O-nitrobenzyl Group Research Articles

Photo-activation of Tolane-based Synthetic Ion Channel for Transmembrane Chloride Transport.

While natural channels respond to external stimuli to regulate ion concentration across cell membranes, creating a synthetic version remains challenging. Here, we present a photo-responsive uncaging technique within an artificial ion channel system, which activates the ion transport process from a transport-inactive o-nitrobenzyl-based caged system. From the comparative ion transport screening, 1 b emerged as the most active transporter. Interestingly, its bis(o-nitrobenzyl) derivative, i.e., protransporter 1 b' was inefficient in transporting ions. Detailed transport studies indicated that compound 1 b is an anion selective transporter with a prominent selectivity towards chloride ions by following the antiport mechanism. Compound 1 b' did not form an ion channel, but after the o-nitrobenzyl groups were photocleaved, it released 1 b, forming a transmembrane ion channel. The channel exhibited an average diameter of 6.5±0.2 Å and a permeability ratio of . The geometry-optimization of protransporter 1 b' indicated significant non-planarity, corroborating its inefficient self-assembly. In contrast, the crystal structure of 1 b demonstrates strong self-assembly via the formation of an intermolecular H-bond. Geometry optimization studies revealed the plausible self-assembled channel model and the interactions between the channel and chloride ion.

Photo and pH dual stimuli-responsive block copolymer micelles with defined incorporation of o-nitrobenzyl units in poly(ɛ-caprolactone) block for controlled release

A series of dual stimuli-responsive block copolymers with varying content of photocleavable o-nitrobenzyl (ONB) ester group pendent in the hydrophobic poly(ɛ-caprolactone) block and pH-cleavable acetal linkage at the junction with hydrophilic poly(ethylene glycol) block is synthesized. The hydrophobic block is a random copolymer synthesized by ring-opening copolymerization of ɛ-caprolactone and ONB-substituted ɛ-caprolactone containing varying compositions of the two monomers. Kinetics of polymerization shows that ONB-functionalized monomer has lower reactivity than that of the unsubstituted monomer. The series of block copolymers shows self-assembly into well-defined spherical micelles of average size of 150–200 nm in aqueous solution. Photocleavage of ONB groups is studied by NMR and UV–vis spectroscopy, and its extent is determined. The two stimuli viz. UV light and pH are used individually as well as simultaneously to study the controlled release of the encapsulated drug Camptothecin and the synergistic effect of the two stimuli is demonstrated. The effect of varying content of ONB groups is observed on drug release profile. MTT assay showed non-cytotoxic nature of the polymer. Cell uptake and photoinduced release of doxorubicin (DOX) from the micelles in MDA-MB-231 cells is demonstrated.

Photo-Responsive Materials for Drug Delivery System

Recently, much research has focused on photo-responsive materials since the responsiveness of materials is convenient to control. The application of photo-responsive materials in drug delivery is widely reported. The o-nitrobenzyl group and coumarin group are two common functional groups that can respond to lights. The o-nitrobenzyl group is photo-cleavable and responds to 365 nm UV lights, while the coumarin group is both photo-cleavable and photo-dimerizable and responds to lights with various wavelengths. The dimerization process of the coumarin group is reversible. Materials based on these two groups are also easy to be prepared. In this review, photo-responsive materials for drug delivery systems are introduced. The whole delivery strategy for each work will be described in detail. All delivery systems show good drug-releasing ability in light stimuli in vitro. Due to limited experiment data, the effectiveness of the delivery system in vivo cannot be determined. The near-infrared ray responsive coumarin group-based materials are more recommended due to the better penetrability of near-infrared rays.

Effect of N-o-nitrobenzylation on conformation and membrane permeability of linear peptides

In this study, we explored the potential of the photoremovable o-nitrobenzyl (oNB) group as a tool to manipulate the membrane permeability and regulate the conformation of linear peptides by means of experimental and computational studies. We found that the introduction of one or more oNB groups markedly increased the permeability and altered the conformation, as compared to the corresponding unmodified peptides. We thoroughly investigated the impact of peptide length, number of oNB group, oNB insertion position, and introduction of N- and C-terminal protecting groups on the passive membrane permeability by means of parallel artificial membrane permeability assay (PAMPA). Photoreaction of peptides containing one or two oNB groups proceeded cleanly in moderate to high yields, releasing the unprotected parent linear peptide. The oNB-modified peptides showed a cis/trans conformational equilibrium, while after photolysis, the unprotected linear peptides showed only the trans-amide conformation. Furthermore, a comprehensive comparison of oNB-modified peptides and N-methylated peptides was conducted, encompassing conformational analysis and physicochemical properties. N-Substituted peptides favored a folded-like structure, which may contribute to the improvement in permeability.

