A scalable process for the synthesis of (E)-pterostilbene involving aqueous Wittig olefination chemistry

A synthetic approach toward the pharmacologically active (E)-stilbene pterostilbene is described using a Wittig reaction conducted under mildly basic, aqueous conditions. A surprising, non-intuitive difference in (E)/(Z) stereoselectivity was observed comparing the two possible isomeric Wittig routes, allowing for the development of a highly efficient process to access the title stilbene derivative through a one-pot olefination deprotection sequence.     

Structure and Polymorphism of M(thd)3 (M = Al,Cr, Mn,Fe, Co,Ga, and In)

Formation, crystal structure, polymorphism, and transition between polymorphs are reported for M(thd)₃, (M = Al, Cr, Mn, Fe, Co, Ga, and In) [(thd)^– = anion of H(thd) = C₁₁H₂₀O₂ = 2, 2, 6, 6‐tetramethylheptane‐3, 5‐dione]. Fresh crystal‐structure data are provided for monoclinic polymorphs of Al(thd)₃, Ga(thd)₃, and In(thd)₃. Apart from adjustment of the M–O_k bond length, the structural characteristics of M(thd)₃ complexes remain essentially unaffected by change of M. Analysis of the M–O_k, O_k–C_k, and C_k–C_k distances support the notion that the M–O_k–C_k–C_k–C_k–O_k– ring forms a heterocyclic unit with σ and π contributions to the bonds. Tentative assessments according to the bond‐valence or bond‐order scheme suggest that the strengths of the σ bonds are approximately equal for the M–O_k, O_k–C_k, and C_k–C_k bonds, whereas the π component of the M–O_k bonds is small compared with those for the O_k–C_k, and C_k–C_k bonds. The contours of a pattern for the occurrence of M(thd)₃ polymorphs suggest that polymorphs with structures of orthorhombic or higher symmetry are favored on crystallization from the vapor phase (viz. sublimation). Monoclinic polymorphs prefer crystallization from solution at temperatures closer to ambient. Each of the M(thd)₃ complexes subject to this study exhibits three or more polymorphs (further variants are likely to emerge consequent on systematic exploration of the crystallization conditions). High‐temperature powder X‐ray diffraction shows that the monoclinic polymorphs convert irreversibly to the corresponding rotational disordered orthorhombic variant above some 100–150 °C (depending on M). The orthorhombic variant is in turn transformed into polymorphs of tetragonal and cubic symmetry before entering the molten state. These findings are discussed in light of the current conceptions of rotational disorder in molecular crystals.     

On the difference in material structure and fatigue properties of nylon specimens produced by injection molding and selective laser sintering

This paper describes the influence of dynamic tension/compression loading on notched and unnotched nylon specimens fabricated by Injection Molding (IM) and Selective Laser Sintering (SLS). The main objective of this work is to analyze and describe the differences in material structure and fatigue properties of as-built nylon parts produced by IM and SLM from the same polyamide 12 powder. The differences in dimensional quality, density, surface roughness, crystal structure and crystallinity are systematically measured and linked to the mechanical fatigue properties. The fatigue properties of the unnotched SLS specimens are found to be equal to those of the unnotched IM specimens. The presence of pores in the sintered samples does not lead to rapid failure, and the microvoid coalescence failure mechanism is delayed. The notched specimens show more brittle failure and increased fatigue resistance which is caused by local notch-strengthening. The results enable improved understanding of the difference in material structure and fatigue behavior of selective laser sintered and injection molded polyamide.     

