Solid-state dynamics and single-crystal to single-crystal structural transformations in octakis(3-chloropropyl)octasilsesquioxane and octavinyloctasilsesquioxane.

Reactive octahedral silsesquioxanes of rod-like [octakis(3-chloropropyl)octasilsesquioxane - T8(CH2CH2CH2Cl)8] and spherical [octavinyloctasilsesquioxane - T8(CH[double bond, length as m-dash]CH2)8] structure can undergo reversible thermally induced phase transitions in the solid state. The phase behaviour has been studied with differential scanning calorimetry (DSC, including temperature modulated DSC), X-ray diffraction, dielectric relaxation spectroscopy (DRS), and nuclear magnetic resonance spectroscopy in the solid state (SS NMR), as well as positron annihilation lifetime spectroscopy (PALS) and polarized optical microscopy (POM). The mechanisms involving fitting the molecules into most symmetrical crystal lattices vary for species of different structure. Thermal energy can be used to expand the crystal lattice leading to thermochromism in the case of T8(CH[double bond, length as m-dash]CH2)8 or conversely to an unusual negative thermal expansion of crystals of T8(CH2CH2CH2Cl)8 that results in their self-actuation. The complex behaviour is reflected in unusual changes in the capacitance and fractional free volume of the material. These phenomena can be used for molecular design of advanced well-defined hybrid materials capable of reversible thermally induced structural transformations. The findings present a new perspective for POSS-based flexible metal-organic frameworks (MOF) of cooperative structural transformability via entropy-based translational sub-net sliding.

Role of titin in nonmuscle and smooth muscle cells.

Extensive investigation of vertebrate striated muscle titin has yielded significant insight into its structure and function in striated muscle. We have begun to investigate other members of the titin protein family found in vertebrate smooth muscle and nonmuscle cells. Smooth and nonmuscle titins resemble striated muscle titin in molecular size and morphology but differ in their interactions with myosin II filaments and in the structural contexts in which they exist in vivo. Divergence of these titins from the muscle titin paradigm demonstrates the versatility of this remarkable family of giant proteins.

13C high-resolution solid state NMR studies of the structure and dynamics of 1,6:3,4-dianhydro-2-O-tosyl-beta-D-galactopyranose.

13C CP/MAS, dipolar dephasing MAS and theoretical GIAO calculations were employed to assign 13C resonances to the molecular structure of 1,6:3,4-dianhydro-2-O-tosyl-beta-D-galactopyranose 1. From spinning sideband intensities, employing the graphical method of Herzfeld and Berger the 13C delta(ii) parameters for aromatic residue were calculated. The experimental data were compared with computed results obtained by means of the B3PW91 hybrid method and 6-311G (df, p) basis set. The X-ray geometry of 1 with the correlated position of hydrogen atoms was taken as input data for theoretical calculations. As concluded from Cambridge Crystallographic Database (CSD) search, there are two reports describing the X-ray studies of 1 that show the slightly different geometry of the compound under investigation. This work shows that such discrepancies in geometry can generate differences between computed 13C delta(ii) parameters up to 6 ppm. 13C T1 and 1H T1rho relaxation times reveal that 1 is very rigid in crystal lattice. This structure is characterized by extremely long 1H T1rho, found to be in range ca. 200 ms.

Nucleophilic N1-->N3 rearrangement of 5'-O-trityl-O2,3'-cycloanhydrothymidine.

5'-O-Trityl-O2,3'-cycloanhydrothymidine (1) heated at 150 degrees C in the presence of O,O-diethyl phosphate or O,O-diethyl phosphorothioate anions undergoes rearrangement into N3-isomer (2); its structure was established by both advanced NMR methods and X-ray crystallographic studies. The most probable mechanism of 1-->2 rearrangement relies upon reversibility of glycosidic bond cleavage process.

Novel internucleotide 3'-NH-P(CH3)(O)-O-5' linkage. Oligo(deoxyribonucleoside methanephosphonamidates); synthesis, structure and hybridization properties.

