Exopolysaccharides as bio-based rheology modifiers from microalgae produced on dairy industry waste: Towards a circular bioeconomy approach

The feasibility of exopolysaccharides (EPS) production from cheese whey using Chlorella vulgaris was investigated as an example of circular bioeconomy application. The effects of dairy waste utilization in EPS biosynthesis and rheological properties were evaluated, comparing with both control conditions and commercial xanthan gum (CXG). A twofold increase in yield, up to 0.32 g L-1, was observed when Chlorella vulgaris was used for EPS production from whey rather than conventional fertilizers. Additionally, the EPS produced using cheese whey exhibited superior pseudoplasticity in the 0.4-1.0 (w/v) range compared to the control. The EPS from the whey wastewater contained functional groups similar to those of CXG (82.7 %). Moreover, the solutions containing 1 % biopolymer showed rheological profiles similar to those of the 0.4 % CXG. The molecular weight averages predominantly fell within the range of 284 to 324 kDa, as deduced using diffusion NMR, an innovative and rapid determination method for estimating EPS size. The potential applications of EPS notably extend beyond the dairy industry, reaching diverse market sectors, and thereby enhancing the competitiveness of microalgal biorefineries while contributing to the achievement of Sustainable Development Goals.

Optimizing the Structure of a Pt Metal-Chelating Polymer to Reduce Nonspecific Binding for Mass Cytometry

Mass cytometry is a bioanalytic tool based on atomic mass spectrometry for detecting biomarker expression on individual cells. Current reagents employ metal-chelating polymers binding isotopes of hard metal ions. Polymers bearing chelators for soft metal ions offer the promise for a large increase in multiplexing capabilities, but examples reported so far often have unacceptably high levels of nonspecific binding (NSB). We recently reported a new class of metal-chelating polymers with dipicolylamine (DPA) chelators that could bind Re and Pt. They also showed significant levels of NSB. Here, to reduce the NSB of the Pt-DPA polymer, we grafted water-soluble oligomers to the distal end of the dipicolylamine pendant group. Methoxy(polyethylene glycol) (DP = 24) was effective as was poly(sulfobetaine methacrylate) (DP = 29). Reacting the Pt-Cl bond of the metalated polymer with glutathione was remarkably effective at suppressing NSB. These results open the door to Pt-isotope-based metal-chelating polymers as new mass tags for mass cytometry.

Comparative biochemistry of PET hydrolase-carbohydrate-binding module fusion enzymes on a variety of PET substrates

Enzyme-driven recycling of PET has now become a fully developed industrial process. With the right pre-treatment, PET can be completely depolymerized within workable timeframes. This has been realized due to extensive research conducted over the past decade, resulting in a large set of engineered PET hydrolases. Among various engineering strategies to enhance PET hydrolases, fusion with binding domains has been used to tune affinity and boost activity of the enzymes. While fusion enzymes have demonstrated higher activity in many cases, these results are primarily observed under conditions that would not be economically viable at scale. Furthermore, the wide variation in PET substrates, conditions, and combinations of PET hydrolases and binding domains complicates direct comparisons. Here, we present a self-consistent and thorough analysis of two leading PET hydrolases, LCCICCG and PHL7. Both enzymes were evaluated both without and with a substrate-binding domain across a range of industrially relevant PET substrates. We demonstrate that the presence of a substrate-binding module does not significantly affect the affinity of LCCICCG and PHL7 for PET. However, significant differences exist in how the fusion enzymes act on different PET substrates and solid substrate loading, ranging from a 3-fold increase in activity to a 6-fold decrease. These findings could inform the tailoring of enzyme choice to different industrial scenarios.

Poly(Sitosterol)-Based Hydrophobic Blocks in Amphiphilic Block Copolymers for the Assembly of Hybrid Vesicles

Amphiphilic block copolymer and lipids can be assembled into hybrid vesicles (HVs), which are an alternative to liposomes and polymersomes. Block copolymers that have either poly(sitostryl methacrylate) or statistical copolymers of sitosteryl methacrylate and butyl methacrylate as the hydrophobic part and a poly(carboxyethyl acrylate) hydrophilic segment are synthesized and characterized. These block copolymers assemble into small HVs with soybean L-α-phosphatidylcholine (soyPC), confirmed by electron microscopy and small-angle X-ray scattering. The membrane's hybrid nature is illustrated by fluorescence resonance energy transfer between labeled building blocks. The membrane packing, derived from spectra when using Laurdan as an environmentally sensitive fluorescent probe, is comparable between small HVs and the corresponding liposomes with molecular sitosterol, although the former show indications of transmembrane asymmetry. Giant HVs with homogenous distribution of the block copolymers and soyPC in their membranes are assembled using the electroformation method. The lateral diffusion of both building blocks is slowed down in giant HVs with higher block copolymer content, but their permeability toward (6)-carboxy-X-rhodamine is higher compared to giant vesicles made of soyPC and molecular sitosterol. This fundamental effort contributes to the rapidly expanding understanding of the integration of natural membrane constituents with designed synthetic compounds to form hybrid membranes.

Development of a dexamethasone-hyaluronic acid conjugate with selective targeting effect for acute lung injury therapy

Acute lung injury (ALI), a critical complication of COVID-19, is characterized by widespread inflammation and severe pulmonary damage, necessitating intensive care for those affected. Although glucocorticoids (GCs), such as dexamethasone (Dex), have been employed clinically to lower mortality, their nonspecific systemic distribution has led to significant side effects, limiting their use in ALI treatment. In this study, we explored the conjugation of Dex to hyaluronic acid (HA) to achieve targeted delivery to inflamed lung tissues. We achieved a conjugation efficiency exceeding 98 % using a cosolvent system, with subsequent ester bond cleavage releasing the active Dex, as verified by liquid chromatography. Biodistribution and cellular uptake studies indicated the potential of the HA conjugate for cluster of differentiation 44 (CD44)-mediated targeting and accumulation. In a lipopolysaccharide-induced ALI mouse model, intravenous (IV) HA-Dex administration showed superior anti-inflammatory effects compared to free Dex administration. Flow cytometry analysis suggested that the HA conjugate preferentially accumulated in lung macrophages, suggesting the possibility of reducing clinical Dex dosages through this targeted delivery approach.

