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71.
In this paper we study the hyperstructures, saidP-hypergroupoids, (H, P*) in whichH is a set andP* is one of the hyperoperations defined as follows: ?(x, y) εH 2,xP*y=xyP orxP*y=Pxy whereP is a subset ofH. In particular we give a general formula for to express the simple hyperproducts ofn elements and then we consider some cases in which (H, P*) is feebly associative. We study, in such cases theβ-relations. 相似文献
72.
Signori AM Santos Kde O Eising R Albuquerque BL Giacomelli FC Domingos JB 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17772-17779
A new and straightforward method for screening highly catalytically active silver nanoparticle-polymer composites derived from branched polyethyleneimine (PEI) is reported. The one-step systematic derivatization of the PEI scaffold with alkyl (butyl or octyl) and ethanolic groups led to a structural diversity correlated to the stabilization of silver nanoparticles and catalysis. Analysis of PEI derivative libraries identified a silver nanoparticle-polymer composite that was able to efficiently catalyze the p-nitrophenol reduction by NaBH(4) in water with a rate constant normalized to the surface area of the nanoparticles per unit volume (k(1)) of 0.57 s(-1) m(-2) L. Carried out in the presence of excess NaBH(4), the catalytic reaction was observed to follow pseudo-first-order kinetics and the apparent rate constant was linearly dependent on the total surface area of the silver nanoparticles (Ag-NPs), indicating that catalysis takes place on the surface of the nanoparticles. All reaction kinetics presented induction periods, which were dependent on the concentration of substrates, the total surface of the nanoparticles, and the polymer composition. All data indicated that this induction time is related to the resistance to substrate diffusion through the polymer support. Hydrophobic effects are also assumed to play an important role in the catalysis, through an increase in the local substrate concentration. 相似文献
73.
George Zonios Aikaterini Dimou Mauro Carrara Renato Marchesini 《Photochemistry and photobiology》2010,86(1):236-240
We present an in vivo study of the optical properties of common nevi, dysplastic nevi and malignant melanoma skin lesions in human subjects. Reflectance spectra were measured on 1379 skin lesions, in the visible and near-infrared spectral regions, using a spectral imaging system, in a clinical setting. Analysis of the data using a reflectance model revealed differences between the optical properties of melanin present in nevi and melanoma lesions. These differences, which are in agreement with our previous observations on average reflectance spectra, may be potentially useful for the noninvasive characterization of pigmented skin lesions and the early diagnosis of melanoma. 相似文献
74.
Francesca Tessore Dr. Elena Cariati Prof. Franco Cariati Prof. Dominique Roberto Prof. Renato Ugo Prof. Patrizia Mussini Prof. Cristiano Zuccaccia Dr. Alceo Macchioni Prof. 《Chemphyschem》2010,11(2):495-507
A series of 4‐X‐1‐methylpyridinium cationic nonlinear optical (NLO) chromophores (X=(E)‐CH?CHC6H5; (E)‐CH?CHC6H4‐4′‐C(CH3)3; (E)‐CH?CHC6H4‐4′‐N(CH3)2; (E)‐CH?CHC6H4‐4′‐N(C4H9)2; (E,E)‐(CH?CH)2C6H4‐4′‐N(CH3)2) with various organic (CF3SO3?, p‐CH3C6H4SO3?), inorganic (I?, ClO4?, SCN?, [Hg2I6]2?) and organometallic (cis‐[Ir(CO)2I2]?) counter anions are studied with the aim of investigating the role of ion pairing and of ionic dissociation or aggregation of ion pairs in controlling their second‐order NLO response in anhydrous chloroform solution. The combined use of electronic absorption spectra, conductimetric measurements and pulsed field gradient spin echo (PGSE) NMR experiments show that the second‐order NLO response, investigated by the electric‐field‐induced second harmonic generation (EFISH) technique, of the salts of the cationic NLO chromophores strongly depends upon the nature of the counter anion and concentration. The ion pairs are the major species at concentration around 10?3 M , and their dipole moments were determined. Generally, below 5×10?4 M , ion pairs start to dissociate into ions with parallel increase of the second‐order NLO response, due to the increased concentration of purely cationic NLO chromophores with improved NLO response. At concentration higher than 10?3 M , some multipolar aggregates, probably of H type, are formed, with parallel slight decrease of the second‐order NLO response. Ion pairing is dependent upon the nature of the counter anion and on the electronic structure of the cationic NLO chromophore. It is very strong for the thiocyanate anion in particular and, albeit to a lesser extent, for the sulfonated anions. The latter show increased tendency to self‐aggregate. 相似文献
75.
Zhongchen Wu Konstantin Chingin Huanwen Chen Liang Zhu Bin Jia Renato Zenobi 《Analytical and bioanalytical chemistry》2010,397(4):1549-1556
The development of analytical techniques suitable for sensitive, high-throughput, and nondestructive food analysis has been
of increasing interest in recent years. In this study, mass-spectral fingerprints of various cheese products were rapidly
recorded in the mass range of m/z 50–300 Da without any sample pretreatment, using neutral desorption extractive electrospray ionization mass spectrometry
(ND-EESI-MS) in negative ion mode. The results demonstrate that both volatile and nonvolatile analytes on greasy cheese surfaces
can be directly sampled by a neutral desorption gas beam. The influence of the neutral desorption gas flow on the analyte
signal was systematically investigated. Under optimized experimental conditions, reproducible results were obtained using
ND-EESI-MS. Principal component analysis was applied to differentiate a total of 49 individual cheese samples (four different
types), which were purchased from three different supermarkets. All samples were successfully classified according to their
types; but distributors and sensory properties were not distinguishable from the spectra data. The principal components 2,
3, and 4 scores showed an excellent capacity of distinguishing types of cheese. Molecular markers of interest can be identified
using tandem mass spectrometry and matching the data with those from reference compounds. The experimental data show that
ND-EESI-MS is able to sensitively and directly detect analytes on greasy surfaces without chemical contamination, providing
a convenient method for high-throughput food analysis with a high degree of safety. 相似文献
76.
