The Monolayer Behavior of Amphiphilic Polymer and Heterostructure of Polymer LB Film/CdS Clusters

In this paper we report the behavior of an amphiphilic polymer monolayer on pure water and Cd2+ subphase. This polymer was composed of hydrophilic ethylene diamine epichlorohydrin slightly crosslinked microgel and hydrophobic stearic chains, noted as ES-1. The introduction of Cd2+ ions in subphase had a marked effect on the process of the organization of the amphiphilic polymer at the air/water interface due to the association of Cd2+ ions with the hydrophilic network, which could be indicated by the pressure-area isotherms and Brewster Angle Microscopy. Ordered ES-1/Cd2+ LB multilayers were fabricated. After the multilayers reacted with H2S gas, CdS clusters were synthesized within the film, which was characterized by X-ray diffraction and UV-visible spectroscopy. Copyright 1999 Academic Press.     

In Situ Electrodeposition of an Asymmetric Sol–Gel Membrane Based on an Octadecyltrimethoxysilane Langmuir Film

The unique properties of Langmuir film formation were utilized in assembling a thin skin of an asymmetric membrane. An octadecyltrimethoxysilane (ODTMS) Langmuir monolayer was formed at the air–water interface and served as the substrate for growing a bulky sol–gel polymer in situ. The latter was based on the electrochemical deposition of tetramethoxysilane dissolved in the water subphase by means of horizontal touch electrochemistry. The resultant asymmetric layer that consisted of a thin hydrophobic ODTMS Langmuir film connected to a bulk hydrophilic sol–gel network was studied in situ and ex situ by using various techniques, such as cyclic voltammetry, electrochemical impedance spectroscopy (EIS), scanning electron microscopy, transmission electron microscopy (TEM), and goniometry. We found that a porous hydrophilic film grew on top of a hydrophobic layer as was evident from TEM, contact angle, and EIS analyses. The film thickness and film permeability could be controlled by changing the deposition conditions such as the potential window applied and its duration. Hence, this method offers an alternative approach for assembling asymmetric films for various applications     

Adsorption and orientation kinetics of self‐assembled films of octadecyltrimethoxysilane on aluminium oxide surfaces

X‐ray photoelectron spectroscopy (XPS) and near‐edge x‐ray absorption fine structure (NEXAFS) spectroscopy have been used to study the time‐dependent adsorption and molecular orientation behaviour of octadecyltrimethoxysilane (ODTMS) on native aluminium oxide surfaces. By measuring the adsorption isotherm using XPS, we show that ODTMS molecules exhibit oscillatory adsorption. The oscillatory adsorption behaviour for ODTMS is analogous to that observed for its simpler short‐chain ‘cousin’—propyltrimethoxysilane (PTMS)—and suggests that the length of the functional alkyl chain on an organosilane does not have a significant influence upon the oscillatory adsorption mechanism. The oscillation in the ODTMS adsorption isotherm shows a maximum and a minimum in coverage at an adsorption time of ～30 and ～65 s, respectively, for a 0.75% ODTMS solution in a 90% ethanol–10% water mixture at pH 4. The time‐dependent orientation behaviour of the ODTMS molecules during adsorption was examined using angular‐dependent carbon K‐edge NEXAFS spectroscopy. We show that the alignment of the ODTMS film changes systematically with deposition time and appears to be correlated with coverage measurements obtained using XPS. In particular, by combining the XPS and NEXAFS results we demonstrate that the minimum ODTMS coverage corresponds to a film whose alignment appears to be predominantly randomized. Copyright © 2005 John Wiley & Sons, Ltd.     

Surface chemistry and annealing-driven interfacial changes in organic semiconducting thin films on silica surfaces

