The role of 18-methyleicosanoic acid in the structure and formation of mammalian hair fibres

Although branched chain fatty acids perform many functions in biological systems, the importance of the anteiso 18 methyleicosanoic acid (MEA) has only recently been recognized. In this first review on MEA its role and distribtuion is explored MEA has been found in minor amounts in the fatty acid components of a wide range of biological materials, but the current interest results from it being the major covalently bound fatty acid in mammalian hair fibres, a finding which is unusual because protein-bound fatty acids are typically straight-chain, even-numbered acids (C14–C18). MEA is released by surface restricted reagents indicating that it is located exclusively in or on the surface of the cuticle cells, a conclusion that has been verified by analysis of isolated cuticle cells. X-ray photoelectron spectroscopy (XPS) and secondary-ion mass spectroscopy (SIMS) studies support these results in that they show the surface of the cuticle to be predominantly hydrocarbon. When either neutral hydroxylamine or acidic chlorine solutions are applied to hair and wool fibres fatty acids are liberated, indicating the presence of thioester bonds. Calculations, based on fatty acid and amino acid analysis, indicate that approximately one residue in 10 of the cuticular membrane protein is a fatty acid thioester of cysteine. Removal of this covalently linked fatty acid renders the fibre hydrophilic, thus offering a chemical explanation for many technological and cosmetic treatments of mammalian fibres. Examination of the fibre surface and that of isolated cuticle cells by transmission electron microscopy (TEM) confirms the presence of a thin non-staining continuous layer surrounding the cuticle cells. Alkaline treatments which remove the bound fatty acids were found to disrupt this layer. TEM examination of developing hair fibres has indicated that the fatty acid layer on the upper surface and scale edges of the cuticle cell differs from that of the underside of the cell. Similar structural studies of hair from patients with maple syrup urine disease (MSUD) support the findings that thioester-bound MEA is limited to the upper surface of fibre cuticle cells. The current model proposed for the boundary layer consists of crosslinked protein with surface thioester-linked fatty acids. forming a continuous hydrophobic layer on the upper surface and scale edges of the cells.     

单层型氧化铁催化剂的制备及其前体的表征:Ⅱ.催化剂前体的表征

用三种方法，即草酸络铁（Ⅱ）酸铵的过量水溶液含浸，三乙酰丙酮铁的甲苯溶液热吸附和硝酸铁溶液饱和浸渍法制备了种载体上氧化铁的负载样品，对用不同方法制备的催化剂前体中表面铁物种的存在形式，结构和分散度等进行了细致的表征和详细的讨论，并与焙烧后样品中Ｆｅ＾３＋的最终形态进行了关联。     

Characterisation of alkyl-functionalised Si(1 1 1) using reflectometry and AC impedance spectroscopy

The past few years have seen a dramatic increase in the study of organic thin-film systems that are based on silicon-carbon covalent bonds for bio-passivation or bio-sensing applications. This approach to functionalizing Si wafers is in contrast to gold-thiol or siloxane chemistries and has been shown to lead to densely packed alkyl monolayers. In this study, a series of alkyl monolayers [CH₃(CH₂)_nCH=CH₂; n = 7, 9, 11, 13, 15] were directly covalent-linked to Si(1 1 1) wafers. The structures of these monolayers were studied using X-ray reflectometry (XRR) and AC impedance spectroscopy. Both techniques are sensitive to the variation in thickness with each addition of a CH₂ unit and thus provide a useful means for monitoring molecular-scale events. The combination of these techniques is able to probe not only the thickness, but also the interfacial roughness and capacitance of the layer at the immobilized surface with atomic resolution. Fundamental physical properties of these films such as chain canting angles were also determined.     

