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Yes / In this work, an analytical study of the electromagnetic propagation in a complex medium-based suspended three-layer coplanar waveguide (CPW) is carried out. The study aims at a numerical calculation of the dominant hybrid mode complex propagation constant in the CPW printed on a bianisotropic substrate. The herein considered bianisotropy is characterized by full 3×3 tensors of permittivity, permeability and magnetoelectric parameters. The study is based on the numerical derivation of the Green's functions of such a complex medium in the spectral domain. The study is carried out using the Full Generalized Exponential Matrix Technique based on matrix- shaped compact mathematical formulations. The Spectral Method of Moments (SMoM) and the Galerkin's procedure are used to solve the resulting homogeneous system of equations. The effect of the chiral and achiral bianisotropy on the complex propagation constant is particularly investigated. Goo d agreements with available data for an anisotropic-medium-based suspended CPW structure are achieved. Various cases of chiral and achiral bianisotropy have been investigated, and particularly, the effect on the dispersion characteristics is presented and compared with cases of isotropic and bianisotropic Tellegen media. / FCT/MEC through national funds and when applicable co-financed by the ERDF, under the PT2020 Partnership Agreement under the UID/EEA/50008/2019 project.

Although gas and liquid chromatography have emerged as dominant separation techniques in environmental analytical chemistry, these methods do not allow for the concurrent analysis of chemically diverse groups of persistent organic pollutants (POPs). There are also a small number of compounds which are not easily amenable to either of these traditional separation techniques. The main objective of this thesis was to address these issues by demonstrating the applicability of packed column supercritical fluid chromatography (pSFC) coupled to mass spectrometry (MS) in various aspects of environmental chemistry. First, pSFC/MS analytical methods were developed for legacy POPs (PCDDs, PCDFs, and PCBs) as well as the emerging environmental contaminant Dechlorane Plus (DP), and issues relating to the ionization of target analytes when pSFC was coupled to MS were explored. Novel APPI and APCI reagents (fluorobenzene and triethylamine) were optimized and real samples (water and soil) were analyzed to demonstrate environmental applicability. The possibility of chiral and preparative scale pSFC separations was then demonstrated through the isolation and characterization of thermally labile hexabromocyclododecane (HBCDD) stereoisomers. The analytical pSFC separation of the α-, β-, and γ-HBCDD enantiomers as well as the δ and ε meso forms was shown to be superior to results obtained using a published LC method. Finally, technical mixtures of phosphorus flame retardants (RBDPP, BPA-BDPP, and DOPO; a group of related compounds which are challenging to analyze concurrently) were examined using multiple analytical techniques and pSFC was found to be the only method which facilitated the accurate determination of the components of all 3 mixtures. This thesis confirms the potential of pSFC/MS as a fast, green, and cost effective means of separating and analyzing environmental contaminants.

Yes / In this paper, we present an analytical study for the investigation of the effects of the magnetoelectric elements of a reciprocal and nonreciprocal bianisotropic grounded substrate on the input impedance, resonant length of a dipole antenna as well as on the mutual coupling between two element printed dipole array in three configuration geometries: broadside, collinear and echelon printed on the same material. This study examines also the effect of the considered bianisotropic medium on the electric and magnetic field distributions that has been less addressed in the literature for antenna structures. Computations are based on the numerical resolution, using the spectral method of moments, of the integral equation developed through the mathematical derivation of the appropriate spectral Green’s functions of the studied dipole configuration. Original results, for chiral, achiral, Tellegen and general bi-anisotropic media, are obtained and discussed with the electric and magnetic field distributions for a better understanding and interpretation. These interesting results can serve as a stepping stone for further works to attract more attention to the reciprocal and non-reciprocal Tellgen media in-depth studies.

