Thermoluminescence of photostimulable materials after X irradiation below room temperature

Thermoluminescence glow peaks in the temperature range 100 to 400 K are investigated for BaFX (X = Cl, Br) crystals after X irradiation at 100 K. A prominent glow peak of BaFCl around 210 K is found to be composed of a few recombination roots, that is, the peak corresponds to the recombination of hole trapped centres such as an O- centre and a dissociated Cl2- centre with the F (F-) centre and the O2--F(Cl-) pair defect. Another small glow peak around 270 K is likely to occur from thermal dissociation of the O2- -F(Cl-) pair defect. The main glow peak of BaFBr:O2- at 170 K may be attributed to a recombination of an O- centre with the F(Br-) centre.     

23Na-n.m.r. experiments on sodalites

²³Na-n.m.r. and two-dimensional (2-D) nutation n.m.r. spectra have been measured for dehydrated and hydrated Cl-, Br-, and I-sodalite. From simulations of the spectra, quadrupole parameters could be determined. For hydrated Cl-sodalite, rapid spin relaxation in the rotating frame, brought about by rapid rotation of water molecules in the β-cages, was observed. Using rotary echo nutation n.m.r., two sodium sites could be discerned.     

Retention of ions on nonporous charged stationary phases

The interactions between ion-exchange resins and counterions consist of several mechanisms, such as ion-pair formation between active sites and counterions, specific adsorption, solvation changes, and double-layer accumulation. The double-layer accumulation of ions, which is a typical nonstoichiometric mechanism, is an important factor governing overall ion-exchange chromatographic retention when a major part of the stationary-phase surface is in contact with eluent flows. Nonporous stationary phases, where solutes are accessible to the surfaces by convection as well as by diffusion, possibly highlight this nonstoichiometric contribution through the coupling of a flow profile with an electrostatic potential function. The retention of ions on nonporous stationary phases has been interpreted by a model derived on the basis of the Poisson-Boltzmann equation including solvation change terms. Unusual retention behaviors have been confirmed only for anions, and can be explained by the model including the assumption that anions undergo solvation changes in a thin layer (approximately 5 nm thickness) at the vicinity of the stationary phase; the thickness should be a function of eluent flow rates. This strongly suggests that there is a difference in solvation nature between cations and anions. It can be inferred that water molecules interacting with polymer domains of the stationary phase behave like single molecules and cannot form a stable hydration shell around an anion as usually seen in bulk solution.     

Development of mass spectrometric method for analysis of cyclic nitramine explosives DTIW and HNIW

Mass spectrometric (MS) methods are used for the analysis of two novel nitramine explosives-hexanitrohexaazaisowurzitane (HNIW) and 4,10-dinitro-2,6,8,12-tetraoxa-4,10-diazaisowurzitane (DTIW). The methods include electrospray (ESI) and atmospheric pressure chemical ionization techniques for liquid chromatography/MS (LC/MS), chemical ionization for direct introduction (DCI), and gas chromatography/MS (CI-GC/MS). It is found that HNIW (438 Da) is detectable using both positive and negative modes of DCI and in the negative mode ESI-MS. Several anions were found to complex with HNIW, e.g., CF3CO2-, Cl-, Br-, I-, NO3-, and NO2-. On the other hand, DTIW could only be detected using positive DCI and CI-GC/MS, where an MH+ ion (m/z 263) was formed. The fragmentation pathways of the two nitramines were further studied by MS2 experiments. Apparently, the main fragmentation pathway of the MH+ ion of DTIW involves the loss of nitrous acid. Several anion adducts of HNIW that were studied dissociate to afford neutral HNIW and the added anions. However, Cl-, Br-, I-, and NO2- afford a series of fragments that resulted from the dissociation of the isowurzitane structure. For these anions, limit of detection was also found. To understand some of the HNIW fragmentation pathways, DFT calculations were used.     

