Trapped Water Molecules Research Articles

Correlation between Metal–Insulator Transition and Hydrogen-Bonding Network in the Organic Metal δ-(BEDT-TTF)4[2,6-Anthracene-bis(sulfonate)]·(H2O)4

The sensitivity of electronic properties of organic conductors to minute modifications of their solid-state structure is investigated here within BEDT-TTF (ET) salts with organic bis-sulfonate anions, where specific hydrogen bonds between water molecules and sulfonate moieties are shown to dynamically control the organic slabs’ electronic structure. While the mixed-valence, 2,6-naphthalene-bis(sulfonate) salt, (ET)4(NBS)·4H2O, exhibits a charge order state already at room temperature, the corresponding salt with the 2,6-anthracene-bis(sulfonate) dianion, formulated as (ET)4(ABS)·4H2O, is metallic at RT and exhibits a metal–insulator transition at TMI = 85 K. The origin of the MI transition is revealed from a combination of temperature-dependent spectroscopic (Raman) measurements, X-ray structure elucidations (from 300 to 15 K), and theoretical investigations, demonstrating that the charge disproportionation observed below TMI is associated here with the progressive switching of bifurcated OH···O hydrogen bonds between the sulfonate moieties of the anion and the trapped water molecules. These movements within the anion layer are transmitted through weaker C–H···O interactions to the two A and B donor molecules, modifying the details of the overlap interactions within AA and BB pairs and opening a gap in the band structure.

Plasma Proteins Adsorption Mechanism on Polyethylene-Grafted Poly(ethylene glycol) Surface by Quartz Crystal Microbalance with Dissipation

Protein adsorption has a vital role in biomaterial surface science because it is directly related to the hemocompatibility of blood-contacting materials. In this study, monomethoxy poly(ethylene glycol) (mPEG) with two different molecular weights was grafted on polyethylene as a model to elucidate the adsorption mechanisms of plasma protein through quartz crystal microbalance with dissipation (QCM-D). Combined with data from platelet adhesion, whole blood clotting time, and hemolysis rate, the blood compatibility of PE-g-mPEG film was found to have significantly improved. Two adsorption schemes were developed for real-time monitoring of protein adsorption. Results showed that the preadsorbed bovine serum albumin (BSA) on the surfaces of PE-g-mPEG films could effectively inhibit subsequent adsorption of fibrinogen (Fib). Nonspecific protein adsorption of BSA was determined by surface coverage, not by the chain length of PEG. Dense PEG brush could release more trapped water molecules to resist BSA adsorption. Moreover, the preadsorbed Fib could be gradually displaced by high-concentration BSA. However, the adsorption and displacement of Fib was determined by surface hydrophilicity.

Aragonite Crystal Growth and Solid-State Aragonite–Calcite Transformation: A Physico–Geometrical Relationship via Thermal Dehydration of Included Water

A relationship between the physico–geometrical mechanisms of aragonite crystal growth and the thermally induced aragonite–calcite transformation was revealed by focusing on the morphological changes during these processes. Thermal dehydration of the included water during the aragonite–calcite transformation was investigated to characterize the relationship. The trapping of water molecules at the twin boundaries is expected from the aragonite crystal growth mechanism of the twinning of poorly crystalline needle-like crystals to form pseudohexagonal columnar crystals. Heating the aragonite gives the two-step thermal dehydration of the included water (total mass loss due to the dehydration is less than 2% of original sample mass), in which the second dehydration process with rapid water vapor release simultaneously occurs with the aragonite–calcite transformation. During the transformation, the morphology of the aragonite crystal dramatically changes to form dumbbell-like crystal with cauliflower-like struct...

Dielectric permittivity enhancement in hydroxyl functionalized polyolefins via cooperative interactions with water

Recent experiments have shown that polypropylene (PP) with a small fraction of hydroxyl (-OH) side groups displays a two-fold increase in the dielectric permittivity. It has been suggested that both the -OH groups and trapped water molecules may contribute to the dielectric constant increase. In this first principles computational study, using short polyolefin chains as models of PP, we shed light on the role played by -OH functional groups and the trapped moisture. Our results reveal that the trapped water molecules will inevitably accompany -OH incorporation (due to hydrogen bonding) and that both the -OH groups and water molecules will contribute cooperatively to the increase of the PP dielectric constant. These findings also provide insights into the effects of moisture on other molecularly functionalized materials systems.