Vibrational sum frequency generation (VSFG) spectroscopy was used in conjunction with steady-state IR spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry to characterize organic semiconductor thin films that were vapor deposited on silica- and trimethoxy(octadecyl)silane (ODTMS)-functionalized silica surfaces. The growth of perylene derivative N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C(8)) was found to proceed differently on simple glass slides relative to that of native oxide on silicon and fused quartz slides. VSFG was applied to these samples to isolate structural changes that occurred specifically at the buried interface between the organic semiconductor and the silica dielectric upon thermal annealing. A model was introduced to globally fit the imide carbonyl symmetric and asymmetric interfacial spectra that included contributions from both inner and outer interfaces. The fits to the VSFG data and AFM topographic images revealed significant reordering at the outer interface on all substrates upon thermal annealing. Within the model, the spectroscopic data reported that the inner interfacial PTCDI-C(8) monolayer reoriented to a more reclined phase on bare substrates after annealing but remained essentially unchanged on ODTMS monolayers. Electrical characterization of PTCDI-C(8) field-effect transistors indicated that electron mobilities were higher on bare substrate devices but could be improved by a factor of 2 on both surface types by thermal annealing. The mobility effects were attributed to the annealing-driven coalescence of PTCDI-C(8) grain boundaries. Consistent with previous structural reports, the molecular rearrangements of the first monolayer of PTCDI-C(8) on bare substrates that were reported by VSFG spectroscopy had a noticeable impact on the device performance.     

Time resolved resonance Raman observation of the extreme protonation forms of a radical zwitterion in water

The reactions of the aqueous proton with the zwitterionic p-aminophenoxyl radical in strongly basic to extremely acidic aqueous solutions have been investigated using time-resolved resonance Raman spectroscopy. The dynamic stability of the different protonation forms of the radical, observed on the microsecond time scale in this work, has been achieved by controlling the proton exchange rate in water. In strongly acidic solutions we observe a rare ring-H+ bonded dication species, a key intermediate in the amine hydrolysis. The neutral p-aminophenoxyl radical undergoes NH2-deprotonation in strongly basic aqueous solutions, which has no analogues in closed-shell amines.     

Hydrolysis characterization of phospholipid monolayers catalyzed by different phospholipases at the air-water interface

Combination of some newly developed microscopic and spectroscopic techniques with conventional Langmuir monolayer method can provide more quantitative information with the molecular orientation and reorganization process of spread amphiphilic molecules at the air/water interface. These techniques are extended to investigate the hydrolysis process of spreading lipid monolayer catalyzed by different enzymes, phospholipases A2, C and D, respectively. Synchrotron X-ray diffraction and infrared reflection absorption spectroscopy are able directly to give the structural information of the assembled monolayer, interfacial activity of amphiphiles and their components at the interface. Microscopic technique such as Brewster angle microscopy (BAM), fluorescence microscopy (FM) can be used to trace the morphological changes dynamically as the spreading lipid monolayer is hydrolyzed at the air/water interface. We summary here some latest progress in this filed and give a brief review over the hydrolysis features of phospholipid monolayer catalyzed by different enzymes. It is attempted to establish a model of membrane hydrolysis process in order to better understand the mechanism of membrane metabolism and signal transduction in a living system.     

Hydrolysis reaction analysis of L-alpha-distearoylphosphatidylcholine monolayer catalyzed by phospholipase A2 with polarization-modulated infrared reflection absorption spectroscopy

The hydrolysis reaction of L-alpha-distearoylphosphatidylcholine (DSPC) monolayers catalyzed by phospholipase A2 (PLA(2)) has been studied using polarization-modulated infrared reflection absorption spectroscopy (PM-IRRAS) with film balance measurements. The PM-IRRAS analysis provides quantitative information about the reaction efficiency at different surface pressures. It was found that the reaction efficiency of L-DSPC monolayer hydrolysis catalyzed by PLA(2) decreased with increasing surface pressure. At zero pressure (lift-off point), the hydrolysis reaction efficiency has the highest value of 45%. Increasing surface pressure leads to the decrease of the hydrolysis efficiency. Since the surface pressure is above 20 mN/m, the hydrolysis reaction nearly stopped. PM-IRRAS technique provides a powerful means to study the hydrolysis process catalyzed by phospholipase A2 at the air/water interface.     

