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1.
Nature ; 577(7788): 60-63, 2020 01.
Artigo em Inglês | MEDLINE | ID: mdl-31894149

RESUMO

The formation and growth of water-ice layers on surfaces and of low-dimensional ice under confinement are frequent occurrences1-4. This is exemplified by the extensive reporting of two-dimensional (2D) ice on metals5-11, insulating surfaces12-16, graphite and graphene17,18 and under strong confinement14,19-22. Although structured water adlayers and 2D ice have been imaged, capturing the metastable or intermediate edge structures involved in the 2D ice growth, which could reveal the underlying growth mechanisms, is extremely challenging, owing to the fragility and short lifetime of those edge structures. Here we show that noncontact atomic-force microscopy with a CO-terminated tip (used previously to image interfacial water with minimal perturbation)12, enables real-space imaging of the edge structures of 2D bilayer hexagonal ice grown on a Au(111) surface. We find that armchair-type edges coexist with the zigzag edges usually observed in 2D hexagonal crystals, and freeze these samples during growth to identify the intermediate edge structures. Combined with simulations, these experiments enable us to reconstruct the growth processes that, in the case of the zigzag edge, involve the addition of water molecules to the existing edge and a collective bridging mechanism. Armchair edge growth, by contrast, involves local seeding and edge reconstruction and thus contrasts with conventional views regarding the growth of bilayer hexagonal ices and 2D hexagonal matter in general.


Assuntos
Gelo , Microscopia de Tunelamento , Cristalização
2.
Science ; 367(6476): 368, 2020 01 24.
Artigo em Inglês | MEDLINE | ID: mdl-31974236
3.
Adv Exp Med Biol ; 1174: 35-60, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31713196

RESUMO

This chapter intends to review the progress in obtaining site-specific structural information for peptide assemblies using scanning tunneling microscopy. The effects on assembly propensity due to mutations and modifications in peptide sequences, small organic molecules and conformational transitions of peptides are identified. The obtained structural insights into the sequence-dependent assembly propensity could inspire rational design of peptide architectures at the molecular level.


Assuntos
Imagem Molecular , Peptídeos , Microscopia de Tunelamento , Mutação , Peptídeos/química , Peptídeos/metabolismo , Estrutura Secundária de Proteína
4.
Nat Commun ; 10(1): 4599, 2019 10 10.
Artigo em Inglês | MEDLINE | ID: mdl-31601813

RESUMO

Host-guest interactions are of central importance in many biological and chemical processes. However, the investigation of the formation and decomplexation of host-guest systems at the single-molecule level has been a challenging task. Here we show that the single-molecule conductance of organoplatinum(II) metallocycle hosts can be enhanced by an order of magnitude by the incorporation of a C60 guest molecule. Mechanically stretching the metallocycle-C60 junction with a scanning tunneling microscopy break junction technique causes the release of the C60 guest from the metallocycle, and consequently the conductance switches back to the free-host level. Metallocycle hosts with different shapes and cavity sizes show different degrees of flexibility to accommodate the C60 guest in response to mechanical stretching. DFT calculations provide further insights into the electronic structures and charge transport properties of the molecular junctions based on metallocycles and the metallocycle-C60 complexes.


Assuntos
Fulerenos/química , Compostos Organoplatínicos/química , Teoria da Densidade Funcional , Eletrodos , Ouro , Espectroscopia de Ressonância Magnética , Microscopia de Força Atômica , Microscopia de Tunelamento , Espectrofotometria Ultravioleta
5.
Molecules ; 24(16)2019 Aug 20.
Artigo em Inglês | MEDLINE | ID: mdl-31434280

RESUMO

The synthesis and surface self-assembly behavior of two types of metal-porphyrin dimers is described. The first dimer type consists of two porphyrins linked via a rigid conjugated spacer, and the second type has an alkyne linker, which allows rotation of the porphyrin moieties with respect to each other. The conjugated dimers were equipped with two copper or two manganese centers, while the flexible dimers allowed a modular built-up that also made the incorporation of two different metal centers possible. The self-assembly of the new porphyrin dimers at a solid-liquid interface was investigated at the single-molecule scale using scanning tunneling microscopy (STM). All dimers formed monolayers, of which the stability and the internal degree of ordering of the molecules depended on the metal centers in the porphyrins. While in all monolayers the dimers were oriented coplanar with respect to the underlying surface ('face-on'), the flexible dimer containing a manganese and a copper center could be induced, via the application of a voltage pulse in the STM setup, to self-assemble into monolayers in which the porphyrin dimers adopted a non-common perpendicular ('edge-on') geometry with respect to the surface.


