Aqueous Solution Chemistry Research Articles

Aqueous fluid composition in CI chondritic materials: Chemical equilibrium assessments in closed systems

Solids of nearly solar composition have interacted with aqueous fluids on carbonaceous asteroids, icy moons, and trans-neptunian objects. These processes altered mineralogy of accreted materials together with compositions of aqueous and gaseous phases. We evaluated chemistry of aqueous solutions coexisted with CI-type chondritic solids through calculations of chemical equilibria in closed water–rock–gas systems at different compositions of initial fluids, water/rock mass ratios (0.1–1000), temperatures (<350°C), and pressures (<2kbars). The calculations show that fluid compositions are mainly affected by solubilities of solids, the speciation of chlorine in initial water–rock mixtures, and the occurrence of Na-bearing secondary minerals such as saponite. The major species in modeled alkaline solutions are Na+, Cl−, CO32-,HCO3-, K+, OH−, H2, and CO2. Aqueous species of Mg, Fe, Ca, Mn, Al, Ni, Cr, S, and P are not abundant in these fluids owing to low solubility of corresponding solids. Typical NaCl type alkaline fluids coexist with saponite-bearing mineralogy that usually present in aqueously altered chondrites. A common occurrence of these fluids is consistent with the composition of grains emitted from Enceladus. Na-rich fluids with abundant CO32-,HCO3-, and OH− anions coexist with secondary mineralogy depleted in Na. The Na2CO3 and NaHCO3 type fluids could form via accretion of cometary ices. NaOH type fluids form in reduced environments and may locally occur on parent bodies of CR carbonaceous chondrites. Supposed melting of accreted HCl-bearing ices leads to early acidic fluids enriched in Mg, Fe and other metals, consistent with signs of low-pH alteration in chondrites. Neutralization of these solutions leads to alkaline Na-rich fluids. Sulfate species have negligible concentrations in closed systems, which remain reduced, especially at elevated pressures created by forming H2 gas. Hydrogen, CO2, and H2O dominate in the gaseous phase, though the abundance of methane cannot be fairly estimated.

Speed Limits for Acid–Base Chemistry in Aqueous Solutions

Proton transfer reactions, including acid-base recombination, are commonly considered to occur 'nearly instantaneously'. However, their actual time scales may stretch far into the microsecond range, as acid-base reactions are diffusion controlled and the concentrations are low near neutral pH. The interplay of competing bases in the pH relaxation is illustrated using a model acid-base system consisting of o-nitrobenzaldehyde (oNBA) as a proton cage and acetate ions and hydroxyl ions as bases. The kinetically controlled behavior leads to highly counterintuitive states, i.e. acetate ions are transiently protonated for hundreds of nanoseconds despite the presence of a much stronger base OH-.

Aqueous phase separation as a possible route to compartmentalization of biological molecules.

How could the incredible complexity of modern cells evolve from something simple enough to have appeared in a primordial soup? This enduring question has sparked the interest of researchers since Darwin first considered his theory of natural selection. Organic molecules, even potentially functional molecules including peptides and nucleotides, can be produced abiotically. Amphiphiles such as surfactants and lipids display remarkable self-assembly processes including the spontaneous formation of vesicles resembling the membranes of living cells. Nonetheless, numerous questions remain. Given the presumably dilute concentrations of macromolecules in the prebiotic pools where the earliest cells are thought to have appeared, how could the necessary components become concentrated and encapsulated within a semipermeable membrane? What would drive the further structural complexity that is a hallmark of modern living systems? The interior of modern cells is subdivided into microcompartments such as the nucleoid of bacteria or the organelles of eukaryotic cells. Even within what at first appears to be a single compartment, for example, the cytoplasm or nucleus, chemical composition is often nonuniform, containing gradients, macromolecular assemblies, and/or liquid droplets. What might the internal structure of intermediate evolutionary forms have looked like?The nonideal aqueous solution chemistry of macromolecules offers an attractive possible answer to these questions. Aqueous polymer solutions will form multiple coexisting thermodynamic phases under a variety of readily accessible conditions. In this Account, we describe aqueous phase separation as a model system for biological compartmentalization in both early and modern cells, with an emphasis on systems that have been encapsulated within a lipid bilayer. We begin with an introduction to aqueous phase separation and discuss how this phenomenon can lead to microcompartmentalization and could facilitate biopolymer encapsulation by partitioning of solutes between the phases. We then describe primitive model cells based on phase separation inside lipid vesicles, which mimic several basic properties of biological cells: microcompartmentation, protein relocalization in response to stimulus, loss of symmetry, and asymmetric vesicle division. We observe these seemingly complex phenomena in the absence of genetic molecules, enzymes, or cellular machinery, and as a result these processes could provide clues to possible intermediates in the early evolution of cell-like assemblies.

