Anisotropic structure building unit involving diverse chemical bonds: a new opportunity for high-performance second-order NLO materials.

We define the anisotropic structure building unit that encompasses diverse chemical bonds (ABUCB). The ABUCB is highly likely to cause anisotropy in both crystallographic structure and spatial electron distribution, ultimately resulting in enhanced macroscopic optical anisotropy. Accordingly, the (PO3F)2- or (SO3F)- tetrahedron involving the unique P-F or S-F bond serves as such an ABUCB. The distinct chemical bond effectively alters the microscopic nature of the structure building unit, such as polarizability anisotropy, hyperpolarizability, and geometry distortion; this consequently changes the macroscopic second-order nonlinear optical (2nd-NLO) properties of the materials. In this review, we summarize both typical and newly emerged compounds containing ABUCBs. These compounds encompass approximately 90 examples representing six distinct categories, including phosphates, borates, sulfates, silicates, chalcogenides and oxyhalides. Furthermore, we demonstrate that the presence of ABUCBs in DUV/UV NLO compounds contributes to an increase in birefringence and retention of a large band gap, facilitating phase matching in high-energy short-wavelength spectral ranges. On the other hand, the inclusion of ABUCBs in IR NLO compounds offers a feasible method for increasing the band gap and consequently enhancing the larger laser-induced damage threshold. This review consolidates various trial-and-error explorations and presents a novel strategy for designing 2nd-NLO compounds, potentially offering an opportunity for the development of high-performance 2nd-NLO materials.

Overdamped Phonon Diffusion and Nontrivial Electronic Structure Leading to a High Thermoelectric Figure of Merit in KCu5Se3.

Thermoelectric copper selenides are highly attractive owing to not only their constituent nontoxic, abundant elements but also their ultralow liquid-like lattice thermal conductivity (κlat). For the first time, the promising thermoelectric properties of the new KCu5Se3 are reported herein, showing a high power factor (PF = 9.0 µWcm-1 K-2) and an intrinsically ultralow κlat = 0.48 Wm-1 K-1. The doped K1-xBaxCu5Se3 (x = 0.03) realizes a figure-of-merit ZT = 1.3 at 950 K. The crystallographic structure of KCu5Se3 allows complex lattice dynamics that obey a rare dual-phonon transport model well describing a high scattering rate and an extremely short phonon lifetime that are attributed to interband phonon tunneling, confinement of the transverse acoustic branches, and temperature-dependent anharmonic renormalization, all of which generate an unprecedently high contribution of the diffusive phonons (70% at 300 K). The overall weak chemical bonding feature of KCu5Se3 gives K+ cations a quiescence behavior that further blocks the heat flux transfer. In addition, the valence band edge energy dispersion of KCu5Se3 is quasilinear that allows a large Seebeck coefficient even at high hole concentrations. These in-depth understandings of the ultralow lattice thermal conductivity provide new insights into the property-oriented design and synthesis of advanced complex chalcogenide materials.

Inorganic Solid-State Nonlinear Optical Switch with a Linearly Tunable Tc Spanning a Wide Temperature Range.

Nonlinear optical (NLO) switch materials that turn on/off second-harmonic generation (SHG) at a phase transition temperature (Tc ) are promising for applications in the fields of photoswitching and optical computing. However, precise control of Tc remains challenging, mainly because a linearly tunable Tc has not been reported to date. Herein, we report a unique selenate, tetragonal P 4 ‾ ${\bar{4}}$ 21 c [Ag(NH3 )2 ]2 SeO4 with a=b=8.5569(2) Šand c=6.5208(2) Šthat exhibits a strong SHG intensity (1.3×KDP) and a large birefringence (Δnobv. =0.08). This compound forms a series of isostructural solid-solution crystals [Ag(NH3 )2 ]2 Sx Se1-x O4 (x=0-1.00) that exhibit excellent NLO switching performance and an unprecedented linearly tunable T c , x , e x p . = T 0 - k x ${{T}_{\left(c,{\rm \ }x\right),{\rm \ }\left({\rm e}{\rm x}{\rm p}.\right)}{\rm \ }={T}_{0}-kx}$ spanning 430 to 356 K. The breaking of localized hydrogen bonds between SeO4 2- and the cation triggers a phase transition accompanied by hydrogen bond length changes with increasing x and a linear change in the enthalpy Δ H x = Δ U 1 - Δ U 2 x + Δ U 2 ${{{\rm { \Delta{}}}H}_{x}=\left({\rm { \Delta{}}}{U}_{1}-{\rm { \Delta{}}}{U}_{2}\right)x+{\rm { \Delta{}}}{U}_{2}}$ .

Hydrogen Bond-Driven Order-Disorder Phase Transition in the Near-Room-Temperature Nonlinear Optical Switch [Ag(NH3)2]2SO4.

Herein, we report a near-room-temperature nonlinear optical (NLO) switch material, [Ag(NH3)2]2SO4, exhibiting switching performance with strong room-temperature second harmonic generation (SHG) intensity that outperforms the UV-vis spectral region industry standard KH2PO4 (1.4 times stronger). [Ag(NH3)2]2SO4 undergoes a reversible phase transition (T c = 356 K) from the noncentrosymmetric room-temperature phase (P4̅21 c, RTP) to a centrosymmetric high-temperature phase (I4/mmm, HTP) where both the SO4 2- anions and [Ag(NH3)2]+ cations are highly disordered. The weakening of hydrogen bond interactions in the HTP is also evidenced by the lower energy shift of the stretching vibration of the N-H···O bonds revealed by the in situ FT-IR spectra. Such weakening leads to an unusual negative thermal expansion along the c axis (-3%). In addition, both the atomic displacement parameters of the single-crystal diffraction data and the molecular dynamics-simulated mean squared displacements suggest the motions of the O and N atoms. Such a structural disorder not only hinders the phonon propagation and dramatically drops the thermal conductivity to 0.22 W m-1 K-1 at 361 K but also significantly weakens the optical anisotropy and SHG as verified by the DFT theoretical studies.

