Hydrogen-bonding Capability Research Articles

Computational modeling of air pollutants for aquatic risk: Prediction of ecological toxicity and exploring structural characteristics

Assessing the aquatic toxicity originating from air pollutants is essential in sustaining water resources and maintaining the ecosystem's safety. Quantitative structure-activity relationship (QSAR) models provide a computational tool for predicting pollutant toxicity, facilitating the identification/evaluation of the contaminants and identifying responsible structural fragments. One-vs-all (OvA) QSAR is a tailored approach to address multi-class QSAR problems. The study aims to determine five distinct levels of aquatic hazard categories for airborne pollutants using OvA-QSAR modeling containing 254 air contaminants. This QSAR analysis reveals the critical descriptors of air pollutants to target for molecular modification. Various factors, including the selection of relevant mechanistic descriptors, data quality, and outliers, determine the reliability of QSAR models. By employing feature selection and outlier identification approaches, the robustness and accuracy of our QSAR models were significantly increased, leading to more reliable predictions in chemical hazard assessment. The results revealed that models using the Random Forest algorithm performed the best based on the selected descriptors, with internal and external validation accuracy ranging from 71.90% to 97.53% and 76.47%–98.03%, respectively. This study indicated that the aquatic risk of air contaminants might be attributed predominantly to their sp3/sp2 carbon ratio, hydrogen-bond acceptor capability, hydrophilicity/lipophilicity, and van der Waals volumes. These structures can be critical in developing innovative strategies to mitigate or avoid the chemicals' harmful effects. Supporting air quality improvement, this study contributes to the rapid implementation of measures to protect aquatic ecosystems affected by air pollution.

Copper-Mediated -CF(OCF3)(CF2H) Transfer to Organic Electrophiles.

The integration of fluorine into medicinal compounds has become a widely used strategy to improve the biochemical and therapeutic properties of drugs. Inclusion of -CF2H and -OCF3 fluoroalkyl groups has garnered attention due to their bioisosteric properties, enhanced lipophilicity, and potential hydrogen-bonding capability in bioactive substances. In this study, we prepared a series of stable Cu[CF(OCF3)(CF2H)]L n complexes by insertion of commercially available perfluoro(methyl vinyl ether), CF2=CF(OCF3), into Cu-H bonds derived from Stryker's reagent, [CuH(PPh3)]6, using ancillary ligands L. Notably, certain of these complexes effectively transfer the fluoroalkyl group to aroyl chlorides. Through reaction optimization and computational analysis, we identified dimethylsulfoxide as a pivotal coligand, playing a distinctive role in enabling the fluoroalkylation of a range of aroyl chlorides and aryl iodides. The latter also benefits from addition of CuBr to abstract PPh3, generating solvent-stabilized Cu[CF(OCF3)(CF2H)]. These methodologies allow for the introduction of geminal -OCF3 and -CF2H groups in a single transformation.

Relationship between the polyurea underlayer structure and PEG surface coverage

Increasing the surface coverage of antifouling materials is essential to enhance the performance of antifouling coatings. In this study, polyurea thin-film underlayers were fabricated by co-depositing difunctional isocyanates with difunctional or trifunctional amines. The relationships among the underlayer structure, terminal group density before polyethylene glycol (PEG) termination, and PEG surface coverage were investigated. The results showed that employing trifunctional amines in the underlayer led to increased terminal group density before PEG termination. Moreover, the reduced hydrogen-bonding capability between the polyurea molecules contributes to enhanced PEG surface coverage.

In-Depth Understanding of the Effect of the Distribution of Substituents on the Morphology and Physical Properties of Ethylcellulose: Molecular Dynamics Simulations Insights.

Ethylcellulose (EC) is a crucial cellulose derivative with widespread applications, particularly in the pharmaceutical industry, where precise property adjustments through chemical modification are imperative. The degree of substitution (DS) and the localization of substituents along the cellulose chains are pivotal factors in this process. However, the impact of the substituent location within the repeating unit of EC remains unexplored. To address this gap, we conducted molecular dynamics simulations on amorphous EC, comparing randomly and uniformly substituted ethyl groups in the repeating units. This comprehensive study of pairwise interactions revealed significant differences in intramolecular and intermolecular hydrogen-bonding capabilities, depending on whether the hydroxyl groups were substituted at C2, C3, or C6. While our simulations demonstrated that substituent localization in the repeating unit influenced the density, number of hydrogen bonds, and conformations, the DS emerged as the dominant determinant. This insight led us to propose and validate a hypothesis: a straightforward linear function using the properties of uniform models and molar fractions can predict the properties of randomly substituted EC with a given DS. This innovative approach is anticipated to contribute to the selection of cellulose derivatives with desirable properties for the pharmaceutical industry and new applications in other fields.

