<p>This dissertation hypothesizes,</p><p><italic>"It is possible to design a self-assembled, nanoscale, high-speed, resonance energy transfer device exhibiting non-linear gain with a few molecules."</italic></p><p>The report recognizes DNA self-assembly, a relatively inexpensive and a massively parallel fabrication process, as a strong candidate for self-assembled RET systems. It successfully investigates into the design and simulations of a novel sequential self-assembly process employed to realize the goal of creating large, scalable, fully-addressable DNA nanostructure-substrate for future molecular circuitry. </p><p>As a pre-cursor to the final device modeling various RET wire designs for interconnecting nanocircuits are presented and their modeling and simulation results are discussed. A chromophore RET system using a biomolecular sensor as a proof-of-concept argument that shows it is possible to model and characterize chromophore systems as a first step towards device modeling is also discussed. </p><p>Finally, the thesis report describes in detail the design, modeling, characterization, and fabrication of the Closed-Diffusive Exciton Valve: a self-assembled, nanoscale (area of 17.34 nm<super>2</super>), high-speed (3.5 ps to 6 ps) resonance energy transfer device exhibiting non-linear gain using only 10 molecules, thus confirming the hypothesis. It also recognized improvements that can be made in the future to facilitate better device operation and suggested various applications.</p> / Dissertation

The unique environment of CubeSat and small satellite missions allows certain accepted paradigms of the larger satellite world to be investigated in order to trade performance for simplicity, mass, and volume. Peak Power Tracking technologies for solar arrays are generally implemented in order to meet the End-of-Life power requirements for satellite missions given radiation degradation over time. The short lifetime of the generic satellite mission removes the need to compensate for this degradation. While Peak Power Tracking implementations can give increased power by taking advantage and compensating for the temperature cycles that solar cells experience, this comes at the expense of system complexity and, given smart system design, this increased performance is negligible and possibly detrimental. This thesis investigates different Peak Power Tracking implementations and compares them to two Fixed Point implementations as well as a Direct Energy Transfer system in terms of performance and system complexity using computer simulation. This work demonstrates that, though Peak Power Tracking systems work as designed, under most circumstances Direct Energy Transfer systems should be used in small satellite applications as it gives the same or better performance with less complexity.

The use of microfluidic tools to develop two novel approaches to surface-based oligonucleotide hybridization assays has been explored. In one of these approaches, immobilized oligonucleotide probes on a glass surface of a microfluidic channel were able to quantitatively hybridize with oligonucleotide targets that were electrokinetically injected into the channel. Quantitative oligonucleotide analysis was achieved in seconds, with nM detection limits and a dynamic range of 3 orders of magnitude. Hybridization was detected by the use of fluorescently labeled target. The fluorescence intensity profile evolved as a gradient that could be related to concentration, and was a function of many factors including hybridization reaction rate, convective delivery speed, target concentration and target diffusion coefficient. It was possible to acquire kinetic information from the static fluorescence intensity profile to distinguish target concentration, and the length and base-pair mismatches of target sequences. Numerical simulations were conducted for the system, and fit well with the experimental data. In a second approach, a solid-phase nucleic acid assay was developed using immobilized Quantum Dot (QD) bioprobes. Hybridization was used to immobilize QDs that had been coated with oligonucleotides having two different sequences. The hybridization of one oligonucleotide sequence conjugated to a QD (a linker sequence) with a complementary sequence that was covalently attached to a glass substrate of a microfluidic channel was shown to be an immobilization strategy that offered flexibility in assay design, with intrinsic potential for quantitative replacement of the sensing chemistry by control of stringency. A second oligonucleotide sequence conjugated to the immobilized QDs provided for the selective detection of target nucleic acids. The microfluidic environment offered the ability to manipulate flow conditions for control of stringency and increasing the speed of analytical signal by introduction of convective delivery of target sequences to the immobilized QDs. This work introduces a stable and adaptable immobilization strategy that facilitates solid-phase QD-bioprobe assays in microfluidic platforms.

