Monitoring the aggregation processes of amyloid-β using a spin-labeled, fluorescent nitroxyl radical

Amyloid nitroxyl radical (nitroxide) ligands were used to detect amyloid-β fibrils, the main constituents of senile plaques in Alzheimer's disease, using anisotropic ESR spectra, and were found to affect the aggregation process due to the radical functionality. These compounds have great potential as novel and multifunctional probes, combining spin labels, spin probes, and fluorescence probes.     

Structure and molecular dynamics of host–guest complexes of TEMPO with cucurbituryl: An ESR and DFT study

Host–guest complexes are of interest as promising nanodevices for molecular recognition and chemosensors. In this work, the structure and molecular dynamics of complexes of the nitroxyl radical TEMPO (I), as models of indicator and analyte, with cucurbituril CB[7] in solution and in the solid phase have been studied by ESR and DFT methods. The kinetic accessibility of the NO group of I for water-soluble reagents has been determined. By simulation of the ESR spectra of the complex, the rotational diffusion coefficients and the anisotropy of its rotation have been determined. To study the rotational mobility of the guest in the CB[7] cavity, solid solutions of I@CB[7] in the CB[7] matrix have been obtained. The ESR spectra indicate rapid jump-like rotation of I about an axis oriented along the normal to the CB[7] portals. The formation energy and the spatial structure of the complex have been calculated by the DFT method; a change in the spin density on the NO group with changing the orientation of I in the CB[7] cavity has been found.     

Synthesis,characterization, equilibrium studies,and biological activity of complexes involving copper(II), 2-aminomethylthiophenyl-4-bromosalicylaldehyde Schiff base,and selected amino acids

Ternary complexes of copper(II) with 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS) and some amino acids have been isolated and characterized by elemental analyses, IR, magnetic moment, molar conductance, UV–vis, mass spectra, and ESR. The proposed general formulas of the prepared complexes are [Cu(ATS)(AA)]·nH₂O (where AA?=?glycine, alanine, and valine). The low molar conductance values suggest the non-electrolytic nature of the complexes. IR spectra show that ATS is coordinated to copper in a bidentate manner through azomethine-N and phenolic-OH. The amino acids also are monobasic bidentate ligands via amino and ionized carboxylate groups. The magnetic and spectral data indicate the square-planar geometry of Cu(II) complexes. The geometry of the Cu(II) complexes has been fully optimized using parameterized PM3 semiempirical method. The Cu–N bond length is longer than that of Cu–O in the isolated complexes. Also, information is obtained from calculations of molecular parameters for all complexes including net dipole moment of the metal complexes, values of binding energy, and lipophilicity value (log P). The antimicrobial activity studies indicate significant inhibitory activity of complex 3 against the selected types of bacteria. The mixed ligand complexes have also been studied in solution state. Protonation constants of ATS and amino acids were determined by potentiometric titration in 50% (v/v) DMSO–water solution at ionic strength of 0.1?M NaCl. ATS has two protonation constants. The binary and ternary complexes of copper(II) involving ATS and some selected amino acids (glycine, alanine, and valine) were examined. Copper(II) forms [Cu(ATS)], [Cu(ATS)₂], [Cu(AA)], [Cu(AA)₂], and [Cu(ATS)(AA)] complexes. The ternary complexes are formed in a simultaneous mechanism.     

Fluorescence study of inclusion complexes between star-shaped cholic acid derivatives and polycyclic aromatic fluorescent probes and the size effects of host and guest molecules

Star-shaped host molecules containing two, three, and four cholic acid moieties have been used to form inclusion complexes with polycyclic aromatic hydrocarbon probes (guests) varying in size from four (pyrene) to five (benzo(e)pyrene) and seven aromatic rings (coronene) and investigated by steady-state fluorescence measurements and fluorescence lifetime techniques. The results indicated that these hydrophobic guest probes prefer to locate in the hydrophobic cavities formed by the host molecules in an aqueous solution. Further studies showed that the stoichiometric ratios of the complexes depended on the relative size of both the host and the guest. The complexes of 1:1 ratio (guest:host) were formed between pyrene and the host molecules of different sizes, while the complexes of 1:2 ratio (guest:host) were found for coronene in all cases. For benzo(e)pyrene with an intermediate size, the complexes with 1:1 and 1:2 ratios (guest:host) were formed depending on the relative sizes of the host molecules. The stability of the inclusion complexes was observed to change with the solvent polarity, indicative of an adaptation of the hydrophobicity of the host pockets to the polarity of the solvent. The formation of the complexes was driven by the solvophobic interactions.     

