Studies on electron spin resonance spectroscopy of biradical molecules containing (14)N-O and (15)N-O moieties

The biradicals with (14)N-Oxide and (15)N-Oxide at the both ends of a molecule are synthesized for the molecular ruler of protein structure, and a potential device for quantum computing. We also establish a general synthetic method for reliable biradical formation. ESR spectra are recorded for the biradicals containing (15)N-Oxide and (14)N-Oxide with various interdistance separations. We find that two types of biradicals yielded different ESR spectra depending upon the distance between the (15)N-O and (14)N-O moieties in a molecule. This is due to electron spin dipole-dipole interaction occurring between the radicals. We also find that there is an indication of isotopic nuclear effects in the dipole-dipole interactions. The present study implies feasibility of the distance measurement between two different N-Oxides containing (14)N and (15)N isotopes. We conclude that quantum entanglement effects are observed through the dipolar interactions, which enable application of quantum computing devices operating in the liquid state.     

The rα-structure of thieno[2,3-b] thiophene. A H-NMR study in a nematic phase including C-satellites in natural abundance

The ¹H-NMR spectrum of thieno[2,3-b]thiophene in a nematic phase has been recorded and analysed. The ¹H,¹³C dipole—dipole couplings were obtained from ¹³C satellites in natural abundance. The indirect ¹H,¹H and ¹H,¹³C spin—spin coupling constants were determined from an isotropic sample. The dipole—dipole couplings were corrected for harmonic vibrational contribution. The corrected dipole—dipole couplings were used to evaluate the r_α-structure of the molecule.     

Effects of alkali-metal cations on nitrate-ion N-O bond force constants in ionic melts

Measured frequencies from pure nitrate liquids have been used to calculate the force constants for the nitrate ion and the M⁺-NO₃ ^– systems (M⁺ = Li⁺, Na⁺, K⁺, Rb⁺, and Cs⁺) by a matrix successive-approximation method based on perturbation theory in dependent coordinates. The valency force constants K_q for the N-O bonds are increased by comparison with free NO ₃ ^– . The N-O bond strengthening is not adequately explained by cation-anion interaction because there is electron-density transfer mainly by the mechanism within the NO ₃ ^– . Correction for the vibrational parameters of the interacting particles confirms the previously demonstrated acid-base mechanism for the cation-anion interaction in liquids containing nitrate.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 25, No. 2, pp. 230–234, March–April, 1989.     

Noncovalent Interaction of Uridine 5′-Monophosphate with Adenosine, Cytidine, and Thymidine, as well as Adenosine 5′-Monophosphate and Cytidine 5′-Monophosphate in Aqueous Solution

Adduct formation has been studied in the systems of uridine 5′-monophosphate (UMP) with adenosine (Ado), cytidine (Cyd), thymidine (Thd), adenosine 5′-monophosphate (AMP), and cytidine 5′-monophosphate (CMP) by the potentiometric method with computer analysis of the data and ¹³C and ³¹P NMR spectroscopic measurements. It has been established that in the complexes identified, ion–dipole and dipole–dipole interactions occur with the positive reaction centers being protonated nitrogen atoms N(3) of UMP or Thd, and at low pH values, endocyclic nitrogen atoms of the other nucleosides and nucleotides, as e.g., in (UMP)H₂(Ado). The negative reaction centers are the high-electron density atoms N(1) and N(7) from Ado or AMP and N(3) from Cyd or CMP, and the phosphate group of the nucleotides studied, which already undergo partial deprotonation at low pH values. The NMR results have established the presence of noncovalent stacking-type interactions in certain molecular complexes, e.g., (UMP)H₂(AMP). The sites of ion–dipole or dipole–dipole interactions are generated as a result of deprotonation of the nucleosides and nucleotides in the pH range of formation of molecular complexes. Analysis of the equilibrium constants of the reaction allowed a determination of the effectiveness of the phosphate groups and donor atoms of heterocyclic rings in the process of molecular complex formation.     

