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991.
992.
993.
Makarov A Denisov E Lange O Horning S 《Journal of the American Society for Mass Spectrometry》2006,17(7):977-982
Using a novel orbitrap mass spectrometer, the authors investigate the dynamic range over which accurate masses can be determined (extent of mass accuracy) for short duration experiments typical for LC/MS. A linear ion trap is used to selectively fill an intermediate ion storage device (C-trap) with ions of interest, following which the ensemble of ions is injected into an orbitrap mass analyzer and analyzed using image current detection and fast Fourier transformation. Using this technique, it is possible to generate ion populations with intraspectrum intensity ranges up to 10(4). All measurements (including ion accumulation and image current detection) were performed in less than 1 s at a resolving power of 30,000. It was shown that 5-ppm mass accuracy of the orbitrap mass analyzer is reached with >95% probability at a dynamic range of more than 5000, which is at least an order of magnitude higher than typical values for time-of-flight instruments. Due to the high resolving power of the orbitrap, accurate mass of an ion could be determined when the signal was reliably distinguished from noise (S/Np-p)>2...3). 相似文献
994.
Wenhui Zhang Allen G. Oliver Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(1):o7-o11
Methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐xylopyranoside, C12H22O10, (II), crystallizes as colorless needles from water with positional disorder in the xylopyranosyl (Xyl) ring and no water molecules in the unit cell. The internal glycosidic linkage conformation in (II) is characterized by a ϕ′ torsion angle (C2′Gal—C1′Gal—O1′Gal—C4Xyl) of 156.4 (5)° and a ψ′ torsion angle (C1′Gal—O1′Gal—C4Xyl—C3Xyl) of 94.0 (11)°, where the ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH2OH) C atoms in the β‐Xyl and β‐Gal residues, respectively. By comparison, the internal linkage conformation in the crystal structure of the structurally related disaccharide, methyl β‐lactoside [methyl β‐d ‐galactopyranosyl‐(1→4)‐β‐d ‐glucopyranoside], (III) [Stenutz, Shang & Serianni (1999). Acta Cryst. C 55 , 1719–1721], is characterized by ϕ′ = 153.8 (2)° and ψ′ = 78.4 (2)°. A comparison of β‐(1→4)‐linked disaccharides shows considerable variability in both ϕ′ and ψ′, with the range in the latter (∼38°) greater than that in the former (∼28°). Inter‐residue hydrogen bonding is observed between atoms O3Xyl and O5′Gal in the crystal structure of (II), analogous to the inter‐residue hydrogen bond detected between atoms O3Glc and O5′Gal in (III). The exocyclic hydroxymethyl conformations in the Gal residues of (II) and (III) are identical (gauche–trans conformer). 相似文献
995.
Thomas E. Klepach Meredith Reed Bruce C. Noll Allen G. Oliver Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(12):o601-o606
Methyl β‐allolactoside [methyl β‐d ‐galactopyranosyl‐(1→6)‐β‐d ‐glucopyranoside], (II), was crystallized from water as a monohydrate, C13H24O11·H2O. The βGalp and βGlcp residues in (II) assume distorted 4C1 chair conformations, with the former more distorted than the latter. Linkage conformation is characterized by ϕ′ (C2Gal—C1Gal—O1Gal—C6Glc), ψ′ (C1Gal—O1Gal—C6Glc—C5Glc) and ω (C4Glc—C5Glc—C6Glc—O1Gal) torsion angles of 172.9 (2), −117.9 (3) and −176.2 (2)°, respectively. The ψ′ and ω values differ significantly from those found in the crystal structure of β‐gentiobiose, (III) [Rohrer et al. (1980). Acta Cryst. B 36 , 650–654]. Structural comparisons of (II) with related disaccharides bound to a mutant β‐galactosidase reveal significant differences in hydroxymethyl conformation and in the degree of ring distortion of the βGlcp residue. Structural comparisons of (II) with a DFT‐optimized structure, (IIC), suggest a link between hydrogen bonding, pyranosyl ring deformation and linkage conformation. 相似文献
996.
