Pulse radiolysis study of one-electron oxidation of thionine in aqueous solutions

One-electron oxidation of thionine has been studied using specific oxidizing radicals such as Cl⁻Tl(II) and N₃ generated by pulse radiolysis of aqueous solutions. The semioxidized thionine exhibited threepK’s indicating four conjugate acid-base forms. N₃ radicals were found to be less efficient in oxidizing thionine as compared to Cl ₂ ⁻ , Tl²⁺ and Tl(OH)⁺. The rate constants for electron abstraction from thionine by Cl ₂ ⁻ , Tl²⁺, Tl(OH)⁺, Tl(OH)₂ and N₃ were evaluated. The spectra of different protonated forms of semioxidized thionine and the extinction coefficients at λ_max are presented. Reaction of OH radicals with thionine gave transient products whose spectra and acid-base properties were different from those of semioxidized thionine. The rate constant for formation of the product transient agrees well with competition kinetic value for reaction of OH with thionine reported earlier.     

Halide‐Anion Binding by Singly and Doubly N‐Confused Porphyrins

The halide‐binding properties of N‐confused porphyrin (NCP, 1 ) and doubly N‐confused porphyrins (trans‐N₂CP ( 2 ), cis‐N₂CP ( 3 )) were examined in CH₂Cl₂. In the free‐base forms, cis‐N₂CP ( 3 ) showed the highest affinity to each anion (Cl^?, Br^?, I^?) with association constants K_a=7.8×10³, 1.9×10³, and 5.8×10² M ^?1, respectively. As metal complexes, on the other hand, trans‐N₂CP 2–Cu exhibited the highest affinity to Cl^?, Br^?, and I^? with K_a=9.0×10⁴, 2.7×10⁴, and 1.9×10³ M ^?1, respectively. The corresponding K_a values for cis‐N₂CP 3–Cu and NCP 1–Cu were about 1/10 and 1/2, respectively, of those of 2–Cu . With the help of density functional theory (DFT) calculations and complementary affinity measurements of a series of trisubstituted N‐confused porphyrins, the efficient anion binding of NCPs was attributed to strong hydrogen bonding at the highly polarized NH moieties owing to the electron‐deficient C₆F₅ groups at meso positions as well as the ideally oriented dipole moments and large molecular polarizability. The orientation and magnitude of the dipole moments in NCPs were suggested to be important factors in the differentiation of the affinity for anions.     

Free radical inactivation of trypsin

Reactivities of free radical oxidants, ^.OH, Br^-·₂ and Cl₃COO^. and a reductant, CO^-·₂, with trypsin and reactive protein components were determined by pulse radiolysis of aqueous solutions at pH 7, 20°C. Highly reactive free radicals, ^.OH, Br^-·₂ and CO^-·₂, react with trypsin at diffusion controlled rates, k(^.OH + trypsin) = 8.2 × 10¹⁰ M^-1 s^-1, k(Br^-·₂ + trypsin) = 2.55 × 10⁹ M^-1 s^-1 and k(CO^-·₂ + trypsin) = 2.6 × 10⁹ M^-1 s^-1. Moderately reactive trichloroperoxy radical, k(Cl₃COO^. + trypsin) = 3 × 10⁸ M^-1 s^-1, preferentially oxidizes histidine residues. The efficiency of inactivation of trypsin by free radicals is inversely proportional to their reactivity. The yields of inactivation of trypsin by ^.OH, Br^-·₂ and CO^-·₂ are low, G(inactivation) = 0.6-0.8, which corresponds to ∾ 10% of the initially produced radicals. In contrast, Cl₃COO^. inactivates trypsin with ∾ 50% efficiency, i.e. G(inactivation) = 3.2.     

Quelques precisions sur les effets catalytiques des micelles cationiques hydroxylees

The alkaline hydrolysis of p-nitrophenyl acetate and of CH₃CO₂(CH₂)₂N⁺(CH₃)₂C₁₆H₃₃, Br^? was studied in the presence of micelles C₁₆H₃₃N⁺(CH₃)₂CH₂CH₂OH, Br^? and CTAB, C₁₆H₃₃N⁺(CH₃)₃,Br^?. A pathway involving an intermediate is suggested for the hydrolysis of the ester. Hydrolysis rate of the intermediate in the presence of micelles is the same as hydrolysis rate for the ester in the absence of micelles. Consequently, hydrolysis of p-nitrophenyl acetate is not catalysed by one type of micelle, while it is enhanced by another type of micelle.     

