Impact of Precooling and Controlled-Atmosphere Storage on γ‑Aminobutyric Acid (GABA) Accumulation in Longan (Dimocarpus longan Lour.) Fruit

Longan (Dimocarpus longan Lour.) fruit cultivars ‘Chuliang’ and ‘Shixia’ were analyzed for γ-aminobutyric acid (GABA) accumulation after precooling and in controlled-atmosphere storage. Fruit were exposed to 5% O₂ plus 3%, 5%, or 10% CO₂ at 4 °C, and GABA and associated enzymes, aril firmness, and pericarp color were measured. Aril softening and pericarp browning were delayed by 5% CO₂ + 5% O₂. GABA concentrations and glutamate decarboxylase (GAD; EC 4.1.1.15) activities declined during storage at the higher-CO₂ treatments. However, GABA aminotransferase (GABA-T; EC 2.6.1.19) activities in elevated CO₂-treated fruit fluctuated during storage. GABA concentrations increased after precooling treatments. GAD activity and GABA-T activity were different between cultivars after precooling. GABA concentrations in fruit increased after 3 days of 10% CO₂ + 5% O₂ treatment and then declined as storage time increased. GABA accumulation was associated with stimulation of GAD activity rather than inhibition of GABA-T activity

Metal Thiophosphates with Good Mid-infrared Nonlinear Optical Performances: A First-Principles Prediction and Analysis

The family of metal thiophosphates is an important but long-ignored compound system of the nonlinear optical (NLO) materials with desirable properties for the mid-infrared (mid-IR) coherent light generation. In the present work, the mid-IR NLO capabilities of metal thiophosphate crystals are systematically investigated based on their structure–property relationship. The linear and nonlinear optical properties of these crystals are predicted and analyzed using the first-principles calculations. In particular, several metal thiophosphate compounds are highlighted to exhibit good mid-IR NLO performances, as supported by the primary experimental results. These candidates would greatly promote the development of the mid-IR NLO functional materials

Midinfrared Nonlinear Optical Thiophosphates from LiZnPS₄ to AgZnPS₄: A Combined Experimental and Theoretical Study

Our earlier theoretical calculation and preliminary experiment highlighted LiZnPS₄ as a good mid-infrared (mid-IR) nonlinear optical (NLO) material. However, this compound suffers from problems including corrosion of the silica tubes, a pungent smell, deliquescence, and incongruent-melting behavior in the further single crystal growth and applications. In order to overcome these problems, herein, we investigate the analogues of LiZnPS₄ and propose that AgZnPS₄ would be a good candidate. The combination of experimental and theoretical study demonstrates that AgZnPS₄ exhibits a much stronger NLO effect than that of LiZnPS₄ despite the relatively smaller energy band gap. More importantly, AgZnPS₄ melts congruently with a melting point as low as 534 °C, much lower than those of traditional IR NLO crystals, and is nondeliquescent with enough stability in the air. Such a good crystal growth habit and chemical stability enable AgZnPS₄ to possess much better overall performance for the practical mid-IR NLO applications

Hg-Based Infrared Nonlinear Optical Material KHg₄Ga₅Se₁₂ Exhibits Good Phase-Matchability and Exceptional Second Harmonic Generation Response

High-performance infrared (IR) nonlinear optical (NLO) materials with large NLO response and suitable birefringence are urgently needed for various applications. A Hg-based IR NLO material KHg₄Ga₅Se₁₂ with such desirable properties has been newly discovered. In the structure, obviously distorted HgSe₄ and GaSe₄ tetrahedra are connected to each other by vertex-sharing to form a three-dimensional framework with the counterion K⁺ residing in the cavities. Remarkably, all the NLO-active building units in the title compound are arranged in a completely parallel manner. Such a topological structure and the large susceptibility of the Hg–Se bonds enable the material to achieve good phase-matchability with a tremendous powder second harmonic generation (SHG) response at 2.09 μm that is about 20-times that of the benchmark material AgGaS₂ (one of the largest responses among all the phase-matchable IR NLO chalcogenides reported to date). The optical band gap of KHg₄Ga₅Se₁₂ was determined as 1.61 eV. Moreover, on the basis of the electronic band structure, the real-space atom-cutting analysis, the SHG-weighted electronic densities, and the local dipole moments calculations, the origin of the superior linear and nonlinear optical properties of the title compound is ascribed to the (Hg/Ga)­Se₄ group. The calculated values for the maximum coefficient <i>d</i>₃₃ and birefringence (Δn) at 2.09 μm are −65.257 pm/V and 0.072, respectively. Such values agree well with experimental observations. Our study demonstrates that Hg-based metal chalcogenides are a class of IR NLO material with competitive features (good phase-matchability, very large SHG efficiency, wide transparency) desirable for practical applications

