Negative Enthalpy Change Research Articles

Separation of platinum group metals from model chloride solution using phosphonium-based ionic liquid

• Liquid-liquid separation of PGMs’ from HCl medium using Cyphos IL 101 was studied. • Increasing acid and total Cl – ion concentration inhibited the extraction efficiency. • Poorly extracted Rh(III) efficiently scrubbed from organic phase in high acid solution. • Outer sphere complexation of [PtCl 6 ] 2− and [PdCl 4 ] 2− with ionic liquid was observed. • Quantitative stripping of Pt(IV) with NaSCN and Pd(II) with CH 4 N 2 S was achieved. The present study dealt with liquid–liquid separation of PGMs (Pt, Pd, and Rh) from a model chloride-based leach solution using an undiluted phosphonium-based ionic liquid, Cyphos IL 101. Based on the parametric optimization studies, 30 min equilibration of both phases at an organic-to-aqueous volume ratio of 1 showed the highest PGMs’ extraction of > 99% Pt(IV) and Pd(II), and ~ 22% Rh(III). Depending upon the HCl and total Cl − ions concentrations, species like [PtCl 6 ] 2− and [PdCl 4 ] 2− exhibited remarkable ability for ion-pairing with Cyphos IL 101 unlike the higher charge density of [RhCl 6 ] 3− which significantly lowered down to be < 5% at an aqueous feed of 0.1 mol.L −1 HCl. Thermodynamic properties with negative changes in enthalpy and entropy indicated that the PGMs’ extraction process exhibit exothermic behaviour with the formation of outer -sphere complexes in the ionic liquid phase. With the supports of experimental results and spectral analysis, the possible structure of Pt(IV)-Pd(II)-loaded ionic liquid could also be revealed. The poorly extracted Rh(III) was efficiently scrubbed by contacting with 5.0 mol.L −1 HCl solution, leaving the organic phase free from Rh(III). The selectivity in back-extraction of Pt(IV) and Pd(II) was achieved by first contacting the loaded ionic liquid with 1 × 10 −1 mol.L −1 NaSCN in two stages, which exhibiting ~ 99% efficacy of Pt(II) stripping. Subsequently, Pt(IV)-depleted organic phase was stripped with 1 × 10 −2 mol.L −1 CH 4 N 2 S that yielded > 99% Pd(II) recovery in a single contact. Results of extraction-stripping cycles that were showing similar efficiency of PGMs extractability clearly indicated the stability and reusability of ionic liquid.

Conformational heterogeneity coupled with \u03b2-fibril formation of a scaffold protein involved in chronic mental illnesses

Chronic mental illnesses (CMIs) pose a significant challenge to global health due to their complex and poorly understood etiologies and hence, absence of causal therapies. Research of the past two decades has revealed dysfunction of the disrupted in schizophrenia 1 (DISC1) protein as a predisposing factor involved in several psychiatric disorders. DISC1 is a multifaceted protein that serves myriads of functions in mammalian cells, for instance, influencing neuronal development and synapse maintenance. It serves as a scaffold hub forming complexes with a variety (~300) of partners that constitute its interactome. Herein, using combinations of structural and biophysical tools, we demonstrate that the C-region of the DISC1 protein is highly polymorphic, with important consequences for its physiological role. Results from solid-state NMR spectroscopy and electron microscopy indicate that the protein not only forms symmetric oligomers but also gives rise to fibrils closely resembling those found in certain established amyloid proteinopathies. Furthermore, its aggregation as studied by isothermal titration calorimetry (ITC) is an exergonic process, involving a negative enthalpy change that drives the formation of oligomeric (presumably tetrameric) species as well as β-fibrils. We have been able to narrow down the β-core region participating in fibrillization to residues 716–761 of full-length human DISC1. This region is absent in the DISC1Δ22aa splice variant, resulting in reduced association with proteins from the dynein motor complex, viz., NDE-like 1 (NDEL1) and lissencephaly 1 (LIS1), which are crucial during mitosis. By employing surface plasmon resonance, we show that the oligomeric DISC1 C-region has an increased affinity and shows cooperativity in binding to LIS1 and NDEL1, in contrast to the noncooperative binding mode exhibited by the monomeric version. Based on the derived structural models, we propose that the association between the binding partners involves two neighboring subunits of DISC1 C-region oligomers. Altogether, our findings highlight the significance of the DISC1 C-region as a crucial factor governing the balance between its physiological role as a multifunctional scaffold protein and aggregation-related aberrations with potential significance for disease.

