An official website of the United States government
Abstract The cytochrome P450 homolog, TxtE, efficiently catalyzes the direct and regioselective aromatic nitration of the indolyl moiety of L‐tryptophan to 4‐nitro‐L‐tryptophan, using nitric oxide (NO) and dioxygen (O2) as co‐substrates. Pathways for such direct and selective nitration of heteroaromatic motifs present platforms for engineering new nitration biocatalysts for pharmacologically beneficial targets, among a medley of other pivotal industrial applications. Precise mechanistic details concerning this pathway are only weakly understood, albeit a heme iron(III)‐peroxynitrite active species has been postulated. To shed light on this unique reaction landscape, we investigated the indole nitration pathway of a series of biomimetic ferric heme superoxide mimics, [(Por)FeIII(O2−⋅)], in the presence of NO. Therein, our model systems gave rise to three distinct nitroindole products, including 4‐nitroindole, the product analogous to that obtained with TxtE. Moreover,15N and18O isotope labeling studies, along with meticulously designed control experiments lend credence to a heme peroxynitrite active nitrating agent, drawing close similarities to the tryptophan nitration mechanism of TxtE. All organic and inorganic reaction components have been fully characterized using spectroscopic methods. Theoretical investigation into several mechanistic possibilities deem a unique indolyl radical based reaction pathway as the most energetically favorable, products of which, are in excellent agreement with experimental findings.
more »
« less
This content will become publicly available on June 26, 2026
On the Preparation of Nickel Porphyrins Bearing Two to Four Nitro Groups at β ‐Positions
The preparation, isolation, and identification of dinitro, trinitro, and tetranitro metalloporphyrins bearing nitro groups on pyrrole rings—desirable intermediates that enable fundamental changes in the chemico‐physical properties of the porphyrin core—are studied. All six possible dinitro‐Ni‐TPP isomers are formed; three are isolated as pure substances using column chromatography, while the remaining three are inseparable. All possible trinitro‐Ni‐TPP isomers are prepared and isolated, except for the 2,7,13 isomer. Attempts to synthesize tetranitro‐Ni‐TPP either through direct nitration of metalloporphyrin or via direct condensation of the nitropyrrole building blocks are unsuccessful. The molecular structures are unambiguously identified using 2D NMR experiments. Some experimental observations, though not all, are consistent with quantum chemical calculations performed on the geometry, energy, Fukui indices, dipole moments of nitroporphyrins, and the energy of nitration intermediates.
more »
« less
- Award ID(s):
- 2102581
- PAR ID:
- 10628801
- Publisher / Repository:
- Wiley
- Date Published:
- Journal Name:
- European Journal of Organic Chemistry
- ISSN:
- 1434-193X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Functionalization of planar aromatic rings is very straightforward, up scalable, and economical in comparison with many azole, caged, linear or cyclic structures. In our present work, a facile synthesis of N , N ′-(4,6-dinitro-1,3-phenylene)dinitramide (3) is obtained by a single-step nitration of 4,6-dinitrobenzene-1,3-diamine (2). Compound 3 exhibits a surprisingly high density of 1.90 g cm −3 at 100 K (1.87 g cm −3 at 298 K). Its reactions with bases result in the formation of a series of energetic salts (4–7) which exhibit relatively high densities (1.74 to 1.83 g cm −3 ), and acceptable thermal sensitivities (177 to 253 °C). Energetic salt formation increases intermolecular hydrogen bonding while the planarity of the aromatic ring maximizes weak non-covalent interactions (π-stacking, cation/π, anion-π, X-H/π, etc. ,). The synergetic effect of these stabilizing interactions plays a crucial role in increasing thermal stability and decreasing sensitivity toward the external stimuli. Overall, these easily accessible new energetic compounds exhibit high densities and good denotation properties with potential applications as new high-energy materials.more » « less
-