Photogenerated lectin sensors produced by thiol-ene/yne photo-click chemistry in aqueous solution

The photoinitiated radical reactions between thiols and alkenes/alkynes (thiol-ene and thiol-yne chemistry) have been applied to a functionalization methodology to produce carbohydrate-presenting surfaces for analyses of biomolecular interactions. Polymer-coated quartz surfaces were functionalized with alkenes or alkynes in a straightforward photochemical procedure utilizing perfluorophenylazide (PFPA) chemistry. The alkene/alkyne surfaces were subsequently allowed to react with carbohydrate thiols in water under UV-irradiation. The reaction can be carried out in a drop of water directly on the surface without photoinitiator, and any disulfide side products were easily washed away after the functionalization process. The resulting carbohydrate-presenting surfaces were evaluated in real-time studies of protein–carbohydrate interactions using a quartz crystal microbalance (QCM) flow-through system with recurring injections of selected lectins, with intermediate regeneration steps using low pH buffer. The resulting methodology proved fast, efficient and scalable to high-throughput analysis formats, and the produced surfaces showed significant protein binding with expected selectivities of the lectins used in the study.

Aquation and dimerization of osmium(ii) anticancer complexes: a density functional theory study

In this paper, the hydrolytic and aqueous solution chemistry of two half-sandwich OsII arene complexes [(η6-p-cym)Os(pic)Cl] (1) and [(η6-p-cym)Os(mal)Cl] (2) (pic = 2-picolinic acid and mal = maltolate) have been investigated using density functional theory (DFT). For aquation (substitution of chloride by H2O) of the complexes, three attacking models were explored, including two forms of side attack (A and B) and back attack C. Side attack A required the lowest free energy of activation of the three, both in the gas phase and in aqueous solution, suggesting that it best describes the hydrolysis of the complexes. Both the activation and reaction energies indicated faster aquation for 2 than 1, which was in accordance with previous experimental observations. With the side attack model of the complexes, it was found that the conformations of complexes had little effect on the aquation process. Moreover, mechanistic pathways have been obtained for the dimerization of aqua adducts. As for 1a, the ligand departure was the rate-determining step with an activation free energy of 26.1 kcal mol−1, while for 2a, the first step of ring opening and protonation is rate-determining with a free energy of activation of 24.8 kcal mol−1, suggesting that 1a was kinetically more stable toward dimerization. There were three factors presented to explain the stability of 1a: differences in HOMO/LUMO densities, the large activation energy of 1a, and stabilization of Os-pic bonding. This study assists in understanding the aqueous solution chemistry of the anticancer complexes and in the design of novel anticancer drugs.

