Isothermal Titration Microcalorimetry Research Articles

Microwave-Assisted Synthesis of β-N-Aryl Glycoamphiphiles with Diverse Supramolecular Assemblies and Lectin Accessibility.

Glycoamphiphiles have attracted considerable interest in a broad range of application fields owing to their solution and bulk-state self-assembly abilities. Despite their importance, the straightforward synthesis of glycoamphiphiles consisting of a hydrophilic carbohydrate linked to a hydrophobic aglycone remains one of the major challenges in glycosciences. Here, a rapid, simple, and efficient synthetic access to chemically stable glycoamphiphiles at physiological pH, namely, N-(β-d-glycosyl)-2-alkylbenzamide, is reported. It leverages the nonreductive amination of unprotected carbohydrates with ortho-substituted aniline derivatives which could be readily obtained by reacting commercially available primary alkylamines with isatoic anhydride. This strategy avoids protection and deprotection of sugar hydroxyl groups and the use of reductive agents, which makes it advantageous in terms of atom and step economy. Moreover, in order to circumvent the cons of classical N-aryl glycosylation, we investigate the use of microwave as a heat source that provides fast, clean, and high-yield β-N-arylation of unprotected carbohydrates. Their self-assembly into water led to multiple morphologies of dynamic supramolecular glycoamphiphiles that were characterized to assess their ability to bind to lectins from pathogenic bacteria. Biophysical interactions probed by isothermal titration microcalorimetry revealed micromolar affinities for most of the synthesized glycoamphiphiles.

Binding Thermodynamics of Ferrocenyl Ammoniums by Sulfonated Calix[4]arenes

AbstractThe binding constants (Ka), standard molar enthalpy changes (ΔH°), and entropy changes (TΔS°) between two sulfonated calix[4]arene hosts including rigid p‐sulfonatocalix[4]arene (SC4A) and flexible p‐sulfonatothiacalix[4]arene (STC4A), and three ferrocenyl ammonium guests modified by different aliphatic chains were determined in aqueous solution (pH 7.0 and pH 2.0) by isothermal titration microcalorimetry (ITC). The gained data indicated that for the flexible host STC4A, the host‐guest binding affinities increased with the increase of length of the aliphatic chain of guests whereas the rigid host SC4A behaved almost oppositely. Compared with those at pH 2.0, the binding affinities between the hosts and the guests were much stronger at pH 7.0. This should be attributed to the higher π‐electron density and the extra negative charge of calixarene cavities owing to one of the phenolic hydroxyl groups is deprotonated at pH 7.0, thus affording stronger π⋯π, C−H⋯π and electrostatic interactions. Job plot and ITC confirmed that the molecular binding were stoichiometric 1 : 1 between hosts and guests. NMR experiments showed that the signals of the guest protons with addition of hosts underwent pronounced upfield shifts suggesting the effective binding between hosts and guests. In addition, the molecular selective binding behavior was discussed from the perspective of thermodynamics.

Molecular toxicity of Cr(III) and Cr(VI) to defensive protein lysozyme and their differential mechanisms

Chromium (Cr) poses potential threats on human and ecological health through both food and environmental pathways. However, the response mechanisms of Cr to function-related proteins in human subjects and the differential effects in the case of different valence states of Cr are still lacking. Herein, the binding interactions and mechanisms of lysozyme to Cr(III) and Cr(VI) were investigated by isothermal titration microcalorimetry, multi-spectroscopy, enzyme activity assay, and molecular simulations. Our results indicated that the binding of Cr in different valence states with lysozyme was a relatively affinity process and mainly driven by hydrophobic forces. Both Cr species induced the looseness of backbone for lysozyme and the enhancement of hydrophilicity around the backbone microenvironment. Otherwise, the α-helix of lysozyme was decreased with different valence states of Cr, while Cr(III) showed a greater degree of influence and a stronger regularity. Interestingly, no significant changes in the microenvironment around aromatic amino acid residues were observed under the exposure of different valence states of Cr. Differential structural changes of lysozyme resulted in activity alterations. At 80 mg·L−1 of Cr, Cr (VI) reduced the lysozyme activity to 81.44% of the control, while the lysozyme activity was significantly reduced to 24.45% under the exposure of Cr (III). Further molecular docking showed that amino acids near the binding sites of different valence states of Cr with lysozyme were not identical, but the enzyme active site, Asp52, was all within the binding pocket. This study elucidates the differential toxicity effects and interaction mechanisms of Cr in different valence states, and offers a comprehensive strategy for exploring the in vitro responses of toxicants exposure.

