Thermal and dissolution kinetics of ampicillin drug and capsules

This work aims to compare the thermal decomposition and dissolution kinetics of ampicillin drug and products A, B and C. The thermal decomposition reaction rate constants (kT) were determined by isothermal thermogravimetric method using the classical Arrhenius equations. The dissolution profiles were obtained using USP 23 method and rate constants (kD) were determined by Kitazawa equation. The results showed correlation between kT and kD can be used in the study of preformulation of drugs and also as a parameter in the studies of pharmaceutical equivalence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrogen bonding abilities and self-association of thiazolidin-and imidazolidin-2-ones and 2-selenones

The hydrogen bonding abilities of iV-methylimidazolidin-2-one and -2-selone and thiazolidin-2-one and -2-selenone have been studied by ir spectroscopy at 25° in carbon tetrachloride solutions, using dimethyl sulphoxide and 4-chlorophenol as proton acceptor (K_A) and proton donor (K_B), respectively. The results are compared with those previously reported for N-methylimidazolidine-2-thione and thiazolidine-2-thione. The K_A values increase in each series in the order O < S < Se and Kg in the reverse order. The and K_B values are discussed in terms of the substituent in ring. The self-association constants (K_D) are dependent on both K_A and K_B, although K_A seems to be much more important.     

Rotational analysis of the v7,v11 (a′,a″) pair of bands of the infrared spectrum of the deuterium substituted propynal molecule C2H-CDO

The mid-infrared spectrum of the v₇,v₁₁ (a′,a″) pair of bands of the deuterium substituted propynal molecule C₂H-CDO was recorded at a resolution of about 0.08 cm⁻¹. An analysis of the pair of bands was completed using the method of simulation of the observed bands with synthetic spectra taking into account the effects of second order Coriolis interactions between the energy levels of the two bands. Best fit values for the changes in the rotational constants (A″ − A′), (B″ − B′) and (C″ − C′), the second order Coriolis constant ζ_7,11 and the δ_7,11 = v₁₁ − v₇ constant have been derived.     

Diffusion in a multicomponent inhomogeneous system with moving boundaries. I. Swelling at constant volume

A medium B contains a substance C which can diffuse. This mixture of B and C is brought into contact with a medium A which itself can diffuse into B. Now C diffuses through a swollen layer of A and B into A. The present study examines mathematically this process which, among other things, could serve as a model for migration in a system consisting of plastic packaging (polymer plus an additive) and the contents of the package. It is assumed that medium A (contents) with a constant diffusion coefficient diffuses into medium B (plastics) and that the diffusion of substance C (additive) in the pure B and into A can also be described by constant diffusion coefficients. The diffusion coefficient of substance C in the zone of mixed A and B is taken to be dependent on the concentration of A in B. Partition coefficients are assumed to exist at all interfaces between the media. The general equations of this coupled diffusion process are solved explicitly. The solutions are discussed and illustrated by several special cases. Furthermore, the total amount of C in A is calculated as a function of the diffusion coefficients of the partition coefficients of time, and of the concentration of A in B.     

Influence of the force interaction on accumulation of macroscopic correlations in elementary reaction <Emphasis Type="Italic">A</Emphasis> + <Emphasis Type="Italic">B</Emphasis> → <Emphasis Type="Italic">C</Emphasis>

The applicability of the Encounter Theory (ET) (the prototype of the Collision Theory) concepts for widely occurring diffusion assisted irreversible bulk reaction A + B →C (for example, radical reaction) in dilute solutions taking account of initial microscopic correlations and force interactions between reactants has been treated theoretically with modern many-particle method for the derivation of non-Markovian binary kinetic equations. The method shows that taking into consideration initial correlations and force interactions leads to the redefinition of the Markovian rate constant only in the expressions derived earlier. Thus, just as in the reaction A + A →C and the reaction A + B →C neglecting force and initial correlations, the Modified Encounter Theory (MET), when reduced to equations of a Regular Form, both extends the time applicability range of ET homogeneous rate equation, and yields the inhomogeneous equation of the Generalized Encounter Theory (GET). It reveals macroscopic correlations induced by the encounters in the reservoir of free walks in full agreement with physical considerations. Time accumulation of macroscopic correlations obeys the same time law as in the previously considered case neglecting force interactions. Just the rate of the process will change, according to traditional redefinition of the steady-state constant of the reaction.     

