Preparation, characterization, and chemical stability of gold nanoparticles coated with mono-, bis-, and tris-chelating alkanethiols

A systematically varying series of monolayer-protected clusters (MPCs) was prepared by exposing small gold nanoparticles ( approximately 2 nm in diameter) to the following four adsorbates: n-octadecanethiol ( n - C18), 2-hexadecylpropane-1,3-dithiol ( C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol ( C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane ( t - C18). The resultant MPCs were characterized by solubility studies, UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). All of the MPCs were soluble in common organic solvents; moreover, analysis by TEM showed that the core dimensions were unaffected by exposure to any of the adsorbates. Separate studies by XPS revealed that the sulfur atoms in all MPCs were predominantly bound to the surface of gold (i.e., approximately 85% or better). Analysis by FT-IR showed that MPCs functionalized with n - C18 possessed alkyl chains having the greatest conformational order in both the solid-state and dispersed in solution; in contrast, those generated from the other three adsorbates were more liquid-like with reduced conformational order (or crystallinity). The rate of nanoparticle decomposition induced by cyanide ions was monitored by UV-vis spectroscopy. While MPCs functionalized with n - C18 showed the fastest rate of decomposition, those functionalized with C18C3 were the most resistant to decomposition. Overall, the following trend in chemical stability was observed, C18C3 > C18C2 > t - C18 > n - C18.     

Influence of alkyl chain length on phosphate self-assembled monolayers

A series of alkyl phosphates with alkyl chain lengths ranging from C10 to C18 have been synthesized. Self-assembled monolayers (SAMs) of these molecules were prepared on titanium oxide surfaces by immersion of the substrates in alkyl phosphate solutions of 0.5 mM concentration in n-heptane/isopropanol. The SAMs were characterized by means of dynamic water contact angle (dCA) measurements, variable-angle spectroscopic ellipsometry (VASE), X-ray photoelectron spectroscopy (XPS), and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). A higher degree of order and packing density within the monolayers was found for alkyl phosphates with alkyl chain lengths exceeding 15 carbon atoms. This is reflected in a lower dCA hysteresis, as well as a film thickness measured by VASE and XPS close to the expected values for SAMs with an average alkyl chain tilt angle of 30 degrees to the surface normal. Additionally a shift of the symmetric and antisymmetric C-H stretching modes in the PM-IRRAS spectra to lower wave numbers was observed. These findings imply a higher two-dimensional crystallinity of the films derived from alkyl phosphates with a longer alkyl chain length.     

溶胶-凝胶法制备C18固相微萃取头及其在有机氯农药残留检测中的应用

以十八烷基三乙氧基硅烷(C18-TEOS)、四乙氧基硅烷(TEOS)、乙醇、盐和水酸为原料,采用溶胶-凝胶法制备了十八烷基(C18)固相微萃取头,利用所制备萃取头实现了水样中11种有机氯农药的检测。在优化条件下,使用该萃取头对有机氯农药(OCPs)萃取后用气相色谱/电子捕获检测器(GC/ECD)测定,检出限为0.01～0.24μg/L,相对标准偏差为3.0%～13.3%。该方法用于鱼塘水、湖水及自来水中OCPs的检测,结果满意。所制备的萃取头在不同溶剂中浸泡后,对有机氯农药的萃取性能无明显变化。使用50次后,C18萃取头的萃取性能未变化。结果表明,所制备的C18固相微萃取头涂层均匀,具有多孔结构,稳定性高,有很好的实用价值。     

含酰胺结构的巯基自组装膜的设计与结构表征

提出了一种简便通用的合成巯基化合物的途径，以分子中的羧基CO2H为起始基团，与2-流基乙胺的氨基选择性缩合；合成了一系列具有RC（O）NHCH2CH2SH（R分别为偶氯苯衍生物，双炔衍生物及直链烷基）结构的化合物，并用接触角测量，电化学和掠角反射红外光谱（GIR-IR）等手段对这些化合物在金表面形成的自组装单分子膜进行了表征。发现4-（N－（2‘-巯基已基））酰胺偶氮苯的自组装膜表现出良好的电活性，电化学测定表面浓度为4．21×10(－10)mol·cm(-2)．当R为烷基链时，随烷基链的增长，膜的致密度与有序度增加GIR-IR证明在自组装腹中CH3（CH2）6C（O）NHCH2CH2SH的C＝O和N－H键与Au表面平行，分子轴线与Au表面近似垂直．     

