Self-assembly of DNA-tetraphenylethylene amphiphiles into DNA-grafted nanosheets as a support for the immobilization of gold nanoparticles: a recyclable catalyst with enhanced activity

Two-Dimensional Supramolecular Polymerization of DNA Amphiphiles is Driven by Sequence-Dependent DNA-Chromophore Interactions

Two-dimensional (2D) assemblies of water-soluble block copolymers have been limited by a dearth of systematic studies that relate polymer structure to pathway mechanism and supramolecular morphology. Here, we employ sequence-defined triblock DNA amphiphiles for the supramolecular polymerization of free-standing DNA nanosheets in water. Our systematic modulation of amphiphile sequence shows the alkyl chain core forming a cell membrane-like structure and the distal π-stacking chromophore block folding back to interact with the hydrophilic DNA block on the nanosheet surface. This interaction is crucial to sheet formation, marked by a chiral "signature", and sensitive to DNA sequence, where nanosheets form with a mixed sequence, but not with a homogeneous poly(thymine) sequence. This work opens the possibility of forming well-ordered, bilayer-like assemblies using a single DNA amphiphile for applications in cell sensing, nucleic acid therapeutic delivery and enzyme arrays.

Galactose Grafted Two-Dimensional Nanosheets as a Scaffold for the In Situ Synthesis of Silver Nanoparticles: A Potential Catalyst for the Reduction of Nitroaromatics

Two major hurdles in NP-based catalysis are the aggregation of the NPs and their recycling. Immobilization of NPs onto a 2D support is the most promising strategy to overcome these difficulties. Herein, amphiphilicity-driven self-assembly of galactose-hexaphenylbenzene-based amphiphiles into galactose-decorated 2D nanosheet is reported. The extremely dense decoration of reducing sugar on the surface of the sheets is used for the in situ synthesis and immobilization of ultrafine catalytically active AgNPs by using Tollens' reaction. The potential of the system as a catalyst for the reduction of various nitroaromatics is demonstrated. Enhanced catalytic activity is observed for the immobilized AgNPs when compared to the corresponding discrete AgNPs. Recovery of the catalytic system from the reaction mixture by ultrafiltration and its subsequent recycling for several cycles without dropping its activity is shown. This is the first report demonstrating the in situ synthesis and immobilization of ultrafine AgNPs onto a 2D nanosheet that exhibits excellent catalytic performance for the reduction of nitroaromatics.

DNA Condensation Triggered by the Synergistic Self-Assembly of Tetraphenylethylene-Viologen Aggregates and CT-DNA

Development of small organic chromophores as DNA condensing agents, which explore supramolecular interactions and absorbance or fluorescence-based tracking of condensation and gene delivery processes, is in the initial stages. Herein, we report the synthesis and electrostatic/groove binding interaction-directed synergistic self-assembly of the aggregates of two viologen-functionalized tetraphenylethylene (TPE-V) molecules with CT-DNA and subsequent concentration-dependent DNA condensation process. TPE-V molecules differ in their chemical structure according to the number of viologen units. Photophysical and morphological studies have revealed the interaction of the aggregates of TPE-V in Tris buffer with CT-DNA, which transforms the fibrous network structure of CT-DNA to partially condensed beads-on-a-string-like arrangement with TPE-V aggregates as beads via electrostatic and groove binding interactions. Upon further increasing the concentration of TPE-V, the "beads-on-a-string"-type assembly of TPE-V/CT-DNA complex changes to completely condensed compact structures with 40-50 nm in diameter through the effective charge neutralization process. Enhancement in the melting temperature of CT-DNA, quenching of the fluorescence emission of ethidium bromide/CT-DNA complex, and the formation of induced CD signal in the presence of TPE-V molecules support the observed morphological changes and thereby verify the DNA condensation abilities of TPE-V molecules. Decrease in the hydrodynamic size, increase in the zeta potential value with the addition of TPE-V molecules to CT-DNA, failure of TPE-V/cucurbit(8)uril complex to condense CT-DNA, and the enhanced DNA condensation ability of TPE-V2 with two viologen units compared to TPE-V1 with a single viologen unit confirm the importance of positively charged viologen units in the DNA condensation process. Initial cytotoxicity analysis on A549 cancer and WI-38 normal cells revealed that these DNA condensing agents are non-toxic in nature and hence could be utilized in further cellular delivery studies.

