Superior photoswitchable fluorescent polymer nanoparticles (PFPNs) are highly desirable for photo-rewritable data storage and ultrahigh-resolution bioimaging. Herein, 2-(3′,3′-dimethyl-6-nitrospiro[chromene-2,2′-indolin]-1′-yl)ethyl 2-(((dodecylthio)-carbonothioyl)thio)-2-methylpropanoate (SPTTC), a novel photochromic spiropyran-based reversible addition–fragmentation chain transfer (RAFT) reagent, and 5-dimethylaminonaphthalene-N-allyl-1-sulfonamide (DNS), the energy-level matched green fluorescent dye, were firstly synthesized. Then, they are used as donor and acceptor of the designed fluorescence resonance energy transfer (FRET) system to help fabricate superior dual-color PFPNs via a simple one-pot RAFT miniemulsion method. Thanks to its multiple merits such as the photochromic property, improved miscibility, and the ability to control polymerization rate, not only did the designed SPTTC provide the PFPNs with superior photoswitchable fluorescence properties such as high energy transfer efficiency (up to 91%), high dual-color contrast (green and red), rapid photoresponsiveness (2–4 min) and outstanding photoreversibility upon irradiation with UV and visible light, but it also endowed PFPNs with controllable molecular weight and narrow polydispersity index (PDI), excellent cell membrane permeability and long-term fluorescence stability. Moreover, the as-prepared PFPNs were successfully used for rewritable fluorescence patterning and intracellular dual-color imaging due to its prominent properties.

•The CCDs sensor was prepared by surface modification of prepared carbon dots.•The sensor can selectively sense Cu2+ and S2− in water.•The detection limit of sensor is 100 nM for Cu2+ and 130 nM for S2−.•The sensor has excellent longterm photostability and low cytotoxicity.•The sensor can realize monitoring of Cu2+ and S2− in live cells.The detection of copper ion (Cu2+) and sulfide anion (S2−) is of vital importance since the abnormal level of Cu2+ or S2− can lead to many diseases. Herein, a highly sensitive and selective fluorescent sensor, 1,4,8,11-tetraazacyclotetradecane (Cyclam)-functionalized carbon dots (CCDs), has been designed, synthesized and evaluated for Cu2+ and S2−. For this nanoprobe, a specific fluorescence resonance energy transfer (FRET) process can be effectively take place between carbon dots and the surface Cu2+-Cyclam complex, the as-prepared CCDs display high sensitivity (detection limit: 100 nM) and selectivity toward Cu2+ among many other metal cations (such as Mg2+, Co2+, Pb2+, Ni2+, Mn2+, Hg2+, Fe2+, Ca2+ and Zn2+) in 100% aqueous solution. Moreover, it is worth to point out that the subsequent addition of S2− can extract Cu2+ from the CCDs-Cu2+ complex and recover the fluorescence of carbon dots, the detection limit for S2− can reach to 130 nM in the aqueous medium. And no statistically significant interference was observed among the other 10 anions (HCO3−, SO42−, NO3−, Cl−, CO32−, S2O32−, F−, Br−, HPO4−, ClO4−) for S2− through the study. In addition, the novel type of multifunctional fluorescent sensor has a relatively wide pH range (pH 4–10). At the same time, it exhibited remarkable longterm fluorescence stability (≥35 days) for Cu2+ detection. In addition, this nanoprobe exhibits very low cytotoxicity and can easily permeate the cell membrane and realize Cu2+ and S2− monitoring and imaging in live cells. Therefore, this novel approach can be used in various fields, such as the detection of multiplex analytes in biological applications and environment, and it will reveal great application prospects.Novel Cyclam-functionalized carbon dots for highly sensitive (detection limit: 100 nM for Cu2+ and 130 nM for S2−) and selective detection of Cu2+ and S2− in water were prepared by surface modification of prepared carbon dots. The prepared dual-ion sensor can be reversibly switched for several times by selective addition of adequate Cu2+ or S2−, and exhibited excellent longterm photostability for Cu2+ detection (≥35 days) in aqueous media. More importantly, the CCDs sensor also displayed low cytotoxicity and can be utilized to monitor Cu2+ and S2− level change in live cells.

