6-S-Alkyl-6-thiohexonolactones and 6-S-Alkyl-6-thiohexitols: Efficient synthesis and new smectic liquid crystal phases

The mesophasic properties of S-alkylthiohexonolactones (d-galactono- and d-mannono-) and the corresponding itol derivatives with general formula Su-SR (R = C₁₁H₂₃) have been investigated. The observation that the synthesized compounds of this series has been studied using crossed polarized optical microscopy. This study involves the discovery of new chiral Smectic A liquid crystal phase through direct comparison with the defective texture of known Smectic A phase of available commercially biphenyls 8CB and 10CB.     

Reflections on Ernest Roy Davidson: the UW years 1962–1984

In the following research acetylation as an unexplored factor in the anomeric effect in carbohydrate chemistry has been examined. Crystallographic data for methyl glycosides and their acetates have been compared and discussed. Some of the methyl glycosides form hydrogen bonding with the participation of acetal oxygen atoms. This seems to have the most significant influence on the structural diagnostic parameters for anomeric effect.

Abbreviations: Me-α-Glc: methyl α-D-glucopyranoside; Me-β-Glc: methyl β-D-glucopyranoside; Me-α-Gal: methyl α-D-galactopyranoside; Me-β-Gal: methyl β-D-galactopyranoside; Me-α-Man: methyl α-D-mannopyranoside; Me-β-Man: methyl β-D-mannopyranoside; Ac-Me-α-Glc: methyl 2,3,4,6-tetra-O-acetyl-α-D-glucopyranoside; Ac-Me-β-Glc: methyl 2,3,4,6-tetra-O-acetyl-β-D-glucopyranoside; Ac-Me-α-Gal: methyl 2,3,4,6-tetra-O-acetyl-α-D-galactopyranoside; Ac-Me-β-Gal: methyl 2,3,4,6-tetra-O-acetyl-β-D-galactopyranoside; Ac-Me-α-Man: methyl 2,3,4,6-tetra-O-acetyl-α-D-mannopyranoside; Ac-Me-β-Man: methyl 2,3,4,6-tetra-O-acetyl-β-D-mannopyranoside; GIPAW (Gauge Including Projector Augmented Waves) calculations: a DFT based method used for calculating nuclear magnetic resonance parameters; CP/MAS NMR: cross-polarisation (CP) magic angle spinning (MAS) NMR spectroscopy; δ_ss: chemical shift in ¹³C CP/MAS NMR spectrum; δ_t: theoretical chemical shift: as derived from GIPAW DFT; dis: distorted multiplet in ¹H NMR spectrum.     

The oxidation of fullerene [C70] with various oxidants by ultrasonication

The reaction of C₇₀ by ultrasonication with various oxidants such as 3-chloroperoxy benzoic acid (Fluka 99%), 4-methyl morpholine N-oxide (Aldrich 97%), chromium (VI) oxide (Aldrich 99.9%), and oxone^® monopersulfate compound, at room temperature causes the oxidation of fullerene [C₇₀(O)_n] (n=1–2 or n=1). The FAB-MS, UV–visible, FT-IR spectra, and HPLC analysis confirmed that products of fullerene oxidation are [C₇₀(O)_n] (n=1–2 or n=1).     

Modeling of the molecular and electronic structures of multiple-decker sandwich macromolecules with η5-π bonds on the basis of biscyclopentadienyl derivatives 60H10 of a C60 fullerene

