Formation Of Ester Bonds Research Articles

Nanotherapeutics-mediated restoration of pancreatic homeostasis and intestinal barrier for the treatment of severe acute pancreatitis.

Severe acute pancreatitis (SAP) is an inflammatory disease of the pancreas accompanied with intestinal injury, and effective therapeutic modalities are still highly lacking. Herein, a facile and effective nanotherapeutics (pHA@IBNCs) is developed to alleviate pancreatic inflammation and restore intestinal barrier for SAP treatment. Epigallocatechin gallate (EGCG, an anti-oxidant), interleukin-22 (IL-22, an anti-inflammatory and epithelial barrier-protecting cytokine), and bovine serum albumin (a framework protein), are assembled via non-covalent interactions to form nanocomplexes (IBNCs). Then, phenylboronic acid-modified hyaluronic acid (pHA) is synthesized and coated onto IBNCs via formation of the reversible boronate ester bonds to obtain pHA@IBNCs. Upon intravenous injection, pHA@IBNCs could efficiently accumulate at the lesion sites of sodium taurocholate (STC)-induced SAP mice, based on their prolonged blood circulation time and pHA-mediated targeting of activated intestinal epithelial cells and macrophages. Inside the inflammatory microenvironment, over-produced reactive oxygen species (ROS) trigger the shedding of the pHA layer and release of the drug payloads. Thereby, EGCG cooperates with IL-22 to attenuate pancreatitis and restore the intestinal barrier by scavenging ROS, suppressing pro-inflammatory cytokines secretion, and promoting the repair of intestinal epithelia. Such a nano-therapeutic approach targeting multiple pathological events may serve as a promising paradigm for the effective management of SAP.

Development of polyvinyl alcohol/carboxymethylcellulose-based bio-packaging film with citric acid crosslinking and clove essential oil encapsulated chitosan nanoparticle pickering emulsion

This study developed polyvinyl alcohol (PVA)/carboxymethylcellulose (CMC)-based films, using citric acid (CA) as a non-toxic crosslinking agent, to enhance the shelf life of water-soluble packaging films. Clove essential oil (CEO)-loaded chitosan nanoparticles (CSNPs) were prepared via Pickering emulsion and incorporated into PVA/CMC/CA composite films. The encapsulation of CEO was confirmed by FTIR and optical microscopy. Thermal properties were analyzed using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), revealing improved thermal stability and a decrease in glass transition temperature (Tg) upon crosslinking. The formation of ester bonds was confirmed by ATR-FTIR and 13CNMR. Water contact angle (WCA) measurements showed a decrease in hydrophilicity, enhancing the barrier properties of the films. SEM images demonstrated good dispersion of CSNP/CEO within the matrix, improving mechanical and barrier properties. The films exhibited a 30 % reduction in water vapor permeability and water solubility. Controlled release studies indicated that the composite films sustained CEO release, extending the shelf life of cherry tomatoes. Thus, these PVA/CMC/CA-CSNP/CEO composite films offer strong potential for food preservation applications.

Facile fabrication of a starch-based wood adhesive showcasing water resistance, flame retardancy, and antibacterial properties via a dual crosslinking strategy

The demand for non-toxic, environmentally friendly, easily processable, water-resistant, flame-retardant and antimicrobial adhesives in the wood processing industry is becoming increasingly urgent. Few adhesives can both simultaneously possess these functions and synthesis easily. This paper presents a one-pot process utilizing corn starch, sodium hypochlorite, itaconic acid, and borax to synthesize a starch-based adhesive with dual crosslinking. Initial crosslinking takes place between the carboxyl groups of itaconic acid and hydroxyl groups on oxidized starch due to the formation of ester bonds. Secondary crosslinking occurs borate ester bonds between starch hydroxyl groups and boric acid. The entire reaction process is environmentally benign, generating no waste, with all reactants converted into final products, aligning with “green” chemistry principles. When used to bond wooden boards, this adhesive achieved a dry shear strength of 5.34 ± 0.24 MPa, and a wet shear strength of 1.22 ± 0.06 MPa after soaking in water. Additionally, this starch-based adhesive exhibited antibacterial properties against Escherichia coli (ATCC 8739) and Staphylococcus aureus. Moreover, with borax incorporated, the adhesive demonstrated flame-retardancy. The limiting oxygen index for bonded wooden boards was 30.9 %, qualifying it as a flame-retardant material. These multiple functions render it promising for applications in the wood processing industry.

