Development of Birdcage Resonators for the 3 Tesla NMR Imaging System

An optimized birdcage resonator configuration with a low-pass filter was designed and built to facilitate the acquisition of high-resolution three-dimensional images of small animals on the 3 T nuclear magnetic resonance imaging system. The birdcage resonator had a 12-element structure in order to ensure B ₁ homogeneity over the image volume and for obtaining the maximum filling factor. The quality of the manufactured birdcage resonators was evaluated on the basis of the return loss following the matching and tuning process. The experimental magnetic resonance images of the phantoms were obtained by the various manufactured birdcage resonators to compare the signal-to-noise ratio (SNR) in accordance with the size of the objects. The ratio of the size of an object to the size of the coil was identified by the parameters that were estimated from the images of a phantom. This study demonstrated that the SNR could be different depending on the size of the object even if birdcage resonators have the same cylindrical forms. Authors' address: Bo-Young Choe, Department of Biomedical Engineering, Kangnam St. Mary's Hospital, College of Medicine, Catholic University of Korea, 505 Banpo-Dong, Seocho-Gu, Seoul 137-040, Korea     

Prelminary Reports on Structural Study via Mercury-Sensitized Photolysis and Gas Chromatography

The combination of photolysis and gas-liquid chromatography results in “fingerprints” which are much superior to the pyrolysis gas chromatography method for the identification of organic compounds. With this photolysis-GIC method, a number of methyl ethers, benzyl ethers, isopropyl ethers and tert-butyl ethers were chromato-graphically purified and photolytically decomposed by way of mercury sensitization. The photolytic degration products were temperature programmed in a sensitive gas-liquid chromatograph. The “fingerprint” product peaks were calculated into retention indices, Δ I-values and I-values, and grouped into homologous peaks, common peaks and distinctive peaks. Identification of parent structures is obtained by the correlation of retention indices in the above three groups of peaks.     

Monte Carlo simulation and self-consistent integral equation theory for polymers in quenched random media

The conformational properties and static structure of freely jointed hard-sphere chains in matrices composed of stationary hard spheres are studied using Monte Carlo simulations and integral equation theory. The simulations show that the chain size is a nonmonotonic function of the matrix density when the matrix spheres are the same size as the monomers. When the matrix spheres are of the order of the chain size the chain size decreases monotonically with increasing matrix volume fraction. The simulations are used to test the replica-symmetric polymer reference interaction site model (RSP) integral equation theory. When the simulation results for the intramolecular correlation functions are input into the theory, the agreement between theoretical predictions and simulation results for the pair-correlation functions is quantitative only at the highest fluid volume fractions and for small matrix sphere sizes. The RSP theory is also implemented in a self-consistent fashion, i.e., the intramolecular and intermolecular correlation functions are calculated self-consistently by combining a field theory with the integral equations. The theory captures qualitative trends observed in the simulations, such as the nonmonotonic dependence of the chain size on media fraction.     

A rigorous theory of ring tensiometry: Addendum on the wall effect

Summary As a supplement to our theoretical calculations for the ring method of measuring surface and interfacial tensions of liquids, the effect of the finite size of the liquid container on the measurement has been studied employing (i) an exact analysis for the case of an infinite straight cylinder midway between two parallel walls and (ii) an approximate analysis for a ring in a circular container. The parameters which can cause errors are identified, and their magnitude is estimated and compared with the experimental results for surface tension of water in air. It is shown that conditions can be readily adjusted to produce negligrors.Nomenclature a radius of cylinder or ring wire; - C ₂₃ (₂ –₃)g/ ₂₃ D=semi-gap width between parallel walls, or radius of liquid container; - f Harkins-Jordan (1) factor - F, E elliptic integrals of the first and second kind (k = modulus) - F equilibrium capillary force on ring or per unit length of a straight cylinder; - F _D,F maximumF for finiteD andD = - g gravity - r _i,z _i r- andz-coordinates of the inner (i =1) and outer (i = 2) contact line circles on ring; - z _c vertical coordinate of the contact line on cylinder; - Y23, YD interfacial tension (D= ; uncorrected interfacial tension measured in container of radiusD - _i density of thei phase - _i slope angle of the inner (i = 1) and outer (i = 2) menisci on ring - 180° - _c slope angle of cylindrical meniscus at the contact line - ₂ 180° – ₂ - Oo contact angle at container wall - (F _D -F )/F for cylinder; (YD - ₂₃)/Y23 for ring     

Degradation of myoglobin by polymeric artificial metalloproteases containing catalytic modules with various catalytic group densities: site selectivity in peptide bond cleavage

