Thermal precipitation or gelling behaviour of dissolved methylcellulose (MC) derivatives—Behaviour in water and influence on the extrusion of ceramic pastes. Part 1: Fundamentals of MC-derivatives

Methylcelluloses dissolved in water show a temperature dependent gelling behaviour. The gel temperatures depend mainly on the degree of substitution with methyl groups. The behaviour of methylcellulose containing pastes is of high importance in various applications. The paper describes the influence of the degree of substitution on the thermal characteristics of methylcelluloses in water and in ceramic pastes. The gelation temperature of the methylcellulose in both systems is increasing with decreasing degree of substitution. This enables a broader temperature window in the ceramic extrusion process. Extrusion near the gelation temperature normally leads to many defects in the extrudate. However, close to the gelation temperature the extruded profiles show more defects with methylcelluloses having a higher degree of substitution. Methylcelluloses having a low degree of substitution also enable a paste extrusion above the gelation temperature (up to 90 °C). This is not possible with currently commercially available methylcelluloses.     

Silicatein-Mediated Polycondensation of Orthosilicic Acid: Modeling of a Catalytic Mechanism Involving Ring Formation

The sponge protein silicatein is the first enzyme that has been described to form an inorganic polymer (silica) from a monomeric precursor (tetraethoxysilane or orthosilicic acid). The models proposed for silicatein-mediated silica formation are mainly based on the use of synthetic substrates (hydrolytic cleavage of tetraethoxysilane to silanol compounds) or only consider the formation of less reactive silicic acid dimers (disilicic acid). Here we propose a new model for the catalytic mechanism of silicatein that leads to the formation of reactive, cyclic silicic acid species (trisiloxane rings and higher-membered siloxane rings) which easily promote the silica polycondensation reaction.     

Potent Inhibitors of Plasmodial Serine Hydroxymethyltransferase (SHMT) Featuring a Spirocyclic Scaffold

With the discovery that serine hydroxymethyltransferase (SHMT) is a druggable target for antimalarials, the aim of this study was to design novel inhibitors of this key enzyme in the folate biosynthesis cycle. Herein, 19 novel spirocyclic ligands based on either 2‐indolinone or dihydroindene scaffolds and featuring a pyrazolopyran core are reported. Strong target affinities for Plasmodium falciparum (Pf) SHMT (14–76 nm ) and cellular potencies in the low nanomolar range (165–334 nm ) were measured together with interesting selectivity against human cytosolic SHMT1 (hSHMT1). Four co‐crystal structures with Plasmodium vivax (Pv) SHMT solved at 2.2–2.4 Å resolution revealed the key role of the vinylogous cyanamide for anchoring ligands within the active site. The spirocyclic motif in the molecules enforces the pyrazolopyran core to adopt a substantially more curved conformation than that of previous non‐spirocyclic analogues. Finally, solvation of the spirocyclic lactam ring of the receptor‐bound ligands is discussed.     

Cholesteric and photoreactive polyesters

Several classes of cholesteric and photoreactive homo- and copolyesters were synthesized and characterized. Most of these polyesters were prepared in such a way that a chiral spacer (e.g. isosorbide) was polycondensed with a photoreactive dicarboxylic acid, such as 4-carboxycinnamic acid, benzene- 1,4-bisacrylic acid, 4-(4′-carboxyphthalimido)cinnamic acid. In several cases other dicarboxylic acids, such as naphthalene-2,6-dicarboxylic acid or 4-aminobenzoic acid trimellitimide were cocondensed to favor the formation of a Grandjean texture. When ‘sugar diols’ such as isosorbide or isomannide were used as chiral building blocks, suitable diphenols were required as comonomers to stabilize the LC phase. Most polyesters were capable of forming a selectively reflecting Grandjean texture, which can be fixed by crosslinking using UV light. An alternative synthetic strategy based on chiral, substituted terephthalic acids is discussed.     

Dispersion and Phase Separation of Water‐Oil‐Amphiphile Systems in Stirred Tanks

Drop size distributions and phase separation behavior of water‐oil‐nonionic amphiphile systems are investigated using an in situ endoscope measurement technique and an external camera in stirred tanks in batch mode. The fitting procedure and the simulation results of a phase separation model are analyzed under the condition that either the swarm sedimentation speed or the mean drop size during sedimentation is known. The steady‐state drop size distributions are self‐similar over the whole range of process parameters, but not in the decaying turbulence field after agitation stop. The coalescence rate in the first seconds after agitation stop clearly affects the separation behavior, so that a prediction of the separation time based on the initial conditions in steady state is not trivial.     

