Langmuir and Langmuir‐Blodgett Asphaltene Films at Heptane‐water Interface

Monolayer characteristics of subfractions and unfractionated whole asphaltenes from Athabasca oil sands bitumen were studied at heptane‐water interface. The transferred Langmuir‐Blodgett films of asphaltenes were characterised with atomic force microscopy and contact angle measurements. Monolayers prepared from the three asphaltene samples are found to behave similarly at heptane‐water interface. The high molecular weight asphaltene monolayer is the most expanded one whereas the low molecular weight asphaltene monolayer is the most condensed one. An asphaltene monolayer behaves differently at an airwater interface to a heptane‐water interface. The presence of the bulk heptane phase renders the interfacial asphaltene monolayer more flexible as compared to that at air‐water interface.     

Hierarchical structures of dendritic polymers

Dendritic polymers' highly specific and three‐dimensional architectures set them apart from linear and slightly branched polymers. Their unique properties also allow them to form hierarchical organizations, which can be classified as planar or non‐planar. The preparation of a planar hierarchy consisting of dendritic polymers can be achieved by conventional techniques of adsorption or Langmuir monolayer and Langmuir–Blodgett accumulation, and the resultant hierarchy is well ordered. Non‐planar hierarchies are built on non‐planar scaffolds, for example by self‐assembly. In this mini‐review, the practical/potential applications of dendritic polymers such as for electrical or optical devices, sensing systems, or medical diagnosis are also reviewed in association with their structures. Copyright © 2009 Society of Chemical Industry     

Mapping the structure-activity relationship of β-sitosteryl fatty acid esters in condensing phospholipid monolayers

The phase behavior of twelve synthesized β-sitosteryl fatty acid esters with acyl moieties with different chain lengths (C2:0-C18:0) and different degrees of unsaturation (C18:1-C18:3) were investigated in pure and mixed Langmuir monolayers with phospholipids. The surface-pressure isotherms showed that short chain β-sitosteryl fatty acid esters gave smaller mean molecular areas and had decreased monolayer stability and the long chain steryl esters did not produce collapsed plateaus. All the steryl esters displayed strong condensing effects, but there was a pronounced structural dependency: medium chain esters (C8 and C10) were less efficient than short and long chain esters. Atomic force microscopy imaging demonstrated that monolayers mixed with dipalmitoyl phosphatidylcholine (DPPC) displayed both DPPC-rich and steryl lipid-rich domains. However, the height and area differences between the two phases and the roughness and morphologic patterns were very dependent on the steryl lipid concentrations as well as the length, the degree of unsaturation and the molecular conformations of the acyl segments. These findings not only provide a better understanding of the interactions between phytosteryl hydrophobic derivatives and biomembranes, but also may be of general use for the design and engineering of phytosterol structural derivations for specific food and pharmaceutical applications.     

Langmuir and Langmuir–Blodgett films of low‐bandgap polymers

Low‐bandgap conjugated polymers have provided a considerable increase in organic photovoltaic efficiencies, however, an understanding of class‐specific nanostructures, necessary to further improve device qualities, remains scarce. Their self‐assembly and associated electronic behaviors in Langmuir?Blodgett (LB) films are used here to provide relationships specific to each polymer, clarifying their structure?property characteristics. The behavior of two low‐bandgap polymers based on cyclopentadithiophene (PCPDTBT) and dithienosilole (Si‐PCPDTBT) units in the Langmuir trough were investigated and it is shown that it is possible to fabricate nanostructured films of low‐bandgap polymers on solid substrates with the LB deposition technique. The polymers were mixed with amphiphilic molecules at well‐defined concentrations to improve the formation of the LB films. The polymers were also deposited by drop‐casting and LB techniques onto interdigitated electrodes to evaluate their electrical properties, and the LB films were characterized for their optical and morphological properties. It was found that both LB and drop‐cast films of PCPDTBT showed higher electrical conductivities than those of Si‐PCPDTBT. Importantly, LB films resulted in higher electrical conductivities – by an order of magnitude ? compared to their equivalent mixtures with stearic acid in drop‐cast films, although drop‐cast films without stearic acid gave higher conductivities. This fine‐tuning of the molecular architectures of the films is thus demonstrated to directly affect the physical properties and may lead to an improvement in device efficiencies in future applications. © 2018 Society of Chemical Industry     

Crystallographic order and decomposition of [MnIII6CrIII]3+ single-molecule magnets deposited in submonolayers and monolayers on HOPG studied by means of molecular resolved atomic force microscopy (AFM) and Kelvin probe force microscopy in UHV

Monolayers and submonolayers of [Mn ^III ₆ Cr ^III ] ³⁺ single-molecule magnets (SMMs) adsorbed on highly oriented pyrolytic graphite (HOPG) using the droplet technique characterized by non-contact atomic force microscopy (nc-AFM) as well as by Kelvin probe force microscopy (KPFM) show island-like structures with heights resembling the height of the molecule. Furthermore, islands were found which revealed ordered 1D as well as 2D structures with periods close to the width of the SMMs. Along this, islands which show half the heights of intact SMMs were observed which are evidences for a decomposing process of the molecules during the preparation. Finally, models for the structure of the ordered SMM adsorbates are proposed to explain the observations.     