Equilibrium and NMR Studies of Noncovalent Interactions in Binary Systems: Uridine,Adenosine, Cytidine and Thymidine,and Adenosine (or Cytidine) 5′-Monophosphate in Aqueous Solution

The molecular complex formation reactions of uridine (Urd) with adenosine (Ado), cytidine (Cyd), thymidine (Thd), adenosine 5-monophosphate (AMP) and cytidine 5-monophosphate (CMP) have been studied at 20°C. It was found that the main positive noncovalent centers of ion–dipole and dipole–dipole type interactions are the protonated N(3) atoms of Urd, whereas the negative centers are the endocyclic atoms of the bases characterized by high electron density from the second molecule involved in the reaction. Moreover, NMR results indicate the occurrence of stacking in the complex (Urd)H(Cyd), whereas in the complex, (Urd)H₂(Thd), it is the only type of interaction. Deprotonation of the latter species brings about a change in the character of the reaction and ion–dipole interactions have been detected in the adduct, (Urd)H(Thd). Interestingly, no involvement of the phosphate groups in the formation of AMP and CMP adducts has been evidenced and the main centers of the reactions were found to be the N(7)and N(1) atoms of AMP, or the N(3) atoms of CMP and Urd. Moreover, in the Urd/CMP system the NMR results suggest stacking-type interactions.     

Single crystal ESR and ENDOR of bis-(salicylaldoximato) Cu(II): Bis-(Salicylaldoximato)Ni(II): Copper,nitrogen and proton hyperfine data and structure of the internal H-bond

An investigation of the ESR and ENDOR spectra of the complex Cusal₂ substituted into single crystals of Nisal₂ is reported. An analysis of the spectra is presented yielding g tensor, the hyperfine interaction tensors of ⁶³Cu, ¹⁴N and four protons and the quadrupole tensor of ¹⁴N, as well as the orientation of the principal axes systems of these quantities. Interpretation of the hyperfine pattern of the set of two perfectly equivalent ¹⁴N nuclei is shown to require a detailed analysis of the second order perturbation terms expressed in the coupled spin basis. For certain orientations of the crystal the ¹⁴N hyperfine pattern shows up to sixteen lines. Analysis of this phenomenon is achieved by exact diagonalization of the energy matrix and is traced back to noncrossing of energy levels. From the magnetic data bonding parameters of Cusal₂ in an extended Maki—McGarvey picture and spin densities on Cu and ¹⁴N are derived. Cusal₂ features an intramolecular hydrogen bridge of type OH…O. Based on some assumptions concerning spin densities, the experimentally determined magnetic constants and a seven-center dipole—dipole interaction model, the structure of the H-bond is inferred to be bent and nonsymmetric, with the angle ∠ OH…O lying in the range 130–143°.     

Toward the Experimental Structure Determination of Larger Molecular Clusters: Application and Limitations of the Weak Interaction Model to the (C6H6)13B2u ← A1g00 0 Spectrum

The experimental B_2u A_1g0⁰ ₀ spectrum of (C₆H₆)₁₃ was analyzed within the weak-interaction model using minimum energy structures calculated from six different potential energy surfaces. The coexistence of two isomers—both of C₃ symmetry and with nearly equal populations—is supported. Structures predicted by two of the six potential energy surfaces are strongly favored. The transition dipole of benzene moieties within the cluster has a magnitude of 0.23 Debye. Weak transition dipole–dipole interactions fall between –1.95 and +2.24cm^–1 and site shifts of ligand molecules range from –160.3 to –153.8cm^–1. Although the weak-interaction transition dipole–dipole model falls short of unambiguously determining isomeric structures of benzene-13, it establishes a solid foundation on which modeling can be based for determining structures of larger, high-symmetry, molecular clusters.     

