Influence of the ligand-field on EPR parameters of cis- and trans-isomers in Mo systems relevant to molybdenum enzymes: Experimental and density functional theory study.

The electron paramagnetic resonance (EPR) investigation of mononuclear cis- and trans-(L1O)MoOCl complexes [L1OH = bis(3,5-dimethylpyrazolyl)-3-tert-butyl-2-hydroxy-5-methylphenyl)methane] reveals a significant difference in their spin Hamiltonian parameters which reflect different equatorial and axial ligand fields created by the heteroscorpionate donor atoms. Density functional theory (DFT) was used to calculate the values of principal components and relative orientations of the g and A tensors, and the molecular framework in four pairs of isomeric mononuclear oxo‑molybdenum(V) complexes (cis- and trans-(L1O)MoOCl, cis,cis- and cis,trans-(L-NS)MoOCl [L-NSH = N,N'-dimethyl-N,N'-bis(mercaptophenyl)ethylenediamine], cis,cis- and cis,trans-(L-NS)MoO(SCN), and cis- and trans-[(dt)MoO(OMe)] [dtH = 2,3-dimercapto-2-butene]). Scalar relativistic DFT calculations were conducted using three different exchange-correlation functionals.

Steam-Stable Basic Immobilized Amine Sorbent Pellets for CO Capture Under Practical Conditions.

Pelletization of basic immobilized amine sorbent (BIAS) particles is required to improve their mechanical strength and facilitate their practical CO capture application under fixed or dynamic reactor conditions. Herein, we utilized two methods to prepare amine-functionalized BIAS pellets. Method (ii-a) involved combining latex polychloroprene (PC)/polyamine solutions with fly ash (FA)/BIAS powder to form sorbent pellets.

Novel Rapid Screening of Basic Immobilized Amine Sorbent/Catalyst Water Stability by a UV/Vis/Cu Technique.

Time-consuming thermogravimetric analysis (TGA) decomposition study is a typical practice to assess the stability of fresh and water-treated basic immobilized amine sorbents (BIAS)/catalysts. This work presents a faster and more precise spectroscopic UV/Vis/Cu sorbent screening technique that quantifies aqueous amines washed from the BIAS by using UV-active amine/Cu complexes. Six BIAS-based catalysts, containing different amine species and a crosslinker within silica, were treated with ultrapure water and then analyzed for their CO capture performance and amine leach resistance/stability by using TGA (catalysts, approximately 4 h) and UV/Vis/Cu techniques (wash solution, few minutes).

Recovering Rare Earth Elements from Aqueous Solution with Porous Amine-Epoxy Networks.

Recovering aqueous rare earth elements (REEs) from domestic water sources is one key strategy to diminish the U.S.'s foreign reliance of these precious commodities.

Spectroscopic Investigation of the Mechanisms Responsible for the Superior Stability of Hybrid Class 1/Class 2 CO2 Sorbents: A New Class 4 Category.

Hybrid Class 1/Class 2 supported amine CO2 sorbents demonstrate superior performance under practical steam conditions, yet their amine immobilization and stabilization mechanisms are unclear. Uncovering the interactions responsible for the sorbents' robust features is critical for further improvements and can facilitate practical applications. We employ solid state (29)Si CP-MAS and 2-D FSLG (1)H-(13)C CP HETCOR NMR spectroscopies to probe the overall molecular interactions of aminosilane/silica, polyamine [poly(ethylenimine), PEI]/silica, and hybrid aminosilane/PEI/silica sorbents.

Rapid Screening of Immobilized Amine CO2 Sorbents for Steam Stability by Their Direct Contact with Liquid H2 O.

Rapid testing of hydrophilic and hydrophobic basic immobilized amine sorbents (BIAS) for CO2 capture stability under practical conditions was achieved by direct contact of the sorbents with flowing liquid water. Losses in both CO2 capture capacity and amine content of sorbents after exposure to 0.5 mL min(-1) of H2 O at 25 °C for 40 min followed similar trends as losses observed after exposure to N2 /steam (105 °C, 7 % H2 O) for 10 h.

Nuclear spin relaxation and molecular interactions of a novel triazolium-based ionic liquid.