Polymerization kinetics of 10,12-pentacosadiynoic acid monolayer and possible acceleration effect of visible light

The molecular area change of 10,12-pentacosadiynoic acid (PDA) monolayer was recorded and large molecular area expansion was observed during UV-polymerization. The expansion speed experienced a quick increase to maximum and then a steady decrease to zero and finally the area change was converted into a slow contraction. The rate of molecular area change depended on the reaction temperature. Turning off the UV-light during the experiments resulted in area contraction. The contraction speed was described with a kinetic equation, which suggested an accompanied area relaxation during the polymerization. A model for the reaction kinetics (both based on the polymerization and the area relaxation) was proposed and well corresponded to the experimental data. By using this model, the ‘activation area’ was calculated to be 0.127 nm² which was little dependence of the reaction temperature. The positive activation area during the monolayer polymerization indicated that there was an increase in area when the activated complex was formed. The rate constant decreased upon elevated surface pressure. The possible effect of visible-light on the monolayer UV-polymerization was investigated in detail by periodically switching on and off the visible light while keeping the UV-light on. An acceleration phenomenon of the visible light on the monolayer UV-polymerization was observed. The acceleration effect was illustrated by the polymerization mechanism and the electronic state of the polymerization intermediates.     

Effect of ethanol on monoglyceride monolayers at the air-aqueous phase interface

We have studied the behavior of monopalmitin and monoolein monolayers, spread at the air-aqueous phase interface, as a function of temperature and surface pressure. The subphases were aqueous ethanol solutions at 0.5 and 1 mol/L. The structural characteristics of these films at interface were deduced from the π-A isotherms, as measured with an automated Langmuir-type film balance. The monolayer structure and stability were functions of hydrocarbon chain length and the presence of a double bond. Generally, the factors that decreased monolayer stability produced transformations toward configurations with more expanded structures. Changes in the subphase composition had a direct influence on the monolayer molecular structure. This study showed the existence of interactions between film and ethanol molecules at the interface. As a consequence of these interactions, a contraction in the monolayer structure was observed. The magnitude of interactions between monoglyceride and ethanol molecules at the interface depends on the surface pressure, temperature, and surface composition. Stronger film-substrate interactions produced changes in monolayer stability. Relationships between film elasticity and structural characteristics are also discussed.     

金属表面烷基硫醇类自组装膜的研究进展

自组装膜(SAMs)是活性分子通过化学键自发吸附在基底上的有序分子膜,由于其排列紧密、结构稳定,因此对基底金属具有良好的防腐蚀作用.本文综述了近年来烷基硫醇类自组装膜在金、铜、铁和其他金属表面缓蚀中的发展和现状.     

Determination of iodine value of palm oil based on triglyceride composition

The triglyceride (TG) composition of palm oil is normally determined by high-performance liquid chromatography (HPLC). The HPLC chromatograms indicated a good separation of most of the TG components in the oil. The TG can be classified based on either the TG groups, i.e., triunsaturated, monosaturated, disaturated, or trisaturated, or the number of double bonds, i.e., zero, one, two, three, or four double bonds. The more unsaturated the fatty acid, the greater the iodine value (IV). Therefore, it is hypothesized that the IV of an oil can be determined based upon the TG composition of the oil. Based on the TG groups, stepwise regression analysis showed that the areas of the disaturated, trisaturated, and triunsaturated TG peaks could predict the IV with a coefficient of determination (R ²) of 0.990. The regression based on the number of double bonds yielded a good regression equation with R ²=0.992. The important variables were the peak area of the fatty acids that contained zero, one, two, and three double bonds. This study concludes that the TG composition can be used to predict the IV of palm oil. The best prediction model is obtained by using the number of double bonds in the TG as the independent variable.     

