Sodium ion interactions with aqueous glucose: insights from quantum mechanics, molecular dynamics, and experiment

Sodium Ions Affect Pyrraline Formation in the Maillard Reaction With Lys-Containing Dipeptides and Tripeptides

Advanced glycation end products (AGEs) are potentially-hazardous chemical compounds, produced by the Maillard reaction between reducing sugars and Lysine side-chain amino groups in proteins. AGEs are strongly associated with diabetes, Alzheimer's disease and atherosclerosis. Pyrraline, a sugar derivative of Lysine, is a major AGE and an established marker for the presence of dietary AGEs. In this study, the effects of NaCl and different dipeptide and tripeptide structures were compared on the formation of pyrraline-containing peptides and the glucose derivative 3-deoxyglucosone in the presence of glucose and at different NaCl concentrations. The physicochemical properties (polarizability, dipole moment, molecular volume and dissociation constant) and the thermodynamic properties of the peptides were determined. The amount of the pyrraline decreased significantly in the following order of peptides (at the same concentrations): Lys-Phe > Lys-Ala > Lys-Gly; Lys-Gly-Phe > Lys-Gly-Ala > Lys-Gly-Gly. The highest levels of both pyrraline and 3-deoxyglucosone occurred at 0.2 mol/L Na⁺. Sodium ions appear to alter the intramolecular electron density and charge distribution of the peptides and facilitate the reaction by stabilizing some of the intermediates in the reaction sequence.

Following in Emil Fischer's Footsteps: A Site-Selective Probe of Glucose Acid-Base Chemistry

Liquid-jet photoelectron spectroscopy was applied to determine the first acid dissociation constant (pKa) of aqueous-phase glucose while simultaneously identifying the spectroscopic signature of the respective deprotonation site. Valence spectra from solutions at pH values below and above the first pKa reveal a change in glucose's lowest ionization energy upon the deprotonation of neutral glucose and the subsequent emergence of its anionic counterpart. Site-specific insights into the solution-pH-dependent molecular structure changes are also shown to be accessible via C 1s photoelectron spectroscopy. The spectra reveal a considerably lower C 1s binding energy of the carbon site associated with the deprotonated hydroxyl group. The occurrence of photoelectron spectral fingerprints of cyclic and linear glucose prior to and upon deprotonation are also discussed. The experimental data are interpreted with the aid of electronic structure calculations. Our findings highlight the potential of liquid-jet photoelectron spectroscopy to act as a site-selective probe of the molecular structures that underpin the acid-base chemistry of polyprotic systems with relevance to environmental chemistry and biochemistry.

Cooperative Activation of Cellulose with Natural Calcium

Naturally occurring metals, such as calcium, catalytically activate the intermonomer β-glycosidic bonds in long chains of cellulose, initiating reactions with volatile oxygenates for renewable applications. In this work, the millisecond kinetics of calcium-catalyzed reactions were measured via the method of the pulse-heated analysis of solid and surface reactions (PHASR) at high temperatures (370-430 °C) to reveal accelerated glycosidic ether scission with a second-order rate dependence on the Ca²⁺ ions. First-principles density functional theory (DFT) calculations were used to identify stable binding configurations for two Ca²⁺ ions that demonstrated accelerated transglycosylation kinetics, with an apparent activation barrier of 50 kcal mol^-1 for a cooperative calcium-catalyzed cycle. The agreement of the mechanism with calcium cooperativity to the experimental barrier (48.7 ± 2.8 kcal mol^-1) suggests that calcium enhances the reactivity through a primary role of stabilizing charged transition states and a secondary role of disrupting native H-bonding.

Mass transfer in aerated culture media combining mixed electrolytes and glucose

The combined effects of mixed electrolyte species and glucose on oxygen transfer were studied in a bubble column with aqueous solutions. Of particular interest was the presence of electrolytes containing ions which are prone to present solute-solute interactions or to crystallize. Without and at low concentration of glucose (≤ 5 g/L), the increasing concentration of electrolytes (nominal ionic strength: 0-0.43 M), up to a critical value, enhanced the volumetric mass transfer coefficient (k_La) and the availability of specific interfacial area (a), due to the inhibition of bubble coalescence. As the glucose concentration increased (10-40 g/L), the enhancing effects of electrolytes were gradually lost. The glucose interacted with electrolytes, reducing their ability to inhibit coalescence and to enhance the k_La. Salt crystallization occurred independently of the addition of glucose; however, it did not have significant effect on mass transfer. Finally, the changes in physicochemical properties were highly collinear with composition variables.

