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The study delves into the binding properties of acridine-9-amine and its selected, mainly N-substituted derivatives (A9As), with calf thymus deoxyribonucleic acid (CT-DNA). This investigation, conducted using UV-Vis spectrophotometry, steady-state fluorescence spectroscopy and isothermal titration calorimetry, provides insights into the relationship between their structure and activity. The absorption spectra of the A9As exhibited a slight red shift and significant hypochromic effects, while the fluorescence emission intensities decreased in the presence of CT-DNA. These results suggest that all fluorescent substrates intercalate into the double helix of native DNA to varying degrees. The binding constants for the A9As/CT-DNA complexes (log(K A ) were determined using various techniques in the range from 2.59 to 5.50). The thermodynamic parameters of A9As binding to DNA were obtained from ITC measurements (ΔG from - 7.51 to - 6.75 kcal·mol -1 , ΔH from - 11.58 to - 3.83 kcal·mol -1 , and TΔS from - 4.83 to 3.68 kcal·mol -1 ) and indicated that the formation of all the investigated A9As-DNA complexes is an enthalpy-driven process. The study also discusses the influence of the emitters' structure and electronic properties of substituents on intercalation efficiency. This knowledge serves as a guide for further research and offers directions for functionalising new acridines as potential reagents. It also provides the latest information on the ability of intercalation to DNA, which can be instrumental in studies on the mechanism of binding small aromatic molecules to DNA and can potentially contribute to new anticancer drug designs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In this article, the binding interactions between bovine serum albumin (BSA) and three 1-alkylsulfonates, namely sodium 1-dodecanesulfonate, sodium 1-decanesulfonate, and sodium 1-octanesulfonate, have been thoroughly investigated. The study employed various experimental techniques such as isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), circular dichroism spectroscopy (CD), and molecular dynamics-based simulations. The objective was to understand the influence of the alkyl chain length of the investigated ligands on several aspects, including the strength of the interaction, the stoichiometry of the resulting complexes, the number of BSA binding sites, and the underlying mechanisms of binding. Notably, the study also demonstrated that sodium dodecyl sulfate (S12S) can serve as an effective site marker for BSA when studying ligands with similar structural and topological features. These findings may have significant implications for enhancing our understanding of the interactions between small amphiphilic molecules and proteins., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In this article, the implications of binding competition of vanadates(V) with dodecyl sulfates for bovine serum albumin on cytotoxicity of vanadium(V) species against prostate cancer cells have been investigated. The pH- and SDS-dependent vanadate(V)-BSA interactions were observed. At pH 5, there is only one site capable of binding ten vanadates(V) ions (logK (ITC)1  = 4.96 ± 0.06; ΔH (ITC)1  = -1.04 ± 0.03 kcal mol -1 ), whereas at pH 7 two distinctive binding sites on protein were found, saturated with two and seven V(V) ions, respectively (logK (ITC)1  = 6.11 ± 0.06; ΔH (ITC)1  = 0.78 ± 0.12 kcal mol -1 ; logK (ITC)2  = 4.80 ± 0.02; ΔH (ITC)2  = - 4.95 ± 0.14 kcal mol -1 ). SDS influences the stoichiometry and the stability of the resulting V(V)-BSA complexes. Finally, the cytotoxicity of vanadates(V) against prostate cancer cells (PC3 line) was examined in the presence and absence of SDS in the culture medium. In the case of a 24-h incubation with 100 μM vanadate(V), a ca. 20 % reduction in viability of PC3 cells was observed in the presence of SDS. However, in other considered cases (various concentrations and time of incubation) SDS does not affect the dose-dependent action of vanadates(V) on the investigated prostate cancer cells., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

Human serum albumin (HSA) effectively binds different types of low-molecular-weight compounds and thus enables their distribution in living organisms. Recently, it has been reported that the protein-ligand interactions play a crucial role in bioaccumulation processes and provide an important sorption phase, especially for ionogenic compounds. Therefore, the binding interactions of such compounds with proteins are the subject of an ongoing interest in environmental and life sciences. In this paper, the influence of some counter-ions, namely [B(CN) 4 ] - and [C(CN) 3 ] - on the affinity of the [IM1-12] + towards HSA has been investigated and discussed based on experimental methods (isothermal titration calorimetry and steady-state fluorescence spectroscopy) and molecular dynamics-based computational approaches. Furthermore, the thermal stability of the resulting HSA/ligand complexes was assessed using DSC and CD spectroscopy. As an outcome of the work, it has been ascertained that the protein is able to bind simultaneously the ligands under study but in different regions of HSA. Thus, the presence in the system of [IM1-12] + does not disturb the binding of [C(CN) 3 ] - and [B(CN) 4 ] - . The presented results provide important information on the presence of globular proteins and some ionogenic compounds in the distribution and bioaccumulation of ILs in the environment and living organisms., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Piotr Stepnowski reports financial support was provided by National Science Centre Poland. Sergey Samsonov reports financial support was provided by National Science Centre Poland., (Copyright © 2023 The Authors. Published by Elsevier B.V. All rights reserved.)