Anticoincidence INAA capabilities for analysis of FDA Total Diet Study seafoods

Anticoincidence instrumental neutron activation analysis was used to analyze three portions each of five fresh-weight FDA Total Diet Study seafoods from 3 Market Basket collections for fiscal years 2006–2008. Portions were treated with l-cysteine solutions to enhance retention of Hg during irradiation then dried at room temperature over magnesium perchlorate. Results or limits of detection were obtained for 33 elements. In general, results agreed with those available from FDA’s Kansas city field laboratory (KAN-DO). Of three shrimp composites analyzed, one showed mass fractions of Ag, Fe, rare earths, U, Th, and Mo significantly higher (up to a factor of 10) than the other two shrimp composites. The same shrimp composite showed a lower Hg result (about 50 % after accounting for any irradiation loss) compared to the KAN-DO value. This may represent a drying loss. There were other indications of Hg loss during the drying process. SRM 1947 Lake Michigan Fish Tissue, run as a control, yielded an INAA Hg mass fraction 20 % lower (corrected for irradiation losses) than the certified value, similar to the difference between the INAA (0.171 mg/kg Hg) and KAN-DO (0.211 mg/kg Hg) results for a TDS canned tuna composite. Because previous studies showed that l-cysteine effectively sequesters inorganic Hg, these discrepancies likely represent methyl mercury loss. INAA results for As, Fe, Rb, and Se were in good agreement with SRM 1947 certified values.     

Theory of an electric field induced periodic phase in a nematic film

The elastic theory of nemtatic liquid crystals is used to determine whether it gives support for recent experimental observations of a novel periodic phase occurring in homeotropically aligned films when an electric field is applied in the plane of the film. The director remains in the plane defined by the film normal and the field, and the wavevector of the periodicity is parallel to the field. It is found that the theory is consistent with experiment.     

Orientational ordering in the nematic phase of 4-alkyl-4'-cyanobicyclohexanes

The orientational ordering of three liquid crystals (trans,trans-4-n-alkyl-4'-cyanobicyclohexanes) has been investigated using ¹³C NMR. 2D proton-encoded local field spectroscopy was used to determine the ¹³C-¹H dipolar coupling constants, from which the order parameters were calculated. Semi-empirical linear relations between the obtained order parameters and anisotropic ¹³C chemical shifts were established. It was found that the order parameters of the major axis of the cyclohexane rings are smaller than those of liquid crystals with phenyl rings, and the order parameters of the C-H bonds in the aliphatic chains also behave differently.     

Supramolecular main-chain liquid crystalline polymers and networks with competitive hydrogen bonding

A series of supramolecular polymers and networks with variable liquid crystalline characteristics have been created. These species are formed though the benzoic acid/pyridine associations of a flexible bisacid and a mixture of a rigid bispyridyl and a non-mesogenic tetrapyridyl. The networked systems displayed liquid crystalline characteristics up to and including 22.5% netpoint inclusion. Above this concentration, only crystalline and melting behaviours were observed. This observed phenomenon would seem to be linked to the statistical correlation of hydrogen bond acceptors and donors. There was also no observed phase segregation of the species after multiple heat/cool cycles and extended periods of time in the isotropic state. This would indicate that the thermodynamically more stable mesogenic phase cannot out-compete the non-liquid crystalline network. Computational analysis indicates no significant difference in hydrogen bond strength between the two different hydrogen bond acceptors.     

Application of a new focused microwave technology with species-specific isotope dilution analysis for the quantitative extraction of organometallic contaminants in solid environmental matrices

A new self-tuning single-mode-focused microwave technology has been evaluated in this work to perform the quantitative routine extraction of organometallic species from solid matrices of environmental interest. Species-specific isotope dilution analysis has been employed to better investigate the real influence of the microwave-assisted extractions on the final results. The advantages of such methodology in comparison with other established microwave units for the routine speciation analysis of organomercury and organotin compounds are discussed (such as the capability of using disposable glass vials, a self-tuning mode to provide an accurate control of the temperature and pressure inside of the vials, and the possibility of performing automated sequence of extractions with low sample size). The results obtained in this work demonstrated that such technology provides a fast and reliable quantitative extraction of the organometallic species in a wide range of extraction conditions even when the multi-elemental (Sn and Hg) species-specific determination is carried out.