Rhodium-Catalyzed ortho-Bromination of O-Phenyl Carbamates Accelerated by a Secondary Amide-Pendant Cyclopentadienyl Ligand

It has been established that a newly developed cyclopentadienyl rhodium(III) [Cp^ARh^III] complex, bearing an acidic secondary amide moiety on the Cp ring, is able to catalyze the ortho-bromination of O-phenyl carbamates with N-bromosuccinimide (NBS) at room temperature. The presence of the acidic secondary amide moiety on the Cp^A ligand accelerates the bromination by the hydrogen bond between the acidic NH group of the Cp^A ligand and the carbonyl group of NBS.     

Electrospray multistage mass spectrometry in the negative ion mode for the unambiguous molecular and structural characterization of acidic hydrolysates from 4‐O‐methylglucuronoxylan generated by endoxylanases

A rapid analytical methodology is proposed to answer the two questions about the molecular and structural features of the acidic xylo‐oligosaccharides (XOSs) formed upon the enzymatic hydrolysis of 4‐O‐methylglucuronoxylan. The shortest acidic XOSs carrying a methylglucuronic acid moiety and the possible distribution of larger products (molecular feature) are instantly found by electrospray ionization mass spectrometry (ESI‐MS) in the negative ion mode, which filters the unwanted neutral XOS. The acidic moiety is then unambiguously localized along the xylose backbone (structural feature) by ESI‐MSⁿ in the negative ion mode via the selection/activation/dissociation of the product ions formed upon the one‐way and stepwise glycosidic bond cleavage at the reducing end. Using the shortest acidic XOS with a known shape generated by glycoside hydrolase family (GH) 10 and GH11 xylanases as a proof of principle, pairs of diagnostic ions are proposed to instantly interpret the MSⁿ fingerprints and localize the acidic moiety along the xylose chain of the activated ion. The original structure of the acidic XOS is then reconstructed by adding as many xylose units at the reducing end as MSⁿ steps. Relying on pairs of ions, the methodology is robust enough to highlight the presence of isomeric products. Mass spectra reported in the present article will be conveniently used as reference data for the forthcoming analysis of acidic XOS generated by new classes of enzymes using this multistage mass spectrometry methodology.     

Effects of acidic peptide size and sequence on trivalent praseodymium adduction and electron transfer dissociation mass spectrometry

Using the lanthanide ion praseodymium, Pr(III), metallated ion formation and electron transfer dissociation (ETD) were studied for 25 biological and model acidic peptides. For chain lengths of seven or more residues, even highly acidic peptides that can be difficult to protonate by electrospray ionization will metallate and undergo abundant ETD fragmentation. Peptides composed of predominantly acidic residues form only the deprotonated ion, [M + Pr ‐ H]²⁺; this ion yields near complete ETD sequence coverage for larger peptides. Peptides with a mixture of acidic and neutral residues generate [M + Pr]³⁺, which cleaves between every residue for many peptides. Acidic peptides that contain at least one residue with a basic side chain also produce the protonated ion, [M + Pr + H]⁴⁺; this ion undergoes the most extensive sequence coverage by ETD. Primarily metallated and non‐metallated c‐ and z‐ions form for all peptides investigated. Metal adducted product ions are only present when at least half of the peptide sequence can be incorporated into the ion; this suggests that the metal ion simultaneously attaches to more than one acidic site. The only site consistently lacking dissociation is at the N‐terminal side of a proline residue. Increasing peptide chain length generates more backbone cleavage for metal‐peptide complexes with the same charge state. For acidic peptides with the same length, increasing the precursor ion charge state from 2+ to 3+ also leads to more cleavage. The results of this study indicate that highly acidic peptides can be sequenced by ETD of complexes formed with Pr(III). Copyright © 2017 John Wiley & Sons, Ltd.     

Ionic‐Liquid‐Based Acidic Aqueous Biphasic Systems for Simultaneous Leaching and Extraction of Metallic Ions

The first instance of an acidic aqueous biphasic system (AcABS) based on tributyltetradecyl phosphonium chloride ([P₄₄₄₁₄][Cl]) and an acid is here reported. This AcABS exhibits pronounced thermomorphic behavior and is shown to be applicable to the extraction of metal ions from concentrated acidic solutions. Metal ions such as cobalt(II), iron(III), platinum(IV) and nickel(II) are found to partition preferentially to one of the phases of the acidic aqueous biphasic system and it is here shown that it successfully allows the difficult separation of Co^II from Ni^II, here studied at 24 and 50 °C.     

