Shell Water Research Articles

Raman structural study of ethylene glycol and 1,3-propylene glycol aqueous solutions

Raman spectra of ethylene glycol (EG) and 1,3-propylene glycol (1,3-PG) aqueous solutions with the diol content from 10 to 90 mol% were measured. The diol content weakly influences the EG and 1,3-PG Raman bands in the spectra of the solutions in the region 250–1800 cm−1. This fact means that the conformational compositions of both the diols do not change significantly with dissolving in water. The intensity of the OH stretching band with respect to the diol bands intensities is the linear function of the ratio of the mole contents of water and the diol in the solutions. The spectral region 2800–3800 cm−1 can be used to evaluate the chemical composition of these binary solutions. DFT modeling of the Raman spectra of EG molecule in water shell confirms the prevalence of the gauche-conformation of EG in the aqueous solutions.

A simple and feasible fluorescent approach for rapid detection of hexavalent chromium based on gold nanoclusters

Hexavalent chromium (Cr6+) owns hypertoxicity, non-biodegradability, and carcinogenicity, thus the detection of Cr6+ is of paramount significance for environmental monitoring and human health maintenance. Herein, a simple, rapid, and feasible fluorescent method based on gold nanoclusters (AuNCs) was established for determination of Cr6+. The AuNCs was coated by a simple and fast one-pot method using d-histidine (d-His) and polylysine (P-Lys) as stabilizers and reductants, which could be quenched by the addition of Cr6+ owing to the aggregation of AuNCs and fluorescence resonance energy transfer (FRET) between AuNCs and Cr6+. Under the optimal conditions, the fluorescent sensor exhibited good linearity within 10–10000 μg/L with limit of detection of 7.2 μg/L. The developed sensor possessed favorable sensitivity and selectivity. Additionally, the proposed method also had favorable recovery with good precision and accuracy within the actual sample, including celery cabbage, rice, capsule shell, and river water.

Water Defect Stabilizes the Bi3+ Lone-Pair Electronic State Leading to an Unusual Aqueous Hydration Structure.

The aqueous hydration structure of the Bi3+ ion is probed using a combination of extended X-ray absorption fine structure (EXAFS) spectroscopy and density functional theory (DFT) simulations of ion-water clusters and condensed-phase solutions. Anomalous features in the EXAFS spectra are found to be associated with a highly asymmetric first-solvent water shell. The aqueous chemistry and structure of the Bi3+ ion are dramatically controlled by the water stabilization of a lone-pair electronic state involving the mixed 6s and 6p orbitals. This leads to a distinct multimodal distribution of water molecules in the first shell that are separated by about 0.2 Å. The lone-pair structure is stabilized by a collective response of multiple waters that are localized near the lone-pair anti-bonding site. The findings indicate that the lone-pair stereochemistry of aqueous Bi3+ ions plays a major role in the binding of water and ligands in aqueous solutions.

V2O5 intercalated with polyaniline for improved kinetics in aqueous ammonium-ion batteries

The use of non-metal ammonium ions (NH 4 + ) as effective charge carriers in battery systems is receiving widespread attention because of their light weight and small hydration shells in water as well as abundancy of the elements. The research concerning NH 4 + ion redox chemistry in batteries is still in its infancy, mainly because the large ionic radius of NH 4 + would require a host material to have a wider open structure and thus limits the choice of electrode materials. NH 4 + ion redox chemistry is dominated by non-ionic chemical bonding such as hydrogen bonding with some covalent bonding in nature which plays a significant role in electrochemical performance of the battery. In this work, an in-situ intercalation technique is utilized to synthesize polyaniline-intercalated vanadium oxide with a nanoflower morphology for increased surface area and enhanced NH 4 + ion (de)intercalation kinetics. Through this strategy, an interlayer spacing of 13.99 Å between V-O layers is reached, offering large diffusion channels to accommodate NH 4 + ions which have an ionic radius of 1.48 Å and a hydrated radius of 3.31 Å. The diffusion kinetics of the NH 4 + ions, influenced by the hydrogen bonds formed between NH 4 + ion and O 2− in the host structure, are thus effectively enhanced by the unique π-conjugated structure of PANI, leading to high capacity, improved rate capability and improved cycle life. The as-prepared PANI-intercalated V 2 O 5 (PVO) demonstrates stable, ultrafast NH 4 + ion electrochemical storage based on hydrogen bond chemistry as elucidated by X-ray photoelectron spectroscopy and Raman spectroscopy characterizations. Additionally, the composition of the PVO electrode is optimized with respect to the amount of PANI between the V-O layers. The PVO with an optimal composition exhibits the best overall electrochemical performance, delivering a high capacity of 192.5 mA hg −1 and 39 mA hg −1 at specific currents of 1 and 20 A g −1 respectively, as well as a stable cycle life with a capacity retention of 98% at a specific current of 10 and 20 A g −1 . As such, the present work provides critical insights into the design of promising electrode materials for emerging aqueous non-metal batteries with intrinsic safety and reduced cost.

