Palladium catalysed carbonylation of 2-iodoglycals for the synthesis of C-2 carboxylic acids and aldehydes taking formic acid as a carbonyl source

Pd catalyzed carbonylative reaction of 2-iodo-glycals has been developed taking formic acid as a carbonyl source for the synthesis of 2-carboxylic acids of sugars by the hydroxycarbonylation strategy. The methodology was successfully extended to the synthesis of 2-formyl glycals by using a reductive carbonylation approach. Both ester and ether protected glycals undergo the reaction and furnished sugar acids in good yield which is otherwise not possible by literature methods. The C-2 sugar acids were successfully utilized for the construction of 2-amido glycals, 2-dipeptido-glycal by Ugi reaction and C-1 and C-2 branched glycosyl esters.

Pd catalyzed carbonylative reaction of 2-iodo-glycals has been developed taking formic acid as a carbonyl source for the synthesis of 2-carboxylic acids of sugars by the hydroxycarbonylation strategy.

Sugar acids constitute a diverse family of carbohydrates¹ which play a crucial role in cell–cell recognition, cellular adhesion, and virus–host recognition processes, for protection of cells from pathogen attachment, and in the synthesis of biologically active natural products.² α,β-Unsaturated sugar acids such as zanamivir and ianinamivir (Fig. 1) are subjects of particular interest because of their application as inhibitors of different glycoproteins such as hemagglutinin (HA) and neuraminidase (NA),³ the major glycoproteins expressed by influenza viruses. While several reports dealing with the synthesis of carboxylic acids at C-6 and C-1 positions of sugars exist,^4a,b there is no established procedure for the synthesis of C-2 carboxylic acids. In glycals accessing carboxylic group at C-1 position required t-butyl lithium and carbon dioxide treatment at −78 °C.^4c There is only one report available in the literature in which carboxylic group was introduced to the C-2 position of glycals by Furstner et al.^4c,d where the C-2 carboxylic acid was derived from the Pinnick oxidation of 2-formyl glycal obtained by classical Vilsmeier–Haack reaction⁵ and thereafter utilized in the total synthesis of bioactive natural orevactaene (exhibits HIV-1 inhibitory property). This strategy has certain drawbacks like long reaction times with cocktails of oxidants and limited substrate specificity. For example, it works only with ether protected sugars like tri-O-benzyl-d-glycal and fails with other base labile and silyl protecting groups. Further, recovery of 2-formyl glycals after base workup is rather low in our hand. Our experience with glycals^6a–f encouraged us to formulate an attractive way to launch carboxylic acid at C-2 position of glycals as shown in Scheme 1 and apply them in the synthesis of C-2 glycoconjugates.Open in a separate windowFig. 1Glycal based acids in drugs.Open in a separate windowScheme 1Art of launching carboxyl group in sugars.This is pertinent to mention that carbonylation reactions of C-2 glycals have been successfully carried out by using metal carbonyl for the synthesis of C-2 branched glycoconjugates.^7a,b In these reaction stoichiometric amount of costly Mo(CO)₆ is required for such transformation that too ends up with some non-carbonylative side products. CO surrogates^8,9 such as formic acid, formamide, chloroform and anhydride have been explored in recent times obviating metal carbonyls and CO gas. Among all formic acid is an attractive candidate for insertion of CO in an organic molecule,¹⁰ because it liberates one water molecule after releasing one CO molecule thereby making the process environmentally benign. We felt that palladium catalyzed hydroxycarbonylation of stable glycal halides, which are conveniently accessed from glycals in good yield, may prove to be the most effective and environmentally benign method to prepare such molecules. With our continuous interest in synthesis of C-2 branched sugars,¹¹ this time we developed a reagent system for the direct synthesis of C-2 sugar carboxylic acids from 2-iodo glycals using formic acid as carbonyl source. Further, we transformed the synthesized acid for the synthesis of different C-2 branched glycoconjugates.Preliminary experiments were conducted by using 2-iodoglycal 1a, HCOOH as carbonyl source, N,N′-dicyclohexylcarbodiimide, (DCC) as an activator and xantphos as a ligand. When 1a was reacted with 5 mol% Pd(OAc)₂, 10 mol% of xantphos, 1 equiv. of DCC, 2 equiv. of formic acid and 2 equiv. of triethyl amine as base in DMF at 90 °C for 16 h the desired product 3a was obtained along with 3a′ in 60 : 40 ratio with overall 63% yield (

Visible light photocatalytic one pot synthesis of Z-arylvinyl halides from E-arylvinyl acids with N-halosuccinimide

An efficient visible light photocatalytic strategy to synthesize thermodynamically less stable Z-arylvinyl halides (with up to >99/1 Z/E ratio and 86% yield) was developed. The reaction combined base-mediated halodecarboxylation of E-arylvinyl acids with N-halosuccinimide and visible light Ir-photocatalyzed isomerization of E-arylvinyl halides in a one pot sequential catalytic process.

An efficient visible light photocatalytic strategy to synthesize Z-arylvinyl halides from E-arylvinyl acids using N-halosuccinimide through a sequential halodecarboxylation/photoisomerization with up to >99/1 Z/E ratio and 86% yield under mild reaction conditions.