Molecular architecture: construction of self-assembled organophosphonate duplexes and their electrochemical characterization

Self-assembled monolayers of phosphonates (SAMPs) of 11-hydroxyundecylphosphonic acid, 2,6-diphosphonoanthracene, 9,10-diphenyl-2,6-diphosphonoanthracene, and 10,10'-diphosphono-9,9'-bianthracene and a novel self-assembled organophosphonate duplex ensemble were synthesized on nanometer-thick SiO(2)-coated, highly doped silicon electrodes. The duplex ensemble was synthesized by first treating the SAMP prepared from an aromatic diphosphonic acid to form a titanium complex-terminated one; this was followed by addition of a second equivalent of the aromatic diphosphonic acid. SAMP homogeneity, roughness, and thickness were evaluated by AFM; SAMP film thickness and the structural contributions of each unit in the duplex were measured by X-ray reflection (XRR). The duplex was compared with the aliphatic and aromatic monolayer SAMPs to determine the effect of stacking on electrochemical properties; these were measured by impedance spectroscopy using aqueous electrolytes in the frequency range 20 Hz to 100 kHz, and data were analyzed using resistance-capacitance network based equivalent circuits. For the 11-hydroxyundecylphosphonate SAMP, C(SAMP) = 2.6 ± 0.2 μF/cm(2), consistent with its measured layer thickness (ca. 1.1 nm). For the anthracene-based SAMPs, C(SAMP) = 6-10 μF/cm(2), which is attributed primarily to a higher effective dielectric constant for the aromatic moieties (ε = 5-10) compared to the aliphatic one; impedance spectroscopy measured the additional capacitance of the second aromatic monolayer in the duplex (2ndSAMP) to be C(Ti/2ndSAMP) = 6.8 ± 0.7 μF/cm(2), in series with the first.     

Structural effects on the barrier properties of self-assembled monolayers formed from long-chain omega-alkoxy-n-alkanethiols on copper

The adsorption of long-chain omega-alkoxy-n-alkanethiols [CH(3)(CH(2))(p-1)O(CH(2))(m)SH; m = 11, 19, 22; p = 18, 22] onto copper produces self-assembled monolayers (SAMs) that can provide protection against corrosion of the underlying metal substrate. The resulting films are 40-60 A in thickness and are isostructural with SAMs formed on copper from unsubstituted n-alkanethiols. As evidenced by electrochemical impedance spectroscopy (EIS), the barrier properties of these ether-containing SAMs depend on the chain length of the adsorbate and the position of the ethereal unit along the hydrocarbon chain. For SAMs where the ether substitution is farther from the copper surface, the initial coating resistances are similar to those projected for unsubstituted n-alkanethiolate SAMs of similar thickness. For SAMs where the ether substitution is nearer to the copper surface (m = 11), the resistances are significantly less than those for unsubstituted n-alkanethiolate SAMs of similar thickness, reflecting the effect of the molecular structure on the barrier properties of the film. Upon exposure to 1 atm of O(2) at 100% RH, the SAMs become less densely packed as observed by infrared (IR) spectroscopy, and their barrier properties deteriorate as observed by EIS. The rate that the SAMs lose their barrier properties upon exposure to oxidizing conditions is correlated to the strength of intermolecular interactions within the bulk state of the adsorbate.     

Characterization and Wettability of ZnO Film Prepared by Chemical Etching Method

ZnO thin films were prepared by a chemical etching method and their wettability was investigated. The structure and surface composition structure were characterized by means of scanning electron microscopy, X-ray photoelectronic spectrometry(XPS), X-ray diffraction(XRD) and Raman spectrometry. These analyses reveal that the etched films were large-scale micro-nanohierarchical structures composed of a Zn core and a ZnO coating. Superhydrophobic surfaces with water contact angles of over 150o were obtained by n-octadecanethiol(ODT) modification. The XPS and Raman results indicate that ODT molecules were bound to the ZnO surface with the S head group by forming Zn-S bond.     