Alpha-substituent effect on the photodeprotection of 4,5-dimethoxy-2-nitrobenzyl acetate

Since the first report of caged ATP, o-nitrobenzyl groups have been widely used as photolabile protecting groups, and analogue compounds have been used to study hydrogen abstraction reactions. In this work, a caged compound containing acetic acid was used to directly analyse the multiple steps of the deprotection reaction, with the aim of elucidating how and during which steps the α-substituent (αR) effect occurs. UV pump–visible probe spectroscopy was used to observe the ultrafast generation of biradicals and zwitterions as reaction intermediates. These experimental results and the results of DFT calculations suggested that the reaction proceeded in the four steps. During the αH abstraction reaction, the small αR volume results in a small energy gap between the S*(n-π*) and ground states and thus a fast rate of αH abstraction. Conversely, during the cyclization reaction, the small αR volume results in a high activation energy and thus a slow rate of cyclization.

Carbamate-Protected (BOC and O-NB) 2-Aminopyrimidinedione-Based Janus G-C Nucleobase Motifs as Building Blocks for Supramolecular Assembly and Smart Polymers.

In this paper, we report "carbamate protected" 2-aminopyrimidinedione-based Janus G-C nucleobases (2-APD Janus G-C nucleobases) featuring polymerizable groups and self-complementary triple H-bonding motifs DDA and AAD as building blocks for developing smart polymers and self-healing materials. The carbamate-masked H-bonding motif, cleavable under acidic (BOC group) or photocleavable (O-nitrobenzyl group) conditions, would facilitate the synthesis of smart polymers by alleviating aggregation during polymerization which in turn would exclude self-assembly-assisted solubility issues. Ready accessibility in excellent yields coupled with the possibility for facile introduction of polymerizable groups would make these building blocks excellent candidates for diverse polymerization applications.

Mitochondria-targeted melatonin photorelease supports the presence of melatonin MT1 receptors in mitochondria inhibiting respiration

The presence of signaling-competent G protein-coupled receptors in intracellular compartments is increasingly recognized. Recently, the presence of Gi/o protein-coupled melatonin MT1 receptors in mitochondria has been revealed, in addition to the plasma membrane. Melatonin is highly cell permeant, activating plasma membrane and mitochondrial receptors equally. Here, we present MCS-1145, a melatonin derivative bearing a triphenylphosphonium cation for specific mitochondrial targeting and a photocleavable o-nitrobenzyl group releasing melatonin upon illumination. MCS-1145 displayed low affinity for MT1 and MT2 but spontaneously accumulated in mitochondria, where it was resistant to washout. Uncaged MCS-1145 and exogenous melatonin recruited β-arrestin 2 to MT1 in mitochondria and inhibited oxygen consumption in mitochondria isolated from HEK293 cells only when expressing MT1 and from mouse cerebellum of WT mice but not from MT1-knockout mice. Overall, we developed the first mitochondria-targeted photoactivatable melatonin ligand and demonstrate that melatonin inhibits mitochondrial respiration through mitochondrial MT1 receptors.

Macroscopic Property Evaluation of Titania Nanocomposite Polymer Capable of Drawing Double-Network Macrostructure Using Photolithography.

In this study, we developed a double-network hybrid polymer that controls the strength and density of cross-linking points by utilizing the bonds of titania and catechol groups with an o-nitrobenzyl group (ONBg) as the photoreactive cross-linking points. In addition, this hybrid material system, which is composed of thermally dissociable bonds between titania and carboxyl groups, can be molded before light irradiation. The Young's modulus increased by approximately 1000 times upon irradiation with UV light. Moreover, introducing microstructures using the photolithography technique improved the tensile strength and fracture energy by approximately 32 and 15 times, respectively, compared to the sample without the photoreaction. The improved toughness was achieved by the macrostructures, which enhanced the effective cleavage of sacrificial bonds between the carboxyl groups and titania.

