Water Molecules Research Articles

Crystal structure and cryomagnetic study of a mononuclear erbium(III) oxamate inclusion complex.

The synthesis, crystal structure and magnetic properties of an oxamate-containing erbium(III) complex, namely, tetrabutylammonium aqua[N-(2,4,6-trimethylphenyl)oxamato]erbium(III)-dimethyl sulfoxide-water (1/3/1.5), (C16H36N)[Er(C11H12NO3)4(H2O)]·3C2H6OS·1.5H2O or n-Bu4N[Er(Htmpa)4(H2O)]·3DMSO·1.5H2O (1), are reported. The crystal structure of 1 reveals the occurrence of an erbium(III) ion, which is surrounded by four N-phenyl-substituted oxamate ligands and one water molecule in a nine-coordinated environment, together with one tetrabutylammonium cation acting as a counter-ion, and one water and three dimethyl sulfoxide (DMSO) molecules of crystallization. Variable-temperature static (dc) and dynamic (ac) magnetic measurements were carried out for this mononuclear complex, revealing that it behaves as a field-induced single-ion magnet (SIM) below 5.0 K.

Unveiling the Behavior of Perfluoro (2-Ethoxyethane) Sulfonic Acid Potassium (PESK) in Water/Gas System: Molecular Dynamics Simulation

Molecular dynamics method (MD) was used to study the distribution of potassium perfluoro (2-ethoxyethane) sulfonic acid (PESK) in water/gas systems. When the PESK aqueous solution system reaches equilibrium, the vast majority the fluorocarbon chain is facing toward the gas phase, while the sulfonic acid radical faces toward the water, with a very small quantity of PES− is still in the bulk solution. The weak intermolecular interactions were analyzed by IGMH method, and the interaction energy between PES− and water mainly comes from the h-bonds formed by the oxygen atom in the sulfonic acid group and hydrogen atom in water molecules. K+ are mainly distributed inside the aqueous solution, and there is only van der Waals interaction between K+ and H2O molecules. According to the distribution of ESP analysis of PES−, it is mainly the sulfonic acid groups that are negatively charged.

Dynamic interchange between two protonation states is characteristic of active sites of cholinesterases.

Cholinesterases are well-known and widely studied enzymes crucial to human health and involved in neurology, Alzheimer's, and lipid metabolism. The protonation pattern of active sites of cholinesterases influences all the chemical processes within, including reaction, covalent inhibition by nerve agents, and reactivation. Despite its significance, our comprehension of the fine structure of cholinesterases remains limited. In this study, we employed enhanced-sampling quantum-mechanical/molecular-mechanical calculations to show that cholinesterases predominantly operate as dynamic mixtures of two protonation states. The proton transfer between two non-catalytic glutamate residues follows the Grotthuss mechanism facilitated by a mediator water molecule. We show that this uncovered complexity of active sites presents a challenge for classical molecular dynamics simulations and calls for special treatment. The calculated proton transfer barrier of 1.65 kcal/mol initiates a discussion on the potential existence of two coupled low-barrier hydrogen bonds in the inhibited form of butyrylcholinesterase. These findings expand our understanding of structural features expressed by highly evolved enzymes and guide future advances in cholinesterase-related protein and drug design studies.

Multi-Template-Guided Synthesis of High-Dimensional Molecular Assemblies for Humidity Gradient-Based Power Generators.

