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1. Templated Growth of a Homochiral Thin Film Oxide

   https://doi.org/10.1021/acsnano.0c00398  

   Schilling, Alex C.; Therrien, Andrew J.; Hannagan, Ryan T.; Marcinkowski, Matthew D.; Kress, Paul L.; Patel, Dipna A.; Balema, Tedros A.; Larson, Amanda M.; Lucci, Felicia R.; Coughlin, Benjamin P.; et al (April 2020, ACS Nano)

   Chiral surfaces are of growing interest for enantioselective adsorption and reactions. While metal surfaces can be prepared with a wide range of chiral surface orientations, chiral oxide surface preparation is much more challenging. Herein, we demonstrate that the chirality of a metal surface can be used to direct the homochiral growth of a thin film chiral oxide. Specifically, we study the chiral ‘29’ copper oxide, formed by oxidizing a Cu(111) single crystal at 650 K. Surface structure spread single crystals which expose a continuous distribution of surface orientations as a function of position on the crystal, enabled us to systematically investigate the mechanism of chirality transfer between metal and oxide with high-resolution scanning tunneling microscopy. We discovered that the local underlying metal facet directs the orientation and chirality of the oxide overlayer. Importantly, single homochiral domains of the ‘29’ oxide were found in areas where the Cu step edges that templated growth were ≤20 nm apart. We used this information to select a Cu(239 241 246) oriented single crystal and demonstrate that a ‘29’ oxide surface can be grown in homochiral domains by templating from the subtle chirality of the underlying metal crystal. This work demonstrates how a small degree of chirality induced by very slight misorientation of a metal surface (~1 sites/ 20 nm2) can be amplified by oxidation to yield a homochiral oxide with a regular array of chiral oxide pores (~75 sites/ 20 nm2). This offers a general approach for making chiral oxide surfaces via oxidation of an appropriately miscut metal surface. 

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2. Chiral plasmonic metasurface absorbers in the mid-infrared wavelength range

   https://doi.org/10.1364/OL.404192  

   Mahmud, Md_Shamim; Rosenmann, Daniel; Czaplewski, David_A; Gao, Jie; Yang, Xiaodong (September 2020, Optics Letters)

   Chiral metamaterials in the mid-infrared wavelength range have tremendous potential for studying thermal emission manipulation and molecular vibration sensing. Here, we present one type of chiral plasmonic metasurface absorber with high circular dichroism (CD) in absorption of more than 0.56 across the mid-infrared wavelength range of 5–5.5 µm. The demonstrated chiral metasurface absorbers exhibit a maximum chiral absorption of 0.87 and a maximum CD in absorption of around 0.60. By adjusting the geometric parameters of the unit cell structure of the metasurface, the chiral absorption peak can be shifted to different wavelengths. Due to the strong chiroptical response, the thermal analysis of the designed chiral metasurface absorber further shows the large temperature difference between the left-handed and right-handed circularly polarized light. The demonstrated results can be utilized in various applications such as molecular detection, mid-infrared filter, thermal emission, and chiral imaging. 

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3. Chiral Grayscale Imaging with Plasmonic Metasurfaces of Stepped Nanoapertures

   https://doi.org/10.1002/adom.201801467  

   Chen, Yang; Gao, Jie; Yang, Xiaodong (January 2019, Advanced Optical Materials)

   Abstract Optical chiral imaging, as an important tool in chemical and biological analysis, has recently undergone a revolution with the development of chiral metamaterials and metasurfaces. However, the existing chiral imaging approaches based on metamaterials or metasurfaces can only display binary images with 1 bit pixel depth having either black or white pixels. Here, the unique chiral grayscale imaging based on plasmonic metasurfaces of stepped V‐shaped nanoapertures is reported with both high circular dichroism and large polarization linearity in transmission. By interlacing two subarrays of chiral nanoaperture enantiomers into one metasurface, two specific linear polarization profiles are independently generated in transmission under different incident handedness, which can then be converted into two distinct intensity profiles for demonstrating spin‐controlled grayscale images with 8 bit pixel depth. The proposed chiral grayscale imaging approach with subwavelength spatial resolution and high data density provides a versatile platform for many future applications in image encryption and decryption, dynamic display, advanced chiroptical sensing, and optical information processing. 