Effect of cholesterol and phospholipid on the behavior of dialkyl polyoxyethylene ether surfactant (2C18E12) monolayers and bilayers

Surface pressure-area isotherm, neutron specular reflection, and small-angle neutron scattering studies have been carried out to determine the effects of added cholesterol and distearoylphosphatidylcholine (DSPC), on the molecular structures of monolayers and vesicles containing the dialkyl polyoxyethylene ether surfactant, 1,2-di-O-octadecyl-rac-glyceryl-3-(alpha-dodecaethylene glycol) (2C18E12). Previous neutron reflectivity studies on 2C18E12 monolayers at the air/water interface have shown them to possess a thickness of approximately 24 angstoms and highly disordered structure with significant intermixing of the polymer headgroups and alkyl chains. SANS studies of 2C18E12 vesicles gave a bilayer thickness of approximately 51 angstroms. Addition of cholesterol to 2C18E12 monolayers (1:1 molar ratio), produced a marked condensing effect coupled with an increased the layer thickness of approximately 7 angstroms, and in vesicles, increased bilayer thickness by approximately 16 angstroms. Monolayers consisting of 2C18E12:DSPC:cholesterol (1:1:2 molar ratio), showed a layer thickness of approximately 31 angstroms, whereas in vesicles, three-component bilayer was found to be only approximately 9 angstroms thicker than those possessed by vesicles composed solely of 2C18E12. Mixing between the molecules in three-component monolayers was shown to be ideal through analysis of the neutron reflectivity data. These findings are discussed in relation to increased ordering and decreased headgroup/hydrophobe intermixing within both monolayers and vesicle bilayers containing 2C18E12. The inferred increase in molecular order within vesicles composed of 2C18E12 with additional cholesterol and phospholipid is used as a model for explaining theoretical differences in bilayer permeability.     

Isostructural self-assembled monolayers. 2. Methyl 1-(3-mercaptopropyl)-oligo(ethylene oxide)s

The structural order and ordering conditions of the self-assembled monolayers (SAMs) of HSCH2CH2CH2O(EO)xCH3, where EO = CH2CH2O and x = 3-9, on polycrystalline gold (Au) were determined by reflection-absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and electrochemical impedance spectroscopy. For x = 5-7, RAIRS and SE data show that the oligo(ethylene oxide) [OEO] segments adopt the near single phase, 7/2 helical conformation of the folded-chain crystal polymorph of crystalline poly(ethylene oxide), oriented normal to the substrate. These SAMs exhibit OEO segment structure and orientation identical to that found in a previous isostructural series [HS(CH2CH2O)6-8C18H37 SAMs. Vanderah, D. J., et al. Langmuir 2003, 19, 3752] and are anisotropic films for surface science metrology where structure is constant and thickness increases in 0.30 nm increments. In addition, this is the first example of OEO SAMs to attain this highly ordered, helical conformation where the (EO)x segment is separated from the Au-sulfur headgroup by a polymethylene chain. For x = 4, 8, and 9, the SAMs are largely helical but show evidence of nonhelical conformations and establish the upper and lower limits of the isostructural set. For x = 3, the SAMs are largely disordered containing some all-trans conformation. SAM order as a function of immersion time from 100% water and 95% ethanol indicates that the HSCH2CH2CH2O(EO)5-7CH3 SAMs order faster and under a wider range of conditions than omega-alkyl 1-thiaolio(ethylene oxide) [HS(EO)xCH3] SAMs, reported earlier (Vanderah, D. J., et al. Langmuir 2002, 18, 4674 and Vanderah, D. J., et al. Langmuir 2003, 19, 2612).     

Study of alkyl organic monolayers with different molecular chain lengths directly attached to silicon

Alkyl organic monolayers with different alkyl molecular chain lengths directly attached to silicon were prepared at 160 degrees C from 1-decene (C10), 1-dodecene (C12), 1-tetradecene (C14), 1-hexadecene (C16), and 1-octadecene (C18). These monolayers were characterized on the basis of water contact angle measurement, ellipsometry, X-ray reflectivity (XR), X-ray photoelectron spectroscopy (XPS), and grazing incidence X-ray diffraction (GIXD) to elucidate the effect of the molecular chain length on the molecular arrangement and packing density of the monolayers. Water contact angle and XPS measurements showed that C12, C14, and C16 monolayers have a comparably higher quality, while the quality of C10 and C18 monolayers is worse. GIXD revealed that the alkyl monolayers directly attached to the Si were all amorphously structured regardless of their alkyl chain length. The amorphous structure of the alkyl monolayers could be attributed to the rigid Si-C bonding, low quality of hydrogen-terminated silicon substrate, and/or low mobility of physisorbed molecules.     

