Neat H2O Research Articles

Spectroscopic and TD-DFT studies on the chromo-fluorogenic detection of cyanide ions in organic and aquo-organic media

A new naked-eye chromogenic and fluorogenic probe KS5 has been developed for the detection of CN– ions in neat DMSO and H2O:DMSO (1:1 v/v) media. The probe KS5 exhibited selectivity towards CN– and F− ions in organic and high selectivity towards CN– ions in aquo-organic media resulting in a colour change from brown to colourless and a turn-on fluorescence response. The probe could able to detect CN– ions via a deprotonation process, which was conceived by consecutive addition of hydroxide and hydrogen ions and confirmed using 1H NMR studies. The limit of detection (LOD) of KS5 towards CN– ions were in the range of 0.07–0.62 µM in both these solvent systems. Suppression of intra-molecular charge transfer (ICT) transition and photoinduced electron transfer (PET) process of KS5 by the added CN– ions are responsible for the chromogenic and fluorogenic changes observed, respectively. Density Functional Theory (DFT) and Time-Dependent Density Functional Theory (TD-DFT) calculations strongly supported the proposed mechanism along with the optical properties of the probe before and after the addition of CN– ions. To prove the practical applicability, KS5 was successfully utilized to detect CN– ions in cassava powder and bitter almonds as well as to determine CN– ions in various real water samples.

Solubility and Thermodynamic Properties of Febuxostat in Various (PEG 400 + Water) Mixtures.

The solubility of the poorly soluble medicine febuxostat (FXT) (3) in various {polyethylene glycol 400 (PEG 400) (1) + water (H2O) (2)} mixtures has been examined at 298.2–318.2 K and 101.1 kPa. FXT solubility was measured using an isothermal method and correlated with “van’t Hoff, Apelblat, Buchowski–Ksiazczak λh, Yalkowsky–Roseman, Jouyban–Acree, and Jouyban–Acree-van’t Hoff models”. FXT mole fraction solubility was enhanced via an increase in temperature and PEG 400 mass fraction in {(PEG 400 (1) + H2O (2)} mixtures. Neat PEG 400 showed the highest mole fraction solubility of FXT (3.11 × 10–2 at 318.2 K), while neat H2O had the lowest (1.91 × 10–7 at 298.2 K). The overall error value was less than 6.0% for each computational model, indicating good correlations. Based on the positive values of apparent standard enthalpies (46.72–70.30 kJ mol−1) and apparent standard entropies (106.4–118.5 J mol−1 K−1), the dissolution of FXT was “endothermic and entropy-driven” in all {PEG 400 (1) + H2O (2)} mixtures examined. The main mechanism for FXT solvation in {PEG 400 (1) + H2O (2)} mixtures was discovered to be an enthalpy-driven process. In comparison to FXT-H2O, FXT-PEG 400 showed the strongest molecular interactions. In conclusion, these results suggested that PEG 400 has considerable potential for solubilizing a poorly soluble FXT in H2O.

Cononsolvency of the responsive polymer poly(N-isopropylacrylamide) in water/methanol mixtures: a dynamic light scattering study of the effect of pressure on the collective dynamics

The collective dynamics of 25 wt% poly(N-isopropylacrylamide) (PNIPAM) solutions in water or an 80:20 v/v water/methanol mixture are investigated in the one-phase region in dependence on pressure and temperature using dynamic light scattering. Throughout, two dynamic modes are observed, the fast one corresponding to the relaxation of the chain segments within the polymer blobs and the slow one to the relaxation of the blobs. A pressure scan in the one-phase region on an aqueous solution at 34.0 °C, i.e., slightly below the maximum of the coexistence line, reveals that the dynamic correlation length of the fast mode increases when the left and the right branch of the coexistence line are approached. Thus, the chains are rather swollen far away from the coexistence line, but contracted near the phase transition. Temperature scans of solutions in neat H2O or in H2O/CD3OD at 0.1, 130, and 200 MPa reveal that the dynamic correlation length of the fast mode shows critical behavior. However, the critical exponents are significantly larger than the value predicted by mean-field theory for the static correlation length, ν = 0.5, and the exponent is significantly larger for the solution in the H2O/CD3OD mixture than in neat H2O.

