Dorota Zarzeczańska

Synthesis, redox properties, and basicity of substituted 1-aminoanthraquinones: spectroscopic, electrochemical, and computational studies in acetonitrile solutions

Abstract1-Amino-, 1-ethylamino-, and 1-(diethylamino)-anthraquinone were characterized by UV–Vis spectroscopy, acid–base titration, electrochemical methods, and quantum-chemical (QM) calculations at the B3LYP/6-31 ++G** level. Acid–base titration and the relative differences between the free energies of the basic and acidic forms of the studied species show that 1-(diethylamino)anthraquinone is the strongest base in an acetonitrile solution. Moreover, the structural differences between the B3LYP-optimized neutral and protonated anthraquinones, notably the presence or the absence of internal hydrogen bonds, account well for the sequence of the measured/calculated basicity. The basicity of the investigated compounds strongly influences their electrochemical properties in acetonitrile. Indeed, the cyclic voltammograms of 1-aminoanthraquinone and 1-(ethylamino)anthraquinone display two well-resolved reduction waves that indicate a two-step reduction process (EE mechanism). On the other hand, the electroreduction of 1-(diethylamino)anthraquinone becomes complicated by the interaction of its reduced forms with traces of water present in an acetonitrile solution (ECE mechanism). The mechanism of this reaction is proposed, and its possibility to occur is examined based on QM calculations.

Influence of different amino substituents in position 1 and 4 on spectroscopic and acid base properties of 9,10-anthraquinone moiety.

A series of novel 1-amino and 1,4-diamino-9,10-anthraquinones, substituted with different alkyl groups, were synthesized as the result of alkylation with amino substituents. All the obtained aminoanthraquinone derivatives were characterized by NMR, IR spectroscopy and mass spectrometry. The spectroscopic properties of these compounds were determined by using UV-Vis spectroscopy in acetonitrile, and in the mixture of acetonitrile and methanol at different pH ranges. The effects of various substituents present in the newly developed anthraquinone derivatives and their ability to form hydrogen bonds between the carbonyl oxygen atom of anthraquinone moiety and nitrogen atom of N-H group in 1-aminoanthraquinone (1-AAQ) and 1,4-diaminoanthraquinone (1,4-DAAQ) were studied. Additionally, the effects of hydrogen bond formation between O-H group in hydroxyethylamino substituent and the carbonyl oxygen atom of anthraquinone were investigated. The spectroscopic behavior of the studied derivatives strongly depended on the solvent-solute interactions and the nature of solvent. The values of pKa for the new anthraquinones were determined by the combined potentiometric and spectrophotometric titration methods.

Potentiometric, spectrophotometric, and AM1d studies of the equilibria between silver(I) ion and monoaza-crown ethers with anthraquinone in various solvents

Complex formation and stability constants between silver(I) and monoaza-12-crown, monoaza-15-crown, and monoaza-18-crown ethers with anthraquinone were determined in acetonitrile, methanol, and propylene carbonate by potentiometric and UV-spectrophotometric methods. Complexes of 1 : 1 and 1 : 2 metal-to-ligand stoichiometry were formed. The solvent composition and the size of the macrocyclic ring affect the stability constants of the complexes. The energetically most favorable structures of the 1 : 1 metal-to-ligand complexes were calculated and visualized by the AM1d method at a semiempirical level of theory.

Structure investigation of intramolecular hydrogen bond in some substituted salicylaldehydes and 4-aminoantipyrine derivatives in solution and in the solid state.

Seven imine derivatives obtained by condensation of appropriate aldehydes and salicylaldehydes with 4-aminoantipyrine were investigated in terms of intramolecular hydrogen bond structure. On the base of (1)H, (13)C and (15)N NMR measurements in solution and in the solid state we found out that all compounds which can form such structure exist as OH forms with strong H-bonds to nitrogen atom. The structure conclusions taken from NMR study were confirmed by pKa measurements. Surpassingly, the positions of protons in H-bridges only very slightly depend on the substituents in aldehyde used for condensation and on the phase (solution vs. solid state). The influence of antipyrine moiety seems to be the major factor defining H-bond structure.

Polyether precursors of molecular recognition systems based on the 9,10-anthraquinone moiety.

A series of novel polyether derivatives of 9,10-anthraquinone (AQ) was synthesized and characterized by means of UV-Vis spectroscopy, acid-base titration and complexometric titration. The results were compared with 1-NEt2AQ and 1-NHEtAQ--model compounds of alkylaminoanthraquinones. Acetonitrile and methanol were used as solvents for determination of spectroscopic and acid-base properties. Complexometric titrations were carried out exclusively in acetonitrile. Spectral characteristic of these compounds strongly depends on pH. Addition of acid causes the decrease of absorption intensity and in some cases also a shift of the visible range band. The weakest base is the compound (2), and the strongest--compound (1), both in methanol and acetonitrile solution. The introduction of an additional substituent in the position 8 of the anthraquinone compound increases its basicity. The presence of metal ions causes changes in intensity of absorption (decrease for compounds (2) and (3) and increase with bathochromic shift for (1) and (4)). For the determination of the coordination properties aluminum (III) ions were chosen. The highest complex stability constant with Al (III) ions is observed for compound (1), and the weakest for compound (3). The elongation of the polyether chain decreases the stability of the complex formed.

1H NMR and spectrophotometric study of alkaline metal ion complexes with N-dansyl aza-18-crown-6

Formation of complexes of A18C6-Dns and metal cations (Ca2+, Sr2+, Ba2+ and Mg2+) in acetonitrile has been studied by NMR, absorption and fluorescence spectroscopy and PM5 semi-empirical methods. A18C6-Dns forms stable complexes with Ca2+, Sr2+ and Ba2+ cations. The stability constants of various complexes are determined by different methods and their structures are visualised by the PM5 semi-empirical calculations.

The electrochemical and spectroscopic characterization of 1,4 and 1,8-aminoanthraquinone derivatives

The acid base properties of 1,4 and 1,8-anthraquinone derivatives were determined in methanol and acetonitrile by pH-spectroscopic measurements. The examined compounds was also characterized by electrochemically using cyclic voltammetry in DMSO solutions.

Influence of substituent on spectroscopic and acid-base properties of anthraquinone derivatives

A series of 1,4-disubstituted aminoanthraquinones has been prepared from 1,4 ditosyloksyanthraquinone. The potentiometric and UV-spectrophotometric method have been used to study the acid-base properties of obtained compounds. The absorption spectra revealed the presence of vibroelectronic band in visible region for compounds containing two tertiary nitrogen groups. It indicates the separation of vibronic states in the molecule. Determined pKa values in acetonitrile used as a solvent indicate the influence of substitution of amino group on basicity of the anthraquinone moiety.

Pyrazino[2,3-b]indolizine-10-carbonitrile.

In the crystal structure of the title compound, C11H6N4, neighbouring molecules are linked into inversion dimers through pairs of weak C—H⋯N hydrogen bonds, forming an R 2 2(10) ring motif. The dimers forming this motif are further linked by π–π interactions. With respective average deviations from planarity of 0.004 (2) and 0.004 (1) Å, the pyrazino[2,3-β]indolizine and cyano fragment are oriented at 0.8 (1)° to each other. The mean planes of the pyrazino[2,3-b]indolizine skeleton either lie parallel or are inclined at an angle of 28.7 (2)° in the crystal.