A Spectroscopic Study of Charge Transfer Complexes of Tetraphenylporphyrin

The fluorescence quenching and complexation behaviour of tetraphenylporphyrin (TPP) with some organic acceptors such as chloranilic acid (CHL), 5,5-dithiobis-2-nitrobenzoic acid (DTNB), or 3,4-dinitrobenzoic acid (DNB) and tetravalent metal ions such as Th⁴⁺ and Zr⁴⁺ have been studied in methanol. The second-order fluorescence quenching rate constant (k_q), the association constant (K), the molar absorption coefficient (), and the thermodynamic parameters of the complexation process (G°, H°, and S°) have been evaluated using different organic solvents.     

Marked differences between acetonitrile/water and methanol/water mobile phase systems on the thermodynamic behavior of benzodiazepines in reversed phase liquid chromatography

Summary Two different methods were used to determine the separation factor at different temperatures and the Gibbs-Helmholtz parameters ((H), (S)) of two adjacent benzodiazepines on a chromatogram were obtained from plots of ln versus 1/T. We first studied each factor (fraction of water in the ACN/water mixture and column temperatureT), which controls the retention mechanism, and then we examined the simultaneous variation of all these factors. The changes in (H) and (S) in relation to a volume fraction of water in an ACN/water mixture were examined. In the ACN/water system, (H) was fairly constant in the acetonitrile region of 0.52 and appears to be a roughly linear function of for 0.52. In this system (S) is approximately a parabolic function of with an optimum at 0.52. The retention mechanism of ten benzodiazepines was found to be significantly different in the methanol/water and ACN/water mixtures. The separation optimization of these ten benzodiazepines was then considered. A fraction of water of 0.43 in the ACN/water mixture and a column temperature of 44°C gave the most efficient separation conditions in the ACN/water mixture.     

Relativistic perturbation theory of molecular structure

Summary The recently developed relativistic double perturbation theory is extended to handle relativistic changes of molecular structure more easily. This is achieved by simple coordinate scalings. Accurate higher order mixed perturbation energies for H ₂ ⁺ are calculated. The relativistic changes of bond energy,DE, of bond length,R _e , and especially of force constant,k, and of anharmonicity,a, are large, up to 100%·(Z/c)². The dominant contributions tok anda are due to the indirect change of the nonrelativistick anda connected with the relativistic change of bond length. Accordingly the relativistic changes obey Badger's and Gordy's rules (–RDEk).Dedicated to Prof. Klaus Ruedenberg in appreciation of his fundamental contributions to both formal theory and physical explanations in quantum chemistry     

The Influence of Dimerization of Water-Soluble Metalloporphyrins as Photosensitizers on the Efficiency of Generation of Singlet Oxygen

Quantum yields () for the generation of singlet oxygen sensitized by Pd(II) complexes of water-soluble porphyrins: meso-tetrakis(4-N-methylpyridyl)porphine [PdTMPyP]⁴⁺ ( = 0.9), meso-tetrakis(4-N,N,N-trimethylaminophenyl)porphine [PdTTMAPP]⁴⁺ ( = 0.8), meso-tetrakis(4-carboxyphenyl)porphine [PdTCPP]^4– ( = 0.7), and meso-tetrakis(4-sulfonatophenyl)porphine [PdTSPP]^4– ( = 0.5) were determined using a chemical method. It was found that the dimerization and aggregation of metalloporphyrins greatly influence the value. The quantum yields evaluated for the formation of singlet oxygen sensitized by metalloporphyrin monomeric and dimeric forms are _{, M} 0.9 and _{, D} 0.2, respectively, and do not depend on the porphyrin nature.     

Numerische Auswertung von Enzymanalysen

Zusammenfassung Für eine numerische Auswertung von Enzymanalysen erscheint es zunächst naheliegend, in die Meßpunkte eine Ausgleichsgerade einzupassen und deren Steigung als Schätzwert für die gesuchte Anfangsgeschwindigkeit E/t ₀ zu nehmen. Die Steigung der Ausgleichsgeraden liefert aber die mittlere Reaktionsgeschwindigkeit über die gesamte Meßzeit und unterschätzt E/t ₀ immer dann, wenn die Reaktion gegen Ende der Meßzeit etwas langsamer läuft. Bei automatischen Geräten muß das Auswerteverfahren auch in solchen Fällen E/t ₀ richtig schätzen. In der vorliegenden Arbeit wird eine einfache Möglichkeit, die zu diesem Ziel führt, diskutiert, nämlich die Schätzung von E/t ₀ mit einer Ausgleichsparabel, die dem Reaktionsverlauf folgen kann.

