Center for Magnetic Resonance

A. I. Solomatina, P.S. Chelushkin, D.V. Krupenya, I.S. Podkorytov∥, T.O. Artamonova, V.V. Sizov, A.S. Melnikov, V.V. Gurzhiy, E.I. Koshel, V.I. Shcheslavskiy, S.P. Tunik

“Coordination to Imidazole Ring Switches on Phosphorescence of Platinum Cyclometalated Complexes: The Route to Selective Labeling of Peptides and Proteins via Histidine Residues”

Bioconjugate Chem., 2017, 28 (2), 426–437.
DOI: 10.1021/acs.bioconjchem.6b00598

In this study, we have shown that substitution of chloride ligand for imidazole (Im) ring in the cyclometalated platinum complex Pt(phpy)(PPh3)Cl (1; phpy, 2-phenylpyridine; PPh3, triphenylphosphine), which is nonemissive in solution, switches on phosphorescence of the resulting compound. Crystallographic and nuclear magnetic resonance (NMR) spectroscopic studies of the substitution product showed that the luminescence ignition is a result of Im coordination to give the [Pt(phpy)(Im)(PPh3)]Cl complex. The other imidazole-containing biomolecules, such as histidine and histidine-containing peptides and proteins, also trigger luminescence of the substitution products. The complex 1 proved to be highly selective toward the imidazole ring coordination that allows site-specific labeling of peptides and proteins with 1 using the route, which is orthogonal to the common bioconjugation schemes via lysine, aspartic and glutamic acids, or cysteine and does not require any preliminary modification of a biomolecule. The utility of this approach was demonstrated on (i) site-specific modification of the ubiquitin, a small protein that contains only one His residue in its sequence, and (ii) preparation of nonaggregated HSA-based Pt phosphorescent probe. The latter particles easily internalize into the live HeLa cells and display a high potential for live-cell phosphorescence lifetime imaging (PLIM) as well as for advanced correlation PLIM and FLIM experiments.

A.S. Konevaa, E. Ritter, Y.A. Anufrikova, A.A. Lezova, A.O. Klestovaa, N.A. Smirnova, E.A. Safonova, I. Smirnova

“Mixed aqueous solutions of nonionic surfactants Brij 35/Triton X-100: Micellar properties, solutes’ partitioning from micellar liquid chromatography and modelling with COSMOmic”

Colloids and Surfaces A, 2018, 538, 45–55.
DOI: 10.1016/j.colsurfa.2017.10.044

Aqueous solutions of nonionic surfactants are of interest for bioprocesses, particularly as solubilizing agents for hydrophobic substances. To design such processes, the data on partition coefficients of solutes between micelles and their aqueous surrounding (Pmw) are of high value. An extended understanding of the partition behavior can be achieved from the structural information such as the micelle size and micelles composition.
In this work, mixtures of nonionic surfactants Triton X-100 and Brij 35 were under study. The data on critical micelle concentrations showed partly non-ideal behavior of the solutions. The compositions of mixed micelles at different molar Brij 35/Triton X-100 ratios in the surfactant mixture were estimated from the data on selfdiffusion coefficients (NMR diffusometry) and were calculated within the regular solution approach and predicted by Motomura’s model. The change of the mixed micelle composition in dependence on the total surfactant concentration was observed. It has been found, that the average value of the mixed micelles radii is∼4 nm. Whereas, the polydispersity indexes and the aggregation numbers increased with Triton X-100 fraction. Moreover, the Pmw values of different non-dissociated solutes (phenyl derivatives with various functional groups) were determined by means of micellar liquid chromatography (MLC) and were predicted using the thermodynamic model COSMOmic, an extension of COSMO-RS. In general, it has been proved that COSMOmic is able to predict Pmw in the mixed micellar system formed by nonionic surfactants. The obtained data show the possibility of modulating the partition behavior of solutes using the mixtures of nonionic surfactants. Apart from the hydrophobicity, the «surfactants – solute» specific interactions play an important role in the partition behavior of the investigated systems.