ESR molecular dynamics study at the oxidation sites of polypropylene with nitroxyl spin labels and spin probes

Novel methods suitable for the selective insertion of nitroxyl spin labels and spin probes at the oxidation sites of isotactic polypropylene have been developed based on reactions with the oxidation products, on spin trapping with nitroso and nitrone compounds and taking advantage of the spontaneous generation of nitroxyl radicals as intermediates in the stabilization mechanism by the HALS. The analysis of the esr spectra of the doxyl spin label and of the spin probes from the HALS, performed according to the stochastic Liouville theory, has allowed information to be obtained on the molecular mobility at the oxidation sites as a function of the temperature.     

A new series of lipophilic pH-sensitive spin probes

A series of new lipophilic spin probes with pH-dependent ESR spectra was synthesized: cyano-substituted enamino ketones, viz., derivatives of imidazolidine nitroxyl radicals. The use of these compounds makes it possible to measure the acidity of the medium in the pH 6—12 range.     

Low‐frequency ESR studies on permeable and impermeable deuterated nitroxyl radicals in corn oil solution

Low‐frequency electron spin resonance studies were performed for 2 mM concentration of deuterated permeable and impermeable nitroxyl spin probes, 3‐methoxycarbonyl‐2,2,5,5‐tetramethyl‐pyrrolidine‐1‐oxyl and 3‐carboxy‐2,2,5,5,‐tetramethyl‐1‐pyrrolidinyloxy in pure water and various concentrations of corn oil solution. The electron spin resonance parameters such as the line width, hyperfine coupling constant, g factor, rotational correlation time, permeability, and partition parameter were estimated. The broadening of line width was observed for nitroxyl radicals in corn oil mixture. The rotational correlation time increases with increasing concentration of corn oil, which indicates the less mobile nature of spin probe in corn oil mixture. The membrane permeability and partition parameter values were estimated as a function of corn oil concentration, which reveals that the nitroxyl radicals permeate equally into the aqueous phase and oil phase at the corn oil concentration of 50%. The electron spin resonance spectra demonstrate the permeable and impermeable nature of nitroxyl spin probes. From these results, the corn oil concentration was optimized as 50% for phantom studies. In this work, the corn oil and pure water mixture phantom models with various viscosities correspond to plasma membrane, and whole blood membrane with different hematocrit levels was studied for monitoring the biological characteristics and their interactions with permeable nitroxyl spin probe. These results will be useful for the development of electron spin resonance and Overhauser‐enhanced magnetic resonance imaging modalities in biomedical applications.     

Localized excited triplet states in mixed charge-transfer single crystals: formation of excited multicomplexes

Single crystals of charge-transfer (CT) complexes between tetracyanobenzene as acceptor and different aromatic donors were doped with guest donors. The molecular arrangements of the guest CT complexes forming triple energy traps in the host crystal were determined from the triplet ESR spectra of the traps. A method for the determination of relative charge-transfer triplet energies is proposed. Extended electron delocalization over more than one donor-acceptor pair has been found.     

对叔丁基杯[8]芳烃/12-钨(钼)磷(硅)杂多酸超分子包合物的合成与性质

用自识别自组装法合成了三种新型对叔丁基杯[8]芳烃/12-钨(钼)磷(硅)杂多酸超分子包合物,C88H115～116O8[XM12-040](X=P,Si;M=w,Mo),用元素分析,IR,UV,1H NMR,31P NMR,ESR,XPS,Fluorescence光谱进行了表征.结果表明,对叔丁基杯[8]芳烃主体化合物与12-钨(钼)磷(硅)杂多酸客体分子发生了主-客体包合反应,生成了稳定的发光包合物.     

