Interaction of Ca2+ with mannose: a density functional study

Lead removal from the aqueous solution by extracellular polymeric substances produced by the marine diatom Navicula salinicola

Microbial extracellular polymeric substances (EPS) have recently emerged as significant contributors in diverse biotechnological applications. Extracellular polymeric substances (EPS), produced by a Navicula salinicola strain, have been studied for potential applications in a specific heavy metal (lead (Pb II)) removal from wastewater. The optimisation of operational parameters, mainly pH, Pb and EPS concentrations, using the Box-Behnken design (BBD) was undertaken to enhance lead uptake. The higher Pb adsorption capacity reached 2211.029 mg/g. Hydroxyl, carbonyl, carboxyl, phosphoric, and sulfhydryl groups were identified quantitatively as potential sites for Pb adsorption. EPS exhibited a notable flocculation rate of 70.20% in kaolin clay at a concentration of 15 mg/L. They demonstrated an emulsifying activity greater than 88%, showcasing their versatile potential for both sedimentation processes and stabilising liquid-liquid systems. EPS could be excellent nonconventional renewable biopolymers for treating water and wastewater.

Pyranose ring conformations in mono- and oligosaccharides: a combined MD and DFT approach

A two-step computational protocol is proposed to efficiently study the conformational properties of hexopyranoses with a special emphasis on their ring-inversion-properties. By applying it, the errors resulting from overestimating the contribution of the hydrogen bond-rich, low-energy structures that are not abundant in aqueous solutions are avoided.

Density functional conformational study of 2-O-sulfated 3,6 anhydro-α-D-galactose and of neo-κ- and ι-carrabiose molecules in gas phase and water

We examined the conformational preferences of the 2-O-sulfated-3,6-α-D-anhydrogalactose (compound I) and two 1,3 linked disaccharides constituting-κ or ι-carrageenans using density functional and ab initio methods in gas phase and aqueous solution. Systematic modifications of two torsion angles leading to 324 and 144 starting geometries for the compound I and each disaccharide were used to generate adiabatic maps using B3LYP/6-31G(d). The lower energy conformers were then fully optimized using B3LYP, B3PW91 and MP2 with several basis sets. Overall, we discuss the impact of full relaxation on the energy and structure of the dominant conformations, present the performance comparison with previous molecular mechanics calculations if available, and determine whether our results are impacted, when polarization and diffuse functions are added to the 6-31G(d) basis set, or when the MP2 level of theory is used.

Sugar-induced blue membrane: release of divalent cations during phase transition of purple membranes observed in sugar-derived glasses

The formation of blue membrane from purple membranes (PM) has been observed in glassy films made from PM and various sugars. The phase transition of PM at about 70 degrees C causes the complexation of divalent cations to be weakened. The vicinal diol structures in sugars are capable to complex divalent cations and delocalize them throughout the matrix as long as its glass transition temperature is lower than the phase transition temperature of PM. The loss of divalent cations from bacteriorhodopsin (BR), the only protein in PM, causes the formation of blue membrane (BM), which is accompanied by a loss of beta-sheet structure observable in the infrared spectrum. Glassy sugars are particular useful to observe this transition, as sugar entrapment does not restrict conformational changes of BR but rather retards them. The material obtained was named sugar-induced blue membrane (SIBM). The formation of SIBM is inhibited by the addition of divalent cations. Furthermore, SIBM is reverted immediately to PM by addition of water. A characteristic time dependence of the thermal reversion of SIBM to PM proves that the phase transition of PM triggers the release and uptake of divalent cations and the corresponding color change.

DFT study of alpha- and beta-D-mannopyranose at the B3LYP/6-311++G** level

Thirty-five conformations of alpha- and beta-d-mannopyranose, the C-2 substituted epimer of glucopyranose, were geometry optimized using the density functional (B3LYP), and basis set (6-311++G**). Full geometry optimization was performed on the hydroxymethyl rotamers (gg/gt/tg) and an analytical hessian program was used to calculate the harmonic vibrational frequencies, zero point energy, enthalpy, and entropy. The lowest energy conformation investigated is the beta-tg in the (4)C(1) chair conformation. The in vacuo calculations showed little energetic preference for either the alpha or beta anomer for mannopyranose in the (4)C(1) chair conformation. Results are compared to similar glucopyranose calculations in vacuo where the alpha anomer is approximately 1kcal/mol lower in electronic energy than the beta anomer. In the case of the generally higher energy (1)C(4) chair conformations, one low-energy, low-entropy beta-gg-(1)C(4) chair conformation was identified that is within approximately 1.4kcal/mol of the lowest energy (4)C(1) conformation of mannopyranose. Other (1)C(4) chair conformations in our investigation are approximately 2.9-7.9kcal/mol higher in overall energy. Many of the (3,O)B, B(3,O), (1,4)B, and B(1,4) boat forms passed through transitions without barriers to (1)S(3), (5)S(1), (1)S(5) skew forms with energies between approximately 3.6 and 8.9kcal/mol higher in energy than the lowest energy conformation of mannopyranose. Boat forms were found that remained stable upon gradient optimization. As with glucopyranose, the orientation and interaction of the hydroxy groups make a significant contribution to the conformation/energy relationship in vacuo.

Gas-phase reactivity of silver and copper coordinated monosaccharide cations studied by electrospray ionization and tandem mass spectrometry

The analytical distinction of the most common isomeric underivatized hexoses was investigated by means of mass spectrometry experiments. Electrospray ionization and tandem mass spectrometry were used in the analysis of silver and copper-coordinated monosaccharides (D-glucose, D-galactose, D-fructose, O-methyl-alpha-D-glucose and O-methyl-beta-D-glucose). The results show that cationization by Ag(+) allows the differentiation of the three first monosaccharides while the complexes formed by association of Cu(+) with these three monosacharides display a similar reactivity that prevents stereoisomer distinction. Unlike copper, silver adduct-ions of both alpha and beta anomeric O-methyl-D-glucoses exhibit specific decomposition patterns (i.e. a loss of methanol for the alpha-anomer and a loss of silver hydride for the beta-anomer), which allow an easy characterization. A theoretical survey of selected complexes, based on the use of DFT calculations were carried out on both anomers in order to rationalize the experimental findings.