A study of the interactions between ephedrine and human serum albumin based on spectroscopic, electrochemical and docking assessments

The aim of this study was to explore the efficiency of ephedrine binding to human serum albumin (HSA) as a protein model using spectroscopic, electrochemical, and molecular docking methods. A reduction in UV absorbance at 280 nm of HSA was attributed to the interaction between ephedrine and HSA. The apparent binding constant (Kapp) values at different temperatures were about 104M−1, which showed high affinity of ephedrine for HSA. The calculated negative enthalpy change (ΔH) and entropy change (ΔS) values suggested that the binding process was mainly driven by van der Waals force and hydrogen bonds. The negative value of free energy change (ΔG) indicated that the interaction process was spontaneous. The results of cyclic voltammetry (CV) further confirmed the high affinity of ephedrine for HSA with an association constant of 2.73 ± 0.17 × 104M−1 at room temperature. Furthermore, molecular docking results revealed that ephedrine bound to site I in subdomain IIA via 2 hydrogen bonds with Phenylalanine 211 (Phe211) and Alanine 215 (Ala215) of HSA, and that Arginine 218 (Arg 218), Lysine 199 (Lys 199), and Serine 202 (Ser202) residues became involved in electrostatic interactions with ephedrine. Also, Leucine 198 (Leu198), Phe211, Tryptophan 214 (Trp214), Leu238, and Histidine 242 (His242) residues were responsible for the stability of the complex via hydrophobic interactions. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was used to investigate the conformational changes of HSA during the interaction of ephedrine and HSA.

Liquid chromatographic study of two structural isomeric pentacyclic triterpenes on reversed-phase stationary phase with hydroxypropyl-β-cyclodextrin as mobile phase additive

Retention behavior of two structural isomeric pentacyclic triterpenic acids, maslinic acid and corosolic acid, was investigated by reverse phase high performance liquid chromatography (HPLC) with hydroxypropyl-β-cyclodextrin (HP-β-CD) as mobile phase additive. Inclusion complexation of maslinic acid, corosolic acid with hydroxypropyl-β-cyclodextrin was evaluated under different concentration of hydroxypropyl-β-cyclodextrin. Apparent formation constant (Km) between methanol and hydroxypropyl-β-cyclodextrin was determined to be 13.82 L mol−1 under 25 °C using UV-spectrophotometry. Two retention models were employed individually for evaluation of inclusion complexation between the two pentacyclic triterpenic acids and hydroxypropyl-β-cyclodextrin. It was found that a higher apparent formation constant (Kf) for corosolic acid and hydroxypropyl-β-cyclodextrin was obtained, 19115 L mol−1, indicating that a greater affinity of hydroxypropyl-β-cyclodextrin with corosolic acid was produced compared with that of maslinic acid, 11775 L mol−1, in the selected mobile phase, and stoichiometric ratio for both of inclusion complex was found to be 1:1. Thermodynamic analysis showed that a negative standard enthalpy change (ΔH) and an entropy change (ΔS*) for analyte transfer were obtained, where ΔH of maslinic acid and corosolic acid was found to be −10.188 kJ mol−1 and −10.650 kJ mol−1, ΔS* of two compounds was −2.092 and −2.180, respectively, indicating that transfer of structural isomers from mobile phase to stationary phase was enthalpically driven. Meanwhile, positive values were obtained for standard enthalpy change and standard entropy change, 136 kJ mol−1 and 274 kJ mol−1 and 536 J mol−1 K−1and 1004 J mol−1 K−1, for inclusion complexation between maslinic acid, corosolic acid and hydroxypropyl-β-cyclodextrin, while negative values were obtained for Gibbs free energy during formation of inclusion complex, −160 kJ mol−1 and −299 kJ mol−1, indicating a spontaneous inclusion reaction happened.

