Vishesh Saxena

Universität Hamburg

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Kirsten von Bergmann

Universität Hamburg

André Kubetzka

Universität Hamburg

Arturo Rodríguez-Sota

Universität Hamburg

Roberto Lo Conte

Universität Hamburg

R. Wiesendanger

Universität Hamburg

Jonas Spethmann

Universität Hamburg

Thomas L. C. Jansen

University of Groningen

Roland Wiesendanger

Universität Hamburg

Sravendra Rana

University of Petroleum and Energy Studies

D.B. Wetlaufer

University of Delaware

Cooperative Institutions

University of Groningen

Universität Hamburg

Kiel University

Nanyang Technological University

University of Petroleum and Energy Studies

University of Delaware

University of Minnesota Medical Center

University of Minnesota

Indiana University School of Medicine

Indiana University – Purdue University Indianapolis

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Distinguishing islet amyloid polypeptide fibril structures with infrared isotope-label spectroscopy

The Journal of Chemical Physics (2022)

Vishesh Saxena Ruben Steendam Thomas L. C. Jansen

Here, we performed spectral simulations of the amide-I vibrational spectra for three proposed fibril structures of the human islet amyloid polypeptide, which is involved in type II diabetes. We modeled both the overall absorption and two-dimensional infrared spectra for these structures. We further analyzed the isotope-labeled spectra, including the variation between structures. The analysis suggests that the infrared spectra of the cryo-electron microscopy structure provide the best match with experimental data. We further simulated isotope-labeled dilution spectroscopy investigating the correlation between the predicted spectral peak shift and the coupling between the amide units. While this correlation works in most cases, failures were observed when the isotope-labeled spectra were broad compared to the coupling or exhibited structure. These findings will be useful in the quest for potential toxic fibril formation intermediates.

Amyloid (mycology)

10.1063/5.0082322

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Citations (7)

Contribution of Ex-Situ and In-Situ X-ray Grazing Incidence Scattering Techniques to the Understanding of Quantum Dot Self-Assembly: A Review

Nanomaterials (2020)

Vishesh Saxena Giuseppe Portale

Quantum dots are under intense research, given their amazing properties which favor their use in electronics, optoelectronics, energy, medicine and other important applications. For many of these technological applications, quantum dots are used in their ordered self-assembled form, called superlattice. Understanding the mechanism of formation of the superlattices is crucial to designing quantum dots devices with desired properties. Here we review some of the most important findings about the formation of such superlattices that have been derived using grazing incidence scattering techniques (grazing incidence small and wide angle X-ray scattering (GISAXS/GIWAXS)). Acquisition of these structural information is essential to developing some of the most important underlying theories in the field.

Grazing-incidence small-angle scattering

10.3390/nano10112240

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Phase Coexistence of Mn Trimer Clusters and Antiferromagnetic Mn Islands on Ir(111)

arXiv (Cornell University) (2023)

Arturo Rodríguez-Sota Vishesh Saxena Jonas Spethmann Roland Wiesendanger Roberto Lo Conte

Clusters supported by solid substrates are prime candidates for heterogeneous catalysis and can be prepared in various ways. While mass-selected soft-landing methods are often used for the generation of monodisperse particles, self-assembly typically leads to a range of different cluster sizes. Here we show by scanning tunneling microscopy measurements that in the initial stages of growth Mn forms trimers on a close-packed hexagonal Ir surface, providing a route for self-organized monodisperse cluster formation on an isotropic metallic surface. For an increasing amount of Mn, first a phase with reconstructed monolayer islands is formed, until at full coverage a pseudomorphic Mn phase evolves which is the most densely packed one of the three different observed Mn phases on Ir(111). The magnetic state of both the reconstructed islands and the pseudomorphic film is found to be the prototypical antiferromagnetic N\'eel state with 120{\deg} spin rotation between all nearest neighbors in the hexagonal layer.

Trimer

Nanoclusters

10.48550/arxiv.2311.10506

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Phase Coexistence of Mn Trimer Clusters and Antiferromagnetic Mn Islands on Ir(111)

ACS Nano (2024)

Arturo Rodríguez-Sota Vishesh Saxena Jonas Spethmann R. Wiesendanger Roberto Lo Conte

Clusters supported by solid substrates are prime candidates for heterogeneous catalysis and can be prepared in various ways. While mass-selected soft-landing methods are often used for the generation of monodisperse particles, self-assembly typically leads to a range of different cluster sizes. Here we show by scanning tunneling microscopy measurements that in the initial stages of growth, Mn forms trimers on a close-packed hexagonal Ir surface, providing a route for self-organized monodisperse cluster formation on an isotropic metallic surface. For an increasing amount of Mn, first a phase with reconstructed monolayer islands is formed, until at full coverage a pseudomorphic Mn phase evolves, which is the most densely packed one of the three different observed Mn phases on Ir(111). The magnetic state of both the reconstructed islands and the pseudomorphic film is found to be the prototypical antiferromagnetic Néel state with a 120° spin rotation between all nearest neighbors in the hexagonal layer.

