Some theoretical considerations in analytical chemistry : The influence of absolute concentration on the parameters of redox titrimetry

Redox reactions are classified into symmetrical, homogeneous and inhomogeneous reactions. Reaction deficiencies when expressed as concentrations are dependent on absolute reactant concentrations, but have been proved to be independent of dilution when expressed as ratios in symmetrical and homogeneous reactions. An expression relating change of reaction deficiency with dilution for inhomogeneous reactions has been derived ; dilution of the reactants very rapidly decreases the reaction deficiency.Expressions for potentials in terms of concentration ratios have been derived for homogeneous and symmetrical reactions and prove to be independent of dilution. For inhomogeneous reactions the absolute potential falls on dilution, although the relative potential change, e.g., from the midpoint of a titration, increases asymptotically to a maximum.New derivations of the equivalence point potential and of an expression for the quantitativeness, for symmetrical and homogeneous reactions confirm the classical expressions and demonstrate their independence of dilution. For inhomogeneous reactions, methods of calculation of quantitativeness and equivalence point potentials through reaction deficiencies are proposed. For such reactions, the equivalence point potential rises sharply with dilution, giving titration curves of increasing steepness. The dependence of mid-point potentials and relative change of potential during titration upon dilution are also examined.     

The equation of state of hard hyperspheres in four and five dimensions

The equation of state of hard hyperspheres in four and five dimensions is calculated from the value of the pair correlation function at contact, as determined by Monte Carlo simulations. These results are compared to equations of state obtained by molecular dynamics and theoretical approaches. In all cases the agreement is excellent.     

Micropatterning chemical oscillations: waves, autofocusing, and symmetry breaking

Arrays of chemical oscillators are micropatterned by Wet Stamping. The technique is used to demonstrate that chemical waves can be initiated and controlled in oscillatory systems and that such waves can give rise to phenomena not observed in excitable media. Interoscillator coupling and synchronization, kinetic autofocusing, and twist-symmetry breaking are a consequence of the dependence of the oscillation phase on the local concentrations of reagents and on systems' geometry. Conditions under which a generic oscillatory system would exhibit such behaviors are determined.     

The behavior of the form factor in two dimensions for linear polymers in different regimes

Off-lattice Monte Carlo simulations employing the PIVOT algorithm are used to generate ideal and excluded volume linear polymers in two dimensions. The form factor at small and large wave vectors is calculated from the resulting configurations and compared to the exact equation for ideal chains and to both scaling and renormalization group predictions for excluded volume chains. It is found that using the des Cloizeaux form for the distance distribution function in an analytic calculation of the form factor leads to close agreement with the Monte Carlo data and that simple expressions for both the small and large wave vector expansions reproduce the essential features of the form factor.     

Rapid synthesis of the N-methylwelwitindolinone skeleton

An efficient, convergent synthesis of the core bicyclo[4.3.1]decane ring system of welwitindolinones is described. Key steps in the synthesis include an intramolecular palladium-catalyzed enolate arylation reaction to create the desired bicyclic skeleton and a Curtius rearrangement to install the bridgehead isocyanate unit. [reaction: see text]