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121.
Elizabeth Suk‐Hang Lam Daniel Ping‐Kuen Tsang Dr. Wai Han Lam Dr. Anthony Yiu‐Yan Tam Dr. Mei‐Yee Chan Prof. Dr. Wing‐Tak Wong Prof. Dr. Vivian Wing‐Wah Yam 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(20):6385-6397
A series of luminescent platinum(II) complexes of tridentate 1,3‐bis(N‐alkylbenzimidazol‐2′‐yl)benzene (bzimb) ligands has been synthesized and characterized. One of these platinum(II) complexes has been structurally characterized by X‐ray crystallography. Their electrochemical, electronic absorption, and luminescence properties have been investigated. Computational studies have been performed on this class of complexes to elucidate the origin of their photophysical properties. Some of these complexes have been utilized in the fabrication of organic light‐emitting diodes (OLEDs) by using either vapor deposition or spin‐coating techniques. Chloroplatinum(II)? bzimb complexes that are functionalized at the 5‐position of the aryl ring, [Pt(R‐bzimb)Cl], not only show tunable emission color but also exhibit high current and external quantum efficiencies in OLEDs. Concentration‐dependent dual‐emissive behavior was observed in multilayer OLEDs upon the incorporation of pyrenyl ligand into the Pt(bzimb) system. Devices doped with low concentrations of the complexes gave rise to white‐light emission, thereby representing a unique class of small‐molecule, platinum(II)‐based white OLEDs. 相似文献
122.
Zinc chemicals are used as activators in the vulcanization of organic polymers with sulfur to produce elastic rubbers. In this work, the reactions of Zn(2+), ZnMe(2), Zn(OMe)(2), Zn(OOCMe)(2), and the heterocubane cluster Zn(4)O(4) with the vulcanization accelerator tetramethylthiuram disulfide (TMTD) and with the related radicals and anions Me(2)NCS(2)(*), Me(2)NCS(3)(*), Me(2)NCS(2)(-), and Me(2)NCS(3)(-) have been studied by quantum chemical methods at the MP2/6-31+G(2df,p)//B3LYP/6-31+G* level of theory. More than 35 zinc complexes have been structurally characterized and the energies of formation from their components calculated for the first time. The binding energy of TMTD as a bidendate ligand increases in the order ZnMe(2)相似文献
123.
James Chung Wah Lam Yiu Chung Yip Wai Fong Tong 《Accreditation and quality assurance》2008,13(6):311-319
A quadrupole inductively coupled plasma mass spectrometer (Q-ICP-MS) has been used for determination of lead in plant materials
using isotope-dilution inductively coupled plasma mass spectrometry. The accuracy of the method was demonstrated by analysis
of a matrix certified reference material, NIST SRM 1547 Peach Leaves. Specific instrumental parameters of Q-ICP-MS, including
isotope analysis mode, integration time per point, number of points per mass, and number of measurements, were optimized to
obtain the best measurement precision. The precision (expressed as relative standard deviation) associated with replicate
measurement of the 208Pb/206Pb isotope ratio and its mass-bias correction factor was <0.2%. Following “Example A7” of the Eurachem/CITAC Guide, the relative
expanded uncertainty, U
rel, (coverage factor k = 2) was found to be ±1.1%, which fulfilled the target value of ±2% maximum and was lower than the uncertainty of ±3.4% reported
by NIST based on isotope-dilution thermal ionization mass spectrometry. Sample recovery of 99% was obtained. 相似文献
124.
Seah Ling Kuan Christina Förtsch David Yuen Wah Ng Stephan Fischer Yu Tokura Weina Liu Yuzhou Wu Kaloian Koynov Holger Barth Tanja Weil 《Macromolecular bioscience》2016,16(6):803-810
Nature has provided a highly optimized toolbox in bacterial endotoxins with precise functions dictated by their clear structural division. Inspired by this streamlined design, a supramolecular approach capitalizing on the strong biomolecular (streptavidin (SA))–biotin interactions is reported herein to prepare two multipartite fusion constructs, which involves the generation 2.0 (D2) or generation 3.0 (D3) polyamidoamine‐dendronized transporter proteins (dendronized streptavidin (D3SA) and dendronized human serum albumin (D2HSA)) non‐covalently fused to the C3bot1 enzyme from Clostridium botulinum, a potent and specific Rho‐inhibitor. The fusion constructs, D3SA‐C3 and D2HSA‐C3, represent the first examples of dendronized protein transporters that are fused to the C3 enzyme, and it is successfully demonstrated that the C3 Rho‐inhibitor is delivered into the cytosol of mammalian cells as determined from the characteristic C3‐mediated changes in cell morphology and confocal microscopy. The design circumvents the low uptake of the C3 enzyme by eukaryotic cells and holds great promise for reprogramming the properties of toxin enzymes using a supramolecular approach to broaden their therapeutic applications.
125.
Non-fluorescence compounds were detected by a fluorescence detector based on scattering light. The fluorescence detector was used without any modification, and the scattering light was observed at the wavelength twice as long as the excitation wavelength. Actually the wavelength of the observed scattering light was the same as that of the excitation light. The maximum signal was achieved at around 280 nm. The signal was increased with increasing molecular weight or size of analytes. Colloidal silica with nanometer sizes, ethylene glycol oligomers, saccharides and cyclodextrins could be visualized by the present detection method. The detection limit at S/N=3 for colloidal silica with 78 nm was 39 pg for 20-microL injection. 相似文献
126.
