Photo-polymerisation and study of the ice recrystallisation inhibition of hydrophobically modified poly(vinyl pyrrolidone) co-polymers

Tailor-Made Poly(vinylamine) via Purple LED-Activated RAFT Polymerization of N-vinylformamide

Photo-iniferter reversible addition-fragmentation chain transfer (PI-RAFT) polymerization of N-vinylformamide (NVF) is demonstrated by using purple light. PNVFs with predetermined molar masses and narrow molar mass distributions are obtained. High RAFT chain-end fidelity is confirmed by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) and electrospray-ionization time-of-flight mass spectrometry (ESI-TOF-MS), and chain extension experiment. To demonstrate the potential of this approach, an original poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PNVF) diblock copolymer is synthesized and characterized by aqueous size-exclusion chromatography (SEC), asymmetric flow field-flow fractionation (A4F), and ¹ H diffusion-ordered spectroscopy nuclear magnetic resonance (¹ H DOSY NMR). Finally, selective hydrolysis of PNVF block to corresponding pH-responsive poly(N-vinylpyrrolidone)-b-poly(N-vinylformamide) (PVP-b-PVAm) is performed.

Synthesis of poly(vinyl alcohol) by blue light bismuth oxide photocatalysed RAFT. Evaluation of the impact of freeze/thaw cycling on ice recrystallisation inhibition

Poly(vinyl alcohol), PVA, is the most potent polymeric ice recrystallisation inhibitor (IRI), mimicking a complex function of ice binding proteins. The IRI activity of PVA scales with its molecular weight and hence broad molecular weight distributions in free radical-derived PVAs lead to activity measurements dominated by small amounts of heavier fractions. Well-defined PVA can be prepared by thermally initiated RAFT/MADIX polymerization using xanthates by the polymerization of the less activated monomer vinyl acetate. The low conversions and molecular weights obtained during this approach, often requires feeding of additional initiator and bulk polymerization. Here we employ bismuth oxide photo-RAFT in solution, using blue light (450 nm), rather than previously reported white light, to obtain a library of PVA's. The use of blue light enabled quantitative conversion and acceptable dispersities. Purple light (380 nm) was also used, but asymmetric molecular weight distributions were obtained in some cases. High concentrations of high molecular weight PVA is known to form cryogels during freeze/thaw which has led to speculation this might limit the use of PVA in environments where the temperature cycles e.g. the construction industry. After 4 freeze/thaw cycles there was only small changes in observable IRI for all synthesised PVAs and two commercial standards. In an extended test, activity was retained after 100 freeze/thaw cycles, mitigating concerns that PVA could not be used in situations where freeze/thaw cycles occur. This work presents a convenient method to obtain well-defined PVAs for cryoscience studies compared to conventional thermal-RAFT and indicates that cryogelation concerns may not prevent their use.

Poly(vinyl alcohol) is synthesised using blue light bismuth oxide photo-RAFT, to high conversion. The ice recrystallisation inhibition activity of these polymers was shown to be retained over 100 freeze/thaw cycles.

Application of Polymers as a Tool in Crystallization-A Review

The application of polymers as a tool in the crystallization process is gaining more and more interest among the scientific community. According to Web of Science statistics the number of papers dealing with “Polymer induced crystallization” increased from 2 in 1990 to 436 in 2020, and for “Polymer controlled crystallization”—from 4 in 1990 to 344 in 2020. This is clear evidence that both topics are vivid, attractive and intensively investigated nowadays. Efficient control of crystallization and crystal properties still represents a bottleneck in the manufacturing of crystalline materials ranging from pigments, antiscalants, nanoporous materials and pharmaceuticals to semiconductor particles. However, a rapid development in precise and reliable measuring methods and techniques would enable one to better describe phenomena involved, to formulate theoretical models, and probably most importantly, to develop practical indications for how to appropriately lead many important processes in the industry. It is clearly visible at the first glance through a number of representative papers in the area, that many of them are preoccupied with the testing and production of pharmaceuticals, while the rest are addressed to new crystalline materials, renewable energy, water and wastewater technology and other branches of industry where the crystallization process takes place. In this work, authors gathered and briefly discuss over 100 papers, published in leading scientific periodicals, devoted to the influence of polymers on crystallizing solutions.

