Layer‐by‐layer Assembled Multilayers of Graphene/Mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin for Detection of Dopamine

Graphene/mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin multilayer films composed of graphene sheet (GS) and mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin (NH₂‐β‐CD) were fabricated easily by two steps. First, negatively charged graphene oxide (GO) and positively charged mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin (NH₂‐β‐CD) were layer‐by‐layer (LBL) self‐assembled on glassy carbon electrode (GCE) modified with a layer of poly(diallyldimethylammonium chloride) (PDDA). Then graphene/mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin (GS/NH₂‐β‐CD) multilayer films were built up by electrochemical reduction of graphene oxide/mono‐(6‐amino‐6‐deoxy)‐β‐cyclodextrin (GO/NH₂‐β‐CD). Combining the high surface area of GS and the active recognition sites on β‐cyclodextrin (β‐CD), the GS/NH₂‐β‐CD multilayer films show excellent electrochemical sensing performance for the detection of DA with an extraordinary broad linear range from 2.53 to 980.05 µmol·L^?1. This study offers a simple route to the controllable formation of graphene‐based electrochemical sensor for the detection of DA.     

掠射椭偏术对K_4〔Fe(CN)_6〕/K_3〔Fe(CN)_6〕电极反应的研究

提出掠射椭圆偏振测试技术的实验方案,应用该掠射式技术结合循环伏安法研究了在镀有Ｉｎ２Ｏ３玻璃片上进行的Ｋ４〔Ｆｅ（ＣＮ）６〕／Ｋ３〔Ｆｅ（ＣＮ）６〕电极反应．结果证明：掠射椭圆偏振术可在电化学反应过程中现场测定椭圆偏振参数及其变化规律,这些规律与所发生的表面电化学反应规律相对应,由此可以对电极体系进行研究;现场掠射椭圆偏振术还能用于分析表面扩散层的性质,弥补其它界面研究方法的缺陷．     

Enantioselective Synthesis of (−)‐(R)‐Cordiachromene and (−)‐(R)‐Dictyochromenol Utilizing Intramolecular SNAr Reaction

A simple and efficient enantioselective synthesis of chromene, (?)‐(R)‐cordiachromene ( 1 ), and (?)‐(R)‐dictyochromenol ( 2 ) has been accomplished. This convergent synthesis utilizes intramolecular S_NAr reaction for the formation of chroman ring, and Seebach's method of ‘self‐reproduction of chirality’ should establish the (R)‐configuration of the C(2) side chain as key steps.     

Synthesis of (−)‐Pinellic Acid and Its (9R,12S,13S)‐Diastereoisomer

The total synthesis of (?)‐pinellic acid with (9S,12S,13S)‐configuration and its (9R,12S,13S)‐diastereoisomer was achieved in high overall yields from a common intermediate derived from (+)‐L ‐diethyl tartrate.     

Comparative Electrochemical Study of N‐, C‐terminal and Integral Centrin on Adsorption and Metal‐Binding Properties

The adsorption behavior of apo‐ciliate Euplotes octocarinatus centrin (EoCen) and N(C)‐terminal domain of EoCen (N(C)‐EoCen) at a glassy carbon (GC) electrode is studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). Interestingly, the adsorption isotherms of C‐EoCen, N‐EoCen and EoCen at a GC surface differ from one another. It is considered to be associated with the different aggregation properties of three proteins. Furthermore, we analyze the metal‐binding properties of centrin and the followed changes in protein structure upon metal‐binding. Corresponding to the four binding sites of EoCen, it shows four no‐equiv signals of CV or EIS change. It indicates that the four different binding sites of EoCen can be discriminated by the EIS titration curves, which is in contrast with conventional use of spectral method. According to the electrostatic potential at the molecular surface of proteins, the favored orientation of N‐EoCen and C‐EoCen on the GC surface is modeled. These models can well explain the results of titration curves of Eu³⁺ to N(C)‐EoCen. This work has established the electrochemical methodology which can be used to measure metal‐binding sites involved and reveal the contribution of each metal site to the whole protein conformational change.     

