Polyphenolic truxillic acid crosslinked sodium alginate film with notable antimicrobial and biodegradable properties for food packaging.

This work demonstrated an innovative antimicrobial and biodegradable food packaging film CBDA-10-SA which was prepared by crosslinking a natural polyphenolic truxillic acid (cyclobutane-dicarboxylic acid, CBDA-10) and sodium alginate (SA). The CBDA-10-SA film exhibited improved tensile strength (148 MPa) and UV shielding capabilities. The maximum thermal decomposition temperature was achieved of 249 °C. Compared to SA film, CBDA-10-SA showed increased antibacterial activities. In food packaging test, the CBDA-10-SA inhibited the rapid growth of potential of hydrogen (pH) value, slowed down the weight loss, reduced total plate count (TPC) value of pork, and delayed the spoilage process of pork. Notably, CBDA-10-SA displayed remarkable degradability in soil, with 60 % degrading in four weeks. In this study, CBDA-10-SA showed enhanced physicochemical and mechanical properties compared to traditional SA film. Those improvements make it anticipated to be used in not only food packaging but also mechanical, pharmaceutical, and agricultural fields.

Stability Indicating Method Development and Validation for the Estimation of Bempedoic Acid by RP-HPLC.

BACKGROUND: Bempedoic acid (BEM) belongs to a category of drugs known as Adenosine triphosphate-citrate Lyase (ACL) inhibitors. It is a prodrug with intracellular activation that is administered orally. Bempedoic acid is used to treat existing atherosclerotic cardiovascular diseases, mainly hypercholesterolemia. METHODS: For the stability-indicating assay, the HPLC method was employed using a Kromasil 100-5-C8 column (100 mm × 4.6 mm), a UV detector set at 230 nm, and a mobile phase comprising a 70:30 v/v mixture of acetonitrile and 0.1% Orthophosphoric Acid (OPA) buffer. The method was operated at an ambient temperature with a flow rate of 1 mL/min. The method developed has been statistically validated according to ICH guidelines. RESULTS: The stability-indicating method was executed using a Kromasil 100-5-C8 (100 mm × 4.6 mm) column at a 1.0 mL/min flow rate. A mixture of acetonitrile and 0.1% Orthophosphoric Acid (OPA) buffer in a 70:30 v/v ratio made up the mobile phase. BEM's retention times were discovered to be 1.88 minutes each. The temperature was kept at room temperature. 234 nm was the ideal wavelength for BEM. According to ICH criteria, the approach developed has undergone statistical validation. BEM's % RSD was discovered to be 0.6, respectively. For BEM, the % recovery was determined to be 100.0%. Regression models for bempedoic acid yielded LoD and LoQ values of 3.3 and 10.1 g/mL, respectively. The method showed good reproducibility and recovery with a % RSD less than 2. Studies on forced degradation confirmed the method's capacity to indicate stability in the presence of stress conditions, such as acid, basic, peroxide, UV, heat, and humidity. Both the retention times and the run time were shortened. CONCLUSION: In accordance with ICH Q2 (R1) guidelines, this method was successfully tested with HPLC to confirm the chemical structures of newly produced degradation products of bempedoic acid.

New insights into the anti-inflammatory and anti-melanoma mechanisms of action of azelaic acid and other Fusarium solani metabolites via in vitro and in silico studies.

