Residual Water Molecules Research Articles

Directing self-assembly in solution towards improved cooperativity in Fe(iii) complexes with amphiphilic tridentate ligands.

An amphiphilic iron(iii) complex with a tridentate Schiff-base ligand was prepared by condensation of a hexadecyloxy functionalised salycylaldehyde with a diamine followed by complexation with FeCl2 and anion methathesis with NaClO4. The complex shows spin crossover both in the solid state and solution. However in solution self-assembly and consequently aggregation of individual molecules form concentration dependent particles with sizes of 300 nm for higher concentrations, or 5 nm for lower concentrations. Aggregate formation was confirmed by NANO-flex 180° DLS Size, scan-rate dependent cyclic voltammetry and scanning electron microscopy. Molecular simulations were used to investigate the self-assembly of the complex in solution, including the role of residual water molecules. The simulations showed the self-assembly of reverse micelle-like structures when a small water cluster is inserted in solution, whereas no large aggregates formed in dehydrated environments. The perchlorate anions were found near the metal centres, stabilizing the aggregates around the water pool. Simulations of pre-assembled structures further showed the lack of stability of large aggregates in the absence of water. The larger aggregates promoted efficient communication between the iron(iii) centres and the compound displayed spin crossover in solution at around 220 K with a 10 K hysteresis window, as measured by NMR and SQUID magnetometry.

Shape memory effect of chitosan/glycerol composite film in mixed water/ethanol solution

ABSTRACTIn this paper, a chitosan (CS)/glycerol (GL) composite film was prepared, and the solution‐responsive feature of the composite film in a mixed water/ethanol solution was investigated. The composite film began to show obvious shape recovery behavior when the water content of the mixed solution was more than 50% v/v. In mixed solutions, when the molar ratio of water molecules and ethanol molecules was more than 2:1, apart from the combination with the ethanol molecules, the residual water molecules could interact with the CS molecules, promoting the formation of hydrogen bonds. The stress stored in CS molecules was released, and the shape memory effect of the composite film was triggered. In addition, the effect of water content in the mixed solutions on the structural, crystal, thermal stability and mechanical properties of the composite film was characterized. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47037.

Cover Feature: Enhanced Crystallization by Methanol Additive in Antisolvent for Achieving High‐Quality MAPbI3 Perovskite Films in Humid Atmosphere (ChemSusChem 14/2018)

The Cover Feature shows a diagram of how the use of methanol can help to remove water during the fabrication of perovskite thin films. Because of the presence of methanol, residual water molecules can be efficiently removed from the gaps of the perovskite precursors and the perovskite film formation can be slightly controlled, leading to pinhole-free and low roughness films. This method presents a new path for controlling the growth and morphology of perovskite films in humid climates and laboratories with uncontrolled environments. More information can be found in the Full Paper by Yang et al. on page 2348 in Issue 14, 2018 (DOI: 10.1002/cssc.201800625).

Factors affecting the separation performance of graphene oxide membranes: mechanical support, properties of graphene oxide, and exotic species

AbstractBACKGROUNDGraphene oxide (GO) membrane with 2‐dimensional nanocapillaries has gained worldwide attention. To manipulate the membrane separation performance, most existing studies focused on sandwiching appropriate species between GO layers. This study aimed to provide multiple strategies to manipulate the GO membrane separation performance, including the mechanical support, properties of GO nanosheets, and exotic species (i.e. cross‐linkers and residual water molecules).RESULTSUsed as the support material, compared with the nitrocellulose membrane, the polyvinylidene fluoride membrane offered stronger mechanical strength to ensure a stable flux. Additional mechanical support could be provided by the non‐woven cloth underneath the GO membrane. The use of GO nanosheets with smaller sizes obtained by centrifugation of the GO suspension increased the water flux and NaCl rejection. Cross‐linking GO layers by Ca2+ resulted in a decreased water flux but increased salt rejection. The same phenomena was observed for the GO membranes post‐treated by vacuum drying, which, compared with air drying, evaporated more residual water molecules from the nanocapillaries.CONCLUSIONResults suggested that the mechanical support, properties of GO nanosheets, cross‐linkers, and residual water molecules greatly affected the membrane water flux and rejections, which could be utilized as strategies to manipulate the GO membrane separation performance. © 2017 Society of Chemical Industry

Coupled Valence-Bond State Molecular Dynamics Description of an Enzyme-Catalyzed Reaction in a Non-Aqueous Organic Solvent.

