Theoretical study of two-photon circular dichroism on molecular structures simulating aromatic amino acid residues in proteins with secondary structures

Herein, we report on the calculation and the comparative analysis of the theoretical two-photon circular dichroism (TPCD) spectra of L-histidine (His), L-phenylalanine (Phe), and L-tyrosine (Tyr) simulating residues in proteins with secondary structures (alpha-helix, beta-strand and random coil), down to the far-UV region (FUV). This work exposes unique signatures in the FUV for each conformer in each configuration. The outcomes of this research show how FUV-TPCD can be used to study peptide and protein structures in a region never evaluated before but packed with important structural information

Cálculo de variables termodinámicas de la difusión de especies iónicas dentro de los poros de un recubrimiento bioactivo mediante espectroscopia de impedancia electroquímica

La investigación en el área de los biomateriales, apunta hacia el desarrollo de nuevos materiales aplicables en implantes médicos. Uno de los biomateriales más usados en la actualidad es el acero inoxidable 316L, ya que es un material que a pesar de su bajo costo presenta unas condiciones satisfactorias de uso en cuanto a su baja velocidad de corrosión; sin embargo, a pesar de considerarse inoxidable cuando se expone a atmósferas tan corrosivas como los fluidos corporales presenta un proceso de degradación del material, permitiendo la liberación de iones dentro del organismo causando a su vez la degradación del tejido circundante al mismo. Con el fin de reducir este efecto se están proponiendo modificaciones superficiales a los biomateriales metálicos, consistentes en recubrimientos con biomateriales activos específicamente, fases apatíticas, las cuales son aplicadas por distintos métodos entre los cuales se encuentra la técnica sol-gel. Teniendo como finalidad el aumento de la resistencia a la corrosión y con el fin de impulsar la osteointegración y la bioactividad de los implantes de acero inoxidable AISI 316L, se depositaron por inmersión-extracción recubrimientos híbridos doble capa, de sílice con partículas de wollastonita dispersas, usando como precursores en la preparación del sol alcóxidos de tetraetilortosilicato (TEOS) y metil-trietoxsilano (MTES). La aplicación de cada una de las capas, la primera de sílice y la segunda de sílice con un 10% p/p de partículas de wollastonita dispersas en el vidrio de sílice, se hizo mediante inmersión-extracción a una velocidad de 4cm/min. Para estabilizar las partículas en suspensión, se utilizo el éster de fosfato como agente dispersante. Una vez obtenido el recubrimiento vítreo bioactivo de composición silícea, se investigó su comportamiento electroquímico, para diferentes tiempos de inmersión en Fluido Fisiológico Simulado (SBF) en un intervalo de tiempo que va desde las 24horas hasta 18 días, para un potencial de circuito abierto. Se realizaron medidas de curvas de polarización a 25°C, 37°C y 56°C y 8 días de envejecimiento de la muestra en SBF y de esta manera, se predijo un comportamiento termodinámico del sistema. Para la temperatura corporal específica, 37°C, se realizaron medidas de impedancia que permitieron modelar la interfase sustrato/recubrimiento por medio de un circuito eléctrico equivalente y a partir de los datos obtenidos de EIS (espectroscopia de impedancia electroquímica) se calculó el valor de la Resistencia de Transferencia de Carga, se determinó el valor de la corriente de corrosión y se obtuvo un valor de energía de activación como variable termodinámica. /Abstract Research in the area of biomaterials, aimed at developing new materials applied in medical implants. One of the most widely used biomaterials is now 316L stainless steel as a material that despite its low cost presents a satisfactory standard for use in their low corrosion rate, however, although considered stainless when exposed to corrosive atmospheres such as body fluids presents a material degradation process, allowing the release of ions in the body while causing degradation of the tissue surrounding it. To reduce this effect are proposing amendments to the biomaterials surface metal coatings consisting of active biomaterials specifically apatitic phases, which are applied by different methods among which is the sol-gel. Taking aim of increasing the corrosion resistance and to promote osseointegration and bioactivity of stainless steel implants AISI 316L were deposited by dip-extraction double-layer hybrid coatings of silica particles dispersed wollastonite, using as precursors in the preparation of alkoxide sol of tetraethylorthosilicate (TEOS) and methyl-trietoxsilano (MTES). The implementation of each of the layers, the first and second silica silica with 10% w / w of wollastonite particles dispersed in the silica glass was made by immersion-extraction 4cm/min speed. To stabilize the particles in suspension, was used as the phosphate ester dispersing agent. Once the coating composition bioactive vitreous silica, we investigated its electrochemical performance for different periods of immersion in simulated body fluid (SBF) at an interval of time ranging from 24 hours to 18 days for an open circuit potential. Measurements of polarization curves at 25 ° C, 37 ° C and 56 ° C and 8 days of aging of the sample in SBF and in this way, it was predicted thermodynamic behavior of the system. For specific body temperature, 37 ° C, impedance measurements were performed for modeling the interface substrate / coating by means of an equivalent electrical circuit and from the data obtained from EIS (electrochemical impedance spectroscopy) was calculated the value of Charge Transfer Resistance, we determined the value of the corrosion current and obtained a value of activation energy as a thermodynamic variable.Maestrí

