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51.
Capillary electrophoresis with ultraviolet detection (CE-UV) was used to perform competitive binding tests to demonstrate the selective recognition of bisphenol A (BPA) by molecularly imprinted polymer (MIP) particles. Cross-linking polymerization of methacrylic acid (MAA) and ethylene glycol dimethacrylate (EGDMA) in the presence of BPA yielded MIP particles with an average diameter of 164 ± 15 nm. Their ability to recognize BPA in the presence of nonionic, anionic, and cationic water contaminants was investigated. Binding efficiency was rapidly determined, after sequential injection of particles first and compounds next into the fused-silica capillary provided a short overlapping time during their electrophoretic migrations. The MIP particles exhibited high-binding efficiency (99 ± 1%) for BPA. Neither diclofenac nor metformin affected BPA binding, and 2-hydroxy-4-methoxybenzophenone was even displaced from the particles by BPA. These results verified the high selectivity of MIP toward its target compound. 相似文献
52.
Garton EM Pixton DA Petersen CA Eady RR Hasnain SS Andrew CR 《Journal of the American Chemical Society》2012,134(3):1461-1463
Cytochromes c' are pentacoordinate heme proteins with sterically hindered distal sites that bind NO and CO but do not form stable complexes with O(2). Removal of distal pocket steric hindrance via a Leu→Ala mutation yields favorable O(2) binding (K(d) ~49 nM) without apparent H-bond stabilization of the Fe-O(2) moiety, as well as an extremely high distal heme-NO affinity (K(d) ~70 fM). The native Leu residue inhibits distal coordination of diatomic ligands by decreasing k(on) as well as increasing k(off). The connection between distal steric constraints, k(off) values, and distal to proximal heme-NO conversion is discussed. 相似文献
53.
James Doutch Michael A. Hough S. Samar Hasnain Richard W. Strange 《Journal of synchrotron radiation》2012,19(1):19-29
The sulfur SAD phasing method allows the determination of protein structures de novo without reference to derivatives such as Se‐methionine. The feasibility for routine automated sulfur SAD phasing using a number of current protein crystallography beamlines at several synchrotrons was examined using crystals of trimeric Achromobacter cycloclastes nitrite reductase (AcNiR), which contains a near average proportion of sulfur‐containing residues and two Cu atoms per subunit. Experiments using X‐ray wavelengths in the range 1.9–2.4 Å show that we are not yet at the level where sulfur SAD is routinely successful for automated structure solution and model building using existing beamlines and current software tools. On the other hand, experiments using the shortest X‐ray wavelengths available on existing beamlines could be routinely exploited to solve and produce unbiased structural models using the similarly weak anomalous scattering signals from the intrinsic metal atoms in proteins. The comparison of long‐wavelength phasing (the Bijvoet ratio for nine S atoms and two Cu atoms is ~1.25% at ~2 Å) and copper phasing (the Bijvoet ratio for two Cu atoms is 0.81% at ~0.75 Å) for AcNiR suggests that lower data multiplicity than is currently required for success should in general be possible for sulfur phasing if appropriate improvements to beamlines and data collection strategies can be implemented. 相似文献
54.
Mark J. Ellis Steven G. Buffey Michael A. Hough S. Samar Hasnain 《Journal of synchrotron radiation》2008,15(5):433-439
X‐ray‐induced redox changes can lead to incorrect assignments of the functional states of metals in metalloprotein crystals. The need for on‐line monitoring of the status of metal ions (and other chromophores) during protein crystallography experiments is of growing importance with the use of intense synchrotron X‐ray beams. Significant efforts are therefore being made worldwide to combine different spectroscopies in parallel with X‐ray crystallographic data collection. Here the implementation and utilization of optical and X‐ray absorption spectroscopies on the modern macromolecular crystallography (MX) beamline 10, at the SRS, Daresbury Laboratory, is described. This beamline is equipped with a dedicated monolithic energy‐dispersive X‐ray fluorescence detector, allowing X‐ray absorption spectroscopy (XAS) measurements to be made in situ on the same crystal used to record the diffraction data. In addition, an optical microspectrophotometer has been incorporated on the beamline, thus facilitating combined MX, XAS and optical spectroscopic measurements. By uniting these techniques it is also possible to monitor the status of optically active and optically silent metal centres present in a crystal at the same time. This unique capability has been applied to observe the results of crystallographic data collection on crystals of nitrite reductase from Alcaligenes xylosoxidans, which contains both type‐1 and type‐2 Cu centres. It is found that the type‐1 Cu centre photoreduces quickly, resulting in the loss of the 595 nm peak in the optical spectrum, while the type‐2 Cu centre remains in the oxidized state over a much longer time period, for which independent confirmation is provided by XAS data as this centre has an optical spectrum which is barely detectable using microspectrophotometry. This example clearly demonstrates the importance of using two on‐line methods, spectroscopy and XAS, for identifying well defined redox states of metalloproteins during crystallographic data collection. 相似文献
55.
