Studies of Interactions between Beta-Cyﬂuthrin and BSA Based on Fluorescence Spectrometry and Ultraviolet Degradation

: Pesticides play a pivotal role in modern agriculture, but their potential environmental and health impacts necessitate a comprehensive understanding of their interactions with biological molecules. Beta-cyﬂuthrin, a widely used synthetic pyrethroid insecticide, is known for its efﬁciency in pest control. However, its interaction with bovine serum albumin (BSA), a crucial transport protein in living organisms, has not been extensively studied. The interaction between beta-cyﬂuthrin, a prominent synthetic pyrethroid insecticide, and bovine serum albumin (BSA) was comprehensively investigated using ﬂuorescence spectrometry. Furthermore, the inﬂuence of ultraviolet (UV) degradation on the interaction parameters was explored, enhancing our understanding of the impact of environmental conditions on this interaction. The Stern–Volmer equation was employed to determine quenching constants, revealing that the ﬂuorescence quenching mechanism primarily involved static quenching. The temperature variations were studied, showing an increase in the binding constant with rising temperature prior to degradation, while post-UV degradation, an inverse correlation between the binding constant and temperature was observed. The thermodynamic parameters were derived through appropriate equations, unveiling the underlying reaction forces. In the absence of degradation, hydrophobic interactions dominated, whereas after UV degradation, interactions shifted to hydrogen bonding and van der Waals forces. The ﬁndings elucidate the nuanced effects of UV degradation on the interaction between beta-cyﬂuthrin and BSA. This study furnishes critical insights that serve as a scientiﬁc foundation for pesticide production and application strategies, accounting for the inﬂuence of UV degradation on the intricate interplay between pesticides and BSA.


Introduce
Beta-cyfluthrin is a kind of pyrethroid.It is developed from the structure change of natural pyrethroids.It has the characteristics of contact and stomach toxicity, wide insecticidal spectrum, rapid knockdown, and long duration [1].Pyrethroid insecticides have been widely used in recent years, so the neurotoxic effects of these pesticides have attracted much attention.Relevant studies have shown that pyrethroid insecticides can accumulate in nerve tissue [2], which may have an impact on the human nervous system and may even cause severe neurotoxic symptoms when the amount of it reaches a certain level [3].Moreover, beta-cyfluthrin is an environmental hormone with a long residual period, which can accumulate in surface water, soil, and food, thus affecting human health [4].The sequence homology between bovine serum albumin (BSA) and human serum albumin (HSA) is 72%, and bovine serum albumin has been well used in scientific research because of its cheapness and easy accessibility [5].
Previous studies have explored the binding interactions between various pesticides and proteins using fluorescence spectrometry, shedding light on the mechanisms and thermodynamics of these interactions.Additionally, research focusing on the effects of environmental stressors, such as UV degradation, on these interactions has grown, reflecting the need to understand how such stressors might alter the behavior of pesticide-protein systems.Qi et al. [6] studied the interaction of paclitaxel and artemisinin on BSA using ultraviolet visible spectroscopy, far-UV CD spectroscopy, and synchronous fluorescence spectroscopy and found that the formed complexes could cause static quenching of BSA.Sharma et al. [7] found the binding and quenching constants for the BSA-rifampicin (an anti-tuberculosis drug) with the steady-state absorption and emission spectroscopies.Dahiya et al. [8] investigated the binding interaction of BSA with a widely used organophosphorous insecticide, chlorpyrifos (CPF), and its stable metabolite, 3,5,6-trichloro-2-pyridinol (TCPy), to provide a comparative analysis of the two molecules by using UV-vis absorption, circular dichroism, and fluorescence spectroscopy.It has been found that both the molecules cause static quenching of BSA.However, there is still relatively little research on the changes in the interaction parameters between pesticides and serum albumin combined with UV degradation.Yuan et al. [9] found that ultrasound (US), ultraviolet irradiation (UV), and combined (US/UV) treatment degraded chlorpyrifos residues in milk by up to 97%.In addition, US/UV treatment that degraded nearly all chlorpyrifos residues had a negligible effect on the nutrients, physicochemical properties, and color of the milk and should, therefore, minimally affect its quality and sensory attributes.By analyzing the impact of degradation on the molecular level of pesticides, the characteristics of degraded pesticides could be explored, which has practical significance for protecting human health.Previous research has reported that dyes, antibiotics, pesticides, and other emerging pollutants have been degraded by photocatalytic degradation.UV illumination played a significant role in visible light-catalyzed reaction due to the superiority of ultraviolet light [10].Therefore, the changes in the interaction between pesticides and bovine serum albumin after ultraviolet degradation are of great interest to us.In this study, fluorescence spectroscopy was used to study the interaction between beta-cyfluthrin and BSA, and ultraviolet degradation of pesticides was carried out to obtain the changes in interaction parameters before and after degradation.By applying established analytical methods and techniques, this research aims to contribute valuable insights into the complex interplay between pesticides and biological molecules, shedding light on potential ecological and health implications and guiding sustainable pesticide practices.

