Water Adduct Research Articles

An unexpected deamination reaction after hydrolysis of the pyrimidine (6-4) pyrimidone photoproduct.

Pyrimidine (6-4) pyrimidone photoproduct (6-4PP), a common DNA photolesion formed under solar irradiation, was indicated to hydrolyze under strong basic conditions, breaking the N3–C4 bond at the 5′-thymine. The reanalysis of this reaction revealed that the resulting water adduct may not be stable as previously proposed; it readily undergoes an esterification reaction induced by the 5-OH group at 6-4PP to form a five-membered ring, eliminating a molecule of ammonia.

Swain-Scott Relationships for Nucleophile Addition to Ring-Substituted Phenonium Ions.

The products of the reactions of 2-(4-methoxyphenyl)ethyl tosylate (MeO-1-Ts) and 2-(4-methyphenyl)ethyl tosylate (Me-1-Ts) with nucleophilic anions were determined for reactions in 50/50 (v/v) trifluoroethanol/water at 25°C. In many cases the nucleophile selectivity kNu/ks (M-1) for reactions of nucleophile and solvent, calculated from the ratio of product yields, depends upon [Nu-]. This demonstrates the existence of competing reaction pathways, which show different selectivities for reactions with nucleophiles. A carbon-13 NMR analysis of the products of the reactions of substrate enriched with carbon-13 at the α-carbon, X-1-[α-13C]Ts, (X = -OCH3, -Me) with nucleophilic anions in 50/50 (v/v) trifluoroethanol/water at 25°C shows the formation of X-1-[β-13C]OH, X-1-[β-13C]OCH2CF3 and X-1-[β-13C]Nu (Nu = Br, Cl, CH3CO2, Cl2CHCO2) from the trapping of symmetrical 4-substituted phenonium ion reaction intermediates X-2+ . The observation of excess label in the α-position, [α-13C]/[β-13C] > 1.0, for both the water and nucleophile adducts, shows that water and anionic nucleophiles also react by direct substitution at X-1-[α-13C]Ts. The ratios of product yields, [α-13C]/[β-13C], and observed nucleophile selectivity (kNu/ks)obs were used to dissect the contribution of direct nucleophile addition at Me-1-Ts and trapping of X-2+ to the product yields. The product yields from partitioning of the intermediate gave the nucleophile selectivity kNu/ks (M-1) for X-2+ . Swain-Scott plots of log (kNu/ks) are correlated by slopes of s = 0.78 and s = 0.73 for reactions of MeO-2+ and Me-2+ , respectively. This shows that the sensitivity of bimolecular substitution at X-2+ to changes in nucleophile reactivity is smaller than for nucleophilic substitution at the methyl iodide. Evidence is presented that nucleophile addition to X-2+ proceeds through an "exploded" transition state.

Direct spectroscopic observation of closed-shell singlet, open-shell singlet, and triplet p-biphenylyloxenium ion.

The photophysics and photochemistry of p-biphenylyl hydroxylamine hydrochloride was studied using laser flash photolysis ranging from the femtosecond to the microsecond time scale. The singlet excited state of this photoprecursor is formed within 350 fs and partitions into three different transients that are assigned to the p-biphenyloxy radical, the open-shell singlet p-biphenylyloxenium ion, and the triplet p-biphenylyloxenium ion, having lifetimes of 40 μs, 45 ps, and 1.6 ns, respectively, in CH3CN. The open-shell singlet p-biphenylyloxenium ion predominantly undergoes internal conversion to produce the closed-shell singlet p-biphenylyloxenium ion, which has a lifetime of 5-20 ns. The longer-lived radical is unambiguously assigned by nanosecond time-resolved resonance Raman (ns-TR(3)) spectroscopy, and the assignment of the short-lived singlet and triplet oxenium ion transient absorptions are supported by matching time-dependent density functional theory (TD-DFT) predictions of the absorptions of these species, as well as by product studies that implicate the intermediacy of charged electrophilic intermediates. Product studies from photolysis give p-biphenylol as the major product and a chloride adduct as the major product when NaCl is added as a trap. Thermolysis studies give p-biphenylol as a major product, as well as water, ammonium, and chloro adducts. These studies provide a rare direct look at a discrete oxenium ion intermediate and the first detection of open-shell singlet and triplet configurations of an oxenium ion, as well as providing an intriguing example of the importance of excited state dynamics in governing the electronic state population of reactive intermediates.