Adsorption states of dialkyl ditelluride autooxidized monolayers on Au(111)

Organic ditellurides (R2Te2 where R = n-butyl (C4), n-octyl (C8), and n-cetyl (C16)) were synthesized, and their adsorption states after oxidation on Au(111) surfaces were studied by X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), theoretical analyses, near-edge X-ray absorption fine structure (NEXAFS) measurements, contact angle measurements, and atomic force microscopy (AFM). The obtained results show that dialkyl ditellurides form autooxidized monolayers (AMs) on the surfaces under ambient conditions and that the oxidation process is accelerated by ambient light. XPS, UPS, and theoretical analyses suggest that the autooxidized ditelluride species consist of polymers or oligomers with Te-O-Te-O network structures stabilized by oxygen bridges between tellurium molecules following the cleavage of tellurium-gold bonds. NEXAFS and contact angle measurements indicate that the average tilt angles of the alkyl chains from the surface normal are smaller for the AMs of dialkyl ditellurides having longer alkyl chains. AFM measurements show defects and roughness features around a few angstroms in height on the surfaces of the dialkyl ditelluride AMs.     

Self-assembled monolayers derived from alkoxyphenylethanethiols having one, two, and three pendant chains

This article describes the design, synthesis, and study of alkoxyphenylethanethiol-based adsorbates with one (R1ArMT), two (R2ArMT), and three (R3ArMT) pendant octadecyloxy chains substituted at the 4-, 3,5-, and 3,4,5-positions, respectively, of the phenylethanethiol group. These adsorbates are being developed for use in the preparation of compositionally versatile "mixed" self-assembled monolayer (SAM) coatings. The resultant SAMs were characterized by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and X-ray photoelectron spectroscopy (XPS). The studies revealed that R1ArMT generates a well-ordered monolayer film, while R2ArMT and R3ArMT generate monolayer films with diminished conformational order in which the degree of crystallinity decreases as follows: C18 ～ R1ArMT > R3ArMT > R2ArMT. In addition, comparison of the molecular and chain packing densities of SAMs derived from these new adsorbates reveals that the R2ArMT and R3ArMT adsorbates give rise to SAMs with reduced chain tilt and smaller surface area per chain when compared to the SAMs derived from C18 and R1ArMT.     

Host-guest interactions at self-assembled monolayers of cyclodextrins on gold

We have developed synthesis routes for the introduction of short and long dialkylsulfides onto the primary side of alpha-, beta-, and gamma-cyclodextrins. Monolayers of these cyclodextrin adsorbates were characterized by electrochemistry, wettability studies, X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and atomic force microscopy (AFM). The differences in thickness and polarity of the outerface of the monolayers were measured by electro-chemistry and wettability studies. On average about 70% of the sulfide moieties were used for binding to the gold, as measured by XPS. Tof-SIMS measurements showed that the cyclodextrin adsorbates adsorb without any bond breakage. AFM measurements revealed for beta-cyclodextrin monolayers a quasi-hexagonal lattice with a lattice constant of 20.6 A, which matches the geometrical size of the adsorbate. The alpha-cyclodextrin and gamma-cyclodextrin monolayers are less ordered. Interactions of the anionic guests 1-anilinonaphthalene-8-sulfonic acid (1,8-ANS) and 2-(p-toluidinyl)naphthalene-6-sulfonic acid (2,6-TNS) and the highly ordered monolayers of heptapodant beta-cyclodextrin adsorbates were studied by surface plasmon resonance (SPR) and electrochemical impedance spectroscopy. The SPR measurements clearly showed interactions between a beta-cyclodextrin monolayer and 1,8-ANS. Electrochemical impedance spectroscopy measurements gave high responses even at low guest concentrations (< or = 5 microM). The association constant for the binding of 1,8-ANS (K = 289,000 +/- 13,000M-1) is considerably higher than the corresponding value in solution. (Partial) methylation of the secondary side of the beta-cyclodextrin strongly decreases the binding.     

Langmuir-Blodgett-Kuhn and self-assembled films of asymmetrically substituted poly(paraphenylene)

