Amine Sites Research Articles

Identification of a UDP-Glucosyltransferase favouring substrate- and regio-specific biosynthesis of flavonoid glucosides in Cyclocarya paliurus

Cyclocarya paliurus (Batalin) Iljinsk is a medicinal plant belonging to the Juglandaceae family, and its leaves are used for a traditional sweet herbal tea with bioactivity against obesity and hyperglycaemia in China. It contains various bioactive specialised metabolites, such as flavonoids, triterpenes and their glucosides, while no glycosyltransferases (GTs) have been reported in C. paliurus to date. Herein, we identified and cloned the first glucosyltransferase C. paliurus GT1. The expression profiles of C. paliurus GT1 showed very high expression in young leaves, callus and branches, but relatively low expression in old leaves and bark and no expression in root. The recombinant C. paliurus GT1 protein was heterologously expressed in Escherichia coli and exhibited catalytic activity towards multiple flavonoids favouring substrate- and regio-specific biosynthesis. Further enzyme assays indicated a preference for certain hydroxyl group glucosylation by C. paliurus GT1. C. paliurus GT1 actively catalysed the glucosylation of flavones and flavonols, but it was less active towards isoflavones, flavanones or triterpenes. C. paliurus GT1 was also able to catalyse the attachment of sugars to the thiol (S-) or amine (N-) sites on aromatic compounds but not on aliphatic compounds. Molecular docking and site-directed mutagenesis analyses indicated that A43F, V84P, and M201Y dramatically altered the regio-selectivity and activity, and the W283M mutation and deletion of the V309-D320 region enhanced the activity and the formation of disaccharides. Herein, we present the identification and characterization of the first multi-functional glucosyltransferase in C. paliurus and provide a basis for understanding the biosynthesis of flavonoid glucosides. C. paliurus GT1 could be utilized as a synthetic biology tool for the synthesis of O-, N-, or S-glucosylated natural/unnatural products.

An experimental based optimization of a novel water lean amine solvent for post combustion CO2 capture process

The development of new amine solvents without the major drawbacks of conventional amines is crucial to industrial applications of CO2 capture. This paper presents a water-lean CO2 capture solvent having a low regeneration energy and low degradation. The water-lean solvent, K2Sol, is a sterically hindered diamine; because of the hindered amine site, K2Sol easily forms bicarbonate, resulting in a high absorption capacity. The minimum solvent regeneration energy is obtained using Gaussian process Bayesian optimization (GPBO) and bench-scale pilot plant experiments. GPBO finds the optimal solution using the input and output relationship of experiments; thus, expensive first-principle model construction can be avoided. According to the pilot plant experiment, the optimal regeneration energies of monoethanolamine (MEA) and K2Sol are 4.3 and 2.8 GJ/t CO2, respectively, indicating that K2Sol requires only 65% of the regeneration energy of MEA. Fewer than 30 experiments are required to find the optimal pilot plant operation for both the MEA and K2Sol experiments. We also describe the superior properties of K2Sol in terms of the CO2 loading, cyclic capacity, regeneration temperature, and degradation.

Fabrication, characterization and electrochemical simulation of AlN-gate ISFET pH sensor

This paper presents fabrication, characterization and modeling of aluminum nitride (AIN)-gate ion-sensitive field-effect transistor based pH sensor. The AIN sensing film is deposited using pulsed DC magnetron assisted reactive sputtering technique and the process optimization has been described. Material characterization was carried out for the deposited film by X-ray diffraction, field-emission scanning electron microscopy and energy dispersive spectroscopy and it was found that AlN film has polycrystalline structure. The fabricated device is tested in different pH buffer solutions (pH 4, 7 and 10) and a sensitivity of 33 mV/pH is obtained. A simulation program with integrated circuit emphasis (SPICE) macromodel was created by introducing electrochemical parameters in a metal-oxide field-effect transistor model for performing electrochemical simulations. We performed parametric sweep of electrochemical parameters to theoretically estimate the experimental results and we observed that the inclusion of amine sites in the SPICE macromodel is essential in determining precise sensor characteristics.

