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Kang, Philjae,Mai, Hien Duy,Yoo, Hyojong The Royal Society of Chemistry 2018 Dalton Transactions Vol.47 No.19
<P>A cobalt (Co) supramolecular triple-stranded helicate, [Co8(PDA)6(<I>Br</I>-PTA)3(DMF)4(H2O)2] (1) (PDA = 2,6-pyridinedicarboxylate, <I>Br</I>-PTA = 5-bromoisophthalate, DMF = dimethylformamide), is successfully synthesized and fully characterized. The solid-state structure of 1 shows that four cobalt atoms are coordinated by three PDA ligands to form a tetranuclear cobalt cluster with three extension points and the ditopic <I>Br</I>-PTA ligands interlink two basic assembly units. In crystal packing, the bromo group is surrounded by the cavity-like tetranuclear cobalt cluster, which acts as a metallocavitand, to generate a unique cage-like crystal packing geometry. The isomorphous molecular cage, which exhibits a similar crystal-packing geometry as observed in 1, is also successfully isolated. This is an unusual example of a highly symmetric cage-like crystal packing architecture, resulting from the interaction among metallocavitands of <I>in situ</I> generated supramolecular modules.</P>
Effect of carbon on the growth of TaC crystal derived from organometallic precursors
Lee Yoonjoo,Kang Philjae,정수용,Bae Seonggun,김정일,Lee Manyoung,Shin Dong-Geun 한국세라믹학회 2021 한국세라믹학회지 Vol.58 No.1
TaC, which is an ultra-high-temperature structural material, was derived from two types of organometallic precursors: Me 3 CCH = Ta(CH 2 CMe 3 ) 3 and Cp*-TaMe 4 . Both compounds are kinds of single-source precursors composed only of tantalum, carbon, and hydrogen, which should be converted into carbide material without oxygen contamination. The carbide material was formed through several processes such as pyrolysis, nucleation, and crystal growth, which are dependent on heat treatment temperature. However, organometallic precursor usually leaves residual carbon, and the crystallization of carbide is aff ected by the carbon. In this study, two types of organometallic precursors containing diff erent amounts of carbon in the organic part were used to prepare TaC, and the crystallization behavior of TaC in rich carbon was investigated. The amount of residual carbon was estimated by thermogravimetry (TG) analysis, and the TaC crystals were characterized using X-ray diff raction (XRD) and transmission electron microscopy (TEM). Nano-sized TaC particles were obtained by heat treatment without any by-products but with excess carbon. The TaC crystal was formed starting from 1300 °C, but the crystals grew better with less carbon, while the carbon barrier prevented agglomeration of the atoms.
Lee, Jaeyeon,Jang, Geunhyeok,Kang, Philjae,Choi, Moon-Gun,Choi, Soo Hyuk The Royal Society of Chemistry 2016 Organic & biomolecular chemistry Vol.14 No.36
<P>Short alpha/beta-peptides that consist of alternating L-a-amino acids and trans-2-aminocyclopentanecarboxylic acid are known to adopt both 11- and 14/15-helical conformations in solution. We report short alpha/beta-depsipeptides containing (S)-lactic acid as the third residue from the N-terminus. The alpha/beta-depsipeptide pentamers and heptamers adopt 14/15-helical conformations analogous to the a-helix in the crystal state and display 14/15-helical conformations predominantly in solution.</P>
Helical folding of α/β-peptides containing β-amino acids with an eight-membered ring constraint
Lee, Woohyung,Kwon, Sunmi,Kang, Philjae,Guzei, Ilia A.,Choi, Soo Hyuk The Royal Society of Chemistry 2014 Organic & Biomolecular Chemistry Vol.12 No.17
<P>αβα-Tripeptide that contains a cyclic β-amino acid with an eight-membered ring, a <I>cis</I>-2-aminocyclooct-5-enecarboxylic acid (<I>cis</I>-ACOE) or a <I>cis</I>-2-aminocyclooctanecarboxylic acid (<I>cis</I>-ACOC) displayed an 11/9-helical turn in the crystal state. The related α/β-peptide oligomers were shown to adopt 11/9-helical conformations in solution.</P> <P>Graphic Abstract</P><P>Cyclic β-amino acid that contains a cyclooctane or a cyclooctene ring promotes 11/9-helical folding of α/β-peptides. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4ob00266k'> </P>
