Colored Charge-transfer Complexes Research Articles

A New Spectrophotometric Method for Determination of Carvedilol from Tablet

In this study, a new spectrophotometric method was developed for the quantitative analysis of Carvedilol and the method was validated. The method depends on the reaction between the carvedilol and 1,2,5,8-tetrahydroxyanthraquinone in methanol to yield colored charge transfer complex giving maximum absorbance at 560 nm. For optimization of the proposed method, several parameters were investigated such as solvent type, reaction time, and quinalizarin concentration. The stoichiometry of colored charge transfer complex was found to be 2:1(reagent: drug) by Job’s method. Beer’s Law is obeyed in the concentration range of 0.5-60 µg/mL with 0.9986 correlation efficient. Limit of detection (LOD) and limit of quantifiqation (LOQ) were found 0.147 µg/mL, 0.491 µg/mL, respectively. The proposed method can be successfully applied pharmaceutical formulation.

Spectrophotometric Study of Charge-Transfer Complexes of Ruxolitinib with Chloranilic Acid and 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone: An Application to the Development of a Green and High-Throughput Microwell Method for Quantification of Ruxolitinib in Its Pharmaceutical Formulations

Ruxolitinib (RUX) is a potent drug that has been approved by the Food and Drug Administration for the treatment of myelofibrosis, polycythemia vera, and graft-versus-host disease. This study describes the formation of colored charge-transfer complexes (CTCs) of RUX, an electron donor, with chloranilic acid (CLA) and 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), the π-electron acceptors. The CTCs were characterized using UV-visible spectrophotometry. The formation of CTCs in methanol was confirmed via formation of new absorption bands with maximum absorption at 530 and 470 nm for CTCs with CLA and DDQ, respectively. The molar absorptivity and other physicochemical and electronic properties of CTCs were determined. The molar ratio was found to be 1:1 for both CTCs with CLA and CTCs with DDQ. The site of interaction on RUX molecules was assigned and the mechanisms of the reactions were postulated. The reactions were employed as basis for the development of a novel green and one-step microwell spectrophotometric method (MW-SPM) for high-throughput quantitation of RUX. Reactions of RUX with CLA and DDQ were carried out in 96-well transparent plates, and the absorbances of the colored CTCs were measured by an absorbance microplate reader. The MW-SPM was validated according to the ICH guidelines. The limits of quantitation were 7.5 and 12.6 µg/mL for the methods involving reactions with CLA and DDQ, respectively. The method was applied with great reliability to the quantitation of RUX content in Jakavi® tablets and Opzelura® cream. The greenness of the MW-SPM was assessed by three different metric tools, and the results proved that the method fulfills the requirements of green analytical approaches. In addition, the one-step reactions and simultaneous handling of a large number of samples with micro-volumes using the proposed method enables the high-throughput analysis. In conclusion, this study describes the first MW-SPM, a valuable analytical tool for the quality control of pharmaceutical formulations of RUX.

Development of novel green and high-throughput microwell spectrophotometric assay for one-step determination of dacomitinib, a recently approved potent drug for first-line treatment of metastatic non-small cell lung cancer

Dacomitinib (DAC) is the most recent drug approved drug for the first-line treatment of patients with metastatic non-small cell lung cancer. This study describes, for the first time, the development of a novel green and high-throughput microwell spectrophotometric assay (MW-SPA) for one-step determination of DAC. The assay was based on formation of a colored charge transfer complex between DAC, as electron donor, with 2,3-dichloro-3,5-dicyano-1,4-benzoquinone, as π-electron acceptor. Ultraviolet–visible spectrophotometry was used to characterize the complex and proposing the reaction mechanism. Under refined optimum reaction conditions, it was employed as a basis for the development of the proposed MW-SPA. The assay was conducted in 96-well assay plates, and the absorbances were measured by an absorbance plate reader. Validation of the assay was performed in accordance with guidelines of the International Council on Harmonization, and all validation parameters were acceptable. The limits of detection and quantitation of the MW-SPA were 1.2 and 3.7 μg/well, respectively. The assay was applied with great distinct success for determining DAC in its bulk form and vizimpro® tablets. The greenness of the assay was ascertained by three distinct metric tools, which conclusively demonstrated the adherence of the assay to principles of green analytical chemistry approach. Moreover, the assay has high throughput capacity as it can simultaneously process large number of micro-volume samples. In conclusion, the proposed MW-SPA is valuable for the rapid and routine determination of DAC for the purposes of quality control.