Hydrolysis and grafting of dimethylalkoxysilanes onto stainless steel

The grafting of trialkoxysilane molecules should also give rise to the formation of a siloxane network at the substrate's surface when trialkoxysilanes are used. Other candidates that might be able to act as adhesion promoters at metallic surfaces are dimethylalkoxysilanes. The advantage of dimethylalkoxysilanes is that only one silanol group is produced during the hydrolysis step, leading to the formation of a grafted monolayer onto the steel. Moreover, the chemical grafting of stainless steel, which exhibits a low surface reactivity, is of great interest for industrial applications such as adhesive bonding or coatings. The objective of this work was to chemically graft dimethylalkoxysilanes onto AISI 316L stainless steel and to analyze the grafted layer by X‐ray photoelectron spectroscopy (XPS). Investigation of the hydrolysis of these molecules in aqueous solutions was also performed by proton nuclear magnetic resonance spectroscopy (¹H NMR). The grafting of 3‐(ethoxydimethylsilyl)propylamine (APDES) and 3‐glycidoxypropyldimethylethoxysilane (GPDES) was achieved onto stainless steel after a controlled hydrolysis reaction. A pH inferior or equal to 5 was necessary to obtain a sufficient hydrolysis of silanes. XPS results have evidenced the grafting of the silanes onto stainless steel. The signal of the Si 2p peak clearly showed the formation of a covalent bond between APDES and the stainless steel surface through the O atoms giving rise to a uniform layer of adsorbed molecules. Moreover, this grafted layer is strongly stable as no removal of the alkoxysilane was observed after immersion in hot water which is very critical for these molecules. Copyright © 2015 John Wiley & Sons, Ltd.     

Equilibrium study of selected divalent d-electron metals adsorption on A-type zeolite

The objective of the presented study was to investigate the adsorption of Cu, Co, Mn, Zn, Cd and Mn on A-type zeolite. The isotherms for adsorption of metals from their nitrates were registered. The following adsorption constants K of metals were found: 162,890, 124,260, 69,025, 16,035, 10,254, and 151 [M(-1)] for Cu, Co, Mn, Zn, Cd, and Ni, respectively, for the concentration range 10(-4)-10(-3) M. On the other hand, the investigation of pH influence on the distribution constants of metals showed that the adsorption of metals proceeds essentially through an ion-exchange process, surface hydrolysis, and surface complexation. The supplementary results from DRIFT, scanning electron microscopy, and X-ray diffraction methods confirmed the presumption about the possible connection between the electronic structure of divalent ions and their adsorption behavior, showing that ions with d5 and d10 configurations such as Mn2+, Zn2+, Cd2+, with much weaker hydrolytic properties than Cu2+ and Ni2+, strongly interact with the zeolite framework and therefore their affinity to the zeolite phase is much stronger when compared with that of the Ni2+ ion, but at the same time not as strong as the affinity of the Cu2+ ion, the latter forming a new phase during the interaction with zeolite framework. For Zn2+, during inspection of the correlation between the proton concentration H/Al and zinc concentration Zn/Al on the zeolite surface, the formation of the surface complex [triple bond]S-OZn(OH) was proposed. A correlation between the heterogeneity of proton concentrations H/Al on Me-zeolite surfaces and the hydrolysis constants pKh of Me2+ ions was found.     

Tailor-made functionalization of silicon nitride surfaces

This communication presents the first functionalization of a hydrogen-terminated silicon-rich silicon nitride (Si3Nx) surface with a well-defined, covalently attached organic monolayer. Properties of the resulting monolayers are monitored by measurement of the static water contact angle, X-ray photoelectron spectroscopy (XPS), and infrared reflection absorption spectroscopy (IRRAS). Further functionalization was performed by reaction of Si3Nx with a trifluoroethanol ester alkene (CH2=CH-(CH2)8CO2CH2CF3) followed by basic hydrolysis to afford the corresponding carboxylic acid-terminated monolayer with hydrophilic properties. These results show that Si3Nx can be functionalized with a tailor-made organic monolayer, has highly tunable wetting properties, and displays significant potential for further functionalization.     

