KuQuinones Equilibria Assessment for Biomedical Applications

Synthesis of Highly Functionalized Spirocycles and Pentafulvene-Containing Dyes Involving 2-(2'-ketoalkyl)-1,3-indandiones

Synthesis of highly functionalized spiro[4.4]nonane and spiro[4.5]decane motifs by the reaction of dimethylacetylenedicarboxylate (DMAD) with 2-(2'-ketoalkyl)-1,3-indandiones and 2-(3'-ketoalkyl)-1,3-indandiones, respectively, has been developed by utilizing a catalytic amount of DABCO. The tertiary hydroxy-containing spiro[4.4]nonane products were converted into fully conjugated pentafulvene π-systems in an acidic medium through dehydration and unprecedented C-C bond rearrangement.

KuQuinones: a ten years tale of the new pentacyclic quinoid compound

Quinones are widespread in nature, as they participate, mainly as redox mediators, in several biochemical processes. Up to now, various synthetic quinones have been recommended in the literature as leading molecules in energy, biomedical and catalytic fields. In this brief review, we retraced our research activity in the last ten years, mainly dedicated to the study of a new class of peculiar pentacyclic conjugated quinoid compounds, synthesized in our group. In particular, their application as sensitive materials in photoelectrochemical devices and in biosensors, as photocatalysts in selective oxidation reactions, and their anticancer activity is here reviewed.

An Accurate Approach for Computational pKa Determination of Phenolic Compounds

Computational chemistry is a valuable tool, as it allows for in silico prediction of key parameters of novel compounds, such as pKa. In the framework of computational pKa determination, the literature offers several approaches based on different level of theories, functionals and continuum solvation models. However, correction factors are often used to provide reliable models that adequately predict pKa. In this work, an accurate protocol based on a direct approach is proposed for computing phenols pKa. Importantly, this methodology does not require the use of correction factors or mathematical fitting, making it highly practical, easy to use and fast. Above all, DFT calculations performed in the presence two explicit water molecules using CAM-B3LYP functional with 6-311G+dp basis set and a solvation model based on density (SMD) led to accurate pKa values. In particular, calculations performed on a series of 13 differently substituted phenols provided reliable results, with a mean absolute error of 0.3. Furthermore, the model achieves accurate results with -CN and -NO₂ substituents, which are usually excluded from computational pKa studies, enabling easy and reliable pKa determination in a wide range of phenols.

3-Morpholino-7-[N-methyl-N-(4′-carboxyphenyl)amino]phenothiazinium Chloride

The synthesis of 3-morpholino-7-[N-methyl-N-(4′-carboxyphenyl)amino]phenothiazinium chloride is reported here. Interestingly, non-symmetric phenothiazinium salt is functionalized with a carboxylic acid group that allows the easy and stable anchoring on metal oxides. In addition, the morpholine unit reduces the dye aggregation tendency; thus, improving its potential applications in the biomedical and photo-electrocatalytic field.

KuQuinone as a Highly Stable and Reusable Organic Photocatalyst in Selective Oxidation of Thioethers to Sulfoxides

A chemoselective photocatalytic system to perform thioether oxidation to sulfoxide is presented. The light-induced oxidation process is here promoted by a metal-free quinoid catalyst, namely 1-hexylKuQuinone (KuQ). Reactions performed in a fluorinated solvent (i.e., HFIP), using O₂ as the oxidant, at room temperature, lead to complete thioanisole conversion to methyl phenyl sulfoxide in 60 min. Remarkably, the system can be recharged and recycled without a loss of activity and selectivity, reaching turnover numbers (TONs) higher than 4000. Excellent catalytic performances and full selectivity have also been obtained for the photocatalytic oxidation of substituted thioanisole derivatives, aliphatic, cyclic, and diaryl thioethers. Likewise, the oxidation of heteroaromatic organosulfur compounds can be accomplished, with longer reaction times.

