Programmable and Sequence-Selective Supramolecular Assembly of Two Different Chromophores along DNA Templates

Aggregation-induced emission by sequence-selective assembly of cyanolytated distyrylbenzene in supramolecular DNA architectures

The cyanolated distyrylbenzene conjugated to 2’-deoxyuridine is a new building block for supramolecular DNA architectures combining aggregation-induced emission and sequence-selective binding. A high number of binding sites at the DNA...

Fluorescence detected circular dichroism (FDCD) for supramolecular host-guest complexes

Fluorescence-detected circular dichroism (FDCD) spectroscopy is applied for the first time to supramolecular host-guest and host-protein systems and compared to the more known electronic circular dichroism (ECD). We find that FDCD can be an excellent choice for common supramolecular applications, e.g. for the detection and chirality sensing of chiral organic analytes, as well as for reaction monitoring. Our comprehensive investigations demonstrate that FDCD can be conducted in favorable circumstances at much lower concentrations than ECD measurements, even in chromophoric and auto-emissive biofluids such as blood serum, overcoming the sensitivity limitation of absorbance-based chiroptical spectroscopy. Besides, the combined use of FDCD and ECD can provide additional valuable information about the system, e.g. the chemical identity of an analyte or hidden aggregation phenomena. We believe that simultaneous FDCD- and ECD-based chiroptical characterization of emissive supramolecular systems will be of general benefit for characterizing fluorescent, chiral supramolecular systems due to the higher information content obtained by their combined use.

Stacked Thiazole Orange Dyes in DNA Capable of Switching Emissive Behavior in Response to Structural Transitions

Functional nucleic acids with the capability of generating fluorescence in response to hybridization events, microenvironment or structural changes are valuable as structural probes and chemical sensors. We now demonstrate the enzyme-assisted preparation of nucleic acids possessing multiple thiazole orange (TO) dyes and their fluorescent behavior, that show a spectral change from the typical monomer emission to the excimer-type red-shifted emission. We found that the fluorescent response and emission wavelength of the TO dyes were dependent on both the state of the DNA structure (single- or double-stranded DNA) and the arrangement of the TO dyes. We showed that the fluorescent behavior of the TO dyes can be applied for the detection of RNA molecules, suggesting that our approach for preparing the fluorescent nucleic acids functionalized with multiple TO dyes could be useful to design a fluorescence bioimaging and detection technique of biomolecules.

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”.

Molecular Chromophore-DNA Architectures With Fullerenes: Optical Properties and Solar Cells

Supramolecular chemistry allows the construction of complex molecular architectures and the design of collective photophysical properties. DNA is an attractive template to build such supramolecular architectures due to its helical structure, the defined distances between the bases and the canonical base pairing that results in precise control of the chromophore position. The tailored properties of DNA-templated supramolecules eventually allow their implementation into optoelectronic applications. For the generation of free charge carriers from photo-generated excitons, fullerenes can be utilized. We synthesized two fullerene derivates, one of which binds by electrostatic interactions to single-stranded DNA, while the other contains two 2'-deoxyuridine moieties and assembles specifically along oligo-2'-deoxyadenosines (dA20) as DNA template. The DNA-directed assembly of both fullerenes in aqueous solution was investigated by UV/Vis absorbance and circular dichroism (CD) spectroscopy. The specific interactions with DNA make fullerenes with the 2'-deoxyuridine moieties a significantly better component for supramolecular DNA architectures. We studied the fluorescence quenching of both fullerenes with a DNA chromophore assembly. To investigate one of the key properties for optoelectronic applications, that is the supramolecular structure of the DNA-based assemblies in the solid phase, we characterized the CD of supramolecular chromophore-DNA architectures in thin films. Remarkably, the helical chirality of the chromophore assemblies that is induced by the DNA template is conserved even in the solid state. Upon implementation into organic solar cells, the external quantum efficiency measurements showed charge carrier generation on all three chromophore components of the DNA assemblies. The fullerenes with the 2'-deoxyuridine moieties enhance the quantum efficiency of the conversion process significantly, demonstrating the potential of DNA as structural element for ordering chromophores into functional π-systems, which may be employed in future organic solar cells.

Control of Energy Transfer Between Pyrene- and Perylene-Nucleosides by the Sequence of DNA-Templated Supramolecular Assemblies

DNA was used as supramolecular scaffold to order chromophores and control their optical properties. Ethynylpyrene as energy donor was attached to 2'-desoxy-2-aminoadenosine that binds selectively to thymidines (T) in the template. Ethynylperylene as acceptor was attached to 2'-desoxyuridine that is complementary to 2'-desoxyadenosine (A). This donor-acceptor pair was assembled along single-stranded DNA templates of different A-T sequences to investigate the sequence control of the energy transfer between the chromophores. The fluorescence intensities increase in the mixed assemblies along the DNA templates from A10T10 over (AATT)5 to (AT)10, although these templates provide equal numbers of potential binding sites for the two different nucleoside chromophore conjugates and exhibit similar absorbances. This shows that the sequence selective assembly of the two building blocks along DNA templates is programmable and alters the fluorescence readout. Such sequence-controlled supramolecular chemistry represents the key element for future functional π-systems in materials for light harvesting of solar energy.

