One-Pot Synthesis of Layered Disodium Zirconium Phosphate: Crystal Structure and Application in the Remediation of Heavy-Metal-Contaminated Wastewater.

Inorganic ion exchangers offer advantages whenever operation at high temperatures or in oxidizing environments is required. A novel two-dimensional disodium zirconium phosphate, Zr(NaPO4)2·H2O, was reported and investigated as an ion exchanger for heavy metals. The material was synthesized by a novel minimalistic solventless approach, and its solid-state structure was determined from powder X-ray diffraction data. Zr(NaPO4)2·H2O crystallizes in the space group P21/c with cell parameters a = 8.7584(1) Å, b = 5.3543(1) Å, c = 18.1684(3) Å, ß = 109.053 (1)°, and Z = 4. Its layered structure is similar to that of α-zirconium phosphate, Zr(HPO4)2·H2O. However, unlike α-zirconium phosphate which is limited in practical applications by its narrow interlayer spacing (d = 7.6 Å), the disodium zirconium phosphate has a larger spacing of 8.6 Å between planes. The material with inherent structural advantages displays excellent sorption for heavy metals such as Pb2+, Cu2+, Cd2+, and Tl+, maintaining its high selectivity with distribution coefficients, Kd, of 104-105 mL/g even in the presence of a large excess of Na+, K+, Mg2+, and Ca2+, which are commonly present in underground water. In particular, the maximum sorption capacity for the highly toxic Tl+ is a record high, 5.07 mmol/g (1036 mg/g). The fast reaction kinetics indicate that the exchangeable positions in Zr(NaPO4)2·H2O are readily accessible, in contrast to Zr(HPO4)2·H2O. The ease of preparation, benign nature, and advantageous ion-exchange properties make Zr(NaPO4)2·H2O a highly promising sorbent for the treatment of water polluted with heavy metals.

Mechanochemistry-Based Synthesis of Highly Crystalline γ-Zirconium Phosphate for Selective Ion Exchange.

Highly crystalline γ-zirconium phosphate has been synthesized by a novel minimalistic approach and investigated as a selective ion exchanger for cesium, ammonium and potassium. In contrast to current solution-based preparations, the mechanochemistry-based synthesis provides easy access to γ-zirconium phosphate with short synthesis times and low crystallization temperature. The addition of NaF as a mineralizer increases the crystallinity of γ-zirconium phosphate, which forms micrometer-sized uniformly shaped rectangular platelets. The crystalline material has extremely high selectivity to cesium even in the presence of 1000- or 500-fold excess Na+ or Ca2+, respectively. The removal efficiency was >98% in the pH range of 2-5.5. As an ion exchanger for purification of dialysate, crystalline γ-zirconium phosphate shows higher uptake of ammonium and potassium ions than the amorphous gel compound currently used in sorbent cartridges. This sustainable protocol opens up opportunities for many practical applications of γ-zirconium phosphate.

Reagent-controlled regiodivergent intermolecular cyclization of 2-aminobenzothiazoles with ß-ketoesters and ß-ketoamides.

Two regiodivergent approaches to intermolecular cyclization of 2-aminobenzothiazoles with ß-ketoesters and amides have been developed, controlled by the reagents employed. With the Brønsted base KOt-Bu and CBrCl3 as radical initiator, benzo[d]imidazo[2,1-b]thiazoles are synthesized via attack at the α-carbon and keto carbon of the ß-ketoester moiety. In contrast, switching to the Lewis acid catalyst, In(OTf)3, results in the regioselective nucleophilic attack at both carbonyl groups forming benzo[4,5]thiazolo[3,2-a]pyrimidin-4-ones instead.

Synthesis of Disubstituted 3-Phenylimidazo[1,2-a]pyridines via a 2-Aminopyridine/CBrCl3 α-Bromination Shuttle.

A versatile protocol for the synthesis of disubstituted 3-phenylimidazo[1,2-a]pyridines by coupling 2-aminopyridine with phenylacetophenones, phenylacetones, or ß-tetralone has been developed. Isolated yields of up to 97% were obtained at 80 °C within 5 h. The 2-aminopyridine/CBrCl3 system acts as an α-bromination shuttle by transferring Br from CBrCl3 to the α-carbon of the carbonyl moiety. This triggers a series of steps with double C-N/C-N bond formation to the final product. The distinct advantages of this protocol include the use of commercially available inexpensive substrates, simplicity of a metal-free one-pot synthesis, and ease of scale-up to multigram quantities.

