Fluorescence light-up recognition of DNA nucleotide based on selective abasic site binding of an excited-state intramolecular proton transfer probe

3-Hydroxyflavone derivatives: promising scaffolds for fluorescent imaging in cells

As a typical class of excited-state intramolecular proton transfer (ESIPT) molecules, 3-hydroxyflavone derivatives (3HF, also known as flavonols) have received much attention recently. Thereinto, the role of hydrophobic microenvironment is significant importance in promoting the process and effects of ESIPT, which can be regulated by the solvents, the existence of metal ions and proteins rich with α-helix structures or the advanced DNA structures. Considering that plenty of biological macromolecules offer cellular hydrophobic microenvironment, enhancing the ESIPT effects and resulting in dual emission, 3HF could be a promising scaffold for the development of fluorescent imaging in cells. Furthermore, as the widespread occurance of compounds with biological activity in plants, 3HF derivatives are much more secure to be cellular diagnosis and treatment integrated fluorescent probes. In this review, multiple regulatory strategies for the fluorescence emission of 3HF derivatives have been collectively and comprehensively analyzed, including the solvent effects, metal chelation, interaction with proteins or DNAs, which would be beneficial for ESIPT-promoting or ESIPT-blocking processes and then enhance or control the fluorescence emission of 3HF effectively. We expect that this review would provide a new perspective to develop novel 3HF-based fluorescent sensors for imaging in cells and plants.

Supramolecular and suprabiomolecular photochemistry: a perspective overview

In this perspective review article, we have attempted to bring out the important current trends of research in the areas of supramolecular and suprabiomolecular photochemistry. Since the spans of the subject areas are very vast, it is impossible to cover all the aspects within the limited space of this review article. Nevertheless, efforts have been made to assimilate the basic understanding of how supramolecular interactions can significantly change the photophysical and other related physiochemical properties of chromophoric dyes and drugs, which have enormous academic and practical implications. We have discussed with reference to relevant chemical systems where supramolecularly assisted modulations in the properties of chromophoric dyes and drugs can be used or have already been used in different areas like sensing, dye/drug stabilization, drug delivery, functional materials, and aqueous dye laser systems. In supramolecular assemblies, along with their conventional photophysical properties, the acid-base properties of prototropic dyes, as well as the excited state prototautomerization and related proton transfer behavior of proton donor/acceptor dye molecules, are also largely modulated due to supramolecular interactions, which are often reflected very explicitly through changes in their absorption and fluorescence characteristics, providing us many useful insights into these chemical systems and bringing out intriguing applications of such changes in different applied areas. Another interesting research area in supramolecular photochemistry is the excitation energy transfer from the donor to acceptor moieties in self-assembled systems which have immense importance in light harvesting applications, mimicking natural photosynthetic systems. In this review article, we have discussed varieties of these aspects, highlighting their academic and applied implications. We have tried to emphasize the progress made so far and thus to bring out future research perspectives in the subject areas concerned, which are anticipated to find many useful applications in areas like sensors, catalysis, electronic devices, pharmaceuticals, drug formulations, nanomedicine, light harvesting, and smart materials.

Recognition of DNA abasic site nanocavity by fluorophore-switched probe: Suitable for all sequence environments

Removal of a damaged base in DNA produces an abasic site (AP site) nanocavity. If left un-repaired in vivo by the specific enzyme, this nanocavity will result in nucleotide mutation in the following DNA replication. Therefore, selective recognition of AP site nanocavity by small molecules is important for identification of such DNA damage and development of genetic drugs. In this work, we investigate the fluorescence behavior of isoquinoline alkaloids including palmatine (PAL), berberine (BER), epiberberine (EPI), jatrorrhizine (JAT), coptisine (COP), coralyne (COR), worenine (WOR), berberrubine (BEU), sanguinarine (SAN), chelerythrine (CHE), and nitidine (NIT) upon binding with the AP nanocavity. PAL is screened out as the most efficient fluorophore-switched probe to recognize the AP nanocavity over the fully matched DNA. Its fluorescence enhancement occurs for all of the AP nanocavity sequence environments, which has not been achieved by the previously used probes. The bridged π conjugation effect should partially contribute to the AP nanocavity-specific fluorescence, as opposed to the solvent effect. Due to the strong binding with the AP nanocavity, PAL will find wide applications in the DNA damage recognition and sensor development.

