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1.
J Am Chem Soc ; 2020 Nov 10.
Artigo em Inglês | MEDLINE | ID: mdl-33167615

RESUMO

Biomolecules function by adopting multiple conformations. Such dynamics are governed by the conformation landscape whose study requires characterization of the ground and excited conformation states. Here, the conformational landscape of a molecule is sampled by exciting an initial gas-phase molecular conformer into diverse conformation states, using soft molecule-surface collision (0.5-5.0 eV). The resulting ground and excited molecular conformations, adsorbed on the surface, are imaged at the single-molecule level. This technique permits the exploration of oligosaccharide conformations, until now, limited by the high flexibility of oligosaccharides and ensemble-averaged analytical methods. As a model for cellulose, cellohexaose chains are observed in two conformational extremes, the typical "extended" chain and the atypical "coiled" chain-the latter identified as the gas-phase conformer preserved on the surface. Observing conformations between these two extremes reveals the physical properties of cellohexaose, behaving as a rigid ribbon that becomes flexible when twisted. The conformation space of any molecule that can be electrosprayed can now be explored.

2.
ACS Nano ; 2020 Apr 17.
Artigo em Inglês | MEDLINE | ID: mdl-32283013

RESUMO

Formation and characterization of low-dimensional nanostructures is crucial for controlling the properties of two-dimensional (2D) materials such as graphene. Here, we study the structure of low-dimensional adsorbates of cesium iodide (CsI) on free-standing graphene using aberration-corrected transmission electron microscopy at atomic resolution. CsI is deposited onto graphene as charged clusters by electrospray ion-beam deposition. The interaction with the electron beam forms two-dimensional CsI crystals only on bilayer graphene, while CsI clusters consisting of 4, 6, 7, and 8 ions are exclusively observed on single-layer graphene. Chemical characterization by electron energy-loss spectroscopy imaging and precise structural measurements evidence the possible influence of charge transfer on the structure formation of the CsI clusters and layers, leading to different distances of the Cs and I to the graphene.

3.
Angew Chem Int Ed Engl ; 58(25): 8336-8340, 2019 06 17.
Artigo em Inglês | MEDLINE | ID: mdl-31018027

RESUMO

Saccharides are ubiquitous biomolecules, but little is known about their interaction with, and assembly at, surfaces. By combining preparative mass spectrometry with scanning tunneling microscopy, we have been able to address the conformation and self-assembly of the disaccharide sucrose on a Cu(100) surface with subunit-level imaging. By employing a multistage modeling approach in combination with the experimental data, we can rationalize the conformation on the surface as well as the interactions between the sucrose molecules, thereby yielding models of the observed self-assembled patterns on the surface.

4.
Anal Chem ; 90(5): 3328-3334, 2018 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-29376333

RESUMO

Desorption/ionization induced by neutral SO2 clusters (DINeC) is used for mass spectrometry (MS) of surface-adsorbed molecules. The method is shown to be a surface-sensitive analysis tool capable of detecting molecular adsorbates in a wide range of molecular weights as well as their reactions on surfaces, which are otherwise difficult to access. Two different surface/adsorbate systems prepared by means of electrospray ion beam deposition (ES-IBD) were investigated: For the peptide angiotensin II on gold, intact molecules were desorbed from the surface when deposited by soft landing ES-IBD. By comparison to the well-controlled amount of substance deposited by ES-IBD, the sensitivity of DINeC-MS was shown to be on the order of 0.1% of a monolayer coverage, corresponding to femtomoles of analyte. Depending on deposition and sample conditions, the original state of charge of the molecules could be retrieved. Reaction of the adsorbed molecules both with surface atoms as well as with coadsorbed D2O was monitored. Rhodamine 6G was also desorbed as an intact molecule when deposited with kinetic energies below 50 eV. For higher deposition energy, fragmentation of the dye molecules was observed by means of DINeC-MS.

