Enzyme‐Mediated In Situ Buildup and Site‐Specific Addressing of Polymeric Coatings

Formation of site‐specific deposition of polymeric particles and films with controllable parameters via enzyme‐mediated addressing is investigated. The polymers are synthesized in situ by combining the addressing process with enzyme‐mediated radical polymerization, using the enzyme horseradish peroxidase. As a model system, the technically important poly(methyl methacrylate) is formed and addressed on both glass‐ and polyethylene supports. The key to the controllability is the influence of different reaction parameters on particle formation, namely, the concentration of H₂O₂ and the pH show the most significant impact. With higher concentrations of H₂O₂, size and amount of gained particles increases, due to H₂O₂ being a limiting factor to the reaction. Moreover, since acetyl acetone forms the end‐group of the polymer chains, the pH directly influences the particle stability in addition to affecting the enzyme activity. This effect can be utilized to gain either films or particle assemblies at will. Deposition occurs highly site‐specific, exclusively on enzyme‐functionalized areas, enabling patterned coating structures within a safe, energy efficient, and easy‐to‐apply process.     

One‐Pot Synthesis of Spirooxazino Derivatives via Enzyme‐ Initiated Multicomponent Reactions

A novel enzyme‐initiated multicomponent reaction from readily available aldehyde, nitrostyrene, cyclohexanone and acetamide substrates was discovered, enabling the facile construction of six new C C/ N bonds and two rings in single step, one‐pot operation, for the synthesis of spirooxazino derivatives in moderate to high yields. Several methods such as isotope labelling and enzyme mutation were used to probe the possible mechanism of this complex synthesis.

     

Tough and Enzyme‐Degradable Hydrogels

Mechanically robust hydrogels that degrade only via cell action have potential as scaffolds for the generation of load‐bearing soft connective tissue. This study demonstrates that terminally acrylated 4‐arm‐poly(ethylene glycol)‐block‐oligo(trimethylene carbonate) (4a‐PEG‐(TMC)_n) can be readily reacted with a collagenase‐degradable bis‐cysteine peptide to form hydrogels. The inclusion of the TMC blocks renders the hydrogels mechanically tough when tested under compression, with modulus and toughness values within the range of those of articular cartilage. Moreover, the hydrogels formed are resistant to degradation by hydrolysis in the absence of collagenase but degrade via surface erosion in the presence of collagenase. The strategy employed to form these hydrogels is readily tailored to create a variety of tough, enzyme‐degradable hydrogels of varying mechanical and degradation properties.     

Enzyme‐Catalyzed Synthesis of Conducting Polyaniline Nanocomposites with Pure and Functionalized Carbon Nanotubes

The in situ enzymatic polymerization of aniline onto multi‐walled carbon nanotubes (MWCNT) and carboxylated MWCNT (COOH‐MWCNT) is reported. Nanostructured composites were prepared by this method. Polymerization was catalyzed with the enzyme horseradish peroxidase at room temperature in aqueous medium of pH 4. Hydrogen peroxide was used in low concentration as the oxidant. The nanocomposites were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). The TEM studies showed tubular morphology with uniformly distributed MWCNT in the nanocomposites. The SEM and TEM investigations revealed wrapping of the MWCNT with polyaniline (PANI) chains. TGA demonstrated that the PANI component is thermally more stable in PANI/COOH‐MWCNT compared to the PANI/MWCNT composites. The synthesized nanocomposites showed higher conductivity than pure PANI, which may be due to the strong interaction between the PANI chains and the MWCNT.     

Data Preprocessing of In Situ Laser‐Backscattering Measurements

In situ measurement techniques are promising tools to aid process development. However, they also pose new challenges in evaluating large amounts of recorded data. A new procedure for in situ laser‐backscattering devices has been developed that allows transformation of the raw recorded data, a chord length distribution, into a format suitable for population balance modeling. Emphasis is thereby laid on the influence of the suspension density on the measured data. Experimental data are recorded using a batch laboratory crystallizer equipped with an in situ 3D‐ORM laser backscattering device and an ultrasound probe. The new proposed five‐step procedure for data preprocessing is based on several independently developed tools from literature and is exemplarily illustrated with results on the crystallization of ascorbic acid. The proposed method is a step forward to use in situ laser‐backscattering devices also for quantitative purposes.     