Enzymes are widely used in nonaqueous solvents to catalyze non-natural reactions. While experimental measurements showed that the solvent nature has a strong effect on the reaction kinetics, the molecular details of the catalytic mechanism in nonaqueous solvents have remained largely elusive. Here we study the transesterification reaction catalyzed by the paradigm subtilisin Carlsberg serine protease in an organic apolar solvent. The rate-limiting acylation step involves a proton transfer between active-site residues and the nucleophilic attack of the substrate to form a tetrahedral intermediate. We design the first coupled valence-bond state model that simultaneously describes both reactions in the enzymatic active site. We develop a new systematic procedure to parametrize this model on high-level ab initio QM/MM free energy calculations that account for the molecular details of the active site and for both substrate and protein conformational fluctuations. Our calculations show that the reaction energy barrier changes dramatically with the solvent and protein conformational fluctuations. We find that the mechanism of the tetrahedral intermediate formation during the acylation step is similar to that determined under aqueous conditions, and that the proton transfer and nucleophilic attack reactions occur concertedly. We identify the reaction coordinate to be mostly due to the rearrangement of some residual water molecules close to the active site.

Structure and Dynamics of Alginate Gels Cross-Linked by Polyvalent Ions Probed via Solid State NMR Spectroscopy.

Alginate gels are an outstanding biomaterial widely applicable in tissue engineering, medicine, and pharmacy for cell transplantation, wound healing and efficient bioactive agent delivery, respectively. This contribution provides new and comprehensive insight into the atomic-resolution structure and dynamics of polyvalent ion-cross-linked alginate gels in microbead formulations. By applying various advanced solid-state NMR (ssNMR) spectroscopy techniques, we verified the homogeneous distribution of the cross-linking ions in the alginate gels and the high degree of ion exchange. We also established that the two-component character of the alginate gels arises from the concentration fluctuations of residual water molecules that are preferentially localized along polymer chains containing abundant mannuronic acid (M) residues. These hydrated M-rich blocks tend to self-aggregate into subnanometer domains. The resulting coexistence of two types of alginate chains differing in segmental dynamics was revealed by 1H-13C dipolar profile analysis, which indicated that the average fluctuation angles of the stiff and mobile alginate segments were about 5-9° or 30°, respectively. Next, the 13C CP/MAS NMR spectra indicated that the alginate polymer microstructure was strongly dependent on the type of cross-linking ion. The polymer chain regularity was determined to systematically decrease as the cross-linking ion radius decreased. Consistent with the 1H-1H correlation spectra, regular structures were found for the gels cross-linked by relatively large alkaline earth cations (Ba2+, Sr2+, or Ca2+), whereas the alginate chains cross-linked by bivalent transition metal ions (Zn2+) and trivalent metal cations (Al3+) exhibited significant irregularities. Notably, however, the observed disordering of the alginate chains was exclusively attributed to the M residues, whereas the structurally well-defined gels all contained guluronic acid (G) residues. Therefore, a key role of the units in M-rich blocks as mediators promoting the self-assembly of alginate chains was experimentally confirmed. Finally, combining 2D 27Al 3Q/MAS NMR spectroscopy with density functional theory (DFT) calculations provided previously unreported insight into the structure of the Al3+ cross-linking centers. Notably, even with a low residual amount of water, these cross-linking units adopt exclusively 6-fold octahedral coordination and exhibit significant motion, which considerably reduces quadrupolar coupling constants. Thus, the experimental strategy presented in this study provides a new perspective on cross-linked alginate structure and dynamics for which high-quality diffraction data at the atomic resolution level are inherently unavailable.

Low-temperature direct heterogeneous bonding of polyether ether ketone and platinum

Direct heterogeneous bonding between polyether ether ketone (PEEK) and Pt was realized at the temperatures lower than 150°C. In order to create sufficient bondability to diverse materials, the surface was modified by vacuum ultraviolet (VUV) irradiation, which formed hydrate bridges. For comparison, direct bonding between surfaces atomically cleaned via Ar fast atom bombardment (FAB) was conducted in a vacuum. The VUV irradiation was found to be effective for creating an ultrathin hydrate bridge layer from the residual water molecules in the chamber. Tight bonds were formed through dehydration of the hydrate bridges by heating at 150°C, which also contributed to enhancing interdiffusion across the interface. The VUV-modified surfaces showed bondability as good as that of the FAB-treated surfaces, and the VUV-modified samples had shear strengths at the same level as those of FAB-treated surfaces. This technology will be of practical use in the packaging of lightweight, flexible biomedical devices.

