Gold Entities Research Articles

Ratiometric and Colorimetric Optical Thermometers Using Emissive Dimeric and Trimeric {[Au(SCN)2]−}n Moieties Generated in d–f Heterometallic Assemblies

AbstractGold complexes can generate excimers ([Au2]→[Au2]*) and exciplexes ([Au3]→[Au3]*) with light excitation. Four GdIII and YIII complexes were assembled with dimeric {[Au(SCN)2]−}2 and trimeric {[Au(SCN)2]−}3 bis(thiocyanato)gold(I) counterions. The vibrational signature associated with the Au⋅⋅⋅Au vibrational mode was probed with ultralow frequency (ULF) Raman spectroscopy as a function of temperature. Emission spectroscopy was used to explore photophysical properties. Two broad features in the high‐ and low‐energy regions were associated with the fluorescence and phosphorescence of the gold entities, respectively. Temperature‐dependent luminescence measurements showed that the emission color can be tuned from blue to green via cyan and white. Hence, these complexes can act as colorimetric thermometers. Additionally, a ratiometric thermal sensing ability was incorporated with high sensitivity up to 5 % K−1 in the cryogenic temperature range.

Ratiometric and Colorimetric Optical Thermometers Using Emissive Dimeric and Trimeric {[Au(SCN)2 ]- }n Moieties Generated in d-f Heterometallic Assemblies.

Gold complexes can generate excimers ([Au2 ]→[Au2 ]*) and exciplexes ([Au3 ]→[Au3 ]*) with light excitation. Four GdIII and YIII complexes were assembled with dimeric {[Au(SCN)2 ]- }2 and trimeric {[Au(SCN)2 ]- }3 bis(thiocyanato)gold(I) counterions. The vibrational signature associated with the Au⋅⋅⋅Au vibrational mode was probed with ultralow frequency (ULF) Raman spectroscopy as a function of temperature. Emission spectroscopy was used to explore photophysical properties. Two broad features in the high- and low-energy regions were associated with the fluorescence and phosphorescence of the gold entities, respectively. Temperature-dependent luminescence measurements showed that the emission color can be tuned from blue to green via cyan and white. Hence, these complexes can act as colorimetric thermometers. Additionally, a ratiometric thermal sensing ability was incorporated with high sensitivity up to 5 % K-1 in the cryogenic temperature range.

Modulation of the Activity of Gold Clusters Immobilized on Functionalized Mesoporous Materials in the Oxidation of Cyclohexene via the Functional Group. The Case of Aminopropyl Moiety.

Gold nanoclusters and isolated gold atoms have been produced in a two-liquid phase procedure that involves a solution of gold in aqua regia and rosemary essential oil as organic layer. These gold entities have been immobilized on the ordered mesoporous silica material SBA-15 functionalized with different amounts of aminopropyl groups. The resulting materials have been characterized by XRD, N2 adsorption, chemical analysis, TGA, 29Si MAS NMR, 13C CP/MAS NMR, UV-vis spectroscopy, XPS, and STEM. The Au-containing materials retain the ordering and porosity of the pristine support. Gold content varies in the range of 0.07–0.7 wt% as a function of the specific immobilization conditions, while STEM evidences the presence of isolated gold atoms. XPS shows a shift of the Au 4f BE toward values lower than those of metallic gold. The catalytic activity in the oxidation of cyclohexene with molecular oxygen at atmospheric pressure parallels the Au content of the aminopropyl-SBA-15 supports. This activity is higher than that of analogous Au entities immobilized on SBA-15 functionalized with thiol or sulfonate groups, the activity decreasing in the order Au-NH2 > Au-SO3− > Au-SH. This behavior has been attributed to differences in the interaction strength between the functional group and the Au entities, which is optimum for the aminopropyl groups.

