EPR of gamma irradiation induced radicals in NaHCO3, CsHCO3 and Na2CO3

In this study gamma irradiated NaHCO₃, CsHCO₃ and Na₂CO₃ were investigated at room temperature. The radicals induced by gamma irradiation in NaHCO₃ were found to be CO⁻₃, HCO₃ and CO⁻₂; in CsHCO₃ the species were attributed to HCO₃; and in Na₂CO₃ to CO⁻₃ and CO⁻₂ radicals. The hyperfine parameters for the hydrogen in HCO₃, and the ¹³C nucleus in CO⁻₂ radical have been determined. The results were compared with literature data for similar compounds and the EPR properties of the CO⁻₂ radical were discussed.     

Studies on the reactions of sylvatesmin and lantbeside with oxidizing free radicals

Sylvatesmin (SYL) and lantbeside (LAN) are two lignans, isolated from a Chinese folk medicinal herb, Lancea tibetica. Their abilities of scavenging oxidizing free radical models, OH, SO₄⁻ and N₃, were investigated in aqueous solution by pulse radiolysis techniques. The OH-adduct radicals with small amount of oxidized products were formed by the reaction of SYL or LAN with OH radical. SYL undergoes one-electron oxidation either by SO₄⁻ or N₃ radicals, LAN can only be detected to react with stronger oxidant SO₄⁻ radical anion. No reaction between LAN and N₃ radical was detectable. The relationship of structure with the abilities of scavenging free radicals was discussed. The reaction rate constants were determined by analysis of the build-up trace of the radical products.     

Thermochemical studies of 1-hydroxyisoquinoline, 5-hydroxyisoquinoline and 1,5-dihydroxyisoquinoline

The standard (p^° = 0.1 MPa) molar enthalpies of formation, , for crystalline 1-hydroxyisoquinoline, 5-hydroxyisoquinoline and 1,5-diidroxyisoquinoline, were derived from the standard molar enthalpies of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry. The standard molar enthalpies of sublimation, , at T = 298.15 K, were determined by Calvet microcalorimetry. The results were as follows:

1-Hydroxyisoquinoline	4395.1 ± 1.5	113.6 ± 2.2
5-Hydroxyisoquinoline	4455.2 ± 1.9	109.6 ± 2.1
1,5-Dihydroxyisoquinoline	4194.1 ± 2.2	123.6 ± 2.2

Full-size table

     

Synthesis, structure and optical limiting effect of a novel inorganic-organic hybrid polymer containing mixed chains of copper(I)/iodine

In this paper, treatment of N-ethyl-benzo[f]quinolium (ebq) iodide and CuI with excess KI afforded an unusual coordination polymer [(ebq)₂(Cu₃I₄)(CuI₂)]_n (1). 1 crystallizes in tetragonal system, space group P4(2)bc with cell parameters of , , , Z=8, , R₁=0.0447 and wR₂=0.0974. A highly interesting feature of 1 is its presence of mixed types of chains [ and chain] in one crystal lattice based on supramolecular self-assembly directed by cations. The infinite chains and in 1 could be described as the edge-sharing arrangement of CuI₄ tetrahedron. Furthermore, IR, EA, UV-Vis, thermal analysis and optical limiting measurements were adopted to characterize polymer 1. The optical limiting experiment shows that the present polymer exhibits a large optical limiting capacity.     

Cyclic voltammetry and theoretical calculations of silyl-substituted 1,4-benzoquinones

Cyclic voltammograms of 2,3,5,6-tetrakis(trimethylsilyl)-1,4-benzoquinone (1a), 2,3,5,6-tetrakis(dimethylvinylsilyl)-1,4-benzoquinone (1b), 2,3,5,6-tetrakis(dimethylsilyl)-1,4-benzoquinone (1c), 4,4,6,6,10,10,12,12-octamethyl-4,6,10,12-tetrasilatricyclo[7.3.0.0^3,7]dodeca-1(9),3(7)-diene-2,8-dione (1d), and 5-t-butyl-2-(pentamethyldisilanyl)-1,4-benzoquinone (5h) showed that the first reduction step was reversible and that the second step was irreversible. The first half-wave reduction potentials of 1a, 1b, 1c, and 1d shifted negatively relative to 1,4-benzoquinone by −0.31, −0.24, −0.03, and −0.18 V, respectively. These results demonstrated that the electron-accepting ability of the chair-form quinones 1a and 1b was lower than that of the planar quinones 1c and 1d. The of 5h (−0.93 V vs. Ag/Ag⁺) was quite similar to that of 5-t-butyl-2-trimethylsilyl-1,4-benzoquinone (5a, −0.94 V). A cyclic voltammogram of dimethylsilylene-bridged 1,4-benzoquinone dimer 7 showed two kinds of (−0.76 and −0.94 V). The electrochemical behavior of 7 would be interpreted in terms of near-neighbor interactions between reduced and non-reduced quinone units. Theoretical calculations of the silyl-1,4-benzoquinones reproduced well the solid state structures of the compounds. Also, the computed vibrational frequencies of the silyl-1,4-benzoquinones were in good agreement with the IR absorption frequencies of the CO units in the compounds. The LUMO energy levels of the silyl-1,4-benzoquinones were quantitatively proportional to the .     