Chemisorption of 4-(4-amino-phenylazo) benzoic acid molecule on the Si(0 0 1)-(4 × 2) surface

Structural and electronic properties of self-assembled monolayer with 4-(4-amino-phenylazo) benzoic acid (APABA) on the Si(0 0 1)-(4 × 2) surface are investigated by ab initio calculation based on density functional theory. For the APABA chemisorption on the silicon surface, we have assumed two different binding sites: (i) amino group of molecule and (ii) carboxyl group of molecule. Considering amino-site, we have assumed two possible models for the chemisorption of molecules on the Si(0 0 1)-(4 × 2) surface: (i) an intrarow position between two neighboring Si dimers in the same dimer row (Model I), (ii) on-dimer position (Model II). We have found that Model II is 1.10 eV energetically more favorable than Model I. The Si-N bond length was calculated as 1.85 Å which is in excellent agreement with the sum of the corresponding covalent radii of 1.87 Å. Considering carboxyl-site, we have assumed exactly the same model as mentioned above. Again we have found that Model II is energetically favorable than Model I. The calculated bond lengths for Si-O and O-C are 1.76 and 1.35 Å, respectively.     

Tribological behaviors of lanthanum-based phosphonate 3-aminopropyltriethoxysilane self-assembled films

Lanthanum-based thin films deposited on the phosphonate 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM) were prepared on the hydroxylated glass substrate by a self-assembling process from specially formulated solution. Chemical compositions of the films and chemical state of the elements were detected by X-ray photoelectron spectrometry (XPS). The thickness of the films was determined with an ellipsometer, while the morphologies of the original and worn surfaces of the samples were analyzed by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM), respectively. The tribological properties of the films sliding against GCr15 steel ball were evaluated on a UMT-2MT reciprocating friction and wear tester. As the results, the target film was obtained and reaction may have taken place between the film and the glass substrate. The tribological results show that lanthanum-based thin films are superior in reducing friction and resisting wear compared with APTES-SAM and phosphorylated APTES-SAM. SEM observation of the morphologies of worn surfaces indicates that the wear of APTES-SAM and the phosphorylated APTES-SAM is characteristic of brittle fracture and severe abrasion. Differently, slight abrasion and micro-crack dominate the wear of lanthanum-based thin films. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate.     

Configuration dependence of photon stimulated ion desorption from methyl ester compounds induced by core excitation

Photon stimulated ion desorption (PSID) from methyl ester terminated self-assembled monolayer (MHDA-SAM, HS(CH₂)₁₅COOCH₃) and methyl mercaptoacetate (MA, HSCH₂COOCH₃) on Ag has been investigated using soft X-ray in the C and O K-edge regions. In MHDA-SAM on Ag, site-selective ion desorption has been clearly observed at resonant core excitations of C_1s, O_1s(OCH₃) → σ^∗(OCH₃) and O_1s(OCH₃) → σ^∗(COCH₃). Ion intensity in MA on Ag is obviously reduced for (n = 1-3) at C_1s, O_1s(OCH₃) → σ^∗(OCH₃) excitations, and no site-selective reaction at O_1s(OCH₃) → σ^∗(COCH₃) excitations has been observed. These reactions may be influenced by configurational difference of reactive sites. It is suggested that surface effects on the selective reaction due to positioning methyl ester group near the surface plays an important role.     

Prediction of semiconducting SiP_2 monolayer with negative Possion's ratio,ultrahigh carrier mobility and CO_2 capture ability

Using particle swarm optimization(PSO) methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D) monolayer of silicide diphosphorus compound:SiP_2,which exhibits good stability as examined via cohesive energy,mechanical criteria,molecular dynamics simulation and all positive phonon spectrum,respectively.The SiP_2 monolayer is an indirect semiconductor with the band gap as 1.8484 eV(PBE) or 2.681 eV(HSE06),which makes it more advantageous for high-frequencyresponse optoelectronic materials.Moreover,the monolayer is a relatively hard auxetic material with negative Possion's ratios,and also possesses a ultrahigh carrier mobility(1.069 × 10~5 cm~2 V~1 s~1) which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers.Furthermore,the effects of strains on band structures and optical properties of SiP2 monolayer have been studied,as well as CO_2 molecules can be strongly chemically adsorbed on the SiP_2 monolayer.A semiconductor-to-metal transition for-9.5% strain ratio case and a huge optical absorption capacity on the order of 106 cm ~1 in visible region present.These theoretical findings endow SiP2 Monolayer to be a novel 2 D material holding great promises for applications in highperformance electronics,optoelectronics,mechanics and CO_2 capturing material.     

