New Photolabile BAPTA-Based Ca2+ Cages with Improved Photorelease

Highly efficient Ca2+ chelation activated by visible light

Calcium ion (Ca2+) control is an essential tool in neuronal research. Herein, we report three thiocoumarin-based, visible light-activated Ca2+ chelators with quantum yields of 0.39, 0.52, and 0.83. The chelators demonstrated an over 105-fold increase in Ca2+ binding affinity upon irradiation. These chelators are efficiently triggered by biologically safer wavelengths, rendering them excellent candidates for use in neurological research and medicine.

In silico strategy to design an efficient organic photoswitch based on excited-state cation transfer

A new class of photoswitches and the corresponding elementary photoinduced reaction, the so-called Excited-State Cation Transfer (ESCT), are investigated. This reaction relies on an intramolecular photo-release/photo-complexation of cation: after irradiation, the cation is translocated from a complexation site 1 to a site 2 during the excited state lifetime. Our purpose is thus to develop a computational strategy based on Density Functional theory (DFT) and its time-dependent counterpart (TD-DFT) to improve the different properties of the ESCT photoswitches, namely (i) the ground state complexation constant K, (ii) the excited state complexation constant K*, (iii) the photoejection properties and (iv) the population of the triplet states from a singlet state via intersystem crossing to increase the lifetime of the excited state. In this work, we are interested in optimizing the ESCT properties of a betaine pyridinium chromophore substituted by a 15-aza-5-crown, that was previously shown to efficiently photoeject a Ca2+ cation from the site 1 but no photo-recapture was observed in the site 2 [Aloïse et al., Phys. Chem. Chem. Phys., 2016, 22, 15384]. To this purpose, we have investigated the impact of the modification of the site 1 on the ESCT properties by introducing different substituents (EDG groups, halogen atoms) at different positions. So far, promising systems have been identified but a simultaneous improvement of all the ESCT photoswitches properties has yet not been achieved.

o-Nitrobenzyl-Based Caged exo-16,17-Dihydro-gibberellin A5-13-acetate for Photocontrolled Release of Plant Growth Regulators

Caged plant growth regulators (caged PGRs) that release bioactive molecules under irradiation are critical in enhancing the efficacy and mitigating the negative environmental effects of PGRs. The synthetically derived plant growth inhibitor exo-16,17-dihydro-gibberellin A5-13-acetate (DHGA5) regulates the development and stress resilience of plants. We report here the conception of novel caged DHGA5 derivatives wherein the photoremovable protecting groups (PRPGs) serve not only to enable light-controlled release but also to protect the carboxyl group during chemical synthesis. Three o-nitrobenzyl-based caged DHGA5 derivatives with different substituents on the nitrobenzyl moiety were obtained and evaluated for their properties in vitro and in vivo. The photolysis half-life values of caged DHGA5 derivatives 7a, 7b, and 7c under a UV lamp were 15.6 h, 1.2 h, and 28.2 h, respectively. Experiments in vivo showed that 0.2 mM of the caged compounds significantly inhibited the growth of the model plant Arabidopsis thaliana and important crop rice in a precise photoactivated form.

Synthesis and Photolytic Assessment of Nitroindolinyl-Caged Calcium Ion Chelators

Neuroactive amino acids derivatised at their carboxylate groups with a photolabile nitroindolinyl group are highly effective reagents for the sub-µs release of neuroactive amino acids in physiological solutions. However, the same does not apply in the case of calcium ion chelators. In this study, nitroindolinyl-caged BAPTA is found to be completely photostable, whereas nitroindolinyl-caged EDTA photolyses only when saturated with calcium ions.

Controlled release and characterisation of photocaged molecules using in situ LED illumination in solution NMR spectroscopy

We demonstrate that photo-uncaging reactions triggered by LED illumination can be conveniently monitored in situ by solution NMR, offering new ways to characterise and optimise photocages.

Caged Phytohormones: From Chemical Inactivation to Controlled Physiological Response

Plant hormones, also called phytohormones, are small signaling molecules regulating a wide range of growth and developmental processes. These unique compounds respond to both external (light, temperature, water, nutrition, or pathogen attack) and internal factors (e.g., age) and mediate signal transduction leading to gene expression with the aim of allowing plants to adapt to constantly changing environmental conditions. Within the regulation of biological processes, individual groups of phytohormones act mostly through a web of interconnected responses rather than linear pathways, making elucidation of their mode of action in living organisms quite challenging. To further progress with our knowledge, the development of novel tools for phytohormone research is required. Although plenty of small molecules targeting phytohormone metabolic or signaling pathways (agonists, antagonists, and inhibitors) and labeled or tagged (fluorescently, isotopically, or biotinylated) compounds have been produced, the control over them in vivo is lost at the time of their administration. Caged compounds, on the other hand, represent a new approach to the development of small organic substances for phytohormone research. The term "caged compounds" refers to light-sensitive probes with latent biological activity, where the active molecule can be freed using a light beam in a highly spatio/temporal-, amplitude-, or frequency-defined manner. This review summarizes the up-to-date development in the field of caged plant hormones. Research progress is arranged in chronological order for each phytohormone regardless of the cage compound formulation and bacterial/plant/animal cell applications. Several known drawbacks and possible directions for future research are highlighted.

