Aspartic Acid Molecules Research Articles

The Feasibility of Targeted Magnetic Iron Oxide Nanoagent for Noninvasive IgA Nephropathy Diagnosis.

IgA nephropathy is the most common glomerular disease in the world and has become a serious threat to human health. Accurate and non-invasive molecular imaging to detect and recognize the IgA nephropathy is critical for the subsequent timely treatment; otherwise, it may progress to end-stage renal disease and lead to glomerular dysfunction. In this study, we have developed a sensitive, specific, and biocompatible integrin αvβ3-targeted superparamagnetic Fe3O4 nanoparticles (NPs) for the noninvasive magnetic resonance imaging (MRI) of integrin αvβ3, which is overexpressed in glomerular mesangial region of IgA nephropathy. The rat model of IgA nephropathy was successfully established and verified by biochemical tests and histological staining. Meanwhile, the clinical 18F-AlF-NOTA-PRGD2 probe molecule was utilized to visualize and further confirmed the IgA nephropathy in vivo via positron emission computed tomography. Subsequently, the Fe3O4 NPs were conjugated with arginine–glycine–aspartic acid (RGD) molecules (Fe3O4-RGD), and their integrin αvβ3-targeted T2-weighted imaging (T2WI) potential has been carefully evaluated. The Fe3O4-RGD demonstrated great relaxation in vivo. The T2WI signal of renal layers in the targeted group at 3 h after intravenous injection of Fe3O4-RGD was distinctly lower than baseline, indicating MRI signal decreased in the established IgA nephropathy rat model. Moreover, the TEM characterization and Prussian blue staining confirmed that the Fe3O4-RGD was located at the region of glomerulus and tubular interstitium. Moreover, no obvious signal decreased was detected in the untargeted Fe3O4 treated and normal groups. Collectively, our results establish the possibility of Fe3O4-RGD serving as a feasible MRI agent for the noninvasive diagnosis of IgA nephropathy.

Assessment of Electrochemical Activity of some Amino acids on the Modified Carbon Electrode Surface

The present work analyzed the electrochemical activity of certain amino acids on the modified carbon electrode as-prepared, such as glycine, threonine and aspartic acid. The electrochemical methods used to investigate surface electrode behavior through amino acid molecules at a fixed concentration and temperature of 298.15 K in the perchloric acid electrolyte solution. The findings showed that the surface electrode was ideal for the analysis of glycine, threonine, and aspartic acid molecules. Aspartic acid showed electrochemical activity by voltage and polarization resistance to 0.533 mV and 9.557 ohms, respectively. In addition, the FE-SEM images showed the thin film layer on the surface electrode from the amino acid molecules in different shapes and dense aggregations, more with aspartic acid under optimum experimental conditions.

Investigation of the phosphorene nano-sheet as a sensor for detecting aspartic-acid, alanine and glycine amino acids: A first principle study

In this study, we have theoretically investigated the application of phosphorene nano-sheet as a biosensor for detecting some amino acids such as alanine, glycine and aspartic-acid using density functional theory (DFT). The results of the electronic properties show that the phosphorene nano-sheet has a direct band gap of about 0.84 eV and the presence of alanine, glycine and aspartic-acid adsorbed on the surface of phosphorene reduces the band gap slightly. The charge transfer analysis between phosphorene nano-sheet and the amino acid molecules shows that aspartic-acid molecule acts as an electron donor, while alanine and glycine molecules act as electron acceptors. Our calculations demonstrate that there is a strong anisotropy in electron/hole effective mass mh*) mh*)along armchair and zigzag directions of pristine and molecular adsorbed phosphorene. This leads to a quenching of conductivity in the zigzag direction with respect to the armchair direction. Based on the changes of electron/hole effective mass of phosphorene under the influence of the adsorption of the amino acid molecules, we have suggested a phosphorene-based biosensor. This biosensor has the best sensibility and selectivity when measuring hole effective mass along the armchair direction. The maximum sensibility was found to be around 59.3% to aspartic acid molecule. Our findings confirm that phosphorene nano-sheet can be applied as a promising biosensor for detecting amino acid molecules.

