O-nitrobenzyl Group Research Articles

Crystallization behavior of poly(ε-caprolactone) chains confined in lamellar nanodomains

The crystallization behavior of poly(ε-caprolactone) (PCL) homopolymers and PCL blocks confined in identical lamellar nanodomains (L-domains) has been examined using differential scanning calorimetry and synchrotron small-angle X-ray scattering as a function of PCL layer thickness d and crystallization temperature. The PCL homopolymers confined in the L-domains with d = 8.7 nm (small L-domain) and 15.8 nm (large L-domain) were prepared using microphase separation of PCL-block-polystyrene (PCL-b-PS) copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks, followed by the photocleavage of ONB with UV-irradiation. The PCL crystallinity showed a conventional sigmoidal evolution both for PCL blocks and PCL homopolymers confined in the large L-domain. However, it increased monotonously with no induction time for PCL blocks but sigmoidally for PCL homopolymers confined in the small L-domain. The substantial differences in crystallization mechanism between PCL blocks and PCL homopolymers confined in the small L-domain are discussed on the basis of chain mobility during crystallization.

Controlled Release of Hydrophilic Guest Molecules from Photoresponsive Nucleolipid Vesicles

We here report a novel design and synthesis of a light-responsive nucleolipid by introducing an o-nitrobenzyl group that acts as a linker between a nucleotide and a lipid. The nucleolipid was applied readily to preparing smart vesicles and encapsulating hydrophilic guest molecules 5(6)-carboxyfluorescein (CF) in their inner aqueous phase. Upon light irradiation, their vesicular structure was disrupted as a result of the photolytic degradation of the nucleotide, resulting in CF release. Furthermore, temporally controlled CF release from these vesicles could be readily realized by turning on and off light. By demonstrating the molecular assembly and photo-disassembly cycle, this report aims to stimulate further research exploring practical applications of nucleolipids.

Wavelength-selective cleavage of o-nitrobenzyl and polyheteroaromatic benzyl protecting groups

Evaluation of the wavelength-selective cleavage of five photolabile protecting groups from two different families has been performed. Alanine, as a model bifunctional target molecule was masked at the amino terminal with o-nitrobenzyl group and at the carboxylic terminal with benzyl-type nitrogen and oxygen polyheteroaromatics, namely acridine, (thioxo)benzocoumarin and a coumarin built on the julolidine nucleus. The photosensitivity of the corresponding alanine conjugates was studied at selected wavelengths with HPLC/UV and 1H NMR monitoring. The release of the fully deprotected molecule could be achieved by sequential irradiation in variable irradiation times, which were dependent on the heteroaromatic group used.

Controlled Release of Hydrophilic Guest Molecules from Photoresponsive Nucleolipid Vesicles

Amphiphilic hybrid nucleolipids bear the structural and functional hallmarks of both lipids and nucleic acids and hold great potential for biotechnological applications. However, further tailoring of their structures and properties for specific applications represents a major challenge. We here report a novel design and synthesis of a light-responsive nucleolipid by introducing an o-nitrobenzyl group that acts as a linker between a nucleotide and a lipid. The nucleolipid was applied readily to preparing smart vesicles and encapsulating hydrophilic guest molecules 5(6)-carboxyfluorescein (CF) in their inner aqueous phase. Upon light irradiation, their vesicular structure was disrupted as a result of the photolytic degradation of the nucleotide, resulting in CF release. Furthermore, temporally controlled CF release from these vesicles could be readily realized by turning on and off light. By demonstrating the molecular assembly and photodisassembly cycle, this report aims to stimulate further research exploring practical applications of nucleolipids.

