Syntheses, structures, and magnetic characterizations of cyanide-bridged Fe(III)Mn(III) chains constructed by mer-Fe(III)tricyanide and Mn(III) Schiff bases: magnetostructural relationship

Five Fe(III)Mn(III) bimetallic compounds [Fe(iqc)(CN)(3)][Mn(5-Xsalen)]·pMeOH·qMeCN·rH(2)O [Hiqc = N-(quinolin-8-yl)isoquinoline-1-carboxamide; salen = N,N'-ethylenebis(salicylideneiminato) dianion; X = H(2), F(3, 3a), Cl(4), Br(5)] were prepared by assembling a newly designed mer-Fe tricyanide (Ph(4)P)[Fe(iqc)(CN)(3)]·0.5H(2)O (1) and the respective Mn Schiff bases Mn(5-Xsalen)(+). Compounds 2-4 show linear chain structures in which trans-positioned cyanides of the Fe precursor bridge neighbouring Mn atoms, while 5 is a zigzag chain coordination polymer where two cyanide groups of the precursor in the cis mode act as bridges. The structural change from linear to zigzag may arise from the size effect of the halogens. The reversible structural transformation occurs between 3 and 3a upon the solvation-desolvation protocol and the corresponding magnetic behaviours are affected. Furthermore, in 4 and 5, the helical chains are established through hydrogen bonding of solvent molecules. From a magnetostructural point of view, within the linear chain system, the ferromagnetic coupling in 2, contrary to antiferromagnetic interactions in 3-4, is associated with the large torsion angle of C(eq)-Fe-Mn-N(O)(eq) (eq = equatorial) as well as almost the linear Mn-N≡C angle.     

Oligoethylene glycols as highly efficient mutifunctional promoters for nucleophilic-substitution reactions

Herein, we report the promising use of n-oligoethylene glycols (oligoEGs) as mutifunctional promoters for nucleophilic-substitution reactions employing alkali metal salts. Among the various oligoEGs tested, pentaethylene glycol (pentaEG) had the most efficient catalytic activity. In particular, when compared with other nucleophiles examined, a fluorine nucleophile generated from CsF was significantly activated by the pentaEG promoter. We also performed various facile nucleophilic-displacement reactions, such as the halogenation, acetoxylation, thioacetoxylation, nitrilation, and azidation of various substrates with potassium halides, acetate, thioacetate, cyanide, and sodium azide, respectively, in the presence of the pentaEG promoter. All of these reactions provided their desired products in excellent yields. Furthermore, the combination of pentaEG and a tert-alcohol medium showed tremendous efficiency in the nucleophilic-displacement reactions (fluorination and methoxylation) of base-sensitive substrates with basic nucleophiles (cesium fluoride and potassium methoxide, respectively). The catalytic role of oligoEGs was examined by quantum-chemical methods. The oxygen atoms in oligoEGs were found to act as Lewis bases on the metal cations to produce the "flexible" nucleophile, whereas the two terminal hydroxy (OH) groups acted as "anchors" to orientate the nucleophile and the substrate into an ideal configuration for the reaction.     

Radiation-grafted proton exchange membranes based on co-grafting from binary monomer mixtures into poly(ethylene-co-tetrafluoroethylene) (ETFE) film

In this study, proton exchange membranes (PEMs) based on a poly(ethylene-co-tetrafluoroethylene) (ETFE) film were synthesized through the graft copolymerization of styrene and VTMS (vinyltrimethoxysilane), or styrene and TMSPM (3-(trimethoxysilyl) propyl methacrylate) binary monomer systems using a simultaneous irradiation method. The prepared membranes with the similar degrees of grafting were investigated by measuring ion exchange capacity, proton conductivity, water uptake, chemical stability, and dimensional stability. The results indicate that the silane-crosslinked proton exchange membrane (PEM) has not only lower water uptake and dimensional change but also high proton conductivity at low humidity condition compared to non-crosslinked poly(ethylene-co-tetrafluoroethylene)-g-poly(styrene sulfonic acid) (ETFE-g-PSSA). Also, the chemical stability of silane-crosslinked fuel cell membranes was more improved than that of non-crosslinked fuel cell membrane.     