Asymmetrically substituted poly(paraphenylene) (PhPPP) with hydrophilic and hydrophobic side chains was investigated. The polymer behavior at the air-water interface was studied on the basis of surface pressure-area (pi-A) isotherms and compression/expansion hysteresis measurements. PhPPP can form stable monolayers with an area per repeat unit of A=0.20+/-0.02 nm2 and a collapse pressure in the range of pi=25 mN/m. Then, Langmuir-Blodgett-Kuhn (LBK) films of PhPPP were prepared by horizontally and vertically transferring the Langmuir monolayers onto hydrophilic solid substrates at pi=12 mN/m. Cross-section analysis of the AFM tapping-mode topography images of a single transferred monolayer reveals a thickness of d0=0.9+/-0.1 nm. Taking into account the obtained monolayer thickness, curve-fitting calculations of angular scan data of LB monolayers measured using surface plasmon resonance (SPR) spectroscopy lead to a value for the refractive index of n=1.78+/-0.02 at lambda=632.8 nm. Next, the spontaneous formation of a PhPPP monolayer by adsorption from solution was studied ex situ by atomic force microscopy and UV-vis spectroscopy and in situ by using SPR spectroscopy. Stable self-assembled monolayers of PhPPP can be formed on hydrophilic surfaces with a thickness similar to that of the monolayer obtained using the LB method. The characterization results confirmed the amphiphilic character and the self-assembly properties of PhPPP, as well as the possibility of preparing homogeneous monolayer and multilayer films.     

Hydrolytic stability of organic monolayers supported on TiO2 and ZrO2

The hydrolytic stability of C18 monolayers supported on TiO2 and ZrO2 was studied. Three types of monolayers were prepared from the following octadecyl modifiers: (1) octadecyldimethylchlorosilane (C18H37Si(CH3)2Cl); (2) octadecylsilane (C18H37SiH3); and (3) octadecylphosphonic acid (C18H37P(O)(OH)2). The hydrolysis of the surfaces prepared was studied under static conditions at 25 and 65 degrees C at pH 1-10. On the basis of the loss of grafted material, the stability of the monolayers fall in the following range: C18H37P(O)(OH)2 > or = C18H37SiH3 > C18H37Si(CH3)2Cl. At 25 degrees C, monolayers from C18H37P(O)(OH)2 showed only approximately 2-5% loss in grafting density after one week at pH 1-10. The high stability of these monolayers was explained because of the strong interactions of the phosphonic acids with the substrates. Monolayers from C18H37Si(CH3)2Cl showed poor hydrolytic stability at any pH, which was explained because of the low stability of Ti-O-Si and Zr-O-Si bonds. Unlike monofunctional silanes, trifunctional silane (C18H37SiH3) yielded surfaces that showed good hydrolytic stability. This suggests that the stability of the monolayers from trifunctional silanes is primarily due to "horizontal" bonding (Si-O-Si or Si-OH...HO-Si) rather than due to bondingwith the matrix (M-O-Si). At 65 degrees C, all C18 surfaces become more susceptible to hydrolysis; however, the trend observed for 25 degrees C remained unchanged. Low-temperature nitrogen adsorption was used to study the adsorption properties of the monolayers as a function of their grafting density. The energy of adsorption interactions showed a significant increase as the grafting density of the monolayers decreased. The order of the alkyl groups in the monolayers, as assessed from CH2 stretching, decreased as the grafting density of the monolayers decreased.     

Lower homologues (methyl, ethyl) of diorganotin derivatives of germyl (substituted) propanoic acids: spectroscopic elucidations and biological studies

Some novel lower homologues of diorganotin derivatives of germyl substituted propanoic acids with general formula [Ar(3)GeCH(R(1))CH(R(2))COO](2)SnR(2)(3), where Ar = p-CH(3)C(6)H(4), C(6)H(5), R(1) = p-CH(3)C(6)H(4), p-CH(3)OC(6)H(4), o-CH(3)OC(6)H(4), C(6)H(5), R(2) = H, CH(3), R(3) = CH(3), C(2)H(5) have been prepared by the condensation reaction of dialkyltin oxide and triarylgermyl(substituted) propanoic acid in 1 : 2 M ratio, respectively, and were characterized by IR, multinuclear ((1)H, (13)C, (119)Sn) NMR, (119 m)Sn M?ssbauer spectroscopy. The synthesized compounds were also screened for their toxicity and possible antibacterial, antifungal activities and found some encouraging results.     

硫醇-烯点击化学法制备C18毛细管电色谱开管柱及其性能研究

基于十八烷基硫醇与乙烯基功能化毛细管(Vinyl capillary)的硫醇-烯点击化学反应,制备了一种新型的C18毛细管电色谱开管柱(C18capillary).采用乙烯基三甲氧基硅烷对毛细管内壁进行乙烯基功能化,然后通过硫醇-烯点击化学反应共价键合十八烷基硫醇于Vinyl capillary内表面.采用环境扫描电镜对C18 capillary进行了形貌表征.考察了缓冲溶液pH值对C18 capillary、Vinyl capillary和裸毛细管柱(Bare capillary)电渗流的影响.结果表明;在相同实验条件下,C18capillary的电渗流最小.以3种多环芳烃为模型化合物,评价了C18capillary的电色谱柱性能;同时考察了模型化合物在C18capillary上的电色谱保留行为.实验表明,其保留机理是基于典型的反相作用.当C18 capillary用于碱性模型化合物分离时,碱性物质在C18 capillary上的峰形较好,无明显的峰拖尾现象,这可能是由于C18capillary表面含有极性的S基团能够屏蔽残留硅羟基对碱性化合物的吸附作用.     