Photoswitchable fluorescent polymeric nanoparticles (PFPNs) with controllable molecular weight, high contrast, biocompatibility, and prominent photostability are highly desirable but still scarce for rewritable printing, super-resolution bioimaging, and rewritable data storage. In this study, novel amphiphilic BODIPY-based PFPNs with considerable merits are first synthesized by a facile one-pot RAFT-mediated miniemulsion polymerization method. The polymerization is performed by adopting polymerizable BODIPY and spiropyran derivatives, together with MMA as monomer, and mediated by utilizing biocompatible PEO macro-RAFT agent as both control agent and reactive stabilizer. The amphiphilic BODIPY-based PFPNs not only exhibit reversibly photoswitchable fluorescence properties under the alternative UV and visible light illumination through induced intraparticle fluorescence resonance energy transfer (FRET) but also display controllable molecular weight with narrow polydispersity index (PDI), high contrast of fluorescence, tunable energy transfer efficiency, good biocompatibility, excellent photostability, favorable photoreversibility, etc. The as-prepared PFPNs are successfully demonstrated for rewritable fluorescence patterning and high-contrast dual-color fluorescence imaging of living cells, implying its potential for rewritable data storage and broad biological applications in cell biology and diagnostics.

•The interaction of bovine serum albumin (BSA) and Tropicamide (TA) was studied.•The fluorescence quenching mechanism is static quenching.•The binding constants and binding sites were calculated.•Hydrogen binds and vander Waals interaction force played a major role in stabilizing the complex.•The TA affects the conformation of BSA.The fluorescence and ultraviolet–visible (UV–Vis) spectroscopy were explored to study the interaction between Tropicamide (TA) and bovine serum albumin (BSA) at three different temperatures (292, 301 and 310 K) under imitated physiological conditions. The experimental results showed that the fluorescence quenching mechanism between TA and BSA was static quenching procedure. The binding constant (Ka), binding sites (n) were obtained. The corresponding thermodynamic parameters (ΔH, ΔS and ΔG) of the interaction system were calculated at different temperatures. The results revealed that the binding process is spontaneous, hydrogen binds and vander Waals were the main force to stabilize the complex. According to Förster non-radiation energy transfer theory, the binding distance between TA and BSA was calculated to be 4.90 nm. Synchronous fluorescence spectroscopy indicated the conformation of BSA changed in the presence of TA. Furthermore, the effect of some common metal ions (Mg2+, Ca2+, Cu2+, and Ni2+) on the binding constants between TA and BSA were examined.

•We explored the interaction between BSA and PRX by spectroscopic methods.•The mainly binding forces are hydrophobic interactions.•The fluorescence quenching mechanism is static quenching.•The binding constants and binding sites were calculated.•The conformation of BSA was changed due to the impact of PRX.This work concerns the interaction of prenoxine sodium (PRX) and bovine serum albumin (BSA), which was conducted by spectroscopic means: fluorescence spectra, ultraviolet–visible spectra (UV–vis) and circular dichroism spectra (CD spectra) in physiological conditions. The results revealed the PRX can quench the fluorescence of BSA remarkably in aqueous solution. The quench mechanism has been obtained after corrected the fluorescence intensities for inner filter effects. The binding constants (Ka) were calculated according to the relevant fluorescence data at different temperatures. Moreover, from a series of analyses, we have obtained the binding sites, the binding distance and binding force. The effect of PRX on the conformation of BSA has been analyzed using synchronous fluorescence under experimental conditions. In addition, the CD spectra proved that the secondary structure of BSA changed in the presence of PRX in aqueous solution.Graphical abstractThe interaction between prenoxine sodium (PRX) and bovine serum albumin (BSA) was studied by fluorescence, circular dichroism (CD) and UV–vis spectroscopy. The quenching mechanism, binding constants, and binding distance were determined. Conformation change of BSA was also observed.

