Ultraviolet-visible Titration Research Articles

Synthesis, Spectroscopic Evaluations and UV-Vis Titration Studies of New Symmetrical Amide Compounds Derived from N-6-[(4-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic Acid Methyl Ester

In this study, 2 flexible and pre-organized tetraamide compounds derived from N-6-[(4-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic acid methyl ester namely 1,2-bis[N,N’-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]pentane (L1) and 1,2-bis[N,N’-6-(4-pyridylmethylamido)pyridyl-2-carboxyamido]hexane (L2) have been successfully synthesized when reacted with diamines in 1:2 ratio. These new compounds were built from combination of 3 main components, as a trend requires for anion receptor which are (i) 2,6-pyridine dicarboxamide moieties as targeted anion binding host, (ii) amino methyl pyridine pendants arms as the flexible moieties and (iii) pentyl (-C5H10-) and hexyl (-C6H12-) unit as the spacer. Compounds L1-L2 were fully characterized by using elemental analyzer, Fourier transform infrared (FTIR) spectroscopy, gas chromatography-mass spectroscopy (GC-MS), 1H, 2D NOESY and 13C Nuclear Magnetic Resonance (NMR) spectroscopies, and Ultraviolet-visible (UV-Vis) spectroscopies. In this study, anion titration methods were used to identify the affinity towards selected anions. The results showed that L1 (having a pentyl spacer) had the highest affinity towards phosphate anions as compared to L2, where the red shift changes were observed in the UV-vis spectrum at the amide region. HIGHLIGHTS Two novel amide compounds with flexible and pre-organized structure are designed for use as potential anion receptors The flexible moieties at the amide and the linker allow hydrogen bonding interaction of the molecules with variety anions with different geometries Anion titration studies revealed good affinities towards phosphate anions as suggested in Hofmeister trend GRAPHICAL ABSTRACT

Supramolecular Chirogenesis in Bis-Porphyrin: Crystallographic Structure and CD Spectra for a Complex with a Chiral Guanidine Derivative

The complexation of (3aR,7aR)-N-(3,5-bis(trifluoromethyl)phenyl)octahydro-2H-benzo[d]imidazol-2-imine (BTI), as a guest, to ethane-bridged bis(zinc octaethylporphyrin), bis(ZnOEP), as a host, has been studied by means of ultraviolet-visible (UV-Vis) and circular dichroism (CD) absorption spectroscopies, single crystal X-ray diffraction, and computational simulation. The formation of 1:2 host-guest complex was established by X-ray diffraction and UV-Vis titration studies. Two guest BTI molecules are located at the opposite sides of two porphyrin subunits of bis(ZnOEP) host, which is resting in the anti-conformation. The complexation of BTI molecules proceed via coordination of the imine nitrogens to the zinc ions of each porphyrin subunit of the host. Such supramolecular organization of the complex results in a screw arrangement of the two porphyrin subunits, inducing a strong CD signal in the Soret (B) band region. The corresponding DFT computational studies are in a good agreement with the experimental results and prove the presence of 1:2 host-guest complex as the major component in the solution (97.7%), but its optimized geometry differs from that observed in the solid-state. The UV-Vis and CD spectra simulated by using the solution-state geometry and the TD-DFT/ωB97X-D/cc-pVDZ + SMD (CH2Cl2) level of theory reproduced the experimentally obtained UV-Vis and CD spectra and confirmed the difference between the solid-state and solution structures. Moreover, it was shown that CD spectrum is very sensitive to the spatial arrangement of porphyrin subunits.

Electrochromic and bipolar memory switching properties of novel Eu(III)-polymer of multidentate Schiff’s base ligand

In the past thirty years, scientists have put enormous efforts into developing smart materials with multiple functionalities. Among such existing intelligent materials, electrochromic and non-volatile memory materials synthesized via organic–metallic hybrid polymers have shown their remarkable presence. To date, a wide variety of transition metal ions have been adopted for forming these polymers. However, reports on the use of lanthanide metal ion for observing such smart behaviour are uncommon. Therefore, the present report focuses on synthesizing a novel Eu(III) metal ion-based organic–metallic hybrid polymer for observing the smart properties using previously reported Schiff’s base polydentate organic ligand. Further, its different possible coordination modes with the ligand have been discussed. The structure of the polymer has been fully supported by Nuclear Magnetic Resonance and Ultraviolet–visible titration. Along with this, the reversible redox properties of this polymer have also been established along with the study of their spectroelectrochemical properties between yellow and bleached colour. The Resistive Random Access Memory properties of this polymer have been observed by spin coating polymer on Indium Tin Oxide coated substrate for fabricating a Metal–Insulator–Metal structure. The bipolar Current–Voltage (I–V) characteristics of this polymer in both the biasing directions have been observed, with the repeatability of about 1000 cycles for Write-Read-Erase-Read operation. The retention capability of this polymer has also been established for 2000 pulses. Thus, the current work presents fascinating aspects of using a lanthanide metal ion collectively for studying both the redox-active properties, i.e. electrochromic and non-volatile memristive properties.