Molecular Characterization of a Mesophilic Cellobiose 2-Epimerase That Maintains a High Catalytic Efficiency at Low Temperatures.

Cellobiose 2-epimerase (CE) can catalyze bioconversion of lactose to its prebiotic derivative epilactose. The catalytic property of a novel CE from Treponema brennaborense (Trbr-CE) was investigated. Trbr-CE showed the highest catalytic efficiency of epimerization toward lactose among all of the previously reported CEs. This enzyme's specific activity could reach as high as 208.5 ± 5.3 U/mg at its optimum temperature, which is 45 °C. More importantly, this enzyme demonstrated a considerably high activity at low temperatures, suggesting Trbr-CE as a promising enzyme for industrial low-temperature production of epilactose. This structurally flexible enzyme exhibited a comparatively high binding affinity toward substrates, which was confirmed by both experimental verification and computational analysis. Molecular dynamics (MD) simulations and binding free energy calculations were applied to provide insights into molecular recognition upon temperature changes. Compared with thermophilic CEs, Trbr-CE presents a more negative enthalpy change and a higher entropy change when the temperature drops.

Cross-linked γ-cyclodextrin metal-organic framework-a new stationary phase for the separations of benzene series and polycyclic aromatic hydrocarbons.

The cross-linked γ-cyclodextrin metal-organic framework (CL-CD-MOF) was synthesized by crosslinking γ-cyclodextrin metal-organic framework (γ-CD-MOF) with diphenyl carbonate to separate benzene series and polycyclic aromatic hydrocarbons (PAHs). The separation ability of the CL-CD-MOF packed column was assessed in both reverse-phase (RP-) and normal-phase (NP-) modes. The retention mechanisms of these compounds were discussed and confirmed by combining molecular simulations in detail. It was found that baseline separation could be obtained in RP-HPLC mode and it was superior to commercial C18 column in separating xylene isomers. The interaction between CL-CD-MOF and analytes, such as dipole-dipole interaction, π-electron transfer interaction, hydrophobic interaction, and van der Waals force, may dominate the chromatographic separation, and CL-CD-MOF column had a certain shape recognition ability. In addition, the composition of the mobile phase also had a crucial effect. Moreover, the column demonstrated satisfactory stability and repeatability (the relative standard deviations of retention time, peak height, peak area, and half peak width for six replicate separations of the tested analytes were within the ranges 0.17-1.1%, 0.96-1.9%, 0.23-1.7%, and 0.32-1.9%, respectively) and there was no significant change in the separation efficiency for at least 3 years of use. Thermodynamic characteristics indicated that the process of separations on the CL-CD-MOF column was both negative enthalpy change (ΔH) and entropy change (ΔS) controlled. The excellent performance made CL-CD-MOF a promising HPLC stationary phase material for separation and determination of benzene series and PAHs.

First Report on the Complexation of Uranyl Ion with Two Diglycolamide Ligands in a Room Temperature Ionic Liquid: Optical Spectroscopy and Calorimetric Studies

