<p>Oscillations in cytoplasmic Ca²⁺ concentration ([Ca²⁺]_i) is the key signal in glucose-stimulated β-cells governing pulsatile insulin release. The glucose response of mouse β-cells is often manifested as slow oscillations and rapid transients of [Ca²⁺]_i. In the present study, microfluorometric technique was used to evaluate the role of amino acids, glucagon, ryanodine and caffeine on the generation and maintenance of [Ca²⁺]_i oscillations and transients in individual murine β-cells and isolated mouse pancreatic islets. The amino acids glycine, alanine and arginine, at around their physiological concentrations, transformed the glucose-induced slow oscillations of [Ca²⁺]_i in isolated mouse β-cells into sustained elevation. Increased Ca²⁺ entry promoted the reappearance of the slow [Ca²⁺]_i oscillations. The [Ca²⁺]_i oscillations were more resistant to amino acid transformation in intact islets, supporting the idea that cellular interactions are important for maintaining the oscillatory activity. Individual rat β-cells responded to glucose stimulation with slow [Ca²⁺]_i oscillations due to periodic entry of Ca²⁺ as well as with transients evoked by mobilization of intracellular stores. The [Ca²⁺]_i oscillations in rat β-cells had a slightly lower frequency than those in mouse β-cells and were more easily transformed into sustained elevation in the presence of glucagon or caffeine. The transients of [Ca²⁺]_i were more common in rat than in mouse β-cells and often appeared in synchrony also in cells lacking physical contact. Depolarization enhanced the generation of [Ca²⁺]_i transients. In accordance with the idea that β-cells have functionally active ryanodine receptors, it was found that ryanodine sometimes restored oscillatory activity abolished by caffeine. However, the IP3 receptors are the major Ca²⁺ release channels both in β-cells from rats and mice. Single β-cells from ob/ob mice did not differ from those of lean controls with regard to frequency, amplitudes and half-widths of the slow [Ca²⁺]_i oscillations. Nevertheless, there was an excessive firing of [Ca²⁺]_i transients in the β-cells from the ob/ob mice, which was suppressed by leptin at close to physiological concentrations. The enhanced firing of [Ca²⁺]_i transients in ob/ob mouse β-cells may be due to the absence of leptin and mediated by activation of the phospholipase C signaling pathway.</p>

Oscillations in cytoplasmic Ca2+ concentration ([Ca2+]i) is the key signal in glucose-stimulated β-cells governing pulsatile insulin release. The glucose response of mouse β-cells is often manifested as slow oscillations and rapid transients of [Ca2+] i. In the present study, microfluorometric technique was used to evaluate the role of amino acids, glucagon, ryanodine and caffeine on the generation and maintenance of [Ca2+] i oscillations and transients in individual murine β-cells and isolated mouse pancreatic islets. The amino acids glycine, alanine and arginine, at around their physiological concentrations, transformed the glucose-induced slow oscillations of [Ca2+] i in isolated mouse β-cells into sustained elevation. Increased Ca2+ entry promoted the reappearance of the slow [Ca2+] i oscillations. The [Ca2+] i oscillations were more resistant to amino acid transformation in intact islets, supporting the idea that cellular interactions are important for maintaining the oscillatory activity. Individual rat β-cells responded to glucose stimulation with slow [Ca2+] i oscillations due to periodic entry of Ca2+ as well as with transients evoked by mobilization of intracellular stores. The [Ca2+] i oscillations in rat β-cells had a slightly lower frequency than those in mouse β-cells and were more easily transformed into sustained elevation in the presence of glucagon or caffeine. The transients of [Ca2+] i were more common in rat than in mouse β-cells and often appeared in synchrony also in cells lacking physical contact. Depolarization enhanced the generation of [Ca2+] i transients. In accordance with the idea that β-cells have functionally active ryanodine receptors, it was found that ryanodine sometimes restored oscillatory activity abolished by caffeine. However, the IP3 receptors are the major Ca2+ release channels both in β-cells from rats and mice. Single β-cells from ob/ob mice did not differ from those of lean controls with regard to frequency, amplitudes and half-widths of the slow [Ca2+] i oscillations. Nevertheless, there was an excessive firing of [Ca2+] i transients in the β-cells from the ob/ob mice, which was suppressed by leptin at close to physiological concentrations. The enhanced firing of [Ca2+] i transients in ob/ob mouse β-cells may be due to the absence of leptin and mediated by activation of the phospholipase C signaling pathway.

