Annulative π-Extension by Rhodium(III)-Catalyzed Ketone-Directed C−H Activation: Rapid Access to Pyrenes and Related Polycyclic Aromatic Hydrocarbons (PAHs)

Annulative π-extension (APEX) reaction has become a powerful tool for the precise synthesis of well-defined polycyclic aromatic hydrocarbons (PAHs) such as nanographene, graphene, and other PAHs possessing unique structure. Herein, an APEX reaction has been realized at the masked bay-region for the efficient and rapid synthesis of valuable PAH, pyrene, bearing substitutions at the most challenging K-region. Rh^III-catalyzed ketone-directed C−H activation at the peri-position of a naphthyl-derived ketone, alkyne-insertion, intramolecular nucleophilic attack at the carbonyl-group, dehydration, and aromatization steps occurred in one-pot to effectuate the protocol. Employing this strategy, a two-fold APEX reaction on enantiopure BINOL-derived ketones provided access to axially-chiral bipyrene derivatives. The detailed DFT study to support proposed mechanism, and synthesis of helical PAHs like dipyrenothiophene and dipyrenofuran are other highlights of the present study.     

Incorporation of Cell-Adhesive Proteins in 3D-Printed Lipoic Acid-Maleic Acid-Poly(Propylene Glycol)-Based Tough Gel Ink for Cell-Supportive Microenvironment

In extrusion-based 3D printing, the use of synthetic polymeric hydrogels can facilitate fabrication of cellularized and implanted scaffolds with sufficient mechanical properties to maintain the structural integrity and physical stress within the in vivo conditions. However, synthetic hydrogels face challenges due to their poor properties of cellular adhesion, bioactivity, and biofunctionality. New compositions of hydrogel inks have been designed to address this limitation. A viscous poly(maleate-propylene oxide)-lipoate-poly(ethylene oxide) (MPLE) hydrogel is recently developed that shows high-resolution printability, drug-controlled release, excellent mechanical properties with adhesiveness, and biocompatibility. In this study, the authors demonstrate that the incorporation of cell-adhesive proteins like gelatin and albumin within the MPLE gel allows printing of biologically functional 3D scaffolds with rapid cell spreading (within 7 days) and high cell proliferation (twofold increase) as compared with MPLE gel only. Addition of proteins (10% w/v) supports the formation of interconnected cell clusters (≈1.6-fold increase in cell areas after 7-day) and spreading of cells in the printed scaffolds without additional growth factors. In in vivo studies, the protein-loaded scaffolds showed excellent biocompatibility and increased angiogenesis without inflammatory response after 4-week implantation in mice, thus demonstrating the promise to contribute to the printable tough hydrogel inks for tissue engineering.     

Effect of gamma irradiation on X‐ray absorption and photoelectron spectroscopy of Nd‐doped phosphate glass

X‐ray absorption near‐edge structure (XANES) and X‐ray photoelectron spectroscopy (XPS) of Nd‐doped phosphate glasses have been studied before and after gamma irradiation. The intensity and the location of the white line peak of the L₃‐edge XANES of Nd are found to be dependent on the ratio O/Nd in the glass matrix. Gamma irradiation changes the elemental concentration of atoms in the glass matrix, which affects the peak intensity of the white line due to changes in the covalence of the chemical bonds with Nd atoms in the glass (structural changes). Sharpening of the Nd 3d_5/2 peak profile in XPS spectra indicates a deficiency of oxygen in the glasses after gamma irradiation, which is supported by energy‐dispersive X‐ray spectroscopy measurements. The ratio of non‐bridging oxygen to total oxygen in the glass after gamma radiation has been found to be correlated to the concentration of defects in the glass samples, which are responsible for its radiation resistance as well as for its coloration.     

Femtosecond solvation dynamics in different regions of a bile salt aggregate: excitation wavelength dependence

Solvation dynamics of coumarin 480 (C480) in the secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied using femtosecond up-conversion. The secondary aggregate resembles a long (approximately 40 A) hollow cylinder with a central water-filled tunnel. Different regions of the aggregate are probed by variation of the excitation wavelength (lambdaex) from 375 to 435 nm. The emission maximum of C480 displays an 8 nm red shift as the lambdaex increases from 345 to 435 nm. The 8 nm red edge excitation shift (REES) suggests that the probe (C480) is distributed over regions of varied polarity. Excitation at a short wavelength (375 nm) preferentially selects the probe molecule in the buried locations and exhibits slow dynamics with a major (84%) slow component (3500 ps) and a small (16%) contribution of the ultrafast component (2.5 ps). Excitation at lambdaex=435 nm (red end) corresponds to the exposed sites where solvation dynamics is very fast with a major (73%) ultrafast component (相似文献   

Improved lithium cyclability and storage in mesoporous SnO2 electronically wired with very low concentrations (≤1 %) of reduced graphene oxide

On the wire: Mesoporous tin dioxide (SnO(2)) wired with very low amounts (≤1?%) of reduced graphene oxide (rGO) exhibits a remarkable improvement in lithium-ion battery performance over bare mesoporous or solid nanoparticles of SnO(2). Reversible lithium intercalation into SnO(2)/SnO over several cycles was demonstrated in addition to conventional reversible lithium storage by an alloying reaction.     