On-column ion-exchange preconcentration of inorganic anions in open tubular capillary electrochromatography with elution using transient-isotachophoretic gradients. 3. Implementation and method development

A solid-phase extraction method based on an ion-exchange retention mechanism has been used for in-line preconcentration of inorganic anions prior to their separation by capillary electrophoresis (CE). A single capillary containing a preconcentration and a separation zone has been used in a commercial CE instrument without instrumental modification. Analyte anions were retained on a preconcentration zone comprising an adsorbed layer of cationic latex particles, while separation was achieved in a separation zone comprising fused silica modified by adsorption of a cationic polymer. Elution of the adsorbed analytes was achieved using an eluotropic gradient formed by a transient isotachophoretic boundary between a fluoride electrolyte and a naphthalenedisulfonate electrolyte. Optimization of the electrolyte concentrations, sample injection times, and back-flushing times allowed the successful separation of sub-ppb levels of inorganic anions using a 100-min injection at 2 bar pressure, introducing over 40 capillary volumes of sample. A method based on a 10-min injection allowed a 100-fold increase in sensitivity over conventional hydrodynamic injection for Br-, I-, NO3-, CrO4(2-), and MoO4(2-) with a total analysis time of 25 min. Detection limits were dependent on the injection time but were in the range 2.2-11.6 ppb for a 10-min injection time. This approach was used to determine NO3- in Antarctic ice cores where the analysis could be performed using a sample volume 100 times less than that used for ion chromatography.     

Effects of coexisting anions on removal of bromide in drinking water by coagulation

Bromo-DBPs (disinfection by-products) are generated by bromide and disinfectant in drinking water disinfection, which have adverse effects on human health. In this study, effects of coexisting anions on removal of bromide by aluminium coagulation were investigated. It was observed that bromide was removed of 62.1-87.0% in raw water, while the removal efficiency of bromide was achieved 82.8-99.2% in deionized water through the combination of Br- with Al(III) in various pathways. The coexisting anions in raw water significantly affected the removal of bromide. Removal efficiency decreased by 11.5, 21.2, 14.6, 8.0 and 40.8% with the addition of HCO3-, SO4(2-), Cl-, NO3- and H2PO4-, respectively, for their affinities with Al(III) or accelerating the formation of Al(OH)3(am). These results demonstrated that bromo-DBPs in drinking water could be controlled though removing bromide by enhanced coagulation.     

Elution of propranolol as an ion-pair complex by buffer solutions on C18-silica

Propranolol (pK(a) = 9.4) was eluted on C(18)-bonded Kromasil, equilibrated with buffer solutions of methanol and water (40/60, v/v) containing a constant concentration of a counteranion (12 mM). Nine different counteranions were studied: Cl(-), I(-), NO(3)(-), SO(4)(2-), CH(3)COO(-), HOOCC(2)H(4)COO(-), (-)OOCC(2)H(4)COO(-), HOOCCOHCOOHCOO(-), HOOCCOHCOO(-)COO(-), and (-)OOCCOHCOO(-)COO(-). The co-cation was K(+) or Na(+). Vacancy perturbations were measured on three concentration plateaus of propranolol hydrochloride, at 1.2, 12, and 24 mM, by injecting 100 microL of a pure mixture of methanol and water (40/60, v/v). Indirect detection of the solvent, the counteranion, the co-cation, and the chloride ion was carried out at 325 nm, a wavelength at which only propranolol responds. In a 1.2 mM propranolol hydrochloride solution, there is a 10-fold excess of counteranions and only a positive perturbation peak, due to the excluded co-cation and eluting before the column hold-up time, and a large vacancy peak, associated with propranolol, were recorded. Association between propranolol and the counteranion in excess determines the retention time of this second perturbation. The hydrophobicity of the complexes increases in the order Cl(-) < CH(3)COO(-) approximately HOOCC(2)H(4)COO(-) < NO(3)(-) < I(-) < HOOCCOHCOOHCOO(-) < (-)OOCC(2)H(4)COO(-) < SO(4)(2-) approximately HOOCCOHCOO(-)COO(-) < (-)OOCCOHCOO(-)COO(-). Propranolol retention is larger in the presence of the trivalent citrate anion than in that of the bivalent citrate, succinate, or sulfate anions. It is larger with these bivalent anions than with any monovalent anion. Equal concentration of propranolol hydrochloride and buffer in the mobile phase reveals five system peaks associated with the five components (solvent, counteranion, co-cation, chloride, propranolol molecules). In contrast with monovalent anions, bivalent anions (sulfate, succinate, citrate) or trivalent anions (citrate) cause a reversal of the elution order of the perturbation peaks of chloride anions and buffer molecules. This confirms a competition between chloride and buffer anions to form ion pairs with propranolol. The retention of the perturbation signal of the buffer increases with increasing anion charge because multivalent anions can bind to several molecules of propranolol. The perturbation measurements demonstrate the influence of the valence and hydrophobicity of the buffer on the retention of ionizable compounds. The inverse method allowed the derivation of the isotherm parameters from the overloaded band profiles of propranolol. These values confirm that adsorbate-adsorbate interactions increase with increasing valence of the anions.     