The Effect of Trehalose Coating for Magnetite Nanoparticles on Stability of Egg White Lysozyme.

In this study, the protein stability of hen egg-white lysozymes (HEWL) by Fe3O4 and Fe3O4-coated trehalose (Fe3O4@Tre) magnetic nanoparticles (NPs) is investigated. For this purpose, the co-precipitation method was used to synthesize magnetic NPs. The synthesized NPs were characterized by XRD, FT-IR spectroscopy, FE-SEM, and VSM analysis. In addition, the stability of HEWLs exposed to different NP concentrations in the range of 0.001–0.1 mg mL−1 was investigated by circular dichroism (CD) spectroscopy, fluorescence, and UV-Vis analysis. Based on the results, in the NP concentration range of 0.001–0.04 mg mL−1 the protein structure is more stable, and this range was identified as the range of kosmotropic concentration. The helicity was measured at two concentration points of 0.02 and 0.1 mg mL−1. According to the results, the α-helix at 0.02 mg mL−1 of Fe3O4 and Fe3O4@Tre was increased from 35.5% for native protein to 37.7% and 38.7%, respectively. The helicity decreased to 36.1% and 37.4%, respectively, with increasing the concentration of Fe3O4 and Fe3O4@Tre to 0.1 mg mL−1. The formation of hydrated water shells around protein molecules occurred by using Fe3O4@Tre NPs. Hence, it can be concluded that the trehalose as a functional group along with magnetic NPs can improve the stability of proteins in biological environments.

High-Efficient Dust Trapping Performance of AES/Polyacrylamide Strengthen Foam Based on the Structure Stability and Dust Wettability.

The atmospheric dust has a great negative impact on the societal harmonious development that starves for an efficient dust suppressant. This paper proposes a novel AES/polyacrylamide strengthen foam (APSF) to improve the dust trapping effectiveness. The APSF structure property and dust suppression capacity are studied and evaluated through the molecular dynamics simulation and experimental tests. The results express that APSF exhibits the stronger structure stability, superior water retention, and slower drainage performance than the traditional water-based foam (WBF). APSF dynamic simulation is studied by the relative concentration, radial distribution function, head group orientation, and mean square displacement. Research shows that APSF introduces water to thicken the hydration layer. The interaction strength between water and surfactant head groups is enhanced by 22.62 and 31.37% in the first and second hydrated water shells. APSF improves the sodium fatty alcohol ether sulfate (AES) orientation and weakens the diffusion of water molecules, which favors the foam stability. APSF exerts a better wettability on the coal dust through the wet settlement and contact angle tests. The APSF liquid film thickness reduces to 58.05 from 64.80 μm that is 3.14 times of WBF according to the foam liquid film decay experiment. Fourier transform infrared (FTIR) spectroscopy analysis indicates that there is an evident reinforcement on the coal surface absorption peak intensity of hydroxyl- and oxygen-containing functional groups treated by APSF. FTIR results are further determined by energy-dispersion spectrum analysis.