Experimental Sample
Beta-cyfluthrin was purchased from Longxi Plant Protection Co., Ltd.(Dezhou, China).It was a suspension agent with an active ingredient content of 75 g/L.Bovine serum albumin (BSA) was purchased from Feijing Biotechnology Co., Ltd.(Fuzhou, China) and was a white to light-yellow powder with a purity greater than 98%.

Experimental Instrument
The fluorescence spectrophotometer (LS55) purchased from PerkinElmer Co., Ltd.(Waltham, MA, USA) was used to measure fluorescence spectra, and its parameters were set as follows: sampling interval: 0.5 nm; wavelength range: 200-600 nm; and slit width: 10.0 nm.
The water-bath heating instrument was the H.SVX series digital display electric thermostatic water temperature box.The heating method was the closed stainless steel electric heater.The temperature control range was room temperature +5 • C to 100 • C, the temperature resolution was 0.1 • C, and the constant temperature fluctuation was ±0.5 • C.
A low-voltage ultraviolet mercury lamp of the quartz type was selected as the ultraviolet light source, and its light transmittance was greater than 90%.The emission wavelength was set to be 253.7 nm, the power was set as 3 W, the tube voltage was 10 V, and the current was 300 mA.The equipment structure of ultraviolet irradiation degradation is shown in Figure 1, and it contained 5 parts.The numerical label 1 represents the closed system, 2 represents the switching device of the closed system, 3 is the sample pool, 4 is the ultraviolet light source module, and 5 is the control switch of the power supply.
Photonics 2023, 10, x FOR PEER REVIEW 3 of 13 A low-voltage ultraviolet mercury lamp of the quartz type was selected as the ultraviolet light source, and its light transmittance was greater than 90%.The emission wavelength was set to be 253.7 nm, the power was set as 3 W, the tube voltage was 10 V, and the current was 300 mA.The equipment structure of ultraviolet irradiation degradation is shown in Figure 1, and it contained 5 parts.The numerical label 1 represents the closed system, 2 represents the switching device of the closed system, 3 is the sample pool, 4 is the ultraviolet light source module, and 5 is the control switch of the power supply.(2) Ultraviolet degradation and water-bath heating of samples To initiate the experimental process, an optimal quantity of bovine serum albumin (BSA) solid powder was meticulously dissolved in distilled water.This meticulous procedure facilitated the creation of a BSA stock solution characterized by a precisely calibrated concentration of 5 × 10 −7 mol/L.Concurrently, beta-cyfluthrin, the subject of investigation, was systematically dissolved in pure water.To introduce variations in pesticide concentrations for subsequent analysis, the beta-cyfluthrin solutions were subjected to ultraviolet (UV) degradation for distinct periods of time.This methodologically controlled degradation strategy allowed for the generation of a collection of ten standard solution samples.These samples spanned a range of diverse pesticide concentrations, thereby enabling a comprehensive investigation of the interaction dynamics between beta-cyfluthrin and BSA.After thoroughly shaking the mixed solution, the colorimetric tube was put into the water tank for water-bath heating, with the temperatures set at 303 K and 309 K, respectively.After heating for 20 min, the colorimetric tube was taken out, and the fluorescence spectra of the mixture of different concentrations of beta-cyfluthrin and BSA solution was measured by a LS55 fluorescence spectrophotometer.

