Dimethylformamide Solvent Research Articles

Solvent-Assisted Hot Melt Extrusion of a Thermally Labile, High Melting Point Compound

Molecular dispersions are a highly effective method of increasing bioavailability for a poorly soluble active pharmaceutical ingredient (API) and can be prepared on a large scale by hot melt extrusion (HME). Processing thermally labile active pharmaceutical ingredients (APIs) via HME is generally more difficult, with operating temperatures limited to below that of the API melting point. API melting is considered essential to facilitate the formation of a fully homogeneous amorphous system. Processing below the melting point renders the system much more susceptible to residual crystalline content; hence, HME is not suitable for APIs which degrade upon melting. In the following work, meloxicam (MEL) was used as a model API, possessing properties of high melting temperature and thermal lability. In this proof of concept work, a modified HME method, termed solvent-assisted HME, was used to overcome this issue and prepare an amorphous solid dispersion using HME, wherein a solvent was incorporated in the formulation blend during extrusion and removed post-processing. Formulations containing 10%wt meloxicam (MEL) and 90%wt polyvinylpyrrolidone vinyl acetate (PVPVA) copolymer were extruded using a twin-screw extruder at temperatures below the melting point of MEL. Dimethylformamide (DMF) solvent was added directly into the extruder barrel through a liquid addition port, resulting in extrudate products having a higher conversion of API to the amorphous form. The incorporation of solvent allowed a significant reduction in processing temperatures due to its increased mobility, while also driving the conversion of the API to its amorphous form. The solvent was successfully reduced through a secondary drying step using a vacuum oven. This advancement has demonstrated the potential for thermally labile APIs to be processed via HME expanding the applications of this technology.

Effect of chlorobenzene on the optical and structural properties of CH3NH3PbI3:DMF perovskite films

Methylammonium lead iodide perovskites (MAPbI3) thin films were prepared by changing the molarity concentration of methylammonium iodide and lead iodide in the N,N- dimethylformamide solvent, with and without chlorobenzene (CB). Rietveld refinement analysis revealed that all prepared samples belong to tetragonal CH3NH3PbI3 phase (sp. gr. I4/mcm). The effect of MAPbI3 concentration on the lattice parameters, crystallite size, lattice microstrain and dislocation density of the prepared films with and without CB was investigated in detail. The FESEM images of perovskite films indicated the presence of pinholes in each sample, and the number of pinholes reduced as CB added to MAPbI3. Generally, the transmission and reflection spectra decreased as the amount of MAPbI3 increased in the films; also, both are reduced as CB added to films. The value of the reflectivity over measured wavelengths changed from about 1% to about 18% and 12% in the case of films without and with CB, respectively. Without CB, the highest absorbance intensity was obtained for 1.3 M films, while with CB the 1.5 M film has the highest absorbance. The number of bandgaps appeared in different samples depending on the concentration of MAPbI3 and CB. The refractive index at 500 nm for (1, 1.3 and 1.5 M) MAPbI3 films without CB are 1.6, 1.44, 1.43 and 1.31 respectively, where its value in the corresponding films with CB are 1.34, 1.3, 1.3 and 1.28, respectively. The effect of MAPbI3 concentration and the existence of CB during the film preparation on the extinction coefficient, refractive index, dielectric constant, the photoluminescence peak position, and PL intensity for the different films were explored.

New Coordination Polymers of Selected Lanthanides with 1,2-Phenylenediacetate Linker: Structures, Thermal and Luminescence Properties

