Relativistic effect influencing the diverse bonding character of the interfacial Ag staple motifs in thiolate-protected nanoclusters.

Thiolate-protected noble-metal nanoclusters have recently attracted extensive attention due to their appealing properties in optics, catalysis, etc. Within the same group element, experiments indicate that Ag staples exhibit di-, tri-, or even tetra-coordination, in contrast to the di-coordination observed in Au staples, rendering the structures of Ag nanoclusters more intricate. However, the underlying chemical insight of the bonding feature of multiple-coordinated Ag staples remains unclear. In this study, we employed density functional theory coupled with all-electron scalar relativistic calculations to elucidate the critical role of relativistic effect in determining the conformational complexity of Ag staples. Unlike Au, the relatively weaker relativistic effect induces fewer contributions of d orbitals in bonding for the Ag atom, showing an extreme sensitivity to the structural architecture in liganded clusters. A relatively higher d orbital percentage favors di-coordination with a shortened Ag-S bond, while a relatively lower d orbital percentage favors tri- and tetra-coordinations with an elongated Ag-S bond. The Lewis structures of the multi-coordinated Ag motifs were also unveiled. In addition, two AgNCs, including the [Ag29(SCH3)18]3- cluster with tri-coordinated Ag motifs and [Ag29(SCH3)18(PCH3)6]3- with tetra-coordinated Ag motifs, were predicted after clarifying the bonding characters of the multiple-coordinated Ag motifs. This work not only deepens the understanding of the bonding characteristics of the Ag staple motif in AgNCs and AuAg alloy clusters but also provides a new perspective to understand the relativistic effect in the thiolate-protected noble-metal nanocluster.

H2 + H2O → H4O: Synthesizing Hyperhydrogenated Water in Small-Sized Fullerenes?

Nanoscale confinement provides an ideal platform to rouse some exceptional reactions which cannot happen in the open space. Intuitively, H2 and H2O cannot react. Herein, through utilizing small-sized fullerenes (C24, C26, C28, and C30) as nanoreactors, we demonstrate that a hyperhydrogenated water species, H4O, can be easily formed using H2 and H2O under ambient conditions by ab initio molecular dynamics simulations. The H4O molecule rotates freely in the cavity of the cages and maintains its structure during the simulations. Further theoretical analysis indicates that H4O in the fullerene possesses high stability thermodynamically and chemically, which can be rationalized by the electron transfer between H4O and the fullerene. This work highlights the possibility of utilizing fullerene as a nanoreactor to provide confinement constraints for unexpected chemistry.

Predatory mite Amblyseius orientalis prefers egg stage and low density of Carpoglyphus lactis prey.

Amblyseius orientalis (Ehara) (Acari: Phytoseiidae) is an effective predatory mite for spider mite control on fruit trees in China. In recent decades, it has been produced massively at a commercial natural enemy producer, feeding on the storage mite Carpoglyphus lactis (L.). In the predator production process, the ratio of predatory mites to their prey was found to be critical for the population increase of A. orientalis in large-scale rearings. In this study, we investigated the predatory capacity of A. orientalis on various developmental stages of the prey C. lactis, and the effect of prey numbers on predator reproduction. The maximum predation rate of A. orientalis adults on C. lactis adults was 2.21 per day at the lowest density of five prey adults, and on C. lactis eggs it was 45.07 at the highest density of 60 prey eggs. The preference index Ci of A. orientalis on C. lactis eggs and adults was 0.4312 and - 0.9249, respectively, suggesting that A. orientalis preferred eggs to adults. Amblyseius orientalis could reproduce when it preyed on either eggs or deutonymphs of C. lactis. However, the fecundity of the predatory mites is not always proportional to the provided prey number. Higher density of prey deutonymphs resulted in lower fecundity, whereas more prey eggs resulted in higher fecundity of A. orientalis. Therefore, our study indicated that the choice of suitable density and developmental stage of prey can significantly improve A. orientalis production on a large scale.

Expression and functional analysis of Niemann-Pick C2 gene in Phytoseiulus persimilis.

