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No description available.

Maintenance of reduced protein sulfhydryl groups is an important function of lens metabolism. In an attempt to inter-relate how lens sulfhydryl metabolism, low molecular weight peptides and trace molecular weight Zn-containing protein population was studied. The concentration of rate lens Zn-containing protein population was studied. The concentration of rat lens Zn decreased 30% from day 10 to day 35 postpartum. After 6 weeks on a low-Zn diet, rats had 25% less lens Zn than control groups. Selenite-induced cataract did not affect lens Zn concentration. Of the total lens Zn, 25% was recovered in the ultrafiltration fraction of less than 20,000 molecular weight which contained 1% of the total soluble protein. Lens tissue has low molecular weight TCA-soluble components that can bind Hg. Isoelectric points of low molecular weight protein fractions were between pI 5.2-5.5. Polypeptide molecular weight was determined to be less than 5,000 daltons by gel filtration chromatography. Aggregation on SDS-polyacrylamide gel electrophoresis yielded apparent higher molecular weights of these proteins. Although the proteins isolated had metallothionein-like character in that they were of low molecular weight, contained Zn and had acidic pI values, the paucity of cysteine residues indicates that metallothionein is not a component of low molecular weight Zn-containing lens proteins. / Master of Science

No / Two force fields, the GROMOS53A5/53A6 (united atom) and the AMBER95 (all atom) parameter sets, coupled with partial atomic charges derived from quantum mechanical calculations were evaluated for their ability to reproduce the known crystalline forms of the polyols mannitol and sorbitol. The force fields were evaluated using molecular dynamics simulations at 10 K (which is akin to potential energy minimization) with the simulation cell lengths and angles free to evolve. Both force fields performed relatively poorly, not being able to simultaneously reproduce all of the crystal structures within a 5% deviation level. The parameter sets were then systematically optimized using sensitivity analysis, and a revised AMBER95 set was found to reproduce the crystal structures with less than 5% deviation from experiment. The stability of the various crystalline forms for each of the parameter sets (original and revised) was then assessed in extended MD simulations at 298 K and 1 bar covering 1 ns simulation time. The AMBER95 parameter sets (original and revised) were found to be effective in reproducing the crystal structures in these more stringent tests. Remarkably, the performance of the original AMBER95 parameter set was found to be slightly better than that of the revised set in these simulations at 298 K. The results of this study suggest that, whenever feasible, one should include molecular simulations at elevated temperatures when optimizing parameters.

No / The two known crystalline phases of resorcinol and their phase transitions are of considerable interest. The crystals exhibit pyro- and piezo-electricity and, remarkably, the higher temperature phase is the denser phase. Furthermore, crystals of the phase, by virtue of having a polar axis, have played a crucial role in investigating fundamental issues of crystal growth. We report an optimized force field for the molecular simulation of crystalline phases of resorcinol. The hydroxyl groups of the resorcinol molecule have a torsional degree of freedom and the molecule adopts a different conformation in each of the two phases of resorcinol. The torsional barrier, therefore, was considered to be critical and has been characterized using ab initio methods. Although the atomic partial charges showed some dependence on the molecular conformation, a single set of partial charges was found to be sufficient in describing the electrostatic potential for all conformations. The parameters for the van der Waals interactions were optimized using sensitivity analysis. The proposed force field reproduces not only the static structures but also the stability of the crystalline phases in extended molecular dynamics simulations.

Yes / Background: The aim was to profile transient accommodative axial length changes from early adulthood to advanced presbyopia and to determine whether any differences exist between the responses of myopic and emmetropic individuals. Methods: Ocular biometry was measured by the LenStar biometer (Haag-Streit, Switzerland) in response to zero, 3.00 and 4.50 D accommodative stimuli in 35 emmetropes and 37 myopes, aged 18 to 60 years. All results were corrected to reduce errors arising from the increase in crystalline lens thickness with accommodation. Accommodative responses were measured sequentially by the WAM 5500 Auto Ref/Keratometer (Grand Seiko, Hiroshima, Japan). Results: Axial length increased significantly with accommodation (p < 0.001), with a mean corrected increase in axial length of 2 18 μm and 8 16 μm observed at 3.00 and 4.50 D, respectively. The magnitude of accommodative change in axial length was not dependent on refractive error classification (p = 0.959); however, a significant reduction in the magnitude and variance of axial length change was evident after 43 to 44 years of age (p < 0.002). Conclusion: The negative association between transient increase in axial length and age, in combination with reduced variance of data after age 43 to 44 years, is consistent with a significant increase in posterior ocular rigidity, which may be influential in the development of presbyopia. / DL received funds from the College of Optometrists, UK