The molecular and electronic structures of the (CpFe)₂C₆₀H₁₀ complex of the D _5d symmetry, where Cp is the $^ \cdot C_5 H_5 $ cyclopentadienyl radical, are simulated using the ab initio Hartree-Fock-Roothaan method in the 3–21G basis set. In this complex, hydrogen atoms are attached to carbon atoms of the C₆₀ fullerene which occupy α-positions with respect to two oppositely lying five-membered rings. Each FeCp semisandwich moiety is linked to atoms of one of these five-membered rings by the η⁵-π-type bond. It is found that the energy of the η⁵-π Fe-C₆₀H₁₀ bonds in the (CpFe)₂C₆₀H₁₀ complex is comparable to that of the η⁵-π Fe-Cp bond in the FeCp₂ ferrocene molecule. The optimum geometry calculated for the (CpFe)₂C₆₀H₁₀ complex is used for modeling of the structure of the quasi-linear macromolecule [-FeC₆₀H₁₀-]_n, (I). The band structure of the energy spectrum of macromolecule I is calculated in the valence approximation of the extended Hückel method within the crystalline-orbital approach. The band gap in the spectrum of macromolecule I is ～2.27 eV. The band structure of the spectrum of this macromolecule is compared with the spectra of the hypothetical molecules [-FeCp-]_n and [-FeC₂₀-]_n.     

Electronic properties of charged fullerenes characterized by EPR and Vis-NIR spectroscopy

EPR and Vis-NIR absorption spectra have both been measured for clarification of contradictory statements about the para-and diamagnetic states of fullerenes. Thereby identification of one sharp EPR signal in solution at room temperature to C ₆₀ ^? (g=2.000±4.0001; ΔB=0.07±0.01 mT) could be made upon using different fullerene sources (TechnoCarbo, Hoechst) and methods of anion generation (chemically, electrochemically, and photochemically). This fact is also supported by the similar observation for a monosubstituted derivative (g=1.9999; ΔB=0.10 mT), in which a small broadening of this sharp signal is found originating from additional¹H hyperfine interactions. Furthermore theg-values of the radical anions of C₆₀ increase with charge (g(C ₆₀ ^? <g(C ₆₀ ^2? ) < <g(C ₆₀ ^3? ) <g(C ₆₀ ^5? )) indicating largest contributions from spin-orbit coupling for the monoanion. No diamagnetic states for the dianions of [60]- and [70]- fullerenes could be found so far but biradical species with largest zero field splittingsD=2.7 mT (C ₆₀ ^2? ), andD=3.1 mT (C ₇₀ ^2? ), respectively. The cation formation of C₆₀ (g=2.0023-2.0029; ΔB=0.15-0.20 mT) with antimony pentachloride was controlled by mass spectrometry. Stable cations were found only in methylenechloride. In other solvents like toluene addition reactions seem to occur.     

EPR of a fullerene-molecule-derived paramagnetic center as a mesoscopic conducting object

Discussion of theg-factor value of fullerene is based on the model of itinerant electrons restricted to the surface of the fullerene molecule C₆₀. The Ag shift, i.e., the difference between the experimentalg-factor and theg-factor of free electron Δg = g ? 2.0023 for C ₆₀ ^?1 is negative as for a very small metallic conducting particle.g-factor value is proportional to the interaction between itinerant electrons in the conduction band, thus the Δg is negative for C ₆₀ ^?1 and C ₆₀ ^?3 having less than half filled conduction band, while Δg is positive for C ₆₀ ⁺ where the conduction band is almost filled.     

X-ray study of some spinels containing gallium and manganese

The ternary oxides CrMnGaO₄, NiMnGaO₄, CuMnGaO₄ and ZnMnGaO₄, crystallize in the cubic spinel structure with lattice parametera=8.41±0.02 Å, 8.34±0.02 Å, 8.36±0.02 Å and 8.32±0.02 Å, respectively. The oxidation state of manganese in these spinels was determined x-ray spectroscopically. The site distribution was determined from the structural properties and calculated site preference energies of cations in the lattice. The ionic structures were found to be Ga³⁺ [Mn²⁺ Cr³⁺] O ₄ ^2? . Ga³⁺ [Cu²⁺ Mn³⁺] O ₄ ^2? , Mn²⁺ [Ga³⁺ Ni³⁺] O ₄ ^2? and Zn²⁺ [Mn³⁺ Ga³⁺] O ₄ ^2? .     

