N,N′-dichloro-p-nitrobenzenesulfonamide (dichloramine-N) as a new oxidimetric reagent: Synthesis and analytical application

A new oxidimetric reagent, dichloramine-N (N,N′-dichloro-p-nitrobenzenesulfonamide; DCN) has been synthesized and its structure elucidated from the spectral data and elemental analyses. The ultraviolet, infrared, nuclear magnetic resonance, and mass spectral data have been presented. Analytical applications of DCN as a potential redox titrant in the determination of diverse reductants such as ascorbic acid, methionine, sulfite, arsenite, glutathione, and indigocarmine have been described.     

Synthesis of Macrocyclic Compounds Using Diorganotin(IV) Dicarboxylates as Covalent Templates

A series of new macrocyclic compounds have been prepared by treating di- n -butyltin(IV) dicarboxylates of diphenic acid (biphenyl-2,2′-dicarboxylic acid), thiodiacetic acid and maleic anhydride with succinyl, adipoyl and sebacoyl dichlorides. The compounds have been characterized with the help of elemental analyses and spectral data (mass, IR, ^IH and ¹³C NMR).     

Apparent molar and partial molar volumes of aqueous ceric ammonium nitrate solutions at 20, 25, 30, and 35°C

Present paper reports the measured densities (ρ) and refractive indices (n _D) of aqueous solutions of ceric ammonium nitrate (CAN) at 20, 25, 30, and 35°C in different concentrations of solution. Apparent molar volumes (φ_v) have been calculated from the density data at different temperatures and fitted to Massons relation to get limiting partial molar volumes (? _v ⁰ ) of CAN. Refractive index data were fitted to linear dependence over concentration of solutions and values of constant K and n _D ⁰ for different temperatures were evaluated. Specific refractions (R _D) of solutions were calculated from the refractive index and density data. Concentration and temperature effects on experimental and derived properties have been discussed in terms of structural interactions.     

Nature of light-absorbing pigments from Brazilian lichens identified by Raman spectroscopy

Light-absorbing pigments from different chemical classes have been identified from the lichens Usnea sp. and Crocodia aurata using Raman spectroscopy supported by quantum mechanical DFT calculations. Raman spectra were obtained directly from the lichen tissues as well as from isolated extracts. Usnic acid, a chemomarker of Usnea spp has been reported together with a minor constituent, namely stictic acid, which has been unambiguously identified by ¹H and ¹³C NMR spectral analysis. The structures of calycin and pulvinic dilactone isolated from Crocodia aurata have been confirmed by single crystal X-ray diffraction. The ubiquitous carotenoids have been characterized by FT-Raman and dispersive Raman microimaging in tissues of Usnea sp. and C. aurata, respectively. The Raman map has revealed the presence of a mixture of carotenoids heterogeneously distributed in the upper layer of C. aurata. In this work we have demonstrated that Raman spectroscopy can be used to monitor aromatic and conjugated polyenic pigments in different layers of lichen tissues.     

Organotin(IV) derivatives as biocides: An investigation of structure by IR, solution NMR, electron impact MS and assessment of structure correlation with biocidal activity

A brief account is given of the synthesis, structural chemistry and the antibacterial, antifungal and cytotoxic effects of organotin complexes of 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid. The unimolar and bimolar substitution products have been characterized by elemental analysis and spectral studies, including IR, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR, and mass spectra. The data support the binding of the oxygen atom to the tin atom in [R₂Sn(OOCR’)₂] and [R₃Sn(OOCR’)] (R = Me, Bu, and Ph, R’ = 2-[(2,4-dichloroanilinocarbonyl)]benzoic acid). Based on these studies, with a coordination number of four, a distorted tetrahedral geometry has been proposed for the resulting derivatives in solution. The free ligand (R’/COOH) and its respective tin complexes were tested in vitro against a number of microorganisms to assess their biocidal properties and to correlate them with the structures of the derivatives.     

