Use of multiple acoustic wave modes for assessment of long bones: model study

Multiple acoustic wave mode method has been proposed as a new modality in axial bone QUS. The new method is based on measurement of ultrasound velocity at different ratio of wavelength to the bone thickness, and taking into account both bulk and guided waves. It allows assessment of changes in both the material properties related to porosity and mineralization as well as the cortical thickness influenced by resorption from inner layers, which are equally important in diagnostics of osteoporosis and other bone osteopenia. Developed method was validated in model studies using a dual-frequency (100 and 500 kHz) ultrasound device. Three types of bone phantoms for long bones were developed and tested: (1) tubular specimens from polymer materials to model combined changes of material stiffness and cortical wall thickness; (2) layered specimens to model porosity in compact bone progressing from endosteum towards periosteum; (3) animal bone specimens with both cortical and trabecular components. Observed changes of the ultrasound velocity of guided waves at 100 kHz followed gradual changes in the thickness of the intact cortical layer. On the other hand, the bulk velocity at 500 kHz remained nearly constant at the different cortical layer thickness but was affected by the material stiffness. Similar trends were observed in phantoms and in fragments of animal bones.     

Enumeration of Łukasiewicz paths modulo some patterns

For any pattern $\alpha$ of length at most two, we enumerate equivalence classes of ?ukasiewicz paths of length $n\ge 0$ where two paths are equivalent whenever the occurrence positions of $\alpha$ are identical on these paths. As a byproduct, we give a constructive bijection between Motzkin paths and some equivalence classes of ?ukasiewicz paths.     

Synthesis and Use of Trifluoromethylthiolated Ketenimines

The synthesis of trifluoromethylthiolated ketenimines is herein described. They are easily synthesized from the corresponding α-trifluoromethylthiolated oximes upon activation with triflic anhydride and a base. The presumed nitrilium ion resulting from the Beckmann rearrangement is deprotonated to lead to the key intermediate, whose stability brought by the fluorinated substituent was unforeseeable. The reaction of these new building blocks with a variety of nucleophiles affords a vast array of cyclic and acyclic products bearing the valuable SCF₃ moiety.     

GIANT ANHYSTERETIC RESPONSE OF FERROELECTRIC SOLID SOLUTIONS WITH MORPHOTROPIC BOUNDARIES: THE ROLE OF POLAR ANISOTROPY

Computer modeling and simulation for the Pb(Zr 1 x Ti x )O 3 (PZT) system reveal the role of polar anisotropy on the giant anhysteretic response and structural properties of morphotropic phase boundary (MPB) ferroelectrics. It is shown that a drastic reduction of the composition- dependent polar anisotropy near the MPB flattens energy surfaces and thus facilitates reversible polarization rotation. It is further shown that the polar anisotropy favors formation of polar domains, promotes phase decomposition and results in a two-phase multidomain state, which response to applied electric field is anhysteretic when the polar domain reorientation is only caused by polarization rotation other than polar domain wall movement. This is the case for the decomposing ferroelectrics under a poling electric field with the formation of a two-phase multidomain microstructure, wherein most domain walls are pinned at the two-phase boundaries. Indication of the microstructure dependence of the anhysteretic strain response opens new avenues to improve the piezoelectric properties of these materials through the microstructure engineering.     

Highly modular P-OP ligands in asymmetric allylic substitution

A library of highly modular P-OP ligands have been evaluated in Pd-catalysed allylic substitutions with C- and N-nucleophiles. Catalyst optimisation via a variation of the phosphino and phosphite substituents led to a ‘lead’ catalyst, which efficiently mediated the allylic substitutions when various combinations of substrates and nucleophiles were tested. Ground-state calculations were carried out and these allowed a clearer understanding of the stereochemical outcome of the reaction.     

Approaches to dihydrooxazine ring systems and application in the synthesis of bioactive natural products

This review describes selected approaches to the synthesis of 4H-5,6-dihydro-1,2-oxazines and application of these methods to the synthesis of natural products containing this heterocyclic ring system. The focus is on applications and on interesting aspects of chemistry related to this subclass of natural products, as well as newer methods for the synthesis of oxazines.     

Spongipyran synthetic studies. Total synthesis of (+)-spongistatin 2

Evolution of a convergent synthetic strategy to access (+)-spongistatin 2 (2), a potent cytotoxic marine macrolide, is described. Highlights of the synthesis include: development of a multicomponent dithiane-mediated linchpin union tactic, devised and implemented specifically for construction of the spongistatin AB and CD spiro ring systems; application of a Ca^II ion controlled acid promoted equilibration to set the thermodynamically less stable axial-equatorial stereogenicity in the CD spiroketal; use of sulfone addition/Julia methylenation sequences to unite the AB and CD fragments and introduce the C(44)-C(51) side chain; and fragment union and final elaboration to (+)-spongistatin 2 (2) exploiting Wittig olefination to unite the advanced ABCD and EF fragments, followed by regioselective Yamaguchi macrolactonization and global deprotection. Correction of the CD spiro ring stereogenicity was subsequently achieved via acid equilibration in the presence of Ca^II ion to furnish (+)-spongistatin 2 (2). The synthesis proceeded with a longest linear sequence of 41 steps.