Visible light photocatalysis has received considerable attention in recent years owing to the mild reaction conditions, green and sustainable chemistry features, and high atom-economy.¹ As reported in the literature, two different activation modes are commonly used. Most of the photochemical reactions proceed through a single-electron transfer (SET) process from the excited photosensitizers to the organic substrates or reagents. The other activation mode is an energy transfer (EnT) process in which no charge separation is involved in the whole process. This EnT activation pathway mainly depends on the triplet-state energies of the photosensitizers and the organic substrates. Synthetically useful visible light-induced organic transformation reactions through the EnT process have been successfully developed in the past decades.^1n,2The synthesis of multisubstituted alkenes is an important reaction because of their versatile utility as synthetic building blocks for organic synthesis and as structural elements contributing to the significant biological properties of natural products and pharmaceuticals.³ Unlike E-alkenes, the strategies for synthesis of thermodynamically less stable Z-alkenes are not readily accessible.⁴ Hammond and Arai developed pioneering photochemical E → Z isomerisations of stilbenes and styrenes and delineated the reaction mechanisms.⁵ Inspired by these mechanistic studies, visible light induced E → Z isomerization has attracted great interest. In 2014, Weaver and co-workers reported Ir(ppy)₃ catalyzed E to Z isomerization of allylamines proceeding via an EnT mechanism.⁶ In 2015, the Gilmour group developed photoisomerization of activated alkenes using (−)-riboflavin as an EnT photocatalyst.⁷ Furthermore, Gilmour and co-workers have reported photoisomerization of styrenyl boron species and selective isomerization of β-borylacrylates.⁸ In 2020, the same group reported a synthetic procedure for E → Z isomerization of β-borylacrylates via EnT using thioxanthone as the sensitizer eliminating the need of an aryl unit for alkene isomerization, and the inert aryl rings were replaced by a traceless BPin handle.⁹Arylvinyl halides are versatile synthetic intermediates for organic synthesis. In particular, transition metal-catalyzed cross couplings of vinyl halides with organometallics, such as, organo boronic and organozinc reagents, are efficient methods for synthesis of multisubstituted alkenes.¹⁰ However, synthesis of the thermodynamically less stable Z-isomer still poses a great challenge. In 2019, Yu''s group demonstrated a synthetically useful E → Z photocatalytic isomerization of styrenyl halides (Scheme 1).¹¹ On the other hand, decarboxylation of α,β-unsaturated arylvinyl acids accompanied by simultaneous replacement by halogen is a useful reaction for the synthesis of styrenyl halides.¹² Considering the importance of Z-vinyl halides in the synthesis of multisubstituted alkenes, we hypothesize that it would be interesting to combine the halodecarboxylation of α,β-unsaturated arylvinyl acids and photoisomerization of E-arylvinylhalides in a one pot sequential catalytic process. Herein, we report a novel method to synthesize Z-arylvinyl halides by visible light Ir-photocatalyzed reaction of E-arylvinyl acids with N-halosuccinimide.Open in a separate windowScheme 1Photocatalytic synthesis of multisubstituted alkenes.Our group has synthesized a series of new fluorescent quinolizinium compounds from quinolines and alkyne substrates.¹³ Due to the high tunability and high excited state reduction potentials of the fluorescent quinolizinium compounds, we proposed that the quinolizinium compounds could be used as photocatalysts for the synthesis of Z-arylvinyl halides from α,β-unsaturated arylvinyl acids.With this idea in mind, we started the initial investigation by treatment of (2E)-3-phenyl-2-butenoic acid (1a) with 2 equiv. of N-bromosuccinimide (NBS) in the presence of 5 mol% of photocatalyst 3a in CH₃CN at room temperature under 30 W blue LEDs irradiation. 36% NMR yield of the desired product (Z/E)-(1-bromoprop-1-en-2-yl)benzene (Z/E-2a) was obtained with modest selectivity (Z/E = 44/56). Next, we optimized the reaction conditions by varying the additives. Adding K₂CO₃ and TBAI, E-2a was obtained only (entries 2–3, EntryPhotocatalyst (PC)AdditiveYield^b Z/E^c13a—4544/5623a1 eq. K₂CO₃880/10033a1 eq. TBAI750/10043a1 eq. CH₃CO₂H4356/4453a2 eq. CH₃CO₂H3577/2363a3 eq. CH₃CO₂H5866/3473a2 eq. PhCO₂H2199/183a0.3 eq. PhCO₂H3294/693b0.3 eq. PhCO₂H2986/14103c0.3 eq. PhCO₂H2291/9113d0.3 eq. PhCO₂H3884/16123e0.3 eq. PhCO₂H2488/12133f0.3 eq. PhCO₂H3394/6143g0.3 eq. PhCO₂H3586/14153h0.3 eq. PhCO₂H4969/31163i0.3 eq. PhCO₂H6360/40 Open in a separate window^aReaction conditions: treatment of E-1a (0.2 mmol), NBS (0.4 mmol) and photocatalyst (5 mol%) in 2 mL of CH₃CN under N₂ and blue LEDs light for 17 hours at room temperature.^bYield was determined by ¹H NMR using dibromomethane as internal standard.^cThe Z/E ratio was determined by ¹H NMR spectroscopy.Then, we screened the reaction conditions with metal photocatalyst Ir(ppy)₃. Styrenyl hailde 2a was obtained in 48% NMR yield in a Z/E ratio (52 : 48) (entry 1, EntryPhotocatalyst (PC)AdditiveYield^b Z/E^c1^dIr(ppy)₃0.3 eq PhCO₂H4852/482Ir(ppy)₃0.3 eq PhCO₂H0—3Ir(ppy)₃—0—4Ir(ppy)₃0.3 eq. K₂CO₃3161/395Ir(ppy)₃2 eq. K₂CO₃6097/36Ir(ppy)₃2.5 eq. K₂CO₃5695/57Ir(ppy)₃3 eq. K₂CO₃4996/48Ir(ppy)₃2 eq. Na₂CO₃5795/59Ir(ppy)₃2 eq. Cs₂CO₃5494/610Ir(ppy)₃2 eq. K₃PO₄6489/1111Ir(ppy)₃2 eq. tBuOK3892/812Ir(ppy)₃2 eq. DBU4794/613Ir(ppy)₃2 eq. Et₃N967/3314Ir(Fppy)₃2 eq. K₂CO₃5689/1115Ir(diFppy)₃2 eq. K₂CO₃7379/2116Mes-Acr-BF₄2 eq. K₂CO₃3010/9017Ru(bpy)₃(PF₆)₂2 eq. K₂CO₃645/9518Ru(bpy)₃Cl₂2 eq. K₂CO₃480/10019^eIr(ppy)₃2 eq. K₂CO₃740/10020—2 eq. K₂CO₃544/96Open in a separate window^aReaction conditions: treatment of E-1a (0.2 mmol), NBS (0.4 mmol) and photocatalyst (2 mol%) in 2 mL of MeOH under N₂ and blue LEDs light for 17 hours at room temperature.^bYield was determined by ¹H NMR using dibromomethane as internal standard.^cThe Z/E ratio was determined by ¹H NMR spectroscopy.^dThe reaction solvent was CH₃CN.^eNo light irradiation.After optimizing the reaction conditions, we next sought to explore the scope of the reaction. The results summarized in Open in a separate window^aReactions were performed with 0.2 mmol substrate at room temperature in MeOH (2.0 mL) using 2 mol% fac-Ir(ppy)₃ under 30 W blue LEDs irradiation. Z/E ratios were determined by ¹H NMR spectroscopy. Isolated yields.^b5.0 mmol scale.^c5 mol% fac-Ir(ppy)₃.^d1 mol% fac-Ir(ppy)₃.To gain mechanistic insight on this reaction, the reaction progress was monitored under the optimized reaction conditions (Scheme 2). Complete halodecarboxylation of E-1c was observed in 1 hour to give E-2c, which suggests that the isomerisation is the rate-determining step. Some product Z-2c was obtained after 2 hours. Almost complete E → Z isomerization was observed over the course of 16 hours.Open in a separate windowScheme 2Reaction progress monitoring of E-1c.At last, we performed two Pd-catalyzed coupling reactions with styrenyl bromide Z-2j to further illustrate the synthetic utility of this cascade reaction (Scheme 3). When 4-methoxyphenylboronic acid was treated with bromide Z-2j using Pd(PtBu₃)₂ as catalyst, Suzuki–Miyaura cross coupling reaction¹⁴ successfully afforded trisubstituted alkene Z-4 (Z/E = 98/2) in 78% yield. Moreover, Sonogashira coupling reaction¹⁵ with 1-ethynyl-4-methylbenzene gave enyne Z-5 (Z/E = 98/2) in 87% yield.Open in a separate windowScheme 3Pd-catalyzed coupling reactions of styrenyl bromide Z-2j.     