Metabolites exploration of the ethyl acetate extract of Fusarium solani culture broth that was isolated from Euphorbia tirucalli root afforded five compounds; 4-hydroxybenzaldehyde (1), 4-hydroxybenzoic acid (2), tyrosol (3), azelaic acid (4), malic acid (5), and fusaric acid (6). Fungal extract as well as its metabolites were evaluated for their anti-inflammatory and anti-hyperpigmentation potential via in vitro cyclooxygenases and tyrosinase inhibition assays, respectively. Azelaic acid (4) exhibited powerful and selective COX-2 inhibition followed by fusaric acid (6) with IC50 values (2.21 ± 0.06 and 4.81 ± 0.14 µM, respectively). As well, azelaic acid (4) had the most impressive tyrosinase inhibitory effect with IC50 value of 8.75 ± 0.18 µM compared to kojic acid (IC50 = 9.27 ± 0.19 µM). Exclusive computational studies of azelaic acid and fusaric acid with COX-2 were in good accord with the in vitro results. Interestingly, this is the first time to investigate and report the potential of compounds 3-6 to inhibit cyclooxygenase enzymes. One of the most invasive forms of skin cancer is melanoma, a molecular docking study using a set of enzymes related to melanoma suggested pirin to be therapeutic target for azelaic acid and fusaric acid as a plausible mechanism for their anti-melanoma activity.

Analytical method development and validation for simultaneous estimation of Bempedoic acid and Ezetimibe in pure and its pharmaceutical dosage form by RP-HPLC.

A simple, accurate and precise method was developed for the simultaneous estimation of the bempedoic acid and ezetimibe in pure and tablet dosage form. The developed method was validated as per International Conference on Harmonization guidelines. The chromatographic separation was achieved isocratically on a Waters- C18, 250 × 4.6 mm, 5 µm column. Mobile phase containing K2HPO4-methanol in the ratio 60:40 in buffer at pH 4.3 was pumped through column at a flow rate of 1.0 ml/min. The temperature was maintained at 25°C. The optimized wavelength selected was 242 nm. The separation of bempedoic acid and ezetimibe showed retention times of 3.090 and 4.268 min respectively. The RSD values of the bempedoic acid and ezetimibe were 0.34 and 0.08 respectively. The accuracy of method was determined at three levels (50,100 and 150%). The percentage recovery was obtained as 100.0 and 100.0% for bempedoic acid and ezetimibe, respectively. The limits of determination and quantitation obtained from regression equations of bempedoic acid and ezetimibe were 1.065, 3.550 and 0.203, 0.677, respectively. The regression equation of bempedoic acid is y = 20,795x + 24,168, and it is y = 6,885.7x + 11,000 for ezetimibe. The retention times were decreased and the run time was decreased, so that the method developed is simple and economical that can be adopted for regular quality control tests in industry.

Hair Follicle-Targeted Delivery of Azelaic Acid Micro/Nanocrystals Promote the Treatment of Acne Vulgaris.

Purpose: Acne vulgaris is a chronic inflammatory skin disorder centered on hair follicles, making hair follicle-targeted delivery of anti-acne drugs a promising option for acne treatment. However, current researches have only focused on the delivering to healthy hair follicles, which are intrinsically different from pathologically clogged hair follicles in acne vulgaris. Patients and Methods: Azelaic acid (AZA) micro/nanocrystals with different particle sizes were prepared by wet media milling or high-pressure homogenization. An experiment on AZA micro/nanocrystals delivering to healthy hair follicles was carried out, with and without the use of physical enhancement techniques. More importantly, it innovatively designed an experiment, which could reveal the ability of AZA micro/nanocrystals to penetrate the constructed clogged hair follicles. The anti-inflammatory and antibacterial effects of AZA micro/nanocrystals were evaluated in vitro using a RAW264.7 cell model stimulated by lipopolysaccharide and a Cutibacterium acnes model. Finally, both the anti-acne effects and skin safety of AZA micro/nanocrystals and commercial products were compared in vivo. Results: In comparison to commercial products, 200 nm and 500 nm AZA micro/nanocrystals exhibited an increased capacity to target hair follicles. In the combination group of AZA micro/nanocrystals and ultrasound, the ability to penetrate hair follicles was further remarkably enhanced (ER value up to 9.6). However, toward the clogged hair follicles, AZA micro/nanocrystals cannot easily penetrate into by themselves. Only with the help of 1% salicylic acid, AZA micro/nanocrystals had a great potential to penetrate clogged hair follicle. It was also shown that AZA micro/nanocrystals had anti-inflammatory and antibacterial effects by inhibiting pro-inflammatory factors and Cutibacterium acnes. Compared with commercial products, the combination of AZA micro/nanocrystals and ultrasound exhibited an obvious advantage in both skin safety and in vivo anti-acne therapeutic efficacy. Conclusion: Hair follicle-targeted delivery of AZA micro/nanocrystals provided a satisfactory alternative in promoting the treatment of acne vulgaris.

