Synthesis and Affinity Evaluation of a Small Library of Bidentate Cholera Toxin Ligands: Towards Nonhydrolyzable Ganglioside Mimics

A small library of nonhydrolyzable mimics of GM1 ganglioside, featuring galactose and sialic acid as pharmacophoric carbohydrate residues, was synthesized and tested. All compounds were synthesized from readily available precursors using high‐performance reactions, including click chemistry protocols, and avoiding O‐glycosidic bonds. Some of the most active molecules also feature a point of further derivatization that can be used for conjugation with polyvalent aglycons. Their affinity towards cholera toxin was assessed by weak affinity chromatography, which allowed a systematic evaluation and selection of the best candidates. Affinity could be enhanced up to one or two orders of magnitude over the affinity of the individual pharmacophoric sugar residues.     

The Synthesis of Blood Group Antigenic A Trisaccharide and Its Biotinylated Derivative

Blood group antigenic A trisaccharide represents the terminal residue of all A blood group antigens and plays a key role in blood cell recognition and blood group compatibility. Herein, we describe the synthesis of the spacered A trisaccharide by means of an assembly scheme that employs in its most complex step the recently proposed glycosyl donor of the 2-azido-2-deoxy-selenogalactoside type, bearing stereocontrolling 3-O-benzoyl and 4,6-O-(di-tert-butylsilylene)-protecting groups. Its application provided efficient and stereoselective formation of the required α-glycosylation product, which was then deprotected and subjected to spacer biotinylation to give both target products, which are in demand for biochemical studies.     

Simultaneous forward and reverse ABO blood group typing using a paper-based device and barcode-like interpretation

A new platform of a paper-based analytical device (PAD) for simultaneous forward and reverse ABO blood group typing has been reported. This platform can overcome the discrepancy results as influenced by the individual haematocrit. The test and the control of non-haemagglutination on each channel were performed in parallel. The PAD was fabricated by printing six parallel channels with wax onto Whatman No. 4 filter paper. An LF1 blood separation membrane was used for the separation of plasma from whole blood for reverse grouping. The blood group was identified by haemagglutination of the corresponding antigen–antibody. For forward grouping, Anti-A, -B and –A,B were treated on the test line of PAD, and inactivated Anti-A, -B and –A,B were immobilized on the control line. For reverse grouping, 30% standard A-cells, B- and O- were added to the test channel after plasma separation, and O-cells were used as a control. Then, 0.9% normal saline (NSS) containing 1% Tween-20 was bi-functionally used for dilution of the blood sample and elution of the non-agglutinated RBCs within the channels. The distance of agglutinated RBCs in each test line was compared with the distance of non-agglutinated RBCs in the parallel control line. The forward and reverse patterns of blood groups A, B, AB and O were a barcode-like chart in which the results can be visually analysed. The PAD has excellent reproducibility when 10 replications of the A, B, AB or O blood groups were performed. The results of both forward and reverse grouping were highly correlated with conventional methods compared with the slide method and tube method, respectively (n = 76). Thus, this ABO typing PAD holds great potential for future applications in blood typing point-of-care testing.     

Saccharide‐Modified Nanodiamond Conjugates for the Efficient Detection and Removal of Pathogenic Bacteria

The detection and removal of bacteria, such as E. coli in aqueous environments by using safe and readily available means is of high importance. Here we report on the synthesis of nanodiamonds (ND) covalently modified with specific carbohydrates (glyco–ND) for the precipitation of type 1 fimbriated uropathogenic E. coli in solution by mechanically stable agglutination. The surface of the diamond nanoparticles was modified by using a Diels–Alder reaction followed by the covalent grafting of the respective glycosides. The resulting glyco–ND samples are fully dispersible in aqueous media and show a surface loading of typically 0.1 mmol g^?1. To probe the adhesive properties of various ND samples we have developed a new sandwich assay employing layers of two bacterial strains in an array format. Agglutination experiments in solution were used to distinguish unspecific interactions of glyco–ND with bacteria from specific ones. Two types of precipitates in solution were observed and characterized in detail by light and electron microscopy. Only by specific interactions mechanically stable agglutinates were formed. Bacteria could be removed from water by filtration of these stable agglutinates through 10 μm pore‐size filters and the ND conjugate could eventually be recovered by addition of the appropriate carbohydrate. The application of glycosylated ND allows versatile and facile detection of bacteria and their efficient removal by using an environmentally and biomedically benign material.     

