A novel crystal form of metacetamol: the first example of a hydrated form

We report the crystal structure and crystallization conditions of a first hydrated form of metacetamol (a hemihydrate), C₈H₉NO₂·0.5H₂O. It crystallizes from metacetamol‐saturated 1:1 (v/v) water–ethanol solutions in a monoclinic structure (space group P2₁/n) and contains eight metacetamol and four water molecules per unit cell. The conformations of the molecules are the same as in polymorph II of metacetamol, which ensures the formation of hydrogen‐bonded dimers and R₂²(16) ring motifs in its crystal structure similar to those in polymorph II. Unlike in form II, however, these dimers in the hemihydrate are connected through water molecules into infinite hydrogen‐bonded molecular chains. Different chains are linked to each other by metacetamol–water and metacetamol–metacetamol hydrogen bonds, the latter type being also present in polymorph I. The overall noncovalent network of the hemihydrate is well developed and several types of hydrogen bonds are responsible for its formation.     

Polymorphic form IV of olanzapine

2‐Methyl‐4‐(4‐methylpiperazin‐1‐yl)‐10H‐thieno[2,3‐b][1,5]benzodiazepine, C₁₇H₂₀N₄S, commonly known as olanzapine, is a psychotropic agent that belongs to the thienobenzodiazepine class of drugs. A new polymorph form IV was obtained upon attempted cocrystallization with nicotinamide in a 1:1 ratio from an ethyl acetate solution. Two butterfly‐like molecules form centrosymmetric dimers stabilized by weak C—H...π interactions between the 4‐methylpiperazin‐1‐yl fragment and the benzene/thiophene aromatic system. Form IV consists of a herringbone arrangement of dimers, whereas the previously reported form II has parallel dimers. Both crystal structures are sustained by an N—H...N hydrogen bond.     

Polytopal form and isomerism

A thesis is developed that accurate structural data for molecules in the solid state can be utilized to derive direct information about the geometric parameters for solution reaction mechanisms, This is specifically illustrated for intramolecular rearrangements but the basic approach should be applicable to bimolecular reactions. A dihedral angle criterion is employed to quantitatively assess shape parameters for polyhedra found in coordination compounds and cluster molecules. These data are expressed in reaction coordinate form whereby a real structure is related to two idealized polyhedra (a reaction path) or to three or more idealized polyhedra (a reaction cycle or chain). It is demonstrated through an analysis of structural data for five coordinate complexes that the Berry type of rearrangement is the lowest energy physical pathway for rearrangements in ML₅ molecules or ions. Solvents may alter the relative energies of ground and excited state forms but should not significantly alter the physical character of the rearrangement process unless the solvent strongly interacts with the molecules. This feature is discussed with respect to polytopal polymorphism in clusters, e.g., B₈H₈^2?.     

Micelle form and stability

Calculations of the elastic bending energy (E _bend) of several equilibrium forms of micelles belonging to a binary water-surfactant system (O/W) have been performed in a wide range of micelle volumes by using the surfactant parameter model proposed by Hyde (see ref.[4]). The micelle forms, differently from the vesicle forms, obey restrictive requirements concerning the structure of their bulk, so the micelle forms are, to a large extent, predictablea priori. Each form shows a distinctiveE _bend/micelle volume curve which depends on the value of the surfactant parameterP ₀ characteristic of the amphiphilic molecule in absence of external stresses. Transitions between different forms can occur —in principle — when and where two of these curves intersect each other.     

Another form of the transmission function

The transmission function describes the passage of the electric current from one point of an electric circuit to another. By now, this is also applied to molecules which are potential candidates for uses in the molecular electronics. We mean the modern branch of electronics which has a goal of reducing the sizes of its devices down to molecular ones and planning indeed to apply single molecules as conducting wires and functional components of microcircuits. For calculating the transmission function, some authors utilize the well-known idea of representing a molecule by a (molecular) graph, which allows them to apply for treating the latter also powerful methods of spectral graph theory. For instance, we refer to the paper by Fowler et al. (Chem Phys Lett. 465 2008) 142–146, where one such expression for this function is given. Our objective is to demonstrate that the same calculational result can be obtained using a different set of characteristic polynomials of graphs (which also slightly reduces a mathematical notation). Specifically, we apply one theorem of Kolmykov to the basic formula derived by these authors.     