Diacetone Alcohol as Complex Ligand. Crystal Structures of [MnBr2{O=C(Me)CH2–C(Me)2OH}2] and [M{O=C(Me)CH2–C(Me)2OH}2][MCl4] with M = Fe, Co, and Zn The metal halides MnBr2 and MCl2 (M = Fe, Co, Zn) react with diacetone alcohol (4-hydroxy-4-methyl-2-pentanon) forming the title compounds, which are characterized by IR spectroscopy and crystal structure analyses. [MnBr2{O=C(Me)CH2–C(Me2)OH}2] ( 1 ): Space group C2/c, Z = 4, lattice dimensions at 293 K: a = 1189.2(4), b = 1317.2(3), c = 1200.0(3) pm, β = 102.25(3)°, R1 = 0.0256. In 1 the manganese atom is coordinated in a distorted octahedral fashion by the two cis bromine atoms and by the four oxygen atoms of the two diacetone alcohol chelating molecules. The distances Mn–[OH] (223.8 pm) and Mn–[O=C] (222.1 pm) are only slightly different. [M{O=C(Me)CH2–C(Me)2OH}2][MCl4] [M = Fe ( 2 ), Co ( 3 ), Zn ( 4 )]: 2 and 3 crystallize isotypically with each other in the space group Pc, Z = 4. Lattice dimensions for 2 at 293 K: a = 865.8(3), b = 926.3(2), c = 1401.5(1) pm, β = 104.19(2)°, R1 = 0.0421. Lattice dimensions for 3 at 293 K: a = 872.3(1), b = 925.7(1), c = 1394.2(3) pm, β = 104.79(2)°, R1 = 0.0481. As in 1 , the metal atoms of the [M{O=C(Me)CH2–C(Me)2OH}2]2+ ions in 2 and 3 are chelated in a distorted octahedral fashion by two diacetone alcohol molecules and associated cis via two μ-Cl atoms of the [MCl4]2– anions to form strands. [Zn{O=C(Me)CH2–C(Me)2OH}2][ZnCl4] ( 4 ): Space group C2/c, Z = 4. Lattice dimensions at 213 K: a = 1582.27(13), b = 1356.15(13), c = 941.93(7) pm, β = 107.283(10)°, R1 = 0.0328. The zinc atom of the dication in 4 is associated in a distorted octahedral fashion by the two diacetone alcohol chelating molecules in the equatorial positions and trans by two μ-Cl atoms of the [ZnCl4]2– ions to form strands. 相似文献
997.
Wenhui Zhang Allen G. Oliver Henry M. Vu John G. Duman Anthony S. Serianni 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(12):o502-o506
Methyl β‐D‐mannopyranosyl‐(1→4)‐β‐D‐xylopyranoside, C12H22O10, (I), crystallizes as colorless needles from water, with two crystallographically independent molecules, (IA) and (IB), comprising the asymmetric unit. The internal glycosidic linkage conformation in molecule (IA) is characterized by a ϕ′ torsion angle (O5′Man—C1′Man—O1′Man—C4Xyl; Man is mannose and Xyl is xylose) of −88.38 (17)° and a ψ′ torsion angle (C1′Man—O1′Man—C4Xyl—C5Xyl) of −149.22 (15)°, whereas the corresponding torsion angles in molecule (IB) are −89.82 (17) and −159.98 (14)°, respectively. Ring atom numbering conforms to the convention in which C1 denotes the anomeric C atom, and C5 and C6 denote the hydroxymethyl (–CH2OH) C atom in the β‐Xylp and β‐Manp residues, respectively. By comparison, the internal glycosidic linkage in the major disorder component of the structurally related disaccharide, methyl β‐D‐galactopyranosyl‐(1→4)‐β‐D‐xylopyranoside), (II) [Zhang, Oliver & Serriani (2012). Acta Cryst. C 68 , o7–o11], is characterized by ϕ′ = −85.7 (6)° and ψ′ = −141.6 (8)°. Inter‐residue hydrogen bonding is observed between atoms O3Xyl and O5′Man in both (IA) and (IB) [O3Xyl...O5′Man internuclear distances = 2.7268 (16) and 2.6920 (17) Å, respectively], analogous to the inter‐residue hydrogen bond detected between atoms O3Xyl and O5′Gal in (II). Exocyclic hydroxymethyl group conformation in the β‐Manp residue of (IA) is gauche–gauche, whereas that in the β‐Manp residue of (IB) is gauche–trans. 相似文献
998.
Ming Ding Oliver FenwickFrancesco Di Stasio Jun-Yu OuNeil Sessions Yongmin JungFranco Cacialli Gilberto Brambilla 《Optics Communications》2012,285(23):4688-4697
Nanostructured optical microfiber tips are proposed and experimentally demonstrated to efficiently confine light beyond the diffraction limit at high powers. Focused ion beam milling was used for the nanostructuring of gold-coated optical microfiber tips with both single-ramp and wedge geometries. Small apertures were formed by flat cutting or hole drilling and optical spot sizes of ∼λ/10 with high transmission efficiency were achieved. Numerical simulations were carried out to optimize the device design with circularly polarized light. Enhanced transmission efficiencies (higher than 10−2) were recorded by optimizing the overall light throughput along the fiber tips. The tip thermal behavior was investigated by launching high powers into the device and recording the tip position in a scanning near-field optical microscopy set-up. This nanostructured optical microfiber tip has the potential for applications in optical recording, scanning near-field optical microscopy and lithography. 相似文献
999.
Frequency-shifted feedback (FSF) lasers have emerged as powerful tools for precision distance metrology. At the output of a Michelson interferometer, the detected rf spectra of the FSF laser light contain a length-dependent heterodyne beat signal whose linewidth ultimately limits the achievable accuracy of length measurements. Here, we demonstrate a narrow-linewidth chirped frequency comb from an FSF Ti:sapphire ring laser seeded by a phase-modulated, ultra-low-phase-noise, single-frequency fiber laser. We experimentally investigate the influence of the seed laser linewidth on the resulting width and shape of the length-dependent rf beat signal. An ultranarrow heterodyne beat linewidth of <20 Hz is observed. 相似文献
1000.