Influence of Electrostatic Field on Mixed Aqueous Solution of Calcium and Ferrous Ions: Insights from Molecular Dynamics Simulations

In order to investigate the anti-scaling and anti-corrosion characteristics of an electrostatic anti-fouling system in the application process, the influence of an electrostatic field (EF) on the structure and dynamics of hydrated Ca2+ and hydrated Fe2+ in a mixed aqueous system was studied through the calculation and analysis of the radial distribution function (RDF), self-diffusion coefficients, viscosity, and hydrogen bond structure by using molecular dynamics simulation. The study results show that the EF can decrease the radius of the first water shell of hydrated Ca2+ but increase that of Fe2+, which will reduce the possibility of forming calcite. The EF can make water molecules and Fe2+ more active, which can hinder iron release and thus decrease iron corrosion products. In addition, the EF can enhance the hydrogen structure of water molecules in the aqueous solution.

Direct and Water-Mediated Adsorption of Stabilizers on SERS-Active Colloidal Bimetallic Plasmonic Nanomaterials: Insight into Citrate-AuAg Interactions from DFT Calculations.

In previous studies, AuAg colloidal nanostar formulations were developed with the two-fold aim of producing optimized surface-enhanced Raman spectroscopy (SERS) substrates and investigating the nature of the capping process itself. Findings demonstrated that the nanoparticle metals are alloyed and neutral, and capping by stabilizers occurs via chemisorption. This study utilizes citrate as the model stabilizer and investigates the mechanistic aspects of its interaction with mono- (Au20) and bimetallic (Au19Ag) surfaces by density functional theory (DFT) calculations. Citrate was modeled according to the colloid's pH and surrounded by a water and sodium first solvation shell. A population of stable cluster-citrate structures was obtained, and energies were refined at the uB3LYP//LANL2TZ(f)/cc-pVTZ level of theory. Solvation was accounted for both explicitly and implicitly by the application of the continuum model SMD. Results indicate that both direct binding and binding by water proxy through the charge-transfer complex formation are thermodynamically favorable. Water participation in citrate adsorption is supported by the adsorption behavior observed experimentally and the comparison between experimental and DFT-simulated IR spectra. Vibrational mode analysis suggests the possible presence of water within a crystal in dried nanostar residues. All ΔGads(aq) indicate a weak chemisorptive process, leading to the hypothesis that citrate could be displaced by analytes during SERS measurements.

Pathogenicity of Indigenous Entomopathogen Liquid Formulation to Paddy Bugs Nymphs (Leptocorisa acuta Thunberg)

The purpose of this study was to determine the effectiveness of bio insecticide liquid formulations made from indigenous entomopathogens against paddy bugs nymphs. The study used a non-factorial Complete Randomized Design with 9 treatments and 1 control with five replications. The treatments studied consisted of E0: Control, E1: Beauveria sp Pky isolate + coconut water (CW), E2: Metarhizium sp isolate Jjt + AK, E3: Beauveria sp isolate Jts + CW, E4: Metarhizium sp isolate Lcc + CW, E5: Beauveria sp Pky isolate + shrimp shell extract (SSE), E6: Metarhizium sp isolate Jjt + SSE, E7: Beauveria sp isolate Jts + SSE, E8: Metarhizium sp isolate Lcc + SSE, E9: Synthetic insecticide b a Carbamate (Dharmabas 500 EC 2 ml L-1). The result showed that liquid bioinsecticide formulations were effective against mortality, infected nymphs and nymph death time. All entomopathogenic fungi isolates were able to cause infections in paddy bugs nymphs of 68% - 84%. Beauveria sp Pky isolate and Metarhizium sp isolate Jjt caused nymph mortality of 72% - 84% and the effectivity did not differ from insecticide b.a. Carbamate. Conidia viability of all entomopathogenic isolates in liquid media within 24 hours reached more than 80%. The fastest time to death of paddy bugs nymph occurred at 5.44 days ( Metarhizium sp. isolate) and 5.92 days (Beauveria sp. isolate) in coconut water media. Metarhizium sp. and Beauveria sp. in the medium of coconut water or shrimp shell extract has a very high potential to be developed as a bio insecticide, but it still needs to be further tested for its effectiveness in field conditions.Keywords: indigenous entomopathogen, coconut water, shrimp shell extract, paddy bugs nymph