Crystalline complexes of fullerene with anisole derivatives

For the first time, bis(anisole)chromium fulleride (PhOMe)₂Cr^+·[C₆₀]^−· and a crystalline complex of fullerene with ortho-butoxyanisole have been obtained. The temperature dependence of the parameters of the EPR spectrum of bis(anisole)chromium fulleride (PhOMe)₂Cr^+·[C₆₀]^−· has been studied. The molecular structure of the complex of fullerene with ortho-butoxyanisole has been established.     

Simultaneous electrochemical and electron paramagnetic resonance studies of fullerene anion radicals C 60 1− and C 60 3−

Simultaneous electrochemical and electron paramagnetic resonance experiments have been carried out on the reduced C₆₀ fullerene to examine theg-factor assignment of the radical species. C ₆₀ ^1? and C ₆₀ ^3? show the following EPR characteristics at room temperature: C ₆₀ ^1? :g _1?=2.0002±0.0001, 2ΔB _1s=0.17 mT, and C ₆₀ ^3? :g _{3?=2.0008±0.0002}, 2ΔB _1s=0.07 mT. EPR linewidths are apparently narrower compared to those in most of the spectra previously reported. Variable temperature EPR study on solution containing C ₆₀ ^1? has shown thatg _1? value is not while the linewidth is only slightly temperature dependent.     

Stoichiometric synthesis of fullerene compounds with lithium and sodium and analysis of their IR and EPR spectra

A modified method is proposed for preparing fullerene compounds with alkali metals in a solution. The compounds synthesized have the general formula Me _n C₆₀(THF)_x, where Me = Li or Na; n=1–4, 6, 8, or 12; and THF = tetrahydrofuran. The use of preliminarily synthesized additives MeC₁₀H₈ makes it possible to prepare fullerene compounds with an exact stoichiometric ratio between C ₆₀ ^n? and Me ⁺. The IR and EPR spectra of the compounds prepared are analyzed and compared with the spectra of their analogs available in the literature. The intramolecular modes T _u (1)-T _u (4) for the C ₆₀ ^n? anion are assigned. The splitting of the T _u (1) mode into a doublet at room temperature for Me _n C₆₀(THF)_x (n=1, 2, 4) compounds indicates that the fullerene anion has a distorted structure. An increase in the intensity of the T _u (2) mode, a noticeable shift of the T _u (4) mode toward the long-wavelength range, and an anomalous increase in the intensity of the latter mode for the Li₃C₆₀(THF)_x complex suggest that, in the fullerene anion, the coupling of vibrational modes occurs through the charge-phonon mechanism. The measured EPR spectra of lithium-and sodium-containing fullerene compounds are characteristic of C ₆₀ ^? anions. The g factors for these compounds are almost identical and do not depend on temperature. The g factor for the C ₆₀ ^n? anion depends on the nature of the metal and differs from the g factor for the C ₆₀ ^? anion.     

Localization in the ground state of the ising model with a random transverse field

We study the zero-temperature behavior of the Ising model in the presence of a random transverse field. The Hamiltonian is given by $$H = - J\sum\limits_{\left\langle {x,y} \right\rangle } {\sigma _3 (x)\sigma _3 (y) - \sum\limits_x {h(x)\sigma _1 (x)} } $$ whereJ>0,x,y∈Z ^d, σ₁, σ₃ are the usual Pauli spin 1/2 matrices, andh={h(x),x∈Z ^d} are independent identically distributed random variables. We consider the ground state correlation function 〈σ₃(x)σ₃(y)〉 and prove:

1. Letd be arbitrary. For anym>0 andJ sufficiently small we have, for almost every choice of the random transverse fieldh and everyx∈Z ^d, that $$\left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle \leqq C_{x,h} e^{ - m\left| {x - y} \right|} $$ for ally∈Z ^d withC _{x h} <∞.
2. Letd≧2. IfJ is sufficiently large, then, for almost every choice of the random transverse fieldh, the model exhibits long range order, i.e., $$\mathop {\overline {\lim } }\limits_{\left| y \right| \to \infty } \left\langle {\sigma _3 (x)\sigma _3 (y)} \right\rangle > 0$$ for anyx∈Z ^d.

