Shattering of Peptide ions on self-assembled monolayer surfaces

Time- and collision energy-resolved surface-induced dissociation (SID) of des-Arg(1)- and des-Arg(9)-bradykinin on a fluorinated self-assembled monolayer (SAM) surface was studied by use of a novel Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially equipped to perform SID experiments. Time-resolved fragmentation efficiency curves (TFECs) were modeled by an RRKM-based approach developed in our laboratory that utilizes a very flexible analytical expression for the internal energy deposition function capable of reproducing both single- and multiple-collision activation in the gas phase and excitation by collisions with a surface. Both experimental observations and modeling establish a very sharp transition in the dynamics of ion-surface interaction: the shattering transition. The experimental signature for this transition is the appearance of prompt (time-independent) fragmentation, which becomes dominant at high collision energies. Shattering opens a variety of dissociation pathways that are not accessible to slow collisional and thermal ion activation. This results in much better sequence coverage for the singly protonated peptides than dissociation patterns obtained with any of the slow activation methods. Modeling demonstrated that, for short reaction delays, dissociation of these peptides is solely determined by shattering. Internal energies required for shattering transition are approximately the same for des-Arg(1) and des-Arg(9)-bradykinin, resulting in the overlap of fragmentation efficiency curves obtained at short reaction delays. At longer delay times, parent ions depletion is mainly determined by a slow decay rate and fragmentation efficiency curves for des-Arg(1) and des-Arg(9)-bradykinin diverge. Dissociation thresholds of 1.17 and 1.09 eV and activation entropies of -22.2 and -23.3 cal/(mol K) were obtained for des-Arg(1) and des-Arg(9)-bradykinin from RRKM modeling of time-resolved data. Dissociation parameters for des-Arg(1)-bradykinin are in good agreement with parameters derived from thermal experiments. However, there is a significant discrepancy between the thermal data and dissociation parameters for des-Arg(9)-bradykinin obtained in this study. The difference is attributed to the differences in conformations that undergo thermal activation and activation by ion-surface collisions prior to dissociation.     

Ozonolysis-based route to the in situ formation of aldehyde-bearing self-assembled monolayer surfaces

While ozonolysis of a terminal carbon-carbon double bond to produce aldehydes is a well-established synthetic strategy for conventional solution chemistry, exposure of vinyl-terminated self-assembled monolayers to ozone has been reported to yield carboxylic acids. By using a cold solution of ozone in methanol and then adding a reducing agent to this solution, acid formation is minimized and near-quantitative aldehyde formation is achieved. The aldehyde-bearing surface is characterized by its physical and chemical properties and by ATR-FTIR spectroscopy showing a characteristic aldehyde C-H peak at 2715 cm(-1) and carbonyl peak at 1729 cm(-1). The reactivity of the aldehyde-bearing surface is shown by its reaction with amines and amine derivatives to give surface-bound imines and by the reversible cycling between aldehyde and acetal. The acetal also provides a useful way to mask the aldehyde and store readily released aldehyde surface functionality for subsequent surface elaboration.     

Soft-landing of peptides onto self-assembled monolayer surfaces

Mass-selected peptide ions produced by electrospray ionization were deposited as ions by soft-landing (SL) onto fluorinated and hydrogenated self-assembled monolayer (FSAM and HSAM) surfaces using a Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS) specially designed for studying collisions of large ions with surfaces. Analysis of modified surfaces was performed in situ by combining 2 keV Cs(+) secondary ion mass spectrometry with FT-ICR detection of the sputtered ions (FT-ICR-SIMS). Similar SIMS spectra obtained following SL at different collision energies indicate that peptide fragmentation occurred in the analysis step (SIMS) rather than during ion deposition. The effect of the surface on SL was studied by comparing the efficiencies of SL on gold, FSAM, HSAM, and COOH-terminated SAM surfaces. It was found that FSAM surfaces are more efficient in retaining ions than their HSAM analogues, consistent with their larger polarizability. The efficiency of soft-landing of different peptides on the FSAM surface increases with the charge state of the ion, also consistent with an ion-polarizable molecule model for the initial stage of soft-landing on SAM surfaces. The gradual decrease of peptide ion deposition efficiency with an increase in collision energy found experimentally was quantitatively rationalized using the hard-cube model.     