Carbon monoxide poisoning and pulmonary injury from the mixture of formic and sulfuric acids

Context: The inhalation of carbon monoxide produced by the incomplete combustion of carbon remains a popular method of suicide. A much less common method of producing carbon monoxide for suicide is by mixing formic and sulfuric acids. Case details: We describe a patient who attempted suicide by mixing formic and sulfuric acids. He presented with a depressed level of consciousness, chemical burns of his airway and skin, and respiratory distress. He was found to have a metabolic acidosis, a carboxyhemoglobin of 36.8%, hyperkalemia, and rhabdomyolysis. His hospital course was notable for copious pulmonary secretions and hypoxia, but he ultimately recovered with supportive care. Discussion: The case highlights the potential toxicity, particularly from inhaled carbon monoxide and formic acid, with this method of suicide.     

Selective and clean synthesis of aminoalkyl-H-phosphinic acids from hypophosphorous acid by phospha-Mannich reaction

Aminoalkyl-H-phosphinic acids, also called aminoalkylphosphonous acids, are investigated as biologically active analogues of carboxylic amino acids and/or as valuable intermediates for synthesis of other aminoalkylphosphorus acids. Their synthesis has been mostly accomplished by phospha-Mannich reaction of a P–H precursor, an aldehyde and an amine. The reaction is rarely clean and high-yielding. Here, reaction of H₃PO₂ with secondary amines and formaldehyde in wet AcOH led to aminomethyl-H-phosphinic acids in nearly quantitative yields and with almost no by-products. Surprisingly, the reaction outcome depended on the basicity of the amines. Amines with pK_a > 7–8 gave the desired products. For less basic amines, reductive N-methylation coupled with oxidation of H₃PO₂ to H₃PO₃ became a relevant side reaction. Primary amines reacted less clearly and amino-bis(methyl-H-phosphinic acids) were obtained only for very basic amines. Reaction yields with higher aldehydes were lower. Unique carboxylic–phosphinic–phosphonic acids as well as poly(H-phosphinic acids) derived from polyamines were obtained. Synthetic usefulness of the aminoalkyl-H-phosphinic was illustrated in P–H bond oxidation and its addition to double bonds, and in selective amine deprotection. Compounds with an ethylene-diamine fragment, e.g. most common polyazamacrocycles, are not suitable substrates. The X-ray solid-state structures of seventeen aminoalkyl-phosphinic acids were determined. In the reaction mechanism, N-hydroxyalkyl species R₂NCH₂OH and [R₂N(CH₂OH)₂]⁺, probably stabilized as acetate esters, are suggested as the reactive intermediates. This mechanism is an alternative one to the known phospha-Mannich reaction mechanisms. The conditions can be utilized in syntheses of various aminoalkylphosphorus compounds.

Acetic acid was used as a new solvent for phospha-Mannich reaction leading to clear reaction mixtures and high yields of the aminoalkylphosphonous acids (AHPA), and hydroxymethylated species were suggested as key intermediates in the reaction.     

Oxidative radical coupling of hydroquinones and thiols using chromic acid: one-pot synthesis of quinonyl alkyl/aryl thioethers

An efficient, simple and practical protocol for one-pot sequential oxidative radical C–H/S–H cross-coupling of thiols with hydroquinones (HQs) and oxidation leading to the formation of quinonyl alkyl/aryl thioethers using H₂CrO₄ was developed. This cross-coupling of thiyl and aryl radicals offers mono thioethers in good to moderate yield and works well with a wide variety of thiols. Similarly, this method works well for coupling of 2-amino thiophenol and HQs to form phenothiazine-3-ones 5a–c. C–S bond formation via thioether synthesis was observed using a chromium reagent for the first time. Theoretical studies on the pharmacokinetic properties of compounds 5a–c revealed that due to drug-like properties, compound 5b strongly binds with Alzheimer''s disease (AD) associated AChE target sites.

Oxidative radical C–H/S–H cross coupling of hydroquinones and thiols and oxidation to quinone using a H₂CrO₄ system was developed.     

