An attempt was made to calculate 13C NMR chemical shifts of poly(β-benzyl L-aspartate) having the right-handed α-helix (αR-helix) and left-handed α-helix (αL-helix) forms by a tight-binding MO sum-over-states theory within the extended Hückel framework, in order to examine whether or not the conformation-dependent 13C chemical shifts previously determined by the cross polarization-magic angle spinning technique are reproduced by a change of electronic structure of the polymer. It is found that the relative displacements of the observed Cα, Cβ and carbonyl 13C chemical shifts between the αR- and αL-helices are reproduced qualitatively by the calculation. 相似文献
A certified reference material (CRM) for the determination of perfluorooctane sulfonate (PFOS) in acrylonitrile-butadiene-styrene (ABS) resin (NMIJ CRM 8155-a) has been issued by the National Metrology Institute of Japan (NMIJ). The bulk material was prepared by mixing commercial ABS resin powder and potassium PFOS and cut into square plates (20 × 20 mm, 2 mm thick) as the CRM. Analytical processes combined with isotope-dilution mass spectrometry and liquid chromatography/mass spectrometry were optimised and applied for characterisation. One of the approaches adopted by NMIJ for certification is that results from two or more primary methods of measurement should be used; thus, two optimised isotope-dilution mass spectrometric methods (Methods 1 and 2 with reprecipitation and with reprecipitation/solid phase extraction, respectively, were validated mutually and employed) were used to determine the certified value. Homogeneity and stability of the square plates were evaluated and their uncertainty contributions (as relative standard uncertainties) were 1.43% for inhomogeneity and 6.96% for approximately two years’ instability. The certified mass fraction of linear PFOS (heptadecafluoro-1-octanesulfonic acid) in the CRM with expanded uncertainty (coverage factor k = 2, approximately 95% confidence interval) was (33.1 ± 5.0) mg kg?1 as free acid of PFOS. 相似文献
The photophysical properties and photoswitching scheme of the reversible photoswitchable green fluorescent protein-like fluorescent proteins Dronpa-2 and Dronpa-3 were investigated by means of ensemble and single-molecule fluorescence spectroscopy and compared to those of the precursor protein Dronpa. The faster response to light and the faster dark recovery of the new mutants observed in bulk also hold at the single-molecule level. Analysis of the single-molecule traces allows us to extract the efficiencies and rate constants of the pathways involved in the forward and backward switching, and we find important differences when comparing the mutants to Dronpa. We rationalize our results in terms of a higher conformational freedom of the chromophore in the protein environment provided by the beta-can. This thorough understanding of the photophysical parameters has allowed us to optimize the acquisition parameters for camera-based sub-diffraction-limit imaging with these photochromic proteins. We show that Dronpa and its mutants are useful for fast photoactivation-localization microscopy (PALM) using common wide-field microscopy equipment, as individual fluorescent proteins can be localized several times. We provide a new approach to achieve fast PALM by introducing simultaneous two-color stroboscopic illumination. 相似文献
A chemically grafted tris(trimethylsiloxy)silyl (tris(TMS)) monolayer on a silicon oxide substrate was used as a template for creating nanoclusters of polymer brushes. Polymer brushes were synthesized by surface-initiated polymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) and tert-butyl methacrylate (t-BMA) via atom transfer radical polymerization (ATRP) from alpha-bromoester groups tethered to the residual silanol groups on the silicon surface after generating a range of tris(TMS) coverage. CuBr/bpy and CuBr/PMDETA were used as the catalytic system for PMPC and Pt-BMA synthesis, respectively. The percentage of tris(TMS) coverage significantly influenced the thickness and morphology of the polymer brushes. Protrusions representing self-aggregation of PMPC brushes in nanopores as visualized by AFM analysis evidently suggested that PMPC brushes were distributed nanoscopically on the surface. The protrusion size and surface roughness corresponded quite well with the graft density of PMPC brushes. The fact that Pt-BMA brushes grown from nanopores were almost featureless implies that self-aggregation of PMPC brushes is truly a consequence of phase incompatibility between hydrophilic PMPC brushes and hydrophobic tris(TMS). The anti-fouling characteristic of PMPC brushes, inferred from plasma protein adsorption, was subsequently varied by controlling the surface coverage ratio between PMPC brushes and tris(TMS). 相似文献
To improve interfacial phenomena of poly(dimethylsiloxane) (PDMS) as biomaterials, well-defined triblock copolymers were prepared as coating materials by reversible addition-fragmentation chain transfer (RAFT) controlled polymerization. Hydroxy-terminated poly(vinylmethylsiloxane-co-dimethylsiloxane) (HO–PVlDmMS–OH) was synthesized by ring-opening polymerization. The copolymerization ratio of vinylmethylsiloxane to dimethylsiloxane was 1/9. The molecular weight of HO–PVlDmMS–OH ranged from (1.43 to 4.44) × 104, and their molecular weight distribution (Mw/Mn) as determined by size-exclusion chromatography equipped with multiangle laser light scattering (SEC-MALS) was 1.16. 4-Cyanopentanoic acid dithiobenzoate was reacted with HO–PVlDmMS–OH to obtain macromolecular chain transfer agents (macro-CTA). 2-Methacryloyloxyethyl phosphorylcholine (MPC) was polymerized with macro-CTAs. The gel-permeation chromatography (GPC) chart of synthesized polymers was a single peak and Mw/Mn was relatively narrow (1.3–1.6). Then the poly(MPC) (PMPC)–PVlDmMS–PMPC triblock copolymers were synthesized. The molecular weight of PMPC in a triblock copolymer was easily controllable by changing the polymerization time or the composition of the macro-CTA to a monomer in the feed. The synthesized block copolymers were slightly soluble in water and extremely soluble in ethanol and 2-propanol.
