This article illustrates the importance of having analytical data on the vitamin and mineral contents of dietary supplements
in nutrition studies, and describes efforts to develop an analytically validated dietary supplement ingredient database (DSID)
by a consortium of federal agencies in the USA. Preliminary studies of multivitamin mineral supplements marketed in the USA
that were analyzed as candidates for the DSID are summarized. Challenges are summarized, possible future directions are outlined,
and some related programs at the Office of Dietary Supplements, National Institutes of Health are described. The DSID should
be helpful to researchers in assessing relationships between intakes of vitamins and minerals and health outcomes. 相似文献
The reaction of [Ru3III (μ3-O)(μ-O2CCF3)6(H2O)3](O2CCF3) in methanol gives two solvates, [Ru3O(O2CCF3)6(DMSO)3] · 1/2H2O (I) and [Ru3O(O2CCF3)6(DMSO)3] · H2O (II), of a novel trinuclear mixedvalence Ru(II,III,III) trifluoroacetate complex, where two DMSO molecules are coordinated to the Ru atoms through the O atom, while the third DMSO molecule is coordinated through the S atom. According to the X-ray diffraction data, the complex can crystallize in two crystal systems: triclinic (I) (space group P\(\overline 1 \)) and monoclinic (II) (space group P21/m). The unit cell parameters for I are: a = 9.354, b = 11.005, c = 20.846 Å, α = 99.10, β = 96.38, γ = 92.17, Z = 2; R = 7.27%; for I are: a = 9.186, b = 17.044, c = 13.091 Å, β = 101.10, Z = 2; R = 14.18%. 相似文献
The reversible red and far-red light-induced transitions of cyanobacterial phytochrome Cph1 from Synechocystis PCC 6803 were investigated by Fourier transform infrared (FTIR) difference spectroscopy. High-quality light-induced Pfr-Pr difference FTIR spectra were recorded for the 58 kDa N-terminal domain of Cph1 by repetitive photochemical cycling and signal averaging. The Pfr-Pr difference spectra in H(2)O and D(2)O were very similar to those previously reported for full-length 85 kDa Cph1.(1) Published assignments were extended by analysis of the effects of (13)C and (15)N isotope substitutions at selected sites in the phycocyanobilin chromophore and by (15)N global labeling of the protein. The Pfr-Pr difference spectra were dominated by an amide I peak/trough at 1653 cm(-1)(+)/1631 cm(-1)(-) and a smaller amide II band at 1554 cm(-1). Labeling effects allowed specific chromophore assignments for the C(1)=O (1736 cm(-1)(-)/1724 cm(-1)(+)) and C(19)=O (1704 cm(-1)(-)) carbonyl vibrations, C=C vibrations at 1589 cm(-1)(+), and bands at 1537(-), 1512(+), 1491(-), 1163(+), 1151(-), 1134(+), 1109(-), and 1072(-) cm(-1) that must involve chromophore C-N bonds. A variety of additional changes were insensitive to isotope labeling of the chromophore. Effects of (15)N labeling of the protein were used to tentatively assign some of these to specific amino acid changes. Those insensitive to (15)N labeling included a protonated aspartic or glutamic acid at 1734 cm(-1)(-)/1722 cm(-1)(+) and a cysteine at 2575 cm(-1)(+)/2557 cm(-1)(-). Bands sensitive to (15)N protein labeling at 1487 cm(-1)(+)/1502 cm(-1)(-) might arise from trytophan and bands at 1261 cm(-1)(+)/1244 cm(-1)(-) and 1107 cm(-1)(-)/1095 cm(-1)(+) might arise from a histidine environment or protonation change. These assignments are discussed in light of the 15Z-E photoisomerization model of phototransformation and the associated protein conformational changes. 相似文献
We assessed the ability of luminescent quantum dots (QDs) to function as energy acceptors in fluorescence resonance energy transfer (FRET) assays, with organic dyes serving as donors. Either AlexaFluor 488 or Cy3 dye was attached to maltose binding protein (MBP) and used with various QD acceptors. Steady-state and time-resolved fluorescence measurements showed no apparent FRET from dye to QD. We attribute these observations to the dominance of a fast radiative decay rate of the donor excitation relative to a slow FRET decay rate. This is due to the long exciton lifetime of the acceptor compared to that of the dye, combined with substantial QD direct excitation. 相似文献
The thermal decomposition of sodium ethyl xanthate (SEX) was used to compare the techniques of pyrolysis-gas chromatography-mass
spectrometry (py-GC-MS), thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR), and TG-MS.
In the py-GC-MS analysis, SEX was pyrolysed at 400°C in an inert atmosphere. Major gases evolved were carbon disulfide, diethyl
sulfide, ethanol, and carbonyl sulfide. The TG of SEX exhibited a sharp mass loss at 201°C (42.3%) and a gradual mass loss
at 217-325°C (20.8 %). The MS spectra of the evolved gases were complex due to overlapping of molecular, isotope, and fragment
ion signals. Using the MS in selected ion monitoring mode, the major gases evolved were found to be carbon disulfide and carbonyl
sulfide. The FTIR spectra of the evolved gases displayed vibrational frequencies due to alkanes, carbonyls, carbonyl sulfide,
and carbon disulfide.