Aspartic acid adsorption on thermoelectric surfaces

Using molecular dynamics based on density functional theory, interaction of aspartic acid (C4H7NO4) with room-temperature thermoelectrics Bi2Te3, SnSe, MgAgSb, and TiO2 alloyed with V is investigated. Aspartic acid is a common amino acid in mammals, decorating a cell membrane, and hence relevant for biocompatibility. Ti(0001), Zn(0001), Pd(111), Pb(111), and Cu(111) surfaces are employed to gauge such interactions, yielding an approximate adsorption energy threshold of −0.060 eV atom−1. Based on this threshold, Bi2Te3(0001) and SnSe(001) are rendered inert, while MgAgSb(001) and TiO2(001) alloyed with V are proposed to be biocompatible. An aspartic acid molecule undergoes a non-dissociative adsorption on MgAgSb(001). The interaction of aspartic acid with TiO2(001) alloyed with V is characterized by deprotonation of a carboxyl group, a subsequent TiO interfacial bond formation, and a reaction of an amino functional group with Ti. Short covalent-ionic bonds across these interfaces support the findings. These results may inspire future research on self-powered biomedical devices.

Experimental and theoretical study of Aspartic acid

The aim of this research is to detect zwittterionic structure of the aspartic acid and confirm the experimental spectra with quantum chemical calculations. The experimental IR and Raman spectra of aspartic acid powder show no vibrational bands of OH and NH stretching in expected spectral region. We assume that zwitterionic structure of aspartic acid is responsible for lowering the frequencies of these vibrations. An extensive experimental and computational research supports this assumption. Our DFT calculation strongly suggests the need for the dielectric environment in order to stabilize the zwitterionic structure of a single molecule. The network of intermolecular hydrogen bonding between aspartic acid molecules provides this dielectric environment. The DFT quantum mechanical calculations corroborate this assumption by optimizing a four-member group of molecules, which also gives an explanation of broad IR spectrum lines.

Deciphering the Adsorption Mechanisms of RGD Subunits: l-Aspartic Acid on Cu(110)

In this work we present a detailed surface science characterization of l-aspartic acid adsorption on a Cu(110) surface. Aspartic acid is one of the main components of the tripeptide RGD (arginine–glycine–aspartic acid). We replaced the traditional sublimation method to obtain molecular films by dosing aspartic acid directly from an aqueous solution through an electrospray ionization (ESI) device. X-ray photoelectron spectroscopy (XPS) and polarization modulation reflection absorption infrared spectroscopy (PM-RAIRS) evidenced different adsorption states ranging from a submonolayer regime up to multilayers. Molecule–substrate interactions guide the creation of the pattern observed in the submonolayer, but molecule–molecule interactions are prevailing from a certain coverage stage, promoting the overlayer growth while leaving exposed areas of bare copper. This is evidenced by scanning tunneling microscopy (STM) results, showing that single aspartic acid molecules self-organize in a two-dimensional (2D) chiral network at low coverage and start originating new molecular layers even before a saturated monolayer has been reached.

Physicochemical properties of aqueous solutions of L-aspartic acid containing chitosan

Physicochemical properties of aqueous solutions of L-aspartic acid with and without addition of chitosan have been studied by conductometry, potentiometry, refractometry, tensiometry, and viscosimetry. It has been shown that aspartic acid molecules take a cyclic configuration stabilized by hydrogen bonds in aqueous solution at c > 0.04 g/dL (298 K). The interaction of chitosan with aspartic acid results in the formation of the polymeric salt that dissociates in aqueous solution to give chitosan polycation [~(NH3)+] and aspartate counterions. The addition of chitosan to solutions of L-aspartic acid results in progressive increase in the surface tension, absorbance, and refractive index as well as the change in hydrodynamic properties of the macromolecules. The polymeric salt exhibits polyelectrolyte properties in dilute aqueous solutions. The increase in temperature impairs the thermodynamic quality of the solvent for chitosan leading to the shrinkage of the polymer coils and, hence, to the decrease in the intrinsic viscosity of the system.

Resonant electron capture by aspartame and aspartic acid molecules

The processes for dissociative electron capture are the key mechanisms for decomposition of biomolecules, proteins in particular, under interaction with low-energy electrons. Molecules of aspartic acid and aspartame, i.e. modified dipeptides, were studied herein to define the impact of the side functional groups on peptide chain decomposition in resonant electron-molecular reactions. The processes of formation and decomposition of negative ions of both aspartame and aspartic acid were studied by mass spectrometry of negative ions under resonant electron capture. The obtained mass spectra were interpreted under thermochemical analysis by quantum chemical calculations. Main channels of negative molecular ions fragmentation were found and characteristic fragment ions were identified. The СООН fragment of the side chain in aspartic acid is shown to play a key role like the carboxyl group in amino acids and aliphatic oligopeptides. Copyright © 2016 John Wiley & Sons, Ltd.

Structural evidence for solvent-stabilisation by aspartic acid as a mechanism for halophilic protein stability in high salt concentrations.