Isolation and identification of dipeptidyl peptidase-IV inhibitory peptides from Sacha inchi meal.

Sacha inchi meal (SIM) is a by-product of oil processing. Our previous studies showed that SIM hydrolysates exhibited dipeptidyl peptidase-IV (DPP-IV) inhibition activity. The objective of the present work was to identify and characterize the bioactive peptides from protein hydrolysates of SIM; enzyme kinetics and peptide-enzyme interaction were also investigated. From SIM hydrolysates, ten peptides responsible for the activity were identified: GPSRGF (GF-6), FPILSPDPA (FA-9), APYRRGGKI (AI-9), WPYH (WH-4), DPATWLALPT (DT-10), NPEDEFRQQ (NQ-9), APESKPVGV (AV-9), LEWRDR (LR-6), APVYWVQ (AQ-7) and LLMWPY (LY-6). The IC50 values of five peptides (GF-6, WH-4, AQ-7, AV-9 and LY-6) with better inhibitory activity on DPP-IV were within the range of 23.43-128.40 μmol L-1 . AQ-7 had the best activity, with an IC50 value of 23.43 μmol L-1 . Enzyme kinetics indicated the presence of various inhibition types (mixed, non-competitive and competitive). Isothermal titration microcalorimetry showed that the main forces of the binding sites between peptide (GF-6 or AQ-7) and DPP-IV were hydrogen bond, hydrophobic interaction and van der Waals force. The key residues involved in peptide-enzyme interaction were determined by molecular docking. Furthermore, at a concentration of 800 μmol L-1 , GF-6 was found to significantly increase the glucose consumption in insulin-resistant HepG2 cells (P < 0.05) compared with the model group. Sacha inchi meal-derived peptides displayed potent DPP-IV inhibition activity and could be used in the health food industry and as lead compounds for diabetes therapy. © 2023 Society of Chemical Industry.

Assessing the Contribution of the Neutral Blocks in DNA/Block-Copolymer Polyplexes: Poly(acrylamide) vs. Poly(ethylene Oxide).

The interaction of DNA with different block copolymers, namely poly (trimethylammonium chloride methacryloyoxy)ethyl)-block-poly(acrylamide), i.e., (PTEA)-b-(PAm), and poly (trimethylammonium chloride methacryloyoxy)ethyl)-block-poly(ethylene oxide), i.e., (PTEA)-b-(PEO), was studied. The nature of the cationic block was maintained fixed (PTEA), whereas the neutral blocks contained varying amounts of acrylamide or (ethylene oxide) units. According to results from isothermal titration microcalorimetry measurements, the copolymers interaction with DNA is endothermic with an enthalpy around 4.0 kJ mol-1 of charges for (PTEA)-b-(PAm) and 5.5 kJ mol-1 of charges for (PTEA)-b-(PEO). The hydrodynamic diameters of (PTEA)-b-(PEO)/DNA and (PTEA)-b-(PAm)/DNA polyplexes prepared by titration were around 200 nm at charge ratio (Z+/-) &lt; 1. At Z+/- close and above 1, the (PTEA)50-b-(PAm)50/DNA and (PTEA)50-b-(PAm)200/DNA polyplexes precipitated. Interestingly, (PTEA)50-b-(PAm)1000/DNA polyplexes remained with a size of around 300 nm even after charge neutralization, probably due to the size of the neutral block. Conversely, for (PTEA)96-b-(PEO)100/DNA polyplexes, the size distribution was broad, indicating a more heterogeneous system. Polyplexes were also prepared by direct mixture at Z+/- of 2.0, and they displayed diameters around 120-150 nm, remaining stable for more than 10 days. Direct and reverse titration experiments showed that the order of addition affects both the size and charge of the resulting polyplexes.

A Fucosylated Lactose-Presenting Tetravalent Glycocluster Acting as a Mutual Ligand of Pseudomonas aeruginosa Lectins A (PA-IL) and B (PA-IIL)-Synthesis and Interaction Studies.

