Molecular and technical aspects on the interaction of serum albumin with multifunctional food preservatives

Characterization of perceptual interactions among aroma compounds found in Rose damascena and Angelica dahurica root essential oil with threshold, S-curve, σ-τ plot and molecular docking

The study investigated the perceptual interaction between two types of Rose damascena essential oil and two types of Angelica dahurica root essential oil. Using gas chromatography-olfactometer (GC-O) and gas chromatography-mass spectrometer (GC-MS), 24 and 25 aromatic compounds in Rose damascena essential oil and Angelica dahurica root essential oil were identified and quantified, respectively. Based on flavor dilution (FD) values and odor activity values (OAVs), 10 important aroma compounds in Rose damascena essential oil and 6 in Angelica dahurica root essential oil were identified. The perceptual interactions between these aroma compounds were explored by using the threshold method, S-curve, and σ-τ plot. Additionally, molecular docking analysis revealed changes in binding energy and binding sites. Notably, when aroma compounds shared similar structures and fragrances, they exhibited additive or synergistic effects. Conversely, dissimilar compounds showed different interactions. The molecular docking results aligned with our experimental findings. Overall, our study demonstrates that the threshold method, S-curve, σ-τ plot, and molecular docking enhance our understanding of aroma compound perceptual interactions between Rose damascena essential oil and Angelica dahurica root essential oil. These insights provide a theoretical foundation and practical guidance for improving the aroma of Angelica dahurica root essential oil and studying perceptual interactions among essential oils.

Binding interaction of sodium benzoate, potassium sorbate and sodium dihydrogen citrate with BSA as food preservatives: in Vitro analysis and computational studies

Advanced glycation end products (AGEs) are obtained intermediate from nonenzymatic reactions between reducing sugars and proteins, lipids, or nucleic acids and it's associated with diabetic complications. Today, potassium sorbate (PS), sodium citrate (CIT) and sodium benzoate (SB) were widespread used as food preservatives that can easily enter biological matrices. Here, the interaction between glycosylation Bovine Serum Albumin (BSA) and food preservatives individually and combination of two and three was studied by biochemical and simulation analysis. The results revealed that an increase in absorption and fluorescent intensity in all treated groups. The most carbonyl and glycosylated compounds were observed in the treatment with PS and its combined groups with two preservatives. Treatment with three preservatives alone or combination caused a significant increase in red blood cell hemolysis and MDA level (p < 0.05). The results of the in vitro experiments were in line with the docking studies and the interaction of the compounds with albumin was observed in important subdomain of BSA that show the stability of the BSA-ligand complex. Simultaneous treatment and the combination of two or three food preservatives cause their synergistic effect in possible harm to the body. In addition, the molecular docking experiment suggests that Sodium Benzoate, Potassium Sorbate and Sodium Dihydrogen Citrate can interact with BSA.

In Vitro Cytotoxicity and Mechanistic Investigation of Quinazolin-4(1H)-One Linked Coumarin as a Potent Anticancer Agent

Quinazolinone-coumarin conjugates synthesized through Late-Stage Functionalization approach are evaluated for their in vitro biological activity for 60 human cancer cell lines representing nine different cancer types. Among the synthesized compounds, eight displayed significant growth inhibitory activity across a spectrum of cancer types, with compound 23 demonstrating particularly notable cytotoxicity. Further investigation involved a five-dose assay of compound 23 against NCI-60 cancer cell lines, revealing its efficacy at different concentrations. Additionally, binding studies elucidated its interaction with Human Serum Albumin (HSA) and DNA. The results indicated a strong binding affinity of 23 with HSA, evidenced by a high binding constant (2.26 × 105 M-1). Moreover, its interaction with DNA occurred via intercalation, specifically between the base pairs of DNA strands, with a binding constant of 5.51 × 104 M-1. This suggests that compound 23 has the ability to bind to both DNA and transport proteins, making it a promising pharmacophore with potential therapeutic applications.

