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51.
Focsan AL Bowman MK Konovalova TA Molnár P Deli J Dixon DA Kispert LD 《The journal of physical chemistry. B》2008,112(6):1806-1819
Pulsed electron nuclear double resonance (ENDOR) and two-dimensional (2D)-hyperfine sublevel correlation spectroscopy (HYSCORE) studies in combination with density functional theory (DFT) calculations revealed that photo-oxidation of natural zeaxanthin (ex Lycium halimifolium) and violaxanthin (ex Viola tricolor) on silica-alumina produces the carotenoid radical cations (Car*+) and also the neutral carotenoid radicals (#Car*) as a result of proton loss (indicated by #) from the C4(4') methylene position or one of the methyl groups at position C5(5'), C9(9'), or C13(13'), except for violaxanthin where the epoxide at positions C5(5')-C6(6') raises the energy barrier for proton loss, and the neutral radicals #Car*(4) and #Car*(5) are not observed. DFT calculations predict the largest isotropic beta-methyl proton hyperfine couplings to be 8 to 10 MHz for Car*+, in agreement with previously reported hyperfine couplings for carotenoid pi-conjugated radicals with unpaired spin density delocalized over the whole molecule. Anisotropic alpha-proton hyperfine coupling tensors determined from the HYSCORE analysis were assigned on the basis of DFT calculations with the B3LYP exchange-correlation functional and found to arise not only from the carotenoid radical cation but also from carotenoid neutral radicals, in agreement with the analysis of the pulsed ENDOR data. The formation of the neutral radical of zeaxanthin should provide another effective nonphotochemical quencher of the excited state of chlorophyll for photoprotection in the presence of excess light. 相似文献
52.
53.
54.
Jozsef Bako Marta Szepesi Adrienn J. Veres Csaba Cserhati Zsuzsa M. Borbely Csaba Hegedus Janos Borbely 《Colloid and polymer science》2008,286(3):357-363
Nanocomposite biocompatible hydrogels (NCHG) were synthesised as model systems for in situ cured potentially local drug delivery
devices for curing periodontal infections. The composite consists of the following components: nanoparticles (NPs), matrix
gel, and chlorhexidine (CHX) as antibacterial drug. The NPs were obtained by free radical initiated copolymerization of the
monomers, 2-hydroxyethyl methacrylate (HEMA) and polyethyleneglycol dimethacrylate (PEGDMA), in aqueous solution. The same
monomers were used to prepare crosslinked matrices by photopolymerization. NCHGs were obtained by mixing NPs, monomers, and
drug in an aqueous solution then crosslinked by photopolymerization. Mechanical properties, swelling behavior, and the kinetics
of drug release have been investigated. It was found that compression strength values increased with increasing ratio of the
crosslinker PEGDMA. Incorporation of NPs into the matrix resulted similar compression strength as the matrix hydrogel. The
hydrated NCHGs swelled more slowly but admitted more water. The drug was incorporated in NPs by swelling in CHX aqueous solution
or added to the solution of monomer mixture followed by photopolymerization. Studies of release kinetics revealed that on
average 60% of the loaded drug was released. The most rapid release was observed over a 24 h period for matrix gels with low
crosslinking density. For NCHGs, the release period exceeded 48 h. An unexpected result was observed for NCHGs without drug
in the NPs. In this case, increasing release was observed for the first 24 h. Thereafter, however, the apparent quantity of
detectable drug decreased dramatically. 相似文献
55.
Jozsef Garai 《Solid State Communications》2010,150(35-36):1710-1714
It is suggested that at the melting temperature the wavelength of the average thermal phonon vibration is equal to or is a harmonic of the distance separating the atomic layers in the crystal. This resonance between the phonon and lattice vibrations equals out the energy of the vibrating atoms in the surface layer. If this “uniform” energy is higher than the energy corresponding to the metastable transition state then all the surface atoms lose its position stability. In order to make the jump to the next potential well energy is required to overcome on the viscous resistance of the liquid. If this energy, latent heat of fusion, is supplied then the atomic/molecular sheet or platelets from the surface are detached and melting occurs. The proposed model is consistent with all of the characteristic features of melting and freezing. Equations calculating the average phonon wavelength and the corresponding lattice distance at the melting temperature are derived from fundamental thermodynamic relationships. The required thermodynamic parameters are determined from experiments of the nine selected highly symmetrical solids. The calculated wavelengths of the phonon vibration are equal to or is a harmonic of the -spacing of the atomic/molecular layers in agreement with theory. 相似文献
56.