Assuntos
Porfirinas/química , Cobre/química , Dimerização , Manganês/química , Microscopia de Tunelamento , Porfirinas/síntese química , Imagem Individual de Molécula/métodos
6.
Adv Mater ; 31(35): e1902816, 2019 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-31265189

RESUMO

The quest for a suitable molecule to pave the way to molecular nanoelectronics has been met with obstacles for over a decade. Candidate molecules such as carbon nanotubes lack the appealing trait of self-assembly, while DNA seems to lack the desirable feature of conductivity. Silver-containing poly(dG)-poly(dC) DNA (E-DNA) molecules have recently been reported as promising candidates for molecular electronics, owing to the selectivity of their metallization, their thin and uniform structure, their resistance to deformation, and their maximum possible high conductivity. Ultrahigh vacuum (UHV) scanning tunneling microscopy (STM) of E-DNA presents an elaborate high-resolution morphology characterization of these unique molecules, along with a detailed depiction of their electronic level structure. The energy levels found for E-DNA indicate a novel truly hybrid metal-molecule structure, potentially more conductive than other DNA-based alternatives.


Assuntos
DNA/química , Microscopia de Tunelamento , Poli G/química , Prata/química , Análise Espectral , Poli C/química
7.
Med Sci Monit ; 25: 4560-4568, 2019 Jun 19.
Artigo em Inglês | MEDLINE | ID: mdl-31216267

RESUMO

BACKGROUND Surgery has been considered to be the primary approach for resection of esophageal muscularis propria tumors. With the development of endoscopic technology, new techniques such as endoscopic submucosal dissection (ESD) and submucosal tunneling endoscopic resection (STER) have emerged for resecting these lesions. Previous studies have demonstrated that STER might be an intriguing alternative. This study aimed to evaluate the clinical value of STER by comparing it to other resecting modules. MATERIAL AND METHODS Clinical outcome and data were retrospectively collected from patients with esophageal muscularis propria tumors who underwent resection either endoscopically or thoracoscopically. The clinical data were statistically analyzed. RESULTS A total of 137 patients were enrolled. They were divided into 3 groups: a STER group (27 patients), an ESD group (42 patients), and a thoracoscopic enucleation (TE) group (68 patients). There were no significant differences among the 3 groups in gender, age, pathological type of tumors, or major adverse events (P>0.05). However, the STER group had the shortest duration of hospitalization and the lowest cost (P<0.05). Furthermore, the STER group was superior in operation time and the location of tumors to the TE group. Moreover, STER outperformed ESD in the resection of large tumors (P<0.05). Although STER had the lowest en bloc resection rate, no recurrence or metastasis was noted during a mean follow-up of 22.14 months (range 3 to 60 months). CONCLUSIONS STER is a feasible, safe, and effective approach for the resection of esophageal muscularis propria tumors ≤40 mm. We recommend STER as a potent alternative for these tumors.


Assuntos
Ressecção Endoscópica de Mucosa/métodos , Neoplasias Esofágicas/cirurgia , Microscopia de Tunelamento/métodos , Adulto , Idoso , China , Neoplasias Esofágicas/patologia , Esôfago/patologia , Feminino , Mucosa Gástrica/metabolismo , Mucosa Gástrica/cirurgia , Gastroscopia/métodos , Humanos , Masculino , Pessoa de Meia-Idade , Membrana Mucosa , Recidiva Local de Neoplasia/patologia , Duração da Cirurgia , Estudos Retrospectivos , Neoplasias Gástricas/patologia , Resultado do Tratamento
8.
J Vis Exp ; (145)2019 03 24.
Artigo em Inglês | MEDLINE | ID: mdl-30958467

RESUMO

The quest to understand correlated electronic systems has pushed the frontiers of experimental measurements toward the development of new experimental techniques and methodologies. Here we use a novel home-built uniaxial-strain device integrated into our variable temperature scanning tunneling microscope that enables us to controllably manipulate in-plane uniaxial strain in samples and probe their electronic response at the atomic scale. Using scanning tunneling microscopy (STM) with spin-polarization techniques, we visualize antiferromagnetic (AFM) domains and their atomic structure in Fe1+yTe samples, the parent compound of iron-based superconductors, and demonstrate how these domains respond to applied uniaxial strain. We observe the bidirectional AFM domains in the unstrained sample, with an average domain size of ~50-150 nm, to transition into a single unidirectional domain under applied uniaxial strain. The findings presented here open a new direction to utilize a valuable tuning parameter in STM, as well as other spectroscopic techniques, both for tuning the electronic properties as for inducing symmetry breaking in quantum material systems.