Electrochemical formation and investigation of a self-assembled [60]fullerene monolayer

The formation and characterisation of a C(60) monolayer at the electrode|electrolyte interface has been studied by cyclic voltammetry, potential step chronoamperometry and ac voltammetry. The presence of the monolayer is evidenced by the presence of a very sharp peak P in the voltammogram, attributed to the faradaic phase formation of an ordered monolayer, and of a reduction post peak Q associated with the reduction of adsorbed species. The chronoamperograms exhibit a well-defined maximum, characteristic of a nucleation and growth mechanism. By comparison with existing models of phase transitions, a progressive polynucleation and growth mechanism is demonstrated. The monolayer is proposed to consist of a 2D fulleride salt. It is suggested that the formation of the monolayer can take place for a broad range of solution compositions, but requires an atomically smooth substrate such as mercury.     

Template-assisted patterning of nanoscale self-assembled monolayer arrays on surfaces

We report a general, simple, and inexpensive approach to pattern features of self-assembled monolayers (SAMs) on silicon and gold surfaces using porous anodic alumina films as templates. The SAM patterns, with feature sizes down to 30 nm and densities higher than 10(10)/cm(2), can be prepared over large areas (>5 cm(2)). The feature dimensions can be tuned by controlling the alumina template structure. These SAM patterns have been successfully used as resists for fabricating gold and silicon nanoparticle arrays on substrates by wet-chemical etching. In addition, we show that arrays of gold features can be patterned with 10-nm gaps between the dots.     

Effect of formation temperature and roughness on surface potential of octadecyltrichlorosilane self-assembled monolayer on silicon surfaces

Kelvin probe force microscopy (KPFM) and atomic force microscopy (AFM) are employed to probe the surface potential and topography of octadecyltrichlorosilane [OTS, CH3(CH2)17SiCl3] self-assembled monolayers (SAMs) on oxidized Si(100) and polycrystalline silicon surfaces as a function of deposition temperature and substrate roughness with particular attention paid to the monitoring of SAM adsorption on highly rough surfaces. In these studies, it is found that the surface potential magnitude of the adsorbed layer is larger for monolayers formed in the liquid-condensed (LC) phase than for those formed in the liquid-expanded (LE) phase. Experiments on individual islands in the LC phase show that surface potential and monolayer thickness increase with increasing island size; islands larger than about 1.5 microm reach maximum potential and height values of 48+/-4 mV and 2.7+/-0.1 nm, with respect to the underlying oxidized surface. It is also shown that KPFM is suitable for the study of monolayer adsorption on polycrystalline surfaces, for which preexisting surface texture makes the use of traditional scanning probe techniques for molecular recognition difficult. In these scenarios it is shown that OTS growth occurs preferentially along grain boundaries in fingerlike patterns having a molecular arrangement comparable to that of LC phase islands on atomically smooth silicon. These findings indicate that surface potential measurements provide a highly accurate, local means of probing monolayer morphology on rough surfaces encountered in many applications.     

Adsorption behavior of DNA-wrapped carbon nanotubes on self-assembled monolayer surfaces

We have examined the adsorption of DNA-wrapped single-walled carbon nanotubes (DNA-SWNTs) on hydrophobic, hydrophilic, and charged surfaces of alkylthiol self-assembled monolayers (SAMs) on gold. Our goal is to understand how DNA-SWNTs interact with surfaces of varying chemical functionality. These samples were characterized using reflection absorption FTIR (RAIRS), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. We have found that DNA-SWNTs preferentially adsorb to positively charged amine-terminated SAMs and to bare gold surfaces versus hydrophobic methyl-terminated or negatively charged carboxylic acid-terminated SAMs. Examination of the adsorption on gold of single-strand DNA (ssDNA) of the same sequence used to wrap the SWNTs suggests that the DNA wrapping plays a role in the adsorption behavior of DNA-SWNTs.     