Fabrication of PBAT/lignin composite foam materials with excellent foaming performance and mechanical properties via grafting esterification and twin-screw melting free radical polymerization

As one of the mainstream biodegradable materials, poly(butylene adipate-co-terephthalate) (PBAT) foams offer a sustainable alternative to traditional plastic foams, effectively reducing environmental pollution. However, the high cost and poor mechanical performance of PBAT foams impede their practical application. Herein, the glycidyl methacrylate-grafted biomass lignin (GML) was used to produce a PBAT/GML composite foam with good foaming performance and mechanical properties at high lignin-filling amounts by twin-screw melting free radical polymerization and supercritical CO2 foaming process. The compatibility of GML in the PBAT matrix was improved due to the formation of ester bonds in modified lignin, endowing the PBAT/GML (PGML) composite foam with exceptional foaming performance. Additionally, the mechanical properties of PGML composite foam were remarkably enhanced due to the introduction of the abundant aromatic structures of GML and the construction of a stable covalent crosslinking network. The compressive strengths and compression modulus of the PGML foam were improved by 2.53 times and 2.47 times, while its bending strength and bending modulus were improved by 1.27 times and 3.92 times compared to the neat PBAT. This research affords a new strategy for developing low-cost biodegradable biomass PBAT/lignin composite foam materials with good foaming performance and mechanical properties.Graphical abstract

Impact of citrus pectin on the foaming behavior, structures, and barrier properties of the starch foam blocks

The starch foam displays weak barrier properties under humid storage, which limits its applications in the food industry. In this study, citrus pectin was loaded to strengthen the starch foam. Results showed that the pectin (4 wt% ∼ 8 wt%) effectively modified the cell structures of the starch foam block. This was attributed to the increased viscosity of the starch melt during foaming and the enhanced cell stability during cooling, which was promoted by the formation of entanglements, hydrogen bonds, and ester bonds between pectin and starch, as confirmed by FTIR and DSC. Moreover, the pectin-starch foam displayed improved mechanical properties under wet storage conditions, mainly due to the limited moisture adsorption and water migration. The foam containing 4 wt% of pectin exhibited the highest compression-recovery ratio (76.7 %) and a reduced adsorbed moisture content (19.22 %) under 95 % RH. Overall, citrus pectin could improve the starch foaming process and the foam blocks barrier properties.

Ubiquitylation of nucleic acids by DELTEX ubiquitin E3 ligase DTX3L

The recent discovery of non-proteinaceous ubiquitylation substrates broadened our understanding of this modification beyond conventional protein targets. However, the existence of additional types of substrates remains elusive. Here, we present evidence that nucleic acids can also be directly ubiquitylated via ester bond formation. DTX3L, a member of the DELTEX family E3 ubiquitin ligases, ubiquitylates DNA and RNA in vitro and that this activity is shared with DTX3, but not with the other DELTEX family members DTX1, DTX2 and DTX4. DTX3L shows preference for the 3′-terminal adenosine over other nucleotides. In addition, we demonstrate that ubiquitylation of nucleic acids is reversible by DUBs such as USP2, JOSD1 and SARS-CoV-2 PLpro. Overall, our study proposes reversible ubiquitylation of nucleic acids in vitro and discusses its potential functional implications.

Celastrol Derivative/DOX Co-Assembled Nanodrug for Enhanced Antitumor Therapy.