Nuclear spin relaxation, small-angle X-ray scattering (SAXS), and electrospray ionization mass spectrometry (ESI-MS) techniques are used to determine supramolecular arrangement of 3-methyl-1-octyl-4-phenyl-1H-triazol-1,2,3-ium bis(trifluoromethanesulfonyl)imide [OMPhTz][Tf2N], an example of a triazolium-based ionic liquid. The results obtained showed first-order thermodynamic dependence for nuclear spin relaxation of the anion. First-order relaxation dependence is interpreted as through-bond dipolar relaxation.

Quantitation of the ligand effect in oxo-transfer reactions of dioxo-Mo(VI) trispyrazolyl borate complexes.

The oxygen atom transfer reactivity (OAT) of dioxo-Mo(VI) complexes of hydrotrispyrazolyl borate (hydrotris(3,5-dimethylpyrazolyl)borate, Tp(Me2); hydrotris(3-isopropylpyrazol-1-yl)borate, Tp(iPr)) with tertiary phosphines (PMe(3), PMe(2)Ph, PEt(3), PEt(2)Ph, PBu(n)(3), PMePh(2), or PEtPh(2)) has been investigated. In acetonitrile, these reactions proceed via the formation of a phosphoryl intermediate complex that undergoes a solvolysis reaction. We report the synthesis and characterization of several phosphoryl complexes.

Determination of free fatty acids and triglycerides by gas chromatography using selective esterification reactions.

A method for selectively determining both free fatty acids (FFA) and triacylglycerides (TAGs) in biological oils was investigated and optimized using gas chromatography after esterification of the target species to their corresponding fatty acid methyl esters (FAMEs). The method used acid catalyzed esterification in methanolic solutions under conditions of varying severity to achieve complete conversion of more reactive FFAs while preserving the concentration of TAGs. Complete conversion of both free acids and glycerides to corresponding FAMEs was found to require more rigorous reaction conditions involving heating to 120°C for up to 2 h.

Influence of the oxygen atom acceptor on the reaction coordinate and mechanism of oxygen atom transfer from the dioxo-Mo(VI) complex, Tp(iPr)MoO(2)(OPh), to tertiary phosphines.

The oxygen atom transfer reactivity of the dioxo-Mo(VI) complex, Tp(iPr)MoO(2)(OPh) (Tp(iPr) = hydrotris(3-isopropylpyrazol-1-yl)borate), with a range of tertiary phosphines (PMe(3), PMe(2)Ph, PEt(3), PBu(n)(3), PEt(2)Ph, PEtPh(2), and PMePh(2)) has been investigated. The first step in all the reactions follows a second-order rate law indicative of an associative transition state, consistent with nucleophilic attack by the phosphine on an oxo ligand, namely, Tp(iPr)MoO(2)(OPh) + PR(3) --> Tp(iPr)MoO(OPh)(OPR(3)). The calculated free energy of activation for the formation of the OPMe(3) intermediate (Chem.

Mechanistic investigation of the oxygen-atom-transfer reactivity of dioxo-molybdenum(VI) complexes.

The oxygen-atom-transfer (OAT) reactivity of [LiPrMoO2(OPh)] (1, LiPr=hydrotris(3-isopropylpyrazol-1-yl)borate) with the tertiary phosphines PEt3 and PPh2Me in acetonitrile was investigated. The first step, [LiPrMoO2(OPh)]+PR3-->[LiPrMoO(OPh)(OPR3)], follows a second-order rate law with an associative transition state (PEt3, DeltaH not equal=48.4 (+/-1.

Solvent effects in the geometric reorganization of an oxo-molybdenum(V) system.

We have previously postulated a serine gated electron transfer hypothesis (Inorg. Chem, 2002, 41, 1281-1291) to possibly be involved in gating electron transfer between the Mo(V) and Mo(IV) states. In this study we explored the effect of solvent dielectric upon the rate and mechanism of isomerization of an oxo-Mo(V) core in attempt to understand the effect of solvent polarity to the isomerization reaction.

Donor atom dependent geometric isomers in mononuclear oxo-molybdenum(V) complexes: implications for coordinated endogenous ligation in molybdoenzymes.

We have previously demonstrated that the complex [(L1O)MoOCl(2)], where L1OH = (2-hydroxy-3-tert-butyl-5-methylphenyl)bis(3,5-dimethylpyrazolyl)methane, exists as both cis and trans isomers (Kail, B.; Nemykin, V. N.