Assuntos
Ferro/química , Fenômenos Magnéticos , Microscopia de Tunelamento , Telúrio/química , Temperatura
9.
Int J Mol Sci ; 20(8)2019 Apr 24.
Artigo em Inglês | MEDLINE | ID: mdl-31022934

RESUMO

Chiral recognition among helical molecules is of essential importance in many chemical and biochemical processes. The complexity necessitates investigating manageable model systems for unveiling the fundamental principles of chiral recognition at the molecular level. Here, we reported chiral recognition in the self-assembly of enantiopure and racemic hexahelicene on a Au(111) surface. Combing scanning tunneling microscopy (STM) and atomic force microscopy (AFM) measurements, the asymmetric heterochiral trimers were observed as a new type of building block in racemic helicene self-assembly on Au(111). The intermolecular recognition of the heterochiral trimer was investigated upon manual separation so that the absolute configuration of each helicene molecule was unambiguously determined one by one, thus confirming that the trimer was "2+1" in handedness. These heterochiral trimers showed strong stability upon different coverages, which was also supported by theoretical calculations. Our results provide valuable insights for understanding the intermolecular recognition of helical molecules.


Assuntos
Compostos Policíclicos/química , Dimerização , Ouro/química , Microscopia de Força Atômica , Microscopia de Tunelamento , Modelos Moleculares , Estereoisomerismo , Propriedades de Superfície
10.
Chemphyschem ; 20(1): 103-107, 2019 01 07.
Artigo em Inglês | MEDLINE | ID: mdl-30467942

RESUMO

The abnormal accumulation of beta-amyloids (Aß) in brain is considered as a key initiating cause for Alzheimer's disease (AD) due to their richness in plaques and self-aggregate propensity. In recent studies, N-terminally extended Aß peptides (NTE-Aß) with the N-terminus originating prior to the canonical ß-secretase cleavage site were found in humans and suggested to have possible relevance to AD. However, the effects of the extended N-terminus on the amyloidegenic structure and aggregation propensity have not been fully elucidated. Herein, we characterized the assembly structures of Aß1-42, Aß(-5)-42, Aß(-10)-42 and Aß(-15)-42 with both normal and reversed sequences on highly oriented pyrolytic graphite (HOPG) surfaces with scanning tunneling microscopy (STM). The molecularly resolved surface-mediated peptide assemblies enable identification of amyloidegenic fragments. The observations reveal that the assembly propensity of the C-terminal strand of Aß1-42 is highly conserved and insensitive to N-terminal extensions. In contrast, different assembly structures of the N-terminal strand of Aß variants can be observed with possible assignment of varied amyloidegenic fragments in the extended N-termini, which may contribute to the varied aggregation propensities of Aß42 species.


Assuntos
Peptídeos beta-Amiloides/química , Microscopia de Tunelamento , Doença de Alzheimer/metabolismo , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Grafite/química , Humanos , Propriedades de Superfície
11.
Sci Adv ; 4(11): eaau4886, 2018 11.
Artigo em Inglês | MEDLINE | ID: mdl-30430137

RESUMO

The impact of nonmagnetic and magnetic impurities on topological insulators is a central focus concerning their fundamental physics and possible spintronics and quantum computing applications. Combining scanning tunneling spectroscopy with transport measurements, we investigate, both locally and globally, the effect of nonmagnetic and magnetic substituents in SmB6, a predicted topological Kondo insulator. Around the so-introduced substitutents and in accord with theoretical predictions, the surface states are locally suppressed with different length scales depending on the substituent's magnetic properties. For sufficiently high substituent concentrations, these states are globally destroyed. Similarly, using a magnetic tip in tunneling spectroscopy also resulted in largely suppressed surface states. Hence, a destruction of the surface states is always observed close to atoms with substantial magnetic moment. This points to the topological nature of the surface states in SmB6 and illustrates how magnetic impurities destroy the surface states from microscopic to macroscopic length scales.


