Stereoelective polymerization of D,L-lactide using N-heterocyclic carbene based compounds

A new Zn alkoxide catalyst supported by an N-heterocyclic carbene rapidly polymerizes D,L-lactide (D,L-LA) to heterotactic enriched poly(lactide)(PLA), while the free carbene and analogs instead yield highly isotactic enriched PLA.     

Syntheses and Properties of New Layered Alkali-Metal/Ammonium Vanadium(V) Methylphosphonates: M(VO(2))(3)(PO(3)CH(3))(2) (M = NH(4), K, Rb, Tl). Single-Crystal Structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2)

The hydrothermal syntheses of a family of new alkali-metal/ammonium vanadium(V) methylphosphonates, M(VO(2))(3)(PO(3)CH(3))(2) (M = K, NH(4), Rb, Tl), are described. The crystal structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) have been determined from single-crystal X-ray data. Crystal data: K(VO(2))(3)(PO(3)CH(3))(2), M(r) = 475.93, trigonal, R32 (No. 155), a = 7.139(3) ?, c = 19.109(5) ?, Z = 3; NH(4)(VO(2))(3)(PO(3)CH(3))(2), M(r) = 454.87, trigonal, R32 (No. 155), a = 7.150(3) ?, c = 19.459(5) ?, Z = 3. These isostructural, noncentrosymmetric phases are built up from hexagonal tungsten oxide (HTO) like sheets of vertex-sharing VO(6) octahedra, capped on both sides of the V/O sheets by PCH(3) entities (as [PO(3)CH(3)](2-) methylphosphonate groups). In both phases, the vanadium octahedra display a distinctive two short + two intermediate + two long V-O bond distance distribution within the VO(6) unit. Interlayer potassium or ammonium cations provide charge balance for the anionic (VO(2))(3)(PO(3)CH(3))(2) sheets. Powder X-ray, TGA, IR, and Raman data for these phases are reported and discussed. The structures of K(VO(2))(3)(PO(3)CH(3))(2) and NH(4)(VO(2))(3)(PO(3)CH(3))(2) are compared and contrasted with related layered phases based on the HTO motif.     

Aggregation and dispersion characteristics of calcium oxalate monohydrate: effect of urinary species

In this research, screening and central composite experimental designs are used to determine the effect of various factors on the aggregation and dispersion characteristics of previously grown calcium oxalate monohydrate (COM) crystals in artificial urinary environments of controlled variables. The variables examined are pH and calcium, oxalate, pyrophosphate, citrate, and protein concentrations in ultrapure water and artificial urine. Optical density measurements, particle size analysis, optical microscopy, AFM force measurements, and protein adsorption have been used to assess the state of aggregation and dispersion of the COM crystals and to elucidate the mechanisms involved in such a complex system. The data indicate that our model protein, mucin, acts as a dispersant. This is attributed to steric hindrance resulting from the adsorbed mucoprotein. Oxalate, however, promotes aggregation. Interesting interactions between protein and oxalate along with protein and citrate are observed. Such interactions (synergistic or antagonistic) are found to depend on the concentrations of these species. Surface responses for these interactions are presented and discussed in this paper. In summary, solution, surface, and interface chemistries interact in a complex manner in the physiological environment to either inhibit or promote aggregation, and an understanding of such interactions may help determine and control the factors affecting kidney stone formation.     

On the West Decomposition of Riesz Operators

Let T be a Riesz operator on a Banach space and let {_n} be anenumeration of the nonzero eigenvalues of T, each repeated accordingto algebraic multiplicity. Then a sufficient condition thatT admit a West decomposition T = C + Q, where C is compact andQ is quasinilpotent, is that n[_n] < . Furthermore, C andQ can be chosen to have a quasinilpotent commutator.     

Quantum Chemistry Comes of Age

On December 10, 1998, the 102nd anniversary of Alfred Nobels death, in Stockholms Konserthus (Concert Hall), Swedens King Carl XVI Gustav awarded one half of the 1998 Nobel Prize in Chemistry (3,800,000 kronor, about $489,000) to Professor John A. Pople, 73, of Northwestern University, Evanston, Illinois for his development of computational methods in quantum chemistry.The remaining half of the prize, the ne plus ultra of chemistry, was awarded to Professor Walter Kohn, 75, of the University of California, Santa Barbara for his development of the density-functional theory [1–9]. Because of health problems in his family, Kohn was unable to attend the ceremony but presented his Nobel lecture in Stockholm on January 28, 1999. According to the Royal Swedish Academy of Sciences: The laureates have each made pioneering contributions in developing methods that can be used for theoretical studies of the properties of molecules and the chemical processes in which they are involved [7].     

Scaffold Effects on Osteogenic Differentiation of Equine Mesenchymal Stem Cells: An In Vitro Comparative Study

The in vitro viability, osteogenic differentiation, and mineralization of four different equine mesenchymal stem cells (MSCs) from bone marrow, periosteum, muscle, and adipose tissue are compared, when they are cultured with different collagen‐based scaffolds or with fibrin glue. The results indicate that bone marrow cells are the best source of MSCs for osteogenic differentiation, and that an electrochemically aggregated collagen gives the highest cell viability and best osteogenic differentiation among the four kinds of scaffolds studied.

     

Amidrazones 9. Convenient Syntheses of 1-Alkyl-1-Phenylhydrazines and α,β-Unsaturated Amidrazones Via Base-Promoted Reactions of 1,1-Disubstituted-3-Amino-4,5-Dihydro-1H-Pyrazolium Salts

A simple, efficient procedure for the conversion of phenylhydrazine to 1-alkyl-1-phenylhydrazines via base-promoted hydrolysis of 1-alkyl-3-amino-4,5-dihydro-1-phenyl-1H-pyrazolium iodides (2) is described. N¹, N¹-disubstituted hydrazones of trans-cinnamamide and acrylamide are obtained by Hofmann-type ring openings of 1,1 -disubstituted-3-amino-4,5-dihydro-5-phenyl (or 5-unsubstituted) -1H-pyrazolium halides (5, 7).     

Polymer microfluidic devices

Since the introduction of lab-on-a-chip devices in the early 1990s, glass has been the dominant substrate material for their fabrication (J. Chromatogr. 593 (1992) 253; Science 261 (1993) 895). This is primarily driven by the fact that fabrication methods were well established by the semiconductor industry, and surface properties and derivatization methods were well characterized and developed by the chromatography industry among others. Several material properties of glass make it a very attractive material for use in microfluidic systems; however, the cost of producing systems in glass is driving commercial producers to seek other materials. Commercial manufacturers of microfluidic devices see many benefits in employing plastics that include reduced cost and simplified manufacturing procedures, particularly when compared to glass and silicon. An additional benefit that is extremely attractive is the wide range of available plastic materials which allows the manufacturer to choose materials' properties suitable for their specific application. In this article, we present a review of polymer-based microfluidic systems including their material properties, fabrication methods, device applications, and finally an analysis of the market that drives their development.