Perturbation theory for open-shell systems: Simulation of the UHF states by means of the perturbed RHF wave functions

Second-, third-, and selected fourth-order contributions to the correlation energy were calculated for a series of simple open-shell systems by means of the previously developed double-perturbation theory in the restricted MO formalism. It was found possible to assign some of the diagrams to self-consistency effects and to approximate in this way the E – E energy difference. A comparison is made with a more rigorous approach, in which the UHF ground-state wave function is expressed as a first-order perturbation expansion based on the RHF reference wave function. Distinguishing between “self-consistency” and “correlation” diagrams for open-shell systems in the RHF formulation represents a special case of a more general problem met in any double-perturbation treatment, such as, e.g., treatments of systems in the external field or perturbation expansions with noncanonical orbitals.     

Asymmetric synthesis of [7]helicene-like molecules

[reaction: see text] A new approach to nonracemic [7]helicene-like molecules has been developed. Stereoselective Co(I)-mediated [2 + 2 + 2] cycloisomerization of aromatic triynes containing an asymmetric carbon atom produces [7]helicene-like scaffolds in diastereomeric ratios up to 100:0. This central-to-helical chirality transfer can be controlled by the absolute configuration at the asymmetric center and by the presence of carbon substituents.     

Synthesis of protected peptides from the human IgG1 hinge region on PEG support using disulfide bond synthons and alkaline or enzymatic detachment

Peptides from the hinge region of human IgG1 are potential defined carriers of synthetic immunogens. Their synthesis was carried out on the soluble support—PEG-OMe 2000 using disulfide bond synthons. The loading capacity of the polymer was increased twofold by anchoring the lysine as a simple branching unit. The amino acid leucine was used as an enzymatically cleavable linker. Peptide detachment from the polymer was performed either by classical ester bond saponification or newly by peptide bond cleavage catalyzed by thermolysin in water.     

Structural basis for recognition of bacterial cell wall teichoic acid by pseudo-symmetric SH3b-like repeats of a viral peptidoglycan hydrolase

Endolysins are bacteriophage-encoded peptidoglycan hydrolases targeting the cell wall of host bacteria via their cell wall-binding domains (CBDs). The molecular basis for selective recognition of surface carbohydrate ligands by CBDs remains elusive. Here, we describe, in atomic detail, the interaction between the Listeria phage endolysin domain CBD500 and its cell wall teichoic acid (WTA) ligands. We show that 3′O-acetylated GlcNAc residues integrated into the WTA polymer chain are the key epitope recognized by a CBD binding cavity located at the interface of tandem copies of beta-barrel, pseudo-symmetric SH3b-like repeats. This cavity consists of multiple aromatic residues making extensive interactions with two GlcNAc acetyl groups via hydrogen bonds and van der Waals contacts, while permitting the docking of the diastereomorphic ligands. Our multidisciplinary approach tackled an extremely challenging protein–glycopolymer complex and delineated a previously unknown recognition mechanism by which a phage endolysin specifically recognizes and targets WTA, suggesting an adaptable model for regulation of endolysin specificity.

Combining genetic, biochemical and computational approaches, we elucidated the molecular mechanisms underlying the recognition of Listeria wall teichoic acid by bacteriophage-encoded SH3b repeats.     

Template evaporation method for controlling anatase nanocrystal size in ordered macroporous TiO2

The importance of pure-phase titanium oxide materials as catalysts, sensors, and photonic band-gap materials has been growing steadily. Recently, more attention has been focused on nanostructured titanium oxide showing controlled and periodic porosity on a nanometric scale. The nanocrystal size control of porous nanostructured titanium oxide in an anatase form is a crucial step for the organic template method. Simple template removal by evaporation in an inert atmosphere is reported in this article and compared with the calcination technique usually reported in the literature. The proposed method allows the formation of a double-porous (macro and meso) anatase phase. We demonstrate that it highly preserves the macropore order into a titanium oxide material and induces narrowly dispersed mesopores by controlling the nano-crystal size that is kept around 6 nm. For the proposed method, polystyrene beads are particularly suitable as templates, being evaporated in the temperature range of anatase existence. The final high surface area makes the materials appealing for applications as photocatalysts or sensors.     

The SO(3,3) group as a common basis for Dirac's and Proca's equations

Dirac's and Proca's equations are unified in the sense that the algebras of Dirac -matrices and Duffin-Kemmer-matrices are shown to furnish two distinct matrix representations of the Lie algebra of the SO(3,3)-group. This fact is then interpreted as evidence for the classical picture of particles described by the above-mentioned equations to be a relativistic top. It is also argued that the shape of the top is rod-like.     

Generation of Ethyl Metathiophosphate by Thermal Fragmentation of O-Ethyl N-Substituted Phosphoramidothioates

O-Ethyl N-1-adamantylphosphoramidothioate was synthesized and found to fragment on heating in inert solvents to form the pyrophosphate AdNHP(S)(OEt)OP(S)(OEt)OH. The proposed mechanism involves an elimination of the amine portion with release of ethyl metathiophosphate (EtOP(S)O), as was confirmed in previous work for the comparable structure with oxygen. This transient compound then phosphorylates the starting phosphoramidothioate. O-Ethyl N,N-diethylphosphoramidothioate was also synthesized, and while it gave a similar pyro compound on heating, the reaction mixture was more complex. Both phosphoramidothioates, however, served effectively as thiophosphorylating agents toward alcohols, a silanol, and the silanol groups on the surface of silica gel. Exploratory experiments showed that these phosphoramidothioates also could thiophosphorylate the OH group of a monoester of phosphoric acid, as well as that of phosphinic acids, forming anhydrides with the partial structure     

Intermolecular contact interactions and their temperature dependence

A model, based on inverse gas chromatography experiments, has been developed for intermolecular interaction and its temperature dependence. The model ascribes to each substance a four-component solubility parameter; the four components reflect the van der Waals, polar, electron donor, and electron acceptor interactive properties. Their values depend on temperature in the same manner as does the cohesive energy. The latter was found to depend only on the critical temperature, the acentric factor, and the reduced temperature. The model was used for evaluation of the solubility parameters from polymer-solvent interaction coefficients and their temperature dependence with high accuracy. For binary solventsolvent mixtures, the free energy of mixing and its temperature dependence, as well as enthalpy of mixing can be derived from this model with a good accuracy.     

Charge location and fragmentation under electron impact. IV—the behaviour under electron impact of some N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds

The ionization potentials of a series of N-methyl,N′-R-1,2,4-phosphadiazetidine-3-ones and related compounds have been determined. The nature of the highest occupied orbital of the molecules and the use of empirical rules to rationalize the variations in the ionization potentials are discussed. The changes in the fragmentation patterns are related to the different low ionization potential site(s) in each molecule. The occurrence of various rearrangement ions are discussed on a similar basis.     

Detecting proximities between quadrupolar nuclei by double-quantum NMR

A robust, easy to optimize, and efficient homonuclear correlation NMR experiment for half-integer quadrupolar nuclei in solids is described and has been experimentally tested on anhydrous Na2HPO4-(23Na, S= 3/2 nucleus) and as-synthesized AlPO4-14 (27Al, S= 5/2 nucleus), an aluminophosphate molecular sieve.