Functional group divergence and the structural basis of acridine photocatalysis revealed by direct decarboxysulfonylation

The reactivity of the sulfonyl group varies dramatically from nucleophilic sulfinates through chemically robust sulfones to electrophilic sulfonyl halides—a feature that has been used extensively in medicinal chemistry, synthesis, and materials science, especially as bioisosteric replacements and structural analogs of carboxylic acids and other carbonyls. Despite the great synthetic potential of the carboxylic to sulfonyl functional group interconversions, a method that can convert carboxylic acids directly to sulfones, sulfinates and sulfonyl halides has remained out of reach. We report herein the development of a photocatalytic system that for the first time enables direct decarboxylative conversion of carboxylic acids to sulfones and sulfinates, as well as sulfonyl chlorides and fluorides in one step and in a multicomponent fashion. A mechanistic study prompted by the development of the new method revealed the key structural features of the acridine photocatalysts that facilitate the decarboxylative transformations and provided an informative and predictive multivariate linear regression model that quantitatively relates the structural features with the photocatalytic activity.

Carboxylic acids can now serve as a single point of entry to several sulfonyl functional groups by a one-step organophotocatalytic sulfonylation, revealing structural effects that enable the photocatalysis.     

Analog calorimetry and UNIQUAC group contributions approaches to the miscibility of pvc with eva copolymers

The miscibility of blends of poly(vinyl-chloride) (PVC) with poly(ethylene-co-vinyl acetate) (EVA) was investigated through analog calorimetry and a group contribution procedure based on the UNIQUAC model. The group contribution parameters quantifying the pair interactions between the structural features of the above polymers were calculated from experimental excess enthalpies of a series of binary mixtures of chlorocompounds, esters and hydrocarbons. Enthalpy data were also collected for the ternary mixtures (2-chloropropane+ethyl acetate+n-heptane) and (2-chlorobutane + methyl acetate+n-heptane), chosen as possible models for the studied macromolecular mixtures. The miscibility window of the PVC-EVA blends is fairly predicted by the group contribution method. It is also acceptably predicted by the enthalpic behaviour of the first ternary set, but only when the latter is calculated with binary data. A slightly narrower miscibility range is predicted by the binary interaction model. The results of these procedures are compared and the higher reliability of the group contribution procedure is emphasized in terms of its capability to reproduce the exact structure of the macromolecules and the non-univocal choice of the model molecules involved in the analog calorimetry approach. This revised version was published online in July 2006 with corrections to the Cover Date.     

Application of the unitary group approach to evaluate spin density for configuration interaction calculations in a basis of S2 eigenfunctions

We present an implementation of the spin‐dependent unitary group approach to calculate spin densities for configuration interaction calculations in a basis of spin symmetry‐adapted functions. Using S² eigenfunctions helps to reduce the size of configuration space and is beneficial in studies of the systems where selection of states of specific spin symmetry is crucial. To achieve this, we combine the method to calculate U(n) generator matrix elements developed by Downward and Robb (Theor. Chim. Acta 1977, 46, 129) with the approach of Battle and Gould to calculate U(2n) generator matrix elements (Chem. Phys. Lett. 1993, 201, 284). We also compare and contrast the spin density formulated in terms of the spin‐independent unitary generators arising from the group theory formalism and equivalent formulation of the spin density representation in terms of the one‐ and two‐electron charge densities.     