Synthesis of a series of oligo(ethylene glycol)-terminated alkanethiol amides designed to address structure and stability of biosensing interfaces.

A strategy for the synthesis of a series of closely related oligo(ethylene glycol)-terminated alkanethiol amides (principally HS(CH(2))(m)CONH(CH(2)CH(2)O)(n)H; m = 2, 5, 11, 15, n = 1, 2, 4, 6, 8, 10, 12) and analogous esters has been developed. These compounds were made to study the structure and stability of self-assembled monolayers (SAMs) on gold in the prospect of designing new biosensing interfaces. For this purpose, monodisperse heterofunctional oligo(ethylene glycols) with up to 12 units were prepared. Selective monoacylation of the symmetrical tetra- and hexa(ethylene glycol) diols as their mesylates with the use of silver(I) oxide was performed. The synthetic approach was based on carbodiimide couplings of various oligo(ethylene glycol) derivatives to omega-(acetylthio) carboxylic acids via a terminal amino or hydroxyl function. SAM structures on gold were studied with respect to thickness, wettability (water contact angles approximately 30 degrees ), and conformation. A good fit was obtained for the relation between monolayer thickness (d) and the number of units in the oligo(ethylene glycol) chain (n): d = 2.8n + 21.8 (A). Interestingly, the corresponding infrared spectroscopy analysis showed a dramatic change in conformation of the oligomeric chains from all-trans (n = 4) to helical (n > or = 6) conformation. A crystalline helical structure was observed in the SAMs for n > 6.     

Structure of the complex monolayer of gemini surfactant and DNA at the air/water interface

The properties of the complex monolayers composed of cationic gemini surfactants, [C(18)H(37)(CH(3))(2)N(+)-(CH(2))(s)-N(+)(CH(3))(2)C(18)H(37)],2Br(-) (18-s-18 with s = 3, 4, 6, 8, 10 and 12), and ds-DNA or ss-DNA at the air/water interface were in situ studied by the surface pressure-area per molecule (π-A) isotherm measurement and the infrared reflection absorption spectroscopy (IRRAS). The corresponding Langmuir-Blodgett (LB) films were also investigated by the atomic force microscopy (AFM), the Fourier transform infrared spectroscopy (FT-IR), and the circular dichroism spectroscopy (CD). The π-A isotherms and AFM images reveal that the spacer of gemini surfactant has a significant effect on the surface properties of the complex monolayers. As s ≤ 6, the gemini/ds-DNA complex monolayers can both laterally and normally aggregate to form fibril structures with heights of 2.0-7.0 nm and widths of from several tens to ~300 nm. As s > 6, they can laterally condense to form the platform structure with about 1.4 nm height. Nevertheless, FT-IR, IRRAS, and CD spectra, as well as AFM images, suggest that DNA retains its double-stranded character when complexed. This is very important and meaningful for gene therapy because it is crucial to maintain the extracellular genes undamaged to obtain a high transfection efficiency. In addition, when s ≤ 6, the gemini/ds-DNA complex monolayers can experience a transition of DNA molecule from the double-stranded helical structure to a typical ψ-phase with a supramolecular chiral order.     

Characterization of monolayer formation on aluminum-doped zinc oxide thin films

The optical and electronic properties of aluminum-doped zinc oxide (AZO) thin films on a glass substrate are investigated experimentally and theoretically. Optical studies with coupling in the Kretschmann configuration reveal an angle-dependent plasma frequency in the mid-IR for p-polarized radiation, suggestive of the detection of a Drude plasma frequency. These studies are complemented by oxygen depletion density functional theory studies for the calculation of the charge carrier concentration and plasma frequency for bulk AZO. In addition, we report on the optical and physical properties of thin film adlayers of n-hexadecanethiol (HDT) and n-octadecanethiol (ODT) self-assembled monolayers (SAMs) on AZO surfaces using reflectance FTIR spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Our characterization of the SAM deposition onto the AZO thin film reveals a range of possible applications for this conducting metal oxide.