Structural,Spectroscopic and Thermal Analysis of Cocrystals of Carbamazepine and Piracetam with Hydroquinone

Abstract  

Cocrystals of two important active pharmaceutical ingredients, carbamazepine and piracetam, with hydroquinone are reported. Cocrystal formation between the selected APIs and hydroquinone is investigated with the aid of solid-state grinding methods. Both the crystal structures belong to the triclinic, P [`1]P bar{1} space group, with the cocrystal involving carbamazepine and hydroquinone having the unit cell parameters a = 6.9725 (14) ?, b = 8.8175 (18) ?, c = 15.083 (3) ?, α = 106.96 (3)°, β = 92.16 (3)°, γ = 103.23 (3)°, V = 858.0 (4) ?³ and Z = 2; and the cocrystal involving piracetam and hydroquinone has the unit cell parameters a = 6.4909 (13) ?, b = 6.5410 (13) ?, c = 11.612 (2) ?, α = 103.92 (3)°, β = 104.53 (3)°, γ = 91.06 (3)°, V = 461.59 (18) ?³ and Z = 2. Analysis of the cocrystals revealed that they are sustained by an alcohol–carboxamide heterosynthon. In addition, the cocrystal of carbamazepine and hydroquinone features an amide–alcohol heterosynthon and an alcohol–alcohol homosynthon. The cocrystal of piracetam and hydroquinone features an amide–amide dimer synthon. Cocrystal formation was evidenced from the shifts in the vibrational frequencies corresponding to the functional groups present on the cocrystal components.     

Heavier alkali-metal monosulfides (KS, RbS, CsS, and FrS) and their cations

The heavier alkali-metal monosulfides (KS, RbS, CsS, and FrS) have been studied by high-level ab initio calculations. The RCCSD(T) method has been employed, combined with large flexible valence basis sets. All-electron basis sets are used for potassium and sulfur, with effective core potentials being used for the other metals, describing the core electrons. Potential-energy curves are calculated for the lowest two neutral and cationic states: all neutral monosulfide species have a (2)Pi ground state, in contrast with the alkali-metal monoxide species, which undergo a change in the electronic ground state from (2)Pi to (2)Sigma(+) as the group is descended. In the cases of KS, RbS, and CsS, spin-orbit curves are also calculated. We also calculate potential-energy curves for the lowest (3)Sigma(-) and (3)Pi states of the cations. From the potential-energy curves, spectroscopic constants are derived, and for KS the spectroscopic results are compared to experimental spectroscopic values. Ionization energies, dissociation energies, and heats of formation are also calculated; for KS, we explore the effects of relativity and basis set extrapolation on these values.     

On a problem of heat conduction with time-dependent boundary conditions

Zusammenfassung Das folgende Wärmeleitungsproblem wird analytisch behandelt. Auf dem Mantel und den Deckflächen eines Kreiszylinders sei einezeitlich veränderliche Temperaturverteilung und ausserdem die Temperatur einer Kurve zur Zeitt=0 gegeben. Gesucht ist die Innentemperatur für alle Zeiten. Die verwendete Separationsmethode kann auch auf andere Randwertprobleme angewendet werden.

---

---

The author wishes to thank the Corporation for permission to publish this paper.     

Novel behavior of bond-centered muonium in heavily doped n-type silicon: Curie-like spin susceptibility and charge screening

Bond-centered muonium ( Mu(0)(BC)) has been observed in very heavily doped n-type Si:P. It exhibits a Curie-like electronic spin susceptibility which leads to a giant negative shift in the muon spin precession frequency. At high dopant levels, the Mu(0)(BC) hyperfine parameters, deduced from a model involving spin exchange with free carriers, are significantly reduced from those in intrinsic Si. This indicates that the spin density distribution for Mu(0)(BC) in metallic Si:P is altered significantly by charge screening effects, likely a general phenomenon for deep impurities in materials with high carrier concentrations.     

Finite element error estimates for non-linear elliptic equations of monotone type

Summary In this paper we shall consider the application of the finite element method to a class of second order elliptic boundary value problems of divergence form and with gradient nonlinearity in the principal coefficient, and the derivation of error estimates for the finite element approximations. Such problems arise in many practical situations — for example, in shock-free airfoil design, seepage through coarse grained porous media, and in some glaciological problems. By making use of certain properties of the nonlinear coefficients, we shall demonstrate that the variational formulations associated with these boundary value problems are well-posed. We shall also prove that the abstract operators accompanying such problems satisfy certain continuity and monotonicity inequalities. With the aid of these inequalities and some standard results from approximation theory, we show how one may derive error estimates for the finite element approximations in the energy norm.     

Spin dynamics in conducting polymers studied by μSR

We report studies of spin dynamics in the conducting polymers polyaniline and polypyrrole using both μ⁺SR and μ^-SR techniques. These measurements reveal characteristic field dependences and cutoff frequencies for the muon spin relaxation which can be related to the spin diffusion process. Clear evidence is seen for increased spin localisation at low temperatures where a crossover occurs from two or three dimensional spin diffusion to a one dimensional diffusion regime. This revised version was published online in August 2006 with corrections to the Cover Date.