Development and Validation of 96-Microwell-Based Spectrophotometric and High-Performance Liquid Chromatography with Fluorescence Detection Methods with High Throughput for Quantitation of Duvelisib and Seliciclib in Their Bulk Forms and Capsules

The Food and Drug Administration (FDA) has approved duvelisib (DUV) for managing follicular lymphoma, small lymphocytic lymphoma, and relapsed or refractory chronic lymphocytic leukemia. Seliciclib (SEL) is a candidate drug for these cancers, neurodegenerative disorders, renal diseases, several viral infections, and chronic inflammation disorders. This work describes the development and validation of a 96-microwell-based spectrophotometric method (MW-SPM) and a high-performance liquid chromatography with fluorescence detection method (HPLC-FD) for the quantitation of DUV and SEL in their bulk forms and capsules. The MW-SPM is based on the formation of colored charge transfer complexes (CTCs) as products for the reactions of DUV and SEL, as n-electron donors, with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), as a π-electron acceptor. The absorption intensity of the CTCs was measured by using an absorbance plate reader at 450 nm. The stoichiometric ratios of DUV:DDQ and SEL:DDQ were 1:1 and 1:2, respectively, and accordingly the reaction mechanisms were postulated. The HPLC-FD involved the chromatographic separation of DUV and SEL on a Hypersil™ Phenyl HPLC column (250 mm length × 4.6 mm i.d., 5 μm particle diameter) with a mobile phase composed of acetonitrile:acetate buffer, pH 4.5 (35:65, v/v) at a flow rate of 2.2 mL/min. DUV and SEL were detected at 370 nm after excitation at 280 nm. SEL was used as an internal standard (IS) for quantitation of DUV, and DUV was used as an IS for quantitation of SEL. Both MW-SPM and HPLC-FD were validated according to the guidelines of the International Council for Harmonization (ICH) for validation of analytical procedures. The linear ranges for both DUV and SEL were 14.52–200 µg/well (100 µL) and 0.12–3.2 µg/mL for MW-SPM and HPLC-FD, respectively. LOD values in MW-SPM for DUV and SEL were 4.4 and 3.17 µg/well, respectively; however, those for HPLC-FD were 0.03 and 0.05 µg/mL, respectively. The accuracy and precision of both methods were confirmed as the recovery values were ≥98.5% and the values of relative standard deviations (RSD) were ≤2.41%. Both methods were satisfactorily applied to the quantitation of DUV and SEL in their capsules; the mean recovery values were ≥99.2%. Both methods have simple procedures and high analytical throughput. Moreover, they consume a small volume of organic solvent; thus, they are economic and eco-friendly. Accordingly, the methods are valuable for routine use in quality control (QC) laboratories for quantitation of DUV and SEL in their bulk forms and capsules.

Development and validation of three colorimetric charge transfer complexes for estimation of fingolimod as an antineoplastic drug in pharmaceutical and biological samples

An inexpensive, simple, sensitive and validated approach is developed for estimation of fingolimod through production of colored charge transfer complexes of fingolimod with different electron acceptor reagents, including a reaction of fingolimod as n-donor with 7,7,8,8-tetracyanoquinodimethane, tetrachloro 1,4-benzoquinone and tetracyanoethylene and as n-acceptors, yielding colored and stable anions which were measured spectrophotometrically. The range that obeyed Beer’s law is 50–300 µg mL−1 for fingolimod with all the studied reagents. The various parameters that affect the reaction were studied and optimized. The results were statistically compared with a reported method showing equal precision and accuracy. The researched approaches were utilized to determine the cited drug in its pharmaceutical form and spiked human plasma with accepted accuracy and precision.

