Water-rich Region Research Articles

Future Mars Rover Named for DNA Pioneer Rosalind Franklin

The rover will explore a once water rich region on Mars’s surface and search for evidence of current and past life.

Forward Modeling of Water-Rich Regions in Mines Based on Unconditional Stability Finite-Difference Time-Domain

Forward Modeling of Water-Rich Regions in Mines Based on Unconditional Stability Finite-Difference Time-Domain

The water footprint of coal-fired electricity production and the virtual water flows associated with coal and electricity transportation in China

Coal-fired electricity industry is the high-water-consumption sector and the coal and electricity trade among different regions drives virtual water flow which embedded in the coal and coal-fired electricity products. In North China regions, a large amount of water was consumed by coal and electricity products, and transferred to the South China in terms of virtual water. This study calculated the water footprint of coal and coal-fired electricity products in seven regions all over China and established a theoretical system to analyse the virtual water flow regime associated with the coal and electricity trade. Besides, a map of the virtual water flow in China is drawn. The results show that the water footprint of the energy industry in the Eastern and North-western regions is much higher than that of other areas, the water footprint in 2015 is 2.4×109m3 and 3.2×109m3, which is mainly due to the large demand for electricity production in the Eastern regions. And the Northwest region is rich in energy resources, which require large amount of water resources for coal mining and electricity generation. However, in the recent years, the Northwest regions are the highest output of virtual water regions, from 3.7×108m3 in 2000 to 8.6×108m3 in 2015, accounting for 35% of the water footprint of the coal power industry in the region. There is almost no out-flow virtual water in the Eastern and Southern regions. The virtual water of water resources in water-scarce regions is transported to the water-rich regions, which will lead to larger pressure on the water resources in the Northwest region. Therefore, the physical water transfer (e.g. South-to-North Water Diversion Project) is not only the efficient measure to cope with the water issues related to energy production, and the virtual water regulation is also an efficient way for sustainable water management in the future.

Thermodynamics of clouding process in 1-butanol + water mixtures in the presence and absence of sugars

This paper deals with liquid-liquid equilibrium of binary {1-butanol + water} and ternary {1-butanol + aqueous sugar solutions} systems in both water-rich and butanol-rich environments. Immiscibility region of 1-butanol-water system is expanded by addition of sugars, and this effect becomes stronger by increasing hydrophilicity and molality of sugars. The soluting-out ability of sugars follows the order maltitol ≈ maltose > sucrose > D-(+)-glucose > D-(−)-fructose > xylitol > D-(+)-xylose. The experimental cloud point data were successfully correlated by Setschenow's equation. Thermodynamic functions and relative contributions of entropy and enthalpy to Gibbs free energy of clouding were calculated. From the obtained results, the clouding process of 1-butanol in water mixtures is more spontaneous than that of water in 1-butanol ones. The presence of sugars, in both water-rich and alcohol-rich environments, leads to a more spontaneous liquid-liquid demixing process. The clouding process in the water-rich region is entropy-driven, while in the butanol-rich region is enthalpy-driven.

Phase equilibria of (water + [EMIM] bromide) and (water + [EMIM] tosylate)

This work presents a detailed phase equilibria study on the aqueous solutions of two hydrophilic ILs that are solid at room temperature: 1-ethyl-3-methylimidazolium bromide ([EMIM][Br]) and 1-ethyl-3-methylimidazolium tosylate ([EMIM][TOS]). The melting temperatures of the pure ILs were measured to discriminate between existing literature data that show some disparity. Solid-liquid equilibrium (SLE) data for (water + [EMIM][Br]), so far lacking in the literature, were determined by a dynamic method over the major portion of the entire composition range. Using a chilled mirror dew point technique, extensive and accurate vapor-liquid equilibrium (water activity) measurements were further conducted for the aqueous solutions of both ILs. The temperature and concentration dependences of the activity data were correlated simultaneously by an extended NRTL model, whereby establishing a common description of pertinent equilibria and related thermodynamic behavior of these systems. Good performance of this model was verified against other experimental data from the literature and this work. In particular, correct predictions of experimental SLE data proved the model to extrapolate well beyond the temperature range of data underlying the correlation. Excess thermodynamic properties calculated from the model revealed that these systems exhibit large negative deviations from Raoult's law, a strongly exothermic mixing and, except for (water + [EMIM][TOS]) in the water-rich region, positive excess entropies. Comparing the two ILs, the observed deviations from ideality are always more pronounced for [EMIM][Br], which indicates that [Br]– is a more hydrophilic anion than [TOS]–. The observed pattern of thermodynamic behavior was rationalized on the molecular level by means of simple MD simulations. They showed that while there are more H-bonds formed between water and [TOS]–, these bonds are weaker than those between water and [Br]–.