AbstractThe complexation of UO22+ with N,N,N′,N′‐tetraoctyl diglycolamide (TODGA) and N,N,N′,N′‐tetra‐2‐ethylhexyl diglycolamide (T2EHDGA) was investigated in ionic liquid using UV−vis absorption spectrophotometry and isothermal titration calorimetry. Spectrophotometric titration suggested the formation of two successive complexes, [UO2L]2+ and [UO2L2]2+ where L=TODGA or T2EHDGA. The formation constant values obtained in ionic liquid medium were several orders of magnitude higher than those observed with the analogous DGA ligands in aqueous medium. The stability constant (logβ) for UO22+/TODGA complex was at least an order of magnitude higher than those observed for UO22+/T2EHDGA complex. The speciation of UO22+/DGA complex obtained by spectrophotometric titration was in conformity with those observed in biphasic solvent extraction. Energetically the UO22+/DGA complexation was mainly driven by negative enthalpy and large positive entropy changes as a result of the release of entire water molecules from the solvation sphere of the hydrated UO22+ ions. The results from this work gave an insight understanding of the complexation behaviour of UO22+ ions with DGA ligands in ionic liquid. It is anticipated that such understanding will give valuable information for understanding the extraction behavior of uranyl ions by DGA ligands in ionic liquid.

Biomolecular interaction mechanism of an anticancer drug, pazopanib with human serum albumin: a multi-spectroscopic and computational approach

Pazopanib (PZP) is a multi-targeting tyrosine kinase inhibitor and is currently approved by FDA for the treatment of soft tissue sarcoma and renal cancer. Molecular interaction mechanism of PZP with human serum albumin (HSA) was explored under simulated physiological conditions (pH = 7.4), using fluorescence and UV absorption spectroscopy along with computational methods. Based on the inverse correlation between the Stern-Volmer constant (Ksv ) and temperature, it was concluded that PZP quenched the protein fluorescence through static quenching mechanism. This was also confirmed from the UV-vis absorption spectral results. Moderate binding affinity between PZP and HSA was evident from the Ka values (5.51 − 1.05 × 105 M−1) while PZP-HSA complex formation was driven by hydrophobic and van der Waals interactions as well as hydrogen bonds, as revealed by positive entropy change (ΔS = +98.37 J mol−1 K−1) and negative enthalpy change (ΔH = −60.31 kJ mol−1). Three-dimensional fluorescence spectral results disclosed microenvironmental perturbations around Trp and Tyr residues of the protein upon PZP binding. Interestingly, the addition of PZP to HSA significantly protected the protein against thermal stress. Competitive drug displacement results obtained with warfarin, phenylbutazone and diazepam elucidated Sudlow's Site I, positioned in subdomain IIA of HSA, as the preferred binding site of PZP which was well supported by molecular docking analysis, while molecular dynamics simulation results suggested the stability of the PZP-HSA complex. Communicated by Vsevolod Makeev

Effective removal of arsenate from wastewater using aluminium enriched ferric oxide-hydroxide recovered from authentic acid mine drainage

This study explored an eco-friendly approach for the synthesis of novel aluminium enriched ferric oxide-hydroxide (Fe/AlO(OH)) from authentic acid mine drainage (AMD). The synthesized Fe/AlO(OH) was subsequently tested for arsenate removal capabilities. Fe/AlO(OH) was synthesized from bona fide AMD via selective precipitation, thermal activation, and vibratory ball milling. One-factor-at-a-time (OFAAT) method was used to optimize operational parameters, which include adsorbent dosage, concentration, pH, agitation time, and temperature. Optimized conditions were observed to be 150 ppm of As(V), Solid: Liquid ratio – 1 g: 250 mL, contact time of 60 min, and ambient temperature and pH. Limited temperature and pH effects on adsorption were observed. Equilibrium data fits using Langmuir-, Freundlich-, Two surface Langmuir-, Dubinin-Radushkevich-, and Dubinin-Astokov isotherm models showed highly favorable adsorption conditions, the highest known maximum adsorption capacity for As(V) of 102–129 mg g−1, and coupled physisorption/diffusion limited adsorption. Thermodynamic analysis showed positive Gibbs free energy (ΔG°), negative enthalpy change (ΔH°), and positive entropy change (ΔS°) – likely a result of an inner sphere complexation of the As(V) with the Fe/Al surface. Considering the obtained results, valorization of AMD for the synthesis of Fe/AlO(OH) was viable and effective. This initiative could potentially minimize the footprints of AMD and arsenic pollution.

