Hybrids and biohybrids as green materials for a blue planet

There is an urgency to identify novel technological answers to the decreasing availability of important resources together with increasing accumulation of pollution. Among the many ways materials science can contribute to these issues, the enhanced use of renewable resources, the optimal production of alternative energies and the improved monitoring/cleaning of contaminated environments can be identified as area where the sol–gel technology has, and will have, a major role to play. In this short review, we more specifically illustrate recent developments in biohybrid chemistry applied to bioplastics, biofuel cells, biosensors and bioremediation.     

Combined spectroscopic studies on post-functionalized Au25 cluster as an ATR-FTIR sensor for cations

Recently, significant research activity has been devoted to thiolate-protected gold clusters due to their attractive optical and electronic properties. These properties as well as solubility and stability can be controlled by post-synthetic modification strategies. Herein, the ligand exchange reaction between Au₂₅(2-PET)₁₈ cluster (where 2-PET is 2-phenylethanethiol) and di-thiolated crown ether (t-CE) ligands bearing two chromophores was studied. The post-functionalization aimed to endow the cluster with ion binding properties. The exchange reaction was followed in situ by UV-vis, ¹H NMR and HPLC. MALDI mass analysis revealed the incorporation of up to 5 t-CE ligands into the ligand shell. Once functionalized MALDI furthermore showed complexation of sodium ions to the cluster. ATR-FTIR spectroscopic studies using aqueous solutions of K⁺, Ba²⁺, Gd³⁺ and Eu³⁺ showed noticeable spectral shifts of the C–O stretching band around 1100 cm⁻¹ upon complexation. Further spectral changes point towards a conformational change of the two chromophores that are attached to the crown ether. Density functional theory calculations indicate that the di-thiol ligand bridges two staple units on the cluster. The calculations furthermore reproduce the spectral shift of the C–O stretching vibrations upon complex formation and reveal a conformational change that involves the two chromophores attached to the crown ether. The functionalized clusters have therefore attractive ion sensing properties due to the combination of binding properties, mainly due to the crown ether, and the possibility for signal transduction via an induced conformational change involving chromophore units.

Using ligand exchange reactions an atomically precise gold cluster was functionalized with a di-thiolated crown ether. Using in situ infrared spectroscopy films of the resulting composite were shown to incorporate metal cations.     

Comparaison de la reactivite du bromure d'ethylmagnesium et du diethylmagnesium vis-a-vis des cetones α,β-ethyleniques dans divers solvants

The reactivity of diethylmagnesium and ethylmagnesium bromide towards 2-cyclohexenone in various solvents is studied. The 1,2 addition is always predominant, but diethylmagnesium adds almost exclusively in 1,2 manner to this ketone while ethylmagnesium bromide gives both 1,2 and 1,4 addition products with a ratio dependent of the solvent basicity. Thus, in hydrocarbons (hexane, benzene), the magnesium reagents behave similary; and with more basic solvents, for EtMgBr the yield of the 1,4 addition product increases and that of the 1,2 addition product decreases.With another α,β-ethylenic ketone, trans-3-penten-2-one, 1,4 addition occurs predominantly with both magnesium reagents, diethylmagnesium and ethylmagnesium bromide, but diethylmagnesium gives again much more 1,2 addition product than ethylmagnesium bromide.     

Study of surfactant–siloxane interfaces in spray-dried mesoporous silica-based spheres

We have undertaken the synthesis of spray-dried mesoporous silica-based micrometric spheres using various synthetic procedures. In this article, we focus on the relationship between textural properties and small organic groups bound to the siloxane network (residual alkoxy groups or added functions). A correlation has been found between the characteristic XRD distance and the quantity of Si-bound organic groups (measured by ¹H solid-state NMR) located at the surfactant–siloxane interface which demonstrates the effect of these organic groups. However, under certain circumstances, Si-bound organic groups can be trapped inside the siloxane network. They have then a different effect on the texture, and are less accessible for further applications. In that sense, this study can also be used in a predictive way for the synthesis of mesoporous spheres with surfaces of functionalised channels.     

