Preparation and characterization of pure and mixed monolayers of poly(ethylene glycol) brushes chemically adsorbed to silica surfaces

We prepared pure and mixed monolayers of methoxy-terminated poly(ethylene glycol)s (m-PEG's) chemically attached to silica surfaces by using m-PEG silane coupling agents of three different molecular weights. These films were subsequently characterized in water by atomic force microscopy (AFM). Images of pure m-PEG monolayers showed the formation of polymer brushes on silica. Force curves between two modified surfaces suggested that an increase in the number of oxyethylene (OE) groups from 6 (PEG6 surface) to 43 (PEG43 surface) to 113 (PEG113 surface) decreased the flexibility of the m-PEG chains in the m-PEG brushes. Frictional force measurements also showed that the friction increased in the order PEG6 < PEG43 相似文献   

Colloidal crystals of core-shell type spheres with poly(styrene) core and poly(ethylene oxide) shell

Elastic modulus and crystal growth kinetics have been studied for colloidal crystals of core–shell type colloidal spheres (diameter = 160–200 nm) in aqueous suspension. Crystallization properties of three kinds of spheres, which have poly(styrene) core and poly(ethylene oxide) shell with different oxyethylene chain length (n = 50, 80 and 150), were examined by reflection spectroscopy. The suspensions were deionized exhaustively for more than 1 year using mixed bed of ion-exchange resins. The rigidities of the crystals range from 0.11 to 120 Pa and from 0.56 to 76 Pa for the spheres of n = 50 and 80, respectively, and increase sharply as the sphere volume fraction increase. The g factor, parameter for crystal stability, range from 0.029 to 0.13 and from 0.040 to 0.11 for the spheres of n = 50 and 80, respectively. These g values indicate the formation of stable crystals, and the values were decreased as the sphere volume fraction increased. Two components of crystal growth rate coefficients, fast and slow, were observed in the order from 10⁻³ to 10¹ s⁻¹. This is due to the secondary process in the colloidal crystallization mechanism, corresponding to reorientation from metastable crystals formed in the primary process and/or Ostwald-ripening process. There are no distinct differences in the structural, kinetic and elastic properties among the colloidal crystals of the different core–shell size spheres, nor difference between those of core–shell spheres and silica or poly(styrene) spheres. The results are very reasonably interpreted by the fact that colloidal crystals are formed in a closed container owing to long-range repulsive forces and the Brownian movement of colloidal spheres surrounded by extended electrical double layers, and their formation is not influenced by the rigidity and internal structure of the spheres.     

Bioreductive activation and drug chaperoning in cobalt pharmaceuticals

The potential for cobalt(III) complexes in medicine, as chaperones of bioactive ligands, and to target tumours through bioreductive activation, has been examined over the past 20 years. Despite this, chemical properties such as reduction potential and carrier ligands required for optimal tumour targeting and drug delivery have not been optimised. Here we review the chemistry of cobalt(III) drug design, and recent developments in the understanding of the cellular fate of these drugs.     

Chemical and electrochemical oxidation of thiophene-pyridine and thiophene-pyrimidine co-oligomers in solutions

Chemical and electrochemical oxidation (or p-doping) of three types of pi-conjugated co-oligomers, Py-Th-(Th)n-Th-Py (Py = pyridine unit; Th = thiophene unit; 5a, n = 1; 6a, n = 2), Th-Py-(Th)n-Py-Th (5b: n = 1; 6b: n = 2), and Pym-Th-(Th)n-Th-Pym (Pym = pyrimidine unit; 5c: n = 1; 6c: n = 2), in solution systems has been studied. The chemical oxidation with NOBF(4) proceeded with isosbestic points in the UV-vis spectrum. The UV-vis absorption peak of 5a at 418 nm in CH(2)Cl(2) shifted to 456 nm after oxidation of 5a with NOBF(4). The oxidized 5a was easily reduced by N(2)H(4) to give the original UV-vis spectrum of 5a, and 5b, 6b, and 5c behaved similarly in the oxidation and reduction. In the oxidation by NOBF4, an (oxidized co-oligomer)/(original neutral co-oligomer) ratio of 1 was attained at [NOBF4] = 1.3 x 10(-6), 4 x 10(-6), 7 x 10(-6), and 9 x 10(-6) M for 5a, 6b, 5b, and 5c, respectively. The obtained data are considered to reflect the ease of oxidation of the co-oligomer, which is affected by the electron-accepting nature of the N-containing aromatic unit in the co-oligomer and effective pi-conjugated length of the co-oligomer. The cyclic voltammogram of 5a showed three redox couples with anodic peak current potentials of Epa = 0.75, 1.10, and 1.34 V versus Ag+/Ag, respectively. The first oxidation peak was assigned to one-electron oxidation of 5a, and electronic current of the first anodic peak (i) of 5a and 5c was proportional to (scanning rate)1/2. From the i- (scanning rate)1/2 relationship, diffusion constants, D's, of 5a and 5c were estimated to be 9.6 x 10(-6) and 1.7 x 10(-5) cm2 s(-1), respectively. CV data of 5b with the terminal thiophene units indicated occurrence of electrochemical oxidative polymerization of 5b.     