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Numerical evaluation of enzyme analyses

To calculate enzyme concentrations numerically, it seems obvious to fit a straight line into the data points and take the slope as an estimate for the starting velocity E/t ₀. This slope, however, is proportional to the average reaction rate over the total measurement interval and always underestimates E/t ₀ when the reaction is slowing down towards the end. Automatic analyzers must correctly estimate E/t ₀ even in such cases. As discussed in this article, this can be achieved by fitting a second order parabola, that can follow the reaction, into the data points.

     

Band structure of even and ions of odd polyenes

The analysis of experimental data for singlet transitions (E _n) of even polyenes (I), cations (II) and anions (III) of odd polyenes show that for infinite chains E (I)/E (II)=E (I)/E (III) = 2:1. It is shown that the energy gap is equal for the three systems. In cases (II) and (III) there is a level (NBMO) in the gap which is vacant in (II) and occupied in (III). That is why the first optical transition in (II) and (III) depends on the semiwidth of the gap.     

Chiroptical detection during liquid chromatography,part 5: On-line measurement of circular dichroism spectra Δε(λ) during stops of chromatographic flow

Summary A procedure is described which serves to measure circular dichrograms () on line during stops of flow in liquid chromatography. Since the concentration of substrate in the spectrometer cell during the stop is not known, the differential absorption coefficients are calculated from the experimental differential absorbances A by means of UV absorption (i. e. photomultiplier voltage) data. Verifications of the procedure are obtained by its application to three substrates (Table 1), the () spectra of which were known. The present on-line technique is compared with a corresponding off-line method.The N,N-dimethylthiobenzamides1 and2 as well as the 9,10-phenanthrenequinone7 consist of interconvertible enantiomers because their planar states are destabilized by steric overcrowding of groups. The unknown dichrograms () of1, 2 and7 are obtained (Figs. 2 and 4) and discussed with reference to the helicities of these molecules.In memory of the late Professor Dr. Dr. h. c. Günther Snatzke.     

Plastic deformation kinetics for glassy polymers and blends

Measurements of the plastic deformation kinetics for several glassy (PS, PC, PI-polyimide, PET, epoxy-amine network), semi crystalline polymers (PBT, PET) and blends (ABS, PC:ABS, PC: PBT) were performed for the unidirectional compression loading conditions by using constant temperature deformation calorimetry. The experiments have permitted us to follow the changes of the mechanical work (A), the heat of deformation (Q) and differences between these quantities, i.e., internal energy (U) stored in samples during their loading and unloading. Experiments have shown that the large portion (45–85%) of the mechanical work of deformation (A) is converted to heat (Q). The rest ofA is converted to internal energy (U) stored in deformed samples. U is quite high as compared with metals [1,2]. After complete unloading of plastically deformed samples, i.e., samples carrying irreversible atT _def plastic deformation ( _irr ), some amount (U) of stored energy disappeared. The amount of (U and (U) are different for different polymers. All data are analyzed in the framework of the model proposed in [3,4]. The experiments support the deformation model where the plasticity of glassy polymers is the process of nucleation and development of so-called PDs-plastic local shear defects of nonconformational and nondilatational nature.Dedicated to Prof. Dr. W. Pechhold on the occasion of his 60th birthday     

NMR Study of Non-freezing Water in Protein-Modified Carbon Adsorbents

Temperature dependences of ¹H NMR spin–spin relaxation were studied for the non-freezing water at the surface of carbon matrices modified with proteins (human serum albumin (HSA) and mouse immunoglobulin (MIG)) in the presence of water-soluble carbodiimide. The entropy, S , and enthalpy, H , values characterizing molecular mobility in non-freezing water were estimated. The compensation effect was observed for all modified samples, which is well approximated by the linear dependence of the type H = T ₀S + H ₀. The compensation temperature T ₀ = 231 ± 33 corresponds to such a state of non-freezing water, when the effect of modifying additives on the isobaric potential of molecular mobility activation in the non-freezing water, G , is minimal. The G has approximately constant value equal to H ₀ = 24.2 ± 0.5 kJ/mol. Modification of the base carbon matrix with MIG protein results in higher structurization of the non-freezing water, whereas HSA reduces this structurization. The observed effects are explained in terms of the hydration of modifying agents and also by the peculiarities of their location on the surface of carbon adsorbent.     