Evidence for Dual Site Binding of Nile Blue A toward DNA: Spectroscopic, Thermodynamic, and Molecular Modeling Studies.

Binding of Nile Blue (NB) with calf thymus DNA has been studied using molecular modeling, spectroscopic, and thermodynamic techniques. Our study revealed that NB binds to the DNA helix by two types of modes (groove binding and intercalation) simultaneously. The thermodynamic study showed that the overall binding free energy is a combination of several negative and positive free energy changes. The binding was favored by negative enthalpy and positive entropy changes (due to the release of water from the DNA helix). The docking study validated all experimental evidence and showed that NB binds to a DNA minor groove at low concentrations and switches to intercalation mode at higher concentrations.

Applicability of gypsum in selective removal of anionic dye molecules from aqueous medium

This article describes how selectively anionic organic molecules could be removed from aqueous medium using naturally available gypsum (GS) adsorbent. Gypsum (CaSO4.2H2O) shows strong interactions with anionic dye molecules while it dos not show any affinity towards cationic dye molecules. We have shown the removal efficiency of gypsum taking chlorazole yellow (anionic dye) and methylene blue (cationic dye) as examples of adsorbates. The GS has been to be even more effective than activated carbon in attaining chlorazole yellow (CY) removal. Three well-known kinetic equations e.g. pseudo-first-order, pseudo-second order and intraparticle diffusion were exploited to interpret the experimental data. Results show best fitting with second order kinetic process with excellent regression coefficient (r2 = 0.99) for the adsorption process. The equilibrium data were analyzed exploiting some adsorption isotherm models. It was apparent that the Freundlich isotherm model superbly fitted for CY dye adsorption process. And the maximum adsorption capacity, Qm, was obtained as 12.85 mg g−1 at room temperature. The negative values of Gibb’s free energy change (ΔGo) suggests that the CY dye molecule adsorption process is spontaneous in nature. Moreover, negative enthalpy change (ΔHo) indicates the exothermic nature of the adsorption process. The outcome could be exploited where anionic organic molecules are required to be separated, selectively.

Molecular interaction of fluorescent carbon dots from mature vinegar with human hemoglobin: Insights from spectroscopy, thermodynamics and AFM

Foodborne nanoparticles have attracted considerable interest due to their distinctive fluorescence and physicochemical properties. The discovery of vinegar carbon dots (VCDs) has drawn our attention to study their effect on human plasma protein. Herein, spectral, constructional, morphological, and enzymatic activity assessments were carried out to investigate the interaction of VCDs with human hemoglobin (HHb). The intrinsic fluorescence of HHb was quenched significantly by the VCDs through a static quenching process. Furthermore, binding constants and important thermodynamic parameters were calculated, the negative enthalpy and entropy changes were accompanied by a negative Gibbs energy, which proposed the binding between VCDs with HHb was spontaneous. Moreover, negative enthalpy and entropy change corroborated the involvement of van der Waals force and hydrogen bonds in the binding process. Results from FTIR, atomic force microscopy and circular dichroism revealed change of HHB after binding with VCDs although their essential morphological features were unaffected. The esterase activity of HHb decreased after VCDs treatment in a dose-dependent manner, which further confirmed the effect of VCDs on HHb. The results offered detailed information about the interaction between VCDs and HHb.

Selective Binding of Cyclodextrins with Leflunomide and Its Pharmacologically Active Metabolite Teriflunomide.

The selectivity of encapsulation of leflunomide and teriflunomide by native α-, β- and γ-cyclodextrins was investigated through 1H NMR and molecular modeling. Thermodynamic analysis revealed the main driving forces involved in the binding. For α-cyclodextrin, the partial encapsulation was obtained while deep penetration was characterized for the other two cyclodextrins, where the remaining polar fragment of the molecule is located outside the macrocyclic cavity. The interactions via hydrogen bonding are responsible for high negative enthalpy and entropy changes accompanying the complexation of cyclodextrins with teriflunomide. These results were in agreement with the molecular modeling calculations, which provide a clearer picture of the involved interactions at the atomic level.

