Safety study of intravitreal and suprachoroidal Laponite clay in rabbit eyes.

PURPOSE: To study the safety and biocompatibility of Laponite clay (LAP) within an intravitreal and suprachoroidal administration in rabbit eyes. METHODS: Thirty-two New Zealand albino rabbits were divided into two experimental groups to test intravitreal (IVT group) and suprachoroidal (SCS group) administration of a 100-µl and 50-µl Laponite suspension respectively. Following injection, the eyes were monitored by ocular tonometry, slit-lamp eye examination and indirect ophthalmoscopy, at 24 h, 1, 4, 12, and 14 weeks post administration. Histological examination was also performed to determine whether any ocular pathological change had occurred. Throughout the study, LAP presence in vitreous was estimated by complexometric titration with ethylenediaminetetraacetic acid (EDTA), taking advantage of the Laponite high content of magnesium ions. RESULTS: Neither significant differences in the intraocular pressure, nor relevant ocular complications were found in the two experimental groups after LAP administration. The histology of the retina remained unchanged. LAP presence in vitreous could be indirectly confirmed by complexometric titration until 14 weeks post administration in eyes of IVT group. CONCLUSION: Laponite could be considered as a vehicle for potential clinical use in ocular drug administration, due to its proven ocular biocompatibility and its transparency in gel state.

Glycerol as a source of designer solvents: physicochemical properties of low melting mixtures containing glycerol ethers and ammonium salts.

In this work we report the preparation of mixtures of several alkyl glyceryl ethers, as hydrogen bond donor compounds, with two ammonium salts, choline chloride and N,N,N-triethyl-2,3-dihydroxypropan-1-aminium chloride. The stability of the mixtures at different molar ratios and temperatures has been evaluated in order to determine the formation of low melting mixtures. Liquid and stable mixtures have been characterized and their physico-chemical properties such as density, viscosity, refractive index, conductivity and surface tension have been measured in the temperature range of 293.15 K to 343.15 K. Comparison of the mixtures prepared herein with the ones containing glycerol and choline chloride evidences the possibility of tuning the physico-chemical properties by changing the substitution pattern in the hydrogen bond donor compound or in the ammonium salt, thus broadening the scope of application of these mixtures.

Polytopic bis(oxazoline)-based ligands for recoverable catalytic systems applied to the enantioselective Henry reaction.

Several kinds of polytopic chiral ligands (including ditopic, tritopic and tetratopic), based on the bis(oxazoline) and azabis(oxazoline) motifs, have been tested in the preparation of recoverable catalytic systems for the Henry reaction. The results obtained with the different ligands are, in general, good, but they point to the existence of a delicate balance between the coordinating ability of the ligand, the catalytic activity and the recovery of the catalyst by formation of the coordination polymer, related to the easiness to form oligomeric species in solution.

Corrigendum to "Laponite for biomedical applications: An ophthalmological perspective" [Mater. Today Bio 24 (2024) 100935].

[This corrects the article DOI: 10.1016/j.mtbio.2023.100935.].

Stereochemical outcome of copper-catalyzed C-H insertion reactions. An experimental and theoretical study.

The combination of chiral preparative HPLC separation, VCD measurements, and theoretical calculations allows the unambiguous determination of the absolute configuration of the conformationally flexible products of copper-catalyzed carbene insertion reactions. DFT calculations were used to predict the stereochemical outcome of the copper-bis(oxazoline)-catalyzed C-H insertion reaction between methyl diazophenylacetate and tetrahydrofuran and also to predict the absolute configuration of the major stereoisomers derived from the same reaction with different cyclic ethers. These predictions were verified experimentally through NMR and VCD spectroscopy and allowed rationalization of the stereochemical outcome of these reactions without further derivatization of the products, which can be prblematic under certain conditions as described herein.

CuO/SiO2 as a simple, effective and recoverable catalyst for alkylation of indole derivatives with diazo compounds.

The purely inorganic copper oxide on silica catalyzes the reaction of methyl phenyldiazoacetate with N-methyl indole under mild reaction conditions, giving the alkylation (formally a C-H insertion) in position 3, and the catalyst can be recovered and reused at least in 5 consecutive runs with only minor loss in activity. The scope of the reaction includes various diazo compounds and indole or pyrrole derivatives leading to alkylation or cyclopropanation depending on the heterocycle structure. An alternative mechanism, without reduction of Cu(II) to Cu(I), is proposed on the basis of the obtained results.

