Electrochemical transformations and antioxidant activity of some Schiff bases 1–5 containing ferrocenyl group and (thio‐)phenol, catechol fragments were investigated. Compounds under investigation ...are: 2‐(ferrocenylmethylene)amino)phenol (1), 2‐((ferrocenylmethylene)amino)‐4,6‐di‐tert‐butylphenol (2), 2‐((ferrocenylmethylene)amino)‐thiophenol (3), 3‐((ferrocenylmethylene)hydrazonomethyl)‐4,6‐di‐tert‐butylcatechol (4) and 2‐((3,5‐di‐tert‐butyl‐4‐hydroxybenzylidene)amino)thiophenol (5).
In a case of compounds 1–3 it has shown that the sequence of electrochemical transformations leads to the products of intramolecular cyclization – 2‐ferrocenylbenzoxazole (benzothiazole). o‐Quinone formation occurs during the electrochemical oxidation of catechol‐ferrocene 4 at the first anode stage. Electrochemical oxidation of the redox‐active fragments in Schiff bases 1–4 can be achieved indirectly at a lower potential corresponding to the oxidation of ferrocenyl moiety, consequently these substances can reveal more pronounced antioxidant properties. The antioxidant activities of the compounds were evaluated using 2,2′‐diphenyl‐1‐picrylhydrazyl radical (DPPH) assay, the reaction of 2,2′‐azobis(2‐amidinopropane hydrochloride) (AAPH) induced glutathione depletion (GSH), the oxidative damage of the DNA, the process of lipid peroxidation of rat (Wistar) brain homogenates in vitro. The compounds 1–4 in the antioxidant assays show effectiveness comparable with standard antioxidants (vitamin E, Trolox) and in some parameters superior to them. In the reaction of AAPH with the glutathione compounds 2–5 have a more pronounced protective activity than Trolox. Compounds 1–5 inhibit AAPH induced oxidation damage of the DNA. The more effective inhibitors of the lipid peroxidation process in vitro are molecules containing the bulky tert‐butyl groups: 2 and 4 and Schiff base 3.
Electrochemical oxidation of the redox‐active fragments can be achieved indirectly at a low potential corresponding to the oxidation of ferrocenyl moiety. The Schiff bases can be activated at lower redox potentials and show pronounced antioxidant activity in comparison with the compounds containing phenolic or catecholic groups only.
Two new photoinitiators of the α,α-bis(arylidene)cyclopentanone series having an unsymmetrical structure and containing two methacrylate units have been synthesized. The electrochemical and ...photoluminescent properties of the initiators have been studied. In the presence of the initiators, photopolymerization of pentaerythritol triacrylate was carried using radiation at λ = 365/405 nm (one-photon process) and focused femtosecond laser radiation with a wavelength of 780 nm (two-photon process). For each initiator, “fabrication windows” were determined and 3D microstructures of complex architecture were fabricated by DLW nanolithography.
New 1-hexadecyl derivatives of isatin containing substituents of various natures in the 5-position have been synthesized and characterized. The kinetics of their photoreduction by visible radiation ...in the presence of 4-methyl-
N
,
N
-dimethylaniline and triethylamine has been studied. It has been found that the photoreduction rate constant increases in the following order of substituted isatins: CH
3
< H < Cl < Br. It is shown that the isatin–amine system initiates photopolymerization of oligocarbonate dimethacrylate OKM-2 by visible light. The efficiency of photoinitiation correlates with the activity of isatins in the photoreduction reaction.
A synthetic procedure was developed for the preparation of sterically hindered di- and trisubstituted catechols and
o
-quinones by the reaction of catechol with isopropanol. Compared to sterically ...more hindered analogs,
o
-quinones bearing isopropyl substituents exhibit a higher reactivity toward the formation of oxanthrenequinone derivatives.