     

Localization in the ground state of a disordered array of quantum rotators

We consider the zero-temperature behavior of a disordered array of quantum rotators given by the finite-volume Hamiltonian: $$H_\Lambda = - \mathop \Sigma \limits_{x \in \Lambda } \frac{{h(x)}}{2}\frac{{\partial ^2 }}{{\partial \varphi (x)^2 }} - J\mathop \Sigma \limits_{\left\langle {x,y} \right\rangle \in \Lambda } \cos (\varphi (x) - \varphi (y))$$ , wherex,y∈Z ^d , 〈,〉 denotes nearest neighbors inZ ^d ;J>0 andh={h(x)>0,x∈Z ^d } are independent identically distributed random variables with common distributiondμ(h), satisfying ∫h ^?δ dμ(h)<∞ for some δ>0. We prove that for anym>0 it is possible to chooseJ(m) sufficiently small such that, if 0<J<J(m), for almost every choice ofh and everyx∈Z ^d the ground state correlation function satisfies $$\left\langle {\cos (\varphi (x) - \varphi (y))} \right\rangle \leqq C_{x,h,J} e^{ - m\left| {x - y} \right|} $$ for ally∈Z ^d withC _x,h,J <∞.     

Intermolecular photoinduced electron-transfer processes between C60 and aniline derivatives in benzonitrile

The quenching behavior of the triplets of C₆₀ by various aniline derivatives (1a-d and 2a-e) was investigated by means of laser flash photolysis in benzonitrile at 293 K. Electron transfer process was proposed to be the main mechanism because of the direct detection of radical ions of aniline derivatives and C₆₀ in time-resolved transient absorption spectra. The quenching rate constants (k_q) of by different substrates determined at 740 nm approach or reach the diffusion-controlled limit. DFT method was employed to calculate the unknown oxidation potentials of substrates in solution. With these E_ox values, free energy changes (ΔG) were obtained through Rehm-Weller equation. Dependence of observed quenching rate constants on the free energy changes further indicates the photoinduced reactions between ³C₆₀^* and substrates proceed through an electron transfer mechanism. Obtained k_q values for the aniline derivatives are impacted obviously by ground-state configurations and the kinds substituents quantified by Hammett σ constant. Good correlation between log k_q and σ values conforms to the empirical Hammett equation. A more negative ρ value (−3.356) was gained for anilines (2a-e) than that of N,N-dimethylanilines (1a-d) (−1.382), which suggests a more susceptible reactivity for the former substrates. Charge density distribution of reaction center “N” originated from quantum calculation supports this suggestion. In addition, a relationship between quenching rate constants and solvent viscosity was gained from C₆₀/dimethyl-p-toluidine system in altered mixtures of acetonitrile and toluene.     

Recent results on multiple ionization and fragmentation of negatively charged fullerene ions by electron impact

Employing the dynamic crossed-beams technique, the absolute cross sections of the electron-impact multiple ionization and fragmentation of mass-selected negatively charged fullerene ions C _m ^? → C _m?n ²⁺ (m=60, 70, 84; q=1, 2, 3; n=0, 2, 4) were measured. The electron energy varied from the respective threshold up to 1 keV. A scaling law was observed for the cross-section magnitude as a function of the fullerene size m and the charge state q of product ions. The data indicate that different mechanisms account for the detachment of an extra electron from the negatively charged fullerene and the formation of a positively charged ion, respectively. Moreover, the multiple ionization of a fullerene anion is found to be a sequential process. A novel ionization mechanism is proposed which might be expected to be valid for all negatively charged molecular or cluster ions able to shield the attached electron from the incident electron.     