The Gram-negative bacterium Pseudomonas aeruginosa is an important opportunistic human pathogen associated with cystic fibrosis. P. aeruginosa produces two soluble lectins, the d-galactose-specific lectin PA-IL (LecA) and the l-fucose-specific lectin PA-IIL (LecB), among other virulence factors. These lectins play an important role in the adhesion to host cells and biofilm formation. Moreover, PA-IL is cytotoxic to respiratory cells in the primary culture. Therefore, these lectins are promising therapeutic targets. Specifically, carbohydrate-based compounds could inhibit their activity. In the present work, a 3-O-fucosyl lactose-containing tetravalent glycocluster was synthesized and utilized as a mutual ligand of galactophilic and fucophilic lectins. Pentaerythritol equipped with azido ethylene glycol-linkers was chosen as a multivalent scaffold and the glycocluster was constructed by coupling the scaffold with propargyl 3-O-fucosyl lactoside using an azide-alkyne 1,3-dipolar cycloaddition reaction. The interactions between the glycocluster and PA-IL or PA-IIL were investigated by isothermal titration microcalorimetry and saturation transfer difference NMR spectroscopy. These results may assist in the development of efficient anti-adhesion therapy for the treatment of a P. aeruginosa infection.

Explanation and Exploration of the Isothermal Titration Curve for the NaCl + Na2SO4 + H2O System at 298.15 K and 102.2 kPa.

Isothermal titration microcalorimetry (ITC) is a common and powerful tool in thermodynamics and related fields, and the connection between the solution behavior and raw titration curve is complex, important, and worth studying, so we try to discuss this problem using a complex solid–solid–liquid diagram. Although there are many experimental methods for studying ternary phase diagrams, ITC has been proven to be a simple, universal method at normal temperature and pressure. This method can be extended to investigate phase diagrams of multisalt aqueous solutions and related systems. Here, the phase equilibrium of one common ternary system (NaCl + Na2SO4 + H2O) was determined using the ITC method with the aid of X-ray diffraction measurements. This isothermal and isobaric titration method can be used not only to determine the boundaries of different phase regions by analyzing changes in the slope of the observed heat vs solvent concentration plot but also to provide additional accurate data regarding the solid dissolution enthalpy and the dilution enthalpy. The dissolution enthalpy of 1 mol NaCl (Na2SO4) solid dissolving in water to just form a saturated solution is measured at 1.92 kJ/mol (−15.60 kJ/mol), and the dissolution enthalpy of the mixed solids can be evaluated with these data. The dilution enthalpy is strongly dependent on the solute concentration (0.08–0.23 kJ/mol at the range of concentration studied), and for the same range concentration of a solute, the dilution enthalpy of Na2SO4 is positive and larger than that of NaCl. Therefore, the connection between the observed heat and the microscopic behavior and the separation between the dissolution and dilution data may result in the possibility to gain a clearer understanding about the solution behaviors.

Secondary Ammonium-Based Hyperbranched Poly(amidoamine) with Excellent Membrane-Active Property for Multidrug-Resistant Bacterial Infection.

With the rapid emergence of microbial infections induced by "superbugs", public health and the global economy are threatened by the lack of effective and biocompatible antibacterial agents. Herein, we systematically design a series of secondary ammonium-based hyperbranched poly(amidoamine) (SAHBP) with different alkyl chain lengths for probing high-efficacy antibacterial agents. SAHBP modified with alkyl tails at the hyperbranched core could efficiently kill Escherichia coli and Staphylococcus aureus, two types of clinically important bacteria worldwide. The best SAHBP with 12-carbon-long alkyl tails (SAHBP-12) also showed high activity against problematic multidrug-resistant bacteria, including Pseudomonas aeruginosa and methicillin-resistant S. aureus (MRSA). Based on ζ potential, isothermal titration microcalorimetry (ITC), and membrane integrity assays, it is found that SAHBP-12 could attach to the cell membrane via electrostatic adsorption and hydrophobic interactions, following which the integrity of the bacterial cell wall and the cell membrane is disrupted, resulting in severe cell membrane damage and the leakage of cytoplasmic contents, finally causing bacterial cell death. Impressively, benefiting from excellent membrane-active property, SAHBP-12 exhibited robust therapeutic efficacy in MRSA-infected mice wounds. Moreover, SAHBP-12 also showed excellent biosafety in vitro and in vivo, which undoubtedly distinguished it as a potent weapon in combating the growing threat of problematic multidrug-resistant bacterial infections.