Effect of the Nucleophile Structure on the Relative Mobility of the Nitro Group and Fluorine Atom in Reactions of 3,5-Dinitro- and 3-Fluoro-5-nitrobenzotrifluorides with Phenols in the Presence of Potassium Carbonate

The relative mobility of the nitro group and fluorine atom in 3,5-dinitro- and 3-fluoro-5-nitrobenzofluorides was estimated by the competing reaction technique using phenols in the presence of potassium carbonate (DMF, 65-95°C). Correlation analysis of the relative rate constants k(NO₂)/k(F) and of the differences in the activation parameters (H and S ) of competing reactions showed the existence of two reaction series for the examined phenols. The higher mobility of the nitro group was found to result from the entropy control of the reactivity of arenes. The mechanism of these reactions is discussed.     

A thermodynamic and structural study of the interactions of pyridino- and diketopyridino-18-crown-6 ligands with some primary organic ammonium cations

Equilibrium constant (K), enthalpy change (H), and entropy change (S) values have been determined calorimetrically at 25°C in 90%MeOH 10%H₂O (v/v) for the interactions of pyridino-18-crown-6 (P18C6) and diketopyridino-18-crown-6 (K₂P18C6) with perchlorate salts of ammonium, benzylammonium,-phenylethylammonium,-phenylethylammonium, and-(1-naphthyl)ethyl-ammonium cations. The crystal structure of the complex of P18C6 with benzylammonium perchlorate was determined by X-ray crystallography. The¹H 1D and 2D NMR spectra of some of these complexes were used to elucidate their structural features in solution. The logK values for the interaction of the ammonium cations with P18C6 are larger than those with K₂P18C6, probably due to the higher degree of structural flexibility of P18C6. Ligand K₂P18C6 displays appreciable - interaction with the-(1-naphthyl)ethylammonium cation, but not with the-phenylethylammonium cation.- interaction between ligand and cationSupplementary Data relating to this article are deposited with the British Library as Supplementary Publication No SUP 00000 (22 pages)     

Substituent effect and enthalpy-entropy compensation on the inclusion ofβ-cyclodextrin with 1-substituted naphthalenes

The inclusion complexation of-CD with 1-substituted naphthalenes has been investigated by fluorescence spectroscopy. It was observed that the association constants were influenced by the molar refraction (R _m), hydrophobic constant ( _x ), and Hammett constant ( _x ) of substituents in the guest compounds. The thermodynamic parameters G⁰, H ⁰, and S ⁰ determined by measuring the temperature-dependentK _a values shows that inclusion complex formation is enthalpy driven. The results are discussed in terms of enthalpy-entropy compensation.     

Kinetics and Mechanism of Monomolecular Heterolysis of Commercial Organohalogen Compounds: XXXV.1 Solvation Effects on the Activation Parameters of Heterolysis of 1-Bromo-1-methylcyclopentane and 1-Bromo-1-methylcyclohexane. Correlation Analysis of Solvation Effects

Kinetics of heterolysis of 1-bromo-1-methylcyclopentane and -cyclohexane in protic and aprotic solvents were studied. Correlation analysis of the effect of solvent parameters on G , H , and S was performed.     

Reaction of methylmagnesium iodide with steroid keto oxides

Summary The reaction of the 3-acetate of the 20-ketal of 16,17-oxido-⁵-pregnenol-3-one-20 with methylmagnesium iodide and subsequent hydrolysis of the reaction product yielded 16-methyl-⁵-pregnenediol-3 –17-one –20. 18-Nor-17-methyl-17-iso-^5.11-pregnadienediol-3,16-one-20 was formed as a by-product.     

Gibbs Energy and Entropy of Mixing in the NaNO2-KNO3 System

The activity and activity coefficients of the components of the NaNO₂-KNO₃ system, determined from the experimental data on the saturated vapor pressure at 798, 823, and 848 K, are used to calculate the relative and excess partial molar Gibbs energies (G _i and G _i ^{e x c}), entropies (S _i and S _i ^{e x c}), and integral relative and excess thermodynamic functions (G, G ^{e x c}, S, and S ^{e x c}) of the system.     

Oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82− and by IO4− in binary aqueous solvent mixtures at pressures up to 1.25 kbar

Second order rate constants and activation parameters H, S, and V have been measured for the oxidation of [Co(en)2(SOCH2CO2)]+ by S2O82– and by IO4– in highly aqueous H2O – t-BuOH mixtures. The changes in solvation on going from the initial to the transition state are discussed on the basis of the transfer functions Gto, Hto and Sto. Whereas Gt changes smoothly as the proportion of t-BuOH increases, the plots of Ht and TSt exhibit mirror behaviour and pass through extrema located around x2(t- BuOH)=0.038. Information on the role of solvation is complemented by the determination of activation volumes. These are discussed in terms of intrinsic and solvational contributions. It is proposed that changes in hydrophobic hydration are of principal importance in determining the response of H, S, and V to changes in solvent composition in H2O – t-BuOH mixtures.     

Simulation of adsorption dynamics in adsorbent layers of short length. Estimation of the concentration region of validity of Zeldovich"s equality

The frontal adsorption dynamics with the convex adsorption isotherm at a stage of parallel transfer, was numerically simulated. The change with time in the mean adsorption values a _c in the adsorbent layers of short length L and corresponding concentrations c _L at the outlet from L was calculated. Zeldovich"s equality, which suggests that the ratio of c _L to a _c is equal to the ratio of the inlet fluid phase concentration to the amount adsorbed at equilibrium, is fulfilled at L 0 over the interval of relative concentrations from 10^–4 to 1. This indicates that Zeldovich"s equality is fulfilled as local at any limiting stage of mass transfer. The nonequilibrium dynamics of adsorption always has the finite L value at which the calculated c _L and a _c values approximately coincide with the a and c values of the equilibrium adsorption isotherm.     

Studies of the energy spectrum of α, ω- substituted polymethine chains. II. Polymethine chains with odd number of methine groups

The analysis of the experimental data for the energy of the longest wavelength optical transitions _n,opt of substituted polymethines X (CH)_2n+1 X shows that in the asymptotic case (n) _,opt does not tend to zero, as it follows from the empirically established correlations, but has a finite, non-zero value. It is shown that the energy gap of odd polymethines is the same as that of the even polymethines - the polyenes (E 2 eV). The substituents (X N, O, B) are responsible for the appearance of levels in the gap. These, depending on the substituent character, are vacant (X B) or occupied (X N, O). The transition from or to such a level determines the longest wavelength optical transition energy of polymethines.     

Relative thermodynamic stabilities of isomeric 1,2-dialkoxyethenes

The relative thermodynamic stabilities of the geometrical isomers of a number of 1,2-dialkoxyethenes have been determined by chemical equilibration in the neat liquid and in 1,4-dioxane solution with mercuric acetate as catalyst. From the variation of the value of the equilibrium constant with temperature, the thermodynamic parameters G , H , and S of theE Z isomerization were evaluated. In all cases theZ isomer proved to be thermodynamically the more stable species, its favor increasing with the bulkiness of the alkoxy groups. The thermodynamic data obtained for theEZ isomerization of 1,2-dimethoxyethene differ significantly from those reported in the literature. An attempt to correlate the experimental thermodynamic data with MM2 calculations for the title compounds as well as for 1,2-dimethoxypropenes is presented.     

Einwirkung von Schwefel und Ammoniak auf Methyl-neopentylketon

Zusammenfassung Bei der Einwirkung von Schwefel und Ammoniak auf Methylneopentylketon in Pyridin bei Raumtemp. bilden sich die beiden theoretisch möglichen Thiazoline-³, das 2,4-Dimethyl-2-neopentyl-5-tert. butyl-thiazolin-³ und das 2-Methyl-2,4-di-neopentyl-thiazolin-³ (etwa im Verhältnis 793). Daneben entsteht 2-Methyl-2,4-dineopentyl-imidazolin-³. Die Darstellung und Charakterisierung der sich vom Methylneopentylketon ableitenden reinen isomeren -Brom- bzw. -Mercaptoketone sowie einiger daraus synthetisierter Thiazoline-³ bzw. Thiazole wird beschrieben.Für Korrespondenz ist diese Adresse zu verwenden.49. Mitt.:F. Asinger, W. Schäfer undA. Saus, Mh. Chem.96, 1278 (1965).Teil der DissertationF. Gentz, Techn. Univ. Dresden 1963.