Tailoring the optical and dynamic properties of iminothioindoxyl photoswitches through acidochromism

Multi-responsive functional molecules are key for obtaining user-defined control of the properties and functions of chemical and biological systems. In this respect, pH-responsive photochromes, whose switching can be directed with light and acid-base equilibria, have emerged as highly attractive molecular units. The challenge in their design comes from the need to accommodate application-defined boundary conditions for both light- and protonation-responsivity. Here we combine time-resolved spectroscopic studies, on time scales ranging from femtoseconds to seconds, with density functional theory (DFT) calculations to elucidate and apply the acidochromism of a recently designed iminothioindoxyl (ITI) photoswitch. We show that protonation of the thermally stable Z isomer leads to a strong batochromically-shifted absorption band, allowing for fast isomerization to the metastable E isomer with light in the 500-600 nm region. Theoretical studies of the reaction mechanism reveal the crucial role of the acid-base equilibrium which controls the populations of the protonated and neutral forms of the E isomer. Since the former is thermally stable, while the latter re-isomerizes on a millisecond time scale, we are able to modulate the half-life of ITIs over three orders of magnitude by shifting this equilibrium. Finally, stable bidirectional switching of protonated ITI with green and red light is demonstrated with a half-life in the range of tens of seconds. Altogether, we designed a new type of multi-responsive molecular switch in which protonation red-shifts the activation wavelength by over 100 nm and enables efficient tuning of the half-life in the millisecond-second range.</p

Dataset Collagen Self Assembly in H2O and D2O.

This zip file contains data, and analysis for the paper "Elucidating the role of water in collagen self-assembly by isotopically modulating collagen hydration".Please feel free to contact us in case of questions or details

Solid-State NMR studies of full-length BamA in lipid bilayers suggest limited overall POTRA mobility

The outer membrane protein BamA is the key player in β-barrel assembly in Gram-negative bacteria. Despite the availability of high-resolution crystal structures, the dynamic behavior of the transmembrane domain and the large periplasmic extension consisting of five POTRA (POlypeptide-TRansport- Associated) domains remains unclear. We demonstrate reconstitution of full-length BamA in proteoliposomes at low lipid-to-protein ratio, leading to high sensitivity and resolution in solid-state NMR (ssNMR) experiments. We detect POTRA domains in ssNMR experiments probing rigid protein segments in our preparations. These results suggest that the periplasmic region of BamA is firmly attached to the β-barrel and does not experience fast global motion around the angle between POTRA 2 and 3. We show that this behavior holds at lower protein concentrations and elevated temperatures. Chemical shift variations observed after reconstitution in lipids with different chain lengths and saturation levels are compatible with conformational plasticity of BamA's transmembrane domain. Electron microscopy of the ssNMR samples shows that BamA can cause local disruptions of the lipid bilayer in proteoliposomes. The observed interplay between protein-protein and protein-lipid interactions may be critical for BamA-mediated insertion of substrates into the outer membrane

Probing radical versus proton migration in the aniline cation with IRMPD spectroscopy

Intramolecular radical and proton migration in the gas phase are important processes driving the dissociation reactions underlying common tandem mass spectrometry processes, such as collision-induced and electron-induced dissociation reactions (CID and ExD). Mechanistic insights in these processes requires experiments that probe the molecular structures of ions along the reaction pathways, usually combined with quantum-chemical calculations. The combination of ion trap mass spectrometry with IR laser spectroscopy, pioneered among others by Dieter Gerlich, provides a particularly effective method to explore details of the ion structures. In this work, we employ infrared multiple-photon dissociation (IRMPD) spectroscopy and density functional theory (DFT) calculations to probe the reactant and product ion structures of a homolytic bond cleavage reaction. First, we employ IRMPD spectroscopy to establish that protonation of the 4-bromoaniline precursor occurs on the amine moiety and then that C-Br homolytic cleavage produces the π-radical cation of aniline. Transition-state calculations are performed to compare the various pathways that connect reactant and product ions, including both proton and radical transfer mechanisms.</p