基于超支化温敏聚合物制备温敏金纳米粒子

通过对不同分子量的超支化聚乙烯亚胺(hyperbranched polyethyleni mine,HPEI)的端基进行部分或完全异丁酰胺(isobutyric amide,IBAm)化,可以制备一系列具有不同低临界溶解温度(Lower Critical SolutionTemperature,LCST)的超支化温敏聚合物HPEI-IBAm。通过离子键或氢键之间的相互作用,所得超支化温敏聚合物可以吸附于柠檬酸钠还原并稳定的14nm的金纳米粒子(AuNP)的表面,从而得到具有温敏性质的金纳米粒子。所得温敏金的LCST都低于其相应的温敏聚合物,其差值在0.8至6℃之间。在pH值为9.18的缓冲溶液中,通过改变所用聚合物的分子量以及异丁酰胺基团的取代度,所得温敏金的LCST可控制在21.7~48.2℃之间。此外,所得温敏金的LCST也是pH值敏感的,通过溶液pH值的改变,所得温敏金的LCST值可以在更宽的范围内调节。增加溶液的碱性,LCST可能变化不大或降低,减小溶液的碱性会使LCST升高,直到消失。在偏酸的条件下,所得金复合物通常发生聚集,变得不稳定。此外,溶液中的盐度对所得温敏金的LCST也有影响,氯化钠和硫酸钠会降低其LCST,尤其是硫酸钠的效果更显著。     

Effects of TEMED and EDTA on the structural and mechanical properties of NIPAAm/Na+MMT composite hydrogels

N‐isopropyl acrylamide (NIPAAm) hydrogels are known as thermosensitive crosslinked polymer networks. In this work, the network parameters of their composites, i.e., NIPAAm/sodium montmorillonite (NIPAAm/Na⁺MMT) hydrogels synthesized by free radical solution polymerization in the presence of two different types of accelerator (tetramethyl ethylenediamine (TEMED) and ethylenediamine tetraacetic acid (EDTA)) and initiator (potassium persulphate (K₂S₂O₈) and cerium ammonium nitrate ((NH₄)₂Ce(NO₃)₆), Ce(IV)) using five different clay content (in the range of 1.0–5.0 wt % of total monomer concentration) at 25 °C were presented and discussed. FTIR spectra, XRD patterns, SEM photographs, and network parameters of the samples indicated that the presence of COOH groups on EDTA molecules was resulted in the formation of exfoliated structures and the activity of EDTA/KPS redox pair was higher than those of TEMED/KPS and EDTA/Ce (IV) pairs. The compression moduli (G) of the hydrogels initiated with EDTA/Ce(IV) redox pair showed smooth and continual changings with increase in Na⁺MMT content (for swelling equilibrium at 25 °C) on the contrary of EDTA/KPS and TEMED/KPS pairs. It might be related to low initiator efficiency of cerium ammonium nitrate than KPS molecules, having higher effective crosslinking density with increasing clay content. On the other hand, the G moduli of NIPAAm/Na⁺MMT hydrogels (above their phase transition temperature) initiated with TEMED/KPS redox pair were higher than the others because of the more hydrophobic nature of TEMED molecules. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1256–1264, 2010     

Synthesis and solution properties of a pH‐responsive cyclopolymer of zwitterionic ethyl 3‐(N,N‐diallylammonio)propanephosphonate

The zwitterionic monomer, ethyl 3‐(N,N‐diallylammonio)propanephosphonate, was cyclopolymerized in aqueous solutions using t‐butylhydroperoxide or ammonium persulfate as initiators to afford a polyphosphonobetaine (PPB). The protonation of P(?O)OEtO^– and deprotonation of ? NH⁺ groups in PPB by HCl and NaOH, gave the corresponding cationic polyphosphononic acid (CPP) and anionic polyphosphonate (APP). The presence of two pH‐responsive functionalities in APP has led to establish the equilibria: APP ? PPB ? CPP, the position of which very much dictates the viscosity behavior of its aqueous solution. The PPB demonstrated “antipolyelectrolyte” viscosity behavior; however, in contrast to many polycarbo‐ and polysulfo‐betaines, it was found to be soluble in salt‐free water as well as in salt‐added solutions. Basicity constant (K₁) of the amine group in APP, as determined by potentiometric technique, were found to be “apparent,” and as such followed the modified Henderson‐Hasselbalch equation. The study demonstrated a correlation between the basicity constants and viscosity values. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Comparison of three methods for fractionation and enrichment of low molecular weight proteins for SELDI-TOF-MS differential analysis