Study of seepage field distribution and its influence on urban tunnels in water-rich regions

This paper presents a study of the spatial distribution of pore water pressure on urban tunnels in water-rich regions. Based on Harr’s classical solution for unlined tunnels and the actual hydrological environment, a water pressure formula of the seepage field is derived by regarding the surrounding rock, grouting circle, lining, etc., as a complete system. The seepage model test system developed is applied to test the distribution of water pressure in the surrounding rock for an unlined tunnel and a tunnel that contains both a grouting circle and a lining. For the unlined tunnel, the degree of coincidence between the theoretical and experimental results is higher at a distance from the tunnel center than near the center of tunnel. For the tunnel with the grouting circle and lining, the theoretical solution tallies with the experimental results. The decrease in the permeability coefficient of the grouting circle or the degradation of lining permeability will cause the water pressure in the surrounding rock to rise, with the latter effect being more significant. However, the effect of changing the grouting radius on the tunnel seepage field is not obvious.

195Pt NMR and Molecular Dynamics Simulation Study of the Solvation of [PtCl6]2- in Water-Methanol and Water-Dimethoxyethane Binary Mixtures.

The experimental 195Pt NMR chemical shift, δ(195Pt), of the [PtCl6]2- anion dissolved in binary mixtures of water and a fully miscible organic solvent is extremely sensitive to the composition of the mixture at room temperature. Significantly nonlinear δ(195Pt) trends as a function of solvent composition are observed in mixtures of water-methanol, or ethylene glycol, 2-methoxyethanol, and 1,2-dimethoxyethane (DME). The extent of the deviation from linearity of the δ(195Pt) trend depends strongly on the nature of the organic component in these solutions, which broadly suggests preferential solvation of the [PtCl6]2- anion by the organic molecule. This simplistic interpretation is based on an accepted view pertaining to monovalent cations in similar binary solvent mixtures. To elucidate these phenomena in detail, classical molecular dynamics computer simulations were performed for [PtCl6]2- in water-methanol and water-DME mixtures using the anionic charge scaling approach to account for the effect of electronic dielectric screening. Our simulations suggest that the simplistic model of preferential solvation of [PtCl6]2- by the organic component as inferred from nonlinear δ(195Pt) trends is not entirely accurate, particularly for water-DME mixtures. The δ(195Pt) trend in these mixtures levels off for high DME mole fractions, which results from apparent preferential location of [PtCl6]2- anions at the borders of water-rich regions or clusters within these inherently micro-heterogeneous mixtures. By contrast in water-methanol mixtures, apparently less pronounced mixed solvent micro-heterogeneity is found, suggesting the experimental δ(195Pt) trend is consistent with a more moderate preferential solvation of [PtCl6]2- anions. This finding underlines the important role of solvent-solvent interactions and micro-heterogeneity in determining the solvation environment of [PtCl6]2- anions in binary solvent mixtures, probed by highly sensitive 195Pt NMR. The notion that preferential solvation of [PtCl6]2- results primarily from competing ion-solvent interactions as generally assumed for monatomic ions, may not be appropriate in general.