Experimental Process
(3) Parameters calculation of the interaction between beta-cyfluthrin and BSA After UV light degradation, the equivalent concentration of beta-cyfluthrin was calculated by substituting the measured fluorescence characteristic peak into the concentration prediction model fitted in the first step.Then, the interaction parameters, including the quenching constant, binding constant, number of binding sites, and thermodynamic parameters, were calculated by substituting the pesticide concentration and fluorescence

Experimental Process
(1) Prediction model construction of the beta-cyfluthrin concentration Beta-cyfluthrin was diluted to different concentrations.The peaks of fluorescence spectra of solutions with different concentrations were obtained by a LS55 fluorescence spectrophotometer, and the prediction model of the concentrations of beta-cyfluthrin was able to be established according to the relationship between concentrations and fluorescence peaks.
(2) Ultraviolet degradation and water-bath heating of samples To initiate the experimental process, an optimal quantity of bovine serum albumin (BSA) solid powder was meticulously dissolved in distilled water.This meticulous procedure facilitated the creation of a BSA stock solution characterized by a precisely calibrated concentration of 5 × 10 −7 mol/L.Concurrently, beta-cyfluthrin, the subject of investigation, was systematically dissolved in pure water.To introduce variations in pesticide concentrations for subsequent analysis, the beta-cyfluthrin solutions were subjected to ultraviolet (UV) degradation for distinct periods of time.This methodologically controlled degradation strategy allowed for the generation of a collection of ten standard solution samples.These samples spanned a range of diverse pesticide concentrations, thereby enabling a comprehensive investigation of the interaction dynamics between beta-cyfluthrin and BSA.After thoroughly shaking the mixed solution, the colorimetric tube was put into the water tank for water-bath heating, with the temperatures set at 303 K and 309 K, respectively.After heating for 20 min, the colorimetric tube was taken out, and the fluorescence spectra of the mixture of different concentrations of beta-cyfluthrin and BSA solution was measured by a LS55 fluorescence spectrophotometer.
(3) Parameters calculation of the interaction between beta-cyfluthrin and BSA After UV light degradation, the equivalent concentration of beta-cyfluthrin was calculated by substituting the measured fluorescence characteristic peak into the concentration prediction model fitted in the first step.Then, the interaction parameters, including the quenching constant, binding constant, number of binding sites, and thermodynamic parameters, were calculated by substituting the pesticide concentration and fluorescence intensity into the Stern-Volmer equation, the double logarithm equation, and the thermodynamic equation, respectively.

Content Prediction Modeling of Beta-Cyfluthrin
To accurately predict the equivalent concentrations of beta-cyfluthrin subsequent to UV degradation, the formulation of a robust concentration prediction model was imperative.In pursuit of this objective, beta-cyfluthrin underwent successive dilutions to encompass a spectrum of concentrations.Before measuring the fluorescence spectrum of the sample, the optimal excitation wavelength needed to be determined first.Different excitation wavelengths were set, and the corresponding fluorescence spectra of beta-cyfluthrin were measured.It was found that when the excitation spectrum was 272 nm, the fluorescence intensity was relatively high, and the spectral image was also relatively stable and smooth.The spectrum presented the best effect comprehensively.Therefore, 272 nm was chosen as the excitation wavelength for the beta-cyfluthrin.
Subsequently, the fluorescence spectra of these distinct concentration solutions were meticulously recorded through the employment of the LS55 fluorescence spectrophotometer.Upon examination of the obtained data, which is depicted in Figure 2A, a discernible trend emerged.Specifically, the fluorescence intensity exhibited a consistent escalation in direct proportion to the augmented beta-cyfluthrin concentration.Notably, a distinctive fluorescence peak materialized at 305 nm, corroborating the characteristic fingerprint of beta-cyfluthrin.In addition, the fluorescence characteristic peak of the research object was located at 305 nm, so fluorescence intensity within the range of 295-340 nm was selected for display in Figure 2A, while the spectra at the other bands were not very related to the characteristics of the research object.For example, the Interference peak caused by the excitation wavelength was at 272 nm, and the fluorescence intensity was low in the range of 340-600 nm, which did not change significantly with sample concentration and did not participate in content prediction modeling; therefore, the fluorescence spectrum information outside the 295-340 nm range was not displayed.This distinctive fluorescence peak, observed at 305 nm, emerged as a definitive marker of beta-cyfluthrin.Consequently, this pivotal observation served as the cornerstone for the subsequent development of the pesticide concentration prediction model, ultimately facilitating the accurate anticipation of beta-cyfluthrin concentrations post-UV degradation.
intensity into the Stern-Volmer equation, the double logarithm equation, and the thermodynamic equation, respectively.