Diastereomeric dithymidine methanephosphonamidates (TnpmT) were synthesized by reaction of 3'-amino-3'-deoxythymidine with 3'- O -acetylthymidin-5-yl-methanephosphonochloridate. Separated dinucleotide TnpmT(fast) and TnpmT(slow) diastereomers were used as building blocks to prepare chimeric dodecathy-midylates, possessing one to four modified linkages, by means of phosphoramidite automated solid phase synthesis. As expected, the methanephosphonamidate internucleotide linkage is resistant to nuclease P1, snake venom PDE and 3'-exonuclease from human plasma. Degradation of dodecathymidylates possessing modified internucleotide linkages in alternate positions proved the 'hopping' properties of 3'-exonuclease. Oligo(deoxyribonucleotide methanephosphonamidates) were tested for their binding affinity to complementary oligomers in thermal denaturation experiments. All the oligomers showed lower binding affinity to DNA and RNA targets, however, oligomers originating from the TnpmT(fast) dimeric unit exhibited better hybridization properties than their diastereomeric TnpmT(slow) counterparts. A lowering of T m of approximately 2.4 degrees C (1.0-1.8 degrees C) was observed for each introduced TnpmT(fast) modification and 6.0 degrees C (4.2-5.0 degrees C) for each TnpmT(slow) modification in duplexes of modified dodecathymidylates with dA12(A12) oligomers. The oligo(deoxyribonucleoside methanephosphonamidate) designated F4, possessing four modified methanephosphonate linkages originating from the TnpmT(fast) diastereomeric unit, exhibits a tendency for triplex formation, as was demonstrated in thermal denaturation experiments with the d(A21C4T21) hairpin oligomer.

Interaction of alpha-actinin with cellular titin.

Cellular titin (c-titin) colocalizes with myosin II in cytoskeletal structures containing actin in vivo and organizes highly ordered myosin bipolar filament arrays in the absence of actin in vitro. We report here that the actin-binding protein alpha-actinin associates with coassemblies of c-titin and myosin through direct interaction with c-titin. These results support the possibility that interaction between the myosin-associated protein c-titin and the actin-associated protein alpha-actinin organizes and stabilizes actin-myosin II cytoskeletal structures in vivo.

Learning disabilities, employment discrimination, and the ADA.

The Americans with Disabilities Act (ADA) of 1990 was intended to prohibit discrimination against individuals with disabilities. Although the scope of this legislation is broad, there are aspects of Title I and Title II of the ADA that may be of particular interest to persons with learning disabilities who are preparing for employment. This article discusses those aspects and presents case studies to demonstrate how the ADA could potentially be applied to typical situations. Suggestions are given for individuals with learning disabilities, their parents, and teachers with regard to employment preparation in secondary and postsecondary settings.

Cellular titin localization in stress fibers and interaction with myosin II filaments in vitro.

We previously discovered a cellular isoform of titin (originally named T-protein) colocalized with myosin II in the terminal web domain of the chicken intestinal epithelial cell brush border cytoskeleton (Eilertsen, K.J., and T.C.S. Keller. 1992. J. Cell Biol. 119:549-557). Here, we demonstrate that cellular titin also colocalizes with myosin II filaments in stress fibers and organizes a similar array of myosin II filaments in vitro. To investigate interactions between cellular titin and myosin in vitro, we purified both proteins from isolated intestinal epithelial cell brush borders by a combination of gel filtration and hydroxyapatite column chromatography. Electron microscopy of brush border myosin bipolar filaments assembled in the presence and absence of cellular titin revealed a cellular titin-dependent side-by-side and end-to-end alignment of the filaments into highly ordered arrays. Immunogold labeling confirmed cellular titin association with the filament arrays. Under similar assembly conditions, purified chicken pectoralis muscle titin formed much less regular aggregates of muscle myosin bipolar filaments. Sucrose density gradient analyses of both cellular and muscle titin-myosin supramolecular arrays demonstrated that the cellular titin and myosin isoforms coassembled with a myosin/titin ratio of approximately 25:1, whereas the muscle isoforms coassembled with a myosin:titin ratio of approximately 38:1. No coassembly aggregates were found when cellular myosin was assembled in the presence of muscle titin or when muscle myosin was assembled in the presence of cellular titin. Our results demonstrate that cellular titin can organize an isoform-specific association of myosin II bipolar filaments and support the possibility that cellular titin is a key organizing component of the brush border and other myosin II-containing cytoskeletal structures including stress fibers.

WISC-R stability and re-evaluation of learning-disabled students.

This study investigated the temporal stability of WISC-R IQ scores for learning-disabled subjects (N = 113). All study subjects were administered the WISC-R for an initial evaluation (M age = 8 years, 3 months) and a follow-up re-evaluation (M age = 11 years, 7 months). Pearson product-moment correlations yielded coefficients that were considerably lower than those previously reported: r = .55, p less than .001 for the Verbal IQs; r = .63, p less than .001 for the Performance IQs; and r = .58, p less than .001 for the Full Scale IQs. Results of t-test analyses indicated that only the Verbal IQ scores were significantly different when the initial evaluation (M = 89.4) was compared to the re-evaluation (M = 85.3), p less than .001. The results suggest that the WISC-R may be less stable for the learning-disabled population than for other groups and that the average 3-year test-retest time lapse was an influential factor in the reduced reliability of this instrument.