Zinc oxide growth morphology on self-assembled monolayer modified silver surfaces

Using organic molecules to direct inorganic crystal growth has opened up new avenues for controlled synthesis on surfaces. Combined with soft lithography to form patterned templates, self-assembled monolayers (SAMs) have been shown to be a powerful approach for the assembly of inorganic nanostructures. In this work, we show that the surface free energy of SAM-modified silver, which depends on end groups and deposition method of SAMs, has a dramatic effect on the nucleation and growth of crystalline ZnO, a technologically important material, from supersaturated solutions. For SAMs with inert methyl end groups, ZnO nucleation is inhibited. For SAMs with chemically active (carboxylic or thiol) end groups, the ZnO morphology is found to be three-dimensional nanorods on low-surface-energy surfaces and two-dimensional thin films on high-energy surfaces.     

Gold film surface preparation for self-assembled monolayer studies

Evaporated gold films are frequently used as substrates for the study of biomolecular adsorbates, nanoparticle systems, amd partial and full monolayer films. These studies often benefit from a predeposition cleaning of the surface that removes adventitiously adsorbed material from laboratory contaminants. Scanning tunneling microscopy (STM) is used in this study to explore the microscopic consequences of two pretreatment protocols used in literature reports of self-assembled monolayers, based on sulfochromic and piranha acid solutions. These measurements show that treatment of the Au/mica surface with piranha acid can lead to extensive and uncontrolled etching of the surface and severe disruption of the surface topography; extended exposure causes the precipitation of crystallites on the surface that are highly mobile during STM imaging processes. Exposure of Au/mica surfaces to sulfochromic acid leads to the formation of permanent etch pits of the surface that are exclusively one Au layer deep; extended exposure leads to progressive etching and oxidation of the surface, ultimately leading to the formation of 0.33-0.36 nm high islands on the otherwise flat Au/mica surface. The piranha acid solutions are significantly more likely to cause the Au film to delaminate from the mica support than are the sulfochromic acid solutions. These results show that sulfochromic surface preparation is a direct and reliable method for the elimination of organic residues from Au(111)-textured surfaces, while causing a minimum of structural and chemical surface damage.     

Lipid membrane formation by vesicle fusion on silicon dioxide surfaces modified with alkyl self-assembled monolayer islands

Using atomic force microscopy, we have investigated the formation of the dipalmitoylphosphatidylcholine (DPPC) membrane by the vesicle fusion method on SiO2 surfaces modified with self-assembled monolayer (SAM) islands of octadecyltrichlorosilane (OTS) with sizes comparable to those of the vesicles. OTS-SAM islands with various sizes and coverages can be constructed on the SiO2 surfaces prepared by thermal oxidation followed by partial hydroxylation in a H2O2/H2SO4 solution. When vesicles are sufficiently smaller than the SiO2 domains, DPPC bilayers and DPPC/OTS layers form on the SiO2 and OTS domains, respectively. However, the adhesion of larger vesicles onto SiO2 is prevented by the OTS islands; therefore only DPPC/OTS layers form without formation of DPPC bilayers on the SiO2 domains. On surfaces with domains on the scale of tens to hundreds of nanometers, the relative size between the hydrophilic domains and the vesicles becomes an important factor in the membrane formation by the fusion of vesicles.     

