Intermolecular interactions required for the formation of liquid microcrystals produced by the precursors self-organized from protonated TPP dimers

Alexander V. Udal'tsov

Faculty of Biology, Lomonosov Moscow State University, 119899 Moscow, Russia

E-mail: avu151@yandex.ru; avud151@gmail.com

Precursors of microcrystals produced in thin layer of self-organized protonated meso-tetraphenylporphine dimers have been investigated by electronic absorption and infrared spectroscopy, non-contact AFM/SNOM, and SEM to elucidate the role of water and water-soluble organic solvent in the processes of the liquid microcrystals formation [1]. It has been found that tetrahydrofuran (THF) is the most suitable organic solvent providing proton moving through the aqueous acid solution that is required for the formation of liquid micro-crystals. A band around 3200 cm^–1 corresponds to O–O distance ca. 2.63 Å in the O–H⁺...O moiety that is consistent with the distance providing proton sharing [2]. So that characteristic band at 3207 cm^–1 (or a shoulder at 3228 cm^–1 in the presence of HCl), which have been found in IR spectra of THF with small amounts of water, is the prerequisite for the proton moving through water-porphyrin matrix. As evidenced earlier the latter generates the self-organization of the structure [3-4] that is needed for the crystallization. According to AFM/SNOM images, submicroscopic particles consisting of ~ 60-nm particles are covered by a layer of tight water. The tight water was found previously under comparison of the non-contact and contact AFM images [5]. Regular surface of the tight water layer observed by non-contact AFM attests about proton moving through water with the change of the moving direction. The angle of the direction change is sharp, 46.2° or 180°– 46.2°=133.8° depending on the forward or backward proton moving. Tracks of the structure self-organization due to the proton moving observed by SEM on the surface of precursors support this view on the structure self-organization. Similar processes of proton moving through the water-porphyrin matrix are suggested for the prolongation of crystallization germ observed by contact AFM. No crystallization has been found for nanoparticles obtained under the self-assembling of protonated TPP dimers in 7-9% (v/v) aqueous dioxane.

References

[1] A.V. Udal'tsov, J. Crys. Growth. 448 (2016) 6-16.

[2] A.V. Udal'tsov, J. Mol. Spectr. 11 (2017) in press, https://doi.org/10.1016/j.jms.2017.11.008

[3] A.V. Udal'tsov, A.V. Bolshakova, J.G. Vos, J. Mol. Struct. 1080 (2015), 14-23.

[4] A.V. Udal'tsov, J. Mol. Struct. 1084 (2015) 308-318.

[5] A.V. Udal'tsov, M. Tosaka, G. Kaupp, J. Mol. Struct. 660 (2003) 15-23.