Molar Mass Determination for Small and Large Molecules Using Diffusion-Ordered Spectroscopy

The development of the most comprehensive universal calibration of molar mass dependences will be presented. For the first time, diffusion-ordered spectroscopy (DOSY) can now provide structure-, solvent-, and temperature-independent molar mass determinations for both small and large molecules. This fundamental theoretical approach provides only one single function which could perfectly describe all molar mass dependences. The new development using DOSY was tested on 477 diffusion coefficients representing altogether 56 molar mass dependences of 30 small molecules in 7 solvents, 5 different polymers in 10 solvents, and 11 temperature dependences of 2 polymers in 2 solvents, respectively. These samples cover a very large range of molar masses varying between 70 g/mol until 1 200 000 g/mol. The derived equation for the molar masses delivered a very good accuracy for all samples and might be one of the best tools for molar mass determinations.

Diffusive Trends in Concentrated Oppositely-Charged Polyelectrolyte Solutions and Onset of Glassy Dynamics

We utilize single particle tracking studies to investigate the diffusion of polylysine through concentrated matrices of cationic polylysine and anionic polyglutamic acid with no added salts. These studies show that diffusivity has a strong apparently exponential dependence on concentration in crowded systems that does not appear to be a function of the charge sign. These trends are consistent in both single-phase systems prepared at concentrated conditions and polymer-rich coacervate phases formed from dilute phase-separating systems. The likely origin of this behavior is the onset of glassy dynamics spurred by a decrease in plasticization by water and the large excluded volume associated with charge-bearing species. This effect can be contextualized through free volume-based theories such as the Vrentas-Duda model. Overall, we obtain dynamic behavior that is distinctly different from behavior observed in more dilute systems and warrants further investigation.

UV/Visible Diffusion-Ordered Spectroscopy: A Simultaneous Probe of Molecular Size and Electronic Absorption

Based on concepts from nuclear magnetic resonance, we have developed UV/vis diffusion-ordered spectroscopy, which simultaneously probes the size and electronic absorption spectrum of molecules and particles. We use simple flow technology to create a step-function concentration profile inside an optical sample cell, and by measuring the time-dependent absorption spectrum in an initially solvent-filled part of the sample volume, we obtain the diffusion coefficients and UV/vis spectra of the species present in the sample solution. From these data, we construct a two-dimensional spectrum with absorption wavelength on one axis and diffusion coefficient (or equivalently, size) on the other, in which the UV/vis spectrum of a mixture with different molecular sizes is separated into the spectra of the different species, sorted by size. We demonstrate this method on mixed solutions of fluorescent dyes, biomolecules, and the UV-absorbing components of coffee, caffeine, and chlorogenic acid, all with concentrations in the μM range.

Real-Time Determination of Molecular Weight: Use of MaDDOSY (Mass Determination Diffusion Ordered Spectroscopy) to Monitor the Progress of Polymerization Reactions

Knowledge of molecular weight is an integral factor in polymer synthesis, and while many synthetic strategies have been developed to help control this, determination of the final molecular weight is often only measured at the end of the reaction. Herein, we provide a technique for the online determination of polymer molecular weight using a universal, solvent-independent diffusion ordered spectroscopy (DOSY) calibration and evidence its use in a variety of polymerization reactions.

Micro(nano)plastics from synthetic oligomers persisting in Mediterranean seawater: Comprehensive NMR analysis, concerns and origins

The presence in seawater of low-molecular-weight polyethylene (PE) and polydimethylsiloxane (PDMS), synthetic polymers with high chemical resistance, has been demonstrated in this study for the first time by developing a novel methodology for their recovery and quantification from surface seawater. These synthetic polymer debris (SPD) with very low molecular weights and sizes in the nano- and micro-metre range have escaped conventional analytical methods. SPD have been easily recovered from water samples (2 L) through filtration with a nitrocellulose membrane filter with a pore size of 0.45 μm. Dissolving the filter in acetone allowed the isolation of the particulates by centrifugation followed by drying. The isolated SPD were analysed by 1H nuclear magnetic resonance spectroscopy (1H NMR), identifying PE and PDMS. These polymers are thus persisting on seawater because of their low density and the ponderal concentrations were quantified in mg/m3. This method was used in an actual case study in which 120 surface seawater samples were collected during two sampling campaigns in the Mediterranean Sea (from the Gulf of Salerno to the Gulf of Policastro in South Italy). The developed analytical protocol allowed achieving unprecedented simplicity, rapidity and sensitivity. The 1H and 13C NMR structural analysis of the PE debris indicates the presence of oxidised polymer chains with very low molecular weights. Additionally, the origin of those low molecular weight polymers was investigated by analysing influents and effluents from a wastewater treatment plant (WWTP) in Salerno as a hot spot for the release of SPD: the analysis indicates the presence of low molecular weight polymers compatible with wax-PE, widely used for coating applications, food industry, cosmetics and detergents. Moreover, the origin of PDMS debris found in surface seawater can be ascribed to silicone-based antifoamers and emulsifiers.

Extreme dependence of dynamics on concentration in highly crowded polyelectrolyte solutions

Charge-carrying species, such as polyelectrolytes, are vital to natural and synthetic processes that rely on their dynamic behavior. Through single-particle tracking techniques, the diffusivity of individual polyelectrolyte chains and overall system viscosity are determined for concentrated polylysine solutions. These studies show scaling dependences of D ~ c-6.1 and η ~ c7.2, much stronger than theoretical predictions, drawing the applicability of power law fits into question. Similar trends are observed in concentrated solutions prepared at various pH and counterion conditions. These hindered system dynamics appear universal to polyelectrolyte systems and are attributed to the large effective excluded volumes of polyelectrolyte chains inducing glassy dynamics. The framework of the Vrentas-Duda free-volume theory is used to compare polyelectrolyte and neutral systems. Supported by this theory, excluding counterion mass from total polymer mass results in all environmental conditions collapsing onto a common trendline. These results are applicable to crowded biological systems, such as intracellular environments where protein mobility is strongly inhibited.