Synthesis, characterization, biological and DFT studies of charge-transfer complexes of antihyperlipidemic drug atorvastatin calcium with Iodine, Chloranil, and DDQ

Extremely coloured charge-transfer complexes (CTCs) of antihyperlipidemic drug, atorvastatin calcium (ATC) acting as n-electron donor with the electron acceptors, namely, iodine as σ-acceptor, 2,3,4,6-tetrachloro-1,4-benzoquinone (chloranil, CHL), 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-acceptors have been explored. Elemental analysis, thermal analysis, FTIR spectroscopy, Raman spectroscopy, NMR spectroscopy, and mass spectroscopy techniques were used to explain the chemical mechanism of the synthesized ATC-CTCs. It has been found that the stoichiometry of the complexes was to be 1:1 ratio in ATC-iodine and 1:2 ratio in ATC-CHL; ATC-DDQ. Elemental and mass analysis were confirmed the above ratio of ATC-CTCs which was [(ATC)I]I3, [(ATC)(CHL)2], and [(ATC)(DDQ)2] respectively. The biological activities of the formed ATC-CTCs were also tested against various bacterial strains. In addition, the frontier molecular orbitals (FMO) of the title compound was performed at the HF/6-311G** level to display the favourable reactivity tendency and the best suitable site for the electrophilic and nucleophilic attacks. The natural bond orbital (NBO) analysis was employed to predict the possible non-covalent interactions and its result disclosed that the n → Π* and Π → Π* interactions had a critical role in the enlightening of the stabilization of the compound. The achieved results are more appropriate for the estimation of antihyperlipidemic drug, ATC in pharmaceutical dosage forms.

Ethylenediamine-bound magnetite nanoparticles as dual function colorimetric sensor having charge transfer and nanozyme activity for TNT and tetryl detection.

A reusable, low-cost, and convenient ethylenediamine (EDA)-bound magnetite nanoparticles (MNPs)-based colorimetric sensor has been developed for dual function colorimetric determination of nitroaromatic explosives such as TNT and tetryl. Colorimetric detection of analytes may occur through two independent routes: (1) nano-Fe3O4- EDA- NH2 as σ-donor may interact with the σ- and π-acceptor aromatic-poly(NO2) groups to produce a colored charge-transfer (CT) complex; (2) nano-Fe3O4-EDA-NH2 as a Fenton-type nanozyme may generate reactive species that comprise hydroxyl radicals (•OH) with H2O2 to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) to a blue-colored diimine (oxTMB-TMB) CT complex, where this color is bleached with TNT/tetryl because of donor-acceptor interactions between the explosive -NO2 groups and the -NH2 group of Fe3O4-EDA nanoparticles of restricted nanozyme activity. Both methods can quantify TNT well below the EPA recommended TNT residential screening level in soil, LOD being in the micromolar range. As EDA was covalently bound to MNPs, the same sensor can be separately reused six times for TNT and eight times for tetryl determination, using method(1). Common metal ions, anions, energetic materials, several camouflage materials, and soil components such as humates did not interfere with thenanosensor performance for TNT and tetryl. Thecombination of charge-transfer and nanozyme ability of Fe3O4- EDA-NH2 nanoparticles may bring a new approach to dual function colorimetric sensor design. To the best of our knowledge, this is the first dual function colorimetric sensor for TNT and tetryl using the same nanoparticles as sensing elements in two different detection systems involving either formation or bleaching of colored species. The proposed colorimetric sensor can determine nitroaromatic explosives in two different ways: method-1 for TNT and tetryl sensing with EDA-MNPs relies on the donor-acceptor interaction between the electron-deficient nitroaromatics and electron-rich amine groups covalently functionalized on MNPs to produce an absorbance at 512nm. In method-2, EDA-MNPs having nanozyme activity react with H2O2 to form reactive species that can oxidize TMB to its blue-colored charge-transfer (CT) complex, where TNT and tetryl addition may partially inhibit the nanozyme activity of EDA-MNPs and cause color bleaching (decrement of 650nm absorbance) by disrupting the CT complex formed from TMB. This is the first dual function colorimetric sensor for nitro explosives uniquely combining charge-transfer and nanozyme ability of EDA-Fe3O4 nanoparticles in the same nano-sensor.

