A structural modeling approach to solid solutions based on the similar atomic environment.

A solid solution is one of the important ways to enhance the structural and functional performance of materials. In this work, we develop a structural modeling approach to solid solutions based on the similar atomic environment (SAE). We propose a similarity function associated with any type of atom cluster to describe quantitatively the configurational deviation from the desired solid-solution structure that is fully disordered or contains short-range order (SRO). In this manner, the structural modeling for solid solutions is transferred to a minimization problem in the configuration space. Moreover, we strive to enhance the practicality of this approach. The approach and implementation are demonstrated by cross validations with the special quasi-random structure method. We apply the SAE method to the typical quinary CoCrFeMnNi high-entropy alloy, continuous binary Ta-W alloy, and ternary CoCrNi medium-entropy alloy with SRO as prototypes. In combination with ab initio calculations, we investigate the structural properties and compare the calculation results with experiments.

TGMin: An efficient global minimum searching program for free and surface-supported clusters.

In this article, we introduce an efficient global-minimum structural search program named Tsinghua Global Minimum 2 (TGMin-2), which is the successor of the original TGMin algorithm that was developed in our group in 2011. We have introduced a number of new features and improvements into TGMin-2, including a symmetric structure generation algorithm that can produce good initial seeds for small- and medium-size clusters, the duplicated structure identification algorithm, and the improved structure adaption algorithm that was implemented in the original TGMin code. To predict the simulated photoelectron spectrum (PE spectrum) automatically, we also implemented a standalone program named AutoPES (Auto Photoelectron Spectroscopy), which can be used to simulate PE spectra and compare them with experimental results automatically. We have demonstrated that TGMin-2 and AutoPES are powerful tools for studying free and surface-supported molecules, clusters, and nanoclusters. © 2018 Wiley Periodicals, Inc.

miR1432-OsACOT (Acyl-CoA thioesterase) module determines grain yield via enhancing grain filling rate in rice.

Rice grain filling rate contributes largely to grain productivity and accumulation of nutrients. MicroRNAs (miRNAs) are key regulators of development and physiology in plants and become a novel key target for engineering grain size and crop yield. However, there is little studies, so far, showing the miRNA regulation of grain filling and rice yield, in consequence. Here, we show that suppressed expression of rice miR1432 (STTM1432) significantly improves grain weight by enhancing grain filling rate and leads to an increase in overall grain yield up to 17.14% in a field trial. Molecular analysis identified rice Acyl-CoA thioesterase (OsACOT), which is conserved with ACOT13 in other species, as a major target of miR1432 by cleavage. Moreover, overexpression of miR1432-resistant form of OsACOT (OXmACOT) resembled the STTM1432 plants, that is, a large margin of an increase in grain weight up to 46.69% through improving the grain filling rate. Further study indicated that OsACOT was involved in biosynthesis of medium-chain fatty acids. In addition, RNA-seq based transcriptomic analyses of transgenic plants with altered expression of miR1432 demonstrated that downstream genes of miR1432-regulated network are involved in fatty acid metabolism and phytohormones biosynthesis and also overlap with the enrichment analysis of co-expressed genes of OsACOT, which is consistent with the increased levels of auxin and abscisic acid in STTM1432 and OXmACOT plants. Overall, miR1432-OsACOT module plays an important role in grain filling in rice, illustrating its capacity for engineering yield improvement in crops.

Observation and characterization of the smallest borospherene, B28(-) and B28.

Free-standing boron nanocages or borospherenes have been observed recently for B40(-) and B40. There is evidence that a family of borospherenes may exist. However, the smallest borospherene is still not known. Here, we report experimental and computational evidence of a seashell-like borospherene cage for B28(-) and B28. Photoelectron spectrum of B28(-) indicated contributions from different isomers. Theoretical calculations showed that the seashell-like B28(-) borospherene is competing for the global minimum with a planar isomer and it is shown to be present in the cluster beam, contributing to the observed photoelectron spectrum. The seashell structure is found to be the global minimum for neutral B28 and the B28(-) cage represents the smallest borospherene observed to date. It is composed of two triangular close-packed B15 sheets, interconnected via the three corners by sharing two boron atoms. The B28 borospherene was found to obey the 2(n + 1)(2) electron-counting rule for spherical aromaticity.

[Relationship between serum adiponectin and bone mineral density in preterm infants].

