Disorder Effects in the Bipolaron System Ti4_{4}O7_{7} Studied by Photoemission Spectroscopy

We have performed a photoemission study of Ti$_{4}$O$_{7}$ around its two transition temperatures so as to cover the metallic, high-temperature insulating (bipolaron-liquid), and low-temperature insulating (bipolaron-crystal) phases. While the spectra of the low-temperature insulating phase show a finite gap at the Fermi level, the spectra of the high-temperature insulating phase are gapless, which is interpreted as a soft Coulomb gap due to dynamical disorder. We suggest that the spectra of the high-temperature disordered phase of Fe$_{3}$O$_{4}$, which exhibits a charge order-disorder transition (Verwey transition), can be interpreted in terms of a Coulomb gap.Comment: 4 pages, 3 epsf figures embedde

Spectroscopic evidence for a charge-density-wave condensate in a charge-ordered manganite: Observation of collective excitation mode in Pr0.7_{\text{0.7}}Ca0.3_{\text{0.3}}MnO3_{\text{3}} by using THz time-domain spectroscopy

THz time-domain spectroscopy was used to directly probe the low-energy (0.5--5 meV) electrodynamics of the charge-ordered manganite Pr$_{0.7}$Ca$_{0.3}$MnO$_3$. We revealed the existence of a finite peak structure around 2--3 meV well below the charge gap $\sim300$ meV. In analogy to the low-energy optical properties of the well-studied low-dimensional materials, we attributed this observed structure to the collective excitation mode arising from the charge-density-wave condensate. This finding provides the importance role of the quasi-one dimensional nature of the charge and orbital ordering in Pr$_{0.7}$Ca$_{0.3}$MnO$_3$.Comment: REVTeX4, 8 pages including 7 figures and 2 table

Disorder effects in the bipolaron system

We have performed a photoemission study of Ti4O7 around its two transition temperatures so as to cover the metallic, high-temperature insulating (“bipolaron-liquid”) and low-temperature insulating (bipolaron-crystal) phases. While the spectra of the low-temperature insulating phase show a finite gap at the Fermi level, the spectra of the high-temperature insulating phase are gapless, which is interpreted as a soft Coulomb gap due to dynamical disorder. We suggest that the spectra of the high-temperature disordered phase of Fe3O4, which exhibits a charge order-disorder transition (Verwey transition), can be interpreted in terms of a Coulomb gap

Photoinduced and current-driven insulator/metal transition in manganites : A fluctuating route

A class of perovskite manganese oxides undergo photoinduced and current-driven insulator-to-metal transition. The conductance near the transition is quite "noisy" indicating macroscopic fluctuations. The spatial and temporal magnitude of the fluctuations is too large to be accounted for by simple first- order phase transition. An alternative view is proposed that the material is in the two-phase coexistence regime with extremely large fluctuations, reminiscent of the critical phenomena

Erratum: Synthetic Studies on Selective, Proapoptotic Isomalabaricane Triterpenoids Aided by Computational Techniques (J. Am. Chem. Soc. (2021) 143:4 (2138-2155) DOI: 10.1021/jacs.0c12569)

Figure 2c and the accompanying text on page 2140, as well as the SI, mistakenly stated the use of AD-mix-a. AD-mix- ß was used for the transformation from 11 to (+)-13. All structures drawn are correct, and all conclusions remain the same. A revised Supporting Information document that reflects this correction is also available

Synthetic Studies on Selective, Proapoptotic Isomalabaricane Triterpenoids Aided by Computational Techniques

The isomalabaricanes comprise a large family of marine triterpenoids with fascinating structures that have been shown to be selective and potent apoptosis inducers in certain cancer cell lines. In this article, we describe the successful total syntheses of the isomalabaricanes stelletin A, stelletin E, and rhabdastrellic acid A, as well as the development of a general strategy to access other natural products within this unique family. High-throughput experimentation and computational chemistry methods were used in this endeavor. A preliminary structure-activity relationship study of stelletin A revealed the trans-syn-trans core motif of the isomalabaricanes to be critical for their cytotoxic activity