Infrared spectrometric study of the interaction between 2-dimethylamino-3,3-dimethyl-1 azirine and some phenol derivatives

The H-bonded complexes between 2-dimethylamino-3,3-dimethyl-1-azirine (TMAAZ) and some phenol derivatives have been studied by IR spectrometry in carbon tetrachloride. The equilibrium constants at 300, 315 and 328 K and the ? ΔH°, ? Δν_OH and Δν_CN values have been determined. The comparison with previously studied OH … N complexes shows that TMAAZ forms stronger complexes than would be expected from the pK_a value. These facts are discussed in terms of steric, hybridization, solvation and charge transfer effects. From a pK_a of 8, the IR spectrum shows the appearance of ion pairs N⁺-H …^?O. A predominance of protonated species can be calculated for a pK_a of 6. This can explain why 1,2-ring cleavage whose first step is probably the formation of an azirinium cation, occurs for acids characterized by pK_a values lower than 5 but not for enolizable ketones having pK_a values higher than 9.     

An Electron Diffraction and XRPD Study of Superlattice Ordering in the Elpasolite-Related Oxyfluoride K3MoO3F3

A detailed electron diffraction and XRPD study has been made of the room-temperature α polymorph of K₃MoO₃F₃. It is shown that the true symmetry of this polymorph is neither tetragonal, trigonal, nor triclinic as previously reported but rather monoclinic I1a1, a=2a_p−c_p, b=4b_p, c=a_p+2c_p when expressed in terms of the underlying elpasolite (ordered perovskite) parent structure type. A highly structured, three-dimensional, continuous diffuse intensity distribution (presumably arising from local O/F ordering and associated structural relaxation) is shown to coexist with the sharp satellite reflections characteristic of the monoclinic supercell.     

Further improvements in the 2,4-xylenol spectrophotometric method for nitrate

Improvements are described for the 2,4-xylenol spectrophotometric method for nitrate that reduce the elapsed and working time. Diluted (22 + 3) sulfuric acid is added quickly to the sample solution while the flask is immersed in tap water. 2,4-xylenol solution is added, the 6-nitro-2,4-xylenol formed is steam-distilled into a composite ammonia—isopropanol reagent, and the absorbance of the ammonium salt of 6-nitro-2,4-xylenol is measured. Further possible interferences are described. Br₂, I₂, ClO^-, CIO₃^-, BrO₃^-, and I0₄^-, cause low results by deactivating or destroying the 2,4-xylenol. Azide, hydrazine, and elemental carbon cause low results by reducing the nitrate in the strong sulfuric acid solution. Se⁺ causes low results because 2,4-xylenol is consumed in reducing Se⁴⁺ to the element. Pt⁴⁺ and Os⁸⁺ cause high results. Interferences from Br₂, I₂, ClO^-, ClO₃^- lO₃^-, and I0₄^- can be eliminated by reduction to the halide with sulfurous acid and precipitation with silver sulfate. Sulfurous acid reduction also eliminates interferences from V⁵⁺. Mn⁷⁺, Cr⁶⁺, S₂O₈^2-, and H₂0₂. Interferences from N₃^-, Br₂, I₂, and S₂0₈^2- are eliminated merely by boiling a 0.5% sulfuric acid solution for 30 min (and precipitating any residual halide with silver sulfate).     

Synthesis of substituted quinolines by the electrophilic cyclization of n-(2-alkynyl)anilines

A wide variety of substituted quinolines are readily synthesized under mild reaction conditions by the 6-endo-dig electrophilic cyclization of N-(2-alkynyl)anilines by ICl, I₂, Br₂, PhSeBr, and p-O₂NC₆H₄SCl. The reaction affords 3-halogen-, selenium- and sulfur-containing quinolines in moderate to good yields in the presence of various functional groups. Analogous quinolines bearing a hydrogen in the 3-position have been synthesized by the Hg(OTf)₂-catalyzed ring closure of these same alkynylanilines.     

