基于胆甾相液晶的可调制光子晶体

将胆甾相液晶填充进胶体晶体内部空隙, 通过胆甾相液晶与胶体晶体的耦合, 构建了一种新型可调制液晶光子晶体. 填充于胶体晶体内部的胆甾相液晶织构呈现典型的手性近晶相(S)特征. 由于胆甾相液晶具有特定的选择性反射, 当胶体晶体的带隙处于胆甾相液晶的反射波长范围之内, 则随着温度的改变, 胶体晶体的带隙与胆甾相液晶的带隙同时发生蓝移. 在一定温度条件下, 胆甾相液晶的带隙将与胶体晶体的带隙发生耦合, 实现了光子晶体带隙在单峰与双峰之间的可逆切换.     

Interfacing Formate Dehydrogenase with Metal Oxides for the Reversible Electrocatalysis and Solar‐Driven Reduction of Carbon Dioxide

The integration of enzymes with synthetic materials allows efficient electrocatalysis and production of solar fuels. Here, we couple formate dehydrogenase ( FDH ) from Desulfovibrio vulgaris Hildenborough (DvH) to metal oxides for catalytic CO₂ reduction and report an in‐depth study of the resulting enzyme–material interface. Protein film voltammetry (PFV) demonstrates the stable binding of FDH on metal‐oxide electrodes and reveals the reversible and selective reduction of CO₂ to formate. Quartz crystal microbalance (QCM) and attenuated total reflection infrared (ATR‐IR) spectroscopy confirm a high binding affinity for FDH to the TiO₂ surface. Adsorption of FDH on dye‐sensitized TiO₂ allows for visible‐light‐driven CO₂ reduction to formate in the absence of a soluble redox mediator with a turnover frequency (TOF) of 11±1 s^?1. The strong coupling of the enzyme to the semiconductor gives rise to a new benchmark in the selective photoreduction of aqueous CO₂ to formate.     

On the Possibility of Evanescent Wave Excitation Distal from a Solid-Liquid Interface Using Light Quenching

Abstract— Evanescent wave illumination with total internal reflection is often used to provide excitation near a quartz-water interface. We now show that evanescent illumination at one wavelength and incident angle, coupled with light quenching at a second wavelength and incident angle, can be used for selective excitation of fluorophores located up to 5000 Å into the aqueous phase. The displacement of the fluorophore population from the solid-liquid interface depends on the angles of incidence of the excitation and quenching beams and the optical power of the quenching beam. Light quenching with an evanescent wave was demonstrated to be experimentally possible using Pyridinez and a light-quenching wavelength of 736 nm. The use of combined evanescent wave excitation and evanescent wave quenching could provide selective excitation of fluorophores in the cytoplasmic region of cells and may provide improved response times for optical sensors based on evanescent excitation.     

Intra- and intermembrane pairwise molecular recognition between synthetic hydrogen-bonding phospholipids

Multivalency and preorganization are fundamental aspects of molecular recognition at the lipid membrane-water interface and can render weak monomeric binding interactions selective and robust; this concept is important throughout biology, biotechnology, and materials science. Though hydrogen bonding is typically weakened in water, intramembrane hydrogen bonding between native lipids has been well-studied and is thought to contribute to lipid bioactivity and membrane function. We hypothesized that avidity and preorganization effects at the lipid-water interface could overcome solvent competition and allow for selective hydrogen-bond recognition between small, unstructured components. We have found that electrostatically identical vesicular membranes composed of cyanuric acid and melamine functionalized phospholipids 1 and 2 undergo selective apposition, fusion and adhesion in suspension and on solid support, indicating that their well-known low-dielectric hydrogen bonding properties translate effectively to the lipid-water interface. This work is notable and of general interest given the few detailed studies of aqueous phase hydrogen-bonding systems; we have extensively characterized this system, gaining structural, functional, and thermodynamic data. Furthermore, we have found that the designed lipid-lipid headgroup interactions result in dramatic alteration of the lipid phase morphology, providing insight into the coupling of molecular interactions with assembly state. As such, this work contributes to our understanding of fundamental phenomena such as molecular recognition at the lipid-water interface membrane chemistry and further illustrates the general possibility of designing selective hydrogen-bonding adhesive interactions from simple starting materials at other polar-apolar interfaces; this could have numerous materials and biotechnological applications.     