The general form of pseudopotential operators

The general form of hermitean linear pseudopotential operators, which are independent of the virtual energies, is derived. A special case of this pseudopotential is the usually used one, ¦c>(– _c)<c¦. It is shown that any pseudopotential is of essentially non-local character. The significance of -dependency and non-hermiticity of pseudopotentials is discussed. The advantages of semiempirical model hamiltonians in comparison with exact pseudopotential hamiltonians are stressed.

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Zusammenfassung Die allgemeine Form hermitescher linearer Pseudopotentialoperatoren, die die virtuellen Orbitalenergien nicht enthalten, wird angegeben. Eine spezielle Form hiervon ist das üblicherweise verwendete Potential ¦c>(– _c). Es wird gezeigt, da\ jegliches Pseudopotential wesentlich nichtlokalen Charakter hat. Die Bedeutung von s-AbhÄngigkeit und Nicht-HermitezitÄt von Pseudopotentialen wird diskutiert. Der Vorzug von Modell-Hamiltonoperatoren gegenüber exakten Pseudo-Operatoren wird betont.

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Résumé Expression générale des opérateurs de pseudo-potentiel linéaires hermitiques, indépendants des énergies des orbitales virtuelles. Le pseudo-potentiel ordinairement utilisé ¦c>(– _c) en est un cas particulier. On montre que tout pseudo-potentiel a essentiellement un caractère non local. Discussion de la signification de la dépendance à et de la non-hermiticité des pseudo-potentiels. On souligne les avantages des hamiltoniens modèles semi-empiriques par rapport aux hamiltoniens de pseudo-potentiel exact.

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The pseudo-orbitals so defined are not normalized to unity.     

Photodecomposition of ketene to form methylene

Correlation curves for a least motion departure path of methylene in the photocomposition of ketene are interpreted in terms of least energy paths. It is concluded that the first excited triplet state of ketene can probably form ³CH₂(³B₂) and ¹CH₂(¹ A ₁) relatively rapidly and the first excited singlet state can give ³CH₂(³ B ₂) easily in a near least motion path. However, the formation of ¹CH₂(¹ A ₁) from the first excited singlet state of ketene by a near-least motion path appears to be highly improbable.

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Zusammenfassung Die Korrelationskurven des Reaktionswegs mit dem geringsten anfänglichen Bewegungsaufwand des Methylens, das durch Photozersetzung des Ketens gebildet wird, werden mit Hilfe des Reaktionswegs geringster Energie interpretiert. Es wird gefolgert, daß sich aus dem ersten angeregten Triplettzustand des Ketens wahrscheinlich relativ schnell ³CH₂(³ B ₂) und ¹CH₂(¹ A ₁) bilden können und daß die Bildung von ³CH₂(³ B ₁) aus dem ersten angeregten Singulettzustand auf einem Weg, der näherungsweise dem eingangs genannten entspricht, erfolgt. Die Bildung von ¹CH₂(¹ A ₁) nach diesem Reaktionsweg ist dagegen sehr unwahrscheinlich.

     

Thermal properties of drug polymorphs: A case study with felodipine form I and form IV

Thermal decomposition kinetics and solution thermodynamics of two polymorphs, felodipine form I and form IV, were investigated. The thermal decomposition kinetics of the polymorphs, containing thermal decomposing mechanism and the kinetic parameters were studied under non-isothermal conditions using Popescu method, and the shelf life was simply calculated. The results showed that nucleation and growth (n = 3/4) of Avremi–Erofeev equation is the most probable mechanism function for form I, and the integral form is G(α) = [−ln(1 − α)]^3/4; while the Mample Powel law (n = 1) is the most probable mechanism function for form IV, corresponding to G(α) = α. Notably, the individual amorphous phases of crystal felodipine form I and IV were obtained after the heating–cooling cycle of DSC tests, which were identified by TMDSC and FT-IR measurements. As the interim products before the collapse, it can be inferred that different amorphous intermediates may be the determinant for different thermal decomposition mechanisms of crystal forms I and IV. The solubility data and solution thermodynamic parameters, including enthalpy, entropy and Gibbs free energy have also been calculated by Van’t Hoff equation in ethanol aqueous. The results illustrated the polymorphic pair is enantiotropic with the transition temperature of 322.23 K and the conversion is driven by entropy.     