DNA-templated control of chirality and efficient energy transport in supramolecular DNA architectures with aggregation-induced emission

Two conjugates of tetraphenylethylene with d-2′-deoxyuridine (1d) and l-2′-deoxyuridine (1l) were synthesized to construct new supramolecular DNA-architectures by self-assembly. The non-templated assemblies of 1d and 1l show strong aggregation-induced emission and their chirality is exclusively controlled by the configuration of their sugar part. In contrast, the chirality of the DNA-templated assemblies is governed by the configuration of the DNA, and there is no configuration-selective binding of 1d to d-A₂₀ and 1l to l-A₂₀. The quantum yield of the assembly of 1d along the single-stranded DNA A₂₀ is 0.40; approximately every second available binding site on the DNA template is occupied by 1d. The strong aggregation-induced emission of these DNA architectures can be efficiently quenched and the excitation energy can be transported to Atto dyes at the 5′-terminus. A multistep energy transport “hopping” precedes the final energy transfer to the terminal acceptor. The building block 1d promotes this energy transport as stepping stones. This was elucidated by reference DNA double strands in which 1d was covalently incorporated at two distinct sites in the sequences, one near the Atto dye, and one farther away. This new type of completely self-assembled supramolecular DNA architecture is hierarchically ordered and the DNA template controls not only the binding but also the energy transport properties. The high intensity of the aggregation-induced emission and the excellent energy transport properties make these DNA-based materials promising candidates for optoelectronic applications.

DNA architectures with tetraphenylethylene are assembled in a non-covalent way. The strong aggregation-induced emission of the chromophores is quenched and the energy is transported to Atto dyes by a multistep energy “hopping”.

K. AK, Sagar S, Das S, Varghese R. Blue-emissive two-component supergelator with aggregation-induced enhanced emission

Two-component organogels offer several advantages over one-component gels, but their design is highly challenging. Hence, it is extremely important to design new approaches for the crafting of two-component organogels with interesting optical and mechanical properties. Herein, we report the design of a new class of two-component supergelators obtained from the assembly between acid functionalized tetraphenylethylene (TPE)-based dendrons and alkylated melamine. No gelation behaviour is observed for the individual components, but interestingly, remarkable gelation behaviour is observed for their hydrogen-bonded complex. The primary driving force responsible for the gelation is the strong π–π stacking interaction of TPE units. Because of the strong π-stacking of TPEs in the gel state, the C(sp²)–C(sp²) bond rotation of the TPE segment is completely arrested in the gel state, which results in intense fluorescence emission of the gels. Furthermore, excellent elastic response is observed for the gels as evident from their high storage modulus compared to loss modulus values. Our results clearly demonstrate that by the appropriate selection of the molecular components, this approach can be applied for the creation of functional nanomaterials with emergent properties absent in the individual blocks.

Design of a novel class of two-component, highly emissive, low molecular weight supergelator is reported.

Combination of DNA with polymers

The preparation and applications of DNA containing polymers are comprehensively reviewed, and they are in the form of DNA−polymer covalent conjugators, supramolecular assemblies and hydrogels for advanced materials with promising features.

Supramolecular Two-Dimensional Systems and Their Biological Applications

Various biological systems rely on the supramolecular assembly of biomolecules through noncovalent bonds for performing sophisticated functions. In particular, cell membranes, which are 2D structures in biological systems, have various characteristics such as a large surface, flexibility, and molecule-recognition ability. Supramolecular 2D materials based on biological systems provide a novel perspective for the development of functional 2D materials. The physical and chemical properties of 2D structures, attributed to their large surface area, can enhance the sensitivity of the detection of target molecules, molecular loading, and bioconjugation efficiency, suggesting the potential utility of functional 2D materials as candidates for biological systems. Although several types of studies on supramolecular 2D materials have been reported, supramolecular biofunctional 2D materials have not been reviewed previously. In this regard, the current advances in 2D material development using molecular assembly are discussed with respect to the rational design of self-assembling aromatic amphiphiles, the formation of 2D structures, and the biological applications of functional 2D materials.

DNA-π Amphiphiles: A Unique Building Block for the Crafting of DNA-Decorated Unilamellar Nanostructures

