Solution-phase Synthesis Research Articles

A general strategy for bimetallic Pt-based nano-branched structures as highly active and stable oxygen reduction and methanol oxidation bifunctional catalysts

The morphology and size of Pt-based bimetallic alloys are known to determine their electrocatalytic performance in reactions relevant to fuel cells. Here, we report a general approach for preparing Pt-M (M = Fe, Co and Ni) bimetallic nano-branched structure (NBs) by a simple high temperature solution-phase synthesis. As-prepared Pt-M NBs show a polycrystalline structure and are rich in steps and kinks on the surface, which promote them favorable bifunctional catalytic properties in acidic electrolytes, specifically in terms of the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Specially, Pt-Co NBs/C catalyst shows 6.1 and 5.3 times higher in specific activity (SA) and mass activity (MA) for ORR than state-of-the-art commercial Pt/C catalysts, respectively. Moreover, it exhibits a loss of 4.0% in SA and 14.4% in MA after 10,000 cycles of accelerated durability tests (ADTs) compared with the initial activities. In addition, we also confirmed the superior MOR activity of Pt-Co NBs/C catalyst in acidic electrolytes. For Pt-M NBs with other alloying metals, the ORR and MOR activities are both higher than commercial catalysts and are in the sequence of Pt-Co/C > Pt-Fe/C > Pt-Ni/C > commercial Pt/C (or PtRu/C). The improved activities and durability can benefit from the morphological and compositional effects. This synthesis approach may be applied to develop bifunctional catalysts with enhanced ORR and MOR properties for future fuel cells designs.

Observation of Non-FCC Copper in Alkynyl-Protected Cu53 Nanoclusters.

The only feasible access to non-face-centered cubic (FCC) copper was by physical vapor deposition under high vacuum. Now, non-FCC copper is observed in a series of alkynyl-protected Cu53 nanoclusters (NCs) obtained from solution-phase synthesis. Determined by single-crystal X-ray crystallography, the structures of Cu53 (C≡CPhPh)9 (dppp)6 Cl3 (NO3 )9 and its two derivatives reveal an ABABC stacking sequence involving 41 Cu atoms. It can be regarded as a mixed FCC and HCP structure, which gives strong evidence that Cu can be arranged in non-FCC lattice at ambient conditions when proper ligands are provided. Characterization methods including X-ray absorption fine structure, XPS, ESI-MS, UV/Vis, Auger spectroscopy, and DFT calculations were carried out. CuII was shown to successively coordinate with introduced ligands and changed to CuI after bonding with phosphine. The following addition of NaBH4 and the aging step further reduced it to the Cu53 NC.

Superatomic Gallium Clusters in Dendrimers: Unique Rigidity and Reactivity Depending on their Atomicity.

Superatoms have been investigated due to their possible substitution for other elements. The solution-phase synthesis of superatoms has attracted attention to realize the availability of superatoms. However, the previous approach is basically limited to the formation of a single cluster. Here, superatoms are investigated and the number of valence electrons in these superatoms is changed by designing the number of gallium atoms present. Based on the dendrimer template method, clusters consisting of 3, 12, 13, and other numbers of atoms have been synthesized. The halogen-like superatomic nature of Ga13 is structurally and electrochemically observed as completely different to the other clusters. The gallium clusters of 13 and 3 atoms, which can fill the 2P and 1P superatomic orbitals, respectively, exhibit different reactivities. The 3-atom gallium cluster is suggested as being reduced to Ga3 H2 - due to the lower shift of energy levels in the unoccupied orbitals. The results for these gallium clusters provide candidates for superatoms.

Solution-phase synthesis of the fluorogenic TGase 2 acyl donor Z-Glu(HMC)-Gly-OH and its use for inhibitor and amine substrate characterisation

A reliable solution-phase synthesis of the water-soluble dipeptidic fluorogenic transglutaminase substrate Z-Glu(HMC)-Gly-OH is presented. The route started from Z-Glu-OH, which was converted into the corresponding cyclic anhydride. This building block was transformed into the regioisomeric α- and γ-dipeptides. The key step was the esterification of Z-Glu-Gly-OtBu with 4-methylumbelliferone. The final substrate compound was obtained in an acceptable yield and excellent purity without the need of purification by RP-HPLC. The advantage of this acyl donor substrate for the kinetic characterisation of inhibitors and amine-type acyl acceptor substrates is demonstrated by evaluating commercially available or literature-known irreversible inhibitors and the biogenic amines serotonin, histamine and dopamine, respectively.