A Donor-Acceptor [2]Catenane for Visible Light Photocatalysis.

Colored charge-transfer complexes can be formed by the association between electron-rich donor and electron-deficient acceptor molecules, bringing about the narrowing of HOMO-LUMO energy gaps so that they become capable of harnessing visible light. In an effort to facilitate the use of these widespread, but nonetheless weak, interactions for visible light photocatalysis, it is important to render the interactions strong and robust. Herein, we employ a well-known donor-acceptor [2]catenane-formed by the mechanical interlocking of cyclobis(paraquat-p-phenylene) and 1,5-dinaphtho[38]crown-10-in which the charge-transfer interactions between two 4,4'-bipyridinium and two 1,5-dioxynaphthalene units are enhanced by mechanical bonding, leading to increased absorption of visible light, even at low concentrations in solution. As a result, since this [2]catenane can generate persistent bipyridinium radical cations under continuous visible-light irradiation without the need for additional photosensitizers, it can display good catalytic activity in both photo-reductions and -oxidations, as demonstrated by hydrogen production-in the presence of platinum nanoparticles-and aerobic oxidation of organic sulfides, such as l-methionine, respectively. This research, which highlights the usefulness of nanoconfinement present in mechanically interlocked molecules for the reinforcement of weak interactions, can not only expand the potential of charge-transfer interactions in solar energy conversion and synthetic photocatalysis but also open up new possibilities for the development of active artificial molecular shuttles, switches, and machines.

Innovative use of σ and π electron acceptors in the development of three high throughput 96-microwell spectrophotometric assays for crizotinib

Crizotinib (CZT) is a potent and selective tyrosine kinase inhibitor used for treatment of non-small cell lung cancer (NSCLC). The development of high-throughput assays for its quality control (QC) is very essential to assure its therapeutic benefits. CZT molecule has multiple electron-donating atoms that can contribute to the formation of colored charge-transfer (CT) complex with iodine as σ-electron acceptor and with 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (CHBQ) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) as π-electron acceptors. These reactions were prospective basis for development of three innovative 96-microwell-based spectrophotometric assays for CZT. The reactions of CZT with iodine, CHBQ and TCNQ were performed in 96-microwell assay plates and absorbances of the CT complexes were measured by microwell absorbance reader at their corresponding maximum absorption peaks. The measured absorbances were correlated with the CZT concentrations in its sample solutions. Beer’s law was obeyed with excellent correlation coefficients in the range of 0.5–30, 2–500, and 5–500 µg mL−1 for assays using iodine, CHBQ and TCNQ, respectively. The limits of detection were 2.17, 0.85 and 6.23 µg mL−1 for assays using iodine, CHBQ and TCNQ, respectively. The validation studies confirmed the accuracy and precision of all the proposed assays. The assays were successfully applied in the determination of CZT in Xalkori capsules. The proposed assays have very simple procedures to run in QC laboratories. Also, both assays enable analyst to process large number of samples and use of very small volumes of the organic solvent (ecofriendly and inexpensive).

Dual-Purpose SERS Sensor for Selective Determination of Polycyclic Aromatic Compounds via Electron Donor-Acceptor Traps.

Toxic, carcinogenic, and mutagenic properties of polycyclic aromatic hydrocarbons (PAHs) and environmental pollution caused by polycyclic aromatic sulfur heterocycles (PASHs) postulate the importance of their selective and sensitive determination in environmental and oil fuel samples. Surface-enhanced Raman spectroscopy (SERS) opens up an avenue toward multiplex analysis of complex mixtures, however not every molecule gives high enhancement factors and, thus, cannot be reliably detected via SERS. However, the sensitivity can be drastically increased by additional resonant enhancement as a result of the analyte absorption band overlapping with the surface plasmon band of nanoparticles (NPs) and the laser excitation wavelength. Using this idea, we developed a dual-purpose SERS sensor based on trapping the target PAHs and PASHs into colored charge-transfer complexes (CTCs) with selected organic π-acceptor molecules on the surface of AgNPs. Studying, computing, and then comparing stability constants of the formed CTC served as a powerful explanation and prediction tool for a wise choice of π-acceptor indicator systems for the further silver surface modification. Moreover, we show that CTC formation can be effectively utilized for increasing both selectivity and sensitivity by simple liquid-liquid extraction prior to SERS measurements. For the first time, the dual-purpose SERS sensor allowed determination of two different classes of polycyclic aromatic fuel components down to 10 nM concentration, lower than that restricted by the ASTM regulation, and demonstrated multi-purpose capabilities of the developed approach.