Effects of Solution Chemistry on the Adsorption of Ibuprofen and Triclosan onto Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs), multiwalled carbon nanotubes (MWCNTs), and oxidized MWCNTs (O-MWCNTs) were studied for the adsorption of ibuprofen (IBU) and triclosan (TCS) as representative types of pharmaceutical and personal care products (PPCPs) under different chemical solution conditions. A good fitting of sorption isotherms was obtained using a Polanyi-Manes model (PMM). IBU and TCS sorption was stronger for SWCNTs than for MWCNTs due to higher specific surface area. The high oxygen content of O-MWCNT further depressed PPCP sorption. The sorption capacity of PPCPs was found to be pH-dependent, and more adsorption was observed at pHs below their pK(a) values. Ionic strength was also found to substantially affect TCS adsorption, with higher adsorption capacity observed for TCS at lower ionic strength. In the presence of a reference aquatic fulvic acid (FA), sorption of IBU and TCS was reduced due to the competitive sorption of FA on carbon nanotubes (CNTs). Sorption isotherm results with SWCNTs, MWCNTs and O-MWCNTs confirmed that the surface chemistry of CNTs, the chemical properties of PPCPs, and aqueous solution chemistry (pH, ionic strength, fulvic acid) all play an important role in PPCP adsorption onto CNTs.

Geochemically Based Modeling of pH-Sensitive Polymer Injection in Berea Sandstone

This study aims at developing a robust geochemical simulation model of pH-sensitive polymer flooding in the context of improved oil recovery. The model can accommodate changes in aqueous solution chemistry and mineral surfaces. The model was calibrated using laboratory data for pH and water chemistry during brine flush and subsequent acid flood. This model was validated using experimental data for citric acid and HCl injections in Berea sandstone. The matching procedure consists of adjusting mineral volumes and specific surface area, in contrast with earlier models that required mineral dissolution rates to be changed by as much as 4 orders of magnitude. The model was used in a predictive mode to evaluate penetration depth of acid fronts in a hypothetical sandstone reservoir. Crucial geochemical data were transferred to a multiphase–multicomponent reservoir simulator to allow for the viscosity of pH-sensitive polymers to change in response to water chemistry alteration during acid–polymer injection. The r...

Study of Ni Metallization in Macroporous Si Using Wet Chemistry for Radio Frequency Cross-Talk Isolation in Mixed Signal Integrated Circuits.

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of selected ultra-high-aspect-ratio macroporous regions that were electrochemically etched in p− Si substrates. The metallization process was conducted by means of wet chemistry in an alkaline aqueous solution containing Ni2+ without reducing agent. It is found that at elevated temperature during immersion, Ni2+ was rapidly reduced and deposited into macroporous Si and a conformal metallization of the macropore sidewalls was obtained in a way that the entire porous Si framework was converted to Ni. A conductive moat was as a result incorporated into p− Si substrate. The experimentally measured reduction of crosstalk in this structure is 5~18 dB at frequencies up to 35 GHz.

A Monte–Carlo step-by-step simulation code of the non-homogeneous chemistry of the radiolysis of water and aqueous solutions. Part I: theoretical framework and implementation

The importance of the radiolysis of water in irradiation of biological systems has motivated considerable theoretical and experimental work in the radiation chemistry of water and aqueous solutions. In particular, Monte-Carlo simulations of radiation track structure and non-homogeneous chemistry have greatly contributed to the understanding of experimental results in radiation chemistry of heavy ions. Actually, most simulations of the non-homogeneous chemistry are done using the Independent Reaction Time (IRT) method, a very fast technique. The main limitation of the IRT method is that the positions of the radiolytic species are not calculated as a function of time, which is needed to simulate the irradiation of more complex systems. Step-by-step (SBS) methods, which are able to provide such information, have been used only sparsely because these are time consuming in terms of calculation. Recent improvements in computer performance now allow the regular use of the SBS method in radiation chemistry. In the present paper, the first of a series of two, the SBS method is reviewed in detail. To these ends, simulation of diffusion of particles and chemical reactions in aqueous solutions is reviewed, and implementation of the program is discussed. Simulation of model systems is then performed to validate the adequacy of stepwise diffusion and reaction schemes. In the second paper, radiochemical yields of simulated radiation tracks calculated by the SBS program in different conditions of LET, pH, and temperature are compared with results from the IRT program and experimental data.