Cupric pollution is a global problem, and the development of stable and sensitive fluorescent probes for cupric ions in the water phase has long been sought. In the present study, we report on the fabrication of core–shell nanoparticle-based fluorescent chemosensors for Cu2+ detection in aqueous media. The core–shell nanoparticle sensor was prepared by a facile one-pot miniemulsion polymerization, in which the fluorescent dye (4-methamino-9-allyl-1,8-naphthalimide, MANI) was covalently incorporated into particle core and the Cu2+ ligand i.e. Vinylbenzylcyclam (VBC), chemically linked onto the surface. The cyclam-functionalized fluorescent polymeric nanoparticles exhibit a high affinity for Cu2+ ions in aqueous media. Upon the addition of Cu2+, the fluorescent emission of the MANI dye in nanoparticles can be quenched on the basis of intraparticle fluorescence resonance energy transfer (FRET) from the dye in the hydrophobic PMMA core to the Cu2+–cyclam complexes on the nanoparticle surface, and the nanoparticle sensor can selectively detect the Cu2+ in water with the detection limit of 500 nM. The observed FRET efficiencies (31.6–73.4%), as well as the distance (r) between MANI (donor) and Cu2+–cyclam complexes (acceptor), were also determined. No interference was observed from other metal ions, making it a highly sensitive and selective Cu2+ probe. Moreover, the nanoparticle-based fluorescent sensor was applicable in a relatively wide pH range (pH 4–10) in water and it exhibited excellent long-term photostability for Cu2+ detection (>45 days) in aqueous media; thus, this approach may provide a new strategy for ratiometric detection of analytes in environmental and biological applications.

•We explored the interaction between urea-induced BSA and CTL by spectroscopic methods.•The fluorescence quenching mechanism is static quenching.•The binding constants and binding sites were calculated.•The conformation of urea-induced BSA was changed affected by CTL.•The three temperature influenced the binding affinity of CTL and urea-induced BSA.The interaction of carteolol hydrochloride, to 0.2 mol L−1 urea-induced bovine serum albumin in aqueous solution has been first investigated by fluorescence spectra and ultraviolet–visible (UV–vis) spectra at pH 7.40. The quenching mechanism, binding parameter and sites (n), the binding mode (ΔG, ΔH, and ΔS) as well as the binding distance (r) have been obtained according to the experimental results. We also use the synchronous fluorescence method to study the effect of CTL on the conformation change of urea-induced BSA.Graphical abstractThe interaction between carteolol hydrochloride (CTL) and urea-induced bovine serum albumin was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, and binding distance were determined. Conformation change of BSA was observed from synchronous fluorescence spectra. The comparison of binding potency of SPSD and BSA suggested that the temperature influence the binding affinity of CTL and urea-induced BSA.

The fluorescence and ultraviolet spectroscopy were explored to study the interaction between Oxymetazoline hydrochloride (OMZH) and mucin under imitated physiological condition. The results demonstrated that the fluorescence quenching mechanism between OMZH and mucin is a combined quenching process. The binding constants (Ka), binding sites (n) and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction system were calculated at different temperatures. The hydrogen bonds and van der Waals forces play a major role in the interaction between OMZH and mucin. According to Förster non-radiation energy transfer theory, the binding distance between OMZH and mucin was calculated.Graphical abstractThe interaction between Oxymetazoline hydrochloride (OMZH) and mucin was studied by fluorescence and UV–Vis spectroscopy. The quenching mechanism, binding constants and binding distance were obtained. The binding constants and binding sites were calculated. According to Förster non-radiation energy transfer theory, the binding distance between OMZH and mucin was calculated.Highlights► We explored the interaction of mucin and OMZH by spectroscopic methods. ► The fluorescence quenching mechanism is combined quenching. ► The binding constants and binding sites were calculated. ► Hydrogen bonds and van der Waals forces plays a major role in the interaction. ► The energy transfer between OMZH and mucin with high probability.