Content Prediction Modeling of Beta-Cyfluthrin
To accurately predict the equivalent concentrations of beta-cyfluthrin subsequent to UV degradation, the formulation of a robust concentration prediction model was imperative.In pursuit of this objective, beta-cyfluthrin underwent successive dilutions to encompass a spectrum of concentrations.Before measuring the fluorescence spectrum of the sample, the optimal excitation wavelength needed to be determined first.Different excitation wavelengths were set, and the corresponding fluorescence spectra of beta-cyfluthrin were measured.It was found that when the excitation spectrum was 272 nm, the fluorescence intensity was relatively high, and the spectral image was also relatively stable and smooth.The spectrum presented the best effect comprehensively.Therefore, 272 nm was chosen as the excitation wavelength for the beta-cyfluthrin.
Subsequently, the fluorescence spectra of these distinct concentration solutions were meticulously recorded through the employment of the LS55 fluorescence spectrophotometer.Upon examination of the obtained data, which is depicted in Figure 2A, a discernible trend emerged.Specifically, the fluorescence intensity exhibited a consistent escalation in direct proportion to the augmented beta-cyfluthrin concentration.Notably, a distinctive fluorescence peak materialized at 305 nm, corroborating the characteristic fingerprint of beta-cyfluthrin.In addition, the fluorescence characteristic peak of the research object was located at 305 nm, so fluorescence intensity within the range of 295-340 nm was selected for display in Figure 2A, while the spectra at the other bands were not very related to the characteristics of the research object.For example, the Interference peak caused by the excitation wavelength was at 272 nm, and the fluorescence intensity was low in the range of 340-600 nm, which did not change significantly with sample concentration and did not participate in content prediction modeling; therefore, the fluorescence spectrum information outside the 295-340 nm range was not displayed.This distinctive fluorescence peak, observed at 305 nm, emerged as a definitive marker of beta-cyfluthrin.Consequently, this pivotal observation served as the cornerstone for the subsequent development of the pesticide concentration prediction model, ultimately facilitating the accurate anticipation of beta-cyfluthrin concentrations post-UV degradation.To unravel the intricate connection between beta-cyfluthrin concentration and the corresponding fluorescence intensity, a meticulous analysis entailing exponential fitting was undertaken.This systematic exploration sought to ascertain the exponential correlation characterizing the concentration of the solution and the distinctive peak intensity-emerging at 305 nm-of beta-cyfluthrin.The outcomes of this analytical endeavor, as depicted in Figure 2B, revealed a pronounced exponential association between the concentration of beta-cyfluthrin and the characteristic peak intensity observed at 305 nm.This correlation was characterized by an impressive correlation coefficient, standing at an elevated value of 0.9998.This commendable coefficient attested to the remarkable fidelity of this exponential relationship, substantiating its aptitude for prediction and analysis.
To verify the content prediction model of beta-cyfluthrin, ten beta-cyfluthrin solutions with different concentrations were prepared, as shown in Table 1.The fluorescence spectrum detection was carried out under the same experimental conditions, and the fluorescence intensity corresponding to 305 nm was substituted into Equation (1) to calculate the equivalent concentration of the beta-cyfluthrin.Then, the recovery parameter was able to be calculated according to its actual concentration.The average recovery rate was 100.08%, and the relative standard deviation was 0.8%, which proved the correctness of the fitted exponential model and showed that it can be used to calculate the equivalent content of the beta-cyfluthrin after UV degradation.A total of ten distinct samples comprising mixed solutions containing both betacyfluthrin and BSA were meticulously prepared.Table 2 delineates the specific concentrations of beta-cyfluthrin within these solutions prior to any degradation process.Subsequently, these mixed solutions were subjected to controlled ultraviolet (UV) irradiation for durations of 10 min and 20 min, respectively.Following the degradation treatment, the fluorescence spectra of these mixed solutions were meticulously captured using the LS55 fluorescence spectrophotometer.By leveraging Equation (1), which derives from the exponential relationship established between beta-cyfluthrin concentration and fluorescence intensity at 305 nm, it became feasible to predict the effective concentration of beta-cyfluthrin within these mixed solutions.This predictive approach, based on the substitution of the recorded fluorescence intensity values, facilitated a precise estimation of beta-cyfluthrin concentrations following UV degradation.y = −1397.39782× exp(−x/2.68209× 10 −4 ) + 1432.79184 (1) After calculation, the equivalent concentrations of beta-cyfluthrin after UV degradation are shown in Table 2. Ayare et al. [11] found that when the concentration of tricyclazole is the same, the longer the time of ultraviolet irradiation of the sample, the higher the extent of degradation, indicating that the concentration of tricyclazole will decrease with the increase in ultraviolet degradation time.From the calculation results, it can be found that the longer the degradation time, the lower the effective components of the beta-cyfluthrin.

