Drug/protein interactions studied by time-resolved fluorescence spectroscopy

[EN] We report here on a recent time-resolved fluorescence study [1] of the interaction between flurbiprofen (FBP), a chiral non-steroidal anti-inflammatory drug, and human serum albumin (HSA), the main transport protein in the human body. We compare the results obtained for the drug-protein complex with those of various covalently linked flurbiprofen-tryptophan dyads having well-defined geometries. In all cases stereoselective dynamic fluorescence quenching is observed, varying greatly from one system to another. In addition, the fluorescence anisotropy decays also display a clear stereoselectivity. For the drug-protein complexes, this can be interpreted in terms of the protein microenvironment playing a significant role in the conformational relaxation of FBP, which is more restricted in the case of the (R)-enantiomer.Gustavsson, T.; Markovitsi, D.; Vayá Pérez, I.; Bonancía Roca, P.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2014). Drug/protein interactions studied by time-resolved fluorescence spectroscopy. Proceedings of SPIE. 9165:1-4. doi:10.1117/12.2063917S149165Vayá, I., Bonancía, P., Jiménez, M. C., Markovitsi, D., Gustavsson, T., & Miranda, M. A. (2013). Excited state interactions between flurbiprofen and tryptophan in drug–protein complexes and in model dyads. Fluorescence studies from the femtosecond to the nanosecond time domains. Physical Chemistry Chemical Physics, 15(13), 4727. doi:10.1039/c3cp43847cCohen, B., Martin Álvarez, C., Alarcos Carmona, N., Organero, J. A., & Douhal, A. (2011). Proton-Transfer Reaction Dynamics within the Human Serum Albumin Protein. The Journal of Physical Chemistry B, 115(23), 7637-7647. doi:10.1021/jp200294qVayá, I., Jiménez, M. C., & Miranda, M. A. (2007). Excited-State Interactions in Flurbiprofen−Tryptophan Dyads. The Journal of Physical Chemistry B, 111(31), 9363-9371. doi:10.1021/jp071301zAbad, S., Pischel, U., & Miranda, M. A. (2005). Wavelength-Dependent Stereodifferentiation in the Fluorescence Quenching of Asymmetric Naphthalene-Based Dyads by Amines. The Journal of Physical Chemistry A, 109(12), 2711-2717. doi:10.1021/jp047996aChemPhysChem. (s. f.). doi:10.1002/(issn)1439-7641Schröder, G. F., Alexiev, U., & Grubmüller, H. (2005). Simulation of Fluorescence Anisotropy Experiments: Probing Protein Dynamics. Biophysical Journal, 89(6), 3757-3770. doi:10.1529/biophysj.105.06950

Stereodifferentiation in the intramolecular singlet excited state quenching of hydroxybiphenyl-tryptophan dyads

