固相合成法制备组氨酸-苯丙二肽及其自组装研究

本文以组装性能良好的苯丙氨酸二肽(FF)为母体分子,用组氨酸对其进行化学修饰,通过多肽固相合成法合成了组氨酸-苯丙二肽(HisFF)凝胶因子。合成的HisFF分子通过质谱(MS)、核磁共振(NMR)和液相色谱(HPLC)方法测试确定精确的结构和纯度。HisFF聚集体的形貌结构通过透射电子显微镜(TEM)和扫描电子显微镜(SEM)观察。HisFF分子在甲苯、氯仿和乙酸乙酯溶剂中形成凝胶强度不同,TEM实验结果表明纤维强度和聚集形态影响其凝胶的强度。组氨酸-苯丙二肽在多种溶剂中,通过不同组装方法可以组装成各种各样的纳米结构。例如,HisFF在丙酮、甲醇和乙酸乙酯溶剂中可组装成纳米颗粒、纳米管和螺旋状纳米纤维;组氨酸-苯丙二肽先经HFIP溶解再通过溶剂稀释后,可得到不同直径的纳米纤维。但是在四氢呋喃、乙醇和乙腈溶剂中,两种方法组装的形貌几乎无变化。     

Direct observation of the release of phenylalanine from diphenylalanine nanotubes

The core recognition motif of the amyloidogenic beta-amyloid polypeptide is a dipeptide of phenylalanine. This dipeptide readily self-assembles to form discrete, hollow nanotubes with high persistence lengths. The simplicity of the nanotube formation, combined with ideal physical properties, make these nanotubes highly desirable for a range of applications in bionanotechnology. To fully realize the potential of such structures, it is first necessary to gain a comprehensive understanding of their chemical and physical properties. Previously, the thermal stability of these nanotubes has been investigated by electron microscopy. Here, we further our understanding of the structural stability of the nanotubes upon dry-heating using the atomic force microscope (AFM), and for the first time identify their degradation product utilizing time-of-flight secondary-ion mass spectrometry. We show that the nanotubes are stable at temperatures up to 100 degrees C, but on heating to higher temperatures begin to lose their structural integrity with an apparent collapse in tubular structure. With further increases in temperature up to and above 150 degrees C, there is a degradation of the structure of the nanotubes through the release of phenylalanine building blocks. The breakdown of structure is observed in samples that are either imaged at elevated temperatures or imaged following cooling, suggesting that once phenylalanine is lost from the nanotubes they are susceptible to mechanical deformation by the imaging AFM probe. This temperature-induced plasticity may provide novel properties for these peptide nanotubes, including possible applications as scaffolds and drug delivery devices.     

The gas sensing properties of TiO_2 nanotubes synthesized by hydrothermal method

In this paper,the TiO₂ nanotubes were synthesized by hydrothermal method using a 10 mol/L NaOH aqueous solution at 150℃. The structure of prepared materials was characterized by X-ray diffraction（XRD）,transmission electron microscopy（TEM）. scanning electron microscope（SEM） and Brunauer-Emmett-Teller（BET）.The prepared TiO₂ nanotubes were used to prepare thick film gas sensors and the gas sensing properties to various gases were tested.Results show the prepared TiO₂ nanotube gas sensors responses to ethanol under dry condition at 450℃.This could be attributed to the fact that it had high porous morphology and a higher pore volume,which can promote the diffusion of ethanol deep inside the films and improve the sensor response. Moreover,the gas sensor made with nanotubes exhibit high selective response towards ethanol gas compared with H₂,CO,acetone.     

Preparation and characterization of individual peptide-wrapped single-walled carbon nanotubes

Two challenges for effectively exploiting the remarkable properties of single-walled carbon nanotubes (SWNTs) are the isolation of intact individual nanotubes from the raw material and the assembly of these isolated SWNTs into useful structures. In this study, we present atomic force microscopy (AFM) evidence that we can isolate individual peptide-wrapped SWNTs, possibly connected end-to-end into long fibrillar structures, using an amphiphilic alpha-helical peptide, termed nano-1. Transmission electron microscopy (TEM) and well-resolved absorption spectral features further corroborate nano-1's ability to debundle SWNTs in aqueous solution. Peptide-assisted assembly of SWNT structures, specifically in the form of Y-, X-, and intraloop junctions, was observed in the AFM and TEM images.     