Modelling of ground vibration from tunnels in a poroelastic half-space using a 2.5-D FE-BE formulation

This paper presents an improved two-and-a-half-dimensional (2.5-D) finite element-boundary element (FE-BE) model to predict train-induced vibrations from a tunnel with an arbitrarily shaped cross-section embedded in a poroelastic half-space. The proposed model considers both the saturated porous characteristic of the soil and the free surface effect. A 2.5-D BE model based on the Green’s function for a poroelastic half-space is developed to simulate the soil surrounding the tunnel. The discretization of the infinite ground surface is not required, which avoids spurious reflections induced by mesh truncations and significantly reduces the mesh size of boundary elements. The 2.5-D BE model for saturated soils and the 2.5-D FE model for tunnels are coupled via the boundary conditions on the soil–tunnel interface. The track components are coupled with the tunnel-soil model to more accurately predict vibrations induced by underground railways. After being verified via comparison with an existing model, the proposed model is used to assess train-induced vibrations from a quasi-rectangular tunnel in a poroelastic half-space. Analysis of vibrations induced by the single-line load and double-line load on rails is conducted, respectively. The results show that the insertion gain, which is greater than 30 dB, is highly dependent on the frequency and observation position. When the saturated soil is simplified as the equivalent single-phase elastic soil, the soil displacement tends to be overestimated while the soil stress is underestimated. A saturated soil model may more accurately describe train-induced vibrations from a tunnel in the water-rich region.

Game Theory Analysis of the Virtual Water Strategy

The virtual water strategy (VWS) provides an alternative modelling method to transport virtual water (VW) from water-rich regions to areas with water-scarce resources. This strategy is designed to balance the differences of regional water supplies, improve water-use efficiency, and ensure the environmental sustainability of water resources. However, the practical implementation of VWS still faces resistance due to a poor understanding of VWS and minimal pressure to make hard decisions about sharing water resources. Therefore, it is important to study the decision-making mechanism and behavioral motivation in the implementation process of VWS. Game theory has been extensively applied in economics, political science and natural science to predict and understand decision outcomes. Cost-benefit analysis and behavior incentives using VWS can also be accessed using game theory with a symmetric take out modelling approach. In this approach, efficient and acceptable methods to construct a VWS-based framework of VW trading can implemented. This study builds a semi-quantitative game model to analyze acceptance paradigms for economic development and trade patterns in sharing water. The optional strategies and relevant payoffs are analyzed to explore factors affecting the implementation of VWS. The results show that an equilibrium in which all areas share VWS is the optimal result. However, egoistic motivations, political pressures and risk of loss hinders decision making. Thus, to achieve mutual benefits within an interregional VWS framework, some external interventions are required. Interventions can include: reasonable incentive mechanisms for rewards or punishments, improving technologies and efficiency related to VW production, and promoting long-term trade cooperation between the regions. The uneven distribution and availability of freshwater globally dictates that the sharing and availability of water into the future will require VWS modelling and the political willingness to share resources.

Probing Interfacial (Pt/Ionomer) and Bulk Water Distribution in Ultra-Thin Films of PFSA and Pfia Ionomers on Platinum Using Neutron Reflectometry

