This thesis presents the crystal structures of 2', 5', cyclic and modified nucleosides / nucleotides. Chapter I gives a brief account of the structural studies on 2', 5' and modified nucleotides. It also presents a short, summary of unusual nucleic acids structures studies on hydration patterns and metal ion interactions Nomenclature and conventions used for describing the conformatioNa1 features are presented. FiNa1ly, the crystallographic suite of programs used for processing the intensity data, structure solution, refinement and generating various diagrams are mentioned. Chapter II describes the crystal structures of anhydrous and hydrated sodium salt of N6-methyl adenosine-S'-monophosphate. N6-AMP-A (anhydrous form) belongs to the trigoNa1 space group P3221 with unit cell dimensions a = b = 10.30 A and c= 25.03 A while N6-AMP-H (hydrated form) belongs to orthorhombic space group C222X with a= 6.910 A, b= 19.318 A, and c= 41.070 A. CuKα intensity data consisting of 1740 and 2740 observed reflections were collected on a CAD4 diffractometer. Both structures were solved using SHELXS97 and refined to R factors of 0.0336 and 0 0381 for anhydrous and hydrated forms respectively. In both structures the adenine bases are in the ant% conformation with respect to the ribose but their torsion angles XCN differ significantly by 78° The ribose moiety shows CS-endo puckering and the conformation about the C4/-C5/ bond is g+ and t in the anhydrous and hydrated structures respectively. The two Na+ ions, present m the hydrated form, coordinate with water oxygen atoms only. A notable feature of the Na+ ion coordination in the anhydrous form is the participation of N3 and N7 of the base besides macrochelation between base-ribose and base-phosphate moieties. Adenine bases in both forms stack at a separation of about 3.4 A between them N6-AMP molecules pack as if one set of bases intercalate between the other set in the hydrated structure while they form helix like pattern m the anhydrous structure Molecular dynamics calculations were carried out for both structures with a view to obtain greater insight into the effect of hydration on the conformation of the molecule. Stereochemically permissible models for poly-A using the N6-AMP-H coordinates were generated using the method developed by Srinivasan and Olson. Its features and possible biological relevance are discussed. Chapter III deals with the structure of sodium adenosine-5'-monosulfate trihydrate (5'-AMS). Intensity data for this modified nucleotide were collected at the Brookhaven NatioNa1 Laboratory, Synchrotron facility, USA. 5'-AMS belonged to the orthorhom bic space group P2!2!2i with unit cell parameters a= 20.698 A, b= 24.621 A and c= 25.925 A and eight molecules, eight Na+ ions and 23 water molecules in the asymmetric unit of the lattice. Never before a nucleotide structure having eight molecules in the asymmetric unit has been reported. Out of 84177 reflections collected using a radiation of A =0.92 A, 9108 independent reflections having Io>2a(Io) were considered observed. The structure was solved using the program Shake and Bake (SnB) and refined by, SHELXL97. The fiNa1 R factor for 1971 parameters was 0.0397. Adenine bases of all the eight 5'-AMS molecules are in anti conformation with respect to the ribose moiety with XCN angles varying from -150 to -177°. But the conformations of the ribose moieties and the sulfate groups about the C4/-C5/ bond are not the same for all the molecules. 5'-AMS molecules A, B and D show C2-exo-C3-endo mixed puckering while C has C£-exo puckering. The remaining four molecules E, F, G and H have C3-endo conformation. The conformation about the C4/-C5/ bond for molecules A, B, C and D is g~ while for E, F and G it is g+. Molecule H shows both g+ and g~ since the 05' atom is disordered. An important feature of the metal ion coordination is the bidentate formation by sodium ions Na3 and Na7 with the sulfate group of molecule C and ribose hydroxyl oxygen atoms of molecule D respectively. Another feature which deserves mention is the participation of Nl and N7 of the adenine base m metal coordination Adenine bases of molecules A, B, C and D form self pairs with those of H, G, F and E respectively through N6...N7 and N6...N1 hydrogen bonds. The 5'-AMS molecules pack as duplexes in the unit cell. A Stereochemically permissible model for poly-A with sugar sulfate backbone using the 5'-AMS coordinates were generated using the method developed by Srinivasan and Olson and its features are discussed. Crystal structures of two polymorphs of mixed sodium and potassium salts of cytidine-5'-monophosphate hexahydrate are discussed in Chapter IV. The two polymorphs of 5'-CMP were grown using methanol and DMF respectively m the crystallization experiments. MoKα intensity data for CMP-I were collected on a Rigaku AFC image plate system while that for CMP-II were collected on a Bruker CCD Smart system. Both belong to the monoclinic space group P2X with a= 8.869 A, b= 20 580 A, c= 23.179 A, β= 105.79° and a= 8.929 A, b= 22.257 A and c= 20.545 A, β= 90.02° for CMP-I and II respectively. The the unit cell volume of the two polymorphs differ by just 12 A3 as the unit cell parameters are same, although the b and c axes are interchanged m CMP-II and their β value differs by 16°. Both polymorphs of CMP have four nucleotide molecules in the asymmetric unit of their orthorhombic lattices. But the number of metal ions and solvents are not the same in the two structures. CMP-I has five sodium ions, three potassium ions, 23 water and two methanol molecules while CMP-II has two sodium ions, four potassium ions, 22 water and an unknown solvent molecule (assigned as dimethyl ether) in the asymmetric unit. This is the first nucleotide structure having two different alkali metal ions (Na+ and K4") in the crystal structure. Out of 36946 and 31293 reflections collected 12247 and 15476 independent reflections having IO>2<J(I0) were considered observed for CMP-I and II respectively. Both structures were solved by combination of heavy-atom and direct methods using DIRDIF96 and refined using SHELXL97 to R factors of 0.0819 and 0 0867 for CMP-I and II respectively In both forms all the