Abstract Enzymes as catalysts in organic syntheses can provide high regio‐ and stereo‐selectivity, which is often not possible with chemical catalysts. Biocatalysis with iron heme enzymes has proven efficient when the enzyme is sequestered in thin films. An added feature is improved stability. For example, peroxidases chemically crosslinked in poly‐lysine in films on silica nanoparticles were stable for 9 hrs or more at 90 °C, and were used for biocatalysis up to 90 °C. We show here for a series ofpara‐substituted phenols, single nitro‐phenol products can be selectively synthesized using biocatalytic magnetic beads coated with horseradish peroxidase (HRP) crosslinked in polylysine films. Nitrophenols moieties are important as synthetic intermediates and in drugs. For a series ofpara‐substituted phenols, biocatalytic nitration gave average turnover numbers 1.8‐fold larger at 75 °C than at 25 °C. For phenols giving <50 % conversion after 1 hr at 25 °C, twice the nitration yield was achieved in 1 hr at 75 °C. Results indicate that this approach should be valuable as a general tool for biocatalytic chemical synthesis.more » « less
-
Since the discovery of the B 40 borospherene, research interests have been directed to the structural evolution of even larger boron clusters. An interesting question concerns if the borospherene cages persist in larger boron clusters like the fullerenes. Here we report a photoelectron spectroscopy (PES) and computational study on the structures and bonding of B 41 − and B 42 − , the largest boron clusters characterized experimentally thus far. The PE spectra of both clusters display broad and complicated features, suggesting the existence of multiple low-lying isomers. Global minimum searches for B 41 − reveal three low-lying isomers ( I–III ), which are all related to the planar B 40 − structure. Isomer II ( C s , 1 A′) possessing a double hexagonal vacancy is found to agree well with the experiment, while isomers I ( C s , 3 A′′) and III ( C s , 1 A′) both with a single hexagonal vacancy are also present as minor isomers in the experiment. The potential landscape of B 42 − is found to be much more complicated with numerous low-lying isomers ( VII–XII ). The quasi-planar structure VIII ( C 1 , 2 A) containing a double hexagonal vacancy is found to make major contributions to the observed PE spectrum of B 42 − , while the other low-lying isomers may also be present to give rise to a complicated spectral pattern. Chemical bonding analyses show isomer II of B 41 − ( C s , 1 A′) and isomer VIII of B 42 − ( C 1 , 2 A) are π aromatic, analogous to that in the polycyclic aromatic hydrocarbon C 27 H 13 + ( C 2v , 1 A 1 ). Borospherene cage isomers are also found for both B 41 − and B 42 − in the global minimum searches, but they are much higher energy isomers.more » « less
-
RationaleCoordinatively driven self‐assembly of transition metal ions and bidentate ligands gives rise to organometallic complexes that usually contain superimposed isobars, isomers, and conformers. In this study, the double dispersion ability of ion mobility mass spectrometry (IM‐MS) was used to provide a comprehensive structural characterization of the self‐assembled supramolecular complexes by their mass and charge, revealed by the MS event, and their shape and collision cross‐section (Ω), revealed by the IM event. MethodsSelf‐assembled complexes were synthesized by reacting a bis(terpyridine) ligand exhibiting a 60odihedral angle between the two ligating terpyridine sites (T) with divalent Zn, Ni, Cd, or Fe. The products were isolated as (Metal2+[T])n(PF6)2nsalts and analyzed using IM‐MS after electrospray ionization (ESI) which produced several charge states from eachn‐mer, depending on the number of PF6ˉ anions lost upon ESI. Experimental Ω data, derived using IM‐MS, and computational Ω predictions were used to elucidate the size and architecture of the complexes. ResultsOnly macrocyclic dimers, trimers, and tetramers were observed with Cd2+, whereas Zn2+formed the same plus hexameric complexes. These two metals led to the simplest product distributions and no linear isomers. In sharp contrast, Ni2+and Fe2+formed all possible ring sizes from dimer to hexamer as well as various linear isomers. The experimental and theoretical Ω data indicated rather planar macrocyclic geometries for the dimers and trimers, twisted 3D architectures for the larger rings, and substantially larger sizes with spiral conformation for the linear congeners. Adding PF6ˉ to the same complex was found to mainly cause size contraction due to new stabilizing anion–cation interactions. ConclusionsComplete structural identification could be accomplished using ESI‐IM‐MS. Our results affirm that self‐assembly with Cd2+and Zn2+proceeds through reversible equilibria that generate the thermodynamically most stable structures, encompassing exclusively macrocyclic architectures that readily accommodate the 60oligand used. In contrast, complexation with Ni2+and Fe2+, which form stronger coordinative bonds, proceeds through kinetic control, leading to more complex mixtures and kinetically trapped less stable architectures, such as macrocyclic pentamers and linear isomers.more » « less
