Combination Of Chemical Modification Research Articles

Large control of friction and wear enabled by Ti3AlC2 MAX- multilayer graphene-polydopamine composites

Friction and wear pose significant challenges in moving mechanical systems. Despite efforts to address these challenges with MAX phase materials, many of these materials lack effective lubrication and wear protection under ambient conditions. Here, we developed a composite coating that addresses these challenges through a combination of materials chemistry and engineering. This coating, composed of polydopamine-functionalized Ti3AlC2 MAX (F-MAX) and multilayer graphene (MGr), known as F-MAX + MGr, demonstrated exceptional tribological performance. At its best composition, the F-MAX + MGr composite coating reduced the friction at sliding interfaces by 82 % and decreased the wear on the counterpart ball by 99.76 % compared to bare surfaces. Importantly, its tribological performance surpassed that of pristine MAX, F-MAX, and MGr coatings. This improvement is attributed to the synergistic lubricating effect of the inherently low shear strengths of Ti3AlC2 MAX and MGr, the chemical properties of PDA, and the occurrence of incommensurate contacts at the interfaces. This work pioneers slippery and wear-resistant surfaces via a combination of chemical modification and materials engineering, with implications for both fundamental science and technological advancement.

Fabrication of multi-functional biodegradable liquid mulch utilizing xyloglucan derived from tamarind waste for agricultural application

Biodegradable liquid mulch is considered a promising alternative to plastic mulch for sustainable agriculture. This work proposed a xyloglucan-based liquid mulch with multi-function using a combination of chemical modification and blending methods. The esterification product of tamarind xyloglucan (TXG) from forestry wastes was synthesized with benzoic anhydride (BA). The effect of esterification modification was investigated, and BA-TXG was utilized as a film-forming and sand-fixation agent. The rheological properties, thermal stability, and hydrophobicity were improved following esterification. Additionally, waterborne polyurethane and urea were incorporated into the mulch to enhance its mechanical strength (23.28 MPa, 80.71 %), and homogeneity, as well as improve its nutritive properties. The xyloglucan-based liquid mulch has excellent UV protection, a high haze value (approximately 90 %), and retains water at a rate of 80.45 %. SEM and immersion experiment showed the effect of xyloglucan-based liquid mulch on sustainable sand-fixation. Moreover, the liquid mulch treatment demonstrated an impressive germination rate of 83.8 % and degradation rate of 51.59 % (60 days). The modified polysaccharide film increases stability and slows down the degradation rate. Tamarind xyloglucan-based liquid mulch exhibits powerful and diverse optical properties as well as sand fixation functions, indicating their great potential in sustainable agriculture as an alternative to plastic mulch.

Tuning of Morphology and Surface Properties of Porous Silicones by Chemical Modification

The behavior of materials against water is a key element in many practical applications. Silicones are hydrophobic by nature and can be chemically modified to become hydrophilic or highly hydrophobic, while combining intrinsic surface properties with morphological details may lead to superhydrophobic materials. Chemically modified porous silicones and their surface properties have rarely been investigated. Our aim in this study was to tune the surface properties of porous silicone materials by a combination of chemical modification and emulsion templating The porous silicones were obtained by two cross-linking reactions in toluene–water emulsion, in mild conditions: dehydrocoupling of poly(methylhydrogen)siloxane (PMHS) and dimethyl-methylhydrogensiloxane copolymers and UV-initiated thiol-ene addition on a poly(dimethyl-methylvinyl)siloxane, respectively. Apart from the pores generated by water droplets, in the first process, additional large pores appeared due to hydrogen evolution. Their size and number diminished along with the cross-linking degree; thus, the porosity was tuned by adjusting the composition of the reaction mixture. Chemical modifications were performed in situ to introduce more hydrophobic groups (hexane and trimethylsilane) or hydrophilic groups (thioethanol), modifications that were followed by FT-IR spectroscopy. The inner morphology and powder wetting behavior of the crushed samples were investigated by SEM, tensiometry analyses, and contact angle measurements. The materials showed morphological particularities and surface properties that spanned from hydrophilic to superhydrophobic with lotus or petal effects.

