Pyrene-Based Covalent Organic Frameworks for Photocatalytic Hydrogen Peroxide Production

Four highly porous covalent organic frameworks (COFs) containing pyrene units were prepared and explored for photocatalytic H₂O₂ production. The experimental studies are complemented by density functional theory calculations, proving that the pyrene unit is more active for H₂O₂ production than the bipyridine and (diarylamino)benzene units reported previously. H₂O₂ decomposition experiments verified that the distribution of pyrene units over a large surface area of COFs plays an important role in catalytic performance. The Py-Py-COF though contains more pyrene units than other COFs which induces a high H₂O₂ decomposition due to a dense concentration of pyrene in close proximity over a limited surface area. Therefore, a two-phase reaction system (water-benzyl alcohol) was employed to inhibit H₂O₂ decomposition. This is the first report on applying pyrene-based COFs in a two-phase system for photocatalytic H₂O₂ generation.     

Translating Planar Heterocycles into Three-Dimensional Analogs by Photoinduced Hydrocarboxylation**

The rapid preparation of complex three-dimensional (3D) heterocyclic scaffolds is a key challenge in modern medicinal chemistry. Despite the increased probability of clinical success for small molecule therapeutic candidates with increased 3D complexity, new drug targets remain dominated by flat molecules due to the abundance of coupling reactions available for their construction. In principle, heteroarene hydrofunctionalization reactions offer an opportunity to transform readily accessible planar molecules into more three-dimensionally complex analogs through the introduction of a single molecular vector. Unfortunately, dearomative hydrofunctionalization reactions remain limited. Herein, we report a new strategy to enable the dearomative hydrocarboxylation of indoles and related heterocycles. This reaction represents a rare example of a heteroarene hydrofunctionalization that meets the numerous requirements for broad implementation in drug discovery. The transformation is highly chemoselective, broad in scope, operationally simple, and readily amenable to high-throughput experimentation (HTE). Accordingly, this process will allow existing libraries of heteroaromatic compounds to be translated into diverse 3D analogs and enable exploration of new classes of medicinally relevant molecules.     

Exploitation of Dimeric Cyclic Cysteine as Helix Inducer in Ultra-Short Peptides for Cu(II)-Catalyzed Asymmetric Michael Addition on Chalcones

A dimeric cyclic cysteine analogue, i.e. (1R,1′R,2R,2′R)-2,2′-disulfanediylbis (aminocyclohexane-1-carboxylic acid), was used as a constrained unnatural amino acid and as a folding inducer in ultra-short Leu-Val-containing peptide. Our results showed that both free dimer amino acid L1 and its peptide derivative L2 are able to chelate Cu(II). The obtained complexes resulted to be catalytically active in Michael addition reaction of nitromethane on different types of chalcones. L1-Cu(II) was shown more reactive in terms of conversion, while, in neat conditions, L2-Cu(II) allows to obtain an interesting 60 % e.e. on pyridine chalcone.     

Mechanistic studies of fluorescent sensors for the detection of reactive oxygen species

Two new sensors for the detection of reactive oxygen species have been synthesized and characterized; they contain the 4-amino-7-nitrobenzofurazan (ABF) moiety covalently tethered to a phenol. Comparison of sensors ABFhd and dABFhd (the latter containing two ortho-methyl groups) shows that introduction of steric bulk leads to an improvement of fluorescent sensor performance, thus confirming our previous predictions based on computational chemistry. ABFhd and dABFhd are new tools for biological applications involving reactive oxygen species, in particular oxygen-centered radicals.     

Supramolecular control of a fast and reversible Diels-Alder reaction

A new cyclophane featuring two opposite anthracene units linked in 9,10-positions has been synthesized thanks to the template effect of the Me4N(+) ion. It forms pseudorotaxane complexes with alkylviologen ions and undergoes a fast and reversible reaction with tetracyanoethylene. A quantitative analysis has been carried out of the formation of Diels-Alder adducts, whose distribution can be controlled by host-guest complexation. These findings open interesting perspectives in the field of Dynamic Covalent Chemistry.     

Existence and Exponential Decay of Solutions to a Quasilinear Thermoelastic Plate System

We consider a quasilinear PDE system which models nonlinear vibrations of a thermoelastic plate defined on a bounded domain in , n ≤ 3. Existence of finite energy solutions describing the dynamics of a nonlinear thermoelastic plate is established. In addition asymptotic long time behavior of weak solutions is discussed. It is shown that finite energy solutions decay exponentially to zero with the rate depending only on the (finite energy) size of initial conditions. The proofs are based on methods of weak compactness along with nonlocal partial differential operator multipliers which supply the sought after “recovery” inequalities. Regularity of solutions is also discussed by exploiting the underlying analyticity of the linearized semigroup along with a related maximal parabolic regularity [1, 16, 44]. The research of I. Lasiecka has been partially supported by DMS-NSF Grant Nr 0606882. S. Maad was supported by the Swedish Research Council and by the European Union under the Marie Curie Fellowship MEIF-CT-2005-024191.     

Green dispersive solid-phase microextraction of melamine using crosslinked beta-cyclodextrin with citric acid followed by high-performance liquid chromatography

In this research, a green approach for dispersive solid phase microextraction was introduced for the extraction and determination of melamine in various matrices such as infant formula and hot water in a melamine bowl. In this way, a natural polar polymer called ß-cyclodextrin has been cross-linked with citric acid to create a water-insoluble adsorbent. The extraction was carried out by dispersion of the sorbent into the sample solution. The effective parameters on the extraction efficiency of the melamine, including ion strength, extraction time, sample volume, amount of absorbent, pH, type of desorption solvent, desorption time, and desorption solvent volume were optimized by one variable at a time approach. Under the optimal conditions, the method showed a good linear dynamic range for melamine in the range of 1–1000 μg/L with a coefficient of determination of 0.9985. The obtained limit of detection was 0.3 μg/L. The intra-day and inter-day relative standard deviations (n = 3) were 3.1% and 3.2% respectively. Lastly, this technique was applied to extract and determine the analyte in a melamine bowl and infant formula with acceptable and satisfactory results.     

Organocatalytic synthesis of α-hydroxy and α-aminophosphonates

A new and highly flexible procedure is described for the synthesis of α-amino- and α-hydroxy phosphonates. In the presence of a catalytic amount of oxalic acid (10 mol %), trimethyl phosphite reacts with aldehydes or imines (generated in situ from an aldehyde and an amine) to yield the corresponding coupled products in good yield.     

Sulfonated molecules that bind a partially structured species of beta2-microglobulin also influence refolding and fibrillogenesis

Human beta2-microglobulin (beta2-m) is a small amyloidogenic protein responsible for dialysis-related amyloidosis, which represents a severe complication of long-term hemodialysis. A therapeutic approach for this amyloidosis could be based on the stabilization of beta2-m through the binding to a small molecule, to possibly inhibit protein misfolding and amyloid fibril formation. The search of a strong ligand of this protein is extremely challenging: by using CE in affinity and refolding experiments we study the effect that previously selected sulfonated molecules have on the equilibrium between the native form and an ensemble of conformers populating the slow phase of beta2-m folding. These data are correlated with the effect that the same molecules exert on in vitro fibrillogenesis experiments.