Sequence specific recognition of ssDNA by fluorophore 3-hydroxyflavone

A fully water soluble 3-hydroxyflavone (3HF) derivative, N-(3-hydroxy-4'-flavonyl)-N,N,N-trimethylammonium sulfate (3HFNMe3) was synthesized. Investigation of its emissions at varying wavelengths revealed that it had three emission bands of normal (N(⁎)), anionic (A(⁎)) and tautomeric (T(⁎)), in ultrapure water. Recognition of single-stranded ten ssDNA chains, having different nucleotide sequences was studied, using the ratiometric change of the intensities of the two bands (A(⁎)/T(⁎)), depending upon the varying environment of the 3HFNMe3 with different ssDNA chains. Addition of the ssDNA chains to the 3HFNMe3 solution caused gradual quenching of the A(⁎) band and had almost no effect on the T(⁎) band. As the ratios of the two bands (A(⁎)/T(⁎)) vs increasing amount of the ssDNAs generated characteristic curves for each ssDNA chain, it became possible to identify the chains with their characteristic curves.

Interactions of Ru(ii) polypyridyl complexes with DNA mismatches and abasic sites

Ru(ii) polypyridyl complexes bind to CC mismatch DNA with high selectivity.

Ag nanoclusters as probes for turn-on fluorescence recognition of TpG dinucleotide with a high selectivity

CpG dinucleotide in DNA has a great tendency to mutate to TpG dinucleotide and this transition can cause some serious diseases. In this work, fluorescent Ag nanoclusters (Ag NCs) were employed as useful inorganic fluorophores for the potential of selectively discriminating TpG dinucleotide from CpG dinucleotide. Opposite the base Y of interest in YpG dinucleotide (Y=C or T), a bulge site was introduced so as to make the base Y to be unpaired and ready for Ag(+) binding. Such that the unpaired Y and context base pairs can provide a specific space suitable for creating fluorescent Ag NCs. We found that in comparison with CpG dinucleotide, TpG dinucleotide is much more efficient in growing fluorescent Ag NCs. Therefore, mutation of CpG dinucleotide to TpG can be identified by a turn-on fluorescence response and a high selectivity. More interestingly, Ag NCs exhibit a better performance in the TpG recognition over the other dinucleotides (Y=A and G) than the previously used organic fluorophores. Additionally, the effectiveness of the bulge site design in discriminating these dinucleotides was evidenced by control DNAs having the abasic site structure. We expect that a practical method for TpG dinucleotide recognition with a high selectivity can be developed using the bulge site-grown fluorescent Ag NCs as novel probes.

Probing 3-hydroxyflavone for in vitro glycorandomization of flavonols by YjiC

The glycosylation of five different flavonols, fisetin, quercetin, myricetin, kaempferol, and 3-hydroxyflavone, was achieved by applying YjiC. 3-Hydroxyflavone was selected as a probe for in vitro glycorandomization of all flavonols using diverse nucleotide diphosphate-d/l-sugars. This study unlocked the possibilities of the glycodiversification of flavonols and the generation of novel compounds as future therapeutics.