Systematically orchestrating fundamental building blocks into intricate high-dimensional molecular assemblies at molecular level is imperative for multifunctionality integration. However, this remains a formidable task in crystal engineering due to the dynamic nature of inorganic building blocks. Herein, we develop a multi-template-guided strategy to control building blocks. The coordination modes of ligands and the spatial hindrance of anionic templates are pivotal in dictating the overall structures. Flexible multi-dentate linkers selectively promote the formation of oligomeric assembly ([TeO3(Mo2O2S2)3O2(OH)(C5O2H7)3]4- {TeMo6}) into tetrahedral cages ([(TeO3)4(Mo2O2S2)12(OH)12(C9H9O4P)6]8- {Te4Mo24} and [(AsO4)4(Mo2O2S2)12(OH)12(C9H9O6)4]12- {As4Mo24}), while steric hindrance from anionic templates further assists in assembling cages into an open quadruply twisted Möbius nanobelt ([(C6H5O3P)8(Mo2O2S2)24(OH)24(C8H10O4)12]16- {P8Mo48}). Among these structures, the hydrophilic-hydrophobic hybrid cage {Te4Mo24} emerges as an exemplary molecular model for proton conduction and serves as a prototype for humidity gradient-based power generators (HGPGs). The Te4Mo24-PVDF-based HGPG (PVDF = Poly(vinylidene fluoride)) exhibits notable stability and power generation, yielding an open-circuit voltage of 0.51 V and a current density of 77.8 nA cm-2 at room temperature and 90% relative humidity (RH). Further insights into the interactions between water molecules and microscale molecules within the generator are achieved through molecular dynamics simulations. This endeavor unveils a universal strategy for synthesizing multifunctional integration molecules.

Insight into Anionic Discrepancies in Bipolar Poly(Thionine) Organic Cathodes for Aqueous Zinc Ion Batteries.

Electroactive organic electrode materials exhibit remarkable potential in aqueous zinc ion batteries (AZIBs) due to their abundant availability, customizable structures, sustainability, and high reversibility. However, the research on AZIBs has predominantly concentrated on unraveling the storage mechanism of zinc cations, often neglecting the significance of anions in this regard. Herein, bipolar poly(thionine) is synthesized by a simple and efficient polymerization reaction, and the kinetics of different anions are investigated using poly(thionine) as the cathode of AZIBs. Notably, poly(thionine) is a bipolar organic polymer electrode material and exhibits enhanced stability in aqueous solutions compared to thionine monomers. Kinetic analysis reveals that ClO4 - exhibits the fastest kinetics among SO4 2-, Cl-, and OTF-, demonstrating excellent rate performance (109 mAh g-1 @ 0.5 A g-1 and 92 mAh g-1 @ 20 A g-1). Mechanism studies reveal that the poly(thionine) cathode facilitates the co-storage of both anions and cations in Zn(ClO4)2. Furthermore, the lower electrostatic potential of ClO4 - influences the strength of hydrogen bonding with water molecules, thereby enhancing the overall kinetics in aqueous electrolytes. This work provides an effective strategy for synthesizing high-quality organic materials and offers new insights into the kinetic behavior of anions in AZIBs.

Evidence of ferroelectric features in low-density supercooled water from ab initio deep neural-network simulations

Over the last decade, an increasing body of evidence has emerged, supporting the existence of a metastable liquid-liquid critical point in supercooled water whereby two distinct liquid phases of different densities coexist. Analyzing long molecular dynamics simulations performed using deep neural-network force fields trained to accurate quantum mechanical data, we demonstrate that the low-density liquid phase displays a strong propensity toward spontaneous polarization, as witnessed by large and long-lived collective dipole fluctuations. Our findings suggest that the dynamical stability of the low-density phase, and hence the transition from high-density to low-density liquid, is triggered by a collective process involving an accumulation of rotational angular jumps, which could ignite large dipole fluctuations. This dynamical transition involves subtle changes in the electronic polarizability of water molecules which affects their rotational mobility within the two phases. These findings hold the potential for catalyzing activity in the search for dielectric-based probes of the putative second critical point.

Water retention property and microscopic mechanism of shallow soil in inner dump improved by fly ash and polyacrylamide.

