In this work, the interaction between camptothecin (CPT) analogs and fat mass and obesity associated (FTO) was investigated using spectroscopy and molecular docking. From the experimental results, it was found that the CPT analogs caused the fluorescence quenching of FTO through a static quenching procedure. The binding constants and thermodynamic parameters at three different temperatures, the number of binding sites were obtained, which suggested that the hydrophobic interaction and electrostatic force played major role in the reaction between CPT analogs and FTO. Results revealed that 10-hydroxycamptothecin was the strongest quencher.

In this paper, The binding of twelve 1,3-diazaheterocyclic compounds (1a-1 l) to the fat mass and obesity-associated (FTO) protein was investigated by fluorescence, UV-vis absorption spectroscopy and molecular modeling. Results indicated that the intrinsic fluorescence of FTO is quenched by the nine compounds (1a-1i) with a static quenching procedure. No interaction was observed between FTO protein and compounds (1j-1 l). The thermodynamic parameters obtained from the fluorescence data showed that the hydrophobic force played a major role in stabilizing the complex. The results of synchronous and three-dimensional fluorescence spectra showed that the conformation of FTO was changed. In addition, the influence of molecular structure on the quenching effect has been investigated.

The interactions between human serum albumin (HSA) and 5-epi-taiwaniaquinone G (G2) or its isomeride (G1) was investigated by fluorescence, UV–visible absorption, resonance light scattering, synchronous fluorescence spectroscopy and 3D spectroscopy under mimic physiological conditions in combination with molecular modeling. The results revealed that G1 and G2 caused the fluorescence quenching of HSA by the formation of G1-HSA and G2-HSA complex, respectively. The binding constants and thermodynamic parameters at three different temperatures were obtained. Hydrophobic and electrostatic interactions played a role in the binding process of HSA and G1. Van der Waals force and hydrogen bond interaction played a role in the binding process of HSA and G2. Results showed that G2 was the stronger quencher and the position of methyl influenced the binding process between HSA and G1 (G2).

The fat mass and obesity associated protein (FTO) is a potential target for anti-obesity medicines. In this paper, we have synthesized two potential inhibitors for FTO, three-member-ring compound (W3) and four-member-ring compound (W4). The interactions of fat mass and obesity-associated (FTO) protein with W3 (or W4) have been studied by spectral method. Results show the intrinsic fluorescence is quenched by the W3 (or W4). The thermodynamics parameters indicate hydrophobic interaction play a major role in the interactions. The results of synchronous fluorescence spectra demonstrate that the microenvironments of Trp residue of FTO are disturbed by W3 and W4. Results showed that W3 are stronger quenchers and bind to FTO with the higher affinity than W4. The influence of molecular structure on the binding aspects has been investigated.

•A novel antiviral drug (FNC) has been studied by multi-spectra and molecular modeling methods.•The interaction between FNC and human hemoglobin has been investigated for the first time.•Hydrogen bond and van der Waals force play major role in the binding process.FNC (2′-deoxy-2′-bfluoro-4′-azidocytidine) is a novel nucleoside analogue with pharmacologic effects on several human diseases. In this work, the binding of FNC to human hemoglobin (HHb) have been investigated by absorption spectroscopy, fluorescence quenching technique, synchronous fluorescence, three-dimensional fluorescence and molecular modeling methods. Analysis of fluorescence data showed that the binding of FNC to HHb occurred via a static quenching mechanism. Thermodynamic analysis and molecular modeling suggest that hydrogen bond and van der Waals force are the mainly binding force in the binding of FNC to HHb.The characteristics of the interaction between FNC and human hemoglobin were investigated by spectral methods.

The interaction between norfloxacin (NFA) and FNC has been investigated by fluorescence and UV-vis absorption spectroscopy. It has been found that static quenching of fluorescence of NFA occurs in the presence of FNC. Hydrophobic interactions play an important role in stabilizing the complex. The binding constant (K), binding site number (n) and corresponding thermodynamic parameters have been determined according to the van't Hoff equation. This method is simple, selective and relatively free of interference from coexisting substances. Under optimal conditions, the relative fluorescence intensity is linearly proportional to the concentration of FNC between 1.29 and 36.20 μg mL−1, with a detection limit of 0.2622 μg mL−1. The recovery of the method is in the range of 97.8–99.9%.