The photochemical processes occurring in diastereomeric dyads (S, S)-1 and (S, R)-1, prepared by conjugation of (S)-2-(2-hydroxy-1,1'-biphenyl-4-yl) propanoic acid ((S)-BPOH) with (S)- and (R)-Trp, have been investigated. In acetonitrile, the fluorescence spectra of (S, S)-1 and (S, R)-1 were coincident in shape and position with that of (S)-BPOH, although they revealed a markedly stereoselective quenching. Since singlet energy transfer from BPOH to Trp is forbidden (5 kcal mol(-1) uphill), the quenching was attributed to thermodynamically favoured (according to Rehm-Weller) electron transfer or exciplex formation. Upon addition of 20% water, the fluorescence quantum yield of (S)-BPOH decreased, while only minor changes were observed for the dyads. This can be explained by an enhancement of the excited state acidity of (S)-BPOH, associated with bridging of the carboxy and hydroxy groups by water, in agreement with the presence of water molecules in the X-ray structure of (S)-BPOH. When the carboxy group was not available for coordination with water, as in the methyl ester (S)-BPOHMe or in the dyads, this effect was prevented; accordingly, the fluorescence quantum yields did not depend on the presence or absence of water. The fluorescence lifetimes in dry acetonitrile were 1.67, 0.95 and 0.46 ns for (S)-BPOH, (S, S)-1 and (S, R)-1, respectively, indicating that the observed quenching is indeed dynamic. In line with the steady-state and time-resolved observations, molecular modelling pointed to a more favourable geometric arrangement of the two interacting chromophores in (S, R)-1. Interestingly, this dyad exhibited a folded conformation in the solid state.Financial support from the Spanish Government (CTQ2010-14882, BES-2008-003314, JCI-2011-09926, PR2011-0581), from the Generalitat Valenciana (Prometeo 2008/090) and from the Universitat Politecnica de Valencia (PAID 05-11, 2766) is gratefully acknowledged.Bonancía Roca, P.; Vayá Pérez, I.; Markovitsi, D.; Gustavsson, T.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2013). Stereodifferentiation in the intramolecular singlet excited state quenching of hydroxybiphenyl-tryptophan dyads. Organic and Biomolecular Chemistry. 11(12):1958-1963. https://doi.org/10.1039/c3ob27278hS195819631112Jiménez, M. C., Pischel, U., & Miranda, M. A. (2007). Photoinduced processes in naproxen-based chiral dyads. Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 8(3), 128-142. doi:10.1016/j.jphotochemrev.2007.10.001Abad, S., Pischel, U., & Miranda, M. A. (2005). Wavelength-Dependent Stereodifferentiation in the Fluorescence Quenching of Asymmetric Naphthalene-Based Dyads by Amines. The Journal of Physical Chemistry A, 109(12), 2711-2717. doi:10.1021/jp047996aAbad, S., Vayá, I., Jiménez, M. C., Pischel, U., & Miranda, M. A. (2006). Diastereodifferentiation of Novel Naphthalene Dyads by Fluorescence Quenching and Excimer Formation. ChemPhysChem, 7(10), 2175-2183. doi:10.1002/cphc.200600337Bonancía, P., Vayá, I., Climent, M. J., Gustavsson, T., Markovitsi, D., Jiménez, M. C., & Miranda, M. A. (2012). Excited-State Interactions in Diastereomeric Flurbiprofen–Thymine Dyads. The Journal of Physical Chemistry A, 116(35), 8807-8814. doi:10.1021/jp3063838Paris, C., Encinas, S., Belmadoui, N., Climent, M. J., & Miranda, M. A. (2008). Photogeneration of 2-Deoxyribonolactone in Benzophenone−Purine