Improving the water retention property of shallow soil in the inner dump is the key step in the sustainable development of mines. In recent years, the use of fly ash to improve the structure of the inner dump and polyacrylamide as an additive to enhance water retention was an effective method. The article used a physical model test, filter paper method, and microstructure analysis method to compare and analyze the water retention property and microstructure of slope-improved soil with different fly ash and polyacrylamide content. The results show that the combined use of fly ash and polyacrylamide improved the water retention property of the amended soil. Fly ash and polyacrylamide had a greater effect on the low suction stage of the amended soil. Polyacrylamide reacted with water and bound soil particles to form aggregates, and the structural unit bodies were a block structure. Fly ash was non-sticky and was a matrix of fine particles, which weakened the bonding effect of polyacrylamide, and reduced the aggregates of soil particles, and the structural unit bodies were a flocculated structure of aggregates mixed with matrix. This, in turn, enhanced the capillary action and improved the water retention performance of the improved soil. In addition, polyacrylamide could connect water molecules, further enhancing the water retention property of the improved soil. The combined use of fly ash and polyacrylamide improved the available water content of improved soil, providing a viable and sustainable solution for improving the comprehensive utilization of fly ash, and laid the foundation for land reclamation at the inner dump.

Small, Fluorinated Mn2+ Chelate as an Efficient 1H and 19F MRI Probe.

We explore the potential of fluorine-containing small Mn2+ chelates as alternatives to perfluorinated nanoparticles, widely used as 19F MRI probes. In MnL1, the cyclohexanediamine skeleton and two piperidine rings, involving each a metal-coordinating amide group and an appended CF3 moiety, provide high rigidity to the complex. This allows for good control of the Mn-F distance (rMnF = 8.2±0.2 Å determined from 19F relaxation data), as well as for high kinetic inertness (a dissociation half-life of 1285 h is estimated for physiological conditions). The paramagnetic Mn2+ leads to a ~150-fold acceleration of the longitudinal 19F relaxation, with moderate line-broadening effect, resulting in T2/T1 ratios of 0.8 (9.4 T). Owing to its inner sphere water molecule, MnL1 is a good 1H relaxation agent as well (r1 = 5.36 mM-1s-1 at 298K, 20MHz). MnL1 could be readily visualized in 19F MRI by using fast acquisition techniques, both in phantom images and living mice following intramuscular injection, with remarkable signal-to-noise ratios and short acquisition times. While applications in targeted imaging or cell therapy monitoring require further optimisation of the molecular structure, these results argue for the potential of such small, monohydrated and fluorinated Mn2+ complexes for combined 19F and 1H MRI detection.

The Influence of Acetone on the Kinetics of Water Electrolysis Examined at Polycrystalline Pt Electrode in Alkaline Solution

This study investigated the impact of acetone on the electrochemical behavior of polycrystalline platinum electrodes in 0.1 M NaOH solution, with respect to the kinetics of hydrogen and oxygen evolution reactions (HER and OER) and indirectly to the underpotential deposition of hydrogen (UPDH). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were employed to analyze these processes for acetone concentrations ranging from 1.0 × 10−6 to 1.0 × 10−3 M. The addition of (CH3)2C=O enhanced the catalytic efficiency of alkaline water splitting, which was believed to be a result of a significant reduction in the surface tension phenomenon (due to mutual interaction of acetone and water molecules), thus considerably facilitating hydrogen bubble detachment from the Pt electrode. Key findings in this work are described with respect to facilitation of both the HER and the OER reactions’ kinetics by the presence of acetone (also undergoing Pt electroreduction over the potential range for UPDH) in the working solution, without an electrode surface poisoning effect. The latter implies significant opportunities for traces of organic additives into alkaline electrolyte to improve the industrial alkaline water electrolysis process.

A Bimetallic Electro-Sensitizer Improves ROS Therapy by Relieving Autophagy-Induced ROS Tolerance and Immune Suppression.