Theoretical-Experimental Study of the Two-Photon Circular Dichroism of Helicenes and Aromatic Amino Acids in the UV Region: From the Structure-Property Relationship to the Final Implementation

Two-photon circular dichroism (TPCD) has been recognized for its exceptional spectroscopic ability for the structural and conformational analysis of chiral systems due to its high sensitivity to small peptide structural distortions. In 2008, Hernandez and co-workers demonstrated TPCD experimentally by the development of the Double L-scan technique. Since then, we have been working on a systematic theoretical-experimental study of chiral molecules using TPCD. In this dissertation, I present my contribution to the continuation to the study of the structure-property relationship of TPCD in molecules with axial chirality in solution, as well as the implementation of the TPCD measurements in the near- and far-UV regions. Employing a theoretical-experimental approach I will discuss: 1) the effect of the pulse width of the excitation source on the TPCD spectra of biaryl derivatives, 2) the theoretical study of the TPCD signal in the far-UV on molecular structures simulating aromatic amino acid residues in proteins with secondary structures, and 3) the pros and cons of the implementation of the FUV-TPCD spectrometer. The outcomes of my research reveal the potential of TPCD for the conformational analysis of relatively complex molecular systems such as peptides in the far-UV region, an area never accessed before. Additionally, we exposed the applicability of TPCD as a complimentary method to standard electronic circular dichroism (ECD) for the study of complex structures. Finally, I demonstrate for the very first time experimental evidence of TPCD in the near- to Far-UV region

Two-Photon Absorption And Two-Photon Circular Dichroism Of L-Tryptophan In The Near To Far Uv Region

Herein we report on the first measurements of the two-photon absorption (TPA) spectrum of L-tryptophan in DMSO solution in the near to far UV region and the two-photon circular dichroism (TPCD) signal corresponding to a transition at 200 nm. We demonstrate the application of the Double L-scan technique in the near to far UV region to perform polarization dependent TPA measurements of chiral molecules. TPCD measurements below 400 nm reveal that chiral molecules in solution, such as tryptophan/DMSO, can undergo photochemical reactions in front of prolonged exposure to UV radiation

Study Of The Effect Of The Pulse Width Of The Excitation Source On The Two-Photon Absorption And Two-Photon Circular Dichroism Spectra Of Biaryl Derivatives