Electrochemical detection of chloride by underpotentially deposited silver films on polycrystalline gold

This paper describes an electrochemical method for measuring dilute levels of chloride using an underpotentially deposited (UPD) Ag adlayer on polycrystalline Au substrates as a sensing agent. Specifically, chloride ions adsorb onto the Ag UPD adlayer and effect changes in the electrochemical deposition and stripping characteristics of the silver film. Cyclic voltammograms (CVs) of the native Au/Ag(UPD) electrode in 0.1 M H2SO4(aq) exhibit a primary stripping peak for the Ag UPD adlayer at 550 mV vs Ag(+/0), and chloride adsorption onto the Au/Ag(UPD) surface effects a peak shift to approximately 600 mV vs Ag(+/0), depending on the amount of adsorbed Cl-, as affected by the Cl- concentrations and contact times employed in the derivatization. The chloride-treated electrodes also exhibit a stripping peak at 275 mV that is not observed on the native substrate and increases in intensity with Cl- concentration and derivatization time. The integrated charge density for this latter stripping peak relative to that for the primary stripping peak at 550-610 mV provides a useful metric for quantifying adsorbed Cl- levels, and these values allow measurement of Cl- concentrations in dilute aqueous solutions. For Cl- concentrations between 0.5 and 100 microM, the kinetics of Cl- adsorption followed a transient Langmuir adsorption model and allowed measured surface coverages to be used for determining Cl- solution concentrations. Using contact times of 1 min for Cl- adsorption, the electrodes showed a linear response across Cl- concentrations of 0.5-20 microM.     

Label-free detection of DNA hybridization based on hydration-induced tension in nucleic acid films

The properties of water at the nanoscale are crucial in many areas of biology, but the confinement of water molecules in sub-nanometre channels in biological systems has received relatively little attention. Advances in nanotechnology make it possible to explore the role played by water molecules in living systems, potentially leading to the development of ultrasensitive biosensors. Here we show that the adsorption of water by a self-assembled monolayer of single-stranded DNA on a silicon microcantilever can be detected by measuring how the tension in the monolayer changes as a result of hydration. Our approach relies on the microcantilever bending by an amount that depends on the tension in the monolayer. In particular, we find that the tension changes dramatically when the monolayer interacts with either complementary or single mismatched single-stranded DNA targets. Our results suggest that the tension is mainly governed by hydration forces in the channels between the DNA molecules and could lead to the development of a label-free DNA biosensor that can detect single mutations. The technique provides sensitivity in the femtomolar range that is at least two orders of magnitude better than that obtained previously with label-free nanomechanical biosensors and with label-dependent microarrays.     

Structure and rheology of charge-free reverse micelles in aromatic liquid phenyloctane

Reverse micelles formulation requires an inclusion of water or other polar molecules in the binary mixture of ionic surfactant and oil and generally exhibit spheroid geometry with a small aggregation number. Here, we report structure and rheology of charge-free (nonionic) reverse micelles in surfactant/oil systems. We have systematically investigated intrinsic parameters for the shape, size, and internal cross section structure control of such micelles using small-angle X-ray scattering (SAXS) and the rheometry. We found that diglycerol monomyristate (C14G2) when added into an aromatic organic liquid phenyloctane, spontaneously self-assembles into spheroid micelles with maximum diameter ca. 6.7 nm. Decrease in surfactant chain length favors globular-to-rod type transition and micellar aggregation number (N(agg)) increases significantly. On the other hand, increase in surfactant weight fraction induces one-dimensional (1-D) micellar growth; N(agg) increases in parallel to the surfactant concentration. Reverse micelles shrink with the rise of temperature, which is close to the rod-to-sphere type transition. However, water causes a significant micellar growth; N(agg) increases drastically, which shows that water not only increase reverse micellar size but also increases the number of surfactant molecules per micelle. All these microstructure transitions could be understood in terms of the modification of the critical packing parameter (cpp). The SAXS results are very well supported by the geometrical model fittings and rheometry.     