Reactive oxygen species (ROS)-dependent monotherapy usually demonstrates poor therapeutic outcomes, due to the accompanied activation of protective autophagy in tumor cells, which results in ROS tolerance and immune suppression. In this study, a bimetallic electro-sensitizer, Pt-Ir NPs is constructed, loaded with the autophagy inhibitor chloroquine (Pt-Ir-CQ NPs), to enhance the effectiveness of electrotherapy by inhibiting autophagy and activating anti-tumor immune responses. This novel electrotherapy platform demonstrates unique advantages, particularly in the treatment of hypoxic and immunosuppressive tumors. First, the electro-sensitizer catalyzes water molecules into ROS under electric field, achieving tumor ablation through electrotoxicity. Second, the incorporated CQ inhibits the protective autophagy induced by electrotherapy, restoring the sensitivity of tumor cells to ROS and thereby enhancing the anti-tumor effects of electrotherapy. Third, Pt-Ir-CQ NPs enhance the functionality of antigen-presenting cells and immunogenic cells through inhibiting autophagy, synergistically activating the anti-tumor immune responses along with the immunogenic cell death (ICD) effect induced by electrotherapy. This study provides a novel approach for the effective ablation and long-term inhibition of solid tumors through flexible modulation by an exogenous electric field.

Thermally Degradable Water Diffusion Barrier Assembled by Gelatin and Beeswax toward Edible Electronics.

Making ingestible devices edible facilitates diagnosis and therapy inside the body without the risk of retention; however, food materials are generally soft, absorb water molecules, and are not suitable for electronic devices. Here, we fabricated an edible water diffusion barrier film made by gelatin-beeswax composites for the encapsulation of transient electronics. Hydrophobic beeswax and hydrophilic gelatin are inherently difficult to mix; therefore, we created an emulsion simply by raising the temperature high enough to melt the materials and vigorous stirring them. As they cool, the beeswax with a relatively high solidification temperature aggregates and forms microspheres, which increases the gelatin gel's viscoelasticity and immobilizes the emulsion structure in the film. The thermoresponsive gelatin imparts degradability to the barrier and its stickiness also enables transfer of metal patterned electronics. Furthermore, we designed an edible resonator on the film and demonstrated its operation in an abdominal phantom environment; the resonator was made to be degradable in a warm aqueous solution by optimizing the composition ratio of the gelatin and beeswax. Our findings provide insight into criteria for making transient electronics on hydrophilic substrates with hydrophobic water diffusion barriers. This proof-of-concept study expands the potential of operating edible electronics in aqueous environments in harmony with the human body and nature.

Metal Ion Binding to Human Glutaminyl Cyclase: A Structural Perspective

Glutaminyl-peptide cyclotransferases (QCs) convert the N-terminal glutamine or glutamate residues of protein and peptide substrates into pyroglutamate (pE) by releasing ammonia or a water molecule. The N-terminal pE modification protects peptides/proteins against proteolytic degradation by amino- or exopeptidases, increasing their stability. Mammalian QC is abundant in the brain and a large amount of evidence indicates that pE peptides are involved in the onset of neural human pathologies such as Alzheimer’s and Huntington’s disease and synucleinopathies. Hence, human QC (hQC) has become an intensively studied target for drug development against these diseases. Soon after its characterization, hQC was identified as a Zn-dependent enzyme, but a partial restoration of the enzyme activity in the presence of the Co(II) ion was also reported, suggesting a possible role of this metal ion in catalysis. The present work aims to investigate the structure of demetallated hQC and of the reconstituted enzyme with Zn(II) and Co(II) and their behavior in the presence of known inhibitors. Furthermore, our structural determinations provide a possible explanation for the presence of the mononuclear metal binding site of hQC, despite the presence of the same conserved metal binding motifs present in distantly related dinuclear aminopeptidase enzymes.