Kinetics and mechanism of the iodine oxidation of hydroxylamine

Studies of the stoichiometry and kinetics of the reaction between hydroxylamine and iodine, previously studied in media below pH 3, have been extended to pH 5.5. The stoichiometry over the pH range 3.4–5.5 is 2NH₂OH + 2I₂ = N₂O + 4I^? + H₂O + 4H⁺. Since the reaction is first-order in [I₂] + [I₃^?], the specific rate law, k₀, is k₀ = (k₁ + k₂/[H⁺]) {[NH₃OH⁺]₀/(1 + K_p[H⁺])} {1/(1 + K_I[I^?])}, where [NH₃OH⁺]₀ is total initial hydroxylamine concentration, and k₁, k₂, K_p, and K_I are (6.5 ± 0.6) × 10⁵ M^?1 s^?1, (5.0 ± 0.5) s^?1, 1 × 10⁶ M^?1, and 725 M^?1, respectively. A mechanism taking into account unprotonated hydroxylamine (NH₂OH) and molecular iodine (I₂) as reactive species, with intermediates NH₂OI₂^?, HNO, NH₂O, and I₂^?, is proposed.     

Synthesis and crystal structure of octaaquaerbium(III) 4,7,13,16,21,24-Hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane pentabromide hydrate

A new complex salt [Er(H₂O)₈]³⁺·[H₂(Crypt-222)]²⁺·5Br^?·1.5H₂O(I) is synthesized, and its crystal structure is studied by single-crystal X-ray diffraction analysis (space group P2₁, a = 8.315 Å, b = 32.000 Å, c = 8.383 Å, β = 120.03°, Z = 2; direct method, anisotropic full-matrix least-squares approximation, R = 0.050 for 3755 independent reflections; CAD4 automated diffractometer, λMoK _α radiation). The structural units of crystal I are complex cations [Er(H₂O)₈]³⁺, disordered dications of the 2.2.2-cryptand (with two protonated nitrogen atoms), Br^? anions, and water molecules. The coordination polyhedron of the Er³⁺ cation is a tetragonal antiprism with the oxygen atoms of eight water molecules at its vertices. The disordered [H₂(Crypt-222)]²⁺ dication contains trifurcate hydrogen bonds N⁺-H(?O)₃.     

Synthesis and structure of lower rim C-linked tetra-N-tosyl peptidocalix[4]arenes

Chiral p-tert-butylcalix[4]arenes perfunctionalised at the lower rim with amino acid residues have been prepared. The ¹H and ¹³C NMR spectra indicate that the macrocycles adopt a cone conformation. Calix[4]arenes bearing amino acid moieties 5a shows strong complexation towards Cl⁻, Br⁻, HSO₄⁻, H₂PO₄⁻ and N-tosyl-(l)-alaninate.     

Resonance Raman spectroscopy and DFT calculations of the protonation of 4-(2-pyridylazo)-N,N-dimethylaniline in solution and adsorbed on oxide surfaces

The protonation of 4-(2-pyridylazo)-N,N-dimethylaniline (PYAD) in aqueous solution and its adsorption on oxide surfaces has been studied by resonance Raman (RR) spectroscopy. The gas phase structures of neutral, protonated and diprotonated forms of PYAD were modelled by SCF-DFT calculations at the B3-LYP/DZ level, enabling determination of the simulated vibrational spectra of these species, together with vibrational assignments, and providing confirmation that protonation occurs initially at the pyridyl nitrogen atom. Electronic absorption spectra were interpreted using time-dependent DFT calculations. Adsorption of PYAD on SiO₂ or Al₂O₃ surfaces is mainly via the neutral species, hydrogen bonded to surface OH groups, although a small proportion of adsorbed molecules are protonated. By contrast, adsorption on SiO₂–Al₂O₃ results in complete protonation, indicating the presence of Brønsted acidic sites with pK_a values ? 4.5, whereas adsorption on H-mordenite results in diprotonation, indicating the presence of Brønsted acidic sites with pK_a values ? 2.     