Fixation of a cholesteric helical structure by the photopolymerization of a cholesteryl derived monomer

A cholesteryl derived monomer was synthesized according to a conventional synthetic route; it exhibits a cholesteric phase above 129°C, and shows a red colour due to selective reflection in the cholesteric phase. Photopolymerization of the monomer was carried out at 135°C in the cholesteric phase. The helical structure of the cholesteric phase of the monomer was frozen by photopolymerization. A peak based on the selective reflection of the cholesteric phase was detected at 615 nm in the transmittance UV-Vis spectrum. Mixtures of the monomer with a binaphthyl derivative were prepared to control the selective reflection wavelength; they all also exhibited a cholesteric phase. The selective reflection wavelength of the mixture was dependent upon the ratio of the binaphthyl derivative in the mixture. This wavelength became shorter with increasing ratio of the binaphthyl derivative. The polymer films obtained by photopolymerization displayed almost the same selective reflection wavelength as the corresponding mixtures before photopolymerization. The selective reflection wavelength of the polymer films did not change up to about 250°C.     

Fixation of a cholesteric helical structure by the photopolymerization of a cholesteryl derived monomer

A cholesteryl derived monomer was synthesized according to a conventional synthetic route; it exhibits a cholesteric phase above 129°C, and shows a red colour due to selective reflection in the cholesteric phase. Photopolymerization of the monomer was carried out at 135°C in the cholesteric phase. The helical structure of the cholesteric phase of the monomer was frozen by photopolymerization. A peak based on the selective reflection of the cholesteric phase was detected at 615 nm in the transmittance UV-Vis spectrum. Mixtures of the monomer with a binaphthyl derivative were prepared to control the selective reflection wavelength; they all also exhibited a cholesteric phase. The selective reflection wavelength of the mixture was dependent upon the ratio of the binaphthyl derivative in the mixture. This wavelength became shorter with increasing ratio of the binaphthyl derivative. The polymer films obtained by photopolymerization displayed almost the same selective reflection wavelength as the corresponding mixtures before photopolymerization. The selective reflection wavelength of the polymer films did not change up to about 250°C.     

Adsorption of a protein-porphyrin complex at a liquid-liquid interface studied by total internal reflection synchronous fluorescence spectroscopy

Interfacial analysis has attracted more and more attention owing to its fundamental and biological importance. Total internal reflection fluorescence (TIRF) spectroscopy is a useful method to study interfacial properties. The synchronous scanning fluorescence technique provides a selective tool to analyze a specific component in a complex system. The interaction and adsorption of bovine serum albumin (BSA) and meso-tetrakis(4-sulfonatophenyl)porphyrin (TPPS) at toluene-water interface were studied successfully by the coupling technique of total internal reflection synchronous fluorescence (TIRSF). New methods are provided for the determination of the critical micelle concentration (cmc), apparent adsorption equilibrium constant (K_ad) and maximum amount of adsorption (f_max) at the liquid-liquid interface. The results indicated that BSA could adsorb onto the toluene-water interface as a complex of BSA-TPPS in a ratio of 1:1 ratio based on Langmuir adsorption isothermal model. The cmc, apparent K_ad and f_max for BSA at pH 3.1 were determined to be 1.0 × 10⁻⁴ mol L⁻¹, 1.15 × 10⁵ L mol⁻¹ and 1.14 × 10⁻⁹ mol cm⁻², respectively.     

Helix unwinding process in the chiral smectic C phase of MHPOBC as observed by conoscopy

Conoscopic studies have been made on the helix unwinding process in the chiral smectic C phase of MHPOBC. The unwinding process is rather unique in the sense that abrupt changes of the biaxiality and apparent tilt angle are followed by further gradual changes before the complete helix unwinding. The process is qualitatively explained by simulating the conoscopic images using the 4 ×4 matrix method with consideration of model molecular distributions, by taking account of both the ferroelectric and dielectric coupling between molecules and a field. The transmittance loss due to selective reflection was also measured under the application of a stepwise d.c. field. The shift of the dip position due to the loss, toward a longer wavelength region, was observed at low field. In contrast, the emergence of a transmittance loss at the same wavelength as that of an unperturbed state was observed. This phenomenon is explained by the ferroelectric deformation of a helix with the pitch unchanged.     

