Binding of single/double stranded ct-DNA with graphene oxide­silver nanocomposites in vitro: A multispectroscopic approach.

The fundamental binding of single-stranded (ssDNA) and double-stranded DNA (dsDNA) with graphene oxide-Ag nanocomposites (GO-AgNCPs) has been systematically investigated by multi spectroscopic methods, i.e. ultraviolet-visible (UV-vis) absorption, fluorescence spectroscopy, and circular dichroism (CD). The experimental and theoretical results demonstrate that both ssDNA and dsDNA can be adsorbed onto the GO-AgNCPs surface. All of the evidence indicated that there were relatively strong binding of ssDNA/dsDNA with GO-AgNCPs. The article compares the differences in binding between the two types of DNA and the nanomaterials using spectroscopic and thermodynamic data. UV-vis absorption spectroscopy experiments indicate that the characteristic absorbance intensity of both ss DNA and ds DNA increases, but the rate of change in absorbance is different. The fluorescence results revealed that ss/dsDNA could interact with the GO-AgNCPs surface, in spite of the different binding affinities. The Ka value of ssDNA binding with GO-AgNCPs is greater than that of dsDNA at each constant temperature, indicating that the affinity of dsDNA toward GO-AgNCPs is comparatively weak. Molecular docking studies have corroborated the mentioned experimental results. The calculated thermodynamic parameters showed that the binding process was thermodynamically spontaneous, van der Waals force and hydrogen bonding played predominant roles in the binding process. The mechanism of ss/ds DNA binding with GO-AgNCPs was also investigated, and the results indicated that GO-AgNCPs directly binds to the minor groove of ss/ds DNA by replacing minor groove binders.

Probing the interaction between the metallo-ß-lactamase SMB-1 and ampicillin by multispectral approaches combined with molecular dynamics.

Metallo-ß-lactamases (MßLs) hydrolyze and inactivate ß-lactam antibiotics, are a pivotal mechanism conferring resistance against bacterial infections. SMB-1, a novel B3 subclass of MßLs from Serratia marcescens could deactivate almost all ß-lactam antibiotics including ampicillin (AMP), which has posed a serious threat to public health. To illuminate the mechanism of recognition and interaction between SMB-1 and AMP, various fluorescence spectroscopy techniques and molecular dynamics simulation were employed. The results of quenching spectroscopy unraveled that AMP could make SMB-1 fluorescence quenching that mechanism was the static quenching; the synchronous and three-dimensional fluorescence spectra validated that the microenvironment and conformation of SMB-1 were altered after interaction with AMP. The molecular dynamics results demonstrated that the whole AMP enters the binding pocket of SMB-1, even though with a relatively bulky R1 side chain. Loop1 and loop2 in SMB-1 undergo significant fluctuations, and α2 (71-73) and local α5 (186-188) were turned into random coils, promoting zinc ion exposure consistent with circular dichroism spectroscopy results. The binding between them was driven by a combination of enthalpy and entropy changes, which was dominated by electrostatic force in agreement with the fluorescence observations. The present study brings structural insights and solid foundations for the design of new substrates for ß-lactamases and the development of effective antibiotics that are resistant to superbugs.

Introduction of Electron Donor Groups into the Azulene Structure: The Appearance of Intense Absorption and Emission in the Visible Region.

In this work, through the Suzuki-Miyaura cross-coupling reaction with high yields, new π-conjugated azulene compounds containing diphenylaniline groups at positions 2 and 6 of azulene were synthesized. The obtained diphenylaniline-azulenes have intensely visible-light absorbing and emitting (in the wavelength range from 400 to 600 nm) properties. It has been shown that such unique optical properties, in particular fluorescent emission in the region of blue and green photoluminescence (λem at 495 and 525 nm), which were absent in the original azulene, are the result of the electron donor effect of diphenylaniline groups, which significantly changes the electronic structure of azulene and leads to the allowed HOMO → LUMO electron transition.

Color Polymorphism and Room Temperature Phosphorescence of 4-Bromo-2,7-Di-Tert-Butyl- 9-Methoxypyrene.