全氟并五苯在半金属Ga表面的分子二聚化及自组装单层

利用超高真空扫描隧道显微镜(UHV-STM)和有机分子束沉积(OMBD)方法研究了全氟并五苯(perfluoropentancene,PFP)分子在半金属Ga表面的吸附和两维自组装. 在低覆盖度下单个PFP分子在Ga表面上表现出很高的迁移性. 在1分子单层(monolayer, ML)时PFP分子发生二聚化并在 Ga 表面上无序排列. 轻度热退火可导致PFP两维自组装: 二聚体排列为高度有序的一维分子带阵列, 带中 PFP二聚体排列为砖墙(brick wall)结构. 在高分辨 STM图中, PFP分子两端出现亮暗相反的圆形突起, 并且相邻分子的亮暗极性相反, 表明PFP分子带有电偶极矩, PFP二聚体带有电四极矩. 因此, PFP分子二聚体的形成机制可唯像解释为反向电偶极矩之间的静电吸引作用; 二聚体的砖墙排列结构可归结为同向电四极矩之间的静电排斥作用.     

"Non-evaporating" microdroplets on self-assembled monolayer surfaces under ambient conditions

A unique "non-evaporation" phenomenon, i.e., the unusually slow evaporation process of sessile microdroplets on self-assembled monolayer (SAM) surfaces, is reported. It has been observed that only droplets containing a certain proportion of a volatile and a less-volatile component undergo non-evaporation, which is characterized by hours-long existence of the droplets maintaining constant contact angle, contact area, and volume. We propose that for alcohol-water binary mixtures on SAM surfaces, the highly orientated and closely packed hydrophobic 1-decanethiol molecules induce a concentration gradient of alcohol in water, with a higher concentration of alcohol near the SAM surface. Initial evaporation of the alcohol (more volatile) increased the contact angle until the establishment of a new composition, which contains a strong hydrogen-bonding network among the water molecules in the presence of the alcohol alkyl chains. There is a lessened tendency for the alcohol to evaporate in the presence of a concentration gradient due to such interactions, which results in the observed "non-evaporating" phenomenon. This type of unusual evaporating profile was not observed on conventional substrates, such as polycarbonate sheets and microscope glass slides modified with alkyltrichlorosilanes.     

Micropatterning of lanthanum-based oxide thin film on self-assembled monolayers

We studied the direct micropatterning of a lanthanum-based thin film on a template of self-assembled monolayers in an aqueous solution at 80 degrees C. The template composed of silanol and octadecyl areas was prepared by UV-modified octadecyltrichlorosilane SAMs through a photomask. The amorphous La(2)O(CO(3))(2) x H(2)O thin films were selectively deposited in the silanol regions. Crystallized La(2)O(3) was obtained after heating at 800 degrees C in air.     

Fabrication of surface energy/chemical gradients using self-assembled monolayer surfaces

Direct laser patterning of surface energy gradients for alkanethiols on gold has been demonstrated. A homogeneous 1-hexadecanethiol self-assembled monolayer (SAM) on gold (supported by a glass substrate) was selectively desorbed using a focused laser beam. By continually varying the incident laser intensity along a straight line scan, a gradient in desorption was produced. This desorption gradient was then backfilled with the second SAM (16-mercaptohexadecanoic acid), to produce a wettability gradient. The gradient in wettability was characterized by condensation imaging. Secondary ion mass spectroscopy was also used to show variation of the second SAM population from maximum to zero along the length, representative of the chemical gradient. The hexadecanethiol desorption was found to be the most sensitive in a laser intensity range of 29.15-6.5 kW/cm2. By considering the functional behavior of the governing equations, the theoretical trend for desorption as a function of laser intensity (represented by the out-of-focus distance) was determined. It was found to conform to the experimental data. The proposed method is fast, simple, noncontact, and flexible in terms of producing different types of gradients.     