Assembly of nanotubes of poly(4-vinylpyridine) and poly(acrylic acid) through hydrogen bonding

Nanotubes of poly(4-vinylpyridine) (PVP) and poly(acrylic acid) (PAA) were fabricated by hydrogen bonding based on layer-by-layer (LbL) assembly. The uniform and flexible tubular structures were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). FTIR and X-ray photoelectron spectroscopy (XPS) measurements confirm the formation of hydrogen bonds in the assembled nanotubes. PAA can be released from the assembled PAA/PVP nanotubes in a basic aqueous solution to give the walls of the tubes a porous structure. Such assembled nanotubes can be considered as carriers for catalysts or drugs, especially in aqueous solution against capillary force.     

Biobased films prepared from NaOH/thiourea aqueous solution of chitosan and linter cellulose

In the present study, films based on linter cellulose and chitosan were prepared using an aqueous solution of sodium hydroxide (NaOH)/thiourea as the solvent system. The dissolution process of cellulose and chitosan in NaOH/thiourea aqueous solution was followed by the partial chain depolymerization of both biopolymers, which facilitates their solubilization. Biobased films with different chitosan/cellulose ratios were then elaborated by a casting method and subsequent solvent evaporation. They were characterized by X-ray analysis, scanning electron microscopy (SEM), atomic force microscopy (AFM), thermal analysis, and tests related to tensile strength and biodegradation properties. The SEM images of the biofilms with 50/50 and 60/40 ratio of chitosan/cellulose showed surfaces more wrinkled than the others. The AFM images indicated that higher the content of chitosan in the biobased composite film, higher is the average roughness value. It was inferred through thermal analysis that the thermal stability was affected by the presence of chitosan in the films; the initial temperature of decomposition was shifted to lower levels in the presence of chitosan. Results from the tests for tensile strength indicated that the blending of cellulose and chitosan improved the mechanical properties of the films and that an increase in chitosan content led to production of films with higher tensile strength and percentage of elongation. The degradation study in a simulated soil showed that the higher the crystallinity, the lower is the biodegradation rate.     

Sequential electrochemical oxidation and site-selective growth of nanoparticles onto AFM probes

In this work, we reported an approach for the site-selective growth of nanoparticle onto the tip apex of an atomic force microscopy (AFM) probe. The silicon AFM probe was first coated with a self-assembled monolayer (SAM) of octadecyltrichlorosilane (OTS) through a chemical vapor deposition (CVD) method. Subsequently, COOH groups were selectively generated at the tip apex of silicon AFM probes by applying an appropriate bias voltage between the tip and a flat gold electrode. The transformation of methyl to carboxylic groups at the tip apex of the AFM probe was investigated through measuring the capillary force before and after electrochemical oxidation. To prepare the nanoparticle terminated AFM probe, the oxidized AFM probe was then immersed in an aqueous solution containing positive metal ions, for example, Ag+, to bind positive metal ions to the oxidized area (COOH terminated area), followed by chemical reduction with aqueous NaBH 4 and further development (if desired) to give a metal nanoparticle-modified AFM probe. The formation of a metal nanoparticle at the tip apex of the AFM probe was confirmed by scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA).     

Using the bending beam model to estimate the elasticity of diphenylalanine nanotubes

The core recognition motif of the amyloidogenic beta-amyloid polypeptide, diphenylalanine peptide, has previously been shown to self-assemble into discrete, well-ordered, stiff nanotubes under mild conditions. The nanotubes keep the same morphology from room temperature up to 100 degrees C. In the presented study, we applied the bending beam model to atomic force microscopy images of diphenylalanine nanotubes suspended across cavities and obtained the Young's modulus 27 +/- 4 GPa and the shear modulus 0.21 +/- 0.03 GPa. We also showed that the elasticity of these nanotubes is stable within the same temperature range and at relative humidity from 0% to 70%. This study furthers our understanding of the structure and properties of these nanotubes, which are important for their potential applications in biotechnology.     