Biochemical applications of surface-enhanced infrared absorption spectroscopy

An overview is presented on the application of surface-enhanced infrared absorption (SEIRA) spectroscopy to biochemical problems. Use of SEIRA results in high surface sensitivity by enhancing the signal of the adsorbed molecule by approximately two orders of magnitude and has the potential to enable new studies, from fundamental aspects to applied sciences. This report surveys studies of DNA and nucleic acid adsorption to gold surfaces, development of immunoassays, electron transfer between metal electrodes and proteins, and protein–protein interactions. Because signal enhancement in SEIRA uses surface properties of the nano-structured metal, the biomaterial must be tethered to the metal without hampering its functionality. Because many biochemical reactions proceed vectorially, their functionality depends on proper orientation of the biomaterial. Thus, surface-modification techniques are addressed that enable control of the proper orientation of proteins on the metal surface. Figure Surface enhanced infrared absorption spectroscopy (SEIRAS) on the studies of tethered protein monolayer (cytochrome c oxidase and cytochrome c) on gold substrate (left), and its potential induced surface enhanced infrared difference absorption (SEIDA) spectrum     

Enhanced sensitivity of self-assembled-monolayer-based SPR immunosensor for detection of benzaldehyde using a single-step multi-sandwich immunoassay

This paper describes the fabrication and sensing characteristics of a self-assembled monolayer (SAM)-based surface plasmon resonance (SPR) immunosensor for detection of benzaldehyde (BZ). The functional sensing surface was fabricated by the immobilization of a benzaldehyde–ovalbumin conjugate (BZ–OVA) on Au-thiolate SAMs containing carboxyl end groups. Covalent binding of BZ–OVA on SAM was found to be dependent on the composition of the base SAM, and it is improved very much with the use of a mixed monolayer strategy. Based on SPR angle measurements, the functional sensor surface is established as a compact monolayer of BZ–OVA bound on the mixed SAM. The BZ–OVA-bound sensor surface undergoes immunoaffinity binding with anti-benzaldehyde antibody (BZ-Ab) selectively. An indirect inhibition immunoassay principle has been applied, in which analyte benzaldehyde solution was incubated with an optimal concentration of BZ-Ab for 5 min and injected over the sensor chip. Analyte benzaldehyde undergoes immunoreaction with BZ-Ab and makes it inactive for binding to BZ–OVA on the sensor chip. As a result, the SPR angle response decreases with an increase in the concentration of benzaldehyde. The fabricated immunosensor demonstrates a low detection limit (LDL) of 50 ppt (pg mL⁻¹) with a response time of 5 min. Antibodies bound to the sensor chip during an immunoassay could be detached by a brief exposure to acidic pepsin. With this surface regeneration, reusability of the same sensor chip for as many as 30 determination cycles has been established. Sensitivity has been enhanced further with the application of an additional single-step multi-sandwich immunoassay step, in which the BZ-Ab bound to the sensor chip was treated with a mixture of biotin-labeled secondary antibody, streptavidin and biotin–bovine serum albumin (Bio–BSA) conjugate. With this approach, the SPR sensor signal increased by ca. 12 times and the low detection limit improved to 5 ppt with a total response time of no more than ca. 10 min. Figure A single-step multi-sandwich immunoassay step increases SPR sensor signal by ca. 12 times affording a low detection limit for benzaldehyde of 5 ppt