Alumina-entrapped Ag catalyzed nitro compounds coupled with alcohols using borrowing hydrogen methodology.

Supported silver catalysts were reported for the first time to be able to catalyze the coupling reaction between nitroarenes and alcohols via the borrowing hydrogen scheme. The recyclable, non-leaching catalyst is synthesized by the entrapment method, which allows entrapping of silver nanoparticles in an alumina matrix. Alcohols, acting as the reducing agents for nitro-groups, alkylated the resultant amines smoothly over these silver catalysts giving a yield of >98% towards the N-substituted amines. In this process, multiple steps were realized in one-pot over a single catalyst with very high efficiency. It offers another clean and economic way to achieve amination of alcohols.

How the spontaneous insertion of amphiphilic imidazolium-based cations changes biological membranes: a molecular simulation study.

The insertion of 1-octyl-3-methylimidazolium cations (OMIM(+)) from a diluted aqueous ionic liquid (IL) solution into a model of a bacterial cell membrane is investigated. Subsequently, the mutual interactions of cations inside the membrane and their combined effect on membrane properties are derived. The ionic liquid solution and the membrane model are simulated using molecular dynamics in combination with empirical force fields. A high propensity of OMIM(+) for membrane insertion is observed, with a cation concentration at equilibrium inside the membrane 47 times larger than in the solvent. Once inserted, cations exhibit a weak effective attraction inside the membrane at a distance of 1.3 nm. At this free energy minimum, negatively charged phosphates of the phospholipids are sandwiched between two OMIM(+) to form energetically favorable OMIM(+)-phosphate-OMIM(+) types of coordination. The cation-cation association free energy is 5.9 kJ mol(-1), whereas the activation barrier for dissociation is 10.1 kJ mol(-1). Subsequently, OMIM(+) are inserted into the leaflet of the membrane bilayer that represents the extracellular side. The cations are evenly distributed with mutual cation distances according to the found optimum distance of 1.3 nm. Because of the short length of the cation alkyl chains compared to lipid fatty acids, voids are generated in the hydrophobic core of the membrane. These voids disorder the fatty acids, because they enable fatty acids to curl into these empty spaces and also cause a thinning of the membrane by 0.6 nm. Additionally, the membrane density increases at its center. The presence of OMIM(+) in the membrane facilitates the permeation of small molecules such as ammonia through the membrane, which is chosen as a model case for small polar solutes. The permeability coefficient of the membrane with respect to ammonia increases substantially by a factor of seven. This increase is caused by a reduction of the involved free energy barriers, which is effected by the cations through the thinning of the membrane and favorable interactions of the delocalized OMIM(+) charge with ammonia inside the membrane. Overall, the results indicate the antimicrobial effect of amphiphilic imidazolium-based cations that are found in various common ILs. This effect is caused by an alteration of the permeability of the bacterial membrane and other property changes.

A heterogeneous Pd-Bi/C catalyst in the synthesis of L-lyxose and L-ribose from naturally occurring D-sugars.

A critical step in the synthesis of the rare sugars, L-lyxose and L-ribose, from the corresponding D-sugars is the oxidation to the lactone. Instead of conventional oxidizing agents like bromine or pyridinium dichromate, it was found that a heterogeneous catalyst, Pd-Bi/C, could be used for the direct oxidation with molecular oxygen. The composition of the catalyst was optimized and the best results were obtained with 5 : 1 atomic ratio of Pd : Bi. The overall yields of the five-step procedure to L-ribose and L-lyxose were 47% and 50%, respectively. The synthetic procedure is advantageous from the viewpoint of overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the heterogeneous oxidation catalyst can be easily separated from the reaction mixture and reused with no loss of activity.

Recent Advances in Catalysts for the Conversion of Ethanol to Butadiene.