A chiral indolocarbazole foldamer displaying strong circular dichroism responsive to anion binding
Kim, Dan A,Kang, Philjae,Choi, Moon-Gun,Jeong, Kyu-Sung The Royal Society of Chemistry 2013 Chemical communications Vol.49 No.84
<P>A chiral foldamer that consists of three indolocarbazoles and chiral amide residues folds into a helical conformation with the orientation bias, thus displaying characteristic CD signals. The X-ray crystal structure of its chloride complex was found to be a left-handed (M−) helix which stacks to give one-dimensional columnar arrays.</P> <P>Graphic Abstract</P><P>A chiral indolocarbazole trimer folds into a helical conformation to exhibit strong CD signals which are responsive to solvents and anions. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3cc45989f'> </P>
Stabilization of 11/9-helical α/β-peptide foldamers in protic solvents
Lee, Mihye,Shim, Jihyun,Kang, Philjae,Choi, Moon-Gun,Choi, Soo Hyuk The Royal Society of Chemistry 2016 Chemical communications Vol.52 No.35
<P>alpha/beta-Peptides with alternating alpha-amino acid and cis-2-aminocyclohexanecarboxylic acid (cis-ACHC) residues adopt 11/9-helical conformations, the folding propensity of which decreases as the solvent polarity increases. We report a new cis-ACHC analogue, cis-2-amino-cis-4-methylcyclohexanecarboxylic acid, which significantly stabilizes the 11/9-helix propensity in protic solvents.</P>
Folding-Generated Molecular Tubes Containing One-Dimensional Water Chains
Jeon, Hae-Geun,Jung, Jin Young,Kang, Philjae,Choi, Moon-Gun,Jeong, Kyu-Sung American Chemical Society 2016 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.138 No.1
<P>A series of indolocarbazole-pyridine (IP) oligomers were prepared that fold into helical conformations, and their folding features in solution and in the solid state were revealed. Helical folding of these IP foldamers is induced by dipolar interactions through the ethynyl bond and pi-stacking between two repeating units. Upon helical folding, H-1 NMR signals of aromatic protons were significantly shifted upfield by Delta delta = 0.5-2.2 ppm. In addition, hypochromic shifts and fluorescence quenching were observed in the absorption and emission spectra. X-ray crystal structures clearly demonstrated that IP foldamers folded to helical structures with cylindrical internal cavities wherein 3 or 5 water molecules were occupied by hydrogen-bonding interactions in a 1-D array, reminiscent of transmembrane water channels, called aquaporins.</P>
Oh, Juwon,Yoon, Hongsik,Sung, Young Mo,Kang, Philjae,Choi, Moon-Gun,Jang, Woo-Dong,Kim, Dongho American Chemical Society 2015 The Journal of physical chemistry B Vol.119 No.23
<P><I>N</I>-(<I>p</I>-Methoxycarbonylbenzyl) triazole (BTz) substituents have been introduced to Ni(II) porphyrins (NiPs), in which their modulated axial-coordination processes have been investigated. For this study, the two types of ligands, neutral pyridine versus anionic cyanide, were employed to investigate an effect of BTz substituents. The unique microenvironments given by the BTz substituents provided two different effects on the axial-coordination processes of NiPs on the ground and excited states: (1) steric shielding and (2) donation of hydrogen-bonding sites. The steric shielding diminished the binding affinity of pyridine, while the cooperation of hydrogen bonds extraordinarily strengthened the binding affinity of CN<SUP>–</SUP>. Interestingly, it was observed that the binding of CN<SUP>–</SUP> with the supporting of BTz substituents accompanied nonplanar distortion of NiPs. Such conformational change perturbed the electronic structure of NiPs, which gave rise to the modulation of coordination processes of NiPs in the excited state. As a consequence, photoinudced ligand binding and releasing processes of four- and six-coordinated NiPs were changed into the dominant photoinduced ligand releasing process.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpcbfk/2015/jpcbfk.2015.119.issue-23/acs.jpcb.5b03033/production/images/medium/jp-2015-03033s_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp5b03033'>ACS Electronic Supporting Info</A></P>