Multidrug resistance (MDR) is a key challenge in clinical chemotherapy. The combination of drugs can effectively reverse multi-drug resistance. In this study, doxorubicin (DOX) was capsulated into nanoparticles formed by an amphiphilic PEGylated-poly (α-lipoic acid)-methanamide analogue of celastrol (mPEG-PαLA-CEN) prodrug polymer. CEN was linked to the branched chain of poly (α-lipoic acid) by forming ester bonds. DOX was physically trapped inside the nanoparticles via electrostatic interaction. Both drugs can be simultaneously released in response to low pH and high GSH in order to overcome DOX resistance. The chemical structure of the mPEG-PαLA-CEN-DOX NPs was confirmed through 1H NMR, FT-IR spectroscopy, UV-Vis spectrum, DLS, and TEM. Drug-loading content, efficacy, and drug release were measured using HPLC. Cell toxicity was examined using an MTT assay. CEN/DOX-loaded nanoparticles were found to have spherical shapes with diameters of around 229.7 nm. The NPs exhibited high biocompatibility and released 92% DOX and 71.8% CEN in response to low pH and high GSH of tumor microenvironments. As dual drug-loaded nanoparticles, the efficacy of mPEG-PαLA-CEN-DOX NPs against tumor cell lines in vitro was enhanced for both MCF-7 and MCF-7/ADR compared to free DOX. Compared to free DOX, the IC50 of mPEG-PαLA-CEN-DOX NPs reduced from 46.10 μM to 8.36 μM for the MCF-7/ADR cell line. In conclusion, this study demonstrated that PEGylated poly (α-lipoic acid)-CEN copolymers can be used not only as biocompatible, stimulation-responsive anticancer drug nanocarriers but also as chemosensitizers to overcome multidrug resistance, which provide a theoretical base for clinical application of CEN/DOX nanodrug.

Biosynthesis of Ester-Bond Containing Quinolone Alkaloids with (3R,4S) Stereoconfiguration.

Asperalins represent a novel class of viridicatin natural products with potent inhibitory activities against fish pathogens. In this study, we elucidated the biosynthesis of asperalins in the Aspergillus oryzae NSAR1 heterologous host and identified the FAD-dependent monooxygenase AplB stereoselectively hydroxylates viridicatin to yield a unique 3R,4S configuration. The monomodular NRPS AplJ catalyzes a rare intramolecular ester bond formation reaction using dihydroquinoline as a nucleophile. Subsequent modifications by cytochrome P450 AplF, chlorinase AplN, and prenyltransferase AplE tailor the anthranilic acid portion, leading to the formation of asperalins. Additionally, we explored the potential of AplB for the hydroxylation of viridicatin analogs, demonstrating its relaxed substrate specificity. This finding suggests that AplB could be developed as a biocatalyst for the synthesis of viridicatin derivatives.

Reinforcing thermostability and pH robustness of exo-inulinase facilitated by ReverseTag/ReverseCatcher tagging system

Enhancing protein stability is pivotal in the field of protein engineering. Protein self-cyclization using peptide a tagging system has emerged as an effective strategy for augmenting the thermostability of target proteins. In this study, we utilized a novel peptide tagging system, ReverseTag/ReverseCatcher, which leverages intramolecular ester bond formation. Initially, we employed GFP as a model to validate the feasibility of cyclization mediated by ReverseTag/ReverseCatcher in improving the protein thermostability. Cyclized GFP (cGFP) retained 30 % of its relative fluorescence after a 30-min incubation at 100 °C, while both GFP and linear GFP (lGFP) completely lost their fluorescence within 5 min. Additionally, we applied this method to exo-inulinase (EXINU), resulting in a variant named cyclized EXINU (cEXINU). The T50 and t1/2 values of cEXINU exhibited significant enhancements of 10 °C and 10 min, respectively, compared to EXINU. Furthermore, post-cyclization, EXINU demonstrated a broad operational pH range from 5 to 10 with sustained catalytic activity, and cEXINU maintained a half-life of 960 min at pH 5 and 9. Molecular dynamics simulations were conducted to elucidate the mechanisms underlying the enhanced thermostability and pH robustness of EXINU following cyclization. This study highlights that cyclization substanitially enhances the stability of both highly stable protein GFP and low-stable protein EXINU, mediated by the ReverseTag/ReverseCatcher tagging system. The ReverseTag/ReverseCatcher tagging system proves to be a potent conjugation method, with potential applications in improving thermostability, pH robustness, and other areas of protein engineering.