Noncentrosymmetric Cubic Cyanurate K₆Cd₃(C₃N₃O₃)₄ Containing Isolated Planar π‑Conjugated (C₃N₃O₃)^3– Groups

Single crystals of K₆Cd₃(C₃N₃O₃)₄ (<b>1</b>) were successfully grown via a solid-state cyclotrimerization reaction method from CdCl₂ and KOCN. To our best knowledge, it is the first inorganic compound containing isolated six-membered-ring (6-MR) anionic groups that crystallizes in the cubic system. In the structure, the basic 6-MR anionic unit is a planar π-conjugated (C₃N₃O₃)^3– group that is isoelectronic with the (B₃O₆)^3– group, as observed in the benchmark nonlinear-optical (NLO) crystal β-BaB₂O₄ with strong second-harmonic-generation response. In addition, the electronic structure and linear-optical and NLO properties for <b>1</b> were also investigated by the first-principles calculation. The NLO coefficient (<i>d</i>₁₄ = 1.17 pm/V) of <b>1</b> is about 3 times that of KH₂PO₄

Visible-Light-Responsive Chalcogenide Photocatalyst Ba₂ZnSe₃: Crystal and Electronic Structure, Thermal, Optical, and Photocatalytic Activity

Visible-light-responsive photocatalytic materials have important applications. In this article, through inserting electropositive ion Ba²⁺ into the three-dimensional framework of ZnSe, a one-dimensional chalcogenide Ba₂ZnSe₃ has been obtained by traditional solid-state reaction. It crystallizes in orthorhombic centrosymmetric space group <i>Pnma</i> with unit cell parameters of <i>a</i> = 9.0744(2) Å, <i>b</i> = 4.4229(1) Å, <i>c</i> = 17.6308(4) Å, and <i>Z</i> = 4. Its structure features [ZnSe₃]^4– anionic straight chains parallel to the <i>b</i> direction, which are further separated by Ba²⁺ cations filling in the cavities. On the basis of the UV–vis–NIR diffuse reflectance spectroscopy, Ba₂ZnSe₃ possesses a typical direct band gap of 2.75 eV, which is in good agreement with the electronic structure calculation. Moreover, Ba₂ZnSe₃ shows good visible-light-responsive photocatalytic activity and excellent thermal stability and cyclability, which are favorable for its application

Trigonal Planar [HgSe₃]^4– Unit: A New Kind of Basic Functional Group in IR Nonlinear Optical Materials with Large Susceptibility and Physicochemical Stability

A new mercury selenide BaHgSe₂ was synthesized. This air-stable compound displays a large nonlinear optical (NLO) response and melts congruently. The structure contains chains of corner-sharing [HgSe₃]^4– anions in the form of trigonal planar units, which may serve as a new kind of basic functional group in IR NLO materials to confer large NLO susceptibilities and physicochemical stability. Such trigonal planar units may inspire a path to finding new classes of IR NLO materials of practical utility that are totally different from traditional chalcopyrite materials

BaAu₂S₂: A Au-Based Intrinsic Photocatalyst for High-Performance Visible-Light Photocatalysis

A new Au-based sulfide BaAu₂S₂ was obtained through solid-state reaction. It crystallizes in the tetragonal space group <i>I</i>4₁/<i>amd</i> with unit cell parameters of <i>a</i> = 6.389 72(2) Å, <i>b</i> = 6.389 72(2) Å, <i>c</i> = 12.7872(1) Å, and <i>Z</i> = 4. Its structure features [AuS_2/2]_∞ zigzag chains composed of corner-sharing AuS₂ linear units. With a direct band gap of 2.49 eV, BaAu₂S₂ is suitable for the visible-light harvesting. Moreover, it exhibits excellent visible-light photocatalytic activity, which is 1.3 times that of graphitic carbon nitride (g-C₃N₄) and also demonstrates excellent circulating stability. On the basis of the crystal and electronic structure analysis, the electrons are highly delocalized along the [AuS_2/2] chains, and the electron effective mass of BaAu₂S₂ is only approximately one-fifth of that of g-C₃N₄, which may help the separation of the electron/hole pairs during the photocatalytic process. Additionally, the absorption coefficient of BaAu₂S₂ is extremely high, exceeding 1 × 10⁴ cm^–1 over the entire absorbable visible spectrum (<i>h</i>ν > <i>E</i>_g), which is significantly higher than that of g-C₃N₄. Such factors may contribute to its outstanding photocatalytic performances. According to our best knowledge, BaAu₂S₂ is the first noble metal-based chalcogenide photocatalyst reported as intrinsic light-harvesting and electron/hole-generating centers. This study may provide valuable insights for further research on photocatalytic materials