Catalytic valorisation of biomass levulinic acid into gamma valerolactone using formic acid as a H2 donor: a critical review

This review sheds light on the catalytic valorisation of agroforestry biomass through levulinic acid and formic acid towards γ-valerolactone and other higher-value chemicals. γ-Valerolactone is produced by the hydrogenation of levulinic acid, which can be achieved through an internal hydrogen transfer reaction with formic acid in the presence of catalyst. By reviewing corresponding catalysts, the paper underlines the most efficient steps constituting an integrated sustainable process that eliminates the need for external H₂ sources while producing biofuels as an alternative energy source. Furthermore, the review emphasizes the role of catalysts in the hydrogenation of levulinic acid, with special focus on heterogeneous catalysts. The authors highlighted the dual role of different catalysts by comparing their activity, morphology, electronic structure, synergetic relation between support and doped species, as well as their deactivation and recyclability. Acknowledging the need for green and sustainable H₂ production, the review extends to cover the role of photo catalysis in dissociating H₂-donor solvents for reducing levulinic acid into γ-valerolactone under mild temperatures. To wrap up, the critical discussion presented enables readers to hone their knowledge about different schools and emphasizes research gaps emerging from experimental work. The review concludes with a comprehensive table summarizing the recent catalysts reported between the years 2017–2021.

This review sheds light on the catalytic valorisation of agroforestry biomass through levulinic acid and formic acid towards γ-valerolactone and other higher-value chemicals.     

Amino acid metabolism in endogenous psychoses: significance of amino acids as neurotransmitter, precursor of monoamines and allosteric regulator of neuro-receptors]

Amino acid metabolism in endogenous psychoses has been discussed in relation to monoamine synthesis. There are no consistent findings which prove altered monoamine syntheses to be the primary change. Our finding, which suggests decreased amino acid transport across the blood-brain barrier in schizophrenia, does not necessarily mean an insufficient amino acid supply to the brain. Several lines of investigation have shown the possibility of the involvement of glutamatergic dysfunction in the pathogenesis of schizophrenia. Our recent finding of decreased CSF asparagine concentration in schizophrenia and its positive correlation with the response to neuroleptics may support this hypothesis. Recently, free D-serine, an allosteric agonist on NMDA-receptor, has been reported to exist in the rat brain, suggesting that D-serine is an intrinsic ligand. The pathogeneses of endogenous psychoses might be studied in terms of disturbed metabolism of amino acid, as allosteric regulater of neuro-receptor, as well as neurotransmitter and precursor of monoamines.     

Microwave-assisted synthesis of octahedral Rh nanocrystals and their performance for electrocatalytic oxidation of formic acid

Uniform and well-defined octahedral Rh nanocrystals were rapidly synthesized in a domestic microwave oven for only 140 s of irradiation by reducing Rh(acac)₃ with tetraethylene glycol (TEG) as both a solvent and a reducing agent in the presence of an appropriate amount of KI, didecyl dimethyl ammonium chloride (DDAC), ethylene diamine (EDA) and polyvinylpyrrolidone (PVP). KI, DDAC and EDA were essential for the creation of octahedral Rh nanocrystals. Electrochemical measurements showed a significantly enhanced electrocatalytic activity and stability for the as-prepared octahedral Rh nanocrystals compared with commercial Rh black.

Octahedral Rh nanocrystals were rapidly synthesized in a domestic microwave oven for only 140 s of irradiation by reducing Rh(acac)₃ with tetraethylene glycol as both a solvent and a reducing agent.