Elucidating the effects of hofmeister salts on the formation mechanism and biocompatibility of lysozyme-hyaluronic acid complexes

This study aimed to investigate the morphologies, biocompatibility, and formation mechanism of lysozyme-hyaluronic acid complexes in the presence of various Hofmeister salts. During the complexation of lysozyme (Lys) and hyaluronic acid (HA), salts can control the formation of colloidal nanoparticles, amyloid-like aggregates, and amorphous aggregates. Circular dichroism spectra revealed that the α-helix content of Lys involved in complexation significantly increased from 21.40 % to 34.19 %, whereas the β-sheet content significantly decreased from 38.65 % to 24.42 % with increasing salt concentration. The fluorescence spectra indicated that the number of binding sites for HA and Lys decreased from 2.19 to 0.63 as the salt concentration increased from 0 to 300 mM, which was consistent with the different anion-specific effects (NaCl < NaBr < NaI). Interestingly, in vitro experiment results demonstrated that colloidal nanoparticles and amorphous aggregates have good biocompatibility, with NCM460 cell viability exceeding 85.92 %, whereas amyloid like aggregates exhibit certain cytotoxicity, with cell viability significantly reduced to 50.47 %. Overall, these findings provide a better understanding of the conformational changes of Lys involved in complexation with HA in the presence of salts, expanding its application in the food and pharmaceutical industries.

A unique implementation of Hantzsch reaction for determination of natamycin in Yoghurt: Hyphenated with Box-Behnken-design for optimization

This study aims to develop a novel and selective method for the detection of natamycin (E235) in yoghurt. The suggested method adopts an application of Hantzsch reaction to turn on the fluorescence behavior of natamycin (blue fluorescence), allowing its sensitive and selective determination in yoghurt samples without any overlapping at 485 nm. The originality of the research lies in the fact that this application takes place for the first time, also the detection (LOD) and quantification (LOQ) limits were very low (0.02 and 0.06μg mL-1, respectively) with a linear concentration range of 0.1-1.0 μgmL-1. Moreover, the developed method was employed for the detection of E235 in yoghurt sample with a good recoveries (98.80 ± 1.20-99.20 ± 1.15 (%), over a concentration range of 0.5-1.0 μgmL-1, (LOD = 0.04 and LOQ = 0.12 μgmL-1). Furthermore, the specificity and convenient application of our intended method is an attempt to determine E235 in milk anddairy products with easily followable steps.

Molecular insights into the interactions of theaflavin and epicatechin with different lipid bilayer membranes by molecular dynamics simulation

At present, consumers increasingly favored the natural food preservatives with fewer side-effects on health. The green tea catechins and black tea theaflavins attracted considerable interest, and their antibacterial effects were extensively reported in the literature. Epicatechin (EC), a green tea catechin without a gallate moiety, showed no bactericidal activity, whereas the theaflavin (TF), also lacking a gallate moiety, exhibited potent bactericidal activity, and the antibacterial effects of green tea catechins and black tea theaflavins were closely correlated with their abilities to disrupt the bacterial cell membrane. In our present study, the mechanisms of membrane interaction modes and behaviors of TF and EC were explored by molecular dynamics simulations. It was demonstrated that TF exhibited markedly stronger affinity for the POPG bilayer compared to EC. Additionally, the hydrophobic interactions of tropolone/catechol rings with the acyl chain part could significantly contribute to the penetration of TF into the POPG bilayer. It was also found that the resorcinol/pyran rings were the key functional groups in TF for forming hydrogen bonds with the POPG bilayer. We believed that the findings from our current study could offer useful insights to better understand the stronger antibacterial effects of TF compared to EC.

Associations of exposure to bisphenol-A or parabens with markers of liver injury/function among US adults in NHANES 2011-2016

BACKGROUND

Bisphenol-A (BPA) and parabens are common endocrine-disrupting compounds (EDCs) that are used extensively in consumer products worldwide and are widely found in the environment.

OBJECTIVE

The purpose of this study was to comprehensively explore the correlations between urinary BPA/parabens levels and liver injury/function markers.

METHODS

In this cross-sectional study, we used National Health and Nutrition Examination Survey (NHANES) data from 2011 to 2016. The exposure variables were urinary BPA and four urinary parabens [methylparaben (MPB), ethylparaben (EPB), propylparaben (PPB), and butylparaben (BPB)], while the outcome variables were indicators of liver function/injury [alanine aminotransferase (ALT), aspartate aminotransferase (AST), AST/ ALT, albumin (ALB), total protein (TP), total bilirubin (TBIL), alkaline phosphatase (ALP), and the fibrosis-4 index (FIB-4)]. Multiple linear regression and weighted quantile sum (WQS) regression analyses were applied to explore the relationships between the individual/combined exposure variables and the liver injury/function indicators, respectively. Furthermore, stratified analysis was employed to detect the associations influenced by age and sex.