To survive, neurons and other eukaryotic cells must rapidly repair (seal) plasmalemmal damage. Such repair occurs by an accumulation of intracellular vesicles at or near the plasmalemmal disruption. Diacylglycerol (DAG)-dependent and cAMP-dependent proteins are involved in many vesicle trafficking pathways. Although recent studies have implicated the signaling molecule cAMP in sealing, no study has investigated how DAG and DAG-dependent proteins affect sealing and, whether pharmacological inhibition of such proteins could promote immediate repair of damaged mammalian axons. To this end, I investigated the role of DAG, protein kinase C (PKC) and other DAG-activated proteins in plasmalemmal sealing in B104 neurons in vitro and rat sciatic nerves in vivo. Using dye exclusion to assess Ca2+-dependent vesicle-mediated sealing of transected neurites of individually identifiable rat hippocampal B104 cells, I now report that, compared to non-treated controls, sealing probabilities and rates are increased by DAG and cAMP analogs that activate PKC and Munc13-1, and protein kinase A (PKA). Sealing is decreased by inhibiting DAG-activated novel protein kinase C isozymes η (nPKCη) and θ (nPKCθ) and, Munc13-1, the PKC effector myristoylated alanine rich PKC substrate (MARCKS) or phospholipase C (PLC). DAG-increased sealing is prevented by inhibiting MARCKS or PKA. Sealing probability is further decreased by simultaneously inhibiting nPKCη, nPKCθ and PKA. Extracellular Ca2+, DAG or cAMP analogs do not affect this decrease in sealing. I also report that applying inhibitors of nPKC and PKA to rat sciatic axons crush-severed in vivo under physiological calcium, do not promote immediate repair by polyethylene glycol (PEG), as assessed by compound action potential conduction and dye diffusion through crush sites. These and other data suggest that DAG increases sealing through MARCKS and that nPKCη, nPKCθ and PKA are all required to seal plasmalemmal damage in B104 neurons, and likely all eukaryotic cells. / text

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Biochemical processes all involve associations and dissociations of chemical entities. Understanding these is of substantial importance for many modern pharmaceutical applications. In this thesis, longstanding problems with regard to ligand binding are treated with computational methods, applied to proteins of key pharmaceutical importance. Homology modeling, docking, molecular dynamics simulations and free-energy calculations are used here for quantitative characterization of ligand binding to proteins. By combining computational tools, valuable contributions have been made for pharmaceutically relevant areas: a neglected tropical disease, an ion channel anti-drug-target, and GPCR drug-targets. We report three compounds inhibiting cruzain, the main cysteine protease of the protozoa causing Chagas’ disease. The compounds were found through an extensive virtual screening study and validated with experimental enzymatic assays. The compounds inhibit the enzyme in the μM-range and are therefore valuable in further lead optimization studies. A high-resolution crystal structure of the BRICHOS domain is reported, together with molecular dynamics simulations and hydrogen-deuterium exchange mass spectrometry studies. This work revealed a plausible mechanism for how the chaperone activity of the domain may operate. Rationalization of structure-activity relationships for a set of analogous blockers of the hERG potassium channel is given. A homology model of the ion channel was used for docking compounds and molecular dynamics simulations together with the linear interaction energy method employed for calculating the binding free-energies. The three-dimensional coordinates of two GPCRs, 5HT1B and 5HT2B, were derived from homology modeling and evaluated in the GPCR Dock 2013 assessment. Our models were in good correlation with the experimental structures and all of them placed among the top quarter of all models assessed.  Finally, a computational method, based on molecular dynamics free-energy calculations, for performing alanine scanning was validated with the A2A adenosine receptor bound to either agonist or antagonist. The calculated binding free-energies were found to be in good agreement with experimental data and the method was subsequently extended to non-alanine mutations. With extensive experimental mutation data, this scheme is a valuable tool for quantitative understanding of ligand binding and can ultimately be used for structure-based drug design.

