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The intriguing network of antibody–antigen (Ab–Ag) interactions is highly governed by environmental perturbations and the nature of biomolecular interaction. Protein–protein interactions (PPIs) have potential applications in developing protein-adsorption-based sensors and nano-scale materials. Therefore, characterizing PPIs in the presence of a nanomaterial at the molecular level becomes imperative. The present work involves the investigation of antiferritin–ferritin (Ab–Ag) protein interactions under the influence of tungsten disulfide quantum dots (WS2 QDs). Isothermal calorimetry and contact angle measurements validated the strong influence of WS2 QDs on Ab–Ag interactions. The interfacial signatures of nano–bio-interactions were evaluated using sum frequency generation vibration spectroscopy (SFG-VS) at the air–water interface. Our SFG results reveal a variation in the tilt angle of methyl groups by ∼12° ± 2° for the Ab–Ag system in the presence of WS2 QDs. The results illustrated an enhanced ordering of water molecules in the presence of QDs, which underpins the active role of interfacial water molecules during nano–bio-interactions. We have also witnessed a differential impact of QDs on Ab–Ag by raising the concentration of the Ab–Ag combination, which showcased an increased inter-molecular interaction among the Ab and Ag molecules and a minimal influence on the methyl tilt angle. These findings suggest the formation of stronger and ordered Ab–Ag complexes upon introducing WS2 QDs in the aqueous medium and signify the potentiality of WS2 QDs relevant to protein-based sensing assays. [ABSTRACT FROM AUTHOR]

The silica (SiO2) nanoparticles of a well-known silica precursor tetraethyl orthosilicate (TEOS) are generally synthesized via a promising solution-gelation inorganic polymerization process. The monodisperse silica nanoparticles have potential applications ranging from the formation of dental nanocomposites to antireflective coatings. In the present study, we have systematically investigated the in situ interfacial molecular structure of TEOS and its impact on the interfacial water structure during the processes of hydrolysis and condensation at the air–aqueous interface using sum-frequency generation (SFG) vibrational spectroscopy. With the presence of water, a gradual decrease in the SFG intensity in the CH-stretch region for each concentration of TEOS with time reflects the elimination of ethoxy groups, which is a signature of the hydrolysis process. Further, the impact of the hydrolysis process is revealed from the significant enhancement in the SFG signal in the OH-stretch region. The hydrolysis of TEOS is then followed by condensation in which the SiO– charged species are replaced by forming the SiOSi bridging network. The signature of the condensation process is reflected with the gradual decrease in the observed enhanced SFG signal in the OH-stretch region. The formation of monodispersed silica nanoparticles as an end product of size variation from 1.75 to 4.67 nm with the increase in TEOS concentration is confirmed with the DLS measurements. We have also probed the pH-dependent SFG studies at three different pH values (2.0, 5.8, and 9.0). The dominant pH-dependent hydrolysis process is revealed from the observed molecular structure of TEOS at the air–aqueous interface. [ABSTRACT FROM AUTHOR]

The change induced in the physicochemical properties of polymer while hosting ions provides a platform for studying its potential applications in electrochemical devices, water treatment plants, and materials engineering science. The ability to host ions is limited in very few polymers, which lack a detailed molecular-level understanding for showcasing the polymer-ion linkage behavior at the interfacial region. In the present manuscript, we have employed sum frequency generation (SFG) vibrational spectroscopy to investigate the interfacial structure of a new class phosphazene-based methoxyethoxyethoxyphosphazene (MEEP) polymer in the presence of lithium chloride salt at the air-aqueous interface. The interfacial aspects of the molecular system collected through SFG spectral signatures reveal enhanced water ordering and relative hydrogen bonding strength at the air-aqueous interface. The careful observation of the study finds a synchronous contribution of van der Waals and electrostatic forces in facilitating changes in the interfacial water structure that are susceptible to MEEP concentration in the presence of ions. The observation indicates that dilute MEEP concentrations support the role of electrostatic interaction, leading to an ordered water structure in proximity to diffused ions at the interfacial region. Conversely, higher MEEP concentrations promote the dominance of van der Waals interactions at the air-aqueous interface. Our study highlights the establishment of polymer electrolyte (PE) characteristics mediated by intermolecular interactions, as observed through the spectral signatures witnessed at the air-aqueous interface. The investigation illustrates the polymer-ion linkage adsorption effects at the interfacial region, which explains the macroscopic changes observed from the cyclic voltammetry studies. The fundamental findings from our studies can be helpful in the design and fine-tuning of better PE systems that can offer improved hydrophobic membranes and interface stability for use in electrochemical-based power sources., (© 2023 IOP Publishing Ltd.)