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61.
A novel one-pot pseudo five-component reaction of isocyanides with 2,5-dihydroxycyclohexa-2,5-diene-1,4-dione and various aliphatic and aromatic aldehydes in ethanol at room temperature has been studied. 2,6-Bis(alkylamino)-benzofuro[5,6-b]furan-4,8-dione derivatives were isolated as the products in good yields after 24 h. 相似文献
62.
Andersen NH Olsen KA Fesinmeyer RM Tan X Hudson FM Eidenschink LA Farazi SR 《Journal of the American Chemical Society》2006,128(18):6101-6110
Minimized beta hairpins have provided additional data on the geometric preferences of Trp interactions in TW-loop-WT motifs. This motif imparts significant fold stability to peptides as short as 8 residues. High-resolution NMR structures of a 16- (KKWTWNPATGKWTWQE, DeltaG(U)(298) >or= +7 kJ/mol) and 12-residue (KTWNPATGKWTE, DeltaG(U)(298) = +5.05 kJ/mol) hairpin reveal a common turn geometry and edge-to-face (EtF) packing motif and a cation-pi interaction between Lys(1) and the Trp residue nearest the C-terminus. The magnitude of a CD exciton couplet (due to the two Trp residues) and the chemical shifts of a Trp Hepsilon3 site (shifted upfield by 2.4 ppm due to the EtF stacking geometry) provided near-identical measures of folding. CD melts of representative peptides with the -TW-loop-WT- motif provided the thermodynamic parameters for folding, which reflect enthalpically driven folding at laboratory temperatures with a small DeltaC(p) for unfolding (+420 J K(-)(1)/mol). In the case of Asx-Pro-Xaa-Thr-Gly-Xaa loops, mutations established that the two most important residues in this class of direction-reversing loops are Asx and Gly: mutation to alanine is destabilizing by about 6 and 2 kJ/mol, respectively. All indicators of structuring are retained in a minimized 8-residue construct (Ac-WNPATGKW-NH(2)) with the fold stability reduced to DeltaG(U)(278) = -0.7 kJ/mol. NMR and CD comparisons indicate that -TWXNGKWT- (X = S, I) sequences also form the same hairpin-stabilizing W/W interaction. 相似文献
63.
Hydrophobic poly(lauryl methacrylate)‐coated magnetic nano‐composite particles for removal of organic pollutants 下载免费PDF全文
This paper described a simple novel technique to prepare magnetic nano‐composite particles coated with highly crosslinked poly(lauryl methacrylate) (PLMA), a hydrophobic polymer because of its long chain alkyl group for application in waste water purification. Nano‐sized magnetite (Fe3O4) particles prepared by coprecipitation of Fe2+ and Fe3+ from their alkali aqueous solution were encapsulated with SiO2 following treatment with tetraethylorthosilicate (TEOS). Finally precipitation copolymerization of LMA and divinyl benzene (DVB) in the presence of Fe3O4/SiO2 particles was carried out within stable isolated droplets containing hexadecane–toluene mixture (4:1 mixture HD‐T). The produced PLMA‐coated magnetic composite particles named as Fe3O4/SiO2/P(LMA‐DVB) were characterized by Fourier Transform IR (FTIR), transmission electron microscopy (TEM), thermogravimetry (TG) and X‐ray diffractometer (XRD) analyses. The performance of the composite particles was evaluated for the removal of organic pollutants from water. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
64.