Free-radical photopolymerization has been widely used in additive technologies, in particular, stereolithography using single- and two-photon initiated polymerization. The single-photon ...stereolithography affords the objects with about 100 μm resolution. The two-photon stereolithography initiated with a femtosecond near-infrared laser can afford arbitrary 3D microstructures with ultrahigh resolution at micro- and nanoscale level (~100 nm). Herein each of the mentioned method and the mechanisms of single- and two-photon excitation are reviewed. The recent results on the components of the photopolymerizable resin as well as the approaches to decrease the size of the elements of objects and accelerate their formation have been generalizated and systematized.
New tri- and tetraalkyl-substituted
o
-benzoquinones were synthesized based on 5,5,8,8-tetramethyl-5,6,7,8-tetrahydronaphthalene-2,3-diol derivatives. The new compounds were characterized by ...spectroscopic and electrochemical methods. The reactivity of
o
-benzoquinones was evaluated in the photoreduction and initiation of photopolymerization of oligocarbonate dimethacrylate (OCM-2) in the presence of
N,N
-dimethylcyclohexylamine and in the inhibition of MMA polymerization. The introduction of the methyl substituent into the benzene ring has a weak effect on the inhibitory activity of
o
-benzoquinone, whereas the (3,5-dimethylpyrazol-1-yl)methyl substituent enhances the inhibitory effect of 4,5-di-
tert
-alkyl-substituted
o
-benzoquinone.
A novel sterically hindered
o
-benzoquinone 4,6-di-
tert-
butyl-3-(5,7-di-
tert-
butylbenzooxazole-2-yl)-
o
-benzoquinone containing a benzoxazole moiety is prepared. The interaction of this quinone ...with Cu(0) yielded a cubane copper(II) complex with a Cu
4
O
4
core. Molecular and crystal structures of the
o
-quinone (CCDC 2269708) and the copper complex (CCDC 2269709) are determined by XRD.
Di-
tert
-alkyl-substituted catechols with a heterocyclic imidazole-type substituent were synthesized in three steps from catecholaldehydes. The 1,1,4,4-tetramethylbutanediyl substituent was shown to ...be resistant to the action of acids in the demethylation reaction. The isomerization of 3,4,5-substituted catechols to the 3,4,6-substituted isomers was observed. The molecular structures of the synthesized compounds in the crystalline state were established by X-ray diffraction analysis. For the catechol derivatives, the tertiary substituent in the
ortho
position to the imidazole moiety was shown to have an effect on the mutual arrangement of the catechol and heterocyclic moieties. The electrochemical properties of the synthesized imidazole-containing catechols were studied and their anti-radical activity was evaluated by the 2,2-diphenyl-1-picrylhydrazyl assay.
Six new 1-hexadecyl derivatives of isatin with various substituents at position 5 were synthesized. Their spectral and electrochemical characteristics were determined. All the obtained isatins can ...undergo photoreduction in solution in the presence of tertiary amines upon irradiation with visible light. The effective rate constant of the process increases with a decrease of the amine oxidation potential, an increase of the isatin reduction potential, and it reaches a maximum in the case of the bromo derivative. In the presence of triethylamine, the obtained 1-hexadecylisatins initiate a photopolymerization of dimethacrylate OCM-2 under the action of near UV and visible light in the blue spectral region. The rate constants of photoreduction and photopolymerization during the transition from one isatin to another change in parallel. The highest efficiency of photoinitiation of OCM-2 polymerization is exhibited by 5-bromo-1-hexadecylisatin.
A new representative of sterically hindered 3,6-di-
tert
-butyl-
o
-benzoquinones bearing an annulated tetrahydrooxazolo3,2-
d
1,4oxazine moiety—6,9-di-
tert
-butyl-1,2,3
a
,4-tetrahydrobenzo
b
...oxazolo3,2-
d
1,4oxazine-7,8-dione—was synthesized. The structure of the novel compound was confirmed by IR, UV, and NMR spectroscopy and X-ray diffraction. According to the cyclic voltammetry, the first reduction potential of the quinone in acetonitrile is –0.83 V (Ag/AgCl/KCl reference electrode).
