An Investigation of Photo‐ and Pressure‐Induced Effects in a Pair of Isostructural Two‐Dimensional Spin‐Crossover Framework Materials

Two new isostructural iron(II) spin‐crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)₂(NCX)₂] (dpms=4,4′‐dipyridylmethyl sulfide; X=S ( SCOF‐6(S) ), X=Se ( SCOF‐6(Se) )) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF‐6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high‐spin (HS) to low‐spin iron(II) sites over the temperature range 300–4 K (T_1/2=75 K). In contrast, the NCSe^? analogue, SCOF‐6(Se) , displays a complete SCO transition (T_1/2=135 K). Photomagnetic characterizations reveal quantitative light‐ induced excited spin‐state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF‐6(S) and SCOF‐6(Se) , respectively. Variable‐pressure magnetic measurements were performed on SCOF‐6(S) , revealing that with increasing pressure both the T_1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF‐6(S) at ambient pressure due to an interplay between close T_1/2 and T(LIESST) values.     

Density functional theory on phase space

Forty‐five years after the point de départ [Hohenberg and Kohn, Phys Rev, 1964, 136, B864] of density functional theory, its applications in chemistry and the study of electronic structures keep steadily growing. However, the precise form of the energy functional in terms of the electron density still eludes us—and possibly will do so forever [Schuch and Verstraete, Nat Phys, 2009, 5, 732]. In what follows we examine a formulation in the same spirit with phase space variables. The validity of Hohenberg–Kohn–Levy‐type theorems on phase space is recalled. We study the representability problem for reduced Wigner functions, and proceed to analyze properties of the new functional. Along the way, new results on states in the phase space formalism of quantum mechanics are established. Natural Wigner orbital theory is developed in depth, with the final aim of constructing accurate correlation‐exchange functionals on phase space. A new proof of the overbinding property of the Müller functional is given. This exact theory supplies its home at long last to that illustrious ancestor, the Thomas–Fermi model. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

A copper complex bearing a TEMPO moiety as catalyst for the aerobic oxidation of primary alcohols

A new bifunctional, triazine-based ligand has been designed with the aim to generate a copper(II) complex holding a TEMPO (2,2,6,6-tetramethylpiperidinyloxy) moiety. The coordination compound obtained from the ligand 4-(2-(3-(pyridin-2-yl)-1H-pyrazol-1-yl)ethoxy)-6-(4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl)-N,N-diphenyl-1,3,5-triazin-2-amine (pypzt-1) and copper(II) bromide (i.e. complex 8) is capable of catalysing the selective, aerobic oxidation of benzyl alcohol to 84% of benzaldehyde in 24 h. This "galactose oxidase activity" of the copper/TEMPO complex is observed as well for the conversion of the non-activated alkyl alcohol octan-1-ol to octanal with a yield of 29% after the same reaction time. The single-crystal X-ray structure of 8 shows that its crystal lattice contains [Cu(I)Br(2)](-) anions which appear to be stabilised by means of both anion-pi and hydrogen bonding interactions. In addition, the solid state structure of 8 exhibits (lone-pair)-pi interactions between the nitrogen atom of an acetonitrile molecule and a triazine ring. The magnetic properties of 8 have been investigated by EPR and magnetic susceptibility measurements.     

Highly Enantioselective Synthesis of 1,2,3‐Substituted Cyclopropanes by Using α‐Iodo‐ and α‐Chloromethylzinc Carbenoids

Herein, we report the enantio‐ and diastereoselective formation of trans‐iodo‐ and trans‐chlorocyclopropanes from α‐iodo‐ and α‐chlorozinc carbenoids by using a dioxaborolane‐derived chiral ligand. The synthetically useful iodocyclopropane building blocks were derivatized by an electrophilic trapping of the corresponding cyclopropyl lithium species or a Negishi coupling to give access to a variety of enantioenriched 1,2,3‐substituted cyclopropanes. The synthetic utility of this method was demonstrated by the formal synthesis of an HIV‐1 protease inhibitor. In addition, the related stereoselective bromocyclopropanation was also investigated. New insights about the relative electrophilicity of haloiodomethylzinc carbenoids are also presented.     