RESULTS

A total of 2,179 adults were eligible for the present analysis. Multivariate linear regression analysis revealed positive associations of EPB with AST, ALT, TP, and FIB-4 scores and negative associations of BPA with TP and ALB. The effects of urinary parabens on adverse outcomes in the liver (AST and ALT) were significant in the female and middle-aged subgroups. In addition, the WQS analysis revealed that the mixture of four compounds was negatively associated with ALB. BPA had the greatest effect on the serum ALB concentration (weight = 0.688).

IMPACT

Our present study provided novel evidence of significant associations between BPA or certain parabens and numerous markers of liver injury/function indicators. We found that higher urinary BPA concentrations were associated with worse liver function. Exposure to high EPB/PPB ratios was significantly associated with biomarkers of liver injury.

Ratio-fluorescence detection of tert-butylhydroquinone based on non-conjugated polymer dots and gold nanoclusters

A novel ratiometric fluorescent probe based on non-conjugated polymer dots (NCPDs) and gold nanocluster (AuNCs) was constructed to determine tert-butylhydroquinone (TBHQ). The probe exhibited dual emission peaks at 480 nm and 630 nm under 370 nm excitation. The fluorescence of AuNCs was quenched by TBHQ due to strong electrostatic interactions, whereas the emission of NCPDs increased. The ratio of fluorescence intensity at 480 nm to 630 nm (F480 / F630) was monitored as analytical signal response. The probe have been utilized for the detection of TBHQ with good linear relationship in the range of 0.2 to 60 μg/mL. The limit of detection (LOD) and the limit of quantitation (LOQ) were 0.048 μg/mL and 0.159 μg/L, respectively. Three levels of spiked-in TBHQ concentrations were obtained with recovery rates from 80 % to 102 %. The present study provided an effective ratiometric fluorescence method for selective screening of TBHQ in food samples.

Effects of potassium sorbate on systemic inflammation and gut microbiota in normal mice: A comparison of continuous intake and washout period

Potassium sorbate (PS) is a widely used food preservative in the field of food industry. However, the effects of continuous intake and washout period of PS on host health are still unclear. In this study, to investigate long-term effect and after-effect of different concentrations and time points of PS, healthy mice were orally exposed to 150 mg/kg, 500 mg/kg and 1000 mg/kg of PS for 10 weeks, and washout treatment for another 5 weeks, respectively. The results indicated that PS intake for 10 weeks had no obvious effects on organs and adipose tissue, nor did it noteworthily interfere with glucolipid metabolism in the serum. However, it caused inflammatory cell infiltration in the liver, increased serum interleukin (IL)-1β level, changed abundances of gut microbiota but failed to promote the production of short chain fatty acids in the gut. After washout period for 5 weeks, liver inflammation and IL-1β level were decreased, and gut environment developed towards a healthier condition. Specifically, PS washout significantly increased abundance of Lachnospiraceae_NK4A136_group and the production of isobutyric acid. This study confirmed washout period eliminated negative effects from continuous intake of PS, which provided positive evidence for its safety.

Potential of Syzygnium polyanthum as Natural Food Preservative: A Review

Food preservation is one of the strategies taken to maintain the level of public health. Oxidation activity and microbial contamination are the primary causes of food spoilage. For health reasons, people prefer natural preservatives over synthetic ones. Syzygnium polyanthum is widely spread throughout Asia and is utilized as a spice by the community. S. polyanthum has been found to be rich in phenols, hydroquinones, tannins, and flavonoids, which are potential antioxidants and antimicrobial agents. Consequently, S. polyanthum presents a tremendous opportunity as a natural preservative. This paper reviews recent articles about S. polyanthum dating back to the year 2000. This review summarizes the findings of natural compounds presented in S. polyanthum and their functional properties as antioxidants, antimicrobial agents, and natural preservatives in various types of food.