M. A. Zanjanch Sh. Sohrabnezhad M. Arvand M. F. Mousavi 《Russian Journal of Electrochemistry》2007,43(7):758-763
The electrochemical properties of thionine dye adsorbed into ZSM-5 and HZSM-5 zeolites (TH/ZSM-5, TH/HZSM-5) are studied in
0.5 M KCl solution. The dye is strongly retained and not easily leached from the zeolites matrix. The samples are incorporated
into the carbon paste electrode (TH/ZSM-5/P, TH/HZSM-5/P) for cyclic voltammetric measurements. The redox reactions of thionine
incorporated into ZSM-5 zeolite contain a quasi-reversible, two-electron one proton in the pH range 1 to 10, but thionine-loaded
HZSM-5 zeolite undergoes a quasi-reversible two-electron two-protons redox reaction under acidic conditions and a one proton
two-electron redox reaction takes place under basic conditions. The separation of the anodic and cathodic potentials (E
p) is high in thionine-loaded zeolites (>100) with respect to the solution of thionine (E
p = 34 for ZSM-5/P and 36 mV for HZSM-5/P), indicating that there are strong interaction between thionine molecules and the
zeolites. The midpoint potentials (E
m) for TH/ZSM-5/P and TH/HZSM-5/P are −0.203 and −0.381 V, respectively. However, the midpoint potentials for the solution
of thionine for the electrode system of ZSM-5/P and HZSM-5/P are −0.335 and −0.407 V, respectively. Thus, thionine dye molecules
incorporated into the zeolites can be reduced more easily with respect to solution of thionine. In various electrolyte solutions,
the midpoint potentials remains constant, but the midpoint potential of the thionine-zeolite electrodes depends on the solution
pH. Influence of the pH of the solution on the midpoint potential of an immobilized dye reveals that thionine molecules are
accessible to protons. This property is ascribed to the formation of mesopores in the structure of our zeolites suffering
from a calcination step.
Published in Russian in Elektrokhimiya, 2007, Vol. 43, No. 7, pp. 794–800.
The text was submitted by the authors in English 相似文献
65.
Shabnam Shahida Akbar Ali Muhammad Haleem Khan 《Journal of the Iranian Chemical Society》2014,11(1):1-8
A very sensitive, selective and simple flow injection time-based method was developed for on-line preconcentration and determination of thorium(IV) at micro g L–1 levels in environmental samples. The system operation was based on thorium(IV) ion retention at pH 4.0 in the minicolumn at a flow rate of 15.2 mL min–1. The trapped complex was then eluted with 3.6 mol L–1 HCl at a flow rate of 4.9 mL min–1. The amount of thorium(IV) in the eluate was measured spectrophotometrically at 651 nm using arsenazo-III solution (0.05 % in 3.6 mol L–1 HCl stabilized with 1 % triton X-100, 4.9 mL min–1) as colorimetric reagent. All chemical, and flow injection variables were optimized for the quantitative preconcentration of metal and a study of interference level of various ions was also carried out. The system offered low backpressure and improved sensitivity and selectivity. At a preconcentration time of 60 s and a sample frequency of 40 h–1, the enhancement factor was 97, the detection limit was 0.25 μg L–1, and the precision expressed as relative standard deviation was 1.08 % (at 50 μg L–1), whereas for 300 s of the preconcentration time and a sample frequency of 10 h–1, the enhancement factor of 357, the detection limit (3σ) of 0.069 μg L–1 and the precision of 1.32 % (at 10 μg L–1) was reported. The accuracy of the developed method was sufficient and evaluated by the analysis of certified reference material IAEA-SL-1 (Lake Sediment) and spiked water samples. 相似文献
66.
Shabnam Sheshmani Parvaneh Dalir Kheirollahi Hossein Aghabozorg Ardeshir Shokrollahi Guido Kickelbick Mojtaba Shamsipur Farshid Ramezanipour Abolghasem Moghimi 《无机化学与普通化学杂志》2005,631(15):3058-3065
The two complexes (pydaH)2[Ce(pydc)2(H2O)2]2 · 2H2O (1) and (phenH)2[Bi(pydc)2(H2O)]2 · 5H2O (2) were prepared from the proton transfer compounds containing the 2,6‐pyridinedicarboxylate ion. 1 was synthesized from the reaction of Ce(NO)3 · 6H2O with the proton transfer compound, (pydaH2)(pydc), (pyda=2,6‐diaminopyridine, pydcH2=2,6‐pyridinedicarboxylic acid). 2 was synthesized from the reaction of proton transfer compound, (phenH)2(pydc), (phen=1,10‐phenanthroline), with Bi(NO3)3 · 5H2O. The characterization was carried out using IR, 1H and 13C NMR spectroscopy, elemental analysis and single crystal X‐ray diffraction. The complex 1 crystallizes in the space group of the triclinic system, and contains two molecules per unit cell. The structure has been refined to a final value for the crystallographic R factor of 0.0342 based on 8851 reflections. The unit cell parameters are: a = 9.753(2) Å, b = 10.503(2) Å, c = 10.774(2) Å, α = 83.905(4)°, β = 88.089(4)°, and γ = 82.636(3)°. The crystal structure illustrates that cerium atoms are connected together through the four‐membered ring Ce2O2. 