Synthesis of 3,4-dihydropyridin-2-one derivatives in convergent mode applying bio catalyst vitamin B1 and polymer supported catalyst PEG-SO3H from two different sets of building blocks

Two highly efficient, green protocols have been developed for the synthesis of 3,4-dihydropyridin-2-one derivatives from different starting materials exploring two reaction specific catalysts, vitamin B₁ (VB₁), and PEG-SO₃H. VB₁ catalyzed simple and convenient protocol has been developed for the synthesis of 3,4-dihydropyridin-2-one derivatives by the installation of aldehyde, cyanoacetamide, and 1,3-dicarbonyl compounds. In addition, 3,4-dihydropyridin-2-one derivatives have also been synthesized by simply combining aldehyde, malononitrile, and 1,3-dicarbonyl compounds via the formation of 4H-pyran nucleus and PEG-SO₃H catalyzed one-pot rearrangement.     

Layer-by-layer-assembled microfiltration membranes for biomolecule immobilization and enzymatic catalysis

Multilayer assemblies of polyelectrolytes, for protein immobilization, have been created within the membrane pore domain. This approach was taken for two reasons: (1) the high internal membrane area can potentially increase the amount of immobilized protein, and (2) the use of convective flow allows uniform assembly of layers and eliminates diffusional limitations after immobilization. To build a stable assembly, the first polyelectrolyte layer was covalently attached to the membrane surface and inside the pore walls. Either poly(L-glutamic acid) (PLGA) or poly(L-lysine) (PLL) was used in this step. Subsequent deposition occurs by multiple electrostatic interactions between the adsorbing polyelectrolyte [poly(allylamine) hydrochloride (PAH) or poly(styrenesulfonate) (PSS)] and the oppositely charged layer. Three-layer membranes were created: PLL-PSS-PAH or PLGA-PAH-PSS, for an overall positive or negative charge, respectively. The overall charge on both the protein and membrane plays a substantial role in immobilization. When the protein and the membrane are oppositely charged, the amount immobilized and the stability within the polyelectrolyte assembly are significantly higher than for the case when both have similar charges. After protein incorporation in the multilayer assembly, the active site accessibility was comparable to that obtained in the homogeneous phase. This was tested by affinity interaction (avidin-biotin) and by carrying out two reactions (catalyzed by glucose oxidase and alkaline phosphatase). Besides simplicity and versatility, the ease of enzyme regeneration constitutes an additional benefit of this approach.     

Ultrafast electron transfer in a nanocavity. dimethylaniline to coumarin dyes in hydroxypropyl gamma-cyclodextrin

Photoinduced electron transfer (PET) from N,N-dimethylaniline (DMA) to four coumarin dyes (C151, C481, C153, and C480) inside the cavity of hydroxypropyl gamma-cyclodextrin (hpCD) is studied using femtosecond upconversion. The rate of PET is found to be nonexponential and to vary significantly with the coumarin dyes. The rate for C481 is 100 times faster than that for C480. The PET rate displays a bell-shaped dependence on the free energy change and thus reveals a Marcus-type inverted region. The anisotropy decay of the four dyes in hpCD are found to be very similar, and hence the observed variation in the rate of PET is not due to variation in rotational diffusion of the acceptors (coumarin dyes).     

Ultrafast fluorescence resonance energy transfer in a micelle

Ultrafast fluorescence resonance energy transfer (FRET) from coumarin 153 (C153) to rhodamine 6G (R6G) is studied in a neutral PEO(20)-PPO(70)-PEO(20) triblock copolymer (P123) micelle and an anionic micelle (sodium dodecyl sulfate, SDS) using a femtosecond up-conversion setup. Time constants of FRET were determined from the rise time of the acceptor emission. It is shown that a micelle increases efficiency of FRET by holding the donor and the acceptor at a close distance (intramicellar FRET) and also by tuning the donor and acceptor energies. It is demonstrated that in the P123 micelle, intramicellar FRET (i.e., donor and acceptor in same micelle) occurs in 1.2 and 24 ps. In SDS micelle, there are two ultrafast components (0.7 and 13 ps) corresponding to intramicellar FRET. The role of diffusion is found to be minor in the ultrafast components of FRET. We also detected a much longer component (1000 ps) for intramicellar FRET in the larger P123 micelle.     

Conformational specificity of non-canonical base pairs and higher order structures in nucleic acids: crystal structure database analysis

Non-canonical base pairs contribute immensely to the structural and functional variability of RNA, which calls for a detailed characterization of their spatial conformation. Intra-base pair parameters, namely propeller, buckle, open-angle, stagger, shear and stretch describe structure of base pairs indicating planarity and proximity of association between the two bases. In order to study the conformational specificities of non-canonical base pairs occurring in RNA crystal structures, we have upgraded NUPARM software to calculate these intra-base pair parameters using a new base pairing edge specific axis system. Analysis of base pairs and base triples with the new edge specific axis system indicate the presence of specific structural signatures for different classes of non-canonical pairs and triples. Differentiating features could be identified for pairs in cis or trans orientation, as well as those involving sugar edges or C-H-mediated hydrogen bonds. It was seen that propeller for all types of base pairs in cis orientation are generally negative, while those for trans base pairs do not have any preference. Formation of a base triple is seen to reduce propeller of the associated base pair along with reduction of overall flexibility of the pairs. We noticed that base pairs involving sugar edge are generally more non-planar, with large propeller or buckle values, presumably to avoid steric clash between the bulky sugar moieties. These specific conformational signatures often provide an insight into their role in the structural and functional context of RNA.