Duplex-forming oligocarbamates with tunable nonbonding sites

In biopolymers such as proteins and nucleic acids, monomer sequence encodes for highly specific intra- and intermolecular interactions that direct self-assembly into complex architectures with high fidelity. This remarkable structural control translates into precise control over the properties of the biopolymer. Polymer scientists have sought to achieve similarly precise control over the structure and function of synthetic assemblies. A common strategy for achieving this goal has been to exploit existing biopolymers, known to associate with specific geometries and stoichiometries, for the assembly of synthetic building blocks. However, such systems are neither scalable nor amenable to the relatively harsh conditions required by various materials science applications, particularly those involving non-aqueous environments. To overcome these limitations, we have synthesized sequence-defined oligocarbamates (SeDOCs) that assemble into duplexes through complementary hydrogen bonds between thymine (T) and diaminotriazine (D) pendant groups. The SeDOC platform makes it simple to incorporate non-hydrogen-bonding sites into an oligomer's array of recognition motifs, thereby enabling an investigation into this unexplored handle for controlling the hybridization of complementary ligands. We successfully synthesized monovalent, divalent, and trivalent SeDOCs and characterized their self-assembly via diffusion ordered spectroscopy, 1H-NMR titration, and isothermal titration calorimetry. Our findings reveal that the binding strength of monovalent oligomers with complementary pendant groups is entropically driven and independent of monomer sequence. The results further show that the hybridization of multivalent oligomers is cooperative, that their binding enthalpy (ΔH) and entropy (TΔS) depend on monomer sequence, and that sequence-dependent changes in ΔH and TΔS occur in tandem to minimize the overall change in binding free energy.

Selective and Controlled Grafting from PVDF-Based Materials by Oxygen-Tolerant Green-Light-Mediated ATRP

Poly(vinylidene fluoride) (PVDF) shows excellent chemical and thermal resistance and displays high dielectric strength and unique piezoelectricity, which are enabling for applications in membranes, electric insulators, sensors, or power generators. However, its low polarity and lack of functional groups limit wider applications. While inert, PVDF has been modified by grafting polymer chains by atom transfer radical polymerization (ATRP), albeit via an unclear mechanism, given the strong C-F bonds. Herein, we applied eosin Y and green-light-mediated ATRP to modify PVDF-based materials. The method gave nearly quantitative (meth)acrylate monomer conversions within 2 h without deoxygenation and without the formation of unattached homopolymers, as confirmed by control experiments and DOSY NMR measurements. The gamma distribution model that accounts for broadly dispersed polymers in DOSY experiments was essential and serves as a powerful tool for the analysis of PVDF. The NMR analysis of poly(methyl acrylate) graft chain-ends on PVDF-CTFE (statistical copolymer with chlorotrifluoroethylene) was carried out successfully for the first time and showed up to 23 grafts per PVDF-CTFE chain. The grafting density was tunable depending on the solvent composition and light intensity during the grafting. The initiation proceeded either from the C-Cl sites of PVDF-CTFE or via unsaturations in the PVDF backbones. The dehydrofluorinated PVDF was 20 times more active than saturated PVDF during the grafting. The method was successfully applied to modify PVDF, PVDF-HFP, and Viton A401C. The obtained PVDF-CTFE-g-PnBMA materials were investigated in more detail. They featured slightly lower crystallinity than PVDF-CTFE (12-18 vs 24.3%) and had greatly improved mechanical performance: Young's moduli of up to 488 MPa, ductility of 316%, and toughness of 46 × 106 J/m3.

Visible-Light Driven Control Over Triply and Quadruply Hydrogen-Bonded Supramolecular Assemblies

Supramolecular polymers offer tremendous potential to produce new "smart" materials, however, there remains a need to develop systems that are responsive to external stimuli. In this work, visible-light responsive hydrogen-bonded supramolecular polymers comprising photoresponsive supramolecular synthons (I-III) consisting of two hydrogen bonding motifs (HBMs) connected by a central ortho-tetrafluorinated azobenzene have been characterized by DOSY NMR and viscometry. Comparison of different hydrogen-bonding motifs reveals that assembly in the low and high concentration regimes is strongly influenced by the strength of association between the HBMs. I, Incorporating a triply hydrogen-bonded heterodimer, was found to exhibit concentration dependent switching between a monomeric pseudo-cycle and supramolecular oligomer through intermolecular hydrogen bonding interactions between the HBMs. II, Based on the same photoresponsive scaffold, and incorporating a quadruply hydrogen-bonded homodimer was found to form a supramolecular polymer which was dependent upon the ring-chain equilibrium and thus dependent upon both concentration and photochemical stimulus. Finally, III, incorporating a quadruply hydrogen-bonded heterodimer represents the first photoswitchable AB type hydrogen-bonded supramolecular polymer. Depending on the concentration and photostationary state, four different assemblies dominate for both monomers II and III, demonstrating the ability to control supramolecular assembly and physical properties triggered by light.

MaDDOSY (Mass Determination Diffusion Ordered Spectroscopy) using an 80 MHz Bench Top NMR for the Rapid Determination of Polymer and Macromolecular Molecular Weight

Measurement of molecular weight is an integral part of macromolecular and polymer characterization which usually has limitations. Herein, this article presents the use of a bench-top 80 MHz Nuclear Magnetic Resonance (NMR) spectrometer for diffusion-ordered spectroscopy as a practical and rapid approach for the determination of molecular weight/size using a novel solvent and polymer-independent universal calibration.

Synthetic Strategies for the Selective Functionalization of Carbon Nanodots Allow Optically Communicating Suprastructures

The surface of Carbon Nanodots (CNDs) stands as a rich chemical platform, able to regulate the interactions between particles and external species. Performing selective functionalization of these nanoscale entities is of practical importance, however, it still represents a considerable challenge. In this work, we exploited the organic chemistry toolbox to install target functionalities on the CND surface, while monitoring the chemical changes on the material's outer shell through nuclear magnetic resonance spectroscopy. Following this, we investigated the use of click chemistry to covalently connect CNDs of different nature en-route towards covalent suprastructures with unprecedent molecular control. The different photophysical properties of the connected particles allowed their optical communication in the excited state. This work paves the way for the development of selective and addressable CND building blocks which can act as modular nanoscale synthons that mirror the long-established reactivity of molecular organic synthesis.

Synthetically encoded complementary oligomers

Creating the next generation of advanced materials will require controlling molecular architecture to a degree typically achieved only in biopolymers. Sequence-defined polymers take inspiration from biology by using chain length and monomer sequence as handles for tuning structure and function. These sequence-defined polymers can assemble into discrete structures, such as molecular duplexes, via reversible interactions between functional groups. Selectivity can be attained by tuning the monomer sequence, thereby creating the need for chemical platforms that can produce sequence-defined polymers at scale. Developing sequence-defined polymers that are specific for their complementary sequence and achieve their desired binding strengths is critical for producing increasingly complex structures for new functional materials. In this Review Article, we discuss synthetic platforms that produce sequence-defined, duplex-forming oligomers of varying length, strength and association mode, and highlight several analytical techniques used to characterize their hybridization.