Crystallization Behavior of Poly(ε-caprolactone) Chains Confined in Nanocylinders: Effects of Block Chains Tethered to Nanocylinder Interfaces

The crystallization behavior of poly(e-caprolactone) (PCL) chains (i.e., PCL block + PCL homopolymer systems) spatially confined in nanocylinders with different diameters D has been investigated as a function of the mole fraction of PCL homopolymers fhomo existing in the PCL chains. The nanocylinders with PCL chains inside were prepared using the microphase separation of PCL-block-polystyrene (PCL-b-PS) diblock copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks, and subsequently ONB was cleaved by a controlled irradiation of UV light to get the PCL chains with various fhomo. In the isothermal crystallization process, the crystallinity of PCL chains showed an exponential time evolution (or first-order kinetics) for all the systems investigated. The half-time of crystallization of PCL chains with 0 < fhomo < 1 was found to be intermediate between those of PCL blocks (fhomo = 0) and PCL homopolymers (fhomo ∼ 1); it decreased moderately with increasing fhomo in a smaller nano...

UV-cleavable unimolecular micelles: synthesis and characterization toward photocontrolled drug release carriers

UV-cleavable star polymers composed of a well-defined 6-arm amphiphilic block copolymer and a UV-cleavable core with photolabile o-nitrobenzyl groups have been synthesized and characterized. The core of the star polymer is a cyclotriphosphazene, which can biodegrade to phosphate and ammonium ion. The resultant unimolecular micelles can be dissociated in a controlled manner by UV irradiation. The inner lipophilic poly(methyl methacrylate) (PMMA) and the outer hydrophilic poly[poly(ethylene glycol) methyl ether methacrylate] (PPEGMA) were grafted by atom transfer radical polymerization (ATRP), leading to the formation of star-PMMA-PPEGMA with different compositions. The effects of various factors, such as molecular weight, solution concentration, solvents (THF, toluene, and water) and monomers (MMA, PEGMA, and 2-(dimethylamino)ethyl methacrylate (DMA)) on the photodegradation rate of the star polymers were studied by gel permeation chromatography (GPC). The micellar behavior of star-PMMA-PPEGMA was unambiguously demonstrated by dynamic light scattering (DLS), fluorescence techniques and transmission electron microscopy (TEM). The formation of nanoparticles (star-AGG) from the aggregation of the two star-PMMA-PPEGMA polymer micelles in aqueous solution was detected by DLS with hydrodynamic radii of 86 and 111 nm. The critical aggregation concentration (CAC) of star-AGG-2 from star-PMMA179-PPEGMA89-2 was 0.0026 g L−1 and 0.022 g L−1 before and after UV-irradiation indicating the reduced stability of the polymer micellar structures after UV-irradiation due to the detachment of the amphiphilic arms from the cyclotriphosphazene core. As a result, spontaneous dissociation of cleaved micelles can be induced by the dilution effect in the human body for stimulus-controlled drug release.

Orthogonal Self-Assembly in Folding Block Copolymers

We herein report the synthesis and characterization of ABA triblock copolymers that contain two complementary association motifs and fold into single-chain polymeric nanoparticles (SCPNs) via orthogonal self-assembly. The copolymers were prepared using atom-transfer radical polymerization (ATRP) and possess different pendant functional groups in the A and B blocks (alcohols in the A block and acetylenes in the B block). After postfunctionalization, the A block contains o-nitrobenzyl-protected 2-ureidopyrimidinone (UPy) moieties and the B block benzene-1,3,5-tricarboxamide (BTA) moieties. While the protected UPy groups dimerize after photoinduced deprotection of the o-nitrobenzyl group, the BTA moieties self-assemble into helical aggregates when temperature is reduced. In a two-step thermal/photoirradiation treatment under dilute conditions, the ABA block copolymer forms both BTA-based helical aggregates and UPy dimers intramolecularly. The sequential association of the two self-assembling motifs results in single-chain folding of the polymer, affording nanometer-sized particles with a compartmentalized interior. Variable-temperature NMR studies showed that the BTA and UPy self-assembly steps take place orthogonally (i.e., without mutual interference) in dilute solution. In addition, monitoring of the intramolecular self-assembly of BTA moieties into helical aggregates by circular dichroism spectroscopy showed that the stability of the aggregates is almost independent of UPy dimerization. Size-exclusion chromatography (SEC) and small-angle X-ray scattering analysis provided evidence of significant reductions in the hydrodynamic volume and radius of gyration, respectively, after photoinduced deprotection of the UPy groups; a 30-60% reduction in the size of the polymer chains was observed using SEC in CHCl(3). Molecular imaging by atomic force microscopy (AFM) corroborated significant contraction of individual polymer chains due to intramolecular association of the BTA and UPy groups. The stepwise folding process resulting from orthogonal self-assembly-induced supramolecular interactions yields compartmentalized SCPNs comprised of distinct microdomains that mimick two secondary-structuring elements in proteins.