A new and general procedure is described for a detailed analysis of time-resolved fluorescence depolarisation data in the presence of electronic energy migration. An isotropic ensemble of bifluorophoric molecules (D1-R-D2) has been studied to demonstrate its utility. Intramolecular donor-donor energy migration occurs between the two donor groups (D), which are covalently connected to a rigid linker group (R). These groups undergo restricted reorientational motions with respect to the R group. The analysis of depolarisation data basically involves the search for best-fit parameters which describe the local reorienting motions, the interfluorophore D1-D2 distance, as well as the mutual orientations of the donors. For this, the analysis is partly performed in the Fourier domain and the best-fit parameters are determined by using an approach based on a Genetic Algorithm. The energy migration process has been described by using Monte Carlo simulations and an extended Förster theory. It is found that this theory provides the least time-consuming computational method. Since one-photon and two-photon excited fluorescence experiments can be applied for energy migration studies, a general and unified theoretical formulation is given. To exemplify the developed quantitative approach the depolarisation of the fluorescence in the presence of electronic energy migration within a bis-(9-anthrylmethylphosphonate) bisteroid molecule has been studied by time-resolved two-photon excited fluorescence depolarisation experiments. To solely obtain information about local reorientations of the 9-anthrylmethyl group, also the mono-(9-anthrylmethylphosphonate) bisteroid was studied, which enabled modelling of the ordering potential of the donor. Values of the two-photon absorption tensor components were obtained. To describe the discrepancy between the measured values of the initial anisotropy and fundamental anisotropy predicted by theory the distribution of absorption tensor caused by fast processes have been introduced. An angular parameter of absorption tensor was determined. Reasonable values of the distance between the 9-anthrylmethyl groups, as well as for their mutual orientation were obtained.

Les performances des techniques de bioimagerie et de biodétection peuvent être améliorées grâce aux nanoparticules fluorescentes (NPs) permettant un transfert d’énergie résonante de type Förster (FRET) efficace. Le but de mon projet de thèse est le développement de NPs polymériques brillantes et ultrastables encapsulant des fluorophores, capables de produire un FRET au-delà du rayon de Förster. Il a été montré que les groupements encombrés sont essentiels pour minimiser l’auto-extinction et le blanchiment des fluorophores encapsulés. Par ailleurs, la matrice polymérique joue un rôle crucial dans le contrôle de l’effet collaboratif entre fluorophores du au transfert d’énergie d’excitation. Puis, en utilisant cet effet collaboratif entre fluorophores, nous avons conçu des NPs présentant une photocommutation efficace, ainsi qu'un phénomène de "light harvesting" très important. Enfin, de très petites NPs avec un FRET efficace à leur surface ont été élaborées et appliquées pour la détection ultra-sensible de protéines. Les résultats obtenus fournissent de nouvelles perspectives dans le développement des nanoparticules brillantes avec un transfert d'énergie efficace, ainsi que des nano-sondes pour la détection de molécules uniques. / Performance of biosensing and bioimaging techniques can be improved by fluorescent nanoparticles (NPs) capable of efficient Förster resonance energy transfer (FRET). The aim of my PhD project is to develop bright and photostable dye-loaded polymer NPs capable to undergo efficient FRET beyond the Förster radius. We showed that bulky groups are essential for minimizing self-quenching and bleaching of encapsulated dyes. Moreover, polymer matrix plays a crucial role in controlling the inter-fluorophore communication by excitation energy transfer. Then, by exploiting communication of dyes, we designed NPs exhibiting efficient photoswitching as well as giant light-harvesting. Finally, very small NPs with efficient FRET to their surface were developed and applied for ultra-sensitive molecule detection of proteins. The obtained results provide new insights in the development of bright nanoparticles with efficient energy transfer as well as nano-probes for single-molecule detection.

