TY - JOUR A1 - Dai, Xiaolin A1 - Mate, Diana M. A1 - Glebe, Ulrich A1 - Garakani, Tayebeh Mirzaei A1 - Körner, Andrea A1 - Schwaneberg, Ulrich A1 - Böker, Alexander T1 - Sortase-mediated ligation of purely artificial building blocks JF - Polymers N2 - Sortase A (SrtA) from Staphylococcus aureus has been often used for ligating a protein with other natural or synthetic compounds in recent years. Here we show that SrtA-mediated ligation (SML) is universally applicable for the linkage of two purely artificial building blocks. Silica nanoparticles (NPs), poly(ethylene glycol) and poly(N-isopropyl acrylamide) are chosen as synthetic building blocks. As a proof of concept, NP-polymer, NP-NP, and polymer-polymer structures are formed by SrtA catalysis. Therefore, the building blocks are equipped with the recognition sequence needed for SrtA reaction-the conserved peptide LPETG-and a pentaglycine motif. The successful formation of the reaction products is shown by means of transmission electron microscopy (TEM), matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-ToF MS), and dynamic light scattering (DLS). The sortase catalyzed linkage of artificial building blocks sets the stage for the development of a new approach to link synthetic structures in cases where their synthesis by established chemical methods is complicated. KW - sortase-mediated ligation KW - enzymes KW - block copolymers KW - nanoparticles Y1 - 2018 U6 - https://doi.org/10.3390/polym10020151 SN - 2073-4360 VL - 10 IS - 2 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tan, Li A1 - Liu, Bing A1 - Siemensmeyer, Konrad A1 - Glebe, Ulrich A1 - Böker, Alexander T1 - Synthesis of thermo-responsive nanocomposites of superparamagnetic cobalt nanoparticlesipoly(N-isopropylacrylamide) JF - Journal of colloid and interface science N2 - Novel nanocomposites of superparamagnetic cobalt nanoparticles (Co NPs) and poly(N-isopropylacrylamide) (PNIPAM) were fabricated through surface-initiated atom-transfer radical polymerization (SI-ATRP). We firstly synthesized a functional ATRP initiator, containing an amine (as anchoring group) and a 2-bromopropionate group (SI-ATRP initiator). Oleic acid- and trioctylphosphine oxide-coated Co NPs were then modified with the initiator via ligand exchange. The process is facile and rapid for efficient surface functionalization and afterwards the Co NPs can be dispersed into polar solvent DMF without aggregation. Transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and dynamic light scattering measurements confirmed the success of ligand exchange. The following polymerization of NIPAM was conducted on the surface of Co NPs. Temperature-dependent dynamic light scattering study showed the responsive behavior of PNIPAM-coated Co NPs. The combination of superparamagnetic and thermo-responsive properties in these hybrid nanoparticles is promising for future applications e.g. in biomedicine. (C) 2018 Elsevier Inc. All rights reserved. KW - Nanoparticles KW - Superparamagnetic KW - Surface-initiated atom-transfer radical KW - polymerization KW - Responsivity Y1 - 2018 U6 - https://doi.org/10.1016/j.jcis.2018.04.074 SN - 0021-9797 SN - 1095-7103 VL - 526 SP - 124 EP - 134 PB - Elsevier CY - San Diego ER - TY - JOUR A1 - Tan, Li A1 - Liu, Bing A1 - Siemensmeyer, Konrad A1 - Glebe, Ulrich A1 - Böker, Alexander T1 - Synthesis of Polystyrene-Coated Superparamagnetic and Ferromagnetic Cobalt Nanoparticles JF - Polymers N2 - Polystyrene-coated cobalt nanoparticles (NPs) were synthesized through a dual-stage thermolysis of cobalt carbonyl (Co-2(CO)(8)). The amine end-functionalized polystyrene surfactants with varying molecular weight were prepared via atom-transfer radical polymerization technique. By changing the concentration of these polymeric surfactants, Co NPs with different size, size distribution, and magnetic properties were obtained. Transmission electron microscopy characterization showed that the size of Co NPs stabilized with lower molecular weight polystyrene surfactants (M-n = 2300 g/mol) varied from 12-22 nm, while the size of Co NPs coated with polystyrene of middle (M-n = 4500 g/mol) and higher molecular weight (M-n = 10,500 g/mol) showed little change around 20 nm. Magnetic measurements