Stability In Solvents Research Articles

Trends in lipase engineering for enhanced biocatalysis.

Lipases, also known as triacylglycerol hydrolases (E.C.No. 3.1.1.3), are considered as leading biocatalysts in the lipid modification business. With properties like ease of availability, capability to work in heterogeneous media, stability in organic solvents, property of catalyzing at the lipid-water interface and even in nonaqueous conditions, have made them a versatile choice for applications in the food, flavor, detergent, pharmaceutical, leather, textile, cosmetic, and paper industries [1]. The increasing alertness toward sustainable technologies, lesser waste generation and solvent usage and minimization of energy input has brought light toward the production and usage of recombinant/improved lipases. For example, Novozym 435, a broadly used recombinant lipase isolated from Candida antarctica, dominates the lipase industry and has even created a supplier bias in the market. This shows that there is a desperate need for novel, low-cost lipases with better properties. For this, mining of existing extremophilic genomes seems more rewarding. But considering the diversity of industrial requirements such as types of solvents used or carrier systems employed for enzyme immobilization, tailor-designed enzymes are an unrealized pressing priority. Therefore, protein engineering strategies in collaboration with the discovery of new lipases can serve as a vital tool to obtain tailor-made enzymes with specific characteristics.

Water-Stable Cobalt-Based MOF for Water Oxidation in Neutral Aqueous Solution: A Case of Mimicking the Photosystem II.

Inspired by the highly efficient water oxidation of Mn4CaO5 in natural photosynthesis, development of novel artificial water oxidation catalysts (WOCs) with structure and function mimicked has inspired extensive interests. A novel 3D cobalt-based MOF (GXY-L8-Co) was synthesized for promising artificial water oxidation by employing the Co4O4 quasi-cubane motifs with a similar structure as the Mn4CaO5 as the core. The GXY-L8-Co not only shows good chemical stability in common organic solvents or water for up to 10 days but also exhibits oxygen evolution performance. It has been demonstrated that the uniform distribution of Co4O4 catalytic active sites confined in the MOF framework should be responsible for the good robustness and catalytic performance.

Flexibly regulated electrochemiluminescence of all-inorganic perovskite CsPbBr3 quantum dots through electron bridge to across interfaces between polar and non-polar solvents

All-inorganic perovskite quantum dots (QDs) have attracted great interests due to its outstanding properties. But their poor stability in polar solvents seriously hampered wide applications in analytical chemistry. In this work, strong, stable and flexibly regulated the electrochemiluminescence (ECL) emission form CsPbBr3 QDs was successfully obtained and applied in the analysis of polar solvents through the unique structure of closed bipolar electrode (BPE). To demonstrate the feasibility, it was successfully used in the detection of tetracycline (Tc) aqueous solution. CsPbBr3 QDs was immersed into organic solution in anode microcell of closed BPE while Tc aqueous solution was added into cathode microcell. The two microcells were physically separated and would not interfere with each other. But the bio-recognition event between aptamer and Tc in cathode microcell would induce the ECL signal change in anode microcell through the electrons conducted by BPE as the bridge. The ECL emission can be flexibly regulated by environmental factors of both polar and non-polar solvents and the interface status of the BPE. Compared with traditional methods to overcome the intrinsic instability in polar medium, the reported method does not need any further surface modifications, has no limitations on the targets and can provide wide development space for further deep research, which may open a new direction for the ECL sensing of CsPbBr3 QDs.

Polypyrrole reinforced ZIF-67 with modulated facet exposure and billion-fold electrical conductivity enhancement towards robust photocatalytic CO2 reduction

A novel strategy is deployed to synthesize the ZIF-67 reinforced with polypyrrole (ZIF-67@PPy) where pyrrole monomer modulates the crystal morphology of ZIF-67. The ZIF-67@PPy demonstrated improved catalytic activity and stability for photocatalytic CO 2 reduction. The implementation of metal organic frameworks (MOFs) as the co-catalysts in hybrid photocatalytic systems puts requirements on both their charge-carrying capability and solvent stability. In the current study, in order to simultaneously promote the electrical conductivity and water stability of ZIF-67, an in-situ monomer trapping strategy is deployed to synthesize polypyrrole (PPy)-reinforced ZIF-67 ensembles. Through coordination modulation, the incremental addition of pyrrole monomers enables to alter the crystal morphology of ZIF-67 from rhombic dodecahedra to truncated rhombic dodecahedra, and further to cubes. Upon polymerization, the resulted composite, in comparison to ZIF-67, demonstrates a billion-fold conductivity enhancement, much improved chemical stability in pronated solvents, as well as largely retained specific surface area and porosity, enabling it functioning as an outstanding co-catalyst for catalyzing robust photocatalytic CO 2 reduction. Furthermore, a PPy-mediated electron harvest and relay mechanism is proposed for rationalizing the enhanced photocatalytic performance.