Supported Ni–Au Colloid Precursors for Active, Selective, and Stable Alkyne Partial Hydrogenation Catalysts

Bimetallic NiAu catalysts have garnered broad interest for a variety of reactions including automotive emissions, selective hydrogenation, selective oxidation, hydrodechlorination, and biomass conversion. However, the bulk immiscibility of the two metals, complicating catalyst synthesis, has limited studies of this bimetallic system. We report a solution-phase synthesis for Ni and bimetallic NiAu heterogeneous catalysts. Using oleylamine as a capping agent, an optimized synthesis for Ni catalysts led to supported particles with a narrow size distribution (4.7 ± 0.4 nm). Gold was added to the Ni nanoparticles via galvanic displacement of Ni in organic solution, the particles were deposited onto commercial alumina, and oleylamine capping agent was removed. The catalytic activity of the bimetallic materials in 1-octyne partial hydrogenation was in between the activity of monometallic Ni and Au catalysts. At high space velocity, the bimetallic catalysts largely maintained the high alkene selectivity associate...

Glycine-A bio-capping agent for the bioinspired synthesis of nano-zinc oxide photocatalyst

Structural modification of nanoparticles (NPs) for application-specific study is timely. In the present investigation, an attempt has been made for the bioinspired synthesis of zinc oxide (ZnO) NPs possessing different morphologies using glycine as the bio-capping agent. A variation in the amount of glycine during low-temperature mediated solid-phase synthesis indicated that a higher ratio of glycine directed the ensemble of nanohexagons into nanobundles which further formed nano-flower buds- like morphology, while least concentration formed agglomerated NPs and moderate concentration of glycine was able to modify the NPs’ structure into nanorods. On the other hand, the utilization of solution-phase synthesis methods, i.e. co-precipitation and hydrothermal, led to the formation of thinner and thicker ZnO nanosheets, respectively. In terms of crystalline structure, not much difference was observed in the lattice parameters or the unit cell of the crystal, with approximately similar crystallite sizes. From Fourier transform infrared spectroscopy, the functionalization of glycine from both the amine and the carboxyl group was noted. Further, it was found that the morphology and photoluminescence emission spectra of the samples were inter-related, wherein higher the agglomeration of the particles, greater the intensity of the visible region defect band was observed. The as-synthesized ZnO-photocatalysts were then employed for the degradation of rhodamine B (RhB), a major effluent of the textile industry. The photocatalytic activity of the samples was found to depend upon the surface area, which in turn was related to the morphology and the magnitude of green emission defect states. About 99% RhB degradation was obtained with ZnO possessing nano-flower buds-like morphology within 60 min of sunlight irradiation. Additionally, the role of reactive oxidative species and the stability of this photocatalyst were investigated.

An Exceptionally Mild and Scalable Solution-Phase Synthesis of Molybdenum Carbide Nanoparticles for Thermocatalytic CO2 Hydrogenation.

Transition metal carbides (TMCs) have demonstrated outstanding potential for utilization in a wide range of catalytic applications because of their inherent multifunctionality and tunable composition. However, the harsh conditions required to prepare these materials have limited the scope of synthetic control over their physical properties. The development of low-temperature, carburization-free routes to prepare TMCs would unlock the versatility of this class of materials, enhance our understanding of their physical properties, and enable their cost-effective production at industrial scales. Here, we report an exceptionally mild and scalable solution-phase synthesis route to phase-pure molybdenum carbide (α-MoC1-x) nanoparticles (NPs) in a continuous flow millifluidic reactor. We exploit the thermolytic decomposition of Mo(CO)6 in the presence of a surface-stabilizing ligand and a high boiling point solvent to yield MoC1-x NPs that are colloidally stable and resistant to bulk oxidation in air. To demonstrate the utility of this synthetic route to prepare catalytically active TMC NPs, we evaluated the thermochemical CO2 hydrogenation performance of α-MoC1-x NPs dispersed on an inert carbon support. The α-MoC1-x/C catalyst exhibited a 2-fold increase in both activity on a per-site basis and selectivity to C2+ products as compared to the bulk α-MoC1-x analogue.