four molecules have anti conformation about the glycosidic bond, CS-endo conformation for the ribose moiety and g+ conformation about the C4'-C5' bond but their metal coordination patterns are significantly different. K1 ion in CMP-I forms an intra molecular macrochelate between the ribose and adenine base while K2 and K3 ions form bidentates with the cytosine and phosphate group of molecules A and D respectively. Na1, Na3 and Na5 are all involved in bidentate interactions with the ribose of molecule C, ribose of molecule A and phosphate of molecule D respectively. In contrast, Na2 and Na4 coordinates with solvent atoms only and do not interact with the nucleotide atoms at all. K1 and K2 ions of CMP-II form bidentates with the cytosines of molecules C and D respectively while K2 and K4 form intra molecular macrochela-tion between the base and ribose of molecules C and B respectively. Na1 and Na2 form bidentates with the ribose of molecules C and D respectively Comparison of the two polymorphs of CMP reveals that despite several striking conformatioNa1 similarities there are also significant differences between them. It was noticed that molecules A, B, C and D of CMP-I corresponds to C, B, D and A of CMP-II. Out of eight metal ions (five Na+ and three K+ ions) present in CMP-I four of them (Kl, K2, K3 and Na3) are found to have partners (K4, Kl, K3 and Na1) in CMP-II within a distance of 0.75 A. One of the water molecules OW8 of CMP-I is replaced by a potassium ion K2 in CMP-II within a distance of 0.92 A. Out of 23 water molecules present in the structure 14 are common to both of them and only 8 are different while one is replaced by an ion. The four crystallographically independent 5'-CMP molecules are linked by metal ions Kl, K3, Na1, Na3, Na5 and Kl, K2, K4, Na1 ions forming a tetramers in CMP-I and CMP-II respectively. An interesting feature of CMP-I and CMP-II is the simultaneous display of base-base and base-ribose stacking patterns. The four nucleotide molecules in the asymmetric unit are related by several pseudo two-fold axis and the r.m.s. Deviations between them after applying the pseudo symmetry are 0.21 and 0.17 A for CMP-I and II respectively. The nucleotide molecules in CMP-I and II pack as infinite linear chains parallel to the b and c axis respectively which repeat along the c and b axis respectively. In between these nucleotide columns metal ions and water molecules are located forming channels between them. Chapter V deals with anhydrous cytidine-2/-phosphate and potassium uridine-5'-phosphate hexahydrate structures. 2'-CMP crystallizes m the orthorhombic space group P212121 with a= 6.698 A, b= 7.436 A and c= 25.291 A with one molecule in the asymmetric unit. MoKα intensity data were collected on a CCD SMART system consisting of 7647 reflection of which 1456 independent reflections having lo>2a(lo) were considered observed. The structure was solved and refined to an R factor of 0.0385 for 186 parameters using SHELXL97. The cytosine base is in the anti conformation with respect to the ribose with XCN = -141.1° similar to that in the hydrated structure. But it differs significantly from the syn conformation observed in several 2'-purine and 2'-5' dinucleotide structures containing purine-pyrimidine sequences. The ribose moiety shows Ctf-endo and the conformation about the C4/-C5/ bond is t with (f)α = 169.3° and <pO( = -72 7° The t conformation in the anhydrous form is different from the g+ conformation m the hydrated form of 2'-CMP 5'-UMP.K crystallizes in the monoclinic space group P2;i with a= 13 034 A, b= 8 916 A, c= 16 205 A and β=98 64° with two nucleotides, four K ions and ten water molecules in the asymmetric unit MoKα intensity data of 19261 were measured on a Bruker CCD system of which 6891 independent reflections having lo>2a(lo) were accepted as observed. The structure was solved and refined by full matrix least square methods to an R factor of 0.0324 for 609 parameters. Uracil bases of both nucleotide molecules are in the anti conformation with respect to the ribose with XCN= -129.4° and -132 7°. Uracil bases of both nucleotide molecules are protonated at N3 Both ribose moieties show C2’-endo puckering with C2' atom displaced by 0.57 and 0.59 A from the best plane constituted by the remaining atoms The phosphate group is in a staggered orientation and the conformation about the C4/-C5/ bond is g* with <j>00 = -67.1 and -62.7 and Øoc = 54.6 and 59.5 for molecules A and B respectively. Potassium ion K2 forms a bidentate by coordinating with ribose 02' and 03' atoms of molecule B and a macrochelate between the uracil base and ribose of molecule A by coordinating with 02 and 02' atoms. K4 also forms a bidentate by coordinating with ribose O2' and 03' atoms of molecule A. The two 5'-UMP molecules form a dimer by coordinating with K2 and K3 ions. They are related by a pseudo two-fold axis and the r.m.s. deviation between the coordinates is 0 12 A. Crystal structures of 8-Benzylamino cychc-3'-5'-monophosphate (8-Benz-cAMP) and 8-mercaptoguanosine (8-MERG) are presented in Chapter VI. 8-Benz-cAMP crystallizes in the monoclinic space group P2x with unit cell dimensions a= 7.989 A, b= 12 589 A, c= 11.773 A and β= 93.82°. MoKα data were collected on a CCD system yielded 4331 independent observed reflection with Io2cr(Io) out of 9733 reflections collected. The structure was solved and refined to a R factor of 0 0451 with 367 parameters. The adenine base is in the syn conformation with XCN= 84.7° as in few other 8-substituted cyclic purine nucleotides but different from the simple cyclic purine nucleotides. The phenyl moiety is in the trans conformation with respect to the base. The ribose moiety shows rare C4’-exo puckering with a deviation of 0.70 A from the best plane constituted by the remaining four atoms. The 05' atom is m the t conformation with respect to the ribose with cpα = -174.8° and <pα = -59.6° since only in this conformation 3' and 5' cyclization is possible. Hydrogen bonds Nl. .O1P and N6...O5' link two nucleotide molecules. Adenine bases stack on the phenyl ring from above and below. The only water molecule present in the structure form hydrogen bonds with the nucleotide atoms. 