ESR Studies on a Friedel‐Crafts Alkylation Reaction in [bmim]Cl‐AlCl3 Ionic Liquid

The paramagnetic complexes formed in Friedel‐Crafts alkylation reaction systems are invistigated by electron spin resonance (ESR) spectroscopy, in room temperature ionic liquids system 1‐butyl‐3‐methyl‐limidazolium chloride‐aluminium chloride ([bmim]Cl‐AlCl₃). The results indicate that ESR spectra observed are due to polycyclic aromatic radical cations formed from their parent hydrocarbons. ESR spectrum of spin adduct is obtained in an ionic liquid system composed of [bmim]Cl‐AlCl₃. In acidic solution the ¹⁴N hyperfine coupling constant of 4‐oxo‐TEMPO, 2.15 mT, is appreciably larger due to an adduct formed with AlCl₃.     

Monocyclic biradicals in the imidazolidine series

The reaction of 1-hydroxy-3-imidazoline 3-oxides with alkyl- or phenyliithium followed by oxidation gives stable biradicals with two nitroxyl groups in the imidazolidine ring. Anisotropic ESR spectra of these biradicals are discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 924–927, May, 1993.     

Microwave spectra of [15n] and [13c] pyridines,quadrupole coupling constants,dipole moment and molecular structure of pyridine

The microwave spectra of two ring-substituted species of pyridine have been remeasured, and the spectra of the two remaining species investigated and assigned.¹⁴N quadrupole coupling splittings were analyzed and used to determine the quadrupole coupling constants, while the derived center frequencies were fitted to give improved values for the rotational constants.A complete substitution structure can now be presented.The dipole moment of pyridine was redetermined from Stark measurements in the spectrum of [¹⁵N]pyridine.     

15N and17O NMR spectra of vinyl ethers of pyridine and quinoline

Conclusions ¹⁵N (¹⁴N) and¹⁷O NMR spectra have been obtained on vinyl ethers of pyridine and quinoline, with unenriched samples. The principal factor determining the chemical shifts is p- conjugation of the unshared pairs of the heteroatom with the unsaturated fragments of the molecule; an additional contribution in the case of the¹⁵N signals comes from interaction of the nitrogen atom with a proton through space.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 769–773, April, 1987.     

Energy transfer and migration in highly forbidden transitions of lanthanide ion doped crystals

Förster–Dexter theory for resonant energy transfer is extended to higher order and applied to explain the rates of energy transfer and migration processes in highly forbidden transitions for some solid-state lanthanide (Ln) ion systems for which experimental results are available. The second-order two-body energy transfer mechanism involves two inter-ion correlated dipole electrostatic interactions, i.e. dipole dipole–dipole dipole (dd–dd) energy transfer, also termed Axe–Axe energy transfer in view of the similarity of the theoretical formalism with that for two-photon transitions. Each of the dipolar transitions consists of a transition from the 4fⁿ configuration to an opposite-parity configuration, taken to be 4fⁿ⁻¹5d. dd–dd energy transfer is a short-range (R⁻¹²) interaction so that it is most important in systems with short donor Ln–acceptor Ln separations. The energy transfer formalism is extended to include spin-forbidden transitions at one or two sites, the so-called Axe–Judd–Pooler (Axe–JP) and JP–JP energy transfer. In some cases the dd–dd mechanism is the dominant energy transfer process, as exemplified herein for energy migration in the ⁵D₀ state of Sm²⁺ in SrF₂, and also in the ⁵D₀ state of Eu³⁺ in Cs₂NaEuCl₆.     