Chemical Synthesis of Proteins Using an o-Nitrobenzyl Group as a Robust Temporary Protective Group for N-Terminal Cysteine Protection

We report here a robust and practical strategy for chemical protein synthesis using an o-nitrobenzyl group as a temporary protective group for an N-terminal cysteine residue of intermediate hydrazide fragments. By reinvestigating the photoremoval of an o-nitrobenzyl group, we establish a robust and reliable strategy for its quantitative photodeprotection. The o-nitrobenzyl group is completely stable to oxidative NaNO2 treatment and has been applied to the convergent chemical synthesis of programmed death ligand 1 fragment, providing a practical avenue for hydrazide-based native chemical ligation.

Rapid and Selective Photo-degradation of Polymers: Design of an Alternating Copolymer with an o-Nitrobenzyl Ether Pendant.

The development of polymers with on-demand degradability is required to alleviate the current global issues on polymer-waste pollution. Therefore, we designed a vinyl ether monomer with an o-nitrobenzyl (oNBn) group as a photo-deprotectable pendant (oNBnVE) and synthesized an alternating copolymer with an oNBn-capped acetal backbone via cationic copolymerization with p-tolualdehyde (pMeBzA). The resultant alternating copolymer could be rapidly degraded into lower-molecular-weight compounds upon simple exposure to UV irradiation without any reactants or catalysts, while it was sufficiently stable toward heat and ambient light. This degradation proceeds via cleavage of the hemiacetal structure generated upon photo-deprotection of the oNBn pendant. The oNBn-peculiar degradability allowed the exclusive photo-degradation of the oNBnVE/pMeBzA segments in a diblock copolymer composed of oNBnVE/pMeBzA and benzyl vinyl ether (BnVE)/pMeBzA segments.

A Cell-Anchored and Self-Calibrated DNA Nanoplatform for in Situ Imaging and Quantification of Endogenous MicroRNA in Live Cells: Introducing Two Controls to Normalize the Sensing Signals

A Cell-Anchored and Self-Calibrated DNA Nanoplatform for in Situ Imaging and Quantification of Endogenous MicroRNA in Live Cells: Introducing Two Controls to Normalize the Sensing Signals

Photoimageable Organic Coating Bearing Cyclic Dithiocarbonate for a Multifunctional Surface.

We report the fabrication of photocross-linkable and surface-functionalizable polymeric thin films using reactive cyclic dithiocarbonate (DTC)-containing copolymers. The chemical functionalities of these material surfaces were precisely defined with light illumination. The DTC copolymers, namely, poly(dithiocarbonate methylene methacrylate-random-alkyl methacrylate)s, were synthesized via reversible addition-fragmentation chain transfer polymerization, and the reaction kinetics was thoroughly analyzed. The copolymers were cross-linked into a coating using a bifunctional urethane cross-linker that contains a photolabile o-nitrobenzyl group and releases aniline upon exposure to light. The nucleophilic attack of the aromatic amine opens the DTC group, forming a carbamothioate bond and generating a reactive thiol group in the process. The surface concentrations of the unreacted DTC and thiol were effectively controlled by varying the amounts of the copolymer and the cross-linker. The use of methacrylate comonomers led to additional reactive surface functionality such as carboxylic acid via acid hydrolysis. The successful transformations of the resulting DTC, thiol, and carboxylic acid groups to different functionalities via sequential nucleophilic ring opening, thiol-ene, and carbodiimide coupling reactions under ambient conditions were confirmed quantitatively using X-ray photoelectron spectroscopy. The presented chemistries were readily adapted to the immobilization of complex molecules such as a fluorophore and a protein in lithographically defined regions, highlighting their potential in creating organic coatings that can have multiple functional groups under ambient conditions.

Synthesis of multiple stimuli-responsive degradable block copolymers via facile carbonyl imidazole-induced postpolymerization modification

A robust approach that centers on carbonyl imidazole chemistry was used to synthesize a triple-stimuli-responsive degradable block copolymer labeled with acetal, disulfide, and o-nitrobenzyl groups exhibiting acid, reduction, and light responses.