Color polymorphism combined with crystal packing-dependent luminescence properties of polymorphs reflects differences in intermolecular interactions in different molecular arrangements. The title compound has two polymorphic crystal structures having strikingly different absorption and luminescence spectra that result from different packing motifs in the crystal lattice. The polymorph with brick wall-like packing of molecules is white and shows very weak violet fluorescence whereas the second polymorph, where molecules are arranged in columnar stacks, is bright yellow and displays intense green fluorescence with maximum at 487 nm (20530 cm-1). In the white polymorph, where the distance between neighboring chromophores is increased, absorption and fluorescence spectra are similar to those of monomer in solution, and intersystem crossing to triplet manifold is the dominant pathway of relaxation. In the yellow polymorph, molecules within the columnar stacks are rotated which mitigates the steric hindrance and leads to closer π-stacking of the pyrene cores. That increases the ππ overlap and strengthens intermolecular interactions decreasing energy of the excited states. This affects emission spectra and photophysical processes-fluorescence yield grows whereas triplet formation yield decreases when S1 is lowered below higher triplet states and conditions for effective vibronic spin-orbit coupling are not favorable. The effect is not observed for other similar pyrene derivatives, testifying the uniqueness of the phenomenon.

Molecular Design Using Selected Concentration Effects in Optically Activated Fluorescent Matrices.

Molecular physics plays a pivotal role in various fields, including medicine, pharmaceuticals, and broader industrial applications. This study aims to enhance the methods for producing specific optically active materials with distinct spectroscopic properties at the molecular level, which are crucial for these sectors, while prioritizing human safety in both production and application. Forensic science, a significant socio-economic field, often employs hazardous substances in analyzing friction ridges on porous surfaces, posing safety concerns. In response, we formulated novel, non-toxic procedures for examining paper evidence, particularly thermal papers. Our laboratory model utilizes a polyvinyl alcohol polymer as a rigid matrix to emulate the thermal paper's environment, enabling precise control over the spectroscopic characteristics of 1,8-diazafluoro-9-one (DFO). We identified and analyzed the cyclodimer 1,8-diazafluoren-9-one (DAK DFO), which is a non-toxic and biocompatible alternative for revealing forensic marks. The reagents used to preserve fingerprints were optimized for their effectiveness and stability. Using stationary absorption and emission spectroscopy, along with time-resolved emission studies, we verified the spectroscopic attributes of the new structures under deliberate aggregation conditions. Raman spectroscopy and quantum mechanical computations substantiated the cyclodimer's configuration. The investigation provides robust scientific endorsement for the novel compound and its structural diversity, influenced by the solvatochromic sensitivity of the DFO precursor. Our approach to monitoring aggregation processes signifies a substantial shift in synthetic research paradigms, leveraging simple chemistry to yield an innovative contribution to forensic science methodologies.

Differential fluorescence features and recovery speeds of different scorpion exoskeleton parts during the molting process.

Scorpion fluorescence under ultraviolet light is a well-known phenomenon, but its features under excitation in the UVA, UVB and UVC bands have not been characterized. Systematic fluorescence characterization revealed indistinguishable fluorescence spectra with a peak wavelength of 475 nm for whole exuviae from second-, third- and fifth-instar scorpions under different ultraviolet light ranges. In-depth investigations of the chelae, mesosoma, metasoma and telson of adult scorpions further indicated heterogeneity in the typical fluorescence spectrum within the visible light range and in the newly reported fluorescence spectrum with a peak wavelength of 320 nm within the ultraviolet light range, which both showed excitation wavelength-independent features. Dynamic fluorescence changes during the molting process of third-instar scorpions revealed the fluorescence heterogeneity-dependent recovery speed of scorpion exoskeletons. The typical fluorescence spectra of the molted chelae and telson rapidly recovered approximately 6 h after ecdysis under UVA light and approximately 36 h after ecdysis under UVB and UVC light. However, it took approximately 12 h and 24 h to obtain the typical fluorescence spectra of the molted metasoma and mesosoma, respectively, under UVA irradiation and 72 h to obtain the typical fluorescence spectra under UVB and UVC irradiation. The fluorescence heterogeneity-dependent fluorescence recovery of the scorpion exoskeleton was further confirmed by tissue section analysis of different segments from molting third-instar scorpions. These findings reveal novel scorpion fluorescence features and provide potential clues on the biological function of scorpion fluorescence.

Use of ultrasound to increase the catalytic activity of α-L-rhamnosidase.

