Interactions between hydroxylated polycyclic aromatic hydrocarbons and serum albumins: multispectral and molecular docking analyses.

Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) can bind to serum albumin and influence their distribution and elimination in organisms. Here, multispectral analysis and molecular docking methods were used to investigate the binding mechanism of two OH-PAHs, 1-hydroxyphenanthrene (1-OHPhe) and 9-hydroxyphenanthrene (9-OHPhe), with two homologous serum albumins, human serum albumin (HSA) and bovine serum albumin (BSA). The quenching constants of HSA with 1-OHPhe and 9-OHPhe were much larger than those for BSA. Energy transfer from the tryptophan (Trp) residues in HSA to 1-OHPhe and 9-OHPhe was more probable than from Trp in BSA. The interactions of 1-OHPhe and 9-OHPhe with Trp in HSA and BSA altered the microenvironment of Trp. Molecular docking results revealed that the binding modes and binding forces of 1-OHPhe and 9-OHPhe with HSA and BSA were different. The two OH-PAHs were used as fluorescent probes to analyze the microenvironmental hydrophobicities of HSA and BSA, which were distinctly different. The structural difference between HSA and BSA induced significant variations in their binding behaviour with 1-OHPhe and 9-OHPhe. Moreover, HSA was more susceptible to 1-OHPhe and 9-OHPhe than BSA. This work suggests that the differences between the two serum albumins should be considered in related studies.

Effects of flooding and aging on phytoremediation of typical polycyclic aromatic hydrocarbons in mangrove sediments by Kandelia obovata seedlings.

A laboratory experiment was conducted to evaluate the effects of flooding and aging on the phytoremediation of naphthalene (Nap), anthracene (Ant) and benzo[a]pyrene (B[a]P) in mangrove sediment by Kandelia obovata (K. obovata) Druce seedlings. Flooding increased dissipation efficiency in the rhizosphere zone from 69.47% to 82.45%, 64.27% to 80.41%, and 61.55% to 78.31% for Nap, Ant and B[a]P, respectively. Aging decreased dissipation efficiency significantly. Further investigation demonstrated that increased enzyme activity was one of important factors for increasing PAHs dissipation rates in flooded mangrove sediments. Moreover, a novel method for in situ quantitative investigation of PAHs distribution in root tissues was established using microscopic fluorescence spectra analysis. Subsequently, the effects of flooding and aging on the distribution of PAHs in root tissues were evaluated using this established method. The order of bioavailable fractions of PAHs after phytoremediation was as follows: non-aging/non-flooding>flooding>aging.

In Situ Investigating of the Interaction of Phenanthrene and Alkyl Phenanthrene with Humic Acid with Laser Induced Nanoseconds Time Resolved Fluorescence Quenching Method.

Investigations both on the binding properties and mechanisms of parent polycyclic aromatic hydrocarbons (PAHs) and alkyl PAHs with humic acid (HA) are crucial to understand the environment behavior and bioavailability of PAHs in aquatic ecosystems. Thus, a novel approach for in situ investigation of the interactions between parent PAHs and alkyl PAHs, exemplified by Phenanthrene (Phe), 9-Ethylphenanthrene (9-EP) and Retene (Ret), and HA was established by using fluorescence quenching method with laser-induced nanosecond time-resolved fluorescence (LITRF). By changing the delay time of 50 ns, the fluorescent interference of HA can be eliminated effectively and the concentrations of free Phe, 9-EP and Ret can be determined directly. The binding characteristics of the dissolved HA and Phe, 9-EP and Ret were described by Freundlich nonlinear isothermal model. The results of the model parameters and the single point binding coefficients KOC of Phe, 9-EP and Ret with HA by LITRF quenching method were consistent with those of the conventional fluorescence quenching method. Nonlinear bindings of Phe, 9-EP and Ret to HA were also observed because of the parameter n values below 1, and the degree of nonlinearity of Phe was lower than 9-EP and Ret duo to the n value of Phe larger than 9-EP and Ret. At a same given equilibrium concentration, the KOC of Phe was lower than 9-EP and Ret, and that of 9-EP was near to Ret. The binding affinity of the three PAHs increased with decreasing the equilibrium concentration. The binding characteristics of PAHs with HA largely depends on their hydrophobicity, substituent groups and its ability to fit into hydrophobic cavities in HA. The fluorescence lifetimes of Phe, 9-EP and Ret in presence of HA were 36.90, 35.34 and 35.13 ns, meanwhile the fluorescence lifetimes of Phe, 9-EP and Ret in absence of HA were 36.36, 35.34 and 35.84 ns. There was no significant difference of three PAHs fluorescence lifetime with or without HA, indicating the quenching mechanism for Phe, 9-EP and Ret with HA were primarily static quenching. The LITRF quenching method could be used to in situ explore the interactions between PAHs and HA, which could be contribute to realize the PAHs risk assessment in real time.

