Tuning Photoinduced Electron Transfer Efficiency of Fluorogenic BODIPY-α-Tocopherol Analogues.

Fluorogenic analogues of α-tocopherol developed by our group have been instrumental in monitoring reactive oxygen species (ROS) within lipid membranes. Prepared as two-segment trap-reporter (chromanol-BODIPY) probes, photoinduced electron transfer (PeT) was utilized to provide these probes with an off/on switch mechanism warranting the necessary sensitivity. Herein, we rationalize within the context of Marcus theory of electron transfer how substituents on the BODIPY core and linker length joining the trap and reporter segments, tune PeT efficiency.

Effect of antioxidant supplements on lipid peroxidation levels in primary cortical neuron cultures.

Oxidative stress, specifically lipid peroxidation, is a major driving force in neurodegenerative processes. However, the exact role of lipid peroxidation remains elusive as reliable real-time detection and quantification of lipid peroxyl radicals proves to be challenging in vitro and in vivo. Motivated by this methodological limitation, we have optimized conditions for real-time imaging and quantification of lipid peroxyl radical generation in primary neuron cultures using the lipophilic fluorogenic antioxidant HBPMHC (8-((6-hydroxy-2,5,7,8-tetramethylchroman-2-yl)-methyl)-1,5-di(3-chloropropyl)-pyrromethene fluoroborate), an α-tocopherol analog probe.

Spatio-temporal monitoring of lipid peroxyl radicals in live cell studies combining fluorogenic antioxidants and fluorescence microscopy methods.

Lipid peroxidation of polyunsaturated fatty acids in cells may occur via their catalytic autoxidation through peroxyl radicals under oxidative stress conditions. Lipid peroxidation is related to a number of pathologies, and may be invoked in new forms of regulated cell death, yet it may also have beneficial roles in cell signaling cascades. Antioxidants are a natural line of defense against lipid peroxidation, and may accordingly impact the biological outcome associated with the redox chemistry of lipid peroxidation.

Development of a Fluorogenic Reactivity Palette for the Study of Nucleophilic Addition Reactions Based on -Formyl BODIPY Dyes.

We describe herein a fluorescence-based assay to characterize and report on nucleophilic addition to carbonyl moieties and highlight the advantages a fluorescence-based assay and multiplex analysis can offer. The assay relies on the fluorogenic properties of -formyl boron-dipyrromethene (BODIPY) dyes that become emissive following nucleophilic addition. A reactivity palette is assembled based on the increasing electrophilic character of five -formyl BODIPY compounds tested.

Rate of Lipid Peroxyl Radical Production during Cellular Homeostasis Unraveled via Fluorescence Imaging.

Reactive oxygen species (ROS) and their associated byproducts have been traditionally associated with a range of pathologies. It is now believed, however, that at basal levels these molecules also have a beneficial cellular function in the form of cell signaling and redox regulation. Critical to elucidating their physiological role is the opportunity to visualize and quantify the production of ROS with spatiotemporal accuracy.

Cigarette smoke activates CFTR through ROS-stimulated cAMP signaling in human bronchial epithelial cells.

Air pollution stimulates airway epithelial secretion through a cholinergic reflex that is unaffected in cystic fibrosis (CF), yet a strong correlation is observed between passive smoke exposure in the home and impaired lung function in CF children. Our aim was to study the effects of low smoke concentrations on cystic fibrosis transmembrane conductance regulator (CFTR) function in vitro. Cigarette smoke extract stimulated robust anion secretion that was transient, mediated by CFTR, and dependent on cAMP-dependent protein kinase activation.

Mitochondria Alkylation and Cellular Trafficking Mapped with a Lipophilic BODIPY-Acrolein Fluorogenic Probe.

Protein and DNA alkylation by endogenously produced electrophiles is associated with the pathogenesis of neurodegenerative diseases, to epigenetic alterations and to cell signaling and redox regulation. With the goal of visualizing, in real-time, the spatiotemporal response of the cell milieu to electrophiles, we have designed a fluorogenic BODIPY-acrolein probe, AcroB, that undergoes a >350-fold fluorescence intensity enhancement concomitant with protein adduct formation. AcroB enables a direct quantification of single post-translational modifications occurring on cellular proteins via recording fluorescence bursts in live-cell imaging studies.

