Landau theory-based estimates for viscosity coefficients of uniaxial and biaxial nematic liquid crystals

Using Landau theory, it is shown that eight phenomenological parameters are needed to describe and distinguish the twelve viscosity coefficients of a biaxial nematic phase, or the five viscosity coefficients of a uniaxial nematic phase. The dependence of the coefficients on the macroscopic uniaxial and biaxial order parameters is established. Since these order parameters are determined by the anisotropies of the dielectric constant, we show that it should be possible to determine values for all eight of the phenomenological parameters of the theory from measurements of the temperature dependence of the five viscosities of a uniaxial phase.     

SNaPshot minisequencing to resolve mitochondrial macro‐haplogroups found in Africa

African mitochondrial DNA (mtDNA) haplogroups are divided into seven macro‐haplogroups (L0′1′2′3′4′5′6), while the rest of the world's lineages are classified as subgroups of macro‐haplogroups M, N and R. The most common approach to characterizing mtDNA variation is the sequencing of hypervariable segments I and II of the non‐coding control region of the molecule. Given the higher mutation rate within the control region compared with the coding regions of the molecule, recurrent mutations in the former can sometimes hide possible phylogenetic structure. The incorporation of haplogroup‐defining coding region mutations has helped in overcoming this limitation. By judiciously selecting 14 coding region SNPs and incorporating them into a multiplex minisequencing assay we were able to resolve mtDNA sequences from some sub‐Saharan African populations into ten macro‐haplogroups (L0–L6, M, N and R). We tested the efficacy of the panel by screening 699 individuals, consisting mostly of Khoe‐San, Bantu speakers and individuals with mixed ancestries (Coloreds) and found no inconsistencies compared with hypervariable segment sequencing results. The panel provided a fast and efficient means of classifying mtDNA into the ten mitochondrial macro‐haplogroups and provided a reliable screening to distinguish African from non‐African‐derived mtDNA lineages.     

A multi-element serum standard for neutron activation analysis

An annular ²²⁷AcBe isotopic neutron source, containing 6.6-Ci ²²⁷Ac, is described for application in fast and thermal neutron activation analysis, with high accuracy, for major constituents in ores, alloys and industrial concentrates. The characteristics of the neutron output and of the fast, epithermal and thermal flux and flux gradients is described in detail. The determination of manganese in pyrolusite ores and ferro-manganese is compared to results obtained previously with a cylindrical 1-Ci ²²⁶RaBe source. Two new sources of systematic errors have been discovered.     

A genetic algorithm for structure-based de novo design

Genetic algorithms have properties which make them attractive in de novo drug design. Like other de novo design programs, genetic algorithms require a method to reduce the enormous search space of possible compounds. Most often this is done using information from known ligands. We have developed the ADAPT program, a genetic algorithm which uses molecular interactions evaluated with docking calculations as a fitness function to reduce the search space. ADAPT does not require information about known ligands. The program takes an initial set of compounds and iteratively builds new compounds based on the fitness scores of the previous set of compounds. We describe the particulars of the ADAPT algorithm and its application to three well-studied target systems. We also show that the strategies of enhanced local sampling and re-introducing diversity to the compound population during the design cycle provide better results than conventional genetic algorithm protocols.     

Comparison of substructural epitopes in enzyme active sites using self-organizing maps

Summary This paper presents a new algorithm to compare substructural epitopes in protein binding cavities. Through the comparison of binding cavities accommodating well characterized ligands with cavities whose actual guests are yet unknown, it is possible to draw some conclusions on the required shape of a putative ligand likely to bind to the latter cavities. To detect functional relationships among proteins, their binding-site exposed physicochemical characteristics are described by assigning generic pseudocenters to the functional groups of the amino acids flanking the particular active site. The cavities are divided into small local regions of four pseudocenters having the shape of a pyramid with triangular basis. To find similar local regions, an emergent self-organizing map is used for clustering. Two local regions within the same cluster are similar and form the basis for the superpositioning of the corresponding cavities to score this match. First results show that the similarities between enzymes with the same EC number can be found correctly. Enzymes with different EC numbers are detected to have no common substructures. These results indicate the benefit of this method and motivate further studies.     