Structures of BlEst2 from Bacillus licheniformis in its propeptide and mature forms reveal autoinhibitory effects of the C-terminal domain.

Carboxylesterases comprise a major class of α/β-fold hydrolases responsible for the cleavage and formation of ester bonds. Found ubiquitously in nature, these enzymes are crucial for the metabolism of both endogenous and exogenous carboxyl esters in animals, plants and microorganisms. Beyond their essential physiological roles, carboxylesterases stand out as one of the important classes of biocatalysts for biotechnology. BlEst2, an enzyme previously classified as Bacillus licheniformis esterase, remains largely uncharacterized. In the present study, we elucidate the structural biology, molecular dynamics and biochemical features of BlEst2. Our findings reveal a canonical α/β-hydrolase fold similar to the ESTHER block L of lipases, further augmented by two additional accessory C-terminal domains. Notably, the catalytic domain demonstrates two insertions, which occupy conserved locations in α/β-hydrolase proteins and commonly form the lid domain in lipase structures. Intriguingly, our in vitro cleavage of C-terminal domains revealed the structure of the active form of BlEst2. Upon activation, BlEst2 showed a markedly elevated hydrolytic activity. This observation implies that the intramolecular C-terminal domain serves as a regulatory intramolecular inhibitor. Interestingly, despite exhibiting esterase-like activity, BlEst2 structural characteristics align more closely with lipases. This suggests that BlEst2 could potentially represent a previously unrecognized subgroup within the realm of carboxyl ester hydrolases.

Preparation of Antifog Hard Coatings Based on Carboxy-Functionalized Polyhedral Oligomeric Silsesquioxane Cross-Linked with Oligo(ethylene glycol)s.

In this study, we prepared antifog hard coatings by heating a mixture of carboxy-functionalized polyhedral oligomeric silsesquioxane (POSS-C) and oligo(ethylene glycol)s (OEGs, HO(CH2CH2O) n H, n = 1-6) in N,N-dimethylformamide, applying the mixture onto a glass substrate, and subsequently removing the solvent via heating. In addition, we evaluated the water resistance, hardness, and antifogging performance of the coatings. In particular, the coating produced at a 2:1 functional group ratio of POSS-C to tetraethylene glycol (OEG, n = 4) coating exhibited high surface hardness (6H), as determined using pencil scratch testing. The coating remained clear after exposure to the vapor of warm water at 40 °C at a height of 2 cm for 10 s, demonstrating its antifogging property. Furthermore, no dissolution or cracking was observed when the POSS-C/OEG coating (n = 4, COOH/OH = 2:1) was immersed in water at room temperature for 1 h, confirming its water resistance. The Fourier transform infrared/attenuated total reflectance results showed the formation of ester bonds, indicating the construction of a network structure that enhanced the water resistance and hardness of the coating.

Xanthan gum/Guar gum-based 3D-printed scaffolds for wound healing: production, characterization, and biocompatibility screening

Biodegradable and eco-sustainable medical devices represent an urgent need to face up to the increasing pollution associated to plastic device wastes. The present study aimed to develop semisolid extruded 3D (SSE-3D)-printed medical devices using mixtures of Xanthan gum (XG) and Guar gum (GG) as a green alternative to non-biodegradable synthetic polymers. The final purpose is to prepare biocompatible, biodegradable, and sterilizable implantable scaffolds with pro-regenerative and wound-healing properties. Inks prepared with 12 % w/v XG/GG (50:50) and blended with citric (CA), succinic (SA), or tartaric acid (TA) possessed suitable rheological profiles and allowed the 3D printing of porous scaffolds with high precision and structural control. Steam-heat sterilization triggered the cross-linking through ester bond formation (confirmed by ATR-FTIR and CP/MAS 13C-NMR). The scaffold crosslinked with SA had reproducible porosity (SEM and pycnometer), maintained the initial shape after 7 days swelling in PBS pH 7.4 and subjected to compression cycles (texturometer analysis), showed good cytocompatibility and hemocompatibility, and promoted angiogenesis in ovo in a chorioallantoic membrane model, evidencing tissue integration without toxicity. Furthermore, these scaffolds attenuated collagenase activity by trapping divalent ions (Ca2+ and Zn2+). Hence, by coupling angiogenic and anticollagenase activity, XG/GG scaffolds are promising candidates for wound healing and pro-regenerative applications.