Dyads. Formation of Ketyl−C1′ Biradicals. Organic Letters, 10(20), 4409-4412. doi:10.1021/ol801514vBelmadoui, N., Encinas, S., Climent, M. J., Gil, S., & Miranda, M. A. (2006). Intramolecular Interactions in the Triplet Excited States of Benzophenone–Thymine Dyads. Chemistry - A European Journal, 12(2), 553-561. doi:10.1002/chem.200500345Lhiaubet-Vallet, V., Boscá, F., & Miranda, M. A. (2007). Stereodifferentiating Drug−Biomolecule Interactions in the Triplet Excited State:  Studies on Supramolecular Carprofen/Protein Systems and on Carprofen−Tryptophan Model Dyads. The Journal of Physical Chemistry B, 111(2), 423-431. doi:10.1021/jp066968kVayá, I., Pérez-Ruiz, R., Lhiaubet-Vallet, V., Jiménez, M. C., & Miranda, M. A. (2010). Drug–protein interactions assessed by fluorescence measurements in the real complexes and in model dyads. Chemical Physics Letters, 486(4-6), 147-153. doi:10.1016/j.cplett.2009.12.091Seedher, N., & Bhatia, S. (2005). Mechanism of interaction of the non-steroidal antiinflammatory drugs meloxicam and nimesulide with serum albumin. Journal of Pharmaceutical and Biomedical Analysis, 39(1-2), 257-262. doi:10.1016/j.jpba.2005.02.031SEEDHER, N., & BHATIA, S. (2006). Reversible binding of celecoxib and valdecoxib with human serum albumin using fluorescence spectroscopic technique. Pharmacological Research, 54(2), 77-84. doi:10.1016/j.phrs.2006.02.008Nanda, R. K., Sarkar, N., & Banerjee, R. (2007). Probing the interaction of ellagic acid with human serum albumin: A fluorescence spectroscopic study. Journal of Photochemistry and Photobiology A: Chemistry, 192(2-3), 152-158. doi:10.1016/j.jphotochem.2007.05.018Zhou, B., Li, R., Zhang, Y., & Liu, Y. (2008). Kinetic analysis of the interaction between amphotericin B and human serum albumin using surface plasmon resonance and fluorescence spectroscopy. Photochemical & Photobiological Sciences, 7(4), 453. doi:10.1039/b717897bVahedian-Movahed, H., Saberi, M. R., & Chamani, J. (2011). Comparison of Binding Interactions of Lomefloxacin to Serum Albumin and Serum Transferrin by Resonance Light Scattering and Fluorescence Quenching Methods. Journal of Biomolecular Structure and Dynamics, 28(4), 483-502. doi:10.1080/07391102.2011.10508590Katrahalli, U., Kalalbandi, V. K. A., & Jaldappagari, S. (2012). The effect of anti-tubercular drug, ethionamide on the secondary structure of serum albumins: A biophysical study. Journal of Pharmaceutical and Biomedical Analysis, 59, 102-108. doi:10.1016/j.jpba.2011.09.013El-Kemary, M., Gil, M., & Douhal, A. (2007). Relaxation Dynamics of Piroxicam Structures within Human Serum Albumin Protein. Journal of Medicinal Chemistry, 50(12), 2896-2902. doi:10.1021/jm061421fTormo, L., Organero, J. A., Cohen, B., Martin, C., Santos, L., & Douhal, A. (2008). Dynamical and Structural Changes of an Anesthetic Analogue in Chemical and Biological Nanocavities. The Journal of Physical Chemistry B, 112(43), 13641-13647. doi:10.1021/jp803083yTardioli, S., Lammers, I., Hooijschuur, J.