Evaluation of the electronic density at critical points of hydrogen bonds: PM7 a good alternative to ab-initio methods

Hydrogen bonds are of vital importance in the formation and functioning of organic molecules; their characterization with theoretical tools is a task of interest to the scientific community. Commonly, the electron density at the bond critical point is used to characterize bonds. Generally this task is carried out with ab-initio methods. In this study, the PM7 semi-empirical approach is used to evaluate the quality of the electron density at the hydrogen bond critical points (HBCPs). The research takes into account dimers, nucleobases and alpha-helices bonded by hydrogen bonds: $$, $$, $$, $$, $$, and $$. The results are compared with second-order Møller–Plesset and density functional theory. The findings demonstrate that PM7 is a reliable alternative for explaining the electron density trends at the HBCPs.     

Adamantane-dipyrromethanes: novel anion receptors

New adamantane-dipyrromethanes (AdD 1-4) were synthesized and their anion binding properties investigated. AdD 1-3 form 2:1 complexes with F⁻ (AdD:F = 2:1) characterized by high association constants, and 1:1 complexes with Cl⁻, Br⁻, and . The binding of Cl⁻, Br⁻, and by AdD 1-3 is 2-3 times stronger than for the reference compound, meso-phenyldipyrromethane (5). However, AdD 4 forms complexes with F⁻ characterized by 1:1 and 1:2 stoichiometry (AdD:F = 1:2).     

Comparison of methods for the determination of total selenium in plasma by magnetic sector inductively coupled plasma mass spectrometry

Three sample preparation methods (dilution, microwave digestion and ethanol addition) were evaluated for the determination of Se in human plasma using magnetic sector inductively coupled plasma mass spectrometry (ICP-MS). A number of instrumental parameters were also considered, namely the choice of internal standard (Sc, Rh, In) and pre-defined spectral resolution (m/Δm ∼300 (low resolution, LR) and ∼7500 (high resolution, HR)). The isotopes and were selected for analysis avoiding the major and unresolvable Ar dimer interferences associated with other Se isotopes.Ethanol addition was found to be the most suitable and reliable sample preparation method. The optimum ethanol concentration for a 1+9 dilution of the plasma sample was 0.5% (v/v). Indium or Sc were selected over Rh as internal standards as Seronorm™ Level 1 target values were achieved at lower concentrations of ethanol modifier. Representative ICP-MS detection limits for this method using (HR) and (HR), were 0.1 and 0.2 μg l⁻¹.Accurate analysis of Se in Seronorm™ Level 1 (MI0181) was found using either or and HR (86±5 and 83±5 μg l⁻¹ respectively, n=5, In internal standard, target value=83±6 μg l⁻¹). Although offering improved precision (e.g. LR: 0-3% versus HR: 1-6%), accurate results were only obtained with LR for the Seronorm™ Level 1 sample when using (86±1 μg l⁻¹). The major interference precluded accurate Se analysis using and LR for all samples considered. Reliable Se concentrations were only found for a “real” pooled sample when using (HR), in part a result of non-negligible and unresolved interference when using LR. Consistently elevated Se concentrations were found under all conditions when Seronorm™ Level 2 (NO0371) was analysed. These results were confirmed by independent GF-AAS analysis.Magnetic sector ICP-MS with (HR), in combination with the ethanol addition sample preparation method, was used for the analysis of Se in human plasma samples as part of a small pilot study. Average measured selenium concentrations were 102±18 μg l⁻¹ (n=18).     

Electrogeneration of triplet states of intramolecular anthracene-amine systems

In the electron transfer between the cation radicals

of the amine moiety of four intramolecular anthra cene-amine systems and the anion radicals B^XXX of some heterocyclic and carbonyl compounds in acetonitrile/toluene, the triplet state of the anthracene moiety

is formed. As intermediates in this process, intramolecular and intermolecular triplet exciplexcs

or

and

or

are discussed.