Effect of H2O/DMF mixed solvents on formation of MIL-100(Fe) and dye adsorption

MIL-100(Fe) with microporous structures is often synthesized under conventional hydrothermal conditions using iron ion and trimesic acid. The effect of H2O/dimethylformamide (DMF) mixtures, with variable H2O volume ratios, on the formation of MIL-100(Fe) was investigated under solvothermal conditions. Pure octahedral MIL-100(Fe) could only be formed in neat H2O or DMF. In most cases, the same reaction in mixed H2O/DMF solvents afforded goethite. When a small volume of H2O was used, morphology resembled coexisting octahedra of MIL-100(Fe) and hexagonal platelets of goethite. A subsequent increase in the H2O content yielded pure hexagonal platelets of goethite and then hexagonal bipyramidal structures of hematite. The surface area and pore volume of MIL-100(Fe) were higher than those of goethite. Dye adsorption tests revealed that 80% of methylene blue (MB) was adsorbed on MIL-100(Fe), synthesized in pure DMF, within 5 ​min, whereas only approximately 26% was adsorbed on MIL-100(Fe) synthesized in pure H2O. This can be attributed to the nanoscale hierarchically porous structures with macroporosity in the DMF-synthesized MIL-100(Fe) and enhanced fast diffusion and mass transfer of dye, which demonstrates its potential as an adsorbent for dye removal. Thus, this study provides a new option of solvent for the formation of nanoscale hierarchically porous MIL-100(Fe) with improved performance in various practical applications.

Aggregation Behavior of Structurally Similar Therapeutic Peptides Investigated by 1H NMR and All-Atom Molecular Dynamics Simulations.

Understanding of peptide aggregation propensity is an important aspect in pharmaceutical development of peptide drugs. In this work, methodologies based on all-atom molecular dynamics (AA-MD) simulations and 1H NMR (in neat H2O) were evaluated as tools for identification and investigation of peptide aggregation. A series of structurally similar, pharmaceutically relevant peptides with known differences in aggregation behavior (D-Phe6-GnRH, ozarelix, cetrorelix, and degarelix) were investigated. The 1H NMR methodology was used to systematically investigate variations in aggregation with peptide concentration and time. Results show that 1H NMR can be used to detect the presence of coexisting classes of aggregates and the inclusion or exclusion of counterions in peptide aggregates. Interestingly, results suggest that the acetate counterions are included in aggregates of ozarelix and cetrorelix but not in aggregates of degarelix. The peptides investigated in AA-MD simulations (D-Phe6-GnRH, ozarelix, and cetrorelix) showed the same rank order of aggregation propensity as in the NMR experiments. The AA-MD simulations also provided molecular-level insights into aggregation dynamics, aggregation pathways, and the influence of different structural elements on peptide aggregation propensity and intermolecular interactions within the aggregates. Taken together, the findings from this study illustrate that 1H NMR and AA-MD simulations can be useful, complementary tools in early evaluation of aggregation propensity and formulation development for peptide drugs.

Solubility Determination, Hansen Solubility Parameters and Thermodynamic Evaluation of Thymoquinone in (Isopropanol + Water) Compositions.

This article studies the solubility, Hansen solubility parameters (HSPs), and thermodynamic behavior of a naturally-derived bioactive thymoquinone (TQ) in different binary combinations of isopropanol (IPA) and water (H2O). The mole fraction solubilities (x3) of TQ in various (IPA + H2O) compositions are measured at 298.2–318.2 K and 0.1 MPa. The HSPs of TQ, neat IPA, neat H2O, and binary (IPA + H2O) compositions free of TQ are also determined. The x3 data of TQ are regressed by van’t Hoff, Apelblat, Yalkowsky–Roseman, Buchowski–Ksiazczak λh, Jouyban–Acree, and Jouyban–Acree–van’t Hoff models. The maximum and minimum x3 values of TQ are recorded in neat IPA (7.63 × 10−2 at 318.2 K) and neat H2O (8.25 × 10−5 at 298.2 K), respectively. The solubility of TQ is recorded as increasing with the rise in temperature and IPA mass fraction in all (IPA + H2O) mixtures, including pure IPA and pure H2O. The HSP of TQ is similar to that of pure IPA, suggesting the great potential of IPA in TQ solubilization. The maximum molecular solute-solvent interactions are found in TQ-IPA compared to TQ-H2O. A thermodynamic study indicates an endothermic and entropy-driven dissolution of TQ in all (IPA + H2O) mixtures, including pure IPA and pure H2O.