Andrea Amantonico Pawel L. Urban Renato Zenobi 《Analytical and bioanalytical chemistry》2010,398(6):2493-2504
Single-cell metabolomics is an emerging field that addresses fundamental biological questions and allows one to observe metabolic
phenomena in heterogeneous populations of single cells. In this review, we assess the suitability of different detection techniques
and present considerations on sample preparation for single-cell metabolomics. Although targeted analysis of single cells
can readily be conducted using fluorescent probes and optical instruments (microscopes, fluorescence detectors), a comprehensive
metabolomic approach requires a powerful label-free method, such as mass spectrometry (MS). Mass-spectrometric techniques
applied to study small molecules in single cells include electrospray MS, matrix-assisted laser desorption/ionization MS,
and secondary ion MS. Sample preparation is an important aspect to be taken into account during further development of methods
for single-cell metabolomics. 相似文献
77.
Liang Zhu Zhong Hu Gerardo Gamez Wai Siang Law HuanWen Chen ShuiPing Yang Konstantin Chingin Roman M. Balabin Rui Wang TingTing Zhang Renato Zenobi 《Analytical and bioanalytical chemistry》2010,398(1):405-413
By gently bubbling nitrogen gas through beer, an effervescent beverage, both volatile and non-volatile compounds can be simultaneously sampled in the form of aerosol. This allows for fast (within seconds) fingerprinting by extractive electrospray ionization mass spectrometry (EESI-MS) in both negative and positive ion mode, without the need for any sample pre-treatment such as degassing and dilution. Trace analytes such as volatile esters (e.g., ethyl acetate and isoamyl acetate), free fatty acids (e.g., caproic acid, caprylic acid, and capric acid), semi/non-volatile organic/inorganic acids (e.g., lactic acid), and various amino acids, commonly present in beer at the low parts per million or at sub-ppm levels, were detected and identified based on tandem MS data. Furthermore, the appearance of solvent cluster ions in the mass spectra gives insight into the sampling and ionization mechanisms: aerosol droplets containing semi/non-volatile substances are thought to be generated via bubble bursting at the surface of the liquid; these neutral aerosol droplets then collide with the charged primary electrospray ionization droplets, followed by analyte extraction, desolvation, ionization, and MS detection. With principal component analysis, several beer samples were successfully differentiated. Therefore, the present study successfully extends the applicability of EESI-MS to the direct analysis of complex liquid samples with high gas content. Figure
By gently bubbling nitrogen gas through beer, both volatile and non-volatile compounds can be simultaneously sampled in the form of aerosol for further analysis, allowing fast chemically fingerprinting using extractive electrospray ionization mass spectrometry (EESI-MS). 相似文献
78.
Solvent polarity plays an important role in electrospray ionization-mass spectrometry (ESI-MS), one of the most widely used
analytical methods for biochemistry. To have a comprehensive understanding of how solvent polarity affects ESI-MS measurements,
we systematically investigated the polarity change in the ESI plume formed from an ethanol solution using laser-induced fluorescence
(LIF) spectroscopy. Two solvatochromic dyes (i.e., dyes whose fluorescence emission is sensitive to solvent polarity), Nile
red and DCM (4-dicyanomethylene-2-methyl-6-p-dimethylaminostyryl-4H-pyran), were used as probes. The peak emission wavelengths
of these two dyes exhibited significant red shifts (8–12 nm) when the measuring spot was moved away from the spray tip and
in radial direction in the plume, indicating a dramatic polarity change during shrinking of the droplets. The emission intensities
were also measured with a polarity-insensitive dye as a reference. The results are consistent with the peak wavelength measurements.
Two key mechanisms responsible for the change of solvent polarity in the plume were considered, water entrainment from the
surrounding air and solvent evaporation. Furthermore, quantitative analysis of the solvent polarity change was performed by
using the Lippert-Mataga polarity parameter Δf. The value of Δf reached 0.305–0.307 at the periphery of the ESI plume, which means that the solvent polarity in the smaller droplet is close
to that of a mixture of 30% water and 70% ethanol (Δf = 0.307), even though the bulk solvent was ethanol containing less than 1% water as an impurity. 相似文献
79.
San Martin A Rovirosa J Carrasco A Orejarena S Soto-Delgado J Contreras R Chamy MC 《Natural product communications》2010,5(12):1859-1864
The sesquiterpene pacifenol is one of the main constituents of the red alga Laurencia claviformis. Earlier work on the semisynthetic derivatives of pacifenol afforded a series of halogenated sesquiterpenes. The aim of the present work was to obtain new hydroxylated derivatives of halogenated sesquiterpenes by means of microbial transformation using Aspergillus niger, Gibberella fujikuroi and Mucor plumbeus. The best results were obtained with M. plumbeus. The microbiological transformation by M. plumbeus of pacifenol, and two semisynthetic derivatives, is described. The structures of the new compounds obtained were determined by spectroscopic means. 相似文献
80.