Functional and structural characterization of an IclR family transcription factor for the development of dicarboxylic acid biosensors.

Prokaryotic transcription factors (TFs) regulate gene expression in response to small molecules, thus representing promising candidates as versatile small molecule-detecting biosensors valuable for synthetic biology applications. The engineering of such biosensors requires thorough in vitro and in vivo characterization of TF ligand response as well as detailed molecular structure information. In this work, we functionally and structurally characterize the Pca regulon regulatory protein (PcaR) transcription factor belonging to the IclR transcription factor family. Here, we present in vitro functional analysis of the ligand profile of PcaR and the construction of genetic circuits for the characterization of PcaR as an in vivo biosensor in the model eukaryote Saccharomyces cerevisiae. We report the crystal structures of PcaR in the apo state and in complex with one of its ligands, succinate, which suggests the mechanism of dicarboxylic acid recognition by this transcription factor. This work contributes key structural and functional insights enabling the engineering of PcaR for dicarboxylic acid biosensors, in addition to providing more insights into the IclR family of regulators.

The effect of carbon chain length of cross-linking agent on the functionality of carrier- free immobilized Thermomyces lanuginosa lipase particles.

The cross-linked enzyme (CLEs) of Thermomyces lanuginosa lipase (TLL) was prepared in an isocyanide-based multi-component reactions (ICMRs) platform by applying three di-acidic cross-linkers to unveil more factors contributing to the functional properties of CLEs. The linkers were 1,11-undecanedicarboxylic acid, azelaic acid, and adipic acid with 11, 7, and 4 carbon lengths, respectively, providing a proper tool to investigate the effect of linker length on the activity, stability, and selectivity of the resulting CLEs. The immobilization yields of 60-90 % and the specific activities of 168, 88.4 and 49 U/mg were obtained for the CLEs of 1,11-undecanedicarboxylic acid, azelaic acid, adipic acid, respectively. The lower activity of azelaic and adipic acid-mediated CLEs compared to the soluble TLL (110 U/mg) was explained by in silico calculations. The results revealed that as opposed to 1,11-undecanedicarboxylic acid, both linkers tended to penetrate the enzyme active site, thus resulting in a major inhibitory effect on the enzyme functionality. The thermal and co-solvent stability of the immobilized derivatives improved compared to those of free TLL. The selectivity of CLEs was also examined by catalytic release of main omega-3 fatty acids from fish oil, presenting the highest selectivity of 22 for the CLEs of azelaic acid.

Phase State Regulates Photochemical HONO Production from NaNO3/Dicarboxylic Acid Mixtures.

Field observations of daytime HONO source strengths have not been well explained by laboratory measurements and model predictions up until now. More efforts are urgently needed to fill the knowledge gaps concerning how environmental factors, especially relative humidity (RH), affect particulate nitrate photolysis. In this work, two critical attributes for atmospheric particles, i.e., phase state and bulk-phase acidity, both influenced by ambient RH, were focused to illuminate the key regulators for reactive nitrogen production from typical internally mixed systems, i.e., NaNO3 and dicarboxylic acid (DCA) mixtures. The dissolution of only few oxalic acid (OA) crystals resulted in a remarkable 50-fold increase in HONO production compared to pure nitrate photolysis at 85% RH. Furthermore, the HONO production rates (PHONO) increased by about 1 order of magnitude as RH rose from <5% to 95%, initially exhibiting an almost linear dependence on the amount of surface absorbed water and subsequently showing a substantial increase in PHONO once nitrate deliquescence occurred at approximately 75% RH. NaNO3/malonic acid (MA) and NaNO3/succinic acid (SA) mixtures exhibited similar phase state effects on the photochemical HONO production. These results offer a new perspective on how aerosol physicochemical properties influence particulate nitrate photolysis in the atmosphere.

