ABSTRACT
Shape-controlled nanocrystals, such as nanoflowers, are expected to serve as innovative nanocatalysts with high catalytic activity. It is well-established that these nanocrystals can be readily synthesized with specific shapes using colloidal methods in solutions containing capping agents. However, these capping agents tend to reduce the catalytic activity of nanocatalysts. Therefore, it is imperative to remove these agents without altering the morphology to enhance catalytic efficiency. In this study, we developed a method for eliminating melamine, a common capping agent, from supported Au nanoflowers using water extraction and ultraviolet-ozone treatment. This process significantly enhances the catalytic performance, particularly for alcohol oxidation reactions such as the conversion of 1-phenylethyl alcohol to acetophenone.
ABSTRACT
Supported anisotropic bimetallic nanocrystals are attractive owing to their potential for novel catalytic applications. Au-Pd nanocrystals are expected to have higher catalytic activity for alcohol oxidation than Au nanocrystals. However, only a few studies have reported the application of anisotropic Au-Pd nanocrystals as alcohol-oxidation nanocatalysts. Support materials such as Al2O3 and Fe2O3 influence the catalytic activity of spherical Au nanoparticles. Thus, optimization of the support is expected to improve the catalytic activity of anisotropic Au-Pd nanocrystals. Herein, we report the synthesis and catalytic performances of Al2O3- and Fe2O3-supported Au and Au-Pd nanoflowers. Au99-Pd1 NFs supported on Fe2O3 exhibited the highest catalytic activity for 1-phenylethyl alcohol oxidation.
Subject(s)
Metal Nanoparticles , Metal Nanoparticles/chemistry , Gold/chemistry , Oxidation-Reduction , CatalysisABSTRACT
The interplay of spin-orbit coupling and crystal symmetry can generate spin-polarized bands in materials only a few atomic layers thick, potentially leading to unprecedented physical properties. In the case of bilayer materials with global inversion symmetry, locally broken inversion symmetry can generate degenerate spin-polarized bands, in which the spins in each layer are oppositely polarized. Here, we demonstrate that the hidden spins in a Tl bilayer crystal are revealed by growing it on Ag(111) of sizable lattice mismatch, together with the appearance of a remarkable phenomenon unique to centrosymmetric hidden-spin bilayer crystals: a novel band splitting in both spin and space. The key to success in observing this novel splitting is that the interaction at the interface has just the right strength: it does not destroy the original wave functions of the Tl bilayer but is strong enough to induce an energy separation.
ABSTRACT
Stacking engineering in van der Waals (vdW) materials is a powerful method to control topological electronic phases for quantum device applications. Atomic intercalation into the vdW material can modulate the stacking structure at the atomic scale without a highly technical protocol. Here we report that lithium intercalation in a topologically structured graphene/buffer system on SiC(0001) drives dynamic topological domain wall (TDW) motions associated with stacking order change by using an in situ aberration-corrected low-energy electron microscope in combination with theoretical modelling. We observe sequential and selective lithium intercalation that starts at topological crossing points (AA stacking) and then selectively extends to AB stacking domains. Lithium intercalation locally changes the domain stacking order to AA and in turn alters the neighbouring TDW stacking orders, and continuous intercalation drives the evolution of the whole topological structure network. Our work reveals moving TDWs protected by the topology of stacking and lays the foundation for controlling the stacking structure via atomic intercalation. These findings open up new avenues to realize intercalation-driven vdW electronic devices.
