More Like this

1. Nonionic star polymers with upper critical solution temperature in aqueous solutions

   https://doi.org/10.1039/D2PY00216G  

   Aliakseyeu, Aliaksei; Hlushko, Raman; Sukhishvili, Svetlana A. (May 2022, Polymer Chemistry)

   We report synthesis of temperature-responsive linear and star poly(2-ureido aminoethyl methacrylates) (PUEMs) of matched molecular weights, their phase transitions in aqueous solutions and interactions with hydrogen bonding and hydrophobic small molecules. PUEMs with number of arms up to 8 were synthesized via the activator regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) technique using the core-first approach. The degrees of branching were determined using gel permeation chromatography (GPC) equipped with the multi-angle laser light scattering and viscometry detectors. The polymer molecular architecture had a neglectable effect on the upper critical solution temperature (UCST) behavior in aqueous solutions, while the presence of a strong hydrogen-bonded acceptor – dimethyl sulfoxide (DMSO) – suppressed the transition temperature for both linear and star UCST polymers. Importantly, star PUEMs showed an enhanced ability of trapping model drug molecules – proflavine and pyrene. In particular, an increase in polymer branching led to 4.5-fold more efficient proflavine trapping and stronger binding of pyrene molecules within the hydrophobic domains of star polymers below their UCST. The trapped molecules could be then fully released from the star polymers upon temperature increase, demonstrating potential for controlled delivery applications. 

   more » « less
2. Selective hydrogen bonding controls temperature response of layer-by-layer upper critical solution temperature micellar assemblies

   https://doi.org/10.1039/d0sm01997f  

   Aliakseyeu, Aliaksei; Albright, Victoria; Yarbrough, Danielle; Hernandez, Samantha; Zhou, Qing; Ankner, John F.; Sukhishvili, Svetlana A. (March 2021, Soft Matter)

   null (Ed.)

   This work establishes a correlation between the selectivity of hydrogen-bonding interactions and the functionality of micelle-containing layer-by-layer (LbL) assemblies. Specifically, we explore LbL films formed by assembly of poly(methacrylic acid) (PMAA) and upper critical solution temperature block copolymer micelles (UCSTMs) composed of poly(acrylamide- co -acrylonitrile) P(AAm- co -AN) cores and polyvinylpyrrolidone (PVP) coronae. UCSTMs had a hydrated diameter of ∼380 nm with a transition temperature between 45 and 50 °C, regardless of solution pH. Importantly, micelles were able to hydrogen-bond with PMAA, with the critical interaction pH being temperature dependent. To better understand the thermodynamic nature of these interactions, in depth studies using isothermal titration calorimetry (ITC) were conducted. ITC reveals opposite signs of enthalpies for binding of PMAA with micellar coronae vs. with the cores. Moreover, ITC indicates that pH directs the interactions of PMAA with micelles, selectively enabling binding with the micellar corona at pH 4 or with both the corona and the core at pH 3. We then explore UCSTM/PMAA LbL assemblies and show that the two distinct modes of PMAA interaction with the micelles ( i.e. whether or not PMAA binds with the core) had significant effects on the film composition, structure, and functionality. Consistent with PMAA hydrogen bonding with the P(AAm- co -AN) micellar cores, a significantly higher fraction of PMAA was found within the films assembled at pH 3 compared to pH 4 by both spectroscopic ellipsometry and neutron reflectometry. Selective interaction of PMAA with PVP coronae of the assembled micelles, achieved by the emergence of partial ionization of PMAA at pH 4 was critical for preserving film functionality demonstrated as temperature-controlled swelling and release of a model small molecule, pyrene. The work done here can be applied to a multitude of assembled polymer systems in order to predict suppression/retention of their stimuli-responsive behavior. 

   more » « less
3. Ultrafast Spectroscopies of Nitrophenols and Nitrophenolates in Solution: From Electronic Dynamics and Vibrational Structures to Photochemical and Environmental Implications

   https://doi.org/10.3390/molecules28020601  

   Bailey-Darland, Sullivan; Krueger, Taylor D.; Fang, Chong (January 2023, Molecules)

   Nitrophenols are a group of small organic molecules with significant environmental implications from the atmosphere to waterways. In this work, we investigate a series of nitrophenols and nitrophenolates, with the contrasting ortho-, meta-, and para-substituted nitro group to the phenolic hydroxy or phenolate oxygen site (2/3/4NP or NP−), implementing a suite of steady-state and time-resolved spectroscopic techniques that include UV/Visible spectroscopy, femtosecond transient absorption (fs-TA) spectroscopy with probe-dependent and global analysis, and femtosecond stimulated Raman spectroscopy (FSRS), aided by quantum calculations. The excitation-dependent (400 and 267 nm) electronic dynamics in water and methanol, for six protonated or deprotonated nitrophenol molecules (three regioisomers in each set), enable a systematic investigation of the excited-state dynamics of these functional “nanomachines” that can undergo nitro-group twisting (as a rotor), excited-state intramolecular or intermolecular proton transfer (donor–acceptor, ESIPT, or ESPT), solvation, and cooling (chromophore) events on molecular timescales. In particular, the meta-substituted compound 3NP or 3NP− exhibits the strongest charge-transfer character with FSRS signatures (e.g., C–N peak frequency), and thus, does not favor nitroaromatic twist in the excited state, while the ortho-substituted compound 2NP can undergo ESIPT in water and likely generate nitrous acid (HONO) after 267 nm excitation. The delineated mechanistic insights into the nitro-substituent-location-, protonation-, solvent-, and excitation-wavelength-dependent effects on nitrophenols, in conjunction with the ultraviolet-light-induced degradation of 2NP in water, substantiates an appealing discovery loop to characterize and engineer functional molecules for environmental applications. 

   more » « less
4. Coupled field modeling of thermoresponsive hydrogels with upper/lower critical solution temperature

   https://doi.org/10.1016/j.eml.2024.102222  

   Valverde-González, A; Reinoso, J; Paggi, M; Dortdivanlioglu, B (August 2024, Extreme Mechanics Letters)
5. Unusual Lower Critical Solution Temperature Phase Behavior of Poly(benzyl methacrylate) in a Pyrrolidinium-Based Ionic Liquid

   https://doi.org/10.3390/molecules26164850  

   Carrick, Brian R.; Seitzinger, Claire L.; Lodge, Timothy P. (August 2021, Molecules)

   Polymer/ionic liquid systems are being increasingly explored, yet those exhibiting lower critical solution temperature (LCST) phase behavior remain poorly understood. Poly(benzyl methacrylate) in certain ionic liquids constitute unusual LCST systems, in that the second virial coefficient (A2) in dilute solutions has recently been shown to be positive, indicative of good solvent behavior, even above phase separation temperatures, where A2 < 0 is expected. In this work, we describe the LCST phase behavior of poly(benzyl methacrylate) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide for three different molecular weights (32, 63, and 76 kg/mol) in concentrated solutions (5–40% by weight). Turbidimetry measurements reveal a strong concentration dependence to the phase boundaries, yet the molecular weight is shown to have no influence. The critical compositions of these systems are not accessed, and must therefore lie above 40 wt% polymer, far from the values (ca. 10%) anticipated by Flory-Huggins theory. The proximity of the experimental cloud point to the coexistence curve (binodal) and the thermo-reversibility of the phase transitions, are also confirmed at various heating and cooling rates. 

   more » « less