The interaction between N-confused porphyrins-(4-hydroxycoumarins) diad (NCP-(4-hydroxycoumarins)) and bovine serum albumin (BSA) was studied using fluorescence and ultraviolet spectroscopy at different temperatures under imitated physiological conditions. The experimental results showed that the fluorescence of BSA was quenched by NCP-(4-hydroxycoumarins) through a combined quenching procedure. The binding constants, binding sites and corresponding thermodynamic parameters between NCP-(4-hydroxycoumarins) and BSA at different temperatures were obtained. According to Förster non-radiation energy transfer theory, the binding distance between BSA and NCP-(4-hydroxycoumarins) was calculated to be about 2.1 nm. The effect of NCP-(4-hydroxycoumarins) on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effect of some metal ions Cu2+, Ca2+, Mg2+, and Ni2+ on the binding constant between NCP-(4-hydroxycoumarins) and BSA was examined.Graphical abstractThe interaction between N-confused porphyrins-(4-hydroxycoumarins) diad (NCP-(4-hydroxycoumarins)) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, thermodynamic parameters, and binding distance were obtained.Highlights► The interaction of BSA and NCP-(4-hydroxycoumarins) was explored. ► The fluorescence quenching mechanism is combined quenching. ► Electrostatic force was the main force for the interaction. ► The binding constants, binding sites and thermodynamic parameters were calculated. ► The conformation of BSA is changed in the presence of NCP-(4-hydroxycoumarins).

Spiro pyrrolidines, which were proved with diverse and potent biological activities and they were discovered widespread in nature. In this paper, using fluorescence and ultraviolet spectroscopy, we investigated the interactions between novel spiro pyrrolidine (NSP) and bovine serum albumin (BSA) under the imitated physiological condition. The results show that the NSP binds to BSA molecules. Static quenching and non-radiation energy transfer are the main reasons for fluorescence quenching. We calculated the binding constant (Ka) and binding sites (n) at different temperatures and obtained the binding distance between the tryptophan residue in BSA and the NSP based on the Förster theory of non-radiation energy transfer. In addition, using synchronous fluorescence spectra, we demonstrated conformation changes of BSA caused by NSP. The comparison of binding potency of NSP and BSA suggests that the substituent on the benzene ring influences the binding ability of NSP and BSA.Graphical abstractThe interaction between novel spiro pyrrolidine (NSP) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, and binding distance were obtained. Conformation change of BSA was observed from synchronous fluorescence spectra. The comparison of binding potency of NSP and BSA suggested that the substituents on the benzene ring influence the binding affinity of NSP and BSA.Highlights► We explored the interaction between BSA and NSP by spectroscopic methods. ► The fluorescence quenching mechanism is static quenching. ► The binding constants and binding sites were calculated. ► The conformation of BSA was changed affected by NSP. ► The substituent on the benzene ring influences the binding affinity of NSP and BSA.

The interaction between thiazolo[2,3-b]pyrimidine (TZPM) analogues and bovine serum albumin (BSA) was investigated by fluorescence spectroscopy and UV–Vis spectroscopy at two different temperatures (299 and 307 K) under imitated physiological conditions. The results indicate that both static quenching and dynamic quenching contribute to the fluorescence quenching of BSA by TZPM. The binding constant (Ka) and binding sites (n) were calculated from the obtained spectra. Based on the Förster non-radiation energy transfer theory, the average binding distance between BSA and TZPM was estimated. The synchronous fluorescence spectra indicate that the conformation of BSA has been changed. The comparison of binding potency of TZPM and BSA suggests that the substituents on the benzene ring enhance the binding affinity of TZPM and BSA. We investigated the possible sub-domains on BSA that bind TZPM by displacement experiments. Furthermore, to explore the effect of molecular structure on the binding, a study on quantitative structure–property relationship (QSPR) was performed, the quantitative relationship equation of R0, r and Ka were obtained. We observed that R0, r and Ka between BSA and TZPM is connected with the margin of the highest and the lowest occupied orbital energy (ΔE), dipole moment (μ), Molar Volume (Vm), Mole Mass (M).Graphical abstractThe interaction between thiazolo[2,3-b]pyrimidine (TZPM) analogues and bovine serum albumin (BSA) was studied by fluorescence and UV–Vis spectroscopy. The quenching mechanism, binding constants, and binding distance were obtained. The synchronous fluorescence spectra indicated that the conformation of BSA has been changed. The comparison of binding potency of TZPM and BSA suggested that the substituents on the benzene ring enhance the binding affinity of TZPM and BSA.Highlights► We explored the interaction between BSA and TZPM by spectroscopic methods. ► The fluorescence quenching mechanism is combined quenching. ► The binding constants, binding sites and binding distances were calculated. ► The synchronous fluorescence indicated that the conformation of BSA has changed. ► The substituents on the benzene ring enhance the binding affinity of TZPM and BSA.