From the analyses it was concluded that py-GC-MS provided unambiguous gas identification. Interpretation of the MS results
was reliant on the py-GC-MS results, and the FTIR data was limited to identifying gases with very characteristic vibration
frequencies.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
Gaseous bis(hexamethydisilylamido)mercury(II), Hg{N(SiMe3)2)2}2, has been studied by electron diffraction at a nozzle temperature of ca 390 K.
The diffraction data are consistent with a model consisting only of monomers. By assuming the NHgN chain to be linear and the HgHSi2 fragments to be planar, an equilibrium conformer with a staggered Si2NHgNSi2 skeleton of Dad-symmetry may be brought into a nice agreement with the observed diffraction data. The relatively large value of the vibrational amplitude of the inter-ligand SiSi distance, 0.26(12) A, indicates that the ligands undergo large amplitude vibrations about the NHgN axis. Steric considerations as well as the magnitude of the rotational barrier as estimated from the diffraction data (ca. 2 kcal mol−1) show that this motion is hindered. A model with an eclipsed, co-planar Si2NHgNSi2 backbone of Dadsymmetry could not satisfactorily be brought into agreement with the observed diffraction data.
The values of some relevant key-parameters are: ra(Hg---N) = 2.01(2) A, ra(Si---N) = 1.732(9) A, ra(Si---C) = 1.883(6) A;HgNSi = 116.0(1.0)°, SiNSi = 128.0(2.0)°, NSiC= 111.8(1.2)° and SiCH = 111.0(2.0)°. The trimethylsilyl groups are twisted 25(3)° away from their references positions typified by one Si---C bond of each such group eclipsing the adjacent Hg---N bond, in such a way that the overall symmetry of the model is lowered from Dad to S4. 相似文献
The hydrodynamically thinned diffusion layer at a sinusoidally rocking disc is approximately uniform and can be expressed in terms of a diffusion layer thickness with D, the diffusion coefficient of the redox active species, v, the kinematic viscosity, Θ, the total rocking angle (here 90 degrees), and f, the rocking frequency (ranging here from 0.83 to 25 Hz). For the one‐electron oxidation of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) in aqueous carbonate buffer pH 9.5, it is shown that there is quantitative agreement between the expression for the diffusion layer thickness and experimental data. Next, for seven primary alcohols, the catalytic TEMPO‐mediated oxidation mechanism is investigated under rocking disc conditions. Chemical rate constants are evaluated (by varying the diffusion layer thickness) employing the DigiElch4.F simulation package. Trends in the chemical rate constants (compared with DFT calculations) suggest enhanced reactivity for methanol versus higher primary alcohols and for aromatic versus non‐aromatic primary alcohols. Rocking disc voltammetry allows quantitative mechanistic analysis in the laminar flow regime. 相似文献
Activation of matrix metalloproteinase zymogen (pro-MMP) is a vital homeostatic process, yet its molecular basis remains unresolved. Using stopped-flow X-ray spectroscopy of the active site zinc ion, we determined the temporal sequence of pro-MMP-9 activation catalyzed by tissue kallikrein protease in milliseconds to several minutes. The identity of three intermediates seen by X-ray spectroscopy was corroborated by molecular dynamics simulations and quantum mechanics/molecular mechanics calculations. The cysteine-zinc interaction that maintains enzyme latency is disrupted via active-site proton transfers that mediate transient metal-protein coordination events and eventual binding of water. Unexpectedly, these events ensue as a direct result of complexation of pro-MMP-9 and kallikrein and occur before proteolysis and eventual dissociation of the pro-peptide from the catalytic site. Here we demonstrate the synergism among long-range protein conformational transitions, local structural rearrangements, and fine atomic events in the process of zymogen activation. 相似文献
The excitation and emission properties of several psoralen derivatives are compared using conventional single-photon excitation and simultaneous two-photon excitation (TPE). Two-photon excitation is effected using the output of a mode-locked titanium: sapphire laser, the near infrared output of which is used to promote non-resonant TPE directly. Specifically, the excitation spectra and excited-state properties of 8-methoxypsoralen and 4′-aminomethyl-4,5,8-trimethylpsoralen are shown to be equivalent using both modes of excitation. Further, in vitro feasibility of two-photon photodynamic therapy (PDT) is demonstrated using Salmonella typhimurium. Two-photon excitation may be beneficial in the practice of PDT because it would allow replacement of visible or UV excitation light with highly penetrating, nondamag-ing near infrared light and could provide a means for improving localization of therapy. Comparison of possible laser excitation sources for PDT reveals the titanium: sapphire laser to be exceptionally well suited for nonlinear excitation of PDT agents in biological systems due to its extremely short pulse width and high repetition rate that together provide efficient PDT activation and greatly reduced potential for biological damage 相似文献