3D-QSAR and docking studies of selective GSK-3beta inhibitors. Comparison with a thieno[2,3-b]pyrrolizinone derivative, a new potential lead for GSK-3beta ligands

The three-dimensional structures of 3-anilino-4-arylmaleimides, selective GSK-3beta inhibitors, were correlated to their biological affinities by 3D-QSAR studies (CoMFA method). The cocrystallographic data of GSK-3beta vs 3-anilino-4-arylmaleimide allowed us to compare 3D-QSAR results to experimental intermolecular interactions. The results of the CoMFA analysis did not really correspond to the interactions recorded in the active site, but they characterized fundamental features (areas of the active site) of the interactions ligand-receptor. These studies were the starting point to analyze a new GSK-3beta ligand, a thieno[2,3-b]pyrrolizinone derivative. This comparison based on docking and simulation approaches allowed us to confirm one preferential orientation of this ligand inside the active site, explaining the relationship with the reference 3-anilino-4-arylmaleimide derivatives and its biological affinity.     

Controlled redox conversion of new X-ray-Characterized Mono- and dinuclear heptacoordinated Mn(II) complexes into di-micro-oxo-dimanganese core complexes

Two heptacoordinated Mn(II) complexes are isolated and X-ray characterized using the well-known tpen ligand (tpen = N,N,N',N'-tetrakis(2-pyridylmethyl)-1,2-ethanediamine): [(tpen)Mn(OH(2))](ClO(4))(2) (1(ClO(4))(2)) and [(tpen)Mn(micro-OAc)Mn(tpen)](ClO(4))(3).2H(2)O (2(ClO(4))(3).2H(2)O). Crystallographic data for 1(ClO(4))(2) at 110(2) K (respectively at 293(2) K): monoclinic, space group C2/c, a = 15.049(3) A (15.096(3) A), b = 9.932(2) A (10.105(2) A), c = 19.246(4) A (19.443(4) A), beta = 94.21(3) degrees (94.50(3) degrees ), Z = 4. Crystallographic data for 2(ClO(4))(3).0.5(C(2)H(5))(2)O at 123(2) K: triclinic, space group P, a = 12.707(3) A, b = 12.824(3) A, c = 19.052(4) A, alpha = 102.71(3) degrees, beta = 97.83(3) degrees, gamma = 98.15(3) degrees, Z = 2. Investigation of the variation upon temperature of the molar magnetic susceptibility of compound 2(ClO(4))(3).2H(2)O reveals a weak antiferromagnetic exchange interaction between the two high-spin Mn(II) ions (J = -0.65 +/- 0.05 cm(-)(1), H = -JS(1).S(2)). EPR spectra are recorded on powder samples and on frozen acetonitrile solutions, demonstrating the maintenance upon dissolution of the heptacoordination of Mn in complex 1 while complex 2 partially dissociates. Electrochemical responses of complexes 1 and 2 are investigated in acetonitrile, and bulk electrolyses are performed at oxidative potential in the presence of various amounts of 2,6-lutidine (0-2.65 equiv per Mn ion). The formation from either 1 or 2 of the mixed-valent complex [(tpen)Mn(III)(micro-O)(2)Mn(IV)(tpen)](3+) (3) is established from mass spectrometry and EPR and IR spectroscopy measurements. When reaction is started from 2, formation of [(tpen)Mn(IV)(micro-O)(2)(micro-OAc)Mn(IV)](3+) (4) is evidenced from cyclic voltammetry, EPR, and UV-vis data. The Mn vs tpen ratio in the electrogenerated complexes is accurately controlled by the quantity of additional 2,6-lutidine. The role of tpen as a base is discussed.     