8-mercaptoguanosine crystallizes in the monoclinic space group C2 with unit cell dimensions a= 23.246 A, b=9.751 A, c= 6.406 A and b= 90.91°. MoKα intensity data collected on CAD diffractometer yielded 2683 independent observed reflections having I0>2<r(I0). The structure was solved using SHBLXS 97 and refined using SHELXL97 to a R factor of 0.0565. The guanine base is in the syn conformation with XCN= 64.1°. The ribose ring shows C2-endo puckering with C2' atom deviating by 0.62 A from the best plane. An interesting feature of this structure is the intra-molecular hydrogen bond between the base N3 and the ribose 05' atoms. The last chapter (VII) describes the crystal structures of three modified adenine nucleosides N6-benzyl adenosine (N6-BA), N6-cyclohexyl adenosine (N6-CA) and 5'-trityl adenosine (5'-TA). N6-BA belongs to the triclinic space group PI with a= 5.008 A, b= 8.921 A, c= 9.762 A and a = 111.73°, β= 90.37°, 7 = 91.42° while N6-CA and 5'-TA belong to the monoclinic space group P2i with a= 12.205 A, b=15.265 A, c= 15.095 A, P = 110.64° and a= 8.823 A, b= 15.613 A, c= 10.078 A and β = 115.01° with three and one molecules in their asymmetric units respectively. The three structures of N6-BA, N6-CA and 5'-TA were solved and refined to R factors of 0.0355, 0.0655 and 0.0262 using 1656, 7549, 2473 independent reflections and 244, 677, 360 parameters respectively using SHELX97. The adenine base of N6-BA is in the anti conformation with XCN= 168.9°. The benzyl moiety is in the distal geometry with respect to the imidazole ring. The furanose ring shows CSI-exo-CS'-endo mixed puckering. There are several 7r-7r interactions observed in this structure. In contrast to N6-BA all three molecules of N6-CA show syn conformation about the glycosidic bond with XCN= 47.0°, 54 8°, 49 V for molecules A, B and C respectively. The cyclohexyl moiety of all three molecules are in the chair conformation. The ribose moieties of all three molecules show C2-endo puckering with C2' atom deviating by 0 59, 0 54, 0.57 A for molecules A, B and C respectively. The adenine base of the 5'-TA is in the anti conformation with \Cs= 168.4° and the ribose moiety shows C2-endo puckering The three phenyl rings of the trityl group are in staggered orientation. Interesting tape formation via N6…02' and N7...O3' hydrogen bonds is observed in all three nuclosides.

Dendrimers are highly branched macromolecules which are prepared by a stepwise procedure. The presence of a well-defined core, discrete generations and a large number of terminal groups in dendrimers make them structurally very interesting and potentially useful for a wide variety of applications.1 Hyperbranched polymers,2 on the other hand, do not possess a unique core or discrete generations and they contain a large number of statistically distributed defects. Despite the presence of structural imperfections, studies have indicated that hyperbranched polymers capture many of the essential features of dendrimers, such as adoption of a compact conformation and the presence of a large number of readily accessible terminal functional groups. The first chapter of this thesis provides a brief introduction to hyperbranched polymers, with an emphasis on different methods for synthesizing them, followed by a discussion of the various approaches to control their molecular structural features, such as molecular weight, polydispersity, degree of branching, branching density, terminal end-groups, etc. One of the main objectives of the present study is to develop a simple synthetic strategy to generate peripherally functionalized (or functionalizable) hyperbranched polymers (HBP) that could potentially exhibit core-shell type behavior; in other words, polymers that carry segments of distinctly different solubility preferences within the core-region and the peripheral shell. To this end, in chapter 2 we describe the use of the melt-transetherification process,3 using an AB2 monomer along with a mono-functional A-R type comonomer, to directly generate core-shell type hyperbranched structures in a single step.4 Given that an AB2 monomer carries one equivalent excess of B functionality, copolymerization with an A-R type molecule bearing a single A functional group, readily permits the decoration of the periphery of the hyperbranched structures with these R-units. Thus, hyperbranched polyethers having polyethylene glycol (PEG) segments at their molecular periphery were prepared by a simple procedure wherein an AB2 type monomer was melt-polycondensed with an A-R type monomer, namely heptaethylene glycol monomethyl ether (HPEG). The presence of a large number of PEG units at the termini rendered a lower critical solution temperature (LCST) to these copolymers, above which they precipitated out of an aqueous solution.5 In an effort to understand the effect of various molecular structural parameters on their LCST, the length of the hydrophobic spacer segment within the hyperbranched core and the extent of PEGylation, were varied. Increase in the size and hydrophobicity of the hyper-core resulted in a continuous lowering of its LCST, while an increase in the level of PEGylation, increases the LCST, for a given size of the hyper-core. Additionally, linear analogues that incorporates pendant PEG segments were also prepared and comparison of their LCST with that of the hyperbranched polymer clearly revealed that the hyperbranched topology leads to a substantial increase in the LCST, highlighting the importance of the peripheral placement of the PEG units as shown in figure 1.5 This observation also provided an indirect evidence for the development of core-shell type topology in these peripherally functionalized hyperbranched structures. Figure 1. Transmittance of a 0.4 wt % aqueous solution of the linear and hyperbranched polymers as a function of temperature, measured at 600 nm. Such core-shell type HBPs could be also exploited both as unimolecular micelles and reverse micelles by suitably modifying the nature of the AB2 and A-R type monomers4. In the third chapter, the preparation and dye-encapsulation properties of unimolecular micelles as well as reverse micelles based on core-shell HBPs have been presented. In case of micelle