Fluorescence and ultraviolet spectroscopies were applied to investigate the interaction between five N-benzyl piperidones (NBP) and bovine serum albumin (BSA) under imitated physiological conditions. The experimental results show that these NBPs have a static fluorescence quenching effect on the endogenous fluorescence of BSA at the temperatures 302 and 310 K. According to the fluorescence quenching theory, the Stern–Volmer quenching constant (KSV), the binding constant (Ka), and the number of binding sites (n) were obtained. Also, the effect of substituents on the binding capacity between NBP and BSA is in the order: C6H5 < 4-CH3OC6H4 < 4-CH3C6H4 < 2,4-Cl2C6H3 < 4-ClC6H4. The corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) were obtained at two different temperatures and indicate that hydrogen bonding and van der Waals forces play main roles in stabilizing the BSA–NBP complex. The binding distance between the tryptophan residue in BSA and NBP was found to be much <7 nm based on the Förster theory of non-radiation energy transfer. The effect of NBP on the conformation of BSA was analyzed as well by synchronous fluorescence spectroscopy.

Novel multicolor and photoswitchcable fluorescent polymer nanoparticles were prepared by one-step miniemulsion via methyl methacrylate (MMA) copolymerization with 4-ethoxy-9-allyl-1,8-naphthalimide (EANI), allyl-(7-nitro-benzo[1,2,5]oxadiazol-4-yl)-amine (NBDAA) and spiropyran-linked methacrylate (SPMA). Under visible-light conditions, SPMA moieties in polymer nanoparticles are colorless and nonfluorescent, by varying the incorporating ratio of two dyes (EANI and NBDAA), fluorescence resonance energy transfer (FRET)-mediated emission signatures can be tuned so that the nanoparticles exhibit multiple colors under a single wavelength excitation. Moreover, the fluorescence emission of EANI and NBDAA dyes in nanoparticles can be reversibly switched “on” and “off” through the FRET process by the alternating irradiation of UV and visible light. This class of novel photoswitchable multicolor fluorescent polymer nanoparticles may find potential applications in multiplexed bioanalysis.

The fluorescence and ultraviolet spectroscopies were explored to study the interaction between edaravone (EDA) and bovine serum albumin (BSA) under imitated physiological condition. The experimental results show that the fluorescence quenching mechanism between EDA and BSA is a combined quenching (dynamic and static quenching). The binding constants, binding sites, and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction system were calculated at different temperatures. According to Förster non-radiation energy transfer theory, the binding distance between EDA and BSA was calculated to be 3.10 nm. The effect of EDA on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effects of some common metal ions Mg2+, Ca2+, Cu2+, and Ni2+ on the binding constant between EDA and BSA were examined.Highlights► We explored the interaction of BSA and EDA using spectroscopic methods. ► The fluorescence quenching mechanism is combined quenching. ► Hydrophobic interaction force plays a major role in stabilizing the complex. ► The binding constants, binding sites, and thermodynamic parameters were calculated. ► EDA affects the conformation of tryptophan residue's microregion.

