High resolution mass spectrometric characterization of amino linked oligosaccharides — a preliminary study

In this study maltose, maltotriose and maltotetraose were for the first time, coupled to 4,4′-methylenedianiline (MDA). The aim of this preliminary work was to test the feasibility of oligo- and polysaccharide coupling to MDA and the characterization of the coupling products by high resolution mass spectrometry (MS). (+) nanoESI in combination with a quadrupole time of flight (QTOF) MS in full scan (MS) and MS/MS was optimized first on underivatized maltose, maltotriose and maltotetraose. The optimal screening and sequencing conditions were further applied to the MDA-functionalized oligosaccharides. The obtained results revealed a straightforward MS detection of the functionalized oligomers, high sequence coverage and a fragmentation pathway with the formation of B and Y ions as well as the complementary C and Z ions along with a typical cleavage of the aglycon. We consider that this methodology is fully applicable also to polydisperse mixtures of long chain polysaccharides, which due to the large number of components and their size require a systematic method of development and testing.      

Mass spectrometric behavior of functionalized calix[4]arenes: the screening ability of host�Cguest complex formation with amino acid methyl esters

The ESI?CMS and MS/MS behavior of functionalized calix[4]arenes (1?C5) has been studied in both positive and negative-ion mode. Liquid chromatography coupled to ESI?CMS has been successfully used for separation of the byproducts issuing from the functionalization pathways, through the application of a simple reversed phase mechanism. The ability of (1?C5) to host methyl esters of amino acids, tyrosine, tryptophan, phenylalanine, cysteine, valine, serine, leucine, isoleucine, and threonine has been evaluated by means of MS identification of the host?Cguest resulting in protonated molecular ions. The direct infusion within the ESI source of the solutions containing the two partners (i.e., calixarene and amino acid derivative) could act as a fast screening means for the evaluation of hosting capability. Only positive ionization may offer information about the host?Cguest complexes being formed. The influence of the excess of a partner in the infused solution strongly alters ionization yields, making quantitative approaches meaningless. Attempts to chromatographically isolate the host?Cguest complexes failed, probably due to the fact that interactions of the partners with the mobile and stationary phases are higher than the inclusion interactions. Structures consisting of combined fragments of the host?Cguest partners resulting from the collisional induced dissociation have not been observed.     

Electrospray ionization–tandem mass spectrometric study of fused nitrogen-containing ring systems

Four fused nitrogen-containing ring systems were investigated by electrospray ionization–tandem mass spectrometry: Pyridazino-indoles, pyridazino-quinolines, a pyrimido-quinoline derivative and pyrimido-cinnolines. Fragmentation patterns of these compounds are discussed and compared. Several characteristic cross-ring fragments were formed mainly on the pyridazine and pyrimidine rings of the ring systems. The connected Cl, NO₂, Me, Ph and more extended heterocyclic substituents influenced the fragmentation.     

Chiroptical study of α-aliphatic amino acid films in the vacuum ultraviolet region

A series of natural circular dichroism (CD) and absorption spectra for films of α-aliphatic amino acids--such as alanine, aminobutyric acid, norvaline, norleucine, valine, leucine, and isoleucine--in the vacuum ultraviolet (VUV) region were observed with the absolute values of optical constants at the undulator-based CD beamline TERAS BL5. Preliminary predictions of some CD spectra were also performed, based on quantum-chemical calculations using the crystal structure. Although the absorption spectra show similar features to each other, significant differences between the CD spectra were found, especially in the 7-8 eV region. The CD spectra of aliphatic amino acids with branched alkyl groups in the side-chain--such as valine, leucine, and isoleucine--exhibit strong negative CD peaks in this energy region. In contrast, the corresponding CD peaks were weak or absent in the spectra of amino acids with straight alkyl groups. Our simple calculation, and the absorption spectra of alkanes, suggest that this difference partly originates from the contribution of the alkyl group. Clear discrepancies between the CD spectra of these amino acids in solutions and those in the solid state were also observed; this is probably caused by the different molecular structures in each state. Our results clearly indicated that CD spectra in the VUV region were very sensitive to the conformations of chiral molecules.     

Microbial production of natural poly amino acid

Three kinds of poly amino acids, poly-γ-glutamic acid, poly(ε-L-lysine) and multi-L-arginyl-poly (L-aspartic acid) can be synthesized by enzymatic process independently from ribosomal protein biosynthesis pathways in microorganism. These biosynthesized polymers have attracted more and more attentions because of their unique properties and various applications. In this review, the current knowledge on the biosynthesis, biodegradations and applications of these three poly amino acids are summarized.     