The work summarizes basic theory of relaxation, energy transfer and decoher- ence in photosynthetic molecular aggregates described as open quantum systems and basic theory of third order coherent non-linear spectroscopy. The work presents two methods for calculation of photo-induced dynamics of molecular aggregates. The methods relax certain approximations of the theories commonly used to model the relaxation and energy transfer in the molecular systems on the sub-picosecond time scale. The first theory derived in the formalism of para- metric projection operators accounts for correlations in a second-order non-linear response-function that are usually neglected in the formalism of master equations. The second theory represents stochastic model of exact dynamics via the cumulant expansion. The work also presents an analysis of importance of the secular and the Markov approximations in the description of dynamics derived in the second-order perturbation theory in the system-bath coupling with emphasis on the excitonic coherence lifetime.

Cette thèse s’inscrit dans le cadre d’une collaboration entre Hong Kong Baptist University (Dr. Gary K-L Wong) et le Laboratoire d'Ingénierie Moléculaire Appliquée à l'Analyse (LIMAA - Dr. Loïc Charbonnière) financé par la région Alsace afin de synthétiser des nouvelles nanosondes pour la détection, l’imagerie et le traitement du cancer. Le premier travail a été de synthétiser des nouvelles nanoparticules ultrabrillantes hybrides. Elles ont été obtenues à partir d’un noyau La0.9Tb0.1F3 et recouvertes de différents ligands. Grâce au mécanisme d’effet d’antenne, la brillance des nanoparticules a été considérablement améliorée. Le deuxième travail a été de synthétiser un nouveau ligand pour photosensibiliser les nanoparticules La0.90Eu0.1F3 hydrosolubles afin d’améliorer l’émission de l’europium. Un second ligand et des nouvelles nanoparticules hétérométalliques ont été synthétisées dans le but de favoriser le transfert d’énergie des ions Tb(III) à la surface des NPs vers les ions Eu(III) dans le noyau des nanoparticules pour obtenir des temps de vie très longs et un rendement quantique exceptionnel en solution aqueuse. Le dernier travail a été de fonctionnaliser des nanoparticules de g-C3N4 (graphitic-carbon nitride) par des porphyrines. Les porphyrines ont été synthétisées pour générer de l’oxygène singulet (1O2), pour accueillir un ion Ga3+ dans sa cavité et deux espaceurs différents pour être couplés aux nanoparticules. Ce système a pour objectif d’être sensible au pH, être un agent théranostique pour l’imagerie TEP et la thérapie PDT. / This joint PhD program is part of a collaboration between Hong Kong Baptist University (Dr. Gary K-L Wong) and Laboratoire d'Ingénierie Moléculaire Appliquée à l'Analyse (LIMAA - Dr. Loïc Charbonnière) funded by the Alsace region to synthesize new nanoprobes for sensing, imaging, and inhibiting cancer diseases. The first work was to synthesize new hybrid ultrabright nanoparticles. They have been obtained from a La0.9Tb0.1F3 core and coated by different ligands. Thanks to a mechanism of antenna effect, the brightness of the nanoparticles has been significantly improved. The second work was to synthesize a new ligand to photosensitize water-soluble La0.90Eu0.1F3 nanoparticles in order to improve the emission of europium. A second ligand and new heterometallic nanoparticles have been synthesized with the aim to promote the energy transfer from Tb(III) ions on the surface of the NPs to Eu(III) ions in the core of the nanoparticles and to get a very long excited-state lifetime and an exceptional quantum yield in aqueous solution. The last work was to functionalize water-soluble graphitic-carbon nitride (g-C3N4) nanoparticles by porphyrins. The porphyrins have been synthesized to generate singlet oxygen (1O2), to host a Ga3+ ion inside their cavity and with two different linkers to be coupled to nanoparticles. This system aims to be a pH sensor, and a PDT and PET theranostic agent.