ABSTRACT
Sterols are essential components of eukaryotic cell membranes. However, studies on sterol biosynthesis in bryophytes are limited. This study analyzed the sterol profiles in the bryophyte model plant Marchantia polymorpha L. The thalli contained typical phytosterols such as campesterol, sitosterol and stigmasterol. BLASTX analysis of the M. polymorpha genome against the Arabidopsis thaliana sterol biosynthetic genes confirmed the presence of all the enzymes responsible for sterol biosynthesis in M. polymorpha. We further focused on characterizing two genes, MpDWF5A and MpDWF5B, which showed high homology with A. thaliana DWF5, encoding Δ5,7-sterol Δ7-reductase (C7R). Functional analysis using a yeast expression system revealed that MpDWF5A converted 7-dehydrocholesterol to cholesterol, indicating that MpDWF5A is a C7R. Mpdwf5a-knockout (Mpdwf5a-ko) lines were constructed using CRISPR/Cas9-mediated genome editing. Gas chromatography-mass spectrometry analysis of Mpdwf5a-ko revealed that phytosterols such as campesterol, sitosterol and stigmasterol disappeared, and instead, the corresponding Δ7-type sterols accumulated. The thalli of Mpdwf5a-ko grew smaller than those of the wild type, and excessive formation of apical meristem in the thalli was observed. In addition, the gemma cups of the Mpdwf5a-ko were incomplete, and only a limited number of gemma formations were observed. Treatment with 1 µM of castasterone or 6-deoxocastasterone, a bioactive brassinosteroid (BR), partly restored some of these abnormal phenotypes, but far from complete recovery. These results indicate that MpDWF5A is essential for the normal growth and development of M. polymorpha and suggest that the dwarfism caused by the Mpdwf5a-ko defect is due to the deficiency of typical phytosterols and, in part, a BR-like compound derived from phytosterols.
Subject(s)
Arabidopsis , Marchantia , Phytosterols , Sterols , Oxidoreductases/metabolism , Sitosterols , Marchantia/genetics , Marchantia/metabolism , Stigmasterol , Brassinosteroids , Growth and DevelopmentABSTRACT
The potato cyst nematode (PCN) causes extensive crop losses worldwide. Because the hatching of PCN requires host-derived molecules known as hatching factors (HFs), regulating HF production in host plants may help to control this harmful pest. Solanoeclepin A (SEA), isolated from potato, is the most active HF for PCN; however, its biosynthesis is completely unknown. We discovered a HF called solanoeclepin B (SEB) from potato and tomato root exudates and showed that SEB was biosynthesized in the plant and converted to SEA outside the plant by biotic agents. Moreover, we identified five SEB biosynthetic genes encoding three 2-oxoglutarate-dependent dioxygenases and two cytochrome P450 monooxygenases in tomato. Exudates from tomato hairy roots in which each of the genes was disrupted contained no SEB and had low hatch-stimulating activity for PCN. These findings will help to breed crops with a lower risk of PCN infection.
Subject(s)
Nematoda , Solanum lycopersicum , Solanum tuberosum , Animals , Solanum tuberosum/genetics , Plant Roots/genetics , Plant Breeding , Solanum lycopersicum/genetics , Nematoda/physiologyABSTRACT
Steroidal glycoalkaloids (SGAs) are specialized metabolites found in members of Solanum species, and are also known as toxic substances in Solanum food crops such as tomato (Solanum lycopersicum), potato (Solanum tuberosum), and eggplant (Solanum melongena). SGA biosynthesis can be divided into two main parts: formation of steroidal aglycones, which are derived from cholesterol, and glycosylation at the C-3 hydroxy group. This review focuses on recent studies that shed light on the complete process of the aglycone formation in SGA biosynthesis and structural diversification of SGAs by duplicated dioxygenases, as well as the development of non-toxic potatoes through genome editing using these findings.