The unparalleled ability of DNA to recognize its complementary strand through Watson and Crick base pairing is one of the most reliable molecular recognition events found in natural systems. This highly specific sequence information encoded in DNA enables it to be a versatile building block for bottom-up self-assembly. Hence, the decoration of functional nanostructures with information-rich DNA is extremely important as this allows the integration of other functional molecules onto the surface of the nanostructures through DNA hybridization in a highly predictable manner. DNA amphiphiles are a class of molecular hybrids where a short hydrophilic DNA is conjugated to a hydrophobic moiety. Since DNA amphiphiles comprise DNA as the hydrophilic segment, their self-assembly in aqueous medium always results in the formation of nanostructures with shell made of DNA. This clearly suggests that self-assembly of DNA amphiphiles is a straightforward strategy for the ultradense decoration of a nanostructure with DNA. However, initial attempts toward the design of DNA amphiphiles were primarily focused on long flexible hydrocarbon chains as the hydrophobic moiety, and it has been demonstrated in several examples that they typically self-assemble into DNA-decorated micelles (spherical or cylindrical). Hence, molecular level control over the self-assembly of DNA amphiphiles and achieving diverse morphologies was extremely challenging and unrealized until recently.In this Account, we summarize our recent efforts in the area of self-assembly of DNA amphiphiles and narrate the remarkable effect of the incorporation of a large π-surface as the hydrophobic domain in the self-assembly of DNA amphiphiles. Self-assembly of DNA amphiphiles with flexible hydrocarbon chains as the hydrophobic moiety is primarily driven by the hydrophobic effect. The morphology of such nanostructures is typically predicted based on the volume ratio of hydrophobic to hydrophilic segments. However, control over the self-assembly and prediction of the morphology become increasingly challenging when the hydrophobic moieties can interact with each other through other noncovalent interactions. In this Account, the unique self-assembly behaviors of DNA-π amphiphiles, where a large π-surface acts as the hydrophobe, are described. Due to the extremely strong π-π stacking in aqueous medium, the assembly of the amphiphile is found to preferably proceed in a lamellar fashion (bilayer) and hence the morphology of the nanostructures can easily be tuned by the structural modification of the π-surface. Design principles for crafting various DNA-decorated lamellar nanostructures including unilamellar vesicles, two-dimensional (2D) nanosheets, and helically twisted nanoribbons by selecting suitable π-surfaces are discussed. Unilamellar vesicular nanostructures were achieved by using linear oligo(phenylene ethynylene) (OPE) as the hydrophobic segment, where lamellar assembly undergoes folding to form unilamellar vesicles. The replacement of OPE with a strongly π-stacking hydrophobe such as hexabenzocoronene (HBC) or tetraphenylethylene (TPE) provides extremely strong π-stacking compared to OPE, which efficiently directed the 2D growth for the lamellar assembly and led to the formation of 2D nanosheets. A helical twist in the lamella was achieved by the replacement of HBC with hexaphenylbenzene (HPB), which is the twisted analogue of HBC, directing the assembly into helically twisted nanoribbons. The most beneficial structural feature of this kind of nanostructure is the extremely dense decoration of their surface with ssDNA, which can further be used for DNA-directed organization of other functional nanomaterials. By exploring this, their potential as a nanoscaffold for predefined assembly of plasmonic nanomaterials into various plasmonic 1D, 2D, and 3D nanostructures through DNA hybridization is discussed. Moreover, the design of pH-responsive DNA-based vesicles and their application as a nanocarrier for payload delivery is also demonstrated.

Galactose-Grafted 2D Nanosheets from the Self-Assembly of Amphiphilic Janus Dendrimers for the Capture and Agglutination of Escherichia coli

High aspect ratio, sugar-decorated 2D nanosheets are ideal candidates for the capture and agglutination of bacteria. Herein, the design and synthesis of two carbohydrate-based Janus amphiphiles that spontaneously self-assemble into high aspect ratio 2D sheets are reported. The unique structural features of the sheets include the extremely high aspect ratio and dense display of galactose on the surface. These structural characteristics allow the sheet to act as a supramolecular 2D platform for the capture and agglutination of E. coli through specific multivalent noncovalent interactions, which significantly reduces the mobility of the bacteria and leads to the inhibition of their proliferation. Our results suggest that the design strategy demonstrated here can be applied as a general approach for the crafting of biomolecule-decorated 2D nanosheets, which can perform as 2D platforms for their interaction with specific targets.

Nanosheets and 2D-nanonetworks by mutually assisted self-assembly of fullerene clusters and DNA three-way junctions

Programmable construction of two dimensional (2D) nanoarchitectures using short DNA strands is of utmost interest in the context of DNA nanotechnology. Previously, we have demonstrated fullerene-cluster assisted self-assembly of short oligonucleotide duplexes into micrometer long, semiconducting nanowires. This report demonstrates the construction of micrometer-sized nanosheets and 2D-nanonetworks from the mutual self-assembly of fullerene nanoclusters with three way junction DNA (3WJ-DNA) and 3WJ-DNA with a 12-mer overhang (3WJ-OH), respectively. The interaction of unique sized fullerene clusters prepared from an aniline appended fullerene derivative, F-An, with two 3WJ-DNAs, namely, 3WJ-20 and 3WJ-30, having 20 and 30 nucleobases, respectively at each strand was characterized using UV-visible absorption, circular dichroism and fluorescence techniques. The morphological characterization of nanosheets embedded with F-An clusters was performed via AFM, TEM and DLS analyses. The programmability and structural tunability of the resultant nanostructures were further demonstrated using 3WJ-OH containing a cytosine rich, single stranded DNA 12-mer overhang, which forms entangled 2D-nanonetwork structures instead of nanosheets due to the differential interaction of F-An nanoclusters with single and duplex strands of 3WJ-OH. Moreover, the selective modification of the cytosine rich sequence present in 3WJ-OH with silver nanoclusters (AgNCs) resulted in significant enhancement in silver nanocluster fluorescence (∼40%) compared to 3WJ-OH/AgNCs owing to the additional stability of AgNCs embedded in 2D nanostructures. This unique strategy of constructing DNA based 2D nanomaterials and their utilization in the integration of functional motifs could find application in the area of DNA nanotechnology and bio-molecular sensing.

Reversible morphological tuning of DNA–perylenebisdiimide assemblies through host–guest interaction

A new supramolecular host–guest strategy is developed to reversibly control the morphology of DNA–perylenebisdiimide assemblies in aqueous solution.