Epoxy resins are ubiquitous in high-performance composite applications because of their excellent mechanical strength, thermal and chemical resistance, strong adhesion, and low shrinkage after curing. Bio-based epoxy resins derived from natural products such as carbohydrates offer tremendous potential for creating new polymeric materials. Sugars and their derivatives often offer great biodegradability and functionality such as the presence of multiple hydroxyl groups that impart highly cross-linked polymer networks. Moreover, their ring structures can afford polymers with high glass transition temperatures. To develop epoxy resins containing sustainably sourced feedstocks, we designed and synthesized trehalose-and β-cyclodextrin-based carboxylic acid hardeners for epoxy resins and examined the thermal, mechanical, and adhesive properties of the resulting materials. Trehalose and β-cyclodextrin were succinylated with excess succinic anhydride, and the resulting carboxylic acid hardeners formed homogeneous mixtures with trimethylolpropane triglycidyl ether (TTE) in different carboxyl−epoxide ratios. The cured resins were found to be thermally stable (T d5 > 300 °C) and display high Young's moduli of up to 1.4 and 1.8 GPa with mechanical strengths of 47 and 64 MPa for the trehalose-and β-cyclodextrin-based epoxy resins, respectively. Preliminary adhesion tests showed that the cured resins exhibit excellent lap-shear strengths of 3600 and 2100 psi, respectively. The resins were also degradable into water-soluble components in both aqueous acidic and basic solutions but were relatively stable from hydrolysis in neutral aqueous conditions. These results imply that this novel class of hardeners are promising feedstocks for renewable high performance epoxy resins.
A new iron(II) complex has been prepared and characterized. [Fe(TrImA)2(OTf)2] (1, TrImA = 1-Tritylimidazole-4-carboxaldehyde). The solid state structure of 1 has been determined by X-ray crystallography. Compound 1 crystallizes in monoclinic space group P21/c, with a = 10.8323(18) Å, b = 8.1606(13) Å and c = 24.818(4) Å. The iron center is coordinated to two imidazole groups, two pendant aldehyde-derived carbonyl oxygens and two triflate oxygens. The complex is high spin between 300 and 20 K as indicated by variable field variable temperature magnetic measurements. A fit of the magnetic data yielded g = 2.17 and D = 4.05 cm−1. A large HOMO-LUMO gap energy (4.49 eV) exists for 1 indicating high stability.
a b s t r a c tIn this study we report the synthesis and characterization of [Cu(T1Et4iPrIP)(CH 3 OH)Cl]Cl (1) (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine). T1Et4iPrIP serves as a His 3 biomimetic ligand binding metals through the 3-nitrogen of the imidazolyl group. The structure of 1 features copper(II) bonded to three nitrogen ligands from T1Et4iPrIP along with an oxygen ligand from methanol and a chloride ligand to form slightly distorted square pyramidal geometry with an imidazole group occupying the axial position and the methanol and chloride ligands situated in the basal plane. The weak sigma donation of the ligand set results in low energy d-d electronic transitions and small A k (131 G). Time-dependent DFT calculations (B3LYP, 6-311+G(d,p)) on the optimized structure of 1 in methanol solvent allowed for the assignment of specific electronic transitions in the UV-Vis spectrum. The highest occupied molecular orbital (HOMO) was noted to consist of 65% Cu-d character identified as the d x 2 Ày 2 orbital.
In this study, we report the synthesis and characterization of [Fe(T1Et4iPrIP)(2-OH-AP)(OTf)](OTf) (2), [Fe(T1Et4iPrIP)(2-O-AP)](OTf) (3), and [Fe(T1Et4iPrIP)(DMF)3](OTf)3 (4) (T1Et4iPrIP = tris(1-ethyl-4-isopropyl-imidazolyl)phosphine; 2-OH-AP = 2-hydroxyacetophenone, and 2-O-AP– = monodeprotonated 2-hydroxyacetophenone). Both 2 and 3 serve as model complexes for the enzyme–substrate adduct for the nonheme enzyme 2,4′-dihydroacetophenone (DHAP) dioxygenase or DAD, while 4 serves as a model for the ferric form of DAD. Complexes 2–4 have been characterized by X-ray crystallography which reveals T1Et4iPrIP to bind iron in a tridentate fashion. Complex 2 additionally contains a bidentate 2-OH-AP ligand and a monodentate triflate ligand yielding distorted octahedral geometry, while 3 possesses a bidentate 2-O-AP– ligand and exhibits distorted trigonal bipyramidal geometry (τ = 0.56). Complex 4 displays distorted octahedral geometry with 3 DMF ligands completing the ligand set. The UV–vis spectrum of 2 matches more closely to the DAD-substrate spectrum than 3, and therefore, it is believed that the substrate for DAD is bound in the protonated form. TD-DFT studies indicate that visible absorption bands for 2 and 3 are due to MLCT bands. Complexes 2 and 3 are capable of oxidizing the coordinated substrate mimics in a stoichiometric and catalytic fashion in the presence of O2. Complex 4 does not convert 2-OH-AP to products under the same catalytic conditions; however, it becomes anaerobically reduced in the presence of 2 equiv 2-OH-AP to 2.
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