scholarly journals Spectroscopic Signatures of Nitrogen-Substituted Zeolites

2008 ◽  
Vol 130 (45) ◽  
pp. 14912-14913 ◽  
Author(s):  
Karl D. Hammond ◽  
Fulya Dogan ◽  
Geoffrey A. Tompsett ◽  
Vishal Agarwal ◽  
W. Curtis Conner ◽  
...  
Keyword(s):  
Spectroscopic Signatures

scholarly journals The Three Pillars of Natural Product Dereplication. Alkaloids from the Bulbs of Urceolina peruviana (C. Presl) J.F. Macbr. as a Preliminary Test Case

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 637
Author(s):  
Mariacaterina Lianza ◽  
Ritchy Leroy ◽  
Carine Machado Rodrigues ◽  
Nicolas Borie ◽  
Charlotte Sayagh ◽  
...  
Keyword(s):  
Natural Product ◽  
Spectroscopic Data ◽  
Preliminary Test ◽  
Rapid Identification ◽  
Molecular Structures ◽  
Data Sources ◽  
Test Case ◽  
The Andes ◽  
Spectroscopic Signatures ◽  
Product Chemistry

The role and importance of the identification of natural products are discussed in the perspective of the study of secondary metabolites. The rapid identification of already reported compounds, or structural dereplication, is recognized as a key element in natural product chemistry. The biological taxonomy of metabolite producing organisms, the knowledge of metabolite molecular structures, and the availability of metabolite spectroscopic signatures are considered as the three pillars of structural dereplication. The role and the construction of databases is illustrated by references to the KNApSAcK, UNPD, CSEARCH, and COCONUT databases, and by the importance of calculated taxonomic and spectroscopic data as substitutes for missing or lost original ones. Two NMR-based tools, the PNMRNP database that derives from UNPD, and KnapsackSearch, a database generator that provides taxonomically focused libraries of compounds, are proposed to the community of natural product chemists. The study of the alkaloids from Urceolina peruviana, a plant from the Andes used in traditional medicine for antibacterial and anticancer actions, has given the opportunity to test different approaches to dereplication, favoring the use of publicly available data sources.

scholarly journals Spectroscopy of a tunable moiré system with a correlated and topological flat band

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Xiaomeng Liu ◽  
Cheng-Li Chiu ◽  
Jong Yeon Lee ◽  
Gelareh Farahi ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Band Structure ◽  
Twist Angle ◽  
Bilayer Graphene ◽  
Scanning Tunneling Spectroscopy ◽  
Scanning Tunneling ◽  
Flat Band ◽  
Correlated Electron ◽  
Partial Filling ◽  
Valley Polarization ◽  
Spectroscopic Signatures

AbstractMoiré superlattices created by the twisted stacking of two-dimensional crystals can host electronic bands with flat energy dispersion in which enhanced interactions promote correlated electron states. The twisted double bilayer graphene (TDBG), where two Bernal bilayer graphene are stacked with a twist angle, is such a moiré system with tunable flat bands. Here, we use gate-tuned scanning tunneling spectroscopy to directly demonstrate the tunability of the band structure of TDBG with an electric field and to show spectroscopic signatures of electronic correlations and topology for its flat band. Our spectroscopic experiments are in agreement with a continuum model of TDBG band structure and reveal signatures of a correlated insulator gap at partial filling of its isolated flat band. The topological properties of this flat band are probed with the application of a magnetic field, which leads to valley polarization and the splitting of Chern bands with a large effective g-factor.

scholarly journals Spectroscopic signatures of the T to R conformational transition in the insulin hexamer

1989 ◽  
Vol 264 (32) ◽  
pp. 19081-19085 ◽  
Author(s):  
M Roy ◽  
M L Brader ◽  
R W Lee ◽  
N C Kaarsholm ◽  
J F Hansen ◽  
...  
Keyword(s):  
Conformational Transition ◽  
Spectroscopic Signatures

Tracing absorption and emission characteristics of halogen-bonded ion pairs involving halogenated imidazolium species

2021 ◽  
Vol 23 (12) ◽  
pp. 7480-7494
Author(s):  
Sarah Karbalaei Khani ◽  
Bastian Geissler ◽  
Elric Engelage ◽  
Patrick Nuernberger ◽  
Christof Hättig
Keyword(s):  
Ion Pairs ◽  
Ion Pairing ◽  
Emission Characteristics ◽  
Absorption And Emission ◽  
Spectroscopic Signatures

Spectroscopic signatures of ion-pairing are identified by variation of counterion and substitution and comparison with theory.

X‐Ray Spectroscopic Signatures of the Extended Corona of FK Comae

2008 ◽  
Vol 679 (2) ◽  
pp. 1522-1530 ◽  
Author(s):  
Jeremy J. Drake ◽  
Sun Mi Chung ◽  
Vinay Kashyap ◽  
Heidi Korhonen ◽  
Adriaan Van Ballegooijen ◽  
...  
Keyword(s):  
X Ray ◽  
Spectroscopic Signatures

Spectroscopic signatures of phase transitions in a charge-density-wave system: 1T-TaS2

1992 ◽  
Vol 46 (12) ◽  
pp. 7407-7412 ◽  
Author(s):  
B. Dardel ◽  
M. Grioni ◽  
D. Malterre ◽  
P. Weibel ◽  
Y. Baer ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Charge Density ◽  
Charge Density Wave ◽  
Density Wave ◽  
Wave System ◽  
A Charge ◽  
Spectroscopic Signatures