OBJECTIVE: To examine serum adiponectin level in preterm infants and to evaluate the relationship between serum adiponectin and bone mineral density in preterm infants. METHODS: Seventy-two appropriate-for-gestational-age neonates were classified into three groups according to their gestational ages: early preterm (31-33(+6) weeks, 13 cases), late preterm (34-36(+6) weeks, 16 cases), and full-term (37-42 weeks, 43 cases). Venous blood was collected at one week of their life to measure serum adiponectin concentration. During the period, omnisense ultrasound bone sonometer was applied to measure speed of sound (SOS) of the left tibia. RESULTS: The median of tibia SOS in the early preterm group was significantly lower than in the late preterm and full term groups (P<0.05), and the median of tibia SOS in the late preterm group was lower than in the full-term group (P<0.05). Serum adiponectin level was lowest in the early preterm group, and the full-term group had the highest serum adiponectin level. Serum adiponectin level was positively correlated with tibia SOS in preterm infants (r=0.664, P<0.05). According to the result of multivariate linear stepwise regression analysis, serum adiponectin and birth weight were independent predictor of tibia SOS in preterm infants. CONCLUSIONS: Serum adiponectin level is lower in preterm infants than that in full-term infants. There is a positive correlation between serum adiponectin and bone mineral density in preterm infants.

The B35 cluster with a double-hexagonal vacancy: a new and more flexible structural motif for borophene.

Elemental boron is electron-deficient and cannot form graphene-like structures. Instead, triangular boron lattices with hexagonal vacancies have been predicted to be stable. A recent experimental and computational study showed that the B36 cluster has a planar C6v structure with a central hexagonal hole, providing the first experimental evidence for the viability of atom-thin boron sheets with hexagonal vacancies, dubbed borophene. Here we report a boron cluster with a double-hexagonal vacancy as a new and more flexible structural motif for borophene. Photoelectron spectrum of B35(-) displays a simple pattern with certain similarity to that of B36(-). Global minimum searches find that both B35(-) and B35 possess planar hexagonal structures, similar to that of B36, except a missing interior B atom that creates a double-hexagonal vacancy. The closed-shell B35(-) is found to exhibit triple π aromaticity with 11 delocalized π bonds, analogous to benzo(g,h,i)perylene (C22H12). The B35 cluster can be used to build atom-thin boron sheets with various hexagonal hole densities, providing further experimental evidence for the viability of borophene.

[B30]⁻: a quasiplanar chiral boron cluster.

Chirality is vital in chemistry. Its importance in atomic clusters has been recognized since the discovery of the first chiral fullerene, the D2 symmetric C76. A number of gold clusters have been found to be chiral, raising the possibility to use them as asymmetric catalysts. The discovery of clusters with enantiomeric structures is essential to design new chiral materials with tailored chemical and physical properties. Herein we report the first inherently chiral boron cluster of [B30](-) in a joint photoelectron spectroscopy and theoretical study. The most stable structure of [B30](-) is found to be quasiplanar with a hexagonal hole. Interestingly, a pair of enantiomers arising from different positions of the hexagonal hole are found to be degenerate in our global minimum searches and both should co-exist experimentally because they have identical electronic structures and give rise to identical simulated photoelectron spectra.

[Relationship between bone turnover markers and bone sound of speed in appropriate-for-gestational-age neonates].

OBJECTIVE: To investigate the correlation of gestational age (GA) with carboxyterminal propeptide of type I procollagen (PICP), deoxypyridinoline (DPD), and bone sound of speed (SOS) in appropriate-for-gestational-age (AGA) neonates, as well as the relationship between bone turnover markers and bone SOS. METHODS: Sixty-five AGA neonates were included in the study. The neonates were divided into three groups: preterm infant (GA ≤3 4 weeks, 14 cases), late preterm infant (34 weeks

Adsorption-induced structural changes of gold cations from two- to three-dimensions.

Understanding the geometry structures of gold clusters, especially with adsorbates, is essential for designing highly active gold nanocatalysts. Here, we report a detailed theoretical study of the geometry structures of bare and CO-saturated Au(n)(+) (n = 4-6) clusters. It is found that the chemisorption of CO molecules leads to significant geometry changes of the gold clusters from two- to three-dimensions (3D), even for clusters as small as Au(4)(+). These gold cationic clusters exhibit characteristic coordination binding sites that have distinct electronic structures. We also find that commonly used density functional theory (DFT) methods have difficulty in accurately predicting energies of some isomers of Au(n)(+) clusters or Au(n)(CO)(n)(+) complexes, with the calculated relative energies strongly depending on the exchange-correlation functionals used. Caution must be exercised when using DFT methods as a blackbox for predicting the structures and energies of gold clusters.

Lattice distortion inducing local antiferromagnetic behaviors in FeAl alloys.

In this work, we study the local magnetic moment as a function of order degree in solid-solution FeAl alloys. Using the combination of ab initio method and similar atomic environment model, we find that the decrease of magnetic moment, even antiferromagnetic behavior, of the Fe atoms derives from the distorted local atomic clusters centered at Fe atoms on the Fe-atom sublattice sites in B2 FeAl alloys. While the local magnetic moment of Fe atoms is up to 2.2 µ B on the Al and Fe solid-solution sublattice sites. The ordering results in the decrease of Curie temperature and magnetic moment of solid-solution FeAl alloys.

Experimental and theoretical evidence of an axially chiral borospherene.