Structure and dynamics of 1-butyl-3-methylimidazolium hexafluorophosphate phases on silica and laponite clay: from liquid to solid behavior.

Solid-state NMR experiments show that the behavior of supported 1-butyl-3-methylimidazolium hexafluorophosphate ionic liquid phases depends on the type of support and the phase thickness. A mobile nearly liquid phase is obtained on silica, on the basis of the line widths of the bands in (1)H, (31)P, and (13)C spectra. However, the mobility is somehow restricted, as shown by the possibility of using the cross-polarization technique, although with slow dynamics. On laponite clay, a layered material with a negatively charged surface, a truly solid phase is obtained at low coverage, whereas the increase in ionic liquid loading leads to a second liquid phase, as shown by the presence of two contributions with very different line widths. These two phases seem to coexist without exchange in the NMR time frame. Heteronuclear correlation experiments evidence different relative dispositions of the imidazolium-surface-PF(6) system, with only aromatic protons involved in all the interactions on silica but participation of the benzylic groups (N-CH(3) and/or N-CH(2)) in the case of laponite clay.

Bis(oxazoline)-based coordination polymers: a recoverable system for enantioselective Henry reactions.

An efficient release-capture strategy for the recovery and reuse of enantioselective catalysts in the Henry reaction is described. This strategy is based on the precipitation of an insoluble coordination polymer at the end of each reaction, allowing easy separation from products. The coordination polymer is formed through aggregation of Cu(II) ions with ditopic bisoxazoline-based chiral ligands. Up to 11 catalytic cycles have been conducted keeping good yields and enantioselectivities.

Can enantioselectivity be computed in enthalpic barrierless reactions? The case of Cu(I)-catalyzed cyclopropanation of alkenes.

An extensive computational study has been carried out on different catalytic systems for cyclopropanation reactions based on copper. Most DFT schemes used present drawbacks that preclude the calculation of accurate absolute kinetic properties (energy barriers) of such systems, excepting the M05 and M06 suites of density functionals. On the other hand, there is a wide range of DFT methods capable of reproducing relative energy values, which can be easily translated into selectivities. Most of the theoretical levels used tend to overestimate activation barriers, allowing the location of the transition state (TS) on the potential-energy surface (PES) of the most reactive systems, which are probably artifacts of the method. However, after a thorough analysis of the calculated PES, and the origin of the energy differences obtained for the different alkene approaches in chiral systems, it is found that energy differences are almost constant over a wide range of geometries covering the reaction channel zone in which the true TS on the Gibbs free-energy surface (GFES) lies. Therefore, many computational schemes can still be used confidently to explain and predict enantioselectivities in these systems.

Enantioselective C-H carbene insertions with homogeneous and immobilized copper complexes.

The efficiency of chiral bis(oxazoline)- and azabis(oxazoline)-copper complexes in the enantioselective carbene insertion into C-H bonds of cyclic ethers in homogeneous phase strongly depends on the structure of the substrate. The immobilization on laponite clay by electrostatic interactions not only allows the recovery and reuse of the heterogeneous catalysts, but in some cases also improves enantioselectivity and overall chemoselectivity, making possible reactions that do not take place or lead to low yields in solution, even with the commonly used Rh(2)[S-DOSP](4) catalyst.

Selective oxidation of alkyl and aryl glyceryl monoethers catalysed by an engineered and immobilised glycerol dehydrogenase.

