Polymer brushes grafted to the surface of silica nanoparticles were fabricated by atom‐transfer radical polymerization (ATRP) and investigated as catalysts in the cleavage of phosphodiesters. The surfaces of silica nanoparticles were functionalized with an ATRP initiator. Surface‐initiated ATRP reactions, in varying proportions, of a methacrylate moiety functionalized with a phenylguanidine moiety and an inert hydrophilic methacrylate species afforded hybrid nanoparticles that were characterized with potentiometric titrations, thermogravimetric analysis, and SEM. The activity of the hybrid nanoparticles was tested in the transesterification of the RNA model compound 2‐hydroxypropyl para‐nitrophenylphosphate (HPNP) and diribonucleoside monophosphates. A high catalytic efficiency and a remarkable effective molarity, thus overcoming the effective molarities previously observed for comparable systems, indicate the existence of an effective cooperation of the guanidine/guanidinium units and a high level of preorganization in the nanostructure. The investigated system also exhibits a marked and unprecedented selectivity for the diribonucleoside sequence CpA. The results presented open up the way for a novel and straightforward strategy for the preparation of supramolecular catalysts. 相似文献
Summary Letf: (x, z)∈Rn×Rn→f(x, z)∈[0, +∞] be measurable inx and convex inz.
It is proved, by an example, that even iff verifies a condition as|z|p≤f(x, z)≤Λ(a(x)+|z|q) with 1<p<q,a∈Llocs
(Rn),s>1, the functional
that isL1(Ω)-lower semicontinuous onW1,1(Ω), does not agree onW1,1(Ω) with its relaxed functional in the topologyL1(Ω) given by inf
Riassunto Siaf: (x, z)∈Rn×Rn→f(x, z)∈[0, +∞] misurabile inx e convessa inz.
Si mostra con un esempio che anche sef verifica una condizione del tipo|z|p≤f(x, z)≤Λ(a(x)+|z|q) con 1<p<q,a∈Llocs
(Rn),s>1, il funzionale
, che èL1(Ω)-semicontinuo inferiormente suW1,1(Ω), non coincide suW1,1(Ω) con il suo funzionale rilassato nella topologiaL1(Ω) definito da inf
[graph: see text] Condensation of squaric acid with a number of differently substituted 2-pyrrolyl derivatives afforded three new classes of squaraines. Their sharp and intense absorption bands in the biological window (700-900 nm), inherent singlet oxygen generation capabilities, together with proper functionalization allowing good water solubility make them suitable candidates as new non-porphyrinic singlet oxygen photosensitizers for photodynamic therapy (PDT). 相似文献
New β-lactam antibiotics. Functionalisation of 3-hydroxy-3-cephem-4-carboxylic esters through the Wittig reaction The 3-hydroxy-ceph-3-em-esters 1a, b reacted smoothly with stabilized phosphor-ylids to give a series of derivatives which were converted into the microbiologically active acids 14a, c, 15c and 20 by known procedures. The synthesis of the amides 23, 24, 26 and of the ester 28 from the 3-carboxymethyl-derivative 19 is also reported. 相似文献
[structure: see text] The conventional interpretation of proton NMR chemical shifts is supported by large basis set ab initio quantum mechanical calculations. The benzene protons are predicted to lie within the deshielding zone defined in terms of the out-of-plane magnetic shielding domain. However, ring currents by themselves are not sufficient to account quantitatively for the observed benzene proton downfield chemical shift. sigma-Electron contributions must also be taken into account. The conventional explanation for the ethyne proton chemical shift is valid. 相似文献
We study the polydisperse Baxter model of sticky hard spheres (SHS) in the modified mean spherical approximation (mMSA). This closure is known to be the zero-order approximation C0 of the Percus-Yevick closure in a density expansion. The simplicity of the closure allows a full analytical study of the model. In particular we study stability boundaries, the percolation threshold, and the gas-liquid coexistence curves. Various possible subcases of the model are treated in details. Although the detailed behavior depends upon the particularly chosen case, we find that, in general, polydispersity inhibits instabilities, increases the extent of the nonpercolating phase, and diminishes the size of the gas-liquid coexistence region. We also consider the first-order improvement of the mMSA (C0) closure (C1) and compare the percolation and gas-liquid boundaries for the one-component system with recent Monte Carlo simulations. Our results provide a qualitative understanding of the effect of polydispersity on SHS models and are expected to shed new light on the applicability of SHS models for colloidal mixtures. 相似文献
The spectroscopic emission intensities from excited F atoms in SF6-O2 discharges at 1 torr have been correlated to the densities of atoms in their ground electronic state by measuring the excitation efficiencies of the electrons in the energy range 11 to 17 eV with a method which essentially consists in the analysis of the emission of Ar or N2, added as actinometer gases to the discharge mixtures. The general applicability of the method has been tested by a direct titration of F atoms with chlorine. The spectroscopic analysis has allowed the determination of useful information on the trends of both the electron densities and their energies as a function of the oxygen percent in the feed. 相似文献
The reaction between N-chloro-N'-aroyl-amidines and β,β-disubstituted enamines affords 1 - aroyl - 4 -amino - 4,5 - dihydro - imidazoles in low yields, the main reaction product being N - (2 - morpholino - 2,2 -disubstituted) - ethylidene - N' - aroyl - amidines. A similar reaction course was not observed with enamines bearing a hydrogen atom in the β-position. In this case only products derived from electrophilic chlorination on enamines were isolated. 相似文献