Submitted by Maike Costa (maiksebas@gmail.com) on 2016-05-11T11:38:41Z No. of bitstreams: 1 arquivo total.pdf: 5689290 bytes, checksum: 55be9a3cf14a111bd7b7407cbca5df8e (MD5) / Made available in DSpace on 2016-05-11T11:38:41Z (GMT). No. of bitstreams: 1 arquivo total.pdf: 5689290 bytes, checksum: 55be9a3cf14a111bd7b7407cbca5df8e (MD5) Previous issue date: 2015-08-07 / The photoluminescence efficiency in compounds of lanthanide ions is a result of the complex balance between absorption of photons, energy transfer and quenching mechanisms, among which the multiphonon decay and suppression mediated by low energy ligand-to-metal charge transfer states (LMCT) which might be generated by ligands that have a low oxidation potential, for instance the NCS–. Less than a decade ago, this process was described mainly in terms of the energy transfer between 4f states and LMCT states, not being considered the participation of intraligands states. In the present study, we investigated the photoluminescent properties of new lanthanide isothiocyanates coordination complexes with N-acetyl-2-aminopyridine, N-benzoyl-2-aminopyridine and N-benzoyl-2- aminopyrimidine as ligands. We also synthesized the well-known complexes of formulas [Ln(NCS)3(phen)3] (H2O), and [Ln(NO3)3(Phen)2] with phen = 1,10-phenanthroline. The complexes were characterized via CHN elemental analysis, vibrational spectroscopy, complexometric titration and thermogravimetric analysis. Their spectroscopic properties were investigated via molecular diffuse reflectance, excitation and emission spectroscopy along with time decay of the emitting states. The results from the analysis of emission spectroscopy and photoluminescence excitation, as well as the lifetimes measurements of the emitting states of the investigated complexes provided what we believe to be the most expressive experimental demonstration of the luminescence quenching via triplet-LMCT energy transfer process in Eu(III) complex so far. / A eficiência na fotoluminescência em compostos de íons lantanídeos é o resultado de um balanço complexo entre absorção de fótons, transferência de energia e mecanismos supressores, dentre os quais se destacam o decaimento multifônon e a supressão mediada por estados de transferência de carga ligante-metal (TCLM) de baixa energia, que pode ser gerado por ligantes que apresentam baixo potencial de oxidação, a exemplo do NCS–. Há menos de uma década, este processo era descrito essencialmente em termos da transferência de energia entre estados 4f e os estados TCLM, não sendo considerada a participação dos estados intraligantes. Neste trabalho, investigamos as propriedades fotoluminescentes de novos compostos de coordenação de isotiocianatos de lantanídeos com os ligantes N-acetil- 2-aminopiridina, N-benzoil-2-aminopiridina e N-benzoil-2-aminopirimidina. Sintetizamos, também, os complexos já conhecidos, de fórmulas gerais [Ln(NCS)3(phen)3] (H2O) e [Ln(NO3)3(phen)2] com phen= 1,10-fenantrolina. Os complexos foram caracterizados por análise elementar de CHN, espectroscopia vibracional na região do infravermelho, análise termogravimétrica e titulação complexométrica e suas propriedades espectroscópicas foram investigadas por espectroscopias molecular de reflectância difusa e de excitação e emissão bem como os tempos de decaimento dos estados emissores. Os resultados obtidos a partir das análises de espectroscopia de emissão e excitação da fotoluminescência, assim como as medidas de tempos de vida dos estados emissores dos complexos investigados proporcionaram o que acreditamos ser a demonstração experimental mais expressiva, até então, do processo de supressão da luminescência mediada pelo processo de transferência de energia tripleto-TCLM em complexos do íon Eu(III).