Fully photodegradable block copolymer nanoparticles for dual release of cargo and radicals

When exposed to radiation, photo-responsive block copolymer nanoparticles disassemble to liberate a possible carried guest. However, the particle disruption is rarely accompanied by a polymer chain disintegration into molecular fragments, that would facilitate clearance from the body. We describe herein a novel class of fully photodegradable all-acrylic poly(hydroxyethyl acrylate)-b-poly(o-nitrobenzyl acrylate) (PHEA-PNBA) nanoparticles. Their synthesis proceeds by dispersion polymerization-induced self-assembly (PISA) based on a reversible addition–fragmentation chain transfer mechanism. The self-immolation mechanism is initiated via a dual H-abstraction by the electronically excited o-nitrobenzyl pendant group, first, from the adjacent CH2, second, from CH of the polyacrylate chains. The former results in the release of the protecting group, while the latter initiates a cascade of reactions that fragment the whole polymer backbone. Simultaneous chain scission and cleavage of o-nitrobenzyl group combine in turn to induce a fast and complete degradation of the copolymer particles. Synthesis, structural and colloidal characterization of the diblock copolymer nanoparticles, photochemical mechanism governing self-immolation are described. Emphasis is placed on understanding the reaction parameters which are important in controlling degradation rates, in particular nature of continuous phase and degree of polymerization of the PNBA block. UV exposure is exploited to release a model guest (Nile red) from the particles. Additionally, the burst release of free radicals accompanying the chain degradation can serve to decompose a target molecule (methylene blue).

Photo-Responsive Polymersomes as Drug Delivery System for Potential Medical Applications.

Due to a strong retardation effect of o-nitrobenzyl ester on polymerization, it is still a great challenge to prepare amphiphilic block copolymers for polymersomes with a o-nitrobenzyl ester-based hydrophobic block. Herein, we present one such solution to prepare amphiphilic block copolymers with pure poly (o-nitrobenzyl acrylate) (PNBA) as the hydrophobic block and poly (N,N’-dimethylacrylamide) (PDMA) as the hydrophilic block using bulk reversible addition-fragmentation chain transfer (RAFT) polymerization of o-nitrobenzyl acrylate using a PDMA macro-RAFT agent. The developed amphiphilic block copolymers have a suitable hydrophobic/hydrophilic ratio and can self-assemble into photoresponsive polymersomes for co-loading hydrophobic and hydrophilic cargos into hydrophobic membranes and aqueous compartments of the polymersomes. The polymersomes demonstrate a clear photo-responsive characteristic. Exposure to light irradiation at 365 nm can trigger a photocleavage reaction of o-nitrobenzyl groups, which results in dissociation of the polymersomes with simultaneous co-release of hydrophilic and hydrophobic cargoes on demand. Therefore, these polymersomes have great potential as a smart drug delivery nanocarrier for controllable loading and releasing of hydrophilic and hydrophobic drug molecules. Moreover, taking advantage of the conditional releasing of hydrophilic and hydrophobic drugs, the drug delivery system has potential use in medical applications such as cancer therapy.

Morphological Transitions of Photoresponsive Vesicles from Amphiphilic Polypeptoid Copolymers for Controlled Release.

Photoresponsive polymers have attracted increasing interest for a variety of applications. Here, we report a family of photoresponsive polypeptoid-based copolymer poly(ethylene glycol)-b-poly(N-(S-(o-nitrobenzyl)-thioethyl) glycine)-co-poly(N-(2-phenylethyl) glycine) (PEG-b-PNSN-co-PNPE) synthesized by the controlled ring-opening polymerization (ROP) technique. The key feature of the design is to incorporate both o-nitrobenzyl group moiety to offer the photoresponsive property and phenethyl residues to tune the structural and amphiphilic property of the system. We demonstrate that the cleavage degree of the o-nitrobenzyl group can reach to 100% upon UV-irradiation. With delicate design, a photoresponsive vesicle-to-sphere transition has been observed that facilitates the release of the encapsulants. This work provides a facile approach to prepare a type of photoresponsive polymers with tunable properties for drug delivery.

Methoxy-Substituted Nitrodibenzofuran-Based Protecting Group with an Improved Two-Photon Action Cross-Section for Thiol Protection in Solid Phase Peptide Synthesis.

