25th Anniversary Article: Dynamic Interfaces for Responsive Encapsulation Systems

Encapsulation systems are urgently needed both as micrometer and sub‐micrometer capsules for active chemicals' delivery, to encapsulate biological objects and capsules immobilized on surfaces for a wide variety of advanced applications. Methods for encapsulation, prolonged storage and controllable release are discussed in this review. Formation of stimuli responsive systems via layer‐by‐layer (LbL) assembly, as well as via mobile chemical bonding (hydrogen bonds, chemisorptions) and formation of special dynamic stoppers are presented. The most essential advances of the systems presented are multifunctionality and responsiveness to a multitude of stimuli – the possibility of formation of multi‐modal systems. Specific examples of advanced applications – drug delivery, diagnostics, tissue engineering, lab‐on‐chip and organ‐on‐chip, bio‐sensors, membranes, templates for synthesis, optical systems, and antifouling, self‐healing materials and coatings – are provided. Finally, we try to outline emerging developments.     

Diopside–Ba disilicate glass–ceramic sealants for SOFCs: Enhanced adhesion and thermal stability by Sr for Ca substitution

This article reports on the influence of strontium for calcium substitution in diopside–Ba disilicate glass–ceramics on stabilization thermal parameters and improvement adhesion to interconnect material of SOFCs. Sr replaced 10, 20, 30 and 40% of Ca in the Ca_0.9MgAl_0.1La_0.1Si_1.9O₆ component of the parent glass having the following composition, mol.%: 22.14 CaO, 24.60 MgO, 0.52 BaO, 1.23 Al₂O₃, 1.23 La₂O₃, 47.79 SiO₂, 1.69 B₂O₃, 0.79 NiO. ²⁹Si–MAS–NMR and ²⁷Al MAS–NMR spectra of the glasses revealed irrelevant chemical shifts for silicon and aluminum atoms upon changing the SrO content. T_g decreased and coefficient of thermal expansion (CTE) increased by Sr for Ca substitution in pyroxene glasses. Additionally SrO-containing glasses exhibited a viscosity of ∼10⁶ dPa s at 900 °C, which is suitable for joining of SOFC metallic/ceramic components by glass/glass–ceramic sealing upon stack hermetization. Glass–ceramics revealed long term (up to 1000 h) thermal stability at 900 °C and suitable CTE values (10.0–11.3) × 10⁻⁶ K⁻¹, high electrical resistivity, good adhesion and minimal reactivity with SOFC components.     

Rational protein design of ThDP-dependent enzymes-engineering stereoselectivity

Benzoylformate decarboxylase (BFD) from Pseudomonas putida is an exceptional thiamin diphosphate-dependent enzyme, as it catalyzes the formation of (S)-2-hydroxy-1-phenylpropan-1-one from benzaldehyde and acetaldehyde. This is the only currently known S-selective reaction (92 % ee) catalyzed by this otherwise R-selective class of enzymes. Here we describe the molecular basis of the introduction of S selectivity into ThDP-dependent decarboxylases. By shaping the active site of BFD through the use of rational protein design, structural analysis, and molecular modeling, optimal steric stabilization of the acceptor aldehyde in a structural element called the S pocket was identified as the predominant interaction for adjusting stereoselectivity. Our studies revealed Leu461 as a hot spot for stereoselectivity in BFD. Exchange to alanine and glycine resulted in variants that catalyze the S-stereoselective addition of larger acceptor aldehydes, such as propanal with benzaldehyde and its derivatives-a reaction not catalyzed by the wild-type enzyme. Crystal structure analysis of the variant BFDL461A supports the modeling studies.     

