Carlos Sánchez

Second-order nonlinear optical properties of tetrathiafulvalene-π-(thio)barbituric acid chromophores

Abstract Donor-acceptor polyenes that combine an electron-donating tetrathiafulvalene (TTF) unit with a barbituric or thiobarbituric acid have been prepared for the first time and characterized as nonlinear optical (NLO) chromophores. The electrochemical and thermal properties of these derivatives are also reported.

Inter-subject variability in human atrial action potential in sinus rhythm versus chronic atrial fibrillation

Aims Human atrial electrophysiology exhibits high inter-subject variability in both sinus rhythm (SR) and chronic atrial fibrillation (cAF) patients. Variability is however rarely investigated in experimental and theoretical electrophysiological studies, thus hampering the understanding of its underlying causes but also its implications in explaining differences in the response to disease and treatment. In our study, we aim at investigating the ability of populations of human atrial cell models to capture the inter-subject variability in action potential (AP) recorded in 363 patients both under SR and cAF conditions. Methods and Results Human AP recordings in atrial trabeculae (n = 469) from SR and cAF patients were used to calibrate populations of computational SR and cAF atrial AP models. Three populations of over 2000 sampled models were generated, based on three different human atrial AP models. Experimental calibration selected populations of AP models yielding AP with morphology and duration in range with experimental recordings. Populations using the three original models can mimic variability in experimental AP in both SR and cAF, with median conductance values in SR for most ionic currents deviating less than 30% from their original peak values. All cAF populations show similar variations in GK1, GKur and Gto, consistent with AF-related remodeling as reported in experiments. In all SR and cAF model populations, inter-subject variability in IK1 and INaK underlies variability in APD90, variability in IKur, ICaL and INaK modulates variability in APD50 and combined variability in Ito and IKur determines variability in APD20. The large variability in human atrial AP triangulation is mostly determined by IK1 and either INaK or INaCa depending on the model. Conclusion Experimentally-calibrated human atrial AP models populations mimic AP variability in SR and cAF patient recordings, and identify potential ionic determinants of inter-subject variability in human atrial AP duration and morphology in SR versus cAF.

The Na+/K+ pump is an important modulator of refractoriness and rotor dynamics in human atrial tissue.

Pharmacological treatment of atrial fibrillation (AF) exhibits limited efficacy. Further developments require a comprehensive characterization of ionic modulators of electrophysiology in human atria. Our aim is to systematically investigate the relative importance of ionic properties in modulating excitability, refractoriness, and rotor dynamics in human atria before and after AF-related electrical remodeling (AFER). Computer simulations of single cell and tissue atrial electrophysiology were conducted using two human atrial action potential (AP) models. Changes in AP, refractory period (RP), conduction velocity (CV), and rotor dynamics caused by alterations in key properties of all atrial ionic currents were characterized before and after AFER. Results show that the investigated human atrial electrophysiological properties are primarily modulated by maximal value of Na(+)/K(+) pump current (G(NaK)) as well as conductances of inward rectifier potassium current (G(K1)) and fast inward sodium current (G(Na)). G(NaK) plays a fundamental role through both electrogenic and homeostatic modulation of AP duration (APD), APD restitution, RP, and reentrant dominant frequency (DF). G(K1) controls DF through modulation of AP, APD restitution, RP, and CV. G(Na) is key in determining DF through alteration of CV and RP, particularly in AFER. Changes in ionic currents have qualitatively similar effects in control and AFER, but effects are smaller in AFER. The systematic analysis conducted in this study unravels the important role of the Na(+)/K(+) pump current in determining human atrial electrophysiology.

Second-order nonlinear optical properties of tetrathiafulvalene-π-3-(dicyanomethylidene)indan-1-one chromophores

Novel conjugated donor-acceptor chromophores, based on the strong electron donating tetrathiafulvalene moiety and the strong electron-withdrawing 3-(dicyanomethylidene)indan-1-one acceptor, exhibit large second-order optical nonlinearities. The effect of increasing the length of the polyenic spacer on the NLO properties of the new molecules has been studied by using the electric field-induced second harmonic generation (EFISH) method.

Synthesis and characterization of novel NLO-phores from π-extended tetrathiafulvalene (TTF) derivatives

Abstract Donor-π-Acceptor systems containing extended TTF derivatives with quinonoid structures have been synthesized and characterized. Their properties as second order NLO chromophores have been studied by experimental (EFISH) and theoretical methods.

