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991.
Hatsis P Brombacher S Corr J Kovarik P Volmer DA 《Rapid communications in mass spectrometry : RCM》2003,17(20):2303-2309
In this work, a high repetition rate laser matrix-assisted laser desorption/ionization (MALDI) source is studied on a quadrupole-time-of-flight (QqTOF) and a triple quadrupole (QqQ) mass spectrometer for rapid quantification of small pharmaceutical drugs. The high repetition rate laser allows an up to 100-fold higher pulse frequency as compared with regular MALDI lasers, resulting in much larger sample throughput and number of accumulated spectra. This increases the reproducibility of signal intensities considerably, with average values being around 5% relative standard deviation after taking into account the area ratio of the analyte to an internal standard. Experiments were conducted in MS/MS mode to circumvent the large chemical background due to MALDI matrix ions in the low mass range. The dynamic range of calibration curves on the QqTOF mass spectrometer extended over at least two orders of magnitude, whereas on the QqQ it extended over at least three orders of magnitude. Detection limits ranged from 60-400 pg/microL on the QqTOF and from 6-70 pg/microL on the QqQ for a series of benzodiazepines. The benzodiazepine content of commercial pill formulations was quantified, and less than 5% error was obtained between the present method and the manufacturer's certified values. Furthermore, a high sample throughput was achieved with this method, so that a single MALDI spot could be quantitatively scanned in as little as 15 s, and an entire 96-well MALDI plate in 24 min. 相似文献
992.
993.
The photochemistry of various Roussin's red ester compounds of the general formula Fe(2)(SR)(2)(NO)(4), where R = CH(3), CH(2)CH(3), CH(2)C(6)H(5), CH(2)CH(2)OH, and CH(2)CH(2)SO(3)(-), were investigated. Continuous photolyses of these ester compounds in aerated solutions led to the release of NO with moderate quantum yields for the photodecomposition of the ester (Phi(RSE) = 0.02-0.13). Electrochemical studies using an NO electrode demonstrated that 4 mol of NO are generated for each mole of ester undergoing photodecomposition. Nanosecond flash photolysis studies of Fe(2)(SR)(2)(NO)(4) (where R = CH(2)CH(2)OH and CH(2)CH(2)SO(3)(-)) indicate that the initial photoreaction is the reversible dissociation of NO. In the absence of oxygen, the presumed intermediate, Fe(2)(SR)(2)(NO)(3), undergoes second-order reaction with NO to regenerate the parent cluster with a rate constant of k(NO) = 1.1 x 10(9) M(-1) s(-1) for R = CH(2)CH(2)OH. Under aerated conditions the intermediate reacts with oxygen to give permanent photochemistry. 相似文献
994.
[structure: see text] Post-assembly covalent modification using Wittig chemistry of [2]rotaxane ylides, wherein NH(2)(+) centers in the dumbbell-shaped components are recognized by dibenzo[24]crown-8 (DB24C8) rings, has afforded a [3]catenane and a [3]rotaxane with a precise and synthetically prescribed shortage of DB24C8 rings. The nondegenerate pairs of translational isomers present in both of these interlocked molecular compounds provide the fundamental platform on which to construct sensory devices and nanochemomechanical systems. 相似文献
995.
Singh SB Herath K Guan Z Zink DL Dombrowski AW Polishook JD Silverman KC Lingham RB Felock PJ Hazuda DJ 《Organic letters》2002,4(9):1431-1434
[structure: see text]. Integramides A and B are two novel 16-mer linear peptides rich in C(alpha)-methyl amino acids that were isolated from fungal extracts of Dendrodochium sp. by employing a bioassay-guided isolation procedure using recombinant HIV-1 integrase. The structure and stereochemistry were elucidated by a combination of 2D NMR and ESI- and FAB-MS including MS/MS studies and by Marfey's method. Integramides A and B inhibited the coupled reaction of HIV-1 integrase with IC50 values of 17 and 10 microM, respectively. 相似文献
996.
The metal ion distribution on the two metal sites of monoclinic Mn1?xCux(HCOO)2 · 2(H,D)2O mixed crystals are studied by infrared and Raman spectroscopic methods. The spectral regions 3 200–3 400 cm?1 (vOH), 2 875–2 990 cm?1 (vCH), 2 330–2 500 cm?1 (vOD of matrix isolated HDO molecules), 1 350–1 400 cm?1 (symmetric CO2 stretching modes), 570–950 cm?1 (H2O librations), and 490 cm?1 (M? O lattice modes) are mostly sensitive to the metal ions present. The frequency shifts of these bands with increasing content of copper show that Cu2+ prefers the M(1) site, coordinated by HCOO? only. The strengths of the hydrogen bonds increase on going from manganese to copper formate, due to the increased synergetic effect of Cu2+. Solubility and X-ray data of the mixed crystals are included. Irrespective of the same crystal structure, two series of mixed crystals are formed: eutonic area at 0.65 ≥ x ≥ 0.5. 相似文献
997.