Enhanced mechanical properties of surface modified and silica reinforced nomex sandwich composites

Nomex cored glass fiber sandwich composites find their use in several aerospace, automotive, and military applications due to their high specific mechanical properties. This study reports a novel procedure to modify/enhance the mechanical properties of Nomex sandwich composites through surface modification as well as surface nano-silica reinforcement. Surface modification of Nomex was conducted in dilute phosphoric acid solution with varying soaking times. In another set of experiments, the surface of Nomex was reinforced with different concentrations of silica particles by dipping in nano-silica suspension (NexSil™ 8). A combination of chemical modification and silica reinforcement treatments were investigated. Scanning Electron Microscopy (SEM) was used for morphological characterizations while Energy Dispersive Spectroscopy (EDS), Atomic Force Microscopy (AFM), and Fourier Transform Infrared Spectroscopy (FTIR) were used to analyze the chemical changes at Nomex surfaces. The mechanical properties of the composite samples were investigated using bend tests (i.e., 3-point and 4-point) and flat-wise compression tests. It was observed that the acid treated samples displayed an increase in flexural strength with etch time. Nano-silica reinforced composite samples also led to an enhancement in flexural as well as compressive strengths with each dip. In contrast, it was found that the compression strength values of the composite samples increased only for short acid treatment time (i.e., 30 sec), and decreased thereof for longer duration(s). Enhancement in flexural strength values were attributed mainly to an increase in Nomex-epoxy interfacial physio-chemical changes. This study demonstrates that surface treated Nomex sandwich composites, through the procedures outlined here, possess superior mechanical/structural properties as compared to non-treated ones.

Zero–Zero Birefringence Cellulose Acetate-Based Optical Films by Benzoylation

Zero–zero birefringence film is one of the key components in optical displays, and its design and preparation remain a challenge nowadays. Here, we report the synthesis of benzoylated cellulose acetate (BCA), the preparation of BCA films by solution casting, and the birefringent properties of unstretched and stretched BCA films. It is found that zero–zero birefringence films can be fabricated using both unstretched and stretched BCA films. As the degree of substitution of benzoyl (DSBz) increases, the out-of-plane birefringence (Δnth) gradually decreases and changes from positive to negative. Particularly, for DSBz = 0.511, both the in-plane birefringence (Δnin) and out-of-plane birefringence (Δnth) of stretched BCA films are close to zero. The orientations of the acetyl and benzoyl groups under stretching are measured to interpret the underlying compensation mechanisms. Finally, we show that the wavelength dispersion of BCA films with DSBz = 0.511 varies significantly with the increase in draw ratio, and formulize the normalized birefringence with the relative orientation degree of the benzoyl and acetyl groups. Our results suggest that the birefringence and wavelength dispersion of cellulose acetate-based optical films can be well regulated by a combination of chemical modification and stretching, and have potential significance to the industrial production of zero–zero birefringence films.

Bioactive Bromotyrosine Derivatives from the Pacific Marine Sponge Suberea clavata (Pulitzer-Finali, 1982).

Chemical investigation of the South-Pacific marine sponge Suberea clavata led to the isolation of eight new bromotyrosine metabolites named subereins 1–8 (2–9) along with twelve known co-isolated congeners. The detailed configuration determination of the first representative major compound of this family 11-epi-fistularin-3 (11R,17S) (1) is described. Their chemical characterization was achieved by HRMS and integrated 1D and 2D NMR (nuclear magnetic resonance) spectroscopic studies and extensive comparison with literature data. For the first time, a complete assignment of the absolute configurations for stereogenic centers C-11/17 of the known members (11R,17S) 11-epi-fistularin-3 (1) and 17-deoxyfistularin-3 (10) was determined by a combination of chemical modifications, Mosher’s technology, and ECD spectroscopy. Consequently, the absolute configurations of all our new isolated compounds 2–9 were determined by the combination of NMR, Mosher’s method, ECD comparison, and chemical modifications. Interestingly, compounds 2–7 were obtained by chemical transformation of the major compound 11-epi-fistularin-3 (1). Evaluation for acetylcholinesterase inhibition (AChE), DNA methyltransferase 1 (DNMT1) modulating activity and antifouling activities using marine bacterial strains are also presented.

A well-defined lignin-based filler for tuning the mechanical properties of polymethyl methacrylate

Well-defined lignin fillers were synthesized by using a universal approach, that the combination of chemical modification with lignin fractionation. This study paves the way towards lignin high-value utilization on a broader scale.