Examine stability polyvinyl alcohol-stabilized nanosuspensions to overcome the challenge of poor drug solubility utilizing molecular dynamic simulation

The pharmaceutical industry faces a significant challenge from the low water solubility of nearly 90% of newly developed Active Pharmaceutical Ingredients (APIs). Despite extensive efforts to improve solubility, approximately 40% of these APIs encounter commercialization hurdles, impacting drug efficacy. In this context, a promising strategy will be introduced in which nanosuspensions, particularly polyvinyl alcohol (PVA) as a stabilizer, are applied to increase drug solubility. In this work using molecular dynamics simulations, the nanosuspension of four poorly water-soluble drugs (flurbiprofen, bezafibrate, miconazole, and phenytoin) stabilized with PVA is investigated. The simulation data showed van der Waals energies between polyvinyl alcohol with flurbiprofen and bezafibrate are − 101.12 and − 58.42 kJ/mol, respectively. The results indicate that PVA is an effective stabilizer for these drugs, and superior interactions are obtained with flurbiprofen and bezafibrate. The study also explores the impact of PVA on water molecule diffusion, providing insights into the stability of nanosuspensions. Obtained results also provide valuable insights into hydrogen bond formation, diffusion coefficients, and nanosuspension stability, contributing to the rational design and optimization of pharmaceutical formulations.

Early-age hydration of tricalcium aluminate in chloride solutions

Understanding the kinetics and mechanisms involved in early-age hydration of tricalcium aluminate (C3A) in chloride solutions holds promise for implementing seawater-mixed concrete in the marine environment, as C3A remains the most reactive component of Portland cement (PC), affecting both PC and concrete's early-age hardening and long-term durability. Herein, we conducted a series of meticulously designed ex-situ and in-situ experiments to elucidate the intricate hydration behaviors of C3A in various chloride solutions. The results reveal that C3A exhibits distinct hydration kinetics and structural evolution processes in different solutions. The rapid precipitation of alumino-ferrite-mono (AFm) and C3AH6 phases contributes to the swift development of hydration heat and storage modulus in water and NaCl solutions, with a slight acceleration observed in the later one. Conversely, the formation of C3AH6 is delayed in CaCl2 and MgCl2 solutions before 20 min, with the subsequent precipitation of Cl-AFm enhancing its later production, particularly in CaCl2 solutions. Ab-initio calculations further elucidate that the acceleration effect of Cl ions originates from the ionization and structurization of hydrated surface Ca ions. However, this positive effect is significantly offset by Cl pairing with counterions, resulting in a dramatic adverse effect of solution Ca ions originated from the negative entropy effect of structuralized water molecules and electrostatic repulsion with like-charged surface Ca ions and solvent dipoles. Our findings provide valuable insights for sustainable and durable designs on cement-based materials mixed with seawater.

Synthesis, spectral analysis, XRD, molecular docking simulation of dithranol and glycine mixed ligand complexes and their potential role in suppressing breast cancer cells via down‐regulating the expression of protein metalloproteinase‐9

Five novel complexes of nickel (II)(1), zinc (II)(2), zirconium (IV)(3), lanthanum (III)(4), thorium (IV)(5), with the dithranol (Dithr) ligand and glycine (Gly) were synthesized and characterized. Their structures were investigated using elemental analysis, molar conductance (Λ), magnetic studies (μeff), spectroscopic methods (FT‐IR, UV–Vis., 1H NMR, XRD), mass spectrometry, TG/DTG and DTA. Findings revealed that Dithr was chelated via two hydroxyl oxygen atoms and carbonyl group while, Gly chelated through carboxylic oxygen and nitrogen atom. All complexes appeared with molar ratio 1:1:1 (M:Dithr:Gly) and were electrolytes with 1:1 for (1), (2) and (3) complexes, 1:2 for (4) complex, and 1:3 for (5) complex according to elemental analysis and molar conductivity data. All metal‐chelates, except Th (IV)‐complex, were confirmed to have lattice water molecules based on their thermal behavior. Average crystalline size of all compounds was calculated using XRD analysis and found in the range 35.50–55.57 nm, indicating the compounds existed as nanocrystalline structure, except zirconium (IV) complex. Then, we studied cytotoxic effects of our synthetic drugs on the survival of an aggressive‐breast‐cancer‐histotype“66cl‐4.” Given its involvement in cancer‐metastasis, matrix‐metalloproteinase‐(MMP)‐9 protein expression was evaluated using western‐blotting‐assays. Th(IV)‐complex emerged as the most effective option in inhibiting cancer‐cells‐proliferation (IC50: 9.39 μM), and suppressed expression MMP‐9 levels by 86%, at 25 μM dose, and drug‐binding‐affinity was interpreted via molecular modeling.