Helix unwinding process in the chiral smectic C phase of MHPOBC as observed by conoscopy

Conoscopic studies have been made on the helix unwinding process in the chiral smectic C phase of MHPOBC. The unwinding process is rather unique in the sense that abrupt changes of the biaxiality and apparent tilt angle are followed by further gradual changes before the complete helix unwinding. The process is qualitatively explained by simulating the conoscopic images using the 4 x 4 matrix method with consideration of model molecular distributions, by taking account of both the ferroelectric and dielectric coupling between molecules and a field. The transmittance loss due to selective reflection was also measured under the application of a stepwise d.c. field. The shift of the dip position due to the loss, toward a longer wavelength region, was observed at low field. In contrast, the emergence of a transmittance loss at the same wavelength as that of an unperturbed state was observed. This phenomenon is explained by the ferroelectric deformation of a helix with the pitch unchanged.     

J-aggregation of a sulfonated amphiphilic porphyrin at the air-water interface as a function of pH

π-A isotherms, ellipsometric measurements, Brewster angle microscopy (BAM) and reflection spectroscopy have been utilized to characterize the films of an amphiphilic porphyrin ((OD)(3)TPPS(3)) at the air-water interface as a function of pH. This porphyrin forms stable mono-molecular layers at such interfaces, and exhibits different J-aggregation as a function of pH. The J-aggregation of (OD)(3)TPPS(3) on neutral pH subphases is notable considering that the nitrogen atoms at the central macrocycle have a pK(a)≈4.9. The type of aggregates at neutral pH is like those detected at pH<4, because the central porphyrin ring is already protonated. However at basic pH the aggregation happens without protonation of the central ring but can be instead controlled by application of the surface pressure. At the air-water interface, (OD)(3)TPPS(3) shows two bands, a red component and a blue component, which have characteristics of non-degenerate linear oscillators being perpendicularly polarized between each other. The spectral behavior observed on subphases at different pHs is qualitatively interpreted by means of exciton coupling theory, assuming that the degenerate transitions attributed to the Soret band are split. Additionally, highly oriented molecular films of these J-aggregates were deposited onto transparent quartz slides.     

Assembly of nanozeolite monolayers on the gold substrates of piezoelectric sensors

Colloidal zeolites NaA (LTA structure type) and ZSM-5 (MFI-type) with crystal diameters of about 100 nm were synthesized as building blocks for the formation of microporous self-limiting monolayers on the piezo-active area (gold electrodes) of a quartz crystal microbalance (QCM). Two different coupling strategies were explored, concerning the modification of either the gold substrate or the external zeolite crystal surface with a bifunctional molecular interface. Diverse analytical methods were employed to fully characterize the materials (dynamic light scattering, X-ray diffraction, infrared and Raman spectroscopy, solid state 29Si NMR spectroscopy, N2 sorption) and to study the process of coupling the zeolite crystals to the gold surface (reflection-absorption IR spectroscopy, scanning electron microscopy). The molecularly selective sensing behavior of these zeolite-coated devices is demonstrated by measuring the full adsorption isotherms of n-butane and i-butane in the microporous films.     

Surface orientation of polypropylene. I. Theoretical considerations for the application of internal reflection spectroscopy

A theoretical consideration of the orientation of the transverse magnetic and the transverse electric polarization vectors of the evanescent field in attenuated total reflection spectroscopy was made. It was demonstrated that near the critical angle of total reflection the transverse magnetic polarization vector approaches a purely normal orientation to the interface between the sample and internal reflection element surfaces, while the transverse electric vector is parallel to this interface. With an appropriate experimental design a set of three orthogonal electric vectors can be obtained for the analysis of surface orientations. A method to obtain high-quality infrared spectra of polypropylene surfaces at a fraction of a degree above the critical angle was developed using a KRS-5 internal reflection element specially cut with a 40° entrance aperture. The surface orientation of uniaxially extended polypropylene films was studied by using the proposed experimental design. It was shown that the orientation of the helix axis of the macromolecular chains of polypropylene could be qualitatively detected. A method employing the 841- and 809-cm^?1 bands of polypropylene was used to show that the ratio of absorbances of these bands reflects the surface orientation of the uniaxially extended polypropylene films for a set of films extended 0–500%.     

Selective reflection and textural studies of free-standing films of a chiral liquid crystal

Abstract

We present a detailed study of selective reflection from free-standing films of chiral smectic phases. Free-standing films are drawn of the chiral compound 2-(4-hexyloxyphenyl)-5-[4-(1-chloro-3-methylbutanoyloxy)phenyl]pyrimidine (2f-6) possessing a chiral smectic C and the recently discovered chiral smectic M phase, both phases showing the phenomenon of selective reflection of visible light in a certain temperature range. With linearly polarized incident light two selective reflection maxima are observed which are caused by the presence of π-walls in the film. The wavelength of the selective reflection maxima is independent of the film thickness, whereas the intensity decreases with decreasing film thickness. The dependence of the reflection maxima on temperature and enantiomeric excess is studied.     