α-L-rhamnosidase (Rha) is ubiquitous in nature and has high feasibility in the food and biotechnology industries. A green and environmentally friendly method was used to improve the activity of Rha. Here, we show that the effects of ultrasound treatment on the Rha. Ultrasonic treatment at 80 W for 10 min yielded the highest enzyme activity. Treatment increased enzyme activity by 26.3% and half-life by 124 min. Further, treatment increased the catalytic efficiency of Rha and increased the substrate conversion rate by 33.88%. These results demonstrate that ultrasound increases the catalytic activity and stability of Rha. Thus, ultrasonic treatment of Rha is cost-effective on the industrial scale.

Effect of cationic antiseptics on fluorescent characteristics and electron transfer in cyanobacterial photosystem I complexes.

In this study, the effects of cationic antiseptics such as chlorhexidine, picloxidine, miramistin, and octenidine at concentrations up to 150 µM on fluorescence spectra and its lifetimes, as well as on light-induced electron transfer in protein-pigment complexes of photosystem I (PSI) isolated from cyanobacterium Synechocystis sp. PCC 6803 have been studied. In doing so, octenidine turned out to be the most "effective" in terms of its influence on the spectral and functional characteristics of PSI complexes. It has been shown that the rate of energy migration from short-wavelength forms of light-harvesting chlorophyll to long-wavelength ones slows down upon addition of octenidine to the PSI suspension. After photo-separation of charges between the primary electron donor P700 and the terminal iron-sulfur center(s) FA/FB, the rate of forward electron transfer from (FA/FB)- to the external medium slows down while the rate of charge recombination between reduced FA/FB- and photooxidized P700+ increases. The paper considers the possible causes of the observed action of the antiseptic.

Fluorescence Study of Pr3+ Doped CdS Nanoparticles and its Applications in Sensors and Detectors.

Fluorescence spectra of Pr3+ doped CdS nanoparticles, synthesized by chemical precipitation method, have been recorded at room temperature. The synthesized particles are nearly spherical shaped and the grain size is decreased with the increase in Pr3+ concentration. The chemical identity of the nanoparticles was confirmed by EDAX spectrum, the absorption peaks was confirmed by FTIR spectrum and then the recorded values were compared with the CIE diagram. The oscillator strengths of the 4f ↔ 4I transitions are parameterized in terms of three phenomenological Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6). Using the fluorescence data and these Ωλ parameters, theoretical and experimental study of various radiative properties viz., spontaneous emission probability (A), radiative life time , fluorescence branching ratio and stimulated emission cross-section were evaluated. The values of these parameters indicate that 3P0→ 3H4 transition can be considered to be good laser transition in the visible colour region. Also, excitation with 493 nm, leads to similar blue regions. The synthesized Pr3+ doped CdS nanomaterials could be useful for sensing and detecting devices, particularly for temperature sensing measurement and bio-sensing detection.

Spectral characteristics of the flavones and anthocyanins present in passionflower (Passiflora incarnata).

Rich in antioxidants with a variety of flavones and anthocyanins, passionflower/fruit has been extensively used in food, beverage, medicinal, and natural dyes industries. The individual components present in passionflower are identified by extracting them in methanol, partitioning them between ethyl acetate and aqueous layers, and recording their ESI mass spectrometric data. The steady-state absorption and fluorescence spectra of the extract in methanol and dimethyl sulfoxide are recorded and the lifetime of the fluorescing species is reported. The pH dependence of the absorption spectrum confirms the presence of the anthocyanins.

Interaction between dissolved organic carbon and fungal network governs carbon mineralization in paddy soil under co-incorporation of green manure and biochar.

Legume crops in rice cultivation are typically rotated and incorporated into the soil as green manure to improve soil fertility. Biochar has recently been co-incorporated with green manure to simultaneously stimulate soil organic carbon (SOC) mineralization and increase carbon (C) sequestration. However, few studies examine the effects of the co-incorporation of biochar and green manure on C cycling and the underlying microbial mechanisms in paddy fields. In this study, the effects of the co-incorporation of green manure and biochar on C mineralization, dissolved organic carbon (DOC) characteristics, and microbial community structures were investigated. A pot study was conducted with three treatments: inorganic NPK (NPK), inorganic NPK + green manure (GM), and inorganic NPK + green manure + biochar (GMC). Organic amendments significantly increased cumulative C mineralization, with amounts in the order GMC (3,434 mg·kg-1) > GM (2,934 mg·kg-1) > NPK (2,592 mg·kg-1). Fertilizer treatments had similar effects on DOC concentrations, with amounts in the order GMC (279 mg·kg-1) > GM (255 mg·kg-1) > NPK (193 mg·kg-1). According to fluorescence spectra, the highest microbial humic acid-like fraction and biological index were also in GMC. Co-incorporation of green manure and biochar shifted the composition of bacterial and fungal communities but more importantly, increased fungal network complexity and decreased bacterial network complexity. The increase in fungal network complexity with the increase in DOC concentrations and microbially derived components was the dominant factor in promoting C mineralization. Overall, this study reveals the underlying biochemical mechanism, the interaction between DOC and fungal network of C cycling in paddy soil under the co-incorporation of green manure and biochar management, and provides fundamental knowledge for exploring effective approaches to improve soil fertility and health in the future.

