An efficient copper-catalyzed allylic trifluoromethylation reaction has been developed. This reaction provides a general and straightforward way to synthesize allylic trifluoromethylated compounds under mild conditions.

Whereas numerous asymmetric methods for formation of quaternary carbon stereocenters in cyclic systems have been documented, the construction of acyclic quaternary carbon stereocenters with control of absolute stereochemistry remains a formidable challenge. This review summarizes enantioselective methods for the construction of acyclic quaternary carbon stereocenters from achiral or chiral racemic reactants via transition metal catalysis.

The structure and mechanics of tissues is constantly perturbed by endogenous forces originated from cells, and at the same time regulate many important cellular functions such as migration, differentiation, and growth. Here we show that 3D collagen gels, major components of connective tissues and extracellular matrix (ECM), are significantly and irreversibly remodeled by cellular traction forces, as well as by macroscopic strains. To understand this ECM plasticity, we develop a computational model that takes into account the sliding and merging of ECM fibers. We have confirmed the model predictions with experiment. Our results suggest the profound impacts of cellular traction forces on their host ECM during development and cancer progression, and suggest indirect mechanical channels of cell-cell communications in 3D fibrous matrices.

A novel strategy for aromatic trifluoromethylation by converting aromatic amino group into CF3 group is reported herein. This method, which can be considered as trifluoromethylation variation of the classic Sandmeyer reaction, uses readily available aromatic amines as starting materials and is performed under mild conditions.

Disordered biopolymer gels have striking mechanical properties including strong nonlinearities. In the case of athermal gels (such as collagen-I) the nonlinearity has long been associated with a crossover from a bending dominated to a stretching dominated regime of elasticity. The physics of this crossover is related to the existence of a central-force isostatic point and to the fact that for most gels the bending modulus is small. This crossover induces scaling behavior for the elastic moduli. In particular, for linear elasticity such a scaling law has been demonstrated [Broedersz et al. Nat. Phys., 2011 7, 983]. In this work we generalize the scaling to the nonlinear regime with a two-parameter scaling law involving three critical exponents. We test the scaling law numerically for two disordered lattice models, and find a good scaling collapse for the shear modulus in both the linear and nonlinear regimes. We compute all the critical exponents for the two lattice models and discuss the applicability of our results to real systems.

Collagen gels are widely used in experiments on cell mechanics because they mimic the extracellular matrix in physiological conditions. Collagen gels are often characterized by their bulk rheology; however, variations in the collagen fiber microstructure and cell adhesion forces cause the mechanical properties to be inhomogeneous at the cellular scale. We study the mechanics of type I collagen on the scale of tens to hundreds of microns by using holographic optical tweezers to apply pN forces to microparticles embedded in the collagen fiber network. We find that in response to optical forces, particle displacements are inhomogeneous, anisotropic, and asymmetric. Gels prepared at 21°C and 37°C show qualitative difference in their micromechanical characteristics. We also demonstrate that contracting cells remodel the micromechanics of their surrounding extracellular matrix in a strainand distance-dependent manner. To further understand the micromechanics of cellularized extracellular matrix, we have constructed a computational model which reproduces the main experiment findings.micromechanics | collagen | fiber network T he mechanical properties of the extracellular matrix (ECM) play a central role in developmental biology (1), tissue homeostasis, and remodeling (2). Alteration of the ECM elasticity is a signature of many diseases such as pulmonary and atrial fibrosis, Ehlers-Danlos syndrome, and infantile cortical hyperostosis (3). The mechanical cues from the ECM also strongly correlate with the clinical prognosis of various types of cancers (4).In recent years, many studies have shown that to mimic the physiological conditions in vitro, mechanical cues from a truly 3D ECM are necessary (5). Type I collagen gel has gained popularity as arguably the most used in vitro model of a 3D ECM (2). As the most abundant protein in animal tissue and accounting for 25% of the human whole-body protein content (6), type I collagen is the major component of the ECM in skin, tendon, and organs. Despite its lack of biochemical complexity compared with live tissue, reconstituted type I collagen gel has been successfully used to provide mechanistic insights into processes such as morphogenesis (7), wound repair (8), and cell migration (9). In particular, the rheology and especially the rigidity of collagen gel have been shown to tune the growth and migratory phenotypes of cancer cells in vitro (10, 11).Structurally, collagen gels are formed by fibrous networks and typically have pore sizes of a few to tens of microns (12)(13)(14). The typical size of these structural discontinuities is comparable to the size of cells and is much larger than cell-ECM adhesion complexes (15,16). It is therefore expected that a cell senses the micromechanical properties of its surrounding matrix, rather than the macroscopic rheology of the ECM (16,17). Although many studies have focused on the (nonlinear) bulk rheology of empty and cellularized collagen ECM (18-22), the micromechanics of the porous biopolymer network is largely unexplored, presumably...

Iridium catalyzed primary alcohol oxidation triggers reductive C-O bond cleavage of isoprene oxide to form aldehyde-allyliridium pairs that combine to form products of tert-(hydroxy)-prenylation, a motif found in >2000 terpenoid natural products. Curtin-Hammett effects are exploited to enforce high levels of anti-diastereo- and enantioselectivity in the formation of an all-carbon quaternary center. The present redox-triggered carbonyl additions occur in the absence of stoichiometric byproducts, premetallated reagents and discrete alcohol-to-aldehyde redox manipulations.

The bimolecular rate constants of the addition reaction between hydroxyl radical (*OH) and nitrobenzene (C(6)H(5)NO(2)) were measured in subcritical and supercritical water (SCW) at temperatures between ambient and 390 degrees C. The measured bimolecular rate constants showed distinctly non-Arrhenius behavior (i.e., essentially no increase with temperature) from ambient to 350 degrees C, but increased in the slightly subcritical and supercritical region between 350 and 390 degrees C. These data were modeled reasonably well over the entire temperature range with a three-step reaction mechanism, originally proposed by Ashton et al.(1) This model includes the formation of a pi-complex intermediate as the precursor of the nitrohydroxycyclohexadienyl radical.