1.Strong and fast-recovery organic/inorganic hybrid AuNPs-supramolecular gels based on loofah-like 3D networks.
He H1, Chen S, Tong X, Chen Y, Wu B, Ma M, Wang X, Wang X. Soft Matter. 2016 Jan 21;12(3):957-64. doi: 10.1039/c5sm02269j. Epub 2015 Nov 16.
Super strong and fast-recovery organic/inorganic hybrid gold nanoparticle (AuNPs)-supramolecular gels based on a three-dimensional loofah-like nanoscale network self-assembled by polyhedral oligomeric silsesquioxane (POSS) core supramolecular gelators are reported for the first time. Two series of POSS core organic/inorganic hybrid gelators, POSS-BOC-l-Homophenylalanine (POSS-Hpy) and POSS-Boc-Cys(Bzl)-OH (POSS-Cys), with two types of peripherals having different abilities for driving the self-assembly of AuNPs in gels were designed and synthesized, both of which self-assembled into three-dimensional loofah-like nanoscale gel networks producing hybrid physical gels with fast-recovery behaviors. The mechanical properties of the resultant hybrid gels were dramatically increased by as much as 100 times in the system of sulfur containing POSS-Cys gelators without destroying the fast-recovery behaviors, with the addition of AuNPs, which had direct interaction with AuNPs to give S-Au non-covalent driving force to lead AuNPs self-assemble onto the 3D loofah-like network nanofibres in the supramolecular hybrid gel system.
2.Synthesis of Optically Active beta-Amino Acid N-Carboxyanhydrides.
Cheng J1, Ziller JW, Deming TJ. Org Lett. 2000 Jun 29;2(13):1943-1946.
Methodology has been developed for the general synthesis of optically active beta-amino acid N-carboxyanhydrides (beta-NCAs) through cyclization of N(beta)-Boc or N(beta)-Cbz beta-amino acids using phosphorus tribromide. The formation of beta-NCAs was confirmed by spectroscopy as well as an X-ray structural determination of beta-homoalanine-N-carboxyanhydride. The beta-NCA molecules could be polymerized in good yield to give optically active poly(beta-peptides) that adopt stable chiral conformations in solution. For example, helical oligo(L-beta-homophenylalanine) was synthesized by polymerization of L-beta-homophenylalanine-N-carboxyanhydride.
3.Alpha,beta hybrid peptides: a polypeptide helix with a central segment containing two consecutive beta-amino acid residues.
Roy RS1, Karle IL, Raghothama S, Balaram P. Proc Natl Acad Sci U S A. 2004 Nov 23;101(47):16478-82. Epub 2004 Nov 16.
Conformational studies on the synthetic 11-aa peptide t-butoxycarbonyl (Boc)-Val-Ala-Phe-alpha-aminoisobutyric acid (Aib)-(R)-beta3-homovaline (betaVal)-(S)-beta3-homophenylalanine (betaPhe)-Aib-Val-Ala-Phe-Aib-methyl ester (OMe) (peptide 1; betaVal and betaPhe are beta amino acids generated by homologation of the corresponding l-residues) establish that insertion of two consecutive beta residues into a polypeptide helix can be accomplished without significant structural distortion. Crystal-structure analysis reveals a continuous helical conformation encompassing the segment of residues 2-10 of peptide 1. At the site of insertion of the betabeta segment, helical hydrogen-bonded rings are expanded. A C15 hydrogen bond for the alphabetabeta segment and two C14 hydrogen bonds for the alphaalphabeta or betaalphaalpha segments have been characterized. The following conformational angles were determined from the crystal structure for the beta residues: betaVal-5 (= -126 degrees, = 76 degrees, and psi = -124) and betaPhe-6 (=-88 degrees, = 80 degrees, and psi =-118).
4.Asymmetrically simultaneous synthesis of L-homophenylalanine and N6-protected-2-oxo-6-amino-hexanoic acid by engineered Escherichia coli aspartate aminotransferase.
Lo HH1, Lin WD, Hsu SK, Hsu WH. Biotechnol Prog. 2009 Nov-Dec;25(6):1637-42. doi: 10.1002/btpr.272.
L-Homophenylalanine (L-HPA) and N(6)-protected-2-oxo-6-amino-hexanoic acid (N(6)-protected-OAHA) can be used as building blocks for the manufacture of angiotensin-converting enzyme inhibitors. To synthesize L-HPA and N(6)-protected-OAHA simultaneously from 2-oxo-4-phenylbutanoic acid (OPBA) and N(6)-protected-L-lysine, several variants of Escherichia coli aspartate aminotransferase (AAT) were developed by site-directed mutagenesis and their catalytic activities were investigated. Three kinds of N(6)-protected-L-lysine were tested as potential amino donors for the bioconversion process. AAT variants of R292E/L18H and R292E/L18T exhibited specific activities of 0.70+/-0.01 U/mg protein and 0.67+/-0.02 U/mg protein to 2-amino-6-tert-butoxycarbonylamino-hexanoic acid (BOC-lysine) and 2-amino-6-(2,2,2-trifluoro-acetylamino)-hexanoic acid, respectively. E. coli cells expressing R292E/L18H variant were able to convert OPBA and BOC-lysine to L-HPA and 2-oxo-6-tert-butoxycarbonylamino-hexanoic acid (BOC-OAHA) with 96.
