| 1. |
- Cautela, Jacopo, et al.
(författare)
-
C-12 vs C-3 substituted bile salts : An example of the effects of substituent position and orientation on the self-assembly of steroid surfactant isomers
- 2020
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 185
-
Tidskriftsartikel (refereegranskat)abstract
- Biomolecule derivatives are transversally used in nanotechnology. Deciphering their aggregation behavior is a crucial issue for the rational design of functional materials. To this end, it is necessary to build libraries of selectively functionalized analogues and infer general rules. In this work we enrich the highly applicative oriented collection of steroid derivatives, by reporting a rare example of C-12 selectively modified bile salt. While nature often exploits such position to encode functions, it is unusual and not trivial to prepare similar analogues in the laboratory. The introduction of a tert-butyl phenyl residue at C-12 provided a molecule with a self-assembly that remarkably switched from rigid pole-like structures to twisted ribbons at a biologically relevant critical temperature (∼25 °C). The system was characterized by microscopy and spectroscopy techniques and compared with the C-3 functionalized analogue. The twisted ribbons generate samples with a gel texture and a viscoelastic response. The parallel analysis of the two systems suggested that the observed thermoresponsive self-assemblies occur at similar critical temperatures and are probably dictated by the nature of the substituent, but involve aggregates with different structures depending on position and orientation of the substituent. This study highlights the self-assembly properties of two appealing thermoresponsive systems. Moreover, it adds fundamental insights hereto missing in the investigations of the relation between self-assembly and structure of synthetic steroids, which are valuable for the rational design of steroidal amphiphiles.
|
|
| 2. |
- D'Annibale, Valeria, et al.
(författare)
-
A spectroscopic and structural study on the solvent-promoted stereospecific self-assembly of new Porphyrin-Bile Salt conjugates
- 2024
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 700
-
Tidskriftsartikel (refereegranskat)abstract
- The chiral bile salt sodium cholate has been covalently linked to tetra-aryl-porphyrins, conferring them an extrinsic chirality and obtaining new molecules with high tendency to aggregate in solution. The chirality transfer from the molecular to the nano- and meso-scale has been investigated by promoting the self-assembly of the conjugates balancing the ratio of aqueous/organic solvent mixtures and allowing a fine control of the dimensions and morphology of the final supramolecular architectures. The shift from elongated structures with helical ribbon features to monodisperse tubules or from tightly packed rolled sheets to wrapped scrolls was enabled by changing the solvent composition, with the possibility of forming tubular structures with a hollow cavity. From UV–Vis and Circular Dichroism (CD) spectroscopy the ability to self-assemble into J-type aggregates with a strong induction of supramolecular chirality was revealed, shedding light on a two-step process, with a fast monomer nucleation followed by a slow second step of further stereospecific chiral evolution. The results as a whole promote the new porphyrin-cholate conjugates as promising smart and easily tunable chiral materials for the design of stereoselective sensing devices.
|
|
| 3. |
- Del Giudice, Alessandra, et al.
(författare)
-
Self-Assembly of Model Amphiphilic Peptides in Nonaqueous Solvents : Changing the Driving Force for Aggregation Does Not Change the Fibril Structure
- 2020
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 36:29, s. 8451-8460
-
Tidskriftsartikel (refereegranskat)abstract
- Within the homologous series of amphiphilic peptides AnK, both A8K and A10K self-assemble in water to form twisted ribbon fibrils with lengths around 100 nm. The structure of the fibrils can be described in terms of twisted β-sheets extending in the direction of the fibrils, laminated to give a constant cross section of 4 nm by 8 nm. The finite width of the twisted ribbons can be reasonably explained within a simple thermodynamic model, considering a free energy penalty for the stretching of hydrogen bonds along the twisted β-sheets and an interfacial free energy gain for the lamination of the hydrophobic β-sheets. In this study, we characterize the self-assembly behavior of these peptides in nonaqueous solutions as a route to probe the role of hydrophobic interaction in fibril stabilization. Both peptides, in methanol and N,N-dimethylformamide, were found to form fibrillar aggregates with the same β-sheet structure as in water but with slightly smaller cross-sectional sizes. However, the gel-like texture, the slow relaxation in dynamic light scattering experiments, and a correlation peak in the small-angle X-ray scattering pattern highlighted enhanced interfibril interactions in the nonaqueous solvents in the same concentration range. This could be ascribed to a higher effective volume of the aggregates because of enhanced fibril growth and length, as suggested by light scattering and cryogenic transmission electron microscopy analyses. These effects can be discussed considering how the solvent properties affect the different energetic contributions (hydrophobic, electrostatic, and hydrogen bonding) to fibril formation. In the analyzed case, the decreased hydrogen bonding propensity of the nonaqueous solvents makes the hydrogen bond formation along the fibril a key driving force for peptide assembly, whereas it represents a nonrelevant contribution in water.
|
|
| 4. |
- Del Giudice, Alessandra, et al.
