Paul Hemmes

Study of the lithium thiocyanate quadrupole by ultra-violet absorption spectroscopy

Abstract A spectroscopic method for studying quadrupole formation is described, and experimental results are presented for lithium thiocyanate in a tetrahydrofuran/hexane solvent system. From molar absorptivity equations and an equation by Fuoss and Kraus, a direct relationship is derived between the quadrupole formation constant, KQ, and the dielectric constant of the medium. Experimental results are consistent with the equation and allow an estimate of the distance between lithium and thiocyanate in the ion pair.

Association of optically active ions III: diastereomeric ion pair formation in histidine-glutamic acid mixtures

Abstract Conductometric titrations of equimolar mixtures of L-glutamic acid and L-histidine indicate that these species interact more strongly than L-glutamic acid with D-histidine in dilute solution. The presence of ion pairs is confirmed by the UV spectrum of these solutions. No such stereospecific interactions were found between L-glutamic acid and L-lysine or L-ornithine. The conductometric titration curves of these compounds are identical with that of L-glutamic acid with the DL mixture of the basic amino acids.

A conductometric detection concentration jump study of the kinetics of association of nickel malonate in water-urea media

Abstract A stopped flow study of the kinetics of association of nickel malonate in water-urea has been made. A commercial stopped flow-T-jump instrument was modified for this purpose. Up until 3M urea the rate constants for association depend only upon the solvent dielectric constants. Above 3M, urea enters the first coordinative sphere of nickel (II) and alters the rate. The effect of water activity changes is found to be negligible compared to the changes produced by the variation in dielectric constant.

The Mechanism of Sound Absorption in Solutions of Nucleotides and Nucleosides

The various mechanisms which can lead to concentration independent relaxation frequencies are discussed. Results are presented of base stacking studies of 6-methylpurine in water urea. It is found that 7M urea does not totally eliminate stacking. The major effect of urea is to decrease the rate of formation of stacks. The most probable mechanism for the concentration independent relaxation at low frequencies in nucleotides is shown to be an anion desolvation.

Estimation of the Ratio of Solvent Separated to Contact ion Pairs by High Field Conductivity Measurements

High field conductimetric measurements of the ratio of contact to solvent separated ion pairs have been made on the system ZnSO4 in methanol (K = 5.8 × 104). The method used has quite general applicability for such determination and is one of the few such generally useful methods.

Errors in the electric field jump evaluation of the rate constant for weak acid ionization in aqueous solution

Abstract The experimental evaluation of the rate constant for weak acid ionization in aqueous solution by electric field jump methods is subject to very large errors when pKa for the acid becomes about 6 or greater. For stronger acids the error becomes equal to or less than the experimental precision. It is therefore recommended that for acids with pKa 6 or greater the rate constant for ionization be evaluated from the rate constant for ion combination and the equilibrium constant.

The Association of Optically Active Ions; Ultrasonic Investigation of the Association of Bis and Tris (Orthophenanthroline) Zinc (11) d-Camphorsulfonate

Pfeiffer and Quehl1,2 discovered that the optical rotation of a solution of zinc d-camphorsulfonate vas altered by the addition of three moles of 1,10 phenanthroline. This optical anomaly and similar systems have been designated the Pfeiffer effect. In a further study, Pfeiffer and Nakatsuka3 showed that when racemic Ni (phen)3 SO4 was added to a solution of ammonium d-camphorsulfonate an instantaneous” change of optical rotation was observed which slowly changed to give an equilibrium rotation significantly different from that of the anion alone. This behavior is seemingly similar to the optical absorbance studies by Posey and Taube4 on the system Co (NH3)5 (H2O)+3 + SO 4 -2 . In this system there is an “instantaneous” change in absorbance when the ions are mixed followed by a slow change of absorbance. The mechanism for this latter reaction is the rapid formation of an outer sphere complex, the ion pair Co(NH3)5 (H2O) SO 4 + , followed by replacement of coordinated water by SO4 –2 to form the inner sphere complex. This multistep mechanism of ionic association has been shown by Eigen to have considerable generality5. In view of this mechanism the postulated mechanism for Pfeiffer activity (between unlike charged ions) is as follows.