Selective fluorescence quenching of biologically important acidic and non-acidic indoles by trivalent lanthanide ions and analysis of mixtures by a fluorimetric quenching method

The effects of several lanthanide(II)(Ln³⁺)ions(Dy³⁺,Er³⁺,Eu³⁺,Nd³⁺,Yb³⁺) on the room-temperature fluorescence spectra of 2-indolecarboxylic acid, 5-indolecarboxylic acid, 5-methoxy-2-indolecarboxylic acid and 3-indoleacetic acid were investigated. It was found that the fluorescence quenching by Ln³⁺ ions is much more efficient for the acidic compounds than for non-acidic indoles. Stern-Volmer relationships were obtained for most acidic indoles in the Ln³⁺ concentration range 10^?7–10^?4 M, with quenching constants ranging between 3 × 10³ and 4.6 × 10⁵ l mol^?1. A fluorimetric quenching method was developed for the quantitative analysis of binary mixtures of acidic and non-acidic indoles.     

Spectroscopic studies on the inclusion interaction of p-sulfonatocalix[6]arene with vitamin B6

The formation of the inclusion complex of p-sulfonatocalix[6]arene (SCX6) with different forms of vitamin B₆ (VB₆) was studied by using fluorescence spectroscopy. VB₆ can exist in one of three forms (the acidic form, neutral zwitterionic form and basic form) depending on pH. The fluorescence intensities of acidic and basic forms of VB₆ remarkably decreased in presence of SCX6. SCX6 preferred to form 1:1 inclusion complexes with acidic and basic forms of VB₆ but hardly form inclusion complex with neutral zwitterionic form. According to the nonlinear curve fitting method, the inclusion constant (K) for the formation of inclusion complexes of acidic and basic forms of VB₆ with SCX6 were evaluated to be 1.4?×?10⁴ and 9?×?10³ L/mol, respectively. The binding affinity of SCX6 towards acidic form is attributed to hydrogen bonds and hydrophobic interaction, furthermore, additional electrostatic interaction also plays a crucial role. The possible inclusion mode was given by ¹H NMR technique.     

The Effects of Beating,Web Forming and Sizing on the Surface Energy of <Emphasis Type="Italic">Eucalyptus globulus</Emphasis> Kraft Fibres Evaluated by Inverse Gas Chromatography

In this work attention has been focused on the effects of papermaking beating, web forming and sizing operations on the physical/chemical surface properties of bleached Eucalyptus globulus kraft fibres. Inverse gas chromatography (IGC) was used to determine the dispersive component of surface tension (γ_s^d) as well as the acidic/basic character (according to the Lewis concept) of the solid surfaces (pulp fibres and pulp handsheets). The results have shown that the main effect of beating is to increase the fibre's Lewis acidic character. Web forming caused a strong decrease in γ_s^d and significant increments in the adhesion works of both acidic and basic probes, lowering the ratio between the two. Nevertheless, the surface of handsheets still exhibited a dominant acidic character. The sizing operation did not change the dispersive component of the surface tension significantly but decreased the difference between the adhesion works of the acidic and basic probes, rendering the handsheet surface less Lewis acidic and more Lewis basic. Thus, although internal sizing is expected to strongly influence liquid spreading at the paper surface and liquid penetration of the fibre's network, it is concluded that beating and web forming lead to important changes in the surface energetic properties of the Eucalyptus globulus kraft fibres.     

Potentiometric titration of trace amounts of mercury after a preliminary separation by a reduction method

Isolation and concentration of mercury by reduction of mercury(II) with acidic tin(II) chloride solution and absorption of mercury vapour in acidic permanganate solution is combined with potentiometric titration with dithiooxamide. The simple procedure is applicable to 5–100 ppb mercury in 1-dm³ samples. Recoveries from organomercurials are discussed.     

Continuous time versus reaction events number in stochastic kinetics. A chemical uncertainty principle

The 3609 cm^–1 OH-groups in NaHZSM-5 zeolites are heterogeneous, 5 kinds of OH-groups being found. Benzene is more strongly bonded to more acidic hydroxyls and n-hexane to less acidic hydroxyls.     

Investigation of the reactions of 2-hydrazino-benzimidazoles with β-diketones: Synthesis of 2-(3,5-disubstituted- 1H-pyrazol-1-yl)benzimidazoles

Reaction of 2-hydrazinobenzimidazoles with β-diketones in neutral and acidic media revealed that 2-(3,5-disubstituted-1H-pyrazol-1-yi)benzimidazoles are formed in the former case, whereas hydrazones are obtained in acidic medium. Further the alkylation of > NH of the title compound was investigated. Characterisation of these products have been done by elemental analysis, ir, pmr, ¹⁹F nmr, ¹³C nmr and mass spectral studies.     

Sorption of iodine on Beishan granite: effect of speciation and humic acid

Sorption of iodine on Beishan granite was studied by batch method. Great difference exists in the sorption behaviors of I^? and IO₃^?. Under acidic condition, the sorption of IO₃^? improves dramatically, and IO₃^? could partly convert to I^?. However, the sorption of I^? is close to zero at all studied pH. Humic acid can slight improve the sorption of IO₃^?, but greatly improve the sorption of I^? in acidic condition. The postulated sorption mechanisms of IO₃^? are electrical interaction and followed by reduction.     