On topological form in structures

This paper begins with a review of the Euler relation for the polyhedra and presents the corresponding Schläfli relation in n, the polygonality, and p, the connectivity of the polyhedra. The use of ordered pairs as given by (n, p), the Schläfli symbols, to organize the mapping of the polyhedra and its extension into the two-dimensional (2D) and three-dimensional (3D) networks is described. The topological form index, represented by l, is introduced and is defined as the ratio of the polygonality, n, to the connectivity, p, in a structure, it is given by l = n/p. Next a discussion is given of establishing a conventional metric of length in order to compare topological properties of the polyhedra and networks in 2D and 3D. A fundamental structural metric is assumed for the polyhedra. The metric for the polyhedra is, in turn, used to establish a metric for tilings in the Euclidean plane. The metrics for the polyhedra and 2D plane are used to establish a metric for networks in 3D. Once the metrics have been established, a conjecture is introduced, based upon the metrics assumed, that the area of the elementary polygonal circuit in the polyhedra and 2D and 3D networks is proportional to a function of the topological form index, l, for these structures. Data of the form indexes and the corresponding elementary polygonal circuit areas, for a selection of polyhedra and 2D and 3D networks is tabulated, and the results of a least squares regression analysis of the data plotted in a Cartesian space are reported. From the regression analysis it is seen that a quadratic in l, the form index, successfully correlates with the corresponding elementary polygonal circuit area data of the polyhedra and 2D and 3D networks. A brief discussion of the evident rigorousness of the Schläfli indexes (n, p) over all the polyhedra and 2D and 3D networks, based upon the correlation of the topological form index with elementary polygonal circuit area in these structures, and the suggestion that an Euler–Schläfli relation for the 2D and 3D networks, is possible, in terms of the Schläfli indexes, concludes the paper.     

Ionic liquids form ideal solutions

An understanding of the activity of a solute in solution is vital for utilising the full potential of a reactive species. In this work we determine the activity of metal salts in a variety of ionic liquids. Some solutions behave like classical non-polar solvents whereas other are practically ideal solutions up to 1 mol kg(-1) which allows standard redox potentials to be determined.     

Structure of the quenched form of polypropylene

X-ray diffraction has been used to further investigate the quenched form of polypropylene. The diffractometer traces were analyzed by a mathematical peak separation procedure which assumed a combined Cauchy and Gaussian shape for the peaks. The results confirmed that the quenched form contains about 60% of amorphous polypropylene. In the remainder, the x-ray diffraction peak positions indicate that the chain helices are arranged in a square array and a cubic or tetragonal symmetry is proposed for this phase. The shape of the x-ray diffractometer peaks indicates a degree of strain in the structure. Crystallite sizes, determined from peak breadths, have been estimated as approximately 30 Å.     

A triangular wave form generator

A simple generator for triangular waveforms is described. It uses two operational amplifiers to give triangular waves between 0 V and a preselected voltage. The scan rate and limit can be varied independently.     

Conformal transition of form II to form I in poly(L-proline) and the aggregation of form I. I. Acetic acid–propanol solvent system

The conformational transition of Form II → Form I of Poly-L-proline and the intermolecular aggregation of the product Form I during and after the transition in the HOAc-propanol mixture solvent were studied, the ratio of HOAc:propanol being changed as 1:9, 1:6, and 1:4 v/v. For the study, the viscosity, light scattering, and dynamic light scattering of the system were measured. The experimental results exhibit that the concentration of Form II promotes the end-to-end type aggregation during and after the transition Form II → I. The extent of the aggregation is reduced in the order of the ratios of HOAc/propanol 1:9, 1:6, and 1:4 v/v. The end-to-end type aggregation is also reduced at higher temperatures. It was also observed that the end-to-end type aggregation occurs abruptly and strongly after the transition of Form II → I occurred to some extent. The point of the abrupt occurrence depends on the solvents and temperature. The light scattering and translational diffusion-coefficient measurements showed also similar phenomena. It was also observed that the side-by-side type aggregation occurs when the initial concentration of Form II of poly-L-proline is relatively small, and the transition temperature is relatively high (35 and 45°C). All the above mentioned experimental results are explained by a simple principle described in the text.     

A new equilibrium form of zircon crystal

The surface tensions of the {100}, {110}, {101} and {211} faces are calculated by using Machenzie's method. A new equilibrium form of zircon crystal is then derived on the basis of Wulf's Law. This theoretic form consists of {100} prismatic faces and {211} pyramidal faces, which is different from that of the prediction by the periodic bond chain theory. The discovery of the equilibrium form of zircon crystal provides a clue for understanding of the morphology of zircon crystals formed in deep magma chamber, indicating that zircon morphology is an indicator of crystallization conditions.