Polymorphism of methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate: an experimental and theoretical study

Being a close analogue of amflutizole, methyl 4‐amino‐3‐phenylisothiazole‐5‐carboxylate (C₁₁H₁₀N₂O₂S) was assumed to be capable of forming polymorphic structures. Noncentrosymmetric and centrosymmetric polymorphs have been obtained by crystallization from a series of more volatile solvents and from denser tetrachloromethane, respectively. Identical conformations of the molecule are found in both structures. The two polymorphs differ mainly in the intermolecular interactions formed by the amino group and in the type of stacking interactions between the π‐systems. The most effective method for revealing packing motifs in structures with intermolecular interactions of different types (hydrogen bonding, stacking, dispersion, etc.) is to study the pairwise interaction energies using quantum chemical calculations. Molecules form a column as the primary basic structural motif due to stacking interactions in both polymorphic structures under study. The character of a column (straight or zigzag) is determined by the orientations of the stacked molecules (in a `head‐to‐head' or `head‐to‐tail' manner). Columns bound by intermolecular N—H…O and N—H…N hydrogen bonds form a double column as the main structural motif in the noncentrosymmetric structure. Double columns in the noncentrosymmetric structure and columns in the centrosymmetric structure interact strongly within the ab crystallographic plane, forming a layer as a secondary basic structural motif. The noncentrosymmetric structure has a lower density and a lower (by 0.59 kJ mol^?1) lattice energy, calculated using periodic calculations, compared to the centrosymmetric structure.     

A Ready‐to‐Use Electrochemical Kit Design for the Diagnosis of Single Nucleotide Polymorphisms

In this study, for the first time a model electrochemical kit was constructed for the detection of a functional polymorphism in catechol‐O‐methyl transferase (COMT) gene which is important for diagnosis of neuropsychiatric disorders as Alzheimer disease. The disposable pencil graphite electrode (PGE) is designed as a “kit” and the probe DNA covered PGE can detect single nucleotide polymorphisms (SNPs) from real samples based on the guanine oxidation signal even after 5 months of kit preparation (150 days durability).The detection limit (S/N=3) of the biosensor was calculated as 1.18 pmol of synthetic target sequence and 6.09×10⁵ molecules of real samples in 30 min detection time.     

Isotactic poly(propylene‐co‐1‐pentene‐co‐1‐hexene) terpolymers: Synthesis,molecular characterization,and evidence of the trigonal polymorph

Terpolymers based on propylene with 1‐pentene and 1‐hexene as comonomeric units are satisfactorily synthesized using a metallocene catalyst. Thus, several terpolymers are prepared with distinct overall compositions in comonomers as well as three different 1‐pentene/1‐hexene ratios at a given composition to evaluate the influence on polymerization activity, intrinsic viscosity, and microstructural details. The new trigonal δ polymorph is observed in those quenched terpolymers with a global content in comonomers of about 14 mol %, independently of the ratio between both comonomers. However, preliminary results indicate a profound influence of that ratio on the crystallization rate. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3251–3259     

Simultaneous differential thermal and volume analysis at high pressure

Abstract

A method for simultaneous measurement of heat and volume changes associated with phase transformations is presented. Examples for melting, polymorphism and structural relaxation illustrate the method.     

Crystallization of the mesomorphic form and control of the molecular structure for tailoring the mechanical properties of isotactic polypropylene

The combination of the control of the concentration of stereodefects in isotactic polypropylene using metallocene catalysts and the crystallization via the mesophase is a strategy to tailor the mechanical properties. Stiff materials, flexible materials, and thermoplastic elastomers can be produced depending only on the concentration of rr stereodefects. Modulus, ductility, and strength can be modulated through the crystallization of α and γ forms or of the mesophase. Different morphologies are observed depending on the stereoregularity and conditions of crystallization. Crystals of the mesomorphic form always exhibit a nodular morphology, accounting for the similar good deformability of all quenched samples, whatever the concentration of stereodefects. The mesophase transforms by thermal treatments into the α form preserving the nodular morphology, with increase of strength while maintaining the ductility typical of the mesophase. Annealing of the mesophase permits a precise adjustment of crystallinity and size of nodular crystals offering additional options to modify the mechanical properties. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 677–699     

Joel Bernstein: a crystal engineer's crystal engineer

Joel Bernstein was a gentle giant in the field of organic solid‐state chemistry and a person who inspired anyone who was in his presence and attended his charismatic lectures over the five decades of his academic career. This commentary looks at his scientific publishing career.     

氯吡格雷抵抗机制的研究进展及临床处理策略

冠心病患者尽管接受了标准的氯吡格雷治疗，但仍有一部分患者对氯吡咯雷表现为低反应甚至无反应，称为氯吡格雷抵抗。导致这种抵抗现象的可能原因包括患者个体的基因多态性和药物之间的相互作用等。临床处理的主要对策有提高氯吡格雷的给药剂量和采用新型药物等。笔者就现有的临床研究证据对氯吡格雷抵抗的定义、发生机制及临床干预策略进行了综述。     

Specific features of T-C-P diagrams for binary systems of B-elements

Abstract

The possibility of reaching high pressures gave rise to intense studies of the phase state of substances, their structures, and properties depending on a new thermodynamic parameter-pressure. Characterizing the extensive development of these studies, one should distinguish three stages: (i) the study of polymorphism for elements under high pressure, and the construction of T-P diagrams; (ii) the study of polymorphism for compounds; and (iii) the construction of three-dimensional T- C-P diagrams for binary and multicomponent systems. At present, the first stage is almost completed in the pressure range from ～100 kbar (see Ref. 1) to 1 Mbar. A series of empirical laws have been established that determine the general direction of structural changes for chemical elements with a pressure rise. Thus, for the elements of the B-subgroup of the Periodic Table, the “coordination rule” has been established according to which an increase in pressure produces structural changes in B elements characterized by a higher packing density and coordination number. According to another rule, the so-called homology rule, B-elements under pressure acquire structures typical for their heavier homologues at normal pressure. These rules manifest themselves most clearly for the elements of the IVB subgroup. In a C-Si-Ge-Sn row structure types change with an increase of the coordination number as follows: graphite (3)-diamond (4)-white tin (6). The same sequence is also observed for the elements of the M3 subgroup with a pressure rise: graphite transforms into diamond, and the diamond-like structure of germanium and silicon transforms into the white-tin structure.     

Association of UCP3, APN,and TNF-a Gene Polymorphisms with Type 2 Diabetes in a Population of Northern Chinese Han Patients

We observed the polymorphism distribution and coaction of uncoupling protein 3(UCP3)-55C/T,adiponectin(APN)+45T/G and tumor necrosis factor(TNF)-a-308G/A on the onset and development of T2DM in a North...