Layer‐by‐layer assembly of readily detachable chitosan and poly(acrylic acid) polyelectrolyte multilayer films

Free‐standing layer‐by‐layer (LbL) assembled thin films have recently found utility in a broad range of applications. Previously reported free‐standing LbL films have generally required covalent modifications to improve aqueous stability and render these films suitable for biomedical applications. Here, we engineered chitosan and poly(acrylic acid) containing polyelectrolyte multilayer films, which are readily detached from hydrophilic silicon in aqueous conditions. These films demonstrate remarkable stability over 28 days in simulated in vivo conditions (pH 7.4, phosphate buffered saline at 37 °C) without the incorporation of any covalent crosslinking modifications. These films exhibit moduli (27–420 kPa) resembling that of many biological tissues including tendon, show high visible light transmittance of greater than 50%, and prevent fibronectin adsorption. The properties of this new detachable LbL film architecture indicate its promise for use in a variety of applications, particularly in medicine and biotechnology. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 127–131     

Layer‐by‐layer deposition of nitrilotris(methylene)triphosphonic acid and Zr(IV): an XPS,ToF‐SIMS,ellipsometry, and AFM study

Layer‐by‐layer assemblies consisting of alternating layers of nitrilotris(methylene)triphosphonic acid (NTMP), a polyfunctional corrosion inhibitor, and zirconium(IV) were prepared on alumina. In particular, a nine‐layer (NTMP/Zr(IV))₄NTMP stack could be constructed at room temperature, which showed a steady increase in film thickness throughout its growth by spectroscopic ellipsometry up to a final thickness of 1.79 ± 0.04 nm. At higher temperature (70 °C), even a two‐layer NTMP/Zr(IV) assembly could not be prepared because of etching of the alumina substrate by the heated Zr(IV) solution. XPS characterization of the layer‐by‐layer assembly showed a saw tooth pattern in the nitrogen, phosphorus, and zirconium signals, where the modest increases and decreases in these signals corresponded to the expected deposition and perhaps removal of NTMP and Zr(IV). Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) confirmed the attachment of the NTMP molecule to the surface through PO^?, PO₂^?, PO₃^?, and CN^? signals. Increasing attenuation of the Al signal from the substrate after deposition of each layer was observed by both XPS and ToF‐SIMS. Essentially complete etching of the alumina by the heated Zr(IV) solution was confirmed by spectroscopic ellipsometry, XPS, and ToF‐SIMS. Atomic force microscopy revealed that all the films were smooth with R_q roughness values less than 0.5 nm. Copyright © 2015 John Wiley & Sons, Ltd.     

Total Synthesis of (−)‐Cleistenolide

An efficient and short total synthesis of (?)‐cleistenolide ( 1 ) from D ‐mannitol with an overall yield of 23.6% is described. The chiron approach for the synthesis of (?)‐cleistenolide involves a one‐C‐atom Wittig olefination, a selective allylic triethylsilyl protection, and a Grubbs‐catalyzed ring‐closure‐metathesis (RCM) reaction as the key steps.     

Enantioselective Synthesis of (−)‐(19R)‐Ibogamin‐19‐ol

The first total synthesis of the natural product (?)‐(19R)‐ibogamin‐19‐ol ((?)‐ 1 ) is reported (biogenetic atom numbering). Starting with L ‐glutamic acid from the chiral pool and (2S)‐but‐3‐en‐2‐ol, the crucial aliphatic isoquinuclidine (= 2‐azabicyclo[2.2.2]octane) core containing the entire configurational information of the final target was prepared in 15 steps (overall yield: 15%). The two key steps involved a highly effective, self‐immolating chirality transfer in an Ireland–Claisen rearrangement and an intramolecular nitrone‐olefin 1,3‐dipolar cycloaddition reaction (Scheme 3). Onto this aliphatic core was grafted the aromatic moiety in the form of N(1)‐protected 1H‐indole‐3‐acetic acid by application of the dicyclohexylcarbodiimide (DCC) method (Scheme 4). Four additional steps were required to adjust the substitution pattern at C(16) and to deprotect the indole subunit for the closure of the crucial 7‐membered ring present in the targeted alkaloid family (Schemes 4 and 5). The spectral and chiroptical properties of the final product (?)‐ 1 matched the ones reported for the naturally occurring alkaloid, which had been isolated from Tabernaemonatana quadrangularis in 1980. The overall yield of the entire synthesis involving a linear string of 20 steps amounted to 1.9% (average yield per step: 82%).     

Nucleophilic Addition to (η3-Allyl)Fe(CO)4 Cations with Functionalized Zinc-Copper Reagents RCu(Znl)CN

Regioselectivity of the addition of the highly functionalized zinc-copper reagents to (η³-allyl)Fe(CO)₄ cationic salts was studied. For 1,1-disubstituted allyl cation 1, the zinc-copper reagents added predominantly at the unsubstituted terminus. For 1,1,2-trisubstituted allyl cation 2, reactive zinc-copper reagents attacked mainly at the unsubstituted terminus while less reactive zinc-copper reagents added to a coordinated CO ligand. For 1,1,3-trisubstituted allyl cation 3, the addition occurred at both the less substituted allyl terminus and a coordinated CO ligand.     