Pyrraline Formation Modulated by Sodium Chloride and Controlled by Encapsulation with Different Coating Materials in the Maillard Reaction

Advanced glycation end products (AGEs), which are present in heat-processed foods, have been associated with several chronic diseases. Sodium chloride (NaCl) modulates the formation of furfurals and acrylamide in the Maillard reaction; however, the effects of NaCl on AGE formation are inconsistent. In this study, we investigated the effects of NaCl on pyrraline formation using glucose-lysine model systems. NaCl, especially at 0.50%, promoted Maillard browning and pyrraline formation, with a simultaneous increase in the 3-deoxyglucosone concentration. To reduce the rate of pyrraline formation, NaCl coated with different gums and starches were used. The results showed that NaCl encapsulation is an effective approach to mitigate pyrraline and 3-deoxyglucosone formation. The content of NaCl in the microparticles were 284 ± 12, 269 ± 6, 258 ± 8, 247 ± 10, 273 ± 16, and 288 ± 15 mg/g (coated with waxy maize starch, normal maize starch, HYLON VII high amylose maize starch, gelatinized resistant starch, xanthan gum, and gum arabic, respectively). The heat resistance of the coating material was negatively correlated with the pyrraline and 3-deoxyglucosone formation, whereas the solubility of the coating material had the opposite results. Coating the material with gum had little effects on the reduction of pyrraline and 3-deoxyglucosone.

Microvascular ion transport through endothelial glycocalyx layer: new mechanism and improved Starling principle

Ion transport through the endothelial glycocalyx layer is closely associated with many vascular diseases. Clarification of ion behaviors around the endothelial glycocalyx layer under varying circumstances will benefit pathologies related to cardiovascular and renal diseases. In this research, a series of large-scale molecular dynamics simulations are conducted to study the response of ion transport to the changing blood flow velocity and the shedding of endothelial glycocalyx sugar chains. Results indicate that blood flow promotes the outward Na+ transport from the near-membrane region to the lumen via the endothelial glycocalyx layer. Scrutiny of sugar-chain dynamics and their interactions with Na+ suggests that corner conformation of endothelial glycocalyx sugar chains confines the movement of the Na+, whereas stretching conformation facilitates the motion of Na+ ions. The flow impact on ion transport of Na+ is nonlinear. Based on the findings, the Starling principle and its revised version, which are prevailingly used to predict the ion transport of the endothelial glycocalyx layer, are further improved. An estimation based on the further revised Starling principle indicates that physiological flow changes the osmotic part of transendothelial water flux by 8% compared with the stationary situation.

NEW & NOTEWORTHY The biophysical roles of negatively charged oligosaccharides of the endothelial glycocalyx have gained increasing attention due to their importance in regulating microvascular fluid exchange. The Starling principle and its revisions are at the heart of the understanding of fluid homeostasis in the periphery. Here, the blood flow changes the conformations of glycocalyx sugar chains, thereby influencing availability of Na+ for transport. Based on the findings, the Starling principle and its revision are further improved.

Do soft anions promote protein denaturation through binding interactions? A case study using ribonuclease A

It has long been known that large soft anions like bromide, iodide and thiocyanate are protein denaturing agents, but their mechanism of action is still unclear. In this work we have investigated the protein denaturing properties of these anions using Ribonuclease A (RNase A) as a model protein system. Salt-induced perturbations to the protein folding free energy were determined using differential scanning calorimetry and the results demonstrate that the addition of sodium iodide and sodium thiocyanate significantly decreases the melting temperature of the protein. In order to account for this reduction in protein stability, we show that the introduction of salts that contain soft anions to the aqueous solvent perturbs the protein unfolding free energy through three mechanisms: (a) screening Coulomb interactions that exist between charged protein residues, (b) Hofmeister effects, and (c) specific anion binding to CH and CH2 moieties in the protein polypeptide backbone. Using the micellization of 1,2-hexanediol as a ruler for hydrophobicity, we have devised a practical methodology that separates the Coulomb and Hofmeister contributions of salts to the protein unfolding free energy. This allowing us to isolate the contribution of soft anion binding interactions to the unfolding process. The analysis shows that binding contributions have the largest magnitude, confirming that it is the binding of soft anions to the polypeptide backbone that is the main promoter of protein unfolding.

Pyrolysis of the Cellulose Fraction of Biomass in the Presence of Solid Acid Catalysts: An Operando Spectroscopy and Theoretical Investigation

Biomass pyrolysis by solid acid catalysts is one of many promising technologies for sustainable production of hydrocarbon liquid fuels and value-added chemicals, but these complex chemical transformations are still poorly understood. A series of well-defined model SiO₂ -supported alumina catalysts were synthesized and molecularly characterized, under dehydrated conditions and during biomass pyrolysis, with the aim of establishing fundamental catalyst structure-activity/selectivity relationships. The nature and corresponding acidity of the supported AlO_x nanostructures on SiO₂ were determined with ²⁷ Al/¹ H NMR and IR spectroscopy of chemisorbed CO, and DFT calculations. Operando time-resolved IR-Raman-MS spectroscopy studies revealed the molecular transformations taking place during biomass pyrolysis. The molecular transformations during biomass pyrolysis depended on both the domain size of the AlO_x cluster and molecular nature of the biomass feedstock. These new insights allowed the establishment of fundamental structure-activity/selectivity relationships during biomass pyrolysis.