Electroreduction of laccase covalently bound to organothiol monolayers on gold electrodes

Cerrena unicolor laccase was immobilized on the gold electrode by covalent bonding to self-assembled monolayers of mercaptoundecanoic or mercaptopropionic acids. STM images of immobilized laccase proved high population of the laccase molecules on the monolayer modified electrode. The SERS experiments in concert with resonance Raman effect confirmed that the structure at the “blue” copper site of the immobilized protein remained intact. The accessibility of individual copper sites for electron exchange with the gold electrode surface was investigated by voltammetry. The electrode behavior of laccase is different in the presence and absence of oxygen, showing that the immobilized enzyme is reactive towards oxygen. Addition of two common mediators improved the electrical connectivity of the enzyme with the electrode, increased the catalytic efficiency of immobilized laccase and switched the onset of catalytic current to the potentials of the mediator. Immobilization of laccase on well-organized mercaptoundecanoic acid separates efficiently the enzyme from the electrode and does not allow easy access of mediators to the surface. Attachment of the enzyme at smaller distance from the electrode by means of significantly shorter spacer molecule—mercaptopropionic acid improved the efficiency of catalytic reduction of oxygen on the monolayer modified electrode.     

Diffuse-reflectance Fourier-transform infrared spectroscopy of vegetable oil triglyceride adsorption on silicic acid

The adsorption of triglyceride by silicic acid from hexane miscellas was observed with diffuse-reflectance Fouriertransform infrared spectroscopy. Triglyceride was adsorbed by hydrogen bonding to silanol groups through the ester carbonyl group. Addition of isopropanol (IPA) to the triglyceride-hexane solution prior to adsorption resulted in unchanged triglyceride adsorption on silicic acid despite IPA's ability to adsorb on silicic acid and hydrogen-bond with triglyceride. Washing the triglyceride, adsorbed on silicic acid, with hexane containing IPA resulted in partial desorption of the triglyceride and a small amount of IPA being adsorbed. Triglyceride desorption into fresh hexane-IPA is due to the establishment of a new equilibrium of lipid and IPA between hexane and silicic acid. The relative strengths of all the possible pairwise interactions among triglyceride, IPA and silicic acid are revealed by the relative amounts of adsorption under various conditions.     

Electrochemical studies of self-assembled monolayers using impedance spectroscopy

Self-assembled monolayers (SAMs) using various organic molecules were constructed on thin thermal silicon dioxide on silicon structures. These structures have potential bio-applications. The monolayers are part of a capacitor sensor based on the electrolyte-insulator-silicon (EIS) structure. The main goal of this work is to investigate the ability of SAMs for acting as an intermediate layer between aqueous solutions and silicon based biosensors. This work presents monolayers based on trimethoxy silanes with various functional groups such as: (a) (3-aminopropyl)-trimethoxysilane, (b) octadecyltrimethoxysilane and (c) trimethoxy(3,3,3-trifluoropropyl)silane. The biosensor is a differential sensor with a built in reference based on the structure of electrolyte-insulator-silicon or in ion-sensitive-field-effect-transistors (ISFETs). While the methyl and fluorine groups can act as the reference part, which is passive to the bio-molecules detection, the capacitor containing the amine groups has the sensing capabilities to the biological molecules. The amine (NH₂) tail groups can be active for those attachments via glutaraldehyde.The film's study and characterization was made by spectroscopic ellipsometry, contact angle method (CA) and FT-IR spectroscopy. The electrical methods such as capacitance-voltage (C-V) and electrochemical impedance spectroscopy (IS) were used to investigate the whole electrolyte/SAM/SiO₂/Si structure. We will show the detection capabilities of these 2D structures, its electrical equivalent model through a simulation fitting and will discuss the application of those structures to bio-sensitive metal/oxide/silicon (MOS) devices.     

Nucleation kinetics of emulsified triglyceride mixtures

The purpose of this study is to determine character istic nucleation parameters such as the surface free energy for nucleus formation in mixtures of fully hydrogenated palm oil (HP) in sunflower oil (SF). These parameters will be used to model the bulk crystallization kinetics of the same mixtures. This was achieved by determining the crystallization kinetics in emulsified triglyceride mixtures using differential scanning calorimetry, proton nuclear magnetic resonance, and ultrasound velocity measurements. The latter technique appeared to be very sensitive for monitoring the crystallization kinetics of fat dispersions containing triglycerides with a simple phase behavior. Isothermal crystallization of emulsified HP stabilized by sodium caseinate started at 7 K below the α clear point, and the kinetics were best fitted assuming heterogeneous nucleation. Isothermal crystallization of emulsified 10% HP in SF stabilized by caseinate started at 14 K below the α melting point, and the kinetics were best fitted assuming homogeneous nucleation. If the same dispersion was stabilized by Tween 20, crystallization started at 11 K below the α melting point, and the kinetics were fitted best using heterogeneous nucleation. Analysis of the temperature dependency of the fit parameters yielded a surface free energy of a nucleus of about 4 mJ.m⁻² in the case of homogeneous nucleation. Pre-exponential nucleation frequencies indicated that a large proportion of the triglyceride molecule should be in the right conformation to be incorporated in a nucleus.     