Deconvolution in microcalorimetry and an application to mass-varying systems

The behaviour of the calorimetric response in continuous injection devices, which are well suited for measurement of excess partial molar enthalpies at different concentrations, is analysed by means of heat transport models. Signal analysis of the thermal response gives the enthalpy values at very low concentrations. We establish an operating routine for the identification of the time-varying device, and a generalized deconvolution procedure to obtain, with high accuracy, the power released in the calorimeter as a function of time. The main features considered are the changes in sensitivity and dynamic properties of the experimental system due to the injection of one component in the mixture. A formal decomposition of the heat transport equations shows that typically time-invariant methods are able to deal with deconvolution in non-invariant systems.     

Functionalisation of unactivated methyl groups through cyclopalladation reactions

The transformation of the organopalladium compound (3) into the corresponding deuteriated, chlorinated, or oxidized derivatives (7), (8), or (9), (11), and (12) respectively. is described. The palladation of compound (9) takes place regioselectively leading to the palladated system (13), which is transformed into the difunctionalised oximes (15) and (16). The palladation of $\text{E}$-2,2-dimethyl and 2,2,6,6-tetramethyl-cyclohexanone oxime leads to the corresponding organopalladium compounds (17) and (27), which through deuteriation or oxidation affords the expected products (21) and (31), or (22), (23), (24), and (32), respectively. The second palladation of the compound (22) takes place on the remaining methyl group yielding the organopalladium derivative (26). Finally, $\text{E}$-lupanone oxime is palladated selectively in the 23-position leading to the organopalladium compound (38); the transformation of this compound into its 23-deuterio and 23-acetoxy- derivatives (41) and (42), respectively is also described. The stereochemistry in the palladatlon of lupanone oxime is deduced from NOE studies at 500 MHz.     

RMN 13C d'α alcoxy-indenes et d'α alcoxy-styrenes : Topologie electronique du systeme Π et une reflexion sur la relation entre deplacement chimique et reactivite dans les ethers d'enol

¹³C NMR chemical shifts of ethylenic carbon atom C_β of α alkoxy-indenes and α-alkoxy-styrenes are affected by the conformation of the OR group with respect to the double bond and hence the efficiency of p- Π conjugation but, contrary to previous results, δC_α is not affected. The phenyl group exerts a diamagnetic Π- effect on C_α and C_β which is a function of its dihedral angle with the double bond. Although δC_β is especially sensitive to the Π-electron density, the chemical shifts of the ethylenic carbons are best understood by considering the total charge density. The σ and Π contributions to the total charge density are discussed using the preferred conformation of the molecules. This approach strongly suggests that the correlation between the gradual shift of δC_α to low frequency and the gradual shift of δC_β to high frequency (relative to TMS) as R changes from RCH₃ to RtC₄H₉ in certain series of enol-ethers is not due to pΠ conjugation variations. This method of interpreting ¹³C NMR shifts, as opposed to previous methods, is compatible with explanations of other physico-chemical properties of alkyl vinyl ethers. Although it is sometimes possible to correlate the gradual shifts of δC_β with (σ + Π) electron density variations in a homogeneous series, it seems impossible to predict the relation. In all cases, there is no evident correlation between gradual shifts of δC_β(orδC_α) and the reactivity of enol ethers because one cannot consider the role of the out-of-plane conformation of the alkoxy group (which increases from RCH₃ to RtC₄H₉); however, the out of plane conformation does not have an identical effect on δC_β and the reactivity.     

Nucleation-growth kinetics of the oxidation of silver nanocrystals to silver halide crystals

The electrochemical oxidation of silver nanocrystals to silver halide crystals proceeds by a process of nucleation and growth. The mechanism is confirmed by analyzing chronopotentiograms using a new extension of nucleation theory. The theory makes it possible to derive plots of nucleation-growth currents vs potential, and growth rates vs potential, directly from experimental data. Such plots yield powerful insights into the reaction kinetics. In situ AFM imaging reveals that a few thousand of silver nanocrystals are oxidized to only a few tens of silver halide crystals, without pronounced loss of active material. The mechanism of this remarkable process is described in this paper. In particular, it is shown that the decrease in crystal population proceeds via an oversaturated silver solution, i.e., a process that is mediated by “driven” Ostwald ripening across the electrode surface. At the same time, the low solubility of silver species in bulk solution means that few silver ions escape from the surface. This combination of features explains why the transformation from silver to silver halide is near-stoichiometric yet highly reconstructive.Dedicated to our friend and colleague Professor Dr. Alan Bond on the occasion of his 60th birthday     