Lattice defects and the effect of Melment on the hydration of alite

The hydration of alite has been studied in the presence of different concentrations of the superplasticizer Melment by using various experimental techniques. Heat of hydration and non-evaporable water content determinations show that Melment retards the hydration; pH measurements indicate that in presence of Melment, Ca²⁺ ion dissolution is reduced. Zeta potential measurements give definite proof that Melment molecules are adsorbed at alite surfaces and the retardation of hydration may be due to adsorption. Thermoelectric power measurements prove that the material is an n-type semiconductor, whereas electrical conductivity measurements of solid pellets of C₃S (C = CaO, S = SiO₂) show that the material is an intrinsic semiconductor above 746 K and an extrinsic semiconductor below 746 K. Extrinsic semiconductivity may be due to the presence of defects or impurities in the crystal lattice. The results also show that oxide ion vacancies are created in the crystal lattice and the reactivity of C₃S is related to the defects. Probably Melment molecules are adsorbed at the sites of defects and oxide ion vacancies and hence retard the hydration.     

Electrical quadruple hysteresis in Pd-doped vanadium pentoxide nanowires due to water adsorption

Humidity-dependent current–voltage (I–V) characteristics of Pd-doped vanadium pentoxide nanowires (Pd-VONs) were investigated. Electrical quadruple hysteresis (QH) was observed and attributed to the large amount of water molecules adsorbed on the nanowires. Using QH in Pd-VONs, the reaction of water with PdO was interpreted as the water molecules are desorbed and then dissociated with increasing bias voltage. Owing to the dissociated H⁺ and OH⁻ ions, PdO is reduced and oxidized. As a result, water molecules recombine as the bias voltage is decreased.     

Electrical quadruple hysteresis in Pd-doped vanadium pentoxide nanowires due to water adsorption

Abstract

Humidity-dependent current–voltage (I–V) characteristics of Pd-doped vanadium pentoxide nanowires (Pd-VONs) were investigated. Electrical quadruple hysteresis (QH) was observed and attributed to the large amount of water molecules adsorbed on the nanowires. Using QH in Pd-VONs, the reaction of water with PdO was interpreted as the water molecules are desorbed and then dissociated with increasing bias voltage. Owing to the dissociated H⁺ and OH^? ions, PdO is reduced and oxidized. As a result, water molecules recombine as the bias voltage is decreased.     

Local investigation of electron-induced processes in water-metal systems

Abstract

Electrons tunnelling inelastically in a scanning tunnelling microscope have been used to induce the diffusion of water monomers adsorbed on the (111) faces of Ag, Cu, and Au via electrons coupling to vibrational modes of the molecules. Electrons of higher energies transform amorphous water clusters into crystalline clusters. At energies above 1.6 eV, the water molecules within the clusters are dissociated only after crystallization of the amorphous ice clusters. When the energy is sufficient to populate an anti-bonding orbital at 3 V the surface is oxidized.     

Attenuated total reflection surface-enhanced infrared absorption spectroscopy of carboxyl terminated self-assembled monolayers on gold

A new recipe for surface-enhanced infrared absorption (SEIRA) active island Au films with improved adhesion in aqueous solution, low resistivity, and enhancement of the infrared (IR) absorption of about 300 was developed. The Au films prepared were utilized in studies of the ionization of self-assembled monolayers of 11-mercaptoundecanoic acid in Na2SO4 aqueous solutions by attenuated total reflection surface-enhanced infrared absorption (ATR-SEIRA) spectroscopy. It was found that the carboxyl end groups of the self-assembled monolayer turn into carboxylate anions on going from anodic to cathodic potentials or from acidic to alkaline pH. The water molecules close to the self-assembled monolayer in acidic solutions or at anodic potentials are preferentially aligned with their dipole moments parallel to the interface. This type of alignment can be ascribed to the dipole-dipole interaction between the carboxyl groups and the water molecules. On the other hand, in alkaline solutions or at cathodic potentials the structure of water close to the self-assembled monolayer is essentially bulk-like, with randomly oriented water molecules. This observation suggests that in alkaline solutions or at cathodic potentials the charge of the carboxylate anions is almost completely compensated for by strongly adsorbed counter cations. As a result, the electric field close to the surface of the ionized self-assembled monolayer is weak and has little influence on the orientation and hydrogen bonding of the water molecules.     

