Evaluating river health through respirogram metrics: Insights from the Weihe River basin, China

Human activities pose a significant threat to rivers, requiring robust assessment methods for effective river management. This study focuses on the Weihe River Basin in Shaanxi province and introduces the respirogram as an innovative assessment technique. The respirogram allows the simultaneous assessment of river health from two important aspects: pollution levels and microbial status. Specifically, the in-situ respiration ratio (Rs/t) serves as an indicator of pollution, with higher Rs/t values correlating with increased pollution levels. Conversely, the recovery index (RI) measures microbial vitality, with values below 0.15 indicating greater microbial activity and recovery potential. Using predefined thresholds of Rs/t = 0.3 and RI = 0.15, water bodies were categorized into four types. For example, rivers with Rs/t > 0.3 and RI > 0.15 were identified as receiving sewage, characterized by high pollution and low microbial vitality. Similarly, different assessment criteria delineated urban rivers, natural rivers, and wastewater treatment plants. Based on these classifications, targeted engineering measures were proposed to enhance the self-purification capabilities of rivers of different statuses.

Understanding the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene: A theoretical study

Oligothiophene and its derivatives have broad applications in organic electronics because of its stability, easy functionalization, and broad color adjustability, and excellent charge carrier mobility. However, the effects of sulfur di-oxidation and side alkyl chains on the absorption and fluorescence of oligothiophene are still not well understood. In this article, we have applied density functional theory (DFT) and time-dependent DFT (TDDFT) to study a series of quinquethiophene compounds functionalized with S,S-dioxide and side alkyl chains, which were experimentally synthesized. Through benchmark calculations, we have found a reliable computational method, and successfully reproduced experimental UV-Vis absorption and fluorescence emission spectra well. Furthermore, the calculated reorganization energy of these molecules could explain the energy differences between absorption and emission spectra. Last but not lease, we also have calculated the fluorescence quantum yield efficiency (Фfl) of two compounds with good planarity in this series, and the trend of calculated values is consistent with experiment. Our work gives an insight to the effects of sulfur di-oxidation and side chain engineering on absorption and fluorescence of oligothiophene.

Discovery and experimental verification of the spectral characteristics at different growth stages of Aurelia

Under the dual pressure of human activities and global changes, jellyfish outbreaks have occurred frequently in China's offshore waters in recent years, with serious impacts on marine fisheries, coastal tourism, marine ecology and cooling water systems for coastal industries. In order to accurately identify the origin of Aurelia and to be more proactive in the prevention and control of Aurelia outbreaks, this article proposed the use of ultraviolet (UV) and fluorescence spectroscopy to detect the polyps, ephyrae and larvae of Aurelia at different growth stages. The AvaSpec-2048 UV visible fibre spectrometer and the F-7000 fluorescence spectrophotometer were used to focus on studying the UV absorption spectrum and three-dimensional fluorescence spectrum of the polyps, ephyrae, and larvae of Aurelia cultured under laboratory conditions. The research results showed that the three-dimensional fluorescence spectrum of the three different growth stages of Aurelia, namely polyps, ephyrae and larvae of Aurelia, had relatively similar fluorescence distributions, and the fluorescence intensity was different from each other. However, the absorption peaks of the three UV absorption spectrum appeared in different UV light bands and there were absorption peaks of different intensities. The different spectral characteristics at different growth stages of Aurelia provide new ideas and methods for exploring the birthplace of Aurelia.

The telltale fluorescence fingerprints of sewer flows for interpreting the low influent concentration in wastewater treatment plant

Low degradability of wastewater treatment plant (WWTP) influents negatively affects its ability to effectively remove pollutants through wastewater treatment processes. Proactive assessment of urban sewer system performance is highly valued in the selection of targeted countermeasures for this occurrence. In this study, a fluorescence spectrum interpretation approach was developed to identify the causes of low biodegradability of WWTP influent by using parallel factor analysis (PARAFAC) and fluorescence regional integration (FRI) of excitation-emission matrix spectroscopy. Statistical analysis was also used to further interpret the PARAFAC- and FRI-derived data. The urban sewer catchment served by a WWTP in Wuhan City, China, was used as the test site to demonstrate the effectiveness of this approach. The results showed that electronics manufacturing industrial wastewater and groundwater input into the urban sewer would significantly decrease the biodegradability of the WWTP influents, and these sources were characterized by much lower fluorescence peak intensities, especially for protein-like substances, including tryptophan-like T and tyrosine-like B1 and B2. The potential conversion of high freshness T into low freshness B2 within the sewer may also contribute to this undesirable scenario. The ratio of peak T to peak B2 and the ratio of the FRI fraction of region I to that of region II can be used together to determine the predominance of industrial wastewater and groundwater. T/B2 < 1.3 indicates the entry of industrial wastewater or groundwater into urban sewers, and I/II > 0.5 further confirms the input of industrial wastewater. Accordingly, the low biodegradability of the WWTP influents in our study site is mostly due to the inflow of industrial wastewater rather than groundwater infiltration into the urban sewers. Therefore, actions should be focused on the surveillance of industrial wastewater rather than widespread sewer inspection and repairs. In this way, this methodology is cost-effective in aiding targeted countermeasures to improve the urban sewer system performance.