Στην παρούσα εργασία συνθέσαμε ένα άμινο-άκυλο- και ένα πεπτίδυλο- ανάλογο της χλωραμφαινικόλης. Τα ανάλογα αυτά ήταν η β-αλανίνη-χλωραμφαινικόλη (β-alaCAM) και η φαινυλαλανίνη-φαινυλαλανίνη-χλωραμφαινικόλη (PhePheCAM). Στην συνέχεια μελετήσαμε την βιολογική συμπεριφορά των αναλόγων αυτών μέσα από την μελέτη της κινητικής της αναστολής του σχηματισμού πεπτιδικού δεσμού που επιφέρουν τα εν λόγω ανάλογα. Σε πρωτεϊνοσυνθετικό σύστημα ριβοσωμάτων εκπορευόμενων από Escherichia coli η σύνθεση ακέτυλο-φαινυλαλάνυλο-πουρομυκίνης πραγματοποιείται μέσω μιας αντίδρασης ψευδοπρώτης τάξεως μεταξύ συμπλέγματος C, δηλαδή ακέτυλο-φαινυλαλάνυλο-poly(U)-ριβοσωμάτων, και περίσσειας πουρομυκίνης. Τόσο η β-alaCAM, όσο και η PhePheCAM μελετήθηκαν ως αναστολείς της αντίδρασης σύνθεσης ακέτυλο-φαινυλαλάνυλο-πουρομυκίνης και τα αποτελέσματα της κινητικής της αναστολής που επέφεραν συγκρίθηκαν με γνωστά από την βιβλιογραφία αντίστοιχα αποτελέσματα που αφορούν τόσο την μητρική ένωση, όσο και άλλα άμινο-άκυλο- και πεπτιδικά ανάλογα αυτής. Αρχικά παρατηρήσαμε ότι, απουσία αναστολέα, η αντίδραση ακολουθεί κινητική πρώτης τάξεως καθόλη την χρονική διάρκεια της χημικής αντίδρασης. Ωστόσο, στη συνέχεια παρατηρήσαμε ότι η παρουσία τόσο της β-alaCAM, όσο και της PhePheCAM είχε σαν αποτέλεσμα διφασικές λογαριθμικές συναρτήσεις συγκέντρωσης – χρόνου, όπου υφίστατο μία αρχική ή πρώτη χρονική φάση και μία τελική ή δεύτερη χρονική φάση της χημικής αντίδρασης πουρομυκίνης. Ακολούθησε λεπτομερής κινητική ανάλυση, αρχικά μέσω διαγραμμάτων διπλού αντιστρόφου για τις αρχικές και τις τελικές κλίσεις των λογαριθμικών χρονοκαμπυλών, καθώς και στη συνέχεια μέσω επαναδιαγραμμάτων αρχικών και τελικών κλίσεων έναντι της συγκέντρωσης του αναστολέα. Με τον τρόπο αυτό υπολογίστηκαν οι κινητικές σταθερές αναστολής Κi οι οποίες και συγκρίθηκαν με την κινητική σταθερά αναστολής της μητρικής ένωσης. Τέλος, μέσω υπολογιστικού προγράμματος προσομοίωσης, σχεδιάστηκαν οι συναρτήσεις της φαινομενικής σταθεράς εξισορρόπησης keq έναντι της συγκέντρωσης του αναστολέα και υπολογίστηκαν οι σταθερές k6 και k7. Tόσο η β-alaCAM όσο και η PhePheCAM εμφάνισαν συμπεριφορά βραδέως προσδενομένου συναγωνιστικού αναστολέα ανεξάρτητα από την συγκέντρωσή τους, σε αντίθεση με την μητρική ένωση η οποία εμφανίζει συμπεριφορά συναγωνιστικού αναστολέα σε μικρές συγκεντρώσεις αυτής και συμπεριφορά μικτού μη-συναγωνιστικού αναστολέα σε μεγαλύτερες συγκεντρώσεις αυτής. H β-alaCAM ευρέθηκε 4,6 φορές περισσότερο βιολογικά δραστική από την PhePheCAM και 14,3 βιολογικά ασθενέστερη από την μητρική ένωση. Σε αντίθεση με τη μητρική ένωση, η οποία δεν υφίσταται ισομερισμό, τόσο η β-alaCAM όσο και η PhePheCAM δίνουν, στην τελική ή δεύτερη χρονική φάση της αντίδρασης πουρομυκίνης, γένεση στο ισομερισμένο σύμπλοκο C*I. Αξιοσημείωτη είναι η παρατήρηση ότι ο σχηματισμός του ισομερισμένου συμπλόκου C*I λαμβάνει χώρα μέσω δύο κινητικών βημάτων στην περίπτωση της β-alaCAM, αλλά μέσω ενός μόνο κινητικού βήματος στην περίπτωση της PhePheCAM. Προτείνουμε, ως μοντέλο επεξηγηματικό του μηχανισμού βιολογικής δράσης και χημικής κινητικής των μελετηθέντων συνθετικών αναλόγων, ότι τόσο η β-alaCAM όσο και η PhePheCAM παρουσιάζουν αυξημένη στερεοχημική ομοιότητα με το 3΄-άκρο του άμινο-άκυλο-tRNA ή με το 3΄-άκρο του πεπτίδυλο-tRNA συγκριτικά με τη μητρική ένωση. Η αυξημένη αυτή στερεοχημική ομοιότητα πιθανότατα εξηγεί τον εκσεσημασμένο συναγωνιστικό χαρακτήρα της αναστολής που εμφανίζουν τα μελετηθέντα ανάλογα συγκριτικά με τη μητρική ένωση, ασχέτως του γεγονότος ότι η συνολική αναστολή που επιφέρουν δεν αποδεικνύεται σε καμία περίπτωση ισχυρότερη της αναστολής που επιφέρει η μητρική ένωση. Για τον λόγο αυτό τα εν λόγω συνθετικά ανάλογα της χλωραμφαινικόλης θα πρέπει να θεωρηθούν παλίνδρομα-ανάστροφα ανάλογα (retro-inverso analogs). / One aminoacyl and one peptidyl analog of chloramphenicol (Cl2CHCO-CAM) were prepared. These are L-β-alaCAM and L-PhePheCAM. The kinetics of inhibition of peptide bond formation by these analogs were examined in a cell-free system which had been used previously for the study of Cl2CHCO-CAM [Drainas et al, Eur. J. Biochem. 