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Parallel-stranded G-quadruplex structures are found to be common in the human promoter sequences. We tested highly fluorescent 9-methoxyluminarine ligand (9-MeLM) binding interactions with different parallel G-quadruplexes DNA by spectroscopic methods such as fluorescence and circular dichroism (CD) titration as well as UV melting profiles. The results showed that the studied 9-MeLM ligand interacted with the intramolecular parallel G-quadruplexes (G4s) with similar affinity. The binding constants of 9-methoxyluminarine with different parallel G4s were determined. The studies upon oligonucleotides with different flanking sequences on c-MYC G-quadruplex suggest that 9-methoxyluminarine may preferentially interact with 3′end of the c-MYC promoter. The high decrease in 9-MeLM ligand fluorescence upon binding to all tested G4s indicates that 9-methoxyluminarine molecule can be used as a selective fluorescence turn-off probe for parallel G-quadruplexes.

The i-motif is a four-stranded DNA structure formed from the cytosine (C)-rich ssDNA sequence, which is stabilized in slightly acidic pH. Additionally, labeling of a cytosine-rich sequence with a fluorescent molecule may constitute a way to construct a pH-sensitive biosensor. In this paper, we report tC-modified fluorescent probes that contain RET-related sequence C4GC4GC4GC4A. Results of the UV absorption melting experiments, circular dichroism (CD) spectra, and steady-state fluorescence measurements of tC-modified i-motifs are presented and discussed here. Efficient fluorescence quenching of tC fluorophore occurred upon lowering the pH from 8.0 to 5.5. Furthermore, we present and discuss fluorescence spectra of systems containing tC-modified i-motifs and complementary G-rich sequences in the ratios 1:1, 1:2, and 1:3 in response to pH changes. The fluorescence anisotropy was proposed for the study of conformational switching of the i-motif structure for tC-probes in the presence and absence of a complementary sequence. The possibility of using of the sensor for monitoring pH changes was demonstrated.

This study aimed to evaluate the oxidative stability and surface properties of cold-pressed vegetable oils using the Langmuir monolayer technique. Six oils—milk thistle, evening primrose, flaxseed, camelina sativa, black cumin, and pumpkin seed—were analyzed to investigate their molecular organization and behavior at the air/water interface, particularly after undergoing oxidation. The results showed that oils rich in polyunsaturated fatty acids (PUFAs), such as flaxseed and evening primrose oils, formed monolayers with larger molecular areas and lower stability, which led to faster oxidative degradation, especially under thermal conditions. In contrast, pumpkin seed oil, with a higher content of saturated fatty acids (SFAs), formed more condensed and stable monolayers, enhancing its resistance to oxidation. Black cumin oil, with a balanced profile of SFAs and monounsaturated fatty acids (MUFAs), demonstrated similar stability. The Langmuir technique facilitated a detailed analysis of monolayer phase transitions: PUFA-rich oils transitioned more readily to less stable phases, while SFA-rich oils maintained durable, condensed structures. These findings underscore the utility of this method for assessing the oxidative stability of vegetable oils and highlight key parameters—such as surface pressure, molecular area, and elasticity modulus—that can support the optimization of oil storage and quality in the food industry and related sectors.

The properties of cytosine- and guanine-rich oligonucleotides contributed to employing them as sensing elements in various biosensors. In this paper, we report our current development of fluorescence oligonucleotide probes based on i-motif or G-quadruplex forming oligonucleotides for cellular measurements or bioimaging applications. Additionally, we also focus on the spectral properties of the new fluorescent silver nanoclusters based system (ChONC12-AgNCs) that is able to anchor at the Langmuir monolayer interface, which is mimicking the surface of living cells membrane.

The use of DNA as a scaffold for nanoclusters is particularly interesting due to its structural versatility and easy integration with aptamers. In their structure, aptamers often contain non-canonical forms of DNA, i.e., G-quadruplexes (GQs). Four-stranded GQs are used to construct nanomachines and biosensors for monitoring changes in the concentration of potassium ions. In the present study, we continue our work related to the synthesis of silver nanoclusters formed on a bifunctional DNA template. By attaching a cytosine-rich domain (C12) to a G-quadruplex-forming sequence—human telomeric (Tel22) or thrombin-binding aptamer (TBA)—we constructed bifunctional templates for fluorescent silver nanoclusters (C12) with the ability to detect potassium ions (GQs). The changing localization of the C12 domain from the 3′ to 5′ end of the oligonucleotide was a successful way to improve the fluorescence properties of the obtained fluorescent probes. The best performance as a probe for potassium ions was exhibited by C12Tel22-AgNCs, with an LOD of 0.68 mM in PBS. The introduction of the fluorescent cytosine analog tC leads to an LOD of 0.68 mM in PBS and 0.46 mM in Tris-acetate. Additionally, we performed AFM, TEM, DLS analysis, and cellular studies to further investigate the structural properties and behavior of the Tel22C12-AgNCs in biological contexts.