Numerical Characterization of the Bubble Rise Behavior in Viscoelastic Liquids

The bubble rise behavior in viscoelastic media is analyzed numerically with CFD. Three different constitutive models, Giesekus, linear and exponential Phan‐Thien‐Tanner, are used to evaluate three different biopolymer solutions. The terminal rise velocity over a range of bubble sizes is validated against experimental data. The local velocity fields are compared with respect to the shape and onset of the negative wake. Furthermore, the normal and shear components of the stress fields, transformed according to the local flow direction, are given. The simulations are performed with a volume of fluid solver in OpenFOAM.     

Hidden Specificities in Enzyme Catalysis: Structural Basis of Substrate Structure-Selectivity Relationship of a Ketoreductase

Enzymes often convert both physiological and non-physiological substrates with high stereoselectivity; yet, for some enzymes, opposite product chirality is observed. A possible explanation is the existence of hidden specificities becoming apparent when non-physiological substrates confer different substrate–enzyme interactions than the physiological substrate. To test this hypothesis, a series of α-methylated β-keto esters were converted with Tyl-KR1, a ketoreductase from polyketide synthesis in Streptomyces fradiae. The conversions of six substrates with different physicochemical properties exhibited enantioselectivities ranging from 84 % ee for R,R to 84 % ee for S,S, yet high and uniform diastereoselectivity (anti, d.r.>9:1). The exchange of a single atom, namely an oxygen ester instead of a thioester, led to almost complete loss of enantioselectivity (<5 % ee). An additional S,S-selective binding mode as a hidden specificity in Tyl-KR1 has been identified through molecular modeling and site-directed mutagenesis.     

Genetically Encoded Biotin Analogues: Incorporation and Application in Bacterial and Mammalian Cells

The biotin–streptavidin interaction is among the strongest known in nature. Herein, the site-directed incorporation of biotin and 2-iminobiotin composed of noncanonical amino acids (ncAAs) into proteins is reported. 2-Iminobiotin lysine was employed for protein purification based on the pH-dependent dissociation constant to streptavidin. By using the high-affinity binding of biotin lysine, the bacterial protein RecA could be specifically isolated and its interaction partners analyzed. Furthermore, the biotinylation approach was successfully transferred to mammalian cells. Stringent control over the biotinylation site and the tunable affinity between ncAAs and streptavidin of the different biotin analogues make this approach an attractive tool for protein interaction studies, protein immobilization, and the generation of well-defined protein–drug conjugates.     

Analysis of Human TAAR8 and Murine Taar8b Mediated Signaling Pathways and Expression Profile

The thyroid hormone derivative 3-iodothyronamine (3-T₁AM) exerts metabolic effects in vivo that contradict known effects of thyroid hormones. 3-T₁AM acts as a trace amine-associated receptor 1 (TAAR1) agonist and activates G_s signaling in vitro. Interestingly, 3-T₁AM-meditated in vivo effects persist in Taar1 knockout-mice indicating that further targets of 3-T₁AM might exist. Here, we investigated another member of the TAAR family, the only scarcely studied mouse and human trace-amine-associated receptor 8 (Taar8b, TAAR8). By RT-qPCR and locked-nucleic-acid (LNA) in situ hybridization, Taar8b expression in different mouse tissues was analyzed. Functionally, we characterized TAAR8 and Taar8b with regard to cell surface expression and signaling via different G-protein-mediated pathways. Cell surface expression was verified by ELISA, and cAMP accumulation was quantified by AlphaScreen for detection of G_s and/or G_i/o signaling. Activation of G-proteins G_q/11 and G_12/13 was analyzed by reporter gene assays. Expression analyses revealed at most marginal Taar8b expression and no gender differences for almost all analyzed tissues. In heart, LNA-in situ hybridization demonstrated the absence of Taar8b expression. We could not identify 3-T₁AM as a ligand for TAAR8 and Taar8b, but both receptors were characterized by a basal G_i/o signaling activity, a so far unknown signaling pathway for TAARs.