Abstract-A Study of the Effect of a Protein on the Structure of Water in Solution Using Terahertz Time-Domain Spectroscopy

Nikita Penkov, Valery Yashin, Eugeny Fesenko, Andrew Manokhin, 

https://www.osapublishing.org/as/abstract.cfm?uri=as-72-2-257&origin=search

Terahertz time-domain spectroscopy (THz-TDS) was used to determine the spectra (range = 1.2–120 cm−1) of aqueous solutions of bovine serum albumin (BSA) at pH range 2.5–10. Under each of the selected pH, BSA molecules exist in a different conformation, compared to other pH values. The spectra were used to calculate the functions of the dielectric permittivity of BSA solutions. Dielectric functions of the aqueous phase of BSA solutions were calculated based on the Bruggeman model, without the contribution of BSA itself. Fitting of the dielectric functions was performed using a model which includes three water spectral bands: two relaxation bands with relaxation times of about 8.28 and 0.3 ps and a vibrational band with a maximum of about 180 cm−1. The parameters of these bands were determined through fitting and physical interpretation at the molecular level can be provided for each of them. A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule. At the same time, the structure of more distant layers of the hydration shells is destroyed, with an increased formation of free water molecules. Some differences are observed in the effect of different BSA conformations on the aqueous phase of solution. The proposed approach can be generalized and applied for studying of a wide class of biological macromolecules in aqueous solutions.

© 2017 The Author(s)

Abstract-Signal-to-noise ratio of single-pixel cameras based on photodiodes

Nikita Penkov, Valery Yashin, Eugeny Fesenko, Andrew Manokhin, and Eugeny Fesenko

https://www.osapublishing.org/ao/abstract.cfm?uri=ao-57-7-B67&origin=search

Single-pixel cameras have been successfully used in different imaging applications in the last years. One of the key elements affecting the quality of these cameras is the photodetector. Here, we develop a numerical model of a single-pixel camera, which takes into account not only the characteristics of the incident light but also the physical properties of the detector. In particular, our model considers the photocurrent, the dark current, the photocurrent shot noise, the dark-current shot noise, and the Johnson–Nyquist (thermal) noise of the photodiode used as a light detector. The model establishes a clear relationship between the electric signal and the quality of the final image. This allows us to perform a systematic study of the quality of the image obtained with single-pixel cameras in different contexts. In particular, we study the signal-to-noise ratio as a function of the optical power of the incident light, the wavelength, and the photodiode temperature. The results of the model are compared with those obtained experimentally with a single-pixel camera.

© 2018 Optical Society of America

Abstract-A Study of the Effect of a Protein on the Structure of Water in Solution Using Terahertz Time-Domain Spectroscopy

Nikita Penkov, Valery Yashin, Eugeny Fesenko, Jr, Andrew Manokhin, Eugeny Fesenko

http://journals.sagepub.com/doi/10.1177/0003702817735551

Terahertz time-domain spectroscopy (THz-TDS) was used to determine the spectra (range = 1.2–120 cm⁻¹) of aqueous solutions of bovine serum albumin (BSA) at pH range 2.5–10. Under each of the selected pH, BSA molecules exist in a different conformation, compared to other pH values. The spectra were used to calculate the functions of the dielectric permittivity of BSA solutions. Dielectric functions of the aqueous phase of BSA solutions were calculated based on the Bruggeman model, without the contribution of BSA itself. Fitting of the dielectric functions was performed using a model which includes three water spectral bands: two relaxation bands with relaxation times of about 8.28 and 0.3 ps and a vibrational band with a maximum of about 180 cm⁻¹. The parameters of these bands were determined through fitting and physical interpretation at the molecular level can be provided for each of them. A comparison between the values of model parameters of solutions with BSA and without BSA allowed to conclude that the main effect of BSA is the formation of strongly bound hydration shells in the immediate proximity to the protein molecule. At the same time, the structure of more distant layers of the hydration shells is destroyed, with an increased formation of free water molecules. Some differences are observed in the effect of different BSA conformations on the aqueous phase of solution. The proposed approach can be generalized and applied for studying of a wide class of biological macromolecules in aqueous solutions.