A simple imine as a dual-channel chemosensor for detection of CN− and HS− ions via different mechanisms in organic and aquo-organic media

An imine based easy to make receptor (R) has been synthesized and characterized, which senses CN− and HS− ions selectively and sensitively in neat DMSO and H2O:DMSO (60:40 v/v) media. Upon treatment with these ions, the receptor exhibited instantaneous colour change from yellow to colourless and a fluorescence enhancement and these optical changes are easily detected by direct visualization. Further, other competitive anions didn’t display any observable colour and fluorescence changes, indicating the receptor's high selectivity towards CN− and HS− ions. The nucleophilic addition of cyanide ion to the imine bond induces an increase in fluorescence, while HS− ion triggered cleavage of the imine bond, producing enhancement in fluorescence in both the media. The limits of detection for CN− and HS− ions were calculated to be 0.9 and 0.7 μM, respectively, which are lower than the permissible limit of these ions in drinking water set by the World Health Organization (WHO). The receptor has fruitfully been applied for the detection of these ions in live HeLa cells.

Reorientation-induced relaxation of free OH at the air/water interface revealed by ultrafast heterodyne-detected nonlinear spectroscopy

The uniqueness of water originates from its three-dimensional hydrogen-bond network, but this hydrogen-bond network is suddenly truncated at the interface and non-hydrogen-bonded OH (free OH) appears. Although this free OH is the most characteristic feature of interfacial water, the molecular-level understanding of its dynamic property is still limited due to the technical difficulty. We study ultrafast vibrational relaxation dynamics of the free OH at the air/water interface using time-resolved heterodyne-detected vibrational sum frequency generation (TR-HD-VSFG) spectroscopy. With the use of singular value decomposition (SVD) analysis, the vibrational relaxation (T1) times of the free OH at the neat H2O and isotopically-diluted water interfaces are determined to be 0.87 ± 0.06 ps (neat H2O), 0.84 ± 0.09 ps (H2O/HOD/D2O = 1/2/1), and 0.88 ± 0.16 ps (H2O/HOD/D2O = 1/8/16). The absence of the isotope effect on the T1 time indicates that the main mechanism of the vibrational relaxation of the free OH is reorientation of the topmost water molecules. The determined sub-picosecond T1 time also suggests that the free OH reorients diffusively without the switching of the hydrogen-bond partner by the topmost water molecule.

Effects of soil particles and convective transport on dispersion and aggregation of nanoplastics via small-angle neutron scattering (SANS) and ultra SANS (USANS).

Terrestrial nanoplastics (NPs) pose a serious threat to agricultural food production systems due to the potential harm of soil-born micro- and macroorganisms that promote soil fertility and ability of NPs to adsorb onto and penetrate into vegetables and other crops. Very little is known about the dispersion, fate and transport of NPs in soils. This is because of the challenges of analyzing terrestrial NPs by conventional microscopic techniques due to the low concentrations of NPs and absence of optical transparency in these systems. Herein, we investigate the potential utility of small-angle neutron scattering (SANS) and Ultra SANS (USANS) to probe the agglomeration behavior of NPs prepared from polybutyrate adipate terephthalate, a prominent biodegradable plastic used in agricultural mulching, in the presence of vermiculite, an artificial soil. SANS with the contrast matching technique was used to study the aggregation of NPs co-dispersed with vermiculite in aqueous media. We determined the contrast match point for vermiculite was 66% D2O / 33% H2O. At this condition, the signal for vermiculite was ~50-100%-fold lower that obtained using neat H2O or D2O as solvent. According to SANS and USANS, smaller-sized NPs (50 nm) remained dispersed in water and did not undergo size reduction or self-agglomeration, nor formed agglomerates with vermiculite. Larger-sized NPs (300-1000 nm) formed self-agglomerates and agglomerates with vermiculite, demonstrating their significant adhesion with soil. However, employment of convective transport (simulated by ex situ stirring of the slurries prior to SANS and USANS analyses) reduced the self-agglomeration, demonstrating weak NP-NP interactions. Convective transport also led to size reduction of the larger-sized NPs. Therefore, this study demonstrates the potential utility of SANS and USANS with contrast matching technique for investigating behavior of terrestrial NPs in complex soil systems.