Submitted by ANA KARLA PEREIRA RODRIGUES (anakarla_@hotmail.com) on 2017-07-31T14:45:43Z No. of bitstreams: 1 arquivototal.pdf: 9976488 bytes, checksum: d0e80f609f413107e918fa94fe016bad (MD5) / Made available in DSpace on 2017-07-31T14:45:43Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 9976488 bytes, checksum: d0e80f609f413107e918fa94fe016bad (MD5) Previous issue date: 2017-02-13 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / This work reports the synthesis, characterization and investigation of the luminescent properties of new lanthanide -diketonate complexes, Ln(- dic)2(NO3)L2, Ln(TTA)3L2 and Ln(DBM)3L (TPPO), where thenoyltrifluoroacetone (TTA) and dibenzoylmethane (DBM), L = triphenylphosphine oxide (TPPO), tributylphosphine oxide (TBPO), and trioctylphosphine oxide (TOPO). Eu3+ ion complexes were also synthesized with triphenylarsine oxide (TPAsO) and tricyclohexylphosphine (TCHPO) as auxiliary ligands. The complexes were characterized by complexometric titration with EDTA, CHN elemental analysis, Fourier transform infrared (FTIR) absorption spectroscopy and thermogravimetric analysis (TGA). The photoluminescent properties in the visible and near infrared (NIR) regions of the synthesized complexes were investigated from excitation, emission and luminescence decay curves. The excitation spectra are characterized by the presence of large bands associated with transitions centered on the ligands, evidencing the efficiency of the luminescence sensitization by the antenna ligands. The emission spectra in the visible region of the compounds of the Sm3+ and Eu3+ ions show narrow bands attributed to intraconfigurationtransitions and are dominated by the hypersensitive transitions (~645 nm) and (~612 nm). The values of the intensity parameters and for the complexes of Sm3+ and Eu3+ presented a good correlation, evidencing that the chemical environment influence in a similar way the spectroscopic properties of these ions. The photoluminescent properties of the Eu3+ ion complexes were investigated by the intensity parameters and , radiative and nonradiative ( and ), lifetime of the emitting state () and quantum emission efficience . The highest values of are found for Eu(-dic)2(NO3)L2 complexes, in the range of 51-86%. It was observed that the Eu(-dic)3L2 compounds exhibited shorter lifetimes, which may be related to the presence of a suppressor channel, resulting in higher values of . The intensity parameters and vary only slightly when changes occur in the number and nature of the ligands of the first coordination sphere, with parameter being more sensitive to changes in coordination geometry. The emission spectra in the NIR region of the bis- and trisdiketonate complexes of Pr3+, Nd3+, Sm3+, Er3+ and Yb3+ ions present characteristic luminescence. Changes in the nature and number of ligands coordinated to the Ln3+ ion slightly influence the spectral profiles. The results obtained for the studied systems suggest that these are potential candidates to act as Molecular Light Converting Devices. / Este trabalho reporta a síntese, caracterização e investigação das propriedades luminescentes de -dicetonatos de íons lantanídos, Ln(- dic)2(NO3)L2, Ln(TTA)3L2 e Ln(DBM)3L, em que Ln3+ = Pr3+, Nd3+, Sm3+, Eu3+, Er3+ e Yb3+, -dic = 2-tenoilltrifluoroacetona (TTA) e dibenzoilmetano (DBM), L = óxido de trifenilfosfina (TPPO), tributilfosfina (TBPO) e trioctilfosfina (TOPO). Para os compostos do íon Eu3+, foram também sintetizados os complexos com o óxido de trifenilarsina (TPAsO) e triciclohexilfosfina (TCHPO) como ligantes auxiliares. Os complexos sintetizados foram caracterizados por titulação complexométrica com EDTA, análise elementar CHN, espectroscopia de absorção na região do infravermelho com transformada de Fourier (FTIR) e análise termogravimétrica (TGA). As propriedades fotoluminescentes nas regiões do visível e infravermelho próximo (NIR) dos complexos sintetizados foram investigadas a partir dos espectros de excitação, emissão e curvas de decaimento de luminescência. Os espectros de excitação são caracterizados pela presença de bandas largas associadas às transições centradas nos ligantes , evidenciando a eficiência na