Evolutionary Imprint of Catalytic Domains in Fungal PKS–NRPS Hybrids

Fungal hybrid enzymes consisting of a polyketide synthase (PKS) and a nonribosomal peptide synthetase (NRPS) module are involved in the biosynthesis of a vast array of ecologically and medicinally relevant natural products. Whereas a dozen gene clusters could be assigned to the requisite PKS–NRPS pathways, the programming of the multifunctional enzymes is still enigmatic. Through engineering and heterologously expressing a chimera of PKS (lovastatin synthase, LovB) and NRPS (cytochalasin synthase, CheA) in Aspergillus terreus, we noted the potential incompatibility of a fungal highly reducing PKS (hrPKS) with the NRPS component of fungal PKS–NRPS hybrids. To rationalize the unexpected outcome of the gene fusion experiments, we conducted extensive bioinformatic analyses of fungal PKS–NRPS hybrids and LovB‐type PKS. From motif studies and the function of the engineered chimeras, a noncanonical function of C‐terminal condensation (C) domains in truncated PKS–NRPS homologues was inferred. More importantly, sequence alignments and phylogenetic trees revealed an evolutionary imprint of the PKS–NRPS domains, which reflect the evolutionary history of the entire megasynthase. Furthermore, a detailed investigation of C and adenylation (A) domains provides support for a scenario in which not only the A domain but also the C domain participates in amino acid selection. These findings shed new light on the complex code of this emerging class of multifunctional enzymes and will greatly facilitate future combinatorial biosynthesis and pathway engineering approaches towards natural product analogues.     

Relationship between dissolved organic and inorganic compounds in tributaries of the Lake Baikal

It was shown that the balance between organic and inorganic compounds is mostly conditioned by watershed size and relief, rather than chemistry. The rise and fall of dissolved organic carbon concentration are irreversely proportional to those of acid neutralizing capacity and follow the changes in water flowpaths. This relationship was used to distinguish between dissolved matter sources, and to characterize quantitatively and qualitatively their contribution to surface water chemistry. The proposed approach has restricted applicability to the watersheds composed of sedimentary materials and to the watersheds with high percentage of wetlands. The applicability of the approach is also limited to a variety of environmental conditions. Big watersheds should be divided into lower order subcatchments to reduce uncertainty in interpretation of results. In small and medium watersheds, the proposed approach can be used for predicting water chemistry under different environmental conditions and for tracing contaminants.     

Yolk–Shell Hybrid Materials with a Periodic Mesoporous Organosilica Shell: Ideal Nanoreactors for Selective Alcohol Oxidation

This contribution describes the preparation of multifunctional yolk–shell nanoparticles (YSNs) consisting of a core of silica spheres and an outer shell based on periodic mesoporous organosilica (PMO) with perpendicularly aligned mesoporous channels. The new yolk–shell hybrid materials were synthesised through a dual mesophase and vesicle soft templating method. The mesostructure of the shell, the dimension of the hollow space (4～52 nm), and the shell thickness (16～34 nm) could be adjusted by precise tuning of the synthesis parameters, as evidenced by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen sorption investigations. Various metal nanoparticles (e.g., Au, Pt, and Pd) were encapsulated and confined in the void space between the core and the shell using impregnation and reduction of adequate metal precursors. The selective oxidation of various alcohol substrates was then carried out to illustrate the benefits of such an architecture in catalysis. High conversion (～100%) and excellent selectivity (～99%) were obtained over Pd nanoparticles encapsulated in the hybrid PMO yolk–shell structures.     

Sonochemical Activation of Al/Ni Hydrogenation Catalyst

This paper proposes a sonochemical approach to the nanostructuring of Al/Ni catalyst with high content of accessible Ni centers and a high reusability. The surface and bulk composition as well as pore size distribution of this catalyst are controlled synergistically by adjusting the ultrasound intensity in aqueous solution. Sonochemical activation of Al/Ni alloy leads to formation of mesoporous Al/Ni metallic based frameworks with surface area up to 125 m² g^?1, and regular distribution of nickel active center in the porous matrix. One of the opportunities of porous Al/Ni catalyst is that due to a time‐resolved controllable formation of protective oxide layer it can be stored and handled under air in comparison to traditional Raney catalysts which need inert conditions. The Al/Ni catalyst is characterized by scanning electron microscopy (SEM), electron diffraction spectroscopy (EDS), X‐ray photoelectron spectroscopy (XPS), confocal scanning fluorescence microscopy (CSFM), solid‐state NMR experiments, and powder X‐ray diffraction analysis (PXRD). The catalytic activity was investigated for the hydrogenation of acetophenone.     