Surface Spectroscopic Signatures of Mechanical Deformation in High-Density Polyethylene (HDPE)

2018 ◽  
Vol 72 (7) ◽  
pp. 1057-1068 ◽  
Author(s):  
Shawn C. Averett ◽  
Steven K. Stanley ◽  
Joshua J. Hanson ◽  
Stacey J. Smith ◽  
James E. Patterson
Keyword(s):  
High Density Polyethylene ◽  
Cold Drawing ◽  
Mechanical Deformation ◽  
Sum Frequency Generation ◽  
High Density ◽  
X Ray ◽  
Sum Frequency ◽  
Surface Normal ◽  
Methylene Groups ◽  
Spectroscopic Signatures

High-density polyethylene (HDPE) has been extensively studied, both as a model for semi-crystalline polymers and because of its own industrial utility. During cold drawing, crystalline regions of HDPE are known to break up and align with the direction of tensile load. Structural changes due to deformation should also manifest at the surface of the polymer, but until now, a detailed molecular understanding of how the surface responds to mechanical deformation has been lacking. This work establishes a precedent for using vibrational sum-frequency generation (VSFG) spectroscopy to investigate changes in the molecular-level structure of the surface of HDPE after cold drawing. X-ray diffraction (XRD) was used to confirm that the observed surface behavior corresponds to the expected bulk response. Before tensile loading, the VSFG spectra indicate that there is significant variability in the surface structure and tilt of the methylene groups away from the surface normal. After deformation, the VSFG spectroscopic signatures are notably different. These changes suggest that hydrocarbon chains at the surface of visibly necked HDPE are aligned with the direction of loading, while the associated methylene groups are oriented with the local C2 v symmetry axis roughly parallel to the surface normal. Small amounts of unaltered material are also found at the surface of necked HDPE, with the relative amount of unaltered material decreasing as the amount of deformation increases. Aspects of the nonresonant SFG response in the transition zone between necked and undeformed polymer provide additional insight into the deformation process and may provide the first indication of mechanical deformation. Nonlinear surface spectroscopy can thus be used as a noninvasive and nondestructive tool to probe the stress history of a HPDE sample in situations where X-ray techniques are not available or not applicable. Vibrational sum-frequency generation thus has great potential as a platform for material state awareness (MSA) and should be considered as part of a broader suite of tools for such applications.

Characterization of NH4-montmorillonite coexisting with NH4Cl salt at different aggregation states. Application to Ceres.

2021 ◽  
Author(s):  
Victoria Munoz-Iglesias ◽  
Maite Fernández-Sampedro ◽  
Carolina Gil-Lozano ◽  
Laura J. Bonales ◽  
Oscar Ercilla Herrero ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Spectroscopic Data ◽  
External Surface ◽  
Deionized Water ◽  
Asteroid Belt ◽  
Aqueous Alteration ◽  
Dawn Mission ◽  
Main Asteroid Belt ◽  
Spectroscopic Signatures

<p>Ceres, dwarf planet of the main asteroid belt, is considered a relic ocean world since the Dawn mission discovered evidences of aqueous alteration and cryovolcanic activity [1]. Unexpectedly, a variety of ammonium-rich minerals were identified on its surface, including phyllosilicates, carbonates, and chlorides [2]. Although from the Dawn’s VIR spectroscopic data it was not possible to specify the exact type of phyllosilicates observed, montmorillonite is considered a good candidate owing to its ability to incorporate NH<sub>4</sub><sup>+</sup> in its interlayers [3]. Ammonium-rich phases are usually found at greater distances from the Sun. Hence, the study on their stability at environmental conditions relevant to Ceres’ interior and of its regolith can help elucidate certain ambiguities concerning the provenance of its precursor materials.</p> <p>In this study, it was investigated the changes in the spectroscopic signatures of the clay mineral montmorillonite after (a) being immersed in ammonium chloride aqueous solution and, subsequently, (b) washed with deionized water. After each treatment, samples were submitted to different environmental conditions relevant to the surface of Ceres. For one experiment, they were frozen overnight at 193 K, and then subjected to 10<sup>-5</sup> bar for up to 4 days in a Telstar Cryodos lyophilizer. For the other, they were placed inside the Planetary Atmospheres and Surfaces Chamber (PASC) [4] for 1 day at 100 K and 5.10<sup>-8</sup> bar. The combination of different techniques, i.e., Raman and IR spectroscopies, XRD, and SEM/EDX, assisted the assignment of the bands to each particular molecule. In this regard, the signatures of the mineral external surface were distinguished from the interlayered NH<sub>4</sub><sup>+ </sup>cations. The degree of compaction of the samples resulted crucial on their stability and spectroscopic response, being stiff smectites more resistant to low temperatures and vacuum conditions. In ground clay minerals, a decrease in the basal space with a redshift of the interlayered NH<sub>4</sub><sup>+</sup> IR band was measured after just 1 day of being exposed to vacuum conditions.</p> <p>Acknowledgments</p> <p>This work was supported by the Spanish MINECO projects ESP2017-89053-C2-1-P and PID2019-107442RB-C32, and the AEI project MDM‐2017‐0737 Unidad de Excelencia “María de Maeztu”.</p> <p>References</p> <p>[1] De Sanctis et al.,  Space Sci. Rev. 216, 60, 2020</p> <p>[2] Raponi et al., Icarus 320, 83,  2019</p> <p>[3] Borden and Giese, Clays Clay Miner. 49, 444, 2001</p> <p>[4] Mateo-Marti et al., Life 9, 72, 2019</p>

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