Synthetic Short Peptides for Rapid Fabrication of Monolayer Cell Sheets

Cell sheets are useful materials in regenerative medicine; however, the cell sheet fabrication processes developed to date are associated with several crucial challenges. The aim of this study was to develop a new and simple method for the rapid and efficient fabrication of transferable monolayer cell sheets. Chemoenzymatic synthesis mediated by proteinase K was used to synthesize short co-oligopeptides for cell sheet fabrication, which showed high yield, well-defined structures, and a controllable composition. These co-oligopeptides predominantly adopted a random coil conformation in buffer. Histidine/cysteine co-oligopeptides with a disordered secondary structure displayed cysteine content-dependent esterase activity and cysteine content-independent protease activity. Taking advantage of this enzymatic activity, confluent cell monolayers were detached by simply adding the co-oligopeptides solution to the culture media, and then an intact monolayer cell sheet was prepared with high cell viability and reattachment ability. The method proposed herein for preparing monolayer cell sheets represents a novel concept by using oligopeptides with enzymatic activity that show applied potential in cell sheet technology for tissue engineering and regenerative medicine

DNA-Grafted Polypeptide Molecular Bottlebrush Prepared via Ring-Opening Polymerization and Click Chemistry

A new type of DNA grafted polypeptide molecular brush was synthesized via a combination of ring-opening polymerization (ROP) and click chemistry. This conjugation method provides an easy and efficient approach to obtain a hybrid DNA-grafted polypeptide molecular bottlebrush. The structure and assembly behaviors of this hybrid brush were investigated using electrophoresis, UV–vis spectroscopy, transmission electron microscopy (TEM), and atomic force microscopy (AFM). Hierarchical supramolecular assemblies can be obtained through hybridization of two kinds of polypeptide-<i>g</i>-DNA molecular bottlebrushes containing complementary DNA side chains. We further demonstrated that such polypeptide-<i>g</i>-DNA can be hybridized with ds-DNA and DNA-grafted gold nanoparticles to form a supermolecular bottlebrush and hybrid bottlebrush, respectively. In addition, DNA-polypeptide hydrogel can be prepared by hybridization of polypeptide-<i>g</i>-DNA with a linker-ds-DNA, which contains the complementary “sticky ends” to serve as cross-linkers

Stereoselective Ring-Opening Polymerization of <i>rac</i>-Lactide Using Organocatalytic Cyclic Trimeric Phosphazene Base

Phosphazene base is an important organocatalyst in polymer chemistry owing to its high activity and versatility. In this contribution, we demonstrate that cyclic trimeric phosphazene base (<b>CTPB</b>) can catalyze stereoselective ring-opening polymerization (ROP) of <i>rac</i>-lactide (<i>rac</i>-LA) to produce isotactic stereoblock PLA (<i>P</i>_i up to 0.93). The polymerizations are highly controlled, as evidenced by linear relationship between molecular weights (MW) and monomer conversions and the narrow dispersity (<i>Đ</i> = <i>M</i>_w/<i>M</i>_n) of the resulted polymers with high fidelity of end groups. The investigations on polymerization parameters show that the tacticity of produced PLA depends on the polymerization temperatures and solvents, while the kinetic studies reveal a faster rate for ROP of l-LA as compared to <i>rac</i>-LA under same conditions. Based on these results, the chain end control mechanism is proposed to explain the production of isotactic stereoblock PLA from <i>rac</i>-LA by an achiral catalyst

Janus Silica Hollow Spheres Prepared via Interfacial Biosilicification

A poly­(ethylene glycol)<i>-<i>b</i>-</i>poly­(_L-lysine)<i>-<i>b</i>-</i>poly­(styrene) (PEG-PLL-PS) triblock copolymer, which contains a cationic PLL block as the middle block, is synthesized via a combination of ring-opening polymerization (ROP) and atom-transfer radical polymerization (ATRP). The PEG-PLL-PS (ELS) triblock is employed as a macromolecular surfactant to form a stable oil-in-water (O/W) emulsion, which is subsequently used as the template to prepare Janus silica hollow spheres (JHS) via a one-pot biosilicification reaction. For the emulsion template, the middle PLL block assembles at the O/W interface and directs the biomimetic silica synthesis in the presence of phosphate buffer and silicic acid precursors. This biosilicification process takes place only in the intermediate layer between water and the organic interior phase, leading to the formation of silica JHSs with hydrophobic PS chains tethered to the inner surface and PEG attached to the outer surface. The three-layer JHSs, namely, PEG/silica-polylysine/PS composites, were verified by electron microscopy. Upon further breaking these JHSs into species, polymer-grafted Janus silica nanoplates (JPLs) can be obtained. Our studies provide an efficient one-step method for preparing hybrid silica Janus structures within minutes