Exploring the interaction between lactoferrin and CdTe quantum dots: Energetic and molecular dynamic study

The kinetic and energetic characterization of interactions between quantum dots (QDs) and proteins is fundamental for understanding the toxicity and effectiveness of these nanoparticles in therapeutic applications. In this study, we combined kinetic and thermodynamic data from surface plasmon resonance (SPR) and isothermal titration microcalorimetry (ITC) to explore the complexation mechanism between thioglycolic acid-capped cadmium telluride QD (CdTe@TGA) and bovine lactoferrin (LF) under physiological conditions. The SPR results demonstrated that QD binds to LF forming a 1:1 [LF-CdTe@TGA]° thermodynamically stable complex, whose binding constant (KbSPR) ranged from 7.18 × 104 to 6.75 × 104 M−1. The association rate constant (ka) values were in the order of 103 M−1 s−1 while the complex residence time (tR) was ∼70 s. The formation of both [LF-CdTe@TGA]° and [LF-CdTe@TGA]‡ activated complexes occurred with the compensation of the enthalpic and entropic terms with the increase in temperature, characterizing enthalpy–entropy compensation (EEC), and iso-kinetic (IC) compensation, respectively. Using ITC, we also found the formation of a 1:1 [LF-CdTe@TGA]° complex, but the calculated KbITC values were on the order of 107 L mol−1. Again, we found that the formation of [LF-CdTe@TGA]°was exothermic and entropically favorable at 298.15 K, although ΔHITC° (−20.46 kJ mol−1) and TΔSITC° (24.13 kJ mol−1) values were higher in magnitude than those found by SPR (ΔHSPR°=−17.35 kJ mol−1 and TΔSSPR° = 10.39 kJ mol−1). We believe that this fundamental study will provide new insights into the safe and effective application of QDs in biological and medical fields.

Mechanism of Mucin Recognition by Lectins: A Thermodynamic Study.

Isothermal titration microcalorimetry (ITC) can directly determine the thermodynamic binding parameters of biological molecules including affinity constant, binding stoichiometry, heat of binding (enthalpy) and indirectly the entropy, and free energy of binding. ITC has been extensively used to study the binding of lectins to mono- and oligosaccharides, but limitedly in applications to lectin-glycoprotein interactions. Inherent experimental challenges to ITC include sample precipitation during the experiment and relative high amount of sample required, but careful design of experiments can minimize these problems and allow valuable information to be obtained. For example, the thermodynamics of binding of lectins to multivalent globular and linear glycoproteins (mucins) have been described. The results are consistent with a dynamic binding mechanism in which lectins bind and jump from carbohydrate to carbohydrate epitope in these molecules leading to increased affinity. Importantly, the mechanism of binding of lectins to mucins appears similar to that for a variety of protein ligands binding to DNA. Recent results also show that high-affinity lectin-mucin cross-linking interactions are driven by favorable entropy of binding that is associated with the bind and jump mechanism. The results suggest that the binding of ligands to biopolymers, in general, may involve a common mechanism that involves enhanced entropic effects that facilitate binding interactions.

Influence of cationic groups on the antibacterial behavior of cationic nano-sized hyperbranched polymers to enhance bacteria-infected wound healing.

With the continuous emergence of drug-resistant pathogens, new strategies with high antibacterial efficacy are urgently needed. Herein, five cationic nano-sized hyperbranched polymers (CNHBPs) with cationic functional groups have been constructed, and their antibacterial mechanism has been studied in detail. CNHBPs bearing secondary ammonium salt groups and long alkyl chains (S12-CNHBP) exhibited weak antibacterial and antibiofilm ability, while CNHBPs bearing quaternary ammonium salt groups and long alkyl chains (Q12-CNHBP) showed the highest antimicrobial and strongest antibiofilm activities. ζ potential and isothermal titration microcalorimetry (ITC) results suggest that the negatively charged surfaces of bacterial cells provided Q12-CNHBP with a higher intrinsic electrostatic driving force for bacterial killing than that with S12-CNHBP. Fluorescent tracing and morphological observations indicate that the bacterial genome might be another antibacterial target for S12-CNHBP in addition to the cell wall and membrane, which are mainly antibacterial targets for Q12-CNHBP, making it less likely to induce bacterial resistance. Surprisingly, Q12-CNHBP exhibited superior in vivo therapeutic efficacy in a mouse wound model of methicillin-resistant Staphylococcus aureus (MRSA) infection with low toxicity during treatment. These advantages and ease of preparation will undoubtedly distinguish Q12-CNHBP as a new class of suitable candidates to combat multidrug-resistant pathogen infections. This study opens up a new avenue for exploiting antibacterial biomaterials to treat infections caused by drug-resistant bacteria.