Improved hydrophobicity of inorganic–organic hybrid mesoporous silica with cage-like pores

Hydrophobic ordered mesoporous silica particles with cage-like pores (SBA-1 type) were prepared through co-condensation of phenyltriethoxysilane (PhTES) and tetraethylorthosilicate (TEOS) at different TEOS/PhTES molar ratios. It is shown that the hydrophobic character of the particles is enhanced by increasing the phenyl loading (decreasing the TEOS/PhTES molar ratio) and that it could be further enhanced by subsequent trimethylsilyl (TMS) grafting on remaining silanol groups (TMS-PhSBA-1 sample). This increase of hydrophobicity has been evidenced on the internal surface (mesoporosity) of the particles using water adsorption and, on the external surface of the particles (in the form of a pellet) using contact angle measurements. Interestingly, a high hysteresis was measured on the most hydrophobic sample (TMS-PhSBA-1), both on its internal surface during high pressure intrusion/extrusion of liquid water and on its external surface using advancing/receding contact angle measurements. This hydrophobic/hydrophilic behavior is explained by surface silanol sites, first shielded by hydrophobic organic moieties and, which subsequently trap water molecules within the porosity or on the external surface after a forced contact with liquid water. The absence of water extrusion (bumper behavior) of this material is then related both to the presence of silanol sites and to the restricted aperture of the cage-like pore morphology.

Structural Observations of Heterometallic Uranyl Copper(II) Carboxylates and Their Solid‐State Topotactic Transformation upon Dehydration

The hydrothermal reactions of uranyl nitrate and metallic copper with aromatic polycarboxylic acids gave rise to the formation of five heterometallic UO(2)(2+)-Cu(2+) coordination polymers: (UO(2))Cu(H(2)O)(2)(1,2-bdc)(2) (1; 1,2-bdc = phthalate), (UO(2))Cu(H(2)O)(2)(btec)⋅4 H(2)O (2) and (UO(2))Cu(btec) (2'; btec = pyromellitate), (UO(2))(2)Cu(H(2)O)(4)(mel) (3; mel = mellitate), and (UO(2))(2)O(OH)(2)Cu(H(2)O)(2)(1,3-bdc)⋅H(2)O (4; 1,3-bdc = isophthlalate). Single-crystal X-ray diffraction (XRD) analysis of compound 1 revealed 2D layers of chains of UO(8) and CuO(4)(H(2)O)(2) units that were connected through the phthalate ligands. In compound 2, these sheets were connected to each other through the two additional carboxylate arms of the pyromellitate, thus resulting in a 3D open-framework with 1D channels that trapped water molecules. Upon heating, free and bonded water species (from Cu-OH(2)) were evacuated from the structure. This thermal transition was followed by in situ XRD and IR spectroscopy. Heating induced a solid-state topotactic transformation with the formation of a new set of Cu-O interactions in the crystalline anhydrous structure (2'), in order to keep the square-planar environment around the copper centers. The structure of compound 3 was built up from trinuclear motifs, in which one copper center, CuO(4)(OH(2))(2), was linked to two uranium units, UO(5)(H(2)O)(2). The assembly of this trimer, "U(2)Cu", with the mellitate generated a 3D network. Complex 4 contained a tetranuclear uranyl core of UO(5)(OH)(2) and UO(6)(OH) units that were linked to two copper centers, CuO(OH)(2)(H(2)O)(2), which were then connected to each other through isophthalate ligands and U=O-Cu interactions to create a 3D structure. The common structural feature of these different compounds is a bridging oxo group of U=O-Cu type, which is reflected by apical Cu-O distances in the range 2.350(3)-2.745(5) Å. In the case of a shorter Cu-O distance, a slight lengthening of the uranyl bond (U=O) is observed (e.g., 1.805(3) Å in complex 4).