从月桂烯合成梨圆蚧性信息素

梨圆蚧是对果林危害较大的害虫。该虫的性信息素包括三个组分:3-亚甲基-7-甲基-7-辛烯-1-醇丙酸酯(1)、(2Z)-3,7-二甲基-2,7-辛二烯-1-醇丙酸酯(2)和(2E)-3,7-二甲基-2,7-辛二烯-1-醇丙酸酯(3)。本文介绍了通过对月桂烯进行结构改造来合成梨圆蚧性信息素,从月桂烯到1,总产率为19%。工业上从月桂烯制龋萑花醇和香叶醇,再将橙花醇和香叶醇转变为相应的氯烯醇后再还原、丙酰化即得2和3,其总产率分别为30%和28%。(以橙花醇和香叶醇计)。月桂烯可从β-蒎烯裂解而得。我国有丰富的蒎烯资源,所以开辟从月桂烯合成梨圆蚧性信息素的新途径具有重要的意义。     

A novel MALDI LIFT-TOF/TOF mass spectrometer for proteomics

A new matrix-assisted laser-desorption/ionization time-of-flight/time-of-flight mass spectrometer with the novel "LIFT" technique (MALDI LIFT-TOF/TOF MS) is described. This instrument provides high sensitivity (attomole range) for peptide mass fingerprints (PMF). It is also possible to analyze fragment ions generated by any one of three different modes of dissociation: laser-induced dissociation (LID) and high-energy collision-induced dissociation (CID) as real MS/MS techniques and in-source decay in the reflector mode of the mass analyzer (reISD) as a pseudo-MS/MS technique. Fully automated operation including spot picking from 2D gels, in-gel digestion, sample preparation on MALDI plates with hydrophilic/hydrophobic spot profiles and spectrum acquisition/processing lead to an identification rate of 66% after the PMF was obtained. The workflow control software subsequently triggered automated acquisition of multiple MS/MS spectra. This information, combined with the PMF increased the identification rate to 77%, thus providing data that allowed protein modifications and sequence errors in the protein sequence database to be detected. The quality of the MS/MS data allowed for automated de novo sequencing and protein identification based on homology searching.     

Probing the intestinal α-glucosidase enzyme specificities of starch-digesting maltase-glucoamylase and sucrase-isomaltase: synthesis and inhibitory properties of 3'- and 5'-maltose-extended de-O-sulfonated ponkoranol

The synthesis and glucosidase inhibitory activities of two C-3'- and C-5'-β-maltose-extended analogues of the naturally occurring sulfonium-ion inhibitor, de-O-sulfonated ponkoranol, are described. The compounds are designed to test the specificity towards four intestinal glycoside hydrolase family 31 (GH31) enzyme activities, responsible for the hydrolysis of terminal starch products and sugars into glucose, in humans. The target sulfonium-ion compounds were synthesized by means of nucleophilic attack of benzyl protected 1,4-anhydro-4-thio-D-arabinitol at the C-6 position of 6-O-trifluoromethanesulfonyl trisaccharides as alkylating agents. The alkylating agents were synthesized from D-glucose by glycosylation at C-4 or C-2 with maltosyl trichloroacetimidate. Deprotection of the coupled products by using a two-step sequence, followed by reduction afforded the final compounds. Evaluation of the target compounds for inhibition of the four glucosidase activities indicated that selective inhibition of one enzyme over the others is possible.     

Crystal structure and magnetic structure of TbOOH

The monoclinic modification of terbium oxide hydroxide, TbOOH, was prepared using hydrothermal technique. The crystal structure was investigated by three-dimensional single-crystal X-ray analysis and was refined to a conventional R-value of 8.1%. The space group is $\text{P2}{}_1\text{m}$, No. 11, with a = 6.04 Å, b = 3.69 Å, c = 4.33 Å, and β = 109.0°. The terbium atom is seven coordinated with oxygen atoms, and the structure is not hydrogen bonded.The compound is antiferromagnetic with a Néel temperature of 10°K. Neutron diffraction powder patterns were measured at 300°K and 4.2°K. The magnetic super lattice reflections were indexed on the basis of a monoclinic unit cell with the dimensions a_M = 2a, b_M = b, c_M = c, and β_M = β, where a, b, c, and β are the dimensions of the chemical unit cell. The structure contains two independent magnetic atoms. A nonclinear antiferromagnetic arrangement of the spins describes the magnetic structure. The spin at one atom has an angle of 43° with the ac plane and the projection of the spin on the ac plane has an angle of 59° with the a axis. The spin on the other atom has an angle of ?43° with the ac plane, the projection having the same angle of 59° with the a axis.     

