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Item Open Access The Unique-5 and -6 Motifs of ZO-1 Regulate Tight Junction Strand Localization and Scaffolding Properties(2006) Fanning, Alan S.; Little, Brent P.; Rahner, Christoph; Utepbergenov, Darkhan; Walther, Zenta; Anderson, James M.The proper cellular location and sealing of tight junctions is assumed to depend on scaffolding properties of ZO-1, a member of the MAGUK protein family. ZO-1 contains a conserved SH3-GUK module that is separated by a variable region (unique-5), which in other MAGUKs has proven regulatory functions. To identify motifs in ZO-1 critical for its putative scaffolding functions, we focused on the SH3-GUK module including unique-5 (U5) and unique-6 (U6), a motif immediately C-terminal of the GUK domain. In vitro binding studies reveal U5 is sufficient for occludin binding; U6 reduces the affinity of this binding. In cultured cells, U5 is required for targeting ZO-1 to tight junctions and removal of U6 results in ectopically displaced junction strands containing the modified ZO-1, occludin, and claudin on the lateral cell membrane. These results provide evidence that ZO-1 can control the location of tight junction transmembrane proteins and reveals complex protein binding and targeting signals within its SH3-U5-GUK-U6 region. We review these findings in the context of regulated scaffolding functions of other MAGUK proteinsItem Open Access DFT/TD-DFT molecular design of porphyrin analogues for use in dye-sensitized solar cells(2008) Balanay, Mannix P.; Kim, Dong HeeDensity functional theory (DFT) and time-dependent DFT calculations have been employed to model Zn meso-tetraphenylporphyrin (ZnTPP) complexes having different b-substituents, in order to design an efficient sensitizer for dye-sensitized solar cells. To calculate the excited states of the porphyrin analogues, at least the TD-B3LYP/6-31G* level of theory is needed to replicate the experimental absorption spectra. Solvation results were found to be invariant with respect to the type of model used (PCM vs. C-PCM). Most of the electronic transitions based on Gouterman’s four-orbital model of ZnTPP-A and ZnTPP-B are p - p* transitions, so that cell efficiency can be enhanced by increasing the p-conjugation and electron-withdrawing capability of the bsubstituent. This proposition was tested by inserting thiophene into the b-substituent of ZnTPP-A to form a new analogue, ZnTPP-C. Compared with ZnTPP-A and ZnTPP-B, ZnTPP-C has a smaller band gap, which brings LUMO closer to the conduction band of TiO2, and a red-shifted absorption spectrum with higher extinction coefficients, especially in the Q-band positionItem Open Access Catalytic hydroboration by an imido-hydrido complex of Mo(IV)(2011) Khalimon, Andrey; Farha, Philip; Kuzmina, Lyudmila G.; Nikonov, Georgii I.The imido-hydrido complex (ArN)Mo(H)(Cl)(PMe3)3 catalyses a variety of hydroboration reactions, including the first example of catalytic addition of HBCat to nitriles to form the bis(borylated) amines RCH2N(BCat)2. The latter species easily undergoes chemoselective coupling with aldehydes R0C(O)H to yield imines RCH2NQC(H)R0Item Open Access The p90 Ribosomal S6 Kinase (RSK) Is a Mediator of Smooth Muscle Contractility(2013) Artamonov, Mykhaylo; Momotani, Ko; Utepbergenov, Darkhan; Franke, Aaron; Khromov, Alexander; Derewenda, Zygmunt S.; Somlyo, Avril V.In the canonical model of smooth muscle (SM) contraction, the contractile force is generated by phosphorylation of the myosin regulatory light chain (RLC20) by the myosin light chain kinase (MLCK). Moreover, phosphorylation of the myosin targeting subunit (MYPT1) of the RLC20 phosphatase (MLCP) by the RhoA-dependent ROCK kinase, inhibits the phosphatase activity and consequently inhibits dephosphorylation of RLC20 with concomitant increase in contractile force, at constant intracellular [Ca2+]. This pathway is referred to as Ca2+-sensitization. There is, however, emerging evidence suggesting that additional Ser/Thr kinases may contribute to the