A supported dendrimer with terminal symmetric primary amine sites for adsorption of salicylic acid

The aim of this work is to evaluate the uptake of salicylic acid (SA), an emerging pollutant, using a nano-polar dendrimer containing highly branched terminal symmetric amine groups immobilized on mixed-oxide nanoparticles of SiO2-Al2O3. Several variables, including the effect of initial SA concentration, contact time, temperature, initial pH, adsorbent dosage, interfering ions, and the hydrophobicity of the adsorbent (SANP-G1.0) were studied. Because of the electrostatic and hydrogen bonding interactions between SA and the amine functional sites of the nano-polar dendrimer, the adsorbent featured a remarkable SA uptake capacity of over 254.5 mg/g after 5 min contact time. The solution pH had a considerable impact on SA uptake by SANP-G1.0, with optimal uptake occurring around pH 2–5. Kinetic and isotherm studies confirmed that SA removal could be fit with the Sips and pseudo-second-order kinetic models, respectively, implying that a chemical process dominates SA uptake by the SANP-G1.0. The uptake of SA decreased at elevated temperature, demonstrating that this is a chemically and naturally exothermic process between 15 and 80 °C. The uptake efficiency of the reused nanodendrimer was 54% after the tenth adsorption-desorption cycle. Moreover, the SANP-G1.0 showed a high capacity for adsorbing SA from Cayuga Lake water. We studied the possible mechanism of SA uptake, including the effect of interfering ions, using zeta potential, X-ray photoelectron spectroscopy, infrared spectroscopy, and the hydrophobicity of the nanodendrimer. The prepared supported dendrimer, featuring high chemical and mechanical stability, demonstrates good reusability for SA adsorption from aqueous media. An artificial neural network (ANN) model was also designed to simulate SA uptake by SANP-G1.0. The results revealed an excellent fit between the ANN-modeled and experimental data, with a correlation coefficient (R2) of 0.9841.

Rational design of nucleophilic amine sites via computational probing of steric and electronic effects

Accessibility of the nucleophilic site in organocatalysts is essential to ensure adequate catalytic activity. Gas-phase trimethylborane (TMB) Lewis basicity and Brønsted proton basicity of several amine based organocatalysts have been calculated using the CBS-QB3 model chemistry. This TMB basicity scale can, as opposed to the proton basicity scale, account for steric effects encountered in the initial nucleophilic attack of the nitrogen free electron pair on a substrate. Since such a step is the first one in several amine catalyzed reactions, severe steric hindrance of the nucleophilic center would render the catalyst ineffective. Comparing the TMB basicity and proton basicity with the experimentally observed catalytic activity of both homogeneous and heterogeneously supported amine sites found in literature for the aldol reaction of acetone with 4-nitrobenzaldehyde showed that, due to the inclusion of these steric effects, the TMB basicity scale is a much better predictor of catalytic activity than the proton basicity. According to this computational Lewis basicity scale, potential steric hindrance in alternative nitrogen containing active sites was probed. This resulted in 3-propylpyrrolidine being proposed among the most promising monofunctional amine groups and 1-(methylamino)propan-2-ol among the most promising bifunctional amine-hydroxyl groups for heterogeneous aldol reaction catalysts.

Electrochromic Behavior of Highly Stable, Flexible Electrochromic Electrode Based on Covalently Bonded Polyaniline-Graphene Quantum Dot Composite

Here in this work, a highly stable and flexible electrochromic film based on a composite of polyaniline and graphene quantum dots (PANI-fGQD), has been reported. To ensure the covalent attachment, monomer aniline was first attached to the negatively charged oxygenated groups present on the surface of GQDs followed by in-situ electrochemical polymerization for the composite. These amine sites act as nucleation sites for further growth. These electron rich oxygenated groups also act as secondary doping agents for hole dominating polyaniline (PANI). The prepared composite film has been found to show similar electrochemical response to that of PANI, but with more well-defined redox peaks and higher current densities. The composite (PANI-fGQD) exhibits improved electrochromic behavior with a color change from pale yellow to green to blue color as potential was scanned from −0.2 V to 0.8V. Pani-fGQD exhibits better optical contrast of 62% at 658nm and faster response time of 0.9s and 1.4s for coloration and bleaching, respectively, compared to pristine PANI. The composite also shows outstanding electrochemical stability of 15,000 cycles. The results present the significant potential of PANI-fGQD electrode for highly stable electrochromic application.