Fast Modulation of d-Band Holes Quantity in the Early Reaction Stages for Boosting Acidic Oxygen Evolution

Synthesis of highly active and durable oxygen evolution reaction (OER) catalysts applied in acidic water electrolysis remains a grand challenge. Here, we construct a type of high-loading iridium single atom catalysts with tunable d-band holes character (h-HL−Ir SACs, ∼17.2 wt % Ir) realized in the early OER operation stages. The in situ X-ray absorption spectroscopy reveals that the quantity of the d-band holes of Ir active sites can be fast increased by 0.56 unit from the open circuit to a low working potential of 1.35 V. More remarkably, in situ synchrotron infrared and Raman spectroscopies demonstrate the quick accumulation of *OOH and *OH intermediates over holes-modulated Ir sites in the early reaction voltages, achieving a rapid OER kinetics. As a result, this well-designed h-HL−Ir SACs exhibits superior performance for acidic OER with overpotentials of 216 mV @10 mA cm⁻² and 259 mV @100 mA cm⁻², corresponding to a small Tafel slope of 43 mV dec⁻¹. The activity of catalyst shows no evident attenuation after 60 h operation in acidic environment. This work provides some useful hints for the design of superior acidic OER catalysts.     

Quantitative aspects of electrolysis in electromembrane extractions of acidic and basic analytes

Electrolysis is omnipresent in all electrochemical processes including electromembrane extraction (EME). The effects of electrolysis on quantitative aspects of EME were comprehensively evaluated for a set of acidic (substituted phenols) and basic (basic drugs) analytes. EMEs were carried out across supported liquid membranes formed by 1-ethyl-2-nitrobenzene at standard EME conditions, i.e., acidic analytes were extracted from alkaline into alkaline solutions and basic analytes were extracted from acidic into acidic solutions. Electric potential applied across the EME systems was 50 V and extraction recoveries of analytes as well as pH values of donor and acceptor solutions were determined after each EME. It has been proven that electrolysis plays a more significant role than has ever been thought before in EME. Electrolytically produced H⁺ and OH^– ions had a significant effect on pH values of acceptor solutions and variations of up to 8.5 pH units were obtained at standard EME conditions. pH values of donor solutions were affected only negligibly due to their significantly higher volumes. The observed variations in pH values of acceptor solutions had fatal consequences on quantitative EME results of weak and medium strong acidic/basic analytes. A direct relation was observed between the decrease in extraction recoveries of the analytes, their pK_a values and the acceptor solution pH values. Acceptor solutions consisting of high concentrations of weak bases or acids were thus proposed as suitable EME operational solutions since they efficiently eliminated the electrolytically induced pH variations, offered stable EME performances and were easily compatible with subsequent analytical methods.     

Azolium and acetate ions in DMF: Formation of free N-heterocyclic carbene. A voltammetric analysis

In order to reveal the possible formation of free N-heterocyclic carbene (NHC) in DMF-azolium and acetate solutions, the proton exchange equilibrium between azolium cations and CH₃COO⁻ was investigated (by cyclic voltammetry) by adding CH₃COOH or tetrabutylammonium acetate to DMF solutions of imidazolium or thiazolium salts of different acidity.The voltammetric analysis confirms that the deprotonation of the azolium cation by CH₃COO⁻ (with the formation of free NHC) is significant in the case of the more acidic thiazolium cations, while it is not effective with the less acidic imidazolium ones.Accordingly, the NHC-catalyzed benzoin condensation was carried out in DMF solutions of azolium salts, tetrabutylammonium acetate, and benzaldehyde. Benzoin was isolated only starting from the more acidic thiazolium salts.     

Acidic Media Impedes Tandem Catalysis Reaction Pathways in Electrochemical CO2 Reduction

Electrochemical CO₂ reduction (CO₂R) in acidic media with Cu-based catalysts tends to suffer from lowered selectivity towards multicarbon products. This could in principle be mitigated using tandem catalysis, whereby the *CO coverage on Cu is increased by introducing a CO generating catalyst (e.g. Ag) in close proximity. Although this has seen significant success in neutral/alkaline media, here we report that such a strategy becomes impeded in acidic electrolyte. This was investigated through the co-reduction of ¹³CO₂/¹²CO mixtures using a series of Cu and CuAg catalysts. These experiments provide strong evidence for the occurrence of tandem catalysis in neutral media and its curtailment under acidic conditions. Density functional theory simulations suggest that the presence of H₃O⁺ weakens the *CO binding energy of Cu, preventing effective utilization of tandem-supplied CO. Our findings also provide other unanticipated insights into the tandem catalysis reaction pathway and important design considerations for effective CO₂R in acidic media.     