Thermal and spectroscopic studies of terbium(III) and dysprosium(III) complexes with piperidin-4-ones

Terbium(III) and dysprosium(III) nitrate complexes with variously substituted 2,6-diphenylpiperidin-4-ones (L¹)-(L¹⁰) of general formula [Ln(L)(NO₃)₂(H₂O)₂]NO₃ have been synthesized. These complexes have been characterized by analytical, spectral and thermal studies. Molar conductance data show that these complexes are 1:1 electrolytes. The presence of two coordinated water molecules is confirmed by thermal and infrared spectral studies. IR spectral data indicate that piperidin-4-ones, in spite of having two coordinating sites, are monodentate, coordinating only through ring nitrogen. The IR and conductance data reveal the presence of two bidentate and one ionic nitrate groups. The nephelauxetic ratio (β), covalency factor (b^1/2) and Sinha’s parameter (δ) evaluated from electronic spectral data of dysprosium(III) complexes indicate a little covalency in metal-ligand bonding.     

The infrared,Raman and NMR spectra,conformational properties and values for the ideal gas thermodynamic functions of cis- and trans-1,2-cyclobutanedicarbonitrile

The infrared spectra above 400 cm⁻¹ and the Raman spectra above 30 cm⁻¹ have been recorded for the cis- and trans- 1,2-cyclobutanedicarbonitriles as melts. ¹H and ¹³C NMR data are also reported. The observed spectral data, and notably the Raman depolarization data, are consistent with C₂ symmetry for the trans isomer and C₁ symmetry for the cis isomer. The probable conformations of each compound have been proposed, and evidence is put forward that the cis compound exists with a relatively small degree of ring puckering. Complete vibrational assignments have been proposed for both compounds apart from the cis ring puckering frequency which was assumed to be too low to observe. Values for the thermodynamic functions of the two compounds as ideal gases have been calculated and the possible errors in these values have been described.     

Ruthenium Complexes of Rigid,Dianionic, Tetradentate N-Donor Ligands and their Potential as Catalysts for Water Oxidation

Two mononuclear ruthenium(II) complexes based on dianionic {N₄} ligands and with axial pyridines have been prepared and characterized crystallographically ( 1 ) or by 2D NMR spectroscopy using residual dipolar couplings ( 2 ). The {N₄} ligands provide a constrained equatorial coordination with one large N−Ru−N angle, and additional non-coordinating N atoms in case of 2 . Their redox properties have been investigated (spectro)electrochemically, and their potential to serve as water oxidation catalysts has been probed using cerium ammonium nitrate (CAN) at pH 1.0. Complex 1 undergoes rapid degradation, likely via ligand oxidation, whereas 2 is more rugged and exhibits 80 % efficiency in the Ce^IV-driven water oxidation, with a high initial turnover frequency (TOF_i) of 3.07×10⁻² s⁻¹ (at 100 equiv. CAN). The initial rate of O₂ evolution exhibits 1^st order dependence on catalyst concentration, suggesting a water nucleophilic attack mechanism. Repeated addition of CAN and control experiments show that high ionic strength conditions (both NO₃⁻ and Ce^III) significantly decrease the TOF.     

Synthesis,electronic, photoacoustic and electron spin resonance investigations on some tetrathiocyanate binuclear mixed-metal complexes

Complexes of the type M₁M₂(SCN)₄xL[M₁ = Ni(II); M₂ = Cd(II) and Hg(II) and L = pyridine, morpholine, dioxan, benzo(f)quinoline, 2,2′-bipyridine, 2,2′-bipyridine N,N′-dioxide, isonicotinic acid hydrazide and 1,10-phenanthroline: x = 2 or 4] have been synthesized and characterized by chemical analysis, magnetic susceptibility, infrared, electronic and photoacoustic (PAS) spectra as well as electron spin resonance (ESR) spectral studies in the solid and solution state. The different coordination sites have been investigated in these ligands towards metal coordination and the behaviour of thiocyanate anions studied. Electron spin resonance spectral data for copper complexes show the distorted octahedral stereochemistry around copper(II) in these complexes. The parameters such as g_∥, g_⊥, A_∥, A_⊥, <g>, <A> and α² calculated for the copper complexes from their ESR spectra indicate the presence of unpaired electron in d_x²-y² or d_z² orbitals. The photoacoustic and electronic spectra of these complexes were studied in the solid state to see the nature of thiocyanate and overall symmetry of the complexes. The results on electronic and photoacoustic spectral studies are in good agreement with ESR data.     

