Unveiling the self-assembly process of gellan-chitosan complexes through a combination of atomistic simulations and experiments.

Polyelectrolyte complexes (PECs), formed via the self-assembly of oppositely charged polysaccharides, are highly valued for their biocompatibility, biodegradability, and hydrophilicity, offering significant potential for biotechnological applications. However, the complex nature and lack of insight at a molecular level into polyelectrolytes conformation and aggregation often hinders the possibility of achieving an optimal control of PEC systems, limiting their practical applications. To address this problem, an in-depth investigation of PECs microscopic structural organization is required.

Water slowing down drives the occurrence of the low temperature dynamical transition in microgels.

The protein dynamical transition marks an increase in atomic mobility and the onset of anharmonic motions at a critical temperature ( ), which is considered relevant for protein functionality. This phenomenon is ubiquitous, regardless of protein composition, structure and biological function and typically occurs at large protein content, to avoid water crystallization. Recently, a dynamical transition has also been reported in non-biological macromolecules, such as poly(-isopropyl acrylamide) (PNIPAM) microgels, bearing many similarities to proteins.

Molecular origin of the two-step mechanism of gellan aggregation.

Among hydrocolloids, gellan is one of the most studied polysaccharides due to its ability to form mechanically stable gels. Despite its long-standing use, the gellan aggregation mechanism is still not understood because of the lack of atomistic information. Here, we fill this gap by developing a new gellan force field.

Modeling Solution Behavior of Poly(-isopropylacrylamide): A Comparison between Water Models.

Water is known to play a fundamental role in determining the structure and functionality of macromolecules. The same crucial contribution is also found in the in silico description of polymer aqueous solutions. In this work, we exploit the widely investigated synthetic polymer poly(-isopropylacrylamide) (PNIPAM) to understand the effect of the adopted water model on its solution behavior and to refine the computational setup.

Two-step deswelling in the Volume Phase Transition of thermoresponsive microgels.

Thermoresponsive microgels are one of the most investigated types of soft colloids, thanks to their ability to undergo a Volume Phase Transition (VPT) close to ambient temperature. However, this fundamental phenomenon still lacks a detailed microscopic understanding, particularly regarding the presence and the role of charges in the deswelling process. This is particularly important for the widely used poly(-isopropylacrylamide)-based microgels, where the constituent monomers are neutral but charged groups arise due to the initiator molecules used in the synthesis.

Interaction of Caffeine with Model Lipid Membranes.

Caffeine is not only a widely consumed active stimulant, but it is also a model molecule commonly used in pharmaceutical sciences. In this work, by performing quartz-crystal microbalance and neutron reflectometry experiments we investigate the interaction of caffeine molecules with a model lipid membrane. We determined that caffeine molecules are not able to spontaneously partition from an aqueous environment, enriched in caffeine, into a bilayer.

Thermoresponsivity of poly(N-isopropylacrylamide) microgels in water-trehalose solution and its relation to protein behavior.

Hypotheses: Additives are commonly used to tune macromolecular conformational transitions. Among additives, trehalose is an excellent bioprotectant and among responsive polymers, PNIPAM is the most studied material. Nevertheless, their interaction mechanism so far has only been hinted without direct investigation, and, crucially, never elucidated in comparison to proteins.

Molecular insights on poly(-isopropylacrylamide) coil-to-globule transition induced by pressure.

By using extensive all-atom molecular dynamics simulations of an atactic linear polymer chain, we provide microscopic insights into poly(N-isopropylacrylamide) (PNIPAM) coil-to-globule transition addressing the roles played by both temperature and pressure. We detect a coil-to-globule transition up to large pressures, showing a reentrant behavior of the critical temperature with increasing pressure in agreement with experimental observations. Furthermore, again confirming the experimental findings, we report the existence at high pressures of a new kind of globular state.

Molecular Dynamics and Neutron Scattering Studies of Potassium Chloride in Aqueous Solution.

Neutron diffraction with isotopic substitution (NDIS) experiments were done on both natural abundance potassium and isotopically labeled KCl heavy water solutions to characterize the solvent structuring around the potassium ion in water. Preliminary measurements suggested that the literature value for the coherent neutron scattering length (2.69 fm) for K was significantly in error.

Water-Polymer Coupling Induces a Dynamical Transition in Microgels.

The long debated protein dynamical transition was recently found also in nonbiological macromolecules, such as poly- N-isopropylacrylamide (PNIPAM) microgels. Here, by using atomistic molecular dynamics simulations, we report a description of the molecular origin of the dynamical transition in these systems. We show that PNIPAM and water dynamics below the dynamical transition temperature T are dominated by methyl group rotations and hydrogen bonding, respectively.

Crowding and conformation interplay on human DNA G-quadruplex by ultraviolet resonant Raman scattering.

The G-quadruplex-forming telomeric sequence (TTAGGG)4TT was investigated by polarized Ultraviolet Resonance Raman Scattering (UVRR) at 266 nm. The presence of 40% poly(ethylene glycol) and the so-called "self-crowding" condition were used to induce the hybrid-to-parallel topology transition. Analysis of frequency shifts with temperature showed the role of several functional groups in the topological transitions and provides structural dynamical information.