Peptide-Lipid Interactions of the Stress-Response Peptide TisB That Induces Bacterial Persistence

The bacterial stress-response peptide TisB in Escherichia coli has been suggested to dissipate the transmembrane potential, such that the depletion of ATP levels induces the formation of dormant persister cells which can eventually form biofilms. We studied the structure and membrane interactions of TisB to find out whether it forms pores or other proton-selective channels. Circular dichroism revealed an amphiphilic α-helical structure when reconstituted in lipid vesicles, and oriented circular dichroism showed that the helix assumes a transmembrane alignment. The addition of TisB to dye-loaded vesicles caused leakage only at very high peptide concentration, notably with a Hill coefficient of 2, which suggests that dimers must be involved. Coarse-grained molecular dynamics simulations showed that membrane binding of monomeric TisB is rapid and spontaneous, and transmembrane insertion is energetically feasible. When TisB oligomers are assembled as transmembrane pores, these channels collapse during the simulations, but transmembrane dimers are found to be stable. Given the pattern of charges on the amphiphilic TisB helix, we postulate that antiparallel dimers could be assembled via a ladder of salt bridges. This electrostatic charge-zipper could enable protons to pass along a wire of trapped water molecules across the hydrophobic membrane.

Water-Dependent Reaction Pathways: An Essential Factor for the Catalysis in HEPD Enzyme

The hydroxyethylphosphonate dioxygenase (HEPD) catalyzes the critical carbon-carbon bond cleavage step in the phosphinothricin (PT) biosynthetic pathway. The experimental research suggests that water molecules play an important role in the catalytic reaction process of HEPD. This work proposes a water involved reaction mechanism where water molecules serve as an oxygen source in the generation of mononuclear nonheme iron oxo complexes. These molecules can take part in the catalytic cycle before the carbon-carbon bond cleavage process. The properties of trapped water molecules are also discussed. Meanwhile, water molecules seem to be responsible for converting the reactive hydroxyl radical group ((-)OH) to the ferric hydroxide (Fe(III)-OH) in a specific way. This converting reaction may prevent the enzyme from damages caused by the hydroxyl radical groups. So, water molecules may serve as biological catalysts just like the work in the heme enzyme P450 StaP. This work could provide a better interpretation on how the intermediates interact with water molecules and a further understanding on the O(18) label experimental evidence in which only a relatively smaller ratio of oxygen atoms in water molecules (∼40%) are incorporated into the final product HMP.

Flight of a Cytidine Deaminase Complex with an Imperfect Transition State Analogue Inhibitor: Mass Spectrometric Evidence for the Presence of a Trapped Water Molecule

Cytidine deaminase (CDA) binds the inhibitor zebularine as its 3,4-hydrate (K(d) ~ 10(-12) M), capturing all but ~5.6 kcal/mol of the free energy of binding expected of an ideal transition state analogue (K(tx) ~ 10(-16) M). On the basis of its entropic origin, that shortfall was tentatively ascribed to the trapping of a water molecule in the enzyme-inhibitor complex, as had been observed earlier for product uridine [Snider, M. J., and Wolfenden, R. (2001) Biochemistry 40, 11364-11371]. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) of CDA nebularized in the presence of saturating 5-fluorozebularine reveals peaks corresponding to the masses of E(2)Zn(2)W(2) (dimeric Zn-CDA with two water molecules), E(2)Zn(2)W(2)Fz, and E(2)Zn(2)W(2)Fz(2), where Fz represents the 3,4-hydrate of 5-fluorozebularine. In the absence of an inhibitor, E(2)Zn(2) is the only dimeric species detected, with no additional water molecules. Experiments conducted in H(2)(18)O indicate that the added mass W represents a trapped water molecule rather than an isobaric ammonium ion. This appears to represent the first identification of an enzyme-bound water molecule at a subunit interface (active site) using FTICR-MS. The presence of a 5-fluoro group appears to retard the decomposition of the inhibitory complex kinetically in the vapor phase, as no additional dimeric complexes (other than E(2)Zn(2)) are observed when zebularine is used in place of 5-fluorozebularine. Substrate competition assays show that in solution zebularine is released from CDA (k(off) > 0.14 s(-1)) much more rapidly than is 5-fluorozebularine (k(off) = 0.014 s(-1)), despite the greater thermodynamic stability of the zebularine complex.