forming polymers, an AB2 monomer carrying a decamethylene spacer was used along with heptaethylene glycol monomethyl ether (HPEG) as the A-R type comonomer. One the other hand, for the preparation of reverse micelle forming polymers, an AB2 monomer containing an oligo(oxyethylene) spacer was used along with cetyl alcohol as the A-R type comonomer as shown in scheme 1. The former was readily soluble in water while the latter was soluble in hydrocarbon solvents, like hexane. NMR spectral studies confirmed that both the approaches generated highly branched structures wherein ca. 65-70 % of the terminal B groups were capped by the A-R comonomer. scheme1. Synthesis of the unimolecular micelle and reverse micelle forming polymers using a one step AB2 + A-R type copolymerization. (REFER PDF FILE) One of the approaches commonly used to demonstrate core-shell behavior is to examine the ability of such polymers to encapsulate appropriate dyes from a suitable medium. In the case of the micelle-forming polymer, an aqueous solution of the polymer (6 μM) was sonicated in the presence of excess pyrene for varying periods of time. From the UV-visible spectra (Figure 2) of the aqueous solution (after filtration), it is evident that the saturation uptake is attained in about 7 h. Similar studies were also carried out for reverse-micelle forming polymers in hexane, using methyl orange as the dye. These dye-uptake studies, in conjunction with dynamic light scattering, unequivocally confirmed the formation of unimolecular micelles/reverse micelles. Figure 2. Absorbance as a function of sonication time for micelle-forming polymers (A), and absorbance as a function of the amount of solid dye taken, for reverse micelle-forming polymers (B). (REFER PDF FILE) Another novel approach to generate core-shell systems, using A2 + B3 + A-R type terpolymerization, was also explored in an effort to simplify the synthesis even further. However, dye-uptake measurements revealed that the polymers prepared via the AB2 + A-R approach exhibited a significantly larger uptake compared to those prepared via the A2 + B3 + A-R approach. This suggests that the AB2 + A-R approach generates hyperbranched polymers with better defined core-shell topology when compared to polymers prepared via the A2 + B3 + A-R approach, which is in accordance with previous studies6 that suggest that A2 + B3 approach yields polymers with significantly lower branching levels and consequently less compact structures. In chapter 4, different strategies for functionalization of the core-region and periphery of core-shell type hyperbranched polymers (HBP) using the “click” reaction7 have been explored. For achieving peripheral functionalization, an AB2 + A-R1 + A-R2 type copolymerization approach was used (as depicted in scheme 2), where the A-R1 is heptaethylene glycol monomethyl ether (HPEG-M) and A-R2 is tetraethylene glycol monopropargyl ether (TEG-P). A very small mole-fraction of the propargyl containing monomer, TEG-P was used to ensure that the water-solubility of the core-shell type HBP is minimally unaffected. Scheme 2. Preparation of a hyperbranched polyether having a few percent of propargyl groups at the molecular periphery and further click reaction to place fluorophores at the periphery. Similarly, to incorporate propargyl groups in the core region, a new propargyl group bearing B2-type monomer was designed and utilized in an AB2 + A2 + B2 + A-R1 type copolymerization, such that the total mole-fraction of B2 + A2 is small and their mole-ratio is 1:1 (Scheme 3). Further, using a combination of both the above approaches, namely AB2 + A2 + B2 + A-R1 + A-R2, hyperbranched structures that incorporate propargyl groups both at the periphery and within the core were synthesized. Since the AB2 monomer carries a C-6 alkylene spacer and the periphery is PEGylated, all the derivatized polymers form core-shell type structures in aqueous solutions. In order to ascertain and probe the location of the propargyl groups in these HBP’s, a fluorescent azide, namely azidomethyl pyrene, was quantitatively clicked onto these polymers and their fluorescence properties were examined in solvents of different polarities. Fluorescence spectra in water was unable to differentiate between the fluorophores present at different locations suggesting that the tethered pyrene at the end of a flexible oligoethylene oxide unit is probably tucked within the core-region because of its intrinsic hydrophobic nature. Scheme 3. Preparation of a hyperbranched polyether bearing a few percent of the propargyl groups within the core and further click reaction to place fluorophores in the core-region. The conventional melt-transetherification polymerization proceeds by continuous removal of methanol as volatile by product.3 The fifth chapter describes the design and development of a new AB2 monomer that carries two propargyloxy benzyl groups and one hydroxyl group, which underwent melt-transetherification condensation by exclusion of propargyl alcohol (instead of methanol) to generate a hyperbranched polyether containing numerous propargyl ether groups located on their molecular periphery as shown in scheme 4. These propargyl groups were readily “clickable” under very mild conditions with a variety of azides using the copper (I) catalyzed Huisgen type dipolar cycloaddition, popularly known as click reaction,7 to generate a range of functionalized hyperbranched polymers. The simplicity of the monomer synthesis, the solvent-free melt polymerization process and the mild conditions under which quantitative peripheral derivatization is achievable, makes this process ideally suited for the generation of hyperscaffolds onto which a wide range of functionalities could be placed. This turned out to be a rather remarkable extension of the melt transetherification polymerization that permitted the direct generation of peripherally clickable hyperbranched scaffold that, in principle, could be used to generate a wide range of interesting structures. Scheme 4. Synthesis of the hyperbranched polyether with clickable surface in a single step. (For structural formula pl refer pdf file)