钳形酰腙类阴离子受体的合成及识别性质研究

设计合成了基于吲哚酰腙单元的钳形阴离子受体(1),UV-Vis滴定实验表明,它在含1%DMSO的CH3CN溶液中能选择性识别具有重要生物学意义的F-、Ac O-和H2PO4-(结合比均为1∶1且Ka104L/mol),但对Cl-、Br-、I-、NO3-、N3-、HSO4-和Cl O4-无识别作用。与它相比,端基为苯并呋喃的参照化合物2在同样溶剂中对上述3种阴离子的亲和性减弱,尤其是对H2PO4-。核磁滴定实验表明,受体1中的吲哚环NH和酰胺NH能产生协同效应,从而对阴离子产生了强效键合作用。     

Anion and Cavity Effects on the Complexation Behavior of Di-Aza-Benzo-Crown-Ether Calix[4]arene towards Zn(II) Ions

A novel compound, 25, 27 - N,N - di - ((2 -ethoxy)benzyl)butylenediamine - p - tert- butylcalix[4]arene, 1, has beensynthesized by reducing its Schiff base derivative. Inclusion studies by¹H-NMR spectroscopy in a mixed solvent (CD₃OD/CDCl₃) of25,27-N,N-di-((2-ethoxy)benzyl)propylenediamine-p-tert-butylcalix[4]arene,2, and 1 with Zn(II) ions, where counter anions are Cl^-, Br^-, I^- and NO ₃ ^- ,show that both ligands can bind Zn(II) to a different extent depending onthe counter anions and the cavity size of the ligands. The stabilityconstants of ZnX₂–1 (ZnX₂-2) complexes where X = Cl^-, Br^-, I^- and NO ₃ ^- are 1.4 ± 0.1 (1.6 ± 0.1), 1.7 ± 0.1 (1.9 ±0.1), 2.2 ± 0.1 (2.7 ± 0.1) and 4.7 ± 0.1 (6.0 ±0.1), respectively. The calix[4]arene unit of the ligand 2 was found to havea structural change from cone to partial cone conformation upon binding toZnCl₂, ZnBr₂ and ZnI₂.     

Stability constants of iron(III)-8-hydroxyquinoline complexes

Spectrophotometric determination of the formation constants of iron(III)-8-hydroxyquinoline complexes in 0.1 M sodium perchlorate solution at 25° gave the values K₁=[FeOx²⁺]/([Fe³⁺][Ox^-])=4.9·10¹³, K₂=[FeOx₂⁺]/([FeOx²⁺][Ox^-])=4.2·10¹² and K₃=[FeOx₃]/([FeOx₂⁺][Ox^-])=3.9·10¹⁰. FeOx₂OH and FeOx(OH)₂ are obtainable as solid phases. FeOx₃ (K_sp=3·10^-44, intrinsic solubility 1.6·10^-7 M) dissolves in basic solutions to form FeOx₂(OH)₂ -In a solution saturated with FeOx³, ([FeOx₂(OH)₂^-][Ox^-])/[OH^-]²=7.7·10^-5.     

Different channels of ·OH radical reaction with tryptophanol in aqueous solutions: A pulse radiolysis study

The pulse radiolysis technique has been employed to study the reaction of ·OH radical with tryptophanol (TPN). Reactions of specific one-electron oxidants like Br₂· - and N₃· and ·H atom were carried out to understand the contribution of different channels of · OH radical reaction with TPN. The studies were carried out in the pH range 3 to 10. One-electron oxidation of TPN (pH 3) produced radical cation absorbing at 570 nm. However, at higher pH, deprotonation of TPN cation radical takes place from N(1) position and indolyl radical absorbing at 520 nm with a p ^K a value of 3.6 is formed. Redox titration with TMPD, ABTS^2- and MV²⁺ was performed to determine the total yield of oxidizing and reducing radicals produced during ·OH reaction.     