Development of Mefloquine-Based Bifunctional Secondary Amine Organocatalysts for Enantioselective Michael and Friedel-Crafts Reactions.

The chiral framework based on 11-aminomefloquine has been utilized for the first time to construct bifunctional organocatalysts. These catalysts demonstrate high enantioselectivity in both Michael additions and Friedel-Crafts reactions across a variety of substrates, achieving up to >99% ee. The distinctive feature is the incorporation of a secondary amine group, offering unique tight hydrogen-bonding capabilities in the protonated state, as supported by DFT computation. The diversity of these organocatalysts suggests their broad applicability across multiple reaction classes.

Spectrofluorometric investigations on the solvent effects on the photocyclization reaction of diclofenac

The solvent effects on the photochemical conversion rate of the photosensitizing drug diclofenac (DCF) were investigated using steady-state fluorescence spectroscopy. The spectral information obtained for the photochemical reaction of DCF in a set of neat solvents demonstrates that the photoconversion reaction rate of DCF is not only medium polarity dependent but also hydrogen-bonding dependent. The solvent effects were qualitatively and quantitatively assessed employing various solvatochromic models, including multi-parameter linear regression analysis (MLRA). Interestingly, the MLRA results (R = 0.99) revealed that the photoconversion rate increases with increasing solvent polarizability (π*) and H-bond donor capability (α), whereas the rate decreases with increasing hydrogen-bond acceptor capability (β). However, predominant effect of the solvent acidity compared to basicity and polarizability was observed. A hypothesis rationalizing the effects of H-bonding and medium polarity on DCF photoconversion reaction is presented and discussed.

Elucidating the Mechanisms of R248Q Mutation-Enhanced p53 Aggregation and Its Inhibition by Resveratrol.

Aggregation of p53 mutants can result in loss-of-function, gain-of-function, and dominant-negative effects that contribute to tumor growth. Revealing the mechanisms underlying mutation-enhanced p53 aggregation and dissecting how small molecule inhibitors prevent the conversion of p53 into aggregation-primed conformations are fundamentally important for the development of novel therapeutics for p53 aggregation-associated cancers. A recent experimental study shows that resveratrol (RSV) has an inhibitory effect on the aggregation of hot-spot R248Q mutant of the p53 core domain (p53C), while pterostilbene (PT) exhibits a relatively poor inhibitory efficacy. However, the conformational properties of the R248Q mutant leading to its enhanced aggregation propensity and the inhibitory mechanism of RSV against p53C aggregation are not well understood. Herein, we performed extensive all-atom molecular dynamics simulations on R248Q p53C in the absence and presence of RSV/PT, as well as wild-type (WT) p53C. Our simulations reveal that loop L3, where the mutation resides, remains compact in WT p53C, while it becomes extended in the R248Q mutant. The extension of loop L3 weakens the interactions between loop L3 and two crucial aggregation-prone regions (APRs) of p53C, leading to impaired interactions within the APRs and their structural destabilization as well as p53C. The destabilized APRs in the R248Q mutant are more exposed than in WT p53C, which is conducive to p53C aggregation. RSV has a higher preference to bind to R248Q p53C than PT. This binding not only stabilizes loop L3 of R248Q mutant to its WT-like conformation, preventing L3-extension-caused APRs' destabilization but also reduces APRs' solvent exposure, thereby inhibiting R248Q p53C aggregation. However, PT exhibits a lower hydrogen-bonding capability and a higher self-association propensity, which would lead to a reduced p53C binding and a weakened inhibitory effect on R248Q mutant aggregation. Our study provides mechanistic insights into the R248Q mutation-enhanced aggregation propensity and RSV's potent inhibition against R248Q p53C aggregation.