Assuntos
Compostos de Boro/química , Magnetismo , Microscopia de Tunelamento/métodos , Samário/química , Propriedades de Superfície
12.
Faraday Discuss ; 210(0): 9-28, 2018 10 01.
Artigo em Inglês | MEDLINE | ID: mdl-30264833

RESUMO

The development of nanoscale electrochemistry since the mid-1980s has been predominately coupled with steady-state voltammetric (i-E) methods. This research has been driven by the desire to understand the mechanisms of very fast electrochemical reactions, by electroanalytical measurements in small volumes and unusual media, including in vivo measurements, and by research on correlating electrocatalytic activity, e.g., O2 reduction reaction, with nanoparticle size and structure. Exploration of the behavior of nanoelectrochemical structures (nanoelectrodes, nanoparticles, nanogap cells, etc.) of a characteristic dimension λ using steady-state i-E methods generally relies on the well-known relationship, λ2 ∼ Dt, which relates diffusional lengths to time, t, through the coefficient, D. Decreasing λ, by performing measurements at a nanometric length scales, results in a decrease in the effective timescale of the measurement, and provides a direct means to probe the kinetics of steps associated with very rapid electrochemical reactions. For instance, steady-state voltammetry using a nanogap twin-electrode cell of characteristic width, λ ∼ 10 nm, allows investigations of events occurring at timescales on the order of ∼100 ns. Among many other advantages, decreasing λ also increases spatial resolution in electrochemical imaging, e.g., in scanning electrochemical microscopy, and allows probing of the electric double layer. This Introductory Lecture traces the evolution and driving forces behind the "λ2 ∼ Dt" steady-state approach to nanoscale electrochemistry, beginning in the late 1950s with the introduction of the rotating ring-disk electrode and twin-electrode thin-layer cells, and evolving to current-day investigations using nanoelectrodes, scanning nanocells for imaging, nanopores, and nanoparticles. The recent focus on so-called "single-entity" electrochemistry, in which individual and very short redox events are probed, is a significant departure from the steady-state approach, but provides new opportunities to probe reaction dynamics. The stochastic nature of very fast single-entity events challenges current electrochemical methods and modern electronics, as illustrated using recent experiments from the authors' laboratory.


Assuntos
Técnicas Eletroquímicas/instrumentação , Nanotecnologia/instrumentação , DNA/química , Difusão , Desenho de Equipamento , Cinética , Microeletrodos , Microscopia de Tunelamento/instrumentação , Modelos Moleculares , Nanopartículas/química , Nanoporos/ultraestrutura , Oxirredução , Processos Estocásticos
13.
J Vis Exp ; (135)2018 05 27.
Artigo em Inglês | MEDLINE | ID: mdl-29889192

RESUMO

Water/solid interfaces are ubiquitous and play a key role in many environmental, biophysical, and technological processes. Resolving the internal structure and probing the hydrogen-bond (H-bond) dynamics of the water molecules adsorbed on solid surfaces are fundamental issues of water science, which remains a great challenge owing to the light mass and small size of hydrogen. Scanning tunneling microscopy (STM) is a promising tool for attacking these problems, thanks to its capabilities of sub-Ångström spatial resolution, single-bond vibrational sensitivity, and atomic/molecular manipulation. The designed experimental system consists of a Cl-terminated tip and a sample fabricated by dosing water molecules in situ onto the Au(111)-supported NaCl(001) surfaces. The insulating NaCl films electronically decouple the water from the metal substrates, so the intrinsic frontier orbitals of water molecules are preserved. The Cl-tip facilitates the manipulation of the single water molecules, as well as gating the orbitals of water to the proximity of Fermi level (EF) via tip-water coupling. This paper outlines the detailed methods of submolecular resolution imaging, molecular/atomic manipulation, and single-bond vibrational spectroscopy of interfacial water. These studies open up a new route for investigating the H-bonded systems at the atomic scale.


Assuntos
Microscopia de Tunelamento/métodos , Análise Espectral/métodos , Água/química
14.
ACS Nano ; 12(7): 7067-7075, 2018 07 24.
Artigo em Inglês | MEDLINE | ID: mdl-29932668

RESUMO

In the present study, we demonstrate a tunneling nanogap technique to identify individual RNA nucleotides, which can be used as a mechanism to read the nucleobases for direct sequencing of RNA in a solid-state nanopore. The tunneling nanogap is composed of two electrodes separated by a distance of <3 nm and functionalized with a recognition molecule. When a chemical entity is captured in the gap, it generates electron tunneling currents, a process we call recognition tunneling (RT). Using RT nanogaps created in a scanning tunneling microscope (STM), we acquired the electron tunneling signals for the canonical and two modified RNA nucleotides. To call the individual RNA nucleotides from the RT data, we adopted a machine learning algorithm, support vector machine (SVM), for the data analysis. Through the SVM, we were able to identify the individual RNA nucleotides and distinguish them from their DNA counterparts with reasonably high accuracy. Since each RNA nucleoside contains a hydroxyl group at the 2'-position of its sugar ring in an RNA strand, it allows for the formation of a tunneling junction at a larger nanogap compared to the DNA nucleoside in a DNA strand, which lacks the 2' hydroxyl group. It also proves advantageous for the manufacture of RT devices. This study is a proof-of-principle demonstration for the development of an RT nanopore device for directly sequencing single RNA molecules, including those bearing modifications.


