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891.
This paper presents the problem of scheduling security teams to patrol a mass rapid transit rail network of a large urban city. The main objective of patrol scheduling is to deploy security teams to stations of the network at varying time periods subject to rostering as well as security-related constraints. We present several mathematical programming models for different variants of this problem. To generate randomized schedules on a regular basis, we propose injecting randomness by varying the start time and break time for each team as well as varying the visit frequency and visit time for each station according to their reported vulnerability. Finally, we present results for the case of Singapore mass rapid transit rail network and synthetic instances. 相似文献
892.
Soft,Oxidative Stripping of Alkyl Thiolate Ligands from Hydroxyapatite‐Supported Gold Nanoclusters for Oxidation Reactions
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Bin Zhang Prof. Dr. Jun Fang Jingguo Li Jun Jie Lau Prof. Dr. Davide Mattia Dr. Ziyi Zhong Prof. Dr. Jianping Xie Prof. Dr. Ning Yan 《化学:亚洲杂志》2016,11(4):532-539
A strategy for the mild deprotection of alkyl‐thiolated (6‐mercaptohexanoic acid, MHA, and 3‐mercaptopropanoic acid, MPA) gold nanoclusters (Au NCs) supported on hydroxyapatite (HAP) has been developed by employing a peroxide (tert‐butyl hydroperoxide, TBHP, or hydrogen peroxide, H2O2) as an oxidant. The thiol ligands on the supported Au NCs were removed after oxidation, and the size and integrity of the supported clusters were well‐preserved. The bare gold clusters on HAP after removal of the ligands were catalytically effective for the epoxidation of styrene and the aerobic oxidation of benzyl alcohol. These two reactions were also investigated on calcined Au NCs that were supported on HAP for comparison, and the resulting Au NCs that were prepared by using this new strategy showed superior catalytic activity. 相似文献
893.
Let be a family of contractive mappings on such that the attractor has nonvoid interior. We show that if the 's are injective, have non-vanishing Jacobian on , and have zero Lebesgue measure for then the boundary of has measure zero. In addition if the 's are affine maps, then the conclusion can be strengthened to . These improve a result of Lagarias and Wang on self-affine tiles.
894.
For clinical diagnosis, a small number of targets (2-10 biomarkers) are often all that is required for disease assessment and accurate early disease diagnosis. In the current paper we have developed novel, carrier-resolved, single-label-based multiplexed assays for the simultaneous detection and quantification of a limited number of DNA targets associated with breast cancer. In contrast to current encoding strategies, every hybridization signal for the corresponding DNA target in our protocol is uniquely immobilized onto one carrier vehicle with a unique and intrinsic physico-chemical signature. Moreover, a simple chemiluminescence setup is employed to read the carrier code instead of expensive and complicated flow-cytometer or imaging-systems commonly used for multiplexed assays. Herein we demonstrate a new protocol using three homogeneous carriers, i.e. thermo-sensitive poly(N-isopropylacrylamide) (PNIP), polystyrene beads, and magnetic beads respectively. This new methodology allowed for the simultaneous determination of three oligonucleotide sequences (60 bases in length) associated with the breast cancer gene (BRCA1) and showed high selectivity and attomolar-femtomolar sensitivity. The mixture of three different capture probe conjugates first hybridizes with three corresponding target sequences, sandwiches with three biotinylated DNAs, and then reacts with peroxidase-streptavidin polymer in a single vessel without any washing, leading to the development of a 'one-pot reaction system'. Only one washing step in our protocol is required prior to detection leading to our whole procedure being simple and efficient. The results show that the hybridization response to sample mixtures containing increasing levels of each target is proportional to the amount of corresponding DNA targets, indicating minimal cross-interferences. The work presented here validates the design and concept of a system for the detection of a limited number of DNA targets and provides the foundation for the development of highly sensitive techniques with increased multi-analyte capabilities. 相似文献
895.