To date, platinum group metals play an indispensable role as efficient catalysts for some important reactions in industry. However, due to their limited reserves and high prices, a large number of platinum group metal nanoparticles with different particle sizes, morphologies and surface structures have been synthesized by means of various methods to reduce their cost.¹ As a platinum group metal, Rh has good catalytic activity and stability, and is often used as a typical catalyst for some chemical reactions such as hydrogenation,^2–7 nitrogen oxide reduction,⁸ CO oxidation,^9–11 cross coupling,^12–14 hydroformylation,^15–19 in fuel cells^20,21 and other chemical reactions.²² Therefore, controlled syntheses of Rh nanoparticles with different morphologies have attracted much attention. In recent years, people have successfully prepared Rh nanostructures with various morphologies such as sheet,^23–27 flower,⁶ polyhedron,^28–33 porous ball,⁸ multi branches,^34–39 stars,⁴⁰ nanoframes^13,14,41 and nano nail.⁴² These Rh nanoparticles with unique structures effectively improve the atom utilization as well as their catalytic reaction performances. However, similar to other platinum group metals, the difficulty of large-scale preparation of Rh nanomaterials with single morphology and uniform size still greatly restricts their industrial application.Microwave irradiation has been widely used in chemical synthesis because of its simple, rapid and efficient characteristics as well as special heating mode from the inner. We have synthesized many metallic nanoparticles with different shapes by using microwave irradiation for about 80 to 120 seconds. Herein, we report a simple and fast strategy for the synthesis of octahedral Rh nanocrystals under microwave irradiation with using domestic microwave oven. In a typical synthesis, octahedral Rh nanocrystals with uniform and well-defined morphologies were successfully synthesized with Rh(acac)₃ as the precursor, polyvinyl pyrrolidone (PVP) as the stabilizer, triethylene glycol (TEG) as both a solvent and a reducing agent in the presence of didecyl dimethyl ammonium chloride (DDAC), KI and ethylene diamine (EDA) under microwave irradiation in a very short time. Meanwhile, the electrocatalytical performance of the as-prepared octahedral Rh nanocrystals for the electro-oxidation of formic acid was also investigated with commercial Rh black as a contrast.The TEM and SEM images of the representative Rh nanoparticles obtained under the optimal experimental conditions are shown in Fig. 1, S1 and S2.^† Wherein, the prepared Rh nanoparticles demonstrated uniform and well-defined octahedral structure with sharp edges and corners as well as smooth surfaces (Fig. 1a and b), in which the average side length is about 65 nm. The high-resolution TEM (HRTEM) image (Fig. 1c) shows well-resolved continuous fringes clearly. The corresponding fast Fourier transform (FFT) pattern, as the inset shown in Fig. 1c, shows a lattice distance of 0.194 or 0.216 nm, which can be attributed to the {200} and {111} lattice planes of the octahedral Rh with face-centered cubic structure, respectively, confirming its single-crystal nature. Furthermore, the regular octahedral feature of the as-prepared Rh nanoparticles can be well distinguished from SEM images, as shown in Fig. 1d and S2.^† These results show that the octahedral Rh nanocrystals with a single morphology can be rapidly synthesized in a great quantity by irradiation with domestic microwave oven for only 140 s.Open in a separate windowFig. 1TEM and SEM images of the as-prepared octahedral Rh nanocrystals. (a) and (b) Typical TEM images with different scales. The inset in (b) is the schematic illustration; (c) typical HRTEM image. The inset is the corresponding FFT pattern; (d) SEM image. Fig. 2a shows the XRD pattern of the as-prepared typical octahedral Rh nanocrystals. As can be seen, the diffraction peaks at 2θ values of 41.26, 47.95, 70.18 and 84.33° are observed, which can be well indexed to the diffractions of (111), (200), (220) and (311) lattice facets of metallic Rh referring to the standard powder diffraction card (JCPDS card No. 05-0685), respectively. This observation further confirmed their fcc Rh structure. In addition, the narrow and sharp (111) diffraction peak implied that the typical octahedral Rh nanocrystals exhibited a high purity and crystallinity. The XPS spectrum was taken for the as-prepared octahedral Rh nanocrystals and the result was displayed in Fig. 2b, As it can be seen, two peaks corresponding to the electron binding energies of Rh 3d_3/2 and Rh 3d_5/2 were observed at 311.85 eV and 307.10 eV with an interval of 4.75 eV, respectively, which were consistent with the literature values (311.75 and 307.0 eV),⁴³ revealing Rh(0) metallic state of the octahedral nanocrystals.Open in a separate windowFig. 2XRD pattern (a) and XPS spectrogram (b) of octahedral Rh nanocrystals.The dependence of the morphological evolution of Rh nanocrystals upon irradiation time was investigated. When irradiated for 120 s, the octahedral structural Rh nanocrystals with about 65 nm of the side length produced except for unclear edges and corners as well as a shorter side length, as shown in Fig. 3a. As microwave irradiation progressed to 140 s, uniform and well-defined octahedral Rh nanocrystals with smooth surfaces generated (Fig. 3b). While the irradiation time was extended to 160 s, however, the vertices of some octahedral structures were truncated although with no change of the sizes, as shown in Fig. 3c. As the irradiation time reached 180 s, the octahedral structural feature of most particles disappeared with a further truncation of their vertices (Fig. 3d), which should be ascribed to higher surface free energies for the metallic atoms at the apexes and edges as well as a higher internal temperature due to a longer irradiation time. These results indicated that the optimum microwave irradiation time was 140 s for the creation of regular octahedral Rh nanocrystals.Open in a separate windowFig. 3TEM images of Rh nanoparticles prepared at different reaction time. (a) 120 s; (b) 140 s; (c) 160 s; (d) 180 s.It was noteworthy that KI played a crucial role in controlling synthesis of octahedral Rh nanocrystals. When no KI was used, it would produce irregular Rh nanoparticles, as shown in Fig. 4a. While with addition of 0.6 mmol of KI, octahedral Rh nanostructures with blunt vertices and an average side length of about 50 nm were generated (Fig. 4b), implying an incomplete growth relative to the case of 0.8 mmol of KI as in the typical experimental process (Fig. 1). Nevertheless, the amount of KI was increased to 1.2 mmol, only less octahedral structure features could be observed except for few obscure polyhedral outlines (Fig. 4c). These results indicated that the existence of KI was advantageous to the generation of octahedral Rh nanocrystals. Generally, the eight triangular surfaces of metallic Rh octahedron consists of (111) lattice planes. According to the previous report,^44–49 it can be considered that the preferential adsorption of I⁻ anions on Rh (111) planes is one of the main factors driving the formation of octahedral structure. As a result, a growth along 〈111〉 directions was confined and a growth along 〈100〉 directions was facilitated, which created octahedral structures due to anisotropic growth. However, excessive I⁻ ions would adsorb non-selectively on the surfaces of Rh nanoparticles, which resulted in passivation of the edges and corners of polyhedron. In addition, an equivalent amount of KBr or KCl was used instead of KI, respectively, to clarify the role of I⁻ ions under the same other conditions. As can be seen (Fig. S3, ESI^†), no octahedral Rh nanocrystal except for agglomerated irregular nanosheets was observed in these two contrast experiments. This may be ascribed to the change of the precursor. In the presence of a large number of I⁻ ions, the precursor can be transformed to a more stable [RhI₆]³⁻ complex.^44–47 As a result, the reducing rate of Rh(iii) to Rh atom decreased, which may be favourable for the nucleation of Rh nanoparticles and the oriented growth of Rh octahedra.Open in a separate windowFig. 