Deacon GB Evans DJ Junk PC Lork E Mews R Zemva B 《Dalton transactions (Cambridge, England : 2003)》2005,(13):2237-2238
Addition of 15-crown-5 to [GdF(AsF6)2], both dissolved in liquid SO2, and crystallisation at -30 degrees C has led to the isolation of the tetranuclear ionic complex [Gd4F7(15-crown-5)4][AsF6]5.6 SO2 which is stable up to--10 degrees C where SO2 loss leads to loss of crystallinity. 相似文献
998.
Hert J Willett P Wilton DJ Acklin P Azzaoui K Jacoby E Schuffenhauer A 《Journal of chemical information and computer sciences》2004,44(3):1177-1185
Fingerprint-based similarity searching is widely used for virtual screening when only a single bioactive reference structure is available. This paper reviews three distinct ways of carrying out such searches when multiple bioactive reference structures are available: merging the individual fingerprints into a single combined fingerprint; applying data fusion to the similarity rankings resulting from individual similarity searches; and approximations to substructural analysis. Extended searches on the MDL Drug Data Report database suggest that fusing similarity scores is the most effective general approach, with the best individual results coming from the binary kernel discrimination technique. 相似文献
999.
A differential pulse voltammetric study of complexes of Cd(II) and Pb(II) with crown ethers is reported. Measured log K(1) values for Cd(II) with 18-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane), 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane), and 12-crown-4 (1,4,7,10-tetraoxacyclododecane) are respectively 2.53 (+/-0.06), 1.97 (+/-0.07), and 1.72 (+/-0.08) and for Pb(II) with 18-crown-6 is 4.17 (+/-0.03), all at 25 degrees C in 0.1 M LiNO(3). Cd(II) is smaller than is usually associated with strong bonding with crown ethers. The high log K(1) values for Cd(2+) with crown ethers found here are discussed in terms of distortion of Cd(II) by relativistic effects. The resulting plasticity of the coordination geometry of the Cd(II) ion allows it to meet the metal ion size requirements of all the crown ethers, allowing high log K(1) values to occur. Crystal structures for [Cd(bz-18-crown-6)(SCN)(2)] (1) (bz-18-crown-6 = benzo-1,4,7,10,13,16-hexaoxacyclooctadecane) and [K(18-crown-6)][Cd(SCN)(3)] (2) are reported. 1 was triclinic, space group P1, a = 8.5413(2), b = 10.0389(2), and c = 13.4644(2) A, alpha = 94.424(1), beta = 102.286(1), and gamma = 93.236(1) degrees, Z = 2, and final R = 0.023. 2 was orthorhombic, space group Cmc2(1), a = 14.7309(3), b = 15.1647(3), and c = 10.6154(2) A, Z = 4, and final R = 0.020. In 1, the Cd occupies the cavity of the bz-18-crown-6 with long average Cd-O bond lengths of 2.65 A and is N-bonded to the thiocyanates with short average Cd-N bonds of 2.12 A. In [Cd(bz-18-crown-6)(SCN)(2)], the linear coordination involving the Cd and the two N-bonded thiocyanate groups in 1 is discussed in terms of the role of relativistic effects in the tendency to linear coordination geometry in group 12 metal ions. In 2 Cd forms a polymeric structure involving thiocyanate bridges between Cd atoms and K(+) occupies the cavity of the crown ether. 2 highlights the fact that cadmium is almost never S-bonded to thiocyanate except in bridging thiocyanates. 相似文献
1000.
Peter M.W. Gill Darragh P. O'Neill Nicholas A. Besley 《Theoretical chemistry accounts》2003,109(5):241-250
Two-electron distribution functions and intracules are functions of electronic coordinates and occupy an important, and frequently
overlooked, middle ground between the beguiling simplicity of electron densities and the bewildering complexity of wavefunctions.
We survey the functions that have been considered by earlier workers and introduce two new ones, the Wigner intracule and
the action intracule, that have not previously been discussed. To illustrate their usefulness, we consider the intracules
of jellium, a few small atoms and the dissociating hydrogen molecule.
Received: 26 July 2002 / Accepted: 20 October 2002 /
Published online: 30 January 2003
Correspondence to: P.M.W. Gill e-mail: peter.gill@nott.ac.uk 相似文献