Unveiling the binding details and esterase-like activity effect of methyl yellow on human serum albumin: spectroscopic and simulation study

The food sector uses methyl yellow (MY) extensively as a colorant. The primary transporter in vivo that influences MY absorption, metabolism, distribution, and excretion is human serum albumin (HSA). Exploring the binding process and looking at how HSA and MY work physiologically at the molecular level is therefore very important. Experiments using steady-state fluorescence and fluorescence lifetimes proved that HSA and MY's quenching mechanisms were static. The HSA-MY complex's binding constant was estimated using thermodynamic parameters to be around 10⁴ M^-1. The hydrophobic forces were a major factor in the binding process, as evidenced by the negative ΔG, positive ΔH, and ΔS, which suggested that this contact was spontaneous. Site tests showed that MY linked to HSA's site I. Circular dichroism and three-dimensional fluorescence analysis revealed that the 1.33% α-helix content dropped and the amino acid microenvironment altered. While HSA's protein surface hydrophobicity decreased when engaging MY, the binding of MY to HSA reduced in the presence of urea. The stability of the system was assessed using molecular modeling. Additionally, HSA's esterase-like activity decreased when MY was present, and Ibf/Phz affected the inhibition mechanism of MY on HSA. These findings offer a distinctive perspective for comprehending the structure and functioning of HSA and evaluating the safety of MY.

Occurrence and profile characteristics of environmental phenols in human urine from a rural area in Northwestern China

Many environmental phenols, such as bisphenols, benzophenones and parabens, are known as endocrine disruptors and can adversely affect human health. However, the knowledge of human exposure to common environmental phenols in Chinese rural areas is insufficient. In this context, 181 urine samples were collected from participants in a rural area in Northwest China and were analyzed for nine bisphenols, three benzophenones and four parabens. Bisphenol A (BPA), bisphenol S, benzophenone-1 (BP-1), benzophenone-3 (BP-3), 4-hydroxybenzophenone, methylparaben (MeP), ethylparaben and propylparaben (PrP) were detected in more than 50% of the urine samples, with median concentrations of 0.938 ng/mL, 0.0111 ng/mL, 0.191 ng/mL, 1.30 ng/mL, 0.0320 ng/mL, 25.9 ng/mL, 4.31 ng/mL and 1.94 ng/mL, respectively. A significant positive correlation was observed between BP-1 and BP-3, as well as between MeP and PrP, indicating metabolic transformation and combined use, respectively. The concentrations of MeP and PrP in females were significantly higher than those in males, suggesting that females were exposed to more MeP and PrP than males. Urinary concentrations of BPA, BP-3, MeP and PrP could be influenced by age. Other demographic information, such as annual household income, education and occupation was not associated with the exposure level of the targeted phenols in adults. The estimated daily intakes of the analytes except BPA were all below their respective tolerable/acceptable daily intake levels. This study profiles the demographic differences in the exposure to environmental phenols in general populations from rural areas and provides information on risk assessments.

A Pilot Study on the Concentration, Distribution and Bioaccumulation of Polybrominated Diphenyl Ethers (PBDEs) in Tissues and Organs of Grassland Sheep

Polybrominated diphenyl ether (PBDE) concentrations in various tissues and organs of grassland sheep from Inner Mongolia, China, were determined. The abilities of PBDEs binding to ovine serum albumin (OSA) and Cytochrome P450 enzyme (CYP3A24) were assessed by fluorescence spectroscopy and molecular docking simulations. The PBDE concentrations in the sheep tissue and organ samples were 33.4-167 pg/g dw. The distribution of PBDEs in sheep organs and tissues is affected not only by the function of organs and tissues, but also by the characteristics of PBDEs. Adipose tissue tends to bioaccumulate more-brominated BDEs (BDE-154, -153, and -183), but muscle tissues and visceral organs mainly bioaccumulate less-brominated BDEs. The distribution of PBDEs in visceral organs is mainly affected by the transport of ovine serum albumin (OSA) and the metabolism of CYP3A24 enzyme. The distribution of PBDEs in adipose tissue and brain is mainly affected by their logKOW.

