NMR Spectral Investigations Research Articles

Marihysin B, a new cyclic lipopeptide from culture broth of Staphylococcus sp. - antimicrobial and glucoamylase inhibitory activities

A new cyclic lipopeptide, marihysin B (1) and the well-known marihysin A (2) were isolated from Staphylococcus sp. culture broth obtained from Corallina officinalis L. Extensive 1D (1H and 13C) and 2D (1H–1H COSY, HSQC, HMBC, and NOESY) NMR spectral investigations were used to determine the structures of isolated compounds. With inhibition zone widths of 11 to 25 mm and MICs of 25 µg/mL, compounds 1 and 2 showed marked antifungal activity against Aspergillus niger, Penicillum crustosum, Trichophyton concentricum, and Schizophyllum commune compared to nystatin (inhibition zone diameters 23–31 mm). Additionally, computational study was done to determine the possible mechanism underlying the antifungal activity of the two cyclic lipopeptides against Schizophyllum commune glucoamylase. These substances showed similar binding affinities to the target's reference compound.

NMR spectral, DFT and antibacterial studies of triazole derivatives

A sequence of 1,4-disubstituted 1,2,3-triazole derivatives has been intended and synthesized using cerium-loaded CuO nanoparticles as a cost-effective catalyst. NMR spectral investigations were adopted for structural elucidation of the synthesized compounds. The generous quality of this nanocatalyst is high yield product, short reaction time, and a huge variety of substrates usage. The absorption and emission behavior of triazole derivatives were examined in diverse solvents. From the emission spectral inspections, we have been perceived that the emission band is shifted to a higher energy region by reason of the solvent polarity increases. The antibacterial activity of the compounds was tested with Gram-positive bacteria such as Staphylococcus aureus (S. aureus), Bacillus subtilis (B. subtilis), and Gram-negative such as Klebsiella pneumonia (K. pneumonia), Salmonella typhi (S. typhi) and Escherichia Coli (E.coli). The compounds show excellent antibacterial activity against all the bacterial strains.

Synthesis, Spectral Investigation, DFT, Antibacterial, Antifungal and Molecular Docking Studies of Ni(II), Zn(II), Cd(II) Complexes of Tetradentate Schiff-Base Ligand

By refluxing 4-nitro-o-phenylenediamine and 5-nitro salicylaldehyde, a new Schiff base ligand was synthesized. By reacting the appropriate precursor with the tetradentate Schiff base ligand, three nitro-substituted nickel(II), zinc(II) and cadmium(II) complexes were synthesized. UV-Visible, FTIR and 1H NMR spectral investigations were used to characterize the ligand. Molar conductance, LC-MS, UV-visible and FTIR spectrum analysis were used to characterize the synthesized metal(II) complexes. The ligand and metal(II) complexes were also tested for antibacterial activity. DFT simulations were performed at the B3LYP/6-311G (d,p) and LanL2dz levels of theory were utilized to study the geometry of the Schiff base ligand and the metal(II) complexes. In addition, the molecular orbital occupancy of HOMO and LUMO, as well as the molecular electrostatic potential (MEP), were computed. Molecular docking investigation were conducted utilizing the active sites of the E. coli FabH-CoA complex (PDB ID: 1HNJ) receptor in order to detect the interactions between metal(II) complexes and define their likely binding locations.

Synthesis of pyrimidine linked heterocyclic scaffolds by intramolecular cyclization and study of biological potential

Synthesis of some interesting pyrimidine linked heterocyclic scaffolds by intramolecular cyclization has been worked out. Initially compound (4,6-dimethyl-pyrimidin-2-yl-amino)-acetic acid hydrazide has been prepared by reacting 2-amino-4,6-dimethyl pyrimidine with ethyl chloroacetate, followed by condensation with hydrazine hydrate. It has then been treated with N-aryl/alkyl isothiocyanates, followed by intramolecular cyclization using alkaline ethanolic solution of I2 with KI, o-phosphoric acid and aqueous KOH to afford respective heterocyclic compounds with differently substituted pharmacophores viz. (5-aryl/alkyl-amino-[1,3,4]-oxadiazol-2-yl-methyl)-(4,6-dimethyl-pyrimidin-2-yl)-amines, (5-aryl/alkyl-amino-[1,3,4]-thiadiazol-2-yl-methyl)-(4,6-dimethyl-pyrimidin-2-yl)-amines and (4-aryl/alkyl-5-mercapto-[1,2,4]-triazol-3-yl-methyl)-(4,6-dimethyl-pyrimidin-2-yl)-amines. Developments during the synthesis have been monitored by TLC. Constitution of synthesized compounds have been delineated in accordance with equivalent weight, elemental assay,chemical transformation and IR, 1H NMR and mass spectral investigations. Title compounds have been tested for their biological potential.