Surface modification was performed via hydrosilylation. The block copolymer was coated on the PDMS film whose surface was pretreated with poly(hydromethylsiloxane). The surface wettability and lubrication of the PDMS film were effectively improved by immobilization with the block copolymers. In addition, the number of adherent platelets from human platelet-rich plasma (PRP) was dramatically reduced by surface modification. Particularly, the triblock copolymer having a high composition ratio of MPC units to silicone units was effective in improving the surface properties of PDMS.
By selective decomposition of the Si–H bond at the surface of the PDMS substrate by irradiation with UV light, the coating region of the triblock copolymer was easily controlled, resulting in the fabrication of micropatterns. On the surface, albumin adsorption was well manipulated. 相似文献
The present case study concerns the technology of Byzantine wall paintings from the Mani Peninsula, Greece. An assemblage
of 12 Byzantine churches, constructed in the tenth to fifteenth century, was included in an initial analytical survey. Two
random samples of wall paintings were taken in each monument in order to study their micro stratigraphy and the composition
of pigment and plaster layers. Polished sections were fabricated for examination with optical microscopy and scanning electron
microscopy (SEM). Furthermore, selected samples were powdered and analysed with Fourier-transformed infrared spectroscopy
(FTIR) and X-ray diffraction (XRD). The analytical results achieved in this case study provided general conclusions concerning
painting techniques for wall paintings in a rather provincial area of the Byzantine Empire. The palette comprised mainly earthen
pigments like ochres and carbon black but occasionally also other pigments like cinnabar, minium and ultramarine. In view
of future studies, a portable X-ray fluorescence analysis (XRF) set-up was tested. 相似文献
A new fluorescent probe for Zn2+, namely, 8-hydroxy-5-N,N-dimethylaminosulfonylquinolin-2-ylmethyl-pendant cyclen (L8), was designed and synthesized (cyclen=1,4,7,10-tetraazacyclododecane). By potentiometric pH, 1H NMR, and UV spectroscopic titrations, the deprotonation constants pKa1-pKa6 of L(8)4 HCl were determined to be <2, <2, <2 (for amino groups of the cyclen and quinoline moieties), 7.19+/-0.05 (for 8-OH of the quinoline moiety), 10.10+/-0.05, and 11.49+/-0.05, respectively, at 25 degrees C with I=0.1 (NaNO3). The results of 1H NMR, potentiometric pH, and UV titrations, as well as single-crystal X-ray diffraction analysis, showed that L8 and Zn2+ form a 1:1 complex [Zn(H-1L8)], in which the 8-OH group of the quinoline ring of L8 is deprotonated and coordinates to Zn2+, in aqueous solution at neutral pH. On addition of one equivalent of Zn2+ and Cd2+, the fluorescence emission of L8 (5 microM) at 512 nm in aqueous solution at pH 7.4 [10 mM HEPES with I=0.1 (NaNO3)] and 25 degrees C increased by factors of 17 and 43, respectively. We found that the cyclen moiety has the unique property of quenching the fluorescence emission of the quinolinol moiety when not complexed with metal cations, but enhancing emission when complexed with Zn2+ or Cd2+. In addition, the Zn2+-L8 complex [Zn(H-1L8)] is much more thermodynamically and kinetically stable (Kd{Zn(H-1L8)}=[Zn2+]free[L8]free/[Zn(H-1L8)]=8 fM at pH 7.4) than the Zn2+ complexes of our previous Zn2+ fluorophores ([Zn(H-1L2)] and [Zn(L3)]). Furthermore, formation of [Zn(H-1L8)] is much faster than those of [Zn(H-1L2)] and [Zn(L3)]. The staining of early-stage apoptotic cells with L8 is also described. 相似文献