The Effects of 4'-Esterified Resveratrol Derivatives on Calcium Dynamics in Breast Cancer Cells.

Triple-negative breast cancer is a highly aggressive subtype of breast cancer. Frequently, breast cancer cells modulate their calcium signaling pathways to optimize growth. Unique calcium pathways in breast cancer cells could serve as a way to target tumorigenic cells without affecting normal tissue. Resveratrol has previously been shown to activate calcium signaling pathways. We use cell viability, single-cell calcium microscopy, and RT-PCR assays to determine the activity and mechanism of three different 4'-esterified resveratrol derivatives. We demonstrate that two of the derivatives reduce cell viability more effectively than resveratrol in MDA-MB-231 human breast cancer cells. The derivatives also activate similar pro-apoptotic calcium signaling pathways. In particular, the pivalated and butyrated resveratrol derivatives are intriguing putative chemotherapeutics because they are more effective at decreasing cell viability in vitro and inhibiting the plasma membrane Ca2+-ATPase, a protein that is often modulated in breast cancer.

Nonlinear optical observation of coherent acoustic Dirac plasmons in thin-film topological insulators.

Low-energy collective electronic excitations exhibiting sound-like linear dispersion have been intensively studied both experimentally and theoretically for a long time. However, coherent acoustic plasmon modes appearing in time-domain measurements are rarely observed due to Landau damping by the single-particle continua. Here we report on the observation of coherent acoustic Dirac plasmon (CADP) modes excited in indirectly (electrostatically) opposite-surface coupled films of the topological insulator Bi2Se3. Using transient second-harmonic generation, a technique capable of independently monitoring the in-plane and out-of-plane electron dynamics in the films, the GHz-range oscillations were observed without corresponding oscillations in the transient reflectivity. These oscillations were assigned to the transverse magnetic and transverse electric guided CADP modes induced by the evanescent guided Lamb acoustic waves and remained Landau undamped due to fermion tunnelling between the opposite-surface Dirac states.

Multiferroic BaCoF4 in Thin Film Form: Ferroelectricity, Magnetic Ordering, and Strain.

Multiferroic materials have simultaneous magnetic and ferroelectric long-range orders and can be potentially useful for a wide range of applications. Conventional ferroelectricity in oxide perovskites favors nonmagnetic electronic configurations of transition metal ions, thus limiting the number of intrinsic multiferroic materials. On the other hand, this is not necessarily true for multiferroic fluorides. Using molecular beam epitaxy, we demonstrate for the first time that the multiferroic orthorhombic fluoride BaCoF4 can be synthesized in thin film form. Ferroelectric hysteresis measurements and piezoresponse force microscopy show that the films are indeed ferroelectric. From structural information, magnetic measurements, and first-principles calculations, a modified magnetic ground state is identified which can be represented as a combination of bulk collinear antiferromagnetism with two additional canted spin orders oriented along orthogonal axes of the BaCoF4 unit cell. The calculations indicate that an anisotropic epitaxial strain is responsible for this unusual magnetic ground state.

Phase diagram of a three-dimensional antiferromagnet with random magnetic anisotropy.

Three-dimensional antiferromagnets with random magnetic anisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs.

Thickness tunable quantum interference between surface phonon and Dirac plasmon states in thin films of the topological insulator Bi2Se3.

We report on a >100-fold enhancement of Raman responses from Bi2Se3 thin films if laser photon energy switches from 2.33 eV (532 nm) to 1.58 eV (785 nm), which is due to direct optical coupling to Dirac surface states (SS) at the resonance energy of ∼1.5 eV (a thickness-independent enhancement) and due to nonlinearly excited Dirac plasmon (a thickness-dependent enhancement). Owing to the direct optical coupling, we observed an in-plane phonon mode of hexagonally arranged Se-atoms associated with a continuous network of Dirac SS. This mode revealed a Fano lineshape for films <15 nm thick, resulting from quantum interference between surface phonon and Dirac plasmon states.