Summary For estimating the values corresponding to the oxygen defects in high Tc superconducting oxides, iodometry has been applied for the determination of Cu3+ and Cu2+. The presence of Bi or Pb causes some difficulty in the identification of the end point of this titration, because of the formation of iodine complexes. Therefore, chlorine generation from HCl and iodometry was applied for the determination of Bi5+ or Pb4+ in the oxides, and for the additional determination of Cu3+, O2 generation was used together with Cl2 generation for Bi5+ or Pb4+. 相似文献
Dendritic iron porphyrins were synthesized as functional mimics of globular electron-transfer heme proteins. The cascade molecules 1 · Zn ? 3 Zn of first to third generation were obtained starting from the (meso-diarylporphyrin) zinc 6 · Zn which contains four carboxylate arms for attachment of the poly(ether-amide) dendritic branches by peptide-coupling methodology (Scheme 1). Generation 3 compound 3 · Zn with 108 methyl-carboxylate end groups has a molecular weight of 19054. D, and computer modeling suggests that its structure is globular and densely-packed, measuring ca. 4 nm in diameter and, therefore, similar in dimensions to the electron-transfer protein cytochrome-c. Starting from the generation 1 poly(carboxylic acid) 11 · Zn and the generation 2 analog 12 · Zn the dendritic ZnII porphyrins 4 · Zn and 5 · Zn , respectively, were obtained by esterification with triethyleneglycol monomethyl ether (Schemes 3 and 4). Demetallation followed by insertion of FeII and in situ oxidation afforded the water-soluble dendritic iron porphyrins 4 FeCl and 5 FeCl . The electrochemical behavior of esters 1 · Zn ? 3 · Zn in organic solvents changed smoothly with increasing dendritic generation (Table 1). Progressing from 1 · Zn to 3 · Zn in THF, the first porphyrin-centered oxidation and reduction potentials become more negative by 320 and 210mV, respectively. These changes were attributed to strong microenvironmental effects imposed on the electroactive core by the densely packed dendritic surroundings. The electrochemical properties of 4 · FeCl and 5 · FeCl were investigated by cyclic voltammetry in both CH2Cl2 and H2O (Tables 2 and 3). Progressing from 4 · FeCl to 5 · FeCl in CH2Cl2, the redox potential of the biologically relevant FeIII/FeII couple remained virtually unchanged, whereas in aqueous solution, 5 FeCl exhibited a potential 420 mV more positive than did 4 FeCl. The large difference between these potentials in H2O was attributed to differences in solvation of the core electrophore. Whereas the relatively open dendritic branches in 4 · Fecl do not impede access of bulk solvent to the central core, the densely packed dendritic superstructure of 5 · FeCl significantly reduces contact between the heme and external solvent. As a result, the more charged FeIII state is destabilized relative to FeII, and the redox potential is strongly shifted to a more positive value. 相似文献
The hydrothermal reaction of MnSO4 with the achiral 2-carboxyethyl(phenyl)phosphinate ligand (H2L) afforded a 2?D coordination polymer manganese phosphinate, [Mn(HL)2]n (1) (H2L?=?2-carboxyethyl(phenyl) phosphinic acid). It contains two types of dimeric ring motifs, which can generate a layer structure through edge-sharing. The interlayer stacking by C-H…π interactions between the C-H groups of the phenyl rings of HL- and the phenyl rings of the adjacent layers results in its crystallization in a noncentrosymmetric crystal structure with (43)2(46·66·83) topology. Compound 1 shows a second harmonic generation response that is 0.8 times that of urea. The luminescence spectrum indicates an emission maximum at 457?nm, attributed to an intra-ligand emission state. 相似文献
Developing a bifunctional catalyst with low cost and high catalytic performance in NaBH4 hydrolysis for H2 generation and selective reduction of nitroaromatics will make a significant impact in the field of sustainable energy and water purification. Herein, a low-loading homogeneously dispersed Pd oxide-rich Co3O4 polyhedral catalyst (PdO-Co3O4) with concave structure is reported by using a metal–organic framework (MOF)-templated synthesis method. The results show that the PdO-Co3O4 catalyst has an exceptional turnover frequency (3325.6 molH2 min−1 molPd−1), low activation energy (43.2 kJ mol−1), and reasonable reusability in catalytic H2 generation from NaBH4 hydrolysis. Moreover, the optimized catalyst also shows excellent catalytic performance in the NaBH4 selective reduction of 4-nitrophenol to 4-aminiphenol with a high first-order reaction rate of approximately 1.31 min−1. These excellent catalytic properties are mainly ascribed to the porous concave structure, monodispersed Pd oxide, as well as the unique synergy between PdO and Co3O4 species, which result in a large specific surface area, high conductivity, and fast solute transport and gas emissions. 相似文献