Proline-Modified UIO-66 as Nanocarriers to Enhance Candida rugosa Lipase Catalytic Activity and Stability for Electrochemical Detection of Nitrofen.

Immobilization can be used to improve the stability of lipases and enhances lipase recovery and reusability, which increases its commercial value and industrial applications. Nevertheless, immobilization frequently causes conformational changes of the lipases, which decrease lipase catalytic activity. in the present work, we synthesized UIO-66 and grafted UIO-66 crystals with proline for immobilization of Candida rugosa lipase (CRL). As indicated by steady-state fluorescence microscopy, grafting of proline onto UIO-66 crystals induced beneficial conformational change in CRL. CRL immobilized on UIO-66/Pro (CRL@UIO-66/Pro) demonstrated higher enzyme activity and better recyclability than that immobilized on UIO-66 (CRL@UIO-66) in both hydrolysis (CRL@UIO-66/Pro: 0.34 U; CRL@UIO-66: 0.15 U) and transesterification (CRL@UIO-66/Pro: 0.93 U; CRL@UIO-66: 0.25 U) reactions. The higher values of kcat and kcat/Km of CRL@UIO-66/Pro also showed that it had better catalytic efficiency as compared to CRL@UIO-66. It is also worth noting that CRL@UIO-66/Pro (0.93 U) demonstrated a much higher transesterification activity as compared to free CRL (0.11 U), indicating that UIO-66/Pro has increased the solvent stability of CRL. Both CRL@UIO-66 and CRL@UIO-66/Pro were also used for the fabrication of biosensors for nitrofen with a wide linear range (0-100 μM), lower limit of detection, and good recovery rate.

Preparation of MIL-101-NH2 MOF/triazine based covalent organic framework hybrid and its application in acid blue 9 removals

Due to the increasing environmental pollution from the textile industry, synthesizing efficient adsorbents to remove coloring agents from waste streams is of practical interest and importance to chemists and material scientists. Metal-organic framework (MOF) and covalent organic framework (COF) are multidimensional, porous, and crystalline. Owing to their high BET surface area, they are both right choices for dye adsorption. A superior feature of COF materials compared to MOFs is their stability in organic solvents and acidic environments. Herein, considering the importance of the complete removal of acid blue 9 and economic aspects, a new hybrid of aminated chromium-based MOF and triazine-based COF (MIL-101-NH2@COF) was synthesized and used for the removal of the dye from textile wastewater. These materials were characterized by FT-IR spectra, PXRD, elemental analysis, and BET. Since the hybrid adsorbent had a mesoporous structure of a large surface area for nitrogen adsorption, it would be the right candidate for solving the coloring agent pollution problem. Some essential parameters, such as pH, contact time, temperature, and adsorbent dosage, were optimized. The optimum condition was pH = 2, absorbent dosage 0.01 g, contact time 90 min, and temperature 35 °C. The obtained maximum adsorption capacity was 256 mg g−1. The experimental results, in general, agree with those of the Langmuir model and the pseudo-second-order kinetics, suggesting that acid blue 9 was adsorbed to the hybrid adsorbent in monolayers due to its chemical affinity.

Liquid-Exfoliated Mesostructured Collagen from the Bovine Achilles Tendon as Building Blocks of Collagen Membranes.

Mesoscaled assemblies are organized in native collagen tissues to achieve remarkable and diverse performance and functions. In this work, a facile, low-cost, and controllable liquid exfoliation method was applied to directly extract these collagen mesostructures from bovine Achilles tendons using a sodium hydroxide (NaOH)/urea aqueous system with freeze-thaw cycles and sonication. A series of collagen fibrils with diameters of 26-230 nm were harvested using this process, and in situ observations under polarizing microscopy (POM) and using molecular dynamics simulations revealed the influence of the NaOH/urea system on the tendon collagen. FTIR and XRD results confirmed that these collagen fibrils preserved typical structural characteristics of type I collagen. These isolated collagen fibrils were then utilized as building blocks to fabricate free-standing collagen membranes, which exhibited good stability in solvents and outstanding mechanical properties and transparency, with potential for utility in optical and electronic sensors. Moreover, in vitro and vivo evaluations demonstrated that these new resulting collagen membranes had good cytocompatibility, biocompatibility, and degradability for potential applications in biomedicine. This work provides a new approach for collagen processing by liquid exfoliation with utility for the formation of robust collagen materials that consist of native collagen mesostructures as building blocks.