1987, 164, 53-58]. In a model cell-free system, derived from Escherichia coli, acetylphenylalanyl-puromycin is produced in a pseudo-first-order reaction between the preformed acetylphenylalanyl/tRNA/poly(U)/ribosome complex (complex C) and excess puromycin. Both L-β-alaCAM and L-PhePheCAM were tested as inhibitors in this reaction. In the absence of inhibitor, the reaction follows first-order kinetics for the entire course of the reaction. In the presence of the analog the reaction gives biphasic log-time plots. The kinetic informations pertaining to the initial and the terminal slopes of the plot are analyzed (initial-slope and terminal-slope analysis). Μοreover, through a computer simulation non-linear regression fitting program, the plots between the keq values and the concentration of the inhibitor [I] were constructed, and consequently the values of k6 and k7 were estimated. Detailed kinetic analysis suggests that both these analogs (I) behave as slow-binding inhibitors and react competitively with complex C to form the complex C*I which is inactive towards puromycin. In the presence of L-β-alaCAM, C*I is formed via a two-step mechanism in which C*I is the product of a slow conformational change of the initial encounter complex CI according to the equation C + I CI C*I. Our results, concerning the two-step mechanism of L-β-alaCAM are in agreement with the results of previous investigations evaluating the potency and kinetic mechanisms of other aminoacyl and peptidyl analogs of chloramphenicol [Michelinaki et al, Mol. Pharmacol. 1997, 51, 139-146]. However, in the presence of L-PhePheCAM, our results are unique because we found evidences that C*I is formed via a one-step mechanism as a product of a slow conformational change according to the equation C + I C*I. The parent compound gives complex inhibition kinetics; increasing the concentration of the parent compound changes the inhibition from competitive to mixed noncompetitive [Drainas et al, Eur. J. Biochem. 1987, 164, 53-58]. In contrast, the analogs give competitive kinetics even at high concentrations of the inhibitor. The following Ki and Ki* values have been determined: Ki = 45 μΜ for L-β-alaCAM, Ki* = 10 μΜ for L-β-alaCAM and Ki* = 46 μM for L-PhePheCAM. If we were to assume that both L-β-alaCAM and L-PhePheCAM behave as classical competitive inhibitors, we could say that L-β-alaCAM is 4.6 times more potent than L-PhePheCAM. On this assumption we could also compare chloramphenicol with L-β-alaCAM and see that L-β-alaCAM is 14.3 times weaker than chloramphenicol (Ki = 0.7 μΜ). It is suggested that as compared with chloramphenicol, both L-β-alaCAM and L-PhePheCAM have increased structural similarity to the 3΄-terminus of aminoacyl-tRNA or of peptidyl-tRNA and this similarity results in a more pronounced competitive inhibition. The results are compared with previous data and discussed on the basis of a possible retro-inverso relationship between chloramphenicol analogs and puromycin.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Mercury is an environmental contaminant, and may accumulate in living organisms causing several damage. Studies have shown that this metal causes several physiological and biochemical alterations in young rats which are prevented by zinc. Thus, this work investigated the in vivo and in vitro effects of HgCl2 and ZnCl2 on alanine aminotransferase (ALT), lactate dehydrogenase (LDH) and glucose 6-phosphatase (G6Pase) activities from liver and kidney of young rats to verify if the physiological and biochemical alterations induced by mercury, and prevented by zinc, are related to hepatic and renal metabolism. Glycemia and tissue glycogen levels (liver, kidney and muscle) were also monitored. Wistar rats were treated (s.c.) with saline or ZnCl2 (27 mg/kg/day) and with saline or HgCl2 (5.0 mg/kg/day) from 3rd to 7th and 8th to 12th days of age, respectively. Pups were sacrificed 24h after the last dose and samples were collected (blood, liver, kidney and muscle). For in vitro experimentation, the samples were collected similarly, with rats of 10 to 13 days old. Regarding in vivo experiments, the mercury treated rats presented an increase around 6 folds of the hepatic ALT activity, without alteration of renal ALT and hepatic LDH activities. Still, the mercury exposure significantly increases in 75% the G6Pase activity. The other parameters, glucose and glycogen, were not altered. The pre-exposure to zinc prevented totally the increase of liver ALT activity and partly the increase of hepatic G6Pase activity induced by mercury. In vitro results revealed that the serum and liver