Structural insight into why S-linked glycosylation cannot adequately mimic the role of natural O-glycosylation

There is an increasing interest in using S-glycosylation as a replacement for the more commonly occurring O-glycosylation, aiming to enhance the resistance of glycans against chemical hydrolysis and enzymatic degradation. However, previous studies have demonstrated that these two types of glycosylation exert distinct effects on protein properties and functions. In order to elucidate the structural basis behind the observed differences, we conducted a systematic and comparative analysis of 6 differently glycosylated forms of a model glycoprotein, CBM, using NMR spectroscopy and molecular dynamic simulations. Our findings revealed that the different stabilizing effects of S- and O-glycosylation could be attributed to altered hydrogen-bonding capability between the glycan and the polypeptide chain, and their diverse impacts on binding affinity could be elucidated by examining the interactions and motion dynamics of glycans in substrate-bound states. Overall, this study underscores the pivotal role of the glycosidic linkage in shaping the function of glycosylation and advises caution when switching glycosylation types in protein glycoengineering.

Zwitterionic Polymeric Sulfur Ylides with Minimal Charge Separation Open a New Generation of Antifouling and Bactericidal Materials.

Zwitterionic polymers are widely employed hydrophilic building blocks for antifouling coatings with numerous applications across a wide range of fields, including but not limited to biomedical science, drug delivery and nanotechnology. Zwitterionic polymers are considered as an attractive alternative to polyethylene glycol because of their biocompatibility and effectiveness to preventformation of biofilms. To this end, zwitterionic polymers are classified in two categories, namely polybetaines and polyampholytes. Yet, despite a fundamental interest to drive the development of new antifouling materials, the chemical composition of zwitterionic polymer remains severely limited. Here, we show that poly(sulfur ylides) thatbelongto the largely overlooked class of poly(ylides),effectively prevent theformation of biofilms from pathogenic bacteria. While surface energy analysis reveals strong hydrogen-bond acceptor capabilities of poly(sulfur ylide), membrane damage of pathogenic bacteria induced by poly(sulfur ylides) indicates toxicity towards bacteria while not affecting eucaryotic cells. Such synergistic effect of poly(sulfur ylides) offers distinct advantages over polyethylene glycol when designing new antifouling materials. We expect that our findings will pave the way for the development of a range of ylide-based materials with antifouling properties that have yet to be explored, opening up new directions at the interface of chemistry, biology, and material science.

Encapsulation of hop (Humulus lupulus L.) essential oil for controlled release in the non-alcoholic beverage application

In order to increase the stability of hop ( Humulus lupulus L.) essential oil (HEO) and diversify its application into hot beverages, CAPSUL®, modified food starch, was used as the wall material to encapsulate HEO at the mass ratio of 2:1 through spray drying under 180 °C. The resultant microcapsules were applied to the non-alcoholic hop tea for the first time and their release kinetics in this matrix were analyzed by gas chromatography-mass spectrometry (GC-MS). Results showed that the reconstituted HEO emulsion possessed fine droplet size (3.295 μm) and high zeta potential (−22.50 mV). The resultant HEO microcapsules exhibited low moisture content (1.249%), suitable bulk density (0.2934 g/mL), good swelling capacity (2.235 g/g dry solids), low color difference (6.310), desirable morphological characteristics, high encapsulation efficiency (92.02–95.45%) and high flavor retention (57.13–71.15%). Each target aroma compound had its specific release behavior and mechanism from HEO microcapsules, among which β -myrcene and methyl octanoate showed the highest and lowest cumulative release respectively. This might be associated with their different volatilities, polarities, function groups and molecular sizes, or their varying hydrogen-bond formation capability at the entrance of starch helix. Most importantly, HEO microcapsules showed significant aroma increasing and stabilizing effects on the hop tea product during storage. These ideal characteristics of HEO microcapsules demonstrated the great potential of diverse essential oil microcapsules as the promising flavoring agent in a variety of hot beverage matrices. • Overall desirable physicochemical properties were observed in HEO microcapsules. • HEO microcapsule showed satisfactory encapsulation efficiency and flavor retention. • Each target aroma compound had a specific release mechanism during 40 °C of storage. • HEO microcapsule was an effective flavoring agent in the hot beverage matrix.

Mobile-Phase Contributions to Organic-Solvent Excess Adsorption and Surface Diffusion in Reversed-Phase Liquid Chromatography.