Photoresponsive Poly(S-(o-nitrobenzyl)-l-cysteine)-b-PEO from a l-Cysteine N-Carboxyanhydride Monomer: Synthesis, Self-Assembly, and Phototriggered Drug Release

A photoresponsive S-(o-nitrobenzyl)-l-cysteine N-carboxyanhydride (NBC-NCA) monomer was for the first time designed, and the related poly(S-(o-nitrobenzyl)-l-cysteine)-b-poly(ethylene glycol) (PNBC-b-PEO) block copolymers were synthesized from the ring-opening polymerization (ROP) of NBC-NCA in DMF solution at 25 °C. Their molecular structures, physical properties, photoresponsive self-assembly, and drug release of PNBC-b-PEO were thoroughly investigated. The β-sheet conformational PNBC block within copolymers presented a thermotropic liquid crystal phase behavior, and the crystallinity of PEO block was progressively suppressed over the PNBC composition. The characteristic absorption peaks of these copolymers at about 310 and 350 nm increased over UV irradiation time and then leveled off, indicating that the o-nitrobenzyl groups were gradually photocleaved from copolymers until the completion of photocleavage. The PNBC-b-PEO copolymers self-assembled into spherical nanoparticles in aqueous solution, presenting a photoresponsive self-assembly behavior, together with a size reduction of nanoparticles after irradiation. The anticancer drug doxorubicin can be released in a controlled manner by changing the light irradiation time, which was induced by gradually photocleaving the PNBC core of nanoparticles. This work provides a facile strategy not only for the synthesis of photoresponsive polypeptide-based block copolymers but also for the fabrication of photoresponsive nanomedicine potential for anticancer therapy.

Crystallization Behavior and Crystal Orientation of Poly(ε-caprolactone) Homopolymers Confined in Nanocylinders: Effects of Nanocylinder Dimension

The crystallization behavior and crystal orientation of poly(e-caprolactone) (PCL) homopolymers and PCL blocks spatially confined in identical nanocylinders have been investigated using differential scanning calorimetry (DSC) and two-dimensional wide-angle X-ray diffraction (WAXD) as a function of cylinder diameter D. The PCL homopolymers confined in nanocylinders were prepared using microphase separation of PCL-block-polystyrene (PCL-b-PS) copolymers with a photocleavable o-nitrobenzyl group (ONB) between PCL and PS blocks and the subsequent cleavage of ONB by irradiating UV light. The time evolution of PCL crystallinity χPCL showed a first-order kinetics for both PCL blocks and PCL homopolymers confined in all the nanocylinders investigated. However, the D dependence of crystallization rates for PCL blocks was more drastic than that for PCL homopolymers, and consequently various D-dependent interrelations were observed between crystallization rates of PCL blocks and PCL homopolymers. The crystal orienta...

O-Nitrobenzyl Alcohol Derivatives: Opportunities in Polymer and Materials Science

Polymers featuring photolabile groups are the subject of intense research because they allow the alteration of polymer properties simply by irradiation. In particular, the o-nitrobenzyl group (o-NB) is utilized frequently in polymer and materials science. This Perspective pays particular attention to the increasing utilization of this chemical group in polymer chemistry. It covers the use of (i) o-NB-based cross-linkers for photodegradable hydrogels, (ii) o-NB side chain functionalization in (block) copolymers, (iii) o-NB side chain functionalization for thin film patterning, (iv) o-NB for self-assembled monolayers, (v) photocleavable block copolymers, and (vi) photocleavable bioconjugates. We conclude with an outlook on new research directions in this rapidly expanding area.

