The development of highly sensitive fluorescent probes in combination with innovative optical techniques is a promising strategy for intravital noninvasive quantitative imaging. Cyanine fluorochromes belong to a superfamily of dyes that have attracted substantial attention in probe design for molecular imaging. We have developed a novel paradigm to introduce a Turn-ON mechanism in cyanine molecules, based on a distinctive change in their π-electrons system. Our new cyanine fluorochrome is synthesized through a simple two-step procedure and has an unprecedented high fluorescence quantum yield of 16% and large extinction coefficient of 52,000 M(-1)cm(-1). The synthetic strategy allows one to prepare probes for various analytes by introducing a specific triggering group on the probe molecule. The probe was equipped with a corresponding trigger and demonstrated efficient imaging of endogenous hydrogen peroxide, produced in an acute lipopolysaccharide-induced inflammation model in mice. This approach provides, for the first time, an available methodology to prepare modular molecular Turn-ON probes that can release an active cyanine fluorophore upon reaction with specific analyte.

No abstract

This study focuses on the formation mechanism of the bicontinuous cubic Ia3 j d mesoporous material KIT-6, both on the molecular and on the mesoscopic levels. KIT-6 is synthesized with Pluronic P123 (PEO 20 PPO 70 PEO 20 ), low acid concentration, and n-butanol at 40 °C. Through in situ EPR measurements on a series of spin-labeled Pluronic molecules introduced at minute quantities into the reaction mixture, changes in the hydrophobicity and the mobility of the polymer chains during the reaction were observed. In addition, to learn more on the functionality of the butanol in this synthesis, freeze-quench electron spin-echo envelope modulation (ESEEM) measurements on reaction mixtures in D 2 O and in butanol-d 10 were preformed. The above experiments gave information on variations in the butanol location and content in the micellar structures during the formation of KIT-6. The evolution of the solution nanostructures was determined by cryo-TEM. Five main stages were resolved: the first two occurred during the first 140 min of the reaction, where condensation of the silica oligomers takes place at the micellar/water interface; this induces depletion of water and butanol molecules from the core-corona interface and reduces the mobility of the ends of the Pluronic chains located at the corona-water interface. This in turn leads to a transition from spheroidal micelles to threadlike micelles and to their aggregation toward the end of the second stage. During the third stage, precipitation (140-160 min), reorganization in the micellar structure, and a change in the relative sizes of core and corona take place. The fourth stage, that ends around 6 h, involves the formation of a hexagonal phase, through accelerated condensation of silica oligomers in the corona, accompanied by extensive depletion of water and butanol molecules. The presence of butanol in the micelle corona is essential in the last stage, 6-24 h, where the cubic phase is formed. We show that the addition of butanol to the reaction mixture of SBA-15 after the formation of the hexagonal phase leads to the formation of the cubic phase.

We studied the structural evolution during the formation of large-pore cubic Ia3d silica-based mesoporous materials, synthesized with Pluroinc P123 and butanol as structure directing agents. We used cryogenic high resolution scanning electron microscopy (cryo-HRSEM) and freeze-fracture-replication (FFR) transmission electron microscopy (TEM). Typically a silica precursor is added to an acid-catalyzed solution of Pluronic P123 and butanol. The latter serves as a cosolute, which can be added either at the beginning of the reaction, or after precipitation and the formation of a hexagonal phase. In this study we focused on the structural evolution from the hexagonal phase to the final cubic phase in the two different reactions. The same structural evolution with different kinetics was detected for both reactions. Cryo-HRSEM and FFR-TEM images revealed that from the hexagonal phase a perforated layer (PL) phase is formed, which later evolves into a bicontinuous structure. The final cubic phase forms within the layers, maintaining their orientation. We suggest a formation mechanism involving cylinder merging for the hexagonal to PL transition. Upon additional polymerization of the silica, the PL phase relaxes into the stable Ia3d cubic phase. Another minor mechanism detected involves the direct transition between the hexagonal to the final cubic phase through cylinder branching.