirms its trimeric character.     

“Hole-burning spectra”. A new method for obtaining fine structure in absorption spectra of organic molecules

A new method is proposed for obtaining fine structure in broad-band absorption spectra of organic molecules in solid solutions at low temperature. This method is based on the laser burning of a series of narrow gaps in inhomogeneously broadened absorption spectra. A special spectral set-up has been developed for the measurement of the differential spectrum (a “hole-burning spectrum”) of “burnt” and “unburnt” samples. As an example the hole-burning spectrum of Zn-tetraphenylporphine in ethanol has been considered.     

Comment on “chiral discrimination in spherical tops”

The difference in the interaction energies of two co-rotating, and two counter-rotating, spherical-top molecules is of second order in the rotational constant B, and not first order. Co- and counter-spinning alkali-metal atoms exhibit a similar but numerically much larger “chiral” discrimination.     

“In situ” radiation cleaning of underground water contaminated with cyanides - six years of experience

The locality of underground water, contaminated with cyanides, has been successfully cleaned by using the hydraulic barrier method (assembly of pumped wells) since 1986. The average cyanide concentrations in the outflow exceeded 35 m per litre. Contamination had to be eliminated before the discharge into the sewer system. The radiation approach “in situ” i.e. decomposition of cyanides by barrier, was applied and is still being used today. The cyanide concentration was lowered more than one order of magnitude. This process was approved by the Czechoslovak radiation security authorities and further applications of “in Situ” regeneration of underground water contamination is anticipated.     

On “vapour---liquid” phase equilibrium in a finite system

A system of a finite number of particles (atoms, molecules) is considered under the condition N. T. V. = const. A “one drop-vapour” approximation is proposed, adapting the Mayer cluster-expansion formalism to describe the heterogeneous equilibrium state of the system. The mean cluster size distribution function obtained is compared with computer simulation results by Rao, Berne and Kalos and shows quite good agreement. The difficulties of applying the Boltzmann entropy hypothesis to the heterogenous (i.e. bistable) state of the system are discussed.     

Protein-coated β-ferric hydrous oxide particles: An electrokinetic and electrooptic study

Using microelectrophoresis and electric light scattering techniques, we investigated the adsorption characteristics, surface coverage and surface electric parameters of superstructures from two isoforms of plastocyanin, PCa and PCb, in an oxidized state adsorbed on β-ferric hydrous oxide particles. The surface electric charge and electric dipole moments of the composite particles and the thickness of the protein adsorption layer are determined in a wide pH range, at different ionic strengths and concentration ratios of PC to β-FeOOH. The adsorption of the two proteins was found to shift the particles’ isoelectric point and to alter the total electric charge and the electric dipole moments of the oxide particles to different extent. A “reversal” in the direction of the permanent dipole moment is observed at lower pH for PCb- than for PCa-coated oxide particles. Strict correlation is found between the changes in the electrokinetic charge of the composite particles and the variation in their “permanent” dipole moments. Data suggest that the adsorption of the proteins is driven by electrostatic and/or hydrophobic interactions with the oxide surfaces dependent on pH. The adsorption behaviour is consistent with the involvement of the “eastern” and “northern” patches of the plastocyanin molecules in their adsorption on the oxide surfaces that are differently charged depending on pH.     

Sterilization of foods with low-energy electrons (“soft-electrons”)

Electrons with an energy of 300 keV or lower were defined as “Soft-electrons”, which showed several advantages over conventional irradiation with gamma-rays or high-energy electrons in decontamination of grains and spices. Energies of electrons necessary to reduce microbial loads to levels lower than 10 CFU/g were 60 keV for brown rice, 75 keV for wheat, 100 keV for white pepper, coriander and basil, 130 keV for buckwheat, 160 keV for rough rice, and 210 keV for black pepper. Electrons with such energies did not significantly influence the quality.     

Use of heterodifunctional ligands to bridge “early” and “late” transition metals. Construction and chemistry of complexes containing indirectly linked cobalt carbonyl and zirconocene units

Four zirconocene systems, each containing tertiary phosphine functionality indirectly linked to either or both cyclopentadienyl rings, are described. Unlike the phosphinomethylzirconocenes, in which the metal and the phosphine strongly influence each other's basic chemistry, it has been found that a variety of transformations may be carried out at either site on the more indirectly linked systems without interference from the other. Thus reduction and hydrozirconation proceed normally at the Zr center, and quaternization and complexation to a second metal may be achieved at the phosphine. Two “early-late” multimetallic systems containing Zr and Co have been prepared. Reduction and acylation at Co proceed without interference from Zr; however, attempts to generate hydrides at Zr in the bimetallic systems were unsuccessful.     