Phase-sensitive sum frequency vibrational spectroscopic study of air/water interfaces: H2O, D2O, and diluted isotopic mixtures.

Using phase-sensitive sum-frequency vibrational spectroscopy with a carefully chosen phase reference, we revisited the vibrational spectra of vapor/water interfaces of neat H2O and D2O as well as HDO in diluted isotopic mixtures. Using z-cut quartz as the phase reference, with proper frequency scaling, the gross features of the OH and OD stretching spectra from H2O and D2O and from HDO in two isotopic mixtures look similar and agree with those reported earlier, but differences are also apparent. In particular, a weak positive band at low frequencies, which has been asserted by molecular dynamic simulations but not detectable in the experimental OH spectrum with pure H2O, is now visible in the OD spectrum. The differences must arise from the change of intermolecular interaction of water molecules with their surrounding molecules upon exchange of the isotopes.

A dual-function probe based on naphthalene for fluorescent turn-on recognition of Cu2+ and colorimetric detection of Fe3+ in neat H2O.

A simple naphthalene derivative, 6-hydroxy-2-naphthohydrazide (NAH), was designed and synthesized through two facile steps reactions with the 6-hydroxy-2-naphthoic acid (NCA) as the starting material. In neat H2O (10% 0.01 M HEPES buffer, v/v, pH = 7.4), probe NAH showed a highly selective and sensitive response towards Fe3+ via perceptible color change and displayed "turn-on" dual-emission fluorescence response for Cu2+. The binding stoichiometry ratio of NAH/Cu2+ and NAH/Fe3+ were all confirmed as 1:1 by the method of fluorescence job's plot and UV-Vis job's plot, respectively. Probe NAH can be used over a wide pH range for the determination of Fe3+ (2.0-10.0) and Cu2+ (6.0-10.0) without interference from other co-existing metal ions. A possible detection mechanism was the hydrolysis of NAH upon the addition of Fe3+ or Cu2+, thereby leading to the formation of 6-hydroxy-naphthalene-2-carboxylic acid (NCA) which was further confirmed by the various spectroscopic techniques including FT-IR, 1H NMR titration and HRMS. Moreover, NAH was successfully applied to the detection of Cu2+ and Fe3+ in tap water, ultrapure water and BSA.

Stabilized Palladium Nanoparticles: Synthesis, Multi-spectroscopic Characterization and Application for Suzuki–Miyaura Reaction

The present article demonstrates a simple method for synthesizing the highly stabilized Pd(0) nanoparticles by using supported 12-tungstophosphoric acid as a stabilizer as well as a carrier. The obtained material was characterized by different methods and the presence of nanoparticles on the surface of the carrier was confirmed, especially by TEM and XPS. As an application, the use of material was explored for the well-known fascinating organic transformation, Suzuki–Miyaura cross coupling reaction in aqueous medium as well as in neat H2O. It was found that the material shows an outstanding activity as the heterogeneous catalyst (0.0096 mol% of Pd) for both aqueous medium (99% conversion, TOF 96958 h−1) and in neat H2O (89% conversion, TOF 46390 h−1) towards biphenyl. The catalyst was recovered by filtration only, regenerated and reused without any significant loss in conversion. Study shows that the present catalyst is truly heterogeneous and sustainable for the said reaction, in either of the medium. The viability of the catalyst was learned toward different substrates and found to be excellent in almost all cases. Pd nanoparticles stabilized by supported 12-tungstophosphoric acid is proved to be sustainable and excellent for Suzuki–Miyaura reaction with very high catalyst to substrate ratio as well as TOF.

