The Atomic Weight of Gadolinium, Dysprosium and Erbium

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The distribution of degree of crystallinity—New concept in polymer science

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The nature of the O—O bond in hydroperoxides

Quantum-chemical calculations of the H₂O₂ and F₂ molecules using different computational schemes, basis sets, and procedures for the inclusion of electron correlation were performed. High-resolution X-ray diffraction study of the electron density distribution in the crystals of 2,5-dimethyl-2,5-dihydroperoxyhexane and 2,5-dimethyl-2,5-dihydroperoxyhex-3-yne was carried out. Joint analysis of the results obtained showed that the formally covalent O—O and F—F bonds correspond to a specific type of interatomic interaction. This type is intermediate between the shared and closed-shell interactions (the latter are typical of the ionic systems and van der Waals molecules).     

The Performance of Rhodium Complex—diphosphine Systems in the Hydroformylation of 1—Dodecene

The catalytic performances of four HRh(CO)(PPh3)3-diphosphine (BISBI,BDPX,BDNA and BINAP) systems in 1-dodecene hydroformylation were investigated and compared with HRh(CO)(PPh3)3-PPh3 system.The catalyst system HRb(CO)(PPh3)3-BISBI exhibited very hig regioselectivity for the formation of linear aldehyde.     

Molecular weights in statistical copolymerization—2. An example of calculations

An example of calculations of the average molecular weights of binary copolymers formed during statistical radical copolymerization, proceeding according to the Mayo-Lewis scheme, is presented. The calculations are based on the statistical model developed in the preceding paper. Literature kinetic data describing the polymerization of styrene and methyl methacrylate at 60°C in bulk are used.     

The Role of Guest Molecules in the Self-assembly of Metal—ligand Clusters

Abstract

Understanding the self-assembly of nanoscale metal—ligand clusters is an important research area in supramolecular chemistry, especially, if one wishes to develop a truly predictive design strategy for synthesizing these nanoscale clusters. As the building blocks for forming these clusters have become larger and more complex, spacious clusters have been synthesized which often contain large cavities. These assemblies can house guest molecules which play a previously uncharacterized role in the self-assembly processes. We seek to analyze this role: do these guest molecules act as templates? Are the guest molecules necessary for cluster formation? Does the guest drive cluster assemble by forming a stable host—guest complex with the cluster? Must a truly rational design strategy for forming metal—ligand clusters incorporate the use of templates? The role of guest molecules in the self-assembly of nanoscale coordination clusters is reviewed in this article.     

The mechanism of chemical degradation of polymers: Part III—The anomaly in the hydrolysis of glycolide copolymers

The data published on the chemical and enzymatic degradation of polyesters and some other polymers is analysed. Earlier studies on copolymers have shown that chemical stability changes monotonously with change in composition if the corresponding homopolymers differ in their sensitivity to the action of a degrading agent. The present work shows that anomalous dependence of chemical stability on copolymer composition is observed for a copolymer based on the isomeric monomers, glycolide and ethylene glycol oxalate. In this case the minimum in the chemical stability versus copolymer composition curve corresponds to the minimum in the copolymer melting temperature versus copolymer composition curve. A possible interpretation of the observed phenomenon is given.     

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…     

476 — The role of electrode position in the electrical induction of limb regeneration in subadult rats

Eight-week-old rats were subjected to mid-forearm amputations, then divided into four groups. One group received no further treatment. One received inactive electrical implants, while the others received implants with either a positive or negative electrode at the dorsoulnar surface of an unclosed amputation wound. Controls and sham-implanted animals repaired their wounds, but did not regenerate. Animals with positively charged electrodes at the surface regenerated considerable amounts of connective tissue but no distal limb structures, while those receiving negatively charged electrodes regenerated complex structures reminiscent of carpal elements. The most effective current density level employed was 1.04 × 10⁻⁶ A/mm².The results of these experiments, when compared to those performed previously, demonstrate that the position of the electrode at the wound surface is important for obtaining maximal regenerative response.     