P.A. Sakharov, N.V. Rostovskii, A.F. Khlebnikov, M.S. Novikov

“Annulation of five-membered cyclic enols with 3-aryl-2H-azirines: Catalytic versus non-catalytic cycloaddition”

Tetrahedron, 2017, 73(31), 4663-4670.
DOI: 10.1016/j.tet.2017.06.037

A copper(I)-NHC-catalyzed annulation of 5-membered cyclic enols of furan, thiophene and indene family with 3-aryl-2H-azirines has been developed to provide a rapid access to furo[3,4-b]pyrrole, thieno[3,4-b]pyrrole, indeno[1,2-b]pyrrole derivatives. The reaction proceeds via a copper-initiated N-C² azirine bond cleavage with the retention of the C=N double bond in the annulation product. The reaction of tetronic acids with 3-aryl-2H-azirines can also proceed under catalyst-free conditions, through a double addition of the enol to the azirine, but this route provides poor yields of the annulation products. This is the first example of the N-C² bond cleavage in 2-unsubstituted 2H-azirines in the absence of a transition metal catalyst.

E. Abakumov, E. Maksimova, A. Tsibart

“Assessment of postfire soils degradation dynamics: Stability and molecular composition of humic acids with use of spectroscopy methods”

Land Degrad Dev., 2017, 1–10.
DOI: 10.1002/ldr.2872

The effect of wildfires on the soils of the south taiga and forest-steppe environments of Central Russia (Histic Spodosols and Eutric Fluvic Arenosols) was investigated in terms of the content and quality of humic acids (HAs) using instrumental spectroscopic methods (solid-state carbon-13 nuclear magnetic resonance and electron spin resonance). The bulk elemental composition of HAs was not essentially altered in postfire soils; however, the organic matter of fire-affected superficial soil layers was characterized by changes in the structural composition and biochemical activity levels. Solid-state carbon-13 nuclear magnetic resonance spectroscopy showed that there is an intensive increase in aromatic compounds in HA molecules in soil from both the south taiga and forest-steppe environments. There is a pronounced and statistically significant decline of aliphatic chain content in response to exposure to fire. The free radicals content and the degree of molecular stabilization assessed with electron spin resonance showed an essential alteration of the HAs, expressed in the increase in the radical’s portion, in postfire soils compared with that found in soils not exposed to fire. It was also shown that the accumulation of aromatic compounds indicates only apparent stabilization of HAs due to the loss of periphery alkylic carbon species, which was confirmed by destabilization of the molecules as illustrated by the increase of free radicals.

D.S. Bolotin, M.Ya. Demakova, A.A. Legin, V.V. Suslonov, A.A. Nazarov, M.A. Jakupec, B.K. Kepplerb, V.Yu. Kukushkin

“Amidoxime platinum(II) complexes: pH-dependent highly selective generation and cytotoxic activity”

NewJ.Chem., 2017, 41, 6840
DOI: 10.1039/c7nj00982h

The reaction of cis-[PtCl2(Me2[S with combining low line]O)2] with 1 equiv. of each of the amidoximes RC(NH2)[double bond, length as m-dash]NOH in neutral media in MeOH results in the formation of complexes cis-[PtCl2{RC(NH2)[double bond, length as m-dash][N with combining low line]OH}(Me2[S with combining low line]O)] (5 examples; 83–98% isolated yields). In the presence of 2 equiv. of NaOH in MeOH solution, the reaction of cis-[PtCl2(Me2[S with combining low line]O)2] with 1 equiv. of each of the amidoximes RC(NH2)[double bond, length as m-dash]NOH leads to [Pt{RC([N with combining low line]H)[double bond, length as m-dash]N[O with combining low line]}(Me2[S with combining low line]O)2] (7 examples; 74–95% isolated yields). All new complexes were characterized by C, H, and N elemental analyses, HRESI+-MS, IR, 1H, 13C{1H}, and CP-MAS TOSS 13C{1H} NMR spectroscopies, and additionally by single-crystal XRD (for seven species). The cytotoxic potency of six compounds was determined in the human cancer cell lines CH1/PA-1, A549, SK-BR-3, and SW480. Generally, the second class of complexes containing chelating amidoximato ligands shows much higher cytotoxicity than the non-chelate amidoxime analogs, despite the lack of easily exchangeable chlorido ligands. Especially, the complex [Pt(p-CF3C6H4C([N with combining low line]H)[double bond, length as m-dash]N[O with combining low line])(Me2[S with combining low line]O)2] displays a remarkable activity in the inherently cisplatin resistant SW480 cell line (0.51 μM vs. 3.3 μM).

