Photoactive Moieties Research Articles

Conformational Switching of G‐Quadruplex DNA by Photoregulation

Native, self-assembling nucleic acid nanomachines that can walk, move, or rotate have been developed. Owing to their ability to form diverse secondary structures, for example, by the highly sequence-specific hybridization of complementary sequences, the hybridization of DNA and RNA through Watson–Crick H bonds, and the assembly of triplexes through Hoogsteen bonds, nucleic acids are ideal building blocks for the construction of nanodevices. Quadruplex architecture is a nucleic acid secondary structure that plays an important role in nanomachine research, particularly in the control of reversible folding and extension of the G quadruplex of DNA in the presence of external stimuli. Mergny and coworkers reported that a copper(II)-mediated structural switch with a flexible ligand could regulate the conformation of the G quadruplex. Nanodevices based on a quadruplex-toduplex-transition that rely on the use of single-stranded DNA as fuels have been shown to perform rotary movements. Among external stimuli, such as temperature, pH value, electrical-field strength, and molecular recognition, photoregulation is particularly advantageous for controlling movement and conformation. For example, photoregulation does not require any additional components and does not cause undesirable side reactions. Irradiation is an accurate and simple method, and the timing, location, and strength of light can be controlled readily. Moreover, photoregulation provides a clean source of energy and can be repeated many times without loss of efficiency. The introduction of a photochromic group into biomolecules, such as peptides, oligonucleotides, sugar scaffolds, and phospholipids, can cause conformational changes that alter the photochemical properties of the biomolecule. Accordingly, various biological processes involving modified biomolecules can be regulated in a straightforward manner by irradiation. Recently, Ogasawara and Maeda demonstrated the successful photoregulation of G-quadruplex formation through isomerization of a photochromic nucleobase, G, incorporated in aptamers. Spada and co-workers introduced a photoactive moiety at the C8 position of a lipophilic guanosine derivative to regulate the existence of G quartets. However, all these photocontrollers are photochromic modified nucleobases. Specific molecules have not been shown to function as G-quadruplex photocontrollers; thus, we became interested in designing a photoswitch to regulate the formation of G-quadruplex DNA. The azobenzene moiety is widely used as a photoresponsive molecular tool because it possesses excellent photochemical characteristics. Specifically, azobenzene isomerizes to predominantly trans and cis forms under visible (Vis) and ultraviolet (UV) light, respectively. In this study, we synthesized the azobenzene derivative 1 (Scheme 1) to control the movement and conformation of a G quadruplex by irradiation. Our results suggest that the formation and dissociation of G-quadruplex DNAwas induced by interconversion of the trans and cis forms of compound 1. Compound 1 was synthesized by treating 4,4’-dihydroxyazobenzene with 1-(2-chloroethyl)piperidine hydrochloride

Triggering of Guanosine Self‐Assembly by Light

Light switches: The introduction of a photoactive moiety into a lipophilic guanosine derivative allows photocontrol over the self-assembly of the molecule. The existence of G-quartets can be alternately switched on and off (see picture).

Layer-by-Layer Ultrathin Films of Azobenzene-Containing Polymer/Layered Double Hydroxides with Reversible Photoresponsive Behavior

We report the preparation of a reversible photoresponsive ultrathin film containing a photoactive azobenzene polymer poly{1-4[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl sodium salt} (PAZO) and exfoliated layered double hydroxide (LDH) nanosheets using a layer-by-layer (LBL) self-assembly technique. Alternate irradiation with UV and visible light (lambda > 450 nm) results in a reversible switching between the trans isomer and the cis-rich photostationary state of the azobenzene group with concomitant significant changes in film color. Fluorescence polarization measurements indicated that the orientation of the azobenzene chromophores in the LDH matrix undergoes a reversible realignment during the photoisomerization processes. Photoisomerization induced by alternate UV and visible light irradiation was accompanied by reversible morphological changes of the LBL film, observable by atomic force microscopy (AFM). Molecular dynamics (MD) studies demonstrated that the LDH monolayers allow sufficient free space for the PAZO to undergo isomerization of its azobenzene chromophores. The reversible photoalignment of PAZO was also followed by MD simulations, and the results are in reasonable agreement with the experimental findings, further validating the configurational and orientational changes proposed for PAZO during the reversible photoprocess. It has been demonstrated that the host (LDH nanosheet)-guest (PAZO) interactions are key factors in determining the reversible photoresponsive performances of the film, since the comparative pristine PAZO film shows no such properties. Therefore, the incorporation of a photoactive moiety within the inorganic nanosheets of LDH by the LBL technique provides an attractive and feasible methodology for creating novel light-sensitive materials and devices with potential read-write capabilities.