“Armed-disarmed” glycosidation strategy based on glycosyl donors and acceptors carrying phosphoroamidate as a leaving group: A convergent synthesis of globotriaosylceramide

A stereocontrolled synthesis of globotriaosylceramide with three different glycosidic linkages has been accomplished by linear and convergent routes exploiting “armed-disarmed” glycosidation methodology based on glycosyl donors and acceptors carrying tetramethylphosphoroamidate as a leaving group. In particular, the convergent strategy featuring a coupling of a galactosyl-(1→4)-galactosyl donor with a glucosylceramide derivative has proven to be extremely efficient.     

Coupled Hartree-Fock calculations of the electric dipole polarizability and first hyperpolarizability of some “inorganic benzenes”

Extended basis sets of gaussian functions were used to calculate near Hartree-Fock estimates of the electric dipole polarizabilities, , and first hyperpolarizabilities, β, of the “inorganic benzenes” B₃N₃H₆, B₃O₃H₃, B₃P₃H₃ and Al₃N₃H₆. Assuming that electron delocalization is responsible for the enhanced polarizabilities of aromatic systems, an aromaticity scale can be set up according to the trend of theoretical polarizabilities obtained in this work, i.e. (B₃O₃H₃) < (B₃N₃H₆ ) < (C₆H₆ ), which is consistent with previous calculations of the degree of delocalization in these compounds.     

Spectral interferences in the determination of traces of scandium, yttrium and rare earth elements in “pure” rare earth matrices by inductively coupled plasma atomic emission spectrometry: Part VII — Terbium, Dysprosium, Holmium and Thulium

This article is the seventh part of a series of papers discussing the spectral interferences of rare earth elements (REEs) in ICP-AES. Radial viewing 27.12 MHz inductively coupled plasma atomic emission spectrometry (ICP-AES) was used in the determination of scandium, yttrium and rare earth elements in Tb₂O₃, Dy₂O₃, Ho₂O₃ and Tm₂O₃ as “pure” rare earth matrices. The quantification of the interferences in terms of Q-values for line interference Q_I(_a) and wing background interference Q_W(Δλ_a) were used in accordance with Boumans and Vrakking [Spectrochim. Acta Part B 43 (1988) 69]. The “best” analysis lines from point of view of spectral interferences were selected. The true detection limits by using the “best” analysis lines were calculated.     

Zur nomenklatur der phane—II

The new term “Phanes” has been clearly defined and a nomenclature system tentatively developed. This system is comprehensible and of general application and at the same time relatively simple. The notations “nucleus”, “bridge”, “number of bridge members” and “number of ring members” are defined. In order to get a definite characterisation of the phanes which contain a carbocyclic nucleus, a carbocyclic and heterocyclic bridge the following terms: “carbophanes”, “carba-phanes” and “hetera-phanes” have been newly introduced. The prefix “hetera-” has been proposed as a general expression and as a representative term for the syllables “aza-”, “oxa-”, “thia-” and so on. The so called “a-nomenclature” is clearly called “hetera-nomenclature”. The new expressions “heteralogous” and “substitulogous” are explained. As the various examples will show, the “Phane-Nomenclature” can also be applied to the naming of complicated metallocenophanes.     

Not the enolate Claisen rearrangement. A surprising route to the “right-wing” of indanomycin (X-14547A)

A synthesis of the “right-wing” equivalent 22 of the ionophore antibiotic indanomycin is described, wherein an unexpected retro hetero Diels-Alder/intramolecular Diels-Alder pathway gives the desired product of the planned Claisen [3,3]-shift.     

Crystal structure of Fe(η-C5H5BCMe3)2 a “problem structure”

The complex Fe(η⁶-C₅H₅CMe₃)₂ crystallizes in the centrosymmetric triclinic space group P (C_i¹; No. 2) with unit cell dimensions of a 8.770(1) Å, b 8.878(1) Å, c 11.991(1) Å, 107.56(1)°, β 90.85(1)°, γ 90.13(1)°, V 890.0(2) ų and Z = 2. A full sphere of data was collected on a four-circle diffractometer. The structure was solved and refined to R 7.93% for all 3155 independent reflections and R 4.98% for those 2002 data with | F₀ | > 6σ. | F₀ |. The molecules lie on crystallographic inversion centers at 0, 0, 0 and 1/2, 0, 1/2; the crystallographic asymmetric unit therefore consists of two independent half molecules. The molecule centered at 0, 0, 0 (molecule “A”) is ordered and well-defined; that centered on 1/2, 0, 1/2 (molecule “B”)is probably disordered, as indicated by larger “thermal parameters” and a greater range of apparent interatomic distances. Discussion em phasizes the geometry of molecule A, which has precise C_i symmetry with Fe(1A)-B(1A) 2.297(4) Å and Fe(1A)-C(ring) distances ranging from 2.057(6) Å to 2.138(4) Å.