Establishment and optimization of the three-band fluorometric indices for oil species identification: Implications on the optimal excitation wavelengths and the detection band combinations

BACKGROUND

The oil pollutants have become a major threat to the ocean environment with the rapid development of social economy and offshore production activities. The detection and identification of petroleum pollutants is the foundation and pre-requisite for controlling offshore oil pollution. Spectroscopic analysis using the ultraviolet-induced fluorescence of oil pollutants is a potential way for oil species identification. Nevertheless, the current fluorescence spectroscopic analysis methods, such as excitation-emission matrix, has high requirements on the detection equipment. There is a great need for rapid oil species identification method when it comes to practical applications. (93) RESULTS: This study established the three-band fluorometric index (TBFI) method and examined its capability on the oil species identification. The fluorescence of five different types of oil samples under various excitation wavelengths were excited using a tuneable xenon lamp, and measured using a high-resolution spectrometer. The optimal excitation wavelengths and the corresponding detection band combinations were explored through the iterations of an optimal band combination algorithm through different excitation wavelengths. According to the results, three out of the four TBFIs tested in this study are suitable for oil species identification. They share the same sets of the excitation wavelengths under 365 nm, 375 nm, and 435 nm. The detection band combinations corresponding to each TBFI under each feasible excitation wavelength were also determined in this study. (125) SIGNIFICANCE: The three-band fluorometric index method proposed in this study provides a feasible way for the rapid oil species identification using fluorescence spectroscopic analysis. The optimal excitation and detection wavelengths determined in this study also provide the theoretical basis for the designs of fluorescence sensors for rapid oil spill detection and identification. (51).

Investigating the characteristics of fluorescence features on sweet peppers using UV light excitation

Sweet peppers are popular worldwide due to their nutrition and taste. Conventional vegetable tracing methods have been trialed, but the application of such labels or tags can be laborious and expensive, making their commercial application impractical. What is needed is a label-free method that can identify features unique to each individual fruit. Our research team has noted that sweet peppers have unique textural fluorescence features when observed under UV light that could potentially be used as a label-free signature for identification of individual fruit as it travels through the postharvest supply chain. The objective of this research was to assess the feature of these sweet pepper features for identification purposes. The macroscopic and microscopic images were taken to characterize the fluorescence. The results indicate that all sweet peppers possess dot-like fluorescence features on their surface. Furthermore, it was observed that 93.60% of these features exhibited changes in fluorescence intensity within the cuticle layer during the growth of a pepper. These features on the macro-image are visible under 365 nm UV light, but challenging to be seen under white LEDs and to be classified from the fluorescence spectrum under 365 nm light. This research reported the fluorescence feature on the sweet pepper, which is invisible under white light. The results show that the uniqueness of fluorescent features on the surface of sweet peppers has the potential to become a traceability technology due to the presence of its unique physical modality.

Composition, variation and contribution of chromophoric dissolved organic matter in Laizhou Bay estuaries, North China

To address the complex biogeochemical processes and potential function of dissolved organic matter (DOM) in estuaries before it enters the sea, water samples were collected seasonally in a dozen Laizhou Bay estuaries and in the Yellow River estuary, North China. The results showed that chromophoric dissolved organic matter (CDOM) varied in abundance but had consistent spectral slopes at the same sampling time. Gradually, CDOM decreased while spectral slopes increased from freshwater to seawater. The spectral slope of CDOM varied temporally (higher in October and lower in August) more than it varied spatially. The fluorescent components and biological indices of CDOM indicated that in situ biological activities were the dominant sources in the waters examined in this study. The CDOM was generally more variable than the dissolved organic carbon (DOC) in most of the estuaries. However, marine CDOM may obviously increase in estuaries when indirectly stimulated by rapidly decomposing terrestrial DOM.