Enzymatic Synthesis of Copolyesters with the Heteroaromatic Diol 3,4-Bis(hydroxymethyl)furan and Isomeric Dimethyl Furandicarboxylate Substitutions.

Polyesters from furandicarboxylic acid derivatives, i.e., dimethyl 2,5-furandicarboxylate (2,5-DMFDCA) and 2,4-DMFDCA, show interesting properties among bio-based polymers. Another potential heteroaromatic monomer, 3,4-bis(hydroxymethyl)furan (3,4-BHMF), is often overlooked but holds promise for biopolymer synthesis. Cleaning and greening synthetic procedures, i.e., enzymatic polymerization, offer sustainable pathways. This study explores the Candida antarctica lipase B (CALB)-catalyzed copolymerization of 3,4-BHMF with furan dicarboxylate isomers and aliphatic diols. The furanic copolyesters (co-FPEs) with higher polymerization degrees are obtained using 2,4-isomer, indicating CALB's preference. Material analysis revealed semicrystalline properties in all synthesized 2,5-FDCA-based co-FPEs, with multiple melting temperatures (Tm) from 53 to 124 °C and a glass-transition temperature (Tg) of 9-10 °C. 2,4-FDCA-based co-FPEs showed multiple Tm from 43 to 61 °C and Tg of -14 to 12 °C; one of them was amorphous. In addition, all co-FPEs showed a two-step decomposition profile, indicating aliphatic and semiaromatic segments in the polymer chains.

One-pot Twostep Chemobiocatalytic Synthesis of a Furan Amino Acid from 5-Hydroxymethylfurfural.

Recently, catalytic valorization of biomass-derived furans has received growing interest. 5-Aminomethyl-2-furancarboxylic acid (AMFC), a furan amino acid, holds great promise in the aeras of polymer and pharmaceutical, but its synthesis remains limited. In this work, we report a chemobiocatalytic route toward AMFC by combining laccase-TEMPO system and recombinant Escherichia coli (named E. coli_TAF) harboring ω-transaminase (TA), L-alanine dehydrogenase (L-AlaDH) and formate dehydrogenase (FDH), starting from 5-hydroxymethylfurfural (HMF). In the cascade, HMF is oxidized into 5-formyl-2-furancarboxylic acid (FFCA) by laccase-TEMPO system, and then the resulting intermediate is converted into AMFC by E. coli_TAF via transamination with cheap ammonium formate instead of costly organic amine donors, theoretically generating H2O and CO2 as by-products. The tandem process was run in a one-pot twostep manner, affording AMFC with approximately 81 % yield, together with 10 % 2,5-furandicarboxylic acid (FDCA) as by-product. In addition, the scale-up production of AMFC was demonstrated, with 0.41 g/L h productivity and 8.6 g/L titer. This work may pave the way for green manufacturing of the furan-containing amino acid.

The Formulation and Evaluation of Deep Eutectic Vehicles for the Topical Delivery of Azelaic Acid for Acne Treatment.

The current work was aimed at the development of a topical drug delivery system for azelaic acid (AzA) for acne treatment. The systems tested for this purpose were deep eutectic systems (DESs) prepared from choline chloride (CC), malonic acid (MA), and PEG 400. Three CC to MA and eight different MA: CC: PEG400 ratios were tested. The physical appearance of the tested formulations ranged from solid and liquid to semisolid. Only those that showed liquid formulations of suitable viscosity were considered for further investigations. A eutectic mixture made from MA: CC: PEG400 1:1:6 (MCP 116) showed the best characteristics in terms of viscosity, contact angle, spreadability, partition coefficient, and in vitro diffusion. Moreover, the MCP116 showed close rheological properties to the commercially available market lead acne treatment product (Skinorin®). In addition, the formula showed synergistic antibacterial activity between the MA moiety of the DES and the AzA. In vitro diffusion studies using polyamide membranes demonstrated superior diffusion of MCP116 over the pure drug and the commercial product. No signs of skin irritation and edema were observed when MCP116 was applied to rabbit skin. Additionally, the MCP116 was found to be, physically and chemically, highly stable at 4, 25, and 40 °C for a one-month stability study.

