Littérature scientifique sur le sujet « Amino terminated molecules »

This study investigates the controlled chemical functionalization of silicon oxide nanostructures prepared by AFM-anodization lithography of alkyl-terminated silicon. Different conditions for the growth of covalently bound mono-, multi- or submonolayers of distinctively functional silane molecules on nanostructures have been identified by AFM-height investigations. Routes for the preparation of methyl- or amino-terminated structures or silicon surfaces are presented and discussed. The formation of silane monolayers on nanoscopic silicon oxide nanostructures was found to be much more sensitive towards ambient humidity than, e.g., the silanization of larger OH-terminated silica surfaces. Amino-functionalized nanostructures have been successfully modified by the covalent binding of functional fluorescein dye molecules. Upon excitation, the dye-functionalized structures show only weak fluorescence, which may be an indication of a relatively low surface coverage of the dye molecules on length scale that is not accessible by standard AFM measurements.

Translating sticky biological molecules—such as mussel foot proteins (MFPs)—into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue’s molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces.

In this study, based on the density functional theory, we examine the interaction between the bare, F-, OH-terminated as well as defect patterned Ti2C and selected neurotransmitter (NT) and amino acids (AA) such as dopamine, glutamate, glycine and serine.

ABSTRACT An amylosucrase gene was subjected to high-rate segmental random mutagenesis, which was directed toward a segment encoding amino acids that influence the interaction with substrate molecules in subsites −1 to +3. A screen was used to identify enzyme variants with compromised glucan chain elongation. With an average mutation rate of about one mutation per targeted codon, a considerable fraction (82%) of the clones that retained catalytic activity were deficient in this trait. A detailed characterization of selected variants revealed that elongation terminated when chains reached lengths of only two or three glucose moieties. Sequencing showed that the amylosucrase derivatives had an average of no more than two amino acid substitutions and suggested that predominantly exchanges of Asp394 or Gly396 were crucial for the novel properties. Structural models of the variants indicated that steric interference between the amino acids introduced at these sites and the growing oligosaccharide chain are mainly responsible for the limitation of glucosyl transfers. The variants generated may serve as biocatalysts for limited addition of glucose moieties to acceptor molecules, using sucrose as a readily available donor substrate.

Cadmium (Cd) is one of the most toxic metals found in water and sediments. In the effort to develop an effective adsorbent for aqueous Cd removal, activated carbon (AC) was modified with an amino-terminated organosilicon (3-aminopropyltrimethoxysilane, APS). Response surface methodology was used to optimize selected operational parameters of adsorption of aqueous Cd by considering a central composite design with three input variables, temperature of the mixture solution, the contact time and feed ratio (APS/AC), on the surface modification. Results demonstrated that the strong Cd-binding amine ligands were effectively introduced onto the AC surfaces through the silanol reaction between carbon surface functional groups (–COOH, –COH) and APS molecules. The optimized preparation condition is 77 °C, 4 h and 2.1 ratio. The adsorbent presented a favorable adsorption of the aqueous Cd(II).

Polyvinylcaprolactam (PVCap) is an economic kinetic inhibitor for hydrate formation in pipelines during oil and gas transportation. However, its application is limited because of the low inhibition performance under certain conditions. In this work, a modified PVCap on its chain end is proposed.2-amino-3-propionic acid mercapto-terminated polyvinyl caprolactam (PVCap-NH2-COOH) was synthesized and its performance as a KHI for methane hydrate formation was evaluated under different conditions. Results showed that the performance of PVCap-NH2-COOH as a KHI was better than that of PVCap at the same concentrations. Gas hydrate samples with 1 wt.% PVCap-NH2-COOH were measured using Raman spectroscopy, XRD, and cryo-SEM. PVCap-NH2-COOH had a selective action on a specific crystal surface of the hydrates and could prevent methane molecules from entering large cages. Its inhibition ability increased with the decrease in the occupancy rate of large cages. The morphology of the gas hydrate crystal changed from porous in a pure water system to a chaotic but compact structure state in the system with PVCap-NH2-COOH.