Assuntos
Aprendizado de Máquina , Nanotecnologia , Nucleotídeos/análise , RNA/análise , Microscopia de Tunelamento , Estrutura Molecular , Nanoporos , Tamanho da Partícula , Propriedades de Superfície
15.
Biomed Mater ; 13(4): 045012, 2018 05 04.
Artigo em Inglês | MEDLINE | ID: mdl-29727301

RESUMO

The aim of the present study is to develop keratin nanoparticles (NPs) encapsulated in Dunaliella bardawil (D. bardawil) biomass, in order to improve their glucose uptake in 3T3-L1 adipocytes. The graph theoretical approach has provided a platform to identify PTP-1B and AMPK as an effective drug target. Docking results of the active constituents of D. bardawil showed a strong interaction with binding pockets of identified PTP-1B and AMPK. The encapsulation efficiency, drug release, stability and physicochemical properties of prepared NPs were analyzed using UV-visible spectrophotometry, Fourier transform infrared spectrophotometry, x-ray diffraction, scanning and tunneling electron microscopy, and Zeta size analysis. Further, encapsulated keratin NPs were screened for their in vitro cytotoxicity and glucose uptake studies. The study report of biomass encapsulated keratin NPs showed no toxicity at lower concentrations and 81.23 ± 6.56% cellular viability at 30 µg in 3T3-L1 adipocytes. Moreover, the effect of keratin NPs (30 µg) on glucose utilization (58.56 ± 4.54%) was higher than that of Metformin (10 µM) or insulin (10 µM). The observed higher level of glucose utilization may lead to the development of novel ways to enhance biological activities.


Assuntos
Biomassa , Clorófitas/química , Glucose/química , Queratinas/química , Nanopartículas/química , Células 3T3-L1 , Animais , Simulação por Computador , Cabelo , Humanos , Insulina/química , Masculino , Metformina/química , Camundongos , Microscopia Eletrônica de Varredura , Microscopia Eletrônica de Transmissão , Microscopia de Tunelamento , Simulação de Acoplamento Molecular , Ligação Proteica , Espectroscopia de Infravermelho com Transformada de Fourier , Difração de Raios X
16.
Anal Sci ; 34(5): 521-523, 2018 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-29681565

RESUMO

We report on a method to measure the electron transport of a single molecular assembly by scanning tunneling microscopy (STM). The STM molecular tip together with a chemically modified substrate was utilized to form an assembly with a single target molecule. This method was successfully applied to a heme peptide to reveal the transport property of a single peptide-containing assembly. The present work opens a way to create functional single molecular devices using biomolecules.


Assuntos
Microscopia de Tunelamento , Peptídeos/síntese química , Transporte de Elétrons , Substâncias Macromoleculares/síntese química , Substâncias Macromoleculares/química , Peptídeos/química
17.
Int J Mol Sci ; 19(4)2018 Apr 13.
Artigo em Inglês | MEDLINE | ID: mdl-29652860

RESUMO

Most biological phenomena occur at the nanometer scale, which is not accessible by the conventional optical techniques because of the optical diffraction limitation. Tip-enhanced Raman spectroscopy (TERS), one of the burgeoning probing techniques, not only can provide the topography characterization with high resolution, but also can deliver the chemical or molecular information of a sample beyond the optical diffraction limitation. Therefore, it has been widely used in various structural analyses pertaining to materials science, tissue engineering, biological processes and so on. Based on the different feedback mechanisms, TERS can be classified into three types: atomic force microscopy based TERS system (AFM-TERS), scanning tunneling microscopy based TERS system (STM-TERS) and shear force microscopy based TERS system (SFM-TERS). Among them, AFM-TERS is the most widely adopted feedback system by live biosamples because it can work in liquid and this allows the investigation of biological molecules under native conditions. In this review, we mainly focus on the applications of AFM-TERS in three biological systems: nucleic acids, proteins and pathogens. From the TERS characterization to the data analysis, this review demonstrates that AFM-TERS has great potential applications to visually characterizing the biomolecular structure and crucially detecting more nano-chemical information of biological systems.


