Search results for "Aromaticity"
showing 10 items of 138 documents
Energy interactions in amyloid-like fibrils from NNQQNY.
2014
We use large-scale MP2 calculations to analyze the interactions appearing in amyloid fibers, which are difficult to determine experimentally. To this end, dimers and trimers of the hexapeptide NNQQNY from the yeast prion-like protein Sup35 were considered as model systems. We studied the energy interactions present in the three levels of organization in which the formation of amyloid fibrils is structured. The structural changes in the hydrogen bonds were studied too. It was found that the most energetic process is the formation of the β-sheet, which is equally due to both hydrogen bonds and van der Waals interactions. The aromatic rings help stabilize these aggregates through stacking of t…
N-Methyl-N-(2-nitrophenyl)nitramine andN-methyl-N-(3-nitrophenyl)nitramine
2005
The structures of the two title isomeric compounds (systematic names: N-methyl-N,2-dinitroaniline and N-methyl-N,3-dinitroaniline, both C7H7N3O4) are slightly different because they exhibit different steric hindrances and hydrogen-bonding environments. The aromatic rings are planar. The –N(Me)NO2 and –NO2 groups are not coplanar with the rings. Comparison of the geometric parameters of the ortho, meta and para isomers together with those of N-methyl-N-phenylnitramine suggests that the position of the nitro group has a strong influence on the aromatic ring distortion. The crystal packing is stabilized by weak C—H⋯O hydrogen bonds to the nitramine group.
Substituent effects in trans-p,p'-disubstituted azobenzenes: X-ray structures at 100 K and DFT-calculated structures.
2014
The crystal and molecular structures of twopara-substituted azobenzenes with π-electron-donating –NEt2and π-electron-withdrawing –COOEt groups are reported, along with the effects of the substituents on the aromaticity of the benzene ring. The deformation of the aromatic ring around the –NEt2group inN,N,N′,N′-tetraethyl-4,4′-(diazenediyl)dianiline, C20H28N4, (I), may be caused by steric hindrance and the π-electron-donating effects of the amine group. In this structure, one of the amine N atoms demonstrates clearsp2-hybridization and the other is slightly shifted from the plane of the surrounding atoms. The molecule of the second azobenzene, diethyl 4,4′-(diazenediyl)dibenzoate, C18H18N2O4,…
Synthesis of Isoxazoline Derivatives through Boulton–Katritzky Rearrangement of 1,2,4-Oxadiazoles
2013
The base-induced rearrangement of 1,2,4-oxadiazoles into isoxazoline derivatives is reported. This represents the first example of a three-atom side-chain rearrangement that involves a saturated CCO side chain at C-3 of the oxadiazole. Nonaromatic 3-amino-isoxazoline derivatives are obtained in good yields. Interestingly, this reaction occurs through the rearrangement of aromatic oxadiazoles to form less stable bonds than those that are broken.
CHARACTERIZATION OF CHEMICAL AND PHYSICAL PROPERTIES OF BIOCHAR FOR ENERGY PURPOSES AND ENVIRONMENTAL RESTORATION
2014
Biochar production processes as well as its various applications provide numerous benefits to both environment and economy (Lehmann et al., 2006; Basu, 2010). However, understanding the physicochemical structure of this valuable product has to be improved in order to be able to obtain the aforementioned benefits and to avoid environmental costs. In this study, chicken or poultry manure (PM) was chosen as feedstock for biochar preparation. This biomass is traditionally used by farmers as an effective organic fertilizer (Chan et al., 2008). Indeed, it is considered a valuable source for readily available plant nutrients, such as N, P, K and other micronutrients (Huang et al., 2011). Notwithst…
Hydrogen activation with perfluorinated organoboranes: 1,2,3-tris(pentafluorophenyl)-4,5,6,7-tetrafluoro-1-boraindene
2013
The perfluorinated boraindene was synthesized and fully characterized. Both computational and crystallographic data show that is antiaromatic. Compound was shown to react reversibly with H2 and to catalyse the hydrogenation of cyclohexene. The mechanism of catalysis was probed experimentally and computationally.
A new series of π-extended tetrathiafulvalene derivatives incorporating fused furanodithiino and thienodithiino units: a joint experimental and theor…
2004
A new family of tetrathiafulvalenes has been prepared. The materials exhibit complex redox behaviour related to the electronic influence of the 1,4-dithiin moieties embedded within the framework of the molecules. The X-ray crystal structure of compound 4 reveals an unusual non-planar conformation of the heterocyclic compound, with the TTF fragment adopting a boat conformation. Theoretical calculations, performed at the DFT level (B3P86/6-31G*), confirm the boatlike structure (C2v symmetry) as the most stable conformation for this family of tetrathiafulvalenes. Upon oxidation, electrons are extracted from the whole molecule and the radical cations and dications remain highly distorted from p…
Phosphonic Acid Analogues of Phenylglycine as Inhibitors of Aminopeptidases: Comparison of Porcine Aminopeptidase N, Bovine Leucine Aminopeptidase, T…
2019
The inhibitory activity of 14 racemic phosphonic acid analogs of phenylglycine, substituted in aromatic rings, towards porcine aminopeptidase N (pAPN) and barley seed aminopeptidase was determined experimentally. The obtained patterns of the inhibitory activity against the two enzymes were similar. The obtained data served as a basis for studying the binding modes of these inhibitors by pAPN using molecular modeling. It was found that their aminophosphonate fragments were bound in a highly uniform manner and that the difference in their affinities most likely resulted from the mode of substitution of their phenyl rings. The obtained binding modes towards pAPN were compared, with these predi…
9-Ethoxy-1,5,13-trimethyl-8,10-dioxatetracyclo[7.7.1.02,7.011,16]heptadeca-2,4,6,11,13,15-hexaene
2009
The reaction of ethyl acetoacetate with meta-cresol in an acidic ionic liquid yielded a complex mixture of condensation products. 4,7-Dimethylcoumarin and the title compound, C20H22O3, were isolated. The title compound shows chemical but not crystallographic mirror symmetry. The two aromatic rings are inclined at an angle of 73.55 (6)°.
Carboranylphosphinic Acids: A New Class of Purely Inorganic Ligands
2015
Purely inorganic carboranyl phosphinates were prepared, and the influence of the cluster on the reactivity of the phosphinate group was studied. Electron-withdrawal by the carboranyl carbon atoms, combined with space-filling efficiency and enhanced aromaticity of the cluster cage, renders the phosphorus more difficult to oxidize. This enables carboranyl phosphinates to survive harsh oxidizing conditions, a property which is uncommon in organic phosphinates.