Creating chirality in the inner walls of silica nanotubes through a hydrogel template: chiral transcription and chiroptical switch

An L- or D-glutamic acid based bolaamphiphile was found to form uniform helical nanotubes in water, which were used as the template to generate silica nanotubes. The formed silica nanotubes have supramolecular chirality in the inner walls, and were further used to load photoactive azobenzene moieties to realize a chiroptical switch.

UV-induced graft polymerization of acrylamide on cellulose by using immobilized benzophenone as a photo-initiator

Photo-active moiety, benzophenone, was incorporated onto cotton fabrics by using butyl tetracarboxylic acids (BTCA). Then, grafting of polyacrylamide on the cotton fabrics was performed by exposing the fabrics to longer UV wavelength irradiation. The chemical structure and thermal properties of the polyacrylamide grafted cotton fabrics were investigated by SEM, FTIR, XRD, and TGA, and the results verified the successful grafting of polyacrylamide on cotton fabrics. Also, it was observed that active chlorine contents were created on the polyacrylamide grafted cotton fabrics through simple chlorination process, and the chlorine treated cotton fabrics showed excellent antibacterial abilities like the powerful cyclic amide halamines.

A versatile photoactivatable probe designed to label the diphosphate binding site of farnesyl diphosphate utilizing enzymes

Farnesyl diphosphate (FPP) is a substrate for a diverse number of enzymes found in nature. Photoactive analogues of isoprenoid diphosphates containing either benzophenone, diazotrifluoropropionate or azide groups have been useful for studying both the enzymes that synthesize FPP as well as those that employ FPP as a substrate. Here we describe the synthesis and properties of a new class of FPP analogues that links an unmodified farnesyl group to a diphosphate mimic containing a photoactive benzophenone moiety; thus, importantly, these compounds are photoactive FPP analogues that contain no modifications of the isoprenoid portion of the molecule that may interfere with substrate binding in the active site of an FPP utilizing enzyme. Two isomeric compounds containing meta- and para-substituted benzophenones were prepared. These two analogues inhibit Saccharomyces cerevisiae protein farnesyltransferase (ScPFTase) with IC 50 values of 5.8 ( meta isomer) and 3.0 μM ( para isomer); the more potent analogue, the para isomer, was shown to be a competitive inhibitor of ScPFTase with respect to FPP with a K I of 0.46 μM. Radiolabeled forms of both analogues selectively labeled the β-subunit of ScPFTase. The para isomer was also shown to label Escherichia coli farnesyl diphosphate synthase and Drosophila melanogaster farnesyl diphosphate synthase. Finally, the para isomer was shown to be an alternative substrate for a sesquiterpene synthase from Nostoc sp. strain PCC7120, a cyanobacterial source; the compound also labeled the purified enzyme upon photolysis. Taken together, these results using a number of enzymes demonstrate that this new class of probes should be useful for a plethora of studies of FPP-utilizing enzymes.

Shedding light on surfaces—using photons to transform and pattern material surfaces

The ultimate goal of surface modification is to quantitatively control surface properties by precise manipulation of surface chemical structure at the molecular level. Advances in the understanding of molecular design principles for soft matter surfaces can be combined with the available arsenal of interesting photochemical reactions to create an exciting paradigm for surface modification: the use of photons to both transform and pattern chemical functionality at soft matter surfaces. The success of the paradigm is predicated on the ability to design and synthesize “photochemical surface delivery vehicles”, complex photoactive molecules that form stable surface monolayers and subsequently deliver photoactive moieties to the surface. Shedding light onto these smart, modified surfaces brings about a wide variety of precise photochemical reactions that are preprogrammed within the surface delivery vehicle. Surface chemical patterns are formed by exposure through a mask. Some photochemical surface transformation can be considered as “green” chemistry since only photons are required as reagents. In this review, we provide a brief tutorial on photochemistry fundamentals to illustrate the nature of possible photochemical surface reactions and discuss the principles of design for photochemical surface delivery vehicles. Applications of the paradigm drawn from a variety of fields emphasize the tremendous potential for photochemical surface transformation and patterning on both hard and soft substrates.

