Modified Amino Groups Research Articles

Efficient recovery of acetylene from quaternary mixture by a pillar-layer framework with abundant Lewis basic sites

The efficient recovery of C2H2 from the gas mixtures comprising CO2 and other light hydrocarbons is the key to realize its further value-added production. In view of their similar physical properties, reasonable design of porous physical adsorbents is expected. Here, we report a metal–organic framework bpy-NH2-CuZrF6, which possesses the suitable aperture size and abundant Lewis basic sites derived from the modified amino groups and fluorinated anions, making it the first example of achieving the efficient recovery of C2H2 from a C2H2/C2H4/C2H6/CO2 quaternary mixture. This porous material possesses an excellent C2H2 adsorption capacity (138.9 cm3/g, 298 K and 1 bar) along with considerable IAST selectivities for equimolar C2H2/CO2 (6.6), C2H2/C2H4 (6.3), and C2H2/C2H6 (6.3) simultaneously. Combined with the adsorption heats and theoretical calculations, the preferential binding with C2H2 is demonstrated. And further breakthrough experiments show that the material can efficiently purify C2H2 not only from various binary mixtures (50/50 C2H2/CO2, 50/50 C2H2/C2H4, and 50/50 C2H2/C2H6), but also from the ternary (33.3/33.3/33.3 C2H2/C2H4/CO2) and even quaternary (25/25/25/25 C2H2/C2H4/C2H6/CO2) mixtures. As a result, 32.1 L/kg and 21.9 L/kg C2H2 with fuel-grade (purity ≥ 98 %) are recovered successfully after desorption for ternary (33.3/33.3/33.3 C2H2/C2H4/CO2) and quaternary (25/25/25/25 C2H2/C2H4/C2H6/CO2) mixtures respectively. Further combined with the green scalable synthesis, good recyclability, and high stability, this microporous material is expected to have a promising prospect for practical applications.

Amino-Functionalized Interfacial Layer Enables an Ultra-Uniform Amorphous Solid Electrolyte Interphase for High-Performance Aqueous Zinc-Based Batteries.

Aqueous rechargeable zinc-based batteries (ZBBs) are emerging as desirable energy storage systems because of their high capacity, low cost, and inherent safety. However, the further application of ZBBs still faces many challenges, such as the issues of uncontrolled dendrite growth and severe parasitic reactions occurring at the Zn anode. Herein, an amino-grafted bacterial cellulose (NBC) film is prepared as artificial solid electrolyte interphase (SEI) for the Zn metal anodes, which can significantly reduce zinc nucleation overpotential and lead to the dendrite-free deposition of Zn metal along the (002) crystal plane more easily without any external stimulus. More importantly, the chelation between the modified amino groups and zinc ions can promote the formation of an ultra-even amorphous SEI upon cycling, reducing the activity of hydrate ions, and inhibiting the water-induced side reactions. As a result, the Zn||Zn symmetric cell with NBC film exhibits lower overpotential and higher cyclic stability. When coupled with the V2 O5 cathode, the practical pouch cell achieves superior electrochemical performance over 1000 cycles.

Enhanced adsorption of cadmium from aqueous solution by amino modification biochar and its adsorption mechanism insight

Cadmium (Cd) in industrial wastewater can accumulate in organisms in the aquatic environment, posing a severe threat to human health. Therefore, effective remediation of cadmium-contaminated water is necessary for public health and environmental sustainability. In this study, the amino groups were modified on the corn stalks biochar (CSBC) surface to prepare a highly selective Cd(Ⅱ) adsorbent (NH2-CSBC) by nitrification and reduction. Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis demonstrated that amino groups were modified on the surface of CSBC. The adsorption capacity of NH2-CSBC for Cd(Ⅱ) was 4 times that of the original CSBC. The adsorption kinetics results showed that the Cd(Ⅱ) adsorption process by NH2-CSBC can be well described by the pseudo-second-order kinetic model. The maximum adsorption capacity obtained by the Sips model fitting reached 375.58 mg/g. The adsorption thermodynamic results indicated that Cd(Ⅱ) adsorption by NH2-CSBC was a spontaneous endothermic process. The analysis results based on FTIR and XPS before and after Cd(Ⅱ) adsorption showed that the amino functional groups on the surface of NH2-CSBC have strong complexation with Cd(Ⅱ). In summary, it is feasible to modify amino groups on the surface of biochar, and the obtained amino-modified biochar could adsorb Cd(Ⅱ) quickly and efficiently, showing great potential in the treatment of heavy metal wastewater.

