Isothermal Titration Microcalorimetry Research Articles

Multi‐Colored Fibers by Self‐Assembly of DNA, Histone Proteins, and Cationic Conjugated Polymers

The development of biomolecular fiber materials with imaging ability has become more and more useful for biological applications. In this work, cationic conjugated polymers (CCPs) were used to construct inherent fluorescent microfibers with natural biological macromolecules (DNA and histone proteins) through the interfacial polyelectrolyte complexation (IPC) procedure. Isothermal titration microcalorimetry results show that the driving forces for fiber formation are electrostatic and hydrophobic interactions, as well as the release of counterions and bound water molecules. Color-encoded IPC fibers were also obtained based on the co-assembly of DNA, histone proteins, and blue-, green-, or red- (RGB-) emissive CCPs by tuning the fluorescence resonance energy-transfer among the CCPs at a single excitation wavelength. The fibers could encapsulate GFP-coded Escherichia coli BL21, and the expression of GFP proteins was successfully regulated by the external environment of the fibers. These multi-colored fibers show a great potential in biomedical applications, such as biosensor, delivery, and release of biological molecules and tissue engineering.

Phosphorylation adjacent to the nuclear localization signal of human dUTPase abolishes nuclear import: structural and mechanistic insights

Phosphorylation adjacent to nuclear localization signals (NLSs) is involved in the regulation of nucleocytoplasmic transport. The nuclear isoform of human dUTPase, an enzyme that is essential for genomic integrity, has been shown to be phosphorylated on a serine residue (Ser11) in the vicinity of its nuclear localization signal; however, the effect of this phosphorylation is not yet known. To investigate this issue, an integrated set of structural, molecular and cell biological methods were employed. It is shown that NLS-adjacent phosphorylation of dUTPase occurs during the M phase of the cell cycle. Comparison of the cellular distribution of wild-type dUTPase with those of hyperphosphorylation- and hypophosphorylation-mimicking mutants suggests that phosphorylation at Ser11 leads to the exclusion of dUTPase from the nucleus. Isothermal titration microcalorimetry and additional independent biophysical techniques show that the interaction between dUTPase and importin-α, the karyopherin molecule responsible for `classical' NLS binding, is weakened significantly in the case of the S11E hyperphosphorylation-mimicking mutant. The structures of the importin-α-wild-type and the importin-α-hyperphosphorylation-mimicking dUTPase NLS complexes provide structural insights into the molecular details of this regulation. The data indicate that the post-translational modification of dUTPase during the cell cycle may modulate the nuclear availability of this enzyme.

Comparative studies on the interaction of [C4mim]Br, and [C8mim]Br with β-casein micelles

The comparative studies on the interactions of β-casein micelles (β-CMs) with imidazolium-based ionic liquids (ILs) containing different hydrophobicity (1-octyl-3-methylimidazolium bromide [C8mim]Br and 1-butyl-3-methylimidazolium bromide [C4mim]Br) have been carried out using turbidity, dynamic light scattering (DLS), transmission electron microscopy (TEM), conductivity, steady-state fluorescence and isothermal titration microcalorimetry (ITC) measurements. The structure and microenvironmental polarity of β-CM can be controlled by the addition of ILs. The controlling effect depends much on the alkyl chain that attached to the imidazolium ring and the polarity of the IL. The partitioning of IL molecules in different locations of β-CM depends on the concentration and chain characteristics of ILs. In addition to the electrostatic attraction, the binding of the cationic [Cnmim]+ headgroup to β-CM should be dominated by the hydrophobic interaction among the alkyl tails of the IL and the hydrophobic domain of β-CM. Also, C2-H of [Cnmim]+ could easily participate in hydrogen bonding interaction with the carboxylic moiety of protein molecules. The complementary results obtained from the multitechnique approaches proved useful in drawing out the mechanism of interaction between amphiphilic protein aggregates and ionic liquid with different chain architecture in different IL concentration regimes, which will in turn facilitate the use of protein–IL systems in foods, pharmaceuticals, biotechnology and related industries.