regulatory pathways in SM. Here, we report data implicating the p90 ribosomal S6 kinase (RSK) in SM contractility. During both Ca2+- and agonist (U46619) induced SM contraction, RSK inhibition by the highly selective compound BI-D1870 (which has no effect on MLCK or ROCK) resulted in significant suppression of contractile force. Furthermore, phosphorylation levels of RLC20 and MYPT1 were both significantly decreased. Experiments involving the irreversible MLCP inhibitor microcystin-LR, in the absence of Ca2+, revealed that the decrease in phosphorylation levels of RLC20 upon RSK inhibition are not due solely to the increase in the phosphatase activity, but reflect direct or indirect phosphorylation of RLC20 by RSK. Finally, we show that agonist (U46619) stimulation of SM leads to activation of extracellular signal-regulated kinases ERK1/2 and PDK1, consistent with a canonical activation cascade for RSK. Thus, we demonstrate a novel and important physiological function of the p90 ribosomal S6 kinase, which to date has been typically associated with the regulation of gene expressionItem Open Access Multiple coupling of silanes with imido complexes of Mo(2014) Khalimon, Andrey; McLeod, Nicolas A.; Ignatov, Stanislav K.; Okhapkin, Andrey I.; Kuzmina, Lyudmila G.; Howardd, Judith A. K.; Nikonov, Georgii I.The bis(imido) complexes (tBuNv)2Mo(PMe3)(L) (L = PMe3, C2H4) react with up to three equivalents of silane PhSiH3 to give the imido-bridged disilyl silyl Mo(VI) complex (tBuN){μ-tBuN(SiHPh)2}Mo(H)(SiH2Ph)- (PMe3)2 (3) studied by NMR, IR and X-ray diffraction. NMR data supported by DFT calculations show that complex 3 is an unusual example of a silyl hydride of Mo(VI), without significant Si⋯H interaction. Mechanistic NMR studies revealed that silane addition proceeds in a stepwise manner via a series of Si–H⋯M agostic and silanimine complexes whose structures were further elucidated by DFT calculationsItem Metadata only Synthesis of Hierarchical Porous Sulfur/Polypyrrole/Multiwalled Carbon Nanotube Composite Cathode for Lithium Batteries(Electrochimica Acta, 2014-10-10) Zhang, Yongguang; Zhao, Yan; Bakenov, Zhumabay; Tuiyebayeva, Madina; Konarov, Aishuak; Chen, P.; Yongguang, ZhangAbstract A novel porous sulfur/polypyrrole/multiwalled carbon nanotube composite (S/PPy/MWNT) was synthesized via in situ polymerization of pyrrole monomer with nano-sulfur and MWNT aqueous suspension followed by a low temperature heat-treatment. Scanning electronic microscopy revealed the formation of a highly hierarchical mesoporous and macroporous structure. High resolution transmission electronic microscopy confirmed homogeneous dispersion of S, PPy and MWNT in the composite. In this composite, polypyrrole with its high adhesion ability to MWNT acts as a conductive binder to connect sulfur and MWNT matrix, as well as absorbs polysulfides into its porous structure positively affecting the composite performance as a cathode in a Li/S cell. The resulting S/PPy/MWNT composite cathode exhibited greatly enhanced cyclability and delivered a reversible discharge capacity of 751 mAh g−1 after 100 cycles at 0.2C.Item Open Access Photo Lewis acid generators: photorelease of B(C6F5)3 and applications to catalysis(2015) Khalimon, Andrey; Shaw, Bryan K.; Marwitz, Adam J. V.; Piers, Warren E.; Blackwellc, James M.; Parveza, MasoodA series of molecules capable of releasing of the strong organometallic Lewis acid B(C6F5)3 upon exposure to 254 nm light have been developed. These photo Lewis acid generators (PhLAGs) can now serve as photoinitiators for several important B(C6F5)3-catalyzed reactions. Herein is described the synthesis of the triphenylsulfonium and diphenyliodonium salts of carbamato- and hydridoborates, their establishment as PhLAGs, and studies aimed at defining the mechanism of borane release. Factors affecting these photolytic reactions and the application of this concept to photoinduced hydrosilylation reactions and construction of siloxane scaffolds are also discussedItem Open Access Imido–hydrido complexes of