Nano-sized metal particles are attracting much interest in industrial and biomedical applications due to the recent progress and development of nanotechnology, and the surface-modifications by appropriate polymers are key techniques to stably express their characteristics. Herein, we applied cyclic poly(ethylene glycol) (c-PEG), having no chemical inhomogeneity, to provide a polymer topology-dependent stabilization for the surface-modification of gold nanoparticles (AuNPs) through physisorption. By simply mixing c-PEG, but not linear counterparts, enables AuNPs to maintain dispersibility through freezing, lyophilization, or heating. Surprisingly, c-PEG endowed AuNPs with even better dispersion stability than thiolated PEG (HS–PEG–OMe). The stronger affinity of c-PEG was confirmed by DLS, ζ-potential, and FT-IR. Furthermore, the c-PEG system exhibited prolonged blood circulation and enhanced tumor accumulation in mice. Our data suggests that c-PEG induces physisorption on AuNPs, supplying sufficient stability toward bio-medical applications, and would be an alternative approach to the gold–sulfur chemisorption.
The intramolecular electronic excitation transfer in dithiaanthracenophane (DTA) in THF solution has been investigated by probing the fluorescence anisotropy decay with a femtosecond up-conversion method. In DTA, two anthracene rings are known to be stacked parallel, but with nearly orthogonal orientation. There appeared a damped oscillation of an apparent period of 1.2 ( 0.2 ps and a damping time constant of 1.0 ( 0.1 ps. It has been found that the oscillatory behavior is consistent with the recurrence motion of an excitation between two anthracene moieties, from a theoretical analysis following a manner of Wynne and Hochstrasser (Wynne, K.; Hochstrasser, R. M. J. Raman Spectrosc. 1995, 26, 561). The magnitude of the dipole-dipole energy transfer interaction is estimated to be 40 cm -1 which is in an acceptable agreement with the experimental value (29 cm -1 ) deduced from the oscillation period. In comparison with the similar case of 2,2′-binaphthyl (BN) reported by Zhu et al. (Zhu, F.; Hochstrasser, R. M. J. Chem. Phys. 1993, 98, 1042, the electronic dephasing time T 2 ′ is significantly longer in DTA (1.0 ps) than in BN (0.2 ps). The longer dephasing time in DTA can be explained as arising from a much more fixed and rigid dimeric conformation than in BN.
This paper describes the synthesis of systematic sets of figure-eightand tadpole-shaped amphiphilic block copolyethers (BCPs) consisting of poly(decyl glycidyl ether) and poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether], together with the corresponding cyclic counterparts, via combination of the t-Bu-P 4 -catalyzed ring-opening polymerization (ROP) and click cyclization. The clickable linear BCP precursors, with precisely controlled azido and ethynyl group placements as well as a fixed molecular weight and monomer composition (degree of polymerization for each block was adjusted to be around 50), were prepared by the t-Bu-P 4catalyzed ROP with the aid of functional initiators and terminators. The click cyclization of the precursors under highly diluted conditions produced a series of cyclic, figure-eight-, and tadpole-shaped BCPs with narrow molecular weight distributions of less than 1.06. Preliminary studies of the BCPs self-assembly in water revealed the significant variation in their cloud points depending on the BCP architecture, though there were small architectural effects on their critical micelle concentration and morphology of the aggregates.
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