Charge Transfer Spectrophotometric Determination of Metronidazole in Pharmaceutical Formulations by Normal and Reverse Flow Injection Analysis Coupled with Solid-Phase Reactor Containing Immobilized FePO4

Two rapid, simpleand sensitive flow injection methods were developed for the estimation of metronidazole (MRZ) in pharmaceutical formulations. The proposed methods were based on charge transfer reaction between metol (N-methyl-p-aminophenol sulfate) as a π-acceptorand reduced MRZ as an n-donor to produce a blue colored chargetransfer complex. Method A depends on the reaction of reduced MRZ with metol (MT) in the presence of NaIO4 using two lines manifold to form blue colored product exhibiting absorption maxima at 700 nm.While method B depends on charge transfer reaction of reduced MRZ with MT in presence of a solid phase reactorcontainingfixedFePO4 on cellulose acetateusing reverse flow injection manifold to form a blue colored productwhich was measured spectrophotometrically at690 nm.Various experimental parameters for both methods were studied. Beer's law was obeyed in the ranges of2.5-200 and 2.5-150 μg mL-1,with r2 of 0.9995 and 0.9972;whilethe detection limit values were2.53 and 2.12μg mL-1 for methods A and B, respectively. Both of the suggested methods were successfully applied for the estimation of MRZ in commercial formulations. The results of the developed methods were compared with those obtained by the British pharmacopeia method, showinghigh accuracy and precision.

Synthesis, spectroscopic, thermal, structural investigations and biological activity studies of charge-transfer complexes of atorvastatin calcium with dihydroxy-p-benzoquinone, quinalizarin and picric acid

The charge-transfer interactions between n-electron donor, atorvastatin calcium (ATC) and the electron acceptors, 2,5-dihydroxy-1,4-benzoquinone (DHBQ), 1,2,5,8-tetrahydroxy-9,10-anthraquinone (quinalizarin, Quiz), and 2,4,6-trinitrophenol (picric acid, PA) as π-acceptors have been studied spectrophotometrically in methanol by giving highly colored charge transfer complexes. The isolated solid charge-transfer complexes were characterized by elemental, IR, NMR, mass and thermal analysis to elucidate the chemical structure of the obtained solid CT complexes. The stoichiometry of the complexes was found to be 1:2 in [ATC]:[reagent] at DHBQ, quinalizarin, picric acid. This ratio gave the formed charge-transfer complexes in the formulas [(ATC)(DHBQ)2], [(ATC)(Quiz)2], and [(ATC)(PA)2] which was also confirmed by elemental and mass analysis. Their biological activities were also screened against various bacterial organisms. The obtained results are suitable for the estimation of antihyperlipidemic drug, ATC in pharmaceutical dosage forms.

Validated spectrophotometric determination of maduramicin ammonium using three charge transfer complexation reactions

Direct spectrophotometric determination of Maduramicin ammonium (MAD) represents an analytical challenge since it is a weak UV-absorbing and lacking a strong chromophore. This work represents the first spectrophotometric determination of MAD as no direct spectrophotometric or colorimetric determination methods for MAD are available in the literature. The present study illustrates the development of three simple, rapid and inexpensive colorimetric methods for the routine quality control analysis of MAD based on the formation of colored charge transfer complexes with three electron acceptors namely p-chloranilic acid (p-CA), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) and picric acid (PA). The color products of MAD with p-CA, DDQ and PA were measured at 519, 588 and 405nm respectively. The proposed methods were validated in terms of linearity, ranges, precision, accuracy, robustness and limits of detection and quantification. MAD was effectively determined over concentration ranges of 100-1000, 25-250 and 30-150μg/mL using p-CA, DDQ and PA, respectively with good linearity as shown by the values of correlation coefficients not less than 0.9991. The developed methods were successfully implemented in the assay of MAD powder pharmaceutical formulation for veterinary use.