Exploring the Acid Gas Sorption Properties of Oxidatively Degraded Supported Amine Sorbents

Amine-supported mesoporous oxide materials have proven to be effective acid gas sorbents. While the primary application of these supported amine species has been CO2 capture, they have also shown to be proficient at adsorbing other damaging flue gas impurities such as SOx and NOx. The precise nature of the amine (primary, secondary, or tertiary) is known to dictate the gas–amine interactions, with tertiary amines of particular interest due to their inability to adsorb dry CO2, favoring SOx and NOx species. The different amine sites also provoke differences in oxidative stability, when exposed to temperatures similar to those used for thermal desorption procedures. Herein we focus on the structural and chemical changes that occur in a range of class 1 (amine-impregnated) and class 2 (amine-grafted) sorbents upon oxidation and correlate these with their variation in acid gas (CO2, NO2, and SO2) uptakes, as a function of the oxidation temperature. These studies suggest that oxidatively degraded or “spent” su...

Improving Conductivity Performance of Chitosan by Carboxymethylation Reaction: Synthesis and Characterization

Chitosan has been applied widely in electrical energy storage purposes like battery and fuel cell, as in electrolyte. This research purposed on improving compatibility chitosan as material for electrical energy storage by chemical reaction. Carboxymethylation reaction performed on chitosan to add carboxymethyl groups in either hydroxyl or amine sites or both. The substitution result could effect by optimizing in the ratio of reactants and reaction condition. Carboxymethylation process on chitosan will confirm by FTIR analysis and degree of carboxymethyl substitution can be calculated from 1H NMR. Its ionic conductivity will calculate from EIS. The highest degree of substitution obtained at 64.64%. This reaction had the ratio of chitosan:monochloroacetic acid about 1:6 (m/m) and was reacted in reflux system at 65°C. EIS analysis showed improvement of carboxymethyl chitosan’s conductivity where pure chitosan had 2.7 x 10-6 Scm-1 and CMC-IV had 2.7 x 10-5 Scm-1 at room temperature.

Synthesis and Characterization of Controlled Nitric Oxide Release from S-Nitroso-N-Acetyl-d-Penicillamine Covalently Linked to Polyvinyl Chloride (SNAP-PVC).

Polyvinyl chloride (PVC) is one of the most widely used polymers in medicine but has very poor biocompatibility when in contact with tissue or blood. To increase biocompatibility, controlled release of nitric oxide (NO) can be utilized to mitigate and reduce the inflammatory response. A synthetic route is described where PVC is aminated to a specified degree and then further modified by covalently linking S-nitroso-N-acetyl-d-penicillamine (SNAP) groups to the free primary amine sites to create a nitric oxide releasing polymer (SNAP-PVC). Controllable release of NO from SNAP-PVC is described using photoinitiation from light emitting diodes (LEDs). Ion-mediated NO release is also demonstrated as another pathway to provide a passive mechanism for NO delivery. The large range of NO fluxes obtained from the SNAP-PVC films indicate many potential uses in mediating unwanted inflammatory response in blood- and tissue-contacting devices and as a tool for delivering precise amounts of NO in vitro.

N-Terminus Alkylation of Vancomycin: Ligand Binding Affinity, Antimicrobial Activity, and Site-Specific Nature of Quaternary Trimethylammonium Salt Modification.