A stable terbium(III) metal-organic framework as a dual luminescent sensor for MnO4− ions and nitroaromatic explosives

A new terbium(III) metal-organic framework [Tb2(BTZ)(μ2-H2O)(μ3-OH)2] (ZH-101, H2BTZ ​= ​3.5-bis(4’-carboxy-phenyl)-1,2,4-triazole) was synthesized with BTZ ligands under solvothermal conditions for the luminescent study. It is constructed of [Tb2(μ2-O)(μ3-O)2]n 2D layered structure and is further connected by BTZ ligands with rich triazole-N sites to form a water-stable 3D net framework. ZH-101 displays excellent chemical stability in common organic solvents and water in the wide pH range of 0–11. The luminescence test experiment of ZH-101 in water containing different anions shows selective fluorescence quenching for MnO4− with low detection limit (0.16 ​mM). In addition, ZH-101 also displays excellent luminescence stability in different solvents and can selectively detect nitroaromatic explosives in DMF solutions, especially for 4-nitrophenol with Ksv ​= ​3.38 ​× ​104 ​M-1, and low detection limit of 0.20 ​mM. It still retains original fluorescence intensity and chemical stability after five cycles experiments, exhibiting remarkable long-term cycle and reversibility. Therefore, ZH-101 is a competitive and promising candidate for sensing MnO4− ions and nitroaromatic explosives.

Ultrasound-assisted synthesis of a stable Co(II) coordination polymer as heterogeneous catalyst for CO2 transformation

A stable benzimidazole-containing Co(II) coordination polymer namely [Co(L)0.5(oba)]n (1) (H2oba = 4,4′-oxybis(benzoate), L = 1,6-bis(5,6-dimethylbenzimidazolyl) hexane) was successfully synthesized by ultrasonic technique under mild conditions. In especial, the effects of initial reagent concentration, irradiation time and ultrasonic power on the morphology and size of micron scale 1 were discussed in detail. Micron scale 1 appeared exceptional solvent and pH stabilities. Further, as a heterogeneous Lewis catalyst, 1 exhibited a highly activity and recyclability for CO2 transformation by cycloaddition with epoxide under room temperature.

An anionic potassium-organic framework for selective removal of uranyl ions.

Effective and selective removal of radioactive metal ions from aqueous solutions is of great importance due to their harmful effects on humans and other living species. However, it is a big challenge for researchers to develop effective adsorbents with high selectivity and a wide pH application range even if some progress has been achieved. Herein, we report an anionic potassium organic framework (UPC-K1) with protonated dimethylamine (Me2NH2+) residing inside the rhomboid channels. The unique 3D firm structure of UPC-K1 is constructed by the cross-linking of the 2D arrangement using weak K-O bonds (2.9270 Å) and strong hydrogen bonds (1.6498 Å), which endows it with excellent chemical stability in organic solvents, boiling water, and aqueous solution in the pH range 3-10. Based on the cation exchange, depending on pore size selectivity, UPC-K1 shows excellent adsorption performance towards UO22+ in aqueous solutions at 298 K with the following characteristics: (1) effective removal in the pH range 3-10; (2) high selectivity over other metal cations; (3) a high adsorption capacity of 551.4 mg g-1; (4) a rapid adsorption equilibrium within 3 hours under stirring; and (5) effective adsorption at low concentrations, with a residual concentration of 0.69 ppm even at an initial concentration of 10.3 ppm after stirring for 24 hours. These results indicate the great potential of UPC-K1 in the treatment of uranium-containing nuclear wastewater.

