Thermodynamic properties of the C5, C6, and C8 n-alkanes from ab initio electronic structure theory

The heats of formation for the n-alkanes C(n)H(n+2) for n = 5, 6, and 8 have been calculated using ab initio molecular orbital theory. Coupled-cluster calculations with perturbative triples (CCSD(T)) were employed for the total valence electronic energies. Correlation-consistent basis sets were used, up through the augmented quadruple zeta, to extrapolate to the complete basis set limit. Geometries were optimized at the B3LYP/TZVP and MP2/aug-cc-pVTZ levels. The MP2 geometries were used in the CCSD(T) calculations. Frequencies were determined at the density functional level (B3LYP/TZVP), and scaled zero point energies were calculated from the B3LYP frequencies. Core/valence, scalar relativistic, and spin-orbit corrections were included in an additive fashion to predict the atomization energies. The core/valence corrections are not small, (approximately 1.1 kcal/mol per carbon unit) and cannot be neglected for chemical accuracy. The calculated deltaH(298)f values are -35.0, -40.2, and -50.2 kcal/mol for C5H12, C6H14, and C8H18, respectively, in excellent agreement with the respective experimental values of -35.11 +/- 0.19, -39.89 +/- 0.19, and -49.90 +/- 0.31 kcal/mol. Isodesmic reaction energies are presented for some simple reactions involving C8H18 and are shown not to be strongly method dependent.     

Oxo-Hydroxoferrate K2−xFe4O7−x(OH)x: Hydroflux Synthesis,Chemical and Thermal Instability,Crystal and Magnetic Structures

The reaction of Fe(NO₃)₃⋅9 H₂O with KOH under hydroflux conditions at about 200 °C produces red crystals of K_2−xFe₄O_7−x(OH)_x in a quantitative yield. In the crystal structure, edge-sharing [FeO₆] octahedra form Fe₂O₆] honeycomb nets. Pillars consisting of pairs of vertex-sharing [FeO₄] tetrahedra link the honeycomb layers and form columnar halls in which the potassium ions are located. The trigonal (P 1m) and the hexagonal (P6₃/mcm) polytypes of K_2−xFe₄O_7−x(OH)_x show oriented intergrowth. The sub-stoichiometric potassium content (x≈0.3) is compensated by hydroxide ions. K_2−xFe₄O_7−x(OH)_x is an antiferromagnet above 2 K and its magnetic structure was determined by neutron powder diffraction. Under ambient conditions, K_2−xFe₄O_7−x(OH)_x hydrolyzes and K₂CO₃ ⋅ H₂O forms gradually on the surface of the K_2−xFe₄O_7−x(OH)_x crystals. Upon annealing at air at about 500 °C, the potassium atoms in the columnar halls start to order into a superstructure. The thermal decomposition of K_2−xFe₄O_7−x(OH)_x proceeds via a topotactic transformation into K_1+x′Fe₁₁O₁₇, adopting the rhombohedral β’’ or the hexagonal β-aluminate-type structure, before γ-Fe₂O₃ is formed above 950 °C, which then converts into thermodynamically stable α-Fe₂O₃.     

Uracil–4-Hydroxyuracil tautomerism revisited

The tautomerism of the uracil-4-hydroxyuracil system is examined with the 3–21G basis set and full geometry optimization using gradient techniques. Single-point calculations at the 6-31G level were also done and the results compared with the 2-pyridone–2-hydroxypyridine system. The best ΔE(taut) obtained in this work is 74.1 kJ/mol.     

一种改进的位移反分析方法

为了发展可用于各种岩土工程及工程地质问题的一般的位移反分析系统方法, 本文在边界控制方法的基础上进行了改进。其目的是对于其各种复杂的系统问题确定最重要的力学参数。     

Several Sterilization Strategies Maintain the Functionality of Mucin Glycoproteins

Mucin glycoproteins, the macromolecular components of mucus, combine a broad range of biomedically important properties. Among those is the ability of mucin solutions to act as excellent lubricants. However, to be able to use purified, endogenous mucin glycoproteins as components of a biomedical product, the mucins need to be sterile; this, in turn, makes it necessary to subject the mucins to quite harsh physical treatments, such as heat exposure, autoclaving, UV‐, or γ‐irradiation, which might compromise the functionality of the glycoproteins. Here, it is shown that mucins are indeed able to withstand most of those treatments without suffering significant lubrication impairment or structural degradation. Among those treatments, which left the mucins unharmed, γ‐irradiation is identified to be the most powerful one in terms of inactivating microbial contaminations. The obtained results demonstrate a remarkable sturdiness of mucins, which opens up broad possibilities for them to be further processed into materials, e.g., as parts of biomedical products.     

Conjugation of poor inhibitors with surface binding groups: a strategy to improve inhibition

Conjugation of surface binding groups with inhibitors for carbonic anhydrase leads to the conversion of weak inhibitors to strong inhibitors.     

Ambewelamides A and B, antineoplastic epidithiapiperazinediones isolated from the lichen Usnea sp.

Two potently cytotoxic epidithiapiperazinediones, ambewelamides A (1) and B (2), have been isolated from the lichen Usnea sp. collected in Sri Lanka. The structures were determined by a combination of X-ray crystallographic and spectroscopic analyses.     

Long-term stability of the elemental composition in biological materials

Summary Lyophilized and radiation sterilized biological certified reference materials (CRMs) are believed to be stable in their chemical composition. Generally, the certifying agencies consider the certificates of these biological CRMs valid for a 5-year shelf life, i.e., apart from measurable moisture content, the chemical composition should not change during that time. The long-term behavior of fresh frozen material is not known. In this study the elemental compositions of the Bovine Liver Standard Reference Material (SRM 1577) and human liver tissue samples are evaluated over a time period of more than 7 years. The concentrations of selected elements were determined by neutron activation analysis at various times. The initial evaluation of zinc, selenium and arsenic results gives no indication of changes during 7 years storage of fresh frozen tissues, however, a trend towards lower arsenic concentrations has been observed in SRM 1577 during a 10-year period.

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Langzeitstabilität der Elementzusammensetzung in biologischen Materialien