Lignin from sugar cane bagasse: extraction, fabrication of nanostructured films, and application

Four lignin samples were extracted from sugar cane bagasse using four different alcohols (methanol, ethanol, n-propanol, and 1-butanol) via the organosolv-CO2 supercritical pulping process. Langmuir films were characterized by surface pressure vs mean molecular area (Pi-A) isotherms to exploit information at the molecular level carrying out stability tests, cycles of compression/expansion (hysteresis), subphase temperature variations, and metallic ions dissolved into the water subphase at different concentrations. Briefly, it was observed that these lignins are relatively stable on the water surface when compared to those obtained via different extraction processes. Besides, the Pi-A isotherms are shifted to smaller molecular areas at higher subphase temperatures and to larger molecular areas when the metallic ions are dissolved into the subphase. The results are related to the formation of stable aggregates (domains) onto the water subphase by these lignins, as shown in the Pi-A isotherms. It was found as well that the most stable lignin monolayer onto the water subphase is that extracted with 1-butanol. Homogeneous Langmuir-Blodgett (LB) films of this lignin could be produced as confirmed by UV-vis absorption spectroscopy and the cumulative transfer parameter. In addition, FTIR analysis showed that this lignin LB film is structured in a way that the phenyl groups are organized preferentially parallel to the substrate surface. Further, these LB films were deposited onto gold interdigitated electrodes and ITO and applied in studies involving the detection of Cd+2 ions in aqueous solutions at low concentration levels through impedance spectroscopy and electrochemical measurements. FTIR spectroscopy was carried out before and after soaking the thin films into Cd+2 aqueous solutions, revealing a possible physical interaction between the lignin phenyl groups and the heavy metal ions. The importance of using nanostructured systems is demonstrated as well by comparing both LB and cast films.     

光催化微反应器中水样光催化降解及Cd2+在线检测

本文以粉末法制备TiO₂涂层的玻璃微流控芯片作为光催化反应器,采用UV-LED点光源为紫外光源,实现了水样中EDTA的光催化降解,并用铋膜电极差分脉冲溶出伏安法在线检测微量水样中的重金属离子Cd²⁺。水样中的Cd²⁺由于EDTA的络合作用无法在铋膜电极上产生电流信号,而当水样在光催化微反应器中经紫外光催化后,由于EDTA与Cd²⁺的配合物结构遭破坏,因此释放出游离的Cd²⁺,从而使Cd²⁺的电流信号得到一定程度的恢复。Cd²⁺的电流恢复程度越大,表明EDTA被光催化降解的程度越高。本文考察了光照强度、反应液流速和氧气流速、pH等因素对EDTA光催化降解效率的影响。在光照强度为120 mW/cm²、反应液流速为50 μL/h、氧气流速为850 μL/h、pH为4.4条件下,水样中EDTA的光催化降解率效果最佳,水样中Cd²⁺的电流恢复程度可达92.6%。反应液流速为300 μL/h时,Cd²⁺的电流恢复率为60.0%,重复光催化反应5次的RSD为5.2%,具有较好的重现性。本文建立了水样EDTA光催化降解及Cd²⁺在线检测的微分析系统,在线检测所需的样品体积仅为0.3 mL,完成一个水样分析的时间约为60 min。     

In situ sensing of metal ion adsorption to a thiolated surface using surface plasmon resonance spectroscopy

The kinetics of the adsorption of metal ions onto a thiolated surface and the selective and quantitative sensing of metal ions were explored using surface plasmon resonance (SPR) spectroscopy. The target metal ion was an aqueous solution of Pt2+ and a thin-gold-film-coated glass substrate was modified with 1,6-hexanedithiol (HDT) as a selective sensing layer. SPR spectroscopy was used to examine the kinetics of metal ion adsorption by means of the change in SPR angle. The selectivity of the thiolated surface for Pt2+ over other divalent metal ions such as Cu2+, Ni2+, and Cd2+ was evident by the time-resolved SPR measurement. SPR angle shift, deltatheta(SPR), was found to increase logarithmically with increasing concentration of Pt2+ in the range of 1.0 x 10(-5)-1.0 mM. The rate of Pt2+ adsorption on HDT observed at both 0.1 and 1 mM Pt2+ accelerates until the surface coverage reaches approximately 17%, after which the adsorption profile follows Langmuirian behavior with the surface coverage. The experimental data indicated that heavy metal ions were adsorbed to the hydrophobic thiolated surface by a cooperative mechanism. A mixed self-assembled monolayer (SAM) composed of HDT and 11-mercaptoundecanoic acid was used to reduce the hydrophobicity of the thiol-functionalized surface. The addition of hydrophilic groups to the surface enhanced the rate of adsorption of Pt2+ onto the surface. The findings show that the adsorption of metal ions is strongly dependent upon the hydrophilicity/hydrophobicity of the surface and that the technique represents an easy method for analyzing the adsorption of metal ions to a functionalized surface by combining SPR spectroscopy with a SAM modification.     