Biosynthesis of Gold Clusters and Nanoparticles by Using Extracts of Mexican Plants and Evaluation of Their Catalytic Activity in Oxidation Reactions

This work shows the biosynthesis of gold clusters and nanoparticles (AuNPs) from a solution of gold in a mixture of ammonium chloride and nitric acid treated with two different Mexican plants extracts, Toad Leaf (Eryngium heterophyllum, SF) and Cuachalalate (Amphipterygium adstringens, CF) as bioreductants. Subsequently, the gold entities were supported on the ordered mesoporous material SBA-15 functionalized with mercaptopropyl groups (1.6 wt% of sulphur). The gold contents were 0.7 wt% and 1.1 wt% for the CF and SF samples, respectively. UV–vis spectroscopy and TEM show the presence of gold nanoclusters in both samples, while very minor amount of AuNPs is detected only in the sample with the highest Au content (SF). The Au/SBA-15 materials are active in the aerobic oxidation of cyclohexene at 65 °C and atmospheric pressure. Two of the catalytic reaction products come from the addition of oxygen to the double bond of cyclohexene: cyclohexene epoxide and cyclohexanediol, while the other three come from allylic oxidation of the ring, which is the major reaction pathway: 2-cyclohexen-1-ol, 2-cyclohexen-1-one and 2-cyclohexenyl hydroperoxide, being the two first the major stable reaction products, while the enone/enol ratio is nearly 2. It has been found that the gold nanoclusters initially present in the catalysts evolve toward AuNPs during catalytic reaction.

DeepEventMine: end-to-end neural nested event extraction from biomedical texts.

MotivationRecent neural approaches on event extraction from text mainly focus on flat events in general domain, while there are less attempts to detect nested and overlapping events. These existing systems are built on given entities and they depend on external syntactic tools.ResultsWe propose an end-to-end neural nested event extraction model named DeepEventMine that extracts multiple overlapping directed acyclic graph structures from a raw sentence. On the top of the bidirectional encoder representations from transformers model, our model detects nested entities and triggers, roles, nested events and their modifications in an end-to-end manner without any syntactic tools. Our DeepEventMine model achieves the new state-of-the-art performance on seven biomedical nested event extraction tasks. Even when gold entities are unavailable, our model can detect events from raw text with promising performance.Availability and implementationOur codes and models to reproduce the results are available at: https://github.com/aistairc/DeepEventMine.Supplementary information Supplementary data are available at Bioinformatics online.

Immobilization of gold on short-channel mesoporous SBA-15 functionalized with thiol and hydrophobic groups for oxidation reactions

Abstract Nanosized gold entities immobilized on short-channel SBA-15 mesoporous materials functionalized solely with mercaptopropyl groups and together with propyl and octyl moieties have been prepared following a two-steps procedure. These materials have been used as catalysts for the oxidation of cyclohexene with molecular oxygen in liquid phase at atmospheric pressure. First, SBA-15 materials functionalized only with mercaptopropyl groups and with a combination of these groups with two hydrophobic moieties, namely propyl and octyl, have been synthesized in the presence of the non-ionic surfactant P104. Small particles having short channel length have been identified by TEM and SEM. In order to study the influence of the nature of the sulphur functional group, these S-bearing materials were also oxidized with hydrogen peroxide or dimethyldioxirane (DMD) to sulfonic groups prior to gold immobilization. The effectiveness of these oxidation methods was assessed by 29Si MAS NMR, 13C CP MAS NMR, XPS, chemical and thermal analysis, and it has been found that DMD oxidized efficiently thiol groups to sulfonic groups, but H2O2 leaves a fraction of unreacted thiol. In a second step, nanosized gold entities have been prepared by a two-liquid phases route involving rosemary oil as organic phase and an aqueous phase formed by dissolving gold in a solution of ammonium chloride in concentrated nitric acid (aqua regia). Following this method, a fraction of the Au dissolved in the aqua regia solution is spontaneously reduced and transferred to the essential oil phase. Upon contacting the gold-bearing organic layer with the mesoporous materials, gold is actually immobilized on them, rendering metal contents in the range 1.1-0.2 wt.%, being those functionalized with alkyl chains the least efficient in capturing gold from the organic phase. No surface plasmon resonance band at 520 nm characteristic of gold nanoparticles has been detected by UV–vis spectroscopy in these Au-containing materials. All of them are active and selective for the allylic oxidation of cyclohexene, but their specific activity varies as a function of the nature of the functional groups. It has been found that the most active catalysts are those pre-oxidized with DMD. The presence of hydrophobic octyl groups increases substantially the turnover number of the reaction (TON), while the short-chain propyl moieties hardly affect the activity. It has been found that the nanosized gold entities initially present in the catalysts evolve in the reaction medium towards the formation of nanoparticles.