revealed that the small cobalt particles were superparamagnetic, while larger particles were ferromagnetic and self-assembled into 1-D chain structures. Thermogravimetric analysis revealed that the grafting density of polystyrene with lower molecular weight is high. To the best of our knowledge, this is the first study to obtain both superparamagnetic and ferromagnetic Co NPs by changing the molecular weight and concentration of polystyrene through the dual-stage decomposition method. KW - cobalt nanoparticles KW - polystyrene KW - superparamagnetic KW - ferromagnetic KW - molecular weight Y1 - 2018 U6 - https://doi.org/10.3390/polym10101053 SN - 2073-4360 VL - 10 IS - 10 PB - MDPI CY - Basel ER - TY - JOUR A1 - Tan, Li A1 - Liu, Bing A1 - Glebe, Ulrich A1 - Böker, Alexander T1 - Magnetic Field-Induced Assembly of Superparamagnetic Cobalt Nanoparticles on Substrates and at Liquid-Air Interface JF - Langmuir N2 - Superparamagnetic cobalt nanoparticles (Co NPs) are an interesting material for self-assembly processes because of their magnetic properties. We investigated the magnetic field-induced assembly of superparamagnetic cobalt nanoparticles and compared three different approaches, namely, the assembly on solid substrates, at water-air, and ethylene glycol-air interfaces. Oleic acid- and trioctylphosphine oxide-coated Co NPs were synthesized via a thermolysis of cobalt carbonyl and dispersed into either hexane or toluene. The Co NP dispersion was dropped onto different substrates (e.g., transmission electron microscopy (TEM) grid, silicon wafer) and onto liquid surfaces. Transmission electron microscopy (TEM), scanning force microscopy, optical microscopy, as well as scanning electron microscopy showed that superparamagnetic Co NPs assembled into one-dimensional chains in an external magnetic field. By varying the concentration of the Co NP dispersion (1-5 mg/mL) and the strength of the magnetic field (4-54 mT), the morphology of the chains changed. Short, thin, and flexible chain structures were obtained at low NP concentration and low strength of magnetic field, whereas they became long, thick and straight when the NP concentration and the magnetic field strength increased. In comparison, the assembly of Co NPs from hexane dispersion at ethylene glycol-air interface showed the most regular and homogeneous alignment, since a more efficient spreading could be achieved on ethylene glycol than on water and solid substrates. Y1 - 2018 U6 - https://doi.org/10.1021/acs.langmuir.8b02673 SN - 0743-7463 VL - 34 IS - 46 SP - 13993 EP - 14002 PB - American Chemical Society CY - Washington ER - TY - JOUR A1 - Sun, Zhiyong A1 - Glebe, Ulrich A1 - Charan, Himanshu A1 - Böker, Alexander A1 - Wu, Changzhu T1 - Enzyme-Polymer Conjugates as Robust Pickering Interfacial Biocatalysts for Efficient Biotransformations and One-Pot Cascade Reactions JF - Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition N2 - Despite the rapid development of Pickering interfacial catalysis (PIC) at liquid-liquid interfaces with chemocatalysts, the use of unstable biocatalysts at emulsion interfaces remains a technical challenge. Herein, we present a Pickering interfacial biocatalysis (PIB) platform based on robust and recyclable enzyme-polymer conjugates that act as both catalytic sites and stabilizers at the interface of Pickering emulsions. The conjugates were prepared by growing poly(N-isopropylacrylamide) on a fragile enzyme, benzaldehyde lyase, under physiological conditions. The mild in situ conjugation process preserved the enzyme structure, and the conjugates were used to emulsify a water-organic two-phase system into a stable Pickering emulsion, leading to a significantly larger interfacial area and a 270-fold improvement in catalytic performance as compared to the unemulsified two-phase system. The PIB system could be reused multiple times. Conjugates of other enzymes were also fabricated and applied for cascade reactions. KW - biphasic catalysis KW - cascade reactions KW - enzyme catalysis KW - enzyme-polymer conjugates KW - Pickering interfacial catalysis Y1 - 2018 U6 - https://doi.org/10.1002/anie.201806049 SN - 1433-7851 SN - 1521-3773 VL - 57 IS - 42 SP - 13810 EP - 13814 PB - Wiley-VCH CY - Weinheim ER -