Francisco Santoyo-Gonzalez

Carbon dots for copper detection with down and upconversion fluorescent properties as excitation sources.

Carbon dots were synthesized by a simple and green strategy for selective and sensitive Cu(2+) ion detection using both down and upconversion fluorescence. These fluorescent nanosensors show low cytotoxicity and are applied for intracellular sensing and imaging of Cu(2+) in biological systems.

Ferrocene–β‐Cyclodextrin Conjugates: Synthesis, Supramolecular Behavior, and Use as Electrochemical Sensors

Ferrocene with a beta-cyclodextrin unit bound to one or both cyclopentadienyl rings through the secondary face were conveniently synthesized by regiospecific copper(I)-catalyzed cycloaddition of 2-O-propargyl-beta-cyclodextrin to azidomethyl or bis(azidomethyl)ferrocene. The supramolecular behavior of the synthesized conjugates in both the absence and presence of bile salts (sodium cholate, deoxycholate, and chenodeoxycholate) was studied by using electrochemical methods (cyclic and differential pulse voltammetry), isothermal titration calorimetry, and NMR spectroscopy (PGSE, CPMG, and 2D-ROESY). These techniques allowed the determination of stability constants, mode of inclusion, and diffusion coefficients for complexes formed with the neutral and, in some cases, the oxidized states of the ferrocenyl conjugates. It was found that the ferrocenyl conjugate with one beta-cyclodextrin unit forms a redox-controllable head-to-head homodimer in aqueous solution. The ferrocene-bis(beta-cyclodextrin) conjugate is present in two distinguishable forms in aqueous solution, each one having a different half-wave oxidation potential for the oxidation of the ferrocene. By contrast, only one distinguishable form for the oxidized state of the ferrocene-beta-cyclodextrin conjugate is detectable. The redox-sensing abilities of the synthesized conjugates towards the bile salts were evaluated based on the observed guest-induced changes in both the half-wave potential and the current peak intensity of the electroactive moiety.

Magnetic Nanoparticles-Templated Assembly of Protein Subunits: A New Platform for Carbohydrate-Based MRI Nanoprobes

A new approach for the preparation of carbohydrate-coated magnetic nanoparticles is reported. In a first step, we show that the pH-driven assembly-disassembly natural process that occurs in apoferritin protein is effective for the encapsulation of maghemite nanoparticles of different sizes: 4 and 6 nm. In a second step, we demonstrate that the presence of functional amine groups in the outer shell of apoferritin allows functionalization with two carbohydrates, N-acetyl-D-glucosamine and d-mannose. High-resolution electron microscopy (HREM), high angle annular dark field scanning electron microscopy (HAADF-STEM), electron energy loss spectroscopy (EELS), X-ray diffraction (XRD), and SQUID technique have been used to characterize the magnetic samples, termed herein Apomaghemites. The in vivo magnetic resonance imaging (MRI) studies showed the efficiency in contrasting images for these samples; that is, the r(2) NMR relaxivities are comparable with Endorem (a commercial superparamagnetic MRI contrast agent). The r(2) relaxivity values as well as the pre-contrast and post-contrast T(2)*-weighted images suggested that our systems could be used as perspective superparamagnetic contrast agents for magnetic resonance imaging (MRI). The carbohydrate-functionalized Apomaghemite nanoparticles retained their recognition abilities, as demonstrated by the strong affinity with their corresponding carbohydrate-binding lectins.

Azide–Alkyne 1,3-Dipolar Cycloadditions: a Valuable Tool in Carbohydrate Chemistry

Recent applications of the 1,3-dipolar cycloaddition reaction of azides and alkynes in carbohydrate chemistry are summarized in the present review. The efficient catalyzed version of this reaction, also referred to as one of the so-called click chemistry reactions, has joined in a short period of time a select group of the most efficient and useful organic reactions. In particular, its application in the carbohydrate field has shown its value as a synthetic tool allowing the preparation of a wide range of carbohydrate-containing molecular constructs such as glycopeptides, glycoaminoacids, glycoclusters, glycodendrimers, glycopolymers, glycosylated biomolecules, and immobilization of carbohydrates onto solid surfaces (glycoarrays) as the most representative examples. In the majority of cases, the formed 1,2,3-triazole heterocycle plays the role of a linking tether between the coupling partners.