Molecular Salt Effects in the Gas Phase: Tuning the Kinetic Basicity of [HCCLiCl]− and [HCCMgCl2]− by LiCl and MgCl2

AbstractA combination of gas‐phase ion–molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HCCLiCl]− reacts with water more rapidly than [HCCMgCl2]−, consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HCCLiCl]− or [HCCMgCl2]− enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HCCMgCl2]− enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics.

Molecular salt effects in the gas phase: tuning the kinetic basicity of [HCCLiCl]⁻ and [HCCMgCl₂]⁻ by LiCl and MgCl₂.

A combination of gas-phase ion-molecule reaction experiments and theoretical kinetic modeling is used to examine how a salt can influence the kinetic basicity of organometallates reacting with water. [HC≡CLiCl](-) reacts with water more rapidly than [HC≡CMgCl2](-), consistent with the higher reactivity of organolithium versus organomagnesium reagents. Addition of LiCl to [HC≡CLiCl](-) or [HC≡CMgCl2](-) enhances their reactivity towards water by a factor of about 2, while addition of MgCl2 to [HC≡CMgCl2](-) enhances its reactivity by a factor of about 4. Ab initio calculations coupled with master equation/RRKM theory kinetic modeling show that these reactions proceed via a mechanism involving formation of a water adduct followed by rearrangement, proton transfer, and acetylene elimination as either discrete or concerted steps. Both the energy and entropy requirements for these elementary steps need to be considered in order to explain the observed kinetics.

Analysis of three private hydraulic systems operated in Apamea during the Byzantine period

In this paper, three hydraulic systems (two nymphaea and a private bath), excavated in three houses located in the southeast of the city of Apamea and operated during the Byzantine period, are described from an archaeological point of view and using fluid mechanics. Information (mostly unpublished) about the architecture of these systems, their construction material, their construction date and their operation (water flow rate …) is provided.The cisterns of these three hydraulic systems were previously understood as being dedicated to collect rainwater. It is clear today that these cisterns belonged to larger systems and that they were not meant to simply collect rainwater.There was probably no precise period for building these hydraulic systems. They spread gradually via major projects scattered over time, as they belong to the embellishment of the Apamean houses during the Byzantine period.The similarities and differences between these systems are discussed. This comparison highlights the probable existence of Roman good practice rules in the construction of nymphaea.The analysis of the data presented in this work stresses highly probable evidence about connections between an operative aqueduct and the hydraulic systems analyzed in this work. These are valuable results, as no documented information about water adduction is available for the southern half of the city of Apamea, except for a distribution table.

Fluorination Effects on the Shapes of Complexes of Water with Ethers: A Rotational Study of Trifluoroanisole–Water

The rotational spectra of five isotopologues of the 1:1 complex trifluoroanisole-water have been investigated with pulsed jet Fourier transform microwave spectroscopy. The triple fluorination of the methyl group greatly affects the features of the rotational spectrum of the complex with water, with respect to those of the related complex anisole-water. The shape, the internal dynamics, and the isotopic effects turned out to be quite different from those of the anisole-water adduct ( Giuliano , B. M. ; Caminati , W. Angew. Chem., Int. Ed. 2005 , 44 , 603 - 606 ). However, as in anisole-water, water has the double role as a proton donor and proton acceptor, and it is linked to trifluoroanisole through two, O-H···O and C-H···O hydrogen bonds.

Computational studies of the unusual water adduct [Cp2TiMe(OH2)](+): the roles of the solvent and the counterion.