5.
Proc Natl Acad Sci U S A ; 114(7): 1474-1479, 2017 02 14.
Artigo em Inglês | MEDLINE | ID: mdl-28087691

RESUMO

Imaging single proteins has been a long-standing ambition for advancing various fields in natural science, as for instance structural biology, biophysics, and molecular nanotechnology. In particular, revealing the distinct conformations of an individual protein is of utmost importance. Here, we show the imaging of individual proteins and protein complexes by low-energy electron holography. Samples of individual proteins and protein complexes on ultraclean freestanding graphene were prepared by soft-landing electrospray ion beam deposition, which allows chemical- and conformational-specific selection and gentle deposition. Low-energy electrons do not induce radiation damage, which enables acquiring subnanometer resolution images of individual proteins (cytochrome C and BSA) as well as of protein complexes (hemoglobin), which are not the result of an averaging process.


Assuntos
Holografia/métodos , Proteínas/ultraestrutura , Imagem Individual de Molécula/métodos , Animais , Bovinos , Citocromos c/ultraestrutura , Elétrons , Grafite , Hemoglobinas/ultraestrutura , Holografia/instrumentação , Soroalbumina Bovina/ultraestrutura , Imagem Individual de Molécula/instrumentação , Espectrometria de Massas por Ionização por Electrospray/métodos , Eletricidade Estática , Vácuo
6.
ACS Nano ; 11(3): 2420-2427, 2017 03 28.
Artigo em Inglês | MEDLINE | ID: mdl-28122181

RESUMO

Herein we report the fabrication of molecular nanostructures on surfaces via two-dimensional (2D) folding of the nine amino acid peptide bradykinin. Soft-landing electrospray ion beam deposition in conjunction with high-resolution imaging by scanning tunneling microscopy is used to fabricate and investigate the molecular nanostructures. Subnanometer resolved images evidence the large conformational freedom of the molecules if thermal motion is inhibited and the formation of stable uniform dimers of only one specific conformation when diffusion can take place. Molecular dynamics modeling supported by density functional theory calculations give atomically precise insight into the induced-fit binding scheme when the folded dimer is formed. In the absence of solvent, we find a hierarchy of binding strength from polar to nonpolar, manifested in an inverted polar-nonpolar segregation which suppresses unspecific interactions at the rim of the nanostructure. The demonstrated 2D-folding scheme resembles many key properties of its native 3D counterpart and shows that functional, molecular nanostructures on surfaces fabricated by folding could be just as versatile and specific.


Assuntos
Bradicinina/química , Nanoestruturas/química , Difusão , Modelos Moleculares , Dobramento de Proteína , Teoria Quântica , Propriedades de Superfície
7.
Nat Commun ; 7: 10335, 2016 Jan 12.
Artigo em Inglês | MEDLINE | ID: mdl-26755352

RESUMO

The sequence of a peptide programs its self-assembly and hence the expression of specific properties through non-covalent interactions. A large variety of peptide nanostructures has been designed employing different aspects of these non-covalent interactions, such as dispersive interactions, hydrogen bonding or ionic interactions. Here we demonstrate the sequence-controlled fabrication of molecular nanostructures using peptides as bio-organic building blocks for two-dimensional (2D) self-assembly. Scanning tunnelling microscopy reveals changes from compact or linear assemblies (angiotensin I) to long-range ordered, chiral honeycomb networks (angiotensin II) as a result of removal of steric hindrance by sequence modification. Guided by our observations, molecular dynamic simulations yield atomistic models for the elucidation of interpeptide-binding motifs. This new approach to 2D self-assembly on surfaces grants insight at the atomic level that will enable the use of oligo- and polypeptides as large, multi-functional bio-organic building blocks, and opens a new route towards rationally designed, bio-inspired surfaces.


Assuntos
Angiotensina II/metabolismo , Angiotensina I/metabolismo , Nanoestruturas/ultraestrutura , Oligopeptídeos/metabolismo , Angiotensina I/química , Angiotensina II/química , Microscopia de Tunelamento , Simulação de Dinâmica Molecular , Oligopeptídeos/química , Peptídeos/química , Peptídeos/metabolismo , Conformação Proteica
8.
J Am Chem Soc ; 136(39): 13482-5, 2014 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-25185758

RESUMO

Chemical functionalization of graphene is achieved by hyperthermal reaction with azopyridine molecular ions. The one-step, room temperature process takes place in high vacuum (10(-7) mbar) using an electrospray ion beam deposition (ES-IBD) setup. For ion surface collisions exceeding a threshold kinetic energy of 165 eV, molecular cation beams of 4,4'-azobis(pyridine) covalently attach to chemical vapor deposited (CVD) graphene. A covalent functionalization degree of 3% of the carbon atoms of graphene is reached after 3-5 h of ion exposure of 2 × 10(14) azopyridinium/cm(2) of which 50% bind covalently. This facile approach for the controlled modification of graphene extends the scope of candidate species that would not otherwise react via existing conventional methods.