Herein we report on the expanded theoretical calculations and the experimental measurements of the two-photon absorption (TPA) and two-photon circular dichroism (TPCD) spectra of a series of optically active biaryl derivatives (R-BINOL, R-VANOL, and R-VAPOL) using femtosecond pulses. The comparative analysis of the experimental TPCD spectra obtained with our tunable amplified femtosecond system with those previously measured in our group on the same series of compounds in the picosecond regime reveals a decrease in the amplitude of the signal and an improvement in matching with the theory in the former. These results can be explained based on the negligible contribution of excited state absorption (ESA) using femtosecond pulses compared to the picosecond regime. We show how ESA affects both the strength of the signal and the shape of the TPA and TPCD spectra. TPA and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (450-750 nm) using 90 fs pulses at 50 Hz repetition rate produced by an amplified femtosecond system. The theoretical calculations were performed using modern analytical response theory within the time-dependent density functional theory (TD-DFT) approach using CAM-B3LYP and 6-311++G(d,p) basis sets

Enhanced Two-Photon Absorption And Fluorescence Upconversion In Thioflavin T Micelle-Type Aggregates In Glycerol/Water Solution

In this article, we report the systematic characterization of the two-photon absorption of ThT in different mixtures of glycerol/water solution. The relationships of TPA peak position and amplitude revealed a dependence on particle size suggesting that the curious trend observed in TPA with changing glycerol content can be attributed to the presence of micelle-type aggregates. Consequently, the relatively strong TPA cross-section (δTPA = 300 GM) obtained in 8.75% glycerol/water solutions could be attributed to the immobilization of dye molecules and the strong coupling of the molecular transition dipoles in micelle-type aggregates. This enhancement of TPA, in addition to the already reported significant fluorescence quantum yield of ThT attached to brain tissue, is expected to boost the application of this compound for in vitro and perhaps in vivo high resolution multiphoton bioimaging of amyloids in brain tissue

Two-Photon Absorption And Two-Photon Circular Dichroism Of A Hexahelicene Derivative With A Terminal Donor-Phenyl-Acceptor Motif

Herein, we report on the theoretical-experimental analysis of the two photon absorption and circular dichroism spectra of 1-(2-pyridyl)-4-methoxy-carbo[6]helicene derivative (P6). The primary outcomes of our investigation on this particular helicene derivative with a donor-acceptor motif on one end led to two important conclusions: (1) the lengthening of the π-electron delocalization within the helical core of P6 predominantly increases the contribution of the magnetic dipole transition moment to the two-photon circular dichroism (TPCD) signal; and (2) the electric quadrupole transition moment contribution to the TPCD signal is enhanced by the intramolecular charge transfer (ICT) produced by the donor-acceptor combination on one end of the molecule. To corroborate our results, we performed a comparative theoretical analysis of the effect of the energy gap and ICT on TPCD on a series of P6-like helicenes with different donor-acceptor combinations. Two-photon absorption and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (400-900 nm) using 90 fs pulses at a low repetition rate (2-50 Hz) produced by an amplified femtosecond system. The theoretical simulations were calculated using time dependent density functional theory at the CAM-B3LYP/6-311++G(d,p) level of theory

Two-Photon Absorption and Two-Photon Circular Dichroism of a Hexahelicene Derivative with a Terminal Donor-Phenyl-Acceptor Motif

International audienceHerein, we report on the theoretical-experimental analysis of the two photon absorption and circular dichroism spectra of 1-(2-pyridyl)-4-methoxy-carbo[6]helicene derivative (P6). The primary outcomes of our investigation on this particular helicene derivative with a donor-acceptor motif on one end led to two important conclusions (1) the lengthening of the π-electron delocalization within the helical core of P6 predominantly increases the contribution of the magnetic dipole transition moment to the two-photon circular dichroism (TPCD) signal; and (2) the electric quadrupole transition moment contribution to the TPCD signal is enhanced by the intramolecular charge transfer (ICT) produced by the donor-acceptor combination on one end of the molecule. To corroborate our results, we performed a comparative theoretical analysis of the effect of the energy gap and ICT on TPCD on a series of P6-like helicenes with different donor-acceptor combinations. Two-photon absorption and TPCD spectra were obtained using the double L-scan technique over a broad spectral range (400-900 nm) using 90 fs pulses at a low repetition rate (2-50 Hz) produced by an amplified femtosecond system. The theoretical simulations were calculated using time dependent density functional theory at the CAM-B3LYP/6-311++G(d,p) level of theory