A fuzzy distance metric for measuring the dissimilarity of planar chromatographic profiles with application to denaturing gradient gel electrophoresis data from human skin microbes: demonstration of an individual and gender-based fingerprint

A newly devised fuzzy metric for measuring the dissimilarity between two planar chromatographic profiles is proposed in this paper. It does not require an accurately assigned sample-feature matrix and can cope with slight imprecision of the positional information. This makes it very suitable for 1-D techniques which do not have a second spectroscopic dimension to aid variable assignment. The usefulness of this metric has been demonstrated on a large data set consisting of nearly 400 samples from Denaturing Gradient Gel Electrophoresis (DGGE) analysis of microbes on human skin. The pattern revealed by this dissimilarity metric was compared with the one represented by a sample-feature matrix and highly consistent results were obtained. Several pattern recognition techniques have been applied on the dissimilarity matrix based on this dissimilarity metric. According to rank analysis, within-individual variation is significantly less than between-individual variation, suggesting a unique individual microbial fingerprint. Principal Coordinates Analysis (PCO) suggests that there is a considerable separation between genders. These results suggest that there are specific microbial colonies characteristic of individuals.     

Aggregative growth of silicalite-1

Precursor silica nanoparticles can evolve to silicalite-1 crystals under hydrothermal conditions in the presence of tetrapropylammonium (TPA) cations. It has been proposed that in relatively dilute sols of silica, TPA, water, and ethanol, silicalite-1 growth is preceded by precursor nanoparticle evolution and then occurs by oriented aggregation. Here, we present a study of silicalite-1 crystallization in more concentrated mixtures and propose that growth follows a path similar to that taken in the dilute system. Small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and high-resolution transmission electron microscopy (HRTEM) were used to measure nanoparticle size and to monitor zeolite nucleation and early-stage crystal development. The precursor silica nanoparticles, present in the clear sols prior to crystal formation, were characterized using two SAXS instruments, and the influence of interparticle interactions is discussed. In addition, SAXS was used to detect the onset of secondary particle formation, and HRTEM was used to characterize their structure and morphology. Cryo-TEM allowed for in situ visual observation of the nanoparticle population. Combined results are consistent with growth by aggregation of silica nanoparticles and of the larger secondary crystallites. Finally, a unique intergrowth structure that was formed during the more advanced growth stages is reported, lending additional support for the proposal of aggregative growth.     

Tight integral duality gap in the Chinese Postman problem

LetG = (V, E) be a graph and letw be a weight functionw:E Z ⁺. Let be an even subset of the vertices ofG. AT-cut is an edge-cutset of the graph which dividesT into two odd sets. AT-join is a minimal subset of edges that meets everyT-cut (a generalization of solutions to the Chinese Postman problem). The main theorem of this paper gives a tight upper bound on the difference between the minimum weightT-join and the maximum weight integral packing ofT-cuts. This difference is called the (T-join) integral duality gap. Let _w be the minimum weight of aT-join, and letv _w be the maximum weight of an integral packing ofT-cuts. IfF is a non-empty minimum weightT-join, andn _F is the number of components ofF, then we prove that _w —v _w n _F –1.This result unifies and generalizes Fulkerson's result for |T|=2 and Seymour's result for |T|= 4.For a certain integral multicommodity flow problem in the plane, which was recently proved to be NP-complete, the above result gives a solution such that for every commodity the flow is less than the demand by at most one unit.Research of the first author was partially supported by Technion V.P.R. Fund — C. and J. Bishop Research Fund, and Argentinian Research Fund.Part of this work was done as part of the author's D.Sc. Thesis in the Faculty of Industrial and Management Engineering, Technion — Israel Institute of Technology, Haifa. Research of this author was partially supported by Technion V.P.R. Fund — The Baltimore Fund for Industrial Engineering and Management Research.     