The interaction between dihydromyricetin (DMY) and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopy at different temperatures under imitated physiological conditions. The experimental results revealed that dynamic quenching, static quenching and non-radiation energy transfer led to the fluorescence quenching. The obtained binding constants, binding sites and corresponding thermodynamic parameters at different temperatures indicate that hydrophobic forces play a major role in the interaction of DMY with BSA. According to Förster non-radiation energy transfer theory, the binding distance between BSA and DMY was found to be 3.26 nm. Synchronous fluorescence spectroscopy and FT-IR spectra showed the conformation of BSA changed in the presence of DMY. In addition, the effect of some common metal ions Cu2+, Ca2+, Mg2+, and Zn2+ on the binding constant between DMY and BSA was examined.

Both lomefloxacin (LOM) and ofloxacin (OFL) have a powerful ability to quench the fluorescence of bovine serum albumin (BSA). The fluorescence quenching action is much stronger when the two drugs coexist. The synergism between LOM and OFL was studied using fluorescence and ultraviolet spectroscopy under imitated physiological conditions. The results show that static quenching and non-radiation energy transfer are the main reasons for the fluorescence quenching. The synergism results in both the reduction of the binding stability between drugs and BSA and an increase of the free drug concentration, which will increase the efficacy of drugs. The thermodynamic parameters at different temperatures were calculated and the binding distances r between the drugs and BSA were obtained based on Försters theory of non-radiation energy transfer. The synchronous fluorescence spectra indicated that the effect of synergism affected the conformation of BSA.

The fluorescence and ultraviolet spectroscopy were explored to study the interaction between N-confused porphyrins (NCP) and bovine serum albumin (BSA) under imitated physiological condition. The experimental results indicated that the fluorescence quenching mechanism between BSA and NCP was static quenching procedure at low NCP concentration at 293 and 305 K or a combined quenching (static and dynamic) procedure at higher NCP concentration at 305 K. The binding constants, binding sites and the corresponding thermodynamic parameters ΔH, ΔS, and ΔG were calculated at different temperatures. The comparison of binding potency of the three NCP to BSA showed that the substituting groups in benzene ring could enhance the binding affinity. From the thermodynamic parameters, we concluded that the action force was mainly hydrophobic interaction. The binding distances between NCP and BSA were calculated using Förster non-radiation energy transfer theory. In addition, the effect of NCP on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy.Graphical abstractThe interaction between N-confused porphyrins (NCP) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, thermodynamic parameters, and binding distance were obtained.Highlights► We explored the interaction of BSA and NCP by spectroscopic methods. ► The quenching mechanism is static quenching or static and dynamic quenching. ► Hydrophobic interaction plays a major role in the binding process. ► The binding constants, binding sites and thermodynamic parameters were calculated. ► The substitution in benzene ring affects the interaction.

The interaction between imidazo[2,1-b]thiazole (IMTZ) and bovine serum albumin (BSA) was analyzed by fluorescence and ultraviolet spectroscopy at 302 and 310 K under simulative physiological conditions. The results show that IMTZ can effectively quench the intrinsic fluorescence of BSA via static and dynamic quenching. The binding constant, binding sites of IMTZ with BSA were calculated. According to the Förster non-radiation energy transfer theory, the average binding distance between IMTZ and BSA was obtained. What's more, the synchronous fluorescence spectra indicated that the conformation of BSA has been changed. The results provided the information for the binding of IMTZ to BSA, and the influences of substituent group on the interaction were also discussed.Graphical abstractThe interaction between imidazo[2,1-b]thiazole (IMTZ) analogues and bovine serum albumin (BSA) was studied by fluorescence and UV–Vis spectroscopy. The quenching mechanism, binding constants and binding distance were obtained. The comparison of binding potency of IMTZ and BSA suggested that the substituent on the benzene ring enhance the binding affinity of IMTZ and BSA.Highlights► We explored the interaction of BSA and IMTZ by spectroscopic methods. ► The fluorescence quenching mechanism is static and dynamic quenching. ► The binding constants and binding sites were calculated. ► The synchronous fluorescence spectra indicated that the conformation of BSA has been changed. ► The substituent on the benzene ring enhance the binding affinity of IMTZ and BSA.