Etude des reactions pericycliques sous pression—IV: Cyclodimerisation thermique de l'acroleine et de la methylvinylcetone

The thermal cyclodimerization of acrolein with methyl vinyl ketone gives selectively only one substituted dihydropyran. The rate is only slightly sensitive to the nature of the solvent; however a slight decrease of the reaction rate with increasing solvent polarity was observed. Effects of high pressure give strong support for a one-step mechanism and the formation of a transition state more compact than the adduct.     

Input,flux, and persistence of six select pesticides in San Francisco Bay

Temporal patterns of pesticide inputs to San Francisco Bay were identified and correlated with timing of application and transport mechanism. Fluxes were calculated from measured concentrations and estimated flow. Persistence of the pesticides under typical riverine or estuarine conditions were estimated from laboratory experiments. Simazine was detected most frequently and had the highest flux into the Bay, which could be explained by its continuous use and long half-life. In comparison, diazinon was detected at lower concentrations and had a lower flux which corresponded to its lower use and shorter half-life. The order-of-magnitude lower fluxes of carbofuran and methidathion corresponded to their lower use and expected hydrolysis. Molinate was detected at the highest concentration but its flux was lower than expected, considering its very high use and persistence in the laboratory experiments. Additional loss of molinate is likely to occur from volatilization and photodegradation on the rice fields. Although thiobencarb had the second highest use, it had the lowest flux of the six pesticides, which can be attributed to its loss via hydrolysis, photodegradation, volatilization, and sorption to sediments. Fluxes into San Francisco Bay were equal to or greater than those reported for other estuaries, except for the Gulf of Mexico.     

Symmetry analysis of periodicity and internal torsional conformers around a single bond

A simple formula to predict the number of equivalent conformations upon internal rotation around a single bond is derived. If the separate parts A and B, of a single bonded molecule A-B, possess N_a and N_b symmetry planes that contain the single bond, the number of symmetrical conformations is found to be Z = N_aN_b/J, where J is the number of these planes which are common. The energy potential for internal rotation then has a period of 2π/Z. Unsymmetrical conformations are infinite in number, but are shown to occur in infinite sets, each set with 2N_aN_b/J equivalent conformations. Extension to three-center molecules is also made.     

Use of ir and 13c-nmr data in the retrieval of functional groups for computer-aided structure determination

Computer-aided interpretation of ¹³C-n.m.r. and i.r. spectra of organic molecules (m.w. ? 500) is done by an artificial intelligence approach. The output of the proposed ASSIGNER system is a list of functional groups which are reasonable candidates for the final structural isomers. The procedure of finding possible functional groups and the main features of the filtering steps are outlined. One search is worked out in detail to demonstrate the capability of the system.     

From magnetic molecules to magnetic solids: An ab initio expertise

The efficiency of ab initio wavefunction based methods is demonstrated using various systems characterized by the presence of open shells. It is recalled that the low-energy spectroscopy of molecular architectures as well as extended materials is accessible and can be rationalized by including in a hierarchical way the valence (i.e. non-dynamical) and dynamical correlation effects. Such methodology not only allows one to investigate vertical transition energies but also gives access to a possible reading of the wavefunction in the ground and excited states.     

Three new vinyl acetylenes from the marine red alga laurencia

The structures of three new halogenated vinyl acetylenes are described which are natural products from various species of the red seaweed Laurencia. The structure of chlorofucin (1) isolated from Laurencia snyderae was determined by X-ray diffraction analysis. Poiteol (2) was isolated from Laurencia poitei and its structure was also determined by single crystal X-ray diffraction experiments. The structure of obtusenyne (3) was based on a combination of chemical and spectral methods. The ¹³C NMR spectra of these new compounds are presented and assignments made.     

Synthesis of a mitomycin C–lexitropsin hybrid

We have constructed hybrid drugs where mitomycin C is linked to the N-methylpyrrole carboxamide framework present in lexitropsins. The coupling reactions leading to these products are efficient and the yields are very high. An interesting spectroscopic feature of these hybrids is the red shift observed in the UV–vis spectrum. Although DFT calculations indicate the possible existence of complexes formed during the coupling reactions, these complexes were not detected. The only species produced and isolated were the mitomycin C-mono- and bis-N-methyl pyrrole conjugates.