sensibilização da luminescência pelos ligantes antenas. Os espectros de emissão, na região do visível, dos compostos dos íons Sm3+ e Eu3+, exibem bandas finas oriundas das transições intraconfiguracionaise são dominados pelas transições hipersensíveis (~645 nm) e (~612 nm). Os valores dos parâmetros de intensidade e dos complexos de Sm3+ e Eu3+ apresentaram uma boa correlação, evidenciando que o ambiente químico influência de maneira semelhante as propriedades espectroscópica destes íons. As propriedades fotoluminescentes dos complexos do íon Eu3+ foram investigados por meio dos parâmetros de intensidade e , taxas de radiativa e nãoradiativa ( e ), tempo de vida do estado () e, eficiência quântica de emissão ( ). Os maiores valores de são encontrados para os complexos Eu(- dic)2(NO3)L2, na faixa de 51-86%. Observou-se que os compostos Eu(-dic)3L2 exibiram tempo de vida mais curto, o que pode estar relacionado com a presença de uma canal supressor, resultando assim em maiores valores de . Os parâmetros de intensidade e , variam apenas ligeiramente quando ocorre alterações no número e na natureza dos ligantes da primeira esfera de coordenação, sendo o 2 mais sensível as alterações na geometria de coordenação. Os espectros de emissão na região do NIR dos complexos bis- e tris-dicetonatos dos íons Pr3+, Nd3+, Sm3+, Er3+ e Yb3+ apresentam luminescência característica. As alterações na natureza e número de ligantes coordenados ao íon Ln3+ influenciam ligeiramente os perfis espectrais. Os resultados obtidos para os sistemas estudados sugerem que estes são potenciais candidatos a atuarem como Dispositivos Moleculares Conversores de Luz.

Realizamos estudos, por espectroscopia de fluorescência de estado estacionário e resolvida no tempo, de dinâmica conformacional de três famílias de peptídeos: o terminal carboxílico do peptídeo neuroendócrino (7B2CT); o peptídeo estimulador do melanócito (alfa-MSH); e os peptídeos derivados da seqüência consensual de peptídeos que se ligam a heparina (peptídeo Cardin). Utilizamos os métodos de fluorescência baseados na supressão da emissão do fluoróforo presente no peptídeo, tanto por interação colisional com um supressor como por transferência de energia para um grupo aceitador presente no peptídeo. No segundo caso, dentro da hipótese de que diferentes conformações do peptídeo estão presentes durante o decaimento da fluorescência, supusemos que o decaimento da intensidade era modulado por uma função de distribuição de distâncias doador-aceitador, f(r). Foi desenvolvido um procedimento computacional usando o programa CONTIN, para recuperar, a partir dos dados de fluorescência resolvida no tempo, a distribuição de distância entre o doador e o aceitador presentes nos peptídeos. A metodologia se mostrou útil para obter informações quantitativas sobre a dinâmica conformacional dos peptídeos, sua dependência com o solvente e sua interação com outras moléculas presentes no meio. O peptídeo 7B2CT e seus análogos A12 e A18 foram estudados pela fluorescência da tirosina, presente na posição cinco na seqüência de aminoácidos. Não houve diferenças significativas no decaimento da intensidade, no decaimento da anisotropia e na supressão por iodeto entre os três peptídeos, que pudessem ser correlacionados com as diferenças observadas na inibição da pro-hormone convertase 2 (PC2). O peptídeo alfa-MSH e seu análogo mais potente [Nle(4),0-Phe(7)] alfa-MSH (NDP-alfa-MSH), que contém o resíduo fluorescente triptofano, foram modificados no seu terminal amino com o grupo ácido amino benzóico (Abz), e foram estudados por métodos de fluorescência. Observamos transferência de energia entre o resíduo triptofano, atuando como doador, e o aceitador o-Abz. Verificamos a uma ampla distribuição de distâncias Trp-o-Abz para o alfa-MSH em água, enquanto três populações de distâncias foram observadas para o análogo modificado NDP-alfa-MSH em água, indicando estados com conformações distintas para o petídeo sintético, comparado com o hormônio nativo. Medidas em trifluoroetanol resultaram em duas populações de distâncias, tanto para o hormônio nativo como para o hormônio análogo, refletindo a diminuição, induzida pelo solvente, das conformações