ABSTRACT
Genome editing is highly useful for crop improvement. The method of expressing genome-editing enzymes using a transient expression system in Agrobacterium, called agrobacterial mutagenesis, is a shortcut used in genome-editing technology to improve elite varieties of vegetatively propagated crops, including potato. However, with this method, edited individuals cannot be selected. The transient expression of regeneration-promoting genes can result in shoot regeneration from plantlets, while the constitutive expression of most regeneration-promoting genes does not result in normally regenerated shoots. Here, we report that we could obtain genome-edited potatoes by positive selection. These regenerated shoots were obtained via a method that combined a regeneration-promoting gene with the transient expression of a genome-editing enzyme gene. Moreover, we confirmed that the genome-edited potatoes obtained using this method did not contain the sequence of the binary vector used in Agrobacterium. Our data have been submitted to the Japanese regulatory authority, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and we are in the process of conducting field tests for further research on these potatoes. Our work presents a powerful method for regarding regeneration and acquisition of genome-edited crops through transient expression of regeneration-promoting gene.
ABSTRACT
Introducing magnetic order into a topological insulator (TI) system has attracted much attention with an expectation of realizing exotic phenomena such as the quantum anomalous Hall effect (QAHE) and axion insulator states. The magnetic proximity effect (MPE) is one of the promising schemes to induce the magnetic order on the surface of a TI without introducing disorder accompanied by doping magnetic impurities in the TI. In this study, we investigate the MPE at the interface of a heterostructure consisting of the topological crystalline insulator (TCI) SnTe and Fe by employing polarized neutron reflectometry. The ferromagnetic order penetrates â¼2.2 nm deep into the SnTe layer from the interface with Fe, which persists up to room temperature. This is induced by the MPE on the surface of the TCI preserving the coherent topological states without introducing the disorder by doping magnetic impurities. This would open up a way for realizing next-generation spintronics and quantum computational devices.
ABSTRACT
Cultivated tomato (Solanum lycopersicum) contains α-tomatine, a steroidal glycoalkaloid (SGA), which functions as a defense compound to protect against pathogens and herbivores; interestingly, wild species in the tomato clade biosynthesize a variety of SGAs. In cultivated tomato, the metabolic detoxification of α-tomatine during tomato fruit ripening is an important trait that aided in its domestication, and two distinct 2-oxoglutarate-dependent dioxygenases (DOXs), a C-23 hydroxylase of α-tomatine (Sl23DOX) and a C-27 hydroxylase of lycoperoside C (Sl27DOX), are key to this process. There are tandemly duplicated DOX genes on tomato chromosome 1, with high levels of similarity to Sl23DOX. While these DOX genes are rarely expressed in cultivated tomato tissues, the recombinant enzymes of Solyc01g006580 and Solyc01g006610 metabolized α-tomatine to habrochaitoside A and (20R)-20-hydroxytomatine and were therefore named as habrochaitoside A synthase (HAS) and α-tomatine 20-hydroxylase (20DOX), respectively. Furthermore, 20DOX and HAS exist in the genome of wild tomato S. habrochaites accession LA1777, which accumulates habrochaitoside A in its fruits, and their expression patterns were in agreement with the SGA profiles in LA1777. These results indicate that the functional divergence of α-tomatine-metabolizing DOX enzymes results from gene duplication and the neofunctionalization of catalytic activity and gene expression, and this contributes to the structural diversity of SGAs in the tomato clade.
Subject(s)
Dioxygenases , Solanum lycopersicum , Dioxygenases/metabolism , Fruit/genetics , Fruit/metabolism , Gene Duplication , Solanum lycopersicum/genetics , Solanum lycopersicum/metabolism , Mixed Function Oxygenases/geneticsABSTRACT
Ca-intercalation has enabled superconductivity in graphene on SiC. However, the atomic and electronic structures that are critical for superconductivity are still under discussion. We find an essential role of the interface between monolayer graphene and the SiC substrate for superconductivity. In the Ca-intercalation process, at the interface a carbon layer terminating SiC changes to graphene by Ca-termination of SiC (monolayer graphene becomes a bilayer), inducing more electrons than a free-standing model. Then, Ca is intercalated in between the graphene layers, which shows superconductivity with the updated critical temperature (TC) of up to 5.7 K. In addition, the relation between TC and the normal-state conductivity is unusual, "dome-shaped". These findings are beyond the simple C6CaC6 model in which s-wave BCS superconductivity is theoretically predicted. This work proposes a general picture of the intercalation-induced superconductivity in graphene on SiC and indicates the potential for superconductivity induced by other intercalants.