Over the last decade, proton conducting ionomers in ultra-thin film form have been subjected to scrutiny because of their relevance to fuel cell catalyst layers. The few nanometers thin ionomer film covering the Pt/C catalysts serve multiple functionalities: transport of reactant gases (O2 or H2) through the ionomer film to the Pt catalyst, transport of water across and along the ionomer film, and proton transport along the ionomer film. The ionomer films respond most strongly to the humid environment resulting in proportional uptake of water. The distribution of water at the Pt/ionomer interface and within the ionomer is expected to be a critical factor in controlling key transport phenomena mentioned above. The interfacial water is also expected to directly impact the electrochemical activity – both by affecting the local proton concentration and mobility as well as potentially offering an transport resistance to the reactant gases. One MD simulation study on Nafion/Pt identifies the backbone densification near Nafion/Pt interface is a root cause of high interfacial transport resistance [1]. Recent findings on low catalyst activity due to the dehydration of ionomer have pointed towards the adsorption of side chains on Pt surface which varies with the ionomer structure [2]. Thus, the description of the Pt/ionomer interface is essential in understanding how these two are transported to the reaction sites because ORR is ultimately tied to interfacial O2 transport resistance and catalyst activity. Neutron Reflectometry (NR) has been a heavily exploited as a non-invasive technique to indirectly visualize the interface and material phase distribution within a thin film. Dura et. Al applied NR to measure a 42 nm thick Nafion film coated on planar Pt [3]. Their findings revealed a 1.1 nm thick water rich region near the interface and uniform water containing bulk film at 92% RH. However, in a similar condition, based on a NR study Wood et. al, claims differed greatly and they identified a water scarce region near the interface [4]. So far only these two NR studies have elucidated the Pt/ionomer interface in wet conditions. We have investigated water sorption on bare Pt and in ~15 nm thick ionomer films coated on Pt. Three different ionomers of varying equivalent weight have been examined: Nafion (EW1100), 3M (EW725), and PFIA (EW 625). The presentation will share the results on the effect of ionomer molecular structure on interfacial morphology as well as water distribution within the each ionomer film. Some of the key findings emerging from our work are: (i) the presence of few monolayers equivalent water rich interfacial layer at Pt/ionomer interface (see Figure 1 below) but varying with ionomer EW; (ii) varying water content and water distribution for the different ionomers; (iii) temperature affects water distribution not merely content.

Thermo-Responsive Behavior of Polymer Solutions Coated with Phospholipids

Various kinds of cell model systems have been utilized for fundamental studies on physical properties of cells. Water-in-Oil (W/O) droplet system coated with phospholipids is one of the beneficial simple model systems of living cells. For instance, a biomimetic phase-separated membrane was constructed in the W/O systems with phospholipid mixture (Hamada et al., J. Phys. Chem. Lett., 2010) since phase separation in lipid membrane system corresponds to the separation between lipid raft domains and other soft domains in the living cell membranes. Phase transition of a polymer has been studied for many years, such as coil-globule transition (Nishio et al., Nature, 1979), and helix-coil transition (Tanaka et al., J. Chem. Phys., 1973). In addition to the phase transition of polymers, phase separation in a binary polymer solution was also reported (Yanagisawa et al., J. Mol. Liq., 2014). However, cell-sized confinement effects on polymer solutions have been poorly confirmed. To clarify the cell-sized confinement effects on polymer solutions, we previously observed the dynamic behavior of polymer droplets (Yoshida et al., Polymers, 2017). The previous study revealed that droplet size influences the start time of phase separation in the case of temperature change from 10 to 65 degrees Celsius. In this study, we observed the dynamic behavior of hydroxypropyl cellulose (HPC) solution droplets in response to temperature change from 10 to 65 degrees Celsius using a fluorescence microscope. The droplets were coated with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE). As a control, we observed non-coated water droplets. DPPC and DPPE are widely used for studies on model cell membranes. Using time-lapse images, we confirmed the water/HPC distribution using a spatial autocorrelation function. The results revealed that water-rich region appeared in the case of lipid coated droplets with increase in temperature while such phenomenon was not observed in the case of non-coated droplets.

Tough Photocrosslinked Silk Fibroin/Graphene Oxide Nanocomposite Hydrogels.