Synthesis, Structural and Spectroscopic analysis, Thermodynamic and Micro hardness testing of a Chalcone molecule: (2E)-3-(3, 4 Dimethoxy Phenyl)-1-(1-Hydroxy-2 Napthyl)Prop-2-en-1-one

A novel chalcone derivative, (2E)-3-(3, 4 dimethoxy phenyl)-1-(1-hydroxy-2 naphthyl)prop-2-en-1-one (DHNP), C21H18O4, has been synthesized from the mixture of 4-hydroxy acetophenone (0.05mol) and 4-hydroxy-3-ethoxybenzaldehyde (0.05mol) by Claisen-Schmidt reaction mechanism. The structural features of the grown crystal were elucidated by single X-ray diffraction (XRD) studies which confirm the title compound, belongs to the monoclinic system with the P21/n space group. Functional groups, the number of unique proton and carbon environments were identified using FT-IR, 1H, and 13C NMR spectral investigation. The optical behavior of the crystal was analyzed by UV-Vis absorption studies, and the value of the optical band gap energy (𝐸𝑔) of the crystal is found to be 3.386eV. The Photoluminescence (PL) spectrum of the compound indicates the green to yellow light emission in the visible region. By employing thermogravimetric analysis (TGA), the thermal stability of crystal and the dehydration and decomposition nature were found. The Coats and Redfern relation was applied to evaluate the kinetic and thermodynamic parameters. Mechanical properties such as the Hardness (HV), Meyer's index (n), Newtonian resistance pressure (W), load independent constant (b), and elastic stiffness constant (Cij) were calculated by performing a Vickers hardness test on the compound and found to exhibits an excellent mechanical power.

A broad-range variable-temperature solid state NMR spectral and relaxation investigation of the water state in Nafion 117.

Understanding the water state in Nafion is not only crucial for operating a proton-exchange membrane (PEM)-based fuel cell, but also intimately related to the elucidation of the proton transport mechanism in a PEM. Although many studies have been published on this subject, some controversies and ambiguities remain unresolved. In this work, we design three different types of Nafion samples by substituting protons with lithium or sodium cations. We also pay special attention to the preparation of samples for carrying out broad-range variable temperature solid state NMR experiments so that no membrane dehydration occurs during the long experimental time at low temperatures. With these precautions and improvements, clear and largely straightforward information could be obtained to ensure minimal ambiguity and complexity in the interpretation of the experimental data. Our results show that about 40-60% of water remains unfrozen at -70 °C, depending on the type of the substituting cation. Both the 1H and 2H spectral and relaxation results indicate that water freezing starts from the center of the nanopores inside Nafion and increases gradually as the temperature decreases. The protons remain dissociated with sulfonate groups even at the lowest temperature we reached (-70 °C), whereas both lithium and sodium are associated with sulfonate groups at most temperatures below 0 °C. The experimental data also suggest that besides frozen and unfrozen water, there is broad distribution of water state and dynamics in Nafion as the temperature is lowered from above zero down to -70 °C. The effect of the size of the substituting cation significantly affects the properties of supercooled water by modifying the cation-water interaction and impeding the rotation of sulfonate groups. These novel results not only help us in establishing a better understanding of the water state in Nafion and its performance as a proton exchange mebrane, but also provide insights into water freezing, antifreeze and supercooling in other nanoscopic environments.

Judd-Ofelt analysis and luminescence studies on Dy3+ -doped different phosphate glasses for white light emitting material applications

This article reports detailed analysis of trivalent dysprosium (Dy3+) doped alkali and alkaline earth phosphate glasses prepared by melt quenching technique. From X-ray diffraction, Scanning electron microscope and 31P solid-state NMR spectral investigations, the structural properties have been evaluated. The optical absorption spectra of these Dy3+ doped phosphate glasses have been analyzed and discussed using Judd-Ofelt (J–O) theory and intensity parameters have been evaluated. Different radiative parameters such as radiative lifetimes (τR), branching ratios (βr) and emission cross sections (σP) have been calculated in all the alkali and alkaline earth phosphate glasses and compared. Emission from 4F9/2 state has been identified and the measured lifetimes have been obtained from the decay curves and compared with calculated lifetime values. The CIE chromaticity co-ordinates have been measured from the photoluminescence spectra.