A defects-free ZIF-90/6FDA-Durene membrane based on the hydrogen bonding/covalent bonding interaction for gas separation

Mixed-matrix membranes (MMMs), consisting of nanoparticles and a polymeric matrix, have been proven high-efficiency separation media for gas separations. The interface engineering between the particles and polymeric matrixes is the key-point for MMMs to display an excellent separation performance. Herein, an amine modified ZIF-90 (ZIF-90-NH2) is dispersed in 6FDA-Durene to prepare MMMs, the modified amino groups can form the hydrogen bonding with 6FDA-Durene to enhance the compatibility of ZIF-90-NH2 and 6FDA-Durene. A 45 wt% ZIF-90-NH2/6FDA-Durene MMM demonstrated a high separation performance, surpassing the 2008 Robeson permeability-selectivity upper bounds. This satisfactory gas separation performance can be due to the intimate interactions between the 6FDA-Durene polymer and ZIF-90-NH2 nanoparticles via abundant hydrogen bonding. Furthermore, the covalent linkage of ZIF-90-NH2 with 6FDA-Durene can be driven by the tris(2-aminoethyl) amine (TAEA) vapor thermal modification method to realize the ring opening reaction, which further enhances the particles-polymer connection in the ZIF-90-NH2/6FDA-Durene-TAEA MMMs. Results show that the 45 wt% ZIF-90-NH2/6FDA-Durene-TAEA MMM exhibits a remarkably enhanced H2 permeability of 487.0 Barrer with a H2/CO2 selectivity of 35.8, which is 6.8 times higher than that of ZIF-90/6FDA-Durene-TAEA MMM. This strategy offers new prospects for membrane materials and opens a new way for the precise interface engineering of MMMs, and the resulting high performance for energy-efficient gas separations.

Amino group-driven distinguishing homocysteine from cysteine and glutathione in photoluminesecent signal of the iridium(III) complexes

In this work, six iridium(III) complexes have been designed, synthesized and characterized. The molecular structures of complex 1 ([(pba)2Ir(bpy-2N(CH3)2)]PF6), 2 ([(pba)2Ir(bpy-2NH2)]PF6) and 3 ([(pba)2Ir(bpy-2CH3)]PF6) were determined by single crystal X-ray diffraction. Upon addition of Hcy (homocysteine) to the solution of complex 1, a luminescent variation from orange red to green was observed by the naked eye, corresponding to a large blue shift from 604 nm to 498 nm (~106 nm). While the emission intensity of complex 1 was almost no change after addition of other common amino acids including Cys (cysteine) and GSH (glutathione). The aldehyde group of complex 1 formed a new thiazinane/thiazolidine ring with Hcy/Cys confirmed by 1H NMR and high-resolution mass spectrometry. And the new product 1-Hcy had a higher quantum yield than 1-Cys. Theoretical calculations showed that the HOMO (highest occupied molecular orbital) of 1-Hcy was located on the newly formed six-membered thiazinane ring, which was different from the HOMO of 1-Cys. Compared with the other iridium(III) complexes, we can speculate that the large blue shift and enhancement of the emission intensity of the complex 1 were related to the strong electron donating ability of the modified amino groups on bipyridine ligand. This will provide an idea for the design of ratio-based luminescence probes for Hcy in future.

Wafer-scalable chemical modification of amino groups on graphene biosensors.

Graphene's remarkable attributes make it suitable for application to biosensors for biomolecular recognition. Specific and precise target detection is realized by designing robust methods for immobilization of probe molecules, such as oligonucleotides, antibodies, receptors, and sugar chains, to a device surface. In this research, we developed a chemical modification method with a plasma treatment of amino groups on natural defects of graphene, which is compatible with a wafer-scalable semiconductor process, to prevent deterioration of the carrier mobility. The plasma treatment was optimized in terms of the efficiency of the amino radical generation, length of the mean free path, and reaction energy on graphene. The density of the modified amino groups on graphene was approximately 0.065 groups/nm2, and the change in the ΔId/ΔVg characteristic of the graphene field-effect transistor (FET) was negligible. DNA probes were then attached to the amino groups on the graphene FET. The target complementary DNA was detected at 1 nM after hybridization using the graphene FET devices. The plasma-assisted modification of the amino groups on the graphene surface was developed for immobilization of the DNA probes, and hybridization with the target DNA was demonstrated without deterioration of the carrier mobility.

Hemishell Zeolites Synthesized by Asymmetric Modification as Biphasic Nanoreactors with Tunable Amphiphilicity for Catalysis of Cascade Reactions.