Kinetics of elementary steps in the reactions of atomic bromine with isoprene and 1,3-butadiene under atmospheric conditions

Laser flash photolysis of CF(2)Br(2) has been coupled with time-resolved detection of atomic bromine by resonance fluorescence spectroscopy to investigate the gas-phase kinetics of early elementary steps in the Br-initiated oxidations of isoprene (2-methyl-1,3-butadiene, Iso) and 1,3-butadiene (Bu) under atmospheric conditions. At T ≥ 526 K, measured rate coefficients for Br + isoprene are independent of pressure, suggesting that hydrogen transfer (1a) is the dominant reaction pathway. The following Arrhenius expression adequately describes all kinetic data at 526 K ≤ T ≤ 673 K: k(1a)(T) = (1.22 ± 0.57) × 10(-11) exp[(-2100 ± 280)/T] cm(3) molecule(-1) s(-1) (uncertainties are 2σ and represent precision of the Arrhenius parameters). At 271 K ≤ T ≤ 357 K, kinetic evidence for the reversible addition reactions Br + Iso ? Br-Iso (k(1b), k(-1b)) and Br + Bu ? Br-Bu (k(3b), k(-3b)) is observed. Analysis of the approach to equilibrium data allows the temperature- and pressure-dependent rate coefficients k(1b), k(-1b), k(3b), and k(-3b) to be evaluated. At atmospheric pressure, addition of Br to each conjugated diene occurs with a near-gas-kinetic rate coefficient. Equilibrium constants for the addition/dissociation reactions are obtained from k(1b)/k(-1b) and k(3b)/k(-3b), respectively. Combining the experimental equilibrium data with electronic structure calculations allows both second- and third-law analyses of thermochemistry to be carried out. The following thermochemical parameters for the addition reactions 1b and 3b at 0 and 298 K are obtained (units are kJ mol(-1) for Δ(r)H and J mol(-1) K(-1) for Δ(r)S; uncertainties are accuracy estimates at the 95% confidence level): Δ(r)H(0)(1b) = -66.6 ± 7.1, Δ(r)H(298)(1b) = -67.5 ± 6.6, and Δ(r)S(298)(3b) = -93 ± 16; Δ(r)H(0)(3b) = -62.4 ± 9.0, Δ(r)H(298)(3b) = -64.5 ± 8.5, and Δ(r)S(298)(3b) = -94 ± 20. Examination of the effect of added O(2) on Br kinetics under conditions where reversible adduct formation is observed allows the rate coefficients for the Br-Iso + O(2) (k(2)) and Br-Bu + O(2) (k(4)) reactions to be determined. At 298 K, we find that k(2) = (3.2 ± 1.0) × 10(-13) cm(3) molecule(-1) s(-1) independent of pressure (uncertainty is 2σ, precision only; pressure range is 25-700 Torr) whereas k(4) increases from 3.2 to 4.7 × 10(-13) cm(3) molecule(-1) s(-1) as the pressure increases from 25 to 700 Torr. Our results suggest that under atmospheric conditions, Br-Iso and Br-Bu react with O(2) to produce peroxy radicals considerably more rapidly than they undergo unimolecular decomposition. Hence, the very fast addition reactions appear to control the rates of Br-initiated formation of Br-Iso-OO and Br-Bu-OO radicals under atmospheric conditions. The peroxy radicals are relatively weakly bound, so conjugated diene regeneration via unimolecular decomposition reactions, though unimportant on the time scale of the reported experiments (milliseconds), is likely to compete effectively with bimolecular reactions of peroxy radicals under relatively warm atmospheric conditions as well as in 298 K competitive kinetics experiments carried out in large chambers.     

Comparison of storage stability of odorous VOCs in polyester aluminum and polyvinyl fluoride Tedlar bags

Whole air sampling using containers such as flexible bags or rigid canisters is commonly used to collect samples of volatile organic compounds (VOC) in air. The objective of this study was to compare the stability of polyester aluminum (PEA) and polyvinyl fluoride (PVF, brand name Tedlar^®) bags for gaseous VOC sampling. Eight VOC standards (benzene, toluene, p-xylene, styrene, methyl ethyl ketone, methyl isobutyl ketone, butyl acetate, and isobutyl alcohol) were placed into each bag at storage times of 0, 2, and 3 days prior to analyses by gas chromatography/mass spectrometry (GC/MS). From each bag representing each storage day, samples of 3 different mass loadings were withdrawn and analyzed to derive response factors (RF) of each chemical between the slope of the GC response (y-axis) vs. loaded mass (x-axis). The relative recoveries (RR) of VOC, if derived by dividing RF value of a given storage day by that of 0 day, varied by time, bag type, and VOC type. If the RR values after three days are compared, those of methyl isobutyl ketone were the highest with 96 (PVF) and 99% (PEA); however, the results of isobutyl alcohol were highly contrasting between the two bags with 31 and 94%, respectively. Differences in RR values between the two bag types increased with storage time, such that RR of PEA bags (88 ± 10%) were superior to those of PVF bags (73 ± 22%) after three days, demonstrating that VOC in PEA bags were more stable than in PVF bags.     