As a new protein class of semiochemical binding and transporting, Niemann-Pick proteins type C2 (NPC2) in arthropods have received more attentions in recent decade. However, the gene function has not been studied in phytoseiid mites with biocontrol potential. In the current study, we cloned a NPC2 gene PpNPC2a from the transcriptome of Phytoseiulus persimilis Athias-Henriot. By encoding 181 amino acids with a conserved ML domain, PpNPC2a was found a homolog of NPC2-1 in Galendromus occidentalis Nesbitt. We then measured the spatio-temporal expression of PpNPC2a in P. persimilis, and found the highest expression in female adults compared to other stages. Due to the tiny body size of predatory mites, we only examined tissue expressions in two sections: the anterior part (gnathosoma and the first pair of legs) and the posterior part (idiosoma without the first pair of legs). Higher transcription of PpNPC2a was found in the posterior part. To investigate the potential function of PpNPC2a in P. persimilis, we interfered gene expression in female adults by feeding dsRNA, which resulted in a decrease of relative expression by 59.1 and 78.2% after 24 and 72 h, respectively. Compared with the control, dsNPC2a-treated P. persimilis were insensitive to the scent of leaves or plants infested by spider mites, suggesting a role of PpNPC2a in response to plant volatiles. However, the dsNPC2a-interfered mites could still respond to four representative compounds of herbivore-induced plant volatiles, including 4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT), methyl salicylate (MeSA), ß-caryophyllene and linalool. In short, our results indicated PpNPC2a may be involved in the chemosensory process of P. persimilis in response to whole-plant volatiles.

Amblyseius orientalis shows high consumption and reproduction on Polyphagotarsonemus latus in China.

The broad mite, Polyphagotarsonemus latus (Banks) (Acari: Tarsonemidae), is a cosmopolitan pest that infests many greenhouse crops. Biological control is an important way to control P. latus, with predatory mites being the most widely used natural enemies of this pest. The purpose of this study is to evaluate the capabilities of three native phytoseiids in China (Neoseiulus californicus, Neoseiulus barkeri and Amblyseius orientalis) in controlling P. latus, using Amblyseius swirskii as a control, a commercial biocontrol agent of this pest widely used in Europe. Consumption, development, and reproduction of the four species when fed with P. latus were assessed, and their life table parameters were estimated and compared. Among the three native species, A. orientalis has the highest consumption rate of P. latus (29.0 per day), the shortest developmental duration (5.3 days), and the highest cumulative fecundity (13.5 eggs/female). Overall, its intrinsic rate of increase (rm) is 0.12, comparable to that of A. swirskii. Among the three candidates, A. orientalis is the only one whose population increase might be expected when fed with P. latus. Therefore, we propose A. orientalis to be a potential biocontrol agent for this pest in China.

Expression and functional analysis of transformer-2 in Phytoseiulus persimilis and other genes potentially participating in reproductive regulation.

Transformer-2 (tra-2) is an important sex-determining gene in insects. It also plays a role in the reproduction of phytoseiid mites. We performed bioinformatic analyses for the tra-2 ortholog in Phytoseiulus persimilis (termed Pptra-2), measured its expression at different stages and quantitatively identified its function in reproduction. This gene encodes 288 amino acids with a conserved RRM domain. The peak of its expression was observed in adult females, especially ca. 5 days after mating. In addition, expression is also higher in eggs than in other stages and adult males. When Pptra-2 was silenced through RNA interference with oral delivery of dsRNA, 56% of the females had their egg hatching rates decreased in the first 5 days, from ca. 100% to ca. 20%, and maintained at low levels during the rest of the oviposition period. To detect other genes functionally related to Pptra-2, transcriptome analyses were performed on day 5 after mating. We compared mRNA expressions among interfered females with significantly reduced egg hatching rate, interfered females without significant hatching rate and CK. In total 403 differential genes were identified, of which 42 functional genes involved in the regulation of female reproduction and embryonic development were screened and discussed.

New structural insights into the stability of Au22(SR)16 nanocluster under ring model guidance.