In the present study, novel polymeric nanoparticles of ca. 55 nm in diameter with reversibly photoswitchable fluorescence properties were synthesized using a facile one-step miniemulsion polymerization, in which the donor of fluorescence resonance energy transfer (FRET), 4-methamino-9-allyl-1,8-naphthalimide (MANI), and the acceptor, spiropyran-linked methacrylate (SPMA), were covalently incorporated into a polymeric matrix during the polymerization process. The fluorescence emission of MANI dye in nanoparticles can be reversibly switched using the alternating irradiation of UV and visible light, which can induce the structural interconversion between the SP form and MC form of spiropyran moieties inside nanoparticles and thus reversibly switch on and switch off the FRET process. The prepared photoswitchable fluorescent polymer nanoparticles not only show a high load capacity of dyes, controllable amount and ratio of the two dyes, and tunable FRET efficiency but also exhibit higher spectral stability because of covalent linkage between dye molecules and the particle, relatively fast photoresponsibility, and better photoreversibility compared to some previously reported systems.

The fluorescence and ultraviolet spectroscopies were explored to study the interaction between N-confused porphyrins–edaravone diad (NCP–EDA) and bovine serum albumin (BSA) under simulative physiological condition at different temperatures. The experimental results show that the fluorescence quenching mechanism between NCP–EDA and BSA is a combined quenching (dynamic and static quenching). The binding constants, binding sites and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction system were calculated at different temperatures. According to Förster non-radiation energy transfer theory, the binding distance between NCP–EDA and BSA was calculated to be 3.63 nm. In addition, the effect of NCP–EDA on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy.Graphical abstractThe interaction between N-confused porphyrins–edaravone diad (NCP–EDA) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, thermodynamic parameters, and binding distance were obtained.Highlights► The interaction between BSA and NCP–EDA was investigated by spectroscopic methods. ► The fluorescence quenching mechanism is dynamic and static quenching. ► Hydrophobic interaction force plays a major role in stabilizing the complex. ► The binding constants, ΔG, ΔH, and ΔS of the interaction were calculated. ► The conformation of BSA is changed in the presence of NCP–EDA.

The interaction between salvianic acid A sodium (SAS) and bovine serum albumin (BSA) was investigated using fluorescence and ultraviolet spectroscopy at different temperatures under imitated physiological conditions. The experimental results showed that the fluorescence of BSA was quenched by SAS through a static quenching procedure. The binding constants of SAS with BSA were 2.03, 1.17 and 0.71 × 105 L mol−1 at 291, 298 and 305 K, respectively. Negative values of ΔG, ΔH, and ΔS indicate that the interaction between SAS and BSA is driven by hydrogen bonds and van der Waals forces. According to Förster non-radiation energy transfer theory, the binding distance between BSA and SAS was calculated to be about 2.92 nm. The effect of SAS on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effect of some metal ions Cu2+, Ca2+, Mg2+, and Zn2+ on the binding constant between SAS and BSA was examined.Graphical abstractThe interaction between salvianic acid A sodium (SAS) and bovine serum albumin (BSA) was studied by fluorescence and UV–vis spectroscopy. The quenching mechanism, binding constants, thermodynamic parameters, and binding distance were obtained.Research highlights► We explored the interaction of BSA and SAS by spectroscopic methods. ► The fluorescence quenching mechanism is static quenching. ► Hydrogen bonds and van der Waals forces were the main force. ► The binding constants, binding sites and thermodynamic parameters were calculated. ► The SAS affects the conformation of tryptophan residues’ microregion.