以铜离子为模板的褐藻酸凝胶对铜离子的选择性富集研究

以铜离子为模板，制备了褐藻酸凝胶（Cu-alginate)，通过吸附实验及过柱渗滤实验，试验了该吸附剂对铜离子的选择性吸附性能，并且采用该吸附剂富集了自来水中微量的Cu^2 ，结合原子吸收法测定了水样中Cu^2 的含量。结果表明：该吸附剂对Cu^2 有较高的选择性吸附性能，显著优于一些化学合成铜离子模板缩聚物及非铜模板褐藻酸凝胶（如Ca-alginate),非重金属离子（如K^ 、Na^ 、Ca^2 ）及某些重金属离子（如Ni^2 、Cd^2 ）等对Cu^2 的吸附均不产生明显干扰。用该吸附剂富集水中的微量铜离子，回收率可达97.7%。     

Proximity effects in monolayer films: kinetic analysis of amide bond formation at the air-water interface using (1)H NMR spectroscopy

The kinetics of amide bond formation in a monolayer film has been studied by proton NMR spectroscopy. Compression of a hexadecyl thioester of N-acetyl glycine (1) and a hexadecyl amide of glycine (2) at the air-water interface produces a single dipeptide product (4) that remains at the surface once formed. Extraction of the reaction mixture from the interface, followed by (1)H NMR spectroscopy, provides quantitative data on the rate of product formation. The kinetics of this reaction was examined as a function of surface pressure, subphase pH, and temperature. The monolayer provides an effective molarity for the reaction of approximately 500 M as compared to the bimolecular reaction of 1 and 4 in chloroform solution. The first-order rate constant for the reaction of 1 and 2 in the monolayer is less than 70-fold slower than k(cat) for condensation of the first amide bond in the enzymatic synthesis of the cyclic antibiotic gramicidin S by gramicidin S synthetase. Activation energies of the reaction were extracted from the temperature dependence of the rate constants of the reaction and are 9.9 +/- 1.0 and 2.1 +/- 0.2 kcal/mol for the chloroform solution and monolayer reactions, respectively. The pK(a) of 2 in the monolayer was estimated to be approximately 0.5 pK(a) units lower than that of related amines in solution. The lower pK(a) at the interface as compared to that in solution may be ascribed to increased electrostatic repulsion at the interface relative to solution. The rate of reaction in the monolayer was also followed by monitoring changes in surface area as a function of time. The rate constant for the reaction of 1 and 4 as determined by changes in surface area differs significantly from the rate determined by NMR. The results indicate that measurements of surface area versus time may yield erroneous rate constants for reactions in monolayers.     

Hydrolysis of cephanone in the micelles with different charges

The hydrolysis of cephanone in water and micelles with different charges was studied by UV-vis absorption spectroscopy. The change of pH with the hydrolysis of cephanone was determined. The mechanism of the hydrolysis and the effect of the acidity of the media on the hydrolysis were studied. The results show that the hydrolysis rate of cephanone increases with the acidity. Compared with water, SDS micelles accelerate this hydrolysis, whereas CTAB and Triton X-100 micelles suppress it. The effects of the micelles with different charges on the hydrolysis are explained by the proton concentration of the micro-environment where cephanone exists and by the charge density of the polar group of the cephanone molecules.     

Fluxional behavior of a cadmium zwitterion complex: proton transport and tautomerism in methylene chloride solution

The synthesis and structure of the tautomeric Cd(II) isoindoline zwitterion coordination compound [Cd(4'-MeLH)(NO(3))(2)].CH(3)OH (4'-MeLH = 1,3-bis[2-(4-methylpyridyl)imino]isoindoline) are reported. In methylene chloride solution, tautomer interconversion occurs as the N-H proton moves between the identical imine nitrogen atoms. We report the kinetics of proton transfer as followed by variable temperature (1)H NMR spectroscopy and demonstrate that methanol of solvation and adventitious water facilitate rapid proton transfer.     