Utilizing Black Soldier Fly Larvae to Improve Bioconversion and Reduce Pollution: A Sustainable Method for Efficient Treatment of Mixed Wastes of Wet Distiller Grains and Livestock Manure.

Widespread environmental contamination caused by huge amounts of wastes generated by human activities has become a critical global concern that requires urgent action. The black soldier fly (BSFL) has gradually been used to treat different wastes due to high efficiency and low cost. However, little information is available regarding the treatment of mixed wastes by BSFLs. The impact of BSFLs on conversion of cow manure (COM) and pig manure (PM) via the incorporation of wet distiller grains (WDG) was assessed. Results demonstrate that the waste reduction rate was increased by 20% by incorporating 45% WDG to COM and PM. The bioconversion rate of BSFLs in COM and PM also increased from 1.20 ± 0.02% and 0.92 ± 0.02% to 10.54 ± 0.06% and 10.05 ± 0.11%, respectively. Total nitrogen content and δ15N/14N ratios of WDG + COM and WDG + PM were found to be significantly lower than those of COM and PM alone (p < 0.01). The organic matter changes during manure degradation were further analyzed by combing ultraviolet-visible spectrum (UV-vis) with excitation-emission matrix (EEM) spectroscopy techniques and fluorescence area integration (FRI) method. The UV-vis spectra results indicate that the addition of WDG to manures resulted in the decreased aromaticity and molecular weight of the waste. EEM spectra demonstrated that the accumulative Pi,n values of regions III and V in COM, COM + WDG, PM, and PM + WDG were 58%, 49%, 52% and 63%, respectively. These results not only provide new insights into the potential of mixed wastes for BSFL treatment but also contribute to the basis for the formulation of effective management measurements that reduce and/or reuse these wastes.

A new turn on coumarin-based fluorescence probe for Cr3+ detection in aqueous solution.

Isatin-3-(7'-Methoxychromone-3'-methylidene) hydrazone (L) was synthesized based on chromone schiff base, and used to construct a novel sensor to detect Cr3+. Fluorescence detection experiments were carried out for a range of different concentrations of Cr3+ in aqueous solutions. A concentration calculation model was built on the basis of eliminating interference of excitation spectrum in the fluorescence spectra with mathematical method. Results showed that probe L displayed a 70-fold fluorescence enhancement upon the addition of Cr3+ due to the photo-induced electron transfer (PET) effect. On the other hand, metal ions except Cr3+ did not cause significant change in either the absorption or the fluorescence spectrum of L. In addition, L showed a good selectivity to Cr3+ over other metal cations, especially Al3+ and Cu2+. The probe L can detect Cr3+ highly and selectively by the direct chelation enhanced fluorescence with a detection limit of 3.14 × 10-6 M. Furthermore, benefiting from their good water solubility and biocompatibility, cell imaging and real-time monitoring of Cr3+ in living HepG2 cells were successfully achieved.

4'-(8-(4-Methylimidazole)-octyloxy)-arctigenin: The first inhibitor of fish rhabdovirus glycoprotein.