Solvothermal reactions of lanthanide (III) salts with 1,2-phenylenediacetic acid in N,N′-dimethylformamide (DMF) solvent lead to the formation of the metal complexes of the general formula Ln2(1,2-pda)3(DMF)2, where Ln(III) = Pr(1), Sm(2), Eu(3), Tb(4), Dy(5), and Er(6), 1,2-pda = [C6H4(CH2COO)2]2−. The compounds were characterized by elemental analysis, powder and single-crystal X-ray diffraction methods, thermal analysis methods (TG-DSC and TG-FTIR), infrared and luminescence spectroscopy. They exhibit structural similarity in the two groups (Pr, Sm, and Eu; Tb, Dy, and Er), which was reflected in their thermal behaviours and spectroscopic properties. Single-crystal X-ray diffraction studies reveal that Sm(2) and Eu(3) complexes form 2D coordination polymers with four crystallographically independent metal centers. Every second lanthanide ion is additionally coordinated by two DMF molecules. The 1,2-phenylenediacetate linker shows different denticity being: penta- and hexadentate while carboxylate groups exhibit bidentate-bridging, bidentate-chelating, and three-dentate bridging-chelating modes. The infrared spectra reflect divergence between these two groups of complexes. The complexes of lighter lanthanides contain in the structure coordinated DMF molecules, while in the structures of heavier complexes, DMF molecules appear in the inner and outer coordination sphere. Both carboxylate groups are deprotonated and engaged in the coordination of metal centers but in different ways in such groups of complexes. In the groups, the thermal decomposition of the isostructural complexes occurs similarly. Pyrolysis of complexes takes place with the formation of such gaseous products as DMF, carbon oxides, ortho-xylene, ethers, water, carboxylic acids, and esters. The complexes of Eu and Tb exhibit characteristic luminescence in the VIS region, while the erbium complex emits NIR wavelength.

Synthesis and Characterization of Azido Esters as Green Energetic Plasticizers

AbstractThree azido‐esters based green energetic plasticizers were synthesized from their chlorides including DEGBAA (diethyleneglycol bis(azidoacetate)), DPGBAA (dipropyleneglycol bis(azidoacetate)) and HETTAA (hexanetriol tris(azidoacetate)). The syntheses were carried out in a two‐step process: the first step was esterification of glycol or triol using chloroacetyl chloride, and the second step was substitution of chloracetate with sodium azide that yields corresponding azido derivatives. The parameters of synthesis such as molar ratio of hydroxyl and acyl groups, and amount and type of solvent (dimethyl sulfoxide and dimethyl formamide) were optimized to achieve maximal conversion and purity of the products. The obtained products were characterized by elemental analysis, nuclear magnetic resonance (NMR), and infrared vibrational spectroscopy (IR). Thermal and rheological properties were determined using DSC and Modular Compact Rheometer. Condensed phase heat of formation and several properties important for high‐energy materials were predicted from quantum chemical calculations using CBS‐4M method. Detonation and combustion performance of energetic compounds were calculated with the thermochemical computer code EXPLO5V06.05. using the predicted heats of formation and experimentally determined densities as input. The energetic and physical properties of the synthesized compounds were compared to the literature data for common plasticizers.

XAS Diagnostic of the Photoactive State in Co(II) Azobenzene Complex in Organic Solvents

AbstractX‐ray absorption spectroscopy (XAS) was used to characterize the structure of the photoactive Co(II) azobenzene complex. Optical absorption spectra show that photoinduced changes occur only in dimethylformamide (DMF) solvent, while in acetonitrile, this complex is photochemically inactive. Co K‐edge XAS spectra indicate 6‐coordinated species in acetonitrile with a structure similar to one in the crystalline form of the complex. However, in DMF, an activation process occurs related to the decrease of coordination number, bond shortening and absorption edge shift to the higher energies. Quantitative analysis indicates that observed spectral changes are related to the high spin ‐ low spin transition in the Co complex accompanied by the bond dissociation and solvent coordination.