Combining relation extraction with function detection for BEL statement extraction.

The BioCreative-V community proposed a challenging task of automatic extraction of causal relation network in Biological Expression Language (BEL) from the biomedical literature. Previous studies on this task largely used models induced from other related tasks and then transformed intermediate structures to BEL statements, which left the given training corpus unexplored. To make full use of the BEL training corpus, in this work, we propose a deep learning-based approach to extract BEL statements. Specifically, we decompose the problem into two subtasks: entity relation extraction and entity function detection. First, two attention-based bidirectional long short-term memory networks models are used to extract entity relation and entity function, respectively. Then entity relation and their functions are combined into a BEL statement. In order to boost the overall performance, a strategy of threshold filtering is applied to improve the precision of identified entity functions. We evaluate our approach on the BioCreative-V Track 4 corpus with or without gold entities. The experimental results show that our method achieves the state-of-the-art performance with an overall F1-measure of 46.9% in stage 2 and 21.3% in stage 1, respectively.

Phosphine-Ligated Gold Clusters with Core+ exo Geometries: Unique Properties and Interactions at the Ligand-Cluster Interface.

Over recent years, research on the structures and properties of ligand-protected gold cluster molecules has gained significant interest. The crystal structure information accumulated to date has revealed the structural preference to adopt closed polyhedral geometries, but the use of multidentate ligands sometimes leads to the formation of exceptional structures. This Account describes results of our studies on diphosphine-coordinated [core+ exo]-type gold clusters featuring extra gold atoms outside the polyhedral cores, highlighting (1) their distinct optical properties due to the unique electronic structures generated by the exo gold atoms and (2) electronic/attractive ligand-cluster interactions that cause definite perturbation effects on the cluster properties. Subnanometer gold clusters with [core+ exo]-type geometries (nuclearity = 6, 7, 8, and 11) commonly displayed single absorption bands in the visible region, which are distinct in patterns from those of conventional polyhedral-only homologues. Theoretical studies demonstrated that the exo gold atoms are critically involved in the generation of unique electronic structures characterized by the HOMO-LUMO transitions with dominant oscillator strengths, leading to the appearance of the isolated absorption bands. On the basis of the frontier orbital distributions, the HOMO and LUMO were shown to be localized around the polyhedral cores and exo gold atoms, respectively. Therefore, the HOMO-LUMO transitions responsible for the visible absorptions occur in the core → exo direction. The HOMO-LUMO gap energies showed no clear trends with respect to the nuclearity (size), indicating that the individual geometric features of the inorganic framework primarily govern the clusters' electronic structures and properties. Systematic studies using octagold clusters bearing various anionic coligands revealed that electronic or attractive interactions between the gold framework and ligand functionalities, such as π-electron systems and heteroatoms, cause substantial perturbations of the wavelength of the visible absorption band due to the HOMO-LUMO transitions. Especially, significant red shifts were observed as a result of the electronic coupling with specific π-resonance contributors. It was also found that the orientation of aromatic rings around the inorganic framework is a factor that affects the cluster photoluminescence. These findings demonstrate the utility of the ligand moieties surrounding the gold frameworks for fine-tuning of the optical properties. During these studies, unusual but definite attractive interactions between the gold framework and C-H groups of the diphosphine ligand were found in the hexagold clusters. On the basis of careful crystallographic and NMR analyses, these interactions were deemed as a certain kind of M···H hydrogen bonds, which critically affect the maintenance of the cluster framework. Such unique interaction activities are likely due to the valence electrons in the gold framework, which serve as the hydrogen-bond acceptor for the unfunctionalized C-H groups. Overall, these observations imply the uniqueness of the ligand-cluster interface associated with the partially oxidized gold entities, which may expand the scope of ligand-protected clusters toward various applications.

