Molybdenum and tungsten complexes containing the pypzH (3-(2-pyridyl)pyrazole) ligand as a chelating bidentate are prepared: [Mo(CO)(4)(pypzH)], cis-[MoBr(η(3)-allyl)(CO)(2)(pypzH)], cis-[MoCl(η(3)-methallyl)(CO)(2)(pypzH)], [MI(2)(CO)(3)(pypzH)] (M = Mo, W) from [Mo(CO)(4)(NBD)] or the adequate bis(acetonitrile) complexes. The deprotonation of the molybdenum allyl or methallyl complexes affords the bimetallic complexes [cis-{Mo(η(3)-allyl)(CO)(2)(μ(2)-pypz)}](2) or [cis-{Mo(η(3)-methallyl)(CO)(2)(μ(2)-pypz)}](2) (μ(2)-pypz = μ(2)-3-(2-pyridyl-κ(1)N)pyrazolate-2κ(1)N). The allyl complex was subjected to an electrochemical study, which shows a marked connection between both metallic centres through the bridging pyridylpyrazolates. 相似文献
A family of ligands derived from bis(amino amides) containing aliphatic spacers has been prepared, and their protonation and stability constants for the formation of Cu(2+) complexes have been determined potentiometrically. Important differences are associated to both the length of the aliphatic spacer and the nature of the side chains derived from the amino acid. In general, ligands containing aliphatic side chains display higher basicities as well as stability constants with Cu(2+). In the same way, basicities and stability constants tend to increase when decreasing the steric hindrance caused by the corresponding side-chain. FT-IR, UV-vis and ESI-MS were used for analyzing the complex species detected in the speciation diagram. UV-vis studies showed the presence of different coordination environments for the copper(II) complexes. Complexes with different stoichiometries can be formed in some instances. This was clearly highlighted with the help of ESI-MS experiments. 相似文献
Theoretical investigations concerning possible calcium sulfate, CaSO(4), high-pressure polymorphs have been carried out. Total-energy calculations and geometry optimizations have been performed by using density functional theory at the B3LYP level for all crystal structures considered. The following sequence of pressure-driven structural transitions has been found: anhydrite, Cmcm (in parentheses the transition pressure) → monazite-type, P2(1)/n (5 GPa) → barite-type, Pnma (8 GPa), and scheelite-type, I4(1)/a (8 GPa). The equation of state of the different polymorphs is determined, while their corresponding vibrational properties have been calculated and compared with previous theoretical results and experimental data. 相似文献
Summary: We have developed the first direct, organocatalytic, bulk ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL) with solid cotton and paper cellulose as the initiators. The mild ROPs were performed without solvent, and are operationally simple, inexpensive and environmentally benign. Organic‐acid‐catalyzed heterogeneous derivatization of cellulose provides a novel route to valuable cellulose‐based biocompatible nanomaterials. The furnished polymerization products were characterized by FTIR, 1H and 13C NMR spectroscopy, MALDI‐TOF mass spectrometry and electron microscopy.
Organic acid‐catalyzed ring‐opening polymerization from cellulose fiber. 相似文献
In the present study, the effects of ultrasound (10, 20, and 30 min) on the bioactive compounds, antioxidant capacity, enzymatic inhibition, and in vitro digestion of six honey extracts from the Oaxaca state, Mexico, were analyzed. Significant differences were found in each honey extract with respect to the ultrasonic treatment applied (p < 0.05). In the honey extract P-A1 treated with 20 min of ultrasound, the phenols reached a maximum concentration of 29.91 ± 1.56 mg EQ/100 g, and the flavonoids of 1.92 ± 0.01 mg EQ/100 g; in addition, an inhibition of α-amylase of 37.14 ± 0.09% was noted. There were also differences in the phases of intestinal and gastric digestion, presenting a decrease in phenols (3.92 ± 0.042 mg EQ/100 g), flavonoids (0.61 ± 0.17 mg EAG/100 mg), antioxidant capacity (8.89 ± 0.56 mg EAG/100 mg), and amylase inhibition (9.59 ± 1.38%). The results obtained from this study indicate that, in some honeys, the processing method could increase the concentration of bioactive compounds, the antioxidant capacity, and the enzymatic inhibition; however, when subjected to in vitro digestion, the properties of honey are modified. The results obtained could aid in the development of these compounds for use in traditional medicine as a natural source of bioactive compounds. 相似文献
An Akaike Information Criterion (AIC) procedure (CASE-3D) has been successfully applied to the NMR based configurational assignment of reported hyacinthacines ( 1 – 3 , 5 – 8 ), recently target of configurational analysis using the popular DP4+ methodology. The present analysis makes use of reported 1H and 13C shifts and, in some particular cases, a few 3JHH couplings. The difficulty in proper computational prediction of relative energies, in molecules capable of inter-molecular hydrogen bonding, introduces large errors in the prediction of conformationally averaged NMR properties in methods based on Boltzmann averaging such as DP4 or DP4+. In contrast CASE-3D conformational amplitudes are free parameters in the model. Here we show that the CASE-3D conformational model selection strategy, when combined with a larger energy cutoff in the molecular-modelling conformational exploration, was sufficient to correctly assign the relative configuration in five of seven cases. Introduction of more information, either by supplementing 1H and 13C data with a few J-couplings, or using a cutoff based on computed DFT energies for the definition of the conformational ensembles, allowed the safe assignment of configuration for all compounds. 相似文献
The self-assembly of protein polymers is a promising route to prepare sophisticated functional nanostructures. However, the interplay between protein self-assembly by itself and its co-assembly with a template is not well understood. Silk-based protein polymers that co-assemble with DNA to form rod-like artificial viruses are herein developed and the effects of silk block length, concentration, and temperature in the self-assembly of the proteins alone are characterized by using a combination of bulk dynamic light scattering (DLS) and single-molecule atomic force microscopy (AFM). Protein nanorods were slowly formed (up to hours) through the interaction of the silk-like blocks. The proteins present a silk-length dependent critical elongation concentration, and above it the amount and size of nanorods rapidly increase. Temperature-dependent light scattering data was adequately fitted into a cooperative model of nucleation–elongation. These results are also important to understand the self-assembly of designed viral coat proteins with DNA templates to form artificial virus-like particles and help us to define general guidelines to design proteins with the ability to precisely organize matter at the nanoscale. 相似文献
Second-order polarization propagator approximation (SOPPA) and density functional theory (DFT) B3LYP computations revealed the presence of giant 3JHCCH couplings, up to more than 60 Hz, in conjugated quinonoid systems, very far above the typical limit of ~15 Hz. Strong hyperconjugative interactions of the C–H σ orbitals with the quinonoid 8-e− π system, which allows effective propagation of the spin polarization, seem to be responsible for those extraordinarily large couplings. Computation on several model systems showed the additive nature of the contributions from the available coupling paths to the total coupling. 相似文献