Graphs whose signless Laplacian spectral radius does not exceed the Hoffman limit value

For a graph matrix M, the Hoffman limit value H(M) is the limit (if it exists) of the largest eigenvalue (or, M-index, for short) of M(H_n), where the graph H_n is obtained by attaching a pendant edge to the cycle C_n-1 of length n-1. In spectral graph theory, M is usually either the adjacency matrix A or the Laplacian matrix L or the signless Laplacian matrix Q. The exact values of H(A) and H(L) were first determined by Hoffman and Guo, respectively. Since H_n is bipartite for odd n, we have H(Q)=H(L). All graphs whose A-index is not greater than H(A) were completely described in the literature. In the present paper, we determine all graphs whose Q-index does not exceed H(Q). The results obtained are determinant to describe all graphs whose L-index is not greater then H(L). This is done precisely in Wang et al. (in press) [21].     

Phase formation in mixed TiO<Subscript>2</Subscript>-ZrO<Subscript>2</Subscript> oxides prepared by sol-gel method

Pure titania, zirconia, and mixed oxides (3–37 mol.% of ZrO₂) are prepared using the sol-gel method and calcined at different temperatures. The calcined samples are characterized by Raman spectroscopy, X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption porosimetry. Measurements reveal a thermal stability of the titania anatase phase that slightly increases in the presence of 3–13 mol.% of zirconia. Practically, the titania anatase-rutile phase transformation is hindered during the temperature increase above 700°C. The mixed oxide with 37 mol.% of ZrO₂ treated at 550°C shows a new single amorphous phase with a surface area of the nanoparticles double with respect to the other crystalline samples and the formed srilankite structure (at 700°C). The anatase phase is not observed in the sample containing 37 mol.% of ZrO₂. The treatment at 700°C causes the formation of the srilankite (Ti_0.63Zr_0.37O_x) phase.     

Synthesis of enantiomerically pure (R)-and (S)-1-benzoyloxypropane-2,3-diol and revision of the stereochemical outcome of the Candida antarctica lipase-catalyzed benzoylation of glycerol

Enantiomerically pure (R)- and (S)-1-benzoyloxypropane-2,3-diol have been prepared from (S)-(+)-2,2-dimethyl-1,3-dioxolane-4-methanol and used as reference compounds to correct the reported stereochemical outcome of the Candida antarctica lipase (CAL)-catalyzed benzoylation of glycerol.     

Synthesis of Differently Protected 1‐C‐Methyl‐Ribofuranoses Intermediates for the Preparation of Biologically Active 1′‐C‐Methyl‐Ribonucleosides

Starting from D‐ribose, differently protected 1‐C‐methyl‐D‐ribofuranoses have been prepared as intermediates for the synthesis of variously modified 1′‐C‐methyl‐ribonucleosides, a class of compounds potentially endowed with interesting biological activity.     

Structural and photophysical characterization of multichromophoric pyridylporphyrin-rhenium(i) conjugates

Four porphyrin-Re(I) conjugates, in which a pyridylporphyrin chromophore is directly coordinated to the electron-acceptor fragment [ fac-Re(CO) 3(bipy)] (+), were prepared: the dimeric and pentameric compounds [ fac-Re(CO) 3(bipy)(4'MPyP)](CF 3SO 3) ( 1) (4'MPyP = 4'-monopyridylporphyrin) and [ fac-{Re(CO) 3(bipy)} 4(mu-4'TPyP)](CF 3SO 3) 4 ( 2) (4'TPyP = 4'-tetrapyridylporphyrin), and the corresponding compounds with 3' rather than 4' porphyrins, [ fac-Re(CO) 3(bipy)(3'MPyP)](CF 3SO 3) ( 3) and [ fac-{Re(CO) 3(bipy)} 4(mu-3'TPyP)](CF 3SO 3) 4 ( 4). These adducts proved to be very stable in solution and were also structurally characterized in the solid state by X-ray crystallography. A detailed photophysical study was performed on the zincated adducts of the conjugates 1- 3, labeled 5, 6, and 7, respectively. In all adducts the typical fluorescence of the zinc-porphyrin unit was reduced in intensity and lifetime by the presence of the peripheral rhenium-bipy fragment(s) (heavy-atom effect). For the dyads 5 and 7 the photoinduced charge transfer process from the zinc-porphyrin to the Re(I)-bipy unit is only slightly exoergonic. Ultrafast spectroscopy experiments showed no evidence for electron transfer quenching in the dyads as such, whereas the addition of pyridine (that binds axially to zinc and thus affects the porphyrin redox potential) led to a moderately efficient photoinduced electron transfer process. In perspective, an appropriate functionalization of the bipy ligand and/or of the porphyrin chromophore might improve the thermodynamics and, thus the efficiency, of the photoinduced electron transfer process.     

A facile in situ microfluidic method for creating multivalent surfaces: toward functional glycomics

An in situ method of modifying the chemistry and topology of microfluidic surfaces in order to mimic the cellular environment is described. The binding of functionalised microbeads to microfluidic channels allows the surface-to-volume ratio of the system, and thus the number of biomolecules available for reaction, to be vastly increased, thereby enhancing the sensitivity of biochemical analyses. The sensitivity and specificity of the technique were first investigated via the study of carbohydrate-protein interactions. Beads featuring hydrazide moieties were adhered to the channel surface, after which carbohydrates (galactose and mannose) were bound to the beads in situ and reacted with fluorescently labelled proteins. Results showed a six-fold increase in fluorescent signal compared to the same process performed on a glass surface without the presence of beads, thereby demonstrating the increase in valence afforded by the method. In a subsequent study, beads, modified with galactose moieties via the in situ functionalisation technique, were used to perform studies of colon tumour cells from a cell sample. Here, the carcinoma cells exhibited superior adhesion than the normal cells due to an increased expression of active galactose receptors, thereby demonstrating the success of the biofunctionalisation method for investigating cellular mechanisms.     

Functional characterisation of metal(loid) processes in planta through the integration of synchrotron techniques and plant molecular biology

Functional characterisation of the genes regulating metal(loid) homeostasis in plants is a major focus for phytoremediation, crop biofortification and food security research. Recent advances in X-ray focussing optics and fluorescence detection have greatly improved the potential to use synchrotron techniques in plant science research. With use of methods such as micro X-ray fluorescence mapping, micro computed tomography and micro X-ray absorption near edge spectroscopy, metal(loids) can be imaged in vivo in hydrated plant tissues at submicron resolution, and laterally resolved metal(loid) speciation can also be determined under physiologically relevant conditions. This article focuses on the benefits of combining molecular biology and synchrotron-based techniques. By using molecular techniques to probe the location of gene expression and protein production in combination with laterally resolved synchrotron techniques, one can effectively and efficiently assign functional information to specific genes. A review of the state of the art in this field is presented, together with examples as to how synchrotron-based methods can be combined with molecular techniques to facilitate functional characterisation of genes in planta. The article concludes with a summary of the technical challenges still remaining for synchrotron-based hard X-ray plant science research, particularly those relating to subcellular level research.