Fluorescence Quenching of Beta-Cyfluthrin on BSA
The inherent fluorescence emitted by bovine serum albumin (BSA) predominantly emanates from amino acid residues such as tyrosine and tryptophan, a phenomenon that is susceptible to alterations in the adjacent microenvironment.Consequently, modifications in the microenvironment can induce shifts in the fluorescence intensity of BSA's intrinsic fluorescence.
The optimum excitation wavelength of BSA was 280 nm, according to experimental measurements.Since the main component of the mixture of BSA and beta-cyfluthrin is BSA, the excitation wavelength of the mixture was set to 280 nm. Figure 3A,B elucidates the fluorescence quenching spectra resulting from the interaction between beta-cyfluthrin and BSA at distinct concentrations, examined at temperatures of 303 K and 309 K.The outcomes of these analyses uncovered a consistent trend.Specifically, as the concentrations of beta-cyfluthrin increased, a discernible reduction in the fluorescence intensity of BSA was observed.This systematic attenuation of fluorescence intensity is indicative of regular quenching, implying that beta-cyfluthrin has the capacity to mitigate the fluorescence emission of BSA.Importantly, despite this fluorescence quenching phenomenon, the characteristic shape of BSA's fluorescence spectrum remained unaltered.This preservation of the fluorescence spectrum's profile signifies that while beta-cyfluthrin imparts quenching effects, it does not induce substantial changes in the overall structure of BSA's fluorescence characteristics.Some studies showed that when the maximum emission peak of BSA was redshifted, the hydrophobicity of the microenvironment of amino acid residues decreased, and the polarity increased.The maximum emission peak shifted blue, indicating that hydrophobicity increased, and polarity decreased in the microenvironment of amino acid residues [13].The following experimental studies all found a blue shift in the maximum emission peak of BSA, indicating that beta-cyfluthrin increased the hydrophobicity and decreased This observation corroborates the notion of an interactive engagement between betacyfluthrin and BSA, substantiating the existence of an interaction between these two entities [12].The intricate interplay between the pesticide and the protein engenders fluorescence quenching without significantly perturbing BSA's intrinsic spectral attributes, indicating the dynamic nature of their association.
Some studies showed that when the maximum emission peak of BSA was redshifted, the hydrophobicity of the microenvironment of amino acid residues decreased, and the polarity increased.The maximum emission peak shifted blue, indicating that hydrophobicity increased, and polarity decreased in the microenvironment of amino acid residues [13].
The following experimental studies all found a blue shift in the maximum emission peak of BSA, indicating that beta-cyfluthrin increased the hydrophobicity and decreased the polarity of the microenvironment in which amino acid residues were located.In Figure 3, the fluorescence peak position of BSA shows a significant blue shift, shifting from 344 nm to 335 nm at 303 K and from 344 nm to 333 nm at 309 K. Figures 4 and 5 show the fluorescence quenching spectra of beta-cyfluthrin on BSA after 10 min and 20 min of UV degradation, respectively.It can be seen that the degree of blue shift after ultraviolet degradation is significantly weakened, compared with that before degradation.The results showed that beta-cyfluthrin could change the microenvironment around the tryptophan residue chromophobe of BSA, making it become hydrophobic.However, after UV degradation, its degradation components inhibited this change, which may be a change in structure that reduced the toxicity.Ben Salem et al. [14] confirmed the hydrolysis of the chloropyrifos aliphatic chain after ionizing radiation and UV treatment.Some studies showed that when the maximum emission peak of BSA was redshifted, the hydrophobicity of the microenvironment of amino acid residues decreased, and the polarity increased.The maximum emission peak shifted blue, indicating that hydrophobicity increased, and polarity decreased in the microenvironment of amino acid residues [13].The following experimental studies all found a blue shift in the maximum emission peak of BSA, indicating that beta-cyfluthrin increased the hydrophobicity and decreased the polarity of the microenvironment in which amino acid residues were located.In Figure 3, the fluorescence peak position of BSA shows a significant blue shift, shifting from 344 nm to 335 nm at 303 K and from 344 nm to 333 nm at 309 K. Figures 4 and 5 show the fluorescence quenching spectra of beta-cyfluthrin on BSA after 10 min and 20 min of UV degradation, respectively.It can be seen that the degree of blue shift after ultraviolet degradation is significantly weakened, compared with that before degradation.The results showed that beta-cyfluthrin could change the microenvironment around the tryptophan residue chromophobe of BSA, making it become hydrophobic.However, after UV degradation, its degradation components inhibited this change, which may be a change in structure that reduced the toxicity.Ben Salem et al. [14] confirmed the hydrolysis of the chloropyrifos aliphatic chain after ionizing radiation and UV treatment.The interaction between solvent molecules and fluorescent substances leads to the reduction in fluorescence intensity of fluorescent substances.This phenomenon is called fluorescence quenching, which can be divided into static quenching and dynamic quenching.The weak binding between the ground-state fluorescent molecules and the quencher generates a complex, and the phenomenon where the complex completely quenches the The interaction between solvent molecules and fluorescent substances leads to the reduction in fluorescence intensity of fluorescent substances.This phenomenon is called fluorescence quenching, which can be divided into static quenching and dynamic quenching.The weak binding between the ground-state fluorescent molecules and the quencher generates a complex, and the phenomenon where the complex completely quenches the fluorescence is called static quenching, while dynamic quenching is mainly characterized by the collision between the excited-state molecules of the fluorescent substance and the quencher molecules [15].The quenching type can be determined by the following two methods: (1) Determine the quenching type based on the system changes caused by temperature changes.In dynamic quenching, molecular diffusion plays a dominant role, so the quenching constant increases with the increase in temperature.For static quenching, stability plays a dominant role, due to the generation of new substances, and an increase in temperature will reduce the stability of the complex.Therefore, the quenching rate constant decreases with the increase in temperature.(2) The maximum collision quenching rate constant of various quenching agents on biological macromolecules is 2 × 10 10 mol/(L * s).If the fluorescence quenching rate constant of the quenching agent on BSA is greater than this value, it can be inferred that the type of quenching is not dynamic quenching but static quenching [16].Fluorescence quenching can be analyzed by the Stern-Volmer Equation ( 2): [17] F where F 0 and F are the fluorescence intensities of the fluorescent substance before and after adding the quenching agent; K q is the quenching rate constant in the bimolecular quenching process; τ 0 is the average fluorescence lifetime of fluorescent substances without quencher molecules (10 −8 s for most biomolecules); Q is the concentration of quencher molecules; and K sv is the quenching constant.
According to the beta-cyfluthrin concentration Q, the fluorescence intensities F 0 and F corresponding to BSA before and after adding pesticides, the parameters (K sv , K q ), and correlation coefficients (R) of the Stern-Volmer equation at 303 K and 309 K can be calculated, respectively.The calculation results are shown in Table 3.