Difluoromethylornithine (DFMO), an Inhibitor of Polyamine Biosynthesis,and Antioxidant N-Acetylcysteine Potentiate Immune Response in Mice to the Recombinant Hepatitis C Virus NS5B Protein

Hepatitis C virus (HCV) is one of the main triggers of chronic liver disease. Despite tremendous progress in the HCV field, there is still no vaccine against this virus. Potential vaccines can be based on its recombinant proteins. To increase the humoral and, especially, cellular immune response to them, more effective adjuvants are needed. Here, we evaluated a panel of compounds as potential adjuvants using the HCV NS5B protein as an immunogen. These compounds included inhibitors of polyamine biosynthesis and urea cycle, the mTOR pathway, antioxidants, and cellular receptors. A pronounced stimulation of cell proliferation and interferon-γ (IFN-γ) secretion in response to concanavalin A was shown for antioxidant N-acetylcysteine (NAC), polyamine biosynthesis inhibitor 2-difluoromethylornithine (DFMO), and TLR9 agonist CpG ODN 1826 (CpG). Their usage during the immunization of mice with the recombinant NS5B protein significantly increased antibody titers, enhanced lymphocyte proliferation and IFN-γ production. NAC and CpG decreased relative Treg numbers; CpG increased the number of myeloid-derived suppressor cells (MDSCs), whereas neither NAC nor DFMO affected MDSC counts. NAC and DFMO suppressed NO and interleukin 10 (IL-10) production by splenocytes, while DFMO increased the levels of IL-12. This is the first evidence of immunomodulatory activity of NAC and DFMO during prophylactic immunization against infectious diseases.     

Regeneration of Pd/TiO2 catalyst deactivated in reductive CCl4 transformations by the treatment with supercritical CO2, ozone in supercritical CO2 or oxygen plasma

Carbonaceous deposits formation was established as the primary reason of Pd/TiO₂ catalyst deactivation during reductive processing of CCl₄ to form hydrodechlorination and oligomerization products. Three methods of carbonaceous deposits elimination were tested: (1) extraction by supercritical CO₂, (2) oxidation by ozone in supercritical CO₂, and (3) low-temperature glow-discharge oxygen plasma treatment. Synchronic thermal analysis confirms effective carbonaceous deposits removal during regeneration by ozone or low temperature glow-discharge oxygen plasma; by XPS deep oxidation of surface Pd after oxidative treatment (by ozone or oxygen plasma) was found. Thus H₂ reduction was proposed as the second step making possible full regeneration of initial catalytic activity of Pd/TiO₂.     

Selective Production of 2-Phenylhexane from Benzene and <Emphasis Type="Italic">n</Emphasis>-Hexane Over Pt- and Ga-Modified Zeolites

Abstract  

Alkylation of benzene with n-hexane was performed over H-ZSM-5 and monometallic Ga- and Pt- and bimetallic Ga- and Pt-modified ZSM-5. The influence of the particle size and the method of incorporation of Ga (during hydrothermal synthesis, by solid-state ion exchange, or by liquid-state ion exchange) was determined. The presence of Pt and well-dispersed extraframework Ga in H-ZSM-5 increased the selectivity in alkylation and suppressed cracking reactions. Well-dispersed Pt particles led to better catalytic performance. The method of Ga incorporation played an important role in obtaining higher selectivity to alkylation products and in the suppression of side reactions. Up to 93% selectivity in alkylation (of which >95% was to 2-phenylhexane) was reached over 2 wt% Pt/H-Ga^fZSM5, in which Ga occupied framework positions. We propose that the close proximity of very small Pt nanoparticles and Ga–(OH)–Si acid sites results in the optimal bifunctional catalyst for selective production of 2-phenylhexane from benzene and n-hexane. During the reaction, the catalyst deactivated, most probably due to the sintering of the Pt particles.