Interaction of a hydrophilic molecule with bovine serum albumin: A combined multi-spectroscopic, microscopic and isothermal calorimetric study in the presence of graphene oxide

One of the most widely studied plasma protein is bovine serum albumin (BSA), and it plays a crucial role in the binding and transportation of many exogenous and endogenous drugs. Coumarin derivatives play a crucial role as an analgesic, anticancer, and anticoagulant agent. Here in this report, we have studied the binding interaction between a 7-amino coumarin derivative, namely 7-(N, N′-diethylamino)coumarin-3-carboxylic acid (7-DCCA) with BSA and also have found out the effect of graphene oxide (GO) on the binding interaction. The binding interaction was probed by employing various spectroscopic, microscopic, isothermal titration calorimetric (ITC), and by using molecular docking studies. The change in absorption and emission maxima position of BSA and 7-DCCA in the absence and presence of GO along with the change in absorbance and emission intensity when we titrated by 7-DCCA or BSA respectively indicates the strong complexation between 7-DCCA and BSA. From the fluorescence resonance energy transfer study, the average distance between tryptophan 213 of the BSA (donor), and the 7-DCCA (acceptor) is found ~50 Ǻ. From excited-state lifetime and fluorescence lifetime imaging (FLIM) studies, we observed that the average lifetime of 7-DCCA is much higher in the presence of BSA compared to buffer medium and in the presence of BSA a heterogeneous environment was created around 7-DCCA. Again in the presence of GO, the formation of a complex of 7-DCCA with a low concentration of BSA shows greater binding interaction as compared to that in the absence of GO. Time-resolved fluorescence anisotropy measurement shows that the addition of GO provides a restricted environment surrounding the 7-DCCA molecule in the presence of both low and high concentrations of BSA. CD study demonstrates the same extent of reduction of α-helical content of BSA protein on binding with 7-DCCA in the absence and presence of GO. ITC study revealed that the interaction between 7-DCCA and BSA is favoured by negative enthalpy change and positive entropy change. Also, from the ITC study, we find out that GO doesn't inflict significant change in the overall global binding interaction pattern, rather it inflicts changes in the mechanistic pathways of binding between 7-DCCA and BSA. Step-scan FTIR studies show the modification of amide I and amide II bonds with time when complexation occurs between BSA and 7-DCCA in the absence and presence of GO. The docking result reveals that the deprotonated form of 7-DCCA has positioned at a distance of ~3.7 nm from Trp 213. Thus these interactions play a central role in the development of coumarin derivative based small molecules to be used for both academic and industrial purposes.

Synthesis of nano-ZIF-8@chitosan microspheres and its rapid removal of p-hydroxybenzoic acid from the agro-industry and preservatives

p-Hydroxybenzoic acid is an emerging contaminant because it has multiple sources such as the hydrolysis of methylparaben, ethylparaben and propylparaben used widely as preservatives in food and drinks, and as well as from the agro-industrial wastewaters. In this study, the nano-ZIF-8@chitosan microspheres (ZIF-8@CSM) were fabricated via the combination of inverse emulsion method and in-situ growth method. The performance of ZIF-8@CSM for the adsorption of p-hydroxybenzoic acid from aqueous solution was studied. The adsorption kinetics showed that the adsorption rapidly reached the equilibrium about 30 s. The equilibrium data were well described by the Langmuir isothermal model and the estimated maximum adsorption capacity was 128.70 mg/g. The thermodynamics analysis indicated negative free energy, enthalpy, and entropy changes suggesting that the adsorption process was spontaneous and exothermic. ZIF-8@CSM is promising to be used as a good adsorption material to remove p-hydroxybenzoic acid rapidly from aqueous solutions.