This study presents thorough structural insights into the stability of crystallized Au22(SAdm)16 (HSAdm = 1-adamantanethiol) nanocluster. With the recently developed Ring Model for describing the interaction between inner gold cores and outer protecting ligands in thiolate-protected gold nanoclusters, the experimental spontaneous transformation from the crystallized Au22(SAdm)16 to Au21(SAdm)15 could be well understood as structurally unfavorable for the current Au22(SAdm)16 and could also be attributed to the weaker aurophilic interaction between the inner Au4 core and the surrounding rings in Au22(SAdm)16 over that in Au21(SAdm)15. Furthermore, with the Ring Model and the grand unified model, two new Au22(SCH3)16 isomers with evident lower energies, higher HOMO-LUMO gaps as well as distinct optical properties over the available crystallized isomer were obtained. This study deepens the current knowledge on the structure of the Au22(SR)16 cluster from a new structural point of view and also confirms the validity as well as practicability of the Ring Model in understanding and predicting the stable structures of thiolate-protected gold nanoclusters.

Structural prediction of anion thiolate protected gold clusters of [Au28+7n(SR)17+3n]- (n = 0-4).

Structural prediction of thiolate-protected gold nanoclusters (AuNCs) with diverse charge states can enrich the understanding of this species. Untill now, the number of anion AuNCs is still deficient. In this work, a series of gold nanoclusters with negative total charge, including [Au28(SR)17]-, [Au35(SR)20]-, [Au42(SR)23]-, [Au49(SR)26]-, and [Au56(SR)29]-, are designed. Following a crystallized [Au23(SR)16]- prototype structure, the inner core of the newly predicted clusters is obtained through packing crossed Au7. Next, proper protecting thiolate ligands are arranged to fulfill the duet rule to obtain Au3(2e) and Au4(2e). Extensive analysis indicates that these clusters own high stabilities. Molecular orbital analysis shows that the orbitals for the populations of the valence electron locate at each Au3(2e) and Au4(2e), which demonstrates the reliability of the grand unified model. This work should be helpful for enriching the structural diversity of AuNCs.

Impact of starvation on paternal reproductive investment in Neoseiulus californicus.

Neoseiulus californicus is an important biological control agent of small arthropod pests, widely used in preventive releases at low prey densities. Therefore, it is important to study reproductive investment of this species, both females and males, under environmental pressure of limited prey availability. Laboratory experiments were performed to investigate N. californicus male reproductive investment after short-time fasting or long-term starvation. When fasted for 36 h, males are still able to complete a single mating with no significant change in reproductive parameters of its mate. But the total mating duration became 24% longer, especially timing for the male to fill the first spermatheca of its mate increased by 35%. If daily food availability was less than 20% of demand, males were still able to mate until the end of life, but their fertility reduced after ca. the seventh mating. Mating of some males at the end of their lives are invalid, with their mates failing to oviposit. Overall, we summarized that reproductive investment demand for a single mating was low in N. californicus males, but its priority in energy allocation was high. When starved, males tried to guarantee their mating capability, but their fertility decreased gradually.

Combining predatory mites and film mulching to control Bradysia cellarum (Diptera: Sciaridae) on Chinese chives, Allium tuberosum.

The subterranean insect Bradysia cellarum Frey (Diptera: Sciaridae) is a notorious and major pest of Chinese chives, Allium tuberosum Rottler ex Sprengle (Amaryllidaceae) in China. Current chemical control of B. cellarum results in low insecticide efficacy, high cost and pesticide resistance, therefore there is an urgent need for sustainable management. Here, greenhouse experiments were conducted to evaluate the potential biocontrol agent Stratiolaelaps scimitus Womersley (Acari: Laelapidae) against B. cellarum. The number of B. cellarum larvae in soil declined from 17.6 to 0 in 4 months after releasing predatory mites in high density (5,000 adults per row); treatment was less effective under low densities of 2500 adults per row. To determine whether S. scimitus can be used in combination with soil solarization by film mulching over 40 °C for 4 h, we also evaluated heat tolerance of S. scimitus in laboratory and its control efficacy against B. cellarum after high-temperature treatment mimicking the film mulching in greenhouse. As our results showed that egg hatchability of S. scimitus was 2.6% at 38 °C and adult survival rate was 2% at 40 °C for 4 h, respectively, we concluded S. scimitus was largely inviable and could not reproduce at 40 °C. This temperature was the baseline of soil solarization, suggesting predatory mites should be released after soil solarization. When using S. scimitus after soil solarization or when using soil solarization as single treatment, fly larvae declined similarly from initial density of 18 to 0 or 17.2 to 0, respectively, within a month. Thus, our study suggests the potential of S. scimitus as a biocontrol agent of B. cellarum in greenhouse, and the most effective strategy is to combine film mulching and predatory mites (after soil heating) to control B. cellarum in chive productions.