Chemistry of salts in aqueous solutions: Applications, experiments, and theory

Salts comprise a very large and important group of chemical compounds. Natural occurrence of salts and industrial processes of their recovery, conversion, purification, and use depend on solubility phenomena and their chemistry in aqueous solutions, mostly in multi-ion systems. Modeling of these processes as well as developing new ones requires knowledge of the properties of the aqueous salt solutions in extended T-p-x ranges including a growing number of components in solutions (CO2, SO2, lithium salts, salts of rare earth metals, actinides, etc.). At least for the thermodynamic properties, the general accepted methodology is to use thermodynamic databases of aqueous species and solids in combination with an appropriate ion-interaction model to perform equilibrium calculations for species distributions in solution and phase equilibria. The situation in respect to available thermodynamic models and data for their parameterization is discussed at selected examples. Thereby, the importance of accurate experimental determinations of phase equilibrium data for derivation of model parameters is emphasized. Furthermore, it is concluded that experimental investigations should follow a chemical systematic. Simple physical models or quantum chemical calculations cannot predict unknown quantities in the databases with sufficient accuracy. Finally, solubility changes in salt-water systems at enhanced temperatures are considered. Systems, which can be considered as molten hydrates, display interesting phase behavior and chemical reactivity as protic ionic liquids. The latter can be exploited in chemical syntheses to substitute mixtures of concentrated acids like HNO3/H2SO4 by simple salts like ferric nitrate. For an understanding of the chemical and phase behavior of water-salt systems in terms of structure–property relations, a renaissance of chemical guided basic investigations of such systems would be worthwhile.

Sorption of aqueous palladium onto synthetic hydroxyapatite

The sorption of Pd(II) on hydroxyapatite (Ca10(PO4)6(OH)2) has been studied at 25 °C as a function of pH, in 0.01 M NaClO4, and 0.01 and 0.025 M Ca(ClO4)2 aqueous background electrolytes and Pd(II) concentration (9.3 to 47 μM), trying to minimize some types of reactions, such as solid dissolution of and metal precipitation. The radiotracer palladium, 109Pd, obtained by neutron irradiation, has been used to calculate the palladium’s distribution coefficients Kd between aqueous and solid phase. A mathematical treatment of results has been made by ion-exchange theory in order to interpret palladium sorption onto treated solid. For this, we take into account the existence of active sites at the hydroxyapatite surface, and the aqueous solution chemistry of palladium as well as the effect of phosphate anions from solid dissolution. The results can be explained as evidence of sorption of the species PdOH+, and of a mixed hydroxo complex of Pd2+ like (XCaO−)–PdOH+·nH2O fixed onto {≡Ca–OH} surface sites of the hydroxyapatite.

Assessment of an effective quasirelativistic methodology designed to study astatine chemistry in aqueous solution

A cost-effective computational methodology designed to study astatine (At) chemistry in aqueous solution has been established. It is based on two-component spin-orbit density functional theory calculations and solvation calculations using the conductor-like polarizable continuum model in conjunction with specific astatine cavities. Theoretical calculations are confronted with experimental data measured for complexation reactions between metallic forms of astatine (At(+) and AtO(+)) and inorganic ligands (Cl(-), Br(-) and SCN(-)). For each reaction, both 1:1 and 1:2 complexes are evidenced. The experimental trends regarding the thermodynamic constants (K) can be reproduced qualitatively and quantitatively. The mean signed error on computed Log K values is -0.4, which corresponds to a mean signed error smaller than 1 kcal mol(-1) on free energies of reaction. Theoretical investigations show that the reactivity of cationic species of astatine is highly sensitive to spin-orbit coupling and solvent effects. At the moment, the presented computational methodology appears to be the only tool to gain an insight into astatine chemistry at a molecular level.