Applications of isothermal titration calorimetry in pure and applied research from 2016 to 2020.

The last 5 years have seen a series of advances in the application of isothermal titration microcalorimetry (ITC) and interpretation of ITC data. ITC has played an invaluable role in understanding multiprotein complex formation including proteolysis-targeting chimeras (PROTACS), and mitochondrial autophagy receptor Nix interaction with LC3 and GABARAP. It has also helped elucidate complex allosteric communication in protein complexes like trp RNA-binding attenuation protein (TRAP) complex. Advances in kinetics analysis have enabled the calculation of kinetic rate constants from pre-existing ITC data sets. Diverse strategies have also been developed to study enzyme kinetics and enzyme-inhibitor interactions. ITC has also been applied to study small molecule solvent and solute interactions involved in extraction, separation, and purification applications including liquid-liquid separation and extractive distillation. Diverse applications of ITC have been developed from the analysis of protein instability at different temperatures, determination of enzyme kinetics in suspensions of living cells to the adsorption of uremic toxins from aqueous streams.

Binding interactions of acrylamide with lysozyme and its underlying mechanisms based on multi-spectra, isothermal titration microcalorimetry and docking simulation

Acrylamide is a known carcinogenic and neurotoxic organic compound that is widespread in the environment and poses potential threats to human beings and other living organisms. Herein, we explored the interaction mechanism of acrylamide with lysozyme via multiple spectroscopic approaches, ITC (isothermal titration calorimetry), enzyme activity, as well as molecular docking under physiological conditions. Results suggested that acrylamide can interact with lysozyme fluorophore residues including Trp and Tyr, and exhibit a fluorescence sensitization ability toward these amino acids. The direct interaction of lysozyme with acrylamide resulted in the unfolding of polypeptide chains along with the loosening of protein skeletons, decreasing the α-helical content, and hence a smaller size of lysozyme agglomerated. Moreover, acrylamide docked to lysozyme at relatively low affinity and the interactions were primarily driven by van der Waals and hydrogen bonding interactions. Further molecular analyses illustrated that the binding site was around the active center of lysozyme, acrylamide interacted with Glu 35, Asn 44, Asn 46, Asp 52, Gln 57, Ala 107, Trp 108 and Val 109. The molecular lysozyme activity was repressed due to the direct cross talk of acrylamid with the key residues Glu 35, as well as Asp 52 of the enzyme activity near the active center lysozyme. In addition, the fluorophore residues Trp 108 was also in the binding pocket, which can also explain the fluorescence sensitization phenomenon. Taken together, our study demonstrated the structure and function of lysozyme were both affected by acrylamide.

Gallium-binding peptides as a tool for the sustainable treatment of industrial waste streams

Here we provide a proof of principle for an application-oriented concept for the peptide-based recovery of gallium in industrial wastewater, which was supported by biosorption studies with a real wastewater sample. We investigated the interaction of the gallium-binding peptides TMHHAAIAHPPH, NYLPHQSSSPSR, SQALSTSRQDLR, HTQHIQSDDHLA, and NDLQRHRLTAGP with gallium and arsenic through different experimental and computational approaches. Data obtained from isothermal titration microcalorimetry indicated a competitive influence by the presence of acetate ions with an exothermic contribution to the otherwise endothermic peptide gallium interactions. For peptide HTQHIQSDDHLA, a stabilizing influence of acetate ions on the metal peptide interaction was found. Peptide NYLPHQSSSPSR showed the highest affinity for gallium in ITC studies. Computational modeling of peptide NYLPHQSSSPSR was used to determine interaction parameters and to explain a possible binding mechanism. Furthermore, the peptides were immobilized on polystyrene beads. Thus, we created a novel and exceptionally robust peptide-based material for the biosorption of gallium from an aqueous solution. Data obtained from isothermal titration microcalorimetry indicated a competitive influence by the presence of acetate ions with an exothermic contribution to the otherwise endothermic peptide gallium interactions. For peptide HTQHIQSDDHLA, a stabilizing influence of acetate ions on the metal peptide interaction was found. Peptide NYLPHQSSSPSR showed the highest affinity for gallium in ITC studies. Computational modeling of peptide NYLPHQSSSPSR was used to determine interaction parameters and to explain a possible binding mechanism. Furthermore, the peptides were immobilized on polystyrene beads. Thus, we created a novel and exceptionally robust peptide-based material for the biosorption of gallium from an aqueous solution.