ALT and liver and kidney G6Pase activities were inhibited by mercury. The inhibitory effect may be related to chemical modification of sulfhydryl group of cysteine, since the mercury has great affinity for these groups, which contributes to its toxicity. Zinc inhibited liver and serum ALT activities in concentration of 100 μM. These results show that mercury induces distinct alterations in these enzymes when tested in vivo or in vitro, as well as when different sources of enzyme were used, hepatic and renal. The increased hepatic ALT and G6Pase activities suggest that animals exposed to mercury have an increased gluconeogenic activity in this tissue. Zinc prevents the in vivo effects of mercury on metabolic changes, confirming its important preventive role. / O mercúrio é um elemento tóxico, podendo acumular-se em organismos vivos causando-lhes vários danos. Estudos têm demonstrado que esse metal é capaz de causar várias alterações fisiológicas e bioquímicas em ratos jovens, as quais são prevenidas pela pré-exposição ao zinco. Assim, este trabalho investigou os efeitos in vivo e in vitro do HgCl2 e ZnCl2 sobre as atividades das enzimas alanina aminotransferase (ALT), lactato desidrogenase (LDH) e glicose 6-fosfatase (G6Pase) de fígado e rim de ratos jovens para verificar se as alterações fisiológicas e bioquímicas induzidas pelo mercúrio e impedidas pelo zinco, estão relacionados ao metabolismo hepático e renal. Os níveis glicêmicos e do glicogênio tecidual (fígado, rim e músculo) também foram monitorados. Ratos Wistar com três dias de idade foram tratados (s.c.) com salina ou ZnCl2 (27 mg/kg/dia) durante cinco dias consecutivos (do 3 o ao 7 o dia de idade) e com salina ou HgCl2 (5 mg/kg/dia) por mais cinco dias (do 8 o ao 12 o dia de idade). Os animais foram sacrificados 24 horas após a última dose e as amostras foram coletadas (sangue, fígado, rim e músculo). Para realização dos experimentos in vitro, amostras foram coletadas de maneira similar, com ratos de 10-13 dias de idade. Com relação aos experimentos in vivo, os ratos tratados com mercúrio apresentaram um aumento da atividade da ALT hepática de aproximadamente seis vezes, sem alteração da atividade da ALT renal e LDH hepática. Ainda, a exposição ao mercúrio aumentou significativamente a atividade da G6Pase em 75%. Os outros dois parâmetros, glicose e glicogênio, não foram alterados. A pré-exposição ao zinco preveniu a alteração da atividade da ALT e parcialmente a alteração da atividade da G6Pase hepática induzida pelo mercúrio. Os resultados in vitro demonstraram que as enzimas ALT e LDH sérica e hepática e G6Pase hepática e renal foram inibidas por mercúrio. O efeito inibitório pode estar relacionado às modificações químicas de grupos sulfidrílicos da cisteína, uma vez que o mercúrio tem grande afinidade por esses grupos, o que contribui para a sua toxicidade. O zinco inibiu a atividade da ALT hepática e sérica na concentração de 100 μM. Estes resultados mostram que o mercúrio induziu alterações distintas sobre essas enzimas quando testado in vivo e in vitro, bem como quando testado em enzimas provenientes de diferentes fontes, hepática e renal. O aumento da atividade das enzimas ALT e G6Pase de fígado sugerem que os animais expostos ao mercúrio apresentam um aumento da atividade gliconeogênica. O zinco previne os efeitos in vivo do mercúrio sobre as alterações metabólicas, confirmando seu papel protetor.

VILELA, Rivelino Cunha. Estudo de transições de fase em cristais de l-alanina + ácido oxálico. 2013. 113 f. Tese (Doutorado em Física) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2013. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2015-10-29T21:51:24Z No. of bitstreams: 1 2013_tese_rcvilela.pdf: 12577577 bytes, checksum: 4dc32419c1bbdde79375612c04227181 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2015-11-03T19:48:22Z (GMT) No. of bitstreams: 1 2013_tese_rcvilela.pdf: 12577577 bytes, checksum: 4dc32419c1bbdde79375612c04227181 (MD5) / Made available in DSpace on 2015-11-03T19:48:22Z (GMT). No. of bitstreams: 1 2013_tese_rcvilela.pdf: 12577577 bytes, checksum: 4dc32419c1bbdde79375612c04227181 (MD5) Previous issue date: 2013 / In the present word we have studied the effect of temperature on the Raman spectra of crystals of L-alanine + oxalic acid, C3H8NO2+.C2HO4-. Raman spectroscopy measurements were performed on