FTIR-ATR spectroscopic determination of the distribution of surfactants in latex films

FTIR-ATR (Fourier Transform Infra-Red-Attenuated Total Reflection) has been used to analyze the surface composition of coalesced acrylic latex films. The behavior of two anionic surfactants has been characterized. It has been found that surfactant distribution depends on the nature of the surfactant. A comparison between the normalized absorbance in transmission and in reflection has shown an enrichment of surfactants at the surfaces of films with a coalescence time of 3 days. The surfactant concentration at the film-air interface is higher than at the film substrate interface. A concentration gradient exists through the film thickness. In addition, the incompatible surfactant migrates towards the interface as coalescence proceeds.     

A novel direct coupling of simultaneous thermal analysis (STA) and Fourier transform-infrared (FT-IR) spectroscopy

Evolved gas analysis (EGA) from thermal analyzers such as thermogravimetry (TG) or simultaneous thermal analysis (STA) which refers to simultaneous TG–DSC is well established since it greatly enhances the value of TG or TG–DSC results. The sensitive and selective FT-IR technique is in particular useful for the analysis of organic molecules but also for infrared active permanent gases evolved during most decomposition processes. The coupling interface between thermal analyzers and FT-IR spectrometers usually consists of heated adapters and a flexible, heated transfer line. In this work, a novel direct coupling of an STA instrument and an FT-IR spectrometer without a transfer line is presented. A very small FT-IR spectrometer is directly mounted on top of the STA furnace leading to a compact and fully integrated STA–FT-IR coupling system. The possibilities and the value of simultaneous STA–FT-IR measurements are demonstrated for organic, biomass, and ceramic samples in the temperature range between room temperature and about 1,500 °C. Various samples from the field of inorganics and organics—especially polymers—were furthermore measured showing the advantages of the direct STA–FT-IR coupling compared to state-of-the-art STA–FT-IR coupling using a heated transfer line: we found that the time delay caused by the volume of the transfer line itself is rather negligible whereas a significantly better correlation between gas detection and TG results was observed in case of some highly condensable decomposition gases. Aspects of quantification of evolved gases are furthermore discussed as well as the known nonlinearity of FT-IR detection at higher gas concentrations.     

Anionic synthesis and detection of fluorescence‐labeled polymers with a terminal anhydride group

To monitor polymer–polymer coupling reactions between two different monofunctional polymers in dilute polymer blends, fluorescence‐labeled anhydride‐functional polystyrene (PS) and poly(methyl methacrylate) (PMMA) were prepared by conventional anionic polymerization. Sequential trapping of lithiopolystyrene by 1‐(2‐anthryl)‐1‐phenylethylene (APE) and then di‐t‐butyl maleate (4) provided, after pyrolysis, anhydride‐functional fluorescent PS. Fluorescent PMMA anhydride (8) was synthesized with sec‐butyllithium/APE as an initiator for the anionic polymerization of methyl methacrylate, trapping by 4, and pyrolysis. These polymers could be reacted with amine‐functional polymers by melt blending, and the reaction progress could be monitored by gel permeation chromatography coupled with fluorescence detection. This technique not only allows monitoring of the coupling reaction with high sensitivity (ca. 100 times more sensitive than refractive index detection) but also permits selective detection because unlabeled polymers are invisible to fluorescence detection. This highly sensitive and selective detection methodology was also used to monitor the coupling reaction of 8 with PS‐NH₂ at a thin‐film interface, which was otherwise difficult to detect by conventional methods. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2177–2185, 2000     

形成晶体条纹的一个界面反应-扩散模型

基于晶体生长动力学的非平衡非线性特性和耗散结构的概念,提出了一个非理想的界面反应一扩散模型,其中界面动力学引起的晶面多重态现象和扩散过程的耦合可导致滞后现象。它可以解释某些晶体中有序条纹的形成。     

Width of the hexadecane-water interface: a discrepancy resolved

An existing discrepancy in the determined values of the width of the hexadecane-water interface as determined from X-ray reflection (XR) and recent neutron reflection (NR) measurements has been resolved. The NR-determined width reported here is 6.0 +/- 1.0 Angstroms, which compares extremely well with the XR-determined value of 6.0 +/- 0.2 Angstroms. The origin of the discrepancy has been attributed to the thermal history of the interface rather than sample purity or other technique-dependent reasons.