Tzy‐Jiun M. Luo

With their unique ability to differentiate into all cell types, embryonic stem (ES) cells hold great therapeutic promise. To improve the efficiency of embryoid body (EB)-mediated ES cell differentiation, we studied murine EBs on the basis of their size and found that EBs with an intermediate size (diameter 100-300 microm) are the most proliferative, hold the greatest differentiation potential, and have the lowest rate of cell death. In an attempt to promote the formation of this subpopulation, we surveyed several biocompatible substrates with different surface chemical parameters and identified a strong correlation between hydrophobicity and EB development. Using self-assembled monolayers of various lengths of alkanethiolates on gold substrates, we directly tested this correlation and found that surfaces that exhibit increasing hydrophobicity enrich for the intermediate-size EBs. When this approach was applied to the human ES cell system, similar phenomena were observed. Our data demonstrate that hydrophobic surfaces serve as a platform to deliver uniform EB populations and may significantly improve the efficiency of ES cell differentiation.

The supramolecular chemistry and crystal structures of five bis(2-methylimidazolium 2,6-dicarboxypyridine) M(II) complexes, where M = Zn, Cu, Ni, Co, and 7:3 Mn/Cu (1−5, respectively), are reported. These complexes form building blocks with nearly identical molecular structures that crystallize in the same packing pattern. Anions of 2,6-dicarboxypyridine and cations of 2-methylimidazole form N−H···O and O−H···O hydrogen bonds that dominate crystal packing by forming linear ribbons of molecules. Thus, complexes 1−5 form an isomorphous series with a single robust crystalline architecture that accommodates five different transition metals without altering molecular packing. The growth of crystals from solutions that contain two different metal complexes produces mixed crystals in which mixtures of the different metal complexes are incorporated in the same relative molar ratio present in solution. This technique was used to grow crystals of 5 with Mn and Cu complexes in a 7:3 molar ratio. Complexes 1−5 form crystalline solids that represent a novel class of modular materials in which the organic ligands serve as a structural component that defines a single packing arrangement that persists over a range of structures and in which the metal serves as an interchangeable component with which to vary the physical properties of the material. The molecular and crystal structures of bis(2-methylimidazolium 2,6-dicarboxypyridine) M(II) complexes 1−5 are reported and compared to those of a related family of bis(imidazolium 2,6-dicarboxypyridine) M(II) dihydrate complexes 1‘−5‘ (M = Zn, Cu, Ni, Co, and Mn) reported previously. We show that complexes 1−5 and 1‘−5‘ have similar packing arrangements and that introducing a methyl substituent (similar in size to water) at the C2 position of imidazole displaces water and prevents it from being incorporated into the lattice of 1−5.

In this research, core-shell electrocatalysts comprising a Ru core covered with precisely controlled 1.5-3.6 atomic layers (ALs)-thick Pt atoms are synthesized. The sample with 1.5 ALs shows a 3.2-fold improvement in CO-tolerance and 2.4-fold current enhancement at the conventional battery operation potential (I(300), at 300 mV vs Ag/AgCl) during methanol oxidation as compared with conventional all-Pt nanoparticles. The origin of the enhanced performance and the atomic structure of the core-shell nanoparticles are elucidated to be mainly dominated by the lattice strain (possibly some slight effect of heteroatomic interactions) then by the combination of ligand effects and bifunctional mechanisms when the shell crystal is thicker than 2.7 ALs.

In this study, we examine the noncovalent interactions that occur between the cyclic dipeptide of glycine (GLYDKP) and a carboxylic acid guest. This study complements our earlier studies on the cyclic dipeptide of aspartic acid by exploring further the possibility of using hydrogen-bonded tapes comprised of molecules of GLYDKP, as a scaffold with which to control the location of guest molecules in a crystalline lattice. On the basis of the 11 cocrystals of GLYDKP reported herein, we conclude that guest molecules will be positioned between tapes of GLYDKP if the guest molecules meet the following criteria. First, the width of the guest molecule should be between 4.5 and 8.5 Å. Second, interactions between adjacent guest molecules should be stronger than a van der Waals contact. Third, a hydrogen-bond donor (hydroxyl group) and a hydrogen-bond acceptor (carbonyl group) should be present in the structure of the guest with their separation no greater than two bonds between the carbon atom of the carbonyl group and the oxygen atom of the hydroxyl group. Fourth, the strength of interactions between molecules in the cocrystal should be of the following order: host−host > host−guest > guest−guest. This order ensures the tape superstructure dictates the location of guest molecules in the host lattice.