Synthesis of Cluster N‐Glycosides Based on a β‐Cyclodextrin Core

A convenient method for the synthesis of cluster glycopyranosylamines based on β-cyclodextrin is presented (see diagram).

The Conformational Behaviour of Non-Hydrolizable Lactose Analogues: The Thioglycoside, Carbaglycoside, and Carba-Iminoglycoside Cases

-glycosidic linkages.In fact, the C2S bond length (1.78 A˚ ) and C2S2C bondangle (99°) strongly differ from the values for C2O (1.41A˚ ) and C2O2C (116°). On the other hand, the C2N dis-tance and C2N2C bond angle values are 1.47 A˚ and be-tween 116.52119.6°, according to MM3* calculations. Onthis basis, we report here the conformational study of thethioglycoside- (

Dendritic Galactosides Based on a β‐Cyclodextrin Core for the Construction of Site‐Specific Molecular Delivery Systems: Synthesis and Molecular Recognition Studies

In order to evaluate the ability of multivalent glycosides based on a beta-cyclodextrin core as site-specific molecular carriers, a study on both the inclusion complexation behaviour and lectin binding affinity of branched and hyperbranched beta-cyclodextrins is presented. A series of cluster galactosides constructed on beta-cyclodextrin scaffolds containing seven 1-thio-beta-lactose or beta-lactosylamine bound to the macrocyclic core through different spacer arms were synthesised. In addition, the first synthesis of three first-order dendrimers based on a beta-cyclodextrin core containing fourteen 1-thio-beta-D-galactose, 1-thio-beta-lactose and 1-thio-beta-melibiose residues was performed. Calorimetric titrations performed at 25 degrees C in buffered aqueous solution (pH 7.4) gave the affinity constants and the thermodynamic parameters for the complex formation of these beta-cyclodextrin derivatives with guests sodium 8-anilino-1-naphthalenesulfonate (ANS) and 2-naphthalenesulfonate, and lectin from peanut (Arachis hypogaea) (PNA). The persubstitution of the primary face of the beta-cyclodextrin with saccharides led to a slight increase of the binding constant values for the inclusion complexation with ANS relative to the native beta-cyclodextrin. However, the increase of the steric congestion due to the presence of the saccharide residues on the narrow rim of the beta-cyclodextrin may cause a decrease of the binding ability as shown for sodium 2-naphthalenesulfonate. The spacer arms are not passive elements and influence the host binding ability according to their chemical nature. PNA forms soluble cross-linked complexes with cluster galactosides and lactosides scaffolded on beta-cyclodextrin but not with cluster galactopyranosylamines or melibiose. Both, perbranched and hyperbranched beta-cyclodextrins, form stronger complexes with PNA than the monomeric analogues. However, the use of hyperbranched CDs does not contribute to the improvement of the complex stability relative to heptakis-glycocyclodextrin derivatives. Finally, a titration experiment with PNA and a complex formed by a heptakis lactose beta-cyclodextrin derivative with sodium 2-naphthalenesulfonate showed the formation of a soluble cross-linked complex with stronger affinity constant and higher stoichiometry than those observed for the complex formation of PNA with the same heptakis-lactose beta-cyclodextrin derivative, suggesting the formation of a three component complex.

Vinyl sulfone bifunctional tag reagents for single-point modification of proteins.