The Universal Calibration for Structure- and Solvent-Independent Molar Mass Determinations of Polymers Using Diffusion-Ordered Spectroscopy

It will be shown how diffusion-ordered spectroscopy (DOSY) can produce a universal calibration of molar mass dependences of polymers compared to size exclusion chromatography (SEC) or recently published DOSY methods. Whereas SEC can deliver only structure-independent universal calibrations for a particular solvent, DOSY was used for creating solvent-independent calibrations for a certain polymer. Now, we can demonstrate a universal calibration method that generates both a structure- and solvent-independent molar mass calibration. Only one mathematical function describes the structure- and solvent-independent calibrations for DOSY by implementing the Mark-Houwink approach. The derived equation is tested on polystyrene (PS), poly(ethylene oxide), and poly(methyl methacrylate) of different molar masses and in different solvents. Altogether, 94 diffusion coefficients representing 16 molar mass calibrations of the diffusion coefficients in 10 different solvents could be perfectly matched to one universal calibration function with an average deviation of just 2.5%. It was also found that the Mark-Houwink parameters calculated by DOSY are very close to the SEC data. In any case, this new approach is a very useful tool for the determination of molar masses and new Mark-Houwink parameters via DOSY.

Tools to enable the study and translation of supramolecular amphiphiles

This tutorial review focuses on providing a summary of the key techniques used for the characterisation of supramolecular amphiphiles and their self-assembled aggregates; from the understanding of low-level molecular interactions, to materials analysis, use of data to support computer-aided molecular design and finally, the translation of this class of compounds for real world application, specifically within the clinical setting. We highlight the common methodologies used for the study of traditional amphiphiles and build to provide specific examples that enable the study of specialist supramolecular systems. This includes the use of nuclear magnetic resonance spectroscopy, mass spectrometry, X-ray scattering techniques (small- and wide-angle X-ray scattering and single crystal X-ray diffraction), critical aggregation (or micelle) concentration determination methodologies, machine learning, and various microscopy techniques. Furthermore, this review provides guidance for working with supramolecular amphiphiles in in vitro and in vivo settings, as well as the use of accessible software programs, to facilitate screening and selection of druggable molecules. Each section provides: a methodology overview - information that may be derived from the use of the methodology described; a case study - examples for the application of these methodologies; and a summary section - providing methodology specific benefits, limitations and future applications.

Raman Diffusion-Ordered Spectroscopy

The Stokes-Einstein relation, which relates the diffusion coefficient of a molecule to its hydrodynamic radius, is commonly used to determine molecular sizes in chemical analysis methods. Here, we combine the size sensitivity of such diffusion-based methods with the structure sensitivity of Raman spectroscopy by performing Raman diffusion-ordered spectroscopy (Raman-DOSY). The core of the Raman-DOSY setup is a flow cell with a Y-shaped channel containing two inlets: one for the sample solution and one for the pure solvent. The two liquids are injected at the same flow rate, giving rise to two parallel laminar flows in the channel. After the flow stops, the solute molecules diffuse from the solution-filled half of the channel into the solvent-filled half at a rate determined by their hydrodynamic radius. The arrival of the solute molecules in the solvent-filled half of the channel is recorded in a spectrally resolved manner by Raman microspectroscopy. From the time series of Raman spectra, a two-dimensional Raman-DOSY spectrum is obtained, which has the Raman frequency on one axis and the diffusion coefficient (or equivalently, hydrodynamic radius) on the other. In this way, Raman-DOSY spectrally resolves overlapping Raman peaks arising from molecules of different sizes. We demonstrate Raman-DOSY on samples containing up to three compounds and derive the diffusion coefficients of small molecules, proteins, and supramolecules (micelles), illustrating the versatility of Raman-DOSY. Raman-DOSY is label-free and does not require deuterated solvents and can thus be applied to samples and matrices that might be difficult to investigate with other diffusion-based spectroscopy methods.

Recycled PLA for 3D Printing: A Comparison of Recycled PLA Filaments from Waste of Different Origins after Repeated Cycles of Extrusion

The objective of this work is to evaluate the reprocessing of PLA 3D printing waste from different origins, into filaments and films, and without the addition of any additive. Two types of waste were considered: a blend of different printing wastes (masks, visors, other components) of personal protective equipment coming from an association of Spanish coronamakers, and PLA waste from a single known commercial source. Both types of materials were subjected to repeated extrusion cycles and processed into films by compression molding. Samples were characterized after each cycle and their mechanical and viscosity properties evaluated. Diffusion-ordered NMR spectroscopy (DOSY) experiments were also carried out to estimate molecular weights. The results show a better performance for the PLA waste from the known origin, capable of withstanding up to three re-extrusion cycles per two for the waste blending, without significant degradation. Additionally, a model to address collection and mechanical recycling cycles under two different scenarios (full traceability and not full traceability) was proposed.

Using surface plasmon resonance, capillary electrophoresis and diffusion-ordered NMR spectroscopy to study drug release kinetics

Nanomedicines, including polymer nanocarriers with controlled drug release, are considered next-generation therapeutics with advanced therapeutic properties and reduced side effects. To develop safe and efficient nanomedicines, it is crucial to precisely determine the drug release kinetics. Herein, we present application of analytical methods, i.e., surface plasmon resonance biosensor technology (SPR), capillary electrophoresis, and 1H diffusion-ordered nuclear magnetic resonance spectroscopy, which were innovatively applied for drug release determination. The methods were optimised to quantify the pH-triggered release of three structurally different drugs from a polymer carrier. The suitability of these methods for drug release characterisation was evaluated and compared using several parameters including applicability for diverse samples, the biological relevance of the experimental setup, method complexity, and the analysis outcome. The SPR method was the most universal method for the evaluation of diverse drug molecule release allowing continuous observation in the flow-through setting and requiring a small amount of sample.