Synthesis and antitubercular screening of some novel 4H-1,4- benzothiazines and their sulfones under environment benign solvent free conditions as future anti-tubercular agents.

Some novel analogs of 4H-1,4-benzothiazines were synthesized under environmentally benign solvent free conditions by one pot oxidative cyclocondensation of substituted 2- aminobenzenthiols with compounds having active methylene group and then converted in to sulfones. These compounds were examined as antitubercular agents against Mycobacterium tuberculosis H37Rv using REMA plate method. The best results have MICs from 6.4 to 8.8 μg/mL, comparable to phenothiazines. IR, NMR and mass spectral investigations are included for structural elucidation.

Investigation on growth, structure and characterization of succinate salt of 8-hydroxyquinoline: An organic NLO crystal

8-Hydroxyquinolinium succinate (8-HQSU) has been synthesized and single crystals were grown from ethanol solvent by employing the technique of slow evaporation at room temperature. The structure of the grown crystal has been elucidated by single crystal X-ray diffraction analysis. It reveals that 8-HQSU crystallizes in monoclinic system with non-centro symmetric space group P21. FTIR, 1H and 13C NMR spectral investigations have been carried out to identify the vibrational modes of various functional groups and placement of proton and carbon in the 8-HQSU compound, respectively. UV–vis–NIR transmission spectrum shows the cutoff wavelength around 357nm. In addition, a photoluminescence spectral analysis was carried out for 8-HQSU crystals. The thermal properties of crystals were evaluated from TGA and DTA techniques and the crystal was found to be stable up to 145°C. The dielectric studies show that the dielectric constant and dielectric loss decrease exponentially with frequency at different temperatures. Photoconductivity studies were carried out on the grown crystals it reveals the positive photo conducting nature. Powder second harmonic generation property of the crystal was confirmed by Kurtz and Perry powder SHG technique and it is found to be 1.3 times greater than that of KDP.

Photophysical studies of an encapsulated neutral guest intercalated into the 2-dimensional space of α-Zr(iv) phosphate

Our long-range objective of developing surface anchored supramolecular assemblies as artificial light harvesting systems led us to explore the intercalation of guest molecules confined within octaamine hydrochloride (OAm·HCl) in the 2-dimensional galleries of layered inorganic material α-Zr(IV)phosphate (α-ZrP). Photophysical properties of 4,4'-dimethylbenzil, camphorthione, 4,4'-dimethylstilbene, pyrene and coumarin-1 were used to probe the intercalation behavior of OAm capsules within the galleries of α-ZrP. (1)H NMR and emission spectral investigations suggested the inclusion of guests within OAm and also confirmed the stability of host-guest complexes under acidic conditions in water. Stirring guest encapsulated OAm capsule with exfoliated α-ZrP nanosheets resulted in intercalation of the host-guest assembly as a whole in the case of 4,4'-dimethylbenzil, camphorthione, and 4,4'-dimethylstilbene as guests. According to powder X-ray diffraction and emission data these capsules are stable in the galleries of α-ZrP. The fact that the capsules are stable and can be included in α-ZrP nanosheets opens up further opportunities to explore inclusion of two different capsules, one with a donor and the other with an acceptor, and study the energy and electron transfer phenomenon between neutral molecules in α-ZrP galleries.

Mechanism Inspired Development of Rationally Designed Dihydrofolate Reductase Inhibitors as Anticancer Agents

On the basis of structural analysis of dihydrofolate reductase (DHFR) (cocrystallized separately with NADPH, dihydrofolate and NADPH, trimethoprim), compounds 2 and 3 were optimized for inhibition of DHFR. Appreciable tumor growth inhibitory activities of compounds 2 and 3 over 60 human tumor cell lines were recorded. Combination of syringaldehyde and indole moieties in these two compounds was rationalized by the synthesis of compounds 4-7, 10, and 11, which were found to have less tumor growth inhibitory activities than compounds 2 and 3. Further, UV-vis and NMR spectral investigations showed significant interactions of compounds 2 and 3 with DHFR and inhibition of its catalytic activity was observed in the presence of these compounds. Therefore, modification of trimethoprim, an antibacterial drug with no tumor growth inhibition, led to the development of compounds 2 and 3 having appreciable anticancer activities that seem to be due to inhibition of DHFR.