207Pb-NMR-Untersuchungen an Bleiorganylen

The high-resolution²⁰⁷Pb magnetic resonance spectra ofR _4–n PbX _n (R=Methyl, Ethyl;X=h₁-Cyclopentadienyl, Chloride;n=1, 2) have been studied at 16.72Mc. The²⁰⁷Pb- ·· -¹H spin-spin coupling constants for the molecules described have been obtained by analysis of the first order NMR-patterns as A_xB_yM and A_xB_yC_zM respectively. The experimental spectra have been verified by a computer simulation. The chemical shifts and coupling constants of the lead organyls investigated show similar dependences on moleculare structure as well as number and species of the substituents like analogous organotin compounds.

     

Contributions to the spectroscopic–kinetic analysis of linear reaction systems: Systems with three linearly independent reactions using the concept of parallel projection

Linear reaction systems consist by definition of first-order reaction steps. Linearly independent reactions are independent of reaction order. Each reaction mechanism consists of a distinct number (s) of linearly independent reaction steps. Thus, the mechanism ABCD can be described by three linearly independent reactions as it is also true for A→B→C→D (s=3). In the following, a procedure for the analysis of linear reaction systems consisting of three linearly independent reaction steps is described which is based on absorbance (A) as well as absorbance difference quotient (ADQ) diagrams (two graphs of the ‘Mauser diagrams') and the concept of parallel projection. In this way it is possible to determine the ratio of eigenvalues describing the reaction mechanism. Furthermore, the reaction system (s=3) can be reduced to a system which is described only by two linearly independent concentration variables (s=2). The kinetic equations of evaluation are simplified by the concept of parallel projection. This can be helpful, for example, when one independent reaction step shows poor spectroscopic properties. The method can be extended to the analysis of quasilinear photoreactions. The method is demonstrated using a practical example (A′→B′, C′→D′, E′→F′).     

Yttrium(III) bonding to organic ligands: A comparison with the lanthanoid(III) cations

Summary The yttrium(III) bonding to organic substrates (oximes, -diketonates and (poly)amino-(poly)carboxylates) has been compared with that of the lanthanoid(III) cations. The complexation constants of Y³⁺ with the examined organic ligands are similar to those of some cations of the first half of the lanthanoid series, in contrast with the fact that the Y³⁺ ionic dimensions are similar to those of Ho³⁺. This has been explained by correlating the formation constants of the Y³⁺ and the lanthanoids(III) complexes by the equation logK ₁=C _AC_B+E _AE_B, where the parametersC andE indicate the tendency of each Lewis acidA and Lewis baseB to undergo covalent or ionic bonding, and where the ratioH=E/C indicates the charge control on the bond formation tendency of each speciesA orB. The results are commented in terms of the utility of Y³⁺ in assisting organic reactions.

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Bindung von Yttrium(III) an organische Liganden: Vergleich mit Lanthanoid(III)-Kationen

Zusammenfassung Es wurde die Bindung von Yttrium(III) an organische Substanzen [Oxime, -Diketonate und (Poly)Amino(poly)carboxylate] im Vergleich mit Lanthanoid(III)-Kationen behandelt. Die Komplexierungskonstanten von Y³⁺ sind ähnlich denen einiger Kationen der ersten Hälfte der Lanthanoidenserie; dies steht im Gegensatz zur Tatsache, daß die Dimensionen des Y³⁺-Ions denen des Ho³⁺ entsprechen. Die Erklärung wurde mittels der für die Bildungskonstanten der Y³⁺- und Lanthanoid(III)-Komplexe gültigen Gleichung logK ₁=C _AC_B+E _AE_B gefunden, wobeiC undE Parameter sind, die die Tendenz der Lewis-SäurenA und der Lewis-BasenB zum Eingehen von kovalenten oder ionischen Bindungen charakterisieren und wo das VerhältnisH=E/C den Steuerungseffekt der Ladung auf die Bindungstendenz der SpeziesA oderB beschreibt. Die Ergebnisse werden im Hinblick auf den Nutzen von Y³⁺ zur Unterstützung organischer Reaktionen diskutiert.