Time-dependent yield of the hydrated electron and the hydroxyl radical in D2O: a picosecond pulse radiolysis study.

Picosecond pulse radiolysis measurements were performed in neat D2O and H2O in order to study the isotopic effect on the time-resolved yield of the hydrated electron and hydroxyl radical. First, the absorption band of the hydrated electron in D2O, eD2O-, is measured between 250 and 1500 nm. The molar absorption coefficient of the solvated electron spectrum in D2O was determined using the isosbestic point method by scavenging the solvated electron using methyl viologen. The amplitude and shape of the absorption spectrum of the hydrated electron in D2O are different from those previously reported in the literature. The maximum of the hydrated electron in the D2O absorption band is ca. 704 nm with a molar absorption coefficient of (22 900 ± 500) L mol-1 cm-1. Based on this extinction coefficient, the radiolytic yield of eD2O- just after the 7 ps electron pulse was determined to be (4.4 ± 0.2) × 10-7 mol J-1, which coincides with the one for eH2O- in H2O. The time-dependent radiolytic yield of eD2O- was determined from a few ps to 8 ns. To determine the OD˙ radical yield, the contribution of the solvated electron and of the transient species produced by the electron pulse in the windows of the fused silica optical cell was taken into account for the analysis of the transient absorption measurements at 260 nm. Therefore, an appropriate experimental methodology is used for measuring low absorbance at two different wavelengths in ps pulse radiolysis. The yield of the OD˙ radical just after the 7 ps electron pulse was found to be (5.0 ± 0.2) × 10-7 mol J-1. In the spurs of ionization, the decay rate of eD2O- is slower than eH2O-, whereas the decay rate of OD˙ is similar to the one of OH˙. Here, the established time-dependent yield of the solvated electron and the hydroxyl radical provide the foundation for improving the models used for spur reaction simulations in heavy water mainly for the chemistry of CANDU reactors.

High-Resolution Electron Attachment to the Water Dimer Embedded in Helium Droplets: Direct Observation of the Electronic Conduction Band Formation.

For bulk liquid helium the bottom of the conduction band (V0) is above the vacuum level. In this case the surface of the liquid represents an electronic surface barrier for an electron to be injected into the liquid. Here we study the electronic conduction band for doped helium droplets of different sizes. Utilizing an electron monochromator, the onset of the (H2O)2– ion yield corresponding to V0 is determined for helium droplets doped with the water dimer. While for larger droplets the onset approaches the well-known bulk value of about 1 eV, the barrier does not continuously decrease with smaller droplet size. A minimum value of V0 = 0.76 ± 0.10 eV is observed, which corresponds to a droplet size of Nmin = 1600 ± 900. For droplet sizes below Nmin, a peak at ∼0 eV appears, which is well-known from neat H2O clusters. Hence, we interpret Nmin as the smallest droplet size in which the electronic band structure is formed in liquid helium droplets.

Both Inter- and Intramolecular Coupling of O-H Groups Determine the Vibrational Response of the Water/Air Interface.

Vibrational coupling is relevant not only for dissipation of excess energy after chemical reactions but also for elucidating molecular structure and dynamics. It is particularly important for O-H stretch vibrational spectra of water, for which it is known that in bulk both intra- and intermolecular coupling alter the intensity and line shape of the spectra. In contrast with bulk, the unified picture of the inter/intra-molecular coupling of O-H groups at the water-air interface has been lacking. Here, combining sum-frequency generation experiments and simulation for isotopically diluted water and alcohols, we unveil effects of inter- and intramolecular coupling on the vibrational spectra of interfacial water. Our results show that both inter- and intramolecular coupling contribute to the O-H stretch vibrational response of the neat H2O surface, with intramolecular coupling generating a double-peak feature, while the intermolecular coupling induces a significant red shift in the O-H stretch response.

Interplay of Ion-Water and Water-Water Interactions within the Hydration Shells of Nitrate and Carbonate Directly Probed with 2D IR Spectroscopy.