Macrocycle synthesis strategy based on step-wise "adding and reacting" three components enables screening of large combinatorial libraries.

Macrocycles provide an attractive modality for drug development, but generating ligands for new targets is hampered by the limited availability of large macrocycle libraries. We have established a solution-phase macrocycle synthesis strategy in which three building blocks are coupled sequentially in efficient alkylation reactions that eliminate the need for product purification. We demonstrate the power of the approach by combinatorially reacting 15 bromoacetamide-activated tripeptides, 42 amines, and 6 bis-electrophile cyclization linkers to generate a 3780-compound library with minimal effort. Screening against thrombin yielded a potent and selective inhibitor (Ki = 4.2 ± 0.8 nM) that efficiently blocked blood coagulation in human plasma. Structure–activity relationship and X-ray crystallography analysis revealed that two of the three building blocks acted synergistically and underscored the importance of combinatorial screening in macrocycle development. The three-component library synthesis approach is general and offers a promising avenue to generate macrocycle ligands to other targets.

Highly efficient radiative recombination in intrinsically zero-dimensional perovskite micro-crystals prepared by thermally-assisted solution-phase synthesis.

Zero-dimensional (0D) quantum confinement can be achieved in perovskite materials by the confinement of electron and hole states to single PbX64− perovskite octahedra. In this work, 0D perovskite (Cs4PbBr6) micro-crystals were prepared by a simple thermally-assisted solution method and thoroughly characterized. The micro-crystals show a high level of crystallinity and a high photoluminescence quantum yield of 45%. The radiative recombination coefficient of the 0D perovskite micro-crystals, 1.5 × 10−8 s−1 cm3, is two orders of magnitude higher than that of typical three-dimensional perovskite and is likely a strong contributing factor to the high emission efficiency of 0D perovskite materials. Temperature dependent luminescence measurements provide insight into the role of thermally-activated trap states. Spatially resolved measurements on single 0D perovskite micro-crystals reveal uniform photoluminescence intensity and emission decay behaviour suggesting the solution-based fabrication method yields a high-quality and homogenous single-crystal material. Such uniform emission reflects the intrinsic 0D nature of the material, which may be beneficial to device applications.

Asymmetric PdPtCu mesoporous hemispheres on nitrogen-functionalized graphene for methanol oxidation electrocatalysis

This work reports an easy solution-phase synthesis of asymmetric metallic mesoporous hemispheres on nitrogen-functionalized graphene for fuel cell electrooxidation.

Microdroplet synthesis of azo compounds with simple microfluidics-based pH control.

Conventional solution-phase synthesis of azo compounds is complicated by the need for precise pH and temperature control, high concentrations of pH control reagents, and by-product removal. In this work, we exploited the advantages of microdroplet chemistry to realize the simple and highly efficient synthesis of an azo compound using microfluidics-based pH control. Owing to the small size of microdroplets, heat exchange between a microdroplet and its environment is extremely fast. Furthermore, chemical reactions in microdroplets occur rapidly due to the short diffusion distance and vortex flow. Formation of the azo compound reached completion in less than 3 s at room temperature, compared with 1 h at 0 °C under conventional conditions. pH control was simple, and the pH control reagent concentration could be reduced to less than one-tenth of that used in the conventional method. No by-products were generated, and thus this procedure did not require a recrystallization step. The time course of the chemical reaction was elucidated by observing the growth of azo compound microcrystals in droplets at various locations along the channel corresponding to different mixing times.

Solution Phase Peptide Synthesis: The Case of Biphalin.

Solution phase synthesis was the first developed and the only method for peptide synthesis until the solid phase peptide synthesis (SPPS) introduced by Merrifield revolutionized the way peptides and their analogues are prepared nowadays. However, some peptides because of their chemical structure cannot be synthetized by SPPS, and the "old school" technique is still favorable to make them. Biphalin is a good example. It was first synthesized by Lipkowski almost 40years ago as a dimeric analogue of enkephalin in which two tetra-amino acid fragments (Tyr-D-Ala-Gly-Phe-) are joined tail to tail by a hydrazide bridge. The synthesis of this octapeptide (Tyr-D-Ala-Gly-Phe-NH-NH←Phe←Gly←D-Ala←Tyr) and its analogues requires synthesis in solution because routine synthesis on a polymeric support is not possible. Biphalin shows high affinity at both μ and δ opioid receptors and produces a more robust spinal analgesia than morphine after intrathecal administration. Although biphalin and its analogues have been already deeply investigated, a complete description for its analgesic activity is not yet available.Here, we present a detailed procedure for the solution phase synthesis of biphalin.

