Synthesis of Artificial Glycoconjugate Polymers Carrying 6-O-Phosphocholine α-D-Glucopyranoside,Biologically Active Segment of Main Cell Membrane Glycolipids of Mycoplasma Fermentas

ABSTRACT

The conformation of two mannose-based amidines, the N-benzylmannoamidine and a pseudo (1→6) dimannoside, has been evaluated using semi-empirical AMI calculations and ¹H NMR studies. The most stable conformations of the mannoamidine ring correspond to the half-chair forms ³H₄ and ⁴H₃. The conformations (Z) or (E) about the exocyclic C-N bond depend on the substituents and it was shown that, in solution, the N-benzylmannoamidine was (E)-configured whilst the pseudo (1→6) dimannoside was (Z)-configured. Using the grid-search approach, the potential energy maps of both mannoamidines were calculated as a function of the torsion angles which define the orientation of the amidine substituent. Three stable conformers were identified for the N-benzylmannoamidine and seven for the pseudo (1→6) dimannoside. Inter-glycosidic NOE have provided evidence for a preferred conformation of the pseudo (1→6) dimannoside in solution. The transition state structure of the α-phenylmannose hydrolysis was optimized using the AMI method and compared to the N-benzylmannoamidine. The developing oxocarbenium ion is well matched by the mannoamidine ring but the orientation of the phenyl group in the inhibitor differs significantly from the position of the leaving group in the transition state. The use of sugar type amidines as haptens to obtain catalytic antibodies is then discussed.

     

Glycation sites of human plasma proteins are affected to different extents by hyperglycemic conditions in type 2 diabetes mellitus

Glucose can modify proteins in human blood, forming early glycation products (e.g., Amadori compounds), which can slowly degrade to advanced glycation endproducts (AGEs). AGEs contribute significantly to complications of diabetes mellitus and, thus, represent markers of advanced disease stages. They are, however, currently unsuitable for early diagnosis and therapeutic monitoring. Here, we report sensitive strategies to identify and relatively quantify protein glycation sites in human plasma samples obtained from type 2 diabetes mellitus (T2DM) patients and age-matched nondiabetic individuals using a bottom-up approach. Specifically, Amadori peptides were enriched from tryptic digests by boronic acid affinity chromatography, separated by reversed-phase chromatography, and analyzed on-line by high-resolution mass spectrometry. Among the 52 Amadori peptides studied here were 20 peptides resembling 19 glycation sites in six human proteins detected at statistically significantly higher levels in T2DM than in the normoglycemic controls. Four positions appeared to be unique for T2DM within the detection limit. All 19 glycation sites represent promising new biomarker candidates for early diagnosis of T2DM and adequate therapeutic control, as they may indicate early metabolic changes preceding T2DM. Graphical Abstract

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Simultaneous determination of reduced and oxidized glutathione in tissues by a novel liquid chromatography-mass spectrometry method: application in an inhalation study of Cd nanoparticles

The paper presents the development of an advanced extraction and fast analytical LC MS/MS method for simultaneous analyses of reduced and oxidized glutathione (GSH and GSSG, respectively) in different animal tissues. The simultaneous determination of GSH and GSSG is crucial because the amount and ratio of both GSH and GSSG may be altered in response to oxidative stress, an important mechanism of toxicity. The method uses the derivatization of free thiol groups in GSH. Its performance was demonstrated for less explored tissues (lung, brain, and liver) in mouse. The combined extraction and analytical method has very low variability and good reproducibility, maximum coefficients of variance for within-run and between-run analyses under 8 %, and low limits of quantification; for GSH and GSSG, these were 0.2 nM (0.06 ng/mL) and 10 nM (6 ng/mL), respectively. The performance of the method was further demonstrated in a model experiment addressing changes in GSH and GSSG concentrations in lung of mice exposed to CdO nanoparticles during acute 72 h and chronic 13-week exposures. Inhalation exposure led to increased GSH concentrations in lung. GSSG levels were in general not affected; nonsignificant suppression occurred only after the longer 13-week period of exposure. The developed method for the sensitive detection of both GSH and GSSG in very low tissue mass enables these parameters to be studied in cases where only a little sample is available, i.e. in small organisms or in small amounts of tissue.     

Insights on the Lewis Superacid Al(OTeF5)3: Solvent Adducts,Characterization and Properties**

Preparation and characterization of the dimeric Lewis superacid [Al(OTeF₅)₃]₂ and various solvent adducts is presented. The latter range from thermally stable adducts to highly reactive, weakly bound species. DFT calculations on the ligand affinity of these Lewis acids were performed in order to rank their remaining Lewis acidity. An experimental proof of the Lewis acidity is provided by the reaction of solvent-adducts of Al(OTeF₅)₃ with [PPh₄][SbF₆] and OPEt₃, respectively. Furthermore, their reactivity towards chloride and pentafluoroorthotellurate salts as well as (CH₃)₃SiCl and (CH₃)₃SiF is shown. This includes the formation of the dianion [Al(OTeF₅)₅]²⁻.     