Asymmetrically Doping a Platinum Atom into a Au38 Nanocluster for Changing the Electron Configuration and Reactivity in Electrocatalysis.

It is an obstacle to precisely manipulate a doped heteroatom into a desired position in a metal nanocluster. Herein, we overcome this difficulty to obtain Pt1 Au37 (SCH2 Pht Bu)24 and Pt2 Au36 (SCH2 Pht Bu)24 nanoclusters via controllably doping Pt atoms into the kernels of Au38 (SCH2 Pht Bu)24 . We reveal that asymmetrical doping of one Pt atom into either of the cores of Au38 (SCH2 Pht Bu)24 elevates the relative energy of the HOMO (highest occupied molecular orbital) accompanied by one valence electron loss of Pt1 Au37 (SCH2 Pht Bu)24 , compared to Au38 (SCH2 Pht Bu)24 with 14 electrons, while symmetrical doping of two Pt atoms into the cores of Au38 (SCH2 Pht Bu)24 narrows the HOMO-LUMO gap (LUMO: lowest unoccupied molecular orbital) of Pt2 Au36 (SCH2 Pht Bu)24 with two valence electrons less. Consequently, Pt1 Au37 (SCH2 Pht Bu)24 shows an electron-spin-induced high activity for CO2 electroreduction, whereas Pt2 Au36 (SCH2 Pht Bu)24 is least efficient and Au38 (SCH2 Pht Bu)24 has a decent performance.

Understanding the Chemical Insights of Staple Motifs of Thiolate-Protected Gold Nanoclusters.

Improving the fundamental understanding of the basic structures of ligand-protected gold nanoclusters is essential to their bottom-up synthesis as well as their further application explorations. The thiolate ligands that cover the central metal core in staple motifs are vital for the stability of the gold clusters. However, the knowledge about the geometrical and bonding characters of the thiolate ligands has not been fully uncovered yet. In this work, density functional theory calculations and molecular orbital analysis are applied to show that the Au atoms in the thiolate ligands are hypervalent. The chemical insights of the linear SAuS configuration as well as the lengthened AuS bond by combining the 3-center 4-electron (3c-4e) model and the well-recognized valence shell electron pair repulsion theory are revealed. Valence bond formulations of the motifs are given to provide more chemical insights, for example, the resonant structures, to show how the thiolate motif forms one covalent bond and one dative covalent bond with the Au core. This work provides a thorough understanding of the structure and bonding pattern of thiolate ligands of Au nanoclusters, which is important for the rational design of ligands-protected Au nanoclusters.

Elucidating the stabilities and properties of the thiolate-protected Au nanoclusters with detaching the staple motifs.

Thiolate-protected Au nanoclusters (AuNCs) have been widely studied in areas of catalysis, biosensors, and bioengineering. In real applications, e.g., catalytic reactions, the thiolate groups are normally partially detached. However, which of the thiolate groups are easily detached and how the detachment of the ligands affects the geometries and electronic structures of the Au nanoclusters have been rarely studied. In this work, we employed the density functional theory calculations as well as the molecular orbital analysis to explore the detachment effect of the ligands using nine thiolate-protected AuNCs as examples. Our results showed that there existed a nearly linear relationship between the averaged detachment energies and the numbers of Au atoms in the motifs. Detaching longer motifs normally required more energies owing to the stronger aurophilic effects. For detaching a full motif, based on the structure decomposition via the grand unified model, analysis on the inner Au core indicated that the change in Au-Au bond length was more sensitive for the inter-block compared to the intra-block. The detachment of the -SH fragment generally needs less energy and brings less structural deformations when compared to the removal of a full motif. Molecular orbital analysis showed that the relative energies of the HOMO orbitals were elevated, which led to the narrow down of the HOMO-LUMO gap. This work provides a primary description of the correlation of the ligands' detachment with the relative stabilities and structures of the AuNCs, which would be beneficial for establishing the structure-property relationship of AuNCs in real applications.