Spring viraemia of carp virus (SVCV), a highly pathogenic rhabdovirus, could cause spring viraemia of carp (SVC) with up to 90% lethality. Like other rhabdoviruses, the entry of SVCV into susceptible cells was mediated by a single envelope glycoprotein G. Specific inhibitors targeting the glycoprotein were the most effective means to alleviate the epidemic. The programs including SWISS-MODEL, I-TASSER, Phyre2 and AlphaFold2 were used to build a three-dimensional structural model of glycoprotein. The structural comparison between SVCV-G and homology protein VSV-G revealed that the SVCV glycoprotein ectodomain (residues 19 to 466) folded into four distinct domains. Based on the potential small molecule binding sites on glycoprotein surfaces, virtual screening of the anti-SVCV drug libraries was performed using Autodock software and 4'-(8-(4-Methylimidazole)-octyloxy)-arctigenin (MOA) with a high binding affinity was identified. The solubility enhancer tags including trigger factor and maltose binding protein were fused with the ectodomain of glycoprotein, and the target protein with a purity of about 90% was successfully obtained. The interaction confirmation tests revealed that the fluorescence intensity of a characteristic peak induced by the endogenous chromophores in glycoprotein was decreased with the addition of MOA, indicating changes in the microenvironment of glycoprotein. Moreover, the interaction could cause a slight conformational change in glycoprotein, as shown by the content of ß-turn, ß-folding, and random coil of protein all increased with the decrease of α-helix content after the addition of MOA compound. These results demonstrated that MOA could act as a novel drug against fish rhabdovirus via direct targeting of glycoprotein.

Transformation of organic carbon through medium pressure (polychromatic) UV disinfection of wastewater effluent during wet weather events.

An observed decrease in total organic carbon (TOC) and dissolved organic carbon (DOC) concentrations following wastewater disinfection with medium pressure (MP, polychromatic) ultraviolet (UV) irradiation during wet weather flows is investigated. When antecedent rainfall in the previous 7-days was >2 in (5 cm), TOC and DOC concentrations decreased dramatically following MP-UV disinfection. Organic carbon surrogate measurements of biological oxygen demand (BOD), TOC, DOC, turbidity, UVA - 254 nm, SUVA (specific UVA), scanning UV-Visible spectra (200-600 nm), fluorescence excitation-emission matrix (EEM) spectra, and light scattering data are presented for wastewater resource recovery facility (WRRF) influent, secondary effluent (pre-UV-disinfection), and MP-UV-disinfected (final effluent) samples. TOC and DOC in wastewater influent and secondary effluent (i.e., pre-UV disinfection) correlated with antecedent rainfall conditions. The percent TOC and DOC removal through secondary treatment (i.e., from influent to effluent pre-UV) and the percent TOC and DOC removal through MP-UV disinfection (i.e., from effluent pre-UV to effluent post-UV) were compared and the latter approached 90 % through MP-UV disinfection during high antecedent rainfall conditions. Spectroscopy (UV, visible, or fluorescence) was performed on samples after filtration through 0.45 µm filters, i.e., the operationally defined DOC fraction of aquatic carbon. Scanning UV-visible spectra indicated transformation of an unidentified wastewater component into light-scattering entities regardless of antecedent rainfall conditions. The types of organic carbon (diagenetic, biogenic, or anthropogenic) and the significance of wet weather are discussed. An organic carbon contribution via infiltration and inflow was attributed as a source-of-interest in this research.

A Quantitative Approach to Determine Hydrophobe Content of Associating Polyacrylamide Using a Fluorescent Probe.

Hydrophobically associating polymers have found widespread applications in many domains due to their unique rheological behavior, which is primarily dictated by the hydrophobe content. However, the low fraction of hydrophobic monomers in polymers makes this parameter's precise and straightforward measurement difficult. Herein, a variety of hydrophobically associating polyacrylamides (HAPAM) with different alkyl chain lengths (L) and hydrophobic contents ([H]) were prepared by post-modification and accurately characterized by 1H NMR spectroscopy. The maximal fluorescence emission intensity (I) of 8-anilino-1-naphthalenesulfonic acid, which is sensitive to hydrophobic environments, was then detected in those polymer solutions and shown as a ratio to that in the polymer-free solution (I0). It was found that I/I0 for 0.5 wt% HAPAM can be scaled versus CH, which is a variate related to both L and [H], as I/I0 = 1.15 + 1.09 × 108CH3.42, which was also verified to be applicable for hydrophobic associating hydrolyzed polyacrylamide (HHAPAM). This relationship provides a handy method for determining the hydrophobic content of hydrophobically associating polymers, particularly for field applications.

Regulating the photophysical properties of ESIPT-based fluorescent probes by functional group substitution: a DFT/TDDFT study.