Mo(IV): catalysis and mechanistic aspects of hydroboration reactions(2015) Khalimon, Andrey; Farhaa, Philip M.; Nikonov, Georgii I.Imido–hydrido complexes (ArN)Mo(H)(Cl)(PMe3)3 (1) and (ArN)Mo(H)2(PMe3)3 (2) (Ar = 2,6-diisopropylphenyl) catalyse a variety of hydroboration reactions, including the rare examples of addition of HBCat to nitriles to form bis(borylated) amines RCH2N(BCat)2. Stoichiometric reactivity of complexes 1 and 2 with nitriles and HBCat suggest that catalytic reactions proceed via a series of agostic borylamido and borylamino complexes. For complex 1, catalysis starts with addition of nitriles across the Mo–H bond to give (ArN)Mo(Cl)(NvCHR)(PMe3)2; whereas for complex 2 stoichiometric reactions suggest initial addition of HBCat to form the agostic complex Mo(H)2(PMe3)3(η3-NAr-HBcat)Item Metadata only Molecular engineering of donor–acceptor co-polymers for bulk heterojunction solar cells(Computational and Theoretical Chemistry, 2015-03-01) Balanay, Mannix P.; Kim, Dong Hee; Mannix P., BalanayAbstract We report a computational modeling, based on DFT and TD-DFT methodologies, on the structural, electronic, and optical properties of different donor–acceptor co-polymer system in bulk heterojunction solar cells. The donor moieties that were considered were the derivatives of thienocyclopentathiophene, fluorene, and thienobenzothiophene. We utilized for the acceptor groups the moieties of thieno[3,4-b]pyrrole-4,6-dione; thieno[3,4-b] thiophene-4,6-dione; tetrafluoro-1,3-dihydrothieno[3,4-c]thiophene and its non-fluorinated counterpart; various electron-donating substituents within the fused π-conjugated polymer system; and 3-fluoroselenophenothiophene. Among the donor–acceptor combination, the best in terms of molecular energy levels, energetic driving force, maximum absorption, calculated open-circuit voltage, reorganization energies, ionization potential, and electron affinity are poly[(bisthieno(bisthieno[3,2-b:2′,3′-d]thiophene)- alt-(5-alkyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione)] and poly[(4,8-dimethyl[1,3] oxazolo[5,4-f][1,3]benzoxazole)- alt-(thieno[3,4-d]pyrimidine)].Item Open Access Nano-Mole Scale Side-Chain Signal Assignment by 1H-Detected Protein Solid-State NMR by Ultra-Fast Magic-Angle Spinning and Stereo-Array Isotope Labeling(Public Library of Science, 2015-04) Wang, Songlin; Parthasarathy, Sudhakar; Nishiyama, Yusuke; Endo, Yuki; Nemoto, Takahiro; Yamauchi, Kazuo; Asakura, Tetsuo; Takeda, Mitsuhiro; Terauchi, Tsutomu; Kainosho, Masatsune; Ishii, YoshitakaWe present a general approach in 1H-detected 13C solid-state NMR (SSNMR) for side-chain signal assignments of 10-50 nmol quantities of proteins using a combination of a high magnetic field, ultra-fast magic-angle spinning (MAS) at ~80 kHz, and stereo-array-isotope-labeled (SAIL) proteins [Kainosho M. et al., Nature 440, 52–57, 2006]. First, we demonstrate that 1H indirect detection improves the sensitivity and resolution of 13C SSNMR of SAIL proteins for side-chain assignments in the ultra-fast MAS condition. 1H-detected SSNMR was performed for micro-crystalline ubiquitin (~55 nmol or ~0.5mg) that was SAIL-labeled at seven isoleucine (Ile) residues. Sensitivity was dramatically improved by 1H-detected 2D 1H/13C SSNMR by factors of 5.4-9.7 and 2.1-5.0, respectively, over 13C-detected 2D 1H/13C SSNMR and 1D 13C CPMAS, demonstrating that 2D 1H-detected SSNMR offers not only additional resolution but also sensitivity advantage over 1D 13C detection for the first time. High 1H resolution for the SAIL-labeled side-chain residues offered reasonable resolution even in the 2D data. A 1H-detected 3D 13C/13C/1H experiment on SAIL-ubiquitin provided nearly complete 1H and 13C assignments for seven Ile residues only within ~2.5 h. The results demonstrate the feasibility of side-chain signal assignment in this approach for as little as 10 nmol of a protein sample within ~3 days. The approach is likely applicable to a variety of proteins of biological interest without any requirements of highly efficient protein