Halophilic organisms have adapted to survive in high salt environments, where mesophilic organisms would perish. One of the biggest challenges faced by halophilic proteins is the ability to maintain both the structure and function at molar concentrations of salt. A distinct adaptation of halophilic proteins, compared to mesophilic homologues, is the abundance of aspartic acid on the protein surface. Mutagenesis and crystallographic studies of halophilic proteins suggest an important role for solvent interactions with the surface aspartic acid residues. This interaction, between the regions of the acidic protein surface and the solvent, is thought to maintain a hydration layer around the protein at molar salt concentrations thereby allowing halophilic proteins to retain their functional state. Here we present neutron diffraction data of the monomeric zwitterionic form of aspartic acid solutions at physiological pH in 0.25 M and 2.5 M concentration of potassium chloride, to mimic mesophilic and halophilic-like environmental conditions. We have used isotopic substitution in combination with empirical potential structure refinement to extract atomic-scale information from the data. Our study provides structural insights that support the hypothesis that carboxyl groups on acidic residues bind water more tightly under high salt conditions, in support of the residue-ion interaction model of halophilic protein stabilisation. Furthermore our data show that in the presence of high salt the self-association between the zwitterionic form of aspartic acid molecules is reduced, suggesting a possible mechanism through which protein aggregation is prevented.

Difference in the Conformation and Dynamics of Aspartic Acid on the Flat Regions, Step Edges, and Kinks of a Calcite Surface: A Molecular Dynamics Study

Molecular dynamics simulations were conducted to investigate the conformation and dynamics of an aspartic acid molecule near the {104} and {110} planes of a CaCO3 calcite crystal, near the acute and obtuse [114] step edges on the {104} plane, and near kinks formed at the step edges. The simulations indicate that the amino acid binds indirectly to the {104} plane, whereas it binds directly to the {110} plane. The simulations also indicate that the acid binds directly to the acute step edge but does not bind to the obtuse step edge. These differences in the binding of the acid to the planes and the step edges were attributed to a difference in the structure of the surrounding water. The simulations also indicate that the acid binds to the kink formed at both the acute and the obtuse step edges, if a Ca2+ ion is placed at the corner of the kink. The binding was much stronger at the kink than at the planes and the step edges.

Optical absorption and DFT calculations inL-aspartic acid anhydrous crystals: Charge carrier effective masses point to semiconducting behavior

Density functional theory (DFT) computations within the local-density approximation and generalized gradient approximation in pure form and with dispersion correction (GGA+D) were carried out to investigate the structural, electronic, and optical properties of $L$-aspartic acid anhydrous crystals. The electronic (band structure and density of states) and optical absorption properties were used to interpret the light absorption measurements we have performed in $L$-aspartic acid anhydrous crystalline powder at room temperature. We show the important role of the layered spatial disposition of $L$-aspartic acid molecules in anhydrous $L$-aspartic crystals to explain the observed electronic and optical properties. There is good agreement between the GGA+D calculated and experimental lattice parameters, with ($\ensuremath{\Delta}a$, $\ensuremath{\Delta}b$, $\ensuremath{\Delta}c$) deviations of ($0.029,\ensuremath{-}0.023,\ensuremath{-}0.024$) (units in \AA{}). Mulliken [J. Chem. Phys. 23, 1833 (1955)] and Hirshfeld [Theor. Chim. Acta 44, 129 (1977)] population analyses were also performed to assess the degree of charge polarization in the zwitterion state of the $L$-aspartic acid molecules in the DFT converged crystal. The lowest-energy optical absorption peaks related to transitions between the top of the valence band and the bottom of the conduction band involve O 2$p$ valence states and C 1$p$ and O 2$p$ conduction states, with the carboxyl and COOH lateral chain group contributing significantly to the energy band gap. Among the calculated band gaps, the lowest GGA+D (4.49-eV) gap is smaller than the experimental estimate of 5.02 eV, as obtained by optical absorption. Such a wide-band-gap energy together with the small carrier effective masses estimated from band curvatures allows us to suggest that an $L$-aspartic acid anhydrous crystal can behave as a wide-gap semiconductor. A comparison of effective masses among directions parallel and perpendicular to the $L$-aspartic molecules layers reveals that charge transport must be favored in the former case. Finally, we also show that there is a strong optical anisotropy in the dielectric function of $L$-aspartic acid anhydrous crystals.

Quantum Chemistry on Graphical Processing Units. 3. Analytical Energy Gradients, Geometry Optimization, and First Principles Molecular Dynamics.