Artificial photosynthesis: photoanodes based on polyquinoid dyes onto mesoporous tin oxide surface

Dye-sensitized photoelectrochemical cells represent an appealing solution for artificial photosynthesis, aimed at the conversion of solar light into fuels or commodity chemicals. Extensive efforts have been directed towards the development of photoelectrodes combining semiconductor materials and organic dyes; the use of molecular components allows to tune the absorption and redox properties of the material. Recently, we have reported the use of a class of pentacyclic quinoid organic dyes (KuQuinone) chemisorbed onto semiconducting tin oxide as photoanodes for water oxidation. In this work, we investigate the effect of the SnO₂ semiconductor thickness and morphology and of the dye-anchoring group on the photoelectrochemical performance of the electrodes. The optimized materials are mesoporous SnO₂ layers with 2.5 μm film thickness combined with a KuQuinone dye with a 3-carboxylpropyl-anchoring chain: these electrodes achieve light-harvesting efficiency of 93% at the maximum absorption wavelength of 533 nm, and photocurrent density J up to 350 μA/cm² in the photoelectrochemical oxidation of ascorbate, although with a limited incident photon-to-current efficiency of 0.075%. Calculations based on the density functional theory (DFT) support the role of the reduced species of the KuQuinone dye via a proton-coupled electron transfer as the competent species involved in the electron transfer to the tin oxide semiconductor. Finally, a preliminary investigation of the photoelectrodes towards benzyl alcohol oxidation is presented, achieving photocurrent density up to 90 μA/cm² in acetonitrile in the presence of N-hydroxysuccinimide and pyridine as redox mediator and base, respectively. These results support the possibility of using molecular-based materials in synthetic photoelectrochemistry.

A Sustainable Improvement of ω-Bromoalkylphosphonates Synthesis to Access Novel KuQuinones

Owing to the attractiveness of organic phosphonic acids and esters in the pharmacological field and in the functionalization of conductive metal-oxides, the research of effective synthetic protocols is pivotal. Among the others, ω-bromoalkylphosphonates are gaining particular attention because they are useful building blocks for the tailored functionalization of complex organic molecules. Hence, in this work, the optimization of Michaelis–Arbuzov reaction conditions for ω-bromoalkylphosphonates has been performed, to improve process sustainability while maintaining good yields. Synthesized ω-bromoalkylphosphonates have been successfully adopted for the synthesis of new KuQuinone phosphonate esters and, by hydrolysis, phosphonic acid KuQuinone derivatives have been obtained for the first time. Considering the high affinity with metal-oxides, KuQuinones bearing phosphonic acid terminal groups are promising candidates for biomedical and photo(electro)chemical applications.

Unveiling KuQuinone Redox Species: An Electrochemical and Computational Cross Study

The study of the electrochemical properties of variegated quinones is a fascinating topic in chemistry. In fact, redox reactions occurring with quinoid scaffolds are essential for most of their applications in biological systems, in photoelectrochemical devices, and in many other fields. In this paper, a detailed investigation of KuQuinones' redox behavior is presented. The distinctiveness of such molecules is the presence in the structure of two condensed naphthoquinone units, which implies the possibility to undergo multiple one-electron reduction processes. Solvent, supporting electrolyte, and hydrogen bond donor species effects have been elucidated. Changing the experimental parameters provoked significant shift of the redox potential for each reduction process. In particular, additions of 2,2,2-trifluoroethanol as a hydrogen bond donor in solution as well as Lewis acid coordination were crucial to obtain important shifts of the redox potentials toward more favorable values. UV-vis-NIR spectroelectrochemical experiments and DFT calculations are also presented to clarify the nature of the reduced species in solution.

Hydroxylated 3-(pyridin-2-yl)coumarins as radical scavengers with potent lipoxygenase inhibitor activity

Hydroxylated 3-(pyridin-2-yl)coumarins show radical scavenging activity and are able to inhibit soybean lipoxygenase.

Zinc porphyrin-anthraquinonylimidazole supramolecular dyads

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 [Formula: see text] 10[Formula: see text]–3.9 [Formula: see text] 10[Formula: see text] M[Formula: see text]. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP[Formula: see text]-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

Photoanodes for water oxidation with visible light based on a pentacyclic quinoid organic dye enabling proton-coupled electron transfer

A novel pentacyclic quinoid photosensitizer with extended absorption in the visible region and enabling proton-coupled electron transfer is employed in photoelectrodes for water oxidation in combination with a ruthenium polyoxometalate catalyst.