2,6‐Pyridinedicarboxylate fragment acts as a tridentate ligand. The molecular structure contains four (pydc)2? ligands, two of which are bridge ligands linking the two central atoms. The complex 2 crystallizes in the space group of the triclinic system and contains two molecules per unit cell. The unit cell dimensions are: a = 8.8860(4) Å, b = 12.0132(6) Å, c = 13.0766(6) Å, α = 100.967(1)°, β = 96.681(1)° and γ = 94.191(1)°. The structure has been refined to a final value for the crystallographic R factor of 0.0471 based on 9576 reflections. In this complex, 2,6‐pyridinedicarboxylate moiety has acted as a tridentate ligand and the lattice is composed of binuclear unit, [Bi(pydc)2(H2O)]22?, (phenH)+ counter ions and five lattice waters. In both complexes hydrogen bonds, π‐π stacking and ion‐pairing play important roles in stabilizing the corresponding lattice. The stoichiometry and stability of the ZnII, CdII, PbII, and CeIII complexes with (pydaH2)(pydc) in aqueous solution were investigated by potentiometric pH titration. The solution studies revealed that the stoichiometry of the crystalline complexes of the proton transfer system (pydaH2)(pydc) with CeIII, obtained in this study, and those with ZnII, CdII and PbII, reported in our previous studies, are in close agreements. The complexation reactions of phen, pydc, and 2phen+pydc with BiIII in aqueous solution were investigated by potentiometric pH titrations, and the equilibrium constants for all major complexes formed are described. 相似文献
67.
Shabnam Fakhari Azita Nouri Mina Jamzad Samira Arab‐Salmanabadi Foujan Falaki 《中国化学会会志》2021,68(1):67-75
In this study, the density functional theory computational method is used to investigate the encapsulation process of metformin into three types of the cyclic peptides composed of eight serine (CP1), eight glycine (CP2), and four serine‐glycine (CP3) cyclic peptides as a new model in the process of drug delivery in the gas phase. The obtained results using the B3LYP/6‐31++G (d,p) method indicate that the complexes formed are energetically favored. Furthermore, results reveal that the drug encapsulation process is typically chemisorption. The natural bonding orbital analysis shows that the intermolecular interaction of the C2 complex (metformin/CP2) is stronger than the C1 (Metformin/CP1) and C3 (Metformin/CP3) complexes due to greater total charge transfer energy, and the C1 complex is found to be the most favored complex. The theory of atoms in molecule (AIM) method is used to analyze the nature of interactions in different molecular systems. The results show the investigated cyclic peptides as effective carriers of metformin in the nanomedicine field. 相似文献
68.
A Vaasa K Ligi S Mohandessi E Enkvist A Uri LW Miller 《Chemical communications (Cambridge, England)》2012,48(68):8595-8597
A photoluminescence probe ARC-1185, possessing both high affinity towards basophilic protein kinases (PKs) and microsecond-scale luminescence lifetime when associated with a kinase, was used for the mapping of ARC-1185-PK complexes in living cells with time-gated luminescence microscopy. 相似文献
69.
Influence of the third monomer on lauryl methacrylate–methyl methacrylate emulsion terpolymerization
Rukhsana Shabnam Abu M. I. Ali Muhammad A. J. Miah Klaus Tauer Hasan Ahmad 《Colloid and polymer science》2013,291(9):2111-2120
An experimental study shows how the emulsion terpolymerization of lauryl methacrylate (LMA) and methyl methacrylate is influenced by the nature of the third monomer. The third monomer is either glycidyl methacrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, or styrene. We report the synthesis of terpolymer particles with an appreciably high content of the very hydrophobic LMA (between 0.2515 and 0.238 molar fraction in the monomer mixture) in 60:40 weight water/ethanol mixture as the continuous phase, poly(vinyl pyrrolidone) as a polymeric steric stabilizer, and potassium peroxodisulfate as the initiator. The emulsion terpolymerization proceeds smoothly without the formation of coagulum and leads to particles with an average diameter clearly below 1 μm. We discuss the overall polymerization behavior regarding conversion–time curves, particle morphology, and glass transition temperature of the terpolymers in dependence of the lyophilicity/lyophobicity of the monomer mixture. 相似文献
70.