Freezing-induced proton dynamics in tofu evaluated by low-field nuclear magnetic resonance

The main purpose of the study was to understand and interpret the effects of freezing times on the proton dynamics and chrominance of tofu. Low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI) were used to monitor real-time changes in microstructure and water distribution at different freezing times. The T 2 relaxation parameters included the relative intensity (A 2i) and the population of T 2i component (M 2i). Three proton populations focusing on approximately 0.93–4.72, 25–49, and 402–505 ms were identified as T 2b, T 21, and T 22, respectively. The generated ice crystals damaged the hydration layer of the soybean protein and T 2b increased over the 2 h. The side chains of the soybean protein then began to unite owing to the protein’s reduced affinity for water, making the protons of the hydrophilic groups exchangeable, and resulting in decreased mobility of the T 2b fraction. The appearance of exchangeable hydrophilic group protons caused an increase in A 2b from 2 to 6 h. The subsequent increases in A 2b and M 2b 6 h later were due to access to the unfrozen free water. The water molecules (T 21 fraction) changed into ice crystals, reducing A 21 and M 21. The disappearance of the T 22 fraction peak 6 h later was attributed to residual unfrozen water molecules, with the minor component turning into ice with a fast relaxation time. The MRI results showed that the outline of the sample was blurred at 2 h and could not be detected 6 h later. Significant correlations were further detected between T 2 relaxation parameters and color parameters. LF-NMR has great potential as a reliable tool for the study of tofu.

The properties of residual water molecules in ionic liquids: a comparison between direct and inverse Kirkwood-Buff approaches.

We study the properties of residual water molecules at different mole fractions in dialkylimidazolium based ionic liquids (ILs), namely 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM/BF4) and 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM/BF4) by means of atomistic molecular dynamics (MD) simulations. The corresponding Kirkwood-Buff (KB) integrals for the water-ion and ion-ion correlation behavior are calculated by a direct evaluation of the radial distribution functions. The outcomes are compared to the corresponding KB integrals derived by an inverse approach based on experimental data. Our results reveal a quantitative agreement between both approaches, which paves a way towards a more reliable comparison between simulation and experimental results. The simulation outcomes further highlight that water even at intermediate mole fractions has a negligible influence on the ion distribution in the solution. More detailed analysis on the local/bulk partition coefficients and the partial structure factors reveal that water molecules at low mole fractions mainly remain in the monomeric state. A non-linear increase of higher order water clusters can be found at larger water concentrations. For both ILs, a more pronounced water coordination around the cations when compared to the anions can be observed, which points out that the IL cations are mainly responsible for water pairing mechanisms. Our simulations thus provide detailed insights in the properties of dialkylimidazolium based ILs and their effects on water binding.

Investigating non-fluorinated anions for sodium battery electrolytes based on ionic liquids

In order for sodium batteries to become a safe, lower cost option for large scale energy storage, minimising the price of all components is important. We report here on the application of a pyrrolidinium room temperature ionic liquid comprising the dicyanamide anion as a successful electrolyte system for sodium metal batteries that does not contain expensive fluorinated species. The effects of plating/stripping of sodium from Na metal electrodes has been investigated in a symmetrical Na|electrolyte|Na configuration at a current density of 10μAcm−2. Comparisons are drawn to reference organic electrolytes comprising propylene carbonate-fluoroethylene carbonate. Residual water molecules in the ionic liquid electrolyte are observed to have a significant effect upon the surface film and subsequent favourable plating/stripping behaviour of symmetrical cells and this is explored in detail. An increase of the moisture content from 90ppm to 400ppm impedes both electrodeposition and electrodissolution of the Na+/Na. This is investigated at Ni electrodes using cyclic voltammetry at different Na+-salt concentrations to further understand the mechanism.