Abir S. Abdel-Naby Samar A. Aboubshait 《Journal of Thermal Analysis and Calorimetry》2013,114(3):1279-1286
Cellulose acetate (CA) was blended in different compositions with various acrylonitrile-N-halo phenyl maleimide (AN-XPhM) copolymers to improve the thermal and mechanical properties of cellulose acetate. The structure, morphology, thermal stability, and crystallinity of the blend films were characterized by infrared spectroscopy, scanning electron micrographs, thermogravimetry/differential thermal analysis, differential scanning calorimetry, and X-ray diffraction. The results revealed that the thermal stability was improved by the increase in AN-XPhM content, irrespective of the type of the N-halo phenyl maleimide. The CA/AN-4BrPhM blend films possessed the highest thermal stability compared to the other CA/AN-XPhM blend films. Blending CA with AN-4BrPhM yielded the most homogeneous blend films, irrespective of the composition ratio. The mechanical properties of various compositions of the CA/AN-4BrPhM blend films were also discussed. 相似文献
56.
Chullikkattil P. Pradeep Sabbani Supriya Panthapally S. Zacharias Samar K. Das 《Polyhedron》2006,25(18):3588-3592
A tetra-nuclear copper(II) complex [Cu4(C54H46N4O14)(OH)2] · 10H2O (1) has been synthesized starting from l-tyrosine, NaOH, 2,6-diformyl-4-methylphenol (dfp) and CuSO4 · 5H2O. Compound 1 crystallizes from an ethanol–water mixture in triclinic space group. In the crystal of 1, two binuclear copper units, related by a center of symmetry, are bridged by two hydroxo bridges and results in the formation of a tetra-nuclear {Cu4} structure. Five lattice water molecules, located in the asymmetric unit, interact among themselves and form an unusual form of a water nonamer. In the crystal, the water nonamer is again hydrogen bonded to the next nonamer forming a chainlike polymer. Each {Cu4} complex unit attaches four such water nonamer chains. Variable temperature magnetic data fit to the Bleaney–Bower’s equation with a Curie type of impurity of S = 0.5. The best fit of the magnetic data to this equation yielded 2J = −217, g = 2.019 and a TIP value of 60 × 10−6 cm3 mol−1. 相似文献
57.
Three polyoxometalate based ion pair solids (1-3), in which Co(III) (d(6)), Ni(II) (d(8)) and Zn(II) (d(10)) complexes of a tetra-aza macrocycle, Me(6)-trans-[14]-diene act as the cationic moieties, have been reported. The title complexes, formulated as [Co (C(16)H(32)N(4))(Cl)(2)](2)[Mo(6)O(19)] (1), [Ni(C(16)H(32)N(4))][W(6)O(19)]·DMSO·DCM (2) and [Zn(C(16)H(32)N(4))(Cl)](2)[W(6)O(19)] (3) (C(16)H(32)N(4) = Me(6)-trans-[14]-diene), are the first crystallographic paradigms where transition metal complexes of a Schiff condensed tetra-aza macrocycle have been associated with an isopolyanion, [M(6)O(19)](2-) (M = Mo(vi) and W(vi)). Compounds 1-3 have been characterized through routine spectroscopic analyses including elemental analysis and their structures have been unambiguously determined through single crystal X-ray crystallography. The molecules of compound 1 assemble obeying P1 (#2) space symmetry, whereas those of compounds 2 and 3 follow the higher symmetrical ensemble P2(1)/c (#14). The ESR spectral studies of compounds 1-3 have revealed their diamagnetic (low-spin) nature. The last part of this article describes the electrochemical properties of the title compounds. 相似文献
58.
Trapping cations in specific positions in tuneable "artificial cell" channels: new nanochemistry perspectives 总被引:1,自引:0,他引:1
59.