The recently reported cationic titanocene complex [Cp2TiMe(OH2)](+) was subjected to detailed computational studies using density functional theory (DFT). The calculated NMR spectra revealed the importance of including the anion and the solvent (CD2Cl2) in order to calculate spectra which were in good agreement with the experimental data. Specifically, two organic solvent molecules were required to coordinate to the two hydrogens of the bound OH2 in order to achieve such agreement. Further elaboration of the role of the solvent led to Bader's QTAIM and natural bond order calculations. The zirconocene complex [Cp2ZrMe(OH2)](+) was simulated for comparison.

Lone‐Pair⋅⋅⋅π Interaction: A Rotational Study of the Chlorotrifluoroethylene–Water Adduct

Lone‐Pair⋅⋅⋅π Interaction: A Rotational Study of the Chlorotrifluoroethylene–Water Adduct

A Molecular Dynamics Simulation-Based Interpretation of Nuclear Magnetic Resonance Multidimensional Heteronuclear Spectra of α-Synuclein·Dopamine Adducts

Multidimensional heteronuclear nuclear magnetic resonance (NMR) spectroscopy provides valuable structural information about adducts between naturally unfolded proteins and their ligands. These are often highly pharmacologically relevant. Unfortunately, the determination of the contributions to observed chemical shifts changes upon ligand binding is complicated. Here we present a tool that uses molecular dynamics (MD) trajectories to help interpret two-dimensional (2D) NMR data. We apply this tool to the naturally unfolded protein human α-synuclein interacting with dopamine, an inhibitor of fibril formation, and with its oxidation products in water solutions. By coupling 2D NMR experiments with MD simulations of the adducts in explicit water, the tool confirms with experimental data that the ligands bind preferentially to (125)YEMPS(129) residues in the C-terminal region and to a few residues of the so-called NAC region consistently. It also suggests that the ligands might cause conformational rearrangements of distal residues located at the N-terminus. Hence, the performed analysis provides a rationale for the observed changes in chemical shifts in terms of direct contacts with the ligand and conformational changes in the protein.

Influence of Chlorine Substitution on the Hydrolytic Stability of Biaryl Ether Nucleoside Adducts Produced by Phenolic Toxins

A kinetic study is reported for the acid-catalyzed hydrolysis of oxygen (O)-linked biaryl ether 8-2'-deoxyguanosine (dG) adducts produced by phenolic toxins following metabolism into phenoxyl radical intermediates. Strikingly, the reaction rate of hydrolysis at pH 1 decreases as electron-withdrawing chlorine (Cl) substituents are added to the phenoxyl ring. The Hammett plot for hydrolysis at pH 1 shows a linear negative slope with ρX = -0.65, implying that increased Cl-substitution diminishes the rate of hydrolysis by lowering N(7) basicity. Spectrophotometric titration provided an N(7)H(+) pKa value of 1.1 for the unsubstituted adduct 8-phenoxy-dG (Ph-O-dG). Model pyridine compounds suggest N(7)H(+) pKa values of 0.92 and 0.37 for 4-Cl-Ph-O-dG and 2,6-dichloro-Ph-O-dG (DCP-O-dG), respectively. Density functional theory (DFT) calculations also highlight the ability of the 8-phenoxy substituent to lower N(7) basicity and predict a preference for N(3)-protonation for highly chlorinated O-linked 8-dG adducts in water. The calculations also provide a rationale for the hydrolytic reactivity of O-linked 8-dG adducts in the gas-phase, as determined using electrospray mass spectrometry (ESI-MS). The inclusion of our data now establishes that the order of hydrolytic reactivity at neutral pH for bulky 8-dG adducts is N-linked > C-linked > O-linked, which correlates with their relative ease of N(7)-protonation.

