Thermochemistry of Complexation of 15-Crown-5 and 18-Crown-6 with Na+and NH+4Ions in Aqueous Solutions

The complexation constants and the heats of complexation of 15-crown-5 (15C5) and 18-crown-6 (18C6) with sodium and ammonium ions in aqueous solutions at several temperatures were determined using calorimetry methods. Thermodynamic characteristics (H°, G°, S°, and C _p°) of the formation of Na(15C5)⁺, Na(18C6)⁺, and NH₄(18C6)⁺were calculated.     

Thermodynamics of 15-Crown-5 Complexation with Ag+ and Pb2+ Ions

Heats and constants of 15-crown-5 (R) complexation with silver and lead ions at 298, 308, and 318 K are determined using direct calorimetry. Thermodynamic parameters (G°, H°, S°, and C _p°) of formation of AgR⁺ and PbR²⁺ complexes at various temperatures are calculated. The effects of the properties of the cations and crown ethers on the thermodynamic parameters of complexation are discussed.     

Thermodynamic quantities for the interaction of Cl− with Mg2+, Ca2+ and H+ in aqueous solution from 250 to 325°C

The aqueous reactions, Mg²⁺+Cl^–=MgCl⁺, Ca²⁺+Cl^–=CaCl⁺, and H⁺ +Cl^–=HCl(aq), were studied as a function of ionic strength at 250, 275, 300, and 325°C using a flow calorimetric technique. The logK, H, S and C_p values were determined from the fits of the calculated and experimental heast. The data were reduced assuming a known functionality of the activity coefficient. Hence, the logK, H, S and C_p values determined in this study are dependent on the activity coefficient model used. These thermodynamic values were compared with literature results. The logK values for the formation of MgCl⁺ agree reasonably well with those reported in the literature. The logK values for CaCl⁺ formation agree reasonably well with those reported in the literature at 300 and 325°C. At lower temperatures, the agreement is poorer. The logK values for the formation of HCl(aq) are generally lower than those reported in the literature. The logK, H, S and C_p values for all three ion association reactions are positive and increase with temperature over the temperature range studied. These values are the first determined calorimetrically for the formation of MgCl⁺ and CaCl⁺ in the temperature range 275–325°C.Presented at the Second International Symposium on Chemistry in High Temperature Water, Provo, UT, August 1991.     

Determination of enthalpy of ionization of water from 250 to 350° C

The enthalpy changes at zero ionic strength (H°) for the ionization of water (H₂O=H⁺+OH^–) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of H values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, H°, S°, C _p ^° and V°) for the ionization of water using the H° values determined in this study from 250 to 350°C and literature log K and H° values from 0 to 225°C. Smoothed values of log K, H°, S°, C _p ^° , and V° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.     

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     

Isomerization of 5, 5-dimethylpyrazolines. preparation and properties of 5, 5-dimethyl-Δ1-pyrazoline and 3, 4-dimethyl-Δ2-pyrazoline

Slow distillation of 5, 5, -dimethyl-²-pyrazoline isomerizes it to 5, 5-dimethyl-¹-pyrazoline, and heating the latter with hydrazine hydrochloride reconverts it to the ² isomer. This is the first experimental evidence that the ² double bond in a pyrazoline can move to the ¹ position, i. e., in a direction the reverse of that previously known. The 5, 5-dimethyl-¹ -pyrazoline described is the simplest ¹ pyrazoline hitherto isolated.The authors heartily thank A. A. Petrov for making it possible to chart the PMR spectra, and V. B. Lebedev and V. S. Stopskom for obtaining and treating the spectrograms.     

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.     

NMR Study of the Stoichiometry, Stability, and Ligand Interchange of Silver Ion-Hexathia-18-crown-6 Complex in Binary Dimethyl Sulfoxide Solvent Mixtures at 300 K

Proton NMR was used to study the complexation reaction between silver ion and hexathia-18-crown-6 in a number of binary mixed solvents of dimethyl sulfoxide with acetonitrile and methanol. Formation constants for the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift-mole ratio data. The influence of solvent composition on the stability of the resulting complex is discussed. The exchange kinetics of Ag⁺-hexathia-18-crown-6 in 70-30 wt.% dimethyl sulfoxide-acetonitrile and 75-25 wt.% dimethyl sulfoxide-methanol were studied by proton NMR line-shape analysis. In both solvent mixtures, the exchange of thiacrown ether between the free and complexed sites was found to proceed via a dissociative pathway. The exchange rates and the activation parameters E _a, H , S, and G for the ligand exchange were determined and the influence of solvent properties on these parameters discussed.     

A conductance study of the association of alkali cations with 1,13-dibenzo-24-crown-8 in acetonitrile

A conductance study concerning the association of Na⁺, K⁺, Rb⁺, and Cs⁺ with 1,13-dibenzo-24-crown-8 in acetonitrile has been carried out at 35, 30, 25, 20, and 15°C. The observed molar conductivities were found to decrease significantly for mole ratios less than unity. A model involving 11 stoichiometry has been used to analyze the conductivity data. The stability constant, K, and the molar conductivity _C for each 11 complex were determined from the conductivity data by using a nonlinear least squares curve fitting procedure. The binding sequence, based on the value of log K at 25°C, is found to be Rb⁺>Cs⁺>K⁺>Na⁺. Values of H^o and S^o are reported and their significance is discussed.     