Simultaneous determination of 9-ethylphenanthrene, pyrene and 1-hydroxypyrene in an aqueous solution by synchronous fluorimetry using the double scans method and hydroxyl-propyl beta-cyclodextrin as a sensitizer.

A novel method for the simultaneous determination of 9-ethylphenanthrene (9-EP), pyrene (Pyr) and 1-hydroxypyrene (1-OH-Pyr) in an aqueous solution using hydroxyl-propyl ß-cyclodextrin (HPCD) as a sensitizer has been established. The overlap of the conventional fluorescence spectra of these molecules is resolved using synchronous fluorescence spectrometry with the double scans method. The simultaneous quantitative determination of three compounds was carried out with Δλ=36 nm and Δλ=55 nm. The signals detected at these three wavelengths (i.e., 298 nm, 337 nm and 351 nm) vary linearly when the concentrations of 9-EP, Pyr and 1-OH-Pyr were in the range of 5.00×10(-8)-1.60×10(-6) mol L(-1), 2.00×10(-8)-1.80×10(-6) mol L(-1), and 2.00×10(-8)-1.20×10(-5) mol L(-1), respectively. The limits of detection (LOD) for 9-EP, Pyr and 1-OH-Pyr were 3.97×10(-9) mol L(-1), 5.25×10(-)(9) mol L(-1), 4.20×10(-9) mol L(-1), respectively, with relative standard deviations (R.S.D.) of 1.62%, 2.45% and 1.73% (n=9), respectively. The inclusion behaviors between HPCD and the guest molecules were observed by synchronous fluorimetry and the association constants for the 1:1 complexes with HPCD were determined. The binding and complexation energies for different orientations are discussed. The proposed method was successfully applied to the analysis of 9-EP, Pyr and 1-OH-Pyr in tap and lake water with good recoveries in the range of 92.9-110.0%.

In situ determination mechanisms for the depuration of polycyclic aromatic hydrocarbons adsorbed onto the leaf surfaces of living mangrove seedlings.

To further increase understanding of the mechanisms responsible for air-surface exchange processes, the depuration of adsorbed individual fluorene (Flu), anthracene (Ant), phenanthrene (Phe), fluoranthene (Fla), and pyrene (Pyr) from the leaf surfaces of living Aegiceras corniculatum (Ac) and Kandelia obovata (Ko) seedlings were in situ investigated in real time using laser-induced nanosecond time-resolved fluorescence (LITRF) system. Depuration of the PAHs from the leaf surfaces of the two mangrove seedlings included a rapid and a slow phase, and both of them followed first-order kinetics. Furthermore, significant inter-species and inter-chemical variability existed in terms of the elimination rates and the remaining PAHs residues during the two phases. The rapid phase mainly represented a fast volatilization, of which the volatilization rates moderately correlate with PAH molecular weight, while combined effect of volatilization and photolysis was the dominant mechanism for the slow phase. The retainment of PAHs on the leaf surfaces was associated with the plant species and physicochemical properties of PAHs, especially logKOA.