Emerging Bottom-Up Strategies for the Synthesis of Graphene Nanoribbons and Related Structures.

The solution-phase synthesis is one of the most promising strategies for the preparation of well-defined graphene nanoribbons (GNRs) in large scale. To prepare high quality, defect-free GNRs, cycloaromatization reactions need to be very efficient, proceed without side reaction and mild enough to accommodate the presence of various functional groups. In this Minireview, we present the latest synthetic approaches for the synthesis of GNRs and related structures, including alkyne benzannulation, photochemical cyclodehydrohalogenation, Mallory and Pd- and Ni-catalyzed reactions.

Blue Light Emitting Defective Nanocrystals Composed of Earth-Abundant Elements.

Copper-based ternary (I-III-VI) chalcogenide nanocrystals (NCs) are compositionally-flexible semiconductors that do not contain lead (Pb) or cadmium (Cd). Cu-In-S NCs are the dominantly studied member of this important materials class and have been reported to contain optically-active defect states. However, there are minimal reports of In-free compositions that exhibit efficient photoluminescence (PL). Here, we report a novel solution-phase synthesis of ≈4 nm defective nanocrystals (DNCs) composed of copper, aluminum, zinc, and sulfur with ≈20 % quantum yield and an attractive PL maximum of 450 nm. Extensive spectroscopic characterization suggests the presence of highly localized electronic states resulting in reasonably fast PL decays (≈1 ns), large vibrational energy spacing, small Stokes shift, and temperature-independent PL linewidth and PL lifetime (between room temperature and ≈5 K). Furthermore, density functional theory (DFT) calculations suggest PL transitions arise from defects within a CuAl5 S8 crystal lattice, which supports the experimental observation of highly-localized states. The results reported here provide a new material with unique optoelectronic characteristics that is an important analog to well-explored Cu-In-S NCs.

Solution phase synthesis of large-area ultra-thin two dimensional layered Bi2Se3: role of Cu-intercalation and substitution

Intercalation of high densities of guest species without affecting the host lattice is challenging. Here we report on a general solution-based synthesis route to intercalate high densities of zero-valent copper into layered Bi2Se3 nanosheets at room temperature. We develop a solution phase synthesis route to design large area single-crystalline two-dimensional ultrathin Bi2Se3 nanosheets with micron dimensions. Layered Bi2Se3 nanosheets possess rhombohedral crystal structure where the Bi and Se hexagonal planes remain in close stacked configuration forming quintuple layers along the c-direction. The coupling between two quintuple layers is predominantly van der Waals type, which allows intercalating smaller guest zero-valent copper within the layers of Bi2Se3 nanosheets. Such intercalation of guest species without affecting the lattices of Bi2Se3 is challenging considering the change in oxidation state of copper, which limits the intercalant concentration. Additionally, we show that the use of CuI-amine complex at high temperature reaction conditions yields CuI substituted CuI-Bi2Se3 nanosheets disrupting the host lattice of Bi2Se3 nanosheets. We have explored the role of intercalation and substitution on the electronic properties of pristine Bi2Se3 nanosheets. Development of new synthetic strategy for the synthesis of ultra-thin larger area 2D layered Bi2Se3 nanosheets and understanding the role of metal intercalation and substitution hold promises for fundamental understanding and energy related applications.