Near-Infrared Light-Triggered Dissociation of Block Copolymer Micelles Using Upconverting Nanoparticles

We demonstrate a novel strategy enabling the use of a continuous-wave diode near-infrared (NIR) laser to disrupt block copolymer (BCP) micelles and trigger the release of their "payloads". By encapsulating NaYF(4):TmYb upconverting nanoparticles (UCNPs) inside micelles of poly(ethylene oxide)-block-poly(4,5-dimethoxy-2-nitrobenzyl methacrylate) and exposing the micellar solution to 980 nm light, photons in the UV region are emitted by the UCNPs, which in turn are absorbed by o-nitrobenzyl groups on the micelle core-forming block, activating the photocleavage reaction and leading to the dissociation of BCP micelles and release of co-loaded hydrophobic species. Our strategy of using UCNPs as an internal UV or visible light source upon NIR light excitation represents a general and efficient method to circumvent the need for UV or visible light excitation that is a common drawback for light-responsive polymeric systems developed for potential biomedical applications.

Photoactive SAM surface for control of cell attachment

A new approach to control cell attachment using photochemistry and self-assembled monolayers (SAMs) has been developed. Poly(ethylene glycol) (PEG) was introduced onto a gold SAM surface to initially create a cell repulsive surface via a photo-cleavable o-nitrobenzyl functional group. This cell repulsive surface was subsequently rendered cell adhesive by exposure to UV-irradiation which cleaved the photoactive o-nitrobenzyl group, followed by immobilization of cell adhesive peptides to the irradiated regions. Water contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were used to confirm the photoreactions and to characterize surface properties. To study cell attachment on the prepared surfaces, NIH/3T3 fibroblast cells were used. The cell culture results demonstrated that PEG covered SAMs had the ability to repel cells and that the surface became cell adhesive after UV-irradiation to cleave cell non-adhesive PEG from the exposed surface via photo-labile o-nitrobenzyl groups, followed by immobilization of cell adhesive RGD peptides. In this study, we show that cell attachment can be controlled on photo-cleavable PEG–gold SAMs by UV exposure. We also show that the resulting surface is effective to control cell attachment for up to 5 days in culture.

Dually responsive aqueous gels from thermo- and light-sensitive hydrophilic ABA triblock copolymers

We report in this article the synthesis of a series of thermo- and light-sensitive hydrophilic ABA linear triblock copolymers, poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate)-b-poly(ethylene oxide)-b-poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate) (P(TEGEA-co-NBA)-b-PEO-b-P(TEGEA-co-NBA)), with various NBA molar contents and the study of sol–gel transitions of their aqueous solutions. The copolymers were prepared by ATRP from a difunctional PEO macroinitiator; the polydispersity indexes of all polymers were <1.2. We demonstrated that a 10.0 wt% aqueous solution of a triblock copolymer with a NBA content of 9.3 mol% in the thermosensitive blocks underwent a thermo-induced reversible sol–gel transition and a UV-triggered gel-to-sol transition at a constant temperature. The UV-irradiated solution again can undergo a temperature-induced sol–gel transition but at a higher temperature. The thermo-triggered sol–gel transitions stemmed from the formation of a 3-dimensional network with the dehydrated thermosensitive blocks being associated into hydrophobic cores and the central PEO block forming bridges among micelles. Exposure to UV light cleaved hydrophobic o-nitrobenzyl groups, raised the LCST of thermosensitive blocks, and thus triggered a gel-to-sol transition at a constant temperature. Rheometry was employed to study the sol–gel transitions and gel characteristics. In addition, we studied the effects of polymer concentration and NBA content on sol–gel transition temperature (Tsol–gel) and gel properties before and after UV irradiation. The Tsol–gel increased with the decrease of polymer concentration; the critical gelation concentration for the triblock copolymer with a NBA content of 9.3 mol% was between 3 and 4 wt% before UV irradiation and between 5 and 6% after photocleavage of o-nitrobenzyl groups. The change of Tsol–gel was in general larger for the copolymer with a higher NBA content after UV irradiation.