DNA/BSA binding of a new oxovanadium (IV) complex of glycylglycine derivative Schiff base ligand

In this study, a new oxovanadium (IV) Schiff base complex was synthesized by the reaction of {[5-(triethylammoniummethyl)salicylaldehyde]chloride}triethylammonium and vanadyl sulfate. The complex was characterized by elemental analysis, FT-IR and UV–Vis spectroscopy. The interaction between the complex and bovine serum albumin (BSA) was studied by absorption and emission titration methods. The quality of the spectral changes and the large calculated value of both the binding constant (Kb = 7.53 × 104 M−1) and the Stern-Volmer quenching constant (KSV = 7.65 × 104 M−1) proved the strong affinity of the complex to BSA. The static quenching mechanism was confirmed by comparing the calculated Kb values at four different temperatures. The negative changes in enthalpy and Gibbs free energy, proved that the BSA-complex binding is exothermic and spontaneous. The fluorescence data also indicated 1:1 binding stoichiometry of the complex on one binding site of BSA. Competitive experiments with site markers (phenylbutazone and ibuprofen) and synchronous measurements identified site I of BSA as the main binding site. Molecular docking results confirmed the binding pocket of site I (subdomain IIA) as the binding site. In the second part of the work, the binding of the complex to fish sperm DNA (FS-DNA) was investigated by UV–Vis absorption spectroscopy, fluorescence spectroscopy, viscosity measurement and cyclic voltammetry. The Stern-Volmer quenching and bimolecular quenching rate constants (KSV = 6.13 × 102 M−1, kq = 6.13 × 1010 M−1S−1) were calculated. Absorption and emission studies could present types of interactions for example groove binding and electrostatic. A minor changes in viscosity showed a groove binding mode. In cyclic voltammogram study, decrease in current and also shift of peak potentials positively after adding DNA supported a partial intercalation mode. Theoretical docking study proposed the minor groove as the main part for DNA-complex binding.

Insights into the mechanism of groove binding between 4-octylphenol and calf thymus DNA.

4-Octylphenol is an endocrine disruptor, belonging to environmental estrogens. It can be enriched in the human body through the food chain and may harm human health. Herein, we used a variety of spectroscopic techniques, molecular docking, and gel electrophoresis to study the interaction of 4-octylphenol and ctDNA. It was found that the mechanism of ctDNA quenching the endogenous fluorescence of 4-octylphenol was static quenching, and formed a complex. The negative enthalpy change (ΔH°), entropy change (ΔS°) and Gibbs free energy (ΔG°) have shown that 4-octylphenol and ctDNA spontaneously bind together under the action of hydrogen bonds and van der Waal's force. Viscosity, melting temperature and iodide quenching experiments showed that 4-octylphenol acted on the groove of ctDNA. Insignificant change in circular dichromism spectra further confirmed this binding mode. The binding sites and groups for 4-octylphenol and ctDNA interaction were identified by molecular docking. Gel electrophoresis found that 4-octylphenol at high concentrations caused DNA cleavage. Above findings may lay a theoretical foundation for understanding the toxicity mechanism of 4-octylphenol.

Syntheses, kinetics and thermodynamics of BODIPY-based fluorescent probes with different kinds of hydrophilic groups for the detection of biothiols

A series of BODIPY-based fluorescent probes incorporating different kinds of hydrophilic groups were synthesized for the detection of biothiols (GSH as a representative target), namely BDP (control), BDP-OH (acidic), BDP-OEG (neutral and hydrophilic) and BDP-QA (cationic). The incorporation of nitroolefin unit (-CHCH–NO2) to the BODIPY core enabled the OFF-ON fluorescent probes. The results indicated that the absorption and fluorescence emission spectra of the probes were essentially not affected by the hydrophilic groups attached on the para position of the meso phenyl group. The reaction rate constants were affected by the hydrophilicity of probes. It was highly worth noting that the cationic BDP-QA had the fastest response toward biothiols owing to the best water solubility and the possible formation of ion pairs with thiolate (R-S-). Thermodynamics illustrated that the reactions of probes with GSH all had negative enthalpy changes and negative entropy changes. Moreover, BDP-QA had the highest affinity toward GSH (K = 2.54 × 104 M−1) and the smallest LOD value (182 nΜ), which benefited from its best water solubility. This work has primarily elucidated the effects of hydrophilic groups from the kinetic and thermodynamic perspectives. It will promote better design of fluorescent probes with fast response and high affinity.