The development of protein-based hydrogels for tissue engineering applications is often limited by their mechanical properties. Herein, we present the facile fabrication of tough regenerated silk fibroin (RSF)/graphene oxide (GO) nanocomposite hydrogels by a photochemical cross-linking method. The RSF/GO composite hydrogels demonstrated soft and adhesive properties during initial stages of photocrosslinking (<2 min), which is not observed for the pristine RSF hydrogel, and rendered a tough and nonadhesive hydrogel upon complete cross-linking (10 min). The composite hydrogels exhibited superior tensile mechanical properties, increased β-sheet content, and decreased chain mobility compared to that of the pristine RSF hydrogels. The composite hydrogels demonstrated Young's modulus as high as ∼8 MPa, which is significantly higher than native cartilage (∼1.5 MPa), and tensile toughness as high as ∼2.4 MJ/m3, which is greater than that of electroactive polymer muscles and at par with RSF/GO composite membranes fabricated by layer-by-layer assembly. Small-angle scattering study reveals the hierarchical structure of photocrosslinked RSF hydrogels to comprise randomly distributed water-poor (hydrophobic) and water-rich (hydrophilic) regions at the nanoscale, whereas water pores and channels exhibiting fractal-like characteristics at the microscale. The size of hydrophobic domain (containing β-sheets) was observed to increase slightly with GO incorporation and/or alcohol post-treatment, whereas the size of the hydrophilic domain (intersheet distance containing random coils) was observed to increase significantly, which influences/affects water uptake capacity, cross-link density, and mechanical properties of hydrogels. The presented results have implications for both fundamental understanding of the structure-property relationship of RSF-based hydrogels and their technological applications.

Physical Transfer of Water Versus Virtual Water Trade: Economic and Policy Considerations

This paper provides a comparative economics of physical water transfer and virtual water trade in India to deal with the problem of growing scarcity of water. This is based on a nuanced understanding of the difficulties in operationalizing the concept of virtual water trade from a regional perspective; a better appreciation of the differential economic value of water use of land-rich, water-scarce regions and land-scarce, water-rich regions; and a recognition of the various direct and indirect benefits of large water transfer projects as evident from recent empirical studies. We first attempt a comparative economics of physical water transfer (between water-rich regions of eastern India to water-scarce regions of peninsular India) and the “virtual water transfer” alternative, considering the anecdotal evidence of various direct and indirect costs and benefits. The direct costs included economic cost of infrastructure, and various damage costs and transaction costs. The indirect costs covered economic, social and environmental costs. These cost components are several and are also more pronounced for physical water transfer. The benefits considered in the analysis included direct economic benefits, and various indirect benefits that are social, economic and environmental in nature. These benefits are several and also more pronounced for physical water transfer. The analysis showed that the net benefits of physical water transfer outweigh virtual water transfer. Subsequently, the political transaction costs of executing water transfer projects were examined.

Phoebe: A Surface Dominated by Water

Abstract The Saturnian irregular satellite, Phoebe, can be broadly described as a water-rich rock. This object, which presumably originated from the same primordial population shared by the dynamically excited Kuiper Belt Objects (KBOs), has received high-resolution spectral imaging during the Cassini flyby. We present a new analysis of the Visual Infrared Mapping Spectrometer observations of Phoebe, which critically, includes a geometry correction routine that enables pixel-by-pixel mapping of visible and infrared spectral cubes directly onto the Phoebe shape model, even when an image exhibits significant trailing errors. The result of our re-analysis is a successful match of 46 images, producing spectral maps covering the majority of Phoebe’s surface, roughly a third of which is imaged by high-resolution observations (&lt;22 km per pixel resolution). There is no spot on Phoebe’s surface that is absent of water absorption. The regions richest in water are clearly associated with the Jason and south pole impact basins. Phoebe exhibits only three spectral types, and a water–ice concentration that correlates with physical depth and visible albedo. The water-rich and water-poor regions exhibit significantly different crater size frequency distributions and different large crater morphologies. We propose that Phoebe once had a water-poor surface whose water–ice concentration was enhanced by basin-forming impacts that exposed richer subsurface layers. The range of Phoebe’s water–ice absorption spans the same range exhibited by dynamically excited KBOs. The common water–ice absorption depths and primordial origins, and the association of Phoebe’s water-rich regions with its impact basins, suggests the plausible idea that KBOs also originated with water-poor surfaces that were enhanced through stochastic collisional modification.