Design, synthesis and photo-cross-linking of a new photosensitive macromonomer from tetra-branched poly(ethylene oxide)s

A general procedure to increase the amount of photoreactive chromophore groups per oligoether chain is presented. In this work, a photoreactive macromonomer with four functionalities was synthesized by a four-step synthetic pathway with high yield. The photochemical behavior of this compound was studied with a view to obtaining polymeric networks. The significant advantage in this strategy is that the preparation of this material has as last operation, the obtaining and processing of polymer as thin film. In this way, the synthetic strategy based on assembling: (i) the polyether chains, (ii) a film forming backbone, and (iii) a photoactive moiety to be used for cross-linking, seems a viable solution to the problem of the continuous processing of materials.

Photosensitizer in a Molecular Bowl and its Effect on the DNA-Binding and -Cleavage Activity of 3d-Metal Scorpionates

Ternary 3d -metal complexes [M(Tp (Ph))(B)](ClO 4) ( 1- 8), where M is Co(II), Ni(II), Cu(II) and Zn(II), Tp (Ph) is anionic tris(3-phenylpyrazolyl)borate, and B is N,N-donor heterocyclic base, namely, 1,10-phenanthroline (phen, 1- 4) and dipyrido[3,2- d:2',3'- f]quinoxaline (dpq, 5- 8), were prepared from a reaction of the perchlorate salt of the metal with KTp (Ph) and B in CH 2Cl 2. The complexes were characterized by various physicochemical methods. 4- 6 and 8 were structurally characterized by single-crystal X-ray crystallography. The crystal structures of the complexes show the presence of discrete cationic complexes having a square-pyramidal (4 + 1) coordination geometry in which two nitrogen atoms of the phenanthroline base (B) and two nitrogen atoms of the Tp (Ph) ligand occupy the basal plane and one nitrogen of the Tp (Ph) ligand binds at the axial site. The phenyl groups of the Tp (Ph) form a bowl-shaped structure that essentially encloses the {M(phen/dpq)} moiety. DNA-binding studies were carried out using various spectral techniques and from viscosity measurements. The complexes show moderate binding propensity to calf thymus DNA at the minor groove, giving binding constant values ( K b) of approximately 10 (4) M (-1). The complexes exhibit poor DNA-cleavage activity in the dark in the presence of 3-mercaptopropionic acid (MPA) or hydrogen peroxide (H 2O 2). The photoinduced DNA-cleavage activity of the complexes was investigated using UV-A radiation of 365 nm and visible light of two different wavelengths with a tunable multicolor Ar-Kr mixed gas ion laser source. The dpq complexes show efficient photoinduced DNA-cleavage activity via a metal-assisted photoexcitation process involving the formation of singlet oxygen as the cleavage active species in a type-II pathway. The paramagnetic d (7)-Co(II)-dpq and d (9)-Cu(II)-dpq complexes exhibit efficient DNA-cleavage activity in visible light. The paramagnetic d (8)-Ni(II)-dpq complex displays only minor DNA-cleavage activity in visible light. Diamagnetic d (10)-Zn(II)-dpq complex shows only UV-A light-induced DNA cleavage but no apparent DNA-cleavage activity in visible light. Steric protection of the photoactive quinoxaline moiety of the dpq ligand inside the hydrophobic {M(Tp (Ph))} molecular bowl has a positive effect on the photoinduced DNA-cleavage activity.