Synthesis and properties of ion-exchange materials based on hydrolysis lignins

Hydrolytic lignin is a large-tonnage waste product of ethyl alcohol production and is a renewable resource. The structure of lignin is characterized by the presence of a large number of hydroxyl groups, which provides the value of lignin as a raw material for synthesis in polymer chemistry. But due to their low chemical stability in dilute alkalis, acids and solvents, lignins are of little use for wide practical use. The introduction of additional functional groups into the lignin maromolecule by oxidative modification with the use of resource-saving technologies makes it possible to obtain new products for the synthesis of composite materials. On the basis of electrochemically modified lignin in polycondensation reactions with phthalic acid, ion-exchange materials have been obtained: weakly acidic cation exchangers with a exchange capacity of 0.1 mol/l NaOH 3.5-3.8 mmol/cm3, capable of sorbing cations in a wide range of pH values, and ampholyte (exchange capacity for sodium cation 6.4-6.6 mmol/cm3, for chlorine anion - 1.1-1.3 mmol/cm3). Ion exchangers synthesized on the basis of chlorine and nitro-containing lignins have been investigated in comparison with generally known industrial ion exchangers; they have high exchange and physic-mechanical characteristics and chemical resistance.

The spirobichroman-based polyimides with different side groups: from structure-property relationships to chain packing and gas transport performance.

Spirobichroman-based polymers with high gas permeability and selectivity are promising for their applications as membranes in gas separation. In this study, three spirobichroman-based polyimides (PIs; 6FDA-FH, 6FDA-DH, and 6FDA-MH) were synthesised by the polyreaction between diamines containing different substituents (benzene ring, pyridine ring, and methyl group) and 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA). The physical properties, gas transport behaviour, d-spacing, dihedral angle of molecules, and fractional free volume of the PIs were investigated through experiments and molecular simulations. The PIs exhibited excellent thermal stability and good solubility in common organic solvents. The gas permeability of the PIs was investigated; the results highlighted the critical role of the substituents in the enhancement of the gas separation performance of polymer membranes. Detailed analysis of the PIs showed that 6FDA-FH exhibits the highest gas permeability. This can be ascribed to the loose packing of the polymer chain owing to the increased dihedral angle between the two planes. However, the methyl substituent in 6FDA-MH disrupts the polymer chain packing rather than changing the dihedral angle between the two planes, thus enhancing the gas permeability of 6FDA-MH. Furthermore, 6FDA-DH exhibited the highest CO2/CH4 selectivity, which is attributed to the CO2 affinity of the polymer containing the pyridine unit.

Robust braid reinforced hollow fiber membranes for organic solvent nanofiltration (OSN)

The hollow fiber organic solvent nanofiltration (OSN) membranes have drawn increasing interest for the refining of high value-added products such as nutraceuticals, pharmaceuticals and fine chemicals. The hollow fiber OSN membranes with defined pore size, reliable stability and durability in various harsh solvents are in urgent demand. Herein, for the first time, braid reinforced hollow fiber (BRHF) OSN membranes with defined pore size, robust mechanical strength, and excellent solvent stability were fabricated and used for the recovery of pharmaceuticals. The BRHF nanofiltration membranes can endure an operation pressure over 3 times larger than that of the cross-linked polyimide hollow fiber OSN membranes in aprotic solvents with a DMF flux of 37.9 LMH and a methanol flux of 70.3 LMH at 15 ​bar. The membranes show over 98.8% rejection to the Tetracycline, Chlortetracycline hydrochloride and Vitamin B12. After immersion in DMF for 360 ​h, the membranes maintain over 98% rejection to Chlortetracycline hydrochloride. Moreover, the BRHFs eliminate the risk of module leakage caused by breakage of hollow fibers and surmount the swelling tendency of polymeric OSN membranes in harsh solvents which enables the scaling-up of high-performance hollow fiber OSN membrane modules. The BRHF OSN membranes with robust stability and durability exhibit very promising application prospects in the pharmaceutical and fine chemical industry.

A hydrolytically stable cage-based metal–organic framework containing two types of building blocks for the adsorption of iodine and dyes

A metal–organic framework (SCNU-Z4) with high chemical stability in water and common organic solvents showed ability for iodine and dye adsorption.

Acid and alkali-resistant Dy4coordination clusters: synthesis, structure and slow magnetic relaxation behaviors

Two Dy4coordination clusters with different skeletons exhibit slow magnetic relaxation behaviours and high stabilities in water and common organic solvents, as well as in acid and base solutions.

Construction of a polymeric cobalt phthalocyanine@mesoporous graphitic carbon nitride composite for efficient photocatalytic CO2 reduction.

Herein, we prepare a type of organic/inorganic hybrid photocatalyst by in situ polymerization of cobalt phthalocyanine on mesoporous g-C3N4 (mpg-C3N4) for photocatalytic CO2 reduction. Photocatalytic results indicate that this photocatalyst can effectively reduce CO2 to CO with high activity and remarkable long-term stability in organic solvents under visible-light irradiation. Our work provides a versatile strategy to synthesize a highly active organic/inorganic composite for photocatalysis.