expression systems.Item Metadata only Theoretical design of triphenylamine-based derivatives with asymmetric D–D–π–A configuration for dye-sensitized solar cells(Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2015-04-05) Balanay, Mannix P.; Enopia, Camille Marie G.; Lee, Sang Hee; Kim, Dong Hee; Mannix P., BalanayAbstract The use of theoretical techniques in the structural development of dye-sensitized solar cells helps in the efficient screening of the dyes. To properly rationalize the dye’s design process, benchmark calculations were conducted using long-range corrected exchange–correlation (xc) functionals with varying separation parameters to be able to predict the excited-state energies of triphenylamine-based dyes, namely: PPS, PSP, and PSS, wherein they differ at the π-conjugated bridge using thiophene and/or phenyl moieties. The results show that LC-ωPBE xc functional with an optimized parameter provided better correlation with the experimental results compared to the other functionals. The relative shifts of the absorption spectra, light harvesting efficiency, normal dipole moments, as well as the ionization potentials and electron affinities of the dyes were well-correlated with the experimental data. A new set of dyes was designed in an effort to increase its solar cell efficiency that was patterned after PSS with an additional donor moiety such as fluorene, cyclopentaindole, and pyrene attached asymmetrically at the triphenylamine ring. Among the newly designed dyes, analogs that contain 4-phenyl-1,2,3,4-tetrahydrocyclopenta[b]indole (I) and pyrido[2,3,4-5-imn]phenanthridine-5,10(4H,9H)-dione (P2) as the additional donor moiety produced the best photophysical properties and charge-transfer characteristics for a promising dye for solar cell applications.Item Metadata only Reaction barrier heights for cycloreversion of heterocyclic rings: An Achilles’ heel for DFT and standard ab initio procedures(Chemical Physics, 2015-09-08) Yu, Li-Juan; Sarrami, Farzaneh; O’Reilly, Robert J.; Karton, Amir; Li-Juan, YuAbstract We introduce a database of 20 accurate cycloreversion barrier heights of 5-membered heterocyclic rings (to be known as the CRBH20 database). In these reactions, dioxazole and oxathiazole rings are fragmented to form isocyanates, isothiocyanates, and carbonyls. The reference reaction barrier heights are obtained by means of the high-level, ab initio W1-F12 and W1w thermochemical protocols. We evaluate the performance of 65 contemporary density functional theory (DFT) and double-hybrid DFT (DHDFT) procedures. The CRBH20 database represents an extremely challenging test for these methods. Most of the conventional DFT functionals (74%) result in root-mean-square deviations (RMSDs) between 10 and 81kJmol−1. The rest of the DFT functionals attain RMSDs=5−10kJmol−1. Of the 12 tested DHDFT functionals, only five result in RMSDs<10kJmol−1. The CRBH20 dataset also proves to be a surprisingly challenging target for composite and standard ab initio procedures.Item Metadata only Synthesis, crystal and electronic structure of the quaternary sulfides Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi)(Journal of Solid State Chemistry, 2016-01-01) Kussainova, Ardak M.; Akselrud, Lev G.; Suen, Nian-Tzu; Voss, Leonard; Stoyko, Stanislav; Bobev, Svilen; Ardak M., KussainovaAbstract The series of quaternary sulfides with general formula Ln2CuMS5 (Ln=La, Ce; M=Sb, Bi) have been synthesized by solid-state reactions. Three representative members have been structurally characterized by single-crystal X-ray diffraction. La2CuSbS5 crystallizes in a new structure type (space group Ima2 (no. 46), Z=4, a=13.401(2)Å, b=7.592(1)Å, c=7.598(1)Å, V=773.1(3)Å3). The bismuth analogs of composition La2CuBiS5 and Ce2CuBiS5 crystallize with the La2CuInSe5 structure type (space group Pnma (no. 62), Z=4). Lattice parameters for La2CuBiS5: a=11.9213(5)Å, b=3.9967(2)Å, c=17.0537(8)Å, V=812.56(7)Å3; lattice parameters for Ce2CuBiS5: a=11.9179(15)Å, b=3.9596(5)Å, c=16.955(2)Å, V=800.13(17)Å3). The similarities