Selective Accumulation of Near Infrared-Labeled Multivalent Quinidine Copolymers in Tumors Overexpressing P-Glycoprotein: Potential for Noninvasive Diagnostic Imaging

P-glycoprotein (P-gp) is a promiscuous small molecule transporter whose overexpression in cancer is associated with multidrug resistance (MDR). In these instances, anticancer drugs can select for P-gp-overexpressing cells, leading to cancer recurrence with an MDR phenotype. To avoid selection for MDR cancers and inform individual patient treatment plans, it is critical to noninvasively identify P-gp-overexpressing tumors prior to administration of chemotherapy. We report the facile free radical copolymerization of quinidine, a competitive inhibitor of P-gp, and acrylic acid to generate multiplexed polymeric P-gp-targeted imaging agents with tunable quinidine content. Copolymer targeting was demonstrated in a nude mouse xenograft model. In xenografts overexpressing P-gp, copolymer distribution was enhanced over two-fold compared to the negative control of poly(acrylic acid) regardless of quinidine content. In contrast, accumulation of the copolymers in xenografts lacking P-gp was equivalent to poly(acrylic acid). This work forms the foundation for a unique approach toward the phenotype-specific noninvasive imaging of MDR tumors and is the first in vivo demonstration of copolymer accumulation through the active targeting of P-gp.

A microgel of CdSe quantum dots for fluorescent bisphenol A detection

A fluorescent microgel for BPA detection has been successfully prepared by cross-linking linear poly(styrene-co-glycidyl methacrylate) (poly (STY-co-GMA)) with L-cysteine-capped CdSe quantum dots (Lcys-caped CdSe QDs). The microgel contained specific binding sites created by the covalent grafting of the copolymer onto the QDs via the GMA units, allowing for selective trapping of BPA molecules through π-π and hydrogen bond interactions with phenyl, carboxylic, and amine groups. After binding, electron transfer from the QDs to the analyte quenched the fluorescence at a wavelength of 547 nm when excited at 400 nm. The rational compositional and structural design allows the microgel to accurately detect BPA concentrations over a wide dynamic range of 1.0×10^-1 to 1.0×10⁵ μg/L with a low detection limit (7.0×10^-2 to 8.0×10^-2 μg/L) in deionized, drinking, and tap waters within just 2.0 min. On top of that, the sensitivity for BPA detection was 2.0-4.6 times higher than that of the other 3 structural analogues, even molecular imprinting was not involved. The influence of the STY/GMA compositions in the copolymers and environmental conditions, including pH and ionic strength, on the sensing performance was determined. Moreover, the sensing mechanism and the selectivity with respect to the molecular features were elucidated.

Is acriflavine an efficient co-drug in chemotherapy?

Cancer is a global health problem being the second worldwide cause of deaths right after cardiovascular diseases. The main methods of cancer treatment involve surgery, radiation and chemotherapy with an emphasis on the latter. Thus development of nanochemistry and nanomedicine in a search for more effective and safer cancer treatment is an important area of current research. Below, we present interaction of doxorubicin and acriflavine and the cytotoxicity of these drug nano-complexes towards cervical cancer (HeLa) cells. Experimental results obtained from NMR measurements and fluorescence spectroscopy show that the drugs' interaction was due to van der Waals forces, formation of hydrogen bonds and π-π stacking. Quantum molecular simulations confirmed the experimental results with regard to existing π-π stacking. Additionally it was shown that, at the level of theory applied (DFT, triple zeta basis set), the stacking interactions comprise the most preferable interactions (the lowest ΔG ca. -12 kcal mol^-1) both between the molecules forming the acriflavine system and between the other component - another drug (doxorubicin) dimer. Biological tests performed on HeLa cells showed high cytotoxicity of the complexes, comparable to free drugs (ACF and DOX), both after 24 and 48 hours of incubation. For non-cancerous cells, a statistically significant difference in the cytotoxicity of drugs and complexes was observed in the case of a short incubation period. The results of the uptake study showed significantly more efficient cellular uptake of acriflavine than doxorubicin, whether administered alone or in combination with an anthracycline. The mechanism determining the selective uptake of acriflavine and ACF : DOX complexes towards non-cancer and cancer cells should be better understood in the future, as it may be of key importance in the design of complexes with toxic anti-cancer drugs.

Protein-Inspired Control over Synthetic Polymer Folding for Structured Functional Nanoparticles in Water

The folding of proteins into functional nanoparticles with defined 3D structures has inspired chemists to create simple synthetic systems mimicking protein properties. The folding of polymers into nanoparticles in water proceeds via different strategies, resulting in the global compaction of the polymer chain. Herein, we review the different methods available to control the conformation of synthetic polymers and collapse/fold them into structured, functional nanoparticles, such as hydrophobic collapse, supramolecular self-assembly, and covalent cross-linking. A comparison is made between the design principles of protein folding to synthetic polymer folding and the formation of structured nanocompartments in water, highlighting similarities and differences in design and function. We also focus on the importance of structure for functional stability and diverse applications in complex media and cellular environments.

Thermoplastic starch/polyvinyl alcohol blends modification by citric acid-glycerol polyesters

Thermoplastic starch/polyvinyl alcohol (TPS/PVA) films have limitations for being used in long-term applications due to starch retrogradation. This leads to plasticizer migration, especially when low molecular weight plasticizers such as glycerol, are used. In this work, we employed mixtures of oligomers based on glycerol citrates with higher molecular weight than glycerol as plasticizers for potato-based TPS/PVA blends obtained by melt-mixing. This constitutes an alternative to reduce plasticizer migration while keeping high swelling degree, and to provide high mechanical performance. The novelty lies in the usage of these oligomers by melt-mixing technique, aspect not deeply explored previously and that represents the first step towards industrial scalability. Prior to the blending process, oligomers mixtures were prepared with different molar ratios of citric acid (0-40 mol%) and added them. This minimizes the undesirable hydrolysis effect of free carboxylic groups on starch chains. The results demonstrated that the migration of plasticizers in TPS/PVA blends decreased by up to 70 % when the citric acid content increased. This reduction was attributed to the higher molecular weight (the majority in the range 764-2060 Da) and the 3D structure of the oligomers compared to using raw glycerol. Furthermore, the films exhibited a 150 % increase in Young's modulus and tensile strength without a reduction in elongation at break, while maintaining a high gel content, due to a moderate crosslinking.

Polymer Molecular Weights via DOSY NMR

Diffusion-ordered spectroscopy (DOSY) ¹H nuclear magnetic resonance (¹H NMR) has become a powerful tool to characterize the molecular weights of polymers. Compared to common characterization techniques, such as size exclusion chromatography (SEC), DOSY is faster, uses less solvent, and does not require a purified polymer sample. Poly(methyl methacrylate) (PMMA), polystyrene (PS), and polybutadiene (PB) molecular weights were determined by the linear correlation between the logarithm of their diffusion coefficients (D) and the logarithm of their molecular weights based on SEC molecular weights. Here, we emphasize the importance of the preparation needed to generate the calibration curves, which includes choosing the correct pulse sequence, optimizing parameters, and sample preparation. The limitation of the PMMA calibration curve was investigated by increasing the dispersity of PMMA. Additionally, by accounting for viscosity in the Stokes-Einstein equation, a variety of solvents were used to produce a "universal" calibration curve for PMMA to determine molecular weight. Furthermore, we place a spotlight on the increasing importance of DOSY NMR being incorporated into the polymer chemist's toolbox.