ABSTRACT
A magnetic skyrmion induced on a ferromagnetic topological insulator (TI) is a real-space manifestation of the chiral spin texture in the momentum space and can be a carrier for information processing by manipulating it in tailored structures. Here, a sandwich structure containing two layers of a self-assembled ferromagnetic septuple-layer TI, Mn(Bi1-xSbx)2Te4 (MnBST), separated by quintuple layers of TI, (Bi1-xSbx)2Te3 (BST), is fabricated and skyrmions are observed through the topological Hall effect in an intrinsic magnetic topological insulator for the first time. The thickness of BST spacer layer is crucial in controlling the coupling between the gapped topological surface states in the two MnBST layers to stabilize the skyrmion formation. The homogeneous, highly ordered arrangement of the Mn atoms in the septuple-layer MnBST leads to a strong exchange interaction therein, which makes the skyrmions "soft magnetic". This would open an avenue toward a topologically robust rewritable magnetic memory.
ABSTRACT
Steroidal glycoalkaloids (SGAs) are toxic specialized metabolites found in members of the Solanaceae, such as Solanum tuberosum (potato) and Solanum lycopersicum (tomato). The major potato SGAs are α-solanine and α-chaconine, which are biosynthesized from cholesterol. Previously, we have characterized two cytochrome P450 monooxygenases and a 2-oxoglutarate-dependent dioxygenase that function in hydroxylation at the C-22, C-26 and C-16α positions, but the aminotransferase responsible for the introduction of a nitrogen moiety into the steroidal skeleton remains uncharacterized. Here, we show that PGA4 encoding a putative γ-aminobutyrate aminotransferase is involved in SGA biosynthesis in potatoes. The PGA4 transcript was expressed at high levels in tuber sprouts, in which SGAs are abundant. Silencing the PGA4 gene decreased potato SGA levels and instead caused the accumulation of furostanol saponins. Analysis of the tomato PGA4 ortholog, GAME12, essentially provided the same results. Recombinant PGA4 protein exhibited catalysis of transamination at the C-26 position of 22-hydroxy-26-oxocholesterol using γ-aminobutyric acid as an amino donor. Solanum stipuloideum (PI 498120), a tuber-bearing wild potato species lacking SGA, was found to have a defective PGA4 gene expressing the truncated transcripts, and transformation of PI 498120 with functional PGA4 resulted in the complementation of SGA production. These findings indicate that PGA4 is a key enzyme for transamination in SGA biosynthesis. The disruption of PGA4 function by genome editing will be a viable approach for accumulating valuable steroidal saponins in SGA-free potatoes.
Subject(s)
4-Aminobutyrate Transaminase/metabolism , Solanine/analogs & derivatives , Solanum tuberosum/genetics , 4-Aminobutyrate Transaminase/genetics , Gene Editing , Hydroxylation , Ketocholesterols/biosynthesis , Ketocholesterols/chemistry , Plant Proteins/genetics , Plant Proteins/metabolism , Plant Tubers/enzymology , Plant Tubers/genetics , Plant Tubers/physiology , Saponins/biosynthesis , Saponins/chemistry , Solanine/chemistry , Solanine/metabolism , Solanum tuberosum/enzymology , Solanum tuberosum/physiologyABSTRACT
Tomato (Solanum lycopersicum) contains α-tomatine, a steroidal glycoalkaloid that contributes to the plant defense against pathogens and herbivores through its bitter taste and toxicity. It accumulates at high levels in all the plant tissues, especially in leaves and immature green fruits, whereas it decreases during fruit ripening through metabolic conversion to the nontoxic esculeoside A, which accumulates in the mature red fruit. This study aimed to identify the gene encoding a C-27 hydroxylase that is a key enzyme in the metabolic conversion of α-tomatine to esculeoside A. The E8 gene, encoding a 2-oxoglutalate-dependent dioxygenase, is well known as an inducible gene in response to ethylene during fruit ripening. The recombinant E8 was found to catalyze the C-27 hydroxylation of lycoperoside C to produce prosapogenin A and is designated as Sl27DOX. The ripe fruit of E8/Sl27DOX-silenced transgenic tomato plants accumulated lycoperoside C and exhibited decreased esculeoside A levels compared with the wild-type (WT) plants. Furthermore, E8/Sl27DOX deletion in tomato accessions resulted in higher lycoperoside C levels in ripe fruits than in WT plants. Thus, E8/Sl27DOX functions as a C-27 hydroxylase of lycoperoside C in the metabolic detoxification of α-tomatine during tomato fruit ripening, and the efficient detoxification by E8/27DOX may provide an advantage in the domestication of cultivated tomatoes.