[Ag(NH3 )2 ]2 SO4 : A Strategy for the Coordination of Cationic Moieties to Design Nonlinear Optical Materials*.

Over recent decades, guided by the anionic group theory of nonlinear optical (NLO) materials, rational design strategies have been primarily focused on anionic moieties; consequently, structural modification and design of cationic moieties have long been neglected. Herein, we report a strategy for the coordination of cationic moieties that substantially enhances the optical properties of NLO materials. For an example with well-known crystal structure, [Ag(NH3 )2 ]2 SO4 , we demonstrate that the coordination of the Ag+ cation by the neutral ligand drives the formation of a noncentrosymmetric tetragonal P 4 ‾ 21 c structure as a positive uniaxial crystal. The bending of the [Ag(NH3 )2 ]+ cationic moiety parallel to the z-axis generates an anisotropic arrangement of the dipoles, i.e., a dipole of 0.12 D along the z-direction, yet zero dipole in the xy-plane, which interacts anisotropically with the incident light oscillating electromagnetic wave, leading to optical anisotropy with a large birefringence. The incident beam of 589.3 nm normal to the (110) crystal plane measures Δnobv. =0.08, and [Ag(NH3 )2 ]2 SO4 also exhibits a phase-matching NLO response 1.4 times that of KH2 PO4 (KDP) (obv. 1.4×KDP @1064 nm; cal. d36 =1.50 pm V-1 ).

Effect of GAPT extract on expression of tau protein and its phosphorylation related enzymes in hippocampal neurons of APPV717I transgenic mice.

OBJECTIVE: To investigate the effect of GAPT, an extract mixture from Radix Ginseng, Rhizoma Acor tatarinowii, Radix Polygalae and Radix Curcuma (containing ingredient of turmeric), etc. on expression of tau protein and its phosphorylation related enzyme in hippocampal neurons of APPV717I transgenic mice. METHODS: Sixty three-month-old APPV717I transgenic mice were randomly divided into model group, donepezil group [0.92 mg/(kg•d)], the low, medium and high dosage of GAPT groups [0.075, 0.15, 0.30 g/(kg•d), 12 in each group], and 12 three-month-old C57BL/6J mice were set as a normal control group, treatments were administered orally once a day respectively, and both the normal group and model group were given 0.5% sodium carboxymethyl cellulose solution. Immunohistochemistry (IHC) and Western blot analysis were used to detect the expression of total tau protein (Tau-5), cyclin-dependent kinase 5 (CDK5) and protein phosphatase 2A (PP2A) in hippocampal neurons of experimental mice after 8-month drug administration (11 months old). RESULTS: In the model group, the expression of Tau-5 and CDK5 were increased, whereas the expression of PP2A was decreased in hippocampal neurons, which were signifificantly different compared with that in the normal group (all P<0.01). IHC test indicated the number and area of either Tau-5 or CDK5 positive cells were decreased with a dose-depended way in GAPT groups, and an increase of PP2A. Compared with the model group, the changes were signifificant in GAPT groups (P<0.05 or P<0.01). Similar results were shown by Western blot. CONCLUSION: GAPT could attenuate abnormal hyperphosphorylation of tau protein in hippocampal neurons of APPV717I transgenic mice via inhibiting the expression of CDK5 and activating the expression of PP2A.

Molar mass and molar mass distribution of polystyrene particle size standards.

Monodisperse polystyrene microspheres and nanospheres are often used as particle size standards for calibration of size-measuring instruments. They are potentially useful as the mass standards for particle mass spectrometry as well. We demonstrated in this work that it is possible to achieve high-precision mass determination for single polystyrene spheres using a quadrupole ion trap. We introduced the particles into the trap by laser-induced acoustic desorption and probed them with light scattering. Mass-to-charge ratios of the individual particles were determined from applied trap-driving frequencies, voltage amplitudes and the observed starlike oscillatory trajectories projected on the radial plane. Creation of one-electron differentials through charge-state changes by electron bombardment allowed determination for the absolute mass of a single trapped particle to a precision better than 0.1%. Both molar mass and molar mass distribution were deduced from a large number of measurements for NIST polystyrene particle size standards (SRMs 1690 and 1691). Our results are in excellent agreement with the size measurement for the 0.895-microm spheres (NIST SRM 1690), but a small discrepancy (4%) in number-average mass was found for the 0.269-microm spheres (NIST SRM 1691).

Measuring masses of single bacterial whole cells with a quadrupole ion trap.

A novel method has been developed to precisely measure the masses of single bacterial whole cells using a quadrupole ion trap as an electrodynamic balance. The bacterial cells were introduced into the ion trap by matrix-assisted laser desorption/ionization, confined in space by audio frequency ac fields, and detected by elastic light scattering. Mass measurement accuracy approaching 0.1% was achieved for Escherichia coli K-12 with a mass distribution of +/-3% from 60 repetitive measurements of the particles and their clusters. This is the first high-precision mass measurement reported for any intact microorganisms with masses greater than 1 x 1010 Da. The method opens new avenues for high-precision mass measurement of single microbial particles and offers an alternative approach for rapid identification of microorganisms by mass spectrometry.