M. A. Kinzhalov , A. S. Legkodukh, T. B. Anisimova, A. S. Novikov, V. V. Suslonov, K. V. Luzyanin , V. Yu. Kukushkin

“Tetrazol-5-ylidene Gold(III) Complexes frоm Sequential [2 + 3] Cycloaddition of Azide to Metal-Bound Isocyanides and N4 Alkylation”

Organometallics, 2017, 36, 3974–3980
DOI: 10.1021/acs.organomet.7b00591

The reaction between equimolar amounts of the isocyanide complexes [AuCl₃(CNR)] [R = 2,6-Me₂C₆H₃ (Xyl), 1a; 2,4,6-Me₃C₆H₂ (Mes), 1b; Cy, 1c; t-Bu, 1d] and tetrabutylammonium azide (2) proceeds in CH₂Cl₂ at room temperature for ∼10 min to furnish the gold(III) tetrazolates [n-Bu₄N][AuCl₃(CN₄R)] (3a–d), which were obtained in 89–95% yields after purification. Subsequent reaction between equimolar amounts of 3a–d and methyl trifluoromethanesulfonate (MeOTf) proceeds in CH₂Cl₂ at −70 °C for ∼30 min to give the corresponding gold(III) complexes [AuCl₃(CaN(Me)N₂NbR)]a–b (5a–d) bearing 1,4-disubstituted tetrazol-5-ylidene ligands (69–75%). Complexes 3a–d were obtained as pale-yellow solids and characterized by elemental analyses (C, H, N), HRESI–-MS, FTIR, and 1H and 13C{1H} NMR spectroscopies. Complexes 5a–d were obtained as colorless solids and characterized by elemental analyses (C, H, N), HRESI+-MS, and 1D (¹H and ¹³C{1H}) and 2D (¹H,¹³C-HMBC) NMR spectroscopies. In addition, the structures of 3a, 3b, 3c, and 5a were established by single-crystal X-ray diffraction. Analysis of the Wiberg bond indices (WI) for gas phase-optimized model structures of 3a–c and 5a computed using the natural bond orbital (NBO) partitioning scheme disclosed a higher degree of electron density delocalization in the CN₄ moiety of carbene 5a when compared to tetrazolate 3a–c. Results of DFT calculations for a model system reveal that the mechanism for the cycloaddition of an azide to the isocyanide ligand in [AuCl₃(CNMe)] is stepwise and involves nucleophilic attack of N3– on the N atom of CNMe followed by ring closure. The addition is both kinetically and thermodynamically favorable and occurs via the formation of an acyclic NNNCN intermediate, whereas the cyclization is the rate-determining step.

A.S. Filatov, N.A. Knyazev, A.P. Molchanov, T.L. Panikorovsky, R.R. Kostikov, A.G. Larina, V.M. Boitsov, A.V. Stepakov

“Synthesis of Functionalized 3-Spiro[cyclopropa[a]pyrrolizine]- and 3-Spiro[3-azabicyclo[3.1.0]hexane]oxindoles from Cyclopropenes and Azomethine Ylides via [3 + 2]-Cycloaddition”

J. Org. Chem., 2017, 82 (2), 959–975
DOI: 10.1021/acs.joc.6b02505

3-Spiro [cyclopropa [a]pyrrolizine]- and 3-spiro [3-azabicyclo [3.1.0] hexane] oxindoles were prepared in moderate to high yields via one-pot three-component reactions using substituted isatins, α-amino acids, and cyclopropenes. The key step is an intramolecular [3 + 2]-cycloaddition reaction of an in situ generated azomethine ylide onto a cyclopropene. Both N-substituted and N-unsubstituted α-amino acids, dipeptide Gly-Gly, and also benzylamine were used as the amine component for the azomethine ylide generation. The anticancer activity of some of the obtained compounds against human leukemia K562 cell line was evaluated by flow cytometry in vitro.

