Dissociative ionization of substituted piperideines

The fragmentation of different alkyl(aryl) substituted piperideines [tetrahydro-pyridines] was studied by analyzing high-resolution mass spectra and DADI [Direct Analysis of Daughter Ions] spectra. It was shown that the retrodiene decomposition of the ring is suppressed by competing processes of elimination of ring substitutents. The nature of the substituents and their mutual disposition on the ring have a substantial influence on the extent of their cleavage from the ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 795–800, June, 1988.     

An NMR-Based Approach to the Measurement of High Log K HL Values at Low Ionic Strength. 31P NMR Study of 1,2-Diaminoethane-N,N,N′,N′-tetra(methylenephosphonic Acid) Protonation Equilibrium at pH > 12

A sequential NMR based approach is proposed for measurements of high log K values at low ionic strength. [³¹P] NMR technique is used to determine the protonation constants of 1,2-diaminoethane-N,N,N,N-tetra(methylenephosphonic acid) (EDTPH, H₈L) at 25°C in 0.1 mol-dm^–3 KNO₃ and at 37°C in 0.15 mol-dm^–3 NaCl at pH 11–14. For equilibrium L + H HL log K are found to be 13.3 (0.1) and 12.9 (0.1), respectively.     

Solvent-sensitive dyes to report protein conformational changes in living cells

Covalent attachment of solvent-sensitive fluorescent dyes to proteins is a powerful tool for studying protein conformational changes, ligand binding, or posttranslational modifications. We report here new merocyanine dyes that make possible the quantitation of such protein activities in individual living cells. The quantum yield of the new dyes is sharply dependent on solvent polarity or viscosity, enabling them to report changes in their protein environment. This is combined with other stringent requirements needed in a live cell imaging dye, including appropriate photophysical properties (excitation >590 nm, high fluorescence quantum yield, high extinction coefficient), good photostability, minimal aggregation in water, and excellent water solubility. The dyes were derivatized with iodoacetamide and succinimidyl ester side chains for site-selective covalent attachment to proteins. A novel biosensor of Cdc42 activation made with one of the new dyes showed a 3-fold increase in fluorescence intensity in response to GTP-binding by Cdc42. The dyes reported here should be useful in the preparation of live cell biosensors for a diverse range of protein activities.     

Synthesis of pyridine bases from piperidine derivatives

The corresponding substituted pyridines are obtained in 40–90% yields when N-alkyl-substituted piperidines, gD⁴-piperideines, and secondary and tertiary -piperidols are heated at 240–270C with pyridine N-oxide.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 787–789, June, 1977.     

Magnetic properties of isostructural BaCoP2O7, BaNiP2O7, and BaCuP2O7 studied with dc and ac magnetization and specific heat

Magnetic properties of three isostructural compounds BaMP2O7 (M = Co, Ni, and Cu) were investigated by dc and ac magnetization and specific heat measurements. BaCuP2O7 was shown to be an excellent quasi-one-dimensional linear-chain Heisenberg antiferromagnet with an exchange constant (J/kB) of 103.8 K (Hamiltonian H = J Sigma SiS(i+1)) and a temperature for the long-range magnetic order (TN) of 0.81 K giving the ratio kBTN/J = 0.78%. BaCoP2O7 and BaNiP2O7 exhibited long-range antiferromagnetic order at TN = 10.4 and 10.1 K, respectively. BaCoP2O7 and BaNiP2O7 showed a large contribution of the short-range correlation above TN. BaNiP2O7 remained in the antiferromagnetic state up to 90 kOe at 2 K, whereas BaCoP2O7 demonstrated two metamagnetic phase transitions at about 52 and 71 kOe at 2 K if the magnetic field was parallel to the easy direction. BaMP2O7 melted incongruently at 1323 K (M = Co), 1344 K (M = Ni), and 1338 K (M = Cu).     