Synthesis and Hierarchical Self‐Assembly of Diphenylalanine‐Based Homopolymer and Copolymers By RAFT Polymerization

Dipeptide diphenylalanine has attracted significant research interests because of its ability to self‐assemble into various nanostructures such as nanotubes, nanowires, and nanoribbons. In this article, we present the synthesis and self‐assembly of a novel diphenylalanine‐based homopolymer and block/random copolymers by the reversible addition–fragmentation chain transfer (RAFT) polymerization of an acrylamide having a dipeptide moiety. The RAFT polymerization of N‐acryloyl‐l ,l ‐diphenylalanine (A‐Phe‐Phe‐OH) afforded novel amino acid‐based polymers with predetermined molecular weights and relatively narrow‐molecular weight distributions. The hierarchical self‐assembled structures of poly(A‐Phe‐Phe‐OH), which involve nanorods, larger nanofiber‐like microcrystals, and fiber bundles, were characterized by atomic force microscopy (AFM), transmission electron microscopy, scanning electron microscopy, and dynamic light scattering measurements. The circular dichroic measurements of poly(A‐Phe‐Phe‐OH) revealed its characteristic chiroptical property, which is affected by the nature of the solvents and the addition of urea and salts via hydrophobic, hydrogen bonding, and electrostatic interactions. Thermo‐ and pH‐responsive block and random copolymers composed of A‐Phe‐Phe‐OH and N‐isopropylacrylamide were synthesized by RAFT polymerization, and the thermoresponsive properties and assembled structures of the resulting copolymers were investigated by AFM and turbidity measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2562–2574     

Synthesis of thin dense titania films via an aqueous solution-gel method

Nanostructured titanium dioxide films have been reported to be used in many applications ranging from optics and solar energy devices to gas sensors. This work describes the synthesis of nanocrystalline titania films via an aqueous solution-gel method. The thin films are deposited by spin coating an aqueous citratoperoxo-Ti(IV)-precursor solution onto a silicon substrate. The influence of processing parameters like Ti⁴⁺ concentration and crystallization temperature on the phase formation, crystallite size and surface morphology of the films is studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atomic force microscopy (AFM). Furthermore, the effect of successive layer deposition on the film thickness of the resulting films is studied by means of cross sectional SEM. SEM and TEM micrographs clearly show that, after optimization of the process parameters, thin, smooth, dense nanocrystalline films are synthesized in a reproducible manner. The films are composed of 15–20 nm grains. At higher crystallization temperatures (600, 650°C) also larger particles (40–70 nm) are present. XRD data reveal that a phase pure anatase film is formed at 450°C. Crystallization temperatures equal to or higher than 600 °C however give rise to the formation of both the anatase and rutile crystalline phases. The smoothness of the films is proved by their very low rms surface roughness (≤1.1 nm) measured by AFM.     

海藻酸锌纤维热降解法制备氧化锌纳米结构

采用天然高分子海藻酸钠为原料, 以氯化锌水溶液为凝固浴, 通过湿法纺丝技术成功制备了海藻酸锌(Alg-Zn)纤维.通过在空气中不同温度下对所得海藻酸锌纤维进行热处理, 得到了多种ZnO纳米结构. 利用热失重分析(TG)、X射线衍射(XRD)、电子能量损失谱(EELS)、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段对产物的组成、形貌和微观结构进行了详细表征. 结果表明, 焙烧温度和时间对所得ZnO纳米结构的尺寸和形貌具有重要影响; 800 ℃下热处理24 h以上可以得到直径约为120 nm的ZnO纳米棒. 通过仔细考察不同热处理时间得到的ZnO纳米结构, 提出了在焙烧条件下ZnO纳米棒的生长机理.     

PREPARATION AND PHYSICAL PROPERTIES OF BLEND FILMS FROM SODIUM ALGINATE AND POLYACRYLAMIDE SOLUTIONS

Blend films of sodium alginate and polyacrylamide (PAAm) were prepared by mixing the aqueous solution of both samples at a different ratio. All blend films obtained are optically clear to the naked eye. The structure and physical properties of the films were studied by FT-infrared (FT-IR), wide angle X-ray diffraction (WAXD), differential thermal analysis (DTA), thermogravimetic analysis (TGA), scanning electron microscopy (SEM), and tensile strength test. The results showed that the occurrence of interactions between -COO^?, -OH groups of sodium alginate and -CONH₂ groups of PAAm in the blends through hydrogen formation. The blend films exhibited the higher thermal stability and improved mechanical properties in dry states. These properties had the maximum value around 20 wt% PAAm content in the blend film. The morphological transition of the blend films from sodium alginate-like to PAAm-like was observed by scanning electron microscopy.     