Chen X Chan WY Wong PS Yeung HS Chan TW 《Journal of the American Society for Mass Spectrometry》2011,22(2):233-244
Peptides adducted with different divalent Group IIB metal ions (Zn2+, Cd2+, and Hg2+) were found to give very different ECD mass spectra. ECD of Zn2+ adducted peptides gave series of c-/z-type fragment ions with and without metal ions. ECD of Cd2+ and Hg2+ adducted model peptides gave mostly a-type fragment ions with M+• and fragment ions corresponding to losses of neutral side chain from M+•. No detectable a-ions could be observed in ECD spectra of Zn2+ adducted peptides. We rationalized the present findings by invoking both proton-electron recombination and metal-ion reduction
processes. As previously postulated, divalent metal-ions adducted peptides could adopt several forms, including (a) [M + Cat]2+, (b) [(M + Cat – H) + H]2+, and (c) [(M + Cat – 2H) + 2H]2+. The relative population of these precursor ions depends largely on the acidity of the metal–ion peptide complexes. Peptides
adducted with divalent metal-ions of small ionic radii (i.e., Zn2+) would form predominantly species (b) and (c); whereas peptides adducted with metal ions of larger ionic radii (i.e., Hg2+) would adopt predominantly species (a). Species (b) and (c) are believed to be essential for proton-electron recombination
process to give c-/z-type fragments via the labile ketylamino radical intermediates. Species (c) is particularly important for the formation of
non-metalated c-/z-type fragments. Without any mobile protons, species (a) are believed to undergo metal ion reduction and subsequently induce
spontaneous electron transfer from the peptide moiety to the charge-reduced metal ions. Depending on the exothermicity of
the electron transfer reaction, the peptide radical cations might be formed with substantial internal energy and might undergo
further dissociation to give structural related fragment ions. 相似文献
127.
The ability of a liquid droplet to move on an incline has important ramifications in discrete volume fluidic devices. By taking advantage of the spontaneous and copious formation of visible air bubbles within water droplets on a polytetrafluoroethylene (PTFE) surface, we uncovered a direct correlation between their presence and the ability of droplets to slide down an incline. We forward two possible mechanisms to account for this behavior. The first is attributed to the air bubbles creating regions where additional solid-liquid-vapor phase interfaces are present; wherein due to the buoyancy force acting upwards, the orientation of the contact angles of each bubble (which should also be in hysteresis but in the opposite direction of the hysteresis at the droplet rim contact lines) dictate that the net force of the bubbles in the droplet act down an incline. We show here that this mechanism cannot fully account for the bubble enhanced sliding behavior. The second mechanism is based on the occurrence of the droplet front advancing first, causing the droplet to elongate and thus allowing the receding contact line to partially sweep inwards over the bubbles. This causes a series of point-wise disruptions on the contact line that permits the droplet to slide down more readily. The relatively short time of ~180s during which these micron sized bubbles decrease in size indicates a possibility of this mechanism contributing to a transient means to reduce the retention force of droplets that reside on hydrophobic surfaces. 相似文献
128.
A new type of chiral β-amino acid catalyst has been computationally designed, mimicking the enzyme catalysis of serine proteases. Our catalyst approach is based on the bioinspired catalytic acid/base dyad, namely, a carboxyl and imidazole pair. DFT calculations predict that this designed organocatalyst catalyzes Michael additions of aldehydes to nitroalkenes with excellent enantioselectivities and remarkably high anti diastereoselectivities. The unusual stacked geometry of the enamine intermediate, hydrogen bonding network, and the adoption of an exo transition state are the keys to understand the stereoselectivity. 相似文献
129.
The catalytic mechanism and origin of enantioselectivity of bicyclic guanidine-catalyzed phospha-Michael reaction between diphenyl phosphine oxide and β-nitrostyrene were investigated by DFT calculations at M06-2X/cc-pVTZ//M06-2X/cc-pVDZ level in conjunction with the implicit SMD solvation method. The catalyst is found to be involved in all 3 steps of the proposed catalytic cycle, namely (1) tautomerization of phosphine oxide, (2) C-P bond formation and (3) concerted hydrogen transfer. The bifunctional role of the guanidine catalyst is clearly demonstrated in all 3 key steps. Due to the geometry of the bicyclic guanidine catalyst, the preferred orientation of the reactants in the transition state of enantioselective C-P bond forming step favours the R enantiomer, in excellent accord with the observed enantioselectivity. Analysis of various transition states suggests that the asymmetric C-P bond formation is controlled by the hydrogen bonding interaction and steric effect between the catalyst and substrate. Various weaker C-H···X (X = N, O and π) interactions also play a role in stabilizing the key transition states. 相似文献
130.
Dr. Dik‐Lung Ma Daniel Shiu‐Hin Chan Dr. Bradley Yat‐Wah Man Dr. Chung‐Hang Leung 《化学:亚洲杂志》2011,6(4):986-1003
Metal ions are prevalent in biological systems and are critically involved in essential life processes. However, excess concentrations of metals can pose a serious danger to living organisms. Oligonucleotides represent a versatile sensing platform for the detection of various molecular entities including metal ions. This review summarizes the recent advances in the development of oligonucleotide‐based luminescent detection methods for metal ions. 相似文献