     

The microwave spectrum of 2, 5-dihydropyrrole

The microwave spectrum of 2, 5-dihydropyrrole has been measured up to J = 25 in both the ground and first vibrational excited states. The rotational constants for ν = 0 are A = 7650.61 ± 0.04 MHz, B = 7597.38 ± 0.04 MHz, C = 4085.63 ± 0.04 MHz and for ν = 1 the constants are A = 7650.65 ± 0.04 MHz, B = 7597.12 ± 0.04 MHz and C = 4085.71 ± 0.04 MHz. Centrifugal distortion corrections are included.     

Istamycin aminoglycosides profiling and their characterization in Streptomyces tenjimariensis ATCC 31603 culture using high‐performance liquid chromatography with tandem mass spectrometry

A high‐performance liquid chromatography with electrospray ionization ion trap tandem mass spectrometry method was developed and validated for the robust profiling and characterization of biosynthetic congeners in the 2‐deoxy‐aminocyclitol istamycin pathway, from the fermentation broth of Streptomyces tenjimariensis ATCC 31603. Gradient elution on an Acquity CSH C₁₈ column was performed with a gradient of 5 mM aqueous pentafluoropropionic acid and 50% acetonitrile. Sixteen natural istamycin congeners were profiled and quantified in descending order; istamycin A, istamycin B, istamycin A₀, istamycin B₀, istamycin B₁, istamycin A₁, istamycin C, istamycin A₂, istamycin C₁, istamycin C₀, istamycin X₀, istamycin A₃, istamycin Y₀, istamycin B₃, and istamycin FU‐10 plus istamycin AP. In addition, a total of five sets of 1‐ or 3‐epimeric pairs were chromatographically separated using a macrocyclic glycopeptide‐bonded chiral column. The lower limit of quantification of istamycin‐A present in S. tenjimariensis fermentation was estimated to be 2.2 ng/mL. The simultaneous identification of a wide range of 2‐deoxy‐aminocyclitol‐type istamycin profiles from bacterial fermentation was determined for the first time by employing high‐performance liquid chromatography with tandem mass spectrometry analysis and the separation of istamycin epimers.     

Surface Tension and the Solubility of Polymers and Biopolymers: The Role of Polar and Apolar Interfacial Free Energies

Surface tension data can be used for estimating the solubility of polymers in liquids. By determining the apolar and the polar components of the surface tension of polymers and of solvents, the attractive free energy, δG ₁₂₁, of a polymer (1) in a given solvent (2) can be established. By also taking into account the contactable surface area of two polymer molecules, immersed in a liquid, δG ₁₂₁ can be expressed in units of kT. Solubility then is favored when -1.5 kT < δG ₁₂₁ < 0 for apolar systems, and when -1.5 kT < δG ₁₂₁ for polar systems. In polar solvents, hydrogen bonding can often increase δG ₁₂₁ from <-1.5 kT to > + 1.5 kT. Positive values are frequently attained and this strongly shifts the behavior from insolubility to solubility. A number of proteins exemplify this behavior.     

Acid–base complexes of polymers

The physical interactions of polymers with neighboring molecules are determined by only two kinds of interactions: London dispersion forces and Lewis acid–base interactions. These two kinds of attractive energies (together with certain steric restrictions) determine solubility, solvent retention, plasticizer action, wettability, adsorption, adhesion, reinforcement, crystallinity, and mechanical properties. The London dispersion force interaction energies of polymers have been quantified by the dispersion force contribution to cohesive energy density (δ²_d) and the dispersion force contribution to surface energy (δ^d). The Lewis acid–base interactions, often referred to as “polar” interactions, can be best quantified by Drago's C_A and E_A constants for acid sites and C_B and E_B constants for basic sites. In this article infrared spectral shifts are featured as a method of determining enthalpies of acid–base interaction, and the C and E constants for polymers, plasticizers, and solvents. Examples are given where acid–base complexation of polymers with solvents dominate solubility and swelling phenomena. Enthalpies of acid–base complexation in polymer blends are determined from spectral shifts.     

