Stereoselective total synthesis and absolute configuration of the natural decanolides (-)-microcarpalide and (+)-lethaloxin. Identity of (+)-lethaloxin and (+)-pinolidoxin

[reaction: see text] Convergent, stereoselective syntheses of the pharmacologically active, naturally occurring lactones (-)-microcarpalide and (+)-lethaloxin have been achieved from the commercially available, chiral reagents (R)-glycidol, (S,S)-tartaric acid, and d-ribose as the starting materials. These syntheses have further served to establish the hitherto unknown absolute configuration of (+)-lethaloxin and to show its identity with (+)-pinolidoxin.     

Concise enantioselective total synthesis of neopeltolide macrolactone highlighted by ether transfer

A concise total synthesis of neopeltolide macrolactone has been accomplished in 14 steps in the longest linear sequence, 15 steps overall from commercially available materials. The present synthesis was highlighted by successful exploitation of ether transfer methodology and a radical cyclization reaction to directly establish the requisite stereochemistry of the tetrahydropyran core.     

Analytical validation of quality control materials for Huntington’s disease examination

The expansion of molecular diagnostics using nucleic acid technologies in clinical and public health practice has increased the need for appropriate reference materials and verified quality-control materials for quality assurance, test validation, proficiency testing and the development of new examination procedures. Good laboratory practice requires the use of reference materials to establish an examination procedure and assess the variability of the results. Reference materials are also required to assess the assay on a daily basis and to normalize results collected among different laboratories. Despite the growing volume, the rapidly increasing number of tests being offered, and the necessary routine use, certified reference materials are often not available. There is a wide range of human genetic bio-assays for which there are no available traceable certified reference materials. Several initiatives have been organized to provide well-characterized quality control specimens (e.g., cell lines) with known DNA mutations for use in diagnostics. Mutations are confirmed with bi-directional DNA sequence analysis, which is considered the reference examination procedure. In the field of personalized medicine, NIST has created and validated Standard Reference Material^® 2399 for fragile X examinations. Herein we describe our characterization of candidate reference materials for Huntington’s disease genetic examination. Bi-directional DNA sequencing confirmed the size of the CAG repeat contained on each allele from patient derived materials. Amplification and capillary electrophoresis of the CAG repeats had an uncertainty ranging from 2.06%CV to 7.83%CV.     

The National Bureau of Standards fresh water lake sediment environmental-level radioactivity standard reference material

The National Bureau of Standards has, for the past five years, been developing natural-matrix, environmental-level radioactivity Standard Reference Materials in large quantities to be available to users over a ten year time period. These materials have been found to be useful for the evaluation of radiochemical methods and analysis, as interlaboratory comparison materials, and as quality assurance materials. To date, six Standard Reference Materials have been issued: River Sediment, Human Lung, Human Liver, Rocky Flats Soil-1, Freshwater Lake Sediment, and Peruvian Soil. The concentrations of twenty radionuclides have been certified in these materials.     

Connecting pi-chromophores by sigma-P-P bonds: new type of assemblies exhibiting sigma-pi-conjugation

To study the ability of sigma-P-P skeleton to mediate interaction between pi-chromophores, 1,1'-biphospholes bearing phenyl or thienyl substituents at the 2,2' and 5,5'-position have been prepared and studied. These air-stable derivatives are readily available via a "one-pot" synthesis starting from diynes. Theoretical studies and UV-vis data clearly establish that the two pi-systems interact via the sigma-P-P bridge. This through-bond interaction results in a lowering of the optical HOMO-LUMO gap of the assemblies. The nucleophilic sigma(3)-P centers of these 1,1'-biphospholes allow chemical modifications of the sigma-bridge. These modifications offer further tuning of the optical properties of the assembly. Electrooxidation of the thienyl-substituted 1,1'-biphosphole results in electroactive materials characterized by low optical band gap and reversible p-doping.     