Assuntos
Ácidos Nucleicos/química , Proteínas/química , Microscopia de Força Atômica , Microscopia de Tunelamento , Nanoestruturas/química , Análise Espectral Raman
18.
Langmuir ; 34(9): 3126-3135, 2018 03 06.
Artigo em Inglês | MEDLINE | ID: mdl-29412680

RESUMO

Realization of useful nanometer length scale devices in which metalloproteins are junction-confined in a distinct molecular arrangement for generating practical electronic signals (e.g., in bioelectronic switch configuration) is elusive till date. This is mostly due to difficulties in observing an electronically appropriate signal (i.e., reproducible and controllable), when studied under junction-assembled condition. A useful "ON"-"OFF" behavior, based on the negative differential resistance (NDR) peak characteristics in the current-voltage response curves, acquired using metal-insulator-metal (MIM) configuration, has been observed only in the case of a few proteins, namely, azurin, cytochrome c, bacteriorhodopsin, so far. The case of NDR in ferritin, an iron storage protein having a semiconducting iron core consisting of few thousands of iron atoms connected in an oxide network, has not been studied in the MIM configuration where single (or a few) molecule(s) are junction-trapped, for example, as in the case of local probe configuration of scanning probe microscopy. The present study by scanning tunneling microscopy (STM), using the naturally occurring iron-containing ferritin (human liver), as well as different iron-loaded ferritins, provides clear indication of the capability of ferritins to be NDR capable, at varying sweep conditions. As ferritin can be tailor-made in a structurally conserved manner, metal core-reconstituted ferritins, that is, Mn(III)-ferritin, Cu(II)-ferritin, and Ag-ferritin, were prepared. A correlation between the NDR peak signatures, as observed in the respective current-voltage response curves of these reconstituted ferritins, and the nature of the metal core is demonstrated. In support of our earlier proposition, here, we affirm that the ferritin protein behaves as a conductor-insulator (metal core-polypeptide shell) composite, where the overall electronic structure of the material can alter as a function of the nature of the conducting filler placed inside the insulated matrix.


Assuntos
Ferritinas/química , Metaloproteínas/metabolismo , Humanos , Ferro/química , Metaloproteínas/química , Microscopia de Tunelamento
19.
J Vis Exp ; (131)2018 01 19.
Artigo em Inglês | MEDLINE | ID: mdl-29443038

RESUMO

The miniaturization of semiconductor devices to scales where small numbers of dopants can control device properties requires the development of new techniques capable of characterizing their dynamics. Investigating single dopants requires sub-nanometer spatial resolution, which motivates the use of scanning tunneling microscopy (STM). However, conventional STM is limited to millisecond temporal resolution. Several methods have been developed to overcome this shortcoming, including all-electronic time-resolved STM, which is used in this study to examine dopant dynamics in silicon with nanosecond resolution. The methods presented here are widely accessible and allow for local measurement of a wide variety of dynamics at the atomic scale. A novel time-resolved scanning tunneling spectroscopy technique is presented and used to efficiently search for dynamics.


Assuntos
Microscopia de Tunelamento/métodos , Silício/química
20.
J Phys Chem Lett ; 9(4): 763-767, 2018 Feb 15.
Artigo em Inglês | MEDLINE | ID: mdl-29376375

RESUMO

We measure the conductance of unmodified peptides at the single-molecule level using the scanning tunneling microscope-based break-junction method, utilizing the N-terminal amine group and the C-terminal carboxyl group as gold metal-binding linkers. Our conductance measurements of oligoglycine and oligoalanine backbones do not rely on peptide side-chain linkers. We compare our results with alkanes terminated asymmetrically with an amine group on one end and a carboxyl group on the other to show that peptide bonds decrease the conductance of an otherwise saturated carbon chain. Using a newly developed first-principles approach, we attribute the decrease in conductance to charge localization at the peptide bond, which reduces the energy of the frontier orbitals relative to the Fermi energy and the electronic coupling to the leads, lowering the tunneling probability. Crucially, this manifests as an increase in conductance decay of peptide backbones with increasing length when compared with alkanes.


Assuntos
Microscopia de Tunelamento/métodos , Peptídeos/química , Alcanos/química , Condutividade Elétrica , Transporte de Elétrons , Ouro/química , Modelos Moleculares
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