Colloidal iron oxides play an important role as magnetic resonance imaging (MRI) contrast agents. The superparamagnetic particles actually used are constituted by solid cores (diameter of 5-15 nm), generally coated by a thick polysaccharidic layer (hydrodynamic radii of 30-100 nm), and formulated by direct coprecipitation of iron salts in the presence of polymeric material. To better control the synthesis, we attempted to formulate new stable uncoated superparamagnetic nanoparticles. Colloids were generated by coprecipitation of an aqueous solution of iron salts and tetramethylammonium hydroxide (TMAOH) solution. The influence of parameters such as media composition, iron media, injection fluxes, Fe and TMAOH concentrations, temperature, and oxygen on size, magnetic and magnetic resonance relaxometric properties, and colloidal stability of particles were evaluated. We have determined the relative importance of these parameters as well as the optimal conditions for obtaining uncoated stable particles with an average size of 5 nm and interesting relaxivities. The interpretation of the observed limits takes into account diffusibilities of reactants and product, feeding rates of reactants, and surface properties of nanoparticles. A model of synthesis, related to spontaneous emulsification of suspensions, is proposed. Copyright 1999 Academic Press. 相似文献
New syntheses of 4‐alkoxy‐3‐methoxy‐5H‐benzocycloheptenes and 2‐alkoxy‐3‐methoxy‐5H‐benzocycloheptenes were studied. Based on Claisen rearrangement, O‐alkylation, nucleophilic addition of allyl magnesium bromide, ring‐closing metathesis, and dehydration, a series of new 4‐alkoxy‐3‐methoxy‐5H‐benzocycloheptenes and 2‐alkoxy‐3‐methoxy‐5H‐benzocycloheptenes were respectively synthesized from isovanillin in good overall yields. 相似文献
Electrophoresis 2014, 35, 2673–2680. DOI: 10.1002/elps.201400210 pH‐responsive microcapsules manufactured by combining electrostatic droplets (ESD) and microfluidic droplets (MFD) techniques to produce mono‐disperse core (alginate) ‐ shell (chitosan) structure with controlled drug release behavior. The fabricated core‐shell microcapsules have a pH‐controlled drug delivery function according to acidic and alkaline environment, and present positive biocompatibility, indicating their potential use in biological and biomedical applications, such as pH‐responsive drug‐delivery systems, scaffolding for bone tissues, and as an oral drug‐delivery vehicle.
Novel meso‐ or β‐derivatized porphyrins with a carboxyl group have been designed and synthesized for use as sensitizers in dye‐sensitized solar cells (DSSCs). The position and nature of a bridge connecting the porphyrin ring and carboxylic acid group show significant influences on the spectral, electrochemical, and photovoltaic properties of these sensitizers. Absorption spectra of porphyrins with a phenylethynyl bridge show that both Soret and Q bands are red‐shifted with respect to those of porphyrin 6 . This phenomenon is more pronounced for porphyrins 3 and 4 , which have a π‐conjugated electron‐donating group at the meso position opposite the anchoring group. Upon introduction of an ethynylene group at the meso position, the potential at the first oxidation alters only slightly whereas that for the first reduction is significantly shifted to the positive, thus indicating a decreased HOMO–LUMO gap. Quantum‐chemical (DFT) results support the spectroelectrochemical data for a delocalization of charge between the porphyrin ring and the amino group in the first oxidative state of diarylamino‐substituted porphyrin 5 , which exhibits the best photovoltaic performance among all the porphyrins under investigation. From a comparison of the cell performance based on the same TiO2 films, the devices made of porphyrin 5 coadsorbed with chenodeoxycholic acid (CDCA) on TiO2 in ratios [ 5 ]/[CDCA]=1:1 and 1:2 have efficiencies of power conversion similar to that of an N3 ‐based DSSC, which makes this green dye a promising candidate for colorful DSSC applications. 相似文献