Guest—host complexes of spin-labeled indoles with cyclodextrins in the solid phase: an esr study

Inclusion complexes of spin-labeled pyrrolidine-(1) and piperidine-containing (2) indole derivatives with β-cyclodextrin and γ-cyclodextrin (CD) were prepared in the solid phase and studied by ESR in a wide temperature interval. For all complexes and free spin probes in solvents of different polarity, local environment polarities of the NO group of the guest molecules were determined from the outer extrema separations in the ESR spectra measured at 77 K. From analysis of the Saturation Transfer (ST) ESR spectra and temperature dependences of linear ESR spectra of the complexes it follows that both guest molecules in γ-CD undergo rapid librations. The libration amplitude of the p-orbit axis of the NO group in molecule 2 increases with temperature and reaches about 16° at 333 K. The ESR lineshape of the β-CD complexes depends on the spin probe/β-CD molar ratio (ρ) even at ρ < 0.01. Lineshape analysis of the spectra recorded at different ρ showed that they consist of two components, one of them corresponding to strong spin-spin interaction between guest molecules and the other corresponding to almost absence of this interaction. The spectral components can be attributed to microphases of the complexes and to isolated complexes in the β-CD matrix, respectively. Simulation of the ST ESR and linear ESR spectra of the magnetically diluted complexes showed that the guest motion inside the CD cavity is better described by rotational jumps rather than Brownian diffusion in an orientation potential. In the temperature range 238—333 K, the rotational frequencies of 1 and 2 are in intervals 1.8·10⁷−6·10⁷ s⁻¹ and 4·10⁷⁻¹.3·10⁸ s⁻¹, respectively. The rotation occurs over the whole solid angle. Significant differences in the character of molecular dynamics in the γ-CD and β-CD complexes can be explained by different stoichiometry, namely, 1: 1 for the former and 2: 1 for the latter and by different orientation of guest molecules in the complexes. In both cyclodextrins the rotational mobility of molecules 2 is higher than that of 1 owing to intramolecular conformational transitions in the piperidine ring of 2 and steric hindrances produced by the methyl group in 1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 233—241, February, 2006.     

Spin exchange in solutions of TEMPOL in n-octanol and 1-methyl-3-octylimidazolium hexafluorophosphate in the temperature range from 300 to 500 K

Comprehensive examinations of the motional properties (rotational correlation time τ(R)) and the spin exchange ω(SS) of the spin probe TEMPOL have been carried out using ESR spectroscopy in two different solvents. For the first time, the dynamic parameters τ(R) and ω(SS) have been determined simultaneously by simulation of spectra measured at three different ESR frequencies (L-, X-, and Q-band) between 293 and 500 K using a dynamic model based on a stochastic fitting program and, for comparison, two alternative models involving the shift of the hyperfine lines and considering the line broadening due to spin exchange in a wide range of conditions. Possibilities and limits of the used models are shown upon comparing the obtained results of the spin exchange. Moreover, the analysis of the ESR spectra gave evidence for the existence of cage effects that produce re-encounters of the spin probes. This has been done for the activation energies, which have been calculated from the temperature dependence of the rate constants of the spin exchange. From the ratio of the activation energies and the influence of the viscosities on the dynamics of the examined systems in n-octanol and an ionic liquid, conclusions can be drawn for the re-encounter effects in solvent cages. However, in contrast to n-octanol, the dynamics of the spin probe in the ionic liquid depends on specific and anisotropic interactions. The temperature dependence of the Q-band measurements required the development of a novel Q-band cavity.     

Synthesis, spectra and biomimetic properties of copper(II)-copper(II) and copper(II)-zinc(II) binuclear complexes with CuN5 chromophores

X-band electron spin resonance (ESR) and UV-vis spectra of a homobinuclear [(Bipy)2Cu-E-Im-Cu(Bipy)2](BF4)3 and a heterobinuclear [(Bipy)2Cu-E-Im-Zn(Bipy)2](BF4)3 complexes, E-Im=2-ethylimidazolate ion have been described as possible models for superoxide dismutase (SOD). Magnetic moment and ESR spectral measurements of the homobinuclear complex have shown an antiferromagnetic exchange interaction. From pH-dependent ESR and UV-vis spectral measurements studies, these complexes have been found to be stable over 8.5-10.5 pH range. These complexes catalyze the dismutation of superoxide (O2-) at biological pH. All the observations indicate that these complexes act as good possible models for superoxide dismutase.     