Butadiene is an important monomer for synthetic rubbers. Currently, the annual demand of ∼16 million tonnes is satisfied by butadiene produced as a byproduct of steam naphtha cracking where ethylene and propylene are the main products. The availability of large amounts of shale gas and condensates in the USA since about 2008 has led to a change in the cracker feed from naphtha to ethane and propane, affecting the amount of butadiene obtained. This has provided the impetus to look into direct processes for butadiene production. One option is the eco-friendly conversion of (bio) ethanol to butadiene (ETB). This process had been developed in the 1930s in the then Soviet Union. It was operated on a large scale in USA during World War II but has since been abandoned in favour of petroleum-based processes. The current trend, driven both by the availability of the raw material and ecological considerations, may make this process feasible again, particularly if the catalytic systems can be improved. This critical review discusses recent catalysts for the ETB process with special focus on the development since 2014, benchmarking them against earlier systems with a large database of operational experience.

Ion-exchange Properties of γ-Zirconium Phosphate.

γ-Zirconium phosphate (γ-ZrP) has potential as a very useful inorganic ion-exchanger due to its stability under thermal and acidic conditions. We recently reported its facile synthesis using a modified solventless method, which could make the exploitation of its ion-exchange properties for cleanup of radioactive materials and extraction of valuable ions feasible. The adsorption isotherms of Rb+ and Sr2+ over γ-ZrP are described well with the Langmuir model, with maximum adsorption capacity of 1.52 and 1.31 mmol/g, respectively. Both ions adsorb on γ-ZrP following pseudo-second order kinetics with a much faster uptake of Rb+ than of Sr2+ . γ-Zirconium phosphate shows very high affinity for Rb+ , allowing its enrichment from low-concentration solutions. Notably, Rb+ is selectively removed from complex solutions containing large amounts of Na+ , Mg2+ , Ca2+ , or transition metals such as Cu2+ , Ni2+ , Fe2+ , Fe3+ , Co2+ and Zn2+ . The used sorbent can be fully regenerated by nitric acid, enabling the recovery of Rb+ .

Zr-zeolite beta: a new heterogeneous catalyst system for the highly selective cascade transformation of citral to (+/-)-menthol.

The transformation of citral to menthols involves hydrogenation steps as well as cyclisation of the intermediate, citronellal. The ability of Zr-zeolite beta to catalyse the cyclisation with high diastereoselectivity to (+/-)-isopulegol is the critical step in this cascade transformation. Bifunctional catalysts containing nickel or rhodium supported on Zr-zeolite beta gave menthols in yields of 87-89% and an excellent diastereoselectivity of 94% for the desired (+/-)-menthol. Dual catalyst systems of Zr-zeolite beta and nano-dispersed Ni on an MCM-41 support were equally effective and have the added advantage that the rates of the acid- and hydrogenation-catalysed steps can be independently varied. By applying a pressure ramp of 0.2-2 MPa, the yield of menthols could be increased to 95%, with 94% diastereoselectivity for (+/-)-menthol. The low initial pressure minimises the rates of competing hydrogenation reactions to byproducts such as citronellol and 3,7-dimethyloctanol.

A novel and environmental friendly synthetic route for hydroxypyrrolidines using zeolites.

A critical step in the synthesis of the hydroxypyrrolidines, 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol, from the corresponding d-sugars is the synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses. Instead of applying homogeneous catalysis process with conventional inorganic acid catalysts like HCl and HClO4, it was found that heterogeneous catalysis using zeolites could be used for the one-pot synthesis of O-methyl 2,3-O-isopropylidenepentofuranoses directly from d-sugars, MeOH and acetone at mild condition. The best catalyst was H-beta zeolite containing a Si/Al molar ratio of 150, where a yield of >83% was obtained. The overall yields of the five-step procedure to 1,4-dideoxy-1,4-imino-l-lyxitol and 1,4-dideoxy-1,4-imino-d-lyxitol were 57% and 50%, respectively. This synthetic procedure has several advantages such as competitive overall yield, reduced number of steps, and mild reaction conditions. Furthermore, the zeolite catalyst can be easily recovered from the reaction mixture and reused with no loss of activity.

Efficient photodegradation of chlorophenols by BiOBr/NaBiO3 heterojunctioned composites under visible light.

Forming heterojunctioned composites is an effective way to develop visible-light-driven photocatalysts. A series of BiOBr/NaBiO3 composites were synthesized by surface transformation of NaBiO3 with hydrobromic acid. Commensurate planes of BiOBr and NaBiO3 enabled the formation of a closely bound interface. Composites with <20wt.% BiOBr exhibited excellent photocatalytic activity towards the degradation of chlorophenols under low intensity visible light (λ>400nm). The best photocatalyst was 9% BiOBr/NaBiO3 with a quantum yield of 0.365. No photocorrosion was observed after three cycles. Using radical scavengers and inert atmosphere, holes, superoxide and hydroxyl radicals were found to be involved in the photoactivity of the BiOBr/NaBiO3 composite. Hydroxylated and open-ring diacid molecules were identified as intermediates in the mineralization of 4-chlorophenol.