ABSTRACT We have analysed the structure and composition of the β-core fragment of human chorionic gonadotrophin (βC-hCG) from fresh urine specimens obtained from pregnant women and compared our findings with those previously proposed by other groups using different protocols. SDS-PAGE separation of reduced βC-hCG demonstrated two major bands with apparent molecular weights of Mr 8900 and Mr 7500. The molecular weight of the agalacto βC-hCG was estimated to be Mr 10 218 from the amino acid analysis after high-performance liquid chromatography (HPLC) separation. Moreover, HPLC separation of its reduced and S-carboxymethylated peptides resulted in three peaks, but only two of them could be sequenced and demonstrated to be the previously reported β6-40 (Mr 5000) and β55-92 (Mr 5300) peptides of the βhCG subunit. The results showed that 56-78% of βC-hCG molecules of molecular weight Mr 12 800 were able to bind Concanavalin A (Con A). While most were lacking all the peripheral monosaccharides and terminated in mannose, some retained other sugar residues on their antennae. Direct carbohydrate analysis showed the following molar content normalized to six mannose molecules: galactose 2·8, glucosamine 5·3, galactosamine 0·3, fucose 1·7 and sialic acid 3·0. Approximately 22–44% of the βC-hCG molecules did not bind Con A (Con A non-reactive forms), of which 88% were totally deprived of sugar units and had an apparent molecular weight of approximately Mr 10 000, and 12% were weakly reactive to Con A and reactive to anion exchange (negatively charged forms), being incompletely trimmed of their oligosaccharide chains. Comparison of our results with those of two other groups have indicated that the differences noted among preparations are due to either the source or the methods used to purify and characterize this fragment. In addition, our results showed significant microheterogeneity on the N-linked oligosaccharide moieties with some molecules apparently having no sugar molecules. These results have implications for the origins of βC-hCG, suggesting secretion of some molecules without sugar chains and in other cases possible metabolism of hCG in the peripheral tissues. Journal of Endocrinology (1993) 139, 519–532

Cyclodextrin (CD)-threaded polyrotaxanes (PRXs) with reactive functional groups at the terminals of the axle polymers are attractive candidates for the design of supramolecular materials. Herein, we describe a novel and simple synthetic method for end-reactive PRXs using bis(2-amino-3-phenylpropyl) poly(ethylene glycol) (PEG-Ph-NH2) as an axle polymer and commercially available 4-substituted benzoic acids as capping reagents. The terminal 2-amino-3-phenylpropyl groups of PEG-Ph-NH2 block the dethreading of the α-CDs after capping with 4-substituted benzoic acids. By this method, two series of azide group-terminated polyrotaxanes (benzylazide: PRX-Bn-N3, phenylazide: PRX-Ph-N3,) were synthesized for functionalization via click reactions. The PRX-Bn-N3 and PRX-Ph-N3 reacted quickly and efficiently with p-(tert-butyl)phenylacetylene via copper-catalyzed click reactions. Additionally, the terminal azide groups of the PRX-Bn-N3 could be modified with dibenzylcyclooctyne (DBCO)-conjugated fluorescent molecules via a copper-free click reaction; this fluorescently labeled PRX was utilized for intracellular fluorescence imaging. The method of synthesizing end-reactive PRXs described herein is simple and versatile for the design of diverse functional PRXs and can be applied to the fabrication of PRX-based supramolecular biomaterials.