Oxygen isotopic effect on the IR reflectivity spectra of a La2NiO4.14 single crystal

Infrared reflectivity spectra measurements have been realised at T=300 K on the oxygen–isotope exchanged single crystals (¹⁶O and ¹⁸O) of La₂NiO_4+δ with δ=0.14. One of the main results lies on transfer of the spectral weight from the mid-infrared spectral range to the far-infrared range upon ¹⁸O substitution. This striking effect is studied in the framework of the harmonic oscillator concept by simulating the experimental data with a dielectric function model based on the generalisation of the Lyddane–Sachs–Teller relationship. It suggests that the lattice strongly influences the behaviour of the charge carriers in such 3d transition metal oxides.     

Synthesis of four diastereomers and structural revision of tetradenolide

Four diastereomers of tetradenolide, a cytotoxic α-pyrone isolated from Tetradenia riparia, were synthesized stereoselectively using the Z-selective Horner–Emmons reaction followed by acid catalyzed lactonization. Making comparison of the ¹H and ¹³C NMR spectral data of the four diastereomers with those of the reported value of natural product did not lead to determine the relative stereochemistry of the natural tetradenolide. Thus detailed investigation of the spectral data of the related compounds led us to revise the structure of tetradenolide as deacetylboronolide.     

Distortion of the coordination polyhedron in mononuclear copper(II) complexes. Optical absorption and electron spin resonance studies on some five-coordinate copper(II) complexes

The preparation and spectral properties are reported for a series of ten mixed-ligand copper(II) complexes of the form [Cu(A)(B)_n](X), where A is acetylacetonate anion, B represents a mono- or bidentate ligand such as morpholine, piperidine, isonicotinic acid hydrazide, 2,2′-bipyridine, 1,10-phenanthroline and X is variously NO^?₃ or ClO^?₄ anion and n = 1 or 2. The coordination of the anions and ligands has been demonstrated by infrared and electronic spectral methods. Electron spin resonance spectral data show the square-pyramidal five-coordinated arrangement around copper(II) in these complexes. Parameters such as g₆, g_⊥, A₆, A_⊥, 〈g〉 and 〈A〉 calculated from electron spin resonance data in solid and solution state at room temperature as well as frozen solution indicate the presence of the unpaired electron in the d_x2_?y2 or d_z2 orbital. These results are in good agreement with electronic and photoacoustic spectral studies.     

Extraction and spectrophotometric determination of mercury with N-p-chlorophenylbenzohydroxamic acid (N-p-Cl-BHA)

Extraction and spectrophotometric studies of tracer amounts of mercury with N-p-chlorophenylbenzohydroxamic acid are described. The yellow color mercury complex was extracted from chloroform at pH 9.0. The spectral measurement was made at 388 nm and the molar absorptivity of the complex is 6.0 × 10² liters mol^?1 cm^?1. It gives a clean separation from many commonly occurring metal ions. Effects of pH, solvents, electrolytes, and reagent concentration on the extraction of mercury have been discussed. The mercury is determined in drug samples and industrial effluents. From the extraction data an attempt has been made to calculate the stability constant of mercury complex.     