A series of vancomycin derivatives alkylated at the N-terminus amine were synthesized, including those that contain quaternary trimethylammonium salts either directly at the terminal amine site or with an intervening three-carbon spacer. The examination of their properties provides important comparisons with a C-terminus trimethylammonium salt modification that we recently found to improve the antimicrobial potency of vancomycin analogues through an added mechanism of action. The N-terminus modifications disclosed herein were well-tolerated, minimally altering model ligand binding affinities (d-Ala-d-Ala) and antimicrobial activity, but did not induce membrane permeabilization that was observed with a similar C-terminus modification. The results indicate that our earlier observations with the C-terminus modification are sensitive to the site as well as structure of the trimethylammonium salt modification and are not simply the result of nonspecific effects derived from introduction of a cationic charge.

Hyperbranched polyglycerols containing amine groups — Synthesis, characterization and carbon dioxide capture

Abstract In this article we report an easy synthetic way towards hyperbranched polyglycerols containing primary amine groups (A-HBPGs). A-HBPGs were synthesized in a two-step procedure including an anionic ring opening copolymerization of the phthalimide-epoxy monomer with glycidol followed by hydrazinolysis of phthalimide groups. Polymeric products of both synthetic steps were characterized using NMR, MALDI-TOF, FTIR, viscosimetry and elemental analysis techniques. The maximum amount of the amine containing units in the products was estimated to be 31 mol%. Introduction of higher amounts of these units was limited by the reactivity (sterical) and viscosity reasons. A-HBPGs showed to be effective in CO2 capture from the ambient air. Adsorbents consisting of A-HBPGs and fumed silica in the 1 to 1 wt ratio were capable of adsorbing up to 85.6 mg of CO2, representing 0.82 mmol CO2 per gram or 36.3 mg CO2 per gram of adsorbent. The measurements confirmed that the amount of adsorbed carbon dioxide was proportional to the number of amine sites in a polymer. The obtained CO2 adsorbents could be regenerated upon by heating. Desorption took place above 80 °C, but the optimum temperature seemed to be at least 100 °C. The effect of easier CO2 desorption in presence of HBPG structures reported in the literature in case of our materials has not been confirmed.

DFT-assisted design and evaluation of bifunctional copper(I) catalysts for the direct intermolecular addition of aldehydes and ketones to alkynes

Bifunctional catalysts containing discrete metal pi-acid and amine sites were designed and investigated for the direct intermolecular addition of aldehydes and ketones to unactivated alkynes. Copper(I)-based catalysts were prioritized based on intramolecular (Conia-ene type) reactions, and complexes were designed with tridentate ligands and potentially hemilabile heterocyclic spacers. The structures of the designed catalysts were computed using density functional theory (DFT), and the relative energies of putative catalytic intermediates were estimated and used to prioritize catalyst designs. Novel bifunctional precatalysts containing a thiazole spacer were synthesized via a 9-step sequence and combined with transition metals before screening for the direct addition of aldehydes and ketones to several internal and terminal alkynes. Despite the lack of desired intermolecular reactions, DFT calculations of putative catalyst intermediates appears to be a promising strategy for the design and prioritization of bifunctional catalysts for CC bond formation.

Clay-Based Nanocomposites as Recyclable Adsorbent toward Hg(II) Capture: Experimental and Theoretical Understanding.

Here, we report the development of inorganic–organic hybrid nanocomposites through selective modification of the negative outer surfaces of halloysite nanoclays with two different organosilanes having primary or secondary amine sites to be explored them as novel and cost-effective adsorbents for the extraction of toxic inorganic contaminants from aqueous solution. They possess excellent selectivity for the adsorption of mercury, which shows monolayer molecular adsorption over the nanocomposites. The adsorption kinetics of Hg(II) is very fast and follows pseudo-second-order model compared to pseudo-first-order model. A combined experimental and theoretical study demonstrated that Hg(II) uptake by these nanocomposites is highly favorable and spontaneous up to 40 °C, and beyond this temperature, the uptake capacity gradually reduced. Temperature-dependent adsorption study exhibits endothermicity at low temperature (≤40 °C) and exothermicity beyond 40 °C. pH-dependent adsorption study showed their high uptake capacity until pH 7, which reduced at alkaline pH. All of the nanocomposites hold excellent adsorption capacity even at low concentration of adsorbate, along with multicycle sorption capability. The outstanding adsorption capacity as well as the easy synthetic route to achieve these nanocomposites may attract researchers to develop low-cost adsorbents to capture toxic metals, which in turn regulate the permissible limit of these toxic metals in drinking water.