Thermodynamics of 2,2′,2′'-terpyridinecopper(II) complexes in aqueous solution

Summary The thermodynamic quantities relative to the protonation and the complexation of 2,2,2'-terpyridine with copper(II) ion have been determined at 25° and I=0.1 mol dm^–3 (NaNO₃). The G data was obtained by potentiometric measurements; a copper selective electrode was employed for the study of the complexation equilibria. The H values have been determined by direct calorimetry.The hydrolytic species, existing at pH>6 and their relative G and H values have also been obtained.From the thermodynamic data the importance of enthalpy and entropy terms in stabilizing the complexes is assessed.Moreover some considerations on the chelating effect are reported.Presented in part at 2 Congresso Nazionale di Chimica Analitica, Catania (1977).     

The position of plutonium/III/ in the lanthanide series in respect to thermodynamic functions of complex formation with nitrates and thiocyanates

The position of Pu/III/ within lanthanides in respect to G⁰, H⁰ and S⁰ of complex formation with nitrate and thiocyanate ligands was determined by the extraction method. It was found that in respect to G⁰, Pu/III/ is a light pseudolanthanide for nitrate ligands and a heavy pseudolanthanide for thiocyanate ligands. A comparison of the positions of Pu/III/ and Am/III/ in respect to G⁰, H⁰ and S⁰ shows that the radius of plutonium is greater than that of americium in the An/NO₃/ ₅ ^2– complex and smaller in the An/NCS/₃/TBP/_n complex. The increase in the radii between plutonium and americium in the thiocyanate complex points out to a contribution from 5f orbitals to bonding.     

Thermodynamic behavior of mixed benzodiazepines by a new liquid chromatographic method

Summary Using a rapid chemometric methodology to determine the separation factor, , at different temperatures, Gibbs Helmholtz parameters ( (H), (S), (G)) of two adjacent benodiazepines on a chromatogram were obtained from ln versus T^–1 plots. A temperature dependent reversal of the elution order was studied and the mobile phase composition and column temperature were optimized to obtain the best separation. A flow rate of 0.80 ml min^–1 with 52.6% methanol in the methanol-water mixture and a column temperature of 48°C gave the most efficient separation of ten benzodiazepines.     

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.     

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.     

Thermodynamics of protonation of amino acid carboxylate groups from 50 to 125°C

Flow calorimetry has been used to study the interaction of glycine, DL--alanine, DL-2-aminobutyric acid, -alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, H°, S°, and C _p ^° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, H°, and S° values are close together over the temperature range studied for the protonation of -amino acids, i.e., glycine, DL--alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The C _p ^° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger C _p ^° values which approach those associated with charge reduction reactions. As the temperature increases, C _p ^° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in H° and S° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.     

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.     

The effect of the relative location of the double bond and the alkoxy group on the mass-spectrometric behavior of alkoxydihydropyranes

Conclusions The mass spectra ofthree 6-alkoxy-³-dihydropyranes and of three 6-alkoxy-²-dihydropyranes have been studied. As distinct from the previously studied 2-alkoxy-³-dihydropyranes, the dominant fragmentation pattern for the compounds under investigation is by retrodiene degradation. Furthermore, in the case of the ²-isomers the charge is preferentially localized on the olefin fragment while for the ³-isomers, it is located on the diene fragment.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1442–1444, June, 1970.     

Thermodynamics of Proton Association of Polyacrylates and Polymethacrylates in NaCl(aq)

Enthalpies of protonation of polyacrylates and polymethacrylates with different molecular weights in aqueous NaCl solutions, 0 I 2 mol-L^–1 were determined by titration calorimetry at 25°C. H values are dependent on both the neutralization degree, , and the molecular weight of polyacids. T S of protonation was obtained using pK values already reported and the present H results. Empirical equations for the dependence on I, , and molecular weight are reported for both H and T S.     

Isomeric composition of pyrazolines obtained from unsaturated carbonyl compounds and hydrazine

The ²-pyrazolines synthesized under the usual conditions from unsaturated aldehydes and hydrazine contain from 2 to 3% of the ¹-isomers and considerable amounts of the isomeric 3-alkyl-²-pyrazolines, which are formed as a consequence of migration of the double bond. Mixtures of the stereoisomeric ²-pyrazolines are formed from ,-dialkyl-substituted acroleins. Migration of the double bond does not occur in the condensation of unsaturated ketones with hydrazine, and ²-pyrazolines that are free from admixtures of the structural isomers are obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1225–1229, September, 1971.     

A Spectroscopic Study of Charge Transfer Complexes of Tetraphenylporphyrin

Summary. 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.