Effect of methanol as an amphiphile on water structuring around a hydrate forming gas molecule: Insights from molecular dynamics simulations

Gas hydrates (GH) are crystalline compounds composed of small hydrophobic molecules encapsulated within cavities formed by hydrogen bonded water molecules. These compounds are an important source of fuel and are of application in gas storage and transportation. Processes such as nucleation, crystal growth, stability and decomposition of GH are controlled by the introduction of molecules referred to as additives. A challenging aspect in the study of GH is to explain at a molecular level the influence of additives on these processes. An intriguing case of additives is that of amphiphilic molecules which influence hydrate processes through their complex effects on the organization of water as well as on gas solubility. In this study, we apply molecular dynamics simulations to examine the effect of CH3OH, the simplest amphiphile and the most commonly used additive, on the organization of H2O molecules in the hydration shell of CO2, a hydrate forming gas. The interface between methanol–water liquid mixture and CO2 is examined by applying the Identification of Truly Interfacial Molecules (ITIM) technique, thereby minimizing the errors due to molecular level roughness at the interface. The organizational order of hydration shell water (HSW) is examined by evaluating the F4 order parameter. The results show that the presence of CH3OH enhances the availability of aqueous CO2 near the interface which makes the arrangement of HSW in this region more hydrate-like, resulting in an increase in value of F4 on approaching the interface from the bulk. It is also observed that CH3OH molecules tend to orient their hydrophobic CH3 group towards aqueous CO2 thereby inducing hydrate-like ordering of water in the hydration shell. However, on approaching the liquid surface, hydrate-like organization of HSW is opposed by CH3OH molecules at the surface which, owing to their –OH group oriented towards the liquid phase, significantly influences water orientation near the interface and decreases the value of F4. The net outcome of these opposing effects of CH3OH on hydrate-like ordering of HSW is the observation of a maximum in the value of F4 order parameter at a distance beneath the surface of the liquid and a progressive decrease from this maximum on moving further closer to the surface. The observed features of the value of F4 order parameter profile are explained based on the analysis of the intrinsic structure of the liquid–gas interface. The results indicate that, the presence of CH3OH leads to a region beneath the liquid surface where the extent of hydrate-like organization of HSW becomes maximum. However, CH3OH molecules significantly limits the availability of water molecules around aqueous gas, justifying the action of methanol as an inhibitor for hydrate formation when present at high concentrations. The results indicate that the effect of an amphiphile on GH formation is determined by its interaction with dissolved gas as well as by the influence of surface adsorbed amphiphile on water orientation and gas availability near the interface.

Quantification of Water–Ion Pair Interactions in Polyelectrolyte Multilayers Using a Quartz Crystal Microbalance Method

Water existing within thin polyelectrolyte multilayer (PEM) films has significant influence on their physical, chemical, and thermal properties, having implications for applications including energy storage, smart coatings, and biomedical systems. Ionic strength, salt type, and terminating layer are known to influence PEM swelling. However, knowledge of water’s microenvironment within a PEM, whether that water is affiliated with intrinsic or extrinsic ion pairs, remains lacking. Here, we examine the influence of both assembly and post-assembly conditions on the water–ion pair interactions of poly(styrene sulfonate)/poly(diallyldimethylammonium) (PSS/PDADMA) PEMs in NaCl and KBr. This is accomplished by developing a methodology in which quartz crystal microbalance with dissipation monitoring is applied to estimate the number of water molecules affiliated with an ion pair (i), as well as the hydration coefficient, πsaltH2O. PSS/PDADMA PEMs are assembled in varying ionic strengths of either NaCl and KBr and then exposed post-assembly to increasing ionic strengths of matching salt type. A linear relationship between the total amount of water per intrinsic ion pair and the post-assembly salt concentration was obtained at post-assembly salt concentrations >0.5 M, yielding estimates for both i and πsaltH2O. We observe higher values of i and πsaltH2O in KBr-assembled PEMs due to KBr being more effective in doping the assembly because of KBr’s more chaotropic nature as compared to NaCl. Lastly, when PSS is the terminating layer, i decreases in value due to PSS’s hydrophobic nature. Classical and ab initio molecular dynamics provide a microstructural view as to how NaCl and KBr interact with individual polyelectrolytes and the involved water shells. Put together, this study provides further insight into the understanding of existing water microenvironments in PEMs and the effects of both assembly and post-assembly conditions.