The long-range influence of ions in solution on the water hydrogen-bond (H-bond) network remains a topic of vigorous debate. Recent spectroscopic and theoretical studies have, for the most part, reached the consensus that weakly coordinating ions only affect water molecules in the first hydration shell. Here, we apply ultrafast broadband two-dimensional infrared (2D IR) spectroscopy to aqueous nitrate and carbonate in neat H2O to study the solvation structure and dynamics of ions on opposite ends of the Hofmeister series. By exciting both the water OH stretches and ion stretches and probing the associated cross-peaks between them, we are afforded a comprehensive view into the complex nature of ion hydration. We show in aqueous nitrate that weak ion-water H-bonding leads to water-water interactions in the ion solvation shells dominating the dynamics. In contrast, the carbonate CO stretches show significant mixing with the water OH stretches due to strong ion-water H-bonding such that the water and ion modes are intimately correlated. Further, the excitonic nature of vibrations in neat H2O, which spans multiple water molecules, is an important factor in describing ion hydration. We attribute these complex dynamics to the likely presence of intermediate-range effects influenced by waters beyond the first solvation shell.

Glucose to Fructose Isomerization in Aqueous Media over Homogeneous and Heterogeneous Catalysts

AbstractIsomerization of glucose to fructose is an important reaction with numerous applications in terms of biomass valorization. The reaction is catalyzed enzymatically but may also proceed under alkaline conditions, in which case it is accompanied by low selectivity and formation of byproducts. Solid Lewis acid and basic catalytic materials are being studied as alternative catalysts. In this work, the isomerization of glucose to fructose in aqueous media over homogeneous and heterogeneous catalysts has been investigated. The effect of polar aprotic solvents and their mixtures with water on glucose conversion and fructose selectivity was also studied. Sodium aluminate (NaAlO2) has been proven to be very effective, resulting in high fructose yield (52.1 %) and high selectivity (84.8 %). Among the various solid catalysts tested, MgO afforded glucose conversion of 44 %, with 75.8 % and 33.4 % fructose selectivity and yield, respectively, when the isomerization reaction was conducted in neat H2O.

Strong frequency dependence of vibrational relaxation in bulk and surface water reveals sub-picosecond structural heterogeneity.

Because of strong hydrogen bonding in liquid water, intermolecular interactions between water molecules are highly delocalized. Previous two-dimensional infrared spectroscopy experiments have indicated that this delocalization smears out the structural heterogeneity of neat H2O. Here we report on a systematic investigation of the ultrafast vibrational relaxation of bulk and interfacial water using time-resolved infrared and sum-frequency generation spectroscopies. These experiments reveal a remarkably strong dependence of the vibrational relaxation time on the frequency of the OH stretching vibration of liquid water in the bulk and at the air/water interface. For bulk water, the vibrational relaxation time increases continuously from 250 to 550 fs when the frequency is increased from 3,100 to 3,700 cm−1. For hydrogen-bonded water at the air/water interface, the frequency dependence is even stronger. These results directly demonstrate that liquid water possesses substantial structural heterogeneity, both in the bulk and at the surface.

ChemInform Abstract: Pd(OAc)2 and (DHQD)2PHAL as a Simple, Efficient and Recyclable/Reusable Catalyst System for Suzuki—Miyaura Cross‐Coupling Reactions in H2O at Room Temperature.

Suzuki–Miyaura cross-coupling reaction catalyzed by Pd(OAc)2–(DHQD)2PHAL is a very simple, mild and efficient protocol for the synthesis of biaryls/heterobiaryls in neat H2O at room temperature. The catalyst system is recyclable/reusable and can be employed in several consecutive runs without significant loss in catalytic activity.

Pd(OAc)2 and (DHQD)2PHAL as a simple, efficient and recyclable/reusable catalyst system for Suzuki–Miyaura cross-coupling reactions in H2O at room temperature

Suzuki–Miyaura cross-coupling reaction catalyzed by Pd(OAc)2–(DHQD)2PHAL is a very simple, mild, efficient and recyclable/reusable protocol for the synthesis of biaryls/heterobiaryls in neat H2O at room temperature.