4TEM images of Rh nanoparticles prepared with different amounts of DDAC or KI under the same other conditions. (a) Absence of KI; (b) 0.6 mmol of KI; (c) 1.2 mmol of KI; (d) absence of DDAC; (e) 0.2 mmol of DDAC; (f) 0.6 mmol of DDAC.Meanwhile, the influence of DDAC on the generation of octahedral Rh nanocrystals was also studied under the same other conditions. In the absence of DDAC, only agglomerated irregular Rh nanoparticles were observed (Fig. 4d). When 0.2 mmol of DDAC was added, octahedral Rh nanostructures with an average side length of about 45 nm, a smaller size relative to the case of 0.4 mmol of DDAC as in the typical experiments (Fig. 1), were generated accompanying with a few irregular nanoparticles (Fig. 4e). With increasing the amount of DDAC to 0.6 mmol, agglomerated irregular polyhedral nanostructures formed (Fig. 4f). Thus, the addition of DDAC was also indispensable for the growth of octahedral Rh nanostructures under microwave irradiation. Whereas an excessive amount of DDAC was also unfavourable for creation of the octahedral Rh nanocrystals. Moreover, no octahedral nanostructures generated except for urchin-like Rh hierarchical superstructures when adding an equivalent amount of cetyltrimethylammonium chloride (CTAC) instead of DDAC (Fig. S4a, ESI^†). While didoctyl dimethyl ammonium bromide (DDAB) was used instead of DDAC, the formation of octahedral Rh structures can be still observed although accompanying with other irregular polyhedral (Fig. S4b, ESI^†). These results suggested that the formation of octahedral Rh nanostructures were strongly dependent upon the hydrophobic chains of DDAC or DDAB but nothing to do with Cl⁻ or Br⁻ anions. The effect of other halide ions can be ignored due to the existence of a large number of I⁻ ions. That is because the strength of adsorption of I⁻ ions on metal surfaces is generally stronger than that of Cl⁻ or Br⁻ ions.⁴⁸Accordingly, the generation of octahedral Rh nanocrystals should be ascribed to the synergistic effect of KI and DDAC under the above experimental conditions. We believe that DDAC could enhance the role of I⁻ ions in generating (111) facets of octahedral by adjusting the adsorption selectivity of I⁻ ions on (111), (100) or (110) facets. On the one hand, the amount of KI would manipulate the reducing kinetics to form octahedral Rh nanostructures under microwave irradiation. A slow reducing rate was favourable for the oriented growth of Rh octahedra due to the formation of a more stable coordinated anion [RhI₆]³⁻. On the other hand, the confinement of DDAC induced the selective adsorption of I⁻ ions on Rh {111} facets which restrained the growth along 〈111〉 directions of Rh nuclei and prompted the growth along 〈100〉 directions. In addition, a proper quantity of DDAC confined the deposition of Rh atoms on {111} facets, which may be beneficial to the growth along 〈100〉 directions. However, an excessive amount of DDAC was unfavourable for the formation of shaped Rh nanoparticles since they disturbed the adsorption of I⁻ anions on Rh {111} facets.Furthermore, it was also found that ethylene diamine (EDA) demonstrated an important effect on the creation of octahedral Rh nanostructures. Under keeping the total volume of the reaction system unchanged, the significantly agglomerated irregular polyhedral nanoparticles with sharp horns were observed in absence of EDA (Fig. S5a^†). When 0.5 mL of EDA was added, a few octahedral nanostructures began to generate though accompanying with agglomerated irregular polyhedra (Fig. S5b^†). While the amount of EDA was increased to 1 mL, uniform and well-defined octahedral Rh nanocrystals with flat and smooth surfaces were produced (Fig. S5c^†). However, a more amount of EDA was added, a part of octahedral nanostructures become deformation as well as agglomeration (Fig. S5d^†). In the reaction system, TEG as a solvent was also served as a reducing agent. As can be seen, even though without adding EDA, the rhodium salt was still reduced completely to produce metal Rh nanoparticles. With the addition of EDA, octahedral Rh nanocrystals began to generate, while an excessive amount of EDA resulted in unclear edges and corners of the octahedral structures. Obviously, EDA demonstrated significant effect on the morphology control of octahedral Rh nanocrystals. It should be ascribed to the coordination adsorption of EDA on the surface of metal particles.⁵⁰ Furthermore, no octahedral nanostructures but irregular nanoparticles or Rh dendrites generated with using an equivalent amount of n-butylamine or n-octylamine instead of EDA (Fig. S6a and b^†). Therefore, we suggest that EDA plays a synergistic role together with DDAC in regulating the rate of atomic packing and nanoparticle growth by coordination adsorption. The growth rate of nanoparticles is faster in absence of EDA, while the growth rate slows down with the increase of EDA dosage. An appropriate amount of EDA facilitates the generation of uniform octahedral Rh nanocrystals by adjusting the balance between nucleation rate and growth rate. Nevertheless, excessive EDA makes a slower growth than nucleation due to their extreme adsorption, resulting in obscure appearances of some octahedral Rh nanoparticles.In addition, PVP was also found to be important but not essential for the formation of octahedral Rh nanocrystals. Either without or with a few amount of PVP, octahedral Rh nanocrystals can also produce except for a little agglomeration (Fig. S7a and b^†). An appropriate amount of PVP contributed to uniform and well dispersed octahedral Rh nanocrystals, while excessive PVP caused aggregation (Fig. S7c and d^†). These results indicated that PVP served mainly as a protecting and dispersing agent for the nanocrystals.The catalytic performance of the synthesized octahedral Rh nanocrystals was tested by cyclic voltammetry (CV) and chronoamperometry (CA) with the formic acid electrooxidation reaction as the model reaction system. Fig. 5a exhibits the representative CV curves obtained for the electrochemical oxidation of 0.5 mol L⁻¹ HCOOH over the octahedral Rh nanocrystals and commercial Rh black in 0.5 mol L⁻¹ HClO₄ solution, respectively. CV measurements showed the peak current density for the octahedral Rh nanocrystals was 3.53 mA cm⁻² at 0.544 V, while it was 1.01 mA cm⁻² at 0.609 V for Rh black. The formic acid electrooxidation indicated that the electrocatalytic activity of octahedral Rh nanocrystals was about 3.5 times that of Rh black, demonstrating an obvious morphological dependence for their electrochemical property. The corresponding CA curves of formic acid electro-oxidation at 0.55 V is shown in Fig. 5b. As can be seen, a higher current retention through the whole measuring range were observed over the as-prepared octahedral Rh nanocrystals than Rh black though both of them showed an equivalent attenuation rate in the initial 20 seconds. The CV curve of continuous cycle scanning for octahedral Rh nanocrystals in 0.5 mol L⁻¹ HClO₄ solution showed a decrease of the electrochemical activity only by 9.6% after 2000 cycles (Fig. S8^†). These results reveal that octahedral Rh nanocrystals exhibit a remarkably enhanced electrochemical activity and stability compared with Rh black. Their enhanced catalytic activity should be attributed to the uniform geometric structure with single surface lattice.Open in a separate windowFig. 5The CV (a) and CA (b) curves for the electrochemical oxidation of 0.5 mol L⁻¹ HCOOH over the octahedral Rh nanocrystals and Rh black in 0.5 mol L⁻¹ HClO₄ solution, respectively.Additionally, CO stripping voltammetry measurements were performed. As shown in Fig. S9a,^† no CO electro-oxidation (CO_ox) was observed for the freshly-prepared octahedral Rh nanocrystals in 0.5 M HClO₄ solution. Subsequently, a current peak for CO_ox appeared at 0.550 V (versus SCE) after adorbing CO for the clean octahedral Rh-modified electrode, as shown in Fig. S9b.^† Then CO_ox peak disappeared in the following second potential scanning, as shown in Fig. S9c.^† These results showed that CO adsorbed on Rh surfaces can be easily removed in the process of electrocatalytic oxidation, showing well CO resistence.In summary, uniform octahedral Rh nanocrystals could be rapidly prepared with domestic microwave oven in only 140 s of irradiation by reducing Rh(acac)₃ with TEG as both a solvent and a reducing agent, PVP as a protecting and dispersing agent in the presence of proper quantities of DDAC, KI and EDA. The formation of octahedral Rh nanocrystals was attributed to the synergism of KI, DDAC and EDA. The electrochemical oxidation of formic acid demonstrated higher electrocatalytic activity and stability for the as-prepared octahedral Rh nanocrystals than Rh black, displaying a significant dependence upon their morphologies.     