Susovan Bhowmik Sudip Kumar Ghosh Samar Layek Prof. Harish Chandra Verma Dr. Sankar Prasad Rath 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(41):13025-13037
Reported herein is a hitherto unknown family of diiron(III)‐μ‐hydroxo bisporphyrins in which two different spin states of Fe are stabilized in a single molecular framework, although both cores have identical molecular structures. Protonation of the oxo‐bridged dimer ( 2 ) by using strong Brønsted acids, such as HI, HBF4, and HClO4, produce red μ‐hydroxo complexes with I3? ( 3 ), BF4? ( 4 ), and ClO4? ( 5 ) counterions, respectively. The X‐ray structure of the molecule reveals that the Fe? O bond length increases on going from the μ‐oxo to the hydroxo complex, whereas the Fe‐O(H)‐Fe unit becomes more bent, which results in the smallest known Fe‐O(H)‐Fe angles of 142.5(2) and 141.2(1)° for 3 and 5 , respectively. In contrast, the Fe‐O(H)‐Fe angle remains unaltered in 4 from the corresponding μ‐oxo complex. The close approach of two rings in a molecule results in unequal core deformations in 3 and 4 , whereas the cores are deformed almost equally but to a lesser extent in 5 . Although 3 was found to have nearly high‐spin and admixed intermediate Fe spin states in cores I and II, respectively, two admixed intermediate spin states were observed in 4 . Even though the cores have identical chemical structures, crucial bond parameters, such as the Fe? Np, Fe? O, and Fe???Ctp bond lengths and the ring deformations, are all different between the two FeIII centers in 3 and 4 , which leads to an eventual stabilization of two different spin states of Fe in each molecule. In contrast, the two Fe centers in 5 are equivalent and assigned to high and intermediate spin states in the solid and solution states, respectively. The spin states are thus found to be dependent on the counterions and can also be reversibly interconverted. Upon protonation, the strong antiferromagnetic coupling in the μ‐oxo dimer (J, ?126.6 cm?1) is attenuated to almost zero in the μ‐hydroxo complex with the I3? counterion, whereas the values of J are ?36 and ?42 cm?1, respectively, for complexes with BF4? and ClO4? counterions. 相似文献
60.
Alkali‐Metal Pyrazolate Complexes with Unusual Pyrazolate Coordination Modes and Pseudocubane Motifs
Samar Beaini Glen B. Deacon Prof. Dr. Anja P. Erven Dr. Peter C. Junk Prof. Dr. David R. Turner Dr. 《化学:亚洲杂志》2007,2(4):539-550
The dimeric complex [Li(Ph2pz)(OEt2)]2 ( 1 ) and tetrameric cluster [Na(Ph2pz)(thf)]4 ( 2 ) were prepared by treatment of alkali‐metal reagents (nBuLi and Na{N(SiMe3)2}, respectively) with 3,5‐diphenylpyrazole (Ph2pzH) in Et2O ( 1 ) or THF ( 2 ). The polymer [Na(tBu2pz)]n ( 3 ) was obtained from reaction at elevated temperature in a sealed tube between Na metal and 3,5‐di‐tert‐butylpyrazole (tBu2pzH). The complex [Na4(tBu2pz)2(thf)3(obds)]2 ( 4 ; obds=(OSiMe2)2O) was obtained as a minor product from prolonged treatment of tBu2pzH with elemental sodium in a silicone‐greased flask. All four alkali‐metal pyrazolato complexes were characterized by IR and 1H NMR spectroscopy and X‐ray crystallography.The Li dimer 1 displays μ‐η2:η1 lithium–pyrazolato binding, in which both lithium atoms are four‐coordinate. Room‐ and variable‐temperature NMR studies (1H, 13C, and 7Li) of 1 suggest similar behavior in solution, with peaks coalescing at low temperatures. Complexes 2 and 4 display distorted cubane structures. In 2 , all the sodium atoms are five‐coordinate, whereas 4 contains two sodium/pyrazolate/thf clusters (4:2:3 ratio) bridged by two obds2? units, as well as two four‐coordinate and two five‐coordinate sodium atoms. Compound 3 is composed of two independent chains with the unusual coordination modes μ3‐η5:η2:η2, μ3‐η5:η2:η1, and μ3‐η4:η2:η1, with five‐, six‐, and seven‐coordinate sodium atoms. Two oxo‐centered M8 cage complexes [(tBu2pz)6Li8O] ( 5 ) and [(tBu2pz)6Na8O] ( 6 ) were obtained as by‐products from attempted preparation of [Li(tBu2pz)] and [Na(tBu2pz)], respectively, and their structures were determined. 相似文献