Self-condensation of n-(N-propyl)butanimine: NMR and mass spectral analyses and investigation by theoretical calculation

The stability of N-propylbutanimine (1) was investigated under different experimental conditions. The acid-catalyzed self-condensation that produced the E-enimine (4) and Z-inimine (5) was studied by experimental analyses and theoretical calculations. Since the calculations for the energy of 5 indicated that it had a lower energy than 4, yet 4 was the principal product, the self-condensation of 1 must be kinetically controlled.

Maytenus salicifolia Reissek, Celastraceae: triterpenes isolated from stems and antioxidant property of extracts from aerial parts

Six pentacyclic triterpenes were isolated from hexane extract of stems of Maytenus salicifolia Reissek, Celastraceae: 30-hydroxyfriedelan-3-one (1), 3,16-dioxofriedelane (2), friedeline (3), lupeol (4), betuline (5) and lup-20(29)-en-3,30-diol (6). The structure each one was established on the basis of detailed ¹H and 13C NMR spectral investigation and by comparison with the respective literature values. For compound 1, the complete 2D NMR (HMBC, HMQC and NOESY) spectral data were herein reported for the first time. Compounds 1, 2, 5 and 6 were isolated for the first time from this plant. Antioxidant activity is described for some extracts from species of the Celastraceae family, then, the extracts from aerial parts of M. salicifolia were evaluated in relation to antioxidant potential using the DPPH method. Compared to quecertin, the AcEt extract (EAF) from leaves, AcEt (EAPF) and MeOH (EMPF) from pulp fruit and AcEt (EAT) and MeOH (EMT) from stems showed significant antioxidant property.

Secondary interactions as driving force in heterocomplex formation of 2,7-disubstituted-1,8-naphthyridines: Quantum chemical, NMR and mass spectral investigations

Tautomerism and dimerization of 2,7-disubstituted-1,8-naphtyridines has been studied theoretically by quantum chemical methods and experimentally by liquid and solid state NMR and ESI-TOF mass spectral techniques. The heterocomplex formation has been proven in solution by variable temperature 1H NMR and in solid state by 13C CPMAS NMR spectra of a grinded mixture of two congeners. Secondary interactions have been proposed as driving forces in the heterocomplex formation. The energy differences between homo- and heterocomplexes were calculated with recently developed DFT + D methods. The energy data obtained by the quantum chemical methods are in agreement with the concept of secondary interactions and with the experimental observations.

The Flavonoids and Phenolic Acids of the Genus Silphium and Their Chemosystematic Value

The current review outlines the distribution of flavonoids and phenolic acids in eleven species of Silphium (Asteraceae). The chemosystematic significance of these findings is discussed and compared with DNA and morphological-based assignments for eleven species. Special attention is given to the five flavonol triglycosides that were previously isolated and characterized from Silphium species: isorhamnetin 3-O-alpha-L-rhamnosyl (1""-->6")-O-beta-D-galactopyranoside 7-O-beta-L-apiofuranoside (1), quercetin 3-O-alpha-L-rhamnosyl (1"'-->6")-O-beta-D-galactopyranoside 7-O-beta-L-apiofuranoside (2), quercetin 3-O-beta-L-galactosyl (1"'-->6")-O-beta-D-rhamnopyranoside 7-O-alpha-L-apiofuranoside (3), kaempferol 3-O-beta-D-apiofuranoside 7-O-alpha-L-rhamnosyl (1""-6"')-O-beta-D-galactopyranoside (4) and kaempferol 3-O-beta-D-apiofuranoside 7-O-alpha-L-rhamnosyl (1""-->6"')-O-beta-D (2"'-O-E-caffeoylgalactopyranoside) (5). In addition, several other known mono and diglycosidic flavonoids, along with 18 phenolic acids, were also identified and the structures of all of the compounds were established by LC/MS and NMR spectral investigations.