El present treball té com objectiu l'obtenció de materials entrecreuats conservant una mesofase cristall líquid fixada, comunment denominats LCTs. La majoria de LCTs s'obtenen per entrecreuament de reïnes epoxi cristall líquid amb amines aromàtiques primàries. L'entrecreuament dins de la mesofase porta a materials amb un menor coeficient d'expansió tèrmica i en alguns casos amb un augment considerable del mòdul d'emmagatzematge. L'orientació dels LCTs per entrecreuament dins d'un camp magnètic porta a materials anisòtrops amb una millora de les propietats mecàniques en la direcció del camp aplicat. En aquest cas, s'han sintetitzat sis sèries de monòmers diepoxídics mesomorfs amb estructura de dímer i que contenen un grup imina dins la unitat mesogènica. S'ha estudiat la influència de la diferent llargària de l'espaciador central i la incorporació de grups èter i èster als extrems del mesògen en el comportament mesomorf. L'estudi de les característiques de cristall líquid s'han caracteritzat mitjançant calorimetria diferncial d'escombrat, microscopia òptica de llum polaritzada i difracció de raigs X. A més d'aquestes tècniques, s'han caracteritzat les propietats mecàniques dels LCTs obtinguts mitjançant anàlisi termodinamomecànica. Dues de les sèries han mostrat mesofases esmèctiques i la resta únicament una mesofase nemàtica. Els resultats obtinguts confirmen la importància de la polaritat del mesogen i de la posició del grup ester entre l'espaciador central i els mesògens per a la formació de mesofases esmèctiques.S'han obtingut LCTs a partir de l'entrecreuament d'aquest monòmers amb cantitats estequiomètriques de 2,4-diaminotoluè, 4,4'-aminoacetofenona azina, i 2,4-toluendiisocianat sol i catalitzat per 4-N,N-dimetilaminopiridina. També s'han obtingut LCTs per entrecreuament amb 4-N,Ndimetilaminopiridina i diazabiciclo[2,2,2]octà en quantitats catalítiques. Els LCTs obtinguts s'han caracterizat per fixar majoritàriament ordenacions nemàtiques i en alguns casos ordenacions esmèctiques C. En els LCTs obtinguts s'ha posat de manifest la importància de la polaritat del mesogen per l'obtenció de LCTs i de la posició del grup ester entre l'espaciador central i els mesògens per a la formació de LCTs amb ordenacions esmèctiques.S'han estudiat les propietats mecàniques dels LCTs entrecreuats amb 2,4-diaminotoluè, 4-N,N-dimetilaminopiridina i diazabiciclo[2,2,2]octà. S'han comparat tres tipus diferents de materials, materials isòtrops, orientats en microdominis i materials macroscòpicament orientats. S'han obtingut graus d'orientació petits, tot i que els materials orientats van mostrar anisotropia en el coeficient d'expansió tèrmica.Obtention of LCTs from liquid crystal epoxy resins with dimeric structure. / The search for new materials with unusual mechanical and thermal properties led to research into liquid crystalline thermosets (LCT's). LC epoxies are the monomers that have been most frequently studied to obtain LCT's. If the crosslinking is carried out in the mesophase, the LCTs obtained have unusual mechanical and thermal properties, low shrinkage upon cure, low thermal expansion coefficients, low dielectric constants and enhanced reaction rates because the ordered structures mean that the reacting groups are close to one another. Several publications describe the physical properties of oriented and unoriented LCT's. Macroscopically oriented LCTs obtained by curing in the mesomorphic state inside a magnetic field led to thermal expansion coefficient and storage modulus having anisotropic characteristics. Thus, the thermal expansion coefficient of macroscopically oriented materials must be lower than that of unoriented materials and the storage modulus must be expected to increase considerably in the direction of the orientation. I have synthesized six series of liquid-crystalline epoxy resins with aromatic azomethine groups and dimeric architecture, and varied the length of the alkyl spacer. The liquid crystal behaviour of these dimeric glycidylic compounds was studied by diferential scanning calorimetry (DSC), hot stage polarized optical microscopy (POM) and X-Ray Diffraction (WAXS). Two series of them show smectic mesophases and the other show nematic mesophase. From the results we have confirmed the importance of the polarization of the mesogenic groups and the presence of an ester group in the inner position in the formation of smectic mesophases.I obtained LCT's from these monomers by isothermal curing with equimolecular amounts of 2,4-diaminotoluene, 4,4'-aminoacetophenone azine, and 2-4-toluendiisocyanate alone and catalized with 4-N,N-dimethylaminopyridine. Another LCT's have obtained by isothermal curing with catalytic amounts of 4-N,N-dimethylaminopyridine or diazabicicle[2,2,2]octane. By curing these monomers with primary and tertiary amines we make clear the polarization of the mesogenic groups and the presence of an ester group in the inner position are also determinant to obtain LCTs with a different degree of order. Most monomers produced nematic-like networks, but in one case smectic C mesophase was also locked.Finally, the mechanical characterization of the LCTs obtained by curing with 2,4-diaminotoluene, 4-N,N-dimethylaminopyridine and diazabicicle[2,2,2]octane was studied by thermodinamicmechanical analysis. The orientation experiments were made by conducting the curing in the same conditions in a NMR probe with a magnetic field of 7.1 T. I compare isotropic materials, LCTs and LCTs obtained inside a magnetic field. Low orientation degrees have led. Macroscopically oriented