polycrystalline samples at different temperatures varying in the range from room temperature to T = 20 K; a tentative assignment of all normal modes was furnished. In order to help the understanding of the crystal behavior we have also obtained X-ray diffractograms and studied the dependence of lattice parameters through dilatometry as a function of temperature in the 290 K – 93 K range. The three different techniques allowed us to construct a picture of the material under low temperature conditions. As a consequence we have realized that L-alanine + oxalic acid crystal undergoes three phase transitions at low temperatures. The splitting of a band at 90 cm-1 and an anomaly in one of the lattice parameters are the signature for the first phase transition that is observed at 250 K. At 150 K it was observed the appearance of two new bands in the Raman spectrum and, simultaneously, it was observed change in the curves of a and c lattice parameters. Additionally, it was verified the appearance of new peaks in the X-ray diffractogram at the same temperature, characterizing the second phase transition. At a temperature even lower, at about 43 K, it was verified the occurrence of the third phase transition that has as main characteristic the splitting of two bands that are associated to the lattice modes. Changes in the modes associated with CH3 and NH3+ during the cooling is discussed. An important behavior of the crystal with the cooling process was the red shift of the band of lower frequency, similar to the soft-mode vibration of ferroelectric materials, although the frequency of the mode in L-alanine + oxalic acid does not goes to zero. Based on the results on Raman spectroscopy, dilatometry and X-ray diffraction, and on the possible symmetry sites occupied by the molecules through the O=CC group in the various phases, it is suggested the following sequence of phase transitions D24  C2h5  Cs3  C23, which should occur at 250 K, 150 K and 43 K. / Neste trabalho, estudou-se o efeito da temperatura nos espectros Raman de cristais de L-alanina + ácido oxálico, C3H8NO2+.C2HO4-. Foram realizadas medidas de espectroscopia Raman em policristais a diferentes temperaturas no intervalo compreendido entre a temperatura ambiente e a temperatura de 20 K, sendo fornecida uma identificação tentativa para todos os modos normais de vibração observados. Para auxiliar o entendimento do comportamento do cristal também foram obtidos os difratogramas de raios-X bem como estudada a dependência dos parâmetros de rede em função da temperatura através de dilatometria no intervalo entre 290 K e 93 K. As três técnicas utilizadas em conjunto permitiram mostrar o comportamento estrutural do material em baixas temperaturas. Deste quadro foi possível inferir que os cristais de L-alanina + ácido oxálico apresentam três diferentes transições de fase durante o resfriamento. Em 250 K o aparecimento de um dubleto em 90 cm-1 e a anomalia num dos parâmetros de rede apontam para a ocorrência da primeira transição de fase. Em 150 K surgem pelo menos duas novas bandas no espectro Raman, ao mesmo tempo em que ocorrem bruscas mudanças de inclinação nas curvas que representam as dimensões dos eixos a e c do cristal. Também se verifica que, de forma semelhante ao que ocorre com os espectros Raman, aparecem novos picos no difratograma de raios-X em torno desta temperatura, caracterizando assim a segunda transição de fase. A uma temperatura ainda mais baixa, em torno de 43 K, foi verificada a ocorrência da terceira transição de fase, que tem como principal característica a separação de dois modos Raman associados a modos da rede. Mudanças nos ambientes dos grupos CH3 e do NH3+ durante o resfriamento são discutidas. Um importante aspecto apresentado pelos espectros Raman com o resfriamento da amostra foi o deslocamento da banda de mais baixa energia para menores valores de frequências, semelhantemente ao que ocorre com vibrações do tipo soft-mode em materiais ferroelétricos, embora a frequência do modo no cristal de L-alanina + ácido oxálico não tenha ido à zero. Baseado nos resultados acima e nos possíveis sítios de simetria ocupados pelas moléculas através do grupo O=CC nas diversas fases, sugere-se a seguinte sequência de transições de fase D24 para C2h5 para Cs3 para C23, que aconteceriam, respectivamente, nas temperaturas de 250 K, 150 K e 43 K.