Temperature (K)
Degradation Time (min) K sv (L * mol −1 ) K q (L * mol −1 * s Shahabadi et al. [18] explored the binding interaction of a cobalt (III) complex containing a ligand with human serum albumin (HSA) and found that increasing temperature decreased K q and K sv , and the K q values obtained were greater than the highest scattering collisional quenching constant for quenching the collision; therefore, the type of quenching was clearly static quenching.It can be seen from Table 3 that the quenching constants of the combination of beta-cyfluthrin and BSA increased with the increase in temperature, but K q was greater than the maximum collision quenching rate constant 2 × 10 10 M −1 S −1 , so it can be judged that the quenching type was mainly static quenching.The fluorescence quenching phenomenon of the interaction between beta-cyfluthrin and BSA still existed, indicating that the complex formed by the two will not disappear due to ultraviolet degradation or increasing temperature [19].Paz et al. [20] also encountered a similar situation where Ksv was obtained for the interaction with albumins; the imidazole interaction BSA:P1 increased with the increase in temperature, and K q was greater than 2 × 10 10 M −1 S −1 .By calculating the parameters, they confirmed that the highest percentage was from the static process rather than the dynamic mechanism for the assayed proportion albumin:ligand.In addition, it can be observed from the calculation results that as the UV degradation time was prolonged, the quenching constant also gradually increased.

