Ultrasonic shear spectrum in hydrated diethylamine melanins and its relation to stacking in a planar group

Abstract

Articles you may be interested inAnisotropy in the dielectric spectrum of hydration water and its relation to water dynamics Shear mechanical relaxation and resonance data are reported for 20 wt % hydration of diethylamine melanins with difTerentpH values ranging from 2 to 7. Shear impedance measurements in the temperature range from 60 to -80 o e, with frequencies from I to 362 MHz, indicate a Davidson-Cole spectrum in the primary relaxation and a single relaxation with a characteristic frequency of f = 4 MHz at 6O·C referred to the molecular motions of a group composed of an average molecular weight M. "" 1.4 X 10'. A resonance at 250 MHz is found in the specific melanin called No. I. associated with stacking of indole monomer units. and a single relaxation at f = 270 MHz at 60 ·C is found in the hydrate of melanin No.2. The nature of the stacking is surveyed on account of Fitzgerald's theory. The limiting shear modulus in the primary relaxation related to the molecular motion of backbone chains obeys the modified Hirai-Eyring equation. All the hydrations have an amorphous phase composed of a three-dimensional network structure.

Biomedical overview of melanin. 2. Updating molecular modeling, synthesis mechanism, and supramolecular properties regarding melanoma therapy

“…However, the melanin content of melanomas strongly absorbs US across several frequencies, and can be used as specific sono-sensitizer (SS). The absorption at 4 MHz has been assigned to molecular motions of a melanin protoparticle with an average molecular weight of ~1.4 × 10 4 Da (Kono et al, 1981). Interestingly, this value agrees with the molecular weight of a protoparticle modeled as a 4-turn spiral BQPoe (~1.3 × 10 4 Da).…”

“…These features are also found in graphene and pyrolyzed PDA, as well as carbon spheres and films (Liu et al, 2014). In addition to UV-visible-NIR radiation, eumelanin is capable of absorbing X-and γ-rays (Hill, 1992;Krol and Liebler, 1998), and ultrasound in the MHz range (Kono et al, 1979;Kono et al, 1981;McGinness et al, 1976).…”

“…Eumelanin is practically the ideal photothermal sensitizer, and the massive vibrational decay from photo-excited electrons in melanotic melanomas induces an efficient heating response that results in coagulative necrosis of the tumor (Kostenich et al, 2000;Colombo et al, 2019;Blázquez-Castro and Stockert, 2021). In the case of melanin-PTT, the endogenous chromophore eumelanin is the selective PTT agent for NIR irradiation (Fig.…”

“…Likewise, the diameter of a protoparticle of PDA-melanin by X-ray diffraction studies is ~30 Å (Chen et al, 1994;Bridelli, 1998), which also corresponds closely to the diameter of a 4-turn spiral BQPoe model (~34.3 Å). In addition, a resonance at 250 MHz was found in melanin associated with stacking of the indole monomer (Kono et al, 1981).…”