Manifestation of the dynamics of ultrafast photoprocesses in the transient absorption spectra of diflavonoid solutions

Herein, using the femtosecond absorption spectroscopy method, the dynamics of the nonstationary induced absorption spectra of diflavonoid 3,7-dihydroxy-2,8-di(4-methoxyphenyl)-4H, 6H-pyrano[3,2-g]chromene-4,6-dione (DFV) in solvents of different polarities is studied. It is found that the rapid transformation of the transient absorption spectra of DFV in time is due to the processes of intramolecular protons transfer in excited singlet states. For a nonpolar solvent, two protons are transferred in two stages. Initially, during the sub-picosecond times, a form with a single transferred proton is formed from the Frank-Condon state. From this transition state, in a time range of about 9 ps, the second proton is transferred and the two proton transfer tautomer with a high quantum yield of fluorescence ~0.66 is formed, which has the gain band in the transient absorption spectra. For the polar solvent dimethylformamide only the short-lived form with a single proton transferred is formed also during the subpicosecond times practically the same ones as for the nonpolar solution and has a lifetime of about 20 ps. The polarity of the medium, which affects the formation of a set of the “closed” and “open” forms of DFV in the ground state, differing in relative positions in the space of hydroxyl and carbonyl groups, largely determines the mechanism of the intramolecular proton transfer process in the DFV molecule, which consists in the sequential transfer of two protons in a non-polar solvent to form a fluorescent long-lived tautomer and the transfer of one proton in polar solvents to form a short-lived non-fluorescent form.

Solvent Engineering for Controlled Crystallization and Growth of All-Inorganic Pb-Free Rudorffite Absorbers of Perovskite Solar Cells.

Solution-processed Ag-Bi-I rudorffites with direct band gaps of <2 eV show promise for highly efficient and cost-effective Pb-free solar cells. However, relatively fast crystallization rates of Bi-based films and limited solubility of BiI3 in many solvents result in poor film morphologies, inhibiting their device performance. Here, we conduct a solvent-engineering method to adjust the dynamics of nucleation and growth during film formation. We fabricate Ag2BiI5, AgBiI4, and AgBi2I7 absorber layers using a mixed solvent of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO) and find that a volume percentage of 50% DMSO causes highly uniform and dense perovskite films via a BiI3-DMSO-AgI intermediate phase formation, leading to solar cells with an improved power conversion efficiency of 0.62% for the Ag2BiI5 absorber. These results provide valuable insights into the optimization of the solution processing technique to realize low-toxicity and efficient perovskite solar cells.

A Prospective Concept on the Fabrication of Blend PES/PEG/DMF/NMP Mixed Matrix Membranes with Functionalised Carbon Nanotubes for CO2/N2 Separation.

With an ever-increasing global population, the combustion of fossil fuels has risen immensely to meet the demand for electricity, resulting in significant increase in carbon dioxide (CO2) emissions. In recent years, CO2 separation technology, such as membrane technology, has become highly desirable. Fabricated mixed matrix membranes (MMMs) have the most desirable gas separation performances, as these membranes have the ability to overcome the trade-off limitations. In this paper, blended MMMs are reviewed along with two polymers, namely polyether sulfone (PES) and polyethylene glycol (PEG). Both polymers can efficiently separate CO2 because of their chemical properties. In addition, blended N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) solvents were also reviewed to understand the impact of blended MMMs’ morphology on separation of CO2. However, the fabricated MMMs had challenges, such as filler agglomeration and void formation. To combat this, functionalised multi-walled carbon nanotube (MWCNTs-F) fillers were utilised to aid gas separation performance and polymer compatibility issues. Additionally, a summary of the different fabrication techniques was identified to further optimise the fabrication methodology. Thus, a blended MMM fabricated using PES, PEG, NMP, DMF and MWCNTs-F is believed to improve CO2/nitrogen separation.

Synthesis and Structural Characterization of Isostructural 4-(4-Aryl)-2-(5-(4-fluorophenyl)-3-(1-(4-fluorophenyl)-5-methyl-1H-1,2,3-triazol-4-yl)-4,5-dihydro-1H-pyrazol-1-yl)thiazoles