Preparation of oligonucleotide microarrays on modified glass using a photoreactive heterobifunctional reagent, 1- N-(maleimidohexanoyl)-6- N-(anthraquinon-2-oyl) hexanediamine (MHAHD)

A novel approach for the construction of oligonucleotide microarrays under the influence of light and microwaves is described. For that purpose, a new heterobifunctional crosslinking reagent, 1- N-(maleimidohexanoyl)-6- N-(anthraquinon-2-oyl) hexanediamine (MHAHD), possessing a photoactive anthraquinone moiety on one terminus and an electrophilic maleimide group on the other one, was developed. The immobilization of oligonucleotides using the reagent, MHAHD, was realized via two routes (A and B). In order to speed up the immobilization procedure, the reaction between 3′- or 5′-mercaptoalkylated oligonucleotides and maleimide moiety of MHAHD was carried out under microwaves in just 15 min. The oligonucleotide arrays produced by both the routes were analyzed by hybridization experiments (hybridization efficiency 30.13%) and subsequently used for the discrimination of base mismatches. The constructed microarrays were found to possess good thermal stability (only ∼4.5% loss of fluorescence intensity observed after ten cycles).

Synthesis of a New Photoactive Nanovehicle: A Nanoworm

A nanovehicle with a new photoactive moiety has been synthesized. The incorporation of the azobenzene chassis allows for potential wormlike movement accompanying the rolling behavior of the wheels. Two versions, the fullerene-wheeled and carborane-wheeled nanoworms, were synthesized to examine the solution-based photoisomerization yields of the chassis.

Synthesis of diiodo butadiynyl-bridged bisphthalocyaninatozinc(II) complexes

Two functionalized phthalocyanine-based chromophore systems having two iodophthalocyaninatozinc(II) rings bound together through a butadiynyl linkage 1a, b have been synthesized by oxidative Eglinton coupling of the corresponding monomer, and fully characterized. The electronic characteristics of these extensively linearly π-conjugated compounds were modulated by the introduction of different peripheral substituents into the phthalocyanine moieties and investigated by UV–visible spectroscopy. The reactivity of the two iodo substituents was explored to prepare a novel bisphthalocyanine containing two ethynylphenyl moieties, thus pointing out the possibility of incorporating other electro and/or photoactive moieties in the BisPc system, taking advantage of the iodo-functionalization.

Photocrosslinkable Liquid Crystal Main‐Chain Polymers: Thin Films and Electrospinning

AbstractFor mechanical actuators, a response to external stimuli is required. Main‐chain liquid crystal elastomers (MCLCEs) show high response to changes in temperature especially in the vicinity of a phase transition. Most of these crosslinked materials were synthesized in a one‐step reaction which leads to a macroscopically aligned elastomer. Up to now only macroscopic samples have been prepared. We are presenting a new approach which allows us to prepare thin films as well as aligned fibers. First a liquid crystalline main‐chain polymer with a photoactive moiety was synthesized, which was oriented by a mechanical field and photocrosslinked. The thin films show exceptional mechanical properties such as large temperature‐dependent changes in length and a nonlinear stress–strain relation. To obtain fibers, we used the electrospinning process from solution with in situ UV curing. We obtained crosslinked fibers with a uniform alignment of the nematic director.magnified image

Synthesis of photoactive polyfunctional molecules based on 1-aryloxyanthraquinone aminoderivatives

By alternating stages of condensation of 1-(4-tert-butylphenoxy)-2-amino-9,10-anthraquinone with 5-nitroisophthaloyl dichloride, cyanuric chloride, and 4-aminobenzocrown ethers with stages of catalytic reduction of nitro group photoactive polyfunctional compounds were prepared containing both several photoactive groups and complex-forming crown ether moieties.

PH-tunable equilibria in azocrown ethers with histidine moieties

The crown ethers with electro- and photoactive azo moieties containing substituents with mobile protons such as in the –COOH groups of histidine, show unique effect of pH switched on/off presence of the azo form. The differences observed for the electrochemical behavior of azocrown ethers with N-acetylhistidine and imidazole moieties reveal the interference of a chemical reduction pathway in strongly acidified solutions. This chemical reduction process leads to the formation of a hydrazine derivative which can be detected by its further electroreduction on the electrode surface. The involvement of chemical reduction is seen clearly in the presence of mobile protons of the –COOH group and mercury as the electrode substrate. The behaviour of the N-acetylhistidine azomacrocyle is similar to that of compounds known to exist in quinone–hydrazone tautomeric equilibria.