Original and liposome-modified indocyanine green-assisted fluorescence study with animal models

Medical diagnosis heavily relies on the use of bio-imaging techniques. One such technique is the use of ICG-based biological sensors for fluorescence imaging. In this study, we aimed to improve the fluorescence signals of ICG-based biological sensors by incorporating liposome-modified ICG. The results from dynamic light scattering and transmission electron microscopy showed that MLM-ICG was successfully fabricated with a liposome diameter of 100-300 nm. Fluorescence spectroscopy showed that MLM-ICG had the best properties among the three samples (Blank ICG, LM-ICG, and MLM-ICG), as samples immersed in MLM-ICG solution achieved the highest fluorescence intensity. The NIR camera imaging also showed a similar result. For the rat model, the best period for fluorescence tests was between 10 min and 4 h, where most organs reached their maximum fluorescence intensity except for the liver, which continued to rise. After 24 h, ICG was excreted from the rat's body. The study also analyzed the spectra properties of different rat organs, including peak intensity, peak wavelength, and FWHM. In conclusion, the use of liposome-modified ICG provides a safe and optimized optical agent, which is more stable and efficient than non-modified ICG. Incorporating liposome-modified ICG in fluorescence spectroscopy could be an effective way to develop novel biosensors for disease diagnosis.

Pyrolysis temperature dependent effects of biochar on shifting fluorescence spectrum characteristics of soil dissolved organic matter under warming

Biochar generally shift the content and molecular composition of soil dissolved organic matter (DOM) which represent the reactive components and have essential roles in coupling elemental cycling in soil. However, it is not clear how the effects of biochar on soil DOM composition is shifted under warming. This causes a knowledge gap to fully understand the fate of SOM affected by biochar application in a warming climate. To fill this gap, we conducted a simulated climate warming incubation of soil to study the influence of biochar with different pyrolysis temperatures and feedstock types on soil DOM components composition. Three-dimensional fluorescence spectrum analysis combining excitation emission matrix-parallel factor analysis (EEM-PARAFAC), fluorescence region integral (FRI), UV-vis spectrometry, principal component analysis (PCA), clustering analysis, Pearson correlation and multi-factor analysis of variance on fluorescence parameters (including FRI on Region I-V, FI, HIX, BIX, H/P) and soil DOC and DON content were analyzed for this purpose. Results showed that biochar shifted soil DOM composition and enhanced soil humification, which was dominantly pyrolysis-temperature dependent. Biochar shifted the soil DOM components composition probably through mediating soil microbial processing rather than direct input of their pristine DOM, and the influence of biochar on soil microbial processing was pyrolysis-temperature dependent and highly affected by warming. Medium-temperature biochar was more efficient for enhancing soil humification, by accelerating the transformation of protein-like components into humic-like components. Soil DOM composition presented a rapid response to warming, and long-term incubation may eliminate the effects of warming on shifting soil DOM composition. By revealing the heterogeneous effects of biochar with different pyrolysis temperatures on fluorescence characteristics of soil DOM components, our study provides a hint for the essential role of biochar on enhancing soil humification, and also suggests a vulnerability of biochar for soil carbon sequestration under warming.

Probing the toxic effect of quinoline to catalase and superoxide dismutase by multispectral method

Quinoline is a common nitrogen heterocyclic aromatic hydrocarbon with high water solubility. Studies have shown that quinoline can be teratogenic, carcinogenic and mutagenic. And Hepatocytes are the target cell of quinoline, which contain a large number of mitochondria and are related to cell function and the balance of reactive oxygen species (ROS). However, the research on the effect of quinoline on hepatocyte damage and anti-oxidation system is still unclear. Through the means of multispectral experiments, it is concluded that quinoline can affect the catalase (CAT) and superoxide dismutase (SOD), change their structure and affect their activity. The binding mode and binding site of quinoline to CAT/SOD were analyzed by isothermal calorimetric titration (ITC) and Molecular Operating Environment (MOE). In molecular docking simulation, the binding site of quinoline-CAT system is close to the active site, and affect the microenvironment of Tyr 357. This may be the reason why quinoline affects CAT activity and synchronous fluorescence (Δλ = 15 nm). This study demonstrated that quinoline has a great effect on CAT, which may affect the intracellular ROS balance and become a potential way to cause hepatocyte damage.