Bone Grafts and Substitutes in Dentistry: A Review of Current Trends and Developments

After tooth loss, bone resorption is irreversible, leaving the area without adequate bone volume for successful implant treatment. Bone grafting is the only solution to reverse dental bone loss and is a well-accepted procedure required in one in every four dental implants. Research and development in materials, design and fabrication technologies have expanded over the years to achieve successful and long-lasting dental implants for tooth substitution. This review will critically present the various dental bone graft and substitute materials that have been used to achieve a successful dental implant. The article also reviews the properties of dental bone grafts and various dental bone substitutes that have been studied or are currently available commercially. The various classifications of bone grafts and substitutes, including natural and synthetic materials, are critically presented, and available commercial products in each category are discussed. Different bone substitute materials, including metals, ceramics, polymers, or their combinations, and their chemical, physical, and biocompatibility properties are explored. Limitations of the available materials are presented, and areas which require further research and development are highlighted. Tissue engineering hybrid constructions with enhanced bone regeneration ability, such as cell-based or growth factor-based bone substitutes, are discussed as an emerging area of development.     

Kinetics of adsorption of metal ions on inorganic materials: A review

It is necessary to establish the rate law of adsorbate-adsorbent interactions to understand the mechanism by which the solute accumulates on the surface of a solid and gets adsorbed to the surface. A number of theoretical models and equations are available for the purpose and the best fit of the experimental data to any of these models is interpreted as giving the appropriate kinetics for the adsorption process. There is a spate of publications during the last few years on adsorption of various metals and other contaminants on conventional and non-conventional adsorbents, and many have tried to work out the kinetics. This has resulted from the wide interest generated on using adsorption as a practical method for treating contaminated water. In this review, an attempt has been made to discuss the kinetics of adsorption of metal ions on inorganic solids on the basis of published reports. A variety of materials like clays and clay minerals, zeolites, silica gel, soil, activated alumina, inorganic polymer, inorganic oxides, fly ash, etc. have been considered as the adsorbents and cations and anions of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Se, and Zn as adsorbate have been covered in this review. The majority of the interactions have been divided into either pseudo first order or second order kinetics on the basis of the best fit obtained by various groups of workers, although second order kinetics has been found to be the most predominant one. The discussion under each category is carried out with respect to each type of metal ion separately. Application of models as given by the Elovich equation, intra-particle diffusion and liquid film diffusion has also been shown by many authors and these have also been reviewed. The time taken for attaining equilibrium in each case has been considered as a significant parameter and is discussed almost in all the cases. The values of the kinetic rate coefficients indicate the speed at which the metal ions adsorb on the materials and these are discussed in all available cases. The review aims to give a comprehensive picture on the studies of kinetics of adsorption during the last few years.     

Sensing mechanism of non-equilibrium solid-electrolyte-based chemical sensors

Solid electrolytes can be used in several different types of chemical sensors. A common approach is to use the equilibrium potential generated across a solid electrolyte given by the Nernst equation as the sensing signal. However, in some cases, stable electrode materials are not available to establish equilibrium potentials, so non-equilibrium approaches are necessary. The sensing signal generated by such sensors is often described by the mixed potential theory, in which a pair of electrochemical reactions establishes a steady state at the electrode, such that the electrons produced by an oxidation reaction are consumed by a reduction reaction. The rates of both reactions depend on several factors, such as electron exchange, active area, and gas phase diffusion, so establishment of the steady-state potential is complex and alternative explanations have been proposed. This paper will review and discuss the mechanisms proposed to explain the sensor response of non-equilibrium-based electrochemical sensors.     

Energy absorption buildup factor studies in water, air and concrete up to 100 mfp using G-P fitting formula

The energy absorption buildup factors for water, air and concrete have been calculated up to a penetration depth of 100 mean free paths using 5-parameter Geometric Progression formula, in the energy range of 0.015–15.0 MeV. The results up to 40 mfp have been compared with the available standard data, whereas the buildup factors of these materials beyond 40 mfp and up to 100 mfp are new to the available literature.     

Mesogens with central naphthalene core substituted at various positions

We have prepared liquid crystalline materials based on hydroxynaphthalene carboxylic acids. The mutual location of both functional groups has been varied, which resulted in compounds possessing a bend angle of 120° and 60°, therefore in bent-core and V-shaped compounds, respectively. The mesomorphic properties have been established with polarizing optical microscopy, DSC measurements and X-ray investigation. The properties of the studied have been compared with analogous derivatives to establish the role of ester orientation in the vicinity of the central naphthalene core.