Separation of metal cations in acidic solution by capillary electrophoresis with direct and indirect UV detection

Methods for the detectionn of metal cations under acidic conditions, near PH 2, in capillary electrophoresis (CE) were investigatged. Conditions for direct UV detection of UV absorbing metal cations such as Cr³⁺, Cu²⁺, Fe³⁺, UO₂²⁺, VO²⁺, and VO²⁺ were established With aqueous HCl or HClO₄ as the electroyte carrier. The speciation of vanadium(IV) and vanadium(V) at PH 2.3 by CE was achieved with direct detection at 185 nm. With the strong absorbance at 185 nm, no complexation was needed to detect the metal cations. An indirect UV detrection scheme for acidic conditions was also investigated. Several background carrier electolytes (BCES) were studied including 4-methylbenzylamince, nicontinamide, pyridazine, guanidine, 3-picoline, and chromium (III) to determine their effectivencess under very acidic conditions. The efect of ioni c surfactants and the nonionic surfactant, Trition X-100, on the peak heights and N Values was also studied.     

The Effects of Exposed Specific Facets and Sulfation on the Surface Acidity of Cu2O Solids

Cuprous oxide microcrystals with {111}, {111}/{100}, and {100} exposed facets were synthesized. ³¹P MAS NMR using trimethylphosphine as the probe molecule was employed to study the acidic properties of samples. It was found that the total acidic density of samples increases evidently after sulfation compared with the pristine cuprous oxide microcrystals. During sulfation, new {100} facets are formed at the expense of {111} facets and lead to the generation of two Lewis acid sites due to the different binding states of SO₄²⁻ on {111} and {100} facets. Moreover, DFT calculation was used to illustrate the binding models of SO₄²⁻ on {111} and {100} facets. Also, a Pechmann condensation reaction was applied to study the acidic catalytic activity of these samples. It was found that the sulfated {111} facet has better activity due to its higher Lewis acid density compared with the sulfated {100} facet.     

Synthesis of Keggin-type polyoxometalate crystals

Vanadium-containing polyoxometalates (POM) were synthesized under acidic conditions and characterized by XRD, FT-IR, ⁵¹V MAS-NMR, EXAFS-XANES and SEM.POM crystals were successfully grown under acidic atmosphere, thus forming a self-assembled structure. This self-organized structure was constituted by cubic crystals having between 20 and 80 μm in size.Both ⁵¹V MAS-NMR, EXAFS-XANES and PM6 calculations suggest that non-covalent interactions, such as hydrogen bonding, or shared vanadium atoms of non-complete coordination are the driving force of the self-assembly process.     

Photo‐induced Substitutive Introduction of the Aldoxime Functional Group to Carbon Chains: A Formal Formylation of Non‐Acidic C(sp3)−H Bonds

A photo‐induced substitutive introduction of an aldoxime functional group to carbon chains was achieved using photo‐excited 4‐benzoylpyridine as a C(sp³)?H bond cleaving agent and arylsulfonyl oxime as an aldoxime precursor. The non‐acidic C?H bonds in various substances, including cycloalkanes, ethers, azacycles, and cyclic sulfides, were chemoselectively converted at ambient temperature under neutral conditions. The present transformation is a formal formylation of non‐acidic C(sp³)?H bonds in a single step.     

Adsorption and Surface Properties of Vladipor Cellulose Acetate and Polysulfonamide Membranes

Surface and adsorption characteristics of porous cellulose acetate (UAM) and polysulfonamide (UPM) membranes with pore diameters from 0.015 to 0.1 μm are compared. The specific surface areas of UPM membranes are 130 and 150 cm²/cm², whereas those of UAM membranes vary from 80 to 360 cm²/cm² of the membrane area. The density of negative charges on the pore surface is 5 × 10^{− 8} and about 20 × 10⁻⁸ C/cm² for UAM and UPM membranes, respectively. The adsorption of basic and acidic substances, proteins (cytochrome C and ovalbumin) and dyes (rhodamine 6G and Acid Orange), from aqueous solutions is studied. Far stronger hydrophobic interactions are observed for the UPM than for UAM membranes. The adsorption of basic substances is markedly higher than that of acidic substances because of acidic properties of the membrane surface. The distribution constants for the adsorption of Acid Orange and cytochrome C on the UPM membrane with a pore diameter of 0.1 μm are 50- and 100-fold higher than for the UAM membrane of the same pore diameter and specific surface area. __________ Translated from Kolloidnyi Zhurnal, Vol. 67, No. 6, 2005, pp. 835–838. Original Russian Text Copyright ? 2005 by Khokhlova, Dzyubenko, Berezkin, Bon, Pervov, Shishova, Dubyaga, Mchedlishvili.