The biocompatibility and biodegradability of poly(lactic acid) (PLA) facilitate its use in a variety of biomedical applications, ranging from sutures to drug delivery. However, uncontrolled interactions with cells and insufficient mechanical properties have prevented PLA from reaching its full potential as a scaffold for use in tissue engineering. Methods to improve the mechanical, chemical and biological properties of PLA are limited by the lack of functional groups along the backbone of the polymer. One possible approach towards overcoming these limitations involves the incorporation of functional groups into the backbone of the polymer through the copolymerization of monomers bearing protected functional groups. Deprotection and modification of these functional groups could provide the opportunity to direct the attachment of cells, and enhance to the physical properties of the polymer. We have developed a general methodology for the synthesis of lactide monomers substituted with protected functional groups (alcohols protected as benzyl ethers, amines protected as benzyl carbamates and carboxylic acids protected as benzyl esters). The monomers were homopolymerized, and copolymerized with lactide, and deprotected to give functional PLA copolymers with pendant hydroxyl, amine, and carboxyl groups. A thorough investigation of the chemical modification of PLA copolymers bearing functional groups along the polymer backbone was performed on a copolymer prepared by copolymerizarion of a dibenzyloxy-substituted lactide monomer with lactide followed by reductive debenzylation. Reaction of the resulting hydroxyl-substited PLA with succinic anhydride resulted in an acid-substituted PLA that is amenable to standard EDC/NHS coupling. The utility of this copolymer was illustrated by coupling with an amine derivative of biotin, and an RGD-containing peptide sequence. The preparation of the biodegradable polyester substituted with RGD, a ubiquitous adhesion peptide, provided us with control over cellular attachment to the hybrid material. We also explored approaches to make use of the pendant functional groups on PLA to enhance the physical properties of polymer foams. Copolymers with pendant photocrosslinkable cinnamate groups were prepared by reaction of the hydroxyl-substited PLA copolymers with cinnamoyl chloride. The copolymer was foamed using thermally-induced phase separation (TIPS), and photocrosslinked upon irradiation at 300 nm. Irradiation resulted in an increase in the compressive modulus of the foams. Crosslinking also led to a decrease in the rate of hydrolytic degradation of the foams, thereby demonstrating the potential for use of these strategies in the development of porous scaffolds for bioengineering. Another potential approach towards the preparation of robust polymer foams is the incorporation of a rigid polymer block which can phase separate during foam formation to provide additional structural integrity. Several poly(norbornene)-PLA diblock copolymer compositions were prepared by the ring-opening of lactide by a hydroxyl-terminated poly(norbornene) macroinitiator. The ability of the diblock copolymer to phase separate at elevated temperature was verified using small-angle x-ray scattering and wide-angle x-ray scattering.

Thesis (M. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 98-104). Also available in electronic format on the Internet.

Thesis (Ph. D.)--University of California, Riverside, 2009. / Vita. Includes abstract. Includes bibliographical references (leaves 148-155). Issued in print and online. Available via ProQuest Digital Dissertations.

Os monômeros ligantes 3amdpy2oxaNBE (1), 3imdpyoxaNBE (2) e ácido âmico (3) foram sintetizados e caracterizado por analise elementar (CHN), infravermelho e RMN 1H e 13C. A partir do monômero 1 sintetizou-se compostos partindo de complexos do tipo [RuCl2(LL)], onde foi LL=bpy 37 (complexo 4), phen (complexo 6) ou 5-Cl-phen (complexo 7), e foram realizados estudos de fotoquímica e fotofísica. Os complexos 6 e 7 apresentaram uma eficiente fotofísica e não apresentaram fotoquímica, enquanto os complexos semelhante [Ru(bpy)2(3amnpy)2](PF6)2 (5) e [Ru(phen)2(3amnpy)2](PF6)2 (8) que possui a aminopiridina no lugar do monômero 1, apresentaram fotoquímica. Observou-se que as diferenças na rigidez dos ligantes phen e bpy podem causar diferentes propriedades fotoquímicas e fotofísicasem sistemas do tipo cis-[RuCl2(?-diimina)]. Todos os complexos exibiram absorções na região de 350 nm e entre 420 a 500 nm. Sendo que 5 e 8 apresentaram fotoquímica e os complexos 6 e 7 apresentaram fotofisica. Estes foram estudados em diferentes solventes (DMF, CH3CN, CH2Cl2, THF) e em diferentes comprimentos de onda de irradiação (340, 440 e 500 nm). A emissão dos complexos 6 (580 nm) e 7 (582 nm) em acetonitrila é atribuída a uma MLCT (Ru_phen). Sendo observada a independência do _irr, mas existe dependência da emissão quando a temperatura é abaixada. Além disso, suas propriedades fotocatalíticas são demonstradas pela supressão oxidativa através de íons receptores do metilviologenio. Ainda deve-se levar em conta que, o anel quelante do monômero ligante 1 contribui ainda mais para a estabilização destes complexos, ao contrario, 5 e 8 possuem uma fotolabilização . / The monomer ligands 3amdpy2oxaNBE (1), 3imdpyoxaNBE (2) and amic acid (3) were synthesized and characterized by elementar analysis (CHN), infrared and 1H e 13C NMR. Since monomer 1, it was synthesized complexes of type [RuCl2(LL)], where LL=bpy 37 (complex 4), phen (complex 6) or 5-Cl-phen (complexo 7), with which photophysics and photochemical studies were performed. The complexes 6 and 7 presented efficient photophysics and they do not presented photochemistry, while the similar complexes [Ru(bpy)2(3amnpy)2](PF6)2 (5) and [Ru(phen)2(3amnpy)2](PF6)2 (8), which possess the aminopyridine in place of monomer 1, presented photochemistry. It was observed that the difference in the rigidity of the ligands phen and bpy may cause different photochemical and photophysical properties in systems of type cis-[RuCl2(?- diimine)]. All complexes exhibited absorptions in region of 350 nm and between 420 and 500 nm, where 5 and 8 presented photochemistry and the complexes 6 and 7 presented photophysics. They were studied in different solvents (DMF, CH3CN, CH2Cl2, THF) and in different irradiation wavelength (340, 440 e 500 nm). The emission of the complexes 6 (580 nm) and 7 (582 nm) in acetonitrile is attributed to an MLCT (Ru_phen). It was observed independence of _irr, however there is dependence of emission when the temperature is lowered. Furthermore, their photocatalytic properties are demonstrated by oxidative quenching using methylviologen ion. One should consider that the chelating ring of monomer ligand 1 contributes even more to the stabilization of these complexes, unlike, 5 and 8 that possess photolabilization.