Use of polyols as particle size and shape controllers: application to boehmite synthesis from sol–gel routes

Polyols were successfully used as size and shape controllers of oxide nanoparticles synthesized by soft chemistry in aqueous solution. The efficiency of acyclic polyols as a complexing agent depends obviously on the number of OH groups bonded to the carbon chain (and thus on the carbon chain length), but also on their stereochemistry. This innovating way to control morphology has been experienced for the synthesis of boehmite nanoparticles, whose morphology variations related to xylitol adsorption (C5 alditol) have been previously reported. The use of polyols during synthesis causes a modification of the usual morphologies observed, specifically resulting in an increase of (101) faces area. It is evidenced here that the variations of the nanoparticle aspect ratio are related to polyol complexing ability, and more specifically to molecule topology and configuration. Indeed, the morphology variations increase as a function of polyol carbon chain length and number of hydroxyl groups, and is much pronounced for stereoisomers exhibiting hydroxyl groups all oriented on the same side of the molecule (threo-threo sequences). Thanks to these various polyols used, we showed how the progressive levels of complexing ability allow us to tune boehmite particle size and shape. Material characterizations were performed using relevant methods such as X-ray diffraction powder pattern simulation and zetametry in addition to transmission electron microscopy. Since γ-alumina is obtained from boehmite by a topotactic transformation, we expect that this method will provide a promising way to control surface properties of γ-alumina, an important industrial catalyst support.

Preface

&amp;lt;div&amp;gt;The 14th International Symposium on Solubility Phenomena and Related Equilibrium Processes (ISSP-14) was held at the Montanuniversität, Leoben, Austria, on 25-30 July 2010, co-chaired by Profs. Helmut Antrekowitsch and Heinz Gamsjäger. As part of the scientific program, a workshop on chemical modeling including kinetic effects was held over several days. The Symposium attracted scientists from all continents, save South America. Speakers at the Symposium covered an astonishing range of topics concerned with solubility phenomena in their widest sense. Oral presentations spanned the fields of analytical chemistry, physical chemistry, and modeling of aqueous and nonaqueous solutions, supersaturation, environmental chemistry, ecotoxicology, ionic liquids, solid solutions and phase relationships, and metallurgy. Aside from oral presentations, two lively poster sessions attracted some 43 presentations, also ranging across the above-mentioned topics.&amp;lt;br /&amp;gt;&amp;lt;br /&amp;gt;This volume of &amp;lt;I&amp;gt;Pure and Applied Chemistry&amp;lt;/i&amp;gt; presents papers based on eight of the key lectures and one of the invited oral presentations at the Symposium. Subjects include the applications, experimental data and theory of the chemistry of salts in aqueous solutions, computational thermochemistry, impurities and calcium sulfate hydrates in hydrometallurgical processes, kinetics of diffusive phase transformations, environmental remediation, free energy minimization methods, supersaturation and phase transformations, and melt corrosion of refractories. These papers offer a glimpse of current research activity in diverse practical and applied aspects of solution chemistry and provide an up-to-date commentary on them.&amp;lt;br /&amp;gt;&amp;lt;br /&amp;gt;The Organizing Committee is delighted that these papers have been gathered together in one volume and thanks the International Union of Pure and Applied Chemistry for its continuing support in bringing the above-mentioned topics to the attention of the wider scientific community.&amp;lt;br /&amp;gt;&amp;lt;br /&amp;gt;&amp;lt;b&amp;gt;Peter A. Williams&amp;lt;/b&amp;gt;&amp;lt;br /&amp;gt;Conference Editor&amp;lt;br /&amp;gt;&amp;lt;br /&amp;gt;&amp;lt;/div&amp;gt;

Simultaneously Controlled Directionality and Valency on a Water-Soluble Gold Nanoparticle Precursor for Aqueous-Phase Anisotropic Self-Assembly