Synthesis of Supramolecular A8 Bn Miktoarm Star Copolymers by Host-Guest Complexation

We report a new synthetic method to construct supramolecular A₈ B_n (n=1, 2, 4) miktoarm star copolymers by host-guest complexation between a resorcinarene-based coordination capsule possessing eight polystyrene chains and 4,4-diacetoxybiphenyl guest molecules that retain one, two or four polymethyl acrylate chains. The formation of the supramolecular A₈ B_n (n=1, 2, 4) miktoarm star copolymers was confirmed by dynamic light scattering (DLS), size-exclusion chromatography (SEC), and diffusion-ordered NMR spectroscopy (DOSY). Differential scanning calorimetry (DSC) measurements revealed that the miktoarm copolymers were phase-separated in the bulk. The micro-Brownian motion of the A₈ B₄ structure was markedly enhanced in the bulk due to a weak segregation interaction between the immiscible arms.

Fuzzy Drug Targets: Disordered Proteins in the Drug-Discovery Realm

Intrinsically disordered proteins (IDPs) and regions (IDRs) form a large part of the eukaryotic proteome. Contrary to the structure-function paradigm, the disordered proteins perform a myriad of functions in vivo. Consequently, they are involved in various disease pathways and are plausible drug targets. Unlike folded proteins, that have a defined structure and well carved out drug-binding pockets that can guide lead molecule selection, the disordered proteins require alternative drug-development methodologies that are based on an acceptable picture of their conformational ensemble. In this review, we discuss various experimental and computational techniques that contribute toward understanding IDP "structure" and describe representative pursuances toward IDP-targeting drug development. We also discuss ideas on developing rational drug design protocols targeting IDPs.

Electrochemically Stable Rechargeable Lithium–Sulfur Batteries Equipped with an Electrospun Polyacrylonitrile Nanofiber Film

The high theoretical charge-storage capacity and energy density of lithium–sulfur batteries make them a promising next-generation energy-storage system. However, liquid polysulfides are highly soluble in the electrolytes used in lithium–sulfur batteries, which results in irreversible loss of their active materials and rapid capacity degradation. In this study, we adopt the widely applied electrospinning method to fabricate an electrospun polyacrylonitrile film containing non-nanoporous fibers bearing continuous electrolyte tunnels and demonstrate that this serves as an effective separator in lithium–sulfur batteries. This polyacrylonitrile film exhibits high mechanical strength and supports a stable lithium stripping and plating reaction that persists for 1000 h, thereby protecting a lithium-metal electrode. The polyacrylonitrile film also enables a polysulfide cathode to attain high sulfur loadings (4–16 mg cm−2) and superior performance from C/20 to 1C with a long cycle life (200 cycles). The high reaction capability and stability of the polysulfide cathode result from the high polysulfide retention and smooth lithium-ion diffusion of the polyacrylonitrile film, which endows the lithium–sulfur cells with high areal capacities (7.0–8.6 mA·h cm−2) and energy densities (14.7–18.1 mW·h cm−2).

The Importance of the Purification Step and the Characterization of the Products in the Synthesis of Carbon Nanodots

In the synthesis of carbon nanodots (CNDs), the critical step of the purification from the starting materials and unwanted side products is faced. In the exciting race toward new and interesting CNDs, this problem is often underestimated, leading to false properties and erroneous reports. In fact, on many occasions, the properties described for novel CNDs derive from impurities not completely eliminated during the purification process. Dialysis, for instance, is not always helpful, especially if the side products are not soluble in water. In this Perspective, the importance of the purification and characterization steps, in order to obtain solid reports and reliable procedures, is emphasized.

Coinage Metal Bis(amidinate) Complexes as Building Blocks for Self-Assembled One-Dimensional Coordination Polymers

The pyridyl functionalized amidinate [{PyC≡CC(NDipp)₂ }Li(thf)₂ ]_n was used to synthesize a series of bis-amidinate complexes [{PyC≡CC(NDipp)₂ }₂ M₂ ] (M=Cu, Ag, Au) with fully supported metallophilic interactions. These metalloligands were then used as building blocks for the synthesis of one-dimensional heterobimetallic coordination polymers using Zn(hfac)₂ (hfac=hexaflouroacetylacetonate) for self-assembly. Interestingly, the three coordination polymers [{PyC≡CC(NDipp)₂ }₂ M₂ ][Zn(hfac)₂ ] (M=Cu, Ag, Au), exhibit a zig zag shape in the solid state. To achieve linear coordination geometry other connectors such as M'(acac) (M'=Ni, Co) (acac=acetylacetonate) were investigated. The thus obtained compounds [{PyC≡CC(NDipp)₂ }₂ Cu₂ ][M'(acac)₂ ] (M'=Ni, Co) are indeed linear heterobimetallic coordination polymers featuring a metalloligand backbone with fully supported metallophilic interactions.

Online hyphenation of size-exclusion chromatography and pyrolysis-gas chromatography for polymer characterization

An understanding of the composition and molecular heterogeneities of complex industrial polymers forms the basis of gaining control of the physical properties of materials. In the current work we report on the development of an online method to hyphenate liquid polymer chromatography with pyrolysis-GC (Py-GC). The designed workflow included a 10-port valve for fractionation of the first-dimension effluent. Collected fractions were transferred to the Py-GC by means of a second LC pump, a 6-port valve was used to control injection in the Py-GC, allowing the second pump to operate continuously. The optimized large volume injection (LVI) method was capable of analyzing 117 µL of the LC effluent in a 6 min GC separation with a total cycle time of 8.45 min. This resulted in a total run time of 2.1 h while obtaining 15 Py-GC runs over the molar mass separation. The method was demonstrated on various real-life samples including a complex industrial copolymer with a bimodal molar mass distribution. The developed method was used to monitor the relative concentration of 5 different monomers over the molar mass distribution. Furthermore, the molar mass-dependent distribution of a low abundant comonomer (styrene, <1% of total composition) was demonstrated, highlighting the low detection limits and increased resolving power of this approach over e.g. online NMR or IR spectroscopy. The developed method provides a flexible and widely applicable approach to LC-Py-GC hyphenation without having to resort to costly and specialized instrumentation.

