Rheological Control Of Microemulsions Is Possible By Admixture Of End–Capped Multi–Arm Polymers Of Different Functionality – A Study Of Structure And Dynamics

For many applications the interesting properties of microemulsion, which are thermodynamically stable mixture of oil and water facilitated by the presence of a surfactant, are highly interesting. However, for many of these potential applications a much higher viscosity or even gelation would be asked for. Accordingly, mixtures of telechelic polymers and microemulsions are interesting systems from a practical point of view as by the addition of the polymer one is able to exert rheological control over a rather wide range. Furthermore they are model systems of networks where concentration of nodes and connectivity can be tuned separately, which allows for a systematic understanding of the control of the rheological properties of these materials. In our investigation we employed end-capped multi-arm polymers for the bridging of the microemulsion droplets which leads to network formation. For that purpose we employed tailor-made bridging amphiphilic polymers with multiple linkers, which were synthesized by the RAFT procedure with poly(N,N-dimethylacrylamide) (PDMA) as hydrophilic central block. This synthesis allows to control the number of arms (functionality), the length of the hydrophilic group (maximum length for connection) and of the hydrophobic chain (stickiness). We employed various multiply bridging polymers with 2, 3, or 4 arms (see figure) and investigated their effect on structure and dynamics of nonionic O/W microemulsion droplets with radii in the range of 2.5-7 nm. Please click Additional Files below to see the full abstract

Oil-in-water microemulsion droplets of TDMAO/decane interconnected by the telechelic C18-EO150-C18: clustering and network formation

The effect of a doubly hydrophobically end-capped water soluble polymer (C18-PEO150-C18) on the properties of an oil-in-water (O/W) droplet microemulsion (R [similar] 2.85 nm) has been studied as a function of the amount of added telechelic polymer. Macroscopically one observes a substantial increase of viscosity once a concentration of [similar]5 hydrophobic stickers per droplet is surpassed and effective cross-linking of the droplets takes place. SANS measurements show that the size of the individual droplets is not affected by the polymer addition but it induces attractive interactions at low concentration and repulsive ones at high polymer content. Measurements of the diffusion coefficient by DLS and FCS show increasing sizes at low polymer addition that can be attributed to the formation of clusters of microemulsion droplets interconnected by the polymer. At higher polymer content the network formation leads to an additional slow relaxation mode in DLS that can be related to the rheological behaviour, while the self-diffusion observed in FCS attains a lower plateau value, i.e., the microemulsion droplets remain effectively fixed within the network. The combination of SANS, DLS, and FCS allows us to derive a self-consistent picture of the evolution of structure and dynamics of the mixed system microemulsion/telechelic polymer as a function of the polymer content, which is not only relevant for controlling the macroscopic rheological properties but also with respect to the internal dynamics as it is, for instance, relevant for the release and transport of active agents

One-step RAFT synthesis of well-defined amphiphilic star polymers and their self-assembly in aqueous solution

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Multifunctional chain transfer agents for RAFT polymerisation were designed for the one-step synthesis of amphiphilic star polymers. Thus, hydrophobically end-capped 3- and 4-arm star polymers, as well as linear ones for reference, were made of the hydrophilic monomer N,N-dimethylacrylamide (DMA) in high yield with molar masses up to 150 000 g mol−1, narrow molar mass distribution (PDI ≤ 1.2) and high end group functionality (∼90%). The associative telechelic polymers form transient networks of interconnected aggregates in aqueous solution, thus acting as efficient viscosity enhancers and rheology modifiers, eventually forming hydrogels. The combination of dynamic light scattering (DLS), small angle neutron scattering (SANS) and rheology experiments revealed that several molecular parameters control the structure and therefore the physical properties of the aggregates. In addition to the size of the hydrophilic block (maximum length for connection) and the length of the hydrophobic alkyl chain ends (stickiness), the number of arms (functionality) proved to be a key parameter.EC/FP7/226507/EU/Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy/NMI

Dynamics of microemulsions bridged with hydrophobically end-capped star polymers studied by neutron spin-echo