Amine-based CO2 capture sorbents: A potential CO2 hydrogenation catalyst

Mechanism of CO2 adsorption on amine loaded SBA-15 sorbents with varying amine coverage has been assessed using thermogravimetric analysis (TGA) and in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). TGA study showed that sorbent adsorption capacities increased by 122–153% with CO2 concentrations (5–80%) in the gas at 50/75 °C. The DRIFTS studies indicate that low amine loaded sorbents exhibit higher uptakes with an increase in CO2 concentrations which is attributed to the mode of CO2 adsorption i.e. 1:1 CO2 to amine forming carbamic acid. At higher amine loadings CO2 is adsorbed following the 1:2 CO2 to amine forming carbamate-ammonium ions pair resulting in lower adsorption capacities per amine site. The studies also showed an increase in carbamic acid formation with pressure from 100 to 500 kPa at low amine loadings and both carbamic acid and carbamates at higher amine loadings. The paper provides insights into the mechanistic understanding of CO2 adsorption behaviour of the varyingly covered amines on the SBA-15 support with a change in concentration and pressure of CO2. The current work presents the conditions to alter the CO2 adsorption mechanism on amine sites with potential application in CO2 conversion to chemicals.

Reducing CO2 with Stable Covalent Organic Frameworks

Covalent organic frameworks (COFs) are highly desirable for electrocatalytic applications but not fully explored yet because of their poor stability. In a recently published paper in Chem, Liu et al. describe an approach to construct chemically stable COFs, involving quantitative linkage conversion from imine COFs, and for co-catalysis of electrochemical CO2 reduction by virtue of the resultant amine sites. The reported amine COF/Ag electrode shows enhanced catalytic selectivity. This work provides a new way to access chemically stable COFs for electrochemical catalysts.

Exploiting the hydrophilic role of natural deep eutectic solvents for greening CO2 capture

Abstract CO2 released from fossil fuels has made a great contribution to global warming, and natural deep eutectic solvents (NADES) offer an attractive option for greening CO2 capture. Being economical natural materials, L-arginine (L-Arg) and glycerol (Gly) were used to synthesize a series of novel hydrophilic NADES (L-Arg/Gly, at mole ratios of 1:4, 1:5, 1:6, 1:7, 1:8). The L-Arg/Gly (1:6) DES showed excellent thermal stability (Tmax, 250 °C; Tf, 13.7 °C). The hydrates of L-Arg/Gly DES (at water contents of 0 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt%, 60 wt%) were also prepared. The synthesis process of L-Arg/Gly DES and its hydrate were studied with FT-IR and in situ IR spectroscopy. High hydrophilicity of such solvent was demonstrated with fast and efficient capture of CO2 at a high absorption (0.511 mol CO2/mol NADES) under optimized conditions. In the gas-liquid absorption process, the hydrophilic properties of L-Arg/Gly DES and its hydrate greatly reduced the transfer barrier, and accelerated the phase transfer by increasing accessibility of active amine sites on NADES and CO2. And the dynamics for the CO2 absorption was investigated correspondingly. The absorption behaviors of CO2 in L-Arg/Gly DES and its hydrate were studied by in situ IR spectrometer and nuclear magnetic resonance (1H NMR, 13C NMR), and the characteristic infrared peaks and shifts of CO2 absorption were observed. In addition, the L-Arg/Gly DES could be reused for 5 times without obvious inactivation. Indicating the L-Arg/Gly DES would be a potential substitute of the traditional volatile amine solvents for CO2 capture.

Controlling the Growth of Staphylococcus epidermidis by Layer-By-Layer Encapsulation.