Gold nanoclusters prepared from an eighteenth century two-phases procedure supported on thiol-containing SBA-15 for liquid phase oxidation of cyclohexene with molecular oxygen

The present work describes the incorporation of finely divided and well-dispersed Au species into SBA-15 mesoporous silica functionalized with mercaptopropyl groups, and the catalytic activity of the resulting Au-materials in the liquid phase oxidation of cyclohexene with molecular oxygen at atmospheric pressure. The gold entities have been prepared through a two-phase system described in the eighteenth century involving a solution of gold in a mixture of nitric acid and ammonium chloride (aqua regia) and rosemary oil. Gold nanoclusters, which present a disordered structure and sizes below 3nm, and even single gold atoms which may be anchored/stabilized through sulphur groups are found immobilized on the mesoporous support, but no gold nanoparticles (with well-defined structure and usually over ∼5nm) are detected. Such observations have been carried out by Cs-corrected STEM-HAADF where the visualization of bright spots is attributable to these individual entities. These materials are active in the oxidation of cyclohexene, but their relative activity is governed by the synthesis conditions. Partial aggregation of the gold entities into nanoparticles has been observed during the reaction, which are mainly responsible for the catalytic activity. The allylic oxidation of the cyclohexene ring over the double bond epoxidation is strongly favored, and at high conversion the two dominants products are 2-cyclohexen-1-one and 2-cyclohexen-1-ol.

Gold-Loaded Tin Dioxide Gas Sensing Materials: Mechanistic Insights and the Role of Gold Dispersion

This work focuses on two aspects of gold-loaded tin dioxide gas sensing materials: The influence of the size and dispersion of the gold on the sensing effect and the investigation into the mechanism at the origin of the improved gas sensing performance. For this purpose, a set of selected and well-characterized gold loaded tin dioxide materials were examined. The results show that the beneficial effect of gold on the CO sensing performance is observed for nanosized as well as for micron-sized gold entities, i.e., the effect is related to Au itself. Nevertheless, the response is strongly enhanced with increasing gold dispersion. Deeper insights into the mechanism of the sensitization, obtained by state-of-the-art operando spectroscopic techniques, indicated that oxygen is adsorbed on gold and transferred to the tin dioxide surface. There, it is bound as a negatively charged, ionic species, which gives additional sites for the interaction with target gases, i.e., enhances the gas sensing performance. These ...

A novel laboratory procedure for predicting continuous centrifugal gravity concentration applications: The gravity release analysis

A novel procedure, Gravity Release Analysis (GRA), is introduced for performance prediction of continuous centrifugal concentration, using lab-scale batch tests. Also, linked with the GRA, the Gravity Release Index (GRI) was developed for ranking the ore amenability to centrifugal gravity concentration. Ore samples from the flotation circuit of Myra Falls concentrator were subjected to Multi Pass Test and Gravity Amenability Test for comparison with GRA. Recovery kinetics of batch centrifugal concentration was analysed to establish the Gravity Release Index (GRI). Both Gravity Amenability Test and Multi Pass Test failed to cover the broader mass yield range of continuous centrifugal concentration and this was the main drawback in performance prediction of larger units from lab-scale data. GRA covered a wider mass yield range, yielding better performance prediction of larger continuous units. From the gravity recovery kinetics of the batch unit, varying GRI values for Au, Fe, Zn, Fe and S were obtained, with Au having the highest- GRI and amenability to centrifugal gravity concentration. Varying amenabilities for different Au forms (free Au particles, Au bearing sulphides) to centrifugal gravity concentration could also be distinguished. SEM analysis on recovered gold entities justified the prediction by the GRI. Overall, GRA could effectively predict continuous centrifugal concentration using small amounts of feed with lab-scale batch units. Determination of the GRI for targeted metals would provide further precision for bench-marking and scaling-up of continuous centrifugal concentration.

Formation of gold nanoparticles in polymeric nanowires by low-temperature thermolysis of gold mesitylene

The formation of polymer nanowires containing metal nanoparticle chains by low-temperature thermolyses of metal precursors has remained challenging. We report the block copolymer-assisted generation of locally regular chains of quasi-spherical gold nanoparticles with narrow particle diameter distribution by mild thermolysis of the non-polar gold precursor gold mesitylene inside the cylindrical nanopores of self-ordered anodic aluminium oxide (AAO). The block copolymer separates the gold mesitylene as well as the developing gold nanoparticles from the AAO pore walls so that surface nucleation and pinning of gold clusters are prevented. Growing quasi-spherical gold nanoparticles locally deform the polymer chains irreversibly adsorbed on the AAO pore walls, and the polymer chains are pushed into the space between the gold nanoparticles. The gold nanoparticles have, therefore, larger diameters and smaller specific surface than hypothetical pluglike gold entities with the same volume, the formation of which is suppressed.

