Synthesis and functionalization of dendron‐polymer conjugate based hydrogels via sequential thiol‐ene “click” reactions

Fabrication and functionalization of hydrogels from well‐defined dendron‐polymer‐dendron conjugates is accomplished using sequential radical thiol‐ene “click” reactions. The dendron‐polymer conjugates were synthesized using an azide‐alkyne “click” reaction of alkene‐containing polyester dendrons bearing an alkyne group at their focal point with linear poly(ethylene glycol)‐bisazides. Thiol‐ene “click” reaction was used for crosslinking these alkene functionalized dendron‐polymer conjugates using a tetrathiol‐based crosslinker to provide clear and transparent hydrogels. Hydrogels with residual alkene groups at crosslinking sites were obtained by tuning the alkene‐thiol stoichiometry. The residual alkene groups allow efficient postfunctionalization of these hydrogel matrices with thiol‐containing molecules via a subsequent radical thiol‐ene reaction. The photochemical nature of radical thiol‐ene reaction was exploited to fabricate micropatterned hydrogels. Tunability of functionalization of these hydrogels, by varying dendron generation and polymer chain length was demonstrated by conjugation of a thiol‐containing fluorescent dye. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 926–934     

An expedient solvent-free C-benzylation of 4-hydroxycoumarin with styrenes

1. Download : Download high-res image (163KB)
2. Download : Download full-size image

     

Homogeneous molecular catalysis of the electrochemical reduction of N2O to N2: redox vs. chemical catalysis

Homogeneous electrochemical catalysis of N₂O reduction to N₂ is investigated with a series of organic catalysts and rhenium and manganese bipyridyl carbonyl complexes. An activation-driving force correlation is revealed with the organic species characteristic of a redox catalysis involving an outer-sphere electron transfer from the radical anions or dianions of the reduced catalyst to N₂O. Taking into account the previously estimated reorganization energy required to form the N₂O radical anions leads to an estimation of the N₂O/N₂O˙⁻ standard potential in acetonitrile electrolyte. The direct reduction of N₂O at a glassy carbon electrode follows the same quadratic activation driving force relationship. Our analysis reveals that the catalytic effect of the mediators is due to a smaller reorganization energy of the homogeneous electron transfer than that of the heterogeneous one. The physical effect of “spreading” electrons in the electrolyte is shown to be unfavorable for the homogeneous reduction. Importantly, we show that the reduction of N₂O by low valent rhenium and manganese bipyridyl carbonyl complexes is of a chemical nature, with an initial one-electron reduction process associated with a chemical reaction more efficient than the simple outer-sphere electron transfer process. This points to an inner-sphere mechanism possibly involving partial charge transfer from the low valent metal to the binding N₂O and emphasizes the differences between chemical and redox catalytic processes.

Homogeneous electrochemical catalysis of N₂O reduction to N₂ is investigated with a series of organic catalysts and rhenium and manganese bipyridyl carbonyl complexes.     

A computational framework for fluid–porous structure interaction with large structural deformation

We study the effect of poroelasticity on fluid–structure interaction. More precisely, we analyze the role of fluid flow through a deformable porous matrix in the energy dissipation behavior of a poroelastic structure. For this purpose, we develop and use a nonlinear poroelastic computational model and apply it to the fluid–structure interaction simulations. We discretize the problem by means of the finite element method for the spatial approximation and using finite differences in time. The numerical discretization leads to a system of non-linear equations that are solved by Newton’s method. We adopt a moving mesh algorithm, based on the Arbitrary Lagrangian–Eulerian method to handle large deformations of the structure. To reduce the computational cost, the coupled problem of free fluid, porous media flow and solid mechanics is split among its components and solved using a partitioned approach. Numerical results show that the flow through the porous matrix is responsible for generating a hysteresis loop in the stress versus displacement diagrams of the poroelastic structure. The sensitivity of this effect with respect to the parameters of the problem is also analyzed.