Made available in DSpace on 2015-05-14T13:21:22Z (GMT). No. of bitstreams: 1 ArquivoTotal.pdf: 18195512 bytes, checksum: 6229ab5e9f367190d5f7b4336c07dfec (MD5) Previous issue date: 2013-08-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / This study was designed based on the concept of achiral / meso compound. The importance of preparing achiral compounds is based on their structural simplification, leading to new molecules which require no further investigations pharmacodynamics and pharmacokinetics of the enantiomers. Therefore, it is proposed to the synthesis of analogues tetrahydropyrans achiral/meso using the Prins cyclization reaction. The homoallylic alcohols synthesized in this work were derived from the Barbier reaction obtained in great yields, wherein these products are used as a synthesis intermediate for the preparation of tetrahydropyrans proposed. The Prins cyclization reaction is an efficient method for the preparation of tetrahydropyrans therefore proved to be a powerful tool for synthesis and versatile for the preparation of substituted tetrahydropyrans to give all the compounds synthesized in satisfactory yields. Through spectroscopic and crystallographic studies were possible to determine in detail the relative configuration of the molecules 40a, 41a, 44a, 45a, 46a, 46b and 48b. Furthermore, a theoretical study was developed using the density functional theory to obtain the molecular geometries optimized in the gas phase, making it possible to compare these preferred conformations with geometries defined by crystals. The tetrahydropyrans bioevaluated were synthesized in the leukemic cell line K562 and two types of normal L929 cells and PBMC. The results were very promising in cancer in vitro assays, highlighting the hydrazones 42a-c and the 43a-c aminoguanidines they were the only compounds that were active against resistant cell line K562, highlighting the tetrahydropyran 42c which showed higher activity series counterpart (present value of IC50 7.59 μM) and the tetrahydropyran 42b with an excellent IC50 (8.97 μM) value and a good selectivity index (2.2 in L929 and 1.6 in PBMC). / Este trabalho foi idealizado baseado no conceito de compostos aquirais/meso. A importância da preparação de compostos aquirais está baseada na sua simplificação estrutural, conduzindo a novas moléculas que não necessitam de posteriores investigações farmacodinâmicas e farmacocinéticas dos enantiômeros. Sendo assim, propomos neste trabalho a síntese de análogos tetraidropirânicos aquirais/meso utilizando a reação de ciclização de Prins. Os álcoois homoalílicos sintetizados foram provenientes da reação de Barbier obtidos em ótimos rendimentos, no qual estes produtos foram utilizados como intermediário de síntese para a preparação dos tetraidropiranos propostos. A reação de ciclização de Prins é um método eficiente na preparação dos tetraidropiranos, pois mostrou-se ser uma ferramenta de síntese poderosa e versátil para a preparação dos tetraidropiranos substituídos, obtendo-se todos os compostos sintetizados em rendimentos satisfatórios. Através de estudos espectroscópicos e cristalográficos foi possível determinar detalhadamente a configuração relativa das moléculas 40a, 41a, 44a, 45a, 46a, 46b e 48b. Além disso, foi desenvolvido um estudo teórico utilizando a teoria do funcional densidade para se obter as geometrias moleculares otimizadas em fase gasosa, tornando possível comparar estas conformações preferenciais com as geometrias definidas pelos cristais. Os tetraidropiranos sintetizados foram bioavaliados na linhagem de células leucêmicas K562 e dois tipos de células normais L929 e PBMC. Os resultados em câncer foram bastante promissores nos ensaios in vitro, dando destaque para as hidrazonas 42a-c e as aminoguanidinas 43a-c que foram os únicos compostos que se mostraram ativos contra a linhagem celular resistente K562, destacando-se o tetraidropirano 42c que apresentou maior atividade da série congênere (apresentando valor de CI50 7.59 μM) e o tetraidropirano 42b que apresentou excelente valor de IC50 (8.97 μM) e um bom índice de seletividade (2.2 em L929 e 1.6 em PBMC).