A heparin derivatives library constructed by chemical modification and enzymatic depolymerization for exploitation of non-anticoagulant functions

Non-anticoagulant biological functions of heparin-based drugs have drawn increasing attention. However, the exploration into the non-anticoagulant activities of various low molecular weight heparins was associated with bleeding risks in clinical practice and often led to controversial conclusions due to the structural differences. In this study, we aimed to establish a process to produce a library of heparin derivatives with structural diversity and reduced/abolished anticoagulant activity through the combination of chemical modifications and enzymatic cleavage of heparins. The depolymerization characteristics of various selectively modified heparin derivatives by three heparinases were comprehensively analyzed. The order of periodate treatment and heparinase-I depolymerization was proved to significantly change the structural characteristics of the oligosaccharide products. Finally, among several heparin derivatives that screened in the bleomycin-induced cell apoptosis model, the low molecular weight partially 6-O-/N-desulfated heparins showed the strongest anti-apoptotic activities. This study provided a useful approach for future development of novel heparin-derivative medications.

Insertion of Synthetic Peptides into Proteins by Tandem Protein Trans-Splicing

Engineering proteins through chemical or genetic manipulations offers great potential to design and study proteins with complex properties. Despite tremendous progress, the type and combination of chemical modification (e.g. non-canonical amino acids (ncAAs) or post-translational modifications (PTMs)) that can be incorporated by genetic means (e.g. amber codon suppression) is still limited. Semi-synthetic approaches offer a post-translational alternative to synthetically introduce modifications into proteins, but have typically been performed in vitro and restricted to small proteins that can be easily refolded. Here, we present a method to incorporate synthetic peptides carrying multiple PTMs or ncAAs into both cytosolic and membrane proteins. The work is performed in live eukaryotic cells by tandem protein trans-splicing (PTS) using two orthogonal split intein pairs. We anticipate the approach to be broadly applicable as it allows for the introduction of a virtually limitless array of modifications, including those not accessible by existing methods.

Research of efficiency of lignite chemical modification and steam-gas activation combining for sorbents preparation*

The paper presents the results of research for sorbents preparation when combining the processes of chemical modification and steam-gas activation of lignite from the Kharanorsk deposit (Zabaikalsky Krai). The experimental studies were carried out by two ways of activation methods combination: parallel and successive exposure on feedstock. The lignite processed by chemical reagent (KOH) was exposed to steam during the whole period of thermolysis under the parallel action. Under successive exposure, the thermolysis was performed in two stages - first without steam supply, then with steam-gas activation. In the work the optimal parameters of the process of combining the chemical and steam-gas lignite activation methods were determined and the quality of the generated sorbents was studied. The efficiency of combined activation was estimated by comparing the sorption characteristics of the samples with the results obtained during chemical and steam-gas activation as autonomous processes and with the requirements to these characteristics of industrially produced active carbon grades. Combined activation of lignite allowed to increase the value of iodine adsorption activity in comparison with autonomous steam-gas activation by 1.8-2 times, chemical activation - by 2.7-10 %. The obtained values of iodine adsorption activity at combination of chemical modification and steam-gas activation exceed the value of 100 % (1000 mg/g) that meets the requirements to high quality industrially produced active carbons of SKT-0 grade.

Design, Synthesis and Evaluation of Pentacyclic Triterpenoids Similar to Glycyrrhetinic Acid Via Combination of Chemical and Microbial Modification as Glycogen Phosphorylases Inhibitor.

A series of pentacyclic triterpenoids similar to glycyrrhetinic acid were designed and synthesized via the combination of chemical modification and microbial catalysis. All products were screened for the glycogen phosphorylases inhibitory activities in vitro. Within this series of derivatives, compound 5 displayed good inhibitory activities with IC50 value of 27.7 μM, which is better than that of the other derivatives and glycyrrhetinic acid. Structure-activity relationship (SAR) analysis of these inhibitors was also discussed.

Systems glycomics of adult zebrafish identifies organ-specific sialylation and glycosylation patterns

The emergence of zebrafish Danio rerio as a versatile model organism provides the unique opportunity to monitor the functions of glycosylation throughout vertebrate embryogenesis, providing insights into human diseases caused by glycosylation defects. Using a combination of chemical modifications, enzymatic digestion and mass spectrometry analyses, we establish here the precise glycomic profiles of eight individual zebrafish organs and demonstrate that the protein glycosylation and glycosphingolipid expression patterns exhibits exquisite specificity. Concomitant expression screening of a wide array of enzymes involved in the synthesis and transfer of sialic acids shows that the presence of organ-specific sialylation motifs correlates with the localized activity of the corresponding glycan biosynthesis pathways. These findings provide a basis for the rational design of zebrafish lines expressing desired glycosylation profiles.