Fabrication of Self‐Assembled Tris(1,10‐phenanthroline) ruthenium/12‐Molybdophosphoric Acid Films with Bifunctional Electrocatalytic and Photoluminescent Properties

The thin films containing transition metal complex tris(1,10‐phenanthroline) ruthenium(II) Ru(phen)₃Cl₂ (abbr Ru(phen)₃, phen=1,10‐phenanthroline), and 12‐molybdophosphoric acid [PMo₁₂O₄₀]_3? (abbr PMo₁₂) were fabricated on quartz, silicon and ITO substrates by layer‐by‐layer (LBL) method. The LBL films were characterized by the UV‐vis spectroscopy, X‐ray photoelectron spectroscopy, atomic force microscopy and cyclic voltammetry. The films can catalyze both the reduction of ClO , BrO , IO , and the oxidation of C₂O due to the presence of bifunctional composite, and the redox potentials depend on pH as a result of protonation. The photoluminescence of films were also investigated. The films exhibited photoluminescence arising from π*–t_2g ligand‐to‐metal transition of Ru(phen)₃.     

Exaltone® (=Cyclopentadecanone) from Isomuscone® (=Cyclohexadecanone), a One‐C‐Atom Ring‐Contraction Methodology via a Stereospecific Favorskii Rearrangement: Regioselective Application to (−)‐(R)‐Muscone

Treatment of cyclohexadecanone ( 1g ; with I₂ (2.2 mol‐euqiv.) and KOH in MeOH) furnished the unsaturated (Z)‐ester 2g in 83% yield, via a stereospecific Favorskii rearrangement (Scheme 1). Further treatment with 3‐chloroperbenzoic acid (m‐CPBA) afforded the unreported epoxy ester 3g (88% yield), which was cleaved in 33% yield to Exaltone^® (=cyclopentadecanone; 1f ) with NaOH in MeOH/H₂O and then HCl at 65°. This methodology was similarly extended to higher (C₁₇) and lower (C₁₅ to C₁₁) cyclic ketone analogues, as well as regioselectively to (?)‐(R)‐muscone ( 5c ) and homomuscone ( 5f ) (Scheme 2). Olfactive properties of the corresponding macrocyclic 1‐oxaspiro[2,n]alkanes and ‐alkenes 4 and 8 , resulting from a Corey? Chaykovsky oxiranylation, are also presented.     

A Fluorescent Chemosensor for Dihydrogen Phosphate Ion Based on 2‐[2‐Hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine‐Fe3+ Ensemble

A long wavelength emission fluorescent (612 nm) chemosensor with high selectivity for H₂PO₄^? ions was designed and synthesized according to the excited state intramolecular proton transfer (ESIPT). The sensor can exist in two tautomeric forms ('keto' and 'enol') in the presence of Fe³⁺ ion, Fe³⁺ may bind with the 'keto' form of the sensor. Furthermore, the in situ generated GY‐Fe³⁺ ensemble could recover the quenched fluorescence upon the addition of H₂PO₄^? anion resulting in an off‐on‐type sensing with a detection limit of micromolar range in the same medium, and other anions, including F^?, Cl^?, Br^?, I^?, AcO^?, HSO₄^?, ClO₄^? and CN^? had nearly no influence on the probing behavior. The test strips based on 2‐[2‐hydroxy‐4‐(diethylamino) phenyl]‐1H‐imidazo[4,5‐b]phenazine and Fe³⁺ metal complex ( GY‐Fe³⁺ ) were fabricated, which could act as convenient and efficient H₂PO₄^? test kits.     

Construction of β‐FeOOH nanorod‐filled layer‐by‐layer coating with effective structure to reduce flammability of flexible polyurethane foam

The β‐FeOOH nanorod‐filled coatings were deposited onto flexible polyurethane foam by layer‐by‐layer assembly technique to reduce its flammability. The coatings were constructed by two assembly systems: one was bilayer system, which was comprised of polyethylenimine and β‐FeOOH nanorods; other one was trilayer system, which was comprised of polyethylenimine, β‐FeOOH nanorods, and sodium alginate. Scanning electron microscopy images indicated that the randomly oriented and entangled network structure can only be observed for the coating that assembled by trilayer system. Cone calorimetry test revealed that the coating assembled by trilayer system can lead to significant reduction in peak heat release rate compared with those of control foam, 61.8% peak heat release rate reduction ever occurred to the eight trilayers coated sample, but the coating assembled by bilayer system has slight reduction (<20%). The result is attributed to trilayer approach being beneficial to fabricate coating with sufficient thickness to protect the underlying foams during burning. Copyright © 2016 John Wiley & Sons, Ltd.     

