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961.
Williams DK Hawkridge AM Muddiman DC 《Journal of the American Society for Mass Spectrometry》2007,18(1):1-7
High mass measurement accuracy (MMA) is demonstrated for intact proteins and subsequent collision-induced dissociation product ions using internal calibration. Internal calibration was accomplished using a dual electrospray ionization source coupled with a hybrid quadrupole Fourier transform ion cyclotron resonance (Q-FT-ICR) mass spectrometer. Initially, analyte ions generated via the first electrospray (ESI) emitter are isolated and dissociated in the external quadrupole. This event is followed by a simultaneous switch to the calibrant ion ESI emitter and a disablement of the isolation and activation of the external quadrupole such that a broad m/z range of calibrant ions are accumulated before injecting the analyte/calibrant ion mixture into the ICR cell. Two different internal calibrant solutions were utilized in these studies to evaluate this approach for the top-down characterization of melittin and ubiquitin. While external calibration of protein fragments resulted in absolute MMA greater than 16 ppm, internal standardization significantly improved upon the MMA of both the intact proteins and their products ions which ranged from -2.0 ppm to 1.1 ppm, with an average of -0.9 ppm. This method requires limited modification to ESI-FT-ICR mass spectrometers and is applicable for both positive and negative ionization modes. 相似文献
962.
963.
Woods E Kim HS Wivagg CN Dotson SJ Broekhuizen KE Frohardt EF 《The journal of physical chemistry. A》2007,111(43):11013-11020
Probe molecule spectroscopy and hygroscopic growth curves characterize the morphology of surfactant-coated aerosol particles as a function of relative humidity (RH). This study focuses on particles composed of either potassium iodide or sodium chloride and sodium dodecyl sulfate (SDS). At high RH, these mixed particles assume a reverse micelle type structure, and at low RH, they comprise a solid core of either KI or NaCl coated with SDS and water. The deliquescence relative humidity (DRH) and efflorescence relative humidity (ERH) of the inorganic fraction of the mixed particles are very similar to those of the pure salts. The surface polarity and morphology sampled by the coumarin 314 probe molecule ranges from that of a water-organic interface to that of an ionic surface and depends strongly on the RH and the amount of SDS. When the SDS coverage of the droplet just prior to efflorescence reaches approximately one monolayer, a thin soap film persists on the surface to values of RH much lower than the ERH. Both the electronic spectroscopy and photoelectric charging efficiency show a separate efflorescence for this layer at RH < 5%. The spectroscopy further reveals that there is a hysteresis associated with this low RH phase transition for both KI and NaCl cores. 相似文献
964.
Vaughan JC Hornung T Stone KW Nelson KA 《The journal of physical chemistry. A》2007,111(23):4873-4883
A novel approach to coherent nonlinear optical spectroscopy based on two-dimensional femtosecond pulse shaping is introduced. Multiple phase-stable output beams are created and overlapped at the sample in a phase-matched boxcars geometry via two-dimensional femtosecond pulse shaping. The pulse timing, shape, phase, and spectral content within all beams may be specified, yielding an unprecedented level of control over the interacting fields in nonlinear spectroscopic experiments. Heterodyne detection and phase cycling of the nonlinear signal are easily implemented due to the excellent phase stability among all output beams. This approach combines the waveform generation capabilities of magnetic resonance spectroscopy with the wavevector specification and phase matching of nonlinear optical spectroscopy, yielding the control capabilities and signal selectivity of both. Results on four prototype systems are used to illustrate some of the novel possibilities of this method. 相似文献
965.
Chang-ting Wang Jinfan Chen Jiayuan Xu Fangfang Wei Chi Yung Yam Keith Man-Chung Wong Patrick H.-L. Sit Wey Yang Teoh 《Materials Today Chemistry》2021
The CO2 reduction reaction is an imperative piece of technology that closes the carbon cycle in many critical energy conversion and chemical manufacturing processes. Here, we report two new iridium (III) terpyridine-based photocatalysts capable of selective reduction of CO2 to CO under visible light (λ ≥ 420 nm). The first photocatalyst, [Ir–COOH], was functionalized with the carboxyl group on the phenylpyridine, whereas the second, [Ir-PhCOOH], was attached to a phenyl spacer on the terpyridine. The [Ir-PhCOOH] was characterized by a higher extinction coefficient than [Ir–COOH], thus allowing more absorption of photons. Although both photocatalysts require two-electron activation, the [Ir-PhCOOH] is more readily activated as a result of the more negatively charged Ir center. These photocatalysts show exclusive selectivities in the production of CO. The turnover frequencies for [Ir–COOH] and [Ir-PhCOOH] were 19 and 10 h?1, respectively, under visible light irradiation. The e-e-H-H pathway was identified as the most favorable, consisting of the rate-limiting step in the conversion of 1COOH to 1CO, and where the barrier is significantly lower for [Ir-PhCOOH] than for [Ir–COOH]. 相似文献
966.