Crystal and Molecular Structure of the [6-Deoxy-6-[(2-(4-imidazolyl)ethyl)amino]- cyclomaltoheptaose]copper(II) Ternary Complex with L-Tryptophanate. Role of Weak Forces in the Chiral Recognition Process Assisted by a Metallocyclodextrin

The ternary copper(II) complex of 6-deoxy-6-[(2-(4-imidazolyl)ethyl)amino]cyclomaltoheptaose (CDhm) and L-tryptophanate (L-TrpO(-)) was characterized by ESR and X-ray diffraction. The solid state structure of [Cu(CDhm)(L-TrpO)](+) shows that the aromatic side chain of TrpO(-) is outside the cavity and that the two amino nitrogen atoms, one from the histamine molecule and one from the amino acidate, are in a cis disposition. The two amino nitrogens, the imidazole nitrogen, and the carboxylate oxygen atoms form the base of a square pyramid, which surrounds the copper(II) ion, a water molecule occupying an apical position. Atomic distances suggest for this complex that pi-pi and d-pi interactions could occur in the solid state. Morover, the [Cu(CDhm)(L-TrpO)](+) has a self-assembled structure in which a CDhm molecule behaves as host and as guest. The imidazole and the indole ring are directed into the cavity of an adjacent CDhm molecule from the wider cyclodextrin rim, thus forming a polymeric column structure. ESR spectra were run on the copper(II) ternary complexes with L- or D-tryptophanate and L- or D-alaninate in frozen aqueous solution and on the former pair of enantiomers in the solid state, as well. While in the case of the ternary complex with L- or D-alaninate no differences are observed in their frozen solution spectra, in the case of complexes with TrpO(-) subtle differences are found. These differences, which disappear when excess methanol is used, are ascribed to the presence of weak forces, such as hydrophobic or d-pi interactions.     

Laser spectroscopic and theoretical studies of encapsulation complexes of calix[4]arene

The complexes between the host calix[4]arene (C4A) and various guest molecules such as NH(3), N(2), CH(4), and C(2)H(2) have been investigated via experimental and theoretical methods. The S(1)-S(0) electronic spectra of these guest-host complexes are observed by mass-selected resonant two-photon ionization (R2PI) and laser-induced fluorescence (LIF) spectroscopy. The IR spectra of the complexes formed in molecular beams are obtained by IR-UV double resonance (IR-UV DR) and IR photodissociation (IRPD) spectroscopy. The supramolecular structures of the complexes are investigated by electronic structure methods (density functional and second order perturbation theory). The current results for the various molecular guests are put in perspective with the previously reported ones for the C4A-rare gas (Rg) (Phys. Chem. Chem. Phys. 2007, 126, 141101) and C4A-H(2)O complexes (J. Phys. Chem. A, 2010, 114, 2967). The electronic spectra of the complexes of C4A with N(2), CH(4), and C(2)H(2) exhibit red-shifts of similar magnitudes with the ones observed for the C4A-Rg complexes, whereas the complexes of C4A with H(2)O and NH(3) show much larger red-shifts. Most of the IR-UV DR spectra of the complexes, except for C4A-C(2)H(2), show a broad hydrogen-bonded OH stretching band with a peak at ~3160 cm(-1). The analysis of the experimental results, in agreement with the ones resulting from the electronic structure calculations, suggest that C4A preferentially forms endo-complexes (guests inside the host calizarene cavity) with all the guest species reported in this study. We discuss the similarities and differences of the structures, binding energies, and the nature of the interaction between the C4A host and the various guest species.     

Photoswitching of the magnetic interaction between a copper(II) ion and a nitroxide radical by using a photochromic spin coupler

Photoswitching of an intramolecular spin exchange interaction between a copper(II) ion and a nitroxyl radical by using a metal complex of diarylethene has been studied by means of ESR spectroscopy. As a coordination ligand, a diarylethene with a 1,10-phenanthroline ring and nitronyl nitroxide radical was synthesized. Mixing the diarylethene ligand with [Cu(hfac)(2)] (hfac=hexafluoroacetylacetone) in toluene led to a hypsochromic shift of the absorption maxima of the closed-ring isomer due to complexation. ESR measurement in toluene at room temperature of the open-ring isomer of the Cu(II) complex gave a spectrum that is a superposition of the spectra from the nitroxide radical and Cu(II). When the sample was irradiated with 366 nm light, a new peak due to large exchange interaction appeared between those of the nitroxyl radical and Cu(II). This ESR measurement revealed that the magnitude of the spin exchange interaction was changed by more than 160-fold by photoirradiation. This is the largest magnetic photoswitching phenomenon recorded in diarylethene systems.     