Quantitative electrochemical formation of phosphotungstate heteropolyanion blues

The optical and ESR spectra of electrochemically reduced phosphotungstate and polyphosphotungstate anions in phosphoric acid were examined as quantitative functions of W⁵⁺ concentration. The optical spectra obey Beer-Lambert laws and are similar to the spectra of reduced silicotungstate anions, indicating the secondary nature of the central cluster in the keggin structure with regard to interactions with the reduction electron. ESR spectra indicate an equivalent correspondence for the W⁵⁺ concentration and unpaired spins for the reduced polyphosphotungstate anion but for the reduced phosphotungstate anion monomer the unpaired spin concentration estimated by ESR was much lower than the W⁵⁺ concentration. Reacting reduced phosphotungstate anions with oxygen showed a I-electron reduction of the oxygen molecule with concomitant oxidation of W⁵⁺ to W⁶⁺ and possibly production of high-molecular-weight, polyanion clusters.     

ESR spectra of copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones

ESR spectra of binuclear copper(ii) complexes with 2-hydroxy-5-methyl- and 5-chloro-2-hydroxyacetophenone acyldihydrazones (H₄L) [Cu₂L·2Py], in which the coordination polyhedra are linked by the polymethylene chain with different lengths (from one to five units), were studied. The spectra of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids exhibit weak exchange interactions between the paramagnetic sites. These interactions induce seven HFS lines from two equivalent copper nuclei with the constant 40·10^–4 cm^–1 in the ESR spectra of liquid solutions. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of the complex based on heptadioic acyldihydrazone contains the signal of four HFS lines with the constant 72·10^–4 cm^–1, which is common for the copper(ii) monomeric compounds.     

Modulation effects in the electron spin echo of trans bis-(2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl-4-il) ethylene biradicals

Electron spin echo modulation effects have been investigated in trans bis(2,2,5,5-tetramethyl-3-imidazoline-3-oxide-1-oxyl-4-il) ethylene biradicals involving ¹⁴N or ¹⁵N nuclei in different positions. The modulation frequencies are shown to be the nitrogen nuclear transition frequencies in radical fragments at m_S = 0 of a triplet electronic spin. Quadrupole splitting parameters for these nitrogen nuclei have been determined.     

Quantum chemical calculation of spectroscopic and photoelectronic characteristics of [<Emphasis Type="Italic">n</Emphasis>]staffanes

Structural parameters, IR spectra, ¹H and ¹³C NMR spectra, quadrupole moments, and dipole polarizabilities of seven [n]staffanes with a distance between the terminal carbon atoms of up to 22.0 Å have been determined by DFT quantum chemical calculations at the PBE0/cc-pVTZ level of theory.     

ESR of ortho-dimesitoylbenzene-alkali earth metal chelates

The ESR spectra of rigid glass solutions of biradicals of ortho-dimesitoylbenzene anion and alkali earth ions, were recorded. The zero field splitting parameter D is compared with theoretical values calculated for different interionic distances. The results show that the biradical species should be of the contact type with metal to oxygen distance very close to the sum of the van der Waals radii of oxygen and metal ions.     

Magnetic interactions in supramolecular N-O...H-C[triple bond]C- type hydrogen-bonded nitronylnitroxide radical chains

Two paramagnetic building blocks, 2-(4-ethynyl-1-phenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl (3) and 2-(5-ethynyl-2-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl (4) were synthesized and crystallized. Single crystal X-ray studies of 3 and 4 show the formation of supramolecular head-to-tail one-dimensional H-bonded (N-O...H-C[triple bond]C- type) chain structures with O...C distances of 3.181 and 3.155 A, respectively. High-resolution isotropic liquid state (c相似文献   

An ESR study of electron loss and electron capture by silver (I) ions in methyl cyanide

Exposure of solutions of silver (I) perchlorate in methyl cyanide to ⁶⁰Co γ-rays at 77 K gave Ag(II) and Ag(O) centres in addition to radicals formed from the solvent. Their ESR spectra showed hyperfine features from ¹⁰⁹Ag and ¹⁰⁷Ag together with features from four equivalent ¹⁴N nuclei. The results are contrasted with those previously reported for solutions of silver (I) nitrate in methyl cyanide, which gave Ag(II) and Ag(O) centres whose ESR spectra were devoid of any ¹⁴N hyperfine features.