-H., Ariese, F., van der Zwan, G., & Gooijer, C. (2012). Complementary Fluorescence and Phosphorescence Study of the Interaction of Brompheniramine with Human Serum Albumin. The Journal of Physical Chemistry B, 116(24), 7033-7039. doi:10.1021/jp300055cVayá, I., Jiménez, M. C., & Miranda, M. A. (2007). Excited-State Interactions in Flurbiprofen−Tryptophan Dyads. The Journal of Physical Chemistry B, 111(31), 9363-9371. doi:10.1021/jp071301zCallis, P. R., & Burgess, B. K. (1997). Tryptophan Fluorescence Shifts in Proteins from Hybrid Simulations:  An Electrostatic Approach. The Journal of Physical Chemistry B, 101(46), 9429-9432. doi:10.1021/jp972436fLakowicz, J. R. (2000). On Spectral Relaxation in Proteins†¶‖. Photochemistry and Photobiology, 72(4), 421. doi:10.1562/0031-8655(2000)0722.0.co;2Schuler, B., & Eaton, W. A. (2008). Protein folding studied by single-molecule FRET. Current Opinion in Structural Biology, 18(1), 16-26. doi:10.1016/j.sbi.2007.12.003Shen, X., & Knutson, J. R. (2001). Subpicosecond Fluorescence Spectra of Tryptophan in Water. The Journal of Physical Chemistry B, 105(26), 6260-6265. doi:10.1021/jp010384vBeechem, J. M., & Brand, L. (1985). Time-Resolved Fluorescence of Proteins. Annual Review of Biochemistry, 54(1), 43-71. doi:10.1146/annurev.bi.54.070185.000355Callis, P. R. (1997). [7] 1La and 1Lb transitions of tryptophan: Applications of theory and experimental observations to fluorescence of proteins. Flourescence Spectroscopy, 113-150. doi:10.1016/s0076-6879(97)78009-1Basarić, N., & Wan, P. (2006). Competing Excited State Intramolecular Proton Transfer Pathways from Phenol to Anthracene Moieties. The Journal of Organic Chemistry, 71(7), 2677-2686. doi:10.1021/jo0524728Lukeman, M., & Wan, P. (2003). Excited-State Intramolecular Proton Transfer ino-Hydroxybiaryls:  A New Route to Dihydroaromatic Compounds. Journal of the American Chemical Society, 125(5), 1164-1165. doi:10.1021/ja029376yKeck, J., Kramer, H. E. A., Port, H., Hirsch, T., Fischer, P., & Rytz, G. (1996). Investigations on Polymeric and Monomeric Intramolecularly Hydrogen-Bridged UV Absorbers of the Benzotriazole and Triazine Class. The Journal of Physical Chemistry, 100(34), 14468-14475. doi:10.1021/jp961081hVollmer, F., & Rettig, W. (1996). Fluorescence loss mechanism due to large-amplitude motions in derivatives of 2,2′-bipyridyl exhibiting excited-state intramolecular proton transfer and perspectives of luminescence solar concentrators. Journal of Photochemistry and Photobiology A: Chemistry, 95(2), 143-155. doi:10.1016/1010-6030(95)04252-0Lukeman, M., & Wan, P. (2002). A New Type of Excited-State Intramolecular Proton Transfer:  Proton Transfer from Phenol OH to a Carbon Atom of an Aromatic Ring Observed for 2-Phenylphenol1. Journal of the American Chemical Society, 124(32), 9458-9464. doi:10.1021/ja0267831Jiménez, M. C., Miranda, M. A., Tormos, R., & Vayá, I. (2004). Characterisation of the lowest singlet and triplet excited states of S-flurbiprofen. Photochem. Photobiol. Sci., 3(11-12), 1038-1041. doi:10.1039/b408530bWeller, A. (1982). Photoinduced Electron Transfer in Solution: Exciplex and Radical Ion Pair Formation Free Enthalpies and their Solvent Dependence. Zeitschrift für Physikalische Chemie, 133(1), 93-98. doi:10.1524/zpch.1982.133.1.093Winget, P., Cramer, C. J., & Truhlar, D. G. (2004). Computation of equilibrium oxidation and reduction potentials for reversible and dissociative electron-transfer reactions in solution. Theoretical Chemistry Accounts, 112(4). doi:10.1007/s00214-004-0577-0ÇAKIR, S., & BÇER, E. (2010). SYNTHESIS, SPECTRAL CHARACTERIZATION AND ELECTROCHEMISTRY OF VANADIUM(V) COMPLEX WITH TRYPTOPHAN. Journal of the Chilean Chemical Society, 55(2). doi:10.4067/s0717-9707201000020002