Investigation of ethanol infiltration into demineralized dentin collagen fibrils using molecular dynamics simulations

The purpose of this study is to investigate the interaction of neat ethanol with bound and non-bound water in completely demineralized dentin that is fully hydrated, using molecular dynamics (MD) simulation method. The key to creating ideal resin-dentin bonds is the removal of residual free water layers and its replacement by ethanol solvent in which resin monomers are soluble, using the ethanol wet-bonding technique. The test null hypotheses were that ethanol cannot remove any collagen-bound water, and that ethanol cannot infiltrate into the spacing between collagen triple helix due to narrow interlayer spacing. Collagen fibrillar structures of overlap and gap regions were constructed by aligning the collagen triple helix of infinite length in hexagonal packing. Three layers of the water molecules were specified as the layers of 0.15–0.22nm, 0.22–0.43nm and 0.43–0.63nm from collagen atoms by investigating the water distribution surrounding collagen molecules. Our simulation results show that ethanol molecules infiltrated into the intermolecular spacing in the gap region, which increased due to the lateral shrinkage of the collagen structures in contact with ethanol solution, while there was no ethanol infiltration observed in the overlap region. Infiltrated ethanol molecules in the gap region removed residual water molecules via modifying mostly the third water layer (50% decrease), which would be considered as a loosely-bound water layer. The first and second hydration layers, which would be considered as tightly bound water layers, were not removed by the ethanol molecules, thus maintaining the helical structures of the collagen molecules.

Hydration of magnesia cubes: a helium ion microscopy study.

Physisorbed water originating from exposure to the ambient can have a strong impact on the structure and chemistry of oxide nanomaterials. The effect can be particularly pronounced when these oxides are in physical contact with a solid substrate such as the ones used for immobilization to perform electron or ion microscopy imaging. We used helium ion microscopy (HIM) and investigated morphological changes of vapor-phase-grown MgO cubes after vacuum annealing and pressing into foils of soft and high purity indium. The indium foils were either used as obtained or, for reference, subjected to vacuum drying. After four days of storage in the vacuum chamber of the microscope and at a base pressure of p < 10−7 mbar, we observed on these cubic particles the attack of residual physisorbed water molecules from the indium substrate. As a result, thin magnesium hydroxide layers spontaneously grew, giving rise to characteristic volume expansion effects, which depended on the size of the particles. Rounding of the originally sharp cube edges leads to a significant loss of the morphological definition specific to the MgO cubes. Comparison of different regions within one sample before and after exposure to liquid water reveals different transformation processes, such as the formation of Mg(OH)2 shells that act as diffusion barriers for MgO dissolution or the evolution of brucite nanosheets organized in characteristic flower-like microstructures. The findings underline the significant metastability of nanomaterials under both ambient and high-vacuum conditions and show the dramatic effect of ubiquitous water films during storage and characterization of oxide nanomaterials.

Growth per cycle of alumina atomic layer deposition on nano- and micro-powders

Core–shell powders consisting of a tungsten particle core and thin alumina shell have been synthesized using atomic layer deposition in a rotary reactor. Standard atomic layer deposition of trimethylaluminum/water at 150 °C utilizing a microdosing technique was performed on four different batches of powder with different average particle sizes. The particle size of the powders studied ranges from ∼25 to 1500 nm. The high mass-thickness contrast between alumina and tungsten in transmission electron microscopy images demonstrates that the particle core/shell interface is abrupt. This allows for the uncomplicated measurement of alumina thickness and therefore the accurate determination of growth per cycle. In agreement with prior works, the highest growth per cycle of ∼2 Å/cycle occurred on the batch of powder with the smallest average particle size and the growth per cycle decreased with increasing average particle size of a powder batch. However, the growth per cycle of the alumina film on an individual particle in a batch is shown to be independent of the size of an individual particle, and therefore, a powder batch which consists of particles size spanning orders of magnitude has constant shell thickness on all particles. This uniformity of thickness on different particle sizes in a particular batch is determined to be due to the difficulty of removing residual water molecules from the powder during the purging cycle of the atomic layer deposition (ALD) process. Therefore, rotary ALD on a single batch of powder with wide particle size distribution provides the same shell thickness regardless of individual particle size, which may have positive implications for particle ALD applications where the shell thickness determines critical parameters, such as particle passivation and manipulation of optical properties.