2007/2008
The understanding of the interaction of organic molecules with metal surfaces is crucial for tailoring the desired properties of future devices that can be employed for molecular electronics or biomedical applications. Self-assembly of complex supramolecular structures and charge transfer through molecular films or even through single molecules are some of the properties that have recently attracted much interest both for possible applications and for more fundamental studies. The molecule-surface interaction takes place thanks to the functional groups that constitute the molecule. The choice of appropriate functional groups of the molecules allows their use as building blocks in the fabrication of complicate architectures [1]. In fact, the functional entities can influence molecule-molecule and molecule-surface interactions, governing the self-assembly of the molecules on the surface. In particular, in the thesis I will report on the characterization by means of Helium Atom Scattering (HAS), X-ray Photoemission Spectroscopy (XPS), Near Edge X-ray Absorption Fine Structure (NEXAFS) and Scanning Tunneling Microscopy (STM) of the self-assembly in ultra high vacuum (UHV) conditions of L-methionine molecules on different metal substrates (Ag(111), Cu(111), Au(111), Au(110)). L-methionine is an amino acid with three functional groups which can interact with the substrate or with other molecules: the amino (-NH2), the carboxyl (-COOH) and the thioether (-S-). Moreover, the first two can change their charge state in a protonated amino group (-NH+ 3 ) and a deprotonated carboxyl group (-COO−): the molecules are called zwitterionic and it is allowed the formation of hydrogen bonds between them. Hydrogen bonding between zwitterionic molecules is responsible for the crystallization in the solid state. In the thesis I have studied how, depending on the choice of the substrate and the growth conditions, L-methionine molecules form assemblies with different morphologies and different chemical states of the building blocks. L-methionine molecules deposited on Ag(111) and Au(111) are in the zwitterionic state and interact strongly via hydrogen bonding forming dimers of molecules. The weak interaction with the substrate allows the organization of these dimers in extended bidimensional nanogratings composed of chains of length extending in the micrometer range and with tunable periodicity across the chains. At temperatures below 270K, L-methionine on Cu(111) forms short aggregates of zwitterionic dimers. By increasing the substrate temperature above 300K the charge state of the amino group changes and also the interaction with the surface. Molecules are anionic (-NH2 and -COO−) and form again charged nanogratings. The anionic state of the molecules can also be obtained on the Au(110) surface, where the interaction of the amino and thioether groups with the gold inhibits the formation of zwitterionic dimers via hydrogen bonding. The functional groups in the molecules can also influence their transport properties. The final goal of miniaturization in molecular electronics research is the formation and characterization of a nanoelectronic device in which a molecule between two electrodes plays the role of an active conducting element. In such a device the interaction between the functional groups anchoring the molecule to the electrodes and the electrodes is a crucial element in order to understand and control the conduction. Recent STM-break junction experiments [2] have shown that Au-molecule-Au contacts with amino (- NH2) terminated molecules are better defined than Au-molecule-Au contacts formed with thiol (-SH) terminated molecules [3]. The strong interaction of thiols with gold surfaces is well known in literature and the self-assembly of thiolated molecules is widely employed in many applications. In contrast, the weak interaction of amino terminated molecules with gold is poorly studied. Theoretical calculations suggest that the amine lone pair is responsible for bonding and that it prefers to bind to undercoordinated gold atoms. Within this framework, in the thesis I report on the study of growth of thin films of 1,4-benzenediamine and p-toluidine on two different Au surfaces, where the atoms present different coordination: Au(111) and Au(110). Both molecules interact more strongly with the low coordination (110) surface. By means of Resonant Photoemission Spectroscopy (RPES) it has been possible to disentangle molecular orbitals and determine the ones involved in the charge transfer at the surface. In both cases the charge transfer involves states localized also on the nitrogen atoms indicating a possible interaction of the molecule with the surface through nitrogen atoms. I also studied the assembly of three benzene substituted diamines on Au(111). These results complement very well the results obtained from conduction experiments of different amine-terminated molecules and combined with theoretical investigations can help understanding the basics of the molecular charge transport mechanism. [1] Barth J.V., Costantini G., Kern K., Nature, 437 (2005) 671 [2] Venkataraman L., Klare J. E., Nuckolls C., Hybertsen M. S., Steigerwald M. L., Nature, 442 (7105), 904 (2006) [3] Schreiber F., Progress in Surface Science, 65 (5-8) (2000) 151
Lo studio dell’interazione di molecole organiche con superfici metalliche è di fondamentale importanza per la progettazione di futuri dispositivi che possiedano proprietà ben controllabili in modo tale che possano essere usati per l’elettronica molecolare o per applicazioni biomediche. L’autoassemblaggio di complesse strutture ”supramolecolari” e il trasferimento di carica attraverso film molecolari o anche attraverso singole molecole sono alcune delle proprietà che hanno attratto di recente grande interesse sia per le possibili applicazioni future che per studi di tipo più fondamentale. L’interazione molecola-superficie avviene attraverso i gruppi funzionali che costituiscono le molecole. Molecole con appropriate funzionalizzazioni possono essere usate come mattoni elementari nella fabbricazione di architetture complesse [1]. Infatti, tali gruppi funzionali possono influenzare le interazioni del tipo molecola-molecola e molecola-superficie che governano l’autoassemblaggio delle molecole sulla superficie. In particolare, in questa tesi riporter`o circa la caratterizzazione mediante diffrazione di atomi di elio (HAS), spettroscopia di fotoemissione di raggi X (XPS), misure di assorbimento di raggi X (NEXAFS) e microscopia ad effetto tunnel (STM) dell’autoassemblaggio in condizioni di ultra alto vuoto (UHV) di molecole di L-metionina su diversi substrati metallici (Ag(111), Cu(111), Au(111), Au(110)). La molecola di L-metionina `e un amminoacido che presenta tre gruppi funzionali i quali possono interagire con il substrato o con altre molecole: il gruppo amminico (-NH2), il gruppo carbossilico (- COOH) e il gruppo tioetere (-S-). I primi due possono inoltre cambiare il loro stato di carica originando un gruppo amminico protonato (-NH+ 3 ) e un gruppo carbossilico deprotonato (COO−): in tal caso le molecole sono dette zwitterioniche ed è permessa la formazione di legami a idrogeno tra esse. I legami a idrogeno tra molecole zwitterioniche sono responsabili della loro cristallizzazione nello stato solido. In questa tesi ho studiato come, a seconda della scelta del substrato e delle condizioni di cescita, le molecole di L-metionina formino strutture assemblate che presentano diverse morfologie e diversi stati chimici delle molecole costituenti. Le molecole di L-metionina depositate su Ag(111) e Au(111) sono zwitterioniche e interagiscono fortemente tra di loro tramite legami a idrogeno a formare dimeri di molecole sulla superficie. La debole interazione con il substrato permette l’organizzazione di questi dimeri in estesi reticoli bidimensionali di dimensione nanometrica composti da catene di lunghezza nel range micrometrico e con spaziatura tra le catene controllabile. A temperature sotto 270K, le molecole di L-metionina su Cu(111) formano corti aggregati di dimeri zwitterionici. Aumentando la temperatura del substrato oltre 300K lo stato di carica del gruppo amminico cambia e quindi l’interazione con la superficie. Le molecole sono anioniche (-NH2 e COO−) e formano di nuovo reticoli carichi. Lo stato anionico delle molecole si può ottenere anche sulla superficie di Au(110) dove l’interazione dei gruppi amminico e tioetere con l’oro inibisce la formazione di dimeri zwitterionici via legami a idrogeno. I gruppi funzionali nelle molecole possono anche influenzare le loro proprietà di trasporto. Lo scopo finale della miniaturizzazione nella ricerca nel campo dell’elettronica molecolare è la formazione e caratterizzazione di un dispositivo nanoelettronico in cui una molecola immobilizzata tra due elettrodi gioca il ruolo di elemento conduttivo attivo. In tale dispositivo il controllo dell’interazione tra i gruppi funzionali che tengono la molecola attaccata gli elettrodi e gli elettrodi è un elemento cruciale per la comprensione e il controllo della conduzione. Recenti esperimenti del tipo STM break junction [2] hanno motrato che contatti del tipo Au-molecola-Au con molecole con terminazioni amminiche (NH2) sono meglio definiti che contatti del medesimo tipo con molecole con terminazione tiolica (-SH) [3]. La forte interazione dei tioli con superfici d’oro è ben nota in letteratura e l’autoassemblaggio di molecole con terminazione tiolica è largamente utilizzato in molte applicazioni. In contrasto, la debole interazione di molecole con terminazione amminica con superfici d’oro è stata poco studiata. Recenti calcoli teorici hanno previsto che le molecole si legano alla superficie d’oro attraverso il ”lone pair” localizzato sull’azoto e che sono preferiti i legami con atomi di oro di bassa coordinazione. In particolare, nella tesi riporterò i risultati dello studio della crescita di film sottili di 1,4-benzenediamina e p-toluidina su due diverse superfici d’oro, i cui atomi di superficie presentano diversa coordinazione: Au(111) e Au(110). Ambedue le molecole interagiscono più fortemente con la superficie di bassa coordinazione (110). Tramite la tecnica di fotoemissione risonante (RPES) è stato possibile individuare gli orbitali molecolari e determinare quelli coinvolti nel trasferimento di carica all’interfaccia. In ambedue i casi il trasferimento di carica coinvolge stati che sono localizzati anche sull’atomo di azoto, il che indica una possibile interazione della molecola con la superficie attraverso i gruppi amminici. Ho anche studiato l’assemblaggio su Au(111) di tre diverse benzene-diamine con vii diversi sostituenti legati all’anello. Questi risultati sono un complemento ai risultati ottenuti da esperimenti di conduzione di molecole con diverse terminazioni amminiche e combinati con le investigazioni teoriche possono aiutare nella comprensione dei fondamenti dei meccanismi di trasporto di carica nelle molecole. [1] Barth J.V., Costantini G., Kern K., Nature, 437 (2005) 671 [2] Venkataraman L., Klare J. E., Nuckolls C., Hybertsen M. S., Steigerwald M. L., Nature, 442 (7105), 904 (2006) [3] Schreiber F., Progress in Surface Science, 65 (5-8) (2000) 151
XXI Ciclo
1981