Morphological and electrical characteristics of amino acid–AuNP nanostructured two-dimensional ensembles

The interaction between amino acids (l-cysteine, l-lysine) and gold nanoparticle layers deposited on ITO glasses was investigated. The citrate capped gold nanoparticles (AuNP) were first deposited as a thin layer onto silanized ITO and subsequently linked with an amino acid, due to strong affinity of thiol and amine groups to gold. The gold nanoparticles had an elliptical shape, with size varying between 7 and 14 nm, as indicated by TEM analysis. After deposition on ITO substrate, the nanoparticles self-assembled into large aggregates with poor contact between, as revealed by AFM. After linking l-cysteine or l-lysine to the surface of nanoparticles layer, a change in morphology occured. A better contact between the gold aggregates boundary developed, which improved the conducting properties of the nanostructured layer. The electrical resistance of the AuNPs layer, obtained from I–V measurements, was very high (2.8 × 10¹³ Ω) and slightly decreased after linking the NPs with amino acids.     

Mass spectrometric stereoisomeric differentiation between α- and β-ascorbic acid 2-O-glucosides. Experimental and density functional theory study

L-Ascorbic acid and two distinct anomers, namely the α-D-glucopyranosyl and β-D-glucopyranosyl-(1→2)-L-ascorbic acid (stereoisomers), were studied within the scope of collision-induced dissociation (CID) experiments, performed by linear ion acceleration and collision with argon atoms inside a hexapole quadrupole hexapole ion beam guide, which is coupled to an ion cyclotron resonance (ICR) cell with a 12 Tesla magnet for high-resolution measurements. Loss of C(2)H(4)O(2) neutral from the [M-H](-) anion of L-ascorbic acid was observed. Density functional theory (DFT) calculations on the 6-311+G(2d,p)//6-31+G(d) level of theory reveal a new concerted mechanism for an intramolecular gas-phase rearrangement, through which the observed ejected neutral C(2)H(4)O(2) can take place. A similar rearrangement also occurs in the case of α- and β-D-glucopyranosyl-(1→2)-L-ascorbic acid. For the α isomer, only homolytic glycoside fragmentation was observed. For the β isomer, both homolytic and heterolytic glycoside cleavages were possible. The mechanisms behind all observed fragmentation pathways were fully understood by the implementation of accurate DFT calculations. Stereoisomeric differentiation between α and β isomers of the L-ascorbic acid-2-O-glucoside could be revealed by tandem mass spectrometry (MS/MS) experiments and were explained theoretically.     

Catalytic α-allylation of unprotected amino acid esters

Catalytic α-allylation of unprotected amino acid esters to produce α-quaternary α-allyl amino acid esters is reported. Catalytic loadings of picolinaldehyde and Ni(II) salts induce preferential reactivity at the enolizable α-carbon of amino acid esters over the free nitrogen with electrophilic palladium π-allyl complexes. Fourteen examples are given. Additionally, the use of chiral ligands to access enantioenriched α-quaternary amino acid esters from racemic precursors is demonstrated by the enantioselective synthesis of α-allyl phenylalanine methyl ester from racemic phenylalanine methyl ester.     

Combined FT–Raman spectroscopic and mass spectrometric study of ancient Egyptian sarcophagal fragments

The application of combined Raman spectroscopic and GC–MS analytical techniques for the characterisation of organic varnish residues from Egyptian Dynastic funerary sarcophagal and cartonnage fragments from the Graeco-Roman period, ca. 2200 BP, is described. The nondestructive use of Raman spectroscopy was initially employed to derive information about the specific location of organic material on the specimens, which were then targeted in specific areas using minimal sampling for GC–MS analysis. In the case of the sarcophagal fragment, a degraded yellow-brown surface treatment was identified as a Pistacia spp. resin; this provides additional evidence for the use of this resin, which has previously been identified in Canaanite transport amphorae, varnishes and “incense” bowls in an Egyptian Late Bronze Age archaeological context. The cartonnage fragment also contained an organic coating for which the Raman spectrum indicated a degradation that was too severe to facilitate identification, but the GC–MS data revealed that it was composed of a complex mixture of fatty acid residues. The combined use of GC–MS and Raman spectroscopy for the characterisation of organic materials in an archaeological context is advocated for minimisation of sampling and restriction to specifically identified targets for museum archival specimens.     

Thermochemical study of the reactions of acid–base interaction in an aqueous solution of α-aminobutyric acid

The heat effects of the interaction between a solution of α-aminobutyric acid and solutions of HNO₃ and KОН are measured by means of calorimetry in different ranges of рН at 298.15 K and values of ionic strength of 0.25, 0.5, and 0.75 (KNO₃). The heat effects of the stepwise dissociation of the amino acid are determined. Standard thermodynamic characteristics (Δ_r H ⁰, Δ_r G ⁰, and Δ_r S ⁰) of the reactions of acid–base interaction in aqueous solutions of α-aminobutyric acid are calculated. The connection between the thermodynamic characteristics of the dissociation of the amino acid and the structure of this compound is considered.     