Synergistic Ice Inhibition Effect Enhances Rapid Freezing Cryopreservation with Low Concentration of Cryoprotectants

Despite recent advances in controlling ice formation and growth, it remains a challenge to design anti-icing materials in various fields from atmospheric to biological cryopreservation. Herein, tungsten diselenide (WSe2)-polyvinyl pyrrolidone (PVP) nanoparticles (NPs) are synthesized through one-step solvothermal route. The WSe2-PVP NPs show synergetic ice regulation ability both in the freezing and thawing processes. Molecularly speaking, PVP containing amides group can form hydrogen bonds with water molecules. At a macro level, the WSe2-PVP NPs show adsorption-inhibition and photothermal conversation effects to synergistically restrict ice growth. Meanwhile, WSe2-PVP NPs are for the first time used for the cryopreservation of human umbilical vein endothelial cell (HUVEC)-laden constructs based on rapid freezing with low concentrations of cryoprotectants (CPAs), the experimental results indicate that a minimal concentration (0.5 mg mL-1) of WSe2-PVP NPs can increase the viabilities of HUVECs in the constructs post cryopreservation (from 55.8% to 83.4%) and the cryopreserved constructs can also keep good condition in vivo within 7 days. Therefore, this work provides a novel strategy to synergistically suppress the formation and growth of the ice crystalsfor the cryopreservation of cells, tissues, or organs.

Effect of pH on the activity of ice-binding protein from Marinomonas primoryensis

The ability of an ice-binding protein (IBP) from Marinomonas primoryensis (MpIBP) to influence ice crystal growth and structure in nonphysiological pH environments was investigated in this work. The ability for MpIBP to retain ice interactivity under stressed environmental conditions was determined via (1) a modified splat assay to determine ice recrystallization inhibition (IRI) of polycrystalline ice and (2) nanoliter osmometry to evaluate the ability of MpIBP to dynamically shape the morphology of a single ice crystal. Circular dichroism (CD) was used to relate the IRI and DIS activity of MpIBP to secondary structure. The results illustrate that MpIBP secondary structure was stable between pH 6 and pH 10. It was found that MpIBP did not interact with ice at pH ≤ 4 or pH ≥ 13. At 6 ≤ pH ≥ 12 MpIBP exhibited a reduction in grain size of ice crystals as compared to control solutions and demonstrated dynamic ice shaping at 6 ≤ pH ≥ 10. The results substantiate that MpIBP retains some secondary structure and function in non-neutral pH environments; thereby, enabling its potential utility in nonphysiological materials science and engineering applications.

High-Throughput Tertiary Amine Deoxygenated Photopolymerizations for Synthesizing Polymer Libraries

The huge chemical space potential of synthetic polymers means that in many studies only a small parameter range can be realistically synthesized in a short time and hence the "best" formulations may not be optimum. Throughput is traditionally limited by the need for deoxygenation in radical polymerizations, but advances in photopolymerization now provide opportunities for "in-air" polymerizations. Here, we have developed a protocol using liquid handling robots (or multichannel pipettes) with blue light photolysis of reversible addition fragmentation chain transfer agents and tertiary amine deoxygenation to enable the synthesis of polymer libraries in industry-standard 96-well plates with no specialized infrastructure and no degassing step. The roles of solvents and amine deoxygenators are explored to optimize the polymerization, particularly to look at alternatives to dimethyl sulfoxide (DMSO) for hydrophobic monomer (co)polymerization. DMSO is shown to aid the degassing process but is not easy to remove and hence prevents isolation of pure polymers. In contrast, using dioxane in-plate evaporation or precipitation of the tertiary amine allowed isolation of polymers in-plate. This removed all reaction components yielding pure polymers, which is not easily achieved with systems using metal catalysts and secondary reductants, such as ascorbic acid. As an example of the throughput, in just under 40 h, 392 polymers were synthesized and subsequently analyzed direct from plates by a 96-well plate sampling size exclusion chromatography system to demonstrate reproducibility. Due to less efficient degassing in dioxane (compared to DMSO), the molecular weight and dispersity control were limited in some cases (with acrylates giving the lowest dispersities), but the key aim of this system is to access hundreds of polymers quickly and in a format needed to enable testing. This method enables easy exploration of chemical space and development of screening libraries to identify hits for further study using precision polymerization methods.

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer "Active"?

Antifreeze proteins and ice-binding proteins have been discovered in a diverse range of extremophiles and have the ability to modulate the growth and formation of ice crystals. Considering the importance of cryoscience across transport, biomedicine, and climate science, there is significant interest in developing synthetic macromolecular mimics of antifreeze proteins, in particular to reproduce their property of ice recrystallization inhibition (IRI). This activity is a continuum rather than an "on/off" property and there may be multiple molecular mechanisms which give rise to differences in this observable property; the limiting concentrations for ice growth vary by more than a thousand between an antifreeze glycoprotein and poly(vinyl alcohol), for example. The aim of this article is to provide a concise comparison of a range of natural and synthetic materials that are known to have IRI, thus providing a guide to see if a new synthetic mimic is active or not, including emerging materials which are comparatively weak compared to antifreeze proteins, but may have technological importance. The link between activity and the mechanisms involving either ice binding or amphiphilicity is discussed and known materials assigned into classes based on this.