Exploring the effects of high pressure on hydrogen bonding in pharmaceutical cocrystals: A systematic study of pyridine dicarboxylic acid systems using synchrotron and neutron diffraction.

Pharmaceutical cocrystals use common robust hydrogen bonding synthons to create novel materials with different physicochemical properties. In this systematic study of a series of cocrystals, we explore the effect of high pressure on one of these commonly used motifs, the acid-pyridine motif, to assess the commonality of behaviour under extreme conditions. We have surveyed five pyridine dicarboxylic acid systems using both synchrotron and neutron diffraction methods to elucidate the changes in structure. We observe that the hydrogen bonding in these systems compress at a similar rate despite the changes to the molecular make-up of the solids and that on compression the changes in structure are indicative that the layers move along the major slip planes in the structure. We have observed two phase transitions to new forms of the pyrazine:malonic acid system, one for each stoichiometric ratio. This study demonstrates that the combination of two complementary diffraction approaches is key to understanding polymorphic behaviour at high pressure.

Tricyclic Diester and 2,5-Furandicarboxylic Acid for the Synthesis of Biobased Hydrolysis Copolyesters with High Glass Transition Temperatures.

The reluctance of a polyester with high glass transition temperature (Tg) and mechanical properties to hydrolyze is a well-known fact, for instance, the high hydrolysis resistance of aromatic polyesters based on terephthalic acid and 2,5-furandicarboxylic acid (FDCA). The synthesis of polyesters that have a high Tg (>100 °C) and a fast hydrolytic degradation quality at the same time is a valuable topic. Herein, a renewable rigid diester, N,N'-trans-1,4-cyclohexane-bis(pyrrolidone-4-methyl carboxylate) (CBPC), was obtained via Michael addition. CBPC was copolymerized with FDCA and ethylene glycol to prepare a series of copolyesters PECxEFy with a high Mn over 30 kDa. PECxEFy showed a Tg range of 75.2-109.2 °C which outdistanced the most biobased polyesters. The thermal stability of all PECxEFy remained unchanged with the introduction of CBPC. Moreover, PECxEFy presented superior mechanical performances which were matching or exceeding those of commercial polyethylene terephthalate (PET) and polylactic acid (PLA). PECxEFy was stable in air but was able to undergo noticeable hydrolytic degradation, proving their enhanced degradability. And the regulation between CBPC and FDCA composition can be leveraged to adjust the degradation and environmental durability of PECxEFy, up to practical applications. Computational studies systematically revealed the relationship between CBPC with a tricyclic structure and the improved Tg and hydrolyzation properties. The outstanding thermal and mechanical performances and hydrolysis of these copolyesters appear to be promising candidates for renewable alternatives to industrial petrochemical polyesters.

Impact of pH on Gas-Particle Partitioning of Semi-Volatile Organics in Multicomponent Aerosol.

The partitioning of semivolatile organic compounds (SVOCs) between the condensed and gas phases can have significant implications for the properties of aerosol particles. In addition to affecting size and composition, this partitioning can alter radiative properties and impact cloud activation processes. We present measurements and model predictions on how activity and pH influence the evaporation of SVOCs from particles to the gas phase, specifically investigating aqueous inorganic particles containing dicarboxylic acids (DCAs). The aerosols are studied at the single-particle level by using optical trapping and cavity-enhanced Raman spectroscopy. Optical resonances in the spectra enable precise size tracking, while vibrational bands allow real-time monitoring of pH. Results are compared to a Maxwell-type model that accounts for volatile and nonvolatile solutes in aqueous droplets that are held at a constant relative humidity. The aerosol inorganic-organic mixture functional group activity coefficients thermodynamic model and Debye-Hückel theory are both used to calculate the activities of the species present in the droplet. For DCAs, we find that the evaporation rate is highly sensitive to the particle pH. For acidity changes of approximately 1.5 pH units, we observe a shift from a volatile system to one that is completely nonvolatile. We also observe that the pH itself is not constant during evaporation; it increases as DCAs evaporate, slowing the rate of evaporation until it eventually ceases. Whether a DCA evaporates or remains a stable component of the droplet is determined by the difference between the lowest pKa of the DCA and the pH of the droplet.