Pigment of Ceiba speciosa (A. St.-Hil.) Flowers: Separation, Extraction, Purification and Antioxidant Activity

In this work, the extraction procedure of a natural pigment from the flower of Ceiba speciosa (A. St.-Hil.) was optimized by response surface methodology. It is the first time that the extraction of the flower pigment of C. speciosa (FPCS) has been reported, along with an evaluation of its stability and biological activity under various conditions, and an exploration of its potential use as a food additive and in medicine. Specifically, the effects of ethanol concentration, solid-liquid ratio, temperature and time on the extraction rate of FPCS were determined using a Box-Behnken design. The optimum extraction conditions for FPCS were 75% ethanol with a solid-liquid ratio of 1:75 mg/mL) at 66 °C for 39 min. The purification of FPCS using different macroporous resins showed that D101 performed best when the initial mass concentration of the injection solution was 1.50 mg/mL, resulting in a three-fold increase in color value. The yield of dry flowers was 9.75% of fresh petals and the FPCS extraction efficiency was 43.2%. The effects of light, solubility, pH, temperature, sweeteners, edible acids, redox agents, preservatives and metal ions on FPCS were also investigated. Furthermore, the characteristics of FPCS were determined by spectrophotometry at a specific wavelength using the Lambert-Beer law to correlate the mass of FPCS with its absorbance value. An acute toxicological test performed according to Horne's method showed that FPCS is a non-toxic extract and thus may be used as a food additive or in other ingestible forms. Finally, western blotting showed that FPCS prevents lipopolysaccharide-induced hippocampal oxidative stress in mice. The study suggests that FPCS may function as an antioxidant with applications in the food, cosmetics and polymer industries.

Alarming impact of the excessive use of tert-butylhydroquinone in food products: A narrative review

Tert-butyl hydroquinone (TBHQ) is a food additive commonly used as a more effective protectant in the food, cosmetic and pharmaceutical industries. However, the long-term exposure to TBHQ at higher doses (0.7 mg/kg) results in substantial danger to public health and brings a series of side effects, including cytotoxic, genotoxic, carcinogenic, and mutagenic effects. As a result, the global burden of chronic diseases has fascinated consumers and governments regarding the safety assessment of food additives. Regarding contradictory reports of various research about the application of food additives, the accurate monitoring of food additives is urgent. Notwithstanding, there are reports of the therapeutic effects of TBHQ under pathologic conditions through activation of nuclear factor erythroid 2-related factor 2. Thus, further investigations are required to investigate the impact of TBHQ on public health and evaluate its mechanism of action on various organs and cells. Therefore, this review aimed to investigate TBHQ safety through an overview of its impacts on different tissues, cells, and biological macromolecules as well as its therapeutic effects under pathologic conditions.

Component spectra extraction and quantitative analysis for preservative mixtures by combining terahertz spectroscopy and machine learning

Preservatives are universally used in synergistic combination to enhance antimicrobial effect. Identify compositions and quantify components of preservatives are crucial steps in quality monitoring to guarantee merchandise safety. In the work, three most common preservatives, sorbic acid, potassium sorbate and sodium benzoate, are deliberately mixed in pairs with different mass ratios, which aresupposedto be the "unknown" multicomponent systems and measured by terahertz (THz) time-domain spectroscopy. Subsequently, three major challenges have been accomplished by machine learning methods in this work. The singular value decomposition (SVD) effectively obtains the number of components in mixed preservatives. Then, the component spectra are successfully extracted by non-negative matrix factorization (NMF) and self-modeling mixture analysis (SMMA), which match well with the measured THz spectra of pure reagents. Moreover, the support vector machine for regression (SVR) designed an underlying model to the target components and simultaneously identify contents of each individual component in validation mixtures with decision coefficient R² = 0.989. By taking advantages of the fingerprint-based THz technique and machine learning methods, our approach has been demonstrated the great potential to be served as a useful strategy for detecting preservative mixtures in practical applications.

Interaction of bovine serum albumin with ellagic acid and urolithins A and B: Insights from surface plasmon resonance, fluorescence, and molecular docking techniques

Human serum albumin (HSA) shows the sequence homology and structural similarity with bovine serum albumin (BSA). Therefore, here, the interaction of natural phenolic antioxidants, ellagic acid (ELA), and its derivatives-urolithins A (ULA) and B (ULB)-with BSA was investigated. The results of surface plasmon resonance (SPR) indicated a high affinity of ELA, ULA, and ULB to BSA, with KD value < 1 × 10-6 M. The KD values of binding of the studied compounds to BSA increased with temperature, revealing a reduction in affinity with an increase in temperature. Fluorescence data showed that the quenching of BSA by tested compounds occurred via a static quenching. However, the affinity of ELA for BSA was higher than that of ULA and ULB, which may be because of the presence of a large number of hydroxyl groups in its structure. The assessment of the antioxidant activity of BSA and BSA-ELA/ULA/ULB complexes using the DPPH assay indicated that the DPPH scavenging activity of BSA increased after complex formation with ELA/ULA/ULB in the following order: BSA-ELA > BSA-ULA > BSA-ULB > BSA, which was due to their structural differences. The results of the docking analysis were in agreement with the experimental results.