A biocompatible hydrogel as a template for oxidative decomposition reactions: a chemodosimetric analysis and in vitro imaging of hypochlorite

The self-assembly properties of new biocompatible, thermoreversible fluorescent hydrogels, composed of amino acid residues, e.g., l-phenylalanine (PyL-PheOx) and l-tyrosine (PyL-TyrOx), have been reported. Spectroscopic investigations indicate that PyL-PheOx forms π-stacked ‘compact’ aggregates, while ‘loose’ aggregates with stronger CT characteristics are observed for PyL-TyrOx. Both the compounds showed the presence of fibrous networks in the self-assembled state. Circular dichroism spectral studies indicate the formation of M-helical and P-helical structures for PyL-PheOx and PyL-TyrOx, respectively. A striking gel-to-sol transition, caused by oxidative decomposition, is explicitly noticed in the presence of hypochlorite. A mechanistic investigation reveals the oxidation of the acyl aroyl hydrazine core of the gelators in the presence of ClO⁻. In addition to this, change in the fluorescence emission intensity of the hydrogel in the presence of ClO⁻ is utilized for the analysis of commercial bleach samples. Gel-coated paper strips are also developed for the on-site detection of ClO⁻. Furthermore, the system is utilized for imaging hypochlorite in live mammalian cells.

The self-assembly properties of new biocompatible, thermoreversible fluorescent hydrogels, composed of amino acid residues have been reported. A unique gel-to-sol transition is triggered by chemodosimetric interaction in the presence of hypochlorite.     

Copper(II) and lead(II) complexes based on 2,3,5,6-tetrakis(2-pyridyl)pyrazine as a polydentate ligand

The Cu(II) complexes [Cu(Tppz)(Dipic)] · 8H₂O (I) and [Pb₂(Tppz)Cl₄] _n (II), where Tppz, H2Dipic are 2,3,5,6-tetrakis(2-pyridyl)pyrazine, dipicolinic acid, respectively, have been synthesized and characterized by elemental analyses, IR, cyclic voltammetry, and electronic spectral studies. Solid state structures of both complexes have been determined by single crystal X-ray crystallography. An ORTEP drawing of two complexes shows that the coordination geometry around the metal center is a distorted octahedron. There are extensive conventional intermolecular O-H…O, N-H…O, and weaker C-H…O and C-H…Cl non-classical hydrogen bonds, which cause the stability of the crystal structure. Crystal data for I: monoclinic, space group: C2/c, a = 35.421(3), b = 8.422(6), c = 22.824(8) Å, β = 101.69(2)°, V = 6668(5) ų, Z = 8. Crystal data for II: triclinic, space group P \(\bar 1\) , a = 7.9534(4), b = 8.8682(5), c = 9.4245(5) Å, β = 95.086(2)°, V = 655.93(6) ų, Z = 2.     

Vibrational spectra and structure of crystalline dipicolinic acid and calcium dipicolinate trihydrate

The i.r. (4000-30 cm⁻¹) and Raman (4000-20 cm⁻¹) spectra of 2,6-pyridinedicarboxylic acid C₅H₃N(COOH)₂, C₅H₃N(COOD)₂, 2,6-pyridine-4-d₁ dicarboxylic acid and calcium dipicolinate trihydrate (the equimolar salt of calcium and 2,6-pyridinedicarboxylic acid) at 100 K have been investigated.A tentative assignment is given by referring to the isotopic frequency shifts and group frequency considerations as well as to depolarization ratios. Thirty-four internal vibrations from the 39 expected modes have been observed for the crystalline dipicolinate ion, the relevant molecular point group being C _2ν. Cyclic centrosymmetric dimeric structures involving the carboxyl groups in the acid are proposed to explain the spectral features of this compound.     

Cribrarione A, a new antimicrobial naphthoquinone pigment from a myxomycete Cribraria purpurea

Cribrarione A (1), a new dihydrofuranonaphthoquinone pigment with antimicrobial activity against Bacillus subtilis has been isolated from a myxomycete Cribraria purpurea and its structure was elucidated by spectral data. The ¹H-¹³C long-range couplings through an intramolecular hydrogen bond were clearly observed in the HMBC spectrum of 1.     

