Synthesis and characterization of well‐defined,amphiphilic poly(N‐isopropylacrylamide)‐ b‐[2‐hydroxyethyl methacrylate‐poly(ϵ‐caprolactone)]n graft copolymers by RAFT polymerization and macromonomer method

The well‐defined, thermosensitive and biodegradable graft copolymers, poly(N‐isopropylacrylamide)‐b‐[2‐hydroxyethyl methacrylate‐poly(ε‐caprolactone)]_n (PNIPAAm‐b‐(HEMA‐PCL)_n) (n = 3 or 9), were synthesized by combining reversible addition‐fragmentation chain transfer polymerization and macromonomer method. The copolymers were able to self‐assemble into micelles in water with low critical micellar concentration and demonstrated temperature sensitivity with a lower critical solution temperature at around 36 °C. Transmission electron microscopy shows that the micelles exhibit a nanosized spherical morphology within a size range of 30–100 nm. The PNIPAAm‐b‐(HEMA‐PCL)₃ copolymer exhibited biodegradation and low cytotoxicity. The paclitaxel‐loaded PNIPAAm‐b‐(HEMA‐PCL)₃ micelles displayed thermosensitive controlled release behavior, which indicates potential as drug carriers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5354–5364, 2007     

Two Characterizations of Diffeomorphisms of Euclidean Space

Two characterizations for a local diffeomorphism of R^n to be global one are given in terms of associated Wazewski equations.The two characterizations could be useful for the investigation of the Jacobian conjecture.     

A thermodynamic study of enantiomeric recognition of organic ammonium cations by pyridino-18-crown-6 type ligands in methanol and a 1: 1 methanol-1,2-dichloroethane mixture at 25.0°C

LogK, H, andTS values for interactions of (R) and (S) enantiomers of -(1-naphthyl)ethylammonium perchlorate (NapEt), -phenylethylammonium perchlorate (PhEt), and the hydrogen perchlorate salt of 2-amino-2-phenylethanol (PhEtOH) with a series of chiral and achiral pyridino-18-crown-6 type ligands and 18-crown-6 (18C6) were determined from calorimetric titration data valid in methanol and in a 1: 1 (v/v) methanol-1,2-dichloroethane (MeOH-1,2-DCE) mixture at 25.0°C. In the MeOH-1,2-DCE solvent mixture, the chiral macrocyclic ligands exhibit excellent recognition for enantiomers of the three organic ammonium cations as shown by large differences in logK values ( logK) which range from 0.4 to 0.6 (2.5- to 4.0-fold difference in binding constants). The logK values in the solvent mixture MeOH-1,2-DCE are increased by 0.1–0.5 logK units over those in absolute methanol, indicating a favorable effect of 1,2-dichloroethane on enantiomeric recognition. In 1,2-dichloroethane, however, the interactions are too strong (logK>6) to observe the degree of recognition by a direct calorimetric method. Complexation of organic ammonium cations by these macrocyclic ligands is driven by favorable enthalpy changes. The entropy changes ure unfavorable in all cases. The thermodynamic origin of enantiomeric recognition for NapEt in 1:1 (v/v) MeOH-1,2-DCE is enthalpic, but those for PhEt and PhEtOH are entropic. Effects of the ligand structure and flexibility and of the organic cation structure on recognition and complex stability are discussed on the basis of the thermodynamic quantities. Different thermodynamic behaviors of achiral 5 and 18C6 from those of chiral macrocyclic ligands indicate a difference between chiral and achiral macrocycle interactions with the chiral organic ammonium cations. The different thermodynamic behavior of NapEt enantiomers compared to those of PhEt and PhEtOH enantiomers supports the idea that the solution complex conformation of NapEt is different from those of PhEt and PhEtOH. - interaction is absent for the PhEt and PhEtOH complexes with diesterpyridino-18-crown-6 ligands in solution. Therefore, the higher degree of enantiomeric recognition for NapEt than for either PhEt or PhEtOH by these chiral macrocyclic ligands is a result of the presence of - interaction in the NapEt system.     