Fast transport of retained analytes in reversed-phase liquid chromatography occurs through surface diffusion in the organic-solvent (OS)-enriched interfacial "ditch" region between the hydrophobic stationary phase and the water (W)-OS mobile phase. Through molecular dynamics simulations that recover the OS excess adsorption isotherms of a typical C18-stationary phase for methanol and acetonitrile, we explore the relation between OS properties, OS excess adsorption, and surface diffusion. The emerging molecular-level picture attributes the mobile-phase contribution to surface diffusion to the hydrogen-bond capability and the eluting power of the OS. The higher affinity of methanol for the formation of W-OS hydrogen bonds at the soft, hydrophobic surface presented by the bonded-phase (C18) chains reduces the OS excess and the related viscosity drop in the ditch. The lower eluting power of methanol, however, translates to increased bonded-phase contacts for analytes, which can increase their mobility gain from surface diffusion above the gain observed with acetonitrile.

Hydrogen Evolution Reaction By Metal-Free Poly-Neutral Red Electrocatalyst

While electric power supply by renewable sources such as solar and wind has become viable for their significant cost reduction, its intermittency demands urgent development of large scale storage technologies. Although conversion of electrical energy into storable hydrogen via electrolysis of water is ideal, noble metals and their oxides are used as electrocatalysts for their activities and stabilities. Alternative electrocatalysts out of abundant elements are needed for sustainable technological development.Recently, some metal-free organic conductive polymers with hydrogen-bonding capabilities were found to exhibit high electrocatalytic activities towards hydrogen evolution reaction (HER) [1,2]. We have succeeded electropolymerization of neutral red (NR) resulting in a formation of conductive poly-NR (PNR) that shows a relatively high HER catalytic activity [3]. PNR possesses hydrogen-bonding N atoms as annelated in the phenazine aromatic system as well as those in the amino substituents. Electrochemical analysis combined with in situ spectroscopy as well as DFT calculation was performed to clarify the mechanism and kinetics of HER electrocatalysis by PNR.This films of PNR were obtained by electropolymerization on F-doped SnO2 coated conductive glass (FTO, Asahi Glass) and SIGRATHERM® GFA5 Carbon felt with potential cycling between -0.2 and 1.2 V (vs. Ag/AgCl) at 50 mV s-1 for 50 times in a 5 mM NR - 0.1 M H2SO4 aqueous solution under N2. Polyaniline (PANI) was also obtained by the same method for comparison. The HER catalysis was evaluated by linear sweep voltammetry (LSV) in a 1 M trifluoromethanesulfonic acid (TfOH) under N2. The film samples were characterized by Fourier transform infrared spectroscopy (FT-IR), UV-visible spectroscopy. In-situ UV-visible spectroelectrochemical monitoring of the reaction intermediate was carried out to determine the rate of HER.PNR undergoes a pseudo-reversible reduction that shifts -61.8 mV/pH under acidic conditions and HER takes off right at this point (Fig. 1, a). Coupling of the same number of protons / electrons is expected as the electrochemical stoichometry from the observed Nernstian relationship, namely, resulting in a singly reduced PNR-H or doubly reduced PNR-H2 as depicted in Fig. 1 b. Protonation of N atoms was reasonably expected and also supported by the DFT calculation. The hydrogen atoms stabilized in the reaction intermediate can be associated to release H2 (Tafel mechanism) to complete the cycle of electrocatalysis of HER.Reduction of PNR in fact is associated with a color change. The broad reddish absorption of PNR peaking at around 500 nm attenuates to change the color to a pale yellow by constantly applying -0.15 V vs. RHE to produce PNR-H and/or PNR-H2 state as shown in Fig. 1c. Gradual recovery of the original red PNR was observed under open circuit under N2, associated with the H2 release. Thus, the rate of the spectral change is analyzed to determine the rate of the Tafel process. Pseudo-first order reaction rate law can be applied as proton is abundant and its concentration is constant, so that the rate of HER (r H2) is simply described as the rate of consumption of PNR-H and/or PNR-H2 as, r H2=-dC PNR-H2/dt =-kt (1)The ratio of PNR-H and PNR-H2 as compared to their initial amount (x PNR-red) was defined from the absorbance at 545 nm before and after reduction as, x PNR-red = C PNR-red/C 0-PNR-red = exp (-kt) (2)Good fitting of the experimental data was obtained to yield a pseudo-first order reaction rate constant of 9.98×10-4 s-1 for this rate-limiting step.