Physico-chemical Parameters and Heavy Metals Distribution in Selected Shell Fishes along the Opuro-Ama Creek in Rivers State of Nigeria

The study was conducted to determine the heavy metals concentration in selected shell fishes (U. tangeri, C. amnicola, T. fuscatus, P. monodon), sediment and water. The samples were collected from a fishing port along the Opuro-ama Creek in Rivers State of Nigeria. analysis for Manganese (Mn), Iron (Fe), Cobalt (Co) and Zinc (Zn) were done using Atomic Absorption Spectrophotometer. The order of metal accumulation in these shellfishes, sediment and water were; C. amnicola (Fe > Zn > Cu > Co > Mn); U. tangeri (Fe > Zn > Cu > Co > Mn); T. fuscatus (Fe > Cu > Zn > Co > Mn); P. monodon (Fe > Co > Zn > Cu = Mn); Sediment (Fe > Zn > Co > Cu > Mn); Water (Fe > Cu > Mn > Co = Zn). There was statistical difference (p<0.05) in metals concentration in the soft tissues in all the shellfish. From the results, the concentration of the metals in the tissues of all the shell fishes, the interstitial water and the sediment sampled from the creek were within the permissible limit recommended by the Department of Petroleum Resources (DRP), Environmental Protection Agency (EPA) and World Health Organization (WHO) except for Fe which was above the recommended limit. The physicochemical parameters of the interstitial water such as pH, Temperature, Conductivity, Total Dissolved Solids (TSS) Biological Oxygen Demand (BOD), Dissolved Oxygen (DO), and Salinity were within the acceptable levels in the guidelines for drinking]. Although Chemical Oxygen Demand (COD) and the Total Suspended Solids (TSS) were slightly higher than the recommended limit of these metals by Department of Petroleum Resources (DRP). This indicates that if theses metals are not checked, they may increase the potential for bioaccumulation in the shellfishes and the creek as well. Therefore, there is need for regular monitoring of this creek to avoid future deterioration.

FtsZ filament structures in different nucleotide states reveal the mechanism of assembly dynamics.

Treadmilling protein filaments perform essential cellular functions by growing from one end while shrinking from the other, driven by nucleotide hydrolysis. Bacterial cell division relies on the primitive tubulin homolog FtsZ, a target for antibiotic discovery that assembles into single treadmilling filaments that hydrolyse GTP at an active site formed upon subunit association. We determined high-resolution filament structures of FtsZ from the pathogen Staphylococcus aureus in complex with different nucleotide analogs and cations, including mimetics of the ground and transition states of catalysis. Together with mutational and biochemical analyses, our structures reveal interactions made by the GTP γ-phosphate and Mg2+ at the subunit interface, a K+ ion stabilizing loop T7 for co-catalysis, new roles of key residues at the active site and a nearby crosstalk area, and rearrangements of a dynamic water shell bridging adjacent subunits upon GTP hydrolysis. We propose a mechanistic model that integrates nucleotide hydrolysis signaling with assembly-associated conformational changes and filament treadmilling. Equivalent assembly mechanisms may apply to more complex tubulin and actin cytomotive filaments that share analogous features with FtsZ.