Probing NaCl hydrate formation from aqueous solutions by terahertz time-domain spectroscopy.

The cooling-induced formation of a hydrate in aqueous NaCl solutions was probed using terahertz time-domain spectroscopy (THz-TDS). It was found that the NaCl hydrate formation is accompanied by the emergence of four new absorption peaks at 1.60, 2.43, 3.34 and 3.78 THz. Combining X-ray diffraction measurements with solid-state based density functional theory (DFT) calculations, we assign the observed terahertz absorption peaks to the vibrational modes of the formed NaCl·2H2O hydrate during cooling. This work shows that THz-TDS based analysis has great potential in studying ionic hydrates and the newly revealed collective vibrational modes could be sensitive indicators to achieve quantitative analysis in phase transitions and lattice dynamics.

Spermatophore producing process and sperm transfer in Phytoseiulus persimilis.

In phytoseiid mites, the spermatophore is an intermediate, isolated structure where sperms are stored during mating. In the present study, the producing process of Phytoseiulus persimilis spermatophore is described in details. Its shape, and the number and shape of sperms inside, are also analyzed, each as affected by coupling time. Based on our results, the spermatophore of P. persimilis is pyriform, and is produced from the male genital opening within 3 min since mating started. When produced, the spermatophore is transferred along the capitular groove to the cheliceral base, where it is adhered to one of the two small holes at the bases of the chelicerae. Seminal fluid passes through the hole, the hollow spermatodactyl, the opening on the spermatodactyl tip, and enters the insemination pore to reach the spermatheca of the female. No sperm was observed in spermatophores obtained 5 min after mating started. The number of sperms increased in the next 10 min, reached its maximum (ca. 52 sperms per spermatophore), and then decreased. All sperms were released in 75 min after mating started. Sperms are slender in shape and on average 3.9 ± 0.3 µm long.

Using shadow page cache to improve isolated drivers performance.

With the advantage of the reusability property of the virtualization technology, users can reuse various types and versions of existing operating systems and drivers in a virtual machine, so as to customize their application environment. In order to prevent users' virtualization environments being impacted by driver faults in virtual machine, Chariot examines the correctness of driver's write operations by the method of combining a driver's write operation capture and a driver's private access control table. However, this method needs to keep the write permission of shadow page table as read-only, so as to capture isolated driver's write operations through page faults, which adversely affect the performance of the driver. Based on delaying setting frequently used shadow pages' write permissions to read-only, this paper proposes an algorithm using shadow page cache to improve the performance of isolated drivers and carefully study the relationship between the performance of drivers and the size of shadow page cache. Experimental results show that, through the shadow page cache, the performance of isolated drivers can be greatly improved without impacting Chariot's reliability too much.

Proposed Structural Model for Chiral Au40(SC2H4Ph)24 Nanoclusters.

The structural configuration of thiolate-protected gold nanoclusters plays a pivotal role in elucidating the correlation between their structure and properties, comprehending their stability, and guiding experimental synthesis. In this study, utilizing the grand unified model and the ring model, we employed an innovative strategy of fusing triangular Au3 and tetrahedral Au4 elementary blocks by sharing a gold atom to design the gold core, predicting the structure of the Au40(SR)24 nanoclusters. Density functional theory calculations indicate that with the protective ligands simplified to methyl groups the energy of the predicted Au40(SR)24 is 0.45 eV lower than that of the experimentally reported Au40(o-MBT)24 nanoclusters, implying its substantial stability. Furthermore, the calculated UV absorption spectrum and circular dichroism spectrum of predicted Au40(SR)24 are consistent with the experimental results of Au40(SC2H4Ph)24 nanoclusters, suggesting that the predicted structure is a likely candidate for the structure of Au40(SC2H4Ph)24 nanoclusters.