Stimuli-Induced Multiple Sol−Gel−Sol Transitions of Aqueous Solution of a Thermo- and Light-Sensitive Hydrophilic Block Copolymer

We report in this article that a 20.0 wt % aqueous solution of a thermo- and light-sensitive hydrophilic block copolymer, poly(ethylene oxide)-b-poly(ethoxytri(ethylene glycol) acrylate-co-o-nitrobenzyl acrylate) (PEO-b-P(TEGEA-co-NBA)), can undergo multiple sol−gel−sol transitions in response to temperature changes and UV irradiation. The 20.0 wt % block copolymer solution was a free-flowing liquid at low temperatures. Upon heating above the lower critical solution temperature (LCST) of the thermo- and light-sensitive P(TEGEA-co-NBA) block, micellization occurred with the P(TEGEA-co-NBA) block associating into the core and the PEO block forming the corona. The solution turned into an immobile, optically isotropic gel at 33 °C. The gel exhibited a finite yield stress, and its dynamic storage modulus was essentially independent of frequency, suggesting that the gel was composed of cubic-packed micelles. With further increasing temperature to 50 °C, the gel flowed under its weight. This is because the PEO corona shrank at elevated temperatures, and thus the structural constraint among micelles was released. At 33 °C, we irradiated the micellar gel with 365 nm UV light. The o-nitrobenzyl group of NBA was cleaved, resulting in an increase in the LCST of the thermosensitive block and the dissociation of micelles. Consequently, the gel was transformed into a free-flowing liquid, which upon heating underwent sol−gel−sol transitions, similar to the solution before UV irradiation.

A Multilayered Approach to Complex Surface Patterning

A method for developing complex nanopatterns on surfaces has been developed by combining self-assembly, photolabile protecting groups, and multilayered films. An o-nitrobenzyl protecting group has been incorporated into molecular level films utilizing thiol-gold interactions. When the o-nitrobenzyl group is cleaved by ultraviolet light, a carboxylic acid terminated layer remains on the surface and is available for activation and further functionalization through amide bond formation. Using this method, multilayered films have been constructed and characterized by contact angle goniometry, cyclic voltammetry, grazing incidence infrared spectroscopy, and X-ray photoelectron spectroscopy measurements. Complex surface patterns can be achieved by creating a surface array using a photomask and then further functionalizing the irradiated area through covalent coupling. Fluorophores were attached to the deprotected regions, providing visual evidence of surface patterning using fluorescence microscopy. This approach is universal to bind moieties containing free amine groups at defined regions across a surface, allowing for the development of films with complex chemical and physicochemical properties.

Metastable Supramolecular Polymer Nanoparticles via Intramolecular Collapse of Single Polymer Chains

We present an elegant approach for fabricating polymeric nanoparticles via the reversible noncovalent intramolecular cross-linking of single polymer chains. By protecting the well-studied 2-ureido-pyrimidinone moiety with an o-nitrobenzyl group, we have introduced a latent quadruple hydrogen bonding motif. Incorporating this group into linear poly(norbornenes) creates a class of supramolecular materials that can be readily dissolved and subsequently cross-linked upon irradiation with UV light, eliminating the need for selective solvent techniques. This is a facile method for producing well-defined particles with narrow polydispersity as confirmed by atomic force microscopy. By virtue of the nature of the intramolecular cross-linking (supramolecular interactions of pendant groups), these metastable nanoparticles are akin to folded biomacromolecules, representing the first step in linking synthetic polymers and self-folded biopolymers.

Biotinylated Photocleavable Polyethylenimine: Capture and Triggered Release of Nucleic Acids from Solid Supports

A biotinylated photocleavable polyethylenimine (B-PC-PEI) was designed and synthesized for the capture and controlled release of nucleic acids from solid supports. B-PC-PEI was synthesized via a three-step reaction process and verified by 1H NMR and mass spectrometry. In aqueous solution, the o-nitrobenzyl group within B-PC-PEI was efficiently cleaved by 5 min of 365 nm light exposure from a distance of 20 cm (9 mW/cm2). When coupled to streptavidin-coated beads, the PEI domain of Cy5-labeled B-PC-PEI was released by 365 nm light exposure. In contrast, a Cy5-labeled biotinylated PEI (B-PEI) was used as a control and negligible fluorescence loss was observed. Cy5-labeled siRNA was electrostatically captured to streptavidin-coated beads preabsorbed with B-PC-PEI or B-PEI, and flow cytometry demonstrated significant loss of fluorescence from the bead surface after 5 min of light exposure only for B-PC-PEI, demonstrating controlled release of siRNA from the bead surface. Finally, the release of the Cy5-labeled siRNA into the supernatant was quantified. The release of Cy5-siRNA into the supernatant was significantly greater after 5 min of light exposure for B-PC-PEI/streptavidin beads compared to 0 min exposure and remained unchanged for B-PEI/streptavidin beads. B-PC-PEI facilitates capture and triggered release of surface-tethered nucleic acids with light exposure and is fully compatible with streptavidin-based applications.