LIMA JÚNIOR, José Alves de. Espectroscopia Raman dos Aminoácidos L - metionina e DL - alanina e de Nanotubos de Carbono. 2008. 214 f. Tese (Doutorado) - Programa de Pós-Graduação em Física, Centro de Ciências, Departamento de Física, Universidade Federal do Ceará, Fortaleza, 2008. / Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-05-13T22:56:00Z No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) / Approved for entry into archive by Edvander Pires(edvanderpires@gmail.com) on 2014-05-14T18:26:53Z (GMT) No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) / Made available in DSpace on 2014-05-14T18:26:53Z (GMT). No. of bitstreams: 1 2008_tese_jalimajúnior.pdf: 3662330 bytes, checksum: ad8b8ed63bf2df476f4e050aae5f5d70 (MD5) Previous issue date: 2008 / This work describes polarized Raman scattering measurements in L-methionine and in DL-alanine (two amino acids) crystals and in several samples of single-walled carbon nanotubes (SWNT). In L-methionine crystal the Raman spectra were obtained from 17 K to 295 K in the spectral range from 50 cm-1 to 3100 cm-1, but no indication of a phase transition was observed. At room temperature, Raman scattering measurements were also performed for pressure up to 5 GPa. Several changes observed in the spectra were interpreted as due to structural phase transition undergone by L-methionine crystal at ~ 2.1 GPa. The results for decompression show that the phase transition is reversible with a hysteresis of ~ 0.8 GPa. In DL-alanine crystal the Raman spectra were obtained at temperatures from 15 K to 295 K over the spectral range 50 cm-1 - 3100 cm-1. No evidence of structural phase transition was found in this range of temperature, although information about diverse modes of the crystal were furnished. Samples of SWNT’s studied were prepared with metallic catalysts using the arc voltaic method. MnNiCo was the main compound of the first series and FeNiCo, the main compound of the second. In both sets it was observed that Cerium (Ce) insertion induces in the sub-set, probed with the 2.41 eV excitation energy, a narrowing of the diameter distribution favoring the tubes with smaller diameter. The Raman scattering measurements in a commercial sample of SWNT’s show a discontinuity at about 2 GPa. The discontinuity was represented by a changing in the slope of the frequency versus pressure for tangential modes. The measurement was performed twice, using two different solutions of surfactants, sodium dodecil sulfate (SDS) and plurocic acid F127 (F127), and the results were similar. The anomaly was interpreted as due to the deformation of the tubes as predicted theoretically. Two sets of three samples of SWNT’s containing different levels of lithium insertion were also analyzed by Raman spectroscopy. Each set of sample was formed by a sample with lithium, a sample without lithium and a sample with partial insertion of lithium. The results show that the lithium is efficiently intercalated with both lithium containing compound (LiCO3/NiO/CoO and LiNi0.5Co0.5O2), but the mechanism of intercalation differs from one to the other. The intercalation is unstable when lithium is intercalated interstitially (LiNi0.5Co0.5O2) and it can be removed almost completely by washing the sample, but if the lithium is intercalated inside the tubes (LiCO3/NiO/CoO) it can not be removed by the same process. / No presente trabalho foram realizadas medidas de espalhamento Raman polarizado em cristais de L-metionina e de DL-alanina (dois aminoácidos) e em diversas amostras de nanotubos de carbono de parede simples (SWNT). As medidas de espalhamento Raman em cristais de L-metionina foram realizadas no intervalo espectral entre 50 cm-1 e 3100 cm-1 desde a temperatura ambiente até a temperatura de 17 K. No intervalo de temperatura estudado a estrutura da L-metionina manteve-se estável. À temperatura ambiente também foram realizadas medidas Raman em altas pressões hidrostáticas. A máxima pressão atingida foi de 4,7 GPa e diversas modificações nos modos associados às unidades CO2, NH3, CC, CS, CH, CH2 e CH3 sugerem que a L-metionina sofre um transição estrutural de fase em torno de 2,1 GPa com histerese de aproximadamente 0,8 GPa. No cristal de DL-alanina foram realizadas medidas de espalhamento Raman no intervalo de temperatura de 15 K a 295 K. Embora nenhuma mudança significativa tenha sido observada neste intervalo de temperatura, os resultados são importantes para se entender o comportamento de uma molécula fundamental na constituição das proteínas. Medidas de espalhamento Raman em SWNT’s foram realizadas em amostras preparadas pela técnica de arco voltáico, utilizando-se vários catalisadores metálicos. As amostras foram divididas em duas séries: A primeira com os catalisadores à base de MnNiCo e a segunda à base de FeNiCo. Em ambas as séries observou-se que a inserção de Cério (Ce) foi responsável por tornar a distribuição de diâmetros do subconjunto ressonante com a energia 2,41 eV mais estreita. Além disso, o máximo da distribuição é deslocado para o azul, provavelmente em conseqüência da seleção de tubos de menor diâmetro dentro do subconjunto estudado. A inserção de Zircônio (Zr) à segunda série não trouxe mudanças significativas. Foram realizadas medidas de espalhamento Raman em função da pressão hidrostática em uma amostra comercial de SWNT. Como fluido transmissor foram utilizadas soluções de dois surfactantes: o dodecil sulfato de sódio (SDS) e o ácido plurônico F127 (F127). Devido à baixa relação sinal-ruído, não foi possível estudar o comportamento dos modos de respiração radial (RBM), mas pela descontinuidade do gráfico da freqüência