and the differences between the two structures are discussed. Electronic structure calculations for La2CuSbS5 and La2CuBiS5 are also presented; they suggest semiconducting behavior with energy gaps exceeding 1.7eV.Item Metadata only Homolytic C–Br bond dissociation energies obtained by means of the G4 thermochemical protocol(Chemical Data Collections, 2016-05-01) Kazakbayeva, Zhanna; Zhumagali, Shingis; Mahboob, Abdulla; O'Reilly, Robert J.; Zhanna, KazakbayevaAbstract Knowledge of the energies required to induce homolytic cleavage of the C–Br bonds of brominated organic molecules, a process that affords carbon-centered radicals and Br•, is of fundamental importance. Although some data pertaining to the strength of C–Br bonds can already be found in the literature, the chemical diversity of the species for which bond dissociation energies (BDEs) are available is somewhat limited. In this data article, we report a comprehensive set of homolytic C–Br BDEs, obtained using the G4 thermochemical protocol, for brominated organic molecules with wide structural diversity. The species in this set have C–Br BDEs (at 298K) that differ by as much as 188.3kJmol–1, with α-bromoalanine having the lowest BDE (214.1kJmol–1) and 1-bromobut-1-yne having the largest (402.4kJmol–1). Of particular relevance to biological systems are the BDEs of 8-bromoguanine (345.3kJmol–1), 8-bromoadenine (345.6kJmol–1), 5-bromocytosine (348.8kJmol–1) and 5-bromouracil (350.3kJmol–1).Item Metadata only A dataset of homolytic C–Cl bond dissociation energies obtained by means of W1w theory(Chemical Data Collections, 2016-08-01) Garifullina, Ainash; Mahboob, Abdulla; O'Reilly, Robert J.; Ainash, GarifullinaAbstract We herein report a dataset of 28 homolytic C–Cl bond dissociation energies (BDEs) (to be known as the CCl28 dataset), obtained using the benchmark-quality W1w thermochemical protocol. This set contains chlorinated organic molecules that consist of either sp3-, sp2- or sp-hybridized C–Cl bonds. The species in this set have C–Cl BDEs (at 298K) that differ by as much as 168.4kJ mol–1, with allyl chloride having the lowest BDE (291.7kJ mol–1) and 1-chloroprop-1-yne having the largest (460.1kJ mol–1). Given the benchmark quality of the CCl28 dataset, it may serve as a useful reference for assessing the performance of more approximate quantum chemical methods, such as density functional theory (DFT) and double-hybrid DFT methods.Item Metadata only Synthesis and anodic electrochemistry of cymanquine and related complexes(Journal of Organometallic Chemistry, 2016-08-15) Lam, Kevin; Geiger, William E.; Kevin, LamAbstract Three compounds have been prepared in which a 4-aminochloroquinoline moiety is covalently linked to a cyclopentadienyl manganese tricarbonyl moiety. One of these (“cymanquine”, 4) is the analogue of the potent antimalarial drug ferroquine in which an FeCp group has been replaced by a Mn(CO)3 group. The anodic electrochemistry of the new compounds was investigated in dichloromethane, using [NBu4][B(C6F5)4] as the supporting electrolyte. Compared to ferroquine, oxidations of the new compounds occur at considerably more positive potentials and are highly irreversible, being located at their amine groups rather than at the organometallic center.Item Open Access Bacterial expression, purification and in Vitro phosphorylation of full-length ribosomal S6 kinase 2 (RSK2)(PLoS One, 2016-10-01) Utepbergenov, Darkhan; Hennig, Paulina M.; Derewenda, Urszula; Artamonov, Mykhaylo V.; Somlyo, Avril V.; Derewenda, Zygmunt S.Ribosomal S6 kinases (RSK) play important roles in cell signaling through the mitogen-activated protein kinase (MAPK) pathway. Each of the four RSK isoforms (RSK1-4) is a single polypeptide chain containing two kinase domains connected by a linker sequence with regulatory phosphorylation sites. Here, we demonstrate that full-length RSK2 - which is implicated in several types of cancer, and which is linked to the genetic Coffin-Lowry syndrome - can be overexpressed with high yields in Escherichia coli as a