Recent Progress in Metabolic Engineering of Escherichia coli for the Production of Various C4 and C5-Dicarboxylic Acids.

As an alternative to petrochemical synthesis, well-established industrial microbes, such as Escherichia coli, are employed to produce a wide range of chemicals, including dicarboxylic acids (DCAs), which have significant potential in diverse areas including biodegradable polymers. The demand for biodegradable polymers has been steadily rising, prompting the development of efficient production pathways on four- (C4) and five-carbon (C5) DCAs derived from central carbon metabolism to meet the increased demand via the biosynthesis. In this context, E. coli is utilized to produce these DCAs through various metabolic engineering strategies, including the design or selection of metabolic pathways, pathway optimization, and enhancement of catalytic activity. This review aims to highlight the recent advancements in metabolic engineering techniques for the production of C4 and C5 DCAs in E. coli.

Engineering a Carboxyl Methyltransferase for the Formation of a Furan-Based Bioplastic Precursor.

FtpM from Aspergillus fumigatus was the first carboxyl methyltransferase reported to catalyse the dimethylation of dicarboxylic acids. Here the creation of mutant R166M that can catalyse the quantitative conversion of bio-derived 2,5-furandicarboxylic acid (FDCA) to its dimethyl ester (FDME), a bioplastics precursor, was reported. Wild type FtpM gave low conversion due to its reduced catalytic efficiency for the second methylation step. An AlphaFold 2 model revealed a highly electropositive active site, due to the presence of 4 arginine residues, postulated to favour the binding of the dicarboxylic acid over the intermediate monoester. The R166M mutation improved both binding and turnover of the monoester to permit near quantitative conversion to the target dimethyl ester product. The mutant also had improved activity for other diacids and a range of monoacids. R166M was incorporated into 2 multienzyme cascades for the synthesis of the bioplastics precursor FDME from bioderived 5-hydroxymethylfurfural (HMF) as well as from poly(ethylene furanoate) (PEF) plastic, demonstrating the potential to recycle waste plastic.

A Semicrystalline Furanic Polyamide Made from Renewable Feedstocks.

Semi-aromatic polyamides (SAPs) synthesized from petrochemical diacids and diamines are high-performance polymers that often derive their desirable properties from a high degree of crystallinity. Attempts to develop partially renewable SAPs by replacing petrochemical diacids with biobased furan-2,5-dicarboxylic acid (FDCA) have resulted in amorphous materials or polymers with low melting temperatures. Herein, we report the development of poly(5-aminomethyl-2-furoic acid) (PAMF), a semicrystalline SAP synthesized by the polycondensation of CO2 and lignocellulose-derived monomer 5-aminomethyl-2-furoic acid (AMF). PAMF has glass-transition and melting temperatures comparable to that of commercial materials and higher than that of any previous furanic SAP. Additionally, PAMF can be copolymerized with conventional nylon 6 and is chemically recyclable. Molecular dynamics (MD) simulations suggest that differences in intramolecular hydrogen bonding explain why PAMF is semicrystalline but many FDCA-based SAPs are not.

Preparation and Physiochemical Analysis of Novel Ciprofloxacin / Dicarboxylic Acid Salts.