The introduction of multiple labels onto biomolecules is a challenge. We report herein the synthesis of vinyl sulfone derivatized bifunctional tag single-attachment-point reagents (BTSAP) bearing biotin and a fluorescent tag and their applications in proteins for the introduction of multiple labels by means of the Michael-type addition of the electrophilic vinyl sulfone group. These BTSAP reagents were easily synthesized by a two-step chemical strategy involving the preparation of alkyne vinyl sulfone derivatized tags (AVST) and subsequent click CuAAC attachment of a second azide functionalized tag. The direct coupling of BTSAP reagents with the low reactive protein horseradish peroxidase (HRP) turned it into a dual reporter group (i.e., fluorescence and peroxidase activity) that may be coupled to any recognition system via biotin-avidin affinity. The AVST compounds are not mere synthetic intermediates for the preparation of BTSAP reagents but valuable clickable self-reporting compounds that allow the simultaneous introduction in proteins of an alkyne function and labeling when conjugated via the vinyl sulfone group. The implementation of these clickable AVST compounds in a CuAAC-based sequential approach also allows attainment of the dual labeling of HRP. This approach yields equivalent results in terms of fluorescent labeling, specific activity, and functionality of the biotin tag when compared with the direct bifunctional labeling by the BTSAP reagent. However, for life science this direct approach is more convenient since it avoids the use of copper catalysis, overcoming the toxicity drawback of this metal in biological systems.

Vinyl sulfone functionalized silica: a “ready to use” pre-activated material for immobilization of biomolecules

The combination of silica as support and vinyl sulfone as reactive group led to a pre-activated material that readily reacts to form covalent bonds by Michael-type addition with both amine and thiol groups naturally occurring in biomolecules in mild conditions compatible with the biological nature of the enzymes. A simple two step synthetic strategy was designed to access this functionalized hybrid material. Two types of vinyl sulfone silicas (N-type and S-type) differing in the chemical nature of the linkers between the silica particle and the reactive vinyl sulfone group were prepared by implementation of this strategy. The capabilities of those vinyl sulfone silicas were evaluated with the model enzymes invertase, lactase and lysozyme. Both S-type and N-type vinyl sulfone silicas coupled efficiently with the model enzymes even at 4 °C by simple combination of the species and the immobilized enzymes retained the enzymatic activity. The linker showed to play a major role in the non covalent interactions between the enzymes and the silicas. In terms of capacity, the S-type material is the best option although its poor flow rate when packed in columns invalidates its applications for low pressure liquid chromatography. The capabilities of the N-type material were successfully put to the test as a pre-packed column for the immobilization of invertase and further demonstrated with two real cases of relevance in proteomics: (i) purification of glutathione-S-transferase (GST) and (ii) identification of proteins that interact with thioredoxin h2 from Pisum sativum.

Vinyl Sulfone Functionalization: A Feasible Approach for the Study of the Lectin! Carbohydrate Interactions

Carbohydrate-mediated molecular recognition is involved in many biological aspects such as cellular adhesion, immune response, blood coagulation, inflammation, and infection. Considering the crucial importance of such biological events in which proteins are normally involved, synthetic saccharide-based systems have emerged as powerful tools for the understanding of protein-carbohydrate interactions. As a new approach to create saccharide-based systems, a set of representative monosaccharides (D-mannose, D-glucose, N-acetyl-D-glucosamine, and L-fucose) and disaccharides (lactose, maltose, and melibiose) were derivatized at their anomeric carbon with a vinyl sulfone group spanned by an ethylthio linker. This vinyl sulfone functionalization is demonstrated to be a general strategy for the covalent linkage of a saccharide in mild conditions via Michael-type additions with the amine and thiol groups from functionalized supports and those naturally present in biomolecules. The introduction of the ethylthio linker between the biorecognizable element (i.e., saccharide) and the reactive group (i.e., vinyl sulfone) was found to preserve the functionality of the former. The capability of the vinyl sulfone saccharides for the study of lectin-carbohydrate interactions was demonstrated by (i) immobilizing them on both amine-functionalized supports (glass slides and microwell plates) and polylysine-coated glass slides to create sugar arrays that selectively bind lectins (ii) coupling to model proteins to yield neoglycoproteins that are recognized by lectins and (iii) using vinyl sulfone saccharides as tags to allow the detection of the labeled biomolecule by HRP-lectins. The above results were further put tothe test with a real case: detection of carbohydrate binding proteins present in rice ( Oryza sativa ).