Numerical modelling of non-ionic microgels: an overview.

Microgels are complex macromolecules. These colloid-sized polymer networks possess internal degrees of freedom and, depending on the polymer(s) they are made of, can acquire a responsiveness to variations of the environment (temperature, pH, salt concentration, etc.).

Evidence of a low-temperature dynamical transition in concentrated microgels.

A low-temperature dynamical transition has been reported in several proteins. We provide the first observation of a "protein-like" dynamical transition in nonbiological aqueous environments. To this aim, we exploit the popular colloidal system of poly--isopropylacrylamide (PNIPAM) microgels, extending their investigation to unprecedentedly high concentrations.

Molecular Dynamics and Neutron Scattering Studies of Mixed Solutions of Caffeine and Pyridine in Water.

Insight into the molecular interactions of homotactic and heterotactic association of caffeine and pyridine in aqueous solution is given on the basis of both experimental and simulation studies. Caffeine is about 5 times more soluble in a 3 m aqueous pyridine solution than it is in pure water (an increase from ∼0.1 m to 0.

Myelography Iodinated Contrast Media. 2. Conformational Versatility of Iopamidol in the Solid State.

The phenomenon of polymorphism is of great relevance in pharmaceutics, since different polymorphs have different physicochemical properties, e.g., solubility, hence, bioavailability.

Stacking and Branching in Self-Aggregation of Caffeine in Aqueous Solution: From the Supramolecular to Atomic Scale Clustering.

The dynamical and structural properties of caffeine solutions at the solubility limit have been investigated as a function of temperature by means of MD simulations, static and dynamic light scattering, and small angle neutron scattering experiments. A clear picture unambiguously supported by both experiment and simulation emerges: caffeine self-aggregation promotes the formation of two distinct types of clusters: linear aggregates of stacked molecules, formed by 2-14 caffeine molecules depending on the thermodynamic conditions and disordered branched aggregates with a size in the range 1000-3000 Å. While the first type of association is well-known to occur under room temperature conditions for both caffeine and other purine systems, such as nucleotides, the presence of the supramolecular aggregates has not been reported previously.

Myelography iodinated contrast media. I. Unraveling the atropisomerism properties in solution.

The present work reports a thorough conformational analysis of iodinated contrast media: iomeprol, iopamidol (the world's most utilized contrast agent), and iopromide. Its main aim is the understanding of the complex structural features of these atropisomeric molecules, characterized by the presence of many conformers with hindered rotations, and of the role of atropisomerism in the physicochemical properties of their aqueous solutions. The problem was tackled by using an extensive analysis of (13)C NMR data on the solutions of whole molecules and of simple precursors in addition to FT-IR investigation and molecular simulations.

The Interaction of Sorbitol with Caffeine in Aqueous Solution.

Molecular dynamics simulations were carried out on a system of caffeine interacting with the sugar alcohol sorbitol. The system examined had a caffeine concentration 0.083 m and a sugar concentration 1.

Caffeine and sugars interact in aqueous solutions: a simulation and NMR study.

Molecular dynamics simulations were carried out on several systems of caffeine interacting with simple sugars. These included a single caffeine molecule in a 3 m solution of α-D-glucopyranose, at a caffeine concentration of 0.083 m, a single caffeine in a 3 m solution of β-D-glucopyranose, and a single caffeine molecule in a 1.

Weakly hydrated surfaces and the binding interactions of small biological solutes.

Extended planar hydrophobic surfaces, such as are found in the side chains of the amino acids histidine, phenylalanine, tyrosine, and tryptophan, exhibit an affinity for the weakly hydrated faces of glucopyranose. In addition, molecular species such as these, including indole, caffeine, and imidazole, exhibit a weak tendency to pair together by hydrophobic stacking in aqueous solution. These interactions can be partially understood in terms of recent models for the hydration of extended hydrophobic faces and should provide insight into the architecture of sugar-binding sites in proteins.

Molecular dynamics simulation studies of caffeine aggregation in aqueous solution.

Molecular dynamics simulations were carried out on a system of eight independent caffeine molecules in a periodic box of water at 300 K, representing a solution near the solubility limit for caffeine at room temperature, using a newly developed CHARMM-type force field for caffeine in water. Simulations were also conducted for single caffeine molecules in water using two different water models (TIP3P and TIP4P). Water was found to structure in a complex fashion around the planar caffeine molecules, which was not sensitive to the water model used.

Sugar-binding sites on the surface of the carbohydrate-binding module of CBH I from Trichoderma reesei.

Molecular dynamics simulations were carried out for a system consisting of the carbohydrate-binding module (CBM) of the cellulase CBH I from Trichoderma reesei (Hypocrea jecorina) in a concentrated solution of β-D-glucopyranose, to determine whether there is any tendency for the sugar molecules to bind to the CBM. In spite of the general tendency of glucose to behave as an osmolyte, a marked tendency for the sugar molecules to bind to the protein was observed. However, the glucose molecules tended to bind only to specific sites on the protein.