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in J. Chem. Phys. 140, 034902 (2014) and may be found at https://doi.org/10.1063/1.4861894.The mesoscopic dynamical properties of oil-in-water microemulsions (MEs) bridged with telechelic polymers of different number of arms and with different lengths of hydrophobic stickers were studied with neutron spin-echo (NSE) probing the dynamics in the size range of individual ME droplets. These results then were compared to those of dynamicic light scattering (DLS) which allow to investigate the dynamics on a much larger length scale. Studies were performed as a function of the polymer concentration, number of polymer arms, and length of the hydrophobic end-group. In general it is observed that the polymer bridging has a rather small influence on the local dynamics, despite the fact that the polymer addition leads to an increase of viscosity by several orders of magnitude. In contrast to results from rheology and DLS, where the dynamics on much larger length and time scales are observed, NSE shows that the linear polymer is more efficient in arresting the motion of individual ME droplets. This finding can be explained by a simple simulation, merely by the fact that the interconnection of droplets becomes more efficient with a decreasing number of arms. This means that the dynamics observed on the short and on the longer length scale depend in an opposite way on the number of arms and hydrophobic stickers.BMBF, 05K10KT1, Verbundprojekt NanoSOFT: Teilprojekt 2: Neutronen Spin-Echo Experimente zur Untersuchung komplexer Soft-Matter Systeme mit extremer Präzissio

Self-recovering stimuli-responsive macrocycle-equipped supramolecular ionogels with unusual mechanical properties

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.A chiral, crown-ether-functionalized bisurea gelator forms supramolecular gels in ionic liquids. The resulting ionogels show a remarkably high thermal stability with gel–sol transition temperatures (Tgs) reaching more than 100 °C. The mechanical strength of these ionogels is surprisingly high and even comparable to that of cross-linked protein fibres. Furthermore, the ionogels exhibit rapid self-recovery properties after structural damage caused by deformation. Pseudorotaxanes form from the gelators’ benzo[21]crown-7 ethers as the wheels and secondary ammonium ions as the axles despite the competition between that cation and the imidazolium ions of the ionic liquid for crown ether binding. Pseudorotaxane formation as an external chemical stimulus triggers the gel–sol transition of the ionogels.DFG, SFB 765, Multivalenz als chemisches Organisations- und Wirkprinzip: Neue Architekturen, Funktionen und Anwendunge

Systems chemistry: logic gates based on the stimuli-responsive gel-sol transition of a crown ether-functionalized bis(urea) gelator

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.A quite simple, achiral benzo-21-crown-7-substituted bis(urea) low-molecular weight gelator hierarchically assembles into helical fibrils, which further develop into bundles and finally form a stable gel in acetonitrile. The gel–sol transition can be controlled by three different molecular recognition events: K+ binding to the crown ethers, pseudorotaxane formation with secondary ammonium ions and Cl− binding to the urea units. Addition of a cryptand that scavenges the K+ ions and Ag+ addition to remove the chloride and bases/acids, which mediate pseudorotaxane formation, can reverse this process. With the gelator, and these chemical stimuli, a number of different systems can be designed that behave as logic gates. Depending on the choice of components, OR, AND, XOR, NOT, NOR, XNOR and INHIBIT gates have been realized. Thus, the gel–sol transition as a property of the system as a whole is influenced in a complex manner. For some cases, the type of logic gate is defined by input signal concentration so that an even more complex reaction of the gel towards the two input signals is achieved.DFG, SFB 765, Multivalenz als chemisches Organisations- und Wirkprinzip: Neue Architekturen, Funktionen und Anwendunge

Crowding Effects on the Structure and Dynamics of the Intrinsically Disordered Nuclear Chromatin Protein NUPR1

The intracellular environment is crowded with macromolecules, including sugars, proteins and nucleic acids. In the cytoplasm, crowding effects are capable of excluding up to 40% of the volume available to any macromolecule when compared to dilute conditions. NUPR1 is an intrinsically disordered protein (IDP) involved in cell-cycle regulation, stress-cell response, apoptosis processes, DNA binding and repair, chromatin remodeling and transcription. Simulations of molecular crowding predict that IDPs can adopt compact states, as well as more extended conformations under crowding conditions. In this work, we analyzed the conformation and dynamics of NUPR1 in the presence of two synthetic polymers, Ficoll-70 and Dextran-40, which mimic crowding effects in the cells, at two different concentrations (50 and 150 mg/ml). The study was carried out by using a multi-spectroscopic approach, including: site-directed spin labelling electron paramagnetic resonance spectroscopy (SDSL-EPR), nuclear magnetic resonance spectroscopy (NMR), circular dichroism (CD), small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). SDSL-EPR spectra of two spin-labelled mutants indicate that there was binding with the crowders and that the local dynamics of the C and N termini of NUPR1 were partially affected by the crowders. However, the overall disordered nature of NUPR1 did not change substantially in the presence of the crowders, as shown by circular dichroism CD and NMR, and further confirmed by EPR. The changes in the dynamics of the paramagnetic probes appear to be related to preferred local conformations and thus crowding agents partially affect some specific regions, further pinpointing that NUPR1 flexibility has a key physiological role in its activity