Molecular evidence for the production of labile, sulfur-bearing dissolved organic matter in the seep sediments of the South China Sea

Cold seeps with methane-rich fluids leaking out of the seafloor usually support massive biomass of chemosynthetic organisms and associated fauna. A substantial amount of methane is converted to dissolved inorganic carbon by microbial metabolism, and this process also releases dissolved organic matter (DOM) into pore water. Here, pore water samples from "Haima cold seeps" sediments and the non-seep reference sediments in the northern South China Sea were analyzed for optical properties and molecular compositions of pore water DOM. Our results showed that the relative abundance of protein-like DOM, H/C_wa and molecular lability boundary percentage (MLB_L%) in the seep sediments were significantly higher than those in the reference sediments, indicating that more labile DOM related to unsaturated aliphatic compounds is produced in the seep sediments. Spearman's correlation of the fluoresce and molecular data suggested that the humic-like components (C1 and C2) mainly constituted the refractory compounds (CRAM, highly unsaturated and aromatics compounds). In contrast, the protein-like component (C3) had high H/C ratios featuring high degree of DOM lability. The amount of S-containing formulas (CHOS and CHONS) was greatly elevated in the seep sediments, likely caused by abiotic and biotic sulfurization of DOM in the sulfidic environment. Although the abiotic sulfurization was proposed to have a stabilizing effect on organic matter, our results implied that the biotic sulfurization in the cold seep sediments would increase DOM lability. Overall, the labile DOM accumulated in the seep sediments is closely linked to methane oxidation, which not only support heterotrophic communities and but also likely have an impact on carbon and sulfur cycling in the sediments and the ocean.

Characterization of conidial autofluorescence in powdery mildew

Autofluorescence is produced by endogenous fluorophores, such as NAD(P)H, lipofuscin, melanin, and riboflavin, indicating the accumulation of substances and the state of energy metabolism in organisms. As an obligate parasite, powdery mildew is wildly spread by air and parasitic crops. However, most identification studies have been based on morphology and molecular biology which were far too time- and labor-consuming, thus lacking characteristic, simple, and effective means. Using microscopy under the blue and cyan channels, we elaborated visible conidial autofluorescence in three powdery mildew species, Erysiphe quercicola, E. cichoracearum, and Podosphaera hibiscicola, with a sharp increase during the conidia senescence in E. quercicola. Additionally, the main spectral excitation detected by fluorescence spectrometery was 375 nm for these species, with a common emission peak at approximately 458-463 nm, and an additional trend at 487 nm for P. hibiscicola. Because NAD(P)H has a similar spectral feature, we further investigated the relation between NAD(P)H and conidial autofluorescence by fluorescence spectra. We observed that the reduced coenzymes prominently contributed to conidial autofluorescence; however, the conidial autofluorescence in P. hibiscicola displayed a different trend that may be affected by the oxidized coenzyme -NAD. Finally, the normalized average spectra of these three powdery mildew species and standard samples showed that the spectral trend of each species was similar but that the features in detail were specific and distinct based on principal component analysis. In conclusion, we showed and characterized conidial autofluorescence in three powdery mildew species for the first time. The specific conidial autofluorescence in these species provides a new idea for the development of field spore capture and identification devices for the discrimination of powdery mildew at the species level.

Juggling with fluorescent proteins: Spectrum and structural changes of the mCardinal2 variants

mCardinal2 is a red fluorescent protein developed through the designs of mKate, mNeptune and mCardinal. Fluorescence spectrums of mCardinal2 and its five mutants (T143C, T143G, C158A, C158D and M160E) were measured with their quantum yields. C158A and C158D increased brightness with slight changes in fluorescence spectrums while T143C, T143G and M160E decreased brightness with blue shift in fluorescence spectrums, which resulted in green, cyan and green fluorescent proteins respectively. Crystal structures of all six variants were analyzed and compared together with those of mKate, LSS-mKate1, LSS-mKate2 and mCardinal. Around the Cα-Cβ bond of Tyr64 in the MYG chromophores, only C158A and C158D were in the trans conformation while all others were mostly in the cis conformation. Blue-shift brightness-decreased variants (T143C, T143G and M160E) showed the diminished hydrogen bonds while large-Stoke-shift brightness-increased variant C158D showed the enhanced hydrogen bonds around the chromophore.

Spectral characteristics of dissolved organic carbon derived from biomass-pyrogenic smoke (SDOC) in the aqueous environment and its solubilization effect on hydrophobic organic pollutants