Synthesis and Photophysics of a New Family of Fluorescent 9‐Alkyl‐Substituted Xanthenones

9‐Alkyl xanthenones with different aliphatic pendant groups have been easily prepared by means of nucleophilic addition of the corresponding Grignard derivative to a tert‐butyldimethylsilyl ether (TBDMS)‐protected 3,6‐dihydroxy‐xanthenone. The photophysical behavior of the new dyes has been explored by using absorption, steady‐state‐, and time‐resolved fluorescence measurements. We determined the equilibrium constants, visible spectral characteristics, fluorescence quantum yield, and decay times. Remarkably, they retain similar fluorescent properties of fluorescein including the characteristic phosphate‐mediated excited‐state proton‐transfer (ESPT) reaction. 6‐Hydroxy‐9‐isopropyl‐3H‐xanthen‐3‐one ( 5 ) was investigated in living cells; it presented a good permeability and efficient accumulation inside the cytosol. For the first time, we reported that the requirement of an aryl group at C‐9 is no longer needed and new fluorescent sensors can be therefore easily developed.     

Rational Design and Development of Anisotropic and Mechanically Strong Gelatin‐Based Stress Relaxing Hydrogels for Osteogenic/Chondrogenic Differentiation

Rational design and development of tailorable simple synthesis process remains a centerpiece of investigational efforts toward engineering advanced hydrogels. In this study, a green and scalable synthesis approach is developed to formulate a set of gelatin‐based macroporous hybrid hydrogels. This approach consists of four sequential steps starting from liquid‐phase pre‐crosslinking/grafting, unidirectional freezing, freeze‐drying, and finally post‐curing process. The chemical crosslinking mainly involves between epoxy groups of functionalized polyethylene glycol and functional groups of gelatin both in liquid and solid state. Importantly, this approach allows to accommodate different polymers, chitosan or hydroxyethyl cellulose, under identical benign condition. Structural and mechanical anisotropy can be tuned by the selection of polymer constituents. Overall, all hydrogels show suitable structural stability, good swellability, high porosity and pore interconnectivity, and maintenance of mechanical integrity during 3‐week‐long hydrolytic degradation. Under compression, hydrogels exhibit robust mechanical properties with nonlinear elasticity and stress‐relaxation behavior and show no sign of mechanical failure under repeated compression at 50% deformation. Biological experiment with human bone marrow mesenchymal stromal cells (hMSCs) reveals that hydrogels are biocompatible, and their physicomechanical properties are suitable to support cells growth, and osteogenic/chondrogenic differentiation, demonstrating their potential application for bone and cartilage regenerative medicine toward clinically relevant endpoints.     

Electrochemistry of immobilized redox enzymes: kinetic characteristics of NADH oxidation catalysis at diaphorase monolayers affinity immobilized on electrodes

In the class of NADH:acceptor oxidoreductases, the diaphorase from Bacillus stearothermophilusis a particularly promising enzyme for sensing NADH, and indirectly a great number of analytes, when coupled with a NAD-dependent dehydrogenase as well as for the design of mono- and multienzyme affinity sensors. The design and rational optimization of such systems require devising immobilization procedures that prevent dramatic losses of the enzymatic activity and a full kinetic characterization of the immobilized enzyme system. Two immobilization procedures are described, which involve recognition of the biotinylated diaphorase by a monolayer of neutravidin adsorbed on the electrode surface either directly or through the intermediacy of a monolayer of biotinylated rabbit immunoglobulin. Thorough kinetic characterization of the two systems is derived from cyclic voltammetric responses. A precise estimate of the enzyme coverages is obtained after comparing the enzyme kinetics of the immobilized and the homogeneous system.