Biphotonic holographic gratings in azobenzene polyesters: Surface relief phenomena and polarization effects

Biphotonic holographic gratings have been recorded in a side-chain azobenzene liquid crystalline polyester using a blue incoherent source and a He–Ne laser. Intensity gratings and the appearance of surface relief have been observed when two linearly polarized beams from a He–Ne laser are made to interfere on a film illuminated with blue light. Polarized holographic gratings are also created with two orthogonally circularly polarized He–Ne beams. All these gratings are stable in darkness but can be erased with blue light.

Na/K pump regulation of cardiac repolarization: insights from a systems biology approach

The sodium-potassium pump is widely recognized as the principal mechanism for active ion transport across the cellular membrane of cardiac tissue, being responsible for the creation and maintenance of the transarcolemmal sodium and potassium gradients, crucial for cardiac cell electrophysiology. Importantly, sodium-potassium pump activity is impaired in a number of major diseased conditions, including ischemia and heart failure. However, its subtle ways of action on cardiac electrophysiology, both directly through its electrogenic nature and indirectly via the regulation of cell homeostasis, make it hard to predict the electrophysiological consequences of reduced sodium-potassium pump activity in cardiac repolarization. In this review, we discuss how recent studies adopting the systems biology approach, through the integration of experimental and modeling methodologies, have identified the sodium-potassium pump as one of the most important ionic mechanisms in regulating key properties of cardiac repolarization and its rate dependence, from subcellular to whole organ levels. These include the role of the pump in the biphasic modulation of cellular repolarization and refractoriness, the rate control of intracellular sodium and calcium dynamics and therefore of the adaptation of repolarization to changes in heart rate, as well as its importance in regulating pro-arrhythmic substrates through modulation of dispersion of repolarization and restitution. Theoretical findings are consistent across a variety of cell types and species including human, and widely in agreement with experimental findings. The novel insights and hypotheses on the role of the pump in cardiac electrophysiology obtained through this integrative approach could eventually lead to novel therapeutic and diagnostic strategies.

High diffraction efficiency polarization gratings recorded by biphotonic holography in an azobenzene liquid crystalline polyester

High diffraction efficiencies have been achieved with polarization gratings recorded in thin films of an azobenzene side-chain liquid crystalline polyester by means of biphotonic processes. Efficiency values up to 30% have been reached after an induction period of 300 s and subsequent evolution with the sample in darkness. These values are at least two orders of magnitude higher than those previously reported for biphotonic recording. The gratings can be erased with unpolarized blue light and partial recovery of the diffraction efficiency has been observed after the erasure process when the sample is kept in darkness. Red light illumination of the erased film increases the recovered efficiency value and the recovery rate.

Biphotonic holographic recording in a liquid crystalline cyanoazobenzene side-chain polymethacrylate. Polarization, intensity, and relief gratings

Biphotonic holographic recording has been performed on thin films of a side-chain liquid crystalline p-cyanoazobenzene polymethacrylate. Polarization and intensity holographic gratings have been recorded by irradiation of the films with blue incoherent light and simultaneous or subsequent illumination with the red light pattern generated by the interference of two properly polarized beams from a He–Ne laser. The influence of temperature and illumination conditions on the diffraction efficiency of those gratings has been studied. Surface topography of the films has been explored using a profilometer. The appearance of relief gratings using biphotonic processes has been observed only in gratings recorded with simultaneous illumination of blue light and an intensity modulated light pattern of the red light.

Polarized photoluminescence and order parameters of “in situ” photopolymerized liquid crystal films

Oriented liquid crystal polymer films with different degrees of cross-linking have been obtained by “in situ” photopolymerization of different mesogenic samples at various temperatures. These samples are mixtures of a naphthalene based monoacrylate and a crosslinking agent (diacrylate). Photoluminescence has been obtained by adding a cyanoterphenyl chromophore. The order parameters of the polymer films have been derived from dichroic measurements. An increase of the dichroism has been found when the diacrylate content and/or the polymerization temperature decrease. The dichroism is also bigger if the chromophore is in a “guest-host” configuration than if it is covalently attached to the polymer backbone. The dichroic ratios do not change under annealing up to 200 °C but some photodegradation of the luminescence is observed in the naphthalene containing films.