An efficient and environmentally sustainable domino protocol for the synthesis of structurally diverse spiroannulated pyrimidophenazines using erbium doped TiO2 nanoparticles as a recyclable and reusable heterogeneous acid catalyst

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines involving a four component reaction of 2-hydroxynaphthalene-1,4-dione, benzene-1,2-diamine, cyclic ketones and amino derivatives in the presence of erbium doped TiO₂ nanoparticles as a recyclable and reusable heterogeneous acid catalyst. The present synthetic protocol features mild reaction conditions with operational simplicity, excellent yield with high purity, short reaction time and high atom economy with the use of a recoverable and reusable environmentally sustainable heterogeneous catalyst.

An efficient and environmentally sustainable domino protocol has been presented for the synthesis of structurally diverse spiroannulated pyrimidophenazines using erbium doped TiO₂ nanoparticles as a recyclable and reusable heterogeneous acid catalyst.     

Role of primary and secondary bile acids as feedback inhibitors of bile acid synthesis in the rat in vivo.

The effect of various primary and secondary bile acids on the rates of synthesis of all major bile acids was studied in the live rat with an extracorporal bile duct. Bile acid synthesis was determined using HPLC based on mass or by isotope dilution. Derepressed rates of bile acid synthesis (30-54 h) were inhibited by an infusion of taurocholic acid only at a supraphysiological dose of 500 mumol/kg per h, but not at 300 mumol/kg per h, which approximates the initial bile acid secretion (250 mumol/kg per h). When administered together with taurocholic acid (200 mumol/kg per h) only a high dose of taurochenodeoxycholic acid (100 mumol/kg per h) decreased taurocholic but not tauromuricholic or taurochenodeoxycholic acid synthesis. The only bile acid suppressing taurocholic acid (36-71%) and taurochenodeoxycholic acid (up to 33%) formation at an infusion rate close to the normal portal flux was deoxy- or taurodeoxycholic acid at 15-50 mumol/kg per h. It may be concluded that deoxycholic acid and possibly other secondary bile acids are much more potent inhibitors than primary bile acids.     

Regulation of cephamycin C synthesis, aspartokinase, dihydrodipicolinic acid synthetase, and homoserine dehydrogenase by aspartic acid family amino acids in Streptomyces clavuligerus.

The effect of the cephalosporin precursors and amino acids of the aspartic acid family on antibiotic production by Streptomyces clavuligerus was investigated DL-meso-Diaminopimelate and L-lysine each stimulated specific antibiotic production by 75%. A fourfold increase in specific production was obtained by simultaneous addition of the two compounds. The stimulation could be further increased by adding valine to the two effectors. In the streptomycetes the alpha-aminoadipyl side chain of the cephalosporin antibiotics is derived from lysine. Streptomycetes, like other bacteria, are expected to produce lysine from aspartic acid; therefore, the feedback control mechanisms operating in the aspartic acid family pathway of S. clavuligerus, which may affect the flow of carbon to alpha-aminoadipic acid, were investigated. Threonine inhibited antibiotic production by 41% when added to minimal medium at a concentration of 10 mM. Simultaneous addition of 10 mM lysine completely reversed this inhibition. The aspartokinase of S. clavuligerus was found to be subject to concerted feedback inhibition by threonine and lysine. Threonine may act to limit the supply of lysine available for cephamycin C biosynthesis via this concerted mechanism. Single or simultaneous addition of any other amino acid of the aspartate family in the in vitro assay did not inhibit aspartokinase activity. Activity was stimulated by lysine. Aspartokinase biosynthesis was partially repressed by methionine or isoleucine at concentrations higher than 10 mM. Methionine, but not isoleucine, inhibited cephamycin C synthesis by 27% when added to minimal medium at a concentration of 10 mM. Dihydrodipicolinate synthetase, the first specific enzyme of the lysine branch, was not inhibited by lysine but was partially inhibited by high concentrations of 2,6-diaminopimelate and alpha-aminoadipate; it was slightly repressed by diaminopimelic acid. Homoserine dehydrogenase activity was inhibited by threonine and partially repressed by isoleucine. It appears that S. clavuligerus aspartokinase is a key step in the control of carbon flow toward alpha-aminoadipic acid.     

Utilization for protein synthesis of 2-ketoisocaproate relative to utilization of leucine, as estimated from exhalation of labelled CO2

1. We have previously shown that the ratio (RWBP) of incorporation of label from 2-ketoisocaproate (KIC) into the leucine of whole-body protein to the simultaneous incorporation of label from leucine itself into protein is a measure of the nutritional efficiency of KIC as a substitute for leucine. 2. In order to determine whether RWBP can be estimated indirectly from measurement of labelled CO2 excretion, rats were injected orally or intravenously with [4,5-3H]leucine and either [1-14C]leucine or [1-14C]KIC. Expired CO2 was collected for 6 h. 3. The results show that 9-14% of KIC underwent first-pass oxidation after oral administration. When isotopes were given intravenously, the mean rate of excretion of 14CO2 from KIC, after 20 min, remained 1.8 times the mean rate of excretion of 14CO2 from leucine. 4. Mean RWBP, measured in whole-body protein in rats given isotopes orally or intravenously along with small or large doses of carriers, was the same as mean RWBP estimated from mean cumulative CO2 excretion. 5. We conclude (1) that nutritional efficiency of KIC relative to leucine can be estimated from measurement of labelled CO2 excretion, and (2) that the relative inefficiency of KIC as a substitute for leucine in the rat is attributable to first-pass oxidation of 9-14% (when given orally) and 80% greater susceptibility to systemic oxidation than leucine.     