A.N. Shestakov, A.S. Pankova, P. Golubev, A.F. Khlebnikov, M.A. Kuznetsov

“Brønsted acid mediated cyclizations of ortho-aryl(ethynyl)pyrimidines”

Tetrahedron, 2017, 73 (27-28), 3939–3948
DOI: 10.1016/j.tet.2017.05.070

A high-yielding procedure for the synthesis of 5-aryl-4-(arylethynyl)pyrimidines from easily available 2-aryl-3-hydroxyacrylates is reported. These pyrimidines readily undergo cyclization in strong Brønsted acids and, depending on the substitution in alkynylpyrimidines and the water content of the reaction mixture, yield either benzo[f]quinazolines or derivatives of spiro[cyclohexa-2,5-diene-1,5′-cyclopenta[d]pyrimidin]-4-one. In most cases the cyclization proceeds nearly quantitatively. DFT calculations support the proposed mechanisms induced by the protonation of the triple bond in 5-aryl-4-(arylethynyl)pyrimidines. Fluorescent properties of the obtained heterocycles are also described.

A.I. Solomatina, I.O. Aleksandrova, A.J. Karttunen, S.P. Tunik, I.O. Koshevoy

“Dibenzothiophene-platinated complexes: probing the effect of ancillary ligands on the photophysical performance”

Dalton Transactions, 2017, 46, 3895-3905
DOI: 10.1039/C7DT00349H

Cyclometalation of dibenzothienyl-pyridine (HPyDBT) afforded a series of platinum(II) complexes Pt(PyDBT)(L)Cl (L = DMSO, 1; P(p-C6H4-X)3 (X = H, 2; CF3, 3; OMe, 4; NPh2, 5); 1,3,5-triaza-7-phosphaadamantane, 6; 2,6-dimethylphenyl isocyanide, 7). Chelating bidentate LL ligands formed cationic compounds [Pt(PyDBT)(LL)]+ (LL = 1,2-bis(diphenylphosphino)benzene, 8; 2,2′-bipyridine, 9; 1,10-phenanthroline, 10). Oxidation of a thienyl sulfur atom allowed for the isolation of the sulfone derivative Pt(PyDBT)(PPh3)Cl (11). The title complexes were characterized crystallographically (except 7). Investigation of their photophysical behavior revealed solid state phosphorescence with quantum yields up to 0.45 for neat powders. The ancillary ligands L show a minor influence on the emission energies of the neutral compounds, but affect dramatically the intensity of luminescence. In contrast, the cationic species with diimine ligands demonstrate a significant contribution of the LL fragments into the emissive T1 states that leads to a certain mixing of 3IL and 3LL′CT transitions and causes a substantial bathochromic shift of emission.

E. G. Vlakh, E. V. Grachova, D. D. Zhukovsky, A. V. Hubina, A. S. Mikhailova, J. R. Shakirova, V. V. Sharoyko, S. P. Tunik, T. B. Tennikova

“Self-assemble nanoparticles based on polypeptides containing C-terminal luminescent Pt-cysteine complex”

Scientific Reports, 2017, 7, Article number 41991
DOI: 10.1038/srep41991

The growing attention to the luminescent nanocarriers is strongly stimulated by their potential application as drug delivery systems and by the necessity to monitor their distribution in cells and tissues. In this communication we report on the synthesis of amphiphilic polypeptides bearing C-terminal phosphorescent label together with preparation of nanoparticles using the polypeptides obtained. The approach suggested is based on a unique and highly technological process where the new phosphorescent Pt-cysteine complex serves as initiator of the ring-opening polymerization of α-amino acid N-carboxyanhydrides to obtain the polypeptides bearing intact the platinum chromophore covalently bound to the polymer chain. It was established that the luminescent label retains unchanged its emission characteristics not only in the polypeptides but also in more complicated nanoaggregates such as the polymer derived amphiphilic block-copolymers and self-assembled nanoparticles. The phosphorescent nanoparticles display no cytotoxicity and hemolytic activity in the tested range of concentrations and easily internalize into living cells that makes possible in vivo cell visualization, including prospective application in time resolved imaging and drug delivery monitoring.