Synthesis, spectral, and antifungal studies of transition metal complexes with sixteen-membered hexadentate macrocylic ligand

A novel hexadentate nitrogen donor [N6] macrocyclic ligand viz, 1,5,11,15,21,22-hexaaza-2,14-dimethyl-l4,12-diphenyltricyclo[15.3.1.I(7–11)]docosane[1,4,6,8,10(22)-11,14,16,18,20(21)]decaene (L), has been synthesised. The Co (II), Ni (II), and Cu (II) complexes with this ligand have been prepared and subjected to elemental analysis, molar conductance, magnetic susceptibility measurements, mass, 1H NMR (ligand), IR, electronic, and ESR spectral studies and electrochemical investigation. On the basis of molar conductance the complexes can be formulated as [M(L)]X2 (where M = Co (II), Ni (II), Cu (II) and X = Cl− and NO3−) due to their 1: 2 electrolytic nature in DMSO. All the complexes are of the high-spin type and are six-coordinated. On the basis of IR, electronic, and ESR spectral studies, an octahedral geometry has been assigned for the Co(II) and Ni(II) complexes, whereas a tetragonal geometry for the Cu(II) complexes was found. Antimicrobial activity of L and its complexes as growth inhibiting agents have been screened in vitro against two species (F. moniliformae and R. solani) of plant pathogenic fungi.

Iron(III) complexes: Preparation, characterization, antibacterial activity and DNA-binding

Iron(III) have been combined to well known quinolones (ciprofloxacin) and some Schiff bases with the help of coordination approach. Characterization of these compounds have been done using elemental analysis, magnetic measurements, thermogravimetric analysis, IR, UV-VIS, 1H NMR and 13C NMR spectral investigation. Analytical studies suggest that the iron(III)-quinolone complexes assume a six-coordinated dimeric distorted octahedral geometry. All the compounds show a good antibacterial activity against broad range of bacteria like Bacillus cereus, Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Salmonella typhi and Serratia marcescens, whereas no significant inhibition towards growth of fungal strains like Aspergillus Niger, Aspergillus flavus and Lasiodiplodia theobromae. Analyses of all these compounds show effective sperm herring DNA inhibition.

Synthesis and Spectral Investigations of Manganese(II), Cobalt(II), Nickel(II), Copper(II) and Zinc(II) Complexes of New Polydentate Ligands Containing a 1,8-Naphthyridine Moiety

2-(o-Hydroxyphenyl)-1,8-naphthyridine (HN), 2-(4-hydroxy-6-methylpyran-2-one-3-yl)-1,8-naphthyridine (HMPN) and 2-(benzimidazol-2-yl)-1,8-naphthyridine(BN) react with acetates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) to yield metal ion complexes of definite composition. These compounds were characterized by elemental analyses, molar conductivity, magnetic susceptibility measurements, thermal studies, IR, UV-visible, NMR and mass spectral investigations. The complexes are found to have the formulae [M(HN)2(H2O)2], [M(HMPN)2(H2O)2] and [M(BN)2(OAc)2], respectively.

4-Acyl-5-hydroxy-1-phenyl-3-trifluoromethylpyrazoles: Synthesis and NMR Spectral Investigations

The title compounds were prepared by reaction of l-phenyl-3-trifluoromethyl-1H-pyrazol-5-ol with trimethyl orthoacetate, triethyl orthopropionate and triethyl orthobenzoate, respectively, followed by hydrolytic cleavage of the primarily formed condensation products. Detailed NMR spectroscopic investigations with the obtained products are presented, revealing the title compounds to be present as 5-hydroxypyrazoles stabilized by an intramolecular hydrogen bond in CDCl 3 solution.

Low potential electrosyntheses of free-standing polyfluorene films in boron trifluoride diethyl etherate

High quality free-standing polyfluorene (PFe) films were synthesized electrochemically by direct anodic oxidation of fluorene in pure boron trifluoride diethyl etherate (BFEE) on stainless steel sheet. The oxidation potential of fluorene in this medium was measured to be only 1.1 V versus SCE, which was much lower than that determined in acetonitrile + 0.1 mol L −1 TBATFB. PFe films obtained from this medium showed good electrochemical behavior, good thermal stability with conductivity of 0.25 S cm −1, indicating that BFEE is a better medium than acetonitrile for the electrosyntheses of PFe films. FTIR and 1H NMR spectral investigations indicated that the polymerization of fluorene occurred mainly at 2, 7 position. As-formed PFe films can be partly dissolved in acetone, acetonitrile, tetrahydrofuran, etc.