Three unimolecular peptide channels have been designed and prepared by using the β‐helical conformation of gramicidin A (gA). The new peptides bear one to three NH3+ groups at the N‐end and one to three CO2? groups at the C‐end. These zwitterionic peptides were inserted into lipid bilayers in an orientation‐selective manner. Conductance experiments on planar lipid bilayers showed that this orientation bias could lead to observable directional K+ transport under multi‐channel conditions. This directional transport behavior can further cause the generation of a current across a planar bilayer without applying a voltage. More importantly, in vesicles with identical external and internal KCl concentrations, the channels can pump K+ across the lipid bilayer and cause a membrane potential. 相似文献
Poly(10-undecene-1-ol)s were synthesized by metallocene-catalyzed polymerization. MALDI-TOF MS allows obtaining detailed information on the monomer units in the polymer chains and the nature of the head and end groups of these polymers in dependence on the Al alkyl triisobutyl aluminum (TIBA) as well as methylalumoxan (MAO), both used as protecting agent for the hydroxyl groups of the monomer. The peak-to-peak distances of the main peaks could be distinctly assigned to the monomer unit 10-undecene-1-ol. Evaluating the MALDI-TOF peak distributions, polymers with -H, -C4H9, -CH3 head groups in combination with vinylidene and saturated (–CH3) end groups could be detected. By 1H NMR spectroscopy, it was verified that with the used catalysts polymers with vinylidene end groups were obtained predominantly. The presence of saturated end groups could be proved qualitatively by combination of 1H and 13C NMR spectroscopy for polymers produced by TIBA protection, which strikingly confirm the results from MALDI-TOF MS. For the polymers prepared with only MAO protection, saturated groups are also proved but discrimination between head and end groups was not possible. A polymerization mechanism corresponding to the detected different head and end groups is proposed. 相似文献
The structures of two ammonium salts of 3‐carboxy‐4‐hydroxybenzenesulfonic acid (5‐sulfosalicylic acid, 5‐SSA) have been determined at 200 K. In the 1:1 hydrated salt, ammonium 3‐carboxy‐4‐hydroxybenzenesulfonate monohydrate, NH4+·C7H5O6S−·H2O, (I), the 5‐SSA− monoanions give two types of head‐to‐tail laterally linked cyclic hydrogen‐bonding associations, both with graph‐set R44(20). The first involves both carboxylic acid O—H...Owater and water O—H...Osulfonate hydrogen bonds at one end, and ammonium N—H...Osulfonate and N—H...Ocarboxy hydrogen bonds at the other. The second association is centrosymmetric, with end linkages through water O—H...Osulfonate hydrogen bonds. These conjoined units form stacks down c and are extended into a three‐dimensional framework structure through N—H...O and water O—H...O hydrogen bonds to sulfonate O‐atom acceptors. Anhydrous triammonium 3‐carboxy‐4‐hydroxybenzenesulfonate 3‐carboxylato‐4‐hydroxybenzenesulfonate, 3NH4+·C7H4O6S2−·C7H5O6S−, (II), is unusual, having both dianionic 5‐SSA2− and monoanionic 5‐SSA− species. These are linked by a carboxylic acid O—H...O hydrogen bond and, together with the three ammonium cations (two on general sites and the third comprising two independent half‐cations lying on crystallographic twofold rotation axes), give a pseudo‐centrosymmetric asymmetric unit. Cation–anion hydrogen bonding within this layered unit involves a cyclic R33(8) association which, together with extensive peripheral N—H...O hydrogen bonding involving both sulfonate and carboxy/carboxylate acceptors, gives a three‐dimensional framework structure. This work further demonstrates the utility of the 5‐SSA− monoanion for the generation of stable hydrogen‐bonded crystalline materials, and provides the structure of a dianionic 5‐SSA2− species of which there are only a few examples in the crystallographic literature. 相似文献
The title compound, [Th(C12H15O4)4]n, is the first homoleptic thorium–carboxylate coordination polymer. It has a one‐dimensional structure supported by the bidentate bridging coordination of the singly charged 3‐carboxyadamantane‐1‐carboxylate (HADC−) anions. The metal ion is situated on a fourfold axis (site symmetry 4) and possesses a square‐antiprismatic ThO8 coordination, including four bonds to anionic carboxylate groups [Th—O = 2.359 (2) Å] and four to neutral carboxyl groups [Th—O = 2.426 (2) Å], while a strong hydrogen bond between these two kinds of O‐atom donor [O...O = 2.494 (3) Å] affords planar pseudo‐chelated Th{CO2...HO2C} cycles. This combination of coordination and hydrogen bonding is responsible for the generation of quadruple helical strands of HADC− ligands, which are wrapped around a linear chain of ThIV ions [Th...Th = 7.5240 (4) Å] defining the helical axis. 相似文献