Validated LC-MS/MS method for the determination of 3-hydroxflavone and its glucuronide in blood and bioequivalent buffers: application to pharmacokinetic, absorption, and metabolism studies

The purpose of this study is to develop an UPLC-MS/MS method to quantify 3-hydroxyflavone (3-HF) and its metabolite, 3-hydroxyflavone-glucuronide (3-HFG) from biological samples. A Waters BEH C8 column was used with acetonitrile/0.1% formic acid in water as mobile phases. The mass analysis was performed in an API 5500 Qtrap mass spectrometer via multiple reaction monitoring (MRM) with positive scan mood. The one-step protein precipitation by acetonitrile was used to extract the analytes from blood. The results showed that the linear response range was 0.61-2500.00 nM for 3-HF and 0.31-2500.00 nM for 3-HFG. The intra-day variance is less than 16.5% and accuracy is in 77.7-90.6% for 3-HF and variance less than 15.9%, accuracy in 85.1-114.7% for 3-HFG. The inter-day variance is less than 20.2%, accuracy is in 110.6-114.2% for 3-HF and variance less than 15.6%, accuracy in 83.0-89.4% for 3-HFG. The analysis was done within 4.0 min. Only 10 μl of blood is needed due to the high sensitivity of this method. The validated method was successfully used to pharmacokinetic study in A/J mouse, transport study in the Caco-2 cell culture model, and glucuronidation study using mice liver and intestine microsomes. The applications revealed that this method can be used for 3-HF and 3-HFG analysis in blood as well as in bioequivalent buffers such HBSS and KPI.

Excited-state proton coupled charge transfer modulated by molecular structure and media polarization

Charge and proton transfer reactions in the excited states of organic dyes can be coupled in many different ways. Despite the complementarity of charges, they can occur on different time scales and in different directions of the molecular framework. In certain cases, excited-state equilibrium can be established between the charge-transfer and proton-transfer species. The interplay of these reactions can be modulated and even reversed by variations in dye molecular structures and changes of the surrounding media. With knowledge of the mechanisms of these processes, desired rates and directions can be achieved, and thus the multiple emission spectral features can be harnessed. These features have found versatile applications in a number of cutting-edge technological areas, particularly in fluorescence sensing and imaging.

DNA abasic site-selective enhancement of sanguinarine fluorescence with a large emission shift

Small molecules that can specifically bind to a DNA abasic site (AP site) have received much attention due to their importance in DNA lesion identification, drug discovery, and sensor design. Herein, the AP site binding behavior of sanguinarine (SG), a natural alkaloid, was investigated. In aqueous solution, SG has a short-wavelength alkanolamine emission band and a long-wavelength iminium emission band. At pH 8.3, SG experiences a fluorescence quenching for both bands upon binding to fully matched DNAs without the AP site, while the presence of the AP site induces a strong SG binding and the observed fluorescence enhancement for the iminium band are highly dependent on the nucleobases flanking the AP site, while the alkanolamine band is always quenched. The bases opposite the AP site also exert some modifications on the SG's emission behavior. It was found that the observed quenching for DNAs with Gs and Cs flanking the AP site is most likely caused by electron transfer between the AP site-bound excited-state SG and the nearby Gs. However, the flanking As and Ts that are not easily oxidized favor the enhanced emission. This AP site-selective enhancement of SG fluorescence accompanies a band conversion in the dominate emission from the alkanolamine to iminium band thus with a large emission shift of about 170 nm. Absorption spectra, steady-state and transient-state fluorescence, DNA melting, and electrolyte experiments confirm that the AP site binding of SG occurs and the stacking interaction with the nearby base pairs is likely to prevent the converted SG iminium form from contacting with water that is thus emissive when the AP site neighbors are bases other than guanines. We expect that this fluorophore would be developed as a promising AP site binder having a large emission shift.

Any colour you like. Excited state and ground state proton transfer in flavonols and applications

The photoinduced and ground state proton transfer processes occurring in flavonols are responsible for their multi-wavelength emission. This peculiar behavior has touched on a wide range of research areas, ranging from biology to chemistry of materials leading, among others, to the development of fluorescent probes for physical and biophysical parameters, laser dyes, and wavelentgh shifting devices. This account aims to be a brief introduction to the multi-faceted applications of flavonols.