The kinetics and mechanisms of the oxidation of I (-) and Br (-) by trans-[Ru (VI)(N 2O 2)(O) 2] (2+) have been investigated in aqueous solutions. The reactions have the following stoichiometry: trans-[Ru (VI)(N 2O 2)(O) 2] (2+) + 3X (-) + 2H (+) --> trans-[Ru (IV)(N 2O 2)(O)(OH 2)] (2+) + X 3 (-) (X = Br, I). In the oxidation of I (-) the I 3 (-)is produced in two distinct phases. The first phase produces 45% of I 3 (-) with the rate law d[I 3 (-)]/dt = ( k a + k b[H (+)])[Ru (VI)][I (-)]. The remaining I 3 (-) is produced in the second phase which is much slower, and it follows first-order kinetics but the rate constant is independent of [I (-)], [H (+)], and ionic strength. In the proposed mechanism the first phase involves formation of a charge-transfer complex between Ru (VI) and I (-), which then undergoes a parallel acid-catalyzed oxygen atom transfer to produce [Ru (IV)(N 2O 2)(O)(OHI)] (2+), and a one electron transfer to give [Ru (V)(N 2O 2)(O)(OH)] (2+) and I (*). [Ru (V)(N 2O 2)(O)(OH)] (2+) is a stronger oxidant than [Ru (VI)(N 2O 2)(O) 2] (2+) and will rapidly oxidize another I (-) to I (*). In the second phase the [Ru (IV)(N 2O 2)(O)(OHI)] (2+) undergoes rate-limiting aquation to produce HOI which reacts rapidly with I (-) to produce I 2. In the oxidation of Br (-) the rate law is -d[Ru (VI)]/d t = {( k a2 + k b2[H (+)]) + ( k a3 + k b3[H (+)]) [Br (-)]}[Ru (VI)][Br (-)]. At 298.0 K and I = 0.1 M, k a2 = (2.03 +/- 0.03) x 10 (-2) M (-1) s (-1), k b2 = (1.50 +/- 0.07) x 10 (-1) M (-2) s (-1), k a3 = (7.22 +/- 2.19) x 10 (-1) M (-2) s (-1) and k b3 = (4.85 +/- 0.04) x 10 (2) M (-3) s (-1). The proposed mechanism involves initial oxygen atom transfer from trans-[Ru (VI)(N 2O 2)(O) 2] (2+) to Br (-) to give trans-[Ru (IV)(N 2O 2)(O)(OBr)] (+), which then undergoes parallel aquation and oxidation of Br (-), and both reactions are acid-catalyzed. 相似文献
896.
Man WL Kwong HK Lam WW Xiang J Wong TW Lam WH Wong WT Peng SM Lau TC 《Inorganic chemistry》2008,47(13):5936-5944
Reaction of [Ru (VI)(N)(L (1))(MeOH)] (+) (L (1) = N, N'-bis(salicylidene)- o-cyclohexylenediamine dianion) with excess pyridine in CH 3CN produces [Ru (III)(L (1))(py) 2] (+) and N 2. The proposed mechanism involves initial equilibrium formation of [Ru (VI)(N)(L (1))(py)] (+), which undergoes rapid N...N coupling to produce [(py)(L (1))Ru (III) N N-Ru (III)(L (1))(py)] (2+); this is followed by pyridine substituion to give the final product. This ligand-induced N...N coupling of Ru (VI)N is utilized in the preparation of a series of new ruthenium(III) salen complexes, [Ru (III)(L)(X) 2] (+/-) (L = salen ligand; X = H 2O, 1-MeIm, py, Me 2SO, PhNH 2, ( t )BuNH 2, Cl (-) or CN (-)). The structures of [Ru (III)(L (1))(NH 2Ph) 2](PF 6) ( 6), K[Ru (III)(L (1))(CN) 2] ( 9), [Ru (III)(L (2))(NCCH 3) 2][Au (I)(CN) 2] ( 11) (L (2) = N, N'-bis(salicylidene)- o-phenylenediamine dianion) and [N ( n )Bu 4][Ru (III)(L (3))Cl 2] ( 12) (L (3) = N, N'-bis(salicylidene)ethylenediamine dianion) have been determined by X-ray crystallography. 相似文献
897.
Patrick Federmann Dr. Robert Müller Fabian Beckmann Caroline Lau Dr. Beatrice Cula Prof. Dr. Martin Kaupp Prof. Dr. Christian Limberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(25):e202200404
Frustrated Lewis pairs (FLPs) composed of acidic alane and basic phosphane functions, separated by a xanthene linker, can be prepared through the corresponding Me3Sn derivative and methyl aluminum compounds with elimination of Me4Sn. This way MeClAl-, Cl2Al- and (C6F5)2Al- moieties could be introduced and the resulting FLPs are stabilized by a further equivalent of the alane precursors. In contact with the FLPs CO2 is bound via the C atom at the phosphane functions and the two O atoms at the Al centers. The residues at the latter determine the binding strength. Hence, in case of MeClAl CO2 capture occurs at higher pressure and under ambient conditions CO2 is released again, while for Cl2Al and (C6F5)2Al CO2 binding becomes irreversible. The results of DFT calculations rationalize these findings by the high thermodynamic stabilization in case of more electronegative residues, which concomitantly lead to higher barriers, and in case of (C6F5)2Al further stabilization is achieved through a low reorganization energy. 相似文献
898.