Transient absorption spectroscopy detection of sensitized delayed fluorescence in chiral benzophenone/naphthalene systems

Transient absorption spectroscopy has proven to be a powerful tool to investigate the formation and decay of excited singlet states upon triplet–triplet annihilation, following T–T energy transfer from a selectively excited sensitizer. Thus, upon selective excitation of benzophenone (BZP) by laser flash photolysis (LFP) at λ = 355 nm in the presence of naphthalene (NPT), a negative band centered at 340 nm has been detected, with growth and decay in the microsecond timescale. It has been assigned to the P-type NPT delayed-fluorescence. In the case of chiral BZP/NPT systems, stereodifferentiation has been observed in the kinetics of the involved photophysical processesFinancial support from the MICINN (Grant CTQ2010-14882 and predoctoral fellowship to P. B.) is gratefully acknowledged.Bonancía Roca, P.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2011). Transient absorption spectroscopy detection of sensitized delayed fluorescence in chiral benzophenone/naphthalene systems. Chemical Physics Letters. 515(1-3):194-196. https://doi.org/10.1016/j.cplett.2011.08.096S1941965151-

Especies transitorias en sistemas bioorgánicos modelo conteniendo cromóforos de tipo bifenilo, naftaleno o benzofenona

La espectroscopía de absorción transitoria ha resultado ser una herramienta útil para investigar la formación y desaparición de estados excitados singlete formados por aniquilación triplete-triplete, tras sensibilización. De este modo, tras excitar selectivamente BZP a 355 nm en presencia de NPT, se detectó mediante espectroscopía de absorción transitoria una banda negativa centrada a 340 nm, cuya formación y desaparición ocurría en la escala de los microsegundos. Esta banda fue asignada como fluorescencia retardada tipo P de NPT. En el caso de sistemas BZP/NPT quirales, se observó estereodiferenciación en las cinéticas de los procesos fotofísicos implicados. Se ha profundizado en el comportamiento del estado excitado triplete de pseudopéptidos basados en naftaleno en presencia de benzofenona y/o bifenilo, como cromóforos dadores de energía. Este comportamiento ha sido comparado con el del compuesto modelo DMN. En todos los casos, la absorción triplete-triplete de NPT se ha detectado por espectroscopía de absorción transitoria, tras excitación selectiva de benzofenona a 355 nm. Las cinéticas de desaparición y formación de estas especies resultaron ser menores en los PSP, debido a que son más lentos los procesos de transferencia de energía tripletetriplete y formación de exciplejos. La fluorescencia retardada detectada en el modelo de naftaleno no fue observada en los PSP. Se han estudiado las interacciones entre FBP y dThd unidos covalentemente, formando diadas (S)- o (R)-FBP-dThd. En ellas, la única especie que emisora fue 1 FBP*, pero con rendimientos cuánticos y tiempos de vida de fluorescencia menores que los del FBP libre en disolución. Estos resultados indican una desactivación dinámica debida a una transferencia electrónica o formación de exciplejo, donde FBP es la especie dadora de carga. En acetonitrilo, ambos mecanismos resultaron favorables, mientras que en dioxano predominó la formación de exciplejo. El enantiómero (S)- presentó valores más bajos de ¿F y ¿F que su análogo (R)- indicando que la disposición espacial de ambos cromóforos desempeñaba un papel importante. El rendimiento cuántico de triplete de las diadas resultó ser mayor que el esperado únicamente a partir de los ¿CIS de 1 FBP*-dThd, siendo ¿T ((S)-) > ¿T ((R)-). Este hecho se pudo explicar debido a una recombinación de carga del par de iones radicales y/o exciplejos, que podrían depender de factores geométricos. El tiempo de vida de las diadas resultó ser similar al del FBP libre, indicando ausencia de interacción en el estado excitado triplete. Con el propósito de estudiar las interacciones fármaco/proteína se sintetizaron diadas conteniendo un derivado de bifenilo unido covalentemente a triptófano. En el caso de las diadas FBP-Trp se observó una notable desactivación de la fluorescencia, cuya emisión fue asignada al residuo de Trp. Esta desactivación se asignó a una TESS desde 1 FBP* a Trp que resultó ser muy rápida y estereoselectiva, con una constante de desactivación mayor para el diastereómero (R,S)-FBPTrp. A escalas de tiempo mayores, se observó una desactivación, también estereoselectiva, de la fluorescencia del 1 Trp* debido a una transferencia de electrón y/o la formación de un exciplejo. Para el caso de los sistemas BPOH-Trp, la sustitución de F por OH en FBP produjo una disminución de la ES. La emisión en las diadas fue asignada al residuo de BPOH, este hecho fue debido a una TESS desde el 1 Trp* al BPOH. Se observó una marcada desactivación en las diadas, que resultó ser estereoselectiva, con kD mayor para el diastereómero (S,R)-. La desactivación se explica por transferencia de electrón intramolecular y/o formación de un exciplejo. El diasterómero (S,R)- presentó una conformación plegada que justifica los valores obtenidos de ¿F y ¿F, siendo éstos menores para la diada (S,R)- que para la (S,S)-. El tiempo de vida de las diadas resultó inferior al de BPOH, confirmando que la desactivación de las primeras era de naturaleza dinámica. Por otro lado, se estudiaron las interacciones entre derivados de bifenilo y ASH. En el caso de los sistemas FBP/ASH las cinéticas de desaparición a ¿em = 310 nm revelaron una desactivación dinámica de 1 ASH*, tanto en la escala de picosegundos (FU) como nanosegundos (TCSPC). El proceso de transferencia de energía desde 1 FBP* a la ASH resultó ser estereoselectivo. Las cinéticas de desaparición a ¿em = 380 nm, donde únicamente emite la proteína, también fueron dependientes de la configuración de FBP, aunque en menor medida. La desactivación puede ser debida a una transferencia electrónica y/o formación de exciplejo. Se ha caracterizado fotofísicamente BPOH en ausencia de proteína; el espectro de emisión de fluorescencia en medio acuoso presentó dos bandas, una a 332 nm correspondiente a 1 BPOH* y otra a 414 nm correspondiente al 1 (BPOH- )*. En presencia de ASH se detectó la formación de un complejo BPOH@ASH en el estado fundamental (máximo a ca. 300 nm), cuya intensidad se veía aumentada a concentraciones más elevadas de proteína. Tras adición de ASH se observó una disminución de la banda de emisión del fenolato (a ¿em ca. 410 nm), confirmando la inhibición de la desprotonación en el estado excitado dentro de la cavidad hidrofóbica de la proteína. Tras adición de (S)-IBP, como sonda desplazante del sitio II de la ASH la banda correspondiente al complejo BPOH@ASH disminuyó significativamente; en cambio, reapareció la banda correspondiente al fenolato. También se observó una gran estereodiferenciación tanto en la formación del complejo en el estado fundamental como en la desprotonación en el estado excitado. En el espectro de absorción transitoria del BPOH se observó una banda centrada a 380 nm correspondiente a su estado excitado triplete; en presencia de ASH el tiempo de vida del mismo aumentó de 1.3 a 19 µs; en este caso no se observó diastereodiferenciación.Bonancía Roca, P. (2012). Especies transitorias en sistemas bioorgánicos modelo conteniendo cromóforos de tipo bifenilo, naftaleno o benzofenona [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/27553TESI