Orientador: Luis Alexandre Maffei Sartini Paulillo / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Odontologia de Piracicaba / Made available in DSpace on 2018-08-04T11:11:29Z (GMT). No. of bitstreams: 1 Bueno_VanessaCastroPestanadaSilveira_M.pdf: 10101006 bytes, checksum: 0cdee7488442c7a04cbb64daddf3b98e (MD5) Previous issue date: 2005 / Resumo: O objetivo deste estudo foi avaliar a influência do cimento endodôntico e do sistema de fixação na resistência à tração de pinos pré-fabricados de fibra de vidro. Foram utilizadas sessenta e quatro raízes bovinas extraídas, divididas em oito grupos experimentais resultantes da interação Cimento Endodôntico x Sistema de Fixação. A obturação dos canais radiculares foi realizada com gutapercha e cimento endodôntico contendo eugenol (CC) ou no apenas com gutapercha termo-plastificada (SC), sendo verificada a influência do eugenol presente no cimento endodôntico nos sistemas de fixação. Foram utilizados dois sistemas de fixação RelyX/ Single Bond (SB/RX) e C&B/All-Bond 2 (CB/AB) e a associação dos mesmos RelyX/ All-Bond 2 (RX/AB) e C & B/ Single Bond (CB/SB), distribuídos nos seguintes grupos: GI ¿ SB/RX/CC; GII ¿ AB/CB/CC; GIII ¿AB/RX/CC; GIV ¿ SB/CB/CC; GV ¿ SB/RX/SC; GVI ¿ AB/CB/SC; GVII ¿AB/RX/SC; GVIII ¿ SB/CB/SC. Após a inclusão das raízes, as amostras foram submetidas ao teste de resistência à tração através de uma Máquina de Ensaios Universal ¿ EMIC - modelo DL 5000, regulada a velocidade de 0,5mm/min. Os valores obtidos em quilograma força (kgf) foram tabulados e submetidos à análise estatística. Os resultados mostraram não haver efeito estatístico significativo para o fator cimento endodôntico e para a interação cimento endodôntico x sistema de fixação (teste de Análise de Variância, a= 0,05). Entretanto, a análise do resultado do teste de variação múltipla de Tukey (LSMEANS) mostrou que a maior média de resistência à tração foi apresentada pelo sistema de fixação Single Bond/RelyX 37,41(12,86)a, porém não apresentou diferença estatística significativa da média do sistema All- Bond 2/C&B 27,13 (8,34)ab. Por outro lado, a menor média de resistência à tração foi apresentada pelo sistema Single Bond/C&B 21,36(6,3)c, não apresentando diferença estatística significativa para o sistema All-Bond 2/RelyX 33,45(11,49)bc. Desta forma, concluiu-se que o cimento endodôntico não influenciou a resistência à tração dos sistemas de fixação de pinos intraradiculares de fibra de vidro; os sistemas de fixação All-Bond 2/C&B e Single Bond/RelyX apresentaram o mesmo comportamento em relação a resistência à tração. Além disso, que a associação de adesivo que possui monômeros ácidos, em sua composição, e cimento resinoso quimicamente ativado diminui significantemente a resistência à tração / Abstract: The aim of this study was to evaluate the influence of adhesive system, endodontic and fixation sealer on tensile strengh of prefabricated glass fiber posts. Sixty-four bovin roots were selected and divided in eighth experimental groups resultant in the interation of Endodontics Sealer x Fixation System. The guta-percha plasticized (WS) by heat and a sealer containing eugenol (WOS) were used in root canal filling in the root canal filling was done using guta-percha plasticized by heat, only. So, the influence of eugenol in fixation systems could be analyzed. It was used two adhesive systems: RelyX/ Single Bond e C & B/ All Bond 2 and the association between them (Rely X/ All Bond 2 e C & B/ Single Bond), all divided in 6 groups: GI ¿ SB/RX/WS; GII ¿ AB/CB/WS; GIII ¿ AB/RX/WS; GIV ¿ SB/CB/WS; GV ¿ SB/RX/WOS; GVI ¿ AB/CB/WOS; GVII ¿ AB/RX/WOS; GVIII ¿ SB/CB/WOS. After the inclusion, the specimens were submitted to tensile strengh in a Universal Testing Machine ¿ EMIC - model 5000, under 0,5 mm/min of velocity. The results expressed in Kgf were schedule and submitted into statistical analysis. They showed no significant statistical effect to the sealer agent and to the interaction sealer X fixation system (Analysis of Variance Test, a= 0,05). However, Tukey's test (LSMEANS) showed higher mean of tensile strengh to the system Single Bond/RelyX 37,41(12,86)a, but no statistical difference between this system and the other one - All Bond 2/C&B 27,13(8,34)ab was found. In the other hand, minor average was showed by system Single Bond/C&B 21,36(6,3)c, but no significant difference between this system and the other one All Bond 2/RelyX 33,45(11,49)bc. Thus, it follows that the endodontic sealer didn't affect fixation systems of pins and the system All Bond 2/C&B and Single Bond/RelyX showed similar results of tensile strengh. It also follows that the association between an adhesive with acidic resin monomers and a chemical cured resin sealer can cause drop of potencial bond strengh / Mestrado / Dentística / Mestre em Clínica Odontológica

No description available.