Effect of a U:G mispair on the water around DNA

DNA repair proteins are able to discriminate DNA lesions among an abundance of intact DNA with high selectivity. To investigate detectable characteristics of one specific lesion, we compare statistical results from molecular dynamics simulations of two different DNA in water, one with an intact C:G pair and one that contains a U:G mispair, and perform a comparative analysis of the water dynamics around the two. Our data show that in addition to the local DNA conformation, also the surrounding water shell exhibits significant differences that may help mispair discrimination. The chemical groups which account for a U:G mispair to exhibit a wobble conformation instead of the ‘proper’ Watson-Crick pairing of a C:G pair, that is an oxygen atom (in uracil) instead of an amino group (in cytosine), also order the water molecules around the bases such that they act predominantly as hydrogen-bond donor or acceptor to the uracil or cytosine base, respectively. These changes in water conformation stretch into the second solvation shell, which may be exploited by repair enzymes to achieve lesion detection with high efficiency.

Robot-assisted magnetic capsule endoscopy; navigating colorectal inclinations

Purpose: To investigate the interaction of a robot assisted magnetically driven wireless capsule endoscope (WCE) with colonic tissue, as it traverses the colorectal bends in the dorsal and ventral directions, relying only on the feedback from a 3D accelerometer. We also investigate the impact of shell geometry and water insufflation on WCE locomotion. Methods: A 3D printed incline phantom, lined with porcine colon, was used as the experimental platform, for controlled and repeatable results. The tilt angle of WCE was controlled to observe its influence on WCE locomotion. The phantom was placed underwater to observe the effects of water insufflation. The experiments were repeated using the two capsule shell geometries to observe the effect of shell geometry on WCE locomotion. Results: Friction between WCE and intestinal tissue increased when the tilt angle of the WCE was lower than the angle of the incline of the phantom. Increasing the WCE tilt angle to match the angle of the incline reduced this friction. Water insufflation and elliptical capsule shell geometry reduced the friction further. Conclusion: Tilting of the WCE equal to, or more than the angle of the incline improved the WCE locomotion. WCE locomotion was also improved by using elliptical capsule shell geometry and water insufflation. Abbreviations: CRC: colorectal cancer; GI: gastrointestinal; MRI: magnetic resonance imaging; WCE: wireless capsule endoscope

Broadband acoustic lens design by reciprocity and optimization.

A broadband acoustic lens is designed based on the principle of reciprocity and gradient-based optimization. Acoustic reciprocity is used to define the pressure at the focal point due to a source located in a far-field and to relate the response by a configuration of scatterers for an incident plane wave. The pressure at the focal point is maximized by rearranging the scatterers and supplying the gradients of absolute pressure at the focal point with respect to scatterer positions. Numerical examples are given for clusters of cylindrical voids and sets of elastic thin shells in water.

A New Perspective on the Interiors of Ice-rich Planets: Ice–Rock Mixture Instead of Ice on Top of Rock

Abstract Ice-rich planets are formed exterior to the water ice line and thus are expected to contain a substantial amount of ice. The high ice content leads to unique conditions in the interior, under which the structure of a planet is affected by ice interaction with other metals. We apply experimental data of ice–rock interaction at high pressure, and calculate detailed thermal evolution for possible interior configurations of ice-rich planets, in the mass range of super-Earth to Neptunes (5–15 M ⊕). We model the effect of migration inward on the ice-rich interior by including the influences of stellar flux and envelope mass loss. We find that ice and rock are expected to remain mixed, due to miscibility at high pressure, in substantial parts of the planetary interior for billions of years. We also find that the deep interior of planetary twins that have migrated to different distances from the star are usually similar, if no mass loss occurs. Significant mass loss results in separation of the water from the rock on the surface and emergence of a volatile atmosphere of less than 1% of the planet’s mass. The mass of the atmosphere of water/steam is limited by the ice–rock interaction. We conclude that when ice is abundant in planetary interiors the planet structure may differ significantly from the standard layered structure of a water shell on top of a rocky core. Similar structure is expected in both close-in and further-out planets.

Kinetic Inhibition of Clathrate Hydrate by Copolymers Based on N-Vinylcaprolactam and N-Acryloylpyrrolidine: Optimization Effect of Interfacial Nonfreezable Water of Polymers.

