Dynamics of Oxygen-Independent Photocleavage of Blebbistatin as a One-Photon Blue or Two-Photon Near-Infrared Light-Gated Hydroxyl Radical Photocage

Development of versatile, chemically tunable photocages for photoactivated chemotherapy (PACT) represents an excellent opportunity to address the technical drawbacks of conventional photodynamic therapy (PDT) whose oxygen-dependent nature renders it inadequate in certain therapy contexts such as hypoxic tumors. As an alternative to PDT, oxygen free mechanisms to generate cytotoxic reactive oxygen species (ROS) by visible light cleavable photocages are in demand. Here, we report the detailed mechanisms by which the small molecule blebbistatin acts as a one-photon blue light-gated or two-photon near-infrared light-gated photocage to directly release a hydroxyl radical (•OH) in the absence of oxygen. By using femtosecond transient absorption spectroscopy and chemoselective ROS fluorescent probes, we analyze the dynamics and fate of blebbistatin during photolysis under blue light. Water-dependent photochemistry reveals a critical process of water-assisted protonation and excited state intramolecular proton transfer (ESIPT) that drives the formation of short-lived intermediates, which surprisingly culminates in the release of •OH but not superoxide or singlet oxygen from blebbistatin. CASPT2//CASSCF calculations confirm that hydrogen bonding between water and blebbistatin underpins this process. We further determine that blue light enables blebbistatin to induce mitochondria-dependent apoptosis, an attribute conducive to PACT development. Our work demonstrates blebbistatin as a controllable photocage for •OH generation and provides insight into the potential development of novel PACT agents

Membrane pores induced by magainin and melittin: The threshold pore forming peptide concentration C_pep, the pore model, the number of peptides inside a pore N_pep, and the inner diameter D_pore.

<p>DT denotes the disordered toroidal model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198049#pone.0198049.ref074" target="_blank">74</a>], B denotes the barrel-stave model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198049#pone.0198049.ref075" target="_blank">75</a>], and C denotes the carpet model [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0198049#pone.0198049.ref076" target="_blank">76</a>].</p

Top and cross-sectional views of melittin-induced membrane deformation or perforation at P/L molar ratio of (A) 0.5%, (B) 1%, (C) 2%, (D) 3%, (E) 4%, and (F) 5%.

<p>Top and cross-sectional views of melittin-induced membrane deformation or perforation at P/L molar ratio of (A) 0.5%, (B) 1%, (C) 2%, (D) 3%, (E) 4%, and (F) 5%.</p

Nonadiabatic Curve-Crossing Model for the Visible-Light Photoredox Catalytic Generation of Radical Intermediate via a Concerted Mechanism

Photoredox catalysis relies on the excited-state single-electron transfer (SET) processes to drive a series of unique bond-forming reactions. In this work accurate electronic structure calculations at the CASPT2//CASSCF/PCM level of theory together with the kinetic assessment of SETs and intersystem crossing are employed to provide new insights into the SET initiation, activation, and deactivation by calculating the SET paths for a paradigm example of photoredox α-vinylation reaction mediated by iridium­(III) catalysts. The concerted photocatalysis mechanism described by the nonadiabatic curve-crossing model, in essence of Marcus electron transfer theory, is first applied for the mechanistic description of the SET events in visible-light photoredox catalysis. The C–C bond functionalization has been revealed to take place in a concerted manner along an energy-saving pathway, in which the generated α-amino radical is unlikely independent existence but strongly depends on the mutual interaction with different substrates. These mechanistic insights offer a plausible picture for the excited-state SET-mediated chemical transformations that should be applicable to further studies of photoredox catalysis in organic chemistry

PMFs for DMPC (black), DOPC (red), and DPPC (blue) flip-flop in a bilayer obtained from Ex-DPD (right panel) and Im-DPD (left panel) simulations.

<p>Error bars indicate the standard error based on the asymmetry between the two leaflets of the bilayer.</p

Snapshots of (A) DMPC, (B) DOPC, (C) gel-phase DPPC, and (D) fluid-phase bilayers at zero tension states.

<p>Snapshots of (A) DMPC, (B) DOPC, (C) gel-phase DPPC, and (D) fluid-phase bilayers at zero tension states.</p

Structural properties of phospholipids bilayers: membrane thickness <i>L</i>_<i>mem</i>, area per lipid <i>a</i>₀, and orientation order of the hydrocarbon chain <i>S</i>_<i>chain</i> as well as elastic properties: bending rigidity <i>κ</i> and rupture tension Σ_<i>r</i>.

<p>Structural properties of phospholipids bilayers: membrane thickness <i>L</i>_<i>mem</i>, area per lipid <i>a</i>₀, and orientation order of the hydrocarbon chain <i>S</i>_<i>chain</i> as well as elastic properties: bending rigidity <i>κ</i> and rupture tension Σ_<i>r</i>.</p

Membrane tension as a function of projected area per lipid <i>a</i>_prj for DMPC, DOPC, fluid phase DPPC and gel phase DPPC bilayers.

<p>Membrane tension as a function of projected area per lipid <i>a</i>_prj for DMPC, DOPC, fluid phase DPPC and gel phase DPPC bilayers.</p

Snapshots of self-assemblies of DMPC lipids simulated by different scaling factor <i>s</i>.

<p>(A-I) <i>s</i> equals to 0.1–0.9. Cross-sectional views of half-cut micelles or vesicles are also given in (G-H).</p

DPD force parameters <i>a</i>_<i>ij</i> for Martini-like CG model.

<p>DPD force parameters <i>a</i>_<i>ij</i> for Martini-like CG model.</p