Partitioning of α-lactalbumin and β-lactoglobulin from cheese whey in aqueous two-phase systems containing poly (ethylene glycol) and sodium polyacrylate

Partitioning behavior of the whey proteins α-lactalbumin (α-la) and β-lactoglobulin (β-lg) in aqueous two-phase systems prepared with poly ethylene glycol (PEG) and sodium polyacrilate (NaPA) was investigated as a function of pH and polymer concentrations. It was observed that α-la concentrated in the PEG phase while β-lg concentrated in the NaPA phase. Response surface methodology was applied to optimize protein partitioning and to achieve the best conditions for their fractionation. Thermodynamic analysis based on isothermal titration microcalorimetry indicated that the partitioning of α-la was accompanied by endothermic heat and was entropically driven, while β-lg partitioning was accompanied by exothermic heat and was enthalpically driven at low polymer concentrations and entropically driven at high polymer concentrations. Purification and yield parameters were determined using fresh whey and the results allowed for conclusion of the great applicability of this new system for α-la and β-lg fractionation.

Complex Formation and Aggregate Transitions of Sodium Dodecyl Sulfate with an Oligomeric Connecting Molecule in Aqueous Solution

Anionic single-tail surfactant sodium dodecyl sulfate (SDS) and a molecule with multiple amido and amine groups (Lys-12-Lys) were used as building blocks to fabricate oligomeric surfactants through intermolecular interactions. Their interactions and the resultant complex and aggregate structures were investigated by turbidity titration, isothermal titration microcalorimetry, dynamic light scattering, cryogenic transmission electron microscopy, freeze-fracture transmission electron microscopy, (1)H NMR, and 1D NOE techniques. At pH 11.0, the interaction between SDS and Lys-12-Lys is exothermic and mainly resulted from hydrogen bonding among the amido and amine groups of Lys-12-Lys and the sulfate group of SDS and hydrophobic interaction between the hydrocarbon chains of SDS and Lys-12-Lys. At pH 3.0, each Lys-12-Lys carries four positive charges and two hydrogen bonding sites. Then SDS and Lys-12-Lys form complexes Lys-12-Lys(SDS)6 and Lys-12-Lys(SDS)4 through the head groups by electrostatic attraction and hydrogen bonds assisted by hydrophobic interaction. Moreover, the complexes pack more tightly in their aggregates with the increase of the molar ratio. Especially the Lys-12-Lys(SDS)4 and Lys-12-Lys(SDS)6 complexes behave like oligomeric surfactants taking Lys-12-Lys as a spacer group, exhibiting a series of aggregates transitions with the increase of concentration, i.e., larger vesicles, smaller spherical micelles, and long threadlike micelles. Therefore, oligomeric surfactants Lys-12-Lys(SDS)4 and Lys-12-Lys(SDS)6 have been successfully fabricated by using a single chain surfactant and an oligomeric connecting molecule through noncovalent association.

Molecular Interactions, Proton Exchange, and Photoinduced Processes Prompted by an Inclusion Process and a [2]Pseudorotaxane Formation

Appropriate design of the host and guest components allows formation of a novel [2]pseudorotaxane complex with an interrupted photoinduced electron transfer (PET)-coupled fluorescence resonance energy transfer (FRET) response. This is the first example of an inclusion complex with NO6-based azacrown ether as the host unit (H). Different guest molecules (G1, G2, G3, and G4) with varying stopper size are used for the studies. Unlike G1, G2, and G3, G4 with a relatively bulkier stopper fails to form a [2]pseudorotaxane complex. Isothermal titration microcalorimetry measurements reveal a systematic increase in the association constant for H·G1, H·G2, and H·G3 with a change in the stopper size. Thermodynamic data suggest that the formation of H·G1/H·G2/H·G3 is exclusively driven by a large positive entropic gain (TΔS = 19.69/26.80/21.81 kJ·mol(-1)), while the enthalpy change is slightly negative for H·G1/H·G3 (-2.61/-1.97 kJ·mol(-1)) and slightly positive for H·G2 (ΔH = 5.98 kJ·mol(-1)). For these three inclusion complexes, an interrupted PET-coupled FRET response is observed with varying efficiency, which is attributed to the subtle differences in acidity of the NH2(+) unit of the guest molecules and thus the proton exchange ability between the host and respective guest. This is substantiated by the results of the computational studies.

Microcalorimetric study of the adsorption of lactoferrin in supermacroporous continuous cryogel with immobilized Cu2+ ions

The adsorption affinity of lactoferrin from whey in monolithic supermacroporous cryogel was analyzed using equilibrium data adsorptive isothermal titration microcalorimetry to measure thermodynamic information governing the process. Isotherm data was obtained at temperatures of 20, 30 and 40°C, pH 6, 7 and 8, and ionic strength of 200, 600 and 1000mmolL−1 NaCl. The Langmuir model was fitted to equilibrium data. The binding was tighter at higher temperatures. The adsorption of protein was observed as spontaneous in all cases analyzed. The microcalorimetric study indicated that, in most cases examined, the adsorption of the protein in the matrix was entropy and enthalpy favored and entropy driven. Results provide data to enable the improvement of technical processes for the affinity separation of proteins.