The anisotropic interaction of gold nanoparticles (AuNP's) into a highly accurate, scalable complex structure not only would aid practical nanoscale assembly but also would increase their utility in many applications, including electronics, optics, and biosensing. Particularly for biological purposes, here we demonstrate an aqueous-phase serial solid-phase monofunctionalization approach to synthesize water-soluble AuNP linkers that contain distinctive single or double diametric functionalities in a site-specific way. Using a mild, rapid, effective single-phase 1:1 ligand replacement reaction between mixed-ligand-protected AuNP precursors and ligand-group-attached silica gels, we successfully synthesized (1) two types of monofunctionalized (monof-) carboxyl- or amino-AuNP's with enhanced yield and accuracy and (2) heterobifunctionalized (bif-) AuNP's with one carboxyl and one amine end group at a discrete angle (∼160°). The controlled coupling chemistry in aqueous solution allowed the covalent bond-directed assembly of intentionally designed 1D dimers with monof-AuNP's and 2D rings with heterobif-AuNP's, confirming the highly functional as well as directional selectivity of the functionalized NPs. This study thus represents an important step toward active control over the design and assembly of bottom-up nanostructures with increased complexity and biocompatibility.

Adsorption of tetracycline on single‐walled and multi‐walled carbon nanotubes as affected by aqueous solution chemistry

Carbon nanotubes have shown great potential as effective adsorbents for hydrophobic organic contaminants in water treatment. The present study investigated the influence of aqueous solution chemistry on the adsorption of tetracycline to carbon nanotubes. Specifically, the effects of ionic strength (NaCl and CaCl(2) ) and presence of Cu(2+) ion (7.5 mg/L) or dissolved soil or coal humic acids (50 mg/L) on adsorption of tetracycline to single-walled carbon nanotubes (SWNT), multi-walled carbon nanotubes (MWNT), and nonporous pure graphite as a model of the graphite surface were systematically estimated. The presence of humic acids suppressed tetracycline adsorption on graphite and MWNT prominently, with stronger effects observed on graphite, but only slightly affected tetracycline adsorption on SWNT. The relatively large humic acid components could not readily access the small interstitial spaces of SWNT and thus were less competitive with tetracycline adsorption. The presence of Cu(2+) ion increased tetracycline adsorption to both SWNT and MWNT through the mechanism of cation bridging, with much larger effects observed on MWNT. This was probably because when compared with the Cu(2+) ions complexed on the surface of SWNT, those on the surface of MWNT having larger mesoporous interstices were more accessible to the relatively bulky tetracycline molecule. Increasing the ionic strength from 10 mM to 100 mM decreased tetracycline adsorption on both SWNT and MWNT, which was attributed to electronic shielding of the negatively charged surface sites. These results show that aqueous solution chemistry is important to tetracycline adsorption on carbon nanotubes.

Solution chemistry effects on cracking and damage evolution during chemical-mechanical planarization

We describe progress in understanding the effect of simulated chemical-mechanical planarization (CMP) slurry chemistry on the evolution of defects and formation of damage that occurs during CMP processing. Specifically, we demonstrate the significant effect of aqueous solution chemistry on accelerating crack growth in porous methylsilsesquioxane (MSSQ) films. In addition, we show that the same aqueous solutions can diffuse rapidly into the highly hydrophobic nanoporous MSSQ films containing interconnected porosity. Such diffusion has deleterious effects on both dielectric properties and the acceleration of defect growth rates. Crack propagation rates were measured in several CMP solutions, and the resulting crack growth behavior was used to qualitatively predict the extent of damage during CMP. These predictions are compared with damage formed during actual CMP processes in identical chemistries. We discuss the effects of both the high and low crack growth rate regimes, including the presence of a crack growth threshold, on the predicted CMP damage. Finally, implications for improved CMP processing were considered.

Radiation Chemistry of N-Hexane Aqueous Solutions as Studied by Chromatographic Analysis of Final Products

Radiolysis of dilute oxygen-free hexane aqueous solutions give dodecanes isomers analyzed by capillary gas chromatography. The relative yields for radicals which react by radical-radical recombination reactions are 39 %, 32 % and 29 % for primary hexyl radical, secondary-2 hexyl radical and secondary-3 hexyl radical respectively. This distribution is changed with the N2O saturation before the radiolysis to 22 % 42 % and 37 %. If the first distribution is statistic, the increase of OH available to attack the solute gives the distribution existing in pure alkane radiolysis.