Preparation of Main‐Chain‐Type Quinolinol Polymers by Organometallic Polycondensation

Summary: New main‐chain‐type polymers of 8‐quinolinol were prepared by organometallic polycondensation. They had a poly(aryleneethynylene)‐type structure and exhibited photoluminescence with a peak at about 470 nm and quantum yields of 21–39%. Metal ions such as Zn²⁺ and Al³⁺ modified the photoluminescence.

Structure of the three main‐chain‐type polymers of 8‐quinolinol synthesized and studied here.     

β‐Cyclodextrin Pseudopolyrotaxanes with π‐Conjugated Polymer Axles

Summary: β‐Cyclodextrin (β‐CD) pseudopolyrotaxanes containing poly(thiophene‐2,5‐diyl), PTh , or poly(3‐methylthiophene‐2,5‐diyl)s, P3MeTh s, as an axle were prepared. Structures of the pseudopolyrotaxanes and their inclusion behavior with β‐CD were investigated. The UV‐vis measurements revealed that inclusion of P3MeTh s by β‐CD depended on the flexibility of the main chain and their molecular weight.

Formation of the inclusion complex of β‐CD and PTh .     

Ostwald ripening of protein-stabilized emulsions: effect of transglutaminase crosslinking

Ostwald ripening in n-alkane oil-in-water emulsions stabilized by sodium caseinate at neutral pH has been studied by monitoring time-dependent changes in the number-average droplet diameter and the droplet-size distribution. In qualitative agreement with theory, the destabilization rate has been shown to increase with reduction of the n-alkane chain length and on addition of ethanol to the aqueous phase. Replacement of caseinate by β-lactoglobulin also leads to improved stability, but addition of calcium ions does not. The potential use of transglutaminase-induced crosslinking of adsorbed protein as a way of inhibiting the Ostwald ripening of caseinate-stabilized emulsions has been examined. It is shown that enzymic crosslinking before emulsification can lead to a modest reduction in the coarsening rate at long storage times. Crosslinking of caseinate after emulsification produces enhanced stability at short times, but there is a catastrophic loss of stability at long times due to droplet coalescence.     

Identification of Cavities Inside Two-Dimensional Heterogeneous Isotropic Elastic Bodies

In this paper, we discuss the uniqueness in determining cavities (i.e., nonrectilinear cracks) in a heterogeneous isotropic elastic medium in two dimensions. Our main result asserts that there is at most one cavity in the elastic medium which yields the same surface displacements and stresses on an arbitarily small portion of the boundary. The boundaries of cavities are assumed to be piecewise smooth and admit edges where no net force is exerted. The key of the proof is the unique continuation for the isotropic Lamé system and geometric considerations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Research on the algorithm of binary image cross-correlation for unsteady flow field measurement

In the present paper, the algorithm of Binary Image Cross-Correlation (BICC) was developed to measure the unsteady flow field. A vortex flow field was used to test the algorithm by numerical simulation. The results show that BICC is an effective algorithm for particle identification from consecutive images, the accurate velocity vector field can be obtained. The real velocity field in a valve chamber was measured by BICC in this study. From the full-field velocity information, the pressure and vorticity fields were also extracted by post-processing. The project supported by the National Natural Science Foundation of China