A study of glutathione molecules adsorbed on silver surfaces under different chemical environments by surface-enhanced Raman scattering in combination with the heat-induced sensing method

In this study, surface-enhanced Raman scattering (SERS) in combination with a heat-induced sensing technique has been applied for investigating molecular orientations of glutathione molecules adsorbed on silver colloidal nanoparticles under different chemical environments, which has enabled us to further study how glutathione molecules are adsorbed on the silver surfaces. Factors that may affect the configurations of glutathione molecules adsorbed on the silver nanocolloids have been investigated. By observing the relative enhancement factors of SERS bands due to individual functional groups contributed from different terminals, the affinity between the different functional groups of glutathione and the silver surfaces under different conditions has been sorted and the orientations of glutathione molecules adsorbed on the silver surfaces have been investigated.     

Optical chloride sensor based on dimer-monomer equilibrium of indium(III) octaethylporphyrin in polymeric film

A novel transduction chemistry for preparing optical anion-selective polymeric films that respond reversibly and selectively to chloride ion activity is demonstrated. The chloride sensors are prepared by casting thin (5-10 microm) plasticized PVC films containing indium(III) octaethylporphyrin hydroxide, along with optimized levels of a lipophilic tetraphenylborate salt, onto glass slides. When bathed in low-pH buffered solutions void of chloride, the porphyrin species spontaneously forms a hydroxide ion-bridged dimer, with the added lipophilic borate species serving as the counteranion for this complex. The maximum for the Soret absorption band of this dimeric species is shifted to 390 nm, from 410 nm for the initial monomeric porphyrin. Increases in chloride ion levels in the bathing solution results in chloride extraction and ligation to the In(III) center, and concomitant breaking of the dimer into monomeric porphyrin species, yielding a decrease in absorbance at 390 nm and an increase in optical signal at 410 nm. Under optimized conditions, optical selectivity coefficients toward chloride over a wide range of other anions (NO3-, ClO4-, SCN-, SO4(2-), F-, Br-, H2PO4-) are measured to be < 10(-3). Of all anions tested, only salicylate yields a slightly greater response than chloride. This selectivity is shown to be adequate for reversible and accurate sensing of chloride levels in diluted serum samples.     

Metal dissolution in aqueous electrolyte: Semi-empirical Hartree-Fock and ab initio MD calculations

The semi-empirical Hartree-Fock intermediate neglect of differential overlap (INDO) method and ab initio molecular dynamics (MD) were used to model complementary aspects of the dissolution of metal in aqueous electrolyte. The INDO calculations were used to explore the potential energy surface of adsorbed water molecules and the reaction path followed by metal ions leaving the cluster. The MD calculations showed how the hydration shell formed around the metal ion as it left the surface, starting with one top site adsorbed water and ending with a five waters surrounding the ion.     

A new method for preparing hydrophilic-activated carbon through ester hydrolysis in an alkaline environment

Hydrophilic-activated carbon was prepared by ester hydrolysis reactions, and was characterized by surface area analysis, Fourier transform infrared spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy, and X-ray diffraction. Hydrophilic groups that were introduced on activated carbon surface through ethyl acetate hydrolysis in an alkaline environment were more efficient than those introduced with sodium acetate. During adsorption, the hydrophilic groups on modified activated carbon surface bound with water molecules through H-bonding and increased the adsorption capacity of water vapor. The adsorption isotherms of water vapor were well fitted by the Do model. Water molecules generated larger water clusters around the functional groups at 303 and 313 K. In addition, water desorption from the samples was analyzed by thermogravimetry. Water molecules that were hydrogen-bonded to functional groups exhibited higher thermal stability than those adsorbed in the micropore of activated carbon. Besides, the process of sodium acetate formation on the surface of modified activated carbon was discussed.     

Hole-enhanced Raman scattering

Stokes and anti-Stokes non-resonant hole-enhanced Raman scattering (HERS) spectra with high signal-to-noise ratio (S/N) are reported for the first time for aqueous phase R6G molecules adsorbed onto random nanoholes in thin gold films. Compared to conventional surface-enhanced Raman scattering from nanometric gold colloid particles, HERS exhibits higher strength gain, exceptional reproducibility, simple and reliable substrate preparation, and excellent mechanical stability. By correlating the hole density with Raman scattering gain, we determined optimum HERS gain for 50 nm diameter holes at approximately 100 holes/microm(2). Providing a Raman substrate with uniform "hot spots", we expect that HERS will make the quantitative Raman analysis of biological molecules possible.