Synthesis and Electronic Structure Determination of N-Alkyl-Substituted Bis(imino)pyridine Iron Imides Exhibiting Spin Crossover Behavior

Abstract

Protein folding is a classic grand challenge that is relevant to numerous human diseases, such as protein misfolding diseases like Alzheimer’s disease. Solving the folding problem will ultimately require a combination of theory, simulation, and experiment, with theory and simulation providing an atomically detailed picture of both the thermodynamics and kinetics of folding and experimental tests grounding these models in reality. However, theory and simulation generally fall orders of magnitude short of biologically relevant time scales. Here we report significant progress toward closing this gap: an atomistic model of the folding of an 80-residue fragment of the λ repressor protein with explicit solvent that captures dynamics on a 10 milliseconds time scale. In addition, we provide a number of predictions that warrant further experimental investigation. For example, our model’s native state is a kinetic hub, and biexponential kinetics arises from the presence of many free-energy basins separated by barriers of different heights rather than a single low barrier along one reaction coordinate (the previously proposed incipient downhill folding scenario).

Oxidative Addition of Carbon–Carbon Bonds with a Redox-Active Bis(imino)pyridine Iron Complex

“…However, a change in the magnitude of either of these parameters would not alter the conclusions regarding the initial and final spin states: ( Me PDI)Fe(biphenyl) is an S = 0 to S = 1 spin crossover compound. Similar SCO behavior has been observed with bis(imino)pyridine iron imido ( S = 0 to S = 1) 51 and bis(chelate) bis(imino)pyridine cobalt ( S = 1/2 to S = 3/2) compounds. 52 The variable temperature magnetic data observed for ( iPr PDI)Fe(biphenyl) displays the same general trends as for ( Me PDI)Fe(biphenyl) (see Supporting Information) but the instability of the compound ( vide supra ) made collection of reliable magnetic data more challenging.…”

“…The values of δ are comparable to that measured for ( iPr PDI)Fe(CO) 2 , a highly covalent molecule that is best described by ( iPr PDI 2– )Fe II (CO) 2 and ( iPr PDI 0 )-Fe 0 (CO) 2 resonance forms and the alkyl-substituted iron imido complex, ( iPr PDI)FeN 1 Ad, an established spin crossover compound. 51 …”

“…49,53 In bis(imino)pyridine chemistry, Mössbauer spectroscopy distinguished the low- and high-spin states of ( iPr PDI)FeN 2 Ad and allowed determination of the energetics of the spin transition. 51 To probe whether such behavior could be detected in organometallic iron complexes, variable temperature data were collected on both ( iPr PDI)Fe(biphenyl) and ( Me PDI)Fe-(biphenyl). For the former compound, spectra were obtained at 10, 80, 150, 200, and 250 K. The parameters obtained at 250 K ( δ = 0.01 mm/s and Δ E Q = 3.51 mm/s) are indistiguishable from the values ( δ = 0.07 mm/s and Δ E Q = 3.58 mm/s) obtained at 80 K. Similar behavior was observed with ( Me PDI)Fe(biphenyl), where parameters of δ = −0.02 mm/s and Δ E Q = 3.43 mm/s were measured at 295 K indistiguishable from the values of δ = 0.05 mm/s and Δ E Q = 3.69 mm/s at 80 K. Representative spectra for both compounds are presented in the Supporting Information.…”

Komplexe mit Stickstoffradikalliganden: Einteilung, spektroskopische Eigenschaften, Reaktivität und katalytische Anwendungen

“…[40] So haben die Verbindungen 50-Alk mit R = 1-Adamantyl, Cyclooctyl oder 2-Adamantyl relativ kurze Fe-N Nitren -Bindungen von 1.65-1.66 , und ihre N Py -Fe-N Nitren -Winkel sind stärker linear (q = 168-1758) als bei den Derivaten mit R = Ar. [40] So haben die Verbindungen 50-Alk mit R = 1-Adamantyl, Cyclooctyl oder 2-Adamantyl relativ kurze Fe-N Nitren -Bindungen von 1.65-1.66 , und ihre N Py -Fe-N Nitren -Winkel sind stärker linear (q = 168-1758) als bei den Derivaten mit R = Ar.…”

“…[40] So haben die Verbindungen 50-Alk mit R = 1-Adamantyl, Cyclooctyl oder 2-Adamantyl relativ kurze Fe-N Nitren -Bindungen von 1.65-1.66 , und ihre N Py -Fe-N Nitren -Winkel sind stärker linear (q = 168-1758) als bei den Derivaten mit R = Ar. [39,40] Stickstoffradikalliganden Systemen tritt Spin-Crossover auf. Durch eine "Porphyrinhälfte" stabilisierte Eisen-und Cobalt-Nitrenradikalkomplexe.…”