Investigation into the causes for the changed biodegradation process of dissolved pyrene after addition of hydroxypropyl-ß-cyclodextrin (HPCD).

Bioremediation of surface waters contaminated with polycyclic aromatic hydrocarbons (PAHs) is a serious problem, often limited by the low bioavailability of contaminants as a result of their low aqueous solubility. In this study, we studied the influence of hydroxypropyl-ß-cyclodextrin (HPCD) addition on the biodegradation of dissolved pyrene in aqueous solution. Five types of unidentified bacterial strains were used with a concentration of pyrene under its solubility limit. The reduction of pyrene content was monitored during the biodegradation process using synchronous fluorimetry. The presence of HPCD changed the rate of pyrene biodegradation by microorganisms due to the formation of an inclusion complex between pyrene and HPCD. The hydrophobicity and the emulsifying activity of microorganisms relative to their biodegrading capacity were investigated. The results indicated that hydrophobicity and emulsifying activity of the microorganisms were important factors that can influence the biodegradation process. The hydrophobicity and emulsifying activity were strongly correlated with the biodegrading capacity of the microorganisms toward pyrene in the presence of solubilizing agents or organized media.

The effects of LMWOAs on biodegradation of multi-component PAHs in aqueous solution using dual-wavelength fluorimetry.

Biodegradation of dissolved fluorene (Flu), phenanthrene (Ph) and pyrene (Py), three polycyclic aromatic hydrocarbons (PAHs), singly or as a mixture of the three, by two bacterial strains, MEBIC 5140 (Mycobacterium flavescens) and MEBIC 5141 (Mycobacterium scrofulaceum), as well as the effects of low molecular weight organic acids (LMWOAs), e.g. malic acid, citric acid and butyric acid on biodegradation of the three PAHs in mineral salts medium aqueous solution were investigated using a newly established dual-wavelength fluorimetric method. The results showed that biodegradation processes can be monitored simultaneously, quickly and simply by dual-wavelength fluorimetry. Both co-metabolism and inhibitory effects were found during the biodegradation of the three PAHs by MEBIC 5140 and MEBIC 5141. Positive effects of butyric acid and negative effects of citric acid on biodegradation of the three PAHs in a mixture were observed.

Simultaneous fluorimetric determination of the biodegradation processes of dissolved multi-component PAHs.

A fluorimetric method for simultaneous determination of dissolved acenaphthylene (Ace) phenanthrene (Ph) and pyrene (Py), mixed in an aqueous mineral salts medium (MSM), was developed. The linear ranges for determination of Ace, Ph and Py dissolved in the mixture were 4.00 x 10(-6) to 3.00 x 10(-3)g/L, 2.00 x 10(-6) to 1.00 x 10(-3)g/L and 7.00 x 10(-7) to 1.00 x 10(-4)g/L. The limits of detection for Ace, Ph and Py were 8.53 x 10(-7), 4.98 x 10(-7) and 6.01 x 10(-8)g/L and the relative standard deviations 1.05%, 1.62% and 1.16% (n=8), respectively. Satisfactory results were obtained when this method was used to simultaneously study the biodegradation processes of mixtures of dissolved Ace, Ph and Py in an MSM aqueous solution.

A novel analytical approach for investigation of anthracene adsorption onto mangrove leaves.