The reaction of XeF+MF6− (M = As,Sb) with sulfuranes; preparation of CF3(O)F2+SbF6− and (CF3)2SOXeF+SbF6−

CF₃S(O)F, (CF₃)₂SO, CF₃SF₃, (CF₃)₂SF₂, and SF₄ react in different manner with XeF⁺MF₆^? (M?As, Sb). An oxidative fluorination is observed by CF₃S(O)F forming the persulfonium salt CF₃S(O)F₂⁺SbF₆^?, whereas by (CF₃)₂SO a simple addition product containing xenon can be isolated in form of the sulfonium salt (CF₃)₂SOXeF⁺SbF₆^?. On the contrary, the Lewis-acidic character of the XeF⁺-cation predominates against (CF₃)_nSF_4?n (n = 0 ? 2) leading to the corresponding fluorosulfonium salts (CF₃)_nSF_3?n ⁺MF₆^? (M?As, Sb) and XeF₂.     

A Mössbauer spectroscopy investigation of the Intergrowth Phases LaSr3Fe3−xMx010−δ (M = Al,Cu)

Iron-57 Mössbauer spectroscopy confirms a high sensitivity of the three-dimensional magnetic ordering temperature (T_Néel) for a series of new intergrowth phases to both oxygen stoichiometry and the partial substitution of iron by copper and aluminium in the Ruddlesden-Popper phase LaSr₃Fe₃0_10?δ. The chemical isomer shifts suggest that significant covalent electron delocalization exists in these phases. Spectra for the paramagnetic phases indicate two distinct iron coordination environments consistent with x-ray and neutron diffraction structure determinations. The Mössbauer spectra at 4.8 K exhibit the overlap of two magnetic hyperfine patterns corresponding to cooperative magnetic order at the iron sites with internal fields of 45 and 27 Tesla for nominal Fe³⁺ and Fe⁴⁺ sites respectively.     

Effect of External Pressure on the Excitation Energy Transfer from [Cr(ox)3]3− to [Cr(bpy)3]3+ in [Rh1−xCrx(bpy)3][NaM1−yCry(ox)3]ClO4

Resonant excitation energy transfer from [Cr(ox)₃]^3? to [Cr(bpy)₃]³⁺ in the doped 3D oxalate networks [Rh_1?xCr_x(bpy)₃][NaM^III_1?yCr_y(ox)₃]ClO₄ (ox=C₂O₄^?, bpy=2,2′‐bipyridine, M=Al, Rh) is due to two types of interaction, namely super exchange coupling and electric dipole–dipole interaction. The energy transfer probability for both mechanisms is proportional to the spectral overlap of the ²E→⁴A₂ emission of the [Cr(ox)₃]^3? donor and the ⁴A₂→²T₁ absorption of the [Cr(bpy)₃]³⁺ acceptor. The spin‐flip transitions of (pseudo‐)octahedral Cr³⁺ are known to shift to lower energy with increasing pressure. Because the shift rates of the two transitions in question differ, the spectral overlap between the donor emission and the acceptor absorption is a function of applied pressure. For [Rh_1?xCr_x(bpy)₃][NaM_1?yCr_y(ox)₃]ClO₄ the spectral overlap is thus substantially reduced on increasing pressure from 0 to 2.5 GPa. As a result, the energy transfer probability decreases with increasing pressure as evidenced by a decrease in the relative emission intensity from the [Cr(bpy)₃]³⁺ acceptor.     

Highly Sensitive and Selective Detection of Pb(II) by NH2−SiO2/Ru(bpy)32+−UiO66 based Solid‐state ECL Sensor

In this study, a novel electrochemiluminescence (ECL) sensor for highly sensitive and selective detection of Pb(II) was developed based on Ru(bpy)₃²⁺ encapsulated UiO66 metal‐organic‐framework (Ru(bpy)₃²⁺?UiO66 MOF) and ?NH₂ group functionalized silica (NH₂?SiO₂). The NH₂?SiO₂ with large surface area provided an excellent platform for the ECL sensor. As numerous exposed carboxyl groups were present on UiO66 backbone, the Ru(bpy)₃²⁺?UiO66 could be steadily immobilized to NH₂?SiO₂ by forming amide bonds. Meanwhile, the introduced UiO66 MOF which used for the encapsulation of Ru(bpy)₃²⁺, significantly enhanced the ECL efficiency of the proposed sensor, as it possessed a large specific surface area and porosity for the loading of Ru(bpy)₃²⁺. Moreover, a high quenching effect on ECL intensity was obtained in the presence of Pb(II) in the electrolyte. Under the optimal conditions, the quenched ECL intensity showed a good linear relationship within Pb(II) concentration in the range from 1.0×10^?6 to 1.0×10² μM, with a detection limit of 1.0×10^?7 μM (S/N=3). The proposed sensor for Pb(II) detection was simple in operation, rapid in testing, stable in signal, and showed a good anti‐interference ability to some other metal ions. Besides, its application for detecting Pb(II) in a real sample was also investigated here. This work provides a potential platform for metal ions detection in environmental monitoring field.