Novel molecular detection of Cu2+ in aqueous solution and related chemistry

Rationally-designed sensors for the detection and measurement of Cu2+ continue to receive significant attention. Cu2+ is an essential d-block metal ion in human health, but is also harmful to biological systems in excessive amounts. Alterations in Cu2+ cellular homeostasis are connected to Wilson's Disease and Alzheimer's Disease. Accordingly, the development of Cu2+-specific molecular probes have been of considerable interest in the biological and analytical chemical sciences. While there are various reports that explore Cu2+-selective probes, very few reports involved studies in pure aqueous solution. Herein, we report: I. the synthesis and characterization of the fluorescent dinuclear chiral compound [Zn2(slys)2Cl2] and also [Zn2(slys)2(NO3)2] [H2slys = 6-amino-2-{(2-hydroxybenzylidene) amino}hexanoic acid] II. Rigid indacene-like “BODIPY”-type species are commonly used as fluorescent probes, dyes, and pigments in biological imaging and as molecular sensing components. We are investigating how novel multiple 2- / 3-thienyl substitution imparts UV-vis absorption / emission differences. We have synthesized the isomeric probes: 3-(thienyl)-4,4-di(thienyl)-8-(thienyl)-4-bora-3a,4a-diaza-s-indacenes. I. [Zn2(slys)2Cl2] and also [Zn2(slys)2(NO3)2] [H2slys = 6-amino-2-{(2-hydroxybenzylidene) amino}hexanoic acid] were prepared by a one-pot in situ process. They are isolated with solvents of 1·(CH3OH)2·(H2O)3, and 2·(H2O)3, respectively. II. We have also prepared 3-(thienyl)-4,4-di(thienyl)-8-(thienyl)-4-bora-3a,4a-diaza-s-indacenes with an interest in systematically discerning Mn+ recognition capabilities at a novel tri-thienyl receptor site. The thienyls mark a step away from the commonly used pyridyl groups or crowns for metal cation recognition. I. [Zn2(slys)2X2] engages in selective Cu2+ detection (over other metal ions, e.g.: Hg2+, Cd2+ and Pb2+) through direct displacement in water. Zinc, another metal of neurodegenerative interest is freed (displaced) in the transformation. II. The boron-dipyrrin derivatives 3-(thienyl)-4,4-di(thienyl)-8-(thienyl)-4-bora-3a,4a-diaza-s-indacenes form pink solutions and were treated with dilute concentrations of various Mn+ species in demonstrating selective differences for Cu2+ and Hg2+. Generally, Cu2+ gives fluorescence increases while Hg2+ gives fluorescence decreases; but, for the systems shown herein, there are a variety of optical changes via different mechanisms at low Cu2+ concentration (in various solvents). In particular, the treatment of 3-(2-thienyl)-4,4-di(2-thienyl)-8-(3-thienyl)-4-bora-3a,4a-diaza-s-indacene with Cu2+ gives a clear solution only and this probe may be a promising component in optical sensing.

Tuning of the Thermochemical and Kinetic Properties of Ascorbate by Its Local Environment: Solution Chemistry and Biochemical Implications

Ascorbate (vitamin C) is a ubiquitous biological cofactor. While its aqueous solution chemistry has long been studied, many in vivo reactions of ascorbate occur in enzyme active sites or at membrane interfaces, which have varying local environments. This report shows that the rate and driving force of oxidations of two ascorbate derivatives by the TEMPO radical (2,2',6,6'-tetramethylpiperidin-1-oxyl) in acetonitrile are very sensitive to the presence of various additives. These reactions proceed by the transfer of a proton and an electron (a hydrogen atom), as is typical of biological ascorbate reactions. The measured rate and equilibrium constants vary substantially with added water or other polar solutes in acetonitrile solutions, indicating large shifts in the reducing power of ascorbate. The correlation of rate and equilibrium constants indicates that this effect has a thermochemical origin rather than being a purely kinetic effect. This contrasts with previous examples of solvent effects on hydrogen atom transfer reactions. Potential biological implications of this apparently unique effect are discussed.