Amphiphilic polymers have now been designed to achieve an icephobic performance and have been used for ice adhesion prevention. They may function by forming a strongly bonded but nonfreezable water shell which serves as a self-lubricating interfacial layer that weakens the adhesion strength between ice and the surface. Here, an analogous concept is built to prevent the formation of clathrate hydrate compounds during oil and natural gas production, in which amphiphilic water-soluble polymers act as efficient kinetic hydrate inhibitors (KHIs). A novel group of copolymers with N-vinylcaprolactam and N-acryloylpyrrolidine structural units are investigated in this study. The relationships among the amphiphilicity, lower critical solution temperature, nonfreezable bound water, and kinetic hydrate inhibition time are analyzed in terms of the copolymer compositions. Low-field NMR relaxometry revealed the crucial interfacial water in tightly bound dynamic states which led to crystal growth rates changing with the copolymer compositions, in accord with the rotational rheometric analysis results. The nonfreezable bound water layer confirmed by a calorimetry analysis also changes with the polymer amphiphilicity. Therefore, in the interface between the KHI polymers and hydrate, water surrounding the polymers plays a critical role by helping to delay the nucleation and growth of embryonic ice/hydrates. Appropriate amphiphilicity of the copolymers can achieve the optimal interfacial properties for slowing down hydrate crystal growth.

Investigation of Dipolar Response of the Hydrated Hen-Egg White Lysozyme Complex under Externally Applied Electric Fields: Insights from Non-equilibrium Molecular Dynamics.

Given its ubiquitous presence in the environment of bio-macromolecules, water is well known to play a fundamental part in biological activity, often as a regulating agent. In parallel, with increasing attention focused on the potential damage of microwave-frequency radiation exposure to human health, the effects of extraneous electric and electromagnetic (e/m) fields on water shells surrounding proteins, and, indeed, biomolecules themselves, are becoming a particularly pertinent issue. In this study, non-equilibrium molecular dynamics simulations of hydrated hen-egg white lysozyme have been performed in both the absence and presence of external electric fields of varying intensity (0.005–0.02 V/Å) and frequency (static, i.e., zero-frequency, together with oscillating fields of 2.45–100 GHz). By comparing the effect of different electric-field conditions on both the protein’s and surrounding hydration layer’s dipole moments and their underlying relaxation dynamics, clear and evident non-thermal field effects were observed on the dipolar response of both the protein and hydration layer. This occurred primarily as a consequence of the protein’s dipolar alignment with the external field and increased with the growth of field intensity. In addition, it was found that the lag time of dipolar response to the applied field itself, for both the protein and the first hydration sub-shell (i.e., directly adsorbed layer), under oscillating fields is longer than that in both the second hydration sub-layer and bulk water, owing to strong direct protein–water adsorption. In that respect, we also probe and discuss the effect of protein–water hydrogen bonds, dissecting the subtleties of “bio-water” dipolar response.

Mid-infrared-perturbed molecular vibrational signatures in plasmonic nanocavities

Recent developments in surface-enhanced Raman scattering (SERS) enable observation of single-bond vibrations in real time at room temperature. By contrast, mid-infrared (MIR) vibrational spectroscopy is limited to inefficient slow detection. Here we develop a new method for MIR sensing using SERS. This method utilizes nanoparticle-on-foil (NPoF) nanocavities supporting both visible and MIR plasmonic hotspots in the same nanogap formed by a monolayer of molecules. Molecular SERS signals from individual NPoF nanocavities are modulated in the presence of MIR photons. The strength of this modulation depends on the MIR wavelength, and is maximized at the 6–12 μm absorption bands of SiO2 or polystyrene placed under the foil. Using a single-photon lock-in detection scheme we time-resolve the rise and decay of the signal in a few 100 ns. Our observations reveal that the phonon resonances of SiO2 can trap intense MIR surface plasmons within the Reststrahlen band, tuning the visible-wavelength localized plasmons by reversibly perturbing the localized few-nm-thick water shell trapped in the nanostructure crevices. This suggests new ways to couple nanoscale bond vibrations for optomechanics, with potential to push detection limits down to single-photon and single-molecule regimes.