Study on the Atomization Process of Lithium in Electrothermal Atomic Absorption Spectrometry

A new method for determining the kinetic order and activation energy for atom formation in electrothermal atomic absorption spec-trometry is proposed. The assumption of first order kinetics for atom formation and the steady-state approximation which appeared in the previous models is avoided in the proposed method. The kinetic parameters for atom formation of Li have been obtained, and the effect of the amount of analysed sample, ashing temperature, atomization temperature, heating rate, gas flow and tube surface on the atomization of Li has also been investigated.     

n—π electron-donor—acceptor complexes—IV. The interaction of aliphatic amines with 1,3-dicyanobenzene in n-hexane. The importance of preferred orientation in the stability of the complexes

The stability constants (K) for the electron-donor—acceptor (EDA) complexes formed between aliphatic amines as n-donors and 1,3-dicyanobenzene (1,3-DCB) have been determined in n-hexane as solvent. By means of free energy substitutent parameters and regression analysis, the electronic and steric effects of the N-amine substituents were quantitatively separated. Thus, values of log K were correlated with Taft's polar substituents, σ*, and Hancock's corrected steric substituent constants, E^C_s. Large steric effects are inferred which lead us to propose a preferential site of interaction. This preferential orientation may also explain the greater stability of the 1,3-DCB—amine complexes with respect to the corresponding 1,4-DCB—amine complexes. The proposal is supported by the excess of atomic charge predicted by the Mulliken population analysis, obtained by MNDO calculations for the acceptors and by considering that for weak n—π complexes, the electrostatic energy may be of major importance in the energy of interaction.     

The Nature of Bonding in IrC

Thetheoreticalstudyofsmallmoleculescontainingtransitionmetalatomsisoneofthemostactiveareasinquantumchemistry'becauseofthemanyimportantmaterialsandcatalyticapplicationsofthetransitionmetalsandalsotheirimpoytanceinbiology.Therehavebeenveryextensivestudiesonfirstandsecondrowtransitionmetalhydrides"',oxides4-6andthetransitionmetaldimers7-9.Buttheoreticalstudiesonthethirdrowtransitionmetalcompoundsareratherscarceg-11.Iridiumisanimportantelementforcatalyticreactions,andtheknowledgeoftheinteractionbe…     

The Competition of Charge Remote and Charge Directed Fragmentation Mechanisms in Quaternary Ammonium Salt Derivatized Peptides—An Isotopic Exchange Study

Derivatization of peptides as quaternary ammonium salts (QAS) is a promising method for sensitive detection by electrospray ionization tandem mass spectrometry (Cydzik et al. J. Pept. Sci. 2011, 17, 445–453). The peptides derivatized by QAS at their N-termini undergo fragmentation according to the two competing mechanisms – charge remote (ChR) and charge directed (ChD). The absence of mobile proton in the quaternary salt ion results in ChR dissociation of a peptide bond. However, Hofmann elimination of quaternary salt creates an ion with one mobile proton leading to the ChD fragmentation. The experiments on the quaternary ammonium salts with deuterated N-alkyl groups or amide NH bonds revealed that QAS derivatized peptides dissociate according to the mixed ChR-ChD mechanism. The isotopic labeling allows differentiation of fragments formed according to ChR and ChD mechanisms.     

The Nature of Bonding in PtN

IntroductionThetheoreticstUdyofsmallmoleculescontainingtransitionmetalatomsisoneofthe..mostactiveareasinquantumchemistry'becauseofthemanyimportantmaterialsandcatalyticaPplicationsofthetransitionmetalsandalsotheirimPortanceinbiology.Veryextensivestudieshavebeendoneonthefirstandsecondrowtransitionmetalhydrides"',oxides4-6andthetransitionmetaldimers7-9.Buttheoreticstudiesonthethirdrowtransitionmetalcompoundsaremorescarce9'lo.Platinumisanimportantelementforcatalyticreactions,andtheknowledgeofthe…     

Standard Enthalpies of Formation of β-Aminobutyric Acid and Products of Its Dissociation in Aqueous Solution

Russian Journal of Physical Chemistry A - Heats of dissolution of β-aminobutyric acid in water and aqueous solutions of potassium hydroxide at 298.15 K are measured via direct calorimetry....     

Standard Enthalpies of Formation for Solid Complexes of Chromium Chloride with L—α—Amino Acids

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Structure of hydrated complexes formed by metal ions of Groups I—III of the Periodic Table in aqueous electrolyte solutions under ambient conditions

Published and authors" experimental data on the structures of aqueous electrolyte solutions under ambient conditions are considered. The hydrated metal complexes formed in aqueous solutions are described systematically depending on the size of the cation, the charge, and the structure of the outer electron shell.     

Emulsions in Health Care Applications—An Overview

Pharmaceutical applications of emulsions are reviewed with special emphasis on the main reasons these vehicles are used and on their limitations. The development of current applications and future directions are considered according to their delivery routes: these routes can be either parenteral, ocular, or oral, or even transdermal. We examine the raw materials generally used in the formulation of these emulsions, and we consider the main factors influencing the release and absorption of the drugs from these vehicles. We also treat the pharmaceutical applications of emulsified vehicles, particularly submicron emulsions, multiple emulsions, and microemulsions. We have also developed some interesting applications of these formulations such as self-emulsifying drug delivery systems, fat emulsions, and drug carrier systems.