Influence of Cation Nature on Stabilization of Gold Nanospecies in Mordenites

Gold species deposited on NH4(+)- and H(+)-mordenites were studied by X-ray diffraction, xenon adsorption, NMR of 27Al and 129Xe, UV-Visible spectroscopy and TPR. Mordenite ion-exchange cations exert a significant effect on size distribution and electronic state of gold species supported on the zeolites. AuNH4M contains larger nanoparticles of gold on its external surface than AuHM because protonic form of zeolite has stronger sites for stabilization of gold nanospecies. In the case of NH4(+)-mordenite, Au clusters inside zeolite channels have bigger size and fill the side-pockets completely after gold deposition due to more complete reduction of gold entities, while in H(+)-mordenite only half the side-pockets are filled by gold species. H(+)-mordenite favors the stabilization of both small gold clusters and cations. Even after the reduction of gold by hydrogen flow at 100 degrees C, some gold species are not completely reduced and have certain effective charge (Au(n)delta+ clusters).

Selective oxidation with dioxygen by gold nanoparticle catalysts derived from 55-atom clusters

Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic properties, but the origin of the catalytic activity is still not fully understood. Experimental work on gold particles supported on a titanium dioxide (110) single-crystal surface has established a striking size threshold effect associated with a metal-to-insulator transition, with gold particles catalytically active only if their diameters fall below approximately 3.5 nm. However, the remarkable catalytic behaviour might also in part arise from strong electronic interaction between the gold and the titanium dioxide support. In the case of industrially important selective oxidation reactions, explanation of the effectiveness of gold nanoparticle catalysts is complicated by the need for additives to drive the reaction, and/or the presence of strong support interactions and incomplete understanding of their possible catalytic role. Here we show that very small gold entities ( approximately 1.4 nm) derived from 55-atom gold clusters and supported on inert materials are efficient and robust catalysts for the selective oxidation of styrene by dioxygen. We find a sharp size threshold in catalytic activity, in that particles with diameters of approximately 2 nm and above are completely inactive. Our observations suggest that catalytic activity arises from the altered electronic structure intrinsic to small gold nanoparticles, and that the use of 55-atom gold clusters may prove a viable route to the synthesis of robust gold catalysts suited to practical application.

Phospholipid-assisted synthesis of size-controlled gold nanoparticles

Morphology and size control of gold nanoparticles (AuNPs) by phospholipids (PLs) has been reported. It was found that gold entities could form nanostructures with different sizes controlled by PLs in an aqueous solution. During the preparation of 1.5 nm gold seeds, AuNPs were obtained from the reduction of gold complex by sodium borohydride and capped by citrate for stabilization. With the different ratios between seed solution and growth solution, which was composed by gold complex and PLs, gold seeds grew into larger nanoparticles step by step until enough large size up to 30 nm. The main discovery of this work is that common biomolecules, such as PLs can be used to control nanoparticle size. This conclusion has been confirmed by transmission electron micrographs, particle size analysis, and UV–vis spectra.

Gas-phase epoxidation of propylene over small gold ensembles on TS-1

A series of Au/TS-1 catalysts with varying gold and titanium contents was prepared by deposition–precipitation (DP) and examined at 140–200 °C in a 10/10/10/70 vol.% mixture of hydrogen, oxygen, propylene and helium at a space velocity of 7000 mL/h/g cat. Gold loading was found to be closely related to titanium loading, implying that low gold loadings using deposition–precipitation results in an inherently small number of very active sites. Forcing the gold loading to higher values resulted in poor activity and stability. A catalyst prepared with a Si/Ti = 36 and a gold loading of 0.05 wt% produced 116 g PO/h/kg cat at 200 °C, which is the highest rate thus reported for a TS-1-based catalyst, with no evidence of deactivation during the 40 h temperature program. Catalysts prepared with lower titanium and gold contents resulted in very active catalysts when rates were normalized to the total gold content, 350 g PO/h/g Au at 200 °C for 0.01 wt% Au/TS-1 (Si/Ti = 500), indicative of the more efficient use of gold and titanium for the epoxidation reaction. The low gold loadings coupled with the absence of gold particles in TEM micrographs make it likely that, in these materials, significant activity is attributable to gold entities much smaller than 2 nm.