1H DOSY analysis of high molecular weight acrylamide-based copolymer electrolytes using an inverse-geometry diffusion probe

Copolymers of [2-(acryloyloxy)ethyl]trimethylammonium chloride (AETAC) and acrylamide (AAm) (AETAC-co-AAm) are polyelectrolytes used as flocculants in wastewater purification. Diffusion-ordered two-dimensional NMR spectroscopy (DOSY) experiments for AETAC-co-AAm samples with Mw ranging from 1.9 to 3.9 million and a polyacrylamide sample with Mw of 1.3 million were carried out in pure D2O and in D2O containing 0.1 or 1 M NaCl using an inverse-geometry diffusion probe system. Projections of the DOSY contour plots onto the diffusion coefficient (D) dimension gave distributions of D for the AETAC and AAm units in the samples. The D values at the maximum point of the distribution (Dp) agreed fairly well with those determined by dynamic light scattering.

Infrared Diffusion-Ordered Spectroscopy Reveals Molecular Size and Structure

Inspired by ideas from NMR, we have developed Infrared Diffusion-Ordered Spectroscopy (IR-DOSY), which simultaneously characterizes molecular structure and size. We rely on the fact that the diffusion coefficient of a molecule is determined by its size through the Stokes-Einstein relation, and achieve sensitivity to the diffusion coefficient by creating a concentration gradient and tracking its equilibration in an IR-frequency resolved manner. Analogous to NMR-DOSY, a two-dimensional IR-DOSY spectrum has IR frequency along one axis and diffusion coefficient (or equivalently, size) along the other, so the chemical structure and the size of a compound are characterized simultaneously. In an IR-DOSY spectrum of a mixture, molecules with different sizes are nicely separated into distinct sets of IR peaks. Extending this idea to higher dimensions, we also perform 3D-IR-DOSY, in which we combine the conformation sensitivity of femtosecond multi-dimensional IR spectroscopy with size sensitivity.

Functionalization of Polylactide with Multiple Tetraphenyethane Inifer Groups to Form PLA Block Copolymers with Vinyl Monomers

In the present contribution, a new strategy for preparing block copolymers of polylactide (PLA), a bio-derived polymer of increasing importance, is described. The method should lead to multiblock copolymers of lactide with vinyl monomers (VM), i.e., monomers that polymerize according to different mechanisms, and is based on the introduction of multiple "inifer" (INItiator/transFER agent) groups into PLA's structure. As an "inifer" group, tetraphenylethane (TPE, known to easily thermally dissociate to radicals) was incorporated into PLA chains using diisocyanate. PLA that contained TPE groups (PLA-PU) was characterized, and its ability to form initiating radicals was demonstrated by ESR measurements. PLA-PU was used as a "macroinifer" for the polymerization of acrylonitrile and styrene upon moderate heating (85 °C) of the PLA-PU in the presence of monomers. The formation of block copolymers PLA/PVM was confirmed by ¹H NMR, DOSY NMR, and FTIR spectroscopies and the SEC method. The prepared copolymers showed only one glass transition in DSC curves with T_g values higher than those of PLA-PU.

Bijels as a Fluid Labyrinth for Drugs: The Effect of Nanoparticles on the Release Kinetics of Ethosuximide and Dimethyl Fumarate

Bijels (bicontinuous interfacially jammed emulsion gels) raised an increasing interest as biomaterials for controlled drug delivery due to their biphasic nature organized in mesoscopic tortuous domains. Two bijel formulations were prepared and explored as delivery systems for both hydrophilic and lipophilic drugs, ethosuximide and dimethyl fumarate. The two bijel-like structures, based on polymerized ε-caprolactone/water, differ in the stabilizing nanoparticle hydroxyapatite (inorganic) and nanogel-based nanoparticles (organic). Diffusion nuclear magnetic resonance spectroscopy has been used to characterize the bijel structure and the transport behavior of the drug molecules confined within the water/organic interconnected domains. A reduced diffusion coefficient is observed for several concentrations of the drugs and both bijel formulations. Moreover, in vitro release profiles also reveal the effect of the microstructure and drug-nanoparticle interactions.

Polymerization, Stimuli-induced Depolymerization, and Precipitation-driven Macrocyclization in a Nitroaldol Reaction System

Dynamic covalent polymers of different topology have been synthesized from an aromatic dialdehyde and α,ω-dinitroalkanes via the nitroaldol reaction. All dinitroalkanes yielded dynamers with the dialdehyde, where the length of the dinitroalkane chain played a vital role in determining the structure of the final products. For longer dinitroalkanes, linear dynamers were produced, where the degree of polymerization reached a plateau at higher feed concentrations. In the reactions involving 1,4-dinitrobutane and 1,5-dinitropentane, specific macrocycles were formed through depolymerization of the linear chains, further driven by precipitation. At lower temperature, the same systemic self-sorting effect was also observed for the 1,6-dinitrohexane-based dynamers. Moreover, the dynamers showed a clear adaptive behavior, displaying depolymerization and rearrangement of the dynamer chains in response to alternative building blocks as external stimuli.

A Molecular Description of Hydrogel Forming Polymers for Cement-Based Printing Paste Applications

This research endeavors to link the physical and chemical characteristics of select polymer hydrogels to differences in printability when used as printing aids in cement-based printing pastes. A variety of experimental probes including differential scanning calorimetry (DSC), NMR-diffusion ordered spectroscopy (DOSY), quasi-elastic neutron scattering (QENS) using neutron backscattering spectroscopy, and X-ray powder diffraction (XRD), along with molecular dynamic simulations, were used. Conjectures based on objective measures of printability and physical and chemical-molecular characteristics of the polymer gels are emerging that should help target printing aid selection and design, and mix formulation. Molecular simulations were shown to link higher hydrogen bond probability and larger radius of gyration to higher viscosity gels. Furthermore, the higher viscosity gels also produced higher elastic properties, as measured by neutron backscattering spectroscopy.