Wetting of mixed OHH(2)O layers on Pt(111)

We describe the effect of growth temperature and OHH(2)O composition on the wetting behavior of Pt(111). Changes to the desorption rate of ice films were measured and correlated to the film morphology using low energy electron diffraction and thermal desorption of chloroform to measure the area of multilayer ice and monolayer OHH(2)O exposed. Thin ice films roughen, forming bare (radical39 x radical39)R16 degrees water monolayer and ice clusters. The size of the clusters depends on growth temperature and determines their kinetic stability, with the desorption rate decreasing when larger clusters are formed by growth at high temperature. Continuous films of more than approximately 50 layers thick stabilize an ordered incommensurate ice film that does not dewet. OH coadsorption pins the first layer into registry with Pt, forming an ordered hexagonal (OH+H(2)O) structure with all the H atoms involved in hydrogen bonding. Although this layer has a similar honeycomb OH(x) skeleton to ice Ih, it is unable to reconstruct to match the bulk ice lattice parameter and does not form a stable wetting layer. Water aggregates to expose bare monolayer (OH+H(2)O), forming bulk ice crystallites whose size depend on preparation temperature. Increasing the proportion of water in the first layer provides free OH groups which stabilize the multilayer. The factors influencing multilayer wetting are discussed using density functional theory calculations to compare water adsorption on top of (OH+H(2)O) and on simple models for commensurate water structures. We show that both the (OH+H(2)O) structure and "H-down" water layers are poor proton acceptors, bonding to the first layer being enhanced by the presence of free OH groups. Formation of an ordered ice multilayer requires a water-metal interaction sufficient to wet the surface, but not so strong as to prevent the first layer relaxing to stabilize the interface between the metal and bulk ice.     

Changes in Coordination Number of Co Ion and Fluorescence Spectrum of 1-Naphthol during the Sol-Gel Reaction of TEOS

Changes in coordination number of Co²⁺ and fluorescence spectra of 1-naphthol during the sol-gel transitions of TEOS have been investigated as a function of time. The change in the coordination number of Co²⁺ has been observed as follows. Six-coordinated Co²⁺ decreased quickly within several hours in the first stage of the reaction corresponding to water consumption by initial hydrolysis reaction. Then six-coordinated Co²⁺ increased around gelation due to polycondensation. After the gelation four-coordinated Co²⁺ increased, where isomorphous-replacement of Co²⁺ into the –O–Si–O– networks occurred. In the Co²⁺/1-naphthol mixed system, separate ion pair of 1-naphthol is preferentially coordinated on the six-coordinated Co²⁺ where water molecule(s) plays an important role to geometrical relaxation of excited-state 1-naphthol.     

Dynamics of mononuclear cadmium beta-lactamase revealed by the combination of NMR and PAC spectroscopy

The two metal sites in cadmium substituted beta-lactamase from Bacillus cereus 569/H/9 have been studied by NMR spectroscopy ((1)H, (15)N, and (113)Cd) and PAC spectroscopy ((111m)Cd). Distinct NMR signals from the backbone amides are identified for the apoenzyme and the mononuclear and binuclear cadmium enzymes. For the binuclear cadmium enzyme, two (113)Cd NMR signals (142 and 262 ppm) and two (111m)Cd PAC nuclear quadrupole interactions are observed. Two nuclear quadrupole interactions are also observed, with approximately equal occupancy, in the PAC spectra at cadmium/enzyme ratios < 1; these are different from those derived for the binuclear cadmium enzyme, demonstrating interaction between the two metal ion binding sites. In contrast to the observation from PAC spectroscopy, only one (113)Cd NMR signal (176 ppm) is observed at cadmium/enzyme ratios < 1. The titration of the metal site imidazole (N)H proton signals as a function of cadmium ion-to-enzyme ratio shows that signals characteristic for the binuclear cadmium enzyme appear when the cadmium ion-to-enzyme ratio is between 1 and 2, whereas no signals are observed at stoichiometries less than 1. The simplest explanation consistent with all data is that, at cadmium/enzyme ratios < 1, the single Cd(II) is undergoing exchange between the two metal sites on the enzyme. This exchange must be fast on the (113)Cd NMR time scale and slow on the (111m)Cd PAC time scale and must thus occur in a time regime between 0.1 and 10 micros.