The purpose of the present work was to design, synthesize and spectrally characterize cholesterol-anchored fluorescent oligonucleotide probes (Ch(F-TBA-T), Ch(py-TBA-py)), based on G-quadruplexes, which were able to incorporate into a lipid structure (Langmuir monolayer, living cell membrane). The probes, based on the thrombin-binding aptamer (TBA) sequence, were labeled with fluorescent dyes which enabled simultaneous monitoring of the formation of G-quadruplex structures and visualization of probe incorporation into the cellular membrane. The combinations of fluorophores used included fluorescence resonance energy transfer (FRET) and excimer emission approaches. The structural changes of the probes upon binding with K+ or Na+ ions were monitored with fluorescence techniques. These systems showed a very high binding preference for K+ over Na+ ions. The use of confocal fluorescence microscopy indicated successful anchoring of the cholesterol-bearing fluorescent probes to the living cell membrane. These structurally simple cholesterol-based fluorescent probes have good potential for opening up new and exciting opportunities in the field of biosensors; e.g., in vivo detection of K+ ions.

The antioxidant potential of bird cherry fruit of water, methanol, ethanol, and acetone extracts and their antioxidant efficiency against oxidation of PC liposomes using spectroscopic and chromatographic methods were investigated. The chromatographic methods quantified and specified the presence of phenolic and flavonoid compounds in the investigated extracts. The characteristic peaks in the UV spectrum at 275 nm and 370 nm confirmed the presence of phenols and flavonoids and their derivatives. Their presence was also confirmed by FTIR spectra, which revealed the presence of its functional groups. The total luminescence spectra with maxima at 314–318 nm, 325–355 nm, and 428–435 nm were ascribed to the presence of phenolic acids and tocopherols. The antioxidant properties of extracts and its inhibition properties against lipid peroxidation in PC liposomes were determined by fluorogenic probes DCF-H and C11-BODIPY581/591. The measured antioxidant properties against generated free radicals in aqueous and lipogenic phases revealed differences between extracts depending on their physicochemical properties with the greatest potential for acetone extract and sirup. The presented quantitative analysis indicated that cherry bird extracts possess significant amounts of phenolics and flavonoids, thus having the opportunity to be used as a natural antioxidant agent source with a large potential for application in pharmaceutical and food industries.

In this study, we examined properties of silver nanoclusters, which are AgNCs stabilized by DNA oligonucleotide scaffold containing G-quadruplex-forming sequences: human telomeric (Tel22) or thrombin-binding aptamer (TBA). Thus, we obtained two fluorescent probes abbreviated as Tel22C12-AgNCs and TBAC12-AgNCs, which were characterized using absorption, circular dichroism and fluorescence spectroscopy. Both probes emit green and red fluorescence. The presence of silver nanoclusters did not destabilize the formed G-quadruplexes. The structural changes of probes upon binding K+ or Na+ ions cause quenching in their red emission. Green emission was slightly quenched only in the case of Tel22C12-AgNCs; on the contrary, for TBAC12-AgNC’s green emission, we observed an increasing fluorescence signal. Moreover, the Tel22C12-AgNCs system shows not only a higher binding preference for K+ over Na+, but it was able to monitor small changes in K+ concentrations in the buffer mimicking extracellular conditions (high content of Na+ ions). These results suggest that Tel22C12-AgNCs exhibit the potential to monitor transmembrane potassium transport.

Cytosine-rich nucleic acids undergo pH-stimulated structural transitions leading to formation of an i-motif architecture at an acidic pH. Thus, i-motifs are good foundation for designing simple pH-sensitive fluorescent probes. We report here steady-state and time-resolved fluorescence studies of pyrene-labeled probes based on RET sequence: C4GC4GC4GC4TA (RET21), AC4GC4GC4GC4TA (RET21A) and C4GC4GC4GC4T (RET20). Comparative studies with single- and double-labeled i-motif probes were carried out. For each probe, we have measured fluorescence spectra and decays for emission wavelength of 390 nm over a wide range of pH (from 4.0 to 8.0). Effect of the oligonucleotide sequence and the number of pyrene labels on the spectral characteristics of probes were discussed.

The interactions of G–quadruplexes of different topologies with highly fluorescent 9-methoxyluminarine ligand 9-MeLM were investigated by fluorescence and circular dichroism spectroscopy. The results showed that 9-methoxyluminarine was able to interact and did not destabilize any investigated molecular targets. The studied compound was selectively quenched by parallel c-MYC G-quadruplex DNA, whereas hybrid and antiparallel G4 topology caused only a negligible decrease in the fluorescence of the ligand. A high decrease of fluorescence of the ligand after binding with c-MYC G-quadruplex suggests that this molecule can be used as a selective probe for parallel G-quadruplexes.