Intraprotein formation of a long wavelength absorbing complex and inhibition of excited state deprotonation in a chiral hydroxybiphenyl

The two enantiomers of 2-(2-hydroxybiphenyl-4-yl)propanoic acid ((S)- and (R)-BPOH) have been selected as probes for human serum albumin (HSA). Photophysical characterization in the absence of protein led to emission maxima, singlet energies, quantum yields, and fluorescence lifetime values of 332 nm, 91 kcal mol(-1), and 0.28 and 1.8 ns for BPOH or 414 nm, 79 kcal mol(-1), and 0.31 and 3.3 ns for the corresponding phenolate BPO-; the pK(a)* was found to be 1.17. In the presence of HSA, a light-absorbing ground-state complex (S)-BPOH@HSA was detected (maximum at ca. 300 nm) whose intensity increased with increasing protein concentration. The fluorescence spectra of (S)-BPOH in PBS, after addition of HSA, revealed a progressive diminution of the phenolate band, indicating that excited-state deprotonation is disfavored within the hydrophobic protein cavities. A similar trend was observed for (R)-BPOH, but the extent of deprotonation was significantly lower for this enantiomer. Addition of increasing amounts of the site II displacement probe (S)-ibuprofen ((S)-IBP) to BPOH@HSA led to a significant decrease of the absorption maximum at ca. 300 nm and to a recovery of the phenolate emission band at ca. 410 nm, which were again configuration dependent. The transient absorption spectrum of (S)-BPOH consisted on a broad band centered at 380 nm, attributed to the first triplet excited state. A dramatic enhancement of the triplet lifetimes within HSA was observed (19.0 mu s within protein versus 1.3 mu s in bulk PBS), although no stereodifferentiation was noticed in this case.Financial support from the Spanish Government (CTQ2010-14882, CTQ2009-13699, BES-2008-003314, JCI-2011-09926), from the Generalitat Valenciana (Prometeo 2008/090) and from the Universitat Politecnica de Valencia (PAID 05-11, 2766) is gratefully acknowledged.Bonancía Roca, P.; Vayá Pérez, I.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2012). Intraprotein formation of a long wavelength absorbing complex and inhibition of excited state deprotonation in a chiral hydroxybiphenyl. Journal of Physical Chemistry B. 116(51):14839-14843. https://doi.org/10.1021/jp310587sS14839148431165