Dissolved organic carbon derived from biomass-pyrogenic smoke (SDOC) can be transported and deposited with atmospheric aerosols, enter aqueous environments, and possibly alter aqueous chemistry and quality. However, the characteristics of SDOC in aqueous environments and their effects on the fate of hydrophobic organic pollutants are poorly understood. In this study, we found that the emitted SDOC is 7.2∼19.6 wt.% of biochar retained in situ after biomass pyrolysis, and the emitted SDOC is approximately 1-3 orders of magnitude greater than dissolved organic carbon (DOC) released from biochar in a short term, which indicates that SDOC is a more important source of DOC in aqueous environments relative to biochar-released DOC after a biomass burning/pyrolysis event. The characteristics of SDOC in aqueous environments are dominated by the <1000 Da fraction, which accounts for >96 wt.% of bulk SDOC. In comparison with DOC in biochar, natural water, and soil, the S_275-295 value of SDOC (0.037-0.053) is significantly greater, further indicating that SDOC has a smaller molecular size. Moreover, fluorescence EEM suggests that a fluorescence component located at the Ex/Em of 205/310 nm and the combinational ranges of fluorescence index (1.28-2.28), humification index (0.07-0.80), and biological index (1.16-1.72) can be used to identify SDOC from DOC in other media. Solubilization experiments indicated that SDOC (20 mg/L) improved the solubility of hydrophobic pollutants (pyrene and triclocarban) by 2-6 folds in aqueous environments, which potentially enhances the mobility of pollutants and enlarges the potential risk region. This study indicates that SDOC may cause a severe harm to aqueous environments in addition to the atmosphere. The results have profound implications for comprehensive assessments of the environmental effects of SDOC while promoting its identification and elucidating its behavior in aqueous environments.

Photophysical properties and stimuli-responsive crystal-state luminescence switching of morpholine-modified naphthalic anhydride derivative

Stimuli-response organic solid-state luminescence switching materials are attracting increasing interest due to their smart photophysical properties. In this study, a morpholine-modified naphthalic anhydride derivative, 4-(4-morpholinyl)naphthalic anhydride (MBC), was synthesized and studied. Its two crystal polymorphs, MBC-G and MBC-O, were obtained under different crystallization conditions. These two distinct crystals show significantly different solid-state luminescence behaviors: a green emission at 535 nm for MBC-G, and an orange emission at 572 nm for MBC-O. Upon fiercely grinding the MBC-G crystal or melting and then quickly cooling it, a phase transition occurs from MBC-G to MBC-O, accompanied by a fluorescence change from green to orange. The reverse transformation from MBC-O to MBC-G can be achieved by recrystallization. The X-ray single crystal structures show that the green emission should be attributed to molecular J-aggregation in the crystal packing, and the orange emission may originate from molecular H-aggregation. This switchable color nature gives MBC the promising candidate for potential smart anti-counterfeiting and light-emitting materials.

Near vacuum-ultraviolet aperiodic oscillation emission of AlN films

An accurate measurement of the refractive index is necessary for the optical design of both deep ultraviolet laser diodes and light-emitting diodes. Generally, the refractive indices along different crystallographic axes of anisotropic thin films are measured using variable angle spectroscopic ellipsometry. However, there are still some limitations concerning this method. Here we proposed a potential method to measure the band edge refractive index of wide bandgap semiconductor. An aperiodic oscillation emission phenomenon due to the Fabry-Perot effect was observed in the fluorescence spectrum of an AlN film with a thickness of 1500 nm. Based on the characteristics of the fluorescence spectrum and the definition of Fabry-Perot effect, we obtained the ordinary refractive index of the AlN thin film near the band edge directly. This refractive index measurement method is a supplement to the variable angle ellipsometry, and it is a more direct and effective method for transferred film and thinner samples to measure the fluorescence spectrum.

Improving the analysis accuracy of components in blood by SSP-MCSD and multi-mode spectral data fusion

In recent years, spectral quantitative analysis for blood components has been a research hotspot in biomedical engineering. But researches have been limited to the application of high-sensitivity spectroscopy instruments and the complexity of blood components-the overlapping of absorption curves for many components is severe. This has led to the difficulty in achieving satisfactory results when using spectroscopy to quantify components in blood. In order to enhance the model robustness and improve the model performance, this paper proposed a sample set partitioning strategy based on multi-component spatial distance (SSP-MCSD). Different from the other sample set partitioning strategies, which only consider the uniformity of the concentration distribution of the target component, this strategy also concerns to the concentration distribution of non-target components. The concentration of the target component and non-target components are used to construct a multi-dimensional space, and the Euclidean Distance of sample points in this space is used as the criterion to partition the sample set. At the same time, the spectra collected in multi-modes are fused for increasing the amount of information. So as to enhance the model robustness and to improve the analysis accuracy of the target components. In order to verify the effectiveness of this strategy, the serum of 101 volunteers was analyzed. Taking total protein in serum as the non-target component, the regression model for bilirubin concentration was established by transmission spectra, fluorescence spectra, and the joint spectra after fusion of the above two spectra, respectively. The experimental results showed that the prediction accuracy of the model established by SSP-MCSD combined with multi-mode spectral fusion is obviously higher than that of other methods. It can effectively improve the analysis accuracy of blood components.