Microbial metabolism of caffeic acid and its esters chlorogenic and caftaric acids by human faecal microbiota in vitro.

Caffeic acid and its esters, chlorogenic and caftaric acids, are major dietary polyphenols present in various foods and beverages. Although caffeic acid is easily absorbed in the small intestine, its esterification with quinic acid, as in chlorogenic acid, decreases its gut absorption and increases the quantities reaching the colon and its microbiota. The microbial conversion of caftaric acid, the tartaric acid ester of caffeic acid, has not been studied earlier. In this work we compared the direct action of a human faecal microbiota on the metabolism of caffeic, chlorogenic and caftaric acids in an in vitro fermentation model. All substrates disappeared quickly and none of the free acids (caffeic, quinic or tartaric acids) were detected after 2 hours of incubation. Two major microbial metabolites were identified by HPLC-ESI-MS-MS as 3-hydroxyphenylpropionic (3-HPP) and benzoic acids (BA). Maximal levels of 3-HPP were reached after 2 h of fermentation and accounted for 9-24% of the dose of caffeic acid and its esters. BA was formed steadily throughout the incubation, accounting for 4-5% of the initial dose of the substrates after 24 h of incubation. The similarities in the metabolic patterns observed for caffeic, chlorogenic and caftaric acids suggest that esterification does not influence the metabolism of caffeic acid by the gut microbiota.     

Green synthesis of Pd nanoparticles supported on reduced graphene oxide,using the extract of Rosa canina fruit,and their use as recyclable and heterogeneous nanocatalysts for the degradation of dye pollutants in water

The current study suggests a convenient synthesis of in situ, ecofriendly and well-dispersed palladium nanoparticles with narrow and small dimension distributions on a graphene oxide (GO) surface using a Rosa canina fruit extract as a stabilizer and reducing agent without the addition of any other stabilizers or surfactants. The as-synthesized nanocatalyst (Pd NPs/RGO) was assessed with XRD, UV-vis, FE-SEM, EDS, TEM, ICP and WDX. The obtained heterogeneous nanocatalyst showed catalytic performance for reducing 4-nitrophenol (4-NP), rhodamine B (RhB) and methylene blue (MB) at ambient temperature in an ecofriendly medium. The catalyst was retained by centrifugation and reused several times with no considerable change in its catalytic performance.

We suggests a convenient synthesis of in situ, ecofriendly and well-dispersed Pd nanoparticles with narrow and small dimension distributions on graphene oxide (GO) using Rosa canina extract as a reducing agent and as the only stabilizer.     

Rare earth complexes using azobenzene-containing poly(aryl ether)s with different absorption wavelengths as macromolecular ligands: synthesis,characterization, fluorescence properties and fabrication of fluorescent holographic micropatterns

In this paper, two novel azobenzene-containing poly(aryl ether)s with different absorption wavelengths were synthesized via Ullmann coupling and Sonogashira coupling, respectively. The obtained polymers were characterized and evaluated by elemental analysis, IR, ¹H NMR, UV-vis, DSC and TGA. Rare earth complexes were prepared by using the two novel azobenzene-containing poly(aryl ether)s as macromolecular ligands. The obtained rare earth complexes were characterized by elemental analysis, IR and WAXD. The influence of the absorption wavelength of azobenzene chromophores on the fluorescent properties was investigated. The polymer whose absorption wavelength was far from the excitation wavelengths of the rare earth complexes showed a much larger fluorescence intensity. By exposing the films of the rare earth complexes to two interference laser beams, SRGs can be formed on the films and can also be detected by fluorescence microscopy measurement.

Preparation and fluorescence properties of rare earth complexes using azobenzene-containing poly(aryl ether)s with different absorption wavelengths as macromolecular ligands.     

Use of ammonium salts or binary mixtures derived from amino acids,glycine betaine,choline and indole-3-butyric acid as plant regulators

A simple, efficient, and environmentally friendly synthesis method for bioproducts based on indole-3-butyric acid and amino acids, glycine betaine or choline has been developed. Spectral analysis and molecular calculations were used to determine whether the products were ammonium salts or binary mixtures. Moreover, it was observed that the ammonium salts degraded more rapidly than the binary mixtures when exposed to light. The structures of the products significantly impacted their thermal stability and phase transitions. Biological studies clearly showed that the synthesized products were more effective than a reference commercial preparation as a rooting agent and have significant potential as new biologically active agents with low environmental impact.

Natural origin ammonium salts or binary mixtures including indole-3-butyric acid as novel plant growth regulators.     

Degradation of diuron by heterogeneous electro-Fenton using modified magnetic activated carbon as the catalyst

In this work, polytetrafluoroethylene coating was firstly conducted to make stable and effective magnetic-activated carbon as a heterogeneous electro-Fenton catalyst for diuron oxidation. The catalysts were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). In addition, the effects of operating parameters such as catalyst dosage, current intensity, substrate concentration and pH on the degradation of diuron were investigated. The removal efficiency of diuron was more than 95% within 120 min oxidation under the conditions of I = 100 mA, pH = 6.7 ± 0.2, catalyst loading 3 g L⁻¹ and diuron concentration 10 mg L⁻¹. Moreover, the catalyst durability test demonstrated that the modification of 5% PTFE on the catalyst indeed has a significant beneficial effect on the useful life of the catalyst. We compared the performance of catalysts with or without PTFE modification in consecutive experiments; the modified catalysts exhibited remarkable advantages in that the diuron removal efficiency was stable with relatively low iron leaching (<0.1 mg L⁻¹) during ten consecutive degradation experiments, which proved the durability and reusability of the modified catalyst. This work demonstrates that such a heterogeneous EF using stable magnetic activated carbon catalyst with PTFE modification is promising for organic wastewater treatment in initial neutral pH conditions; at the same time, these good properties of the modified catalyst increase the possibility of practical application.

The magnetic particles were firstly coated with PTFE for the degradation of diuron in a heterogeneous electro-Fenton system.