(författare)
-
Structural response of human serum albumin to oxidation : Biological buffer to local formation of hypochlorite
- 2016
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 120:40, s. 12261-12271
-
Tidskriftsartikel (refereegranskat)abstract
- The most abundant plasma protein, human serum albumin (HSA), plays a key part in the body's antioxidant defense against reactive species. This study was aimed at correlating oxidant-induced chemical and structural effects on HSA. Despite the chemical modification induced by the oxidant hypochlorite, the native shape is preserved up to oxidant/HSA molar ratio <80, above which a structural transition occurs in the critical range 80-120. This conformational variation involves the drifting of one of the end-domains from the rest of the protein and corresponds to the loss of one-third of the α-helix and a net increase of the protein negative charge. The transition is highly reproducible suggesting that it represents a well-defined structural response typical of this multidomain protein. The ability to tolerate high levels of chemical modification in a folded or only partially unfolded state, as well as the stability to aggregation, provides albumin with optimal features as a biological buffer for the local formation of oxidants. (Graph Presented).
|
|
| 5. |
- Del Giudice, Alessandra, et al.
(författare)
-
The effect of fatty acid binding in the acid isomerizations of albumin investigated with a continuous acidification method
- 2018
-
Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765. ; 168, s. 109-116
-
Tidskriftsartikel (refereegranskat)abstract
- The protein Human Serum Albumin (HSA) is known to undergo conformational transitions towards partially unfolded forms triggered by acidification below pH 4.5. The extent of Fatty Acids (FA) binding has been thought to have an impact on the conformational equilibrium between the native and acid forms and to be a possible explanation for the observation of more than one band in early electrophoretic migration experiments at pH 4. We compared the acid-induced unfolding processes of commercial FA-free HSA, commercial “fatted” HSA and FA-HSA complexes, prepared at FA:HSA molar ratios between 1 and 6 by simple mixing and equilibration. We used a method for continuous acidification based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, and followed the average protein changes by the blue shift of the intrinsic fluorescence emission and by performing a small angle X-ray scattering analysis on selected samples. The method also allowed for continuous monitoring of the increase of turbidity and laser light scattering of the protein samples related to the release of the insoluble ligands with acidification. Our results showed that the presence of FA interacting with albumin, an aspect often neglected in biophysical studies, affects the conformational response of the protein to acidification, and slightly shifts the loss of the native shape from pH 4.2 to pH 3.6. This effect increased with the FA:HSA molar ratio so that with three molar equivalents a saturation was reached, in agreement with the number of high-affinity binding sites reported for the FA. These findings confirm that a non-uniform level of ligand binding in an albumin sample can be an explanation for the early-observed conformational heterogeneity at pH 4.
|
|
| 6. |
- Del Giudice, Alessandra, et al.
(författare)
-
Time-Dependent pH Scanning of the Acid-Induced Unfolding of Human Serum Albumin Reveals Stabilization of the Native Form by Palmitic Acid Binding
- 2017
-
Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 121:17, s. 4388-4399
-
Tidskriftsartikel (refereegranskat)abstract
- The most abundant plasma protein, human serum albumin (HSA), is known to undergo several conformational transitions in an acidic environment. To avoid buffer effects and correlate global and local structural changes, we developed a continuous acidification method and simultaneously monitored the protein changes by both small-angle scattering (SAXS) and fluorescence. The progressive acidification, based on the hydrolysis of glucono-δ-lactone from pH 7 to pH 2.5, highlighted a multistep unfolding involving the putative F form (pH 4) and an extended and flexible conformation (pH < 3.5). The scattering profile of the F form was extracted by component analysis and further 3D modeled. The effect of acid unfolding at this intermediate stage was assigned to the rearrangement of the three albumin domains drifting apart toward a more elongated conformation, with a partial unfolding of one of the outer domains. To test the stabilizing effect of fatty acids, here palmitic acid, we compared the acid unfolding process of albumin with and without ligand. We found that when binding the ligand, the native conformation was favored up to lower pH values. Our approach solved the problem of realizing a continuous, homogeneous, and tunable acidification with simultaneous characterization applicable to study processes triggered by a pH decrease.
|
|
| 7. |
- Del Giudice, Alessandra, et al.