碩士
國立臺灣大學
應用物理所
101
Hybrid solar cell is a photovoltaic that combines both organic semiconductors and inorganic semiconductors. Although it has the benefit from both materials, the different surface properties between the semiconducting metal-oxides and polymers is a critical issue that causes the device performance to deteriorate. 　　In order to overcome the above difficulty, we use two hydrophobic molecules, 2-aminoanthracene (2-AA) and 4-amino-p-terphenyl (4-A-p-T), to enhance the compatibility between the polymer blend and metal-oxide materials. It is worth mentioning that because ZnO may be eroded by acid molecules, we use two small alkaline conductive molecules, 2-AA and 4-A-p-T, to modify the ZnO-nanorod surface. The structure of our studied cell is ITO/ZnO-nanorod/2-aminoanthracene or 4-amino-p-terphenyl/poly(3-hexythiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM)/Ag. 　　It is found that after the surface is modified by 2-AA and 4-A-p-T, the cells yield an open circuit voltage of 0.53 and 0.57 V, a short circuit current density of 9.52 mA/cm2 and 9.78 mA/cm2, a fill factor of 45.44 % and 46.65 % leading to increased power conversion efficiencies by about 20 % and 40 %, respectively. 　　Since there is no significant change in the light absorption efficiency after surface modification, the increase in the surface roughness of the photoactive layer after treatment provides a larger charge collection area. Thus, the series resistance of the devices decreases resulting in improved device performance.