SAR—The U.S. Regulatory Perspective

Abstract

Structure-Activity Relationships (SAR) have been used for over a decade by the U.S. EPA's Office of Pollution Prevention and Toxics (OPPT) in their new chemicals program. The development and use of SAR resulted from the need to make rapid risk-based decisions on thousands of new chemicals per year while seldom receiving data on chemical properties, potential exposures, or hazards to humans or organisms in the environment. Qualitative SAR and quantitative SAR methods (QSAR) have been used to fill some of these data gaps by estimating the potential properties and hazards of such chemicals. SAR has been used to assess chemical hazards, identify testing needs, and set priorities. Validation of these SAR assessment tools is an ongoing process.     

The Huge World of Nanomaterials.From Wiley-VCH

~~The Huge World of Nanomaterials.From Wiley-VCH~~     

The Huge World of Nanomaterials. From Wiley-VCH

Nanoparticles From Theory to Application GNTHER SCHMID,Univ. Essen,Germany An introduction to the science of nanoparticles     

The Vast World of Nanomaterials. From Wiley-VCH

Nanotechnology MICHAEL KHLER,llmenau Technical Univ.,Inst. of Physics,llmenau,Germany,and WOLFGANG FRITZSCHE,IPHT Jena     

The binary system benzene—hexafluorobenzene studied by SSOZ theory and computer simulation. I. The charge symmetry model

The symmetry reduction of the SSOZ equation already developed for pure components is extended to binary mixtures. The general formalism is applied to the binary system C₆F₆/C₆H₆, whose “mixing interaction” is described by a simplified “charge symmetry model”. Varying the charge strength in a systematic way the predictions of SSOZ theory are verified by extensive computer simulation (molecular dynamics) studies. Thereby mixtures and pure components are treated in a unified way. Finally, extensions of the “charge symmetry model” are presented and the computed radial excess correlation functions are compared to those measured by neutron and X-ray scattering.     

The correlation of NHn i.r. frequencies in amines

Correlations have been found between the various i.r. frequencies in aromatic and aliphatic amines and the appropriate δ_i substituent constants. This correlation demonstrates that, for aliphatic amines, it is often difficult to distinguish the NH_n stretching peaks from other nearby peaks the correct peak may be chosen with the aid of these correlations. Application to hydrogenated amorphous silicon nitride indicates that an extraneous peak at the same position as the NH_n stretching peaks masks the very low intensity NH₂ peaks, which are present even at low N concentrations.     

The rheological properties of gelatin gels containing κ-carrageenan. The role of polysaccharide

The influence of an anionic polysaccharide, κ-carrageenan, on the rheological properties of low-concentration (1.0 wt %) gelatin gels has been studied in a wide range of low polysaccharide concentrations (1 × 10^?3–5 × 10^?1 wt %) at a temperature of 14.0°C and pH values slightly higher than the isoelectric point of gelatin. The parameters characterizing the rheological properties of the gels are governed by the mass ratio between the polysaccharide and gelatin, which are able to form (bio)polyelectrolyte complexes in aqueous systems. There is a critical κ-carrageenan-to-gelatin mass ratio Z ? 0.1, above which the yield stress of the gels and their effective viscosit at stresses exceeding the yield point drastically rise. The increase in these rheological parameters correlates with a growth in the particle size of κ-carrageenan-gelatin polyelectrolyte complexes, which are formed in the aqueous bulk phase at an elevated temperature and precede gelation.     

The World of Synthetic Polymers. An Industrial Perspective

Synthetic polymers have become the building block in almost every aspects of our daily life. Billions of pounds of polymers are produced each year and the demand is continuously growing both in terms of volume and advanced performance. The general property of a class of polymers is often bounded by the synthetic process that produces the polymer. For example, polyolefins, are non-polar polymers due to the poor tolerance of transition metal catalysts toward polar monomers. Conversely, latices a…     

J. J. Thomson and The Electron: 1897–1899 An Introduction

Three Seminal Papers of J. J. Thomson This being the 100th anniversary of J. J. Thomsons discovery of the electron, the October 1897 paper in which he presented his case that cathode rays are streams of subatomic corpuscles is attracting a great deal of attention. Viewed from 100 years later, this paper stands out as the starting point for the research into the structure of the atom that has dominated 20th-century science. Viewed in its original historical context, however, this paper was but one of a group by Thomson and his Cavendish Laboratory research students and is matched in importance by his two ensuing papers: On the Charge of Electricity carried by the Ions produced by Röntgen Rays published in December 1898 and On the Masses of the Ions in Gases at Low Pressures published in December 1899. All three of these seminal papers, which appeared in the prestigious Philosophical Magazine, are included here, along with the published text of Thomsons talk of April 30, 1897, in which he first put the subatomic proposal forward and George Fitzgeralds commentary on this talk.     

The i.r. spectra of ethylenediamine complexes—I. The tris(ethylenediamine) complexes of first transition series metal(II) sulphates

The i.r. spectra of the complex [Zn(en)₃]SO₄ and its ⁶⁴Zn-, ⁶⁸Zn-, ¹⁵N-, N₂D₄- and C₂D₄-labelled analogues have been determined over the range 4000-50 cm⁻¹. Band assignments are based on the isotopically induced shifts and also those which result from substitution of Zn(II) by the metal(II) ions of the first transition series: Mn(II), Fe(II), Co(II), Ni(II) and Cu(II). The spectrum of the Cu(II) complex yields evidence of Jahn—Teller distortion.     