Mechanical and chemical analysis of plasma and ultraviolet-ozone surface treatments for thermal bonding of polymeric microfluidic devices

Here we have demonstrated that radio frequency plasma and ultraviolet-ozone (UVO) surface modifications are effective treatments for enabling the thermal bonding of polymeric microfluidic chips at temperatures below the T(g) (glass transition temperature) of the polymer. The effects of UVO and plasma treatments on the surface properties of a cyclic polyolefin and polystyrene were examined with X-ray photoelectron spectroscopy (XPS), contact angle measurements, atomic force microscopy (AFM) surface roughness measurements and surface adhesion measurements with AFM force-distance data. Three-point bending tests using a dynamic mechanical analyzer (DMA) were used to characterize the bond strength of thermally sealed polymer parts and the cross-sections of the bonded microchannels were evaluated with scanning electron microscopy (SEM). The experimental results demonstrated that plasma and UVO surface treatments cause changes in the chemical and physical characteristics of the polymer surfaces, resulting in a decrease in T(g) at the surface, and thus allowing the microfluidic chips to be effectively bonded at temperatures lower than the T(g) of the bulk polymer without losing the intended channel geometry.     

Self-assembly of biocidal nanotubes from a single-chain diacetylene amine salt

We describe the facile two-step synthesis of nanotubes that form pure, well-defined, nanostructured materials. We have synthesized a secondary amine HBr salt as the headgroup of a single-chain diacetylenic lipid. This molecule can form a number of different self-assembled nanostructures in aqueous or organic solvents. In water, this lipid forms a monodisperse preparation of nanotubes at high yields. Partially dissolving a preparation of nanotubes dried from aqueous solution results in a remarkably organized structure that resembles a nanocarpet. Details of the nanotube structure were investigated by scanning electron microscopy, transmission electron microscopy, and small-angle X-ray spectroscopy. The aqueous nanotubes have a cross-sectional diameter of 89 nm. The walls of the tubes are an exquisitely uniform 27 nm thick and are shown to consist of five lipid bilayers with a repeat spacing of 57.8 A. The chemical structure of the material shows no chiral centers, but suspensions of the nanotubes in an aqueous medium show an unexpected circular dichroism signal. The versatility of this new material as a platform for nanostructure design and synthesis is enhanced by its biocidal activity. This antimicrobial activity along with the regularity the nanostructures will enhance the development of a range of applications from biosensors to artificial retinas.     

A rapid synthesis of iron phosphate nanoparticles via surface-mediated spontaneous reaction for the growth of high-yield, single-walled carbon nanotubes

The direct formation of iron phosphate nanoparticles on hydroxyl-terminated SiO(2)/Si substrates with a narrow size distribution (average diameter = 2.2 nm) is achieved by a simple room temperature spontaneous reaction of ferric chloride and phosphoric acid. Single-walled carbon nanotubes (SWNTs) are grown in high yield from the synthesized iron phosphate nanoparticles by the thermal chemical vapor deposition (CVD) method, as confirmed by atomic force microscopy (AFM) and Raman spectroscopy. Furthermore, three-terminal, p-type, nanotube network field effect transistor (FET) devices are successfully fabricated using the synthesized SWNTs via the photolithography technique. The reduced solubility of Fe(III) ions when they form iron phosphate salts in aqueous media is the main driving force for the nanoparticle formation. Systematic control experiments reveal that the surface property, concentration, and pH of the reaction solution play equally important roles in the formation of nanoparticles.     

Formation of colloidal suspension of hydrophobic compounds with an amphiphilic self-assembling peptide

The amphiphilic self-assembling peptide EAK16-II was found to be able to stabilize hydrophobic compounds in aqueous solution. Micro/nanocrystals of a hydrophobic compound, pyrene, and a hydrophobic anticancer agent, ellipticine, were stabilized by EAK16-II to form colloidal suspensions in water. Initial evidence of the association between EAK16-II and hydrophobic compounds was the observation of a clouding phenomenon and a difference in fluorescence spectra of the solution. A further investigation on the interaction between EAK16-II and pyrene was carried out using fluorescence spectroscopy and scanning electron microscopy (SEM). It was found that the pyrene–peptide complex formation required mechanical stirring, and the freshly prepared peptide solution (containing peptide monomers and/or peptide protofibrils) was more effective at stabilizing pyrene than the mature fibrils in aged peptide solutions. The time duration over which the complex formed was about 22 h. The data on the complexation of pyrene and EAK16-II at various concentrations suggested that the maximum amount of stabilized pyrene was concentration dependent. SEM images showed that peptide concentration did not significantly affect the size of the complexes/suspensions but altered the structures of the peptide coating on the surface of the complex. Atomic force microscopy (AFM) was conducted to study the interaction of EAK16-II with a model hydrophobic surface, which provided some detailed information of how peptide adsorbed onto the hydrophobic compounds and stabilize them. This study shows the potential of self-assembling peptides for encapsulation of hydrophobic compounds.     