Selective construction and stability studies of a molecular trefoil knot and Solomon link.

Two novel compounds, a molecular trefoil knot and a Solomon link, were constructed successfully through the cooperation of multiple π-π stacking interactions. A reversible transformation between the trefoil knot and the corresponding [2 + 2] macrocycle could be achieved by solvent- and guest-induced effects. However, the Solomon link maintains its stability in different concentrations, solvents and guest molecules. Single-crystal X-ray crystallographic data, NMR spectroscopic experiments and ESI-MS support the synthesis and structural assignments. These synthesis methods open the door to the further development of smart materials, which will push the advancement of rational design of biomaterials.

From absolute potentials to a generalized computational standard hydrogen electrode for aqueous and non-aqueous solvents.

We describe a simple and efficient procedure to compute a conversion factor for the absolute potential of the standard hydrogen electrode in water to any other solvent. In contrast to earlier methods our procedure only requires the pKa of an arbitrary acid in water and few simple quantum chemical calculations as input. Thus, it is not affected adversely by experimental shortcomings related to measurements in non-aqueous solvents. By combining this conversion factor with the absolute potential in water, the absolute potential in the solvent of interest is obtained. Based on this procedure a new generalized computational standard hydrogen electrode for the computation of electron transfer and proton-coupled electron transfer potentials in non-aqueous solvents and ionic liquids is developed. This enables for the first time the reliable prediction of redox potentials in any solvent. The method is tested through calculation of absolute potentials in 36 solvents. Using the Kamlet-Taft linear solvation energy model we find that the relative absolute potentials consistently increase with decreasing polarisability and decreasing hydrogen bonding ability. For protic solvents good agreement with literature is observed while significant deviations are found for aprotic solvents. The obtained conversion factors are independent of the quantum chemical method, while minor differences are observed between solvation models. This does, however, not affect the global trends.

Analysis of flexible operation of CO2 capture plants: Predicting solvent emissions from conventional and advanced amine systems

In our previous work, we reported results on solvent management, emissions, and dynamic behavior from an 18-month testing campaign with monoethanolamine (MEA) at the PCC pilot plant at Niederaussem. In this study, we extended our work to include the CESAR1 solvent, a blend of 2-amino-2-methyl-1-propanol (AMP) and piperazine (PZ) in water, as part of our efforts in the ALING-CCUS project to evaluate if CESAR1 could be established as a new benchmark solvent for post-combustion capture. From our long-term (>12,275 h) testing experience, CESAR1 has shown a substantial promise in terms of lower specific solvent regeneration energy demand and stability to degradation in comparison with MEA. However, during a comprehensive series of parametric tests with the CESAR1 solvent, it was observed that amine emissions are significantly higher, especially under transient operation (AMP: 30 – 100 mg/m3 (STP); PZ: 2 – 30 mg/m3 (STP); MEA: <8 mg/m3 (STP)). This work presents step response functions for predicting the time delay and gain in emissions for each parametric/dynamic test performed. Some dynamic tests show a fast response and high emission values and, therefore, can be used to reduce emissions during flexible plant operation. These control actions are mainly the lean solvent and/or water wash temperature increase and are similar to those observed in the MEA campaign. Our testing campaign helps in advancing the fundamental understanding of emissions, establishing optimal mitigation strategies, and providing important insights for future development of models regarding solvent emissions and degradation.

Triplet stabilization for enhanced drug photorelease from sunscreen-based photocages.

Recently, sunscreen-based drug photocages have been introduced to provide UV protection to photoactive drugs, thus increasing their photosafety. Here, combined experimental and theoretical studies performed on a photocage based on the commercial UVA filter avobenzone (AB) and on the photosensitizing non-steroidal anti-inflammatory drug ketoprofen (KP) are presented unveiling the photophysical processes responsible for the light-triggered release. Particular attention is paid to solvent stabilization of the drug and UV filter excited states, respectively, which leads to a switching between the triplet excited state energies of the AB and KP units. Most notably, we show that the stabilization of the AB triplet excited state in ethanol solution is the key requirement for an efficient photouncaging. By contrast, in apolar solvents, in particular hexane, KP has the lowest triplet excited state, hence acting as an energy acceptor quenching the AB triplet manifold, thus inhibiting the desired photoreaction.