Tracking ultrafast non-adiabatic dissociation dynamics of the deuterated water dication molecule.

We applied reaction microscopy to elucidate fast non-adiabatic dissociation dynamics of deuterated water molecules after direct photo-double ionization at 61eV with synchrotron radiation. For the very rare D+ + O+ + D breakup channel, the particle momenta, angular, and energy distributions of electrons and ions, measured in coincidence, reveal distinct electronic dication states and their dissociation pathways via spin-orbit coupling and charge transfer at crossings and seams on the potential energy surfaces. Notably, we could distinguish between direct and fast sequential dissociation scenarios. For the latter case, our measurements reveal the geometry and orientation of the deuterated water molecule with respect to the polarization vector that leads to this rare 3-body molecular breakup channel. Aided by multi-reference configuration-interaction calculations, the dissociation dynamics could be traced on the relevant potential energy surfaces and particularly their crossings and seams. This approach also unraveled the ultrafast time scales governing these processes.

Tandem catalytic conversion of glucose and cellobiose to 5-ethoxymethylfurfural with record yields

The conversion of biomass-derived carbohydrates to 5-ethoxymethylfurfural (EMF) is a fascinating reaction with 100% carbon atom utilization. Although effective conversion of 5-hydroxymethylfurfural (HMF) and fructose to EMF have been achieved, the direct conversion of glucose only gave low EMF yields. Herein, we reveal that the combinations of common Lewis acid with Brønsted acid in ethanol universally catalyze rapid etherification of glucose to intractable ethyl glucoside (EGL), as impedes the further conversion toward the desired products. The synergy of large-pore tin phosphate (SnPO) bearing strong Lewis acidic sites with acidic ionic liquid 1-(4-sulfobutyl)-3-methylimidazolium chloride (BSO3HMIMCl) enable tandem catalytic conversion of glucose, cellobiose and starch to EMF with record yields (61.7%, 61.8% and 55.7%, respectively), far exceeding previous reports. This transformation probably occurs via multiple parallel pathways, where water molecules generated by dehydration cooperate with acid and Cl- to hydrolyze EGL back to glucose, thus forming a positive feedback on EMF production.

A water-in-lactone electrolyte with controllable water activity for highly reversible zinc anodes

Rechargeable aqueous zinc batteries, offering the advantages of intrinsic safety, affordability, and superior recyclability, represent an emerging technology for stationary energy storage. However, the practical application of the technology is fundamentally blocked by the instability of the zinc anode/electrolyte interface caused by the water-induced hydrogen evolution reaction and Zn dendrite growth. Here, we formulate a water-in-lactone electrolyte to effectively regulate the water activity by adjusting the molar ratio of H2O to green γ-valerolactone. The γ-valerolactone not only enters the solvation shell of Zn2+ ions, excluding nearly all bound water molecules, but also interacts with free water via forming intermolecular hydrogen bonds, thus completely confining water molecules within γ-valerolactone network. As a result, the water-in-lactone electrolyte minimizes hydrogen evolution side reactions and promotes uniform zinc electrodeposition. The coulombic efficiency of Zn ‖ Ti asymmetric cells is improved to 99.6 % over 500 cycles at a current density of 1 mA cm−2 and an areal capacity of 1 mAh cm−2. The cycling lifespan of Zn ‖ Zn symmetric cells is extended to more than 1100 h with the water-in-lactone electrolyte, much higher than that with the pure water electrolyte (less than 250 h). When coupled with polyaniline cathodes, Zn full cells utilizing the newly formulated electrolyte demonstrate enhanced cycling stability with a capacity retention of 73 % after ∼500 cycles at 200 mA g−1. Moreover, the water-in-lactone electrolyte enhances the temperature tolerance of Zn ion capacitors with activated carbon cathodes, allowing stable operation from −20 ℃ to 80 ℃. This work further sheds light on the significant correlation between water activity and the performance of zinc anodes, and hopefully contributes to the advancement of stable aqueous zinc batteries.

