Buffers for the physiological pH range: Thermodynamic constants of substituted aminopropanesulfonic acids from 5 to 55°C

ThepK ₂ values for 3-[(l,l-Dimethyl-2-hydroxymethyl)amino]-2-hydroxypropanesulfonic acid (AMPSO), and 3-[N,N-Bis(-hydroxyethyl)amino]-2-hydroxypropanesulfonic acid (DIPSO) have been determined at 12 temperatures over the range 5 to 55‡C by measurements of the emf of cells without liquid junction containing hydrogen and silver-silver chloride electrodes. The values of pK ₂ for AMPSO and DIPSO were found to be 9.138 and 7.576, respectively, at 25‡C. The thermodynamic quantities, δG‡, δH‡, δS‡, and δC _p ^‡ were calculated from the change of the equilibrium constants with temperature. These buffer substances are useful as secondary pH standards in the physiological region of pH 7 to 9. Camille and Henry Dreyfus Fellow, 1994–1996.     

Voltammetry as a Virtual Potentiometric Sensor in Modeling of a Metal‐Ligand System and Refinement of Stability Constants. Part 1. Polarographic and Glass Electrode Potentiometric Study of a Dynamic Cd‐Glycine System

A mathematical conversion of data coming from nonequilibrium and dynamic voltammetric techniques (a direct current sampled (DC) and differential pulse (DP) polarography) into potentiometric sensor type of data is described and tested on a dynamic metal‐ligand system. A combined experiment involving DCP, DPP and glass electrode potentiometry (GEP) was performed on a single solution sample containing a fixed [L_T] : [M_T] ratio (acid‐base titration). Dedicated potentiometric software ESTA was successfully employed in the refinement operations performed on virtual potentiometric (VP) data obtained from DC and DP polarography. It was possible to refine stability constants either separately, from VP‐DC or VP‐DP, or simultaneously from any combination of VP‐DC, VP‐DP and GEP. The concept of VP‐DC or VP‐DP is reported for the first time and numerous documented and possible advantages are discussed. The proposed procedure can be easily utilized also by nonelectrochemists who are interested in, e.g., the ligand design strategies.     

Molybdenum-95 nuclear magnetic resonance of a series of phosphine and phosphite substituted molybdenum carbonyls Mo(CO)6−n (L) n (n=1, 2, 3, 4, 5)

Molybdenum-95 NMR spectra of a series of phosphine and phosphite substituted molybdenum carbonyls Mo(CO)_6-n L _n [L=P(OCH₃)₃ n=1, 2, 3, 4, 5,L=P(OC₂H₅)₃ n=1, 2, 3,L=P(C₆H₅)₃ n=1] including isomers (cis,trans,fac,mer) are reported, A large range of chemical shifts is found for the title compounds. The coupling constants¹ J(⁹⁵Mo-³¹P) are derived either from⁹⁵Mo-NMR spectra or³¹P-NMR spectra. Syntheses of the measured compounds were performed by thermal or photochemical ligand substitution.

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Molybdän-95 NMR einer Reihe von Phosphin- und Phosphit-substituierten Molybdäncarbonylen Mo(CO)_6–n(L) _n (n=1, 2, 3, 4, 5)

Zusammenfassung Es werden die⁹⁵Mo-NMR-Spektren der im Titel genannten Verbindungen mitL=P(OCH₃)₃ n=1–5,L=P(OC₂H₅)₃ n=1–3 undL=P(C₆H₅)₃ n=1, einschließlich von Isomeren (cis, trans, fac, mer) angegeben. Für die chemischen Verschiebungen wurde ein sehr weiter Bereich beobachtet. Die Kopplungskonstanten¹ J(⁹⁵Mo-³¹P) wurden entweder von den⁹⁵Mo- oder³¹P-NMR-Spektren ermittelt. Die Synthese der Verbindungen erfolgte mittels thermischem oder photochemischem Ligandenaustausch.

     

Hyperfine interactions in aqueous solution of Cr3+: an ab initio molecular dynamics study

We performed an ab initio molecular dynamics simulation of the paramagnetic transition metal ion Cr³⁺ in aqueous solution. Isotropic hyperfine coupling constants between the electron spin of the chromium ion and nuclear spins of all water molecules have been determined for instantaneous snapshots extracted from the trajectory. The coupling constant of first sphere oxygen, A _iso(¹⁷O_I)=1.9±0.3 MHz, is independent on Cr–O_I distance but increases with the tilt angle for the water molecule approaching 180°. First sphere hydrogen spins have A _iso(¹ H_I)=2.1±0.2 MHz which decreases with increasing tilt angle and shows a Cr–H_I distance dependence. The hyperfine coupling constants for second sphere ¹⁷O is negative and an order of magnitude smaller (−0.20±0.02 MHz) compared to first sphere.     