Design of Free Triblock Polylysine‑<i>b</i>‑Polyleucine‑<i>b</i>‑Polylysine Chains for Gene Delivery

Mixing cationic polymer chains with anionic DNA chains in solution results in the polymer/DNA complexes (also known as polyplexes). We recently confirmed that it is those noncomplexed cationic chains free in the mixture that promote the gene transfection, leading to a hypothesis: free cationic chains adsorbed on various anionic membranes interfere with the signal protein interaction, disrupt the intervesicular fusion, and block the endolysosome pathway so that the plasmid DNA (pDNA) chains have a higher chance to enter the nucleus. Accordingly, we design and synthesize linear cationic–hydrophobic–cationic triblock polylysine (K)-<i>b</i>-polyleucine (L)-<i>b</i>-polylysine (K) as free cationic chains by using natural protamine to condense the pDNA. The hydrophobic middle L-block helps its insertion into the membrane, while the interaction of the two cationic side K-blocks with the signal proteins helps the escape of the polyplexes from the lysosome entrapment. We studied the transfection efficiency of these copolymers with different block lengths. We found the optimal length of blocks K and L that allows the free triblock cationic copolymer chains to effectively enhance the gene transfection process. A combination of copolypeptides and protamine provides a new kind of biocompatible and nontoxic gene vectors made of only nontoxic peptides

Hafnium and Zirconium Complexes Bearing ONN-Tridentate Ligands and Their Catalytic Properties toward Olefin Polymerization

The development of high-performance catalysts is a goal that is constantly being pursued in the field of polyolefins. In this study, a class of Hf (Hf1 and Hf2) and Zr (Zr1 and Zr2) dimethyl complexes were prepared by one-pot reactions of phenoxy-imino-quinoline compounds with MMe4 (M = Hf and Zr). Both NMR spectroscopy and X-ray studies suggested the formation of phenoxy-amido-quinoline metal complexes because of methyl migration from the metal center to the carbon atom of imine. These Hf and Zr complexes exhibited moderate to high activity (up to 9060 kg (PE)·mol–1(M)·h–1) toward ethylene homopolymerization and copolymerization with 1-octene in the presence of 1 equiv of [Ph3C][B(C6F5)4] as a cocatalyst. It was significant that Zr complexes were far more active than Hf complexes bearing the same ligand under otherwise identical conditions, revealing a tremendous metal center effect on catalysis. On the other hand, the nature of the ligand also strongly influenced the catalytic properties, including the activity and properties, of resultant polymers. Thus, Zr complex Zr1 with a sterically demanding and electron-donating Me group on the 2-position of quinoline showed the highest activity and good thermal stability

Dinuclear Group 4 Metal Complexes Bearing Anthracene-Bridged Bifunctional Amido-Ether Ligands: Remarkable Metal Effect and Cooperativity toward Ethylene/1-Octene Copolymerization

Two types of bifunctional amido-ether ligands (syn-L and anti-L) with the rigid anthracene skeleton were designed to support dinuclear group 4 metal complexes. All organic ligands and organometallic complexes (syn-M2 and anti-M2; M = Hf, Zr, and Ti) were fully characterized by 1H and 13C NMR spectroscopies and elemental analyses. The anti-Hf2 complex showed two confirmations at room temperature with C2-symmetry or S2-symmetry that can inter-exchange, as indicated by VT NMR, while only a C2-symmetric isomer was observed for syn-Hf2 complex at room temperature. However, for Zr and Ti analogues, both syn and anti complexes exhibited only one conformation at room temperature. The molecular structures of complexes syn-Hf2, anti-Hf2, and syn-Ti2 in the solid state were further determined by single-crystal X-ray diffraction, revealing the distances between two metal centers in syn-M2 from 7.138 Å (syn-Ti2) to 7.321 Å (syn-Hf2) but a much farther separation in anti-M2 (8.807 Å in C2-symmetric anti-Hf2). The mononuclear complex (2-CH3O–C6H4–N–C14H9)Zr(NMe2)3 (mono-Zr1) was also prepared for control experiments. In the presence of alkyl aluminum (AlEt3) as the alkylating agent and trityl borate ([Ph3C][B(C6F5)4]) as the co-catalyst, all metal complexes were tested for copolymerization of ethylene with 1-octene at high temperature (130 °C). The preliminary polymerization results revealed that the activity was highly dependent upon the nature of metal centers, and syn-Zr2 showed the highest activity of 9600 kg(PE)·mol–1 (Zr)·h–1, which was about 17- and 2.2-fold higher than those of syn-Hf2 and syn-Ti2, respectively. Benefitting from both steric proximity and electronical interaction of two metal centers, syn-Zr2 exhibited significant cooperativity in comparison to anti-Zr2 and mono-Zr1, with regard to activity and molecular weight and 1-octene incorporation of resultant copolymers