Monoamine oxidases inhibitors from Colvillea racemosa: Isolation, biological evaluation, and computational study

Bioassay-guided fractionation and chemical investigation of Colvillea racemosa stems led to identification of two new α, β-dihydroxydihydrochalcones, colveol A (1) and colveol B (2) along with fifteen known compounds. The structures were elucidated via interpretation of spectroscopic data. The absolute configurations of the dihydrochalcones 1 and 2 were assigned by a combination of chemical modification and electronic circular dichroism data. The isolated compounds were evaluated for their inhibition activity toward recombinant human monoamine oxidases (rhMAO-A and -B). Compound 1 demonstrated preferential inhibition against hMAO-A isoenzyme (IC50 0.62μM, SIA/B 0.02) while S-naringenin (13) and isoliquiritigein (15) demonstrated preferential hMAO-B inhibition (IC50 0.27 and 0.51μM, SIA/B 31.77 and 44.69, respectively). Fisetin (11) showed inhibition against hMAO-A with IC50 value of 4.62μM and no inhibitory activity toward hMAO-B up to 100μM. Molecular docking studies for the most active compounds were conducted to demonstrate the putative binding modes. It suggested that 1 interacts with Gln215, Ala111, Phe352, and Phe208 amino acid residues which have a role in the orientation and stabilization of the inhibitor binding to hMAO-A, while S-naringenin (13) occupies both entrance and substrate cavities and interacts with Tyr326, a critical residue in inhibitor recognition in hMAO-B.

Protein adsorption, platelet adhesion, and bacterial adhesion to polyethylene-glycol-textured polyurethane biomaterial surfaces.

Traditional strategies for surface modification to enhance the biocompatibility of biomaterials often focus on a single route utilizing either chemical or physical approaches. This study combines the chemical and physical treatments as applied to poly(urethane urea) (PUU) biomaterials to enhance biocompatibility at the interface for inhibiting platelet-related thrombosis or bacterial adhesion-induced microbial infections. PUU films were first textured with submicron patterns by a soft lithography two-stage replication process, and then were grafted with polyethylene glycol (PEG). A series of biological response experiments including protein adsorption, platelet adhesion/activation, and bacterial adhesion/biofilm formation showed that PEG-grafted submicron textured biomaterial surfaces were resistant to protein adsorption, and greatly increased the efficiency in reducing both platelet adhesion/activation and bacterial adhesion/biofilm formation due to the additive effects of physical topography and grafted PEG. Results suggest that a combination of chemical modification and surface texturing will be more efficient in preventing biomaterial-associated thrombosis and infection of biomaterials. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 668-678, 2017.

Facile preparation of superamphiphobic epoxy resin/modified poly(vinylidene fluoride)/fluorinated ethylene propylene composite coating with corrosion/wear-resistance

A robust superamphiphobic epoxy resin (EP)/modified poly(vinylidene fluoride) (MPVDF)/fluorinated ethylene propylene (FEP) composite coating has been prepared through the combination of chemical modification and spraying technique. Nanometer silica (SiO2, 2.5wt.%) and carbon nanotubes (CNTs, 2.5wt.%) were added in the coating to construct the necessary reticulate papillae structures for superamphiphobic surface. The prepared EP composite coating demonstrated high static contact angles (166°, 155°) and low sliding angles (3°, 5°) to water and glycerol, respectively. Moreover, the prepared coating can also retain superhydrophobicity under strongly acidic and alkaline conditions. The brittleness of EP can be avoided by introducing the malleable MPVDF. The wear life of the EP composite coating with 25wt.% FEP was improved to 18 times of the pure EP coating. The increased wear life of the coating can be attributed to the designed nano/micro structures, the self-lubrication of FEP and the chemical reaction between EP and MPVDF. The anti-corrosion performance of the coatings was investigated in 3.5% NaCl solution using potentiodynamic polarization. The results showed that the prepared superamphiphobic composite coating was most effective in corrosion resistance, primarily due to the barrier effect for the diffusion of O2 and H2O molecules. It is believed that this robust superamphiphobic EP/MPVDF/FEP composite coating prepared by the facile spray method can pave a way for the large-scale application in pipeline transport.

Genome-Directed Lead Discovery: Biosynthesis, Structure Elucidation, and Biological Evaluation of Two Families of Polyene Macrolactams against Trypanosoma brucei.