It is strongly desired to design and synthesize amphiphilic nanoreactors with tunable compatibility, which are stable at the biphasic interface in both acidic and alkaline environments. Herein, a novel amphiphilic R1-ZSM-5-R2 nanoreactor with adjustable hydrophilic-lipophilic balance (solid) (HLB(S)) values has been successfully synthesized by hydrophilic/lipophilic asymmetric modification of the surface of hemishell zeolites. The hemishell zeolites obtained by alkali etching have different surfaces for this asymmetric modification. Owing to the unique hemishell structures and asymmetric modification, the R1-ZSM-5-R2 nanoreactors with an optimized type and amount of modified organosilanes show excellent stability and emulsifying properties under extreme environments, which is important for cascade reactions in a biphasic system. The modified amino groups on the surface of the nanoreactors not only enhance the hydrophilicity of the hemishell zeolites and stabilize ultrasmall Pt nanoparticles (1.90 nm) but also used for the catalytic synthesis of trans-cinnamaldehyde. The Pt@R1-ZSM-5-R2 amphiphilic catalysts fabricated through a one-step reduction of Pt nanoparticles present outstanding performances in the biphasic cascade synthesis of cinnamic acid, achieving a very high turnover frequency (TOF) of 978 h-1. The TOF values of the catalysts correspond well to the HLB(S) values of the R1-ZSM-5-R2 nanoreactors.

An electrochemiluminescence aptamer sensor for chloramphenicol based on GO-QDs nanocomposites and enzyme-linked aptamers

In this paper, CdS quantum dots (QDs) were synthesized. Positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged CdS quantum dots were sequentially adsorbed on the surface of graphene oxide (GO). The nano-luminescent materials GO-QDs were prepared and characterized by UV–Vis absorption spectroscopy, fluorescence spectroscopy and transmission electron microscopy. The GO-QDs were then modified on the surface of glassy carbon electrode (GCE). Chloramphenicol aptamer (apt) of 5′-end modified biotin hybridized with the aptamer complementary strand (cDNA) of 5′-end modified amino group into double-stranded DNA (dsDNA). The double-stranded DNA was bonded onto the surface of GO-QDs modified electrode. When the electrode was incubated with streptavidin - labeled horseradish peroxidase (SA-HRP), the biotin modified at the end of the chloramphenicol aptamer can specifically bind directly to the streptavidin labeled HRP. Therefore, HRP was bonded to the surface of the electrode. Hydrogen peroxide was used as the co-reactant of the QDs. HRP can thereby consume hydrogen peroxide and can weaken the electrochemiluminescence intensity. Chloramphenicol in solution can specifically bind to the aptamer to form a composite and to unwind the dsDNA. Then the composite was detached from the surface of the electrode. HRP also left the electrode surface along with the aptamer, so that the electrochemiluminescence signal was significantly enhanced. The electrochemiluminescence intensity of the sensor showed a linear correlation with the logarithm of chloramphenicol concentration. The linear range was 1.0 × 10−12–1.0 × 10−7 M, the detection limit is 0.5 pM. The reproducibility, stability and specificity of the sensor were also studied. The sensor was used for the determination of chloramphenicol in samples and satisfactory results were obtained.

Edge enriched self-assembly of Au nanoparticles: Coffee-ring effect during microcontact printing via agarose stamps

Amino functionalized surfaces were selectively modified via the combination of a wet agarose stamping technique and microcontact printing technique. Because of the specific reaction environments and diffusion of HNO2 confined in agarose stamp, the reaction of amino groups in the edge of the strip pattern was much more intense than other areas. The modified amino groups in the edge areas show higher affinity to Au-NPs than other areas, consequently, edge enriched Au-NPs patterns were observed after the self-assembly of Au-NPs. A “cylindrical droplet” model, in a manner analogous to “coffee-ring” effect, was proposed to describe the diffusion of HNO2 from the bulk to the edge in agarose stamp. By using such density varied Au-NPs patterns as templates for the growth of ZnO nanorods, we observed high density of Au-NPs resulting in high density and highly (0 0 1) oriented ZnO nanorods. In contrast, sparse and non-oriented ZnO nanorods were grew on low density of Au-NPs areas. Our findings might open new routes for the fabrication of gradient patterns and extend applications of Au-NPs patterns in surface enhanced Raman scattering and catalysis.

