Single-atom substitution enables supramolecular diversity from dipeptide building blocks.

Dipeptides are popular building blocks for supramolecular gels that do not persist in the environment and may find various applications. In this work, we show that a simple substitution on the aromatic side-chain of phenylalanine with either fluorine or iodine enables supramolecular diversity upon self-assembly at neutral pH, leading to hydrogels or crystals. Each building block is characterized by 1H- and 13C-NMR spectroscopy, LC-MS, circular dichroism, and molecular models. The supramolecular behaviour is monitored with a variety of techniques, including circular dichroism, oscillatory rheology, transmission electron microscopy, attenuated total reflectance Fourier-transformed infrared spectroscopy, visible Raman spectroscopy, synchrotron-radiation single-crystal X-ray diffraction and UV Resonance Raman spectroscopy, allowing key differences to be pinpointed amongst the halogenated analogues.

UV resonance Raman spectroscopy of weakly hydrogen-bonded water in the liquid phase and on ice and snow surfaces.

The hydrogen bond network has a major role in determining the physical and chemical properties of water both in the solid and in the liquid state. In the bulk liquid phase, there is a coexistence of water molecules with different degrees of coordination and their relative amount changes according to the conditions (e.g., temperature, presence of solutes). Ice shows a larger amount of topologically under-coordinated water molecules at the surface as compared to the bulk. Snow is composed of many ice crystallites, and it differs from bulk ice because of the much larger specific surface area. The OH-stretching band is the most intense signal of the Raman spectrum of water, and it gives direct insight about the hydrogen bond network. In this work we compared the OH-stretching region of the Raman spectra of water, ice and snow acquired with excitations in the visible (532 nm) and in the UV-C range (250-200 nm) by exploiting the tunability of the synchrotron radiation. By moving towards the highest energy excitation we observed in liquid water a monotonic increase of the relative intensities of the peaks associated with weakly hydrogen-bonded water molecules. With visible excitation, the Raman spectrum of snow displays a larger contribution from weakly hydrogen-bonded water molecules at the surfaces when compared to the spectrum of bulk ice. By using excitation sources in the UV-C range, we observe a further enhancement of the contribution of the surfaces in the spectra of snow. By considering the reported changes of the water absorption coefficient in relation to the hydrogen bonding environment, we interpreted our results as a preferential pre-resonance excitation of weakly hydrogen-bonded water molecules induced by the UV-C sources.

Insight into the thermal stability of DNA in hydrated ionic liquids from multi-wavelength UV resonance Raman experiments.

The utility of ionic liquids (ILs) as alternative solvents for stabilizing and preserving the native structure of DNA over the long term may be envisaged for biotechnological and biomedical applications in the near future. The delicate balance between the stabilizing and destabilizing effects of IL-mediated interactions with the structure of DNA is complex and is still not well understood. This work reports a fundamental study dealing with the effect exerted by cations and anions in imidazolium-based ILs on the thermal structural stability of large nucleic acid molecules. Multi-wavelength UV resonance Raman spectroscopy is used for selectively detecting heat-induced structural transitions of DNA localized on specific base tracts. Our study reveals the establishment of preferential interactions between the imidazolium cations of ILs and the guanine bases in the DNA groove that lead to more effective stacking between the guanine bases even at high temperatures. Interestingly, we observe that this trend for ILs sharing the same chloride anion is further enhanced as the alkyl chain on the imidazolium cation gets shorter. The results from the present investigation lead to a more comprehensive view of the IL-mediated interactions with A-T and G-C base pairs during thermal unfolding.

Biocleaning of starch glues from textiles by means of α-amylase-based treatments.

Glues based on starch are widely used for the consolidation of brittle fibres in historic and archaeological textiles. Ageing fabrics are affected by hydrolysis/oxidation and cross-linking of these glues, a decrease of glues' solubility, the formation of cracks, and discoloration. The hydrolytic action of enzymes on starch-based glues is promising, as molecular recognition offers great selectivity. However, a systematic assessment of the best methods for applying enzymatic formulations has not been explored yet. Here, α-amylase was applied either by pipetting a solution or combining with gellan gel (embedded in the gel or spread on the gel surface). The effectiveness of the different formulations on the removal of potato and wheat starch was evaluated by Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) and colorimetric measurements. Enzymes dispersed in gel showed weak diffusion at the surface, resulting in poor starch breakdown and removal. On the contrary, amylase applied by pipette and spread on gel resulted in high starch removal selectivity and efficiency, with neither swelling nor damage to the fibres. These results validate protocols for the assessment of the enzymatic activity on glue-consolidated fibres, identify best application methods and confirm the excellent properties of amylase dispersions for the conservation of historic and archaeological textiles.Key points• Application of α-amylase by pipette and combined with gellan gel to remove starch glues from wool.• Systematic assessment of the best application methods following a multi-analytical protocol.• Enzymes dispersed in gel exhibit poor diffusion at the surface, leading to weak starch removal.• Enzymes applied by pipette and spread on gel are efficient in starch cleaning, without damage to the fibres.

Local and cooperative structural transitions of double-stranded DNA in choline-based deep eutectic solvents.

The possibility of using deep eutectic solvents (DESs) as co-solvents for stabilizing and preserving the native structure of DNA provides an attractive opportunity in the field of DNA biotechnology. The rationale of this work is a systematic investigation of the effect of hydrated choline-based DES on the structural stability of a 30-base-pair double-stranded DNA model via a combination of spectroscopic experiments and MD simulations. UV absorption and CD experiments provide evidence of a significant contribution of DESs to the stabilization of the double-stranded canonical (B-form) DNA structure. Multi-wavelength synchrotron UV Resonance Raman (UVRR) measurements indicate that the hydration shell of adenine-thymine pairs is strongly perturbed in the presence of DESs and that the preferential interaction between H-bond sites of guanine residues and DESs is significantly involved in the stabilization of the dsDNA. Finally, MD calculations show that the minor groove of DNA is significantly selective for the choline part of the investigated DESs compared to the major groove. This finding is likely to have a significant impact not only in terms of thermal stability but also in the modulation of ligand-DNA interactions.