Both host and diet shape bacterial communities of predatory mites.

Microbial communities, derived from food, ambient, and inner, can affect host ecological adaption and evolution. Comparing with most phytophagous arthropods, predators may have more opportunities to develop specific microbiota depending on the level of prey specialization. To explore how diet sources affect host microbial communities and vary across predator species, we considered 3 types of predators from Phytoseiidae (Acari: Mesostigmata): polyphagous (Amblyseius orientalis Ehara, Neoseiulus barkeri Hughes, and Amblyseius swirskii Athias-Henrio), oligophagous (Neoseiulus californicus McGregor), and monophagous (Phytoseiulus persimilis Athias-Henriot) predatory mites. The polyphagous species were fed on 2 types of diets, natural prey and alternative prey. By using 16S rRNA sequencing, we found that diet was the main source of microbiota in predatory mites, while there was no clear pattern affected by prey specialization. Among 3 polyphagous predators, host species had a larger impact than prey on microbial composition. Unlike A. orientalis or N. barkeri which showed consistency in their microbiota, prey switching significantly affected ß-diversity of bacterial composition in A. swirskii, with 56% of the microbial alteration. In short, our results confirmed the substantial influence of diet on host microbial construction in predatory species, and highlighted species differences in shaping the microbiota which are not necessarily related to prey specialization.

Diachronic evolvement from tetra-icosahedral to quasi-hexagonal close-packed bimetal clusters.

Here we report a diachronic evolvement from tetra-icosahedral Au30Ag12(C[triple bond, length as m-dash]CR)24 to quasi-hcp (hexagonal close-packed) Au47Ag19(C[triple bond, length as m-dash]CR)32 via a one-step reduction, in which the size/structure conversion of the two clusters is not a typical Oswald growth process, but involves interface shrinking followed by core rearrangement and surface polymerization. Au30Ag12(C[triple bond, length as m-dash]CR)24 has an aesthetic Au18Ag8 kernel that is composed of four interpenetrating Au10Ag3 icosahedra, while Au47Ag19(C[triple bond, length as m-dash]CR)32 has a twisted Au19 core capped by a Au12Ag19 shell that are stacked in a layer-by-layer manner with a quasi-hcp pattern. The discovery of the two clusters not only provides further evidence for icosahedral clusters with longer excited-state lifetime compared to hcp-like clusters, but also discloses a double increase in catalytic reactivity for electrocatalytic oxidation of ethanol over quasi-hcp clusters in comparison with icosahedral clusters. This work provides the rationale for reversing the bottom-up growth process to remake bimetal clusters.

Decoding Chemical Formula to Spatial Conformation: A Structural Study Targeting the [Au25(SR)19]0 Nanocluster.

Structural global searches employing highly efficient algorithms have been extensively applied for studying molecules and clusters. However, the code-aided spatial conformational determination of thiolated gold nanoclusters (AuNCs) has not been accomplished because of the complex structural architecture of AuNCs, especially when only the chemical formula of the cluster is known. Experiments have shown that the star [Au25(SR)18]-1 cluster can transform into the [Au25(SR)19]0 cluster. However, the crystal structure of the [Au25(SR)19]0 cluster has not been experimentally determined, and theoretical structural predictions for this cluster are challenging because no template cluster presents for [Au25(SR)19]0. Utilizing the grand unified model, this study succeeded in obtaining the structure of the [Au25(SR)19]0 cluster by using minimal computations, which was verified to be reasonable through stability analysis and experimental absorption spectrum confirmation. Although the predicted [Au25(SR)19]0 cluster has the same number of Au atoms as the [Au25(SR)18]-1 cluster, the structure is considerably altered, owing to the presence of a face-centered cubic kernel. This study provides insights for decoding the chemical formulas of AuNCs to determine their spatial conformations.