Aloe emodin inhibits telomerase activity in breast cancer cells: transcriptional and enzymological mechanism.

Telomerase plays an essential role in cancer cell proliferation. In this study, we investigated inhibition mechanism of aloe emodin (AE) on three different types of breast cancer cell lines, MDA-MB-453, MDA-MB-231 and MCF-7. The cells were treated with different concentrations of AE. Relative length of telomere and human telomerase reverse-transcriptase (hTERT) mRNA level was analyzed by quantitative PCR (qPCR). Protein level was assayed by Western blot. Sodium bisulfite methylation sequencing was performed to assess the methylation status of gene promoter. Enzymology kinetics was applied to reveal the interaction between AE and telomerase. Ultraviolet-visible titration and fluorescence resonance energy transfer (FRET) melting experiment were carried out to study the interaction between AE and telomeric DNA. Continuous AE exposure of these cells for 48 h results in shortening of telomeres and inhibition of telomerase. The transcription of hTERT was repressed by activation of E2F1 and inactivation of c-myc proteins. Significant demethylation of CpG islands in hTERT gene promoter was observed in MDA-MB-453 and MCF-7 cells. AE competed with dNTP for occupation of the enzyme active site. AE was a telomeric G-quadruplex structure stabilizer as indicated by titration test and FRET experiments. AE was a competitive inhibitor of telomerase and a G-quadruplex structure stabilizer. AE decreased the transcription of hTERT gene in the three breast cancer cell lines via up-regulation E2F1 and down-regulation c-myc expressions. The suppressed transcription was also related to the demethylation of the gene promoter.

Halogenation as a Strategy to Improve Antiplasmodial Activity: A Report of New 3-Alkylpyridine Marine Alkaloid Analogs

Introduction: Due to the emergence of resistance to antimalarial drugs as well as the lack of vaccination for malaria, there is an urgent demand for the development of new antimalarial alternatives. Recently, our research group developed a new set of 3-alkylpyridine marine alkaloid analogs, of which a compound known as compound 5 was found to be inactive against Plasmodium falciparum.Methods: Herein, we report a successful halogenation strategy to improve the antiplasmodial activity of compound 5 through the replacement of a hydroxyl group by chlorine (compound 6) and fluorine (compound 7) atoms. Results: Compounds 6 and 7 showed improved antiplasmodial activities (IC50 = 7.2 and 8.3 µM, respectively) 20 times higher than that of their precursor, compound 5 (IC50 = 210.7 µM). Ultraviolet-visible titration experiments demonstrated that halogenation of compound 5 did not alter its ability to bind its target, hematin. Conclusion: Halogenation can enhance the antiplasmodial activity of a compound without altering its mechanism of action.

Binding Study of the Fluorescent Carbazole Derivative with Human Telomeric G-Quadruplexes.

The carbazole ligand 3 was synthesized, characterized and its binding interactions with human telomeric (22HT) G-quadruplex DNA in Na+ and K+-containing buffer were investigated by ultraviolet-visible (UV-Vis) spectrophotometry, fluorescence, circular dichroism (CD) spectroscopy, and DNA melting. The results showed that the studied carbazole ligand interacted and stabilized the intramolecular G-quadruplexes formed by the telomeric sequence in the presence of sodium and potassium ions. In the UV-Vis titration experiments a two-step complex formation between ligand and G-quadruplex was observed. Very low fluorescence intensity of the carbazole derivative in Tris HCl buffer in the presence of the NaCl or KCl increased significantly after addition of the 22HT G4 DNA. Binding stoichiometry of the ligand/G-quadruplex was investigated with absorbance-based Job plots. Carbazole ligand binds 22HT with about 2:1 stoichiometry in the presence of sodium and potassium ions. The binding mode appeared to be end-stacking with comparable binding constants of ~105 M−1 as determined from UV-Vis and fluorescence titrations data. The carbazole ligand is able to induce formation of G4 structure of 22HT in the absence of salt, which was proved by CD spectroscopy and melting studies. The derivative of carbazole 3 shows significantly higher cytotoxicity against breast cancer cells then for non-tumorigenic breast epithelial cells. The cytotoxic activity of ligand seems to be not associated with telomerase inhibition.

