Synthesis, conformational stability and molecular structure of 4-aryl- and 4,5-diaryl-1,8-bis(dimethylamino)naphthalenes.

4-Bromo- and 4,5-dibromo-1,8-bis(dimethylamino)naphthalenes were arylated with arylboronic acids under Suzuki reaction conditions to provide 4-aryl- and 4,5-diaryl-1,8-bis(dimethylamino)naphthalenes, respectively. The interaction of 4,5-dibromo-1,8-bis(dimethylamino)naphthalene with pyridin-3-ylboronic acid was accompanied by heterocyclization leading unexpectedly to the formation of N3,N3,N4,N4-tetramethylacenaphtho[1,2-b]pyridine-3,4-diamine. Dynamic 1H NMR experiments showed fast interconversion between syn and anti conformers of 4,5-diaryl-1,8-bis(dimethylamino)naphthalenes in CDCl3 solution at room temperature. The free energy of the rotational isomerization was determined to be ∼14.0 kcal mol-1 for 4,5-di(m-tolyl) and 4,5-di(naphthalen-2-yl) derivatives. X-ray analysis of 4,5-diaryl-1,8-bis(dimethylamino)naphthalenes revealed a high degree of structural deformation due to internal steric repulsions between both peri-dimethylamino and peri-aryl groups. In crystals, 4,5-di(naphthalen-1-yl)-1,8-bis(dimethylamino)naphthalene molecules exist exclusively in the most stable anti-out form, while for 4,5-di(naphthalen-2-yl) and 4,5-di(m-tolyl) counterparts, only the syn-form is realized. The introduction of two peri-aryl substituents in the 1,8-bis(dimethylamino)naphthalene scaffold affected the basic properties, making the 4,5-diphenyl derivative 0.7 pKa units less basic. The protonation of 4,5-diaryl-1,8-bis(dimethylamino)naphthalenes leads to dramatic changes in their structures. Compared to the corresponding bases, the inter-nitrogen distance in these salts noticeably decreases whereas peri-aromatic rings move away from each other demonstrating the so-called "clothespin effect". This lowers the barriers of syn/anti-isomerization; as a result, protonated molecules with peri-m-tolyl and even peri-(naphthalen-2-yl) substituents exist in crystals as mixtures of rotamers.

Magnetically bistable cobalt-dioxolene complexes with a tetradentate N-donor base.

Synthesis and magnetic characterization of a family of cobalt-dioxolene complexes [(Me2TPA)Co(36-DBCat)] (1), [(Me2TPA)Co(36-DBCat)](PF6) (2) and [(Me2TPA)Co(diox-(OMe)3)](BPh4) (3) (Me2TPA = bis(6-methyl-2-pyridyl)methyl-(2-pyridylmethyl)amine; 36-DBCat = dianion of 3,6-di-tert-butylcatechol; diox-(OMe)3 - 2,5-di-tert-butyl-3,3,4-trimethoxy-6-oxocyclohexa-1,4-dienolate) is reported. The neutral complex 1 is found to form hexa- (CoO2N4, 1a) and pentacoordinated (CoO2N3, 1b) isomers. Variable temperature single crystal X-ray diffraction analysis of 1a and 1b clearly indicates the presence of the high-spin divalent metal ion and the dianionic catecholate form of the dioxolene ligand. Oxidation of 1 by ferrocenium hexafluorophosphate results in the formation of the ionic octahedral complex 2, demonstrating thermally induced valence-tautomeric transition (ls-CoIII-36-DBCat ⇄ hs-CoII-36-DBSQ) in the solid state with T1/2 = 175 K (36-DBSQ = radical-anionic semiquinonate form of the redox-ligand). In contrast, aerial oxidation of 1 is accompanied by changes in the structure of dioxolene resulting in oxocyclohexadienolate ligand and the formation of an ionic complex of high-spin divalent cobalt (3). Compounds 1a, 1b, and 3 are found to demonstrate a field-induced single-ion magnet behavior. The analysis of the electronic structures of 1, 2 and 3 with the aid of DFT and SA-CASSCF/NEVPT2 calculations is also given.

Proton-induced fluorescence in modified quino[7,8-h]quinolines: dual sensing for protons and π-donors.