A solid surface fluorimetry approach was established for direct determination of anthracene (An) adsorbed onto fresh mangrove leaves. The experimental results showed that the linear dynamic ranges for determination of An adsorbed onto Avicennia marina (Am), Bruguiera gymnorrhiza (Bg), Kandelia candel (Kc) and Rhizophors stylosa (Rs) leaves varied from 0.92 to 8.71, 0.089 to 0.70, 0.063 to 5.61 and 0.11 to 1.82 microgg(-1), with detection limits of 5.77, 1.79, 4.29 and 1.42 ngg(-1), respectively, and with a relative standard deviation less than 10% (n=5). The experimental recovery results for adsorbed An on Am, Bg, Kc and Rs leaves were among 79.2-85.9, 75.1-102.3, 70.2-93.8 and 73.1-110.8%, respectively. Using the established method, we investigated the effects of exposure time of An and the different quantity of leaf-wax among the four species of mangrove on the amount of An adsorbed. Under the same experimental conditions, the adsorption of An on the upper and lower sides of the same mangrove leaf, and at different regions on the upper side of the same mangrove leaf were also studied. The results demonstrated that the leaves of different mangrove species contained different quantities of leaf-wax, and with the same exposure conditions to An, the quantity of leaf-wax among the four species showed a significant positive correlation with the amount of An adsorbed onto the leaves.

Simultaneous determination of dissolved anthracene and pyrene in aqueous solution by synchronous fluorimetry.

A synchronous fluorimetry for simultaneous determination of dissolved anthracene and pyrene in aqueous solution has been established. The linear ranges for determination of dissolved anthracene and pyrene were 1.00x10(-8) to 4.50x10(-7)molL(-1) and 5.00x10(-9) to 6.50x10(-7)molL(-1), and the limits of detection (LOD) for anthracene and pyrene were 2.23x10(-9) and 8.24x10(-10)molL(-1) with relative standard deviations (R.S.D.) of 2.90 and 2.34% (n=5), respectively. Satisfactory results were obtained when the established method was used to simultaneously determine anthracene and pyrene in spiked water samples.

Room temperature phosphorescence of alpha-bromonaphthalene induced by cyclodextrin in the presence of hexahydropyridine or 1-ethylpiperidine and its application.

Two novel heterocyclic third components, hexahydropyridine (HHP) and 1-ethylpiperidine (EP) were firstly found to enhance room temperature phosphorescence (RTP) of alpha-bromonaphthalene (alpha-BrN) induced by cyclodextrin. The effects of equilibrium time for formation of inclusion complex, temperature, pH values and the variation of concentrations of each component on RTP of alpha-BrN and the RTP lifetime of each ternary complex had been investigated and compared to discuss inclusion mechanism of ternary complexes. The RTP lifetimes of alpha-BrN/beta-CD/HHP, alpha-BrN/beta-CD/cyclohexane (CH) and alpha-BrN/beta-CD/EP were 6.18, 7.71 and 9.36 ms, respectively. Based on the strongest RTP of alpha-BrN induced by CD in the presence of EP, a method for determination of EP was established. Under the optimal conditions, the analytical curve of EP gave a liner dynamic range of 1.50x10(-4) to 1.50x10(-3) mol L(-1) with a detection limit of 4.8x10(-5) mol L(-1). When the established CD-RTP method was applied to determine the concentration of EP synthetic samples in distilled water, the experimental results demonstrated that the recovery was 91.4% with a relative standard deviation less than 2.85% (n=7).

Novel method for determining pyrene biodegradation using synchronous fluorimetry.

To study the biodegradation rate of pyrene dissolved in liquid medium supplemented with mineral salts, a synchronous fluorimetry (SF) method was established. The limit of detection for pyrene dissolved in mineral salts medium (MSM) was determined as 0.19 ng/ml with a relative standard deviation of less than 1.3% (n = 9). The pyrene degrading rates of four bacterial strains were investigated using this method under the same experimental conditions. The degradation rates of the three active strains ranged from 76% to 87% after a 14-h incubation. The results were confirmed by the gas chromatography with a flame ionized detector (GC/FID) method. This implies that pyrene degradation can be directly monitored by the SF method without the solvent extraction of samples. The advantages of SF are that it is less laborious, faster, and less expensive than the GC/FID determination method with solvent extraction. The SF method provides a new tool for studying the degradation of polynuclear aromatic hydrocarbons (PAHs) in the natural environment and under experimental conditions.