From Interaction to Function in DNA-Templated Supramolecular Self-Assemblies

DNA-templated self-assembly represents a rich and growing subset of supramolecular chemistry where functional self-assemblies are programmed in a versatile manner using nucleic acids as readily-available and readily-tunable templates. In this review, we summarize the different DNA recognition modes and the basic supramolecular interactions at play in this context. We discuss the recent results that report the DNA-templated self-assembly of small molecules into complex yet precise nanoarrays, going from 1D to 3D architectures. Finally, we show their emerging functions as photonic/electronic nanowires, sensors, gene delivery vectors, and supramolecular catalysts, and their growing applications in a wide range of area from materials to biological sciences.

A Quencher-Free Linear Probe from Serinol Nucleic Acid with a Fluorescent Uracil Analogue

With the goal of developing a quencher-free probe composed of an artificial nucleic acid, the fluorescent nucleobase analogue 5-(perylenylethynyl)uracil (^Pe U), which was incorporated into totally artificial serinol nucleic acid (SNA) as a substitute for thymine, has been synthesized. In the context of a 12-mer duplex with RNA, these fluorophores reduce duplex stability slightly compared with that of an SNA without ^Pe U modification; thus suggesting that structural distortion is not induced by the modification. If two ^Pe Us were incorporated at separate positions in an SNA, the fluorescent emission at λ≈490 nm was clearly enhanced upon hybridization with complementary RNA. A quencher-free SNA linear probe containing three ^Pe Us, each separated by six nucleobases, has been designed. Detection of target RNA with high sensitivity and discrimination of a single-base mismatch has also been demonstrated.

Influences of Linker and Nucleoside for the Helical Self-Assembly of Perylene Along DNA Templates

Six different conjugates of perylene with 2'-deoxyuridine and with 2-amino-2'-deoxyadenosine were synthesized and applied for DNA-templated assembly in aqueous buffer solutions. They differ by the linkers ethynylene, phenylene, and phenylene-ethynylene between nucleoside and chromophore. The nucleosides were investigated as monomers in CHCl₃ and dimethyl sulfoxide by optical spectroscopy. The properties of the four phenylene-linked conjugates are similar to that of perylene as reference because these linkers separate both aromatic parts. The ethynylene linker electronically couples the chromophore with the respective nucleoside and thus red shifts the absorbance. The DNA-templated assembly properties were elucidated by mixing the templates in aqueous buffer with the perylene-nucleoside conjugates from a dimethyl sulfoxide stock solution. Specific binding of the nucleosides was probed by comparing the results with dA₂₀ and T₂₀ as single-stranded DNA templates. Our studies reveal the structural parameters that are important for the DNA-templated assembly of perylenes. First, perylene-2'-deoxyuridine conjugates do not form DNA-templated helical assemblies, regardless of the choice of linker. Second, the ethynylene linker is crucial for successful DNA-templated chromophore assemblies of perylene-2-amino-2'-deoxyadenosine conjugates. Third, in contrast, the phenylene linker inhibits self-assembly along single-stranded DNA templates. In conclusion, the 2-amino-2'-deoxyadenosin in combination with the ethynylene linker provides the best structural feature for specific and helical DNA-templated assembly of perylenes. This result is important for the design of future DNA-based supramolecular architectures with chromophores, in particular DNA-based light-harvesting systems and DNA systems for emitting or sensing circularly polarized luminescence.

Self-assemblies of nucleolipid supramolecular synthons show unique self-sorting and cooperative assembling process

The inherent control of the self-sorting and co-assembling process that has evolved in multi-component biological systems is not easy to emulate in vitro using synthetic supramolecular synthons. Here, using the basic component of nucleic acids and lipids, we describe a simple platform to build hierarchical assemblies of two component systems, which show an interesting self-sorting and co-assembling behavior. The assembling systems are made of a combination of amphiphilic purine and pyrimidine ribonucleoside-fatty acid conjugates (nucleolipids), which were prepared by coupling fatty acid acyl chains of different lengths at the 2'-O- and 3'-O-positions of the ribose sugar. Individually, the purine and pyrimidine nucleolipids adopt a distinct morphology, which either supports or does not support the gelation process. Interestingly, due to the subtle difference in the order of formation and stability of individual assemblies, different mixtures of supramolecular synthons and complementary ribonucleosides exhibit a cooperative and disruptive self-sorting and co-assembling behavior. A systematic morphological analysis combined with single crystal X-ray crystallography, powder X-ray diffraction (PXRD), NMR, CD, rheological and 3D X-ray microtomography studies provided insights into the mechanism of the self-sorting and co-assembling process. Taken together, this approach has enabled the construction of assemblies with unique higher ordered architectures and gels with remarkably enhanced mechanical strength that cannot be derived from the respective single component systems.

Control of helical chirality in supramolecular chromophore-DNA architectures

Four different d- and l-configured chromophore-2'-deoxyuridine conjugates were applied to elucidate the helical chirality of their non-covalent assemblies along the d- and l-configured DNA templates by optical spectroscopy. There is no configuration-selective recognition between these nucleosides and the DNA templates. The helicity of the DNA assemblies is either controlled by the configuration of the DNA template or by the nucleoside configuration.