Isotope effects in the tyrosinase catalysed hydroxylation of l-tyrosine methyl derivatives

To investigate isotope effects in the hydroxylation of [3′,5′-²H₂]-α-methyl- and [3′,5′-²H₂]-N-methyl-l-tyrosine, they were synthesised using acid catalysed isotope exchange at high temperature. The kinetic and solvent deuterium isotope effects on V_max and V_max/K_m parameters of tyrosinase in its action on methylated derivatives of l-tyrosine were determined using the non-competitive spectrophotometric method. Lineweaver–Burk plots were used to consider the inhibition type of O-methyl-l-tyrosine, revealing that it is an uncompetitive inhibitor of tyrosinase.     

Structure of some FeII − III hydroxysalt green rusts (carbonate, oxalate, methanoate) from Mössbauer spectroscopy

The abundances of Fe^II and Fe^III environments within green rusts one, GR1s, that intercalate carbonate, oxalate and methanoate (formate) anions are found from Mössbauer spectra for compositions corresponding to [Fe $^{\rm II}_{6}$ Fe $^{\rm III}_{2}$ (OH)₁₆]^2?+??[CO $_{3}^{2-}$ ?5H₂O]^2???, [Fe $^{\rm II}_{4}$ Fe $^{\rm III}_{2}$ (OH)₁₂]^2?+??[CO $_{3}^{2-}$ ?3H₂O]^2???, [Fe $^{\rm II}_{6}$ Fe $^{\rm III}_{2}$ (OH)₁₆]^2?+??[C₂O $_{4}^{2-}$ ?4H₂O]^2??? and [Fe $^{\rm II}_{5}$ Fe $^{\rm III}_{2}$ (OH)₁₄]^2?+??[2HCOO^????3H₂O]^2???. These formulae correspond to orders α, β and γ where cation distances are (2 × a ₀), ( $\surd 3$ × a ₀) or a mixture of both leading to (7 × a ₀), where ratio x = {[Fe^III]/[Fe_total]} = 1/4, 1/3 and 2/7, respectively. Anion distributions within interlayers are also devised and long-range orders determined accordingly.     

Charge transport in low-concentration MEH-PPV conjugated polymer/fullerene composites

Charge transport was studied in composites of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene-vinylene] (MEH-PPV) conjugate polymer and low-concentration fullerenes (C₆₀) below the percolation threshold. The electron mobility showed a linear increase with the fullerene concentration, to which the hole mobility was insensitive. Our results indicate that fullerene–polymer networks provide a conduction path to the electrons, whereas the holes are transported through the polymer-only paths. The microscopic environments of the two distinct conduction paths in the composites as revealed by the electric field dependence of the mobilities are also discussed.     

An inequality for Hilbert-Schmidt norm

For the absolute value |C|=(C*C)^1/2 and the Hilbert-Schmidt norm ∥C∥_HS=(trC*C)^1/2 of an operatorC, the following inequality is proved for any bounded linear operatorsA andB on a Hilbert space $$|| |A|---|B| ||_{HS} \leqq 2^{1/2} ||A - B||_{HS} $$ . The corresponding inequality for two normal state ? and ψ of a von Neumann algebraM is also proved in the following form: $$d(\varphi ,\psi ) \leqq ||\xi (\varphi ) - \xi (\psi )|| \leqq 2^{1/2} d(\varphi ,\psi )$$ . Here ξ(χ) denotes the unique vector representative of a state χ in a natural positive coneP ^? forM, andd(?, ψ) denotes the Bures distance defined as the infimum (which is also the minimum) of the distance of vector representatives of ? and ψ. In particular, $$||\xi (\varphi _1 ) - \xi (\varphi _2 )|| \leqq 2^{1/2} ||\xi _1 - \xi _2 ||$$ for any vector representatives ξ _j of ? _j ,j=1, 2.     

EPR spectra of C60 anions

The broad and sharp EPR signals observed in spectra of C₆₀ and C ₆₀ ^3? are summarized and proposed assignments are discussed. The sharp signals in samples of C ₆₀ ^2? are reviewed.