Solution-phase synthesis of ordered mesoporous carbon as resonant-gravimetric sensing material for room-temperature H2S detection

H2S can cause multiple diseases and poses a great threat to human health. However, the precise detection of extremely toxic H2S at room temperature is still a great challenge. Here, a facile solvent evaporation induced aggregating assembly (EIAA) method has been applied for the production of ordered mesoporous carbon (OMCs) in an acidic THF/H2O solution with high-molecular-weight poly(ethylene oxide)-b-polystyrene (PEO-b-PS) copolymers as the structure-directing agent, formaldehyde and resorcinol as carbon precursors. Along with the continuous evaporation of THF from the mixed solution, cylindrical micelles are formed in the solution and further assemble into highly ordered mesostructure. The obtained OMCs possesses a two-dimensional (2D) hexagonal mesostructure with uniform and large pore diameter (∼19.2 nm), high surface area (599 m2/g), and large pore volume (0.92 cm3/g). When being used as the resonant cantilever gas sensor for room-temperature H2S detection, the OMCs has delivered not only a superior gas sensing performance with ultrafast response (14 s) and recovery (21 s) even at low concentration (2 ppm) but also an excellent selectivity toward H2S among various common interfering gases. Moreover, the limit of detection is better than 0.2 ppm, indicating its potential application in environmental monitoring and health protection.

Solution processable transition metal dichalcogenides-based hybrids for photodetection

Abstract Transition metal dichalcogenides (TMDs), as one of the most promising two-dimensional (2D) materials, have attracted considerable attention for use in photodetection applications over the past few years due to their distinct properties, such as atomic-scale thickness, tunable direct bandgaps, and decent carrier mobilities at room temperature. Compared with pure 2D TMDs, the construction of hybrids consisting of TMDs and other low-dimensional materials can further improve the performance of photodetectors including their spectral range, responsivity and detectivity, which significantly boosts interest in the development of TMDs-based photodetectors. On the other hand, solution-phase synthesis methods provide a facile strategy for the scalable production of TMD hybrids, opening an exciting avenue to develop low-cost devices. In this review, we summarize the material synthesis, characterizations, and photodetection applications of the solution processable TMDs-based hybrids, as well as provide insights into their prospects.

Exploration of Ni-X (O, S, Se) for high performance supercapacitor with long-term stability via solution phase synthesis

Here, we report a simple strategy to grow NiSe architectures vertically on nickel foam (NF) via facile solution-based deposition. The as-synthesized NSE7h core-shell nanoplate structure with a mass loading of 6.4mg/cm−2 can be delivered a high specific capacitance of 2234.84Fg−1 at 10mAcm−2 and outstanding rate capability compared to that of NO (708.52Fg−1), NS (968.22Fg−1), NSE1h (1357.43Fg−1), and NSE4h (1675.87Fg−1). The desirable electrochemical performance was mainly attributed to the component’s synergy assuring rich redox reactions, deposition of selenium on the surface of NiO nanotubes, high conductivity, great specific area and furthermore, rapid ion diffusion distance, with effective transport pathway of electrons and electrolyte ions. The existence of selenium vacancies and versatile synthesis of NiSe architectures would open up a wide range of applications in energy storage and conversion applications including supercapacitors, electrocatalysis, and batteries.

Sequences of Acretocins, Peptaibiotics Containing the Rare 1-Aminocyclopropanecarboxylic Acid, from Acremonium crotocinigenum CBS 217.70.

Sequences of Acretocins, Peptaibiotics Containing the Rare 1-Aminocyclopropanecarboxylic Acid, from Acremonium crotocinigenum CBS 217.70.

Parallel Solution Phase Synthesis and Preliminary Biological Activity of a 5'-Substituted Cytidine Analog Library.

A 109-membered library of 5'-substituted cytidine analogs was synthesized, via funding through the NIH Roadmap Initiative and the Pilot Scale Library (PSL) Program. Reaction core compounds contained -NH2 (2) and -COOH (44 and 93) groups that were coupled to a diversity of reactants in a parallel, solution phase format to produce the target library. The assorted reactants included -NH2, -CHO, -SO2Cl, and -COOH functional groups, and condensation with the intermediate core materials 2 and 44 followed by acidic hydrolysis produced 3-91 in good yields and high purity. Linkage of the amino terminus of d-phenylalanine methyl ester to the free 5'-COOH of 44 and NaOH treatment led to core library -COOH precursor 93. In a libraries from libraries approach, compound 93 served as the vital building block for our unique library of dipeptidyl cytidine analogs 94-114 through amide coupling of the -COOH group with numerous commercial amines followed by acidic deprotection. Initial screening of the complete final library through the MLPCN program revealed a modest number of hits over diverse biological processes. These hits might be considered as starting points for hit-to-lead optimization and development studies.