Colorimetric Determination of Uric Acid in Live samples

A simple, sensitive and precise colorimetric method for uric acid determination was described. The method based on the complexion reaction between uric acid, potassium ferricyanide, and ferric chloride in hydrochloric acid medium to form blue colored charge transfer complex measured at maximum wavelength 752 nm. The optimum conditions obtained were volume 0.3 ml for hydrochloric acid, 1.25 ml for both potassium ferricyanide and ferric chloride solutions, 60?C and 8 minutes as maximum temperature and time of reaction, the order of mixing additives was uric acid, ferric chloride, potassium ferricyanide, and hydrochloric acid. The highly accurate and precise results obtained with RSD%, Recovery%, Ere%, and D.L were (0.755 to 4.376), (99.676 to 97.831), (-0.033 to -2.169), and 0.1569 µg mL-1 respectively, the calibration graphs were linear in the concentration range of (2.0-200µg ml-1), the . molar absorptivity (5937.473L mol-1 cm-1) The proposed methods were successfully applied for the determination of uric acid in serum and urine samples for twenty persons.

SYNTHESIS AND CHARACTERIZATION OF THE CHARGE TRANSFER COMPLEXES POLYVINYL CARBAZOLE WITH TRINITROFLUORENONE

Carbazole based polymers are materials of considerable scientific and industrial interest due to their attractive features, such as hole-transporting, high charge-carrier mobility, and electroluminescent properties. Poly (N-vinyl carbazole) (PVK) is easily synthesized, soluble in common organic solvents, poly (N-vinyl carbazole)/2,4,7-trinitro-9-fluorenone (PVK/TNF) charge transfer complex is one of the best-known organic photos conducting materials for application in electrophotography. In the present research, a spectrophotometric method applied for the study of (colored charge transfer complexes) CTC of PVK with TNF reveals the formation of 1:1 (A:D) complex, the formation of CTC with PVK and TNF from the conductivity of the CT Complex. The concentration of the donor is affected when it reacts with the acceptor and that when we increase the concentration of the donor.

Development of two spectrophotometric methods for quantification of certain anti-depressant drug in pure, pharmaceutical formulation and application to content uniformity testing

Two accurate, rapid, simple, robust and extraction-free spectrophotometric techniques were created for assay of Amisulpride (AMS) in pure and tablet preparation. The described methods have been established on the reaction of methanolic solution of AMS with 4-(dimethylamino) benzaldehyde in acidic medium which give yellow product that can be determined at λmax = 400 nm (method-I) and the reaction AMS with tetrachloro-1, 4-benzoquinone (p-Ch) which yields intense blue to purple colored charge transfer complex that can be determined at λmax = 559 nm (method-II). The prescribed assay obeys Beer's law within the range from 20 to 200 and 50–400 micrograms per milliliter for method-I & method-II orderly. Detection limits have been 4.4 & 10.6 μg/mL while quantitation limits have been 13.2 & 32.0 micrograms per milliliter for method-I & method-II orderly. Developed methods were validated according to guidelines of International conference on Harmonization for the detection of cited drug in pure, pharmaceutical preparations and content uniformity testing.