•The interactions between HHb and five alkaloids have been investigated.•Hydrophobic and electrostatic interactions play major role in the binding process.•The influence of molecular structure on the binding aspects has been investigated.•Molecular docking was also applied in the binding study.This work studied the interaction of human hemoglobin (HHb) with aminophylline, acefylline, caffeine, theophylline and diprophylline systematically by UV–vis absorption spectroscopy and fluorescence spectroscopy in combination with molecular modeling. Five alkaloids caused the fluorescence quenching of HHb by the formation of alkaloids-HHb complex. The binding constants and thermodynamic parameters were obtained. The hydrophobic and electrostatic interactions were the predominant intermolecular forces to stabilize these complexes. Results of thermodynamic analysis and molecular modeling showed that aminophylline was the strongest quencher and diprophylline was the weakest quencher.Graphical abstractThe synchronous fluorescence spectra of HHb in the absence and presence of Ami.

•The interactions between BSA and FNC or analogs have been investigated.•Hydrophobic interactions play major role in the binding process.•The influence of molecular structure on the binding aspects has been investigated.•Molecular docking was also applied in the binding study.The binding of 4′-azido-2′-deoxyfluoroarabinocytidine (FNC) or analogs (cytidine and 5′-cytidylate monophosphate) to bovine serum albumin (BSA) was investigated by fluorescence, UV–vis absorption spectroscopy and molecular modeling. The three compounds quenched the intrinsic fluorescence of BSA and the results revealed the presence of static quenching mechanism. The positive ΔH and positive ΔS for the systems suggested that the hydrophobic forces stabilized the interaction between the compounds and protein. Results also showed that FNC was the weakest quencher.Graphical abstractThe fluorescence spectra of BSA in the absence and presence of FNC.

•The interactions between Trypsin and Bicyclol or analogs have been investigated.•Results reveal that Bifendate has the strongest affinity for Trypsin among five compounds.•Hydrophobic and electrostatic interactions play major role in the binding process.•The influence of molecular structure on the binding aspects has been investigated.The interactions between Trypsin and Bicyclol or analogs (Bifendate, I, II and III) were investigated by spectrophotometric methods. It was found that Bicyclol or analogs had strong ability to quench the intrinsic fluorescence of Trypsin by a static quenching procedure. The binding constants were obtained at three temperatures. The thermodynamics parameters reveal that the hydrophobic and electrostatic interactions play an important role in the interaction. Results showed that the microenvironments of tryptophan residue of Trypsin were disturbed by the analogs. Results indicated that Bifendate was the strongest quencher among five compounds.The synchronous fluorescence spectra of Trypsin in the absence and presence of Bicyclol.

The interactions between trypsin and caffeine/theophylline were investigated by fluorescence spectroscopy, UV–visible absorption spectroscopy, resonance light scattering and synchronous fluorescence spectroscopy under mimic physiological conditions. The results revealed that the fluorescence quenching of trypsin by caffeine and theophylline was the result of the formed complex of caffeine–trypsin and theophylline–trypsin. The binding constants and thermodynamic parameters at three different temperatures were obtained. The hydrophobic interaction was the predominant intermolecular forces to stabilize the complex. Results showed that caffeine was the stronger quencher and bound to trypsin with higher affinity than theophylline.Highlights► The fluorescence of trypsin can be quenched by caffeine or theophylline via hydrophobic contacts. ► Caffeine binds to trypsin with higher affinity than theophylline. ► The influence of molecular structure on the binding aspects is reported.

•The interactions between bovine hemoglobin and analogs of DDB have been investigated.•Results reveal that DDB has the strongest affinity for hemoglobin among four compounds.•The van der Waals and hydrogen bonding play major role in the binding process.•The influence of molecular structure on the binding aspects has been investigated.The interaction between bovine hemoglobin and analogs of Biphenyldicarboxylate was investigated by fluorescence, synchronous fluorescence, ultraviolet–vis absorbance, resonance light-scattering spectra and three-dimensional fluorescence spectra at pH 7.40. The quenching mechanism and binding constants were determined by the quenching of bovine hemoglobin fluorescence in presence of analogs. Results showed that the nature of the quenching was of static type. Both the van der Waals and hydrogen bonding played a major role in stabilizing the complex. The distance between donor and acceptors was obtained to be 2.11–2.25 nm according to Förster's theory. The influence of analogs on the conformation of bovine hemoglobin was investigated.

Two novel methods for the determination of kanamycin sulfate (Kan) have been developed. The first method was based on the enhanced fluorescence of thioglycolic acid-capped CdTe quantum dots by Kan in aqueous solutions. The second method was a simple colorimetric method to detect trace amounts of Kan with unmodified gold nanoparticles as the sensing probe. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of Kan between 1.80 × 10−2 μg mL−1 and 8.00 × 10−1 μg mL−1. The linear ranges of the colorimetric sensor for Kan were from 3.75 × 10−3 μg mL−1 to 4.25 × 10−2 μg mL−1 and from 4.40 × 10−2 μg mL−1 to 9.88 × 10−2 μg mL−1, respectively. Comparisons between the two methods were made. Both methods were used for rapid detection of Kan in real samples with satisfactory results.

