Experimental results of a high Q quasioptical reflection cavity

A quasi-optical reflection cavity intended to be used as the resonant load of a submillimeter wavelength oscillator has been designed, constructed, and tested. The resonator consists of three elements in cascade: a high Q, high finesse folded Fabry-Perot resonator, a lower Q, low finesse Fabry-Perot resonator, and a Littrow mounted diffraction grating. The resonator exhibits a Q of 6600 and 2.5 dB of loss at 63 GHz. The design can be scaled to 1 THz, where waveguide structures become impractical, to serve as the resonator for high frequency quantum well resonant tunneling device oscillators.     

Protein encapsulation and release from degradable sugar based hydrogels

Acid labile sugar based hydrogels have been synthesized using a commercially available acid sensitive cross-linker, 3,9-divinyl-2,4,8,10-tetraoxaspiro-[5,5]-undecane. The monomers used for polymerization are N-isopropylacrylamide (NIPAM) and d-gluconamidoethyl methacrylate (GAMA), which when polymerized in the presence of the acid labile cross-linker yield hydrogels that can swell and degrade under acidic conditions, making them ideal for drug delivery. The hydrogels are synthesized using either a photo-initiator, Irgacure-2959 or a conventional initiator, potassium persulfate. The hydrogels obtained by photo-polymerization exhibit defined and unique microstructures, when analyzed by scanning electron microscopy (SEM). The swelling capacity and protein release from the hydrogels as a function of pH is studied. The protein release from the hydrogels is found to be dependent upon the degree of cross-linking and the pH of the environment.     

Density functional theory calculation of (29)Si NMR chemical shifts of organosiloxanes

Density functional theory at the B3LYP/6-311++G(d,p) level is applied to calculate the (29)Si NMR chemical shifts of a variety of organosiloxane moieties including monomers or precursors for polymerization and representative segments of organosiloxane polymers or thin films. The calculated shifts of two linear dimethylsiloxane compounds, hexamethylcyclotrisiloxane (D3) and octamethylcyclotetrasiloxane (D4), compare well with their known values, having an average error of 3.4 ppm. The same method is applied to structures believed to occur in organosilicate glass thin films deposited using hot-filament chemical vapor deposition (HFCVD) from D3 and D4. The chemical shift at -15 ppm is identified as a cross-linking Si-Si bond between two strained D groups and has not previously been reported. Retention of the strained ringed structure in HFCVD films deposited from D3 is confirmed. The rings are bonded to the matrix through either Si-O or Si-Si bonds, with the latter only becoming prevalent when higher filament temperatures are employed. The strained ring structure is also observed in films deposited from a precursor with a larger unstrained ring structure, D4. These observations suggest that the known gas-phase conversion pathways of D4 to D3 and dimethylsilanone as well as the methyl abstraction reaction from D3 operate in the HFCVD reaction chemistry.     

Characteristics and production of thermostable α-amylase

Thermostable α-amylases have application in a variety of industrial processes and enzymes from a substantial number of thermophilic bacteria and fungi have been screened and characterized to varying degrees. The characteristics of these enzymes are summarized in this review. The genetics of α-amylase production inBacillus subtilis is reviewed and classical and recombinant DNA approaches to increasing α-amylase production are discussed.     

PICOSECOND LASER PHOTOLYSIS STUDIES OF FLUORESCENCE QUENCHING MECHANISMS OF FLAVIN: A DIRECT OBSERVATION OF INDOLE-FLAVIN SINGLET CHARGE TRANSFER STATE FORMATION IN SOLUTIONS and FLAVOENZYMES

Formation of singlet charge transfer (heteroexcimer) states in the course of the fluorescence quenching of lumiflavin and riboflavin tetrabutyrate by indole and N-methylindole have been directly observed by means of time-resolved absorption spectral measurements using a picosecond laser photolysis method. Similar transient spectra have been observed also in the case of a flavoenzyme, D-amino acid oxidase.     

Facile syntheses of surface-functionalized micelles and shell cross-linked nanoparticles

Block copolymer micelles and shell cross-linked nanoparticles (SCKs) presenting Click-reactive functional groups on their surfaces were prepared using two separate synthetic strategies, each employing functionalized initiators for the controlled radical polymerization of acrylate and styrenic monomers to afford amphiphilic block copolymers bearing an alkynyl or azido group at the α-terminus. The first route for the synthesis of the azide-functionalized nanostructures was achieved via sequential nitroxide-mediated radical polymerization (NMP) of tert-butyl acrylate and styrene, originating from a benzylic chloride-functionalized initiator, followed by deprotection of the acrylic acids, supramolecular assembly of the block copolymer in water and conversion of the benzylic chloride to a benzylic azide. In contrast, the second strategy utilized an alkynyl-functionalized reversible addition fragmentation transfer (RAFT) agent directly for the RAFT-based sequential polymerization of tetrahydropyran acrylate and styrene, followed by selective cleavage of the tetrahydropyran esters to give the α-alkynyl-functionalized block copolymers. These Click-functionalized polymers, with the functionality located at the hydrophilic polymer termini, were then self-assembled using a mixed-micelle methodology to afford surface-functionalized “Clickable” micelles in aqueous solutions. The optimum degree of incorporation of the Click-functionalized polymers was investigated and determined to be ca. 25%, which allowed for the synthesis of well-defined surface-functionalized nanoparticles after cross-linking selectively throughout the shell layer using established amidation chemistry. Functionalization of the chain ends was shown to be an efficient process under standard Click conditions and the resulting functional groups revealed a more “solution-like” environment when compared to the functional group randomly inserted into the hydrophilic shell layer. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5203–5217, 2006     

Local acid environment in poly(ethylene‐ran‐methacrylic acid) ionomers

The local environment of unneutralized carboxylic acid groups in poly(ethylene‐ran‐methacrylic acid) (E/MAA) ionomers neutralized with monovalent (Li and Na) and divalent (Ca and Zn) ions has been investigated with Fourier transform infrared spectroscopy. These unneutralized acid groups interact with one another to form acid dimers, and they associate with existing neutralized complexes. At room temperature, no free acids can be detected for any system, not even for pure E/MAA. With the acid dimer peak (1700 cm^?1) and a known unneutralized acid concentration, the concentration of acids associated with a neutralized complex can be determined. This concentration of associated acids increases with increasing neutralization, reaches a maximum below 50% neutralization, and then decreases toward zero near 80% neutralization. This behavior is perhaps due to the increased driving force for aggregation of the neutralization acids. Although Li, Na, and Ca contain similar concentrations of associated acids over the range of neutralizations, the Zn system contains far fewer associated acids (i.e., more acid dimers) at any particular neutralization level. These results are confirmed by an analysis of the absorbance in the neutralized region (1650–1500 cm^?1). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2833–2841, 2002     

Labeling of Polymer Nanostructures for Medical Imaging: Importance of crosslinking extent, spacer length, and charge density

Radiolabeling studies were employed to investigate the influence of structure on the efficiency of surface functionalization for poly(acrylic acid)-coated shell crosslinked nanoparticles (SCKs) with two types of amine-terminated DOTA chelators. An intricate interplay between the chemical and physical properties of both the DOTA derivative and the SCK nanostructures was revealed, demonstrating the importance of structural control.