Impact of fibre moisture content on the structure/mechanical properties relationships of PHBV/wheat straw fibres biocomposites

Abstract The objective of the present work was to investigate the impact of fibre moisture, at the moment of the manufacturing process, on the relationships between the structure of PHBV/wheat straw fibres composites and their final mechanical properties, with a focus on the interphase role. For that purpose, wheat straw fibres were equilibrated at extreme relative humidity conditions before extrusion with PHBV, reaching moisture contents of 2 wt% w.b. and 14.2 ± 0.4 wt% w.b. at 0 and 98% RH, respectively. The structure and mechanical properties of resulting composites (prepared with a fibre content of 20 wt%) were compared to those of materials filled with fibres classically dried (moisture content of 3 wt% w.b.). It was shown that the fibre/matrix adhesion was visually not affected by the initial fibre moisture content. However, PHBV molecular weight decreased significantly with increasing fibre moisture content, which was attributed to hydrolysis reactions induced by residual water molecules. The increase in crystallinity along with initial fibre moisture content was put in relation to the observed decrease of molecular weight. In spite of structural differences, the tensile properties were similar for all composites, leading to the conclusion that the initial fibre moisture content was not a predominant factor for controlling the mechanical properties of PHBV/wheat straw fibres composites.

Effect of focused ion beam deposition induced contamination on the transport properties of nano devices

Focused ion beam (FIB) deposition produces unwanted particle contamination beyond the deposition point. This is due to the FIB having a Gaussian distribution. This work investigates the spatial extent of this contamination and its influence on the electrical properties of nano-electronic devices. A correlation study is performed on carbon-nanotube (CNT) devices manufactured using FIB deposition. The devices are observed using transmission electron microscopy (TEM) and these images are correlated with device electrical characteristics. To discover how far Pt-nanoparticle contamination occurs along a CNT after FIB electrical contact deposition careful TEM inspections are performed. The results show FIB deposition efficiently improves electrical contact; however, the practice is accompanied by serious particle contamination near deposition points. These contaminants include metal particles and amorphous elements originating from precursor gases and residual water molecules in the vacuum chamber. Pt-contamination extends for approximately 2 μm from the point of FIB contact deposition. These contaminants cause current fluctuations and alter the transport characteristics of devices. It is recommended that nano-device fabrication occurs at a distance greater than 2 μm from the FIB deposition of an electrical contact.

Residual water in ionic liquids: clustered or dissociated?

How do residual water molecules in ionic liquids (ILs) interact with themselves, as well as with the ions? This question is crucial in understanding why the physical properties of ILs--and chemical reactions performed in them--are strongly affected by the residual water content. There have been three conflicting hypotheses regarding the structure and behaviour of the residual water: (i) water molecules are separated from one another, while interacting strongly with the ions, and dispersed throughout the medium; (ii) water molecules self-associate or form clusters in the ILs; (iii) residual water weakens ion-ion interactions. A satisfactory resolution of these conflicting suggestions has been hindered by the complexity and long range of the interactions in the water-IL mixture and by the often profound differences in physical structure between various different ILs. Here we present a route to resolve this question through a combination of a statistical thermodynamic theory (Kirkwood-Buff theory) with density and osmotic data from the literature. The structure of water-IL mixtures is shown to be water content dependent; at the lowest measured water concentration, strong water-IL interaction and water-water separation are observed in accordance to (i), whereas water in a more hydrophobic IL environment seems to self-associate at moderately low water concentrations, in accordance with (ii).

Structural and dynamical characteristics of trehalose and sucrose matrices at different hydration levels as probed by FTIR and high-field EPR