Photoremovable caging groups are useful for biological applications because the deprotection process can be initiated by illumination with light without the necessity of adding additional reagents such as acids or bases that can perturb biological activity. In solid phase peptide synthesis (SPPS), the most common photoremovable group used for thiol protection is the o-nitrobenzyl group and related analogues. In earlier work, we explored the use of the nitrodibenzofuran (NDBF) group for thiol protection and found it to exhibit a faster rate toward UV photolysis relative to simple nitroveratryl-based protecting groups and a useful two-photon cross-section. Here, we describe the synthesis of a new NDBF-based protecting group bearing a methoxy substituent and use it to prepare a protected form of cysteine suitable for SPPS. This reagent was then used to assemble two biologically relevant peptides and characterize their photolysis kinetics in both UV- and two-photon-mediated reactions; a two-photon action cross-section of 0.71-1.4 GM for the new protecting group was particularly notable. Finally, uncaging of these protected peptides by either UV or two-photon activation was used to initiate their subsequent enzymatic processing by the enzyme farnesyltransferase. These experiments highlight the utility of this new protecting group for SPPS and biological experiments.

Synthesis and characterization of photo-responsive flower-like copolymer micelles with o-nitrobenzyl as the junction point

The photo-responsive ABA amphiphilic triblock copolymers polylactide-block-poly(ethylene glycol)-block-polylactide with o-nitrobenzyl esters as the photocleavable block-linker (defined as PLA-NB-PEG-NB-PLA), were prepared by controlled ring-opening polymerization (ROP) of D, L-lactide (D, L-LA) using two o-nitrobenzyl groups terminated polyethylene glycol as initiator. Flower-like micelles formed after these copolymers were dissolved in aqueous solution. Introduction of shortened PEG and PLA chains, although resulting in the reduction of micelle sizes, would bring about higher photolysis rate and loading efficiency of DOX. The flower-like micelles showed excellent photocleavage properties, thereby, burst release of DOX could be induced after UV irradiation, which will have potential application in biomedical materials.

Control of crystal orientation of spatially confined PCL homopolymers by cleaving chain-ends of PCL blocks tethered to nanolamella interfaces

We have examined the crystalline nanomorphology (i.e., crystallinity, melting temperature (reflecting crystal thickness), and crystal orientation) of poly(ε-caprolactone) (PCL) blocks and PCL homopolymers spatially confined in lamellar microdomain structures (nanolamellae) using two polystyrene (PS)-b-PCL diblock copolymers (with either PCL chain-end anchored to nanolamella interfaces) and one PS-b-PCL-b-PS triblock copolymer (with both chain-ends anchored). These copolymers had photocleavable o-nitrobenzyl groups at all the block junctions, so the PCL blocks could be converted into PCL homopolymers by UV irradiation with keeping the nanolamellar geometry. The crystallization of photocleaved PCL homopolymers was achieved by two procedures; (1) the amorphous PCL blocks were first converted into PCL homopolymers and they were crystallized at room temperature (RT) (one-step crystallization) or (2) the PCL blocks were first crystallized at selected temperatures to form some crystalline nanomorphology and then converted into PCL homopolymers to further crystallize and/or anneal at RT (two-step crystallization). The crystallinity and melting temperature of PCL homopolymers were similar for both procedures, suggesting that a certain amount of PCL homopolymers formed lamellar crystals with a comparable thickness. However, the lamellar crystals showed significantly different orientations between two procedures, because some crystal orientation was made by the advance crystallization of PCL blocks and remained unchanged after UV irradiation/subsequent crystallization in two-step crystallization, yielding a substantial difference in the crystal orientation of PCL homopolymers in nanolamellae.

Two in One: Light as a Tool for 3D Printing and Erasing at the Microscale.

The ability to selectively remove sections from 3D-printed structures with high resolution remains a current challenge in 3D laser lithography. A novel photoresist is introduced to enable the additive fabrication of 3D microstructures at one wavelength and subsequent spatially controlled cleavage of the printed resist at another wavelength. The photoresist is composed of a difunctional acrylate cross-linker containing a photolabile o-nitrobenzyl ether moiety. 3D microstructures are written by photoinduced radical polymerization of acrylates using Ivocerin as photoinitiator upon exposure to 900 nm laser light. Subsequent scanning using a laser at 700 nm wavelength allows for the selective removal of the resist by photocleaving the o-nitrobenzyl group. Both steps rely on two-photon absorption. The fabricated and erased features are imaged using scanning electron microscopy (SEM) and laser scanning microscopy (LSM). In addition, a single wire bond is successfully eliminated from an array, proving the possibility of complete or partial removal of structures on demand.