EPS Glycoconjugate Profiles Shift as Adaptive Response in Anaerobic Microbial Granulation at High Salinity

Anaerobic granulation at elevated salinities has been discussed in several analytical and engineering based studies. They report either enhanced or decreased efficiencies in relation to different Na⁺ levels. To evaluate this discrepancy, we focused on the microbial and structural dynamics of granules formed in two upflow anaerobic sludge blanket (UASB) reactors treating synthetic wastewater at low (5 g/L Na⁺) and high (20 g/L Na⁺) salinity conditions. Granules were successfully formed in both conditions, but at high salinity, the start-up inoculum quickly formed larger granules having a thicker gel layer in comparison to granules developed at low salinity. Granules retained high concentrations of sodium without any negative effect on biomass activity and structure. 16S rRNA gene analysis and Fluorescence in Situ Hybridization (FISH) identified the acetotrophic Methanosaeta harundinacea as the dominant microorganism at both salinities. Fluorescence lectin bar coding (FLBC) screening highlighted a significant shift in the glycoconjugate pattern between granules grown at 5 and 20 g/L of Na⁺, and the presence of different extracellular domains. The excretion of a Mannose-rich cloud-like glycoconjugate matrix, which seems to form a protective layer for some methanogenic cells clusters, was found to be the main distinctive feature of the microbial community grown at high salinity conditions.

IR-IR Conformation Specific Spectroscopy of Na+(Glucose) Adducts

We report an IR-IR double resonance study of the structural landscape present in the Na⁺(glucose) complex. Our experimental approach involves minimal modifications to a typical IR predissociation setup, and can be carried out via ion-dip or isomer-burning methods, providing additional flexibility to suit different experimental needs. In the current study, the single-laser IR predissociation spectrum of Na⁺(glucose), which clearly indicates contributions from multiple structures, was experimentally disentangled to reveal the presence of three α-conformers and five β-conformers. Comparisons with calculations show that these eight conformations correspond to the lowest energy gas-phase structures with distinctive Na⁺ coordination. Graphical Abstract ᅟ.

Interactions of D-cellobiose with selected chloride salts: A ¹³C NMR and FT-IR study

The interactions of cellulose model compound d-cellobiose with chloride salts of Zn(2+), Ca(2+), Li(+), Sn(2+), La(3+), Mg(2+), K(+) and NH4(+) were evaluated by measuring the (13)C NMR chemical shift changes (Δδ) of the disaccharide due to the addition of salts in D2O. The KCl and NH4Cl showed similar Δδ changes due to interactions only with the Cl(-) anion. Whereas other chloride salts showed interactions with both cation and anion. Among these salts the total interactions are in the order: Zn(2+)>Sn(2+)>Li(+)>Ca(2+)~La(3+)>Mg(2+). The FT-IR spectra of D-cellobiose-chloride salt 1:2 mixtures also indicate that KCl and NH4Cl interacts similarly with D-cellobiose in the solid state.

Increasing Glucose Concentrations Interfere with Estimation of Electrolytes by Indirect Ion Selective Electrode Method

The estimation of electrolytes like sodium (Na(+)), potassium (K(+)) and chloride (Cl(-)) using direct and indirect ion-selective electrodes (ISE) is a routine laboratory practice. Interferents like proteins, triglycerides, drugs etc. are known to affect the results. The present study was designed to look into the effect of increasing glucose concentrations on estimation of Na(+), K(+) and Cl(-) by direct and indirect ISE. Pooled sera was mixed with glucose stock solution (20 g/dL) prepared in normal saline to obtain glucose concentrations ranging from ~100 to ~5000 mg/dL. Na(+), K(+) and Cl(-) levels were estimated by direct and indirect ISE analyzers and results were statistically analysed using ANOVA and Pearson's correlation. Similar experiment was also performed in 24 h urine sample from healthy subjects. Significant difference was observed between Na(+) and Cl(-) measurements by direct and indirect ISE, with indirect ISE values being consistently higher than direct ISE. Besides this, significant difference was observed amongst Na(+) and Cl(-) values from baseline values obtained by indirect ISE at glucose concentrations ≥2486 mg/dL. However, no such difference was observed with direct ISE. Na(+) and Cl(-) estimation by indirect ISE showed significant negative correlation with glucose concentration, more so, above ~2000 mg/dL. K(+), however, showed no significant difference with varying glucose. Similar results were observed in 24 h urine samples with a significant difference observed amongst Na(+) and Cl(-) values at ≥2104 mg/dL glucose. Thus we conclude that high glucose concentrations interfere significantly in estimation of Na(+) and Cl(-) by indirect ISE in serum as well as urine.