An A-B monomer containing an ether group, 4(4-acetoxyphenoxy) benzoic acid (PAPBA) was successfully synthesized via a new route using 4-methoxyphenol and 4-chlorobenzonitrile as starting materials. Another ether containing monomer, 4(2-acetoxy-6-naphthoxy) benzoic acid (PANBA), which appears to be a novel monomer, was also prepared in high yields from 6-methoxy-2-bromonaphthalene and ethyl-4-hydroxybenzoate via the Ullmann condensation reaction. These monomers were found to be useful for synthesizing LCP copolymers and segmented copolymers. A variety of polyarylates based on 5-tertiary butylisophthalic acid were synthesized via melt acidolysis techniques. The resulting high molecular weight polyarylates were amorphous polymers and the t-butyl groups along the polymer backbones were found to be thermoxidatively stable. Thermotropic liquid crystalline polyesters (LCPs) are well known for their thermoxidative stability, ductility, solvent resistance and the potential of generating extremely strong, stiff molecular chains. In this dissertation research, several novel liquid crystalline aromatic polyether-ester copolymers were synthesized by the incorporation of an A-B monomer, either PAPBA or PANBA, into the polymer main chain. The corresponding copolymers were thermoxidatively stable and melt processable over a wide compositional range. Novel carboxyl terminated oligomers of an amorphous engineering polymer, poly(arylene ether ketone)(PEK) were successfully synthesized. The synthetic method was somewhat similar to that of carboxyl terminated poly(arylene ether sulfone) oligomers. The PEKCOOH oligomers were quantitatively endcapped and their molecular weights could be controlled. Thermogravimetric analysis revealed that the PEKCOOH oligomers were thermoxidatively stable and therefore suitable for high temperature post-reactions. In general, thermotropic liquid crystalline polymers show excellent properties in the longitudinal direction. Nevertheless, to improve the transverse mechanical properties of liquid crystalline polymers, novel poly(arylene ether ketone)-LCP segmented copolymers were synthesized via melt acidolysis techniques. Chemically bonding an isotropic engineering thermoplastic into a potentially liquid crystalline anisotropic polyester affords segmented copolymers which may possess a balance of mechanical properties in both the longitudinal and transverse directions. In the case of PEK-poly(oxybenzoate)(PEK-POB), a limited amount of POB (~25 wt %) could be incorporated so as to produce segmented copolymers which would yield coherent films. On the other hand, when PEK-POB was modified by adding PAPBA to form PEK-POB-POPB segmented copolymers, a series of the segmented copolymers with various compositions was realized. The liquid crystalline behavior was found to be retained in the segmented copolymers, depending on the degree of the LCP content. The structural analysis of the A-B monomers mentioned earlier was performed by elemental analysis, mass spectroscopy, proton NMR and FT-IR. All the polymers synthesized were characterized by thermal analysis (DSC and TGA). The molecular weight of the carboxyl terminated PEK oligomers was determined by an automatic titration method, and indirectly, by intrinsic viscosity measurements. The latter method was also used to assess the molecular weight of the amorphous polyarylates. For liquid crystalline polyether-ester copolymers and PEK-LCP segmented copolymers, DSC and hot stage optical microscopy were utilized to investigate their thermotropic liquid crystalline behavior. DMTA was used to determine the high temperature properties of the polymers and tensile tests, i.e. stress-strain data, were employed to obtain information on their mechanical properties. / Ph. D.

Yes / The creation of long-lived amorphous phases has potential applications in numerous fields; for example, the instability of the amorphous phase leads to higher solubility of pharmaceutical phases, often leading to higher bioavailability. The rate of recrystallization of an amorphous phase poses a significant limitation to the application of many such phases; however, understanding the energetic and structural factors that control the stability of molecular amorphous phases is limited by empirical classifications based on thermal analysis used to identify materials. From a set of molecularly related benzanilides, examples of all three classes have been identified, allowing use of crystal structural analysis, Raman spectroscopy, and energetic calculations to determine the structural factors playing a role in the different stabilities. While the behavior of most systems reflects the relative energy of the crystalline phase to the amorphous phase, kinetic factors based on whether a NH···O=C hydrogen bond is present in the crystalline phase play a key role in stabilizing the amorphous phase as the loss of this bond reduces the conversion rate. In contrast, systems without this bond display fast recrystallization due to the greater structural similarity between the amorphous and crystalline phases.