The Structure of Cellulose by Conformational Analysis. 1. Cellobiose and Methyl-β-cellobioside

Conformational analysis studies on the tertiary structure of cellobiose and methyl-β-cellobioside were carried out by using calculations of van der Waals, H-bond, electrostatic, and torsional energy interactions between the atoms and groups of the molecules. Energy maps as functions of the rotational anglesΨo and Φ° of the glucosidic bond were obtained in increments of 20° and refined in increments of 1°. Two “primary” and one “secondary” conformations of minimum energy were obtained for both cellobiose and methyl-β-cellobioside, some of which are equivalent to results obtained by x-ray diffraction. The H-bond forces are shown to be, together with the van der Waals forces, the predominant factors in the fixation of the conformations of minimum energy. The position and energy contributions of the H-bonds patterns for the favored conformations are identified.     

The electron-donating properties of 2,2′-bipyridine. Charge-transfer studies

Molecular charge-transfer complexes of 2,2′-bipyridine with iodine and tetracyanoethylene have been investigated. The formation constants of these complexes were determined at different temperatures and the thermodynamic functions, ΔH_f and ΔS_f were calculated. The spectra and stability of the complexes were discussed and interpreted.     

When Is a Bond Broken? The Polarizability Perspective.

The question of when a chemical bond can be said to be broken is of fundamental chemical interest but has not been widely studied. Herein we propose that the maxima of static polarizability along bond dissociation coordinates naturally define cutoff points for bond rupture, as they represent the onset of localization of shared electron density into constituent fragments. Examples of computed polarizability maxima over the course of bond cleavage in main-group and transition metal compounds are provided, across covalent, dative and charge-shift bonds. The behavior along reaction paths is also considered. Overall, the static polarizability is found to be a sensitive reporter of electronic structure reorganization associated with bond stretching, and thus can serve as a metric for describing bond cleavage (or diagnose the absence of a chemical bond).     

The heterometric micro-analysis of cobalt with α-nitroso - β-naphthol. a general study.

1. The reaction between cobaltous or cobaltic and α-nitroso-β-naphthol was extensively studied heterometrically both in water and in alcoholic solutions. The influence of complexing agents and of the acidity on the precipitation of cobalt-α-nitroso-β-naphthol was investigated. In all cases the molar ratios : [Co] [αβ] at the end of the precipitation were established and the possible compounds which were obtained were discussed. 2. Micro-analytical heterometric methods are given for the determination of cobalt or α-nitroso-β-naphthol. The determination can be carried out with precision even in concentrations as low as 0.0001M Co. Conversely, very dilute alcoholic solutions of α-nitroso-β-naphthol may be titrated with precision with a dilute solution of cobalt nitrate. 0.2–0.5 mg cobalt in 20 ml solution are required for the analysis. The error lies between zero and 3%.     

Kekulé-based Valence Bond Model. I. The Ground-state Properties of Conjugated π-Systems

ＩｎｔｒｏｄｕｃｔｉｏｎＩｔｈａｓｂｅｅｎａｃｋｎｏｗｌｅｄｇｅｄｔｈａｔｂｏｔｈｔｈｅＨ櫣ｃｋｅｌｍｏｌｅｃｕｌａｒｏｒｂｉｔａｌ (ＨＭＯ)ａｎｄｖａｌｅｎｃｅｂｏｎｄ (ＶＢ)ｍｅｔｈ ｏｄｓａｒｅｖａｌｉｄｓｔａｒｔｉｎｇｐｏｉｎｔｓｆｏｒｄｅｓｃｒｉｂｉｎｇｔｈｅｃｈｅｍｉｃａｌｂｅｈａｖｉｏｒｓｏｆａｌｔｅｒｎａｎｔｃｏｎｊｕｇａｔｅｄｓｙｓｔｅｍｓｗｉｔｈｏｕｔｄｅｇｅｎｅｒ ａｔｅｇｒｏｕｎｄｓｔａｔｅｓ (ｆｏｒｅｘａｍｐｌｅ ,ｃｙｃｌｏｂｕｔａｄｉｅｎｅｉｓｅｘｃｌｕｄ ｅｄ) .1Ｒｅｃ…     

The hydroperoxysulfonium ylide. An aberration or a ubiquitous intermediate?

An intramolecular isotope effect has been measured for the reaction of singlet oxygen with 2,2,8,8-tetradeuterio-1,5-dithiacyclooctane, 4d₄. The magnitude of the isotope effect, 1.21±0.09, provides verification of removal of an α-hydrogen during the product determining step to form a hydroperoxysulfonium ylide and ultimately the sulfoxide product. The absence of any special structural features in 4d₄ to enhance the propensity of hydrogen removal is used to suggest that the hydroperoxysulfonium ylide is a ubiquitous intermediate in the reactions of sulfides with singlet oxygen.     

Studies on Agarofurans Ⅲ. The Synthesis of 3-Substituted Agarofurans

Agarotlirans were found to be bioactive on nervous system. 3,4-dihydroxy dihydroagarofuran (l)' is only one of this group of natural products, which has substituent on C3 position.We synthesized this compound by the reported nletllod' and tbund it to possess somespecific bioactivity on nervous system. In order to search for more active compounds, wedecided to modify agarofurans on C-3 position beginning with the synthesis of 14-nor-3oxodihydroagarofuran (2).In the initial stage of the synthes…