Neat Protein Single-Chain Nanoparticles from Partially Denatured BSA

The main challenge for the preparation of protein single-chain nanoparticles (SCNPs) is the natural complexity of these macromolecules. Herein, we report the suitable conditions to produce "neat" bovine serum albumin (BSA) single-chain nanoparticles (SCNPs) from partially denatured BSA, which involves denaturation in urea and intramolecular cross-linking below the overlap concentration. We use two disuccinimide ester linkers containing three and six methylene spacer groups: disuccinimidyl glutarate (DSG) and disuccinimidyl suberate (DSS), respectively. Remarkably, the degree of internal cross-linking can be followed simply and efficiently via 1H NMR spectroscopy. The associated structural changes-as probed by small-angle neutron scattering (SANS)-reveal that the denatured protein has a random-like coil conformation, which progressively shrinks with the addition of DSG or DSS, thus allowing for size control of the BSA-SCNPs with radii of gyration down to 5.4 nm. The longer cross-linker exhibits slightly more efficiency in chain compaction with a somewhat stronger size reduction but similar reactivity at a given cross-linker concentration. This reliable method is applicable to a wide range of compact proteins since most proteins have appropriate reactive amino acids and denature in urea. Critically, this work paves the way to the synthesis of "neat", biodegradable protein SCNPs for a range of applications including nanomedicine.The authors acknowledge the financial support received from the IKUR Strategy under the collaboration agreement between the Ikerbasque Foundation and the Materials Physics Center on behalf of the Department of Education of the Basque Government. Financial support by MCIN/AEI/10.13039/501100011033 and “ERDF – A way of making Europe” (grant PID2021-123438NB-I00), Eusko Jaurlaritza – Basque Government (grant IT-1566-22) and the Gipuzkoako Foru Aldundia, Programa Red Gipuzkoana de Ciencia, Tecnología e Innovación (2021-CIEN-000010-01) is gratefully acknowledged. A.I. thanks MICINN for a Personal Técnico de Apoyo contract (PTA2017-14359-I)

Crowding Effects on the Structure and Dynamics of the Intrinsically Disordered Nuclear Chromatin Protein NUPR1

The intracellular environment is crowded with macromolecules, including sugars, proteins and nucleic acids. In the cytoplasm, crowding effects are capable of excluding up to 40% of the volume available to any macromolecule when compared to dilute conditions. NUPR1 is an intrinsically disordered protein (IDP) involved in cell-cycle regulation, stress-cell response, apoptosis processes, DNA binding and repair, chromatin remodeling and transcription. Simulations of molecular crowding predict that IDPs can adopt compact states, as well as more extended conformations under crowding conditions. In this work, we analyzed the conformation and dynamics of NUPR1 in the presence of two synthetic polymers, Ficoll-70 and Dextran-40, which mimic crowding effects in the cells, at two different concentrations (50 and 150 mg/ml). The study was carried out by using a multi-spectroscopic approach, including: site-directed spin labelling electron paramagnetic resonance spectroscopy (SDSL-EPR), nuclear magnetic resonance spectroscopy (NMR), circular dichroism (CD), small angle X-ray scattering (SAXS) and dynamic light scattering (DLS). SDSL-EPR spectra of two spin-labelled mutants indicate that there was binding with the crowders and that the local dynamics of the C and N termini of NUPR1 were partially affected by the crowders. However, the overall disordered nature of NUPR1 did not change substantially in the presence of the crowders, as shown by circular dichroism CD and NMR, and further confirmed by EPR. The changes in the dynamics of the paramagnetic probes appear to be related to preferred local conformations and thus crowding agents partially affect some specific regions, further pinpointing that NUPR1 flexibility has a key physiological role in its activity.This work was supported by Spanish Ministry of Economy and Competitiveness and European ERDF Funds (MCIU/AEI/FEDER, EU) (RTI 2018-097991-B-I00 to JN and PGC 2018-094548-B-I00 to AA and PM), and the Basque Government (IT1175-19 to AA and PM)