Relevance of dissolved organic matter generated from green manuring of Chinese milk vetch in relation to water-soluble cadmium

Dissolved organic matter (DOM) can become a carrier of soil contaminants. Therefore, an understanding of the evolution and characteristics of DOM produced by Chinese milk vetch during green manuring is crucial. In this study, DOM solutions from 28 days' manuring with three different organic materials were characterized using three-dimensional fluorescence excitation-emission matrix (3D-EEM) with parallel factor (PARAFAC) analysis, and ultraviolet-visible spectroscopy. With the green manuring milk vetch at flowering period (MVFP), the DOC and water-soluble cadmium (WS-Cd) in soil solution reached 1875 mg/l and 2.64 μg/l, respectively, on day 6 after manuring. The PARAFAC analysis modeled three components: protein-like (tryptophan) and two humic-like components (humic acid and fulvic acid); DOM produced by MVFP was primarily protein-like during the early stage of decomposition. The aromaticity and molecular weight of DOM in the MVFP treatment was lower than in the other treatments, which could promote the release of soil particle-adsorbed Cd to soil solution. Principal components analysis showed that aromaticity was the main factor affecting Cd solubility, and the negative linear correlation of aromaticity with WS-Cd reached 0.4827. The results of this study supported the idea that manuring with MVFP might accelerate Cd infiltration to deep soil with water under gravity.

A detecting Al3+ ion luminophor 2-(Anthracen-1-yliminomethyl)-phenol: Theoretical investigation on the fluorescence properties and ESIPT mechanism

2-(Anthracen-1-yliminomethyl)-phenol (AYP) had been synthesized recently and used as a chemosensor to detect Al³⁺ ion, while its fluorescent properties and excited-state intramolecular proton transfer (ESIPT) process were not investigated in detail. In this study, the molecular absorption and emission spectra were accurately reproduced by using TDDFT/CAM-B3LYP/6-31 + G(d,p) computational method. The ESIPT- chromophore photochemical behaviors and detecting Al³⁺ ion photophysical changes were explained for the first time at the molecular level. As driving force of ESIPT reaction, the bond parameters and vibrational frequencies of intramolecular hydrogen bond were analyzed by optimizing structures and calculating infrared spectra, analysis of frontier molecular orbitals and reduced density gradient isosurfaces. To further elucidate the proton transfer reactive paths, we scanned the potential energy curves of AYP chemosensor in different electronic states. By comparing potential barriers of the S₀ and S₁ states, the proton transfer is confirmed to occur in the S₁ state. In addition, the experimentally unpresented AYP-Enol fluorescence signal was assigned via analyzing molecular fluorescent properties. Moreover, the calculated fluorescence spectra were employed to explain carefully the mechanism of detection of Al³⁺ ion.

A theoretical method for the high-sensitivity fluorescence detection of PAEs through double-substitution modification

A highly sensitive method for the detection of phthalate acid ester (PAE) derivatives by fluorescence spectroscopy based on a double-substitution modification is reported. The fluorescence intensities of 18 PAE derivatives and the template PAEs after docking with the protein bovine serum albumin (BSA) are compared; the fluorescence intensities of the PAE derivatives increase significantly (28.20 to 110.00 times) with high sensitivities, but the functionalities (stability and insulation) are not affected. The persistence, mobility, and toxicity of the PAE derivatives are reduced by varying degrees, and their amounts of bioaccumulation are not significantly changed, indicating that the derivatives are more environmentally friendly. Within the wavelength range 240-420 nm in the fluorescence spectrum, there is no interference between the PAE derivatives and polycyclic aromatic hydrocarbons (PAHs), and the derivatives can be detected with good precision. Based on the analysis of fluorescence characteristics using a 2D quantitative structure-activity relationship (QSAR) model, the occupied orbital energies and Mulliken charge numbers are the main factors that influence the spectral characteristics of the PAE derivatives.

Substituent effect on the acid-induced isomerization of spiropyran compounds

Spiropyran compounds are well known as an isomeric system, the closed spiropyran (SP) could be converted into the open merocyanine (MC) via acid-induced because stable protonated merocyanine (MCH) were formed by combination of MC and H⁺. In order to understand how the substituent affect the isomerization of spiropyran. A series of the chromene 7-subsituted spiropyran compounds were designed and synthesized. The photophysical properties of them were studied comparatively by UV-absorption and fluorescence spectra in different pH. The results demonstrated that the various substituents influenced not only the photophysical properties of SP, MC and MCH forms, but also the pK_a of the MC-MCH transformation. There was a good linearity relationship between the pK_a and the Hammett constant of substituent, the pK_a was smaller when the Hammett constant of substituent was larger.