Ulam asked in 1945 if there is an everywhere dense rational set, i.e., 1 a point set in the plane with all its pairwise distances rational. Erdős conjectured that if a set S has a dense rational subset, then S should be very special. The only known types of examples of sets with dense (or even just infinite) rational subsets are
lines and circles. In this paper we prove Erdős’ conjecture for algebraic curves by showing that no irreducible algebraic
curve other than a line or a circle contains an infinite rational set. 相似文献
57.
Eva Fenyvesi Katalin Csabai Monika Molnár Katalin Gruiz Attila Murányi Jozsef Szejtli 《Journal of inclusion phenomena and macrocyclic chemistry》2002,44(1-4):413-416
An HPLC method has been developed for determination of RAMEB in soil samplescontaminated with hydrocarbons. The extraction efficiency of RAMEB from soils wasfound to depend on the soil properties. The extraction method elaborated results in agood recovery from sandy and loamy soils, but only a poor recovery was obtained from soils of high clay content.A SPE method was worked out to remove the components disturbing the HPLCanalysis, and a one-peak method has been developed for the quantitative analyses.The isomer distribution of RAMEB was characterized by fingerprint chromatograms.The new methods have been applied for determination of RAMEB content in soilsamples from field treatment. 相似文献
58.
Letn linear formsL
i
onm variables be given, normalized so that all coefficients have absolute value at most unity. Letw
1, ...,w
m
be real numbers andx
1, ...,x
m
be integers. We sayE
i
=L
i
(w
1, ...,w
m
)-L
i
(x
1, ...,x
m
) is the error in approximating thew's by thex's with respect to formL
i
It is shown that given anyw's there is an integral approximation ofx's so that the errorsE
i
are small-roughly that
simultaneously for alli. 相似文献
59.
Kepka C Lemmens R Vasi J Nyhammar T Gustavsson PE 《Journal of chromatography. A》2004,1057(1-2):115-124
An integrated process for purifying a 6.1 kilo base pair (kbp) plasmid from a clarified Escherichia coli cell lysate based on an ultra/diafiltration step combined with polymer/polymer aqueous two-phase system and a new type of chromatography is described. The process starts with a volume reduction (ultrafiltration) and buffer exchange (diafiltration) of the clarified lysate using a hollow fibre membrane system. The concentrated and desalted plasmid solution is then extracted in a thermoseparating aqueous two-phase system, where the contaminants (RNA and proteins) to a large extent are removed. While the buffer exchange (diafiltration) is necessary in order to extract the plasmid DNA exclusively to the top phase, experiments showed that the ultrafiltration step increased the productivity of the aqueous two-phase system by a factor of more than 10. The thermoseparated water phase was then subjected to a polishing step using lid bead chromatography. Lid beads are a new type of restricted access chromatography beads, here with a positively charged inner core that adsorbed the remaining RNA while its inert surface layer prevented adsorption of the plasmid DNA thus passing in the flow-through of the column. Differently-sized plasmid DNA in the range of 2.7-20.5 kbp were also partitioned in the aqueous two-phase system. Within this size range, all plasmid DNA was exclusively extracted to the top phase. The complete process is free of additives and easy scalable for use in large scale production of plasmid DNA. The overall process yield for plasmid DNA was 69%. 相似文献
60.
Jozsef Bordas-Nagy Dominique Despeyroux Keith R. Jennings 《Journal of the American Society for Mass Spectrometry》1992,3(5):502-514
Collision-induced decompositions (CID) of protonated peptides were studied using a four-sector mass spectrometer. The collision gases employed were helium and argon. The CID spectra of several peptides covering the molecular mass region of 905–2465 u were recorded. These investigations established several previously unrecognized differences between the CID spectra obtained with helium and argon as collision gases. These can be summarized as follows: (1) Structurally significant and specific side chain fragmentations (dn f, wn f and vn, ion types) are greatly reduced or completely missing in the CID spectra obtained with helium as a collision gas compared to those obtained with argon. (2) As the peptide molecular mass increases, argon, which is heavier than helium, is increasingly more efficient than helium for generating fragment ions. 相似文献