The synthesis, as well as spectral, structural and photoluminescence properties of dipyrido[3,2-e:2',3'-h]acenaphthene 5 and quinazolino[7,8-h]quinazolines 6 as representatives of the bidentate -N[double bond, length as m-dash]/-N[double bond, length as m-dash] superbases, are reported. These nitrogen bases being more rigid (5) or π-extended (6) analogs of optically-mute quino[7,8-h]quinoline are both active in terms of fluorescence with quantum yields up to φ = 0.71-0.77. At the same time, their luminescence behavior is opposite to that of peri-NMe2/NMe2 naphthalene proton sponges and their hybrid NMe2/-N[double bond, length as m-dash] analogs. Although 5 and 6 exhibit visible region emission upon protonation, for the hybrid systems the fluorescence is manifested only for bases. The most remarkable observation is that the fluorescence of compound 5 can be switched on not only by means of organic or inorganic acids, but also through the formation of chelate complexes with such weak H-donors as water and primary alcohols. It was disclosed that water is present in the complex as a cluster comprising 8 interconnected H2O molecules. Overall, the studied compounds demonstrate a previously unobserved type of dual mode optical response, H-sensing (emission enhancement in 5 and 6 on protonation) and π-sensing (emission quenching in 5H+ and 6H+ on coordination with π-donors). This work seems to be an important contribution to areas such as chemosensorics, the creation of new ligands, hydrogen transfer and some other phenomena representing different types of supramolecular interactions.

10-Dimethylamino Derivatives of Benzo[h]quinoline and Benzo[h]quinazolines: Fluorescent Proton Sponge Analogues with Opposed peri-NMe2/-N═ Groups. How to Distinguish between Proton Sponges and Pseudo-Proton Sponges.

For the first time, 10-dimethylamino derivatives of benzo[h]quinoline 6 and benzo[h]quinazoline 7a-e as mixed analogues of archetypal 1,8-bis(dimethylamino)naphthalene ("proton sponge") 1 and quino[7,8-h]quinoline 2a have been examined. Similar to 1 and 2, compounds 6 and 7 display rather high basicity, forming chelated monocations. At the same time, unexpected specifics of the protonated NMe2/-N═ systems consist of a strong shift of the NH proton to the 10-NMe2 group, contrary to the "aniline-pyridine" basicity rule. In case of 4H(+), a rapid migration (in the NMR time scale) of the NH proton between two nitrogen atoms along the N-H···N hydrogen bond was registered at room temperature and frozen below -30 °C with the proton fixed on the NMe2 group. Two different approaches for classification of strong neutral nitrogen organic bases as proton sponges (kinetically inert compounds) or pseudo-proton sponges (kinetically active) are discussed. On this basis, benzoquinoline 6 was identified as staying closer to pseudo-proton sponges while 7a-e to proton sponges due to the presence in their molecules of bulky substituents in the pyrimidine ring. Other remarkable peculiarities of 6 and 7 are their yellow color and luminescence in the visible region distinguishing them from colorless 1 and 2a.

Interaction of antithyroid drugs with bovine serum albumin: electrophoretic and fluorimetric study.

The pre-equilibrium capillary zone electrophoretic (pre-eq CZE) method to determine association constants of active anionic forms of antithyroid drugs: 6-n-propyl-2-thiouracil (PTU), 6-methyl-2-thiouracil (MTU), 2-thiouracil (TU) with bovine serum albumin (BSA) under physiological pH 7.4 has been developed for the first time. Using the decrease of the selective electrochromatographic peak area of a drug anionic form due to binding with BSA the association constants K of the binary BSA complexes were calculated. It has been found that the binding constants (log K) of BSA with TU, MTU, and PTU are equal to 2.99, 1.85, and 2.11, respectively. The interaction of PTU, MTU, TU, 2-mercapto-1-methylimidazole (MMI), and ethyl-3-methyl-2-thionoimidazoline-1-carboxylate (Carb), which is considered to be a prodrug for MMI, with BSA has been investigated under physiological conditions by means of fluorescence spectroscopy. Fluorescence emission spectra of BSA in the presence of thioamides recorded at 295 nm excitation wavelength clearly show that the studied drugs act as quenchers, except MMI, which acts as quencher when being excited at 280 nm. The 295 nm light excites tryptophan residues, while the 280 nm light excites both tryptophan and tyrosine residues. The binding constants (log K) of BSA with PTU, MTU, TU, MMI, and Carb have been found to be 4.51, 4.30, 4.30, 2.64, and 4.32, respectively.