Search for: All records

Phenolic acids are a class of poorly water‐soluble organic compounds with antioxidant properties that contain a carboxylic acid and a phenol group, common in plants. We used hydroxypropyl‐β‐cyclodextrin (HP‐β‐CD) as a supramolecular host to sense phenolic acids in water near physiological pH. The analytes’ complexation was monitored through changes in the optical absorption and emission properties of a series of six organic dyes, acting as indicators in a displacement assay, that were selected from screening a panel of 17 candidates. Binding constants between these dyes and the HP‐β‐CD were in the 10²–10⁴range. We showed that the nuanced differences in the dyes’ optical signatures associated with this displacement process, when analyzed and summarized using multivariate analysis algorithms such as principal component analysis (PCA), can be used to successfully discriminate among six phenolic acids, and to identify six unknown samples of such acids, down to a 0.02 mM concentration.

 

Conversion of epichlorohydrin to glycidyl ethers creates versatile precursors that can be transformed into a variety of molecular species with glycerol skeletons, enabling the design of molecules with highly tailored functionalities. The synthesis of 2,2,2‐trifluoroethyl glycidyl ether (TFGE, IUPAC name: 2‐[(2,2,2‐trifluoroethoxy)methyl]oxirane, CAS# 1535‐91‐7) was optimized to provide high yield/selectivity and good “green metrics.” TFGE was then used as a platform molecule in the synthesis of asymmetric glycerol 1,3‐diether‐2‐alcohol derivatives, which were subsequently transformed to 1,2,3‐triethers or 1,3‐diether‐2‐ketones. The density, viscosity, and CO₂solubility of each molecule were measured and compared with those of other glycerol‐derived compounds as well as compounds with similar functional groups. Furthermore, quantum chemical calculations were performed to understand the structure–property–performance relationships of these molecules for CO₂absorption. Based on the results in this work, we foresee that TFGE (and similar glycidyl ethers) would offer great flexibility in molecular design of green solvents and precursors to more complex compounds.

 

A new method to synthesize complexes of the type [(CNC)Ru^II(NN)L]ⁿ⁺has been introduced, where CNC is a tridentate pincer composed of two (benz)imidazole derived NHC rings and a pyridyl ring, NN is a bidentate aromatic diimine ligand, L=bromide or acetonitrile, and n=1 or 2. Following this new method a series of six new complexes has been synthesized and characterized by spectroscopic, analytic, crystallographic, and computational methods. Their electrochemical properties have been studiedviacyclic voltammetry under both N₂and CO₂atmospheres. Photocatalytic reduction of CO₂to CO was performed using these complexes both in the presence (sensitized) and absence (self‐sensitized) of an external photosensitizer. This study evaluates the effect of different CNC, NN, and L ligands in sensitized and self‐sensitized photocatalysis. Catalysts bearing the benzimidazole derived CNC pincer show much better activity for both sensitized and self‐sensitized photocatalysis as compared to catalysts bearing the imidazole derived CNC pincer. Furthermore, self‐sensitized photocatalysis requires a diimine ligand for CO₂reduction with catalyst2_ACNbeing the most active catalyst in this series with TON=85 and TOF=22 h⁻¹with an electron donating 4,4′‐dimethyl‐2,2′‐bipyridyl (dmb) ligand and a benzimidazole derived CNC pincer.

 

We report new ruthenium complexes bearing the lipophilic bathophenanthroline (BPhen) ligand and dihydroxybipyridine (dhbp) ligands which differ in the placement of the OH groups ([(BPhen)₂Ru(n,n′‐dhbp)]Cl₂withn = 6 and 4 in 1_Aand 2_A, respectively). Full characterization data are reported for 1_Aand 2_Aand single crystal X‐ray diffraction for 1_A. Both 1_Aand 2_Aare diprotic acids. We have studied 1_A, 1_B, 2_A, and 2_B(B = deprotonated forms) by UV‐vis spectroscopy and 1 photodissociates, but 2 is light stable. Luminescence studies reveal that the basic forms have lower energy³MLCT states relative to the acidic forms. Complexes 1_Aand 2_Aproduce singlet oxygen with quantum yields of 0.05 and 0.68, respectively, in acetonitrile. Complexes 1 and 2 are both photocytotoxic toward breast cancer cells, with complex 2 showing EC₅₀light values as low as 0.50 μM with PI values as high as >200vs. MCF7. Computational studies were used to predict the energies of the³MLCT and³MC states. An inaccessible³MC state for 2_Bsuggests a rationale for why photodissociation does not occur with the 4,4′‐dhbp ligand. Low dark toxicity combined with an accessible³MLCT state for¹O₂generation explains the excellent photocytotoxicity of 2.

 

N-Sulfonyl-activated aziridines are known to undergo anionic-ring-opening polymerizations (AROP) to form polysulfonyllaziridines. However, the post-polymerization deprotection of the sulfonyl groups from polysulfonyllaziridines remains challenging. In this report, the polymerization of tert-butyl aziridine-1-carboxylate (BocAz) is reported. BocAz has an electron-withdrawing tert-butyloxycarbonyl (BOC) group on the aziridine nitrogen. The BOC group activates the aziridine for AROP and allows the synthesis of low-molecular-weight poly(BocAz) chains. A 13C NMR spectroscopic analysis of poly(BocAz) suggested that the polymer is linear. The attainable molecular weight of poly(BocAz) is limited by the poor solubility of poly(BocAz) in AROP-compatible solvents. The deprotection of poly(BocAz) using trifluoroacetic acid (TFA) cleanly produces linear polyethyleneimine. Overall, these results suggest that carbonyl groups, such as BOC, can play a larger role in the in the activation of aziridines in anionic polymerization and in the synthesis of polyimines.