CONTEXT: In recent years, fluorescent probe technology has received more and more attention. However, the photophysical and photochemical properties of probe molecules still need to be further explored. This paper presents the excited state intramolecular proton transfer (ESIPT) processes and photophysical properties of the probe molecule 4-bromo-2-((E)-((Z)-((5-bromo-1H-indol-2-yl) methylene) hydrazono) methyl) phenol (BHPL) and its four derivatives (BHPL2, BHPL3, BHPL4, and BHPL5). Infrared spectra and geometric structure analyses revealed that introducing the -NH2 group on the benzene ring with the hydroxyl group will enhance the intramolecular hydrogen bond, which benefits the ESIPT process. Combining their absorption and fluorescence spectra, it can be concluded that BHPL2 and BHPL4 are both excellent probe candidates due to their large Stokes shift. The hole and electron and root mean square displacement analyses manifest that the fluorescence quenching of BHPL4 may be due to the intramolecular charge transfer process. Potential energy curves of BHPL and its four derivatives noted that ESIPT process of the BHPL2 is the most favorable to occur. The frontier molecular orbital and NBO analyses indicated that besides introducing electron-donating groups to reduce the energy gap and enhance fluorescence emission, introducing double electron-withdrawing groups can also achieve this effect, explaining why the energy barrier of ESIPT process for BHPL2 is lower than BHPL5. This work would provide the theoretical basis for designing novel fluorescence probes with more prominent properties. METHODS: The ground (S0) and excited (S1) state structures of all compounds were optimized by density functional theory (DFT) and time-dependent (TDDFT) method, with B3LYP/6-311+G(d,p) level, respectively. The infrared spectra and potential energy curves were simulated at the same theoretical level. The reduced density gradient scatter plots and interaction region indicator isosurfaces were drawn using Multiwfn and VMD programs. The absorption and fluorescence spectra were simulated by the TDDFT/B3PW91/6-311+G(d,p) method. All the calculations in this work are carried out in Gaussian 16 program package.

Simultaneous Force and Fluorescence Spectroscopy on Single Chains of Polyfluorene: Effect of Intra-Chain Aggregate Coupling.

Conjugated polymer chains in compact conformations or in films exhibit spectral features that can be attributed to interactions between individual conjugated segments of the chain, including formation of aggregates or excimers. Here, we use atomic force microscopy (AFM) on single chains of the conjugated polymer polyfluorene (PFO) to control the intersegment interactions by mechanically unfolding the chain. Simultaneously with the force spectroscopy we monitor fluorescence from the single PFO chains using a fluorescence microscope. We found that mechanical stretching of the chain causes disappearance of the green emission band. This observation provides evidence that the green emission originates from an intrachain aggregated state on the self-folded chain, which is decoupled by the stretching. In addition, the stretching upon laser irradiation leads to the appearance of additional features in the force spectra, small force peaks in the initial stages of the unfolding. These features are attributed to a combination of excitonic and van der Waals coupling of a ground-state intrachain aggregate.

Development of Spectral Imaging Cytometry.

Spectral flow cytometry is a new technology that enables measurements of fluorescent spectra and light scattering properties in diverse cellular populations with high precision. Modern instruments allow simultaneous determination of up to 40+ fluorescent dyes with heavily overlapping emission spectra, discrimination of autofluorescent signals in the stained specimens, and detailed analysis of diverse autofluorescence of different cells-from mammalian to chlorophyll-containing cells like cyanobacteria. In this paper, we review the history, compare modern conventional and spectral flow cytometers, and discuss several applications of spectral flow cytometry.

Study of complexation of single-stranded poly(rA) and poly(rU) with methylene blue.

To reveal the effect of DNA- or RNA-specific low-molecular compounds on cellular processes on the molecular level, we have carried out the studies with the application of spectroscopic methods. It is necessary for the understanding of structural-functional properties of nucleic acids in cell. In this work the interaction of DNA-specific thiazine dye methylene blue (MB) with synthetic polynucleotides poly(rA) and poly(rU) was studied. The interaction of MB with synthetic polyribonucleotides poly(rA) and poly(rU) was examined in the solution with high ionic strength in a wide phosphate-to-dye (P/D) range, using the absorption and fluorescence spectroscopies, as well as the fluorescence 2D spectra and 3D spectra analyses were given. Values of the fluorescence quenching constants for the complexes of MB with poly(rA) and poly(rU) were calculated (KSV is the Stern-Volmer quenching constant). Two different modes of MB binding to single-stranded (ss-) poly(rA) and poly(rU) and to their hybrid double-stranded (ds-) structure - poly(rA)-poly(rU) were identified. This ligand binds to ss-poly(rA) and poly(rA)-poly(rU) by semi-intercalation and electrostatic modes, but to ss-poly(rU) the prevailing mode is the electrostatic interaction.Communicated by Ramaswamy H. Sarma.