     

Cannabinoid Receptor 2 Alters Social Memory and Microglial Activity in an Age-Dependent Manner

Physiological brain aging is characterized by gradual, substantial changes in cognitive ability, accompanied by chronic activation of the neural immune system. This form of inflammation, termed inflammaging, in the central nervous system is primarily enacted through microglia, the resident immune cells. The endocannabinoid system, and particularly the cannabinoid receptor 2 (CB₂R), is a major regulator of the activity of microglia and is upregulated under inflammatory conditions. Here, we elucidated the role of the CB₂R in physiological brain aging. We used CB₂R^−/− mice of progressive ages in a behavioral test battery to assess social and spatial learning and memory. This was followed by detailed immunohistochemical analysis of microglial activity and morphology, and of the expression of pro-inflammatory cytokines in the hippocampus. CB₂R deletion decreased social memory in young mice, but did not affect spatial memory. In fact, old CB₂R^−/− mice had a slightly improved social memory, whereas in WT mice we detected an age-related cognitive decline. On a cellular level, CB₂R deletion increased lipofuscin accumulation in microglia, but not in neurons. CB₂R^−/− microglia showed an increase of activity markers Iba1 and CD68, and minor upregulation in tnfa and il6 expression and downregulation of ccl2 with age. This was accompanied by a change in morphology as CB₂R^−/− microglia had smaller somas and lower polarity, with increased branching, cell volume, and tree length. We present that CB₂Rs are involved in cognition and age-induced microglial activity, but may also be important for microglial activation itself.     

Covalent Modification of Organo‐Functionalized Graphene Oxide and its Scope as Catalyst for One‐Pot Pyrazolo‐Pyranopyrimidine Derivatives

The surface of graphene oxide (GO) was modified using [3‐(2‐aminoethylamino)propyl]trimethoxysilane (diamine), which exhibited excellent catalytic activity for one‐pot multicomponent reactions. The newly synthesized material was fully characterized by various instrumental techniques including Fourier‐transfer infrared (FTIR) and Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The instrumental analysis confirmed the successful grafting of organic amine functional groups onto the graphene oxide surface. The diamine‐functionalized GO proved to be an excellent catalyst for the synthesis of pyrazolo‐pyranopyrimidine derivatives with 93 % yield and high selectivity. The catalytic activity almost remained unaltered up to three cycles. The newly synthesized pyrazolo‐pyranopyrimidine derivatives have potential use as scaffolds in designing new pharmaceutical products.     

Generation of Photocurrent by Visible‐Light Irradiation of Conjugated Dawson Polyoxophosphovanadotungstate–Porphyrin Copolymers

Four hybrid polyoxometalate–porphyrin copolymer films were obtained by the electrooxidation of zinc octaethylporphyrin in the presence of four different Dawson‐type polyoxometalates bearing two pyridyl groups (POM(py)₂) with various spacers. The POM monomers were designed around 1,3,5‐trisubstituted benzene rings. Two of the substituents of the benzene ring are linked to the pyridyl groups, and the third is connected to the POM subunit. The four monomers vary in the relative positions of the nitrogen atoms of the pyridine rings or in the distance from the carbonyl group. The monomers were fully characterized by ¹H, ³¹P, and ¹³C NMR spectroscopy, electrospray mass spectrometry, IR and UV/Vis spectroscopy, and electrochemistry. The copolymers were characterized by UV/Vis spectroscopy, X‐ray photoelectron spectroscopy, electrochemistry, and AFM. Their photovoltaic performance under visible light irradiation was investigated by photocurrent transient measurements under visible illumination.     

Electrochemical oxidation of aldehyde-N-arylhydrazones into symmetrical-2,5-disubstituted-1,3,4-oxadiazoles

A convenient, efficient and one-pot synthesis of chemically and pharmaceutically interesting symmetrical-2,5-disubstituted-1,3,4-oxadiazoles is reported. The protocol involves anodic oxidation of aldehyde-N-arylhydrazones in anhyd. MeCN–LiClO₄. Constant potential electrolysis carried out in an undivided cell and platinum electrodes leads to the formation of the corresponding oxadiazoles under ambient condition and the mechanism was deduced from voltammetry studies. The reaction proceeded smoothly with high atom economy.