Dextran Sulfate/Pramlintide Polyelectrolyte Nanoparticles as a Promising Delivery System: Optimization, Evaluation of Supramolecular Interactions and Effect on Conformational Stability of the Peptide Drug

In this study, we investigated the feasibility to obtain nanoparticles (NPs) by assembling pramlintide (Pram) with dextran sulfate (DexS), as a new approach for mucosal peptide delivery. DexS/Pram NPs were prepared by dropwise addition of a Pram solution to a DexS solution under magnetic stirring. The physicochemical characteristics of NPs and molecular interactions involved in the co-assembling were evaluated by dynamic light scattering (DLS), transmission electronic microscopy (TEM), isothermal titration microcalorimetry, Fourier-transform infrared spectroscopy (FTIR), fluorescence quenching, and circular dichroism (CD). DexS/Pram NPs displayed a narrow size distribution (ca. 200 nm), negative zeta potential (ca. −40 mV), association efficiency close to 100%, and nanogel behavior. The assembling with DexS increased the Pram α-helical content, stabilizing the peptide in its bioactive form. The colloidal stability of nanoparticles was dependent on the salt concentration and it could be assumed that peptide release from nanoparticles occurs by dissociation of the complex at physiological conditions.

Interaction with longan seed polyphenols affects the structure and digestion properties of maize starch

This study investigated effects of longan seed polyphenols (LSPs) on the structure and digestion properties of starch, and discussed the interaction mechanism between starch and LSPs. The results showed cooking with 20 % LSPs did not change amylopectin chain length distribution of normal maize starch, however, the amylose content was reduced from 21.60 to 14.03 %. This suggests LSPs may interact with starch via non-covalent bond. Isothermal titration microcalorimetry and XRD results confirmed the existence of non-covalent interaction, and indicated that LSPs may enter the hydrophobic cavity of amylose, forming V-type inclusion complex. LSPs did not affect gelatinization temperatures of maize starch, whereas 20 % LSPs decreased the enthalpy change by about 26 %. The digestion results indicate significant inhibition effect of LSPs on the digestion of cooked starch, attributing to the interaction of LSPs with starch. These suggest potential applications of LSPs as functional ingredients in modulating postprandial glycemic response of starchy food.

Measuring boundaries in phase diagrams of ternary systems using titration calorimetry

This paper demonstrates how isothermal titration microcalorimetry (ITC) can be used for the global construction of several kinds of phase diagrams for ternary systems at 298.15 K and atmospheric pressure. The solid-solid-liquid system of KCl-KNO3-H2O has not yet been studied using ITC, and thus, it is the main system discussed. It is clear that thermal effects associated with transformations in a system (appearance or disappearance of a phase) change with the composition of the system in ampoule. During titration, the solubility curves (including the liquid-liquid and solid-liquid equilibrium lines) in ternary systems can be detected as changes in the slope of the heat evolved vs time plot or in the slope of the observed heat vs solvent concentration plot. ITC is more precise and repeatable than the visual-cloud-point method. This isothermal and isobaric titration method can also provide additional information regarding the dissolution heat and the dilution heat. On the basis of the three experimental solubilities of KCl, KNO3, and KCl + KNO3 (co-saturated solution) in H2O, the other intermediate points on the solubility curve can be obtained based on the lever rule and the assumption of ideal solution, and these results agree well with the experimental values.