fusion with maltose binding protein (MBP), and can be purified to homogeneity after proteolytic removal of MBP by affinity and size-exclusion chromatography. The purified protein can be fully activated in vitro by phosphorylation with protein kinases ERK2 and PDK1. Compared to full-length RSK2 purified from insect host cells, the bacterially expressed and phosphorylated murine RSK2 shows the same levels of catalytic activity after phosphorylation, and sensitivity to inhibition by RSK-specific inhibitor SL0101. Interestingly, we detect low levels of phosphorylation in the nascent RSK2 on Ser386, owing to autocatalysis by the C-terminal domain, independent of ERK. This observation has implications for in vivo signaling, as it suggests that full activation of RSK2 by PDK1 alone is possible, circumventing at least in some cases the requirement for ERK.Item Metadata only Assessment of quantum chemical methods for the calculation of homolytic N–F bond dissociation energies(Chemical Data Collections, 2016-11-01) Akhmetova, Nuriya; Kaliyeva, Laura; O'Reilly, Robert J.; Nuriya, AkhmetovaAbstract In this article, the performance of a wide range of conventional and double-hybrid DFT methods (in conjunction with Dunning basis sets of double-, triple- and quadruple-zeta quality), as well as a number of Gaussian-n thermochemical protocols are assessed for their ability to compute accurate homolytic N–F bond dissociation energies (BDEs). Their performance is evaluated against a previously reported set of 31 highly accurate gas-phase N–F BDEs obtained using the benchmark-quality W2w thermochemical protocol (See: R.J. O'Reilly, A. Karton, L. Radom, J. Phys. Chem. A2011, 115, 5496.). Out of all of the DFT/basis set combinations investigated, ωB97 and M06-2X (in conjunction with the aug'-cc-pVDZ basis set) offer the lowest mean absolute deviations (MADs= 2.4 and 2.7kJ mol–1, respectively). Of the Gaussian-n procedures, G3X offers the best performance (MAD= 1.4kJ mol–1), whilst the significantly more economical G3X(MP2)-RAD method also offers excellent performance (MAD= 1.8kJ mol–1).Item Metadata only Selective oxidation of styrene catalyzed by cerium-doped cobalt ferrite nanocrystals with greatly enhanced catalytic performance(Journal of Catalysis, 2016-12-01) Tong, Jinhui; Li, Wenyan; Bo, Lili; Wang, Huan; Hu, Yusen; Zhang, Zhixia; Mahboob, Abdulla; Jinhui, TongAbstract The rare earth metal Ce-doped cobalt ferrite samples CexCo1−xFe2O4 (x=0.1, 0.3, 0.5) were prepared by the sol–gel autocombustion route. The as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, ICP–atomic emission spectroscopy, and N2 physisorption. Their catalytic performance was evaluated in oxidation of styrene using hydrogen peroxide (30%) as oxidant. Compared with pristine CoFe2O4, the Ce-doped samples were found to be more efficient catalysts for the oxidation of styrene to benzaldehyde, with greatly enhanced catalytic performance. Especially, when Ce0.3Co0.7Fe2O4 was used as catalyst, 90.3% styrene conversion and 91.5% selectivity for benzaldehyde were obtained at 90°C for 9h reaction. The catalyst can be magnetically separated easily for reuse, and no obvious loss of activity was observed when it was reused in five consecutive runs.Item Metadata only Synthesis and antibacterial activity of silver@carbon nanocomposites(Journal of Inorganic Biochemistry, 2017-01-01) Wang, Kunjie; Ji, Qingjuan; Li, Hongxia; Guan, Feng; Zhang, Deyi; Feng, Huixia; Fan, Haiyan; Kunjie, WangAbstract In this work, hollow multiple-Ag-nanoclustes- C-shell nanocomposites (Ag@C) were synthesized by using silane coupling agent to graft carbon dots (CDs) with silver nanoparticles (AgNPs). CDs act as coating and stabilizing agent, protecting AgNPs from aggregation and oxidation. The resulting Ag@C nanocomposites demonstrate strong bactericidal effect against both gram-negative and gram-positive bacteria in the disk diffusion test. Cellular toxicity evaluation was performed using MTT assay. Meanwhile, the as-prepared Ag@C nanocomposites show a good biocompatibility.