Surface kinetics of nitrogen dissolution and its correlation to the slag structure in the CaO―SiO2, CaO―Al2O3, and CaO―SiO2―Al2O3 slag system

The kinetics of nitrogen dissolution into molten slag at 1873 K was investigated by an isotope exchange technique. Rate constants were correlated with the molten slag structure obtained from FT-IR spectra. The rate constant in the CaO―SiO₂ binary system showed a maximum value at a specific slag composition followed by a decrease in the rate due to excess O²⁻ blocking the surface sites for nitrogen adsorption. The rate constant in the CaO―Al₂O₃ binary system was comparatively constant within the experimental range of 45 mass% to 60 mass%. The rate constant in the CaO―SiO₂―Al₂O₃ ternary slag system was measured within the boundary of the liquidus line and showed a close correlation with the slag structure. Furthermore, the rate constant in the CaO―SiO₂―Al₂O₃ ternary system was found to be significantly higher compared to the binary system due to the correlated effect of lower binding energies of the Al―O bonds and the increased number of reaction sites available when smaller Si―O tetrahedral were simultaneously present with Al―O bonds.     

Cryopreservation of potato cultivated varieties and wild species: critical factors in droplet vitrification

The applicability of cryopreservation protocols to a broad range of genotypes is a key issue for genebanks. We tried to identify the critical factors causing differences in survival of cryopreserved shoot tips using potato varieties coming from cultivated and wild species. The droplet-vitrification method, a combination of droplet-freezing and solution-based vitrification, was selected from several protocols. High survival after freezing was observed after dehydration with PVS2 for 20 min, cooling shoot tips placed in a droplet of PVS2 solution on aluminum foil strips by immersing the foil strips in liquid nitrogen, warming them by plunging the foil strips into a 0.8 M sucrose solution (at 40 degrees C) for 30 s and unloading in 0.8 M sucrose for 30 min. This optimized protocol was successfully applied to 12 accessions with survival ranging between 64.0 and 94.4%.     

Facile nucleophilic fluorination of primary alkyl halides using tetrabutylammonium fluoride in a tert-alcohol medium

Nonpolar protic reaction media such as t-amyl alcohol allow the aliphatic, nucleophilic fluorination reaction of primary haloalkane systems to fluoroalkanes, using tetrabutylammonium fluoride (TBAF), to proceed chemo-selectively at a reasonable reaction rate under mild conditions to afford the fluoro-product in high yield. As an example, the nucleophilic fluorination of 2-(3-iodopropoxy)naphthalene (1a) as the primary haloalkane model compound, with TBAF in acetonitrile as a polar aprotic solvent, CsF in t-amyl alcohol as a nonpolar protic solvent, and TBAF in t-amyl alcohol for 1 h provided 2-(3-fluoropropoxy)naphthalene (2a) in 38, 5, and 76% yields, respectively.     

Separation of phosphorous by liquid–liquid extraction for the measurement of <Superscript>32</Superscript>P

Phosphorous containing radioisotope waste was separated and determined by liquid–liquid extraction method through liquid scintillation counter (LSC). In this process, ammonium phosphate was converted to phosphomolybdate (PMo) by the reaction of ammonium molybdate (Mo) in HCl solution (0.02 M) and maximum UV/VIS absorbance (λ_max) 218 nm was observed. The PMo solution was extracted with TOA (Tri-n-Octylamine)/xylene mixture and λ_max 290 nm was found for this organic layer. Absorbance of aqueous and organic layer was linear through concentration. The impurities such as Co, Cr, Gd, etc. remain in aqueous layer by treating with Mo which was determined by ICP-AES and AAS. The quenching correction curve for ³²P was calculated using LSC results. No counting change was observed as the volume of quenchers increased. The recovery was 98% and 81% for the extraction and separation process from the test using H₃³²PO₄ as standard tracer.