Binding Constants and Number of Binding Sites for the Interaction between Beta-Cyfluthrin and BSA
According to the above analysis results, the fluorescence quenching of beta-cyfluthrin and BSA belongs to static quenching.The binding constant and number of binding sites can be further obtained by applying the following double logarithmic Equation ( 3): [21,22] lg [(F where F 0 and F represent the fluorescence intensities of the BSA before and after adding the beta-cyfluthrin, respectively.K A is the binding constant, and n is the number of binding sites between beta-cyfluthrin and BSA.Q represents concentration of beta-cyfluthrin. With the value of lg[(F 0 − F)/F] as the vertical coordinate and the value of lg[Q] as the horizontal coordinate, the corresponding slope of the line is the number of binding sites (N), and the negative logarithmic value of the line intercept is the binding constant (K A ).The calculation results are shown in Table 4, and R is the correlation coefficient.Table 4 shows that in the case of non-degradation, the binding constant will increase with increasing temperature; however, after degradation, the binding constant decreases with the increase in temperature.For example, 20 min after UV degradation, the binding constant decreases from 8.63 × 10 3 to 1.59 × 10 3 .This indicates that the effective concentration of beta-cyfluthrin after degradation is low, and its binding capacity with BSA also gradually decreases [23], while the increase in temperature accelerates this trend.In addition, at the same temperature, the binding constant increased first and then decreased with the deepening of degradation, and the corresponding number of binding sites also showed the same trend.However, their values were all around 1, indicating that a binding site could be formed after the combination of beta-cyfluthrin and BSA [24].However, the binding capacity would continue to decline with the further extension of degradation time.This phenomenon may be attributed to the fact that a moderate amount of ultraviolet irradiation can help the binding of beta-cyfluthrin and BSA, but excessive ultraviolet irradiation will result in the destabilization of the complex.