Mononuclear, dinuclear, and tetranuclear artificial metalloproteases were prepared by attaching respective catalytic modules containing the Cu(II) complex of cyclen (Cu(II)Cyc) to a derivative of cross-linked polystyrene. The polymeric artificial metalloproteases effectively cleaved peptide bonds of myoglobin (Mb) by hydrolysis. The proteolytic activity increased considerably as the catalytic group density was raised: the ratio of k(cat)/K(m) was 1:13:100 for the mono-, di-, and tetranuclear catalysts. In the degradation of Mb by the dinuclear catalyst, two pairs of intermediate proteins accumulated. One of the two initial cleavage sites leading to the formation of the protein fragments is identified as Gln(91)-Ser(92) and the other is suggested as Ala(94)-Thr(95). On the basis of a molecular modeling study by using the X-ray crystallographic structure of Mb, the site-selectivity is attributed to anchorage of one Cu(II)Cyc unit of the catalytic module to a heme carboxylate of Mb. The high site selectivity for the initial cleavage of a protein substrate and mechanistic analysis of the catalytic action are unprecedented for polymeric artificial enzymes.     

A polydiacetylene-based fluorescent sensor chip

Self-assembled diacetylene vesicles were spotted and immobilized on aldehyde-modified glass substrates using conventional microarray technology. Irradiation of the immobilized diacetylenes allowed generation of nonfluorescent "blue-phase" polydiacetylene (PDA) arrays. Specific interaction of the PDA vesicle arrays with carbohydrates or poly(acrylic acid) solutions afforded fluorescent profiles.     

Synthesis,pharmacokinetics, and biological activity of a series of new pyridonecarboxylic acid antibacterial agents bearing a 5-fluoro-2-pyridyl group or a 3-fluoro-4-pyridyl group at N-1

The 1-(5-fluoro-2-pyridyl) or 1-(3-fluoro-4-pyridyl) group was introduced in the syntheses of new pyridonecarboxylic acid antibacterial agents. 1-(5-Fluoro-2-pyridyl)-6-fluoro-1,4-dihydro-7-(4-methyl-1-piperazinyl)-4-oxoquinolone-3-carboxylic acid 7b (DW-116) showed a moderate in vitro antibacterial activity but it was found to have very excellent pharmacokinetic profiles so that 7b (DW-116) showed dramatic increased in vivo efficacy.     

Studies of organically functionalized mesoporous silicas using heteronuclear solid-state correlation NMR spectroscopy under fast magic angle spinning

Highly resolved solid-state HETCOR NMR spectra between protons and low gamma nuclei ((13)C and (29)Si) can be suitably obtained on surfaces using a "brute force" (1)H-(1)H decoupling by MAS at rates > or =40 kHz. Despite a small rotor volume (<10 microL), a (1)H-(13)C HETCOR spectrum of allyl groups (AL, -CH(2)-CH=CH(2)) covalently anchored to the surface of MCM-41 silica was acquired without using isotope enrichment. The advantages of using fast MAS in such studies include easy setup, robustness, and the opportunity of using low RF power for decoupling. In the case of the (1)H-(29)Si HETCOR experiment, the sensitivity can be dramatically increased, in some samples by more than 1 order of magnitude, through implementing into the pulse sequence a Carr-Purcell-Meiboom-Gill train of pi pulses at the (29)Si spin frequency. The use of low-power heteronuclear decoupling is essential in the (1)H-(29)Si CPMG-HETCOR experiment, due to unusually long acquisition periods. These methods provided detailed structural characterization of the surface of AL-MCM mesoporous silica.     

Optical effects of S-oxidation and M(n+) binding in meso-thienyl dipyrrin systems and of stepwise bromination of 4,4-difluoro-8-(2,5-dibromo-3-thienyl)-4-bora-3a,4a-diaza-s-indacene

We report 16 novel species and 8 molecular structures in studying how meso-thienyl-substituted dipyrrole oxidation, bromination, and metal ion binding impart optical changes, as monitored by UV-vis absorption/emission spectroscopy. Treatment of 4,4-difluoro-8-(3-benzothienyl)-4-bora-3a,4a-diaza-s-indacene (varphi(F) = 0.19) with m-CPBA gives selective S-dioxidation (varphi(F) = 0.006). Results of titrations of transition metal- and "scorpionate"-like dipyrrin species varied under room temperature treatment of m-CPBA. Ni-(thienyl-dipyrrin)(n) (n = 2) degraded significantly in the presence of m-CPBA, whereas related species (M = Cu, Fe, Co; n = 2, 3) were inert. meso-Thienyl group properties were revealed through the use of 3,4,4-triphenyl-8-(thienyl)-4-bora-3a,4a-diaza-s-indacene; Cu(2+) addition resulted in smooth absorption decreases which were modeled to support 1:1 substrate:M(2+) binding; for Hg(2+) 1:2 substrate:M(2+) binding was found. Treatment of 4,4-difluoro-8-(2,5-dibromo-3-thienyl)-4-bora-3a,4a-diaza-s-indacene with Br(2) gave red-shifted UV-vis absorption band features that grow with increasing dipyrrin bromination. Structures of the di- and tetra-substituted bromination products were obtained.