Properties of Bioconjugates of Streptokinase with Anionic Polyamidoamine Dendrimers of Various Generations

Covalent conjugates of streptokinase (SK) with polyamidoamine (PAMAM) dendrimers G1.5, G2.5, and G3.5 (SK–G1.5, SK–G2.5, and SK–G3.5) with the protein–polymer molar ratios of (1: 1), (1: 5), and (1: 10) were obtained and their properties were studied as compared to the properties of free SK. It was shown that the initial rates of formation of the modified Pm. SK complex, activation of plasminogen, and lysis of the plasma clot under the action of SK–dendrimer conjugates decreased with increasing number of bound dendrimers (from 1 to 10) and increased with increasing dendrimer generation (from G1.5 up to G3.5). Conjugates SK–G3.5 (1: 1) and (1: 5) were the most active compared to other conjugates. It was found that the catalytic efficiency of plasminogen activation (kPg/KPg) by conjugates SK–G3.5 (1: 1) (0.15 μM–1 min–1) and SK–G3.5 (1: 5) (0.12 μM–1 min–1) was comparable to the efficiency of free SK (0.18 μM–1 min–1). Probably, small in size, soft, and easily deformable dendrimers G1.5 and G2.5 are able to penetrate into the internal shielded cavities of the native SK molecule and there modify amino groups that are important for the effective formation of the Pm · SK complex. By contrast, the larger and more rigid molecule of dendrimer G3.5 modifies, mainly, exposed lysine residues in the SK molecule, without affecting the latent internal lysines. Conjugates SK–G3.5 (1: 1) and (1: 5), which had the maximum activator activity, retained up to 85% of thrombolytic activity compared to the activity of free SK. In addition, due to modification of the exposed lysines—most sensitive to proteolysis in the SK molecule—with dendrimer G3.5, which has the highest density of negative charge on its surface, SK–G3.5 (1: 1) and (1: 5) conjugates were more stable in plasma and caused less exhaustion of plasma levels of plasminogen, α2-antiplasmin, and fibrinogen than free SK in vitro. Thus, thrombolytic activity of the SK–dendrimer conjugates depends on the degree of modification of the amino groups of SK, size, stiffness, and density of the negative charge on the surface of the PAMAM dendrimer. Conjugates SK–G3.5 (1: 1) and (1: 5) are potential candidates for the development of a new thrombolytic agent.

Aggregation‐Induced Emission, Functionalized Fluorescent Nanoparticles and Cells Imaging of a Water‐Soluble Pyridyl‐Naphthalimide Dendron

AbstractThis paper reports on the design, synthesis and spectral characteristics of a novel pyridyl‐naphthalimide aggregation‐induced emission (AIE) dendron named PADN, and intermediate compound named PAN. PADN and PAN emitted brightly fluorescence in solid state and a maximum emission wavelength at 497 nm (green fluorescence) and 454 nm (blue fluorescence) in pure THF solution respectively. A considerable fluorescence intensity was found for PADN when water fraction reached a high value (the quantum yield of 90% water fraction was 0.15). Because of a stable core‐shell structure by the surface contains easily modified amino groups, the two AIE‐dendrons were successfully encapsulated in silica matrix, emitting bright green fluorescence with 0.33 quantum yield (PADN) and clear blue fluorescence with 0.27 quantum yield (PAN). Additionally, dye PADN was successfully applied for cell imaging, getting clear green‐field photograph, which indicated a better uptake by lung cancer cells A‐549 and suggested its promising application for biosensors.

Template synthesis of imine-based covalent organic framework core-shell structure and hollow sphere: a case of COFTTA-DHTA

Controllably synthesizing well-dispersed covalent organic frameworks (COFs) with uniform both morphology and size is still a challenge. Herein, we report the template-directed synthesis of COFTTA-DHTA-based core-shell hybrids under solvothermal conditions by using amino-functionalized SiO2 microspheres as templates coupled with stepwise addition of initial monomer molecules. The modified amino groups on the surfaces of SiO2 templates play an important role in the formation of well-defined NH2-f-SiO2@COFTTA-DHTA core-shell hybrids. COFTTA-DHTA hollow spheres can be obtained by etching SiO2 cores of NH2-f-SiO2@COFTTA-DHTA. Both the NH2-f-SiO2@COFTTA-DHTA and COFTTA-DHTA hollow spheres possess the well-defined morphology, high crystallinity and porosity, excellent dispersion property and high chemical stability. The template synthesis method demonstrated in this work provides a general method for the shape-controlled synthesis of COF-based materials, which is important for the further applications in the fields such as energy storage, drug delivery and catalysis.