Thermodynamic Parameters and Force Types of Interaction between Beta-Cyfluthrin and BSA
Pesticides and proteins bind through different types of forces, which can be divided into hydrophobic forces, hydrogen bonds, van der Waals forces, and electrostatic attraction [25].Thermodynamic parameters such as enthalpy change (∆H), entropy change (∆S), and Gibbs free energy (∆G) can determine the characteristics of the interaction.These parameters can be calculated by the Van't Hoff equation and the thermodynamic equation as follows [26]: Equations ( 6) and ( 7) can be obtained through the simplification of the above two equations: where K 1 and K 2 correspond to the binding constants of T 1 (303 K) and T 2 (309 K), respectively.R is the general gas constant (8.314J/(mol * K)).∆H is the enthalpy change, ∆S is the entropy change, and ∆G is the Gibbs free energy.The specific calculation results are shown in Table 5.Table 5 shows that before degradation, ∆H > 0, and ∆S > 0, indicating that hydrophobic interaction is the main force [27].∆G < 0 indicates that the binding between beta-cyfluthrin and BSA is spontaneous.∆H > 0 indicates that the interaction between the two is an endothermic reaction, and temperature rise will be conducive to the combination of the two.After ultraviolet degradation, ∆H < 0, and ∆S < 0, indicating that the interactions between the two are hydrogen bond and van der Waals force [28].The observation of a negative enthalpy change (∆H < 0) subsequent to ultraviolet degradation signifies that the binding reaction between beta-cyfluthrin and BSA becomes exothermic.Strikingly, this indicates that cooling conditions foster the progression of the binding reaction-a departure from the situation prior to degradation.This temperature-dependent variation aligns harmoniously with the established trends dictated by the alteration in binding constants.Despite the transformation in enthalpy, the Gibbs free energy change (∆G) retained its negative value, signifying that the fundamental spontaneous nature of the binding mode endured, unaffected by ultraviolet degradation.This steadfast consistency underscores that the degradation process did not precipitate a shift in the inherent binding propensity between beta-cyfluthrin and BSA.

Conclusions
The fluorescence spectra analysis unequivocally revealed that beta-cyfluthrin effectively quenches the intrinsic fluorescence of BSA, with the prevailing quenching mechanism attributed predominantly to static quenching.Notably, the behavior of the binding constant exhibited distinct patterns pre-and post-degradation.In the absence of degradation, an ascending trend with rising temperature was observed, while degradation induced a counterintuitive decrease in the binding constant with elevated temperatures.Additionally, within the context of degradation, as degradation time was extended, the binding constant showcased an initial increase, followed by a subsequent decrease.This phenomenon emanated from the diminishing effective concentration post-degradation, contributing to reduced binding capacity.Before degradation, hydrophobic forces took precedence in driving the interaction between beta-cyfluthrin and BSA.However, UV degradation catalyzed a shift in the driving forces, with hydrogen bonding and van der Waals interactions emerging as dominant factors.This transformation underscores the profound effects of UV degradation on the intimate interaction between beta-cyfluthrin and BSA.In addition, this investigation intricately unravels the microscopic implications of UV degradation on the intricate interplay between pesticides and bovine serum albumin.The disclosed findings stand as a pivotal contribution to the comprehension of the toxicity mechanisms associated with pesticides, equipping us with crucial insights to further our understanding of the potential environmental and health ramifications.

Figure 1 .
Figure 1.Simple structure of the ultraviolet irradiation experiment.

( 1 )
Prediction model construction of the beta-cyfluthrin concentration Beta-cyfluthrin was diluted to different concentrations.The peaks of fluorescence spectra of solutions with different concentrations were obtained by a LS55 fluorescence spectrophotometer, and the prediction model of the concentrations of beta-cyfluthrin was able to be established according to the relationship between concentrations and fluorescence peaks.

Figure 1 .
Figure 1.Simple structure of the ultraviolet irradiation experiment.

Table 1 .
Content prediction and recovery calculation of beta-cyfluthrin.

Table 2 .
The concentration of beta-cyfluthrin before and after degradation.

Table 4 .
Binding constants and number of binding sites of BSA with beta-cyfluthrin.

Table 5 .
Thermodynamic parameters of BSA binding with beta-cyfluthrin.