Subject(s)
Fruit/metabolism , Mixed Function Oxygenases/metabolism , Plant Proteins/metabolism , Solanum lycopersicum/metabolism , Tomatine/analogs & derivatives , Fruit/growth & development , Solanum lycopersicum/genetics , Solanum lycopersicum/growth & development , Mixed Function Oxygenases/genetics , Phylogeny , Plant Proteins/genetics , Plants, Genetically Modified , Recombinant Proteins/genetics , Recombinant Proteins/metabolism , Saponins/metabolism , Substrate Specificity , Tomatine/metabolismABSTRACT
Potato (Solanum tuberosum), a worldwide major food crop, produces the toxic, bitter tasting solanidane glycoalkaloids α-solanine and α-chaconine. Controlling levels of glycoalkaloids is an important focus on potato breeding. Tomato (Solanum lycopersicum) contains a bitter spirosolane glycoalkaloid, α-tomatine. These glycoalkaloids are biosynthesized from cholesterol via a partly common pathway, although the mechanisms giving rise to the structural differences between solanidane and spirosolane remained elusive. Here we identify a 2-oxoglutarate dependent dioxygenase, designated as DPS (Dioxygenase for Potato Solanidane synthesis), that is a key enzyme for solanidane glycoalkaloid biosynthesis in potato. DPS catalyzes the ring-rearrangement from spirosolane to solanidane via C-16 hydroxylation. Evolutionary divergence of spirosolane-metabolizing dioxygenases contributes to the emergence of toxic solanidane glycoalkaloids in potato and the chemical diversity in Solanaceae.
Subject(s)
Biosynthetic Pathways , Dioxygenases/biosynthesis , Dioxygenases/genetics , Solanum tuberosum/enzymology , Solanum tuberosum/genetics , Amino Acid Sequence , Biosynthetic Pathways/genetics , Cholesterol/metabolism , Gene Expression Regulation, Plant , Genes, Plant/genetics , Hydroxylation , Ketoglutaric Acids/metabolism , Solanum lycopersicum/enzymology , Solanum lycopersicum/genetics , Phylogeny , Plants, Genetically Modified , Secondary Metabolism/genetics , Secondary Metabolism/physiology , Solanine/analogs & derivatives , Solanum melongena/enzymology , Solanum melongena/genetics , Tomatine/analogs & derivatives , Tomatine/metabolismABSTRACT
Cyst nematodes (Globodera spp. and Heterodera spp.) are highly evolved sedentary endoparasites that are considered as harmful pests worldwide. The hatching of the dormant eggs of cyst nematodes occurs in response to hatching factors (HFs), which are compounds that are secreted from the roots of host plants. Solanoeclepin A (SEA), a triterpene compound, has been isolated as HF for potato cyst nematode (PCN) eggs, whereas other compounds, such as steroidal glycoalkaloids (SGAs), are also known to show weak hatching stimulation (HS) activity. However, the structures of both compounds are different and the HF-mediated hatching mechanism is still largely unknown. In the present study, we observed specific hatching of PCN eggs stimulated by the hairy root culture media of potato and tomato, revealing the biosynthesis and secretion of HFs. SGAs, such as α-solanine, α-chaconine, and α-tomatine, showed significant HS activity, despite being remarkably less activities than that of SEA. Then, we evaluated the contribution of SGAs on the HS activities of the hairy root culture media. The estimated SGAs content in the hairy root culture media were low and nonconcordant with the HS activity of those, suggesting that the HS activity of SGAs did not contribute much. The analysis of structure-activity relationship revealed that the structural requirements of the HS activity of SGAs are dependent on the sugar moieties attached at the C3-hydoroxyl group and the alkaloid property of their aglycones. The stereochemistry in the EF rings of their aglycone also affected the strength of the HS activity.