Some organisms can survive complete dehydration and high temperatures by adopting an anhydrobiotic state in which the intracellular medium contains large amounts of disaccharides, particularly trehalose and sucrose. Trehalose is most effective also in protecting isolated in vitro biostructures. In an attempt to clarify the molecular mechanisms of disaccharide bioprotection, we compared the structure and dynamics of sucrose and trehalose matrices at different hydration levels by means of high-field W-band EPR and FTIR spectroscopy. The hydration state of the samples was characterized by FTIR spectroscopy and the structural organization was probed by EPR using a nitroxide radical dissolved in the respective matrices. Analysis of the EPR spectra showed that the structure and dynamics of the dehydrated matrices as well as their evolution upon re-hydration differ substantially between trehalose and sucrose. The dehydrated trehalose matrix is homogeneous in terms of distribution of the residual water and spin-probe molecules. In contrast, dehydrated sucrose forms a heterogeneous matrix. It is comprised of sucrose polycrystalline clusters and several bulk water domains. The amorphous form was found only in 30% (volume) of the sucrose matrix. Re-hydration leads to a structural homogenization of the sucrose matrix, whilst in the trehalose matrix several domains develop differing in the local water/radical content and radical mobility. The molecular model of the matrices provides an explanation for the different protein-matrix dynamical coupling observed in dried ternary sucrose and trehalose matrices, and accounts for the superior efficacy of trehalose as a bioprotectant. Furthermore, for bacterial photosynthetic reaction centers it is shown that at low water content the protein-matrix coupling is modulated by the sugar/protein molar ratio in sucrose matrices only. This effect is suggested to be related to the preference for sucrose, rather than trehalose, as a bioprotective disaccharide in some anhydrobiotic organisms.

Water-mediated inclusion of benzoates and tosylates inside the bambusuril macrocycle

A supramolecular complex between benzoates and a bambusuril crystallizes out immediately after mixing in chloroform but only in the presence of residual water molecules. In this complex each of the two portals of the macrocycle is occupied by one benzoate. Carboxylate groups are connected through hydrogen bonding interactions with one molecule of water positioned between them in the center of the bambusuril cavity. Similar water assisted host-guest behavior was also observed when tosylates instead of benzoates were used.

Studies of Size-Based Selectivity in Aqueous Ternary Complexes of Americium(III) or Lanthanide(III) Cations

Spectrophotometric and calorimetric titrations were used to determine the equilibrium constants (log10 K 111) and enthalpies of formation (ΔH 111) for aqueous ternary complexes of the form M(La)(Lb) (M = Nd3+, Sm3+, Tb3+, Ho3+, Er3+, or Am3+; La = DTPA5−, DO3A3−, or CDTA4−; Lb = oxalate (Ox), malonate (Mal), or iminodiacetate (IDA)). Inner-sphere ternary complexes were readily formed with the septadentate DO3A (1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid) and hexadentate CDTA (trans-1,2-diaminocyclohexanetetraacetic acid) ligands, whose binary complexes have residual metal-coordinated water molecules that are readily displaced by the smaller secondary ligands. The stability constants for the formation of lanthanide–CDTA complexes with Ox, Mal, and IDA generally increase with decreasing ionic radius when steric hindrance is minimal, with the trend in the M(CDTA)− formation constants overshadowing any size-based reversal in the stepwise ternary complexation constants. Similar ternary complexes with DO3A showed little increase in thermodynamic stability compared to analogous CDTA complexes and no preference for larger Ln cations. The octadentate DTPA (diethylenetriaminepentaacetic acid) ligand proved too large to form ternary complexes to a measurable extent with any of the secondary ligands investigated, despite the presence of one residual inner sphere water molecule.

Ultrafast Two-Dimensional Infrared Spectroscopy of Guanine–Cytosine Base Pairs in DNA Oligomers

NH and OH stretching excitations of hydrated double-stranded DNA oligomers containing guanine-cytosine (GC) base pairs in a Watson-Crick geometry are studied by two-dimensional (2D) infrared spectroscopy. The 2D spectra measured at a low hydration level (∼4 water molecules/base pair) are dominated by NH stretch contributions from the NH2 groups of G and C and the NH group of G. Partially hydrated NH2 groups display red-shifted NH stretch frequencies and a mixing of the wave functions of the two local NH oscillators via the mechanical vibrational coupling. The NH stretch lifetimes are of the order of 200-300 fs. Weak couplings exist between NH stretch oscillators within a base pair, while interactions between neighboring GC pairs in the double helix are negligible. The absence of spectral diffusion on a 1 ps time scale suggests a relatively rigid structure of the hydrogen bonds between DNA and residual water molecules. 2D spectra recorded with fully hydrated DNA oligomers exhibit NH and OH stretch contributions with a weak influence of water fluctuations on the NH stretch lineshapes. The femtosecond spectral diffusion of OH stretch excitations is slower than that in bulk H2O and originates from structural fluctuations of the water shell and the formation of a vibrationally hot ground state by vibrational relaxation. We compare our findings with measurements on hydrated adenine-thymine DNA oligomers and anhydrous GC base pairs in solution.