Excited-state interactions in diastereomeric flurbiprofen-thymine dyads

Excited-state interactions between (S)- or (R) fluorescence (S)- or (R)-FBP) and thymidine (dThd) covalently linked in dyads 1 or 2 have been investigated. In both dyads, the only emitting species is (FBP)-F-1*, but with a lower fluorescence quantum yield (phi(F)) and a shorter fluorescene lifetime (tau(F)) than when free in solution. These an results indicate that dynamic quenching occurs either by electron transfer or via exciplex formation, with FBP as the charge-donating species. In acetonitrile, both mechanisms are favored, while in dioxane exciplex formation is predominating. Isomer 1 displays lower values of OF and rF than its analogue 2, indicating that the relative spatial arrangement of the chromophores plays a significant role. The triplet quantum yields (0-F) of 1 and 2 are significantly higher than the expectations based solely on 'FBP* dThd intersystem crossing quantum yields (Oisc), with OT (1) > OT (2). This can be explained in terms of intramolecular charge recombination at the radical ion pairs and/or the exciplexes, which would be again dependent on geometrical factors. The triplet lifetimes (IT) of 3FBP* dThd and free 3FBP* are similar, indicating the lack of excited-state interactions at this stage. The FBP dThd dyads could, in principle, constitute appropriate model systems for the elucidation of the excited-state interactions in noncovalent DNA ligand complexes.Financial support from the Spanish Government (Grants CTQ2010-14882 and CTQ2009-13699), Salvador Madariaga Program (Grant to M.C.J.), Juan de la Cierva Program (contract to I.V.), Generalitat Valenciana (Prometeo 2008/090), and the Universitat Politecnica de Valencia (PAID 05-11, ref 2766) is gratefully acknowledged.Bonancía Roca, P.; Vayá Pérez, I.; Climent Olmedo, MJ.; Gustavsson, T.; Markovitsi, D.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2012). Excited-state interactions in diastereomeric flurbiprofen-thymine dyads. Journal of Physical Chemistry A. 116(35):8807-8814. https://doi.org/10.1021/jp3063838S880788141163

Triplet excited state behavior of naphthalene-based pseudopeptides in the presence of energy donors

In this work, the triplet state behavior of naphthalene-based pseudopeptides with amide-based macrocyclic or lateral chain substructures has been investigated in the presence of benzophenone and/or biphenyl, as suitable energy donating chromophores. Their behavior has been compared with that of 1,4-dimethylnaphthalene as model compound.,,In all the cases,. the triplet-triplet absorption of naphthalene is detected by transient absorption spectroscopy, upon selective excitation of benzophenone at 355 nm. The kinetics of formation and decay of this species is markedly slower in the pseudopeptides, due to retardation of triplet-triplet energy transfer and exciplex formation. Finally, the delayed fluorescence detected in the model naphthalene is absent in the pseudopeptides. The concept can, in principle, be exploited for the study of excited state interactions. in supramolecular systemsFinancial support from the MICINN (Grants CTQ-2010-14882, CTQ2009-14366-C02-01 and FPI contract to P.B.), the Generalitat Valenciana (Prometeo 2008/090), the UPV (PAID 05-11 Program, ref 2766), and Fundacio Caixa Castello-UJI (P1 1B-2009-59) is gratefully acknowledged.Bonancía Roca, P.; Vigara, L.; Galindo, F.; Luis, SV.; Jiménez Molero, MC.; Miranda Alonso, MÁ. (2012). Triplet excited state behavior of naphthalene-based pseudopeptides in the presence of energy donors. Journal of Physical Chemistry B. 116(33):9957-9962. https://doi.org/10.1021/jp304883uS995799621163