arXiv subjects

Daniel Hermida-Merino

Publications and source records attributed to Daniel Hermida-Merino.

5 recordsLinked to original sources

arXiv2025

Driving a stimuli-responsive wedge in the packing of phospholipid membranes using bolaamphiphile intercalants

Bolaamphiphilesamphiphilic molecules with polar groups at each of the two ends of a hydrophobic tail with pH-sensitive spontaneous molecular curvaturesendow membranes of extremophiles with an exquisite balance between stability (or robustness) and adaptability (or plasticity). But how the presence (or real-time insertion) of bolaamphiphiles influences lamellar lipid membranes is poorly understood. Using a combination of time-resolved confocal fluorescence microscopy, in situ small angle X-ray and neutron scattering (SAXS, SANS), and neutron spin echo (NSE) measurements, we monitor here the pH-dependent interactions of nanoscopic vesicles of a representative bolaamphiphilea glucolipid consisting of a single glucose headgroup and a C18:1 (oleyl) fatty acid tail (G-C18:1)with the membranes of an essentially cylindrical, fluid-phase phospholipid (dioleoylphosphatidylcholine, DOPC). We find that the two mesophases interact spontaneously at all pH values, producing large-scale morphological remodeling. Under neutral and acidic conditions, when the bolaamphiphile assumes a cylindrical shape, vesicles fuse with one another, producing invaginations, inner tubulation and vesicle-in-vesicle aggregates. Under basic pH, by contrast, when the carboxylic acid is deprotonated and the molecule is inverted-conical in shape, the bolaamphiphile causes phospholipid membranes to undergo poration, budding, and vesiculation. This pH-dependent, environmentally sensitive membrane remodeling without the disruption of the essential bilayer motif illustrates how local, molecular-level packing perturbations can translate into global system-level morphological changes, enabling membranes to acquire environmental sensitivity and real-time adaptability. These results support the notion that molecular fluxeswhich add (or remove) amphiphilic molecules to biological membranescan endow de novo functionalities (e.g., pH sensitivity) and influence global morphologies of cell-sized vesicles.

cond-mat.soft↗

arXiv2024

A Direct Real-Time Observation of Anion Intercalation in Graphite Process and Its Fully Reversibility by SAXS/WAXS Techniques

The process of anion intercalation in graphite and its reversibility plays a crucial role in the next generation energy-storage devices. Herein the reaction mechanism of the aluminum graphite dual ion cell by operando X-ray scattering from small angles to wide angles is investigated. The staging behavior of the graphite intercalation compound (GIC) formation, its phase transitions, and its reversible process are observed for the first time by directly measuring the repeated intercalation distance, along with the microporosity of the cathode graphite. The investigation demonstrates complete reversibility of the electrochemical intercalation process, alongside nano- and micro-structural reorganization of natural graphite induced by intercalation. This work represents a new insight into thermodynamic aspects taking place during intermediate phase transitions in the GIC formation.

cond-mat.mtrl-sci↗

arXiv2020

Synthesis and self-assembly of aminyl and alkynyl substituted sophorolipids

Sophorolipids are one of the most important microbial biosurfactants, because of their large-scale production and applications developed so far in the fields of detergency, microbiology, cosmetics or environmental science. However, the structural variety of native sophorolipids is limited/restricted, a limiting fact for the development of new properties and their potential applications. In their open acidic form, C18:1 sophorolipids (SL) are classically composed of a sophorose headgroup and a carboxylic acid (COOH) end-group. The carboxyl group gives them unique pH-responsive properties, but they are a poorly-reactive group and their charge can only be negative. To develop a new generation of pH-responsive, positively-charged, SL and to improve their reactivity for further functionalization, we develop here SLs with an amine (-NH2) or terminal alkyne (-C$\not\equiv$CH) end-group analogues. The amine group generates positively-charged SL and is more reactive than carboxylic acids, e.g. towards aldehydes; the alkyne group provides access to copper-based click chemistry. In this work, we synthesize (C18:1) and (C18:0) --NH2 and (C18:1) -C$\not\equiv$CH sophorolipid derivatives and we study their self-assembly properties in response to pH and/or temperature changes by means of static and dynamic light scattering, small angle (X-ray, neutron) scattering and cryogenic electron microscopy. Monounsaturated aminyl SL-C18:1-NH2 sophorolipids form a micellar phase in their neutral form at high pH and a mixed micellar-bilayer phase in their positively-charged form at low pH. Saturated aminyl SL-C18:0-NH2 sophorolipids form a micellar phase in their charged form at low pH and a twisted ribbon phase in their neutral form at high pH and monounsaturated alkynyl SL-C18:1-C$\not\equiv$CH sophorolipids form a main micellar phase at T> 51.8{\textdegree}C and a twisted ribbon phase at T< 51.8 {\textdegree}C.

cond-mat.soft↗

arXiv2020

Single-Molecule Lamellar Hydrogels from Bolaform Microbial Glucolipids

Lipid lamellar hydrogels are rare soft fluids composed of a phospholipid lamellar phase instead of fibrillar networks. The mechanical properties of these materials are controlled by defects, induced by local accumulation of a polymer or surfactant in a classical lipid bilayer. Herein we report a new class of lipid lamellar hydrogels composed of one single bolaform glycosylated lipid obtained by fermentation. The lipid is self-organized into flat interdigitated membranes, stabilized by electrostatic repulsive forces and stacked in micrometer-sized lamellar domains. The defects in the membranes and the interconnection of the lamellar domains are responsible, from the nano- to the micrometer scales, for the elastic properties of the hydrogels. The lamellar structure is probed by combining small angle x-ray and neutron scattering (SAXS, SANS), the defect-rich lamellar domains are visualized by polarized light microscopy while the elastic properties are studied by oscillatory rheology. The latter show that both storage G' and loss G'' moduli scale as a weak power-law of the frequency, that can be fitted with fractional rheology models. The hydrogels possess rheo-thinning properties with second-scale recovery. We also show that ionic strength is not only necessary, as one could expect, to control the interactions in the lamellar phase but, most importantly, it directly controls the elastic properties of the lamellar gels.

cond-mat.soft↗

arXiv2019

Extending SAXS instrument ranges through addition of a portable, inexpensive USAXS module

Ultra-SAXS can enhance the capabilities of existing SAXS/WAXS beamlines and laboratory instruments. A compact Ultra-SAXS module has been developed, which extends the measurable $q$-range with $0.0015 \leq q\mathrm{(nm^{-1})} \leq 0.2$, allowing structural dimensions between $30 \leq D$(nm)$ \leq 4000$ to be probed in addition to the range covered by a high-end SAXS/WAXS instrument. By shifting the module components in and out on their respective motor stages, SAXS/WAXS measurements can be easily and rapidly interleaved with USAXS measurements. In this paper, the design considerations, realization and synchrotron findings are presented. Measurements of silica spheres, an alumina membrane, and a porous carbon catalyst are provided as application examples.

physics.ins-det↗