Fluorogenic Ubiquinone Analogue for Monitoring Chemical and Biological Redox Processes.

We report herein the synthesis and characterization of a fluorogenic analogue of ubiquinone designed to reversibly report on redox reactions in biological systems. The analogue, H2B-Q, consists of the redox-active quinone segment found in ubiquinone, 2,3-dimethoxy-1,4-benzoquinone, coupled to a boron-dipyrromethene (BODIPY) fluorophore segment that both imparts lipophilicity in lieu of the isoprenyl tail of ubiquinone, and reports on redox changes at the quinone/quinol segment. Redox sensing is mediated by a photoinduced electron transfer intramolecular switch.

Reactive Oxygen Species Mediated Activation of a Dormant Singlet Oxygen Photosensitizer: From Autocatalytic Singlet Oxygen Amplification to Chemicontrolled Photodynamic Therapy.

Here we show the design, preparation, and characterization of a dormant singlet oxygen ((1)O2) photosensitizer that is activated upon its reaction with reactive oxygen species (ROS), including (1)O2 itself, in what constitutes an autocatalytic process. The compound is based on a two segment photosensitizer-trap molecule where the photosensitizer segment consists of a Br-substituted boron-dipyrromethene (BODIPY) dye. The trap segment consists of the chromanol ring of α-tocopherol, the most potent naturally occurring lipid soluble antioxidant.

When push comes to shove: unravelling the mechanism and scope of nonemissive meso-unsaturated BODIPY dyes.

We report herein spectroscopy and computational results that illustrate an efficient intramolecular deactivation pathway for meso-unsaturated boron-dipyrromethene (BODIPY) dyes in their singlet excited state. Our results show that the mechanism hinges on the structural flexibility imparted by the boron atom and on the energetic stabilization conferred by extending the conjugation into the meso substituent, which is otherwise unconjugated in the ground state. Following photoexcitation, rotation along the dihedral angle of the meso-unsaturated group results in its conjugation at the expense of shifting one pyrrole moiety in dipyrrin out of the plane.

Electronic excited state redox properties for BODIPY dyes predicted from Hammett constants: estimating the driving force of photoinduced electron transfer.

Here we formulate equations based solely on empirical Hammett substituent constants to predict the redox potentials for the electronic excited state of boron-dipyrromethene (BODIPY) dyes. We utilized computational, spectroscopic, and electrochemical techniques toward characterizing the effect of substitution at the positions C2, C6, and C8 of the 1,3,5,7-tetramethyl BODIPY core. Working with a library of 100 BODIPY dyes, we found that highest occupied molecular orbital (HOMO) energies calculated at the B3LYP 6-31g(d) level correlated linearly with the Hammett σm value for substituents at position C8 and with Hammett σp values for substituents at positions C2 and C6.

Fluorogenic α-tocopherol analogue for monitoring the antioxidant status within the inner mitochondrial membrane of live cells.

We report here the preparation of a lipophilic fluorogenic antioxidant (Mito-Bodipy-TOH) that targets the inner mitochondrial lipid membrane (IMM) and is sensitive to the presence of lipid peroxyl radicals, effective chain carriers in the lipid chain autoxidation. Mito-Bodipy-TOH enables monitoring of the antioxidant status, i.e.

Correlations of ion structure with multiple fragmentation pathways arising from collision-induced dissociations of selected α-hydroxycarboxylic acid anions.

Under conditions of collision-induced dissociation (CID), anions of α-hydroxycarboxylic acids usually fragment to yield the distinctive hydroxycarbonyl anion (m/z 45) and/or the complementary product anion formed by neutral loss of formic acid (46 u). Further support for the known two-step mechanism, involving an ion-neutral complex for the formation of the hydroxycarbonyl anion from the carboxyl group, is herein provided by tandem mass spectrometric results and density functional theory computations on the glycolate, lactate and 3-phenyllactate ions. A fourth, structurally related α-hydroxycarboxylate ion, obtained by deprotonation of mandelic acid, showed only loss of carbon dioxide upon CID.