Cyclic acetal-photosensitized polymerization. VIII. Photopolymerizations of diallylidene pentaerythritol and its derivatives

The photopolymerization of diallylidene pentaerythritol (DAPE) was carried out in benzene at 40°C without the use of the usual initiator. DAPE was polymerized with the ester radical generated from DAPE by photoirradiation. To investigate the effect of dimethyl groups at the α,α- or β,β-positions of vinyl groups on the polymerization, photopolymerizations of dimethallylidene pentaerythritol (DMPE) and dicrotylidene pentaerythritol (DCPE) were carried out and kinetically studied from the standpoint of the degradative chain transfer by the allylidene group and cyclization by two double bonds. The results can be summarized as follows: (1) The relation between the rate of polymerization, R_p, and the monomer concentration [M] can be expressed as [M]/R_p = (A[M] + B)/(2[M] + C), where A, B, and C are constants. (2) The ratios of the rate constant of unimolecular cyclization to the total rate constants of bimolecular propagation and the chain transfer of uncyclized radical were estimated as 1.12, 0.26, and 0.16 mole dm^?3 for DAPE, DMPE, and DCPE, respectively; the cyclizations hardly took place. (3) The rate of polymerization and the molecular weight of the polymer were small because of the degradative chain transfer by the allylidene group.     

The microwave spectrum,structure and centrifugal distortion constants of 2-chloroacrylonitrile

The microwave spectrum of 2-chloroacrylonitrile has been studied in the 26.5–40 GHz region. A total of 99 a- and b-type rotational transitions have been measured and assigned for CH₂ =C³⁵Cl(CN),yielding values for the rotational constants (in MHz): A = 6973.27, B = 3148.16, C = 2165.95. For CH₂=C³⁷Cl(CN) a total of 53 transitions have been measured and assigned and the rotational constants obtained are (in MHz): A = 6909.35, B = 3081.17, C = 2127.98. The distortion effects have also been studied and the quartic distortion constants have been evaluated. From the observed hyperfine structure, the chlorine nuclear quadrupole coupling constants have been obtained. The structure of vinyl cyanide and vinyl chloride can be transferred to account remarkably well for the observed rotational constants.     

Configuration interaction calculations on the propane radical cation,C3H 8 +

Summary Proton isotropic hyperfine coupling constants have been calculated for three low-energy nuclear conformations on the ground state potential surface of the propane cation, using a multireference singles and doubles configuration interaction (MR-SDCI) wave function. The lowest point found on the potential surface hadC _2v symmetry and the electronic wave function at this point had²B₂ symmetry. At this point, the largest isotropic coupling constant is calculated to be 88.6 G, which is in fair agreement with the experimental value of 98 G obtained in an SF₆ matrix at 4 K. No support is found for a long-bond ground state of lower symmetry thanC _2v . AnotherC _2v minimum on the ground state potential energy surface was found at which the wave function had² B ₁ symmetry. At this point, two large coupling constants of 198 G and 35 G were calculated. AC _2v stationary point was also found on the ground state potential surface at which the wave function had² A ₁ symmetry. At this point, couplings of 86 G and 25 G were obtained. None of these agree closely with the other experimental result of couplings at both 100–110 G and 50–52.5 G which was obtained in freon matrices. It is suggested that the latter spectra might correspond to a dynamical average of two distorted² A' states inC _s symmetry.     

Microwave spectrum and structure of equatorial chlorocyclohexane

The microwave rotational spectra of C₆H₁₁³⁵Cl and C₆H₁₁³⁷Cl have been measured. The rotational constants A, B and C and quadrupole coupling constants were determined. Some structural information was obtained.     