Structural studies of peptides are of great importance in developing novel and effective biomaterials ranging from drugs and vaccines to nano materials with industrial applications. In addition, they provide model systems to study and mimic the protein conformations. The ability to generate folded intramolecularly hydrogen bonded structures in short peptides is essential for peptide design strategies, which rely on the use of folding nuclei in the construction of secondary structure modules like helices and β-hairpins. In these approaches, conformational choices at selected positions are biased, using local stereochemical constraints, that limit the range of accessible backbone torsion angles. X-ray crystallographic studies of designed peptides provide definitive proof of the success of a design strategy, and provide essential structural information that can be utilized in the future design of biologically and structurally important polypeptides. Recent trends in peptide research focus on the incorporation of β-, γ- and higher homologs of the α-amino acid residues in designed peptides as they confer more proteolytic stability to the polypeptides. X-ray crystallographic studies of such modified peptides containing non-protein residues are essential, since information on the geometric and stereochemical properties of modified amino acids can only be gathered from the systematic structural studies of synthetic peptides incorporating them. This thesis reports a systematic study of the structures and conformations of amino acid derivatives and designed peptides containing stereochemically constrained α-, β- and γ-amino acid residues and the structural studies of polymorphic peptide helices. The structures described in thesis contain the Cα,α-dialkyalted α-residues α-aminoisobutyric acid (Aib) and 1-aminocyclohexane-1-carboxylic acid (Ac6c), the β-amino acid residue 1-aminocyclohexane acetic acid (β3,3Ac6c) and the γ-amino acid residue 1-aminomethylcyclohexaneacetic acid (gabapentin, Gpn). The crystal structure determination of peptides incorporating conformationally constrained α-, β- and γ- amino acid residues permitted the characterization of new types of hydrogen bonded turns and polymorphs. The studies enabled the precise determination of conformational and geometric parameters of two ω-amino acid residues, gabapentin and β 3,3Ac6c and provided detailed information about the conformational excursions possible for peptide molecules. This thesis is divided into 10 chapters. Chapter 1 gives a general introduction to the stereochemistry of the polypeptide chain, description of backbone torsion angles of α- and ω- amino acid residues and the major secondary structures of α-peptides, β-peptides, γ-peptides and hybrid peptides. A brief introduction to polymorphism and weak interactions, in particular aromatic interactions, is also provided, followed by a discussion on X-ray diffraction and solution to the phase problem. Chapter 2 describes the crystal structures of gabapentin zwitterion and its eight derivatives (Ananda, Aravinda, Vasudev et al., 2003). The crystal structure of the gabapentin zwitterions determined in this study is identical to that previously reported (Ibers, J. A. Acta Crystallogr. 2001, C57, 641-643). Eight of the nine achiral compounds crystallized in centrosymmetric space groups P21/c, C2/c or Pbca, while one derivative (Tos-Gpn-OH) crystallized in non-centrosymmetric space group Pna21 with four independent molecules in the asymmetric unit.The structural studies presented in this chapter reveal that the geminal substituents on the Cβ atom limits the values of dihedral angles θ1 and θ2 to ±60°, resulting in folded backbone conformations in all the examples. Intramolecular hydrogen bonds with 7-atoms in the hydrogen bond turn (C7) are observed in three derivatives, gabapentin hydrochloride (GPNCL), Boc-Gpn-OH (BGPNH) and Piv-Gpn-OH (PIVGPN), while a 9-atom hydrogen bonded turn (C9) is observed in Ac-Gpn-OH (ACGPH). Unique structural features, such as an unusual anti conformation of the COOH group (in ACGPH) and positional disorder of the cyclohexane ring (in BGPNN), indicating the co-existence of both the interconvertible chair conformations, are revealed by the crystal structure analyses. Chapter 3 describes the structural characterization of novel hydrogen bonded conformations of homo oligomers of Gpn. The crystal structures of three peptides, Boc-Gpn-Gpn-NHMe (GPN2), Boc-Gpn-Gpn-Leu-OMe (GPN2L) and Boc-Gpn-Gpn-Gpn-Gpn-NHMe (GPN4) provide the first crystallographic characterization of two new families of polypeptide structures, the C9 helices and C9 ribbons (Vasudev et al., 2005, 2007), in which the molecular conformations are stabilized by contiguous C9 turns formed by the hydrogen bonding between the CO group of residue (i) and the NH group of residue (i+2). The C9 hydrogen bond is characterized by a specific combination of the four torsion angles for the Gpn backbone, with the torsion angles θ1 and θ2 adopting g+/g+ or g /g- conformations. The structural analysis also permits precise determination of hydrogen bond geometry for the C9 structures, which is highly linear in contrast to the analogous γ-turn hydrogen bonds in α-peptides. A comparison of the backbone conformations in the three peptides reveals two classes of C9 hydrogen bonded secondary structures, namely C9 helices and C9 ribbons. The packing arrangement in these γ-peptides follows the