Photoreversible stretching of a BAPTA chelator marshalling Ca2+-binding in aqueous media

Free calcium ion concentration is known to govern numerous biological processes and indeed calcium acts as an important biological secondary messenger for muscle contraction, neurotransmitter release, ion-channel gating, and exocytosis. As such, the development of molecules with the ability to instantaneously increase or diminish free calcium concentrations potentially allows greater control over certain biological functions. In order to permit remote regulation of Ca²⁺, a selective BAPTA-type synthetic receptor / host was integrated with a photoswitchable azobenzene motif, which upon photoirradiation would enhance (or diminish) the capacity to bind calcium upon acting on the conformation of the adjacent binding site, rendering it a stronger or weaker binder. Photoswitching was studied in pseudo-physiological conditions (pH 7.2, [KCl] = 100 mM) and dissociation constants for azobenzene cis- and trans-isomers have been determined (0.230 μM and 0.102 μM, respectively). Reversible photoliberation/uptake leading to a variation of free calcium concentration in solution was detected using a fluorescent Ca²⁺ chemosensor.

Photoconversion of an anthraquinone derivative in the presence of human serum albumin

Photconversion of an anthraquinone photochrome (AQP) from Trans to Ana forms were studied by different methods and techniques. Solution of AQP was irradiated under UV light in buffer condition, pH = 7.5, 10 mM phosphate buffer in the absence and presence of human serum albumin at 27 and 37 °C. The results showed that a new peak at higher wavelength was observed that indicative of producing the Ana form. Rate of Trans to Ana conversion increases in the presence of human serum albumin (HSA). Electron transport calculations were carried out from the first principles with a method based on non-equilibrium Green's functions (NEGF) combined with DFT. The results showed that electron transport is easier in Ana form due to increasing the resonance length and electron delocalization. Binding study by docking and spectroscopy showed that Trans form has more tendency to interact with HSA due to higher number of HSA-Trans hydrogen bond. Structural studies by circular dichroism and molecular dynamics results show that at lower concentration of AQP, percentage of helix was increased and then decreases at higher concentration. In addition structural parameters such as RMSD, accessible surface area, hydrogen bond, in associated with experimental results showed that protein folded at low concentration.

Visible light initiated release of calcium ions through photochemical electron transfer reactions

Photolysis of anthraquinone or flavin photosensitizers in the presence of calcium EDTA complexes results in decomposition of the EDTA complex, releasing free Ca²⁺. In the case of the flavin sensitizers, it is shown that millimolar concentrations of Ca²⁺ can be released using visible light (>440 nm) and with quantum yields as high as 0.31. The utility of this system is further demonstrated by in situ photogelation of an alginate solution.

Photo-cleavable analog of BAPTA for the fast and efficient release of Ca2

A new photocleavable analog of BAPTA chelating ligand has a high affinity towards Ca2+ ions (K = 2.5 × 106 M-1). The use of photolabile 3-(hydroxymethyl)-2-naphthol core in the design of photo-BAPTA allows for the efficient (Φ = 0. 63) and very fast (τ < 12 μs) release of Ca2+ ions upon 300 or 350 nm irradiation.

Development and Biological Evaluation of a Photoactivatable Small Molecule Microtubule-Targeting Agent

Photoremovable protecting groups added to bioactive molecules provide spatial and temporal control of the biological effects. We present synthesis and characterization of the first photoactivatable small-molecule tubulin inhibitor. By blocking the pharmacophoric OH group on compound 1 with photoremovable 4,5-dimethoxy-2-nitrobenzyl moiety we developed the photocaged prodrug 2 that had no effect in biological assays. Short UV light exposure of the derivative 2 or UV-irradiation of cells treated with 2 resulted in fast and potent inhibition of tubulin polymerization, attenuation of cell viability, and apoptotic cell death, implicating release of the parent active compound. This study validates for the first time the photoactivatable prodrug concept in the field of small molecule tubulin inhibitors. The caged derivative 2 represents a novel tool in antitubulin approaches.

Design and Synthesis of a 4-Nitrobromobenzene Derivative Bearing an Ethylene Glycol Tetraacetic Acid Unit for a New Generation of Caged Calcium Compounds with Two-Photon Absorption Properties in the Near-IR Region and Their Application in Vivo

Among biologically active compounds, calcium ions (Ca2+) are one of the most important species in cell physiological functions. Development of new calcium chelators with two-photon absorption (TPA) properties is a state-of-the-art challenge for chemists. In this study, we report the first and efficient synthesis of 5-bromo-2-nitrobenzyl-substituted ethylene glycol tetraacetic acid (EGTA) as a platform for a new generation of calcium chelators with TPA properties in the near-infrared region. New calcium chelators with high TPA properties, that is, a two-photon (TP) fragmentation efficiency of δu = 20.7 GM at 740 nm for 2-(4-nitrophenyl)benzofuran (NPBF)-substituted EGTA (NPBF-EGTA, K d = 272 nM) and δu = 7.8 GM at 800 nm for 4-amino-4'-nitro-1,1'-biphenyl (BP)-substituted EGTA (BP-EGTA, K d = 440 nM) derivatives, were synthesized using Suzuki-Miyaura coupling reactions of the bromide with benzofuran-2-boronic acid and 4-(dimethylamino)phenyl boronic acid, respectively. The corresponding acetoxymethyl (AM) esters were prepared and successfully applied to the Ca2+-uncaging reaction triggered by TP photolysis in vivo.

A membrane permeable fluorescent Ca2+ probe based on bis-BODIPY with branched PEG

The cellular uptake of MPFCP-2 is improved by the PEG encapsulation method, and then MPFCP-2 could pass through the cell membrane by itself, and monitor the changes of the intracellular Ca²⁺ signal.

A light-induced reversible phase separation and its coupling to a dynamic library of imines

Irradiation of an acetonitrile–water solution of the bis-pyridyl hydrazone 1 and calcium chloride causes a photo-induced phase separation. It is coupled to a covalent library of imines, undergoing constitutional reorganization upon phase separation.