Trimer

Nanoclusters

10.1021/acsnano.3c11459

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A New Basis for Interpreting the Circular Dichroic Spectra of Proteins

Proceedings of the National Academy of Sciences (1971)

Vishesh Saxena D.B. Wetlaufer

Experimental circular dichroic (CD) spectra of three proteins have been combined with estimates of the content of peptide-chain structural modes obtained from x-ray diffraction studies of the same proteins. Solution of the simultaneous equations at a series of wavelengths permits the construction of a CD spectrum for each of three structural modes: alpha-helix, beta-structure, and the so-called "random". The CD spectra thus obtained are compared with those obtained from polypeptide models. The alpha-helical spectra from the two approaches are nearly congruent, the beta-structure spectra are in fair agreement, and the third forms agree qualitatively, but are substantially different quantitatively. Comparisons are made between the present approach and earlier approaches to interpreting protein CD spectra. Certain advantages of the present approach are indicated.

Dichroic glass

Basis (linear algebra)

Helix (gastropod)

10.1073/pnas.68.5.969

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Citations (277)

Formation of three-dimensional structure in proteins. I. Rapid nonenzymic reactivation of reduced lysozyme

Biochemistry (1970)

Donald B. Wetlaufer Vishesh Saxena

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTFormation of three-dimensional structure in proteins. I. Rapid nonenzymic reactivation of reduced lysozymeDonald B. Wetlaufer and V. P. SaxenaCite this: Biochemistry 1970, 9, 25, 5015–5023Publication Date (Print):December 8, 1970Publication History Published online1 May 2002Published inissue 8 December 1970https://pubs.acs.org/doi/10.1021/bi00827a028https://doi.org/10.1021/bi00827a028research-articleACS PublicationsRequest reuse permissionsArticle Views697Altmetric-Citations308LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts

Muramidase

10.1021/bi00827a028

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Citations (394)

Self-healing epoxy/PDMS/graphene oxide nanocomposites for anti-corrosive applications

Chemical and Process Engineering New Frontiers (2023)

Krishna Moorthi Vishesh Saxena R. Siva Prasanna Sanka Sravendra Rana

This study discusses the synthesis, characterization and development of self-healing nanocomposite of amino-terminated PDMS (Polydimethylsiloxane), Epoxy (EPON828+ Diethylenetriamine (DETA)), and Graphene Oxide (GO).GO was prepared using a modified Hummer's method and was incorporated into the PDMS-Epoxy composite in various ratios (0.1 wt.%, 0.3 wt.%, and 0.5 wt.%) using toluene as the dispersing medium.Fourier Transform Infrared Spectroscopy was used for confirming the presence of the designed/prepared structures, and thermo-mechanical analysis was performed to test the change in glass transition temperature and initiation temperature of self-healing process.The composite resins were coated on mild steel substrates by curing freshly prepared resins over the substrates at elevated temperatures.The corrosion behavior of mild steel in 3.5 wt.% NaCl solution before and after the coatings was studied using Tafel Electrochemical Polarization test.The self-healing properties of the materials were also studied by applying cuts on the material and letting them heal under elevated temperatures, and the results showed that the prepared coating demonstrated an effective corrosion resistance for mild steel for various marine applications.

10.24425/cpe.2022.140816

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Strain-driven domain wall network with chiral junctions in an antiferromagnet

arXiv (Cornell University) (2024)

Vishesh Saxena Mara Gutzeit Arturo Rodríguez-Sota Soumyajyoti Haldar Felix Zahner

Materials with antiferromagnetic order have recently emerged as promising candidates in spintronics based on their beneficial characteristics such as vanishing stray fields and ultra-fast dynamics. At the same time more complex localized non-coplanar magnetic states as for instance skyrmions are in the focus of applications due to their intriguing properties such as the topological Hall effect. Recently a conceptual shift has occurred to envision the use of such magnetic defects not only in one-dimensional race track devices but to exploit their unique properties in two-dimensional networks. Here we use local strain in a collinear antiferromagnet to induce non-coplanar domain wall junctions, which connect in a very specific way to form extended networks. We combine spin-polarized scanning tunneling microscopy with density functional theory to characterize the different building blocks of the network, and unravel the origin of the handedness of triple-junctions and the size of the arising topological orbital moments.

Domain wall (magnetism)

Strain (injury)

10.48550/arxiv.2408.12580

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