The launch of national and international initiatives to reduce pollution, reliance on fossil fuels and increase the beneficiation of agricultural wastes has prompted research into sugar monomer production from lignocellulosic wastes. These sugars can subsequently be used in the production of biofuels and environmentally degradable plastics. This study investigated the use of synergistic combinations of commercial and pure enzymes to lower enzyme costs and loadings, while increasing enzyme activity in the hydrolysis of agricultural waste. Pineapple pomace was selected due to its current underutilisation and the substantial quantities of it produced annually, as a by-product of pineapple canning. One of the primary costs in beneficiating agricultural wastes, such as pineapple pomace, is the high cost of enzyme solutions used to generate reducing sugars. This can be lowered through the use of synergistic combinations of enzymes. Studies related to the inclusion of hemicellulose degrading enzymes with commercial enzyme solutions have been limited and investigation of these solutions in select combinations, together with pineapple pomace substrate, allows for novel research. The use of synergistic combinations of purified cellulosomal enzymes has previously been shown to be effective at releasing reducing sugars from agricultural wastes. For the present study, MannanaseA and XylanaseA from Clostridium cellulovorans were heterologously expressed in Escherichia coli BL21 (DE3) cells and purified with immobilised metal affinity chromatography. These enzymes, in addition to two commercially available enzyme solutions (Celluclast 1.5L® and Pectinex® 3XL), were assayed on defined polysaccharides that are present in pineapple pomace to determine their substrate specificities. The degree(s) of synergy and specific activities of selected combinations of these enzymes were tested under both simultaneous and sequential conditions. It was observed that several synergistic combinations of enzyme solutions in select ratios, such as C20P60X20 (20% cellulose, 60% pectinase and 20% xylanse), C20P40X40 (20% cellulose, 40% pectinase and 40% xylanase) and C20P80 (20% cellulose, 80% pectinase) with pineapple pomace could both decrease the protein loading, while raising the level of activity compared to individual enzyme solutions. The highest quantity of reducing sugars to protein weight used on pineapple pomace was recorded at 3, 9 and 18 hours with combinations of Pectinex® 3XL and Celluclast 1.5L®, but for 27 h it was combinations of both these commercial solutions with XynA. The contribution of XynA was significant as C20P60X20 displayed the second highest reducing sugar production of 1.521 mg/mL, at 36 h from 12.875 μg/mL of protein, which was the second lowest protein loading. It was also shown that certain enzyme combinations, such as Pectinex® 3XL, Celluclast 1.5L® and XynA, did not generate synergy when combined in solution at the initial stages of hydrolysis, and instead generated a form of competition called anti-synergy. This was due to Pectinex® 3XL which had anti-synergy relationships in select combinations with the other enzyme solutions assayed. It was also observed that the degree of synergy and specific activity for a combination changed over time. Some solutions displayed the highest levels of synergy at the commencement of hydrolysis, namely Celluclast 1.5L®, ManA and XynA. Other combinations exhibited the highest levels of synergy at the end of the assay period, such as Pectinex® 3XL and Celluclast 1.5L®. Whether greater synergy was generated at the start or end of hydrolysis was a function of the stability of the enzymes in solution and whether enzyme activity increased substrate accessibility or generated competition between enzymes in solution. Sequential synergy studies demonstrated an anti-synergy relationship between Pectinex® 3XL and XynA or ManA, as well as Pectinex® 3 XL and Celluclast 1.5L®. It was found that under sequential synergy conditions with Pectinex® 3 XL, XynA and ManA, that anti-synergy could be negated and high degrees of synergy attained when the enzymes were added in specific loading orders and not inhibited by the presence of other active enzymes. The importance of loading order was demonstrated under sequential synergy conditions when XynA was added before ManA followed by Pectinex® 3 XL, which increased the activity and synergy of the solution by 50%. This equates to a 60% increase in reducing sugar release from the same concentrations of enzymes and emphasises the importance of removing anti-synergy relationships from combinations of enzymes. It can be concluded that a C20P60X20 combination (based on activity) can both synergistically increase the reducing sugar production and lower the protein loading required for pineapple pomace hydrolysis. This study also highlights the importance of reducing anti-synergy in customised enzyme cocktails and how sequential synergy can demonstrate the order in which a lignocellulosic waste is degraded.