Switch from Anionic Polymerization to Coordinative Chain Transfer Polymerization: A Valuable Strategy to Make Olefin Block Copolymers

Anionic polymerization of butadiene or/and styrene is performed with lithium initiators, functional or not. The polymer chains are subsequently transferred to magnesium. The resulting polymeryl-magnesium compounds were combined with {(Me₂ Si(C₁₃ H₈ )₂ )Nd(μ-BH₄ )[(μ-BH₄ )Li(THF)]}₂ metallocene complex to act as macromolecular chain transfer agents (macroCTAs) in coordinative chain transfer polymerization (CCTP) of ethylene (E) or its copolymerization (CCTcoP) with butadiene (B). Block copolymers were produced for the first time by this switch from anionic polymerization to CCTP. Hard and soft blocks such as PB, polystyrene (PS), poly(styrene-co-butadiene) (SBR) obtained by anionic polymerization and PE or poly(ethylene-co-butadiene) (EBR) produced by CCT(co)P were combined and the corresponding structures were characterized.

Synthesis of N-Methyl-o-phenylenediamine-Bridged Bis(phenolato) Lanthanide Alkoxides and Their Catalytic Performance for the (Co)Polymerization of rac-Butyrolactone and l-Lactide

A series of lanthanide alkoxo complexes supported by ONNO salalen ligands were synthesized and characterized. A one-pot reaction of LH₂ (L = (2-O-C₆H₂-^tBu₂-3,5)CH═N-C₆H₄-N(CH₃)CH₂(2-O-C₆H₂-^tBu₂-3,5)) with LnCp₃(THF) in a 1:1 molar ratio followed by the addition of 1 equiv of ROH (R = Bn, ⁱPr, and CF₃CH₂), afforded the dimeric lanthanide alkoxo complexes [LLn(μ-OCH₂Ph)]₂ [Ln = Lu (1), Yb (2), Sm (3), Nd (4)], [L²Yb(μ-OⁱPr)]₂ (5), and [L²Yb(μ-OCH₂CF₃)]₂ (6) in good isolated yields. All these lanthanide complexes were characterized by elemental analysis and FT-IR spectroscopy. In addition, complex 1 has been characterized by NMR spectroscopy. Single-crystal X-ray diffraction analysis of complexes 1, 2, 5, and 6 showed that these lanthanide alkoxo complexes are dimeric in the solid state. Complexes 1-6 showed good activity toward the homopolymerization of rac-butyrolactone (rac-BBL) to give atactic PHB, and ionic radii of central metals have profound influence on the polymerization. The polymerization behavior of l-lactide (l-LA) initiated by complex 2 was also explored. The kinetic study revealed that the polymerizations of rac-BBL and l-LA initiated by salalen lanthanide akoxide are first order for both the monomer and the initiator concentrations. Furthermore, it was found that complexes 1 and 2 showed good activity in the copolymerization of l-LA and rac-BBL, affording gradient copolymers.

Halogen⋅⋅⋅Halogen and Halogen⋅⋅⋅π Interactions Enabled Reversible Photo-oligomerization of Conjugated Dienones: Visible Light Triggered Single-Crystal-to-Single-Crystal Transformation

The synthesis of reversible oligomer/polymers is fascinating both from the perspective of the fundamental understanding as well as their applications, ranging from biomedical to self-healing smart materials. On the other hand, the reactions that occur in single-crystal-to-single-crystal (SCSC) fashion offer great details of the structure, geometry and stereochemistry of the product. However, SCSC [2+2] oligomerization is rather difficult and rare. Further, till date there are no reports for a reversible [2+2] oligomerization in SCSC fashion. In this work, four halogen-substituted acrylic dienone molecules were deliberately designed and their ability to participate in [2+2] cycloaddition reaction in solid state was studied under visible light. Despite of having the required alignment of double bonds of dienes in all four crystal structures, they were found to exhibit variable reactivities given the differences in their weak intermolecular interactions such as halogen⋅⋅⋅halogen, halogen⋅⋅⋅π and C-H⋅⋅⋅O interactions. Notably, one of these materials exhibits reversible oligomerization in a SCSC manner.

Water-Saturated Ion Gel for Humidity-Independent High Precision Epidermal Ionic Temperature Sensor

Although ion gels are attractive sensing materials for deformable epidermal sensors or implantable devices, their sensing performances are highly affected by environmental humidity change, so that their sensing reliability cannot be secured. This study proposes a new concept of maintaining the high-precision temperature sensing performance of highly deformable ion gel sensors. In this approach, a hydrophobic ion gel sensing layer is kept water-saturated by attaching a hydrogel layer, rather than attempting to completely block water penetration. This study performs experimental and theoretical investigation on water concentration in the ion gel, using the analysis of mass transportation at the interface of the ion gel and the hydrogel. By using the charge relaxation time of the ionic molecules, the temperature sensor is not affected by environmental humidity in the extreme range of humidity (30%-100%). This study demonstrates a highly deformable on-skin temperature sensor which shows the same performance either in water or dry state and while exercising with large strains (ε = 50%).

Pulse-field gradient nuclear magnetic resonance of protein translational diffusion from native to non-native states

Hydrodynamic radii (R_h -values) calculated from diffusion coefficients measured by pulse-field-gradient nuclear magnetic resonance are compared for folded and unfolded proteins. For native globular proteins, the R_h -values increase as a power of 0.35 with molecular size, close to the scaling factor of 0.33 predicted from polymer theory. Unfolded proteins were studied under four sets of conditions: in the absence of denaturants, in the presence of 6 M urea, in 95% dimethyl sulfoxide (DMSO), and in 40% hexafluoroisopropanol (HFIP). Scaling factors under all four unfolding conditions are similar (0.49-0.53) approaching the theoretical value of 0.60 for a fully unfolded random coil. Persistence lengths are also similar, except smaller in 95% DMSO, suggesting that the polypeptides are more disordered on a local scale with this solvent. Three of the proteins in our unfolded set have an asymmetric sequence-distribution of charged residues. While these proteins behave normally in water and 6 M urea, they give atypically low R_h -values in 40% HFIP and 95% DMSO suggesting they are forming electrostatic hairpins, favored by their asymmetric sequence charge distribution and the low dielectric constants of DMSO and HFIP. While diffusion-ordered NMR spectroscopy can separate small molecules, we show a number of factors combine to make protein-sized molecules much more difficult to resolve in mixtures. Finally, we look at the temperature dependence of apparent diffusion coefficients. Small molecules show a linear temperature response, while large proteins show abnormally large apparent diffusion coefficients at high temperatures due to convection, suggesting diffusion reference standards are only useful near 25°C.