Mobility of spin probes having a primary,secondary, tertiary,or quaternary amino group in drawn and undrawn nylon 6 film

The mobility of spin probes having a secondary, tertiary, or quaternary amino group in dried nylon films was investigated by means of electron spin resonance (ESR) measurements and compared with the behavior of previously investigated spin probes having a primary amino group, a carboxylate group, or a sulfate group. The spin probes having a primary or secondary amino group showed effects of drawing on the mobility, while the other probe molecules did not. This result could be interpreted by considering the interactions between the spin probes and the nylon chains. In the undrawn nylon film, the mobilities of the nonionic spin probes were almost the same, and smaller than those of the charged spin probes, suggesting that the location in the nylon film is different for the uncharged and charged spin probes. These results are discussed in detail using separation of extrema of the ESR spectra, rotational correlation times, and anisotropy parameters.     

镧系β-二酮-吡啶衍生物三元体系中f-f跃迁光谱的研究

本文研究了Pr~(3 )、Nd~(3 )、Ho~(3 )、Er~(3 )四种离子在乙醇介质中与噻吩甲酰三氟丙酮(TTA)、1—苯基—3—甲基—4—苯甲酰基—吡唑酮—5(PMBP)、乙酰丙酮(AA)、二苯甲酰甲烷(DBM)或者苯甲酰丙酮(BA)所形成的二元配合物,以及这些二元配合物与吡啶衍生物所形成的三元配合物的吸收光谱,根据Judd—Ofelt方程计算了各跃迁的振子强度以及方程中的强度参数T_2、T_4及T_8,对Nd~(3 )、Ho~(3 )、Er~(3 )的各个体系而言,超灵敏跃迁的振子强度与参数T_2明显相关。其相关系数为0.92—0.99,符合P=aT_2 b直线方程,而Pr~(3 )则例外。根据配合物吸收峰的红移,计算了Ln~(3 )—TTA—吡啶衍生物体系的共价参数。     

Structure and molecular dynamics of the ternary complexes of cyclodextrins with spin-labeled indoles and hydrocarbons in the solid phase. ESR spectroscopy and quantum chemical calculations

The ternary inclusion complexes of two spin-labeled pyrrolidine-and piperidine-containing indole derivatives (1 and 2, respectively) and two hydrocarbons, benzene and cyclohexane, with γ-and β-cyclodextrins (CD) (altogether eight complexes) were prepared and studied by ESR in the solid phase over a broad temperature range. For most ternary complexes, the hydrophobicity of the NO group environment is much higher than for binary complexes devoid of hydrocarbons. The rotational mobility of both spin-labeled indoles in the ternary complexes of γ-CD is much greater than in binary complexes of γ-CD, which is due to transition to the stoichiometry 2γ-CD-1(2)-C₆H₆(C₆H₁₂) from 1: 1 stoichiometry. The guest rotational mobility in the complexes with either of the CD is higher for 2 than for 1. The saturation transfer ESR spectra show that the rotational mobility of 1 in γ-and β-CD in the presence of C₆H₆ or C₆H₁₂ has a character of fast librations in an angular cone, whose amplitude increases with temperature, whereas for radical 2, the rotation occurs in the full solid angle. The structures and energies of all complexes were calculated for different modes of inclusion of guest molecules using the PM3 method with the standard set of parameters. The calculation results are in qualitative agreement with experimental data. The results demonstrate the possibility of substantial modification of the molecular dynamics and hydrophobicity of the environment of “functional” guest molecules by introducing a second regulatory guest molecule into the CD cavity. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2081–2093, December, 2006.     

The nature and dynamics of nonlinear excitations in conducting polymers. Polyaniline

The advantages of using the multifrequency (3-cm, 8-mm, and 2-mm) EPR method in combination with the modified method of spin label and spin probes and the methods of steady-state microwave saturation and microwave saturation transfer of spin packets in studies of the spin and electrodynamic properties of polyaniline are outlined. The methods of determining the composition of localized and delocalized paramagnetic centers and calculating their main parameters from total ESR spectra are described. Original results of investigations of polyaniline modified with sulfuric, hydrochloric, camphorsulfonic, and 2-acrylamido-2-methyl-l-propanesulfonic acids are reported. The dependences of the nature, electronic relaxation, dynamics of paramagnetic centers, and the charge-transfer mechanism on the method of synthesis, the structure of the acid molecule, and the polyaniline oxidation level are shown. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 205–230, February, 2000.     

Paramagnetic π-Allyl complexes of palladium

Paramagnetic π-allyl complexes of palladium with phenoxyl or o-semiquinolate ligands have been prepared and their ESR spectra studied. The stability of the resulting free radicals, the influence of various substituens attached to the palladium atom on the pattern of distribution of spin density of the unpaired electron and the nature of dynamic processes occuring in paramagnetic allyl complexes are discussed.