Water Scarcity in Vietnam: a Point of View on Virtual Water Perspective

This paper quantifies water consumption of Vietnam in agricultural products on virtual water perspective. The calculation of water footprint and virtual water in four major agricultural crops is first implemented for seven regions of the country. The domestic and international trades of virtual water are subsequently investigated to demonstrate the commodity and virtual water flows among regions. The analysis reveals that Mekong River Delta is an important exporter of virtual water in rice product for both domestic and international trades while Central Highland is the main virtual exporter in coffee. The paper also proposes a new water stress index such that it considers both direct and indirect water use given transboundary water resources. The proposed water stress index indicates the actual water scarcity in Vietnam in which the water-rich regions i.e. Red River Delta and Mekong River Delta are in severe water stress.

Role of Transmembrane Potential and Defects on the Permeabilization of Lipid Bilayers by Alamethicin, an Ion-Channel-Forming Peptide.

The insertion and ion-conducting channel properties of alamethicin reconstituted into a 1,2-di- O-phytanyl- sn-glycero-3-phosphocholine bilayer floating on the surface of a gold (111) electrode modified with a 1-thio-β-d-glucose (β-Tg) self-assembled monolayer were investigated using a combination of electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). The hydrophilic β-Tg monolayer separated the bilayer from the gold substrate and created a water-rich spacer region, which better represents natural cell membranes. The EIS measurements acquired information about the membrane resistivity (a measure of membrane porosity), and the PM-IRRAS experiments provided insight into the conformation and orientation of the membrane constituents as a function of the transmembrane potential. The results showed that the presence of alamethicin had a small effect on the conformation and orientation of phospholipid molecules within the bilayer for all studied potentials. In contrast, the alamethicin peptides assumed a surface state, where the helical axes adopted a large tilt angle with respect to the surface normal, at small transmembrane potentials, and inserted into the bilayer at sufficiently negative transmembrane potentials forming pores, which behaved as barrel-stave ion channels for ionic transport across the membrane. The results indicated that insertion of alamethincin peptides into the bilayer was driven by the dipole-field interactions and that the transitions between the inserted and surface states were electrochemically reversible. Additionally, the EIS measurements performed on phospholipid bilayers without alamethicin also showed that the application of negative transmembrane potentials introduces defects into the bilayer. The membrane resistances measured in both the absence and presence of alamethicin show similar dependencies on the electrode potential, suggesting that the insertion of the peptide may also be assisted by the electroporation of the membrane. The findings in this study provide new insights into the mechanism of alamethicin insertion into phospholipid bilayers.

Water footprint characteristic of less developed water-rich regions: Case of Yunnan, China

Rapid industrialization and urbanization pose pressure on water resources in China. Virtual water trade proves to be an increasingly useful tool in water stress alleviation for water-scarce regions, while bringing opportunities and challenges for less developed water-rich regions. In this study, Yunnan, a typical province in southwest China, was selected as the case study area to explore its potential in socio-economic development in the context of water sustainability. Both input-output analysis and structural decomposition analysis on Yunnan's water footprint for the period of 2002–2012 were performed at not only an aggregated level but also a sectoral level. Results show that although the virtual water content of all economic sectors decreased due to technological progress, Yunnan's total water footprint still increased as a result of economic scale expansion. From the sectoral perspective, sectors with large water footprints include construction sector, agriculture sector, food manufacturing & processing sector, and service sector, while metal products sector and food manufacturing & processing sector were the major virtual water exporters, and textile & clothing sector and construction sector were the major importers. Based on local conditions, policy suggestions were proposed, including economic structure and efficiency optimization, technology promotion and appropriate virtual water trade scheme. This study provides valuable insights for regions facing “resource curse” by exploring potential socio-economic progress while ensuring water security.

Divergent trends of open-surface water body area in the contiguous United States from 1984 to 2016.