α,ω-Diphenylpolyisobutylenes produced by the Clt-R-Clt/ø3Al initiating system have been derivatized. Model chloromethylation of t-butylbenzene by CH3OCH2Cl in chloroform indicated that beyond ca. 35% yield significant alkylative side reactions occurred. Phenyl end groups (average 1.5 per chain) and unsaturated chain ends (from proton elimination) have been converted to carboxyl end groups by oxidation with RuO4 in chloroform. Subsequently the carboxyl end groups were converted to acyl chloride termini by reaction with SOCl2. The latter end groups were coupled with living polystyryl anions to form isobutylene-styrene blcok copolymers. 相似文献
The 1,10‐decanedioic acid–1,3,5,7‐tetraazatricyclo[3.3.1.13,7]decane (1/1) system, C10H18O4·C6H12N4, was studied at 215 (2) K. Its analysis provides important information with regard to the long‐standing acid–carboxylate controversy in the urotropine–alkanedioic acid system. In the present structure, all the chain end‐groups display a clear acid character. The asymmetric unit of this commensurate modulated phase contains two molecules of diacid as well as two molecules of urotropine. Furthermore, the chain packing suggests a possible order parameter for the lock‐in transition. 相似文献
Quantum Chemical Model Calculations on the Migration of Si? F Groups in Hexafluorosilicates The transport of different Si? F species was simulated using two [SiF6]2? octahedra as example. Activation barriers and charge distributions were calculated with the EHT method. Bearing in mind the structure of cubic hexafluorosilicates calculations were carried out on the migration both along an edge and along a (110) face of the elementary cell. At first [SiF2]2+ and SiF4 groups were removed from an [Si2F12]4? unit to produce a surface vacancy. During a second step planar SiF4 groups were moved to the neighbouring lattice position. A diffusion of planar SiF4 is favoured, if the electrostatic interaction between moved and fixed fluorine atoms is as small as possible. 相似文献
The crystal structure of cesium phenylacetylide, CsC2C6H5, was solved and refined from synchrotron powder diffraction data (Pbca, Z = 8). Each Cs+ cation is coordinated by five ligands: four acetylide groups coordinate side‐on and one end‐on. A similar arrangement is found in the crystal structure of NaC2H (P4/nmm, Z = 2). There is a group‐subgroup relationship between both structures. Most importantly, the crystal structure of CsC2C6H5 could only be solved with the help of synchrotron data, as the very good peak:noise ratio allowed the assignment of several very weak reflections, which finally led to the correct space group, in which a structural solution was possible using direct space methods. 相似文献
The title compound, tricadmium trizinc tetraborate, Cd3Zn3(BO3)4, is a new non‐linear optical (NLO) crystal and its structure has been determined by single‐crystal X‐ray diffraction. This compound is composed of planar [BO3]3− groups sharing O atoms with CdO4 or ZnO4 tetrahedra. The BO3 triangles are located on threefold axes and are arranged with nearly the same orientation. The Cd and Zn atoms are disordered on the same site in the proportion 1:1. A strong second harmonic generation of Nd:YAG laser radiation (λ = 1064 nm) has been observed for a crystal of the title compound. 相似文献
The syntheses of polylactides (PLAs) with branched peptide end groups containing reactive (ionic) moieties such as amino or carboxyl groups are described and were used to prepare PLA‐based microspheres (MSs) with positively or negatively charged surfaces. Branched peptides with hydroxyl end groups and four protected amino or carboxyl groups, Boc4‐K3‐OH or Bn4‐E3‐OH, were synthesized, and the hydroxyl group converted to an alkoxide and was used as the initiation site for the ring‐opening polymerization of L ‐lactide. Subsequent deprotection gave PLAs end‐capped with branched peptides having four amino or carboxyl groups, respectively (K3‐PLA and E3‐PLA). K3‐PLA and E3‐PLA were converted to K34+‐PLA and E34?‐PLA by acid or base treatment, respectively. MSs with charged surfaces were then prepared using K34+‐PLA or E34?‐PLA as a surfactant [MS(K34+‐PLA) or MS(E34?‐PLA)]. The ionic surface state of the MSs was confirmed by colloidal titration and zeta potential analysis.