Direct Detection and Reactivity of the Short-Lived Phenyloxenium Ion

Photolysis of protonated phenylhydroxylamine was studied using product analysis, trapping experiments, and laser flash photolysis experiments (UV-vis and TR(3) detection) ranging from the femtosecond to the microsecond time scale. We find that the excited state of the photoprecursor is followed by two species: a longer-lived transient (150 ns) that we assign to the phenoxy radical and a shorter-lived (3-20 ns) transient that we assign to the singlet phenyloxenium ion. Product studies from photolysis of this precursor show rearranged protonated o-/p-aminophenols and solvent water adducts (catechol, hydroquinone) and ammonium ion. The former products can be largely ascribed to radical recombination or ion recombination, while the latter are ascribed to solvent water addition to the phenyloxenium ion. The phenyloxenium ion is apparently too short-lived under these conditions to be trapped by external nucleophiles other than solvent, giving only trace amounts of o-/p-chloro adducts upon addition of chloride trap. Product studies upon thermolysis of this precursor give the same products as those generated from photolysis, with the difference being that the ortho adducts (o-aminophenol, hydroquinone) are formed in a higher ratio in comparison to the photolysis products.

Analysis of alcohol polyethoxylates and polyethylene glycols in marine sediments

Alcohol polyethoxylates (AEOs) are the most commercially important type of nonionic surfactants, used in a wide variety of products such as household cleaning detergents, industrial cleaners, textiles, adjuvants in pesticides, wetting and dispersing agents, and emulsifiers. Our main objective in this work was to develop a methodology for the extraction, isolation and analysis of these compounds and their main degradation products and precursors (polyethylene glycols, PEGs) in solid environmental matrices. First, analytes were extracted by pressurized liquid extraction (PLE) using methanol at 120°C as solvent and 3 cycles (5min per cycle). Clean-up and concentration of the extracts were carried out by solid-phase extraction (SPE), using Oasis HLB cartridges and a mixture dicloromethane/methanol 1:1 as eluting solvent. Recovery percentages were usually between 54% and 106% for most compounds. Identification and quantification of analytes were performed using a liquid chromatography–mass spectrometry (LC–MS) system equipped with an electrospray interface (ESI) operating in positive ionization mode. Water content, cone voltage and adduct formation were optimized to this end. Limits of detection were usually below 50ngg−1, being higher for some shorter ethoxymers (>100ngg−1) because of poor ionization. Finally, the protocol proposed here was applied to the determination of the concentration of AEOs and PEGs in selected surface sediment samples collected in Mar Menor Lagoon (Murcia, Spain). In this sense, this paper presents some of the first data relative to the occurrence of these analytes in coastal sediments, showing relatively high concentrations of PEGs (up to 9000ngg−1) compared to those measured for AEOs (<100ngg−1).

The nature of the styrylindolium dye: transformations among its monomer, aggregates and water adducts

The optical properties of styrylindolium dyes are strongly influenced by the external environment. After a detailed investigation by electronic absorption spectroscopy, we found that five states of 2-methoxylstyryl-indolium dye viz. monomer, D-aggregate, H-aggregate, J-aggregate and water adducts can be observed under different conditions. The spectroscopic studies revealed that the conversion rate of the dye among its monomer and the other aggregates is slow due to the steric hindrance of the 3,3-dimethyls. Meanwhile, it could form water adducts by the reaction of the water residue in solvent with the charged electron-deficient CN double bond of the dye. The formation of water adducts is also an important factor that influences the optical properties of the dye because the water addition reaction breaks the dye's π-conjugate. Generally, the dye exists mainly in the monomeric form in freshly prepared solutions. A small portion of the D-aggregate, H-aggregate and J-aggregate can be observed in some cases. In equilibrium solutions, however, significant changes are observed in most solvents with different polarities. The J-aggregate is an unstable state which is irreversibly converted to other species. The monomer converts reversibly among the D-aggregate, H-aggregate and water adducts in the equilibrium state. At the same time, the water adducts are sensitive to the external environment and their content can be modulated by temperature and pH conditions. The dye's prominent optical signal changes arising from pH- and thermal dependence of water addition or the disassociation of the D-aggregate led to potential applications in the field of thermoresponsive probes under given conditions.