Dinuclear Group 4 Metal Complexes Bearing Anthracene-Bridged Bifunctional Amido-Ether Ligands: Remarkable Metal Effect and Cooperativity toward Ethylene/1-Octene Copolymerization

Two types of bifunctional amido-ether ligands (syn-L and anti-L) with the rigid anthracene skeleton were designed to support dinuclear group 4 metal complexes. All organic ligands and organometallic complexes (syn-M2 and anti-M2; M = Hf, Zr, and Ti) were fully characterized by 1H and 13C NMR spectroscopies and elemental analyses. The anti-Hf2 complex showed two confirmations at room temperature with C2-symmetry or S2-symmetry that can inter-exchange, as indicated by VT NMR, while only a C2-symmetric isomer was observed for syn-Hf2 complex at room temperature. However, for Zr and Ti analogues, both syn and anti complexes exhibited only one conformation at room temperature. The molecular structures of complexes syn-Hf2, anti-Hf2, and syn-Ti2 in the solid state were further determined by single-crystal X-ray diffraction, revealing the distances between two metal centers in syn-M2 from 7.138 Å (syn-Ti2) to 7.321 Å (syn-Hf2) but a much farther separation in anti-M2 (8.807 Å in C2-symmetric anti-Hf2). The mononuclear complex (2-CH3O–C6H4–N–C14H9)Zr(NMe2)3 (mono-Zr1) was also prepared for control experiments. In the presence of alkyl aluminum (AlEt3) as the alkylating agent and trityl borate ([Ph3C][B(C6F5)4]) as the co-catalyst, all metal complexes were tested for copolymerization of ethylene with 1-octene at high temperature (130 °C). The preliminary polymerization results revealed that the activity was highly dependent upon the nature of metal centers, and syn-Zr2 showed the highest activity of 9600 kg(PE)·mol–1 (Zr)·h–1, which was about 17- and 2.2-fold higher than those of syn-Hf2 and syn-Ti2, respectively. Benefitting from both steric proximity and electronical interaction of two metal centers, syn-Zr2 exhibited significant cooperativity in comparison to anti-Zr2 and mono-Zr1, with regard to activity and molecular weight and 1-octene incorporation of resultant copolymers

Peptide Hydrogels Assembled from Nonionic Alkyl-polypeptide Amphiphiles Prepared by Ring-Opening Polymerization

Three alkyl-polypeptide (AP) amphiphiles were prepared using ring-opening polymerization of α-amino acid <i>N</i>-carboxyanhydride. The polypeptide segment was composed of diethylene-glycol-monomethyl-ether-functionalized poly-l-glutamate (poly-l-EG₂Glu). These AP amphiphiles can spontaneously self-assemble into transparent hydrogels in water. These hydrogels showed shear thinning properties, and their strength can be modulated by hydrophobic alkyl tails. CryoTEM and AFM characterizations suggested that these hydrogels were formed by nanoribbons arising from intermolecular interactions between nonionic poly-l-EG₂Glu segments

Tailorable Aqueous Dispersion of Single-Walled Carbon Nanotubes Using Tetrachloroperylene-Based Bolaamphiphiles via Noncovalent Modification

The enhanced dispersing capability of these bolaamphiphiles can be attributed to the large aromatic perylene core. The aqueous dispersion efficiency of single-walled carbon nanotubes (SWCNTs) is investigated by UV–vis absorption, fluorescence emission and Raman spectra, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. It is found that the tetrachloroperylene backbone moieties could interact with SWCNT via synergistic π–π and hydrophobic interactions, and the dispersing properties are closely related to the hydrophilic part of bolaamphiles. This study not only demonstrates tetrachloroperylene derivatives are able to stabilize SWCNTs, but also provides the possibility to understand the structure–property relationship between SWCNTs and tetrachloroperylene-based surfactants