Adsorption of ciprofloxacin to functionalized nano-sized polystyrene plastic: Kinetics, thermochemistry and toxicity

Plastic debris is ubiquitous in aquatic systems and has been proven vehicles for the transport of various pollutants including trace organic compounds. Nanoplastics have large specific surface area and hydrophobic characteristics and therefore are capable of adsorbing other organic or inorganic chemicals from the environment. Antibiotics, as another class of emerging contaminants, have raised significant research concern in recent years as they pose threats to the ecosytems and human health. Nevertheless, little information is available on the adsorption behaviors of antibiotics onto nano-sized plastics. The toxicity of combined nanoplastics and antibiotics is also largely unknown. In this study, the physicochemical and thermodynamic interactions between representative nanoplastics, which containing a carboxyl functional group of polystyrene nanoplastics (PS-COOH), and typical antibiotic, i.e., ciprofloxacin (CIP) were investigated in a batch adsorption experiment. The specific thermodynamic correlation function of PS-COOH combined with CIP was obtained through isothermal titration microcalorimetry (ITC) analysis. The adsorption kinetics and isotherm of CIP on PS-COOH closely fit the pseudo-second-order kinetic model (r2 = 0.99) and Freundlich isotherm (r2 = 0.99). The ITC results showed that the adsorption reaction of PS-COOH with CIP was a spontaneous exothermic reaction. The adsorption of antibiotics on nanoplastics may aggravate the negative impacts of these two pollutants on aqueous ecosystems, and we hypothesized that would be reflected in the survival rate of model organism of Caenorhabditis elegans when exposed to this combination. This work used a mechanistic approach to unravel the adsorption behavior of antibiotics on nanoplastics and shed light on their potential impact on aquatic ecosystems.

Structural ensemble and biological activity of DciA intrinsically disordered region

DciA is a newly discovered bacterial protein involved in loading the replicative helicase DnaB onto DNA at the initiation step of chromosome replication. Its three-dimensional structure is composed of a folded N-terminal domain (residues 1–111) resembling K Homology domains and a long disordered C-terminal tail (residues 112–157) which structure–activity relationship remains to be elucidated. In the present study on Vibrio cholerae DciA, we emphasize the importance of its disordered region to load DnaB onto DNA using surface plasmon resonance (SPR) and isothermal titration microcalorimetry (ITC). Then we characterize the conformational ensemble of the full-length protein using a combination of circular dichroism (CD), small angle X-ray scattering (SAXS), and molecular dynamics (MD) simulations. The atomic-level structural ensemble generated by MD simulations is in very good agreement with SAXS data. From initial conformations of the C-terminal tail without any secondary structure, our simulations bring to light several transient helical structures in this segment, which might be molecular recognition features (MoRFs) for the binding to DnaB and its recruitment and loading onto DNA.

Partition and Solubilization of Phospholipid Vesicles by Noncovalently Constructed Oligomeric-like Surfactants.

This work has investigated the interaction of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles with oligomeric surfactants noncovalently formed by sodium dodecyl sulfate (SDS) and a series of polyamines, 1,3-diaminopropane (PDA), triamine, spermidine, and spermine. The partition coefficients (P) of these surfactants between lipid bilayers and the aqueous phase are measured by isothermal titration microcalorimetry (ITC), showing that the P value increases and the Gibbs free energy of the partition becomes more negative with increasing oligomerization degree of the surfactants. This changing trend is similar to that of synthetic oligomeric surfactants regardless of the charge properties, suggesting that the polyamine and SDS molecules interact with the DOPC bilayer simultaneously. Meanwhile, the DOPC solubilization by these surfactants is evaluated by the effective surfactant-to-lipid molar ratios for the onset (Resat) and end (Resol) of the solubilization process, which are determined from the phase boundaries obtained by ITC, turbidity, and dynamic light scattering measurements. With the increment of oligomerization degree, the Resat and Resol values increase anomalously and are much larger than those of the synthetic surfactants with the same oligomerization degree, suggesting that noncovalently constructed oligomeric surfactants exhibit lower solubilization ability to phospholipid vesicles than the corresponding covalent oligomeric surfactants. Therefore, the noncovalently constructed oligomeric-like surfactants facilitate strong partition but weak solubilization to phospholipid vesicles, which may provide a useful strategy to mildly adjust the permeation and fluidity of phospholipid vesicles with solubilization delay.