Purification and identification of high molecular weight products formed during storage of neutral formulation of human insulin.

To identify High Molecular Weight Products (HMWP) formed in human insulin formulation during storage. Commercial formulation of human insulin was stored at 37°C for 1year and HMWP was isolated using preparative size exclusion chromatography (SEC) and reverse phase (RP) chromatography. The primary structure of the isolated species was analysed using liquid chromatography mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS). To test the hypothesis that amino groups of insulin are involved in HMWP formation, the HMWP content of various formulations spiked with amine compounds or formulations of insulin with modified amino groups was measured. More than 20 species of HMWP were observed and 16 species were identified using LC-MS. All identified species were covalent dimers of human insulin linked via A21Asn and B29Lys, formed via the formation of an anhydride intermediate at A21Asn. Two types of HMWP were identified, with the covalent link in the open or closed (succinimidyl) form. Some species also contained single deamidation at B3 or the desPhe(B1)-N-oxalyl-Val(B2) modification. Reduced rate of HMWP formation was observed after addition of L-lysine, L-arginine or piperazine or when insulin analogues with methylated N-terminals and side chain amines and A21Gly mutation were used. Formulations of human insulin without zinc and m-cresol were found to contain a different pool of HMWP. HMWP formed in formulation of human insulin at pH 7.4 with zinc and m-cresol consists primarily of covalent dimers linked via A21Asn and B29Lys. Insulin formulation properties determine the amount and identity of formed HMWP.

Development of a Silica Surface Modified with Reactive Amino Group as an Immobilized Carrier for Use as Biosensor Material

In this study, the surface of a silica particle modified with a reactive amino group was developed as an immobilized carrier for use as a biosensor material. Silica particles with a diameter of 5 μm were modified with N-2(aminoethyl)-3-amino-propyl trimethoxysilane as a silane coupling agent at 100 °C at heating rates of 2.2, 3.0, and 6.0 °C/min. These particles were reacted with various concentrations of fluorescein isothiocyanate (FITC) at room temperature for 5 min. FITC-labeled samples exhibited green fluorescence at 520 nm, which was examined by a fluorescence microscope. The fluorescence intensity of a FITC-labeled silica surface was found to increase in two steps with increasing FITC concentration. The rate of increase in fluorescence intensity was higher in step I than in step II for all samples. However, the rate of increase in fluorescent intensity in step I, as well as the amount of reactive amino groups on a silica surface, was strongly affected by the heating rate in the silane coupling reaction. On the basis of these results, conditions of silane coupling reaction and the effect of the conformation of modified amino groups on the silica surface on reactivity were discussed.

Increased levels of aldehyde-modified collagen type iv in symptomatic atherosclerotic lesions

Objectives: Subendothelial LDL-adhesion and its subsequent oxidation are considered as key events in the development of atherosclerotic lesions. During oxidation of LDL, reactive aldehydes such as malondialdehyde are formed, which modify amino groups of apolipoprotein B100. However, the possibility that these reactive aldehydes could leak out of the LDL-particle and modify surrounding extracellular matrix proteins has been largely unexplored. Here we investigated if aldehyde-modified collagen type IV, one of the major basement membrane components, in plaque extracts is associated with cardiovascular events.

Comparison of modification of a bacterial uricase with N‐hydroxysuccinimide esters of succinate and carbonate of monomethoxyl poly(ethylene glycol)

Uricase after modification with monomethoxy poly(ethylene glycol) (mPEG) is currently the sole agent to treat refractory gout. For formulating Bacillus fastidious uricase, succinimidyl carbonate of mPEG-5000 (SC-mPEG5k) and succinimidyl succinate of mPEG-5000 (SS-mPEG5k) were compared. SC-mPEG5k possessed higher purity, comparable reaction rate constant with glycine but lower hydrolysis rate, and stronger effectiveness to modify amino groups. The uricase possessed two types of amino groups bearing a 25-fold difference in reactivity with SC-mPEG5k or SS-mPEG5k at pH 9.2. Oxonate and xanthine concentration-dependently protected the bacterial uricase from inactivation during PEGylation. With SC-mPEG5k at a molar ratio of 200 to uricase subunits and oxonate of 50µM, the PEGylated uricase (1) retained about 73% of the original activity, (2) displayed about 10% reactivity to rabbit anti-sera recognizing the native uricase, (3) elicited IgG in rats accounting for about 5% of that by the native uricase, (4) exhibited circulation half-life time of about 25H in cock plasma in vivo, and (5) concurrently maintained uric acid at lowered levels for over 20H. Hence, PEGylation with SC-mPEG under the protection of a competitive inhibitor was a practical approach to formulation of the bacterial uricase; protection of enzymes by competitive inhibitors during PEGylation may have universal significance.