Multifunctional Charge and Hydrogen-Bond Effects of Second-Sphere Imidazolium Pendants Promote Capture and Electrochemical Reduction of CO2 in Water Catalyzed by Iron Porphyrins.

Microenvironments tailored by multifunctional secondary coordination sphere groups can enhance catalytic performance at primary metal active sites in natural systems. Here, we capture this biological concept in synthetic systems by developing a family of iron porphyrins decorated with imidazolium (im) pendants for the electrochemical CO2 reduction reaction (CO2 RR), which promotes multiple synergistic effects to enhance CO2 RR and enables the disentangling of second-sphere contributions that stem from each type of interaction. Fe-ortho-im(H), which poises imidazolium units featuring both positive charge and hydrogen-bond capabilities proximal to the active iron center, increases CO2 binding affinity by 25-fold and CO2 RR activity by 2000-fold relative to the parent Fe tetraphenylporphyrin (Fe-TPP). Comparison with monofunctional analogs reveals that through-space charge effects have a greater impact on catalytic CO2 RR performance compared to hydrogen bonding in this context.

Effect of polar molecular organic solvents on non-aqueous solvent extraction of rare-earth elements

The extraction and separation of five different rare-earth elements, La, Nd, Eu, Dy and Yb, from an aqueous chloride solution and from different chloride non-aqueous solutions using the solvating extractant Cyanex 923 was investigated. As previous studies had demonstrated the potential of non-aqueous solvent extraction (NASX) to refine rare earths from ethylene glycol, structural analogues of ethylene glycol (1,2-propanediol and 1,3-propanediol) and to other polar organic solvents (triethylene glycol, dimethylsulfoxide, methanol, N,N-dimethylformamide and N,N-dimethylacetamide) were studied. The extraction data were interpreted in terms of different solvent properties: dielectric constant, Gutmann donor number, molecular structure and hydrogen-bonding capabilities. Remarkable differences were observed between the extraction behaviour from ethylene glycol, 1,2-propanediol and 1,3-propanediol. Therefore, these solvent systems were further studied to elucidate the speciation of the rare-earth elements by optical absorption and luminescence spectroscopy. Based on these studies, both contact-ion-pair formation and solvation strength are assumed to play an important role in the extraction of rare earths by Cyanex 923 from different polar organic solvents. The differences in extraction behaviour can be exploited to fine-tune the separation of rare earths.

All-Atom Molecular Dynamics Simulations of Polyethylene Glycol (PEG) and LIMP-2 Reveal That PEG Penetrates Deep into the Proposed CD36 Cholesterol-Transport Tunnel.

Polyethylene glycol (PEG) is the most prominent clinically administered synthetic polymer. For example, over 300 million people have been administered PEGylated liposome vaccines for SARS-CoV-2. PEG is used in mammals because it has low affinity for most proteins and vice versa. However, this makes it difficult to study the few interactions with proteins that PEG has. On the atomistic level, there are two PEG-protein structures: (1) PEG-LIMP-2 and (2) PEG-αPEG. In the first structure, two monomers of a 1.5 kDa PEG polymer (PEG2) had electron density deep in the postulated cholesterol transport tunnel of LIMP-2, a lysosomal cholesterol transport protein and member of the CD36 super family of proteins. It is unclear how PEG entered this tunnel. In the second structure, PEG wrapped around a surface-exposed tryptophan on its antibody. Since tryptophan is a rare residue, it is unclear if this PEG-Trp interaction is ubiquitous. To gain deeper mechanistic insight into PEG–protein interactions, we surrounded the LIMP-2 apo structure with 13 PEG chains of 10 monomers each (PEG10), water, and KCl and simulated the system using NAMD. One of the 13 chains penetrated LIMP-2 and came within 3 Å of PEG2. This was possible because of the strong hydrogen bonding between multiple oxygens along PEG10 and Arg192 but, most importantly, the clamping of the tertiary structure on PEG10. Clamping stabilized the movements of PEG10, and the leading oxygen of PEG10 was able to penetrate LIMP-2 and head toward to the position occupied by PEG2. Phe383 appears to act as a gate for objects to move through this cavity, which continues to the basal/membrane side of LIMP-2. Of all residues, PEG10 molecules had the most sustained interactions with lysine and arginine because of their strong hydrogen-bonding capabilities. These results show that the oxygens of PEG bind residues with high hydrogen bonding capabilities. However, the PEG–protein interaction is likely to be transient unless groups of resides can clamp down on PEG or a cavity that at least part of the PEG chain can enter is in close proximity to lower PEG’s entropy.