13,13a‐Di­hydro‐13‐methoxy‐9‐methyl‐1‐benzo­pyrano­[4,3‐i]­dinaphtho­[2,1‐c;1′,2′‐f]‐2,8‐dioxa­bicyclo­[3.3.1]­nonane

The crystal structure of the title compound, C₃₂H₂₄O₄, contains three fused di­hydro­pyran rings (A, B and C); ring A is fused with a benzene ring while the other two rings, B and C, are fused with naphthalene rings. Ring A adopts a half‐chair conformation with an equatorial methoxy group, whereas ring B assumes a distorted half‐chair conformation, the A/B ring junction being trans. Ring C adopts a distorted half‐boat conformation and is nearly orthogonal to ring B. Ring C is inclined to the best plane of ring A at an angle of 112.1 (1)°.     

Physicochemical foundations of synthesis of new ferromagnets from chalcopyrites A<Superscript>II</Superscript>B<Superscript>IV</Superscript>C<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>

The results of studying phase equilibria of ternary A^IIB^IVC^V systems have been reported. Physicochemical foundations have been developed for the synthesis of new ferromagnets with Curie temperatures above room temperature structurally compatible with basic semiconducting materials. Methods of synthesis and physicochemical properties of manganese-doped A^IIB^IVC₂^V ferromagnets have been described. The results of theoretical simulation of magnetic properties have been considered and basic approaches to the explanation of the emergence of ferromagnetism in A^IIB^IVC₂^V doped with 3d metals have been surveyed. The most promising ways to produce and study dilute magnetic semiconductors as spintronics materials have been presented.     

Anion radicals of [60]fullerenes. An EPR study

Photochemically induced electron transfer in homogeneous systems (using triethylamine donor) and heterogeneous systems (using photoexcited TiO₂ suspension) was applied in in situ reduction of [60]fullerene. The anion radicals generated were characterized by means of EPR and VIS/near-IR spectroscopy. Narrow EPR lines were found. Radical A with g_A=2.0000 and peak-to-peak width, pp_A=0.09mT was observed as the primary product; followed by its consecutive product B with g_B=2.0006, pp_B=0.04mT, and in some cases product C with g_C=2.0009 and pp_c<0.1 mT. Radical A was assigned to [60]fullerene mono-anion, also characterized by a near-IR band at 1077 nm. B is presumably di-anion or a dimeric form of mono-anion. Identical results were also obtained using cathodic in situ reduction. Applying these generation techniques to [60]fullerene derivatives produced narrow EPR lines analogous to those described for pristine [60]fullerene. This was the case not only in organic solvents, but also in aqueous solutions. The results obtained present a contrast with the original ex situ EPR investigations describing [60]fullerene mono-anion with wide lines. According to the results presented here, the narrow and wide EPR lines do not represent contradictory phenomena, but are an integral part of the relatively complicated manifestations of various fullerene states and both will have to be seriously considered in the future.     

Characterization of surface thermodynamic properties of p-toluene sulfonate-doped polypyrrole by inverse gas chromatography

Summary p-Toluene sulfonate-doped polypyrrole (PPyTos) powder has been characterized by inverse gas chromatography at various temperatures. We have used apolar n-alkanes and polar probes of differing acidity and basicity to interrogate the London dispersive and Lewis acid-base properties of PPyTos, respectively. We have found that the London component of the surface energy (γs^d) is about 90 mJ · m⁻² at 25°C and the acid-base contribution to the free energy of adsorption (ΔG_a ^AB) for Lewis bases is higher than 8 kJ · mol⁻¹. These results show that PPyTos is a high energy material and is capable of very strong specific acid-base interactions. Lewis acidity is, however, dominant and is shown to increase with temperature. The determination of the heats of adsorption for tetrahydrofuran and ethyl acetate enabled us to determine Drago’s E_A, C_A, E_B and C_B parameters. Whilst E_A and C_A are similar to those published for chloride-doped polypyrrole and rank PPyTos as a hard acidic species, the E_B and C_B values suggest that PPyTos is a very soft Lewis base.