The interactions between 3,4-dihydropyrimidin-2(1H)-ones (DHPM) and bovine serum albumin (BSA) were investigated by fluorescence and ultraviolet spectroscopy under imitated physiological conditions. The experimental results showed that all DHPM could form complexes with BSA. Static quenching and non-radiation energy transfer are the main reasons leading to the fluorescence quenching. The binding constants (KA) and the number of binding sites (n) were calculated. According to Förster theory of non-radiation energy transfer, the binding distances (r) between BSA and DHPM are less than 7 nm. The relationship between different aryl groups in pyrimidine ring and the binding ability of DHPM with BSA is preliminarily discussed. Moreover, the synchronous fluorescence spectra indicated that the conformation of BSA has not been changed.

To understand the effects of pyrazole substitution on reaction equilibrium, the interactions between a series of pyrazole-like ligands and [OV(O2)2(D2O)]−/[OV(O2)2(HOD)]− were explored by using multinuclear (1H, 13C, and 51V) magnetic resonance, HSQC, and variable temperature NMR in 0.15 mol/L NaCl ionic medium mimicking physiological conditions. These results show that the relative reactivities among the pyrazole-like ligands are 3-methyl-1H-pyrazole ≈ 4-methyl-1H-pyrazole ≈ 1H-pyrazole > 1-methyl-1H-pyrazole. As a result, the main factor which affects the reaction equilibrium is the steric effect instead of the electronic effect of the methyl group of these ligands. A pair of isomers has been formed resulting from the coordination of 3-methyl-1H-pyrazole and a vanadium complex, which is attributed to different types of coordination between the vanadium atom and the ligands. Thus, the competitive coordination leads to the formation of a series of six-coordinate peroxovanadate species [OV(O2)2L]− (L, pyrazole-like ligands). Moreover, the results of density functional calculations provided a reasonable explanation on the relative reactivity of the pyrazole-like ligands as well as the important role of solvation in these reactions.

To understand the effects of benzimidazole substitution on reaction equilibrium, the interactions between a series of benzimidazole-like ligands and [OV(O2)2(D2O)]−/[OV(O2)2(HOD)]− in solution were explored by a combination of multinuclear (1H, 13C, and 51V) magnetic resonance and variable temperature NMR in 0.15 mol/L NaCl ionic medium for mimicking the physiological condition. Some direct NMR data are reported for the first time. These results show that the relative reactivity among the organic ligands is 2-methyl-1H-benzo[d]imidazole > (1H-benzo[d]imidazol-2-yl)methanol > 1-(1H-benzo[d]imidazol-2-yl)ethanol > 1H-benzo[d][1,2,3]triazole. Both the steric effect and the electron effect of the 2-position substituted groups in benzimidazole ring affect the reaction equilibrium. The competitive coordination results in the formation of a series of new six-coordinated peroxovanadate species [OV(O2)2L]− (L = benzimidazole-like ligands). Moreover, the results of density functional calculations provided a reasonable explanation on the relative reactivity of the benzimidazole-like ligands as well as the important role of solvation in these reactions.

The fluorescence and ultraviolet spectroscopies were explored to study the interaction between edaravone (EDA) and bovine serum albumin (BSA) under imitated physiological condition. The experimental results show that the fluorescence quenching mechanism between EDA and BSA is a combined quenching (dynamic and static quenching). The binding constants, binding sites, and the corresponding thermodynamic parameters (ΔG, ΔH, and ΔS) of the interaction system were calculated at different temperatures. According to Förster non-radiation energy transfer theory, the binding distance between EDA and BSA was calculated to be 3.10 nm. The effect of EDA on the conformation of BSA was analyzed using synchronous fluorescence spectroscopy. In addition, the effects of some common metal ions Mg2+, Ca2+, Cu2+, and Ni2+ on the binding constant between EDA and BSA were examined.Highlights► We explored the interaction of BSA and EDA using spectroscopic methods. ► The fluorescence quenching mechanism is combined quenching. ► Hydrophobic interaction force plays a major role in stabilizing the complex. ► The binding constants, binding sites, and thermodynamic parameters were calculated. ► EDA affects the conformation of tryptophan residue's microregion.