Amyloidogenic and non-amyloidogenic molten globule conformation of ß-lactoglobulin in self-crowded regime.

Molecular insights on the ß-lactoglobulin thermal unfolding and aggregation are derived from FTIR and UV Resonance Raman (UVRR) investigations. We propose an in situ and in real-time approach that thanks to the identification of specific spectroscopic markers can distinguish the two different unfolding pathways pursued by ß-lactoglobulin during the conformational transition from the folded to the molten globule state, as triggered by the pH conditions. For both the investigated pH values (1.4 and 7.5) the greatest conformational variation of ß-lactoglobulin occurs at 80 °C and a high degree of structural reversibility after cooling is observed. In acidic condition ß-lactoglobulin exposes to the solvent its hydrophobic moieties in a much higher extent than in neutral solution, resulting on a highly open conformation. Moving from the diluted to the self-crowded regime, the solution pH and consequently the different molten globule conformation select the amyloid or non-amyloid aggregation pathway. At acidic condition the amyloid aggregates form during the heating cycle leading to the formation of transparent hydrogel. On the contrary, in neutral condition the amyloid aggregates never form. Information on the secondary structure conformational change of ß-lactoglobulin and the formation of amyloid aggregates are obtained by FTIR spectroscopy and are related to the information of the structural changes localized around the aromatic amino acid sites by UVRR technique. Our results highlight a strong involvement of the chain portions where tryptophan is located on the formation of amyloid aggregates.

Attenuated Total Reflection Far-Ultraviolet (ATR-FUV) Spectroscopy is a Sensitive Tool for Investigation of Protein Adsorption.

Attenuated total reflection far-ultraviolet (ATR-FUV) spectra in the 145-250 nm region were studied for four kinds of proteins (two α-helix-rich proteins: bovine serum albumin (BSA) and lysozyme and two ß-sheet rich proteins: concanavalin A and γ-globulin) in different solutions (pure water and phosphate buffered saline, or PBS) with different concentrations. All the spectra show a band at 191 nm due to the π-π* transition of amide bonds of the proteins. The wavelength of the band does not change with their second structures, suggesting that the corresponding electronic transition mode is localized and polarized in the direction that is not affected by the difference in the peptide folding. The intensity of the 191 nm band differs with the concentration of salt in the solution, suggesting that the band intensity reflects the adsorption density of a protein on the internal reflection element (IRE) made of a sapphire glass prism. According to the intensity changes of the band at 191 nm, it is revealed that the properties in adsorption are different from one protein to another. It is assumed that there are two types of forces on the protein adsorption: one is that among the molecules and the other is that between a molecule and a substrate. The origin of force includes localized electrostatic polarity and affinity to water. The ions in the solvent give a marked effect on these forces, resulting in the difference in the response to adsorption density against the salt concentration in the solvent.

A multi-technique approach to unveil the redox behaviour and potentiality of homoleptic CuI complexes based on substituted bipyridine ligands in oxygenation reactions.

The effect of differently substituted 2,2'-bipyridine ligands (i.e. 6,6'-dimethyl-2,2'-bipyridine, 5,5'-dimethyl-2,2'-bipyridine, 6,6'-dimethoxy-2,2'-bipyridine and 2,2'-bipyridine) on the reversible oxidation of the resulting CuI homoleptic complexes is investigated by means of a multi-technique approach (electronic and vibrational spectroscopies, DFT, electrochemistry). Among the four tested complexes, [CuI(6,6'-dimethyl-2,2'-bipyridine)2] (PF6) shows a peculiar behavior when oxidized with an organic peroxide (i.e. tert-butyl hydroperoxide, tBuOOH). The simultaneous use of UV-Vis-NIR and Raman spectroscopy methods and cyclovoltammetry, supported by DFT based calculations, allowed identifying (i) the change in the oxidation state of the copper ion and (ii) some peculiar modification in the local structure of the metal leading to the formation of a [CuIIOH]+ species. The latter, being able to oxidize a model molecule (i.e. cyclohexene) and showing the restoration of the original CuI complex and the formation of cyclohexanone, confirms the potential of these simple homoleptic CuI complexes as model catalysts for partial oxygenation reactions.

Hydrogen Bonding and Solvation of a Proline-Based Peptide Model in Salt Solutions.

The hydrogen bonding of water and water/salt mixtures around the proline-based tripeptide model glycyl-l-prolyl-glycinamide·HCl (GPG-NH2) is investigated here by multi-wavelength UV resonance Raman spectroscopy (UVRR) to clarify the role of ion-peptide interactions in affecting the conformational stability of this peptide. The unique sensitivity and selectivity of the UVRR technique allow us to efficiently probe the hydrogen bond interaction between water molecules and proline residues in different solvation conditions, along with its influence on trans to cis isomerism in the hydrated tripeptide. The spectroscopic data suggest a relevant role played by the cations in altering the solvation shell at the carbonyl site of proline., while the fluoride and chloride anions were found to promote the establishment of the strongest interactions on the C=O site of proline. This latter effect is reflected in the greater stabilization of the trans conformers of the tripeptide in the presence of these specific ions. The molecular view provided by UVRR experiments was complemented by the results of circular dichroism (CD) measurements that show a strong structural stabilizing effect on the ß-turn motif of GPG-NH2 observed in the presence of KF as a co-solute.