Sustainable foams from hemp, lignin, xylan, pectin, and glycerol: tunable via reversible citric acid crosslinking for absorption and insulation applications

This study investigates the development of sustainable multifunctional foams utilizing hemp stalk waste, lignin, xylan, pectin, glycerol, and citric acid. Using the freeze-drying method for foam formation in combination with industrial waste products and renewable resources, we emphasize a green, scalable material development approach. In total, 25 distinct formulations were prepared and methodically examined, mainly focusing on the roles of citric acid, pectin, and glycerol. Thermal crosslinking, conducted at 140°C, was analyzed using FTIR, confirming the formation of ester bonds. The microstructural characterization of the foams revealed distinct variations from nanofibrillar to microfibrillar structures based on composition. The bulk density of the foams ranged from 13 to 152 mg/cm3, and porosity values varied from 97 % to 99 % for most of the compositions. Foams showed up to 50 g/g water, 51 g/g rapeseed oil, and 46 g/g kerosine absorption. Foam absorption capacity changes were examined through 10 iterative cycles in water, demonstrating that most compositions retained near-original absorption capacities. Adding glycerol conferred exceptional hydrophobic properties to the foam surfaces, as evidenced by water contact angles ranging between 140° and 150°. The thermal conductivity of foams ranged from 0.040 to 0.046 W/mK. The mechanical properties of foams were assessed using compression testing, which showed highly tunable structures ranging from soft to rigid. This study illustrates the broad applicability of these foams, emphasizing their utility in thermal insulation, filtration systems, and environmental cleanup, among other potential uses.

Influence of pH on the formation of benzyl ester bonds between dehydrogenation polymer and cellulose

Generation of lignin-carbohydrate complex (LCC) between dehydrogenation polymer (DHP) and pulp fibers may have an important impact on the properties of pulp. In this work, the benzyl ester-type LCC was formed between oxidized cellulose and DHP. The effect of pH on the addition reaction of oxidized cellulose to quinone methide in the synthesis of DHP-cellulose complex (DHPCC) was investigated. The structure of the product was characterized by Fourier Transform Infrared (FTIR), Carbon 13-Nuclear Magnetic Resonance (13C-NMR), and 2-Dimensional Heteronuclear Single Quantum Coherence Nuclear Magnetic Resonance (2D HSQC NMR) analyses. The results indicated that cellulose was indeed oxidized and carboxyl groups were introduced into cellulose by the oxidation process. The formed DHPCC was connected by benzyl ester linkage. In addition, the pH of the reaction system had an important role in the formation of the benzyl ester bonds. The acidic condition (pH = 4.0) was conducive to the addition reaction of quinone methide with carboxyl groups of cellulose. Overall, this study provides helpful guidance for the generation of LCC between DHP and paper pulp fibers.

Hydrostability, mechanical resilience, and biodegradability of paper straws fabricated through lignin-based polyurethane and chitosan binary emulsion bonding

This study focuses on enhancing the strength and water stability of paper straws through a novel approach involving a binary emulsion of lignin-based polyurethane and chitosan. Kraft lignin serves as the raw material for synthesizing a blocked waterborne polyurethane, subsequently combined with carboxylated chitosan to form a stable binary emulsion. The resulting emulsion, exhibiting remarkable stability over at least 6 months, is applied to the base paper. Following emulsion application, the paper undergoes torrefaction at 155 °C. This process deblocks isocyanate groups, enabling their reaction with hydroxyl groups on chitosan and fibers, ultimately forming ester bonds. This reaction significantly improves the mechanical strength and hydrophobicity of paper straws. The composite paper straws demonstrate exceptional mechanical properties, including a tensile strength of 47.21 MPa, Young's modulus of 4.33 GPa, and flexural strength of 32.38 MPa. Notably, its water stability is greatly enhanced, with a wet tensile strength of 40.66 MPa, surpassing commercial paper straws by 8 folds. Furthermore, the composite straw achieves complete biodegradability within 120 days, outperforming conventional paper straws in terms of environmental impact. This innovative solution presents a promising and sustainable alternative to plastic straws, addressing the urgent need for eco-friendly products.