The order of multiple excited state proton transfer in ternary complex of norharmane and acetic acids

Dolores Reyman et al. found the norharmane (9H-pyrido [3,4-b] indole) (NHM) and two acetic acid molecules can form the ternary complex (NHM-2A) in component solvent of dichloromethane and acetic acid via the hydrogen bond chain (J. Lumin. 2014, 148, 64). But the specific reaction details during this process were rarely reported. In this study, we will give an insight into the reasons which promote the occurrence of this reaction as well as its reaction order. The hydrogen bond enhancing behavior in first excited state (S₁) is verified through the analysis of geometric configurations, infrared spectra, frontier molecular orbitals and potential energy curves. The absorption and fluorescence spectra we calculated are well coincident with the experimental results. Meanwhile, it is obvious that the hydrogen bond intensity is gradually enhanced from N₁H₂⋯O₃, O₄H₅⋯O₆ to O₇H₈⋯N₉ by analyzing the reduced density gradient (RDG) isosurface. The hydrogen bond strengthening mechanism has been confirmed in which the hydrogen bond interaction acts as driving force for excited state proton transfer (ESPT) reaction. In order to provide a reliable description of the reaction energy profiles, we compare the barrier differences obtained by m062x and B3LYP methods. We might safely draw the conclusion that the multiple ESPT is a gradual process initiated by the proton transfer of O₇H₈⋯N₉. And we further proof the ESPT process can be completed via the NHM-2A → NHM-2AS → NHM-2AD → NHM-2AT in S₁ state. Theoretical research of NHM-2A has been carried out by density functional theory (DFT) and time-dependent density functional theory (TDDFT). It is worth noting that we predicted that the fluorescence at 400 nm observed in experiment is more likely to be emitted by NHM-2AS in S₁ state.

Interaction of Aldehyde dehydrogenase with acetaminophen as examined by spectroscopies and molecular docking

The interaction of acetaminophen, a non-substrate anionic ligand, with Aldehyde Dehydrogenase was studied by fluorescence, UV-Vis absorption, and circular dichroism spectroscopies under simulated physiological conditions. The fluorescence spectra and data generated showed that acetaminophen binding to ALDH is purely dynamic quenching mechanism. The acetaminophen-ALDH is kinetically rapid reversible interaction with a binding constant, Ka, of 4.91×103 L mol-1. There was an existence of second binding site of ALDH for acetaminophen at saturating acetaminophen concentration. The binding sites were non-cooperative. The thermodynamic parameters obtained suggest that Van der Waal force and hydrogen bonding played a major role in the binding of acetaminophen to ALDH. The interaction caused perturbation of the ALDH structures with an obvious reduction in the α-helix. The binding distance of 4.43 nm was obtained between Acetaminophen and ALDH. Using Ficoll 400 as macro-viscosogen and glycerol as micro-viscosogen, Stoke-Einstein empirical plot demonstrated that acetaminophen-ALDH binding was diffusion controlled. Molecular docking showed the participation of some amino acids in the complex formation with -5.3 kcal binding energy. With these, ALDH might not an excipient detoxifier of acetaminophen but could be involved in its pegylation/encapsulation.

Spectroscopic characterisation of interaction of ferulic acid with aldehyde dehydrogenase (ALDH)

Interaction of a pharmacological important phenolic, ferulic acid, with Aldehyde dehydrogenase (ALDH) at the simulative pH condition, was studied using spectroscopic approach. Ferulic acid caused a decrease in the fluorescence intensity formed from ALDH-ferulic acid complex resulting in mixed inhibition of ALDH activity (IC₅₀=30.65μM). The intrinsic quenching was dynamic and induced altered conformation of ALDH and made the protein less compact but might not unfold it. ALDH has two binding sites for ferulic acid at saturating concentrations having association constant of 1.35×10³Lmol^-1 and a dissociation constant of 9.7×10⁷Lmol^-1at 25°C indicating ALDH-ferulic acid complex formation is more favourable than its dissociation. The interaction was not spontaneous and endothermic and suggests the involvement of hydrophobic interactions with a FRET binding distance of 4.49nm. Change in pH near and far from isoelectric points of ferulic acid did not affect the bonding interaction. Using trehalose as viscosogen, the result from Stoke-Einstein hypothesis showed that ferulic acid-ALDH binding and dissociation equilibrium was diffusion controlled. These results clearly suggest the unique binding properties and lipophilicity influence of ferulic acid.