Investigation on the binding of cyanobacterial metabolite calothrixin A with human serum albumin for evaluating its potential toxicology

Calothrixin A (CLA), as a carbazole-1,4-quinone alkaloid with unique indolo [3,2-j] phenanthridine framework, is a natural metabolite from the Calothrix cyanobacteria. Since the interaction to the functional serum albumins may play an important role in estimating its potential physiological or toxicological effects in vivo, we here explored the binding information of CLA with human serum albumin (HSA) by multi-spectroscopic experiments and computational approaches. The molecular docking results showed that there was one binding site of CLA to the site I (subdomain IIA) of HSA, causing the spontaneous formation of the ground state complex of CLA-HSA through the integration of hydrogen bond, hydrophobic interaction, and electrostatic interaction. Moreover, CLA could effectively trigger the change of HSA's secondary structure because of an obvious decrease of α-helical content in HSA. Taking into consideration of the crucial role of HSA to transport extraneous functional small molecules in vivo, this study may provide a worthy theoretical basis to evaluate the in vivo toxicity of CLA, aiming to reduce/avoid the potential toxic side effects of CLA in the next hit-to-lead campaign.

Effect of nisin and potassium sorbate additions on lipids and nutritional quality of Tan sheep meat

Nisin and potassium sorbate as preservatives are used in a broad range of meat. A lipidomic evaluation was performed on Tan sheep meat treated by two types of preservatives. The addition of potassium sorbate resulted in higher lipid losses compared with nisin treatment. Furthermore, 106 significant lipids of 12 lipid classes (PC, PS, LPS, LPC, PE, PI, LPE, TG, Cer, DG, SM, Sph) with variable importance in projection scores greater than 1.0 were detected and qualified to distinguish different preservatives added meat using UHPLC-Q-Orbitrap MS/MS. LOD and LOQ were 0.12-0.32 μg kg^-1 and 0.35-0.89 μg kg^-1, indicating high sensitivity and excellent analytical characteristics in the study. Nisin was confirmed to be the better preservative for prolonging the shelf life of Tan sheep meat while reducing the loss of nutrients. These results could provide a strong cornerstone for future research on preservatives in meat products.

Probing the Interaction between Human Serum Albumin and 9-Hydroxyphenanthrene: A Spectroscopic and Molecular Docking Study

9-Hydroxyphenanthrene (9-OHPhe), the representative hydroxyl metabolite of phenanthrene, has generated increasing concern as it is potentially hazardous to organisms. Herein, multispectroscopic and molecular docking techniques were applied to investigate the molecular interaction of human serum albumin (HSA) with 9-hydroxyphenanthrene (9-OHPhe) under simulated physiological conditions. Steady-state fluorescence and time-resolved fluorescence spectral analysis showed that 9-OHPhe quenched HSA fluorescence through a mixed static and dynamic process. HSA can bind with 9-OHPhe to form a 1:1 complex, with binding constants of 1.28 × 10⁵, 1.36 × 10⁵, and 1.26 × 10⁵ L·mol^-1 at 298.15, 303.15, and 308.15 K, respectively. The strong binding between HSA and 9-OHPhe is spontaneous and entropy-driven. Molecular docking indicated that the optimal binding site of 9-OHPhe with HSA was located in the IA subdomain of HSA. Thermodynamic analysis and molecular docking results suggested that hydrophobic interactions and hydrogen bond force dominated the binding process of HSA with 9-OHPhe. Specifically, 9-OHPhe formed hydrophobic interactions with LEU134, LEU139, ILE142, LEU154, PHE157, ALA158, and TYR161 and formed a 1.86 Å hydrogen bond with LEU135. Circular dichroism spectral analysis showed that the α-helical content of HSA decreased from 52.3 to 50.9% after adding 9-OHPhe with a ratio of 1:1. The obtained results are hoped to provide basic data for understanding the potential effects of the hydroxyl metabolites of PAHs on functional biomacromolecules.