Mass spectrometric identification of modified urinary nucleosides used as potential biomedical markers by LC–ITMS coupling

In diseases accompanied by strong metabolic disorders, like cancer and AIDS, modifying enzymes are up- or down-regulated. As a result, many different types of metabolic end-products, including abnormal amounts of modified nucleosides, are found in urine. These nucleosides are degradation products of an impaired ribonucleic acid (RNA) metabolism, which affects the nucleoside pattern in urine. In several basic experiments we elucidated the fragmentation pathways of 16 characteristic nucleosides and six corresponding nucleic bases that occur in urine using electrospray ionization ion trap MS⁵ (ESI-ITMS) experiments operated in positive ionization mode. For urinary nucleoside analysis, we developed an auto-LC–MS³ method based on prepurification via boronate gel affinity chromatography followed by reversed phase chromatography. For this purpose, an endcapped LiChroCART Superspher RP 18 column with a gradient of ammonium formate and a methanol–water mixture was used. This method gives a limit of detection of between 0.1 and 9.6 pmol for 15 standard nucleosides, depending on the basicity of the nucleoside. Overall, the detection of 36 nucleosides from urine was feasible. It was shown that this auto-LC–MS³ method is a valuable tool for assigning nucleosides from complex biological matrices, and it may be utilized in the diagnosis of diseases associated with disorders in RNA metabolism.     

Mass spectrometric identification of double bond positional isomers of hexadecenyl acetate without chemical derivatization

A method for the identification of the double bond positional isomers of hexadecenyl acetate has been established by analysing similarity of the mass spectra patterns on a fuzzy classification, in which the intensity ratios of six diagnostic pairs of the predominant ions were selected as standard parameters for the characterization of the double bond position. The procedure was tested with △2 to △15-isomers of chemically unmodified hexadecenyl acetate, and the original double bond position in the acetates was located unambiguously.     

Thermogravimetric study of 8-hydroxyquinoline 5-sulfonic acid–melamine–formaldehyde terpolymer resins-II

The title terpolymer (8-HQ5-SAMF-II) is synthesized by the condensation of 8-hydroxyquinoline 5-sulfonic acid (8-HQ5-SA) and melamine (M) with formaldehyde (F) in the presence of acid catalyst and using 2:1:3 M proportions of the reacting monomers. The synthesized terpolymer resin is then characterized by different physicochemical techniques viz. number average molecular mass determination, intrinsic viscosity determination, and spectral studies like UV–Visible, IR, ¹H NMR, and ¹³C NMR spectra. The morphology of synthesized terpolymer was studied by scanning electron microscopy (SEM). The thermogravimetry of the terpolymer resin prepared in this study has been carried out by non-isothermal thermogravimetry technique in which sample is subjected to condition of continuous increase in temperature at linear rate. Thermal study of the resin was carried out to determine their mode of decomposition and relative thermal stabilities. Thermal decomposition curves were studied carefully with minute details. The Freeman-Carroll and Sharp-Wentworth methods have been used in the present investigation to calculate thermal activation energy and different kinetic parameter of the terpolymer resins. Thermal activation energy E _a calculated with the two above-mentioned methods are in close agreement. The advantage of Freeman-Carroll method is to calculate both the order of reaction n and energy of activation in one single stage by keeping heating rate constant. By using data of thermogravimetry, various thermodynamic parameters like frequency factor Z, entropy change ΔS, free energy change ΔF, and apparent entropy S* have been determined using Freeman-Carroll method.     

Thermophysical property characterization of aqueous amino acid salt solutions containing α-aminobutyric acid

In this study, density, electrical conductivity, refractive index and viscosity of aqueous potassium and sodium salt solutions of α-aminobutyric acid were presented. Measurements were done over the temperature range (303.15 to 343.15) K and atmospheric pressure for salt compositions from x₁ = 0.009 to 0.062. A modified Graber et al. equation was used to correlate the density, electrical conductivity, and refractive index with temperature and composition leading to average absolute deviations (AAD) between the predicted and calculated values of 0.04%, 0.7%, and 0.01%, respectively. The viscosity data were represented as a function of temperature and composition via Vogel–Tamman–Fulcher (VTF) type equation at an AAD of 0.6%.     

A path integral molecular dynamics study on intermolecular hydrogen bond of acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters

We apply ab initio path integral molecular dynamics simulation employing ωB97XD as the quantum chemical calculation method to acetic acid–arsenic acid anion and acetic acid–phosphoric acid anion clusters to investigate the difference of the hydrogen bond structure and its fluctuation such as proton transfer. We found that the nuclear quantum effect enhanced the fluctuation of the hydrogen bond structure and proton transfer, which shows treatment of the nuclear quantum effect was essential to investigate these systems. The hydrogen bond in acetic acid–arsenic acid anion cluster showed characters related to low-barrier hydrogen bonds, while acetic acid–phosphoric acid anion cluster did not. We found non-negligible distinction between these two systems, which could not be found in conventional calculations. We suggest that the difference in amount of atomic charge of the atoms consisting the hydrogen bond is the origin of the difference between acetic acid–arsenic acid and acetic acid–phosphoric acid anion cluster. © 2018 Wiley Periodicals, Inc.     

Synthesis of biologically active nickelocenyl–amino acid conjugates using 1,3-dipolar cycloaddition click reactions

Russian Journal of General Chemistry - Herein we present the study of synthesis of novel bio-organometallic conjugates using 1,3-dipolar cycloaddition click reactions. Amino acid azides such as...