Synthesis and Spectrophotometric Analysis of Microcapsules Containing Immortelle Essential Oil

In this study, microcapsules were prepared by solvent evaporation technique using ethyl cellulose component as wall and essential oil as core material. The synthesis of microcapsules was carried out using different oil masses. The analysis of the microcapsules was carried out using field emission scanning electron microscope (FE-SEM) and UV spectrophotometric analysis using absorption spectrophotometer. The obtained results confirm the regular spherical shape and size of the synthesized microcapsules. The qualitative and quantitative spectrophotometric analysis of the microencapsulated immortelle oil was measured at the wavelength of 265 nm. The calibration diagram was used to calculate the unknown concentrations of the microencapsulated oil. The obtained results confirm the application of the presented method as relevant for the possible determination of microencapsulated oil on textile materials.     

The influence of nitrogen-15 proton-driven spin diffusion on the measurement of nitrogen-15 longitudinal relaxation times

The effect of nitrogen-15 proton-driven spin diffusion on quantitative (15)N T(1) measurements in solid proteins is investigated, and the impact on the measurement of dynamic parameters is assessed. A simple model of exchange between neighboring nitrogens is used to reproduce the evolution of (15)N spin systems whose longitudinal relaxation rates and exchange rates are compatible with experimental measurements. We show that the induced error in the measured T(1) and its effect on the determination of dynamics parameters is likely to be less than the current experimental error. The use of deuterated protein samples is shown to have a small but sometimes visible effect, and may also considerably slow down or even suppress the exchange of magnetization due to spin diffusion.     

Investigations of silicone breast implants with the NMR-MOUSE

Silicone breast implants are used for breast augmentation and breast reconstruction. The issues of concern associated with such implants are: (a) the quality control of each implant before implantation, and (b) the detection of implant bleeding after implantation. We have studied the use of the Nuclear Magnetic Resonance-MObile Universal Surface Explorer (NMR-MOUSE) for the nondestructive testing of (a) the quality of implant shells, and (b) changes in implant gel due to leakage of body fluid into the implant. Depth profiles measured nondestructively through implant shells at different positions of each implant by the Profile NMR-MOUSE assured good reproducibility of the quality and thickness of different shell layers. The leakage of implants upon rupture was mimicked by observing changes in the transverse NMR relaxation time of the implant gel upon ingress of physiological saline solution and safflower oil through the rupture. Results demonstrate that nondestructive testing with unilateral NMR is a potential method for use in the quality control of implants and for the screening of implants for rupture after implantation.     

Elucidating dynamic behavior of synthetic supramolecular polymers in water by hydrogen/deuterium exchange mass spectrometry

A comprehensive understanding of the structure, self-assembly mechanism, and dynamics of one-dimensional supramolecular polymers in water is essential for their application as biomaterials. Although a plethora of techniques are available to study the first two properties, there is a paucity in possibilities to study dynamic exchange of monomers between supramolecular polymers in solution. We recently introduced hydrogen/deuterium exchange mass spectrometry (HDX-MS) to characterize the dynamic nature of synthetic supramolecular polymers with only a minimal perturbation of the chemical structure. To further expand the application of this powerful technique some essential experimental aspects have been reaffirmed and the technique has been applied to a diverse library of assemblies. HDX-MS is widely applicable if there are exchangeable hydrogen atoms protected from direct contact with the solvent and if the monomer concentration is sufficiently high to ensure the presence of supramolecular polymers during dilution. In addition, we demonstrate that the kinetic behavior as probed by HDX-MS is influenced by the internal order within the supramolecular polymers and by the self-assembly mechanism.     

gem‐Difluorocarbadisaccharides: Restoring the exo‐Anomeric Effect

Molecular mimicry is an essential part of the development of drugs and molecular probes. In the chemical glycobiology field, although many glycomimetics have been developed in the past years, it has been considered that many failures in their use are related to the lack of the anomeric effects in these analogues. Additionally, the origin of the anomeric effects is still the subject of virulent scientific debates. Herein, by combining chemical synthesis, NMR methods, and theoretical calculations, we show that it is possible to restore the anomeric effect for an acetal when replacing one of the oxygen atoms by a CF₂ group. This result provides key findings in chemical sciences. On the one hand, it strongly suggests the key relevance of the stereoelectronic component of the anomeric effect. On the other hand, the CF₂ analogue adopts the natural glycoside conformation, which might provide new avenues for sugar‐based drug design.