em função da pressão dos modos tangenciais em aproximadamente 2 GPa é provável que os nanotubos sofram uma transição de fase estrutural nessa pressão, com deformação da seção circular dos tubos como predito por estudos teóricos. Dois conjuntos de amostras contendo diferentes níveis de inserção de lítio também foram estudados por espectroscopia Raman. Cada conjunto era formado por uma amostra sem lítio, uma com lítio e a terceira com inserção parcial de lítio (obtida pela lavagem da amostra que contém lítio). Nos dois conjuntos a inserção foi eficiente, contudo o mecanismo de inserção é diferente de uma série para outra. Na primeira série o catalisador utilizado para a inserção de lítio foi LiNi0,5Co0,5O2. Com este composto o lítio é intercalado intersticialmente e pode ser removido quase que completamente pela lavagem da amostra. Já na segunda série o composto utilizado foi LiCO3/NiO/CoO o que fez com que o lítio fosse intercalado dentro dos tubos de modo a não ser removido pela lavagem da amostra.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Neste trabalho, estudou-se o efeito da temperatura nos espectros Raman de cristais de L-alanina + Ãcido oxÃlico, C3H8NO2+.C2HO4-. Foram realizadas medidas de espectroscopia Raman em policristais a diferentes temperaturas no intervalo compreendido entre a temperatura ambiente e a temperatura de 20 K, sendo fornecida uma identificaÃÃo tentativa para todos os modos normais de vibraÃÃo observados. Para auxiliar o entendimento do comportamento do cristal tambÃm foram obtidos os difratogramas de raios-X bem como estudada a dependÃncia dos parÃmetros de rede em funÃÃo da temperatura atravÃs de dilatometria no intervalo entre 290 K e 93 K. As trÃs tÃcnicas utilizadas em conjunto permitiram mostrar o comportamento estrutural do material em baixas temperaturas. Deste quadro foi possÃvel inferir que os cristais de L-alanina + Ãcido oxÃlico apresentam trÃs diferentes transiÃÃes de fase durante o resfriamento. Em 250 K o aparecimento de um dubleto em 90 cm-1 e a anomalia num dos parÃmetros de rede apontam para a ocorrÃncia da primeira transiÃÃo de fase. Em 150 K surgem pelo menos duas novas bandas no espectro Raman, ao mesmo tempo em que ocorrem bruscas mudanÃas de inclinaÃÃo nas curvas que representam as dimensÃes dos eixos a e c do cristal. TambÃm se verifica que, de forma semelhante ao que ocorre com os espectros Raman, aparecem novos picos no difratograma de raios-X em torno desta temperatura, caracterizando assim a segunda transiÃÃo de fase. A uma temperatura ainda mais baixa, em torno de 43 K, foi verificada a ocorrÃncia da terceira transiÃÃo de fase, que tem como principal caracterÃstica a separaÃÃo de dois modos Raman associados a modos da rede. MudanÃas nos ambientes dos grupos CH3 e do NH3+ durante o resfriamento sÃo discutidas. Um importante aspecto apresentado pelos espectros Raman com o resfriamento da amostra foi o deslocamento da banda de mais baixa energia para menores valores de frequÃncias, semelhantemente ao que ocorre com vibraÃÃes do tipo soft-mode em materiais ferroelÃtricos, embora a frequÃncia do modo no cristal de L-alanina + Ãcido oxÃlico nÃo tenha ido à zero. Baseado nos resultados acima e nos possÃveis sÃtios de simetria ocupados pelas molÃculas atravÃs do grupo O=CC nas diversas fases, sugere-se a seguinte sequÃncia de transiÃÃes de fase D24 para C2h5 para Cs3 para C23, que aconteceriam, respectivamente, nas temperaturas de 250 K, 150 K e 43 K. / In the present word we have studied the effect of temperature on the Raman spectra of crystals of L-alanine + oxalic acid, C3H8NO2+.C2HO4-. Raman spectroscopy measurements were performed on polycrystalline samples at different temperatures varying in the range from room temperature to T = 20 K; a tentative assignment of all normal modes was furnished. In order to help the understanding of the crystal behavior we have also obtained X-ray diffractograms and studied the dependence of lattice parameters through dilatometry as a function of temperature in the 290 K â 93 K range. The three different techniques allowed us to construct a picture of the material under low temperature conditions. As a consequence we have realized that L-alanine + oxalic acid crystal undergoes three phase transitions at low temperatures. The splitting of a band at 90 cm-1 and an anomaly in one of the lattice parameters are the signature for the first phase transition that is observed at 250 K. At 150 K it was observed the appearance of two new bands in the Raman spectrum and, simultaneously, it was observed change in the curves of a and c lattice parameters. Additionally, it was verified the appearance of new peaks in the X-ray diffractogram at the same temperature, characterizing the second phase transition. At a temperature even lower, at about 43 K, it was verified the occurrence of the third phase transition that has as main characteristic the splitting of two bands that are associated to the lattice modes. Changes in the modes associated with CH3 and NH3+ during the cooling is discussed. An important behavior of the crystal with the cooling process was the red shift of the band of lower frequency, similar to the soft-mode vibration of ferroelectric materials, although the frequency of the mode in L-alanine + oxalic acid does not goes to zero. Based on the results on Raman spectroscopy, dilatometry and X-ray diffraction, and on the possible symmetry sites occupied by the molecules through the O=CC group in the various phases, it is suggested the following sequence of phase transitions D24 &#61664; C2h5 &#61664; Cs3 &#61664; C23, which should occur at 250 K, 150 K and 43 K.