阳极氧化法制备二氧化钛纳米管阵列的研究

采用电化学阳极氧化法,将纯钛浸入HF酸水溶液,在钛基体表面原位构建高度有序的二氧化钛纳米管阵列,探讨阳极氧化电压、电解液浓度和电解液温度等对二氧化钛纳米管阵列尺寸和形貌的影响。通过SEM、XRD对二氧化钛纳米管阵列的结构特征进行表征,结果表明,不同的阳极氧化电压、电解液浓度和温度都将影响TiO2纳米管阵列的尺寸和形貌,在阳极氧化电压为20V,HF电解液浓度为0.5%t条件下,可制备出结构规整有序的TiO2纳米管阵列。     

在Ni-B非晶态催化剂作用下生物油水相加氢制备饱和醇

采用化学还原法制备了Ni-B和Ni-Co-B非晶态催化剂, 并采用X射线衍射(XRD)、BET比表面积、扫描电子显微镜(SEM)、透射电子显微镜(TEM)和电感耦合等离子体光谱(ICP)进行了结构表征. 结果表明, 在110 ℃及氢冷压4.0 MPa时, 在Ni-B或Ni-Co-B催化下, 丙酮、糠醛和苯酚的转化率和饱和醇的选择性分别达到99.99% 和95.00%以上. 对于Ni-B催化生物油真实体系, 在150 ℃及氢冷压4.0 MPa下, 饱和醇的收率达到47.54%. 温度过高易导致催化剂转晶从而降低反应活性. 为生物油的有效利用和饱和多元醇的制备提供了新思路.     

Fabrication of Hexagonal Boron Nitride Nanosheets by Using a Simple Thermal Exfoliation Process

A simple and inexpensive method to exfoliate boron nitride powder to form boron nitride nanosheets (BNNSs) with few layers was achieved by using a physically thermal process. The obtained BNNSs were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), IR spectroscopy, and Raman spectroscopy. The size distribution of the sheets and average sheet size is in the range of 80–380 nm and 200±62 nm, respectively, and the pure phase h‐BN products were confirmed. XPS result showed the B/N atomic ratio to be 0.99. In addition, the BNNSs can well disperse in aqueous solution to form a cloudy suspension and importantly, can remain suspended for 1 month without precipitate, which would have good potential in a wide range of applications.     

含辣素衍生结构疏水缔合聚合物PAAH的合成、表征及溶液性质

以辣素功能结构单体N-（4-羟基-3-甲氧基-苄基）-丙烯酰胺（HMBA）为疏水单体,与丙烯酰胺（AM）和2-丙烯酰胺基-2-甲基丙磺酸钠（NaAMPS）通过自由基胶束共聚,制得三元疏水缔合聚合物P（AM-NaAMPS-HMBA）（简称PAAH）. 采用紫外-可见光谱、核磁共振氢谱、热重分析及扫描电子显微镜对共聚物的结构及形貌进行表征,利用原子力显微镜对聚合物水溶液的微观形貌进行观察,并对其溶解性、疏水缔合性、耐温性及抑菌性能进行了研究. 结果表明,所得共聚物中疏水单体含量与投料比基本一致;PAAH具有良好的速溶性,当聚合物浓度超过一定值后,溶液黏度急剧增加,且随着疏水单体含量增加,疏水缔合性能增强;原子力显微镜观察证实了聚合物水溶液中网络结构的存在. 与未改性的P（AM-NaAMPS）（简称PAA）共聚物相比,引入具有生物活性且带有刚性苯环结构的HMBA单体可使PAAH共聚物热稳定性增强,耐温性能提高,并赋予其优良的抑菌性能.