In the present paper, the binding interactions of highly negative-charged ions, namely hexacyanoferrates(II/III), i.e. [Fe(CN) 6 ] 4- and [Fe(CN) 6 ] 3- with bovine and human serum albumins (BSA and HSA, respectively) have been studied for the first time in an aqueous solution (10 mM cacodylate buffer of pH 7.0) using steady-state fluorescence spectroscopy, isothermal titration calorimetry, and CD spectroscopy supported by molecular dynamics-based computational approaches. The Stern-Volmer equation as well as its modifications suggested that hexacyanoferrates(II/III) effectively quenched the intrinsic fluorescence of the albumins through a static mechanism. The proteins under study possess only one binding site on the surface capable of binding one mole of hexacyanoferrates(II/III) ions per one mole of albumin (HSA or BSA). The formation of albumin complexes is an enthalpy-driven process (|ΔH ITC | > |TΔS ITC |). The strength of the interactions depends mainly on the type of albumin, and changes as follows: BSA-K 3 [Fe(CN) 6 ] ∼ BSA-K 4 [Fe(CN) 6 ] > HSA-K 3 [Fe(CN) 6 ] ∼ HSA-K 4 [Fe(CN) 6 ]. Finally, potential binding sites of bovine and human serum albumins have been investigated and discussed based on a competitive fluorescence displacement assay (with warfarin and ibuprofen as site markers) and molecular dynamics simulations., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Steady-state and time-resolved fluorescence quenching measurements supported by Isothermal Titration Calorimetry (ITC) were used to study the interactions of Cu(2+) with four peptides. Two of them were taken from the N-terminal part of the FBP28 protein (formin binding protein) WW domain: Tyr-Lys-Thr-Ala-Asp-Gly-Lys-Thr-Tyr-NH2 (D9) and its mutant Tyr-Lys-Thr-Ala-Asn-Gly-Lys-Thr-Tyr-NH2 (D9_M) as well as two mutated peptides from the B3 domain of the immunoglobulin binding protein G derived from Streptococcus: Asp-Val-Ala-Thr-Tyr-Thr-NH2 (J1) and Glu-Val-Ala-Thr-Tyr-Thr-NH2 (J2). The measurements were carried out at 298.15K in 20mM 2-(N-morpholino)ethanesulfonic acid (MES) buffer solution with a pH of 6. The fluorescence of all peptides was quenched by Cu(2+) ions. The stoichiometry, conditional stability constants and thermodynamic parameters for the interactions of the Cu(2+) ions with D9 and D9_M were determined from the calorimetric data. The values of the conditional stability constants were additionally determined from fluorescence quenching measurements and compared with those obtained from calorimetric studies. There was a good correlation between data obtained from the two techniques. On the other hand, the studies revealed that J1 and J2 do not exhibit an affinity towards metal ions. The obtained results prove that fluorescence quenching experiments may be successfully used in order to determine stability constants of complexes with fluorescent ligands. Finally, based on the obtained results, the coordinating properties of the peptides towards the Cu(2+) ions are discussed., (Copyright © 2015 Elsevier B.V. All rights reserved.)

The fluorescence quenching of 7-amino-4-methylcoumarin by different TEMPO derivatives was studied in aqueous solutions with the use of steady-state, time-resolved fluorescence spectroscopy as well as UV-VIS absorption spectroscopy methods. In order to distinguish each TEMPO derivative from the others and to understand the mechanism of quenching, the absorption and fluorescence emission spectra as well as decays of the fluorescence of 7-amino-4-methylcoumarin were registered as a function of each TEMPO derivative concentration. There were no deviations from a linearity in the Stern-Volmer plots (determined from both, steady-state and time-resolved measurements). The fluorescence quenching mechanism was found to be entirely collisional, what was additionally confirmed by the registration of Stern-Volmer plots at 5 temperatures ranging from 15 to 55°C. Based on theoretical calculations of molecular radii and ionization potentials of all TEMPO derivatives the mechanism of electron transfer was rejected. The fluorescence quenching which was being studied seems to be diffusion-limited and caused by the increase of non-radiative processes, such as an internal conversion and an intersystem crossing. The Stern-Volmer quenching constants and bimolecular quenching constants were determined at the room temperature for all TEMPO derivatives studied. Among all TEMPO derivatives studied TEMPO-4-amino-4-carboxylic acid (TOAC) was found to be the most effective quencher of 7-amino-4-methylcoumarin fluorescence (kq for TOAC was approximately 1.5 higher than kq for other TEMPO compounds studied). The findings demonstrate the possibility of developing an analytical method for the quantitative determination of TOAC, which incorporation into membrane proteins may provide a direct detection of peptide backbone dynamics., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The fluorescence quenching of norfloxacin, danofloxacin, enrofloxacin and levofloxacin, belonging to a group of fluoroquinolone antibiotics, by 4-hydroxy-TEMPO was studied in aqueous solutions with the use of steady-state, time-resolved fluorescence spectroscopy as well as UV-VIS absorption spectroscopy methods. In order to understand the mechanism of quenching the absorption and fluorescence emission spectra of all fluoroquinolone antibiotics studied as well as decreases of their fluorescence were registered as a function of the 4-hydroxy-TEMPO concentration. No deviations from a linearity in the Stern-Volmer plots (determined from both, steady-state and time-resolved measurements) were observed. The fluorescence quenching mechanism was proved to be totally dynamic, what was additionally confirmed by the registration of Stern-Volmer plots at 5 temperatures ranging from 15 to 55°C. On the basis of theoretical calculations of fluoroquinolones' molecular radii and ionization potentials the mechanism of electron transfer was rejected. It seems that the fluorescence quenching is diffusion-limited and is caused by the increase of nonradiative processes, such as internal conversion or intersystem crossing. The Stern-Volmer quenching constants and bimolecular quenching constants were determined at the room temperature for all fluoroquinolone antibiotics studied., (Copyright © 2014 Elsevier B.V. All rights reserved.)