Characteristics of Polypeptide/Phospholipid Monolayers on Water and the Plasma-Activated Polyetheretherketone Support

Polyetheretherketone (PEEK) is a highly biocompatible polymer widely used in medicine as an implant production material. In this article, the PEEK surface was characterized in terms of its wettabillity properties after the physicochemical modifications by treatment with the low-temperature air plasma and covering with the Langmuir–Blodgett (LB) monolayers of polypeptide (cyclosporine A, CsA) and/or phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine, DPPC). The LB deposition was preceded by the analysis of miscibility and morphology of monolayers at the air/water interface by means of the Langmuir technique and Brewster angle microscopy (BAM). Then, wettability of the polymer-supported films was evaluated by the contact angle measurements of three probe liquids of different characters (two polar—water and formamide, one apolar—diiodomethane). The measured contact angles allowed for determination of the surface free energy and its components based on the Lifshitz-van der Waals/acid–base (LWAB) approach. Some relations between the kind and magnitude of interactions within the model membranes on the water subphase and those of the PEEK-supported membranes with the liquids were found out. The results allowed obtaining the interesting models of biological coatings with potential applications.     

Seasonal and regional variation in triglyceride composition of French butterfat

In the present study, high-performance liquid chromatography analysis of butterfat allowed separation of 46 peaks at 32°C. Knowing the theoretical carbon number value of each triglyceride (TG), 32 peaks of the butterfat chromatogram were identified. These TGs were determined by extrapolation of their capacity factor values, and their identifications were confirmed with some standard TGs. Analysis of winter and summer butterfat from five different French areas showed significant seasonal and regional variation in the TG composition. However, the most important contribution to this variation was provided by TG groups represented by only four peaks. To approximately select the predominant TGs in these four peaks, a random distribution hypothesis was used to predict the amount of each TG. This hypothesis allowed the prediction of the TG components that seem to provide the most important contribution to both seasonal and regional variation.     

Selection of surfactant-modified lipases for interesterification of triglyceride and fatty acid

Interesterification of tripalmitin and stearic acid inn-hexane was investigated with surfactant-modified lipases. Various kinds of lipases and surfactants were screened for high interesterification activity of the modified lipases. The modified-lipase hydrophile-lipophile balance value and fatty acid group of the surfactants. The modified lipase obtained fromRhizopus japonicus with sorbitan monostearate as surfactant had the highest activity in then-hexane system. The interesterification activity of the selected modified lipase in molten substrates at 75°C without solvents was the same as that in then-hexane system at 40°C.     

Low-calorie triglyceride synthesis by lipase-catalyzed esterification of monoglycerides

Monoglycerides of erucic acid (C_22:1, Δ13), prepared by conventional methods, were reacted with caprylic acid (octanoic acid, C_8.0) by using lipases as catalysts with the intention of synthesizing a triglyceride that contains two molecules of caprylic acid and one molecule of erucic acid (caprucin). The reaction was carried out by mixing lipase powder, a small quantity of water, and the reactants in a temperature-controlled stirred batch reactor. Organic solvents or emulsifying agents were not required. When the nonspecific lipase fromPseudomonas cepacia was used, a yield of approximately 37% caprucin was obtained, together with a complex mixture of di- and triglycerides that resulted from the random transesterification of the erucic acid. The fatty acid-specific lipase fromGeotrichum candidum promoted minimal transesterification of erucic acid and resulted in a yield of 75% caprucin and approximately 10% interesterification products. Lipase fromCandida rugosa exhibited a similar, although less pronounced, specificity to that fromG. candidum and promoted more transesterification of erucic acid. Optimum conditions forG. candidum lipase were at 50°C and an initial water content of 5.5%. After the reaction, erucic acid was converted to behenic acid by hydrogenation, thereby converting caprucin into caprenin, a commercially available low-calorie triglyceride.     

Relaxation phenomena of stereoregular poly(methyl methacrylate) monolayers at the air/water interface

Relaxation behaviors of isotactic, atactic, and syndiotactic poly(methyl methacrylate) (PMMA) monolayers at the air/water interface were investigated at three different temperatures. The monolayer characteristics of the three stereoisomers were studied in terms of surface pressure–area per molecule (π‐A) isotherm, area relaxation, and pressure relaxation. The results show that pressures at inflection points of π‐A isotherms of PMMA decrease with an increase in temperature. The collapse pressure also decreases as the temperature is elevated. It was shown likely for the first time that the relaxation process of PMMA stereoisomers could be described by a model considering the nucleation and growth mechanisms. The simulation parameters of area relaxation of the three stereoisomers at 30 mN/m are very similar, indicating similar mechanisms. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008