In most diseases, the clinical need for serum/plasma markers has never been so crucial, not only for diagnosis, but also for the selection of the most efficient therapies, as well as exclusion of ineffective or toxic treatment. Due to the high sample complexity, prefractionation is essential for exploring the deep proteome and finding specific markers.In this study, three different sample preparation methods (i.e., highly abundant protein precipitation, restricted access materials (RAM) combined with IMAC chromatography and peptide ligand affinity beads) were investigated in order to select the best fractionation step for further differential proteomic experiments focusing on the LMW proteome (MW inferior to 40,000 Da). Indeed, the aim was not to cover the entire plasma/serum proteome, but to enrich potentially interesting tissue leakage proteins. These three methods were evaluated on their reproducibility, on the SELDI-TOF-MS peptide/protein peaks generated after fractionation and on the information supplied.The studied methods appeared to give complementary information and presented good reproducibility (below 20%). Peptide ligand affinity beads were found to provide efficient depletion of HMW proteins and peak enrichment in protein/peptide profiles.     

Selective synthesis of mono- and distannylpyridines from chloropyridinols via an SRN1 mechanism

A selective two-step synthesis of either mono- or distannylated pyridines from commercially available pyridinols, involving its conversion to the corresponding diethyl pyridyl phosphates (pyDEP) followed by the reaction with Me₃SnNa in liquid ammonia, is described.The results obtained clearly indicate that the reactions proceed through an unimolecular radical nucleophilic substitution mechanism (S_RN1) with intermediacy of a monosubstitution product.     

Open tubular capillary electrochromatography: A useful microreactor for collagen I glycation and interaction studies with low-density lipoprotein particles

Diabetes, a multifunctional disease and a major cause of morbidity and mortality in the industrialized countries, strongly associates with the development and progression of atherosclerosis. One of the consequences of high level of glucose in the blood circulation is glycation of long-lived proteins, such as collagen I, the most abundant component of the extracellular matrix (ECM) in the arterial wall. Glycation is a long-lasting process that involves the reaction between a carbonyl group of the sugar and an amino group of the protein, usually a lysine residue. This reaction generates an Amadori product that may evolve in advanced glycation end products (AGEs). AGEs, as reactive molecules, can provoke cross-linking of collagen I fibrils. Since binding of low-density lipoproteins (LDLs) to the ECM of the inner layer of the arterial wall, the intima, has been implicated to be involved in the onset of the development of an atherosclerotic plaque, collagen modifications, which can affect the affinity of native and oxidized LDL for collagen I, can promote the entrapment of LDLs in the intima and accelerate the progression of atherosclerosis.In this study, open tubular capillary electrochromatography is proposed as a new microreactor to study in situ glycation of collagen I. The kinetics of glycation was first investigated in a fused silica collagen I-coated capillary. Dimethyl sulphoxide, injected as an electroosmotic flow marker, gave information about the charge of coating. Native and oxidized LDL, and selected peptide fragments from apolipoprotein B-100, the protein covering LDL particles, were injected as marker compounds to clarify the interactions between LDLs and the glycated collagen I coating. The method proposed is simple and inexpensive, since only small amounts of collagen and LDL are required. Atomic force microscopy images complemented our studies, highlighting the difference between unmodified and glycated collagen I surfaces.     

Conformation dependence of DNA electrophoretic mobility in a converging channel

The electrophoresis of λ‐DNA is observed in a microscale converging channel where the center‐of‐masses trajectories of DNA molecules are tracked to measure instantaneous electrophoretic (EP) mobilities of DNA molecules of various stretch lengths and conformations. Contrary to the usual assumption that DNA mobility is a constant, independent of field and DNA length in free solution, we find DNA EP mobility varies along the axis in the contracting geometry. We correlate this mobility variation with the local stretch and conformational changes of the DNA, which are induced by the electric field gradient produced by the contraction. A “shish‐kebab” model of a rigid polymer segment is developed, which consists of aligned spheres acting as charge and drag centers. The EP mobility of the shish‐kebab is obtained by determining the electrohydrodynamic interactions of aligned spheres driven by the electric field. Multiple shish‐kebabs are then connected end‐to‐end to form a freely jointed chain model for a flexible DNA chain. DNA EP mobility is finally obtained as an ensemble average over the shish‐kebab orientations that are biased to match the overall stretch of the DNA chain. Using physically reasonable parameters, the model agrees well with experimental results for the dependence of EP mobility on stretch and conformation. We find that the magnitude of the EP mobility increases with DNA stretch, and that this increase is more pronounced for folded conformations.     

Electrochemical reactions at the electrode/solution interface:Theory and applications to water electrolysis and oxygen reduction

Theoretical simulations on complex electrochemical processes have been developed on the basis of the understanding in electrochemistry,which has benefited from quantum mechanics calculations.This article reviews the recent progress on the theory and applications in electrocatalysis.Two representative reactions,namely water electrolysis and oxygen reduction,are selected to illustrate how the theoretical methods are applied to electrocatalytic reactions.The microscopic nature of these electrochemical reaction...