Photosensitized TiO2 films on polymers – Titania-polymer interactions and visible light induced photoactivity

Photocatalytic coatings at polymers, showing a visible light induced photoactivity, can be synthesized using a low temperature oxygen plasma treatment of the polymer (PP) followed by deposition of TiO2 nanoparticles and their sensitization with organic ligands. The whole process consists of three major steps: surface activation involving its partial oxidation, immobilization of TiO2 nanoparticles and photosensitization of titania film by impregnation with the solution of organic ligands forming surface Ti(IV) charge transfer complexes. XPS and IR analysis revealed the formation of oxygen-containing groups at the polymer surface upon plasma treatment. These groups participate in the formation of TiOC bonds which ensure a very good adhesion of titania films to polymeric surface. The dip-coating process using an aqueous colloidal solution of TiO2 nanoparticles allows to synthesize a compact coating with a thickness of 100–300 nm. Coordination of catechol-like ligands to surface Ti(IV) centers results in formation of colored charge transfer complexes responsible for absorption of visible light and an effective photoinduced charge separation. Photogenerated electrons and holes can take part in surface redox reactions responsible for degradation of pollutants. Tests with various organic ligands (catechol, 2,3-naphthalenediol, pyrogallol and rutin) revealed, that the titanium dioxide coating modified with catechol was the most photoactive one when visible light irradiation was applied. Presented photocatalytic coatings can be effectively used as self-sterilizing surfaces activated by visible light.

A Calixarene-Based Metal-Organic Framework for Highly Selective NO2 Detection.

A calixarene-based metal-organic framework (Zr-cal, [Zr6 O4 (OH)4 (FA)6 ]2 (cal)3 ], FA=formate, cal=1,3-alt-25,26,27,28-tetrakis[(carboxy)methoxy]calixarene) was synthesized and characterized by single-crystal X-ray diffraction. The three-dimensional framework is a 4,6-connected network of gar topology and exhibits two equal but nonintersecting three-dimensional pore systems. It has a specific BET surface area of 670 m2 g-1 , and the calixarene cavities are accessible through the pore systems. The exposed calixarenes can be used for the visual detection and encapsulation of NO2 through the formation of deeply colored charge-transfer complexes inside the MOF. The highly selective complexation was analyzed by UV/Vis and IR spectroscopy, and the stability of the material was confirmed by powder X-ray diffraction and 1 H NMR spectroscopy. Finally, the MOF was used as a sensor material in a home-made sensor cell and showed high sensitivity for NO2 .

Visual detection of peroxide-based explosives using novel mimetic Ag nanoparticle/ZnMOF nanocomposite

A simple and selective colorimetric method for the detection of perilous peroxide explosives was developed using the peroxidase mimetic activity of silver nanoparticles/flake-like zinc metal-organic framework nanocomposite (Ag@ZnMOF). The synthesis of Ag@ZnMOF contained the formation of silver nanoparticles (AgNPs) inside the fine pores of Zn metal-organic framework (ZnMOF). High reactive AgNPs as well as great surface area of MOFs provided a synergetic and high improved catalytic activity for the composite which was studied as a peroxidase mimic in hydrogen peroxide (H2O2)-based oxidations. The achieved system was used for detection of Triacetone triperoxide (TATP) as one of the most hazardous peroxide explosives. TATP was decomposed in an acidic condition to generate H2O2, which was then applied to oxidize 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of the Ag@ZnMOF as a catalyst. This reaction led to the production of well-known blue colored charge transfer complex (oxTMB), which was recognized by the colorimetric technique. A linear relationship was obtained between the absorption intensity of the produced blue solution and the TATP concentration in the range of 0.4-15 mg L-1, with a detection limit of 0.1 mg L-1. A portable test kit was prepared using the same reagents for TATP measurement in real samples.

Visualization of Phase-Transfer Catalysis through Charge-Transfer Complexes

Unlike the large number of laboratory experiments on phase-transfer catalysis (PTC) that focus on a catalyzed chemical process, the present laboratory emphasizes the mechanism of phase-transfer catalysis itself. Students can follow visually the actual transfer of the reagent by the catalyst, and its consumption in the organic phase, in a step-by-step process that employs a colored charge-transfer (CT) complex as the transferred reacting species. Consumption of the transferred nucleophile is followed by discoloration of the organic phase. This transfer-consumption cycle can be repeated several times by shaking the two separated phases again, allowing students to finally grasp the whole process as a continuous repetition of these cycles. The experiment also links, through visualization, the important synthetic tool of PTC with abstract concepts based on molecular-orbital and hard–soft acid–base theories, invoked in the formation of a CT complex.