ABSTRACT
Nanoflowers (NFs)-shape-controlled noble metal nanocrystals-have garnered significant attention because of their novel catalytic properties and applicability. In this paper, we report the preparation and catalytic performance of a magnetic Fe3O4-supported AuNF catalyst with a clean surface. The magnetically supported AuNFs were obtained by using magnetic Fe3O4 as the support. However, when nonmagnetic γ-Al2O3 was utilized as the support, the AuNFs did not exhibit a magnetic response. These supported AuNFs were utilized to catalyze the oxidation of 1-phenylethyl alcohol to acetophenone using air (1 atm) as the oxidant. The rate of formation of acetophenone using supported AuNFs was 8-fold higher than that of acetophenone using supported spherical Au nanoparticles of comparable size. In addition, the Fe3O4-supported AuNFs exhibited a higher rate of formation of acetophenone than the Al2O3-supported AuNFs. The Fe3O4-supported AuNFs were recovered using a magnet, and the recovered catalyst was reused under identical catalytic reaction conditions. The rate of formation of acetophenone using recovered Fe3O4-supported AuNFs remained unchanged, demonstrating no loss of catalytic activity.
ABSTRACT
Tomato plants (Solanum lycopersicum) contain steroidal glycoalkaloid α-tomatine, which functions as a chemical barrier to pathogens and predators. α-Tomatine accumulates in all tissues and at particularly high levels in leaves and immature green fruits. The compound is toxic and causes a bitter taste, but its presence decreases through metabolic conversion to nontoxic esculeoside A during fruit ripening. This study identifies the gene encoding a 23-hydroxylase of α-tomatine, which is a key to this process. Some 2-oxoglutarate-dependent dioxygenases were selected as candidates for the metabolic enzyme, and Solyc02g062460, designated Sl23DOX, was found to encode α-tomatine 23-hydroxylase. Biochemical analysis of the recombinant Sl23DOX protein demonstrated that it catalyzes the 23-hydroxylation of α-tomatine and the product spontaneously isomerizes to neorickiioside B, which is an intermediate in α-tomatine metabolism that appears during ripening. Leaves of transgenic tomato plants overexpressing Sl23DOX accumulated not only neorickiioside B but also another intermediate, lycoperoside C (23-O-acetylated neorickiioside B). Furthermore, the ripe fruits of Sl23DOX-silenced transgenic tomato plants contained lower levels of esculeoside A but substantially accumulated α-tomatine. Thus, Sl23DOX functions as α-tomatine 23-hydroxylase during the metabolic processing of toxic α-tomatine in tomato fruit ripening and is a key enzyme in the domestication of cultivated tomatoes.