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4. Accuracy of Quantum Chemistry Structures of Chiral Tag Complexes and the Assignment of Absolute Configuration

   https://doi.org/10.1039/D2CP04060C  

   Mayer, Kevin; West, Channing; Marshall, Frank; Sedo, G; Grubbs II, Smitty; Evangelisti, Luca; Pate, Brooks (August 2022, PCCP Physical chemistry chemical physics)

   The absolute configuration of a molecule can be established by analysis of molecular rotational spectra of the analyte complexed with a small chiral molecule of known configuration. This approach of converting the analyte enantiomers, with identical rotational spectra, into diastereomers that can be distinguished spectroscopically is analogous to chiral derivatization in nuclear magnetic resonance (NMR) spectroscopy. For the rotational chiral tag method, the derivatization uses non-covalent interactions to install the new chiral center and avoids complications due to possible racemization of the analyte when covalent chemistry is used. The practical success of this method rests on the ability to attribute assigned rotational spectra to specific geometries of the diastereomeric homochiral and heterochiral tag complexes formed in the pulsed jet expansion that is used to introduce samples into the microwave spectrometer. The assignment of a molecular structure to an experimental rotational spectrum uses quantum chemistry equilibrium geometries to provide theoretical estimates of the spectrum parameters that characterize the rotational spectrum. This work reports the results of a high-sensitivity rotational spectroscopy study of the complexes formed between (3)-butyn-2-ol and verbenone. The rotational spectra of four homochiral and four heterochiral complexes are assigned. In addition, the 14 distinct, singly-substituted 13C isotopomer spectra of five of these species are assigned in natural abundance. Analysis of these spectra provides direct structural characterization of the complexes through determination of the carbon atom position coordinates. This data set is used to benchmark quantum chemistry calculations of candidate equilibrium geometries of the chiral tag complexes. The quantum chemistry calculations are limited to methods commonly used in the field of rotational spectroscopy. It is shown that the accuracy of the structures from quantum chemistry provides a high-confidence assignment of cluster geometries to the observed spectra. As a result, a high-confidence determination of the analyte (verbenone) absolute configuration is achieved. 

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5. Beyond the “spine of hydration”: Chiral SFG spectroscopy detects DNA first hydration shell and base pair structures

   https://doi.org/10.1063/5.0220479  

   Perets, Ethan A; Konstantinovsky, Daniel; Santiago, Ty; Videla, Pablo E; Tremblay, Matthew; Velarde, Luis; Batista, Victor S; Hammes-Schiffer, Sharon; Yan, Elsa_C Y (September 2024, The Journal of Chemical Physics)

   Experimental methods capable of selectively probing water at the DNA minor groove, major groove, and phosphate backbone are crucial for understanding how hydration influences DNA structure and function. Chiral-selective sum frequency generation spectroscopy (chiral SFG) is unique among vibrational spectroscopies because it can selectively probe water molecules that form chiral hydration structures around biomolecules. However, interpreting chiral SFG spectra is challenging since both water and the biomolecule can produce chiral SFG signals. Here, we combine experiment and computation to establish a theoretical framework for the rigorous interpretation of chiral SFG spectra of DNA. We demonstrate that chiral SFG detects the N–H stretch of DNA base pairs and the O–H stretch of water, exclusively probing water molecules in the DNA first hydration shell. Our analysis reveals that DNA transfers chirality to water molecules only within the first hydration shell, so they can be probed by chiral SFG spectroscopy. Beyond the first hydration shell, the electric field-induced water structure is symmetric and, therefore, precludes chiral SFG response. Furthermore, we find that chiral SFG can differentiate chiral subpopulations of first hydration shell water molecules at the minor groove, major groove, and phosphate backbone. Our findings challenge the scientific perspective dominant for more than 40 years that the minor groove “spine of hydration” is the only chiral water structure surrounding the DNA double helix. By identifying the molecular origins of the DNA chiral SFG spectrum, we lay a robust experimental and theoretical foundation for applying chiral SFG to explore the chemical and biological physics of DNA hydration. 

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