Marine natural products are an important source of lead compounds against many pathogenic targets. Herein, we report the discovery of lobosamides A-C from a marine actinobacterium, Micromonospora sp., representing three new members of a small but growing family of bacterially produced polyene macrolactams. The lobosamides display growth inhibitory activity against the protozoan parasite Trypanosoma brucei (lobosamide A IC50 = 0.8 μM), the causative agent of human African trypanosomiasis (HAT). The biosynthetic gene cluster of the lobosamides was sequenced and suggests a conserved cluster organization among the 26-membered macrolactams. While determination of the relative and absolute configurations of many members of this family is lacking, the absolute configurations of the lobosamides were deduced using a combination of chemical modification, detailed spectroscopic analysis, and bioinformatics. We implemented a "molecules-to-genes-to-molecules" approach to determine the prevalence of similar clusters in other bacteria, which led to the discovery of two additional macrolactams, mirilactams A and B from Actinosynnema mirum. These additional analogs have allowed us to identify specific structure-activity relationships that contribute to the antitrypanosomal activity of this class. This approach illustrates the power of combining chemical analysis and genomics in the discovery and characterization of natural products as new lead compounds for neglected disease targets.

Mechanism of action of thalassospiramides, a new class of calpain inhibitors.

Thalassospiramides comprise a large family of lipopeptide natural products produced by Thalassospira and Tistrella marine bacteria. Here we provide further evidence of their nanomolar inhibitory activity against the human calpain 1 protease. Analysis of structure-activity relationship data supported our hypothesis that the rigid 12-membered ring containing an α,β-unsaturated carbonyl moiety is the pharmacologically active functional group, in contrast to classic electrophilic “warheads” in known calpain inhibitors. Using a combination of chemical modifications, mass spectrometric techniques, site-directed mutagenesis, and molecular modeling, we show the covalent binding of thalassospiramide's α,β-unsaturated carbonyl moiety to the thiol group of calpain's catalytic Cys115 residue by a Michael 1,4-addition reaction. As nanomolar calpain inhibitors with promising selectivity and low toxicity from natural sources are rare, we consider thalassospiramides as promising drug leads.

Synthesis and characterization of lignin-based carbon materials with tunable microstructure

Lignin-based carbons can be used as a low-cost alternative to graphite and petroleum-based carbons enabling the production of sustainable, functional carbon materials for various applications. The microstructure development of these carbons can be controlled through chemical modification of the lignin precursor and choice of carbonization parameters. In this work, microstructured carbon materials are synthesized from lignin using a combination of chemical modification and carbon fiber processing techniques. Lignin is modified by incorporating different ester groups which results in a precursor highly compatible with melt processing using the fiber extrusion technique and conversion into microstructured carbons by oxidative stabilization and subsequent carbonization. Furthermore, the impact of esterifications on precursor chemistry and carbonizations is investigated. A nuclear magnetic resonance study of modified lignins shows characteristic spectral changes as a result of esterifications. Ultrahigh resolution Fourier transform ion cyclotron resonance mass spectrometry shows the modification process does not affect the polymeric character of the lignin backbone. Esterifications result in moderate shifts in O : C and H : C ratios. Thermogravimetric analysis of lignins reveals distinct differences in mass loss trends during oxidations and carbonizations.

Detection and Characterization of 1,2‐Dibromoethane‐Derived DNA Crosslinks Formed with O6‐Alkylguanine‐DNA Alkyltransferase

A combination of chemical modifications and LC-tandem MS was used for the structure elucidation of various ethylene crosslinks of DNA with O(6) -alkylguanine-DNA alkyltransferase (AGT, see picture). The elucidation of the chemical structures of such DNA-protein crosslinks is necessary to understand mechanisms of mutagenesis.

Efficient adsorption of gold ions from aqueous systems with thioamide-group chelating nanofiber membranes

We report on the efficient adsorption of gold ions from aqueous systems with thioamide-group chelating nanofiber membranes. The obtained membranes were prepared by a combination of chemical modification and electrospinning process. It was found that the maximum adsorption capacities of the chelating nanofibers toward Au(III) ions were 15.86mmol/g, 23.50mmol/g and 34.60mmol/g, when the temperature was 298, 323 and 348K, respectively. The nanofibers display a high adsorption efficiency for Au(III) ions. The Langmuir adsorption isotherm was applied to describe the adsorption processes. Kinetics of the Au(III) ions adsorption was found to follow pseudo-second-order rate equation. Furthermore, the as-prepared thioamide-group chelating nanofiber membranes, as well as Au(III) ions adsorbed nanofiber membranes, were carefully examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS). Based on the characterization results, a possible mechanism of Au(III) ions adsorption with the thioamide-group chelating nanofiber membranes was proposed. This study provides a promising nanofiber adsorbent with high and efficient adsorption property for heavy metal ions removal.