A Catalogue of Orthogonal Complementary Ligand Pairings for Palladium(II) Complexes.

Molecular recognition is a form of information transfer, seen in the base pairing in DNA which is derived from the identity (acceptor or donor) and number of hydrogen bond sites within each base. Here we report bis‐ligand palladium(II) complexes that exhibit similar complementarity. Pd(II) has square planar four‐coordinate geometry, giving control over ligand orientation and denticity. Pairings were developed using ligand denticity (3 : 1 or 2 : 2), and hydrogen bond capability (AA:DD or AD:DA) or lack thereof. Five pairings were investigated, with two sets of four being found fully orthogonal. The two 3 : 1 pairings exhibited limited ligand exchange. The extent of this exchange varied dependant on solvent from 2 : 1 (desired to undesired) to 6 : 1. A reliable and varied set of ligand pairs have therefore been developed for bis‐ligand coordination sphere engineering in pursuit of sorting for complex molecular architectures and molecular‐level information storage and transfer events.

Novel insights into the mechanism for protic solvent promoting Pd/C-catalyzed hydrodechlorination of chlorinated organic compounds

• Protic solvents promoted catalytic HDC of 4-CBP with Et 3 N over Pd/C catalyst. • HDC rate of 4-CBP increased with increase of water content in mixed solvent systems. • Mechanism for protic solvents promoting Pd/C-catalyzed HDC reactions was elucidated. • Protic solvents participated in Pd/C-catalyzed HDC and hydrogenation reactions. Solvent effects in liquid-phase hydrodechlorination (HDC) of chlorinated organic compounds (COCs) over Pd/C catalyst were systematically studied. For the HDC of 4-chlorobiphenyl (4-CBP) with triethylamine (Et 3 N), Pd/C exhibited much higher catalytic activity in protic solvents than that in aprotic polar and non-polar solvents, and a clear correlation between the HDC rate and polarity of protic solvents was observed. Moreover, water promoted Pd/C-catalyzed HDC of 4-CBP in homogeneous alcohol-water solvents and biphasic organic-water solvents with Et 3 N, and the HDC rate of 4-CBP increased with the increase of water content in the above solvent systems. Catalyst characterization (FT-IR and XRD) combined with solvent parameters and isotope labelling analysis were introduced to explain in-depth the solvent effects in the HDC of 4-CBP with Et 3 N. It was found that protic solvents would transfer active hydrogen atom (H*) via hydrogen bonding network or exchange their hydroxyl hydrogen with H*, which was beneficial to the stabilization of H* and interface HDC reaction. Thus, the higher HDC rate was achieved in solvent systems contained protic solvents with higher hydrogen-bond donor capability ( α ) values. On the other hand, non-polar and polar aprotic solvents had a negative effect on H* and mass transfer, and thus suppressed interface HDC reaction. Similar solvent effects were observed in Pd/C-catalyzed hydrogenation of unsaturated bonds-containing groups (nitryl group, carbonyl group, and carbon-carbon double bond). The results presented here would provide vital guidance for the rational selection of solvent systems for Pd/C-catalyzed HDC of COCs and hydrogenation of unsaturated bonds-containing groups.

Ion permeation, selectivity, and electronic polarization in fluoride channels

Fluoride channels (Flucs) export toxic F− from the cytoplasm. Crystallography and mutagenesis have identified several conserved residues crucial for fluoride transport, but the permeation mechanism at the molecular level has remained elusive. Herein, we have applied constant-pH molecular dynamics and free-energy-sampling methods to investigate fluoride permeation through a Fluc protein from Escherichia coli. We find that fluoride is facile to permeate in its charged form, i.e., F−, by traversing through a non-bonded network. The extraordinary F− selectivity is gained by the hydrogen-bonding capability of the central binding site and the Coulombic filter at the channel entrance. The F− permeation rate calculated using an electronically polarizable force field is significantly more accurate compared with the experimental value than that calculated using a more standard additive force field, suggesting an essential role for electronic polarization in the F−–Fluc interactions.