Determination of trace arsenic(V) by catalytic solid substrate-room temperature phosphorescence quenching method

In the H2SO4 medium and in the presence of dodecylbenzene sulfonic acid sodiumsalt (DBS), dimethyl yellow (R) could emit strong and stable solid substrate room temperature phosphorescence (RTP) on filter paper. And NaIO4 could oxidize R to cause the RTP quenching. Arsenic(V) could catalyze the reaction of NaIO4 oxidizing R, which caused the RTP sharply quenching. The reducing value of phosphorescence intensity (△Ip) for the system with DBS is 3.3 times higher than that without DBS. Moreover, the△Ip is proportional to the concentration of As(V). Based on the facts above, a new RTP quenching method for the determination of trace As(V) has been established.     

Factors influencing enantiomeric recognition of primary alkylammonium salts by pyridino-18-crown-6 type ligands

Equilibrium constant (K), enthalpy change (H), and entropy change (S) values were determined for the interactions of a series of chiral pyridino-18-crown-6 type ligands with enantiomers of several primary alkylammonium salts in various solvents. Good enantiomeric recognition in terms of logK was observed in many systems with logK values greater than 0.4. The extent of enantiomeric recognition and the stabilities of the chiral crown ether-ammonium salt complexes were found to depend on the rigidity of the macrocyclic frame of the ligand, the type and arrangement of the donor atoms on the ligand, the bulkiness of the substituents on the ligand's chiral centers, the location of the chiral centers on the ligand, and the solvent. The effects of these factors on the extent of enantiomeric recognition and on the stabilities of the complexes were examined for the systems studied.     

烯丙基氯化镁引发己二酸酐开环聚合

以烯丙基氯化镁引发己二酸酐开环聚合制备功能化的聚己二酸酐。考察了引发剂、温度、溶剂对聚合反应的影响.核磁端基分析表明开环聚合反应可能是通过酰氧键断裂,按“配位－插入”机理进行的。     

Prediction of Retention Time of Solutes under Linear Gradient Elution Conditions in RP-HPLC

A model for prediding retention time of solutes undeir linear gradient elulioa conditions has been established. In this model,the theorelkal expressions under different eluflon modes were derived and tested with the retention behaviors of p-hydroxy-benzaldehyde, vanilUn, biphenyl, phenanthrene in gradient elution. With halting into account the dwell time of the instrumeatal system, the theoretically predicted retention times agreewell with those experimentally determined.     

Synthesis of N-methylene phosphonic chitosan （NMPCS） and its potential as gene carder

N-Methylene phosphoulc chitosan (NMPCS),an amphiphilic macromolecule with powerful chelating ability of Ca~(2 ) ions,was synthesized and characterized.The physicochemical properties of NMPCS and the interactions between NMPCS and plasmid DNA were investigated by FTIR,~(13)C NMR,X-ray,agarose gel electrophorcsis retardation assay,atomic force microscopy (AFM) and circular dichroism (CD).The results suggest that at charge ratio 2:1 or above,DNA could be completely entrapped and spherical complexes with mean size of 80-210 nm were formed.Taking HeLa as host cell,luciferase expression mediated by NMPCS improved about 100 times compared to the expression mediated by chitosan.     

壳聚糖-两性聚氨酯接枝共聚物的制备

利用壳聚糖大分子链上的－OH和－NH2基团与两性聚氨酯预聚体的端－NCO基团反应，把两性聚氨酯链接枝到壳聚糖分子链上，为聚电解质及纳米胶体粒子间的组装，复合性质的研究提供模型化合物，红外光谱，热分析方法初步研究表明，采用上述方法能够制备出APU－壳聚糖接枝共聚物，但产物是壳聚糖与接枝共聚物的混合物，研究发现，这种接枝共聚物在盐酸水溶液中呈胶束形态，而且具有独特的流变性。