Synthesis and properties of differently charged chemiluminescent acridinium ester labels

Chemiluminescent acridinium dimethylphenyl esters containing N-sulfopropyl groups in the acridinium ring are highly sensitive, hydrophilic labels that are used in automated immunoassays for clinical diagnostics. Light emission from these labels is triggered with alkaline peroxide in the presence of a cationic surfactant. At physiological pH, N-sulfopropyl acridinium esters exist as water adducts that are commonly referred to as pseudobases. Pseudobase formation, which results from addition of water to the zwitterionic N-sulfopropyl acridinium ring, neutralizes the positive charge on the acridinium nitrogen and imparts a net negative charge to the label due to the sulfonate moiety. As a consequence, N-sulfopropyl acridinium ester conjugates of small molecule haptens as well as large molecules such as proteins gain negative charges at neutral pH. In the current study, we describe the synthesis and properties of two new hydrophilic acridinium dimethylphenyl ester labels where the net charge in the labels was altered. In one label, the structure of the hydrophilic N-alkyl group attached to the acridinium ring was changed so that the pseudobase of the label contains no net charge. In the second acridinium ester, two additional negative charges in the form of sulfopropyl groups were added to the acridinium ring to make this label's pseudobase strongly anionic. Chemiluminescence measurements of these labels, as well as their conjugates of an antibody with a neutral pI, indicate that acridinium ester charge while having a modest effect on emission kinetics has little influence on light output. However, our results demonstrate that acridinium ester charge can affect protein pI, apparent chemiluminescence stability and non-specific binding of protein conjugates to microparticles. These results emphasize the need for careful consideration of acridinium ester charge in order to optimize reagent stability and performance in immunoassays. In the current study, we observed that for a neutral protein, an acridinium ester with a hydrophilic but charge-neutral N-alkyl group afforded faster light emission, lower non-specific binding and better chemiluminescence stability than an analogous label with an anionic N-alkyl group.

Water Network Protection from Intentional Contamination by Sectorization

Each single phase of a water supply network, from water adduction to distribution to end-users, is exposed to many diverse potential sources of intentional contamination (or malicious attacks). One of the most dangerous threats is a backflow attack that occurs when a pump system, easily available on the market, is utilized to overcome the pressure gradient of network pipes. In this work, a simple backflow attack with cyanide being introduced into a real-water system is modeled and the most dangerous introduction points for a contaminant incident are defined. Moreover, the network vulnerability has been analyzed by computing the lethal dose of cyanide ingested by users and the total length of the contaminated water system. Eventually the effects of network partitioning and district isolation to protect water supply systems have been investigated. The results show how district closing - by network sectorization techniques used to improve leakage search and reduction - can significantly decrease contaminant diffusion and protect part of the users from cyanide uptake. Network sectorization can also reduce the risk of simple malicious attacks because several introduction points are necessary to have a massive negative impact on the network. Simulation results also show that in some cases water network partitioning may worsen water network protection and further studies are necessary to design water districts for network security and safety.

Phototransformation of anthraquinone-2-sulphonate in aqueous solution

Anthraquinone-2-sulphonate (AQ2S) is a triplet sensitiser that has recently been used to model the photoreactivity of chromophoric dissolved organic matter (CDOM). We show that the photolysis quantum yield of AQ2S under UVA irradiation varies from (3.4 ± 0.2) × 10(-3) at μM AQ2S levels to (1.8 ± 0.1) × 10(-2) at 3 mM AQ2S (μ±σ). This trend is consistent with a combination of direct phototransformation and transformation sensitised by a photogenerated reactive species. In both cases a transient water adduct of AQ2S would be involved. Depending on the initial quinone concentration, the adduct could undergo transformation, give back ground-state AQ2S or react with it. The prevalence of the latter process at high AQ2S concentration would account for the increased values of the photolysis quantum yield. When using AQ2S as a triplet sensitiser, one should not exceed an initial concentration of 0.1 mM. Under the latter conditions the sensitised process is negligible compared to the direct photolysis, providing a simpler system to be studied, and the photolysis quantum yield is independent of the initial AQ2S concentration. This paper also shows, by adoption of density functional theory calculations, that the triplet state of AQ2S has most of the spin density localised on C[double bond, length as m-dash]O, analogous to other photoactive quinones, which accounts for the oxidising character of the triplet state that tends to be reduced to a semiquinone radical.

