To understand the photochemical behaviour of the polydopamine polymer in detail, one would also need to know the behaviour of its building blocks. The electronic absorption, as well as the fluorescence emission and excitation spectra of the dopamine were experimentally and theoretically investigated considering time-resolved fluorescence spectroscopy and first-principles quantum theory methods. The shape of the experimental absorption spectra obtained for different dopamine species with standard, zwitterionic, protonated, and deprotonated geometries was interpreted by considering the advanced equation-of-motion coupled-cluster theory of DLPNO-STEOM. Dynamical properties such as fluorescence lifetimes or quantum yield were also experimentally investigated and compared with theoretically predicted transition rates based on Fermi’s Golden Rule-like equation. The results show that the photochemical behaviour of dopamine is strongly dependent on the concentration of dopamine, whereas in the case of a high concentration, the zwitterionic form significantly affects the shape of the spectrum. On the other hand, the solvent pH is also a determining factor for the absorption, but especially for the fluorescence spectrum, where at lower pH (5.5), the protonated and, at higher pH (8.0), the deprotonated forms influence the shape of the spectra. Quantum yield measurements showed that, besides the radiative deactivation mechanism characterized by a relatively small QY value, non-radiative deactivation channels are very important in the relaxation process of the electronic excited states of different dopamine species.

Magnetic structures exhibiting large magnetic moments are sought after in theranostic approaches that combine magnetic hyperthermia treatment (MH) and diagnostic magnetic resonance imaging in oncology, since they offer an enhanced magnetic response to an external magnetic field. We report on the synthesized production of a core–shell magnetic structure using two types of magnetite nanoclusters (MNC) based on a magnetite core and polymer shell. This was achieved through an in situ solvothermal process, using, for the first time, 3,4-dihydroxybenzhydrazide (DHBH) and poly[3,4-dihydroxybenzhydrazide] (PDHBH) as stabilizers. Transmission electron microscopy (TEM) analysis showed the formation of spherical MNC, X-ray photoelectronic spectroscopy (XPS) and Fourier transformed infrared (FT-IR) analysis proved the existence of the polymer shell. Magnetization measurement showed saturation magnetization values of 50 emu/g for PDHBH@MNC and 60 emu/g for DHBH@MNC with very low coercive field and remanence, indicating that the MNC are in a superparamagnetic state at room temperature and are thus suitable for biomedical applications. MNCs were investigated in vitro, on human normal (dermal fibroblasts-BJ) and tumor (colon adenocarcinoma-CACO2, and melanoma-A375) cell lines, in view of toxicity, antitumor effectiveness and selectivity upon magnetic hyperthermia. MNCs exhibited good biocompatibility and were internalized by all cell lines (TEM), with minimal ultrastructural changes. By means of flowcytometry apoptosis detection, fluorimetry, spectrophotometry for mitochondrial membrane potential, oxidative stress, ELISA-caspases, and Western blot–p53 pathway, we show that MH efficiently induced apoptosis mostly via the membrane pathway and to a lower extent by the mitochondrial pathway, the latter mainly observed in melanoma. Contrarily, the apoptosis rate was above the toxicity limit in fibroblasts. Due to its coating, PDHBH@MNC showed selective antitumor efficacy and can be further used in theranostics since the PDHBH polymer provides multiple reaction sites for the attachment of therapeutic molecules.

Coating the surfaces of implantable materials with various active principles to ensure inhibition of microbial adhesion, is a solution to reduce infections associated with dental implant. The aim of the study was to optimize the polydopamine films coating on the Ti-6Al-6V alloy surface in order to obtain a maximum of antimicrobial/antibiofilm efficacy and reduced cytotoxicity. Surface characterization was performed by evaluating the morphology (SEM, AFM) and structures (Solid-state 13C NMR and EPR). Antimicrobial activity was assessed by logarithmic reduction of CFU/mL, and the antibiofilm activity by reducing the adhesion of Escherichia coli, Staphylococcus aureus, and Candida albicans strains. The release of NO was observed especially for C. albicans strain, which confirms the results obtained for microbial adhesion. Among the PDA coatings, for 0.45:0.88 (KMnO₄:dopamine) molar ratio the optimal compromise was obtained in terms of antimicrobial activity and cytotoxicity, while the 0.1:1.5 ratio (KMnO₄:dopamine) led to higher NO release and implicitly the reduction of the adhesion capacities only for C. albicans, being slightly cytotoxic but with moderate release of LDH. The proposed materials can be used to reduce the adhesion of yeast to the implantable material and thus inhibit the formation of microbial biofilms.

Dopamine (DA) and its analogues are compounds of interest in polymer science where their properties provide a multitude of applications. However, in elucidating polydopamine structure, there are ambiguities related to the types of bonds, the structure of monomeric units, their ratio, and influence of synthesis parameters. In order to minimize these variables, isotopic labeling presents an optimal alternative. In the diversification and understanding of these polymers, we aim to investigate analogues that by selective isotopic labeling provide possibilities for structure elucidation both of the polymerized analogues as well as polydopamine. In the present paper we report the synthesis of three new dopamine derivatives, labeled *CL ((Z)-3-(3,4-bis(benzyloxy)phenyl)-2-cyano-2-propenamide) and both labeled and unlabeled DL/*DL (2-aminomethyl-3-(3,4-dihydroxyphenyl)propionamide). The labeled *CL and *DL compounds contain selective ¹³C and ¹⁵N labeling in the alkyl chain. For these new compounds, NMR, FT-IR and fluorescence characterization, including by time-resolved laser spectroscopy, are reported.

The equilibrium geometries of the ground and first electronic excited states as well as the radiation-less deactivation channels of catechol in its monomer and dimer configurations were investigated using the standard linear-response and the spin-flipped TDDFT, multireference CASSCF as well as the similarity transformed equation-of-motion coupled cluster built with the domain-based local pair natural orbitals (DLPNO-STEOM-CCSD) methods. For the monomer, it was found that there is a new conical intersection geometry that can explain why catechol exhibits different photochemical behavior. This deactivation pathway involves almost simultaneously, an excited state intramolecular proton transfer between the two O atoms and an O–H bond breaks at the proton that is not between the two O atoms. From an energy balance point of view, these geometries are not associated with high potential barriers, so radiation-less relaxation can be achieved through these geometries. For the cyclohexane solvent, the lowest CI geometry shows an energy gap of about 4 kcal mol⁻¹ lower than that found for acetonitrile, making the relaxation even more easier. In the case of catechol dimer structures, several so-called dimer-type CI geometries were found where both monomers exhibit substantial geometric distortions together with the formation of a weaker C–C bond between the two catechol monomers. These CI geometries are energetically more favorable and, in the case of aggregation processes, more likely to decay the excited states of the catechol through these radiation-less deactivation channels than those found for the monomer.