Investigation on the interactions of scutellarin and scutellarein with bovine serum albumin using spectroscopic and molecular docking techniques

The binding abilities of scutellarin (Scu) and scutellarein (Scue) with bovine serum albumin (BSA) were investigated using equilibrium dialysis, high performance liquid chromatography, fluorescence spectroscopy, competitive site marker and molecular docking. The results showed that the average protein binding ratios of Scu and Scue with BSA were (79.85 ± 1.83) and (85.49 ± 1.21) % respectively. Under simulated physiological conditions, the fluorescence data indicated that Scu and Scue bound with BSA through a static mechanism. The thermodynamic parameters indicated that the interactions of Scu-BSA and Scue-BSA mainly occurred by van der Waals forces and hydrogen bonds and it was easier for Scue to bind with BSA than Scu, indicating that the glucuronic acid molecule in Scu decreased the binding affinity. Site competitive marker experiments showed that the binding sites of Scu and Scue mainly located within the sub-domain IIA of BSA. Furthermore, molecular docking studies indicated that one BSA could bind three Scue, while one BSA could carry only two Scu. All these results clearly indicated the interactions of Scu and Scue with BSA, which will lay the foundation for further research to determine the pharmacology and pharmacodynamics of Scu and Scue for treating ischemic cerebrovascular disease.

Effects of hydrogen bond on 2-aminopyridine and its derivatives complexes in methanol solvent

In the present work, the time-dependent density functional theory (TD-DFT) method was adopted to investigate the excited state hydrogen-bond dynamics of 2-aminopyridine monomer (2AP) and its derivatives in hydrogen donating methanol solvent. The calculated steady-state absorption and fluorescence spectra agree well with the experimental results. Theoretical results state that the bond lengths of both O-H and N-H bands are lengthened, while the intermolecular hydrogen bond lengths are shortened in the excited state. Further, the intermolecular hydrogen bonds are proved to be strengthened according to the calculated binding energy. As a reasonable explanation, the hydrogen bonds binding energy increases with multiple hydrogen-bonding interactions in the electronically excited state. In addition, the hydrogen bonding dynamics in the excited state were visualized by the spectral shifts of vibrational modes. The calculated infrared spectra of both O-H and N-H stretching vibrational regions revealed that the O-H and N-H stretching bands red-shift.

Fluorimetric analysis of the binding characteristics of 5-enolpyruvylshikimate-3-phosphate synthase with substrates in Dunaliella salina

A general model of the catalytic mechanism for 5-enolpyruvylshikimate-3-phosphate synthase (EPSPs) has already been proposed. But whether shikimate-3-phosphate (S3P) alone can cause EPSPs' conformation changes, and whether the binding site of phosphoenolpyruvate (PEP) and glyphosate is the same are still in debate. In this paper, DsaroA gene amplified and cloned from Dunaliella salina (our laboratory's early study) was used for DsEPSPs expression and purification. Then the DsEPSP conformation changes as it bind with different substrates were detected by fluorimetry. The results show that we obtained the DsEPSPs by prokaryotic expression and purification, and the S3P binding with DsEPSPs alone cannot cause DsEPSPs to form "close" conformation directly. However, when S3P exits, DsEPSPs did have a trend to change to the "close" conformation. Then the "close" conformation can be formed completely with the addition of phosphoenolpyruvate (PEP) or glyphosate. The inorganic phosphorus can help S3P to induce two domains of DsEPSPs to form "close" conformation. Besides, when DsEPSPs binds with S3P, in 295 nm, only the intensity of emission peak decreases, however, in 280 nm, not only the peak intensity reduces but also the blue-shift phenomenon takes place. The reason for blue-shift phenomenon was the distribution of aromatic amino acids in EPSPs. EPSPs is a good target for novel antibiotics and herbicides, because of shikimic acid pathway is only present in plants and microorganisms, completely absent in mammals, fish, birds, reptiles, and insects. The results demonstrate that the binding of substrates to EPSPs causes a conformational change from an open form to a closed form, that might be important for designing of novel antimicrobial and herbicidal agents that block closure of the enzyme.

The synthesis and activities of novel mononuclear or dinuclear cyclen complexes bearing azole pendants as antibacterial and antifungal agents

A series of novel compounds containing 1,4,7,10-tetraazacyclododecane and azoles were synthesized and characterized by (1)H NMR, MS and elemental analysis. Bioactive assay manifested that some target compounds, such as 11a, 11b and 11d, displayed good and broad spectrum antimicrobial activities with relative low MIC values against most of tested strains. These dinuclear complexes gave comparable or even better antimicrobial efficiencies than the reference drugs Fluconazole and Chloromycin. The result showed that the metal ions were the key factors to enhance the antimicrobial activities for mononuclear or dinuclear complexed in varying degrees. The interaction evaluation of compound 11b with bovine serum albumin (BSA) as an example was tested by fluorescence method. The thermodynamic parameters indicated that the hydrogen bonds and van der waals forces played the major roles in the strong association between dinuclear compound and BSA. The CCK-8 tests also confirmed the safeties of these dinuclear compounds in vitro.