Reactions of Doubly Ionized Benzene with Nitrogen and Water: A Nitrogen‐Mediated Entry into Superacid Chemistry

Even in the highly diluted gas phase, rather than electron transfer the benzene dication C(6)H(6)(2+) undergoes association with dinitrogen to form a transient C(6)H(6)N(2)(2+) dication which is best described as a ring-protonated phenyl diazonium ion. Isotopic labeling studies, photoionization experiments using synchrotron radiation, and quantum chemical computations fully support the formation of protonated diazonium, which is in turn a prototype species of superacidic chemistry in solution. Additionally, reactions of C(6)H(6)(2+) with background water involve the transient formation of diprotonated phenol and, among other things, afford a long-lived C(6)H(6)OH(2)(2+) dication, which is attributed to the hydration product of Hogeveen's elusive pyramidal structure of C(6)H(6)(2+), as the global minimum of doubly ionized benzene. Nitrogen is essential for the formation of the C(6)H(6)OH(2)(2+) dication in that it mediates the formation of the water adduct, while the bimolecular encounter of the C(6)H(6)(2+) dication with water only leads to (dissociative) electron transfer.

Bifunctional Water Activation for Catalytic Hydration of Organonitriles

Treatment of [Rh(COD)(μ-Cl)]2 with excess tBuOK and subsequent addition of 2 equiv of PIN·HBr in THF afforded [Rh(COD)(κC2-PIN)Br] (1) (PIN = 1-isopropyl-3-(5,7-dimethyl-1,8-naphthyrid-2-yl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene). The X-ray structure of 1 confirms ligand coordination to “Rh(COD)Br” through the carbene carbon featuring an unbound naphthyridine. Compound 1 is shown to be an excellent catalyst for the hydration of a wide variety of organonitriles at ambient temperature, providing the corresponding organoamides. In general, smaller substrates gave higher yields compared with sterically bulky nitriles. A turnover frequency of 20 000 h–1 was achieved for the acrylonitrile. A similar Rh(I) catalyst without the naphthyridine appendage turned out to be inactive. DFT studies are undertaken to gain insight on the hydration mechanism. A 1:1 catalyst–water adduct was identified, which indicates that the naphthyridine group steers the catalytically relevant water molecule to the active metal site...

Linear Trinuclear Copper(II) Complexes Derived from the Nucleophilic Addition Products of Dicyanonitrosomethanide [C(CN)2(NO)]–: Syntheses, Structures, and Magnetic Properties

Two novel trinuclear CuII complexes have been synthesised from the nucleophilic addition derivatives of the small cyano anion, dicyanonitrosomethanide (dcnm). The reaction of CuII with the water adduct ligand, carbamoylcyanonitrosomethanide (ccnm) and teaH3 (triethanolamine) in a basic MeOH/MeCN solution results in the formation of [Cu3(acnm)2(teaH2)2]·2MeOH (1) (acnm = amidocarbonyl(cyano)nitrosomethanide and teaH2– = singly deprotonated triethanolamine). The reaction of CuII with dicyanonitrosomethanide (dcnm) and m-xylenediamine in a basic MeOH/MeCN solution results in the formation of [Cu3(cimm)2(a3acnm)2]·6MeCN (2) (cimm = cyano(imido(methoxy)methyl)nitrosomethanide and a3acnm = {amino(3-aminomethylphenyl)methylimino}methyl(cyanonitrosomethanide)). Both complexes display linear trinuclear CuII metallic cores. Solid state DC magnetic susceptibility studies were performed on 1 and 2. Compound 1 revealed very strong antiferromagnetic interactions between central and terminal Cu atoms, while compound 2 displayed ferromagnetic interactions because of the orthogonal relationship of the terminal and the central ‘magnetic’ orbitals, which contrasts with these orbitals being coplanar in 1 thus providing strong superexchange pathways involving Cu-N-O-Cu moieties.