The polymerization of ε-caprolactone (εCL) initiated with aluminium triisopropoxide (Al(OiPr)3) trimer ( A 3) and/or tetramer ( A 4) was studied. The rate of A 3 ⇔︁ A 4 interconversions in the diluted (≤0,1 mol · L-1) C6D6, C6D6/εCL, and THF/εCL solutions were found to be slow, when compared with the rate of propagation. Comparison of the 1H NMR spectra of the initiators with those of the polymerization mixtures revealed that A 3 is much more reactive than A 4 in their reactions with εCL. From the initiator reacted with εCL all threeOiPr groups from Al(OiPr)3 are transferred into the poly(εCL) as end groups. Kinetic studies of polymerization confirmed the large reactivity difference between A 3 and A 4. 相似文献
We discovered a rare phenomenon wherein a thieno‐pyrrole fused BODIPY dye (SBDPiR690) generates singlet oxygen without heavy halogen atom substituents. SBDPiR690 generates both singlet oxygen and fluorescence. To our knowledge, this is the first example of such a finding. To establish a structure–photophysical property relationship, we prepared SBDPiR analogs with electron‐withdrawing groups at the para‐position of the phenyl groups. The electron‐withdrawing groups increased the HOMO–LUMO energy gap and singlet oxygen generation. Among the analogs, SBDPiR688, a CF3 analog, had an excellent dual functionality of brightness (82290 m ?1 cm?1) and phototoxic power (99170 m ?1 cm?1) comparable to those of Pc 4, due to a high extinction coefficient (211 000 m ?1 cm?1) and balanced decay (Φflu=0.39 and ΦΔ=0.47). The dual functionality of the lead compound SBDPiR690 was successfully applied to preclinical optical imaging and for PDT to effectively control a subcutaneous tumor. 相似文献
Aqueous zinc (Zn) ion batteries are attractive for next generation batteries with high safety, yet their applications are still hindered by the uncontrollable dendrite formation and side reactions on Zn anode. Here, a polyzwitterion protective layer (PZIL) was engineered by polymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) in carboxymethyl chitosan (CMCS), which renders the following merits: the choline groups of MPC can preferentially adsorb onto Zn metal to avoid side reactions; the charged phosphate groups chelate with Zn2+ to regulate the solvation structure, further improving side reaction inhibition; the Hofmeister effect between ZnSO4 and CMCS can enhance the interfacial contact during electrochemical characterization. Consequently, the symmetrical Zn battery with PZIL can keep stable for more than 1000 hours under the ultra-high current density of 40 mA cm−2. The PZIL confers the Zn/MnO2 full battery and Zn/active carbon (AC) capacitor with stable cycling performance under high current density. 相似文献
The 1994 structure of a transition‐state analogue with AlF4− and GDP complexed to G1α, a small G protein, heralded a new field of research into the structure and mechanism of enzymes that manipulate the transfer of phosphoryl (PO3−) groups. The number of enzyme structures in the PDB containing metal fluorides (MFx) as ligands that imitate either a phosphoryl or a phosphate group was 357 at the end of 2016. They fall into three distinct geometrical classes: 1) Tetrahedral complexes based on BeF3− that mimic ground‐state phosphates; 2) octahedral complexes, primarily based on AlF4−, which mimic “in‐line” anionic transition states for phosphoryl transfer; and 3) trigonal bipyramidal complexes, represented by MgF3− and putative AlF30 moieties, which mimic the geometry of the transition state. The interpretation of these structures provides a deeper mechanistic understanding into the behavior and manipulation of phosphate monoesters in molecular biology. This Review provides a comprehensive overview of these structures, their uses, and their computational development. 相似文献