Bias‐Stress‐Induced Charge Trapping at Polymer Chain Ends of Polymer Gate‐Dielectrics in Organic Transistors

AbstractHerein is demonstrated that the polymer chain ends of polymer gate‐ dielectrics (PGDs) in organic field‐effect transistors (OFETs) can trap charges; the bias‐stress stability is reduced without changes in the mobilities of the transistor devices as well as the morphologies of the organic semiconductors. The bias‐stress stabilities of OFETs using PGD with various molecular weights (MWs) are investigated. Under bias stress in ambient air, the drain current decay and the threshold voltage shift are found to increase as the MW of the PGD decreases (MW effect). This MW effect is caused by the variation in the density of polymer chain ends in the PGDs with MW: the free volumes at the polymer chain ends act as charge‐trap sites, resulting in drain current decay during bias stress. The free volumes at polymer chain ends are sufficiently large to allow the residence of water molecules, the presence of which significantly increases the density of charge‐trap sites. In contrast, polymer chain ends without trapped water molecules do not allow charge trapping and so bias‐stress stability is independent of the MW of the PGD. It is also found that the hydrophilicity/hydrophobicity of the chain ends of the PGD can affect bias‐stress stability; carboxyl‐terminated polystyrene exhibits a much higher trap density and lower bias‐stress stability than hydrogen‐terminated polystyrene when these devices are exposed to humid nitrogen.

High electrothermal performance of expanded graphite nanoplatelet-based patch heater

A sub-kilogram scale (∼500 g) of expanded graphite nanoplatelet (EGnP) with multi-layered graphene sheets were successfully fabricated using a simple mild-oxidation of pristine graphite. In particular, a substantial amount of trapped water molecules in EGnP make it a good ionic conductor, while simultaneously allowing it to serve as an electrolyte with ion transport characteristics. Due to its high electrical and thermal conductivity, micro-patterned EGnP can be used to produce electro-heating elements for line heaters. We found that the surface resistance of EGnP-based films was two orders of magnitude smaller than that of graphene-based thin films. The EGnP-based line heater demonstrated efficient heat propagation with uniform temperature distribution, resulting in an energy savings of up to ca. 37% in comparison to the graphene-based flexible heater. Especially, the steady-state temperature increased as the applied voltage increased and it reached to 172.3 °C at a driving voltage of 14 V. In addition, the EGnP-based line heaters under a bending radius of 4 cm had a 25 °C higher temperature as compared with heaters under flat conditions. Most of all, screen printing technique provides the facile formation of shape and size, and makes it possible to be used as a cheap and lightweight patch heater for industrial applications.

Nanoparticle-based PARACEST agents: the quenching effect of silica nanoparticles on the CEST signal from surface-conjugated chelates

Silica nanoparticles of average diameter 53 ± 3 nm were prepared using standard water-in-oil microemulsion methods. After conversion of the surface Si-OH groups to amino groups for further conjugation, the PARACEST agent, EuDOTA-(gly)₄ (-) was coupled to the amines via one or more side-chain carboxyl groups in an attempt to trap water molecules in the inner-sphere of the complex. Fluorescence and ICP analyses showed that approximately 1200 Eu(3+) complexes were attached to each silica nanoparticle, leaving behind excess protonated amino groups. CEST spectra of the modified silica nanoparticles showed that attachment of the EuDOTA-(gly)₄ (-) to the surface of the nanoparticles did not result in a decrease in water exchange kinetics as anticipated, but rather resulted in a complete elimination of the normal Eu(3+) -bound water exchange peak and broadening of the bulk water signal. This observation was traced to catalysis of proton exchange from the Eu(3+) -bound water molecule by excess positively charged amino groups on the surface of the nanoparticles.

An excellent non-wax-stick coating prepared by chemical conversion treatment

The development of non-wax-stick coating is an important issue for petroleum industry. In this letter, an excellent non-wax-stick coating was prepared based on Zn coating by chemical conversion treatment. The chemical conversion coating had hydrophilic and superoleophobic properties in water/oil mixture system, which enabled it to trap water molecules on the surface and reduce wax deposition. The coating was mainly composed of Zn and O elements accompanied by some Si element, and the costing surface showed round bulge structure with different sizes. The combination of chemical composition and structure was considered to play the key role in the special liquid wettability and non-wax-stick properties.