Enhancing Polyvinyl Alcohol Nanocomposites with Carboxy-Functionalized Graphene: An In-Depth Analysis of Mechanical, Barrier, Electrical, Antibacterial, and Chemical Properties.

To enhance the various properties of polyvinyl alcohol (PVA), varying concentrations of carboxy-functionalized graphene (CFG) were employed in the preparation of CFG/PVA nanocomposite films. FTIR and XRD analyses revealed that CFG, in contrast to graphene, not only possesses carboxylic acid group but also exhibits higher crystallinity. Mechanical testing indicated a notable superiority of CFG addition over graphene, with optimal mechanical properties such as tensile and yield strengths being achieved at a 3% CFG concentration. Relative to pure PVA, the tensile strength and yield strength of the composite increased by 2.07 and 2.01 times, respectively. XRD analysis showed distinct changes in the crystalline structure of PVA with the addition of CFG, highlighting the influence of CFG on the composite structure. FTIR and XPS analyses confirmed the formation of ester bonds between CFG and PVA, enhancing the overall performance of the material. TGA results also demonstrated that the presence of CFG enhanced the thermal stability of CFG/PVA nanocomposite films. However, analyses using scanning electron microscopy and transmission electron microscopy revealed that a 3% concentration of CFG was uniformly dispersed, whereas a 6% concentration of CFG caused aggregation of the nanofiller, leading to a decrease in performance. The incorporation of CFG significantly enhanced the water vapor and oxygen barrier properties of PVA, with the best performance observed at a 3% CFG concentration. Beyond this concentration, barrier properties were diminished owing to CFG aggregation. The study further demonstrated an increase in electrical conductivity and hydrophobicity of the nanocomposites with the addition of CFG. Antibacterial tests against E. coli showed that CFG/PVA nanocomposites exhibited excellent antibacterial properties, especially at higher CFG concentrations. These findings indicate that CFG/PVA nanocomposites, with an optimized CFG concentration, have significant potential for applications requiring enhanced mechanical strength, barrier properties, and antibacterial capabilities.

Mechanism Behind the Programmed Biosynthesis of Heterotrimeric Fungal Depside Thielavin A

AbstractThielavin A (1) is a fungal depside composed of one 3‐methylorsellinic acid and two 3,5‐dimethylorsellinic acid units. It displays diverse biological activities. However, the mechanism underlying the assembly of the heterotrimeric structure of 1 remains to be clarified. In this study, we identified the polyketide synthase (PKS) involved in the biosynthesis of 1. This PKS, designated as ThiA, possesses an unusual domain organization with the C‐methyltransferase (MT) domain situated at the C‐terminus following the thioesterase (TE) domain. Our findings indicated that the TE domain is solely responsible for two rounds of ester bond formation, along with subsequent chain hydrolysis. We identified a plausible mechanism for TE‐catalyzed reactions and obtained insights into how a single PKS can selectively yield a specific heterotrimeric product. In particular, the tandem acyl carrier protein domains of ThiA are critical for programmed methylation by the MT domain. Overall, this study highlighted the occurrence of highly optimized domain–domain communication within ThiA for the selective synthesis of 1, which can advance our understanding of the programming rules of fungal PKSs.

Mechanism Behind the Programmed Biosynthesis of Heterotrimeric Fungal Depside Thielavin A.

Thielavin A (1) is a fungal depside composed of one 3-methylorsellinic acid and two 3,5-dimethylorsellinic acid units. It displays diverse biological activities. However, the mechanism underlying the assembly of the heterotrimeric structure of 1 remains to be clarified. In this study, we identified the polyketide synthase (PKS) involved in the biosynthesis of 1. This PKS, designated as ThiA, possesses an unusual domain organization with the C-methyltransferase (MT) domain situated at the C-terminus following the thioesterase (TE) domain. Our findings indicated that the TE domain is solely responsible for two rounds of ester bond formation, along with subsequent chain hydrolysis. We identified a plausible mechanism for TE-catalyzed reactions and obtained insights into how a single PKS can selectively yield a specific heterotrimeric product. In particular, the tandem acyl carrier protein domains of ThiA are critical for programmed methylation by the MT domain. Overall, this study highlighted the occurrence of highly optimized domain-domain communication within ThiA for the selective synthesis of 1, which can advance our understanding of the programming rules of fungal PKSs.