We demonstrate that a video gaming machine containing two consumer graphical cards can outpace a state-of-the-art quad-core processor workstation by a factor of more than 180× in Hartree-Fock energy + gradient calculations. Such performance makes it possible to run large scale Hartree-Fock and Density Functional Theory calculations, which typically require hundreds of traditional processor cores, on a single workstation. Benchmark Born-Oppenheimer molecular dynamics simulations are performed on two molecular systems using the 3-21G basis set - a hydronium ion solvated by 30 waters (94 atoms, 405 basis functions) and an aspartic acid molecule solvated by 147 waters (457 atoms, 2014 basis functions). Our GPU implementation can perform 27 ps/day and 0.7 ps/day of ab initio molecular dynamics simulation on a single desktop computer for these systems.

Aspartic acid nucleates the apatite crystallites of bone: a hypothesis

This review concentrates on the physical state of bone mineral at the nanosize range, where it exists as ultrathin, tiny, platelike particles. They have a distinct X-ray pattern, different from that of apatite crystals, but shared by all bone matter irrespective of source or architecture. The main feature of this diffractogram is a broadened undifferentiated and asymmetric peak at about 32°. The mineral contains several percents of carbonate and also other foreign elements and ions at low concentrations. When new bone is regenerated at a site of damage or resorption, such nanoparticles have to be created as the first step to progressive organizations at higher levels of bone composition. They are generated under cellular control. As they are produced in huge numbers, homogeneous in character, there is no escape from the conclusion that they are nucleated on compounds excreted by the cells and being not foreign to the surrounding. Evidence has been obtained that aspartic acid (AspA), one of the amino acids, which compose all life, has a specific beneficial effect on bone regeneration in an animal model experiment. An analysis of the possible interaction between aspartic acid molecule and the crystallographic unit cell of hydroxyapatite was attempted and is presented in this review. Hydroxyapatite has a large and complex unit cell, and therefore the interaction between such unit and a tiny acid calls for a special array in which the aspartic acid is enclosed inside a carbonated, calcium deficient unit, apparently without changing its external appearance and is able to start assemblage of regular apatite units. The nucleation event depends upon substitution of four carbonate ions in the sites of four phosphate ions. This substitution causes generation of four voids that can accommodate the four terminal oxygen of the aspartic acid. Such unit serves as a nucleating unit.

Adsorption of aspartic acid on kaolinite

The interaction of aspartic acid with kaolinite was studied by potentiometric titrations and by adsorption measurements both at constant aspartate concentration (but varying pH) and at a constant pH of 5.5. The temperature was 25 °C, and the ionic medium 5 mM KNO 3. Aspartic acid dissociation constants estimated from titrations agreed with those from the literature. The adsorption of aspartic acid to kaolinite was weak and varied only slightly with pH; 10–18% of 100 μM aspartic acid adsorbed to kaolinite at 100 m 2 L −1 between pH 3 and 10. Data from the titrations and adsorption experiments were fitted closely by an extended constant-capacitance surface complexation model, in which monodentate outer-sphere complexes formed between deprotonated aspartic acid molecules and protonated sites on the variable-charge edges of the kaolinite crystals. There appeared to be no adsorption to the permanently charged crystal faces.

Kinetics of dehydration–polymerization of aspartic acid and synthesis of polyaspartate catalyzed by potassium bisulfate

The dehydration–polymerization kinetics of DL- and L-aspartic acid, either in the absence or presence of KHSO4, from 323 to 573 K, was studied by thermogravimetric analysis (TGA), and the synthesis of polyaspartate through the polymerization of L-aspartic acid was investigated by a thin-layer polymerization method. The TGA results revealed that the dehydration–polymerization of both type of aspartic acids proceeds in two steps: first, the loss of one water molecule through the reaction of an amino group of one aspartic acid molecule and a hydroxyl group of another aspartic acid molecule, forming amide bonds, and secondly, the loss of another water molecule through the amide hydrogen and another hydroxyl group, leading to the formation of a succinimide ring. The kinetic parameters of the extrapolated onset temperatures of dehydration—the first and the second maxima—were obtained by a method similar to that of Ozawa–Flynn–Wall. The kinetic results indicate that the dehydration of L-aspartic acid is slightly more difficult than for DL-aspartic acid, and that the presence of potassium bisulfate effectively catalyzes the dehydration–polymerization of aspartic acid. In the synthesis of polyaspartate, the product with a weight-average molecular mass (Mw) of 5000 g mol−1 was obtained in the absence of catalyst. However, in the presence of potassium bisulfate, the products obtained had Mws of up to 7000 g mol−1 Copyright © 2003 Society of Chemical Industry

L-Aspartic acid monohydrate

In the title compound, C4H7NO4·H2O, the screw-related aspartic acid molecules are linked along the a axis by N—H⋯O hydrogen bonds to form helical structures. The adjacent helices are inter-linked through O—H⋯O hydrogen bonds and also by the water mol­ecules through N—H⋯O(W) and O(W)—H⋯O hydrogen bonds, to form a three-dimensional network.