Dr. Matthias Tombers Jun. Prof. Dr. Jennifer Meyer Dr. Jonathan Meyer Dr. Arkadiusz Lawicki Dr. Vicente Zamudio-Bayer Dr. Konstantin Hirsch Prof. Dr. J. Tobias Lau Prof. Dr. Bernd von Issendorff Prof. Dr. Akira Terasaki Prof. Dr. Thomas A. Schlathölter Prof. Dr. Ronnie A. Hoekstra Dr. Sebastian Schmidt Prof. Dr. Annie K. Powell Dr. Eva Kessler Dr. Marc H. Prosenc Prof. Dr. Christoph van Wüllen Prof. Dr. Dr. Gereon Niedner-Schatteburg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202102592
The phenomenon of single molecule magnet (SMM) behavior of mixed valent Mn12 coordination clusters of general formula [MnIII8MnIV4O12(RCOO)16(H2O)4] had been exemplified by bulk samples of the archetypal [MnIII8MnIV4O12(CH3COO)16(H2O)4] (4) molecule, and the molecular origin of the observed magnetic behavior has found support from extensive studies on the Mn12 system within crystalline material or on molecules attached to a variety of surfaces. Here we report the magnetic signature of the isolated cationic species [Mn12O12(CH3COO)15(CH3CN)]+ (1) by gas phase X-ray Magnetic Circular Dichroism (XMCD) spectroscopy, and we find it closely resembling that of the corresponding bulk samples. Furthermore, we report broken symmetry DFT calculations of spin densities and single ion tensors of the isolated, optimized complexes [Mn12O12(CH3COO)15(CH3CN)]+ (1) , [Mn12O12(CH3COO)16] (2) , [Mn12O12(CH3COO)16(H2O)4] (3) , and the complex in bulk geometry [MnIII8MnIV4O12(CH3COO)16(H2O)4] (5) . The found magnetic fingerprints – experiment and theory alike – are of a remarkable robustness: The MnIV4 core bears almost no magnetic anisotropy while the surrounding MnIII8 ring is highly anisotropic. These signatures are truly intrinsic properties of the Mn12 core scaffold within all of these complexes and largely void of the environment. This likely holds irrespective of bulk packing effects. 相似文献
899.
The end-of-life treatment for post-consumer plastic waste constitutes one of modern society’s greatest problems, whereby highly unsustainable landfilling and incineration are the two main disposal routes. At present, the chemical upcycling of plastic waste is largely limited to its pyrolytic conversion into hydrocarbon fuels or nanomaterials. Herein, we demonstrate the upcycling of high-volume plastic waste by turning them into catalysts for biomass valorization. Many existing studies synthesize organocatalysts from a bottom-up approach using specialized monomers. Yet, transforming widely available waste polymers into functionalized materials for catalysis remains relatively unexplored. In this study, homogeneous and cross-linked heterogeneous catalysts derived from waste polystyrene food containers are shown to convert readily available saccharide precursors from biomass into 5-hydroxymethylfurfural (5-HMF), a key biorefinery platform chemical, under short reaction times and mild conditions. In addition, the heterogeneous catalyst can be reused multiple times with little loss of yield between repeated runs. Other than 5-HMF, doping the reaction with water or halide salts also allowed the formation of valuable products such as formic acid and diformylfuran. Our work expands on existing upcycling options for post-consumer plastic waste by giving them a new lease of life as value-added catalysts. 相似文献
900.
The mechanism for the diffusion of vinyl bromide (VB) through the nonporous van der Waals organic solid of p-tert-butylcalix[4]arene (tBC) is examined by molecular mechanics calculations. In a "squeeze" mechanism, a VB molecule passes through the interstitial space in the rim regions of tBC bowls, after the partial filling of nearby inclusion sites, and couples with the both the rotation of butyl groups and the translational sliding of the bilayers, until it encounters and falls into a empty site. In a "relay" mechanism, translational sliding shifts the skew angle between two tBC bowls and makes it possible to pass a VB from one bowl to another and throughout the solid. The barrier for the "relay" mechanism is 4 kcal/mol lower than the "squeeze" mechanism, although the "squeeze" mechanism is favored by entropy. The "squeeze" mechanism should be more sensitive to the size of the diffusion molecule and should leave residue VB molecules in the interstitial regions. In contrast, the VB molecule hops from one site to another in the "relay" mechanism, and the kinetically limiting step is the translational sliding of the bilayer. Such contrasts should help resolve the relative importance of the two mechanisms in future kinetic studies. 相似文献