Peptide-functionalized chitosan-based microcapsules for dual active targeted treatment of lung infections

Lung infections, such as: pneumonia, chronic obstructive cystic fibrosis, tuberculosis are generally caused by viruses, bacteria and fungi. As these infections are very difficult to treat, new therapeutic approaches are investigated in order to maximize the efficiency of the treatment and to reduce the major complications that can occur. The main objective of this study was focused on the preparation of drug-loaded peptides-functionalized microcapsules, obtained by a double emulsion, based on carboxylated chitosan (CMCS), poly(vinyl alcohol) (PVA) and an activator [4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride] (DMT-MM), for the dual active targeting and treatment of pulmonary infections. The microcapsules were functionalized on the surface with both CGSPGWVRC and indolicidin (IN) peptides, as effective ligands for the active targeting of both alveolar capillary endothelial cells and bacterial cells. FTIR spectroscopy confirmed the formation of ester and amide bonds into the structure of prepared microcapsules. Microcapsules diameter varied between 893 and 965 nm. The swelling degree in PBS, at pH 7.4, ranged between 1760 %- 2100 %. All the analyzed samples showed hemolysis degrees lower than 2 %, which demonstrated their non-hemolytic character. Evaluation of the impact of microcapsules on WI-38 normal human lung cells and RAW 264.7 mouse macrophages revealed a non-toxic or slightly cytotoxic effect. Internalization assay proved that microcapsules were localized at intracellular level.

Ynamide Coupling Reagents: Origin and Advances.

Since the pioneering work of Curtius and Fischer, chemical peptide synthesis has witnessed a century's development and evolved into a routine technology. However, it is far from perfect. In particular, it is challenged by sustainable development because the state-of-the-art of peptide synthesis heavily relies on legacy reagents and technologies developed before the establishment of green chemistry. Over the past three decades, a broad range of efforts have been made for greening peptide synthesis, among which peptide synthesis using unprotected amino acid represents an ideal and promising strategy because it does not require protection and deprotection steps. Unfortunately, C → N peptide synthesis employing unprotected amino acids has been plagued by undesired polymerization, while N → C inverse peptide synthesis with unprotected amino acids is retarded by severe racemization/epimerization owing to the iterative activation and aminolysis of high racemization/epimerization susceptible peptidyl acids. Consequently, there is an urgent need to develop innovative coupling reagents and strategies with novel mechanisms that can address the long-standing notorious racemization/epimerization issue of peptide synthesis.This Account will describe our efforts in discovery of ynamide coupling reagents and their application in greening peptide synthesis. Over an eight-year journey, ynamide coupling reagents have evolved into a class of general coupling reagents for both amide and ester bond formation. In particular, the superiority of ynamide coupling reagents in suppressing racemization/epimerization enabled them to be effective for peptide fragment condensation, and head-to-tail cyclization, as well as precise incorporation of thioamide substitutions into peptide backbones. The first practical inverse peptide synthesis using unprotected amino acids was successfully accomplished by harnessing such features and taking advantage of a transient protection strategy. Ynamide coupling reagent-mediated ester bond formation enabled efficient intermolecular esterification and macrolactonization with preservation of α-chirality and the configuration of the conjugated α,β-C-C double bond. To make ynamide coupling reagents readily available with reasonable cost and convenience, we have developed a scalable one-step synthetic method from cheap starting materials. Furthermore, a water-removable ynamide coupling reagent was developed, offering a column-free purification of the target coupling product. In addition, the recycle of ynamide coupling reagent was accomplished, thereby paving the way for their sustainable industrial application.As such, this Account presents the whole story of the origin, mechanistic insights, preparation, synthetic applications, and recycle of ynamide coupling reagents with a perspective that highlights their future impact on peptide synthesis.