Xiangyu Teng Dr. Alena Sheveleva Dr. Floriana Tuna Prof. Keith R. Willison Dr. Liming Ying 《Chemphyschem》2021,22(23):2413-2419
The interaction between α-synuclein (αSyn) and Cu2+ has been suggested to be closely linked to brain copper homeostasis. Disruption of copper levels could induce misfolding and aggregation of αSyn, and thus contribute to the progression of Parkinson's disease (PD). Understanding the molecular mechanism of αSyn-Cu2+ interaction is important and controversies in Cu2+ coordination geometry with αSyn still exists. Herein, we find that the pathological H50Q mutation has no impact on the kinetics of Cu2+ binding to the high-affinity site of wild type αSyn (WT-αSyn), indicating the non-involvement of His50 in high-affinity Cu2+ binding to WT-αSyn. In contrast, the physiological N-terminally acetylated αSyn (NAc-αSyn) displays several orders of magnitude weaker Cu2+ binding affinity than WT-αSyn. Cu2+ coordination mode to NAc-αSyn has also been proposed based on EPR spectrum. In addition, we find that Cu2+ coordinated WT-αSyn is reduction-active in the presence of GSH, but essentially inactive towards ascorbate. Our work provides new insights into αSyn-Cu2+ interaction, which may help understand the multifaceted normal functions of αSyn as well as pathological consequences of αSyn aggregation. 相似文献
967.
Kovalishyn Vasyl Zyabrev Volodymyr Kachaeva Maryna Ziabrev Kostiantyn Keith Kathy Harden Emma Hartline Caroll James Scott H. Brovarets Volodymyr 《Journal of computer-aided molecular design》2021,35(12):1177-1187
Journal of Computer-Aided Molecular Design - The problem of designing new antiviral drugs against Human Cytomegalovirus (HCMV) was addressed using the Online Chemical Modeling Environment (OCHEM).... 相似文献
968.
Keith Anguige 《PAMM》2017,17(1):699-700
Consideration is given to the existence of minimisers for a family of variational models of finite-strain single-crystal elastoplasticity with infinite cross-hardening. The non-convex cross-hardening condition on the plastic slip necessitates the use of special analytical tools, in particular the combination of the div-curl Lemma with a slip-exclusion Lemma of Conti & Ortiz [1], if one wishes to prove existence for physically reasonable parameters. A regularised model with a cross-hardening matrix is also briefly discussed - existence of minimisers for this model also follows by a div-curl argument, at least if one goes over to the case of linearised elasticity. Moreover, in this case one can also prove that the regularised model Γ-converges to the infinite-cross-hardening model as the hardening matrix becomes unboundedly large. (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
969.
970.
Day JG Iorenz M Wilding TA Friedl T Harding K Pröschold T Brennan D Müller J Santos LM Santos MF Osório HC Amaral R Lukesova A Hrouzek P Lukes M Elster J Lukavsky J Probert I Ryan MJ Benson EE 《Cryo letters》2007,28(5):359-376
Two cryopreservation methods, colligative cryoprotection coupled with controlled cooling and vitrification-based, encapsulation-dehydration were validated by five members of the EU research infrastructure consortium, COBRA, and two independent external validators. The test strain Chlorella vulgaris SAG 211-11b was successfully cryopreserved using two-step cooling employing passive (Mr Frosty) and Controlled Rate Freezers (CRF) attaining the desired recovery target within 15% of the median viability level (94%). Significant differences (p < 0.05) between cooling regimes were observed where Mr Frosty was more variable (Inter-Quartile Range being 21.5%, versus 13.0% for CRF samples). Viability assessment using fluorescein diacetate gave significantly (P < 0.0001) higher survival than growth in agar with median values being 96% and 89%, respectively. On employing encapsulation-dehydration, greater variability between some validators was observed, with six labs observing recovery in 100% of the beads (84-95% of cells surviving) and one lab observing survival in 80% of the treated beads. Bead disruption followed by algal growth in agar was considered the most reliable and accurate method of assessing cell survival for encapsulation-dehydration. 相似文献