same patterns as the helix packing in crystals of α-peptides. Chapter 4 describes ten crystal structures of short hybrid peptides containing the Gpn residue (Vasudev et al., 2007). In addition to the C7 and C9 hydrogen bonded turns which are defined by the backbone conformations at the Gpn residue, hybrid turns defined by a combination of backbone conformations at the α and γ-residues or at the β and γ-residues have been determined. Peptides Boc-Ac6c-Gpn-OH (ACGPH), Piv-Pro-Gpn-Val-OMe (PPGPV) and Boc-Val-Pro-Gpn-OH (VPGPH) reveal molecular conformation stabilized by intramolecular C9 hydrogen bonds, while Boc-Ac6c-Gpn-OMe (ACGPO) and Boc-Gpn-Aib-OH (GPUH) are stabilized by a C7 hydrogen bonded turn at the Gpn residue. An αγ hybrid turn with 12 atoms in the intramolecular hydrogen bonded rings (C12 turns) has been observed in the tripeptide Boc-Ac6c-Gpn-Ac6c-OMe (ACGP3), while βγ hybrid turns with 13 atoms in the hydrogen bonded ring (C13 turns) have been characterized in the tripeptides Boc-βLeu-Gpn-Val-OMe (BLGPV) and Boc- βPhe-Gpn-Phe-OMe (BFGPF). The two βγ C13 turns belong to two different categories and are characterized by different sets of backbone torsion angles for the β and γ residues. A γα C10 hydrogen bond, which is formed in the N→C direction (NHi ••• COi+2), as opposed to the regular hydrogen bonded helices of α-peptides, has also been observed in BFGPF. The Chapter provides a comparison of the backbone torsion angles of the Gpn residue in various hydrogen bonded turns and a brief comparison of the observed hydrogen bonded turns with those of the α-peptides. Chapter 5 describes the crystal structures of three αγ hybrid peptides which show C12/C10 mixed hydrogen bond patterns (Vasudev et al., 2007, 2008a; Chatterjee, Vasudev et al.,2008a). The insertion of gabapentin in the predominantly α-amino acid sequences in Boc-Ala-Aib-Gpn-Aib-Ala-OMe (AUGP5) and Boc-Leu-Gpn-Aib-Leu-Gpn-Aib-OMe results in the observation of helices stabilized by αα C10 (310-turn) and αγ C12 turns. The tetrapeptide Boc-Leu-Gpn-Leu-Aib-OMe reveals a novel conformation, stabilized by C12 (αγ) and C10 (γα) hydrogen bonds of opposite hydrogen bond directionalities. The conformations observed in crystals have been extended to generate C12 helix and C12/C10 helix with alternating hydrogen bond polarities in ( αγ)n sequences. The structure determination of three crystals, providing five molecular conformations, presented in this chapter provides the first crystallographic characterization of two types of helices predicted for the regular αγ hybrid peptides from theoretical calculations. The crystal structure of Boc-Ala-Aib-Gpn-Aib-Ala-OMe also provides an example for the co-existence of left-handed and right-handed helix in the asymmetric unit. Chapter 6 describes the structural studies of αγ hybrid peptides containing Aib and Gpn residues, and is divided into two parts. The first part presents the crystal structure analysis of peptides of sequence length 2 to 4, with alternating Aib and Gpn residues, and illustrates the conformational variability in αγ hybrid sequences as evidenced by the observation of conformational polymorphs (Chatterjee, Vasudev et al., 2008b; Vasudev et al., 2007; Ananda, Vasudev et al., 2005). The peptide Boc-Gpn-Aib-NHMe (GUN), Boc-Aib-Gpn-Aib-OMe (UGU), Boc-Gpn-Aib-Gpn-Aib-OMe (GU4O), Boc-Aib-Gpn-Aib-Gpn-OMe (UG4O) and Boc-Aib-Gpn-Aib-Gpn-NHMe (UG4N), all of which are potential candidates for exhibiting αγ C12 hydrogen bonds, reveal molecular conformations stabilized by diverse hydrogen bonded turns such as C7, C9, C12 and C17 in crystals. The conformational heterogeneity in this class of hybrid peptides is further evidenced by the observation of three polymorphs in the monoclinic space group P21/c for the tetrapeptide Boc-Aib-Gpn-Aib-Gpn-NHMe (UG4N), providing four independent peptide molecules adopting two distinct backbone conformations. In one polymorph, C12 helices terminated with an unusual three residue ( γαγ) C17 turn is observed, while the unfolding of helical conformation by solvent insertion into the backbone is observed in the other two polymorphs. The studies indicate the possible utility of Gpn residue in stabilizing locally folded conformations in the folding pathway, thus permitting their crystallographic characterization in multiple crystal forms. A discussion of the structural and conformational features of Gpn residues determined from all the crystal structures is presented in the Chapter, along with a φ-ψ plot for the Gpn residue. Part 2 of Chapter 6 describes the crystal structures of two octapeptides, Boc-Gpn-Aib-Gpn-Aib-Gpn-Aib-Gpn-Aib-OMe (GU8) and Boc-Leu-Phe-Val-Aib-Gpn-Leu-Phe-Val-OMe (LFVUG8), featuring C12 turns at the Aib-Gpn segments (Chatterjee, Vasudev et al., 2009). GU8 folds into a C12 