4-(4-Chlorophenyl)-2-(5-(4-fluorophenyl)-3-(1-(4-fluorophenyl)-5-methyl-1H-1,2,3-triazol-4-yl)-4,5-dihydro-1H-pyrazol-1-yl)thiazole (4) and 4-(4-fluorophenyl)-2-(5-(4-fluorophenyl)-3-(1-(4-fluorophenyl)-5-methyl-1H-1,2,3-triazol-4-yl)-4,5-dihydro-1H-pyrazol-1-yl)thiazole (5) have been synthesized in high yields. Crystallization of 4 and 5 from dimethylformamide solvent produced samples suitable for structure determination by single crystal diffraction. The materials are isostructural with triclinic, PĪ and symmetry and comprise two independent molecules in the asymmetric unit. The two independent molecules in the asymmetric unit assume similar conformation. The molecule is essentially planar apart from one of the two fluorophenyl groups, which is oriented roughly perpendicular to the plane of the rest of the molecule.

Dehydration of Natural Gas Using Polyether Sulfone (PES) Membrane and Its Nanocomposite with Silica Particles and Nitrogen Sweeping Gas

Natural gas must be dehydratedbefore being sent to the distribution network to control corrosion and prevent the formation of solid hydrates. Membrane technology is a viable alternative to conventional glycol absorbents and adsorbent solids. This study was performed to evaluate the dehydration of crude natural gas by membrane separation process. Various operating conditions such as the effect of silica nanoparticles, pressure and sweeping gas on the removal of water vapor dissolved in natural gas were investigated using PES membrane and its nanocomposite. PES membranes and their nanocomposites with silica was made by solution mixing method in solvent dimethyl formamide. The properties of silica nanoparticles and fabricated nanocomposite membranes were evaluated by Fourier transfer spectroscopy and scanning electron microscopy. The dehydration rate was from natural gas in the pressure range of 2 to 10 bar and temperature of 30 °C in the presence of nitrogen sweeping gas. The addition of silica nanoparticles to the PolyetherSulfonemembrane significantly reduced the moisture content of natural gas. Also, with increasing feed pressure, the amount of water permeation from the membrane improved. The use of nitrogen sweeping gas reduced the amount of water in natural gas in pure Polyether Sulfone membranes by more than 80% and in nanocomposite membranes by more than 100%.

Solvency and salt addition influence the photoresponsivity and fluorescence in an azobenzene-containing block copolymer

We investigated the effects of solvency and salt addition on the morphology, photoresponsivity, and fluorescence of the block copolymer poly(ethylene glycol)methyl ether-block-poly(6-[4-(4′-methoxyphenylazo)phenoxy]hexyl methacrylate) (PEG-b-PAzo). The morphology of PEG-b-PAzo was manipulated through dissolution in mixed solvents of dimethylformamide (DMF) and H2O. DMF served as a good solvent for both blocks, whereas H2O was a PEG-selective solvent. Increasing the concentration of H2O in the mixed solvent increased the repulsive interaction between H2O and PAzo chains, resulting in the assembly of PEG-b-PAzo into micelles composed of PEG in the corona and PAzo in the core. The confined geometry forced the mesogens to assemble into H-type aggregates. Adding KCl to the PEG-b-PAzo solution increased PEG segment hydrophobicity, causing an increase in the core radius and a reduction in the corona thickness. The opposite effect was observed when KSCN was added to the PEG-b-PAzo solution. The addition of salts led to slight reductions in H-type aggregate percentage and increases in nonassociated mesogen percentage. The fluorescence behavior of PEG-b-PAzo was closely correlated with a mesogen dispersion state. In the saltless PEG-b-PAzo solution, the increase in the percentage of the H-type aggregates, which was due to the addition of H2O, caused fluorescence loss. The small changes in mesogen aggregation upon the addition of salts led to only a small change in fluorescence emission.

Intermolecular interaction study of l-Threonine in polar aprotic Solvent: Experimental and theoretical study

The present paper accounts for the interacting nature of CO, CH and OH vibrational modes of l-Threonine in polar aprotic solvent Dimethyl Formamide(DMF) using Raman spectroscopic and infrared(IR) techniques. The intermolecular interaction between l-Threonine and DMF are analyzed using Density Functional Theory (DFT), IEFPCM