The contiguous United States (CONUS), especially the West, faces challenges of increasing water stress and uncertain impacts of climate change. The historical information of surface water body distribution, variation, and multidecadal trends documented in remote-sensing images can aid in water-resource planning and management, yet is not well explored. Here, we detected open-surface water bodies in all Landsat 5, 7, and 8 images (∼370,000 images, >200 TB) of the CONUS and generated 30-meter annual water body frequency maps for 1984-2016. We analyzed the interannual variations and trends of year-long water body area, examined the impacts of climatic and anthropogenic drivers on water body area dynamics, and explored the relationships between water body area and land water storage (LWS). Generally, the western half of the United States is prone to water stress, with small water body area and large interannual variability. During 1984-2016, water-poor regions of the Southwest and Northwest had decreasing trends in water body area, while water-rich regions of the Southeast and far north Great Plains had increasing trends. These divergent trends, mainly driven by climate, enlarged water-resource gaps and are likely to continue according to climate projections. Water body area change is a good indicator of LWS dynamics in 58% of the CONUS. Following the 2012 prolonged drought, LWS in California and the southern Great Plains had a larger decrease than surface water body area, likely caused by massive groundwater withdrawals. Our findings provide valuable information for surface water-resource planning and management across the CONUS.

Study of electron transfer process in aqueous methanol system by using tryptophan based short peptide – Amino acid pairs

The present study demonstrated the nature of synergistic solvation behaviour in water – methanol binary solvent mixture(s) and its role on photo-induced electron transfer (PET) process during the interactions of different tryptophan based peptide conjugates with selected non-aromatic amino acids and also with standard coumarins – amines pairs. The highest degree of solvation was obtained in water rich region near Xwater = 0.85 with ETN(30) value 1.05, which was observed more compared to both pure water (1.00) and methanol (0.76). An analytical solvent exchange model was used to estimate the extent of synergistic solvation and found ∼2 times stronger than the preferential solvation efficiency. Such unconventional associative solvation behaviour was confirmed by fluorescence study of the solvatochromic probe which suggested that the weak nature of intermolecular interaction is responsible for such behaviour. The selected pairs of different amino acids as donors, and established pre-synthesized new tryptophan based peptide conjugates as acceptors were used to check the PET event in the polar environment(s) to know the reorganization energy of the binary solvent mixture. An inverted region was observed and estimated the value of reorganization energy (λ) in Xwater = 0.85. The values of λ in water, methanol and Xwater = 0.85 solution were further used to determine its dependency on solvent parameters. Interestingly, our observations revealed that the solvent viscosity depicted linear dependence with reorganization energy (λ) where the value of λ increases with increasing solvent viscosity. Therefore, the photo-physical event i.e. PET, in present solvent system, is significantly dependent on the physical properties of polar solvents.

Intermolecular Interactions of Pyridine in Liquid Phase and Aqueous Solution Studied by Soft X-ray Absorption Spectroscopy

Abstract Intermolecular interactions of pyridine in liquid and in aqueous solution are studied by using soft X-ray absorption spectroscopy (XAS) at the C, N, and O K-edges. XAS of liquid pyridine shows that the N 1s→π* peak is blue shifted and the C 1s→π* peak of the meta and para sites is red shifted, respectively, as compared with XAS of pyridine gas. These shifts in liquid are smaller than those in clusters, indicating that the intermolecular interaction of liquid pyridine is weaker than that of pyridine cluster, as supported by the combination of quantum chemical calculations of the core excitation and molecular dynamics simulations of the liquid structure. On the other hand, XAS spectra of aqueous pyridine solutions (C5H5N)x(H2O)1−x measured at different molar fractions show that in the pyridine rich region, x&gt;0.7, the C and N 1s→π* peak energies are not so different from pure liquid pyridine (x=1.0). In this region, antiparallel displaced structures of pyridine molecules are dominant as in pure pyridine liquid. In the O K-edge XAS, the pre-edge peaks sensitive to the hydrogen bond (HB) network of water molecules show the red shift of −0.15 eV from that of bulk water, indicating that small water clusters with no large-scale HB network are formed in the gap space of structured pyridine molecules. In the water rich region, 0.7&gt;x, the N 1s→π* peaks and the O 1s pre-edge peaks are blue shifted, and the C 1s→π* peaks of the meta and para sites are red-shifted by increasing molar fraction of water. The HB network of bulk water is dominant, but quantum chemical calculations indicate that small pyridine clusters with the HB interaction between the H atom in water and the N atom in pyridine are still existent even in very dilute pyridine solutions.