Commensal skin bacteria such as Staphylococcus epidermidis are currently being considered as possible components in skin-care and skin-health products. However, considering the potentially adverse effects of commensal skin bacteria if left free to proliferate, it is crucial to develop methodologies that are capable of maintaining bacteria viability while controlling their proliferation. Here, we encapsulate S. epidermidis in shells of increasing thickness using layer-by-layer assembly, with either a pair of synthetic polyelectrolytes or a pair of oppositely charged polysaccharides. We study the viability of the cells and their delay of growth depending on the composition of the shell, its thickness, the charge of the last deposited layer, and the degree of aggregation of the bacteria which is varied using different coating procedures-among which is a new scalable process that easily leads to large amounts of nonaggregated bacteria. We demonstrate that the growth of bacteria is not controlled by the mechanical properties of the shell but by the bacteriostatic effect of the polyelectrolyte complex, which depends on the shell thickness and charge of its outmost layer, and involves the diffusion of unpaired amine sites through the shell. The lag times of growth are sufficient to prevent proliferation for daily topical applications.

Controllable Adsorption of CO2 on Smart Adsorbents: An Interplay between Amines and Photoresponsive Molecules

Photoresponsive adsorbents for CO2 capture attract significant attention, because the variation of adsorption capacity can be tailored conveniently by light irradiation. However, all photoresponsive adsorbents reported until now capture CO2 via physical interaction (weak sites). Thus, the selectivity of CO2 over other gases like CH4 is low, and the variation of CO2 adsorption capacity originates from pure structural change via isomerization of photoresponsive units. Despite great challenges, photoresponsive adsorbents for CO2 capture based on chemical interaction (strong sites) are extremely desirable. Here, we report for the first time the construction of photoresponsive adsorbents with chemical adsorption sites for CO2. The control of adsorption capacity is based on the interplay between active amine sites {A, [3-(methylamine)propyl]trimethoxysilane} and photoresponsive azobenzene molecules [P, 4-(3-triethoxysilylpropyl-ureido)azobenzene]. Density functional theory (DFT) calculations reveal that the neg...

Exploration of the Glycosyltransferase BmmGT1 from a Marine-Derived Bacillus Strain as a Potential Enzyme Tool for Compound Glycol-Diversification.

Glycosyltransferases (GTs) from microbes are an emerging and rich source for efficient glycol-transformation of natural/unnatural compounds. Here, we probed the catalytic capability and substrate promiscuity of BmmGT1 from marine-derived Bacillus methylotrophicus B-9987. The regioselectivity of BmmGT1 on macrolactin A (1) was explored by optimization of the reaction conditions, in which a series of O-glycosylated macrolactins (1a-1e) were generated, including two new di/tri-O-glucosyl analogs (1b and 1e). Furthermore, BmmGT1 was able to catalyze the glycosylation of the thiol (S-) or amine (N-) sites of phenolic compounds (2 and 3), leading to the generation of N- (2a) or S-glycosides (3a and 3b). The present study demonstrates that BmmGT1 could serve as a potential enzyme tool for O-, N-, or S-glycosyl structural diversification of compounds for drug discovery.

Improved CO2 Sorption in Freeze-Dried Amine Functionalized Mesoporous Silica Sorbent

This work investigates the structural and CO2 sorption properties of amine-functionalized mesoporous silica prepared by a freeze-drying method. It was found that the freeze-dried samples delivered significantly higher CO2 sorption capacities up to a factor of 18 times as compared to samples prepared by the conventional oven-drying evaporation method. The improved performance of the freeze-drying method was attributed to a higher surface area and access to active amine sites for CO2 sorption. The freeze-dried samples also exhibited good stability at a relatively high sorption temperature (90 °C) and flue gas CO2 partial pressure (15 kPa). The freeze-drying method reached the best CO2 sorption capacity of 4.71 mmol g–1 for samples with 70 wt % amine loading. Higher loading (80 and 90 wt %) led to excess amine not being incorporated into the mesoporous silica structure, thus covering active sites and limiting CO2 diffusion.