The crystal structures of four novel dicarboxylic acid salts of ciprofloxacin (CFX) with modified physicochemical properties, prepared by mechanochemical synthesis and solvent crystallization, are reported. A series of dicarboxylic acids of increasing molecular weight was chosen, predicted to interact via a carboxylic acid:secondary amine synthon. These were succinic (SA), glutaric (GA), adipic (AA) and pimelic (PA) acids (4, 5, 6, 7 carbon atoms respectively). Characterized by single crystal and powder X-ray diffraction, Fourier-Transform Infrared Spectroscopy, thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy and aqueous solubility measurements, these salts showed distinct physicochemical properties relative to ciprofloxacin base. Searches of the Cambridge Structural Database (CSD) confirmed CFX-SA, CFX-GA, CFX-AA and CFX-PA to be novel crystal structures. Furthermore, the GA salt has substantially higher solubility than the widely available hydrochloride monohydrate salt (CFX-HCl·H2O). CFX-SA, CFX-GA and CFX-AA showed minimum inhibitory concentration (MIC) of 0.008 g/L and CFX-PA showed MIC of 0.004 g/L. The prepared CFX salts retained antibacterial activity exhibiting equivalent antimicrobial activity to CFX-HCl·H2O. These salts have positive implications for increasing the application of CFX beyond conventional oral formulations and highlight mechanochemical activation as suitable production method.

Displacement of Strong Acids or Bases by Weak Acids or Bases in Aerosols: Thermodynamics and Kinetics.

Depletion of chloride, nitrate, or ammonium from atmospheric aerosols represents a unique class of displacement reactions in which strong acids (HCl and HNO3) or bases (NH3) are substituted by weaker ones (i.e., dicarboxylic acids or dicarboxylate salts, respectively). These reactions alter the aerosol composition and perturb the atmospheric cycle of volatile compounds, thereby affecting environmental systems and climate. Despite the profound implications, the mechanism of these unique displacement reactions remains unclear. Here, we elucidate the thermodynamics and kinetics of these reactions using the multiphase buffer theory and a diffusion-controlled mass-transfer function, respectively. On the thermodynamic aspect, we find that the effective dissociation constants of the strong acids and bases in aerosols are 2 to 10 orders of magnitude lower than those in bulk solutions. On the kinetic aspect, we find that displacement reactions occur rapidly in aerosol microdroplets with a radius below 10 µm. Within this size range, the characteristic reaction time is always shorter than the lifetime of the aerosols in the atmosphere. Our findings suggest that the unique displacement reactions can significantly modify the composition of atmospheric aerosols, and consequentially, these aerosols may manifest distinct properties unforeseen by the chemistry of homogeneous bulk systems.

Bio-based poly(hexamethylene 2,5-furandicarboxylate-co-2,6-naphthalate) copolyesters: a study of thermal, mechanical, and gas-barrier properties.

A series of poly(hexamethylene 2,5-furandicarboxylate-co-2,6-naphthalate) copolyesters were synthesized using various amounts of poly(hexylene 2,5-furandicarboxylate) (PHF) and poly(hexylene 2,6-naphthalate) (PHN) via melt polymerization. The effects of introducing 2,6-naphthalene dicarboxylic acid (NDCA) on the thermal, mechanical, and gas-barrier properties were investigated. When the NDCA content was less than 30 mol%, the temperatures of crystallization (Tc) and melting (Tm) decreased as the amount of NDCA was increased owing to disturbance of the polymer-chain regularity. When the NDCA content was above 50 mol%, the Tc and Tm of the materials increased as the NDCA content was increased, showing that the dominant crystallization behavior varied from 2,5-furandicarboxylic acid to NDCA. Hence, the glass transition temperature (Tg) increased as the NDCA content was increased, which was attributed to the incorporation of NDCA with a more rigid naphthalate structure compared with the furan ring. The gas-barrier properties of the samples were observed to improve with the introduction of NDCA; this tendency could be explained by the ß-relaxation behavior and free volume values of the samples in the amorphous state. The activation energy (Ea) of ß-relaxation increased with the NDCA content, indicating that higher amounts of energy were needed to trigger the onset of long-range molecular motions. Free-volume calculations of the polymer structure showed that the introduction of NDCA hindered the space for gas penetration. For these reasons, the gas-barrier properties were improved and evaluated.