Lomonosov Moscow State University Physics Department SPECIFIC INTERACTION OF ALBUMIN MOLECULES IN WATER SOLUTION, CONTAINING SILICON NANOPARTICLES AT DIFFERENT NET CHARGE OF PROTEIN Ksenia A. Anenkova, Galina P. Petrova, Lubov A. Osminkina, Konstantin P. Tamarov.

Bovine Serum Albumin (BSA) Mesoporous Silicon nanoparticles (MP-Si nanoparticles) Molecular weight – 65 kDa Characteristic sizes – 4*4*14 nm Isoelectric point pH 4.9 Albumin molecules realize transport function and maintenance of colloid-osmotic pressure in blood. Owing to their biological compatibility with living tissues and ability of fast removal from the organism, the silicon nanoparticles may be used as photosensitisers in photodynamic therapy of cancer and as drug delivery systems.

Experimental setup Fig.1. Autocorrelation function of scattered light g (1) (t) is first order field correlation function, g (2) (t) is second order intensity auto-correlation function, accumulated by correlator during the experiment Fundamental formula: In case of a poly-dispersed solution : Main parameters: laser’s wavelength 647nm, power P=25mW

Fig.2. pH dependence of the scattering centers translation diffusion coefficient in BSA water solution According to Scatchar theory nonlinear character of dependence at fig.1 is described by next formula where B is the second virial coefficien in the expansion for free energy, known as coefficient of intermolecular interaction

Fig.3. pH dependence of the scattering centers translation diffusion coefficient in mesoporous silicon nanoparticles water solution Mesoporous silicon nanoparticles are hydrophilic. Due to this property a water shell is formed around them. This leads to a partial shielding of particles net charge. Therefore, the shape of dependence at fig.3 is more smooth.

Fig.4. pH dependence of the scattering centers translation diffusion coefficient in mesoporous silicon nanoparticles + BSA water solution

Images of MP-Si nanoparticles, obtained by TEM In water solution MP-Si nanoparticles exist as clusters with sizes ranging from 100 nm to 1 mm. Ultrasonic treatment, followed by filtration, allows us to select the desired particles size нм

Comparison of the results obtained by dynamic light scattering with TEM нм 1 2 3

IR spectrometer Bruker IFS 66v/S IR spectroscopy is widely used to determine the composition of porous silicon layers. Technical characteristics: Scanning range: 7500 – 370 сm -1 Resolution: 0.25 сm -1 Evacuating the measuring chamber to 3 mbar

Fig.5. IR transmission spectrum for Mp-Si nanoparticles in the range from 800 to 2500 сm -1 SiH 3 antisymmetric deformation vibrations 877сm -1 SiO stretching vibrations in Si-O-Si 1064сm -1 SiH stretching vibrations in O 3 -SiH 2266сm -1

Amide-I (С=O stretching vibrations ) 1650 cm -1 Amide-II (CN stretching vibrations and NH deformational vibrations) 1520 cm -1 COO cm -1 Amide-III (CN stretching vibrations and NH rotating) cm -1 Fig.6. IR transmission spectrum for BSA in the range from 800 to 2000 сm -1

What are we looking for in the IR-spectrum BSA+MP-Si nanoparticles? Fig.7. IR transmission spectra for BSA and BSA+lead acetate in the range from 800 to 2000 сm -1 We are looking for amide-I and amide-II bands frequencies shifts. This shifts detect secondary structural changes caused by interaction of nanoparticles and protein. The examples of such shifts for system BSA+ lead acetate are shown at fig.7 For this system is well known that there is an interaction between BSA macromolecules and lead acetate.

Fig.8. IR transmission spectrum for BSA+Mp-Si nanoparticles in the range from 800 to 1800 сm -1 There is no any shifts of amide-I or amide-II bands in BSA+MP-Si nanoparticles system compared to pure protein. So it means that there is no interaction in this system. Hydrophilic properties of MP-Si nanoparticles can explain the absence of interaction between the nanoparticles’ surface OH groups and CO groups of BSA The absence of OH- CO groups interaction also can be explained by unsufficient for stable bond amount of H on the surface of particles

Conclusions: The investigation of molecular parameters of serum albumin in water solution by DLS method has shown that the addition of nanoparticles does not change the mobility of the scattering particles within the experimental error. In the obtained IR spectra is not observed shift to short wave area, characteristic for the formation of hydrogen bonds between the carbonyl groups of the protein and the OH groups on the silicon nanoparticles surface (shoulder 1650 for C = O stretching vibrations) Present results show that there is no interaction between albumin molecules and silicon nanoparticles in the investigated systems.

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