Ultrafast Click Chemistry with Fluorosydnones

We report the synthesis and reactivity of 4‐fluorosydnones, a unique class of mesoionic dipoles displaying exquisite reactivity towards both copper‐catalyzed and strain‐promoted cycloaddition reactions with alkynes. Synthetic access to these new mesoionic compounds was granted by electrophilic fluorination of σ‐sydnone Pd^II precursors in the presence of Selectfluor. Their reactions with terminal and cyclic alkynes were found to proceed very rapidly and selectively, affording 5‐fluoro‐1,4‐pyrazoles with bimolecular rate constants up to 10⁴ m ^?1 s^?1, surpassing those documented in the literature with cycloalkynes. Kinetic studies were carried out to unravel the mechanism of the reaction, and the value of 4‐fluorosydnones was further highlighted by successful radiolabeling with [¹⁸F]Selectfluor.     

Sugar-derived tricatenar catanionic surfactant: synthesis, self-assembly properties, and hydrophilic probe encapsulation by vesicles

A new sugar-derived tricatenar catanionic surfactant (TriCat) was developed to obtain stable vesicles that could be exploited for drug encapsulation. The presence of the sugar moiety led to the formation of highly hydrophilic stoichiometric catanionic surfactant systems. The three hydrophobic chains permitted vesicles to form spontaneously. The self-assembly properties (morphology, size, and stability) of TriCat were examined in water and in buffer solution. Encapsulation studies of a hydrophilic probe, arbutin, commonly used in cosmetics for its whitening properties, were performed to check the impermeability of the vesicle bilayer. The enhancement of hydrophobic forces by the three chains of TriCat prevented surfactant equilibrium between the bilayer and the solution and enabled the probe to be retained in the aqueous cavity of the vesicles for at least 30 h. Thus, the present study suggests that this tricatenar catanionic surfactant could be a promising delivery system for hydrophilic drugs.     

Thermal and thermo-mechanical degradation of poly(3-hydroxybutyrate)-based multiphase systems

The influence of fermentation residues and quaternary ammonium salts on the thermal and thermo-mechanical degradation of a biodegradable bacterial poly(3-hydroxybutyrate), PHB, was studied. The results obtained from DSC, SEC and TG analyses performed on blends reveal that ammonium cations greatly enhance the degradation leading to a dramatic decrease in PHB molecular weight. These results are confirmed by the thermo-mechanical study. Besides, we show that the presence of fermentation residues does not affect significantly the PHB thermal stability in comparison to the ammonium cations. A kinetic analysis based on the Coats and Redfern model was applied to the non-isothermal TGA data. This method completed by NMR characterizations led us to determine the most probable mechanism for PHB degradation in the presence of the ammonium salts. The results demonstrate that ammonium surfactants commonly found in commercial nanoclays (for nanocomposites' production) effectively have a catalytic effect on the PHB degradation.     

Combination of FTIR spectral imaging and chemometrics for tumour detection from paraffin-embedded biopsies

FTIR spectral imaging was applied on formalin-fixed paraffin-embedded biopsies from colon and skin cancerous lesions. These samples were deposited onto different substrates (zinc selenide and calcium fluoride respectively) and embedded using two types of paraffin. Formalin fixation followed by paraffin embedding is the gold standard in tissue storage. It can preserve molecular structures and it is compatible with immunohistochemistry. However, paraffin absorption bands are significant in the mid-infrared region and can mask some molecular vibrations of the tissue. Direct data processing was applied on spectral images without any chemical dewaxing of the tissues. Extended Multiplicative Signal Correction was used to correct the spectral contribution from paraffin. For this purpose, the signal of paraffin was modelled using Principal Component Analysis and paraffin spectra were removed from the raw images based on an outlier detection. Then, pseudo-colour images were computed by K-means clustering in order to highlight histological structures of interest. This robust chemometrics methodology was applied on the two samples. Tumour areas were successfully demarcated from the rest of the tissue in both colon and skin independently of the embedding material and of the substrate.