Optically active transition metal complexes. Part 117:Synthesis,crystal structure and properties of chiral (η6-arene)ruthenium complexes with N,O- and N,N-ligands

The complexes [(η⁶-p-ⁱPrC₆H₄Me)Ru(NO₂pesa)Cl] 2, [(η⁶-p-ⁱPrC₆H₄Me)Ru(oxazsa)Cl] 3 and [(η⁶-p-ⁱPrC₆H₄Me)Ru(pepy)Cl] 4, chiral in the chelate ligand and chiral at the ruthenium atom, have been prepared by reaction of [(η⁶-p-ⁱPrC₆H₄Me)RuCl₂]₂ with the anions of the (S)-configured bidentate N,O- and N,N-ligands. [(η⁶-p-ⁱPrC₆H₄Me)Ru(pesa)I] 5 was synthesized by halide exchange. The diastereomer ratios of compounds 2–4 with respect to the stereogenic ruthenium atom are in CDCl₃ 2a:2b=81:19, 3a:3b=77:23 and 4a:4b=61:39. Compound 5 is obtained diastereomerically pure. An X-ray structure analysis of 3 shows (R_Ru,S_C)-configuration     

A study of the physico-chemical properties of 1,3,5-trihydroxy-1,3,5-triazin-2,4,6[1H,3H,5H]-trione

Acetyl (Ia) and pivaloyl (Ib) triesters of the 1N,3N,5N-trihydroxy-1,3,5-triazin-2,4,6[1H,3H,5H]-trione (I) were synthesised. The spectrophotometric and potentiometric investigation of I revealed a weak acidic properties of triprotonic acid (pK_a1=5.23, pK_a2=6.32, and pK_a3=7.93). The MS and TGA analyses of I indicated on hydroxyisocyanate as possible degradation product. The chelating ability of I with Fe(III)-ion was preliminary explored. IR measurements of aqueous solutions of I in the presence of Fe(III) ion showed the possible chelating ability of all hydroxamic moieties. The chemical structures and properties of investigated compounds were derived from the results of IR, ¹H and ¹³C NMR, UV and MS spectrometric data, as well as thermogravimetric and potentiometric analysis.     

Transition metal derivatives of arenediazonium ions: XIV. Reactions of arenediazomolybdenum(II) complexes with neutral and anionic Lewis bases

The reactions of arenediazomolybdenum(II) complexes such as [(η-C₅H₅)Mo(N₂C₆H₄CH₃-p)I₂]₂, (η-C₅H₅)Mo(CO species with neutral and anionic monodentate or chelating ligands have been investigated. The new arenediazo complexes isolated from these reactions include neutral species such as (η-C₅H₅)Mo(PPh₃)(N₂C₆H₄CH₃-p)I₂ and (η-C₅H₅)Mo(N₂C₆H₄CH₃-p) cations of the type [η-C₅H₅)Mo(bipy)(N₂C₆H₄CH₃-p)I]⁺ and the anion [(η-C₅H₅)Mo(N₂C₆H₄CH₃-p)I₃]^?. The structures of the new complexes are discussed.     

Interaction of Iodine with Hexaaza-18-crown-6 and Tetraaza-14-crown-4 in Chloroform Solution

Interactions of hexaaza-18-crown-6 (HA18C6) and tetraaza-14-crown-4 (TA14C4) with iodine have been investigated spectrophotometrically in chloroform solution. The observed time dependence of the charge-transfer band and subsequent formation of I₃ ^- in solution were related to the slow transformation of the initially formed 1:1 macrocycle. I₂ outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion, as follows: macrocycle + I₂→_fast ^K _f macrocycle.I₂ (outer complex) macrocycle.I₂ (outer complex) →^slow (macrocycle.I⁺)I^- (inner complex) macrocycle.I⁺)I^- (inner complex) + I²→^slow (macrocycle.I⁺)I₃ ^-. The pseudo-first-order rate constants at various temperatures for thetransformation process were evaluated from the absorbance-time data. The activation parameters (E_a, Δ H^?, and Δ S^?) for thetransformation were obtained from the temperature dependence of the rate constants. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. It was found that the (TA14C4.I⁺)I₃ ^- is more stable the (HA18C6.I⁺)I₃ ^- complex in chloroform solution.