9.
ACS Appl Mater Interfaces ; 5(24): 13006-11, 2013 Dec 26.
Artigo em Inglês | MEDLINE | ID: mdl-24261989

RESUMO

Aiming at future technological applications, we describe the interface and the thin film processes of a pyrene-substituted nitronyl nitroxide radical deposited on Al2O3(11-20) single crystals. Electronic properties, chemical environment at the interface, and morphology of the thin films have been investigated by a multitechnique approach. Spectroscopic and morphologic analyses indicate a Stranski-Krastanov growth mode and weak physisorption of the molecules on the surface. The deposition does not affect the paramagnetic character of the molecules. The results presented in this paper show not only that the investigated system is a promising candidate as a model for understanding thin film processes in purely organic-based magnets, but its characteristics are worth its future use in electronics, because the radical character of the molecules is completely preserved in the thin films.

10.
J Am Chem Soc ; 134(34): 14165-71, 2012 Aug 29.
Artigo em Inglês | MEDLINE | ID: mdl-22880959

RESUMO

Ionic bonding in supramolecular surface networks is a promising strategy to self-assemble nanostructures from organic building blocks with atomic precision. However, sufficient thermal stability of such systems has not been achieved at metal surfaces, likely due to partial screening of the ionic interactions. We demonstrate excellent stability of a self-assembled ionic network on a metal surface at elevated temperatures. The structure is characterized directly by atomic resolution scanning tunneling microscopy (STM) experiments conducted at 165 °C showing intact domains. This robust nanometer-scale structure is achieved by the on-surface reaction of a simple and inexpensive compound, sodium chloride, with a model system for carboxylate interactions, terephthalic acid (TPA). Rather than distinct layers of TPA and NaCl, angle resolved X-ray photoelectron spectroscopy experiments indicate a replacement reaction on the Cu(100) surface to form Na-carboxylate ionic bonds. Chemical shifts in core level electron states confirm a direct interaction and a +1 charge state of the Na. High-temperature STM imaging shows virtually no fluctuation of Na-TPA island boundaries, revealing a level of thermal stability that has not been previously achieved in noncovalent organic-based nanostructures at surfaces. Comparable strength of intermolecular ionic bonds and intramolecular covalent bonds has been achieved in this surface system. The formation of these highly ordered structures and their excellent thermal stability is dependent on the interplay of adsorbate-substrate and ionic interactions and opens new possibilities for ionic self-assemblies at surfaces with specific chemical function. Robust ionic surface structures have potential uses in technologies requiring high thermal stability and precise ordering through self-assembly.

11.
Langmuir ; 28(24): 8874-80, 2012 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-22401603

RESUMO

The plasmonic properties of self-assembled layers of rod- and branched-shaped gold nanoparticles were investigated using optical techniques. Nanoparticles were synthesized by a surfactant-guided, seed-mediated growth method. The layers were obtained by gradual assembly of nanoparticles at the interface between a polar and a nonpolar solvent and were transferred to a glass slide. Polarization and angle-dependent extinction measurements showed that the layers made of gold nanorods were governed by an effective medium response. The response of the layers made by branched gold particles was characterized by random light scattering. Microscopic mapping of the spatial mode structure demonstrates a uniform optical response of the nanoparticle layers down to a submicrometer length scale.


Assuntos
Ouro/química , Membranas Artificiais , Nanopartículas Metálicas/química , Nanotubos/química , Ressonância de Plasmônio de Superfície , Coloides/química , Tamanho da Partícula , Propriedades de Superfície
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