disponíveis para os peptídeos. Os peptídeos Cardin foram estudados na presença de heprarina, de micelas de SDS e na mistura TFE/água. O grupo fluorescente Abz foi incorporado no terminal amino e o grupo aceitador etilenodiamina-N-[2,4- dinitrofenil] (Eddnp) foi incorporado ao terminal carboxílico dos peptídeos. A distribuição de distâncias entre as extremidades, recuperadas dos dados de fluorescência resolvida no tempo, indicaram a presença de conformações estendidas em solução aquosa e a ocorrência de conformações compactas na interação com heparina e SDS ou em soluções com TFE. As distâncias entre as extremidades recuperadas foram maiores que aquelas esperadas para osI peptídeos na conformação hélice alfa, sugerindo a ocorrência de estruturas dobradas além da hélice alfa. A metodologia da transferência de energia se mostrou útil para os estudos de dinâmica de peptídeos em solução. / Steady state and time-resolved fluorescence spectroscopy were used to study the conformational dynamics of three families of peptides: the carboxyl terminal of the neuroendocrine peptide (782Cl), the alpha melanocytestimulating hormone (alpha-MSH) and heparin-binding consensus sequence peptides (Cardin motif peptides). The fluorescence methods were based on quenching of the emission of a fluorophore present in the peptide, either by collisional interaction with a quencher, as by energy transfer to an acceptor group. In the second case, within the hypothesis that different peptide conformations are in equilibrium during the fluorescence decay, we supposed that the intensity decay was modulated by an acceptor-donor distance distribution function, f(r). A computational procedure was developed using the CONTIN program, to recover, from the time-resolved fluorescence data, the distance distribution between donor and acceptor groups attached to the peptides. The methodology proved to be useful to provide quantitative information about conformational dynamics of peptides, its dependency on the solvent and its interaction with other molecules present in the medium. The peptide 782CT and its analogs A12 and A18 were studied by examination of fluorescence from the tyrosine residue present in the position five of the amino acid sequence. There were no appreciable differences in the intensity decay, anisotropy decay and iodide quenching between the three peptides, that could be correlated to observed differences in the inhibition of the pro-hormane convertase 2 (PC2). The peptide hormone alpha-MSH and its more potent analog [Nle(4),0- Phe(7)]alpha-MSH (NDP-alpha-MSH), containing the fluorescent residue tryptophan, were labeled at the amino terminal with the amino benzoic acid (Abz) group, and were also examined by fluorescence methods. We observed energy transfer between the tryptophan residue acting as donor and Abz as acceptor, and verified a broad Trp-o-Abz distance distribution for alpha-MSH in aqueous medium, while three different distance populations could be identified for the labeled analog NDP-alpha-MSH in water, indicating distinct conformational states for the synthetic peptide, compared with the native hormone. Measurements in trifluoroethanol resulted in the recovery of two Abzlrp distance populations, both for the native and the analog hormones, reflecting the decrease, induced by the solvent, of the conformational states available to the peptides. The Cardin motif peptides were examined in the presence of heparin, SDS micelles and in TFE/water mixtures. The fluorescent group Abz was attached to the amino terminal and the acceptor group N-(2,4 dinitrophenyl)ethylenediamine (Eddnp) was bound to the carboxyl terminal of the peptides. The end-to-end distance distribution recovered from time-resolved fluorescence data indicated extend conformation in aqueous medium and the occurrence of compact conformations under interaction with heparin and SDS or in the medium containing TFE. The end-to-end distances recovered were lower than those expected for the peptides in alpha helix conformation, suggesting the occurrence of turned structures beyond the alpha helix. The energy transfer methodology shows to be useful to study conformational dynamics of peptides in solution.