Hydrophobicity plays an important role in numerous physico-chemical processes, from the process of dissolution in water to protein folding, but its origin at the fundamental level is still unclear. The classical view of hydrophobic hydration is that in the presence of a hydrophobic solute, water forms transient microscopic ‘icebergs’ arising from strengthened water hydrogen bonding, yet there is no experimental evidence for enhanced hydrogen bonding and/or ‘icebergs’ in such solutions. Here we have used the redshifts and line-shapes of the isotopically decoupled infrared O-D stretching mode of small, purely hydrophobic solutes (methane, ethane, krypton, xenon) in water to study hydrophobicity at the most fundamental level. We present the first unequivocal and model-free experimental proof for the presence of strengthened water hydrogen bonds near four hydrophobic solutes, matching those in ice and clathrates. The water molecules involved in the enhanced hydrogen bonds display extensive structural ordering resembling that in clathrates. The number of ice-like hydrogen bonds is 10 to 15 per methane molecule. Ab-initio molecular dynamics simulations have confirmed that water molecules in the vicinity of methane form stronger, more numerous and more tetrahedrally oriented hydrogen bonds than those in bulk water, and that their mobility is restricted. We demonstrate the absence of intercalating water molecules that cause the electrostatic screening (shielding) of hydrogen bonds in bulk water as the critical element for the enhanced hydrogen bonding around a hydrophobic solute. Our results confirm the classical view of hydrophobic hydration.
COBISS.SI-ID: 6068250
We have investigated the chemistry of the pH dependent cross-linking of boric acid or borate anions with nanocellulose and shown that the molecular pathway at neutral and alkaline conditions influences strongly the flame retardancy and ignition resistance. The pH dependent speciation of boric acid into borate anions at high pH and the different reactivity of boric acid and borate anion toward the diol and carboxylic acid functional groups on the nanocellulose backbone control the molecular cross-linking pathways. Thermal analysis shows that char oxidation is slowed down and shifted to higher temperatures. Analysis of the thermally annealed residues by a combination of 11B MAS and 13C CP/MAS NMR, Raman, and infrared spectroscopy shows that the formation of a nanocellulose−borate hybrid promotes charring and complete transformation of the polysaccharide at 450 °C into a graphitized structure. Preparation of freeze-cast foams from nanocellulose−borate hybrids with the addition of sepiolite clay results in complete suppression of polymer ignition on radiant heat exposure. The ability to strongly reduce the flammability of nanocellulose hybrid foams is important for the development of sustainable and eco-friendly thermal insulation materials.
COBISS.SI-ID: 6060314
Low temperature Raman spectra of oxalic acid dihydrate (8−300 K) for both the polycrystalline and single crystal phase show strong variation with temperature in the interval from 1200 to 2000 cm−1. Previous low temperature diffraction studies all confirmed the stability of the crystal P21/n phase with no indications of any phase transition, reporting the existence of a strong hydrogen bond between the oxalic acid and a water molecule. A new group of Raman bands in the 1200−1300 cm−1 interval below 90 K is observed, caused by possible loss of the centre of inversion. This in turn could originate either due to disorder in hydroxyl proton positions or due to proton transfer from carboxylic group to water molecule. The hypothesis of proton transfer is further supported by the emergence of new bands cantered at 1600 and 1813 cm−1, which can be explained with vibrations of H3O+ions. The agreement between quantum calculations of vibrational spectra and experimentally observed Raman bands of hydronium ions in oxalic acid sesquihydrate crystal corroborates this hypothesis.
COBISS.SI-ID: 6072602
In this study the conformational properties of biological importance of rat/mouse MOG35-55 epitope were explored. This linear peptide is implicated in chronic EAE induction and multiple sclerosis disease. With the combination of NMR spectroscopy and computational analysis the conformational properties of MOG35-55 in different environments were elucidated. Comparison of conformational features in various solution environments and with the crystallographic data explained that alternations of R41 and R46 residues with alanine amino acid are expected to reduce the severity of MOG induced EAE clinical symptoms.
COBISS.SI-ID: 6015002
We cooperated in a study of a simple synthesis procedure of anatase/rutile/brookite TiO2 nanocomposite material, designed for efficient transformation of emerging water pollutants (e.g., bisphenol (A)) to CO2 and H2O as final products of complete photo-oxidation. Sol–gel procedure with a subsequent hydrothermal treatment carried out at mild temperature and in the presence of 3 M HCl led to the formation of TiO2 nanomaterial, which consists of anatase (43%), rutile (24%) and brookite (33%) polymorph phases within the same material. Newly synthesized TiO2 nanocomposite was highly active in terms of mineralization, since after 60 min of irradiation under UV light almost 60% of water dissolved pollutant bisphenol A was successfully transformed into CO2 in H2O.
COBISS.SI-ID: 5753626