Functionalization of a Rigid Divalent Ligand for LecA,a Bacterial Adhesion Lectin

The bacterial adhesion lectin LecA is an attractive target for interference with the infectivity of its producer P. aeruginosa. Divalent ligands with two terminal galactoside moieties connected by an alternating glucose-triazole spacer were previously shown to be very potent inhibitors. In this study, we chose to prepare a series of derivatives with various new substituents in the spacer in hopes of further enhancing the LecA inhibitory potency of the molecules. Based on the binding mode, modifications were made to the spacer to enable additional spacer–protein interactions. The introduction of positively charged, negatively charged, and also lipophilic functional groups was successful. The compounds were good LecA ligands, but no improved binding was seen, even though altered thermodynamic parameters were observed by isothermal titration calorimetry (ITC).     

Calorimetric investigation of the interaction between a macromolecular prodrug of diflunisal and human platelets

The thermal effect due to the interaction between human platelets and α,β poly(N-hydroxy-ethyl)-DL-aspartamide (PHEA) or the PHEA-Diflunisal conjugate was measured by the calorimetric technique at 25°C. The experimental data confirm that PHEA is a biocompatible macromolecule and that its conjugate influences the physiological activity of human platelets.     

Development and validation of a sensitive enzyme immunoassay for surveillance of Cry1Ab toxin in bovine blood plasma of cows fed Bt-maize (MON810)

The increasing global adoption of genetically modified (GM) plant derivatives in animal feed has provoked a strong demand for an appropriate detection method to evaluate the existence of transgenic protein in animal tissues and animal by-products derived from GM plant fed animals. A highly specific and sensitive sandwich enzyme immunoassay for the surveillance of transgenic Cry1Ab protein from Bt-maize in the blood plasma of cows fed on Bt-maize was developed and validated according to the criteria of EU-Decision 2002/657/EC. The sandwich assay is based on immuno-affinity purified polyclonal antibody raised against Cry1Ab protein in rabbits. Native and biotinylated forms of this antibody served as capture antibody and detection antibody for the ELISA, respectively. Streptavidin-horseradish peroxidase conjugate and TMB substrate provided the means for enzymatic colour development.The immunoassay allowed Cry1Ab protein determination in bovine blood plasma in an analytical range of 0.4-100 ng mL⁻¹ with a decision limit (CCα) of 1.5 ng mL⁻¹ and detection capability (CCβ) of 2.3 ng mL⁻¹. Recoveries ranged from 89 to 106% (mean value of 98%) in spiked plasma.In total, 20 plasma samples from cows (n = 7) fed non-transgenic maize and 24 samples from cows (n = 8) fed transgenic maize (collected before and, after 1 and 2 months of feeding) were investigated for the presence of the Cry1Ab protein. There was no difference amongst both groups (all the samples were below 1.5 ng mL⁻¹; CCα). No plasma sample was positive for the presence of the Cry1Ab protein at CCα and CCβ of the assay.     

Towards a Quantitative Understanding of Protein Hydration and Volumetric Properties

Herein, we probe by pressure perturbation calorimetry (PPC) the coefficient of thermal expansion, the volumetric and the hydration properties of variants of a hyperstable variant of staphylococcal nuclease (SNase), Δ+PHS. The temperature‐dependent volumetric properties of the folded and unfolded states of the wild‐type protein are calculated with previously published data. The present PPC results are used to interpret the volume diagram and expansivity at a molecular level. We conclude that the expansivity of the unfolded state is, to a first approximation, temperature independent, while that of the folded state decreases with increasing temperature. Our data suggest that at low temperature the defining contribution to ΔV comes mainly from excluded volume differences and ΔV for unfolding is negative. In contrast, at high temperatures, differential solvation due to the increased exposed surface area of the unfolded state and, in particular, its larger thermal volume linked to the increased conformational dynamics of the unfolded state ensemble takes over and ΔV for unfolding eventually becomes positive.