The Chromophore of asFP595: A Theoretical Study

We investigate the electronic and structural properties of the chromophore of the asCP/asFP595, a newly discovered protein of the (green) fluorescent protein family. The use of theoretical methods with different degrees of accuracy and efficiency (DFT, TDDFT, CASSCF and perturbative corrections) allows us to compare the properties of a large number of hypothetic molecular models for the chromophore. The models are sorted on the basis of the relative stability and through a comparison with the experimental values of the excitation energy. Our study indicates that the most probable structure of the photoactive moiety in the protein and in water is the one resulting from the GFP-like rather than the "alternative" cyclization scheme.

Syntheses, Structures, and Photoisomerization of (E)- and (Z)-2-tert-Butyl-9-(2,2,2-triphenylethylidene)fluorene

"Sterically geared" 9-(2,2,2-triphenylethylidene)fluorene (1) is of potential interest as a photoactive moiety in molecular devices, and the 2-tert-butyl derivative (6) has been synthesized to investigate photoisomerization. E and Z stereoisomers of 6 were separated and identified by X-ray crystallography. The tert-butyl group does not introduce additional strain, and its close proximity to the trityl group in the Z isomer suggests an attractive van der Waals interaction. The UV spectra of (E)-6 and (Z)-6 are nearly identical, showing absorption bands that are similar to those of fluorene occurring at wavelengths longer than 240 nm. Photoisomerization of 6 was investigated at 266, 280 and 320 nm. Solutions initially containing only (E)-6 or (Z)-6 were irradiated with pulsed laser light, monitoring isomerization by 1H NMR spectroscopy. Negligible photodecomposition was observed when the solutions were agitated by N2 ebullition. Experimental data were fitted to theoretical curves to obtain photoisomerization quantum yields (phi(ZE) and phi(EZ)) ranging from 0.04 to 0.09. This first photoisomerization study of a dibenzofulvene reveals significant quantum yields, despite theoretical prediction of inefficient or negligible isomerization of the parent hydrocarbon, fulvene. Thermal isomerization of 6 at 270 degrees C (t(1/2) = 120 min) was also followed by 1H NMR spectroscopy, resulting in an estimated activation energy (deltaG(double dagger)) of 43 kcal/mol.

Energy and Electron Transfers in Photosensitive Chitosan

Novel photosensitive chitosan was synthesized. The modified chitosan contains photoactive anthracene chromophore moieties. Because of the presence of anthracene chromophores, the polymer absorbs light in the UV-vis spectral region. Electronically excited polymeric chromophores could participate in energy and electron transfer processes to the suitable acceptor molecules. The photosensitive chitosan developed herein could could act as an efficient photosensitizer and lead to the application of the environmentally friendly photocatalytic system for an efficient degradation of a wide range of pollutants.

Photochromic liquid crystalline structures containing azobenzene moieties

AbstractNovel liquid crystalline photochromic materials of the type 4‐R‐C6H4‐N=N‐C6H4‐O(CH2)n‐N(CH2CH2OH)2, where R is NO2, H, CN, O‐n‐C8H17, phenyl, 4‐O2NC6H4, were prepared. Some of them are photoconductive. These materials were used for the preparation of light‐sensitive polymers in which the photoactive moieties were attached to polyurethane chain. Photochromism of these compounds is based on trans‐cis isomerization of azobenzene group. An example of the photochromic activity is presented on solid solution of one material (R = O‐n‐C8H17, n = 5) in poly(methyl methacrylate) matrix.

Slow anion exchange, conformational equilibria, and fluorescent sensing in venus flytrap aminopyridinium-based anion hosts.

The synthesis, anion binding, and conformational properties of a series of 3-aminopyridinium-based, tripodal, tricationic hosts for anions are described. Slow anion and conformational exchange on the (1)H NMR time scale at low temperature, coupled with NMR titration, results in a high level of understanding of the anion-binding properties of the compounds, particularly with respect to significant conformational change resulting from induced fit complexation. Peak selectivity for halides, particularly Cl(-), is observed. The approach has been extended to dipodal and tripodal podands based on 3-aminopyridinium "arms" containing photoactive anthracenyl moieties. The 1,3,5-tripodal host shows a remarkable selectivity for acetate over other anions, in contrast to the analogous unsubstituted tris(3-aminopyridinium) analogue, despite the fact that low-temperature (1)H NMR experiments reveal a total of four acetate-binding conformations. Photodimerization of anthracene units results in the formation of potential fluorescent anion sensors.