Push/Pull Effect as Driving Force for Different Optical Responses of Azobenzene in a Biological Environment

Abstract

The specific relationship between the alkyl tail lengths of four azobenzene probes embedded in DOPC liquid disorder membrane and their (non) linear optical (NLO) properties have been considered in the current study. Using extensive molecular dynamics calculations, the push/pull effect of the alkyl tails on the position and orientation of the probes in the model membrane are discussed. The simulations indicate that with increasing tail lengths the cis isomers are pushed closer to the membrane surface, while the trans ones are rather pulled toward the membrane center. Throughout hybrid quantum mechanics/molecular mechanics calculations, the linear and nonlinear optical properties of these compounds have been investigated. The pushing effect of the tails for cis azobenzene is translated in strong responses in the (non) linear optical spectroscopies, while the opposite is seen for the trans isomers. The cis isomer can be seen as the active state of the azobenzene compound for membrane recognition. The current work highlights the correlation between the tails of photosensitive membrane probes and their NLO properties, and focuses on unexpected behaviors of azobenzene derivatives in biological environments which can be exploited in distinguishing between soft and stiff cellular compartments that are of utmost importance for ion carrier transport.

Influence of Membrane Phase on the Optical Properties of DPH

“…Incorporating an impinging near infrared laser beam ( Figure 4 b), the intensities are ten times enhanced but the relative trend among the different lipid bilayers does not change. Thus, the current work enforces the ample studies performed in the static regime; incorporation of a well-tuned light beam might be opportune to mimic specific experimental conditions [ 50 ] or particular complex probes [ 34 ], but in the context of the current studies it does not incorporate new physics. It can therefore be stated that the static hyperpolarizabilities have a profound universal character.…”

“…Fluorescence spectroscopies are nowadays one of the techniques of choice for the analysis of the behavior of probes in different membrane phases, due to the different responses related to the anisotropy decay [ 51 , 52 , 53 , 54 , 55 , 56 , 57 ]. We focus on the decay time and the fluorescence anisotropy decay as model analyses which can be obtained by computations [ 29 , 30 , 31 , 33 , 34 ]. The decay time analysis, which can be closely related to the fluorescence lifetime imaging (FLIM) technique, allows screening between the membrane phase and gives indication on the phase itself.…”

“…Afterwards, the focus can be put on a smaller part of the system to study optical properties by means of hybrid quantum mechanics/molecular mechanics (QM/MM) methods. In this way, many different properties such as linear and non-linear optical properties, fluorescence and photoselection of an optical probe immersed into the membrane can be assessed [ 28 , 29 , 30 , 31 , 32 , 33 , 34 ]. The ability of the probe to give different optical responses depending on the environment it is embedded in allows to determine the phase of the membrane itself, which, in turn, is strongly related to its fluidity.…”

Multiscale Modeling Unravels the Influence of Biomembranes on the Photochemical Properties of Embedded Anti-Oxidative Polyphenolic and Phenanthroline Chelating Dyes

“…The results in the current work can further on be compared to other studies, which have been performed in similar conditions and which focus on the influence of the membrane on the probe's conformation, position, and orientation. 33,34 The overall planarity conditions of the more flexible Caffest and the flavonoids are estimated against the potential they are sensing in the environment, isotropic (gas phase) or membrane embedding. Hybrid QM/MM calculations are employed to understand how they perform with respect to two different optical spectroscopies, one-and two-photon absorption, OPA and TPA, respectively.…”

Impact of Van der Waals interactions on structural and nonlinear optical properties of azobenzene switches

“…[21][22][23][24] Recent theoretical works also highlighted that azobenzene NLO switches could be exploited as versatile probes for phase recognition in biological environments. 25,26 At the molecular level, it is well known that the nature of the chemical substituents determines the relative thermodynamic stability of the trans and cis forms of azobenzene derivatives and thus plays a critical role in their photo-isomerization process. In particular, chemical functionalization in the meta-position with bulky substituents has been shown to lower the cis !…”