A Dual-Functional Catalyst for Cascade Meerwein-Pondorf-Verley Reduction and Dehydration of 4'-Methoxypropiophenone to Anethole.

Anethole is an ingredient in many flavours, fragrances and pharmaceutical formulations. To reduce the dependence of its supply on natural oils, a green route for anethole synthesis was designed on the basis of Meerwein-Pondorf-Verley (MPV) reduction and dehydration of 4'-methoxypropiophenone. The one-pot cascade reactions were heterogeneously catalysed by dual-functional Zr-MSU-3, a predominantly Lewis-acidic catalyst with a Si/Zr ratio of 10 and pores with sizes in the range of 3.2-4.2 nm. The use of 2-pentanol as solvent and hydrogen donor for the MPV reduction was advantageous, as its high boiling point enhances the rate of the reactions, especially the dehydration of the MPV product, 1-(4-methoxyphenyl)-propan-1-ol. This dispenses with the need for a strong acid catalyst that could result in by-products of acid-catalysed reactions. Anethole yields of 91 % with a trans/cis isomer ratio of about 92:8, similar to that of natural anethole, were obtained. In comparison, microporous Zr-beta (Si/Zr 12.5) gave lower activity owing to pore-size constraints. Hence, through design of the reactions and catalyst, 4'-methoxypropiophenone can be efficiently converted to anethole in a sustainable and green manner.

Minimalistic Liquid-Assisted Route to Highly Crystalline α-Zirconium Phosphate.

Zirconium phosphates have potential applications in areas of ion exchange, catalysis, photochemistry, and biotechnology. However, synthesis methodologies to form crystalline α-zirconium phosphate (Zr(HPO4 )2 ⋅H2 O) typically involve the use of excess phosphoric acid, addition of HF or oxalic acid and long reflux times or hydrothermal conditions. A minimalistic sustainable route to its synthesis has been developed by using only zirconium oxychloride and concentrated phosphoric acid to form highly crystalline α-zirconium phosphate within hours. The morphology can be changed from platelets to rod-shaped particles by fluoride addition. By varying the temperature and time, α-zirconium phosphate with particle sizes from nanometers to microns can be obtained. Key features of this minimal solvent synthesis are the excellent yields obtained with high atom economy under mild conditions and ease of scalability.

Domino-cyclisation and hydrogenation of citronellal to menthol over bifunctional Ni/Zr-Beta and Zr-beta/Ni-MCM-41 catalysts.

The one-pot conversion of (+/-)-citronellal to menthol can be selectively catalysed by either a bifunctional Ni/Zr-zeolite beta catalyst or a dual catalyst system of Zr-beta and Ni/MCM-41, giving a high diastereoselectivity to (+/-)-menthol of 90-94%.

Enhanced Photocatalytic Activity of the AgI/UiO-66(Zr) Composite for Rhodamine†B Degradation under Visible-Light Irradiation.

Visible-light photocatalysts that degrade organic pollutants in an efficient and recyclable way are highly desirable for water treatment. In this study, UiO-66, a zirconium-based metal-organic framework, was conjugated with AgI to obtain a composite for use as photocatalyst. The AgI/UiO-66 composites with different composition ratios were synthesized by a simple solution method and exhibited remarkable activity for the degradation of rhodamine B (RhB) under visible-light irradiation. The scanning electron microscopy and X-ray diffraction results confirmed the outstanding structural stability of the AgI/UiO-66 photocatalysts. The photocatalytic stability of the AgI/UiO-66 composite was further examined by reusing AgI/UiO-66 for long-term dye degradation. The good stability of the AgI/UiO-66 composite can be attributed to the outstanding stability of the UiO-66 framework material, as well as the good interaction between AgI and the UiO-66 framework. The mechanism of the photocatalytic RhB degradation by AgI/UiO-66 was investigated by introducing different scavengers to compete for the possible reactive species involved in the degradation process.

Al-free Zr-zeolite beta as a regioselective catalyst in the Meerwein-Ponndorf-Verley reaction.