The interactions of bifendate (DDB) or analogs (Bicyclol, I, II and III) with catalase are analyzed by spectrophotometric methods. The fluorescence spectra results show the intrinsic fluorescence of catalase is strongly quenched by DDB or analogs with a static quenching procedure. The binding constants are obtained at three temperatures. The thermodynamics parameters (ΔH, ΔS, ΔG) indicate the hydrophobic and electrostatic interactions play a major role in the interaction. The results of synchronous fluorescence, UV–vis absorption and three-dimensional fluorescence spectra demonstrate that the microenvironments of Trp residue of catalase are disturbed by the analogs. Thermodynamic results showed that DDB is the strongest quencher and bind to catalase with the highest affinity among five compounds.Graphical abstractThe synchronous fluorescence spectra of CAT in the absence and presence of DDB.Highlights► The interactions between a serious of analogs and catalase have been investigated. ► Results reveal that DDB has the strongest affinity for catalase among five compounds. ► Hydrophobic and electrostatic interactions play major role in the binding process. ► The influence of molecular structure on the binding aspects has been investigated.

The interactions between pepsin and four alkaloids, including caffeine (Caf), aminophylline (Ami), acefylline (Ace), diprophylline (Dip), were investigated by fluorescence, UV–visible absorption, resonance light scattering, synchronous fluorescence spectroscopy and 3D spectroscopy under mimic physiological conditions. The results revealed that Caf (Ami/Ace/Dip) caused the fluorescence quenching of pepsin by the formation of Caf (Ami/Ace/Dip)-pepsin complex. The binding constants and thermodynamic parameters at three different temperatures, the binding locality and the binding power were obtained. The hydrophobic and electrostatic interactions were the predominant intermolecular forces to stabilize the complex. Results showed that aminophylline was the stronger quencher and bound to pepsin with higher affinity than other three alkaloids.Graphical abstractThe synchronous fluorescence spectra of pepsin in the absence and presence of aminophylline (Ami).Highlights► The interactions between pepsin and four alkaloids have been investigated. ► Results reveal that aminophylline has the strongest affinity for pepsin among four compounds. ► Hydrophobic interaction plays major role in the binding process. ► The influence of molecular structure on the binding aspects has been investigated.

•The interactions between bovine hemoglobin and analogs of DDB have been investigated.•Results reveal that DDB has the strongest affinity for hemoglobin among four compounds.•The van der Waals and hydrogen bonding play major role in the binding process.•The influence of molecular structure on the binding aspects has been investigated.The interaction between bovine hemoglobin and analogs of Biphenyldicarboxylate was investigated by fluorescence, synchronous fluorescence, ultraviolet–vis absorbance, resonance light-scattering spectra and three-dimensional fluorescence spectra at pH 7.40. The quenching mechanism and binding constants were determined by the quenching of bovine hemoglobin fluorescence in presence of analogs. Results showed that the nature of the quenching was of static type. Both the van der Waals and hydrogen bonding played a major role in stabilizing the complex. The distance between donor and acceptors was obtained to be 2.11–2.25 nm according to Förster's theory. The influence of analogs on the conformation of bovine hemoglobin was investigated.

Two novel methods for the determination of kanamycin sulfate (Kan) have been developed. The first method was based on the enhanced fluorescence of thioglycolic acid-capped CdTe quantum dots by Kan in aqueous solutions. The second method was a simple colorimetric method to detect trace amounts of Kan with unmodified gold nanoparticles as the sensing probe. Under optimal conditions, the relative fluorescence intensity was linearly proportional to the concentration of Kan between 1.80 × 10−2 μg mL−1 and 8.00 × 10−1 μg mL−1. The linear ranges of the colorimetric sensor for Kan were from 3.75 × 10−3 μg mL−1 to 4.25 × 10−2 μg mL−1 and from 4.40 × 10−2 μg mL−1 to 9.88 × 10−2 μg mL−1, respectively. Comparisons between the two methods were made. Both methods were used for rapid detection of Kan in real samples with satisfactory results.

The interaction between norfloxacin (NFA) and FNC has been investigated by fluorescence and UV-vis absorption spectroscopy. It has been found that static quenching of fluorescence of NFA occurs in the presence of FNC. Hydrophobic interactions play an important role in stabilizing the complex. The binding constant (K), binding site number (n) and corresponding thermodynamic parameters have been determined according to the van't Hoff equation. This method is simple, selective and relatively free of interference from coexisting substances. Under optimal conditions, the relative fluorescence intensity is linearly proportional to the concentration of FNC between 1.29 and 36.20 μg mL−1, with a detection limit of 0.2622 μg mL−1. The recovery of the method is in the range of 97.8–99.9%.