Efficiency of layered double hydroxides in epoxy coating as corrosion inhibitor reservoirs for carbon steel

Layered double hydroxides (LDH) are considered as interesting containers for corrosion inhibitors, since they exhibit high ability to release inhibitor as well as to capture aggressive ions from aqueous solution. Epoxy containing organo-modified LDH filler intercalated with ethylenediamine-N,N′-disuccinate anions (EDDS), [Zn2Al(OH)6]+ [EDDS]4−0.25 . 2H2O (LDH-EDDS) with loading from 0% to 1.25% were coated onto carbon steel plates. The efficiency of these coatings against corrosion (barrier properties and release of inhibitors) was assessed by using electrochemical impedance spectroscopy. The evolution of the impedance modulus |Z| at low frequency range during time showed that the 0.75% organo-modified LDH-containing epoxy (thickness 80 μm) exhibited the highest corrosion resistance in the series and the associated value of |Z| at 3 mHz (1010 Ω cm2 after 21 days of immersion in 0.1 mol L−1 NaCl solution) placed it among the best solutions published so far using organo-modified LDH as cargo carrying a corrosion inhibitor. The behavior of this polymer composite was compared to the free-LDH coating by plotting the resistivity profiles along the coating thickness as a function of time. These results showed that (i) the presence of 0.75% LDH-EDDS in the epoxy coating delayed the penetration of water molecules, and (ii) limited corrosion of carbon steel. The efficiency of the organo-modified filler to inhibit the corrosion process was explained by an exchange between interleaved species occurring from released EDDS4− anions and aggressive Cl− ions being captured.

Temperature dependence of the near infrared absorption spectrum of single-wall carbon nanotubes dispersed by sodium dodecyl sulfate in aqueous solution: experiments and molecular dynamics study.

Single-wall carbon nanotubes (SWCNT) dispersed in water with the help of sodium dodecyl sulfate (SDS) surfactants exhibit a temperature dependent near infrared (NIR) exciton spectrum. Due to their biocompatibility and NIR spectrum falling within the transparent window for biological tissue, SWCNTs hold potential for sensing temperature inside cells. Here, we seek to elucidate the mechanism responsible for this temperature dependence, focusing on changes in the water coverage of the SWCNT as the surfactant structure changes with temperature. We compare optical absorption spectra in the UV-Vis-IR range and fully atomistic molecular dynamics (MD) simulations. The observed temperature dependence of the spectra for various SWCNTs may be attributed to changes in the dielectric environment and its impact on excitons. MD simulations reveal that the adsorbed SDS molecules effectively shield the SWCNT, with ~ 70% of water molecules removed from the first two adlayers; this coverage shows a modest temperature dependence. Although we are not able to directly demonstrate how this influences the NIR spectrum, this represents a potential pathway given the strong influence of the water environment on the excitons in SWCNTs. Optical absorption measurements were carried out in the UV-Vis-NIR range using a Varian Cary 5000 spectrophotometer in a temperature-controlled environment. PeakFit™ v. 4.06 was used as peak-fitting program in the spectral range 900-1400nm (890-1380meV) as a function of the temperature. Fully atomistic molecular dynamics simulations were conducted using the NAMD2 package. The CHARMM force field comprising two-body bond stretching, three-body angle deformation, four-body dihedral angle deformation, and nonbonded interactions (electrostatic and Lennard-Jones 6-16 potentials) was employed.