(författare)
-
Towards natural care products : Structural and deposition studies of bio-based polymer and surfactant mixtures
- 2024
-
Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - 0927-7757. ; 698
-
Tidskriftsartikel (refereegranskat)abstract
- Oppositely charged polymer-surfactant systems are expected to interact with formation of coacervate complexes near composition of charge-neutrality. Such behaviour is widely used in formulated products (e.g. household and personal care), where the co-deposition of coacervates and active ingredients on various surfaces is triggered by dilution. A transition towards the use of more sustainable ingredients is currently ongoing as a response to the need of more environmentally conscious choices in production, albeit slowed down by the often more complex and not fully understood bulk and interfacial behaviour of new ingredients. In this work, mixtures of a medium-chain fatty acid (sodium decanoate) and two grades of bio-based cationic modified inulin were studied. The phase behaviour was determined in a wide composition matrix. The formation of coacervate complexes was observed for the mixture with the higher charge density polymer at a surfactant concentration of 1–3 wt%, close to the surfactant critical micellar concentration in pure water. Such behaviour was confirmed by DLS and SAXS data, suggesting surfactant-polymer complexation in a concentrated phase of packed micelles with a micelle-to-micelle distance of ∼4.5 nm. In situ ellipsometry and neutron reflectometry experiments were conducted to study the effect on surface deposition when diluting. The ellipsometry showed an adsorbed mass of ∼1.3–1.9 mg/m2, consistent with the deposition of a coacervate layer, and considerably higher than the neat, adsorbed polymer layer of ∼0.3 mg/m2. In the case of the neutron reflectometry experiments, dilution was performed before contact with the surface (pre-mixing), and no adsorption of coacervates was observed, but rather the adsorption of a polymer layer (0.49–0.85 mg/m2). The different results obtained with the different techniques highlight the kinetic nature of bulk coacervate formation and deposition, and the competition between these two phenomena. Maximal deposition can be achieved if one can control this time window either by tuning the composition of the system or the experimental set-up, to mimic the conditions of a specific application.
|
|
| 8. |
|
|
| 9. |
- Del Giudice, Rita, et al.
(författare)
-
Effects of iron on the aggregation propensity of the N-terminal fibrillogenic polypeptide of human apolipoprotein A-I
- 2018
-
Ingår i: BioMetals. - : Springer Science and Business Media LLC. - 0966-0844 .- 1572-8773. ; 31:4, s. 551-559
-
Tidskriftsartikel (refereegranskat)abstract
- Specific mutations in APOA1 gene lead to systemic, hereditary amyloidoses. In ApoA-I related amyloidosis involving the heart, amyloid deposits are mainly constituted by the 93-residue N-terminal region of the protein, here indicated as [1-93]ApoA-I. Oxidative stress is known to be an enhancing factor for protein aggregation. In healthy conditions, humans are able to counteract the formation and the effects of oxidative molecules. However, aging and atmospheric pollution increase the concentration of oxidative agents, such as metal ions. As the main effect of iron deregulation is proposed to be an increase in oxidative stress, we analysed the effects of iron on [1-93]ApoA-I aggregation. By using different biochemical approaches, we demonstrated that Fe(II) is able to reduce the formation of [1-93]ApoA-I fibrillar species, probably by stabilizing its monomeric form, whereas Fe(III) shows a positive effect on polypeptide fibrillogenesis. We hypothesize that, in healthy conditions, Fe(III) is reduced by the organism to Fe(II), thus inhibiting amyloid formation, whereas during ageing such protective mechanisms decline, thus exposing the organism to higher oxidative stress levels, which are also related to an increase in Fe(III). This alteration could contribute to the pathogenesis of amyloidosis.
|
|
| 10. |
- Du, Guanqun, et al.
(författare)
-
Condensed Supramolecular Helices : The Twisted Sisters of DNA
- 2022
-
Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 61:4
-
Tidskriftsartikel (refereegranskat)abstract
- Condensation of DNA helices into hexagonally packed bundles and toroids represents an intriguing example of functional organization of biological macromolecules at the nanoscale. The condensation models are based on the unique polyelectrolyte features of DNA, however here we could reproduce a DNA-like condensation with supramolecular helices of small chiral molecules, thereby demonstrating that it is a more general phenomenon. We show that the bile salt sodium deoxycholate can form supramolecular helices upon interaction with oppositely charged polyelectrolytes of homopolymer or block copolymers. At higher order, a controlled hexagonal packing of the helices into DNA-like bundles and toroids could be accomplished. The results disclose unknown similarities between covalent and supramolecular non-covalent helical polyelectrolytes, which inspire visionary ideas of constructing supramolecular versions of biological macromolecules. As drug nanocarriers the polymer-bile salt superstructures would get advantage of a complex chirality at molecular and supramolecular levels, whose effect on the nanocarrier assisted drug efficiency is a still unexplored fascinating issue.
|
|