helix flanked by C9 hydrogen bonds at both the termini, while LFVUG8 adopts β-hairpin conformation with a chain-reversing C12 turn at the central Aib-Gpn segment. A remarkable feature of the Aib-Gpn turn in the β-hairpin structure is the anti conformation about the Cβ-Cα (θ2) bond, which is the only example of a Gpn residue not adopting gauche conformation for both θ1 and θ2. The crystal structures of the two peptides, mimicking the two major secondary structural elements of α-peptides in hybrid polypeptides, permits a comparative study of the mode of molecular packing in crystals of α-peptides and hybrid peptides. The chapter also discusses theoretical calculations on αγ hybrid sequences, which reveal new types of C12 hydrogen bonded turns. Chapter 7 describes the crystal structures of conformationally biased tert-butyl derivatives of Gpn. The crystallographic characterization of the E (trans) and Z (cis) isomers of the residue,three protected derivatives and a tripeptide provides examples of C7 and C9 hydrogen bonded conformations, suggesting that the C7 and C9 hydrogen bonds can be formed by Gpn residues with both the chair conformations of the cyclohexane ring. Chapter 8 describes the systematic structural studies of the derivatives and peptides of the stereochemically constrained β- amino acid residue, β3,3Ac6c (Vasudev et al., 2008c). The backbone torsion angles φ and θ adopt gauche conformation in majority of the examples, owing to the presence of a cyclohexane ring on the Cβ atom. In contrast to Gpn, β3,3Ac6c does not show strong preference for adopting intramolecularly hydrogen bonded conformations. Of the 16 crystal structures determined, intramolecular hydrogen bonds involving the β-residue are observed only in 4 cases. The amino acid zwitterion (BAC6C), the hydrochloride (BACHCL) and the dipeptide Boc-β3,3Ac6c-β3,3Ac6c-NHMe (BAC62N) form N-H•••O hydrogen bonds with 6-atoms in the hydrogen bond ring (C6 turns). An αβ hybrid C11 hydrogen bonded turn is characterized in the dipeptide Piv-Pro-β3,3Ac6c-NHMe, which is distinctly different from the C11 hydrogen bonds observed in αβ hybrid peptide helices. Several unique structural features such as a dynamic disorder of the hydrogen atom of the carboxylic acid group (in BBAC) and cis geometry of the urethane bond (in BBAC, BAC62N and BPBAC) have been observed in this study. A comparison of the backbone conformations of β3,3Ac6c with other β- amino acid residues is also provided. Chapter 9 describes the crystallographic characterization of a new polymorph of gabapentin monohydrate and crystal structures of the zwitterions of E and Z isomers of tert-butylgabapentin and its hydrochloride and hydrobromide (Vasudev et al., 2009). A comparison of the crystal structures of the monoclinic form (Ibers, J. A. Acta Crystallogr. 2001, C57, 641-643) of gabapentin monohydrate and the newly characterized orthorhombic form reveals identical molecular conformations and intermolecular hydrogen bond patterns in both the polymorphs. The two polymorphs show differences in the orientation of molecules constituting a layer of hydrophobic interactions between the cyclohexyl side chains. A comparison of the packing arrangements of the zwitterionic amino acid molecules in the crystal structures of gabapentin monohydrate, the tert-butyl derivatives and other co-crystals of gabapentin that had been characterized so far, is provided which would facilitate prediction of new polymorphs of the widely used drug molecule, Gpn. Chapter 10 describes the crystallization of α-peptide helices in multiple crystal forms (Vasudev et al., 2008b). Crystal structures of two peptides, Boc-Leu-Aib-Phe-Phe-Leu-Aib-Ala-Ala-Leu-Aib-OMe (LFF), Boc-Leu-Aib-Phe-Ala-Leu-Ala-Leu-Aib-OMe (D1) in two crystal forms and the crystal structure of a related sequence, Boc-Leu-Aib-Phe-Ala-Phe-Aib-Leu-Ala-Leu-Aib-OMe (D10) permit an analysis of the molecular conformation and packing patterns of peptide helices in crystals. The two polymorphs of LFF, crystallized in the space groups P21 and P22121, reveal very similar molecular conformation (α/310-helix) in both the polymorphic crystals; the two forms differ significantly in the pattern of solvation. The crystal structure determination of a monoclinic (P21) and an orthorhombic polymorph (P21212) of D1 provides five different peptide conformations, four of which are α-helical and one is a mixed 310/α-helix. The crystal structure determination of the three peptides provide an opportunity to compare the nature and role of aromatic interactions in stabilizing molecular conformation and packing and its significance in the observation of polymorphism. An analysis of the Cambridge Structural Database and a model for nucleation of crystals in hydrophobic peptide helices are also discussed.