Study on the Polymerization of Aspartic Acid Catalyzed by Phosphoric Acid

The dehydration kinetics of dl- and l-aspartic acid, either in the absence or presence of phosphoric acid, from 323 to 573K were studied with thermogravimetric analysis (TGA), and the polymerization of dl-aspartic acid was studied by a thin-layer polymerization method. The results revealed that the dehydration of both type aspartic acids proceeds in two steps: the first step might be the loss of one water molecule through the reaction of an amino group of one aspartic acid molecule and a hydroxyl of carboxyl group of another aspartic acid molecule, forming amide bonds, and the second step might be the loss of another water molecule through the amide hydrogen and another hydroxyl group, leading to the formation of succinimide ring. The kinetic parameters of the extrapolated onset temperatures of dehydration, the first and the second maximum were obtained by a method similar to the Ozawa–Flynn–Wall method. The results further revealed that the presence of phosphoric acid effectively catalyzed the dehydration of aspartic acid. In the synthesis of polyaspartate, only the product with molecular weight below 5000 was obtained in the absence of phosphoric acid. However, in the presence of phosphoric acid, the product with molecular weight up to 14,000 can be obtained.

Synthesis of New Anthracycline Derivatives Containing Pyruvic, Aspartic, or N‐Acetylaspartic Acid Molecule.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Magnetic Interactions in the Copper Complex (L-Aspartato)(1,10-phenanthroline)copper(II) Hydrate. An Exchange-Coupled Extended System with Two Dissimilar Copper Ions.

We report EPR measurements in single-crystal samples at the microwave frequencies 9.8 and 34.3 GHz and magnetic susceptibility measurements in polycrystalline samples for the ternary complex of copper with aspartic acid and phenanthroline, (L-aspartato)(1,10-phenanthroline)copper(II) hydrate. The crystal lattice of this compound is composed of two dissimilar copper ions identified as Cu(A) and Cu(B), which are in two types of copper chains called A and B, respectively, running parallel to the b crystal axis. The copper ions in the A chains are connected by the aspartic acid molecule, and those in the B chains by a chemical path that involves a carboxylate bridge and a hydrogen bond. Both chains are held together by a complex network of hydrogen bonds and by hydrophobic interactions between aromatic amines. Magnetic susceptibility data indicate a Curie-Weiss behavior in the studied temperature range (2-300 K). The EPR spectra at 9.8 GHz display a single exchange collapsed resonance for any magnetic field orientation, in the so-called strong exchange regime. Those at 34.3 GHz are within the so-called weak exchange regime and display two resonances which belong to each type of copper ion chain. The decoupling of the spectra at 34.3 GHz using a theory based on Anderson's model for the case of two weakly exchange coupled spins S = (1)/(2) allows one to obtain the angular variation of the squares of the g-factor and the peak-to-peak line width of each resonance. This model also allows one to evaluate the exchange parameter |J(AB)/k| = 2.7(6) mK associated with the chemical path connecting dissimilar copper ions. The line width data obtained for each component of the spectra at 34.3 GHz are analyzed in terms of a model based on Kubo and Tomita's theory, to obtain the exchange parameters |J(A)/k| = 0.77(2) K and |J(B)/k| = 1.44(2) K associated with the chemical paths connecting the similar copper ions of types A and B, respectively.

Crystal and molecular structure of DL-aspartic acid nitrate monohydrate

Abstract DL-aspartic acid nitrate monohydrate, (C4H8NO4)+(NO3)− · H2O, M = 214.128, triclinic, P[unk], a = 5.680(1) Å, b = 7.331(2) Å, c = 10.812(1) Å, α = 76.74(1)°, β = 105.33(1)°, γ = 96.41(1)°, V = 422.0 Å3, Dm = 1.66 g cm−3 (flotation), Dc = 1.685 g cm−3 Z = 2, μ = 1.561 cm−1, λ(MoKα = 0.70926 Å. The crystal structure was solved by direct, Fourier and difference-Fourier methods and refined by full-matrix least-squares technique to an R = 0.041 and wR = 0.049 for 1249 unique reflections. The aspartic acid molecule exists in cationic form by the protonation of the α-carboxylic group. All the hydrogen atoms were located by difference-Fourier-syntheses.