Al-free Zr-zeolite beta catalyzes the transfer reduction of ketones to the corresponding alcohols in high yield and with exceptional stereocontrol. Notably, the catalyst is very robust and gives good results even with 10% water content in the reaction mixture.

Impact of ionic liquids in aqueous solution on bacterial plasma membranes studied with molecular dynamics simulations.

The impact of five different imidazolium-based ionic liquids (ILs) diluted in water on the properties of a bacterial plasma membrane is investigated using molecular dynamics (MD) simulations. Cations considered are 1-octyl-3-methylimidazolium (OMIM), 1-octyloxymethyl-3-methylimidazolium (OXMIM), and 1-tetradecyl-3-methylimidazolium (TDMIM), as well as the anions chloride and lactate. The atomistic model of the membrane bilayer is designed to reproduce the lipid composition of the plasma membrane of Gram-negative Escherichia coli. Spontaneous insertion of cations into the membrane is observed in all ILs. Substantially more insertions of OMIM than of OXMIM occur and the presence of chloride reduces cation insertions compared to lactate. In contrast, anions do not adsorb onto the membrane surface nor diffuse into the bilayer. Once inserted, cations are oriented in parallel to membrane lipids with cation alkyl tails embedded into the hydrophobic membrane core, while the imidazolium-ring remains mostly exposed to the solvent. Such inserted cations are strongly associated with one to two phospholipids in the membrane. The overall order of lipids decreased after OMIM and OXMIM insertions, while on the contrary the order of lipids in the vicinity of TDMIM increased. The short alkyl tails of OMIM and OXMIM generate voids in the bilayer that are filled by curling lipids. This cation induced lipid disorder also reduces the average membrane thickness. This effect is not observed after TDMIM insertions due to the similar length of cation alkyl chain and the fatty acids of the lipids. This lipid-mimicking behavior of inserted TDMIM indicates a high membrane affinity of this cation that could lead to an enhanced accumulation of cations in the membrane over time. Overall, the simulations reveal how cations are inserted into the bacterial membrane and how such insertions change its properties. Moreover, the different roles of cations and anions are highlighted and the fundamental importance of cation alkyl chain length and its functionalization is demonstrated.

Cationized bovine serum albumin with pendant RGD groups forms efficient biocoatings for cell adhesion.

Cationized bovine serum albumin (cBSA-147) has been modified by attaching the cyclic pentapeptide cRGDfK to its surface through linkers of different length. Coatings of these bioconjugates on glass surfaces were studied for their ability to stimulate cell adhesion. These chemically modified albumins combine a high number of positive charges which facilitate the initial cell adhesion to the surface with multiple Arg-Gly-Asp groups which enable focal adhesion of fibroblast cells by specific interactions with cell-surface receptors. The biocoatings are easily prepared within a few minutes by simple incubation from a dilute solution of the modified albumin. This constitutes a convenient approach for preparing surfaces for cell adhesion. Excellent focal adhesion of NIH 3T3 fibroblast cells on the biocoatings was observed. About 75% of the seeded cells attached to the cRGDfK-cBSA-147 coated surfaces, and 97% of them underwent focal adhesion. Adhering cells were able to grow and proliferate on the coated surfaces, confirming the outstanding biocompatibility of these biocoatings.

cBSA-147 for the preparation of bacterial biofilms in a microchannel reactor.

Whole cells are attractive biocatalysts, particularly if the reaction requires cofactors or involves multiple transformations. Immobilization of the catalyst is often a prerequisite for continuous processes. The highly cationic chemically modified plasma protein bovine serum albumin (cBSA-147) has been applied for the electrostatically mediated immobilization of the planktonic bacterium E. coli BL21 star (DE3), and the resulting biofilms were superior to those formed on poly-L-lysine coated surfaces. The biocatalyst was immobilized in a capillary column (inside diameter of 530 µm and L=30 m) and evaluated in the enantioselective reduction of ethyl acetoacetate to R-(-)ethyl hydroxybutyrate. In continuous operation in the microreactor format, the productivity of the cells was about 30% higher than that determined in a bench-scale fermentation system. This increase is attributed to the improved mass transfer over short geometrical dimensions. The similarity in the results indicates that studies on a biofilm-coated microreactor can be used for the accelerated collection of data for process optimization.