Polarization-modulation pump-probe spectroscopy for biological molecules: Linear dichroism and birefringence.
Denis A. Volkov1, Maxim V. Belashov1,2, Anastasia V. Dmitrieva1,3, Maria A. Plotitsyna1,3, Maxim E. Sasin1, Oleg S. Vasutinskii1; 1Ioffe Institute, St. Petersburg, Russia; 2ITMO University, St. Petersburg, Russia; 3Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia
Abstract
In this work we present a new method for the separation of linear dichroism (LD) and birefringence (BR) in polarization-modulated pump-probe experiments. The BR signal consists of pronounced Stimulated Raman Scattering (SRS) peak of solvent and linear pump-probe signal of studied molecules, while in the LD signal SRS peak is not present. A comparison of the LD and BR signals shows that LD is preferable for studying fast relaxation processes, such as vibrational relaxation, whereas BR is more suitable for slower relaxation processes, such as rotational diffusion.
This method is applied to investigate picosecond dynamics of nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) in water and ethanol solutions. NADH exhibits fast 1ps vibrational relaxation in water, while for FAD this relaxation takes place within 5ps. With increase of ethanol concentration in solutions, FAD relaxation processes slow down, and the relaxation time increases to 35ps. For FAD, the vibrational relaxation coefficients were obtained and compared with those for NADH measured in the study by Gorbunova et al [Gorbunova I. A. PCCP V. 22, 18155 (2020)]. The coefficients exhibit different trends: in case of FAD, the post‑relaxation transition dipole moment coefficient consistently exceeds the pre‑relaxation one, while for NADH the opposite is true.
The results can be used for interpretation of polarization-resolved signals in pump-probe microscopy and for improving signal-to-noise ratio.
Speaker
Volkov Denis Andreevich
Ioffe Institute
Russia
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