α-Gel Prepared in Sodium Methyl Stearoyl Taurate/Behenyl Alcohol/Water System-Characterization of Structural Changes with Water Concentration

In this study, the changes in the structural and physicochemical properties of an α-crystalline phase (often called an "α-gel") were assessed in a sodium methyl stearoyl taurate (SMT)/behenyl alcohol/water system. The α-gels were characterized focusing on the effects of the alcohol/surfactant ratio and water concentration. Water molecules solubilized in the interlayer of the α-crystalline phase resulting in expanded interlayer spacing. Beyond the solubilization limit of 85 %, water molecules were trapped in the matrix of the α-crystalline phase in non-equilibrium (i.e., two phases). Accordingly, different self-diffusion coefficients for the solubilized and trapped water molecules were measured using a Fourier transform pulsed gradient spin echo technique to monitor the ¹H NMR spectra. It was concluded that the two self-diffusion coefficients correspond to the water solubilized in the interlayer, i.e., "slow water," and trapped in the matrix of the α-crystalline phase, i.e., "fast water."

State of water molecules and silanol groups in opal minerals: a near infrared spectroscopic study of opals from Slovakia

Recently, near infrared spectroscopy in combination with double derivative technique has been effectively used by Christy (Vib Spectrosc 54:42–49, 2010) to study and differentiate between free and hydrogen bonded silanol groups on silica gel surface. The method has given some insight into the type of functionalities, their location in silica gel samples, and the way the water molecules bind onto the silanol groups. The important information in this respect comes from the overtones of the OH groups of water molecules hydrogen-bonded to free silanol groups, and hydrogen-bonded silanol groups absorbing in the region 5,500–5,100 cm−1. Chemically, opal minerals are hydrated silica and the same approach was adapted to study the state of water molecules, silanol functionalities, and their locations in opal samples from Slovakia. Twenty opal samples classified into CT and A classes and one quartz sample were used in this work. The samples were crushed using a hydraulic press and powderized. Each sample was then subjected to evacuation process to remove surface-adsorbed water at 200°C, and the near infrared spectrum of each sample was measured using a Perkin Elmer NTS FT-NIR spectrometer equipped with a transflectance accessory and a DTGS detector. The samples were also heated to 750°C to remove the hydrogen-bonded silanol groups on the surface to reveal their locality. Second derivative profiles of the near infrared reflectance spectra were obtained using the instrument’s software and used in the detailed analysis of the samples. The analysis of the near infrared spectra and their second derivative profiles had the aim in finding relationships between the surface chemical structure and the classification of opal samples. The dry opal samples were also tested for their surface adsorption effectivity toward water molecules. The results indicate that the opal samples contain (1) surface-adsorbed water, (2) free and hydrogen-bonded silanol groups on the surface, (3) trapped water molecules in the bulk, and (4) free and hydrogen-bonded silanol groups in the cavity surfaces in the bulk. A part of the water molecules in the bulk of opal minerals are found as free molecules and the rest are found in hydrogen-bonded state to either free or vicinal or geminal silanol groups.

Effect of Cyclodextrins on the Photophysics of Three Indoloquinoline Derivatives: An Intriguing Fluorometric Study

Effect of cyclodextrin encapsulation on the photophysics of three indoloquinoline derivatives, namely, 5-methyl-5H-indolo[3,2-c]quinoline (MIQ), 8-chloro-5-methyl-5H-indolo[3,2-c]quinoline (CMIQ), and 2,8-dichloro-5-methyl-5H-indolo[3,2-c]quinoline (DCMIQ), has been studied using steady state and time-resolved fluorescence spectroscopy. The three compounds, which are basically cryptosanguinolentines, exist mainly in their zwitterionic forms in the excited state. Appreciable emission from the π-π* state can be observed on excitation of the compounds at a specific wavelength. The existence of zwitterions in the excited state leads to mutual interaction to form dimers triggered by the presence of the hydrophobic nanocavities of cyclodextrins (CDs) through Coulombic interaction. This is evidenced by steady state fluorescence measurements and treating the fluorophores with CDs of different cavity space. The photophysical behavior of the compounds gets dramatically modulated when they are treated with α-, β-, and γ-CD hosts. Presence of chloro substituent/s on the parent molecule and the extent of encapsulation by CDs of different dimensions exhibit enormous alterations in the fluorescence characteristics of the compounds. Solvation of the chromophoric moiety by water molecules deviates in character due to the guest-host interaction. Trapped water molecules inside the bigger cavity of γ-CD seem to play a vital role in quenching the fluorescence of the zwitterions of the molecules.