In Situ Reaction Synthesis of Silicon Carbide–Boron Nitride Composites

SiC–BN composites were prepared via the proposed in situ reaction, which used Si₃N₄, B₄C, and carbon as reactants. Adding SiC powder to the reactants controlled the BN content in the composite. For comparison, SiC–BN composites with the same phase compositions were produced via conventional processing. The in situ process was advantageous for obtaining better composites with fine grain size and homogeneous microstructures. The in situ composite that had a BN content of 53.71 vol% exhibited considerably high strength (342 MPa) and a very low elastic modulus (107 GPa). The SiC–25-vol%-BN in situ composite had a peak strength of 588 MPa, which was 95% of that of monolithic SiC; however, the elastic modulus was as low as half that of monolithic SiC. These in situ SiC–BN composites can be expected to have excellent thermal shock resistance and mechanical strain tolerance.     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.     

Enzyme‐catalyzed regioselective synthesis of sucrose‐based esters

Sucrose‐based esters are nonionic biosurfactants, which can be synthesized from the enzyme‐catalyzed esterification/transesterification of sucrose. The multi‐hydroxyl groups of sucrose and the immiscibility of sucrose with the acyl donors are the main bottlenecks in obtaining highly regioselective sucrose‐based esters. In this mini‐review, the effects of reaction conditions such as biocatalysts, design of solvent systems used as reaction media, modification and denaturation of substrates, and coupling with external auxiliary physical fields such as microwave irradiation and ultrasonic waves on the yield of sucrose esters and regioselectivity of products are highlighted. The existing problems in the field of enzymatic synthesis of sucrose esters as well as its future perspectives were pointed out. Copyright © 2011 Society of Chemical Industry     

In Situ Acetaldehyde Synthesis for Carboligation Reactions

The enzyme 4-oxalocrotonate tautomerase (4-OT) can promiscuously catalyze various carboligation reactions using acetaldehyde as a nucleophile. However, the highly reactive nature of acetaldehyde requires intricate handling, which can impede its usage in practical synthesis. Therefore, we investigated three enzymatic routes to synthesize acetaldehyde in situ in one-pot cascade reactions with 4-OT. Two routes afforded practical acetaldehyde concentrations, using an environmental pollutant, trans-3-chloroacrylic acid, or a bio-renewable, ethanol, as starting substrate. These routes can be combined with 4-OT catalyzed Michael-type additions and aldol condensations in one pot. This modular systems biocatalysis methodology provides a stepping stone towards the development of larger artificial metabolic networks for the practical synthesis of important chemical synthons.     

Synthesis and Characterisation of In Situ Doped Silicon Nanoparticles

In situ boron, or phosphorous doped silicon nanoparticles were synthesised by pyrolysis of monosilane-diborane and monosilane-phosphane mixtures in free-space reactors. The studies were performed under atmospheric pressure in a laboratory reactor and a pilot plant for examination of scale-up effects. In the laboratory scale experiments, 1 vol % monosilane diluted in helium was used. The synthesis temperature varied between 600 and 800 ^°C. Pilot plant tests were run at 600 ^°C with 13.3 vol % silane diluted in hydrogen. The dopant content of the synthesised silicon powders was characterised by ETV-ICP-OES. Further investigations were carried out by using SEM, XRD, particle size analysis and FT-IR. An inhibition of the boron incorporation into the growing silicon lattice was found during the decomposition of the silane-diborane mixtures. This effect is a result of the low thermal stability of diborane. Silicon powders with higher boron contents and a wider particle size distribution leading to bigger particles, which showed no affinity to electrostatic charging, were obtained on the pilot plant scale. In phosphorus doping, reactor temperature was found crucial for the doping process.     