Chirality plays an important role in chemistry, biology, and materials science. The recent discovery of the B40(-/0) borospherenes marks the onset of a class of boron-based nanostructures. Here we report the observation of axially chiral borospherene in the B(39)(-) nanocluster on the bases of photoelectron spectroscopy, global minimum searches, and electronic structure calculations. Extensive structural searches in combination with density functional and CCSD(T) calculations show that B(39)(-) has a C3 cage global minimum with a close-lying C2 cage isomer. Both the C3 and C2 B(39)(-) cages are chiral with degenerate enantiomers. The C3 global minimum consists of three hexagons and three heptagons around the vertical C3 axis. The C2 isomer is built on two hexagons on the top and at the bottom of the cage with four heptagons around the waist. Both the C3 and C2 axially chiral isomers of B(39)(-) are present in the experiment and contribute to the observed photoelectron spectrum. The chiral borospherenes also exhibit three-dimensional aromaticity, featuring σ and π double delocalization for all valence electrons. Molecular dynamics simulations reveal that these chiral B(39)(-) cages are structurally fluxional above room temperature, compared to the highly robust D(2d)B40 borospherene. The current findings add chiral members to the borospherene family and indicate the structural diversity of boron-based nanomaterials.

Planar hexagonal B(36) as a potential basis for extended single-atom layer boron sheets.

Boron is carbon's neighbour in the periodic table and has similar valence orbitals. However, boron cannot form graphene-like structures with a honeycomb hexagonal framework because of its electron deficiency. Computational studies suggest that extended boron sheets with partially filled hexagonal holes are stable; however, there has been no experimental evidence for such atom-thin boron nanostructures. Here, we show experimentally and theoretically that B36 is a highly stable quasiplanar boron cluster with a central hexagonal hole, providing the first experimental evidence that single-atom layer boron sheets with hexagonal vacancies are potentially viable. Photoelectron spectroscopy of B36(-) reveals a relatively simple spectrum, suggesting a symmetric cluster. Global minimum searches for B36(-) lead to a quasiplanar structure with a central hexagonal hole. Neutral B36 is the smallest boron cluster to have sixfold symmetry and a perfect hexagonal vacancy, and it can be viewed as a potential basis for extended two-dimensional boron sheets.

Observation of an all-boron fullerene.

After the discovery of fullerene-C60, it took almost two decades for the possibility of boron-based fullerene structures to be considered. So far, there has been no experimental evidence for these nanostructures, in spite of the progress made in theoretical investigations of their structure and bonding. Here we report the observation, by photoelectron spectroscopy, of an all-boron fullerene-like cage cluster at B40(-) with an extremely low electron-binding energy. Theoretical calculations show that this arises from a cage structure with a large energy gap, but that a quasi-planar isomer of B40(-) with two adjacent hexagonal holes is slightly more stable than the fullerene structure. In contrast, for neutral B40 the fullerene-like cage is calculated to be the most stable structure. The surface of the all-boron fullerene, bonded uniformly via delocalized σ and π bonds, is not perfectly smooth and exhibits unusual heptagonal faces, in contrast to C60 fullerene.

B30H8, B39H9(2-), B42H10, B48H10, and B72H12: polycyclic aromatic snub hydroboron clusters analogous to polycyclic aromatic hydrocarbons.

Calculations performed at the ab initio level using the recently reported planar concentric π-aromatic B(18)H(6)(2+)(1) [Chen Q et al. (2011) Phys Chem Chem Phys 13:20620] as a building block suggest the possible existence of a new class of B(3n)H(m) polycyclic aromatic hydroboron (PAHB) clusters-B(30)H(8)(2), B(39)H(9)(2-)(3), B(42)H(10)(4/5), B(48)H(10)(6), and B(72)H(12)(7)-which appear to be the inorganic analogs of the corresponding C(n)H(m) polycyclic aromatic hydrocarbon (PAHC) molecules naphthalene C(10)H(8), phenalenyl anion C(13)H(9)(-), phenanthrene/anthracene C(14)H(10), pyrene C(16)H(10), and coronene C(24)H(12), respectively, in a universal atomic ratio of B:C = 3:1. Detailed canonical molecular orbital (CMO), adaptive natural density partitioning (AdNDP), and electron localization function (ELF) analyses indicate that, as they are hydrogenated fragments of a boron snub sheet [Zope RR, Baruah T (2010) Chem Phys Lett 501:193], these PAHB clusters are aromatic in nature, and exhibit the formation of islands of both σ- and π-aromaticity. The predicted ionization potentials of PAHB neutrals and electron detachment energies of small PAHB monoanions should permit them to be characterized experimentally in the future. The results obtained in this work expand the domain of planar boron-based clusters to a region well beyond B(20), and experimental syntheses of these snub B(3n)H(m) clusters through partial hydrogenation of the corresponding bare B(3n) may open up a new area of boron chemistry parallel to that of PAHCs in carbon chemistry.