Progress in the optimization of chiral cyclophane synthetic receptors for shape selective molecular recognition in aqueous media through hydrophobic association

Three new synthetic receptors based on Tr?ger’s base are prepared and evaluated. These three receptors are structural isomers of a successful receptor reported earlier from this laboratory, and they are all far inferior to that original receptor. Two of these receptors fail almost entirely and do so for an interesting reason. In water (not in other solvents) they collapse, forming a deflated structure. Collapsed or “sicklied” receptors do not bind to alicyclic or hydrophobic substrates in water because an important component of the driving force, the high energy waters solvating the interior of the macrocyclic structure, is lost when the receptor collapses. The results clearly illustrate how important it is to use computational methods that include good aqueous solvation models when designing new cyclophane receptors.     

2,1-benzisothiazoline 2,2-dioxide. I. Some 3-substituted derivatives

A number of 3-mono- and 3,3-disubstituted derivatives of 1-methyl 2,1-benzisothiazoline 2,2-dioxide (IIa), a unique benzosultam, were synthesized. Starting materials for the condensation and aminoalkylation reactions utilized were IIa and the 3-methyl compound IIb, which were prepared by cyclization of the 2′-chloro-N-methylalkylsulfonanilides, Ia and b, respectively.     

Color-image generation by use of binary-phase holograms

A novel, simple scheme for producing full-color images by use of binary-phase holograms and red (632.8-nm), green (543.5-nm), and blue (488-nm), lasers is reported. The theory and experimental results of the system are also presented.     

Molded polyethylene glycol microstructures for capturing cells within microfluidic channels

The ability to control the deposition and location of adherent and non-adherent cells within microfluidic devices is beneficial for the development of micro-scale bioanalytical tools and high-throughput screening systems. Here, we introduce a simple technique to fabricate poly(ethylene glycol)(PEG) microstructures within microfluidic channels that can be used to dock cells within pre-defined locations. Microstructures of various shapes were used to capture and shear-protect cells despite medium flow in the channel. Using this approach, PEG microwells were fabricated either with exposed or non-exposed substrates. Proteins and cells adhered within microwells with exposed substrates, while non-exposed substrates prevented protein and cell adhesion (although the cells were captured inside the features). Furthermore, immobilized cells remained viable and were stained for cell surface receptors by sequential flow of antibodies and secondary fluorescent probes. With its unique strengths in utility and control, this approach is potentially beneficial for the development of cell-based analytical devices and microreactors that enable the capture and real-time analysis of cells within microchannels, irrespective of cell anchorage properties.     

Nanostructure manipulation device for transmission electron microscopy: application to titania nanoparticle chain aggregates.

Experimental difficulties in studying nanostructures stem from their small size, which limits the use of traditional techniques for measuring their physical properties. We have developed a nanostructure manipulation device to apply tension to chain aggregates mounted in a transmission electron microscope. A 1-mm-long slit was cut in the center of a lead-tin alloy disc, measuring 3 mm in diameter and 200 microm in thickness. The disc was heated to about 140 degrees C before it was pressed between two quartz slides. The disc was then thinned by mechanical dimpling and ion milling until holes developed around the slit. The edges of the slit were 0.2 to 3 microm in thickness while the gap between them was up to a few microns. This disc was bonded to the two plates of a cartridge. The slit could be widened or narrowed at controlled speeds of 0.5 to 300 nm/s. The system was tested using titania (TiO2) nanoparticle chain aggregates (NCA) deposited across the slit. The ends of the NCA remained attached to the edges of the slit, which was widened at about 0.7 nm/s. In this way, the NCA was stretched up to 176% of its initial length before breaking.     

Magnetic and porous nanospheres from ultrasonic spray pyrolysis

We have used an inexpensive high-frequency ultrasound generator from a household humidifier to create a useful source for ultrasonic spray pyrolysis and produced submicrometer silica particles that are porous on the nanometer scale. By using two heated zones, we first initiate polymerization of organic monomers in the presence of silica colloid, which creates in situ a composite of silica with an organic polymer, followed by a second heating to pyrolyze and remove the polymer. The morphology and surface area of the final porous silica are controlled by varying the silica-to-organic monomer ratio. In a single flow process, ferromagnetic cobalt nanoparticles can be easily encapsulated in the porous silica, and the resulting nanospheres are extremely resistant to air oxidation. Products were characterized by SEM, (S)TEM, EDS, XPS, and SQUID.