Thermodynamics of mixtures of amines with n-alkanes and 1-alkanols

The LFAS (Lattice-Fluid Associated Solution) model, which has been applied to alkanol + alkane and to alkanol + alkanol mixtures is now extended to mixtures consisting of one self-associated and one active or weakly self-associated component. The types of association complexes considered are A_nB_m and A_nB with a single A-B bond each. The model is subsequently applied to binary alkanol + amine mixtures with an emphasis on vapor-liquid equilibria. Self-association constants for n-alkyl amines and dialkyl amines are presented along with the pure component lattice-fluid scaling constants. These parameters are used for correlating pure component data on vapor pressures, heats of vaporization, and orthobaric densities as well as mixing properties of amine + alkane mixtures.Communicated at the Festsymposium celebrating Dr. Henry V. Kehiaian's 60^th birthday, Clermont-Ferrand, France, 17–18 May 1990.     

Optical constants and integrated intensities of liquid hexafluorobenzene between 4000 and 250 cm at 25 °C

The optical constants (real and imaginary refractive indices) of hexafluorobenzene were determined at 25 °C via transmission measurements. Experimental absorbance spectra measured on a Nicolet Impact 410 FTIR were converted to imaginary refractive indices using methods described in the literature. The real refractive indices were obtained by Kramers–Kronig transformation of the imaginary refractive indices. From the complex refractive indices, the molar absorption coefficient (E_m) and complex molar polarizability spectra were calculated. The integrated intensities for the E_1u fundamentals were obtained from the areas under the bands in the spectrum. These integrated intensities are compared to those for benzene and benzene-d₆ in the literature.     

Unexpected formation of the copper(II) dinuclear mixed-ligand species in the ternary system of N,N,N′,N″,N″-pentamethyldiethylenetriamine with methionine- or histidinehydroxamic acids in aqueous solution

Equilibrium studies of the mixed-ligand complexes of the copper(II) ion with pentamethyldiethylenetriamine (N,N,N′,N″,N″-pentamethyl-[bis(2-aminoethyl)amine], Me₅dien) as a primary ligand and methioninehydroxamic acid (2-amino-4-(methylthio)butanehydroxamic acid, Metha) or histidinehydroxamic acid (2-amino-3-(4′-imidazolyl)propanehydroxamicacid, Hisha) as a secondary ligand L were performed by potentiometric titration, UV–Vis and EPR spectroscopy. The results show that in these ternary systems the dinuclear [Cu₂(Me₅dien)L₂H₋₁]⁺ mixed-ligand species is formed as a predominant one in the basic solution. The monouclear [Cu(Me₅dien)L]⁺ species is formed in low concentration. Our spectroscopic results indicate that the geometry of these mixed-ligand five-coordinate complexes is strongly distorted towards trigonal-bipyramidal.     

Analysis of Equilibria in the Extraction of Cesium Nitrate by Calix[4]arene-bis(t-Octylbenzo- Crown-6) in 1,2-Dichloroethane

The extraction of CsNO₃ by the highly lipophilic calixarene-crown ether calix[4]arene-bis(t-octylbenzo-crown-6) (CABOBC6) in 1,2-dichloroethane (1,2-DCE) at 25 °C has been shown to be consistent with the formation of both 1 : 1 and 2 : 1 metal : ligand species. Variation of the aqueous-phase CsNO concentration up to 1.0 M and variation of the organic-phase calixarene concentration up to 0.10M was modeled by the program SXLSQI. Formation of the organic-phase species CsBNO₃ (B = calixarene) was confirmed as well as the organic-phase dissociation products CsB⁺ and NO₃ ^-. Good evidence for the 2 : 1 metal : ligand organic-phase species Cs₂B(NO₃)₂ was also found, although the dissociation of nitrate from this complex was not observed. Binding of the second Cs⁺ cation by the ligand is approximately two orders of magnitude weaker than binding of the first Cs⁺ cation. The logarithm of the apparent partition ratio (log P_B) of the calixarene between water and 1,2-DCE was found by ¹H-NMR techniques to be > 5.1.     

The use of a lyotropic liquid-crystalline medium and residual dipolar coupling constants for determination of the spatial structure of thiacalix[4]arenes in solutions

The possibility of using an approach for the elucidation of the spatial structure of functionalized thiacalix[4]arenes based on the determination the residual dipolar coupling constants between the ¹H and ¹³C nuclei separated by one chemical bond (¹ D _CH) in lyotropic liquid-crystalline media (poly--benzyl-L-glutamate and CDCl₃) is demonstrated for the first time. This approach was used to distinguish between the cone and 1,3-alternate conformations of 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis(2-oxopropyloxy)-2,8,14,20-tetrathiacalix[4]arene. The results were confirmed by the data from 2D NMR (¹H—¹H) NOESY experiments for these compounds in an isotropic solvent (CDCl₃).     

Chromoionophores with Chromophores as Integral Part(s) of the Macrocycle in Crown Ethers

Several new types of ionizable chromoionophores have been synthesized. Their reactions with metal cations have been studied by spectroscopic methods. Preferential complexation of lithium ions was found for many of these reagents.