Reaction of quinolines fluorinated at the benzene ring with nitrogen-centered nucleophiles

A primary functionalization of quinolines polyfluorinated at the benzene ring (5,7-difluoro-, 5,7,8-trifluoro-, 5,6,8-trifluoro-, 8-chloro-5,7-difluoro-, 5,6,7,8-tetrafluoro-, and 5,7,8-trifluoro-6-(trifluoromethyl)quinolines) by the reaction with nitrogen-centered nucleophiles (aqueous and liquid ammonia, hydrazine hydrate, piperidine) has been studied. If the molecule of fluorinated quinoline contains three or four halogen atoms, their combined orientation effect outweighs the influence of the heterocycle N atom. It was found that the orientation of substitution in the reactions of 5,6,8-trifluoro- and 5,7,8-trifluoro-6-(trifluoromethyl)quinolines with piperidine depends on temperature, because the enthalpy control of the ratio of the rates of competing reactions changes to the entropy control. Nineteen new quinoline derivatives containing F atoms and amino or modified amino groups in the benzene ring have been obtained.

Chemical modification of Art v 1, a major mugwort pollen allergen, by cis-aconitylation and citraconylation

Art v 1 is the major allergen of mugwort (Artemisia vulgaris) pollen, a significant cause of hay fever all over Europe. Specific immunotherapy is the only treatment modality for allergic disease. Application of modified allergens makes the treatment safer and more efficient. In this work, two out of three (citraconic anhydride, cis-aconitic anhydride, 2,3-dimethylmaleic anhydride) tested anhydrides were proven to be suitable for chemical modifications of allergens. Art v 1 was modified by cis-aconitylation and citraconylation in order to obtain derivatives of Art v 1 that may be suitable for further immunological testing. Acylation of Art v 1 gave derivatives (caaArt v 1 and citArt v 1) with about 80 % modified amino groups. The derivatives were in the monomeric form and had dramatically reduced pI values. Both derivatives were relatively stable at neutral pH values, while the acyl groups undergo hydrolysis under acidic conditions. Modification of allergens by cis-aconitylation and citraconylation could be a new tool for obtaining allergoids.

Hyperbranched poly(L-lysine) modified with histidine residues via lysine terminal amino groups: Synthesis and structure

A method for preparing hyperbranched poly(L-lysine) via the polymerization of Nɛ-carbobenzoxy-L-lysine-N-carboxyanhydride has been developed in order to regulate the molecular mass and size of this polymer and to modify amino groups of its N-terminal lysine residues. This method includes the reductive removal of an Nɛ-carbobenzoxy group by hydrogen over activated palladium in the presence of a chain termination agent, which is the activated ether of Nα-tert-butyloxycarbonylhistidine. The structure of the polymers has been studied by capillary electrophoresis, circular dichroism, and molecular hydrodynamics.

Monitoring the effect of glyoxal and methylglyoxal glycation on the secondary structure of human serum albumin: an analysis based on CD, ESI‐MALDI‐TOF/MS, thermal melting profiles and UV fluorescence spectroscopy

Glyoxal and methylglyoxal (MG) are reactive dicarbonyl compounds, which modify amino groups of proteins to form advanced glycation endproducts (AGEs), that are involved in diabetes complications. The objective of this investigation was to determine the effects of nonenzymatic glycation of glyoxal and MG on the secondary structure of human serum albumin (HSA) and to evaluate the factors that influence the modification of HSA with glyoxal and MG. The formation of AGEs was monitored by HPLC, MALDI‐TOF/MS, UV, and fluorescence spectroscopy. The change in the secondary structure of HSA was determined by circular dichroism (CD) and thermal melting (Tm) profiles of the native and glycated proteins. UV and fluorescence demonstrate that the extent of AGE formation was dependent on both glyoxal and MG concentration and incubation time. The CD profiles demonstrated that HSA was a‐helical in structure, and low concentrations (2 mM) of glyoxal or methylglyoxal destabilized HSA while high concentrations (40 mM) preserved and stabilized the a‐helical structure of the protein. This was confirmed by thermal melting profiles. Finally, MALDI‐TOF/MS was successfully applied for site‐ and product‐specific relative quantification of AGEs. Supported in part by NCRR/NIH Grant # P20 RR16457.