Ultrafast Charge Delocalization Dynamics of Ambient Stable CsPbBr3 Nanocrystals Encapsulated in Polystyrene Fiber

CsPbBr₃ nanocrystals (NCs) encapsulated in a transparent polystyrene (PS) fiber matrix (CsPbBr₃@PS) have been synthesized to protect the NCs. The ultrafast charge delocalization dynamics of the embedded NCs have been demonstrated, and the results are compared with the pristine CsPbBr₃ in toluene. The electrospinning method was employed for the preparation of CsPbBr₃@PS fibers by using a polystyrene solution doped with pre-synthesized CsPbBr₃ and characterized by XRD, HRTEM, and X-ray photoelectron spectroscopy (XPS). Energy level diagrams of CsPbBr₃ and PS suggest that CsPbBr₃@PS fibers make a type I core–shell structure. The carrier cooling for CsPbBr₃@PS fibers is found to be much slower than pure CsPbBr₃ NCs. This observation suggests that photoexcited electrons from CsPbBr₃ NCs get delocalized from the conduction band of the perovskite to lowest unoccupied molecular orbital (LUMO) of the PS fiber matrix. The CsPbBr₃@PS fibers possess remarkable stability under ambient conditions as well as in water over months. The clear understanding of charge carrier relaxation dynamics of CsPbBr₃ confined in PS fibers could help to design robust optoelectronic devices.     

Monobenzylation Of 1,n-Diols via Dibutylstannylene Intermediates

Symmetrical primary l,n-diols, HO(CH_2)nOH, of any chain length from n = 2-10, can be selectively monobenzylated via sequential treatment with dibutyltin oxide and benzyl bromide.     

Bioavailability and biotransformation of sulforaphane and erucin metabolites in different biological matrices determined by LC–MS–MS

The food-related isothiocyanate sulforaphane (SFN), a hydrolysis product of the secondary plant metabolite glucoraphanin, has been revealed to have cancer-preventive activity in experimental animals. However, these studies have often provided inconsistent results with regard to bioavailability, bioaccessibility, and outcome. This might be because the endogenous biotransformation of SFN metabolites to the structurally related erucin (ERN) metabolites has often not been taken into account. In this work, a fully validated liquid chromatography tandem mass spectrometry (LC–MS–MS) method was developed for the simultaneous determination of SFN and ERN metabolites in a variety of biological matrices. To reveal the importance of the biotransformation pathway, matrices including plasma, urine, liver, and kidney samples from mice and cell lysates derived from colon-cancer cell lines were included in this study. The LC–MS–MS method provides limits of detection from 1 nmol L^?1 to 25 nmol L^?1 and a mean recovery of 99 %. The intra and interday imprecision values are in the range 1–10 % and 2–13 %, respectively. Using LC–MS–MS, SFN and ERN metabolites were quantified in different matrices. The assay was successfully used to determine the biotransformation in all biological samples mentioned above. For a comprehensive analysis and evaluation of the potential health effects of SFN, it is necessary to consider all metabolites, including those formed by biotransformation of SFN to ERN and vice versa. Therefore, a sensitive and robust LC–MS–MS method was validated for the simultaneous quantification of mercapturic-acid-pathway metabolites of SFN and ERN.

Open image in new window

Graphical Abstract Biotransformation of sulforaphane and erucin metabolites in mice and cell culture

     

Challenges in determining perchlorate in biological tissues and fluids: implications for characterizing perchlorate exposure

The ability to measure environmental contaminants in biological tissues and fluids is important in the characterization of exposure. However, the analysis of certain contaminants in these matrices presents significant challenges. Perchlorate (ClO₄⁻) has emerged as a potential contaminant of concern primarily in drinking water and also in contaminated food. Significant advances have been made in the analysis of perchlorate in environmental matrices (water, soil) by ion chromatography (IC). In contrast, the analysis of perchlorate in extracts of biological tissues and fluids (vegetation, organs, milk, blood, urine, etc.) presents several challenges including small sample sizes, extracts with high matrix conductivity, and co-elution of other ions during IC analysis. To be able to detect low concentrations of perchlorate in biological samples, interferences must be removed or minimized, such as through the use of preparative chromatography cleanup techniques and/or alternative analytical methods less susceptible to common interferences (preconcentration or mass spectrometric detection). We present discussion and examples of the challenges encountered in the analysis of tissue extracts and fluids for perchlorate by IC and how some of those analytical challenges have been overcome.