Search

NO is well-known for its trans effect. NO binding to ferrous hemes of the form (por)Fe(L) (L = neutral N-based ligand) to give the {FeNO}7 (por)Fe(NO)(L) product results in a lengthening of the axial trans Fe-L bond. In contrast, NO binding to the ferric center in [(por)Fe(L)]+ to give the {FeNO}6 [(por)Fe(NO)(L)]+ product results in a shortening of the trans Fe-L bond. NO binding to both ferrous and ferric centers involves the lowering of their spin states. Density functional theory (DFT) calculations were used to probe the experimentally observed trans-bond shortening in some NO adducts of ferric porphyrins. We show that the strong σ antibonding interaction of d z2 and the axial (L) ligand p orbitals present in the Fe(II) systems is absent in the Fe(III) systems, as it is now in an unoccupied orbital. This feature, combined with a lowering of spin state upon NO binding, provides a rationale for the observed net trans-bond shortening in the {FeNO}6 but not the {FeNO}7 derivatives.

Depression is a recurrent and chronic mental disorder requiring long-term treatment. Major depressive disorder is present in 15-20% of patients with type 1 or type 2 diabetes. Large-scale evidence revealed that depression and depressive symptoms are independent risk factors for the development of type 2 diabetes, and they may contribute to hyperglycemia and even accelerate the premature onset of diabetes complications. Venlafaxine is a clinical first-line antidepressant used for more than 30 years. Recently, clinical reports showed that venlafaxine overdose might cause hypoglycemia. Venlafaxine is insoluble and salt formation technology is the most appropriate method to improve the physicochemical properties and the pharmacokinetic profile of the drug. In the present work, the use of the solvent evaporation method, slurry, and the liquid-assisted grinding method resulted in the crystalline salt venlafaxine-caffeic acid (1:1). The compounds were characterized using a series of solid-state techniques, viz., powder X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared spectroscopy, and solid-state nuclear magnetic resonance, and the crystal structure was determined by single-crystal X-ray diffraction. Besides, a comparative study of solubility, dissolution, and hypoglycemic activity of the parent drug and the new salt has been carried out. The tested venlafaxine-caffeic acid salt showed about 16-fold higher solubility than the pure drug. Moreover, the glucose consumption assay results showed that the novel salt possesses potent hypoglycemic activity in vitro, suggesting that it is a promising candidate effective for major depressive disorder patients with type 2 diabetes.

In this work, coumarin derivatives (C) are used to enhance the fluorescence of graphene quantum dots (GQDs) by covalently linking the carboxyl groups on the edge of the GQD sheet. The as-synthesized coumarin-modified graphene quantum dots (C-GQDs) have a uniform particle size with an average diameter of 3.6 nm. Simultaneously, the C-GQDs have strong fluorescence emission, excellent photostability, and high fluorescence quantum yield. C-GQDs and CN- can form a C-GQDs+CN- system due to deprotonation and/or intermolecular interactions. The introduced hydroquinone (HQ) is oxidized to benzoquinone (BQ), and the interaction between BQ and the C-GQDs+CN- system could lead to fluorescence enhancement of C-GQDs. Meanwhile, the redox reaction between BQ and ascorbic acid (AA) can be used for quantitative detection of AA with CN- and HQ being used as substrates. Based on the above mechanism, C-GQDs are developed as a multicomponent detection and sensing platform, and the detection limits for CN-, HQ, and AA were 4.7, 2.2, and 2.2 nM, respectively. More importantly, satisfactory results were obtained when the platform was used to detect CN-, HQ, and AA in living cells and fresh fruits.

Ceramic dielectrics are reported with superior energy storage performance for applications, such as power electronics in electrical vehicles. A recoverable energy density (Wrec) of ∼4.55 J cm–3 with η ∼ 90% is achieved in lead-free relaxor BaTiO3-0.06Bi2/3(Mg1/3Nb2/3)O3 ceramics at ∼520 kV cm–1. These ceramics may be co-fired with Ag/Pd, which constitutes a major step forward toward their potential use in the fabrication of commercial multilayer ceramic capacitors. Compared to stoichiometric Bi(Mg2/3Nb1/3)O3-doped BaTiO3 (BT), A-site deficient Bi2/3(Mg1/3Nb2/3)O3 reduces the electrical heterogeneity of BT. Bulk conductivity differs from the grain boundary only by 1 order of magnitude which, coupled with a smaller volume fraction of conducting cores due to enhanced diffusion of the dopant via A-site vacancies in the A-site sublattice, results in higher breakdown strength under an electric field. This strategy can be employed to develop new dielectrics with improved energy storage performance.

Catalytic carbene transfer to olefins is a useful approach to synthesize cyclopropanes, which are key structural motifs in many drugs and biologically active natural products. While catalytic methods for olefin cyclopropanation have largely relied on rare transition-metal-based catalysts, recent studies have demonstrated the promise and synthetic value of iron-based heme-containing proteins for promoting these reactions with excellent catalytic activity and selectivity. Despite this progress, the mechanism of iron-porphyrin and hemoprotein-catalyzed olefin cyclopropanation has remained largely unknown. Using a combination of quantum chemical calculations and experimental mechanistic analyses, the present study shows for the first time that the increasingly useful C=C functionalizations mediated by heme carbenes feature an FeII-based, nonradical, concerted nonsynchronous mechanism, with early transition state character. This mechanism differs from the FeIV-based, radical, stepwise mechanism of heme-dependent monooxygenases. Furthermore, the effects of the carbene substituent, metal coordinating axial ligand, and porphyrin substituent on the reactivity of the heme carbenes was systematically investigated, providing a basis for explaining experimental reactivity results and defining strategies for future catalyst development. Our results especially suggest the potential value of electron-deficient porphyrin ligands for increasing the electrophilicity and thus the reactivity of the heme carbene. Metal-free reactions were also studied to reveal temperature and carbene substituent effects on catalytic vs noncatalytic reactions. This study sheds new light into the mechanism of iron-porphyrin and hemoprotein-catalyzed cyclopropanation reactions and it is expected to facilitate future efforts toward sustainable carbene transfer catalysis using these systems.