A multidentate ligand chromophore with rhodamine-triazole-pyridine units and its acting mechanism for dual-mode visual sensing trace Sn2+

A multidentate ligand chromophore, combining rhodamine, triazole, and pyridine units, was identified and developed for the first time. Using triazole and pyridine rings as coordinating functional recognition groups, it was expected to selectively recognize Sn2+ to form some stable 5-member or 6-member rings with nitrogen and oxygen atoms. Under the optimized conditions, the ligand chromophore could selectively react with trace Sn2+ in CH3CN/H2O (99/1, v/v), accompanying with obvious changes in fluorescent spectrum, ultraviolet-visible spectrum and visual color. For fluorescent analysis, a turn-on fluorescence at 587 nm was found and increased linearly in the range of 1.2–6.2 × 10−7 mol L−1 Sn2+ from colorless to orange. For ultraviolet-visible one, a new absorption peak at 560 nm emerged with a linear range of 2.0–11.0 × 10−7 mol L−1 Sn2+ from colorless to pink. The action mechanism between the ligand chromophore and Sn2+ was confirmed basing on ultraviolet-visible titration, 1H NMR titration, Job's plot, binding constants and theoretical calculation in detail.

Coordination study of chitosan and Fe 3+

The coordination of Fe 3+ with chitosan was studied, considering the type of acid for dissolving the ligand, the pH for the medium, and the metal-biopolymer ratio. Potentiometric and ultraviolet–visible titrations, infrared spectroscopy, thermal analysis and X-ray diffraction were employed. The polymer coordinates with the metal cation through the amino and hydroxyl groups in the entire pH range studied, with pH values around 3–6 being the most important region. The logarithms of the overall binding constants for the equilibria were: A: Chit–Fe, β A 16.06 ± 0.07; B: Chit 2–FeH, β B 32.64 ± 0.07; C: Chit 3–Fe, β C 35.6 ± 0.1; D: Chit 3–FeH, β D 49.0 ± 0.2, respectively. The coordination is made either by the amino or/and the hydroxyl groups with water molecules or/and chloride ions completing the coordination sphere for the metal giving rise to among other possible, di- to hexacoordinated complexed species [FeNO 2Cl 3], [FeN 2O 2Cl 2], [FeN 3O 3] and [FeN 2O 4].

Complexes of carboxymethylcellulose in water. 1: Cu 2+, VO 2+ and Mo 6+

The importance of finding alternative materials to remediation of natural and waste waters is undoubted nowadays. The search for inexpensive and renewable substances that could grab metal ions and safely return the used waters to be used again is a matter of great importance. The properties of carboxymethylcellulose (CMC) renewable, inexpensive and water soluble biopolymer, in the absence and in the presence of some metal ions that have varying industrial applications, are reported in this work. Potentiometric and ultraviolet–visible titrations were performed in aqueous solutions of CMC in the absence and in the presence of Cu 2+, VO 2+ and Mo 6+ obtaining the values of the logarithms of the binding constants (stepwise formation constants) considering the complexation towards the monomeric sugar repeating units of CMC (HL) as follows, 10.63 ± 0.08, 12.08 ± 0.02 and 15.89 ± 0.03 for ML, when M was Cu 2+, VO 2+ and Mo 6+, respectively. For ML 2, the calculated values were 8.54 ± 0.08 and 9.1 ± 0.1 for Cu 2+ and VO 2+, respectively. Other binding constants were detected and their values calculated. The quantitatively obtained infrared spectra of the solids precipitated from aqueous systems revealed decreasing intensity in the –OH and –COOH bands as the pH values of the solution in which the solids were obtained were raised. These results matched the species distribution diagrams obtained in the aqueous studied systems. Also the solids were inspected for their thermal behavior and the results showed a more thermally stable complex species than the CMC alone. Scanning Electron Microscopy showed stable, compact and homogeneous films. CMC will be employed as a remediation agent in different aqueous solutions containing metal ions and the results will be released soon.