Hyperthermal organic thin film growth on surfaces terminated with self-assembled monolayers. I. The dynamics of trapping

We have examined the initial stages of growth of a crystalline small molecule organic thin film, diindenoperylene (DIP), on SiO(2) surfaces terminated with a series of self-assembled monolayers (SAMs). In this study we make use of supersonic molecular beam techniques to vary the incident kinetic energy of the DIP molecules, and we use in situ, real time synchrotron x-ray scattering to monitor the buildup of each molecular layer in the growing thin film. We find that the effects of the SAMs are most apparent concerning growth in the sub-monolayer regime, before the substrate is entirely covered by the DIP thin film. In this coverage regime on bare SiO(2), and SiO(2) terminated with either hexamethyldisilazane or perflurooctyltrichlorosilane the adsorption dynamics are consistent with trapping-mediated adsorption as observed in more simple systems, where the probability of adsorption decreases significantly with increasing kinetic energy. Once these surfaces are covered with DIP, however, the adsorption probability increases, particularly at the highest incident kinetic energy, and the probability of adsorption exhibits only a weak dependence on the incident kinetic energy. In contrast, on surfaces terminated by octyl- (OTS) and octadecyltrichlorosilane (ODTS) the trapping probability is high and exhibits little dependence on the incident kinetic energy, essentially the same as what is observed on these same surfaces covered by DIP. We postulate, which is backed by the results of molecular dynamics simulations, that direct molecular insertion into the OTS and ODTS layers is a primary explanation for efficient trapping on these surfaces.     

Soft-landing of peptide ions onto self-assembled monolayer surfaces: an overview

This review is focused on what has been learned in recent research studies concerned with fundamental aspects of soft-landing and reactive landing of peptide ions on self-assembled monolayer surfaces (SAMs). Peptide ions are particularly attractive model systems that provide important insights on the behavior of soft landed proteins, while SAMs provide a convenient and flexible platform for tailoring the interfacial properties of metals and semiconductor surfaces. Deposition of mass-selected ions on surfaces is accompanied by a number of processes including charge reduction, neutralization, covalent and non-covalent binding, and thermal desorption of ions and molecules from the substrate. Factors that affect the competition between these processes are discussed.     

硫辛酸在金电极上自组装成膜动力学研究

自组装单层膜 (ＳＡＭ)应用广泛[1～ 3] 。但对于硫辛酸 (ＴＡ)自组装成膜动力学过程的研究尚未见报道。本研究利用石英晶体微天平 (ＱＣＭ)对ＴＡ自组装成膜过程进行在线监测 ,研究成膜动力学特征 ,并探讨浓度、温度对成膜过程的影响 ,以及在不同ｐＨ值下 ,ＳＡＭ的稳定性 ,推算了不同温度下的速率常数及成膜的活化能。1　实验部分1 1　基本原理通过监测成膜过程中石英晶体微天平 (ＱＣＭ)的振荡频率的变化 ,据Ｓａｕｅｒｂｒｅｙ方程 ,可推知在石英谐振器 (ＱＣＭ)的金电极表面 ,ＴＡ的吸附质量Γ(Γ =Δｍ Ａ ,ｇ ｃｍ2 )与ＱＣＭ的频率…     

A novel photoalignment film for ferroelectric liquid crystal based on self-assembled monolayer method

A novel strategy based on self-assembly technology was devised for design of photosensitive material as a ferroelectric liquid crystal (FLC) alignment layer. This development offers new tools for the study and control at the molecular level of the interaction of FLCs with solid surfaces. The photoreactive material was self-assembled to the substrate by covalent bond linkage due to a special chemical adsorption reaction. Through ester bond linkage, a cyano group with strong polarity was introduced to be terminus of the film. Under irradiation of linearly polarised ultraviolet light, an optically anisotropic self-assembled film was easily obtained. The irradiated film was demonstrated to result in homogenous alignment of FLC by optical transmittance measurements and polarising optical microscopy images of a FLC cell at different rotation angles. The alignment quality of the FLC on this self-assembled monolayer film is comparable to that of commercial rubbed polyimide film. Furthermore, it was also found that the fine alignment of the FLC may be related to the smoothness of the self-assembled film surface owing to its polar end.