Enhancement of charge-assisted hydrogen bond capabilities due to O-alkylation proximity in alkoxy cationic polythiophenes: solution- and solid-state evidence via EPR, AFM and surface free energy.

Despite the array of applications for cationic polythiophenes (CPTs), there is still a need for structure-function guidelines and mechanistic understanding of their solution- and solid-state properties. This work presents a solution- and solid-state investigation of the effect of O-alkylation proximity on the hydrogen bonding (H-bonding) capabilities of alkoxy-CPTs, based on comparing an imidazolium alkoxy CPT with strong cation-pi, pi+ and positive charge-assisted hydrogen bonding (+CAHB) capabilities (PIMa), with two isothiouronium alkoxy CPTs with two-point +CAHB capabilities (PT1 & PT2), which have short and long alkoxy side chains, respectively. Our results show that a closer proximity of O-alkylation strengthens the +CAHB capabilities of PT1: in aqueous solutions, PT2 aggregates have a stronger interaction with cationic EPR spin probes than aggregates of PIMa and PT1, which in turn show a similar extent of repulsion towards the cationic spin probes. In solid-state, atomic force microscopy (AFM) shows that PIMa generates dendritic structures onto mica, with features of diffusion-limited aggregation (DLA), indicating strong interactions with the anionic substrate due to a high configurational entropy during spreading, regardless of being drop-casted from water or 1,4-dioxane-water (W-DI), despite the latter disturbing H-bonding due to selective solvation. PT1 is also capable of generating dendritic structures resembling ballistic aggregation (BA). However, this occurs only when casting from water, since W-DI generates island-like aggregates resembling attachment limited aggregation (ALA), which is the morphology generated by PT2 regardless of the solvent. Finally, spin-coated films of PIMa and PT1 show similar dispersivity of the surface free energy (SFE), which in turn is larger than that in PT2 films, which are also more affected when casted from W-DI, presenting much larger decreases of dispersivity. These results constitute a novel empirical structure-function guideline that could be useful for optimal design and/or processing of alkoxy CPTs. For example, dendritic patterns have recently gained attention since the colloidal droplet drying is related to engineering applications including inkjet printing, biosensing, and functional material design, while the SFE is relevant for opto- and bio-electronic applications of conjugated polyelectrolytes (CPEs). This information could also be useful when analyzing previous results obtained from alkoxy CPTs with different side chain lengths.

The effects of sugars and sugar alcohols on the pasting and granular swelling of wheat starch

Replacing added sugars with low-glycemic, natural, and/or low-calorie sweeteners in baked goods without altering texture or quality traits is challenging. Starch thermal properties (gelatinization, pasting/swelling, retrogradation) determine the final set structure of baked goods and are altered by many variables, including sweetener type and concentration. This study investigated how different sugars and sugar alcohols known to alter starch gelatinization temperatures also affected the pasting behavior and granule swelling of wheat starch. Wheat starch slurries (10% w/v) with increasing concentrations (0–4.0 M and saturated) of sugars and sugar alcohols (glucose, fructose, sorbitol, maltose, isomaltulose, isomalt, and sucrose) were studied. Rapid Visco Analyser (RVA) profiles were generated to observe sweetener effects on starch pasting behavior. Granule particle size measurements were taken at various timepoints during RVA analysis to document sweetener effects on granular swelling. Sweetener type and concentration significantly affected starch pasting and granule swelling. Generally, disaccharides increased starch pasting temperatures more than monosaccharides, while monosaccharides increased peak and final viscosities of starch solutions more than other sweeteners at the same concentrations. Isomers had different effects on starch pasting temperatures and paste properties, as did sugar alcohols compared to their unreduced sugar counterparts. Indicators of intermolecular hydrogen bond capability of sweeteners strongly correlated to many starch pasting properties. Sorbitol, isomaltulose, and isomalt had the most similar effects on starch pasting properties compared to sucrose, on a percent solids basis, and could be useful starting points for reformulation efforts in reduced-sugar products for which control of starch pasting behavior is important.