Enzymes acting over glyceryl ethers are scarce in living cells, and consequently biocatalytic transformations of these molecules are rare despite their interest for industrial chemistry. In this work, we have engineered and immobilised a glycerol dehydrogenase from Bacillus stearothermophilus (BsGlyDH) to accept a battery of alkyl/aryl glyceryl monoethers and catalyse their enantioselective oxidation to yield the corresponding 3-alkoxy/aryloxy-1-hydroxyacetones. QM/MM computational studies decipher the key role of D123 in the oxidation catalytic mechanism, and reveal that this enzyme is highly enantioselective towards S-isomers (ee > 99%). Through structure-guided site-selective mutagenesis, we find that the mutation L252A sculpts the active site to accommodate a productive configuration of 3-monoalkyl glycerols. This mutation enhances the k cat 163-fold towards 3-ethoxypropan-1,2-diol, resulting in a specific activity similar to the one found for the wild-type towards glycerol. Furthermore, we immobilised the L252A variant to intensify the process, demonstrating the reusability and increasing the operational stability of the resulting heterogeneous biocatalyst. Finally, we manage to integrate this immobilised enzyme into a one-pot chemoenzymatic process to convert glycidol and ethanol into 3-ethoxy-1-hydroxyacetone and (R)-3-ethoxypropan-1,2-diol, without affecting the oxidation activity. These results thus expand the uses of engineered glycerol dehydrogenases in applied biocatalysis for the kinetic resolution of glycerol ethers and the manufacturing of substituted hydroxyacetones.

Surface-enhanced stereoselectivity in Mukaiyama aldol reactions catalyzed by clay-supported bis(oxazoline)-copper complexes.

Surface effects on a laponite-exchanged bis(oxazoline)-copper complex modify the stereochemical course of the Mukaiyama aldol reaction between 2-(trimethylsilyloxy)furan and alpha-ketoesters, leading up to 90% ee (dr 86 : 14) becoming the best overall result obtained for this reaction and significantly improving the homogeneous process.

Simple and efficient heterogeneous copper catalysts for enantioselective C-H carbene insertion.

Immobilized box-Cu complexes are able to efficiently catalyze the insertion of a carbene, from methyl phenyldiazoacetate, into C-H bonds of THF, with high enantioselectivity (up to 88% ee). The immobilization not only allows recovery and reuse of the enantioselective catalyst but also provides an improvement in the selectivities from the values obtained in solution, probably due to a confinement effect of the bidimensional support. [reaction: see text].

Determination of Three Corticosteroids in the Biologic Matrix of Vitreous Humor by HPLC-tandem Mass Spectrometry: Method Development and Validation.

PURPOSE: To develop a simple, specific, and rapid method to determine corticosteroid concentrations in vitreous humor. METHODS: An analytical method based on high-pressure liquid chromatography-tandem mass spectrometry (HPLC-MS) with a simple extraction procedure was developed. New Zealand albino rabbits (n = 54) received a single (0.1 mL) intravitreal injection of dexamethasone (DXM, 0.1 mg), methylprednisolone (MP, 2 mg), or triamcinolone acetonide (TA, 10 mg). Eyes were enucleated and mean vitreous steroid levels were quantified at 12 h and 1, 2, 3, 7, and 14 days. RESULTS: Corticosteroids were extracted from the vitreous with acetonitrile, and TA was extracted with ethyl acetate, yielding high protein precipitation and clean solution samples. Vitreous samples were analyzed by isocratic HPLC-MS with mobile phase comprising acetonitrile and 2 mM ammonium formate buffer in water, pH 3.5. The linear range was 50-100,000 ng/g with a lower quantification limit of 45 ng/g for DXM and MP, and 50 ng/g for TA. Vitreous levels of DXM and MP were not detectable 14 days post-administration. Vitreous levels of TA were positive and stable throughout the study in both injected and control eyes. CONCLUSIONS: The HPLC-MS analytical method is an alternative to HPLC-MS/MS methods, sensitive enough for identifying and quantifying steroids in vitreous humor at a therapeutic dosage scale.

Laponite as carrier for controlled in vitro delivery of dexamethasone in vitreous humor models.

Laponite clay is able to retain dexamethasone by simple physisorption, presumably accomplished by hydrogen bonding formation and/or complexation with sodium counterions, as shown by solid state NMR. The physisorption can be somehow modulated by changing the solvent in the adsorption process. This simple system is able to deliver dexamethasone in a controlled manner to solutions used as models for vitreous humor. The proven biocompatibility of laponite as well as its transparency in the gel state, together with the simplicity of the preparation method, makes this system suitable for future in vivo tests of ophthalmic treatment.

The first synthesis of organic-inorganic hybrid materials with chiral bis(oxazoline) ligands.

Condensation of tetraethoxysilane with silane-functionalized bis(oxazolines) in the presence of dodecylamine leads to hybrid materials whose textural and catalytic properties depend on both the ligand and the spacer structure.