Subject(s)
Mixed Function Oxygenases/metabolism , Solanum lycopersicum/enzymology , Solanum lycopersicum/metabolism , Taste , Tomatine/analogs & derivatives , Tomatine/metabolism , Fruit/metabolism , Gene Expression Regulation, Plant , Inactivation, Metabolic , Solanum lycopersicum/genetics , Mixed Function Oxygenases/genetics , Plant Leaves/metabolism , Plants, Genetically Modified/metabolism , Recombinant ProteinsABSTRACT
α-Tomatine and dehydrotomatine are major steroidal glycoalkaloids (SGAs) that accumulate in the mature green fruits, leaves and flowers of tomato (Solanum lycopersicum), and function as defensive compounds against bacteria, fungi, insects and animals. The aglycone of dehydrotomatine is dehydrotomatidine (5,6-dehydrogenated tomatidine, having the Δ5,6 double bond; the dehydro-type). The aglycone of α-tomatine is tomatidine (having a single bond between C5 and C6; the dihydro-type), which is believed to be derived from dehydrotomatidine via four reaction steps: C3 oxidation, isomerization, C5 reduction and C3 reduction; however, these conversion processes remain uncharacterized. In the present study, we demonstrate that a short-chain alcohol dehydrogenase/reductase designated Sl3ßHSD is involved in the conversion of dehydrotomatidine to tomatidine in tomato. Sl3ßHSD1 expression was observed to be high in the flowers, leaves and mature green fruits of tomato, in which high amounts of α-tomatine are accumulated. Biochemical analysis of the recombinant Sl3ßHSD1 protein revealed that Sl3ßHSD1 catalyzes the C3 oxidation of dehydrotomatidine to form tomatid-4-en-3-one and also catalyzes the NADH-dependent C3 reduction of a 3-ketosteroid (tomatid-3-one) to form tomatidine. Furthermore, during co-incubation of Sl3ßHSD1 with SlS5αR1 (steroid 5α-reductase) the four reaction steps converting dehydrotomatidine to tomatidine were completed. Sl3ßHSD1-silenced transgenic tomato plants accumulated dehydrotomatine, with corresponding decreases in α-tomatine content. Furthermore, the constitutive expression of Sl3ßHSD1 in potato hairy roots resulted in the conversion of potato SGAs to the dihydro-type SGAs. These results demonstrate that Sl3ßHSD1 is a key enzyme involved in the conversion processes from dehydrotomatidine to tomatidine in α-tomatine biosynthesis.
Subject(s)
3-Hydroxysteroid Dehydrogenases/metabolism , Plant Proteins/metabolism , Solanum lycopersicum/metabolism , Tomatine/analogs & derivatives , 3-Hydroxysteroid Dehydrogenases/genetics , Genes, Plant/genetics , Solanum lycopersicum/enzymology , Solanum lycopersicum/genetics , Metabolic Networks and Pathways , Phylogeny , Plant Proteins/genetics , Real-Time Polymerase Chain Reaction , Tomatine/metabolismABSTRACT
Shape-controlled metal nanocrystals, such as nanowires and nanoflowers, are attractive owing to their potentially novel catalytic properties and bimetallic nanocrystals composed of two distinct metals are expected to act as highly active catalysts. However, their catalytic activities are limited because of the capping agents adsorbed on the metal surfaces, which are necessary for the preparation and dispersion of these nanocrystals in solvents. Therefore, the preparation of bimetallic shape-controlled noble metal nanocrystals with clean surfaces, devoid of almost all capping agents, are expected to have high catalytic activity. Herein, we report the preparation of bimetallic Au-Ag nanoflowers using melamine as the capping agent. The bimetallic Au-Ag nanoflowers with a clean surface were subsequently obtained by a support and extraction method. The bimetallic nanoflowers with a clean surface were then used for the aerobic oxidation of 1-phenylethyl alcohol and they exhibited high rates for the formation of acetophenone compared to Au nanoflowers and spherical nanoparticles with almost the same size and Au/Ag ratio. We also show that Au-Ag nanoflowers containing only 1 % Ag (Au99 -Ag1 NFs) exhibit the highest rate of acetophenone formation among Au-Ag nanoflowers with different Au/Ag ratios owing to an increase in the electron density of the Au atoms that act as active sites for the oxidation of 1-phenylethyl alcohol.