Molecular Design of o-Nitrobenzyl Phenol Ether for Photo-deprotection Resist; Challenge to half-pitch 22nm using Near-field Lithography

Polyhydroxystyrenes protected with three kinds of o-nitrobenzyl (NB) group are synthesized: 4,5- dimethoxy NB group (DNB), 4- monomethoxy NB group (MNB) and $alpha;-methyl 4,5- dimethoxy NB group (ADNB). Their solutions are formulated as photo-deprotection resists for the near-field lithography (NFL). These resists are evaluated in terms of the fundamental lithographic performances using the propagation i-line light, followed by the NFL experiments. The ADNB has the highest photosensitivity and the DNB provides the resist patterns of the smallest line edge roughness (LER). Hp 22 nm L/S pattern of 10 nm deep is fabricated on the top portion of a single-layer of DNB. Hp 32 nm L/S pattern of 10 nm thick is transferred to the 100 nm thick bottom-layer resist through the tri-layer resist process.

A Versatile Photocleavable Bifunctional Linker for Facile Synthesis of Substrate−DNA Conjugates for the Selection of Nucleic Acid Catalysts

Covalent photocleavable attachment of small molecules or peptides to oligonucleotides is an integral strategic element in the selection of novel nucleic acid enzymes. Here, we report the synthesis of a multipurpose, photocleavable bifunctional linker (PCBL) suitable for nucleic acid selections and other biotechnology applications. PCBL contains a photocleavable O-nitrobenzyl group flanked on one side by an N-hydroxysuccinimidyl ester (reactive toward primary amines) and on the other side by a sulfhydryl. To demonstrate the utility of PCBL, the linker was used to couple an analog of the antibiotic chloramphenicol (Cam) to the 5' end of an amino-modified 8-mer DNA oligo. Coupling was confirmed by MALDI-TOF spectrophotometry. Decoupling was performed by irradiating the coupled species with near-UV light (approximately 360 nm), regenerating the original amino-modified oligo. Ligation of the Cam-PCBL-DNA conjugate to random-sequence RNA generated a diversity library appropriate for the selection of new ribozymes that catalyze reactions involving the tethered substrate. Coupling and decoupling of the Cam analog from the library was monitored on a trilayered organomercurial polyacrylamide gel. The coupling/decoupling strategy described here is readily generalized to many combinations of macromolecules and small molecules. For example, analogs of this small molecule-DNA conjugate can be generated as synthons for ligation to nucleic acid diversity libraries during each round of novel ribozyme selections, or they can be immobilized onto chips for addresssably reversible microarray analysis.

Controlled release of DNA/polyamine complex by photoirradiation of a solid phase presenting o-nitrobenzyl ether tethered spermine or polyethyleneimine

Various gene transfer and automated/monitorized analytical applications require the controlled release of nucleic acid. A solid phase with spermine or polyethyleneimines (PEI, 600 MW) tethered by o-nitrobenzyl linkages was synthesized with polyethylene oxide beads (Argo Gel-NH 2). The photolysis of test compound O-2-nitrophenethyl O, O-diethyl phosphate or solid phase with o-nitrobenzyl group as synthetic linker was completely degradable with photoirradiation at 365 nm for 10–18 min at 3.5 mW/cm 2. DNA binding with polyamine of the solid phase and releasing of DNA/polyamine were monitored by UV measurement and gel electrophoresis. The potential exists to employ a DNA-loaded solid phase for spatially, temporally, or dose-controlled release of DNA, at extracellular or intracellular sites.