Design and synthesis of novel thiopheno-4-thiazolidinylindoles as potent antioxidant and antimicrobial agents

A novel and convenient synthesis of thiopheno-4-thiazolidinyl indole analogues is presented (IVa-IVi), with the aim of obtaining biologically active compounds. 3,5-disubstituted indol-2-carboxyhydrazides (Ia-If) were allowed to react with 3-acetyl-2,5-dichlorothiophene (II) to yield the corresponding 3,5-disubstituted indol-2-carbohydrazides (IIIa-IIIf). The pre-formed indolecarbohydrazides (IIIa-IIIf) were allowed to react with 2-mercaptoacetic acid or 2-mercaptopropanoic acid to produce thiopheno-4-thiazolidinylindoles (IVa-IVi). This reaction protocol affords a simple, eco-friendly, non-hazardous, easier preparation and high yields. The antioxidant (free radical scavenging, total antioxidant capacity and ferric-reducing antioxidant power) and antimicrobial activities of the synthesised compounds were evaluated. The structures and purity of the products were confirmed by their IR, ¹H NMR, ¹³C NMR and mass spectral and analytical data. Most of the compounds tested showed very significant scavenging, antioxidant and antimicrobial activities. Compounds containing electron donor group (CH₃) at the fifth position of indole exhibit an excellent ferric-reducing activity. The present study suggests that compounds IIIa-IIIb, IIIf, IVa-IVc, IVf-IVi, may serve as promising lead scaffolds for antioxidant and antimicrobial agents.     

Design,synthesis and screening of some novel benzoxazole based 1,3,4-oxadiazoles as potential antimicrobial agents

A series of novel 2-(5-substituted-[1,3,4]oxadiazol-2-yl)-benzoxazoles (7a–h) were synthesized in good yields in two different directions by involving benzoxazole-2-carboxylic acid (1) as raw material and benzoxazole-2-carbonyl chloride (2), benzoxazole-2-carboxylic acid methyl ester (3), benzoxazole-2-carboxylic acid hydrazide (4), benzoxazole-2-carboxylic acid N′-acetyl hydrazide (5a–d) and benzoxazole-2-carboxylic acid-ethylidene-hydrazides (6a–d) as reactive intermediates. The chemical structures of all the synthesized compounds were elucidated by their IR, ¹H NMR and ¹³C NMR and mass spectral data. Further, the target compounds were screened for their antimicrobial activity against various Gram-positive and Gram-negative bacteria.     

Carboxylic acid-assisted solid-state synthesis of LiFePO4/C composites and their electrochemical properties as cathode materials for lithium-ion batteries

To enhance the capability of LiFePO₄ materials, we attempted to coat carbon by incorporating various organic carboxylic acids as carbon sources. The purity of LiFePO₄ was confirmed by XRD analysis. Galvanostatic cycling, cyclic voltammetry, electric impedance spectroscopy, and conductivity measurements were used to evaluate the material’s electrochemical performance. The best cell performance was delivered by the sample coated with 60 wt.% malonic acid. Its first-cycle discharge capacity was 149 mA h g^?1 at a 0.2 C rate or 155 mA h g^?1 at a 0.1 C rate. The presence of carbon in the composite was verified by total organic carbon and Raman spectral analysis. The actual carbon content of LiFePO₄ was 1.90 wt.% with the addition of 60 wt.% malonic acid. The LiFePO₄/C samples sintered with 60 wt.% various carboxylic acids were measured by Raman spectral analysis. The intense broad bands at 1,350 and 1,580 cm^?1 are assigned to the D and G bands of residual carbon in LiFePO₄/C composites, respectively. The peak intensity (I _D/I _G) ratio of the synthesized powders is from 0.907 to 0.935. Carbon coatings of LiFePO₄ with low I _D/I _G ratios can be produced by incorporating carboxylic acid additives before the final calcining process. The use of carboxylic acid as a carbon source increases the overall conductivity (～10^?4 S cm^?1) of the material.