Multicomponent T2* mapping of knee cartilage: Technical feasibility ex vivo

Disorganization of collagen fibers is a sign of early-stage cartilage degeneration in osteoarthritic knees. Water molecules trapped within well-organized collagen fibrils would be sensitive to collagen alterations. Multicomponent effective transverse relaxation (T2*) mapping with ultrashort echo time acquisitions is here proposed to probe short T(2) relaxations in those trapped water molecules. Six human tibial plateau explants were scanned on a 3T MRI scanner using a home-developed ultrashort echo time sequence with echo times optimized via Monte Carlo simulations. Time constants and component intensities of T2* decays were calculated at individual pixels, using the nonnegative least squares algorithm. Four T2*-decay types were found: 99% of cartilage pixels having mono-, bi-, or nonexponential decay, and 1% showing triexponential decay. Short T2* was mainly in 1-6 ms, while long T2* was ∼ 22 ms. A map of decay types presented spatial distribution of these T2* decays. These results showed the technical feasibility of multicomponent T2* mapping on human knee cartilage explants.

The thermodynamic influence of trapped water molecules on a protein-ligand interaction

Water molecules doing time: Atomic-resolution crystal structures of the PPIase domain of cyclophilin G, alone and in complex with cyclosporin A, and together with MD simulations and calorimetry, reveal how trapped water molecules influence the thermodynamic profile of a protein-ligand interaction.

Ultrafast and ultraslow proton transfer of pyranine in an ionic liquid microemulsion

Effect of a room temperature ionic liquid (RTIL) and water on the ultrafast excited state proton transfer (ESPT) of pyranine (8-hydroxypyrene-1,3,6-trisulfonate, HPTS) inside a microemulsion is studied by femtosecond up-conversion. The microemulsion consists of the surfactant, triton X-100 (TX-100) in benzene (bz) and contains the RTIL, 1-pentyl-3-methyl-imidazolium tetrafluoroborate ([pmim] [BF(4)]) as the polar phase. In the absence of water, HPTS undergoes ultrafast ESPT inside the RTIL microemulsion (RTIL/TX-100/bz) and the deprotonated form (RO(-)) exhibits three rise components of 0.3, 14, and 375 ps. It is proposed that in the RTIL microemulsion, HPTS binds to the TX-100 at the interface region and participates in ultrafast ESPT to the oxygen atoms of TX-100. On addition of water an additional slow rise of 2150 ps is observed. Similar long rise component is also observed in water/TX-100/benzene reverse micelle (in the absence of [pmim] [BF(4)]). It is suggested that the added water molecules preferentially concentrate (trapped) around the palisade layer of the RTIL microemulsion. The trapped water molecules remain far from the HPTS both in the presence and absence of ionic liquid and gives rise to the slow component (2150 ps) of ESPT. Replacement of H(2)O by D(2)O causes an increase in the time constant of the ultraslow rise to 2350 ps.

The transition state for peptide bond formation reveals the ribosome as a water trap

Recent progress in elucidating the peptide bond formation process on the ribosome has led to notion of a proton shuttle mechanism where the 2'-hydroxyl group of the P-site tRNA plays a key role in mediating proton transfer between the nucleophile and leaving group, whereas ribosomal groups do not actively participate in the reaction. Despite these advances, the detailed nature of the transition state for peptidyl transfer and the role of several trapped water molecules in the peptidyl transferase center remain major open questions. Here, we employ high-level quantum chemical ab initio calculations to locate and characterize global transition states for the reaction, described by a molecular model encompassing all the key elements of the reaction center. The calculated activation enthalpy as well as structures are in excellent agreement with experimental data and point to feasibility of an eight-membered "double proton shuttle" mechanism in which an auxiliary water molecule, observed both in computer simulations and crystal structures, actively participates. A second conserved water molecule is found to be of key importance for stabilizing developing negative charge on the substrate oxyanion and its presence is catalytically favorable both in terms of activation enthalpy and entropy. Transition states calculated both for six- and eight-membered mechanisms are invariably late and do not involve significant charge development on the attacking amino group. Predicted kinetic isotope effects consistent with this picture are similar to those observed for uncatalyzed ester aminolysis reactions in solution.