NAG-thiazoline is a potent inhibitor of the Vibriocampbellii GH20 β-N-Acetylglucosaminidase.

Vibrio spp. play a vital role in the recycling of chitin in oceans, but several Vibrio strains are highly infectious to aquatic animals and humans. These bacteria require chitin for growth; thus, potent inhibitors of chitin-degrading enzymes could serve as candidate drugs against Vibrio infections. This study examined NAG-thiazoline (NGT)-mediated inhibition of a recombinantly expressed GH20 β-N-acetylglucosaminidase, namely VhGlcNAcase from Vibriocampbellii (formerly V.harveyi) ATCC BAA-1116. NGT strongly inhibited VhGlcNAcase with an IC50 of 11.9±1.0μm and Ki 62±3µm, respectively. NGT was also found to completely inhibit the growth of V.campbellii strain 650 with an minimal inhibitory concentration value of 0.5µm. ITC data analysis showed direct binding of NGT to VhGlcNAcase with a Kd of 32±1.2μm. The observed ΔG°binding of -7.56kcal·mol-1 is the result of a large negative enthalpy change and a small positive entropic compensation, suggesting that NGT binding is enthalpy-driven. The structural complex shows that NGT fully occupies the substrate-binding pocket of VhGlcNAcase and makes an exclusive hydrogen bond network, as well as hydrophobic interactions with the conserved residues around the -1 subsite. Our results strongly suggest that NGT could serve as an excellent scaffold for further development of antimicrobial agents against Vibrio infections. DATABASE: Structural data are available in PDB database under the accession number 6K35.

Selective Extraction of Light Lanthanides(III) by N,N-Di(2-ethylhexyl)-diglycolamic Acid: A Comparative Study with N,N-Dimethyl-diglycolamic Acid as a Chelator in Aqueous Solutions.

The complexation and selectivity of N,N-di(2-ethylhexyl)-diglycolamic acid (HDEHDGA/kerosene, HA) toward the light lanthanides, La(III), Ce(III), Pr(III), and Nd(III), are presented for the extraction from chloride media. In the low pH region (pH 1.8–2.8), the obtained data reveal that the extraction of Ln(III) is governed by cation-exchange mechanism and is driven by the negative change in enthalpy. The results from the slope analysis method suggest the formation of LnA3·(HA)1or2 in the extraction process. As major extracted species with a core of LnA3 in the first coordination sphere, LnA3 might connect with one or two additional HA molecules in the second coordination sphere by hydrogen bonding. The LnA3 core might share similar coordination geometry to those of 1:3 Ln(III) complexes (LnA′3) with water-soluble N,N-dimethyl-diglycolamic acid (HDMDGA, HA′) formed in aqueous solutions or in solid-state compounds. The correlation between the extraction with HDEHDGA (HA) as an extractant and the complexation with HDMDGA (HA′) as a chelator has been explored by interpreting the separation factors for HA with the difference in the stability constants for HA′. Consequently, the ratios of the stability constants of the corresponding 1:3 complexes (LnA′3) with HDMDGA could be reasonably translated to the separation factors (SFs) with HDEHDGA, providing a valuable approach for understanding the origin of the extraction/separation mechanism. By comparing the extraction selectivity of HDEHDGA with that of the currently deployed extractants in the industry such as P204, P507, and Cyanex 272, HDEHDGA offers outstanding selectivity with considerable SFs (SFCe/La = 6.68, SFPr/Ce = 2.79, and SFNd/Pr = 2.65) for light Ln(III) pairs under conditions of low acid concentrations.