自分散性棒状纳米碳酸钙的原位合成

通过碳化法原位合成了自分散性棒状纳米碳酸钙粒子,通过FE SEM和XRD对产品形貌和结构进行分析。结果表明,形成棒状碳酸钙粒子的最佳条件是:温度为80℃,搅拌速度为400r/min,CO2流量为4.5mL/min。通过对体系pH值进行监测,表明有机质的加入可缩短碳化反应时间。同时引入了自分散性能,对解决纳米粒子的团聚、分散性差等问题有一定的参考价值。     

Monitoring Early Hydration of Cement by Ex Situ and In Situ ATR‐FTIR – a Comparative Study

Diffuse Reflection Fourier Transform Infrared (DR‐FTIR) spectroscopy has previously proven to provide time‐resolved insights into early cement hydration spanning ~30 s to ~36 h after completing the mixing. Here, a previously validated ex situ freeze‐dry procedure to stop hydration at preset times is complemented by an in situ Attenuated Total Reflectance (ATR) infrared spectroscopy method. The qualitative overall agreement between ex situ freeze‐drying and in situ monitoring is demonstrated. Moreover, water conversion during hydration comes out clearly in the time‐resolved ATR‐FTIR spectra. This information is absent in DR‐FTIR where buildups of crystal water and hydroxides are observed, while quenching of the hydration process requires removal of free water prior to acquiring the spectra. The ability of the IR technique to monitor the initial rate of hydration as a function of time is validated by comparing to calorimetry. The two approaches are understood to be complementary in that the former monitors alite grain surface hydration, while the latter reflects bulk hydration. IR is complementary to the calorimetry in cases of surface processes in conjunction with low enthalpy changes, that is, initial C–S–H formation and additive related surface chemistry.     

Zinc Iodide‐Mediated Direct Synthesis of 2,3‐Dihydroisoxazoles from Alkynes and Nitrones

A zinc diiodide (ZnI₂)‐mediated direct synthesis of 2,3‐dihydroisoxazoles via a [3+2] cycloaddition reaction of the nitrones and non‐electron‐deficient terminal alkynes has been developed. This method was applied in the formal synthesis of HPA‐12 and aminoglucose.

     

Visible Light‐Mediated Metal‐Free Synthesis of Vinyl Sulfones from Aryl Sulfinates

Visible light and eosin Y catalyze the synthesis of vinyl sulfones from aryl sulfinates and alkenes by a photoredox process. The reaction scope is broad in aryl sulfinates and alkenes and the general and simple procedure provides a metal‐free alternative for the synthesis of synthetically valuable vinyl sulfones.

     

Novel Synthesis of ZrB2 Powder Via Molten‐Salt‐Mediated Magnesiothermic Reduction

Zirconium diboride (ZrB₂) powder was synthesized at a low temperature via a molten‐salt‐mediated reduction route using ZrO₂, Na₂B₄O₇ and Mg powders as starting raw materials. By using appropriately excessive amounts of Mg and Na₂B₄O₇ to compensate for their evaporation losses, ZrO₂ could be completely converted into ZrB₂ after 3 h at 1200°C. In addition, the formation of undesirable Mg₃B₂O₆ could be effectively avoided. As‐prepared ZrB₂ powders were phase pure, 300–400 nm in size and generally well dispersed. SEM images showed that to a large extent the reactively formed ZrB₂ retained the morphology and size of the starting ZrO₂. The salt melt formed from MgCl₂ and Na₂B₄O₇ at test temperatures is believed to be responsible for the reduced synthesis temperature and good dispersion of the final ZrB₂ product powder.     

Kinetics of Multi‐Step Redox Processes by Time‐Resolved In Situ X‐ray Diffraction

The kinetics of redox reactions of iron oxide in oxygen carrier 50Fe₂O₃/MgAl₂O₄ are examined using different time‐resolved techniques. Reduction kinetics are studied by H₂ temperature‐programmed reduction (H₂‐TPR) monitored by time‐resolved in situ XRD. In contrast to conventional TPR, in situ XRD distinguishes the three‐stage reduction of Fe₂O₃ → Fe₃O₄ → FeO → Fe. It also shows that the oxidation of Fe → Fe₃O₄ by CO₂ has no intermediate crystalline phases, explaining why its kinetics can easily be investigated by conventional CO₂ temperature‐programmed oxidation (CO₂‐TPO). A shrinking core model which takes into account solid state diffusion allows describing the experimental data.