Electronic state of Fe used as Mössbauer probe in the perovskites LaMO3 (M=Ni and Cu)

For the first time a comparative study of rhombohedral LaNiO₃ and LaCuO₃ oxides, using ⁵⁷Fe Mössbauer probe spectroscopy (1% atomic rate), has been carried out. In spite of the fact that both oxides are characterized by similar crystal structure and metallic properties, the behavior of ⁵⁷Fe probe atoms in such lattices appears essentially different. In the case of LaNi_0.99Fe_0.01O₃, the observed isomer shift (δ) value corresponds to Fe³⁺ (3d⁵) cations in high-spin state located in an oxygen octahedral surrounding. In contrast, for the LaCu_0.99Fe_0.01O₃, the obtained δ value is comparable to that characterizing the formally tetravalent high-spin Fe⁴⁺(3d⁴) cations in octahedral coordination within Fe(IV) perovskite-like ferrates. To explain such a difference, an approach based on the qualitative energy diagrams analysis and the calculations within the cluster configuration interaction method have been developed. It was shown that in the case of LaNi_0.99Fe_0.01O₃, electronic state of nickel is dominated by the d⁷ configuration corresponding to the formal ionic “Ni³⁺-O²⁻” state. On the other hand, in the case of LaCu_0.99Fe_0.01O₃ a large amount of charge is transferred via Cu-O bonds from the O:2p bands to the Cu:3d orbitals and the ground state is dominated by the d⁹L configuration (“Cu²⁺−O” state). The dominant d⁹L ground state for the (CuO₆) sublattice induces in the environment of the ⁵⁷Fe probe cations a charge transfer Fe³⁺+O⁻(L)→Fe⁴⁺+O²⁻, which transforms “Fe³⁺” into “Fe⁴⁺” state. The analysis of the isomer shift value for the formally “Fe⁴⁺” ions in perovskite-like oxides clearly proved a drastic influence of the 4s iron orbitals population on the Fe−O bonds character.     

1,3-diphenyl-2-azaanthracene and 8-aza-7-phenylbenzo[a]fluoranthene in the diene synthesis

The diene condensation of 1,3-diphenyl-2-azaanthracene with maleic anhydride proceeds under more severe conditions than the analogous condensation with anthracene. On the basis of an analysis of the PMR data for the adduct obtained it was assumed that isomers of ,-[9,10-dihydro-2-aza-1,3-diphenylanthrylene(9,10)]succinic anhydride with respect to the position of the anhydride bridge relative to the pyridine ring are formed in this condensation. 9,10-Dihydro-2-aza-1,3-diphenyl-9, 10-(1-cyanoethylene)anthracene was obtained in the condensation of the same azaanthracene with acrylonitrile. ,-[5H-8-Aza-7-phenylbenzo[a]fluoranthrylene (5,12b) ]succinic anhydride is formed as a result of the similar condensation of 8-aza-7-phenylbenzo[a]fluoranthene with maleic anhydride, while isomeric (with respect to the position of the nitrile group in the ethylene bridge) 5H-8-aza-7-phenyl-5,12b-(cyanoethylene)benzo[a]fluoranthenes were isolated in its condensation with the acrylonitrile. Data from the PMR and IR spectra were used to prove the structures of the adducts of the diene synthesis obtained.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1645–1647, December, 1980.     

Long-range magnetic ordering of quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Sr2Cu(PO4)2

Magnetic properties of quasi-one-dimensional S=1/2 Heisenberg antiferromagnet Sr₂Cu(PO₄)₂ were investigated by temperature and field dependence of AC susceptibility down to 0.03 K. A sharp peak was observed at on the temperature dependence of AC susceptibility indicating long-range magnetic ordering. Taking into account the exchange constant, (Hamiltonian =J∑S_iS_i+1), the ratio k_BT_N/J is 0.06%. Sr₂Cu(PO₄)₂ is, therefore, one of the best one-dimensional Heisenberg antiferromagnet known so far.     

Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

Background  

The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible) more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation.     

Synthesis of hexahydroazonino[5,6-b]indoles from hexahydroazepino[4,3-b]-and-[3,4-b]indoles and activated alkynes

A reaction of substituted hexahydroazepino[4,3-b]-and-[3,4-b]indoles with activated alkynes was studied. A one-step method for the synthesis of isomeric hexahydroazonino[5,6-b]indoles different by positions of the double bond in the azonine ring was developed. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2244–2250, November, 2007.