Critical solvent thermodynamic effect on molecular recognition: The case of the complex formation of carboxylates and ammonium-squaramido based receptors

An isothermal titration microcalorimetry (ITC) study on the supramolecular complex formation between carboxylates and ammonium-squaramido based receptors at different ethanol:water proportions is reported. The results obtained show that the formation enthalpy sign of a supramolecular complex in a water–ethanol binary mixture can be influenced by the proportion of the cosolvent. Moreover there is an enthalpy–entropy compensation process in the supramolecular complex formation; in poor water mixtures the process is endothermic, whilst in reach water mixtures the process is exothermic. This behavior is mostly due to the intrinsic nature of the mixture between water and ethanol, and particularly the process of solvation and desolvation of receptor, substrate and complex. When this study is repeated with binary mixtures of water–methanol and water–DMSO it is observed that the nature of the organic solvent affects the results. While the mixture water–methanol has a behavior similar to water–ethanol mixture, the water–DMSO mixture shows clear differences. In order to check this compensation process, △Cp values are calculated at two different proportions water–ethanol, and they are consistent with an enthalpy–entropy compensation process similar to that described by the inclusion process for certain hydrophilic cyclodextrines. The results obtained show that the enthalpy–entropy compensation detected in the supramolecular complex formation between carboxylates and ammonium-squaramido receptors is independent of the spacer used, and more dependent on the microscopic nature and proportion of the binary mixture.

Coassembly of Poly(ethylene glycol)-block-Poly(glutamate sodium) and Gemini Surfactants with Different Spacer Lengths

The coassembly of poly(ethylene glycol)-b-poly(glutamate sodium) copolymer (PEG113-PGlu100) with cationic gemini surfactants alkanediyl-α,ω-bis-(dodecyldimethylammonium bromide) [C12H25(CH3)2N(CH2)SN(CH3)2C12H25]Br2 (designated as C12CSC12Br2, S = 3, 6, and 12) have been studied by isothermal titration microcalorimetry, cryogenic transmission electron microscopy, circular dichroism, small-angle X-ray scattering, zeta potential, and size measurement. It has been shown that the electrostatic interaction of C12CSC12Br2 with the anionic carboxylate groups of PEG113-PGlu100 leads to complexation, and the C12CSC12Br2/PEG113-PGlu100 complexes are soluble even at the electroneutral point. The complexes display the feature of superamphiphiles and assemble into ordered nanosheets with a sandwich-like packing. The gemini molecules which were already bound with PGlu chains associate through hydrophobic interaction and constitute the middle part of the nanosheets, whereas the top and bottom of the nanosheets are hydrophilic PEG chains. The size and morphology of the nanosheets are affected by the spacer length of the gemini surfactants. The average sizes of the aggregates at the electroneutral point are 81, 68, and 90 nm for C12C3C12Br2/PEG113-PGlu100, C12C6C12Br2/PEG113-PGlu100, and C12C12C12Br2/PEG113-PGlu100, respectively. Both C12C3C12Br2/PEG113-PGlu100 and C12C12C12Br2/PEG113-PGlu100 mainly generate hexagonal nanosheets, while the C12C6C12Br2/PEG113-PGlu100 system only induces round nanosheets.

Novel phosphorus-containing cyclodextrin polymers and their affinity for calcium cations and hydroxyapatite

Novel phosphorous-containing β-cyclodextrin (βCD) polymers (CDP) were synthesized easily under “green chemistry” conditions. A simple polycondensation between the hydroxyl groups of βCD and non-toxic sodium trimetaphosphate (STMP) under basic conditions led to soluble, non-reticulated CDPs with molecular weights (Mw) higher than 104gmol−1, the actual value depending on the NaOH:βCD and STMP:βCD weight ratios. The presence of both βCD and phosphate groups in the polymer allows for strong interactions with amphiphilic probes, such as 1-adamantyl acetic acid, or with divalent cations, such as Ca2+, whose strengths were characterized by isothermal titration microcalorimetry. The obtained phosphated compounds also display high affinity towards hydroxyapatite (HA), leading to HA nanoparticles that could easily be recovered by CDPs, as demonstrated by transmission electron microscopy and quantitative determination of the total amount of phosphated molecules fixed on HA.

Potential toxicity of sarafloxacin to catalase: Spectroscopic, ITC and molecular docking descriptions

The interaction between sarafloxacin and catalase (CAT) was studied by fluorescence spectroscopy, UV–visible absorption spectroscopy, circular dichroism (CD) spectroscopy, isothermal titration microcalorimetry (ITC) and molecular docking method. After deducting the inner filter effect, the fluorescence of CAT was quenched regularly by different concentrations of sarafloxacin. The quenching mechanism was studied by lifetime measurement, and it was proved to be mostly due to static quenching. The formation of sarafloxacin–CAT complex alters the micro-environment of amide moieties and tryptophan (Trp) residues, reduces the α-helix content of the enzyme, changes the peripheral substituents on the porphyrin ring of heme and leads to the inhibition of the enzyme activity. Molecular docking study reveals that sarafloxacin is located between two α-helix of CAT near to Trp 182 and Trp 185 residues, which supports the experimental results and helps to have a more clear understanding about the interaction mechanism. The change in the relative position of His 74 to heme induced by the variation of secondary structure is considered to be the major reason for the reduction of CAT activity. Moreover, sarafloxacin binds into a hydrophobic area of CAT mainly through hydrophobic interactions, which is consistent with the ITC analysis.

Synthesis of Multivalent Carbohydrate‐Centered Glycoclusters as Nanomolar Ligands of the Bacterial Lectin LecA from Pseudomonas aeruginosa

A family of fifteen glycoclusters based on a cyclic oligo-(1→6)-β-D-glucosamine core has been designed as potential inhibitors of the bacterial lectin LecA with various valencies (from 2 to 4) and linkers. Evaluation of their binding properties towards LecA has been performed by a combination of hemagglutination inhibition assays (HIA), enzyme-linked lectin assays (ELLA), and isothermal titration microcalorimetry (ITC). Divalent ligands displayed dissociation constants in the sub-micromolar range and tetravalent ligands displayed low nanomolar affinities for this lectin. The influence of the linker could also be demonstrated; aromatic moieties are the best scaffolds for binding to the lectin. The affinities observed in vitro were then correlated with molecular models to rationalize the possible binding modes of these glycoclusters with the bacterial lectin.

Interaction between cationic surfactant of 1-methyl-3-tetradecylimidazolium bromide and anionic polymer of sodium polystyrene sulfonate

The interaction between long-chain imidazolium ionic liquid (C14mimBr) and anionic polyelectrolyte of sodium polystyrene sulfonate (NaPSS) has been studied using surface tension, isothermal titration microcalorimetry (ITC), dynamic light scatting (DLS) and conductance methods. The result shows that the surface tension plots have a pronounced hump in the surface tension at surfactant concentrations below the critical micelle concentration (cmc) of the surfactant. The cooperative adsorption of surfactant and polymer on the surface (PSS) and the formation of polymer/surfactant aggregate in bulk solution (PSM) provide a rational explanation about it. The formation of surfactant/polymer complexes is affected by the concentration of the surfactant or NaPSS, which is also ascertained by ITC and DLS measurements. Further, the thermodynamic parameters are derived from calorimetric titration and conductance curves, and the effects of polymer concentration and temperature on the parameters are evaluated in detail.

Mechanism on the interaction between amimo sulfonate amphoteric surfactant and sodium dodecyl benzene sulfonate in aqueous solution

The micellar properties of binary mixtures of sodium dodecyl diamino sulfonate (C12AS) and sodium dodecyl benzene sulfonate (SDBS) in aqueous solution at the pH of 6.5 have been characterized employing both conductometric techniques and isothermal titration microcalorimetry (ITC). The critical micelle concentration (cmc) values for the individual surfactants and their corresponding mixtures were determined from both the conductivity measurements and ITC. The interaction parameters between the surfactants, the activity coefficients and the molar fractions of components in the mixed micelles, and the thermodynamic parameters calculated by various approaches, like Rubingh models, were evaluated. The results show that the synergistic effect between C12AS and SDBS in all systems plays an vital role in the reduction of the overall cmc value in aqueous solution at 25°C, and that the steric effect of the head group, the lower charge density, and the capability of accepting proton on the molecule for C12AS affect the formation of mixed micelle. Thermodynamic data show that the micellization for binary mixture of C12AS and SDBS can occur spontaneously, and is both enthalpy and entropy driven process.

A Thermodynamic Study of Micellization of 3-Alkyloxy-2-hydroxypropyl Trimethylammonium Chloride in Aqueous Solution

The detailed micellization behavior of 3-alkyloxy-2-hydroxypropyl trimethylammonium chloride (RnHTACl, n = 12, 14, 16) in aqueous solution was studied by electric conductivity, steady-state fluorescence, and isothermal titration microcalorimetry (ITC) methods. The critical micelle concentration (CMC) and degree of counterion dissociation (α0) were estimated from conductivity curves in the temperature range of 293.15 K to 323.15 K. Then the thermodynamic parameters of micellization (ΔGm0, ΔHm0, and ΔSm0) were calculated by applying a mass-action model equation. On the basis of the ITC results, the CMCs and thermodynamic parameters were also estimated at 293.15 K, which were basically consistent with the results from the conductivity method. According to the Turro–Yekta method, the micelle aggregation number (Nagg) of RnHTACl was determined through static luminescence quenching, and found that the decreased temperature, the elongation of the alkyl chain length or the increased concentration of RnHTACl could...

Drug–tea polyphenol interaction

Propericiazine (PCZ) is an antipsychotic agent used for the treatment and the prevention of relapse of schizophrenia. We found that when an oral solution containing PCZ was mixed with a green tea drink, the residual content of PCZ was reduced by forming an insoluble complex between PCZ and tea polyphenol. In this study, the mechanism underlying the incompatibility of PCZ with green tea polyphenol (GTP) in the solution was clarified by isothermal titration microcalorimetry (ITC). Both solutions of 27.4 mM PCZ and 2.2 mM (−)-epigallocatechin gallate (EGCg), which is a main ingredient of GTP, were mixed and then PCZ in the filtrate was reduced to approximately 60 %. According to measurement at 298 K by ITC, PCZ formed an insoluble complex with EGCg at an associate constant (K) of 4.75 × 102 M−1 exothermically, ΔH = −40.0 kJ mol−1. When (−)-epicatechin gallate (ECg) was used as the GTP, PCZ interacted with ECg with K and ΔH values of 3.74 × 102 M−1 and −22.1 kJ mol−1, respectively. On the other hand, little heat of the reaction between PCZ and (−)-epigallocatechin or (−)-epicatechin was observed. The results indicated that the main reason for this incompatibility was the formation of an insoluble complex by PCZ and a gallate-type GTP such as EGCg and ECg in the aqueous solution.

Thermodynamic Investigation on Micellization of Cationic Gemini Surfactants with Nitrophenoxy Groups in Hydrophobic Chains

Isothermal titration microcalorimetry (ITC) is a powerful technique for acquiring thermodynamic information on the micellization process of surfactants. In typical ITC experiments, consecutive injections of small volume of a surfactant micellar solution into water contained in a sample cell are performed. The sample cell is maintained at a constant temperature and the heat of processes occurring during dilution is monitored for each injection and plotted as a function of surfactant concentration in the cell. The interpretation of experimental data obtained by ITC is necessarily based on models describing micellization process. So far, there are two main models to the thermodynamic analysis of the micellization process: the mass action model, considering micelles and unassociated monomers to be in an association-dissociation equilibrium and the phase separation model, which regards micelles as a separate phase at critical micelle concentration (CMC) and assumes that the micellization process is strongly cooperative. The phase separation model is the simplest model for describing micelle forma- tion assuming that this process is akin to a separate phase-precipitation. Based on these two models, an ITC curve of observed enthalpy change versus surfactant concentration allows the determination of CMC and the enthalpy of micellization (ΔHmic) of a surfactant. Other thermodynamic parameters related to micellization, namely the free energy (ΔGmic), the entropy (ΔSmic) and the heat capacity of micellization (ΔCp,mic) can be calculated from the experimentally determined CMC and ΔHmic. In this paper, ITC and electrical conductivity were employed to investigate the micellization process of cationic gemini surfactants, N,N,N',N'-tetramethyl-N,N'-bis(10-(4-nitrophenoxy)alkyl)-1,6-hexanediammonium dibromide (Nm-6-mN, with m=8, 10 and 12, which are the numbers of carbon in the hydrocarbon chains), in aqueous solutions. Both phase separation model and mass action model were used to obtain a series of thermodynamic parameters. The results show that the obtained ΔHmic values based on the two models are very close, however, the obtained ΔGmic values based on the two models are not consistent. In addition, the ΔCp,mic of the micellization process is mainly from the dehydration contribution of hydrophobic alkyl chains of the surfactants, which means the nitrophenoxy group located in the hydrophobic chain still contacts with water after the mi- cellization. Furthermore, the micellar aggregation number n can be obtained by employing the mass action model. The mi- cellar aggregation number n decreases with the increase of the hydrophobic chain length. The reason is that the surfactant with longer hydrophobic chains prefers to form premicelles, leading to the decrease of the average aggregation number. Keywords Gemini surfactant; micellization; isothermal titration microcalorimetry; phase separation model; mass action model

Interaction between β-casein micelles and imidazolium-based ionic liquid surfactant

The interaction of β-casein micelles (β-CMs) with imidazolium based ionic liquid (IL) surfactant ([C12mim]Br) has been studied using turbidity, isothermal titration microcalorimetry, fluorescence spectroscopy, dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements. Below c1, the individual [C12mim]Br monomers bind onto the β-CM shell close to the hydrophobic core to form a β-CM–[C12mim]Br (monomer) complex. The hydrophobic tail of [C12mim]Br leads to a significant decrease in the environmental polarity of β-CM. Just over c1, [C12mim]Br molecules aggregate into micelle-like aggregates on the micellar shell. This leads to the collapse of the N-terminal of β-casein and strengthens the hydrophobicity of the protein molecules, resulting in a more compact structure of β-CM. With a continuous increase in[C12mim]Br concentration, β-CMs associate with each other into a network-like structure. Beyond c3, the net positive charges on the complexes, owing to the binding of more cationic surfactant molecules, lead to redissociation of the complexes, corresponding to the formation of the new nano-sized β-CM–[C12mim]Br complexes. All the β-casein molecules are saturated by [C12mim]Br aggregates above cs, and free [C12mim]Br micelle-like aggregates appear in the bulk phase above critical aggregation concentration (cac). From a combination of experimental results and discussion on various interactions in the β-CM–[C12mim]Br system, the hydrophobic interaction between the hydrophobic tail of ILs and the hydrophobic domain of β-CM, the electrostatic attraction between [C12mim]+ and negative charged amino acid residues on β-CM shell, and the hydrogen bonding between [C12mim]+ and carboxylic moiety on β-CM shell are the main forces for [C12mim]Br binding to β-CM. Modifications in the physicochemical properties of β-CM upon the addition of [C12mim]Br will expand and enhance the overall capabilities and applications of β-CM.

Synthesis of branched-phosphodiester and mannose-centered fucosylated glycoclusters and their binding studies with Burkholderia ambifaria lectin (BambL)

Five fucosylated glycoclusters exhibiting 4, 6 or 8 residues were synthesised with two different spatial environments based on mannose-centered and branched-phosphodiester scaffolds. Their synthesis was performed in solution using phosphoramidite chemistry to generate phosphodiester linkages, combined with Cu(I)-catalyzed azide–alkyne cycloaddition (CuAAC). The multivalent ligands were evaluated for their ability to bind to Burkholderia ambifaria Lectin (BambL). Binding evaluation was performed through inhibition of hemagglutination (HIA), surface plasmon resonance (SPR) and isothermal titration microcalorimetry (ITC). All fucosylated glycoclusters exhibited a higher affinity to BambL than methyl α-L-fucoside. A dissociation constant of 43 nM was observed for the fucocluster exhibiting four residues with the branched-phosphodiester spatial environment corresponding to a 22-fold increase in comparison with methyl α-L-fucoside. These multivalent fucoclusters represent the first example of ligands of high affinity to BambL.

Aromatic thioglycoside inhibitors against the virulence factor LecA from Pseudomonas aeruginosa

Three small families of hydrolytically stable thioaryl glycosides were prepared as inhibitors of the LecA (PA-IL) virulence factor corresponding to the carbohydrate binding lectin from the bacterial pathogen Pseudomonas aeruginosa. The monosaccharidic arylthio β-d-galactopyranosides served as a common template for the major series that was also substituted at the O-3 position. Arylthio disaccharides from lactose and from melibiose constituted the other two series members. In spite of the fact that the natural ligand for LecA is a glycolipid of the globotriaosylceramide having an α-d-galactopyranoside epitope, this study illustrated that the β-d-galactopyranoside configuration having a hydrophobic aglycon could override the requirement toward the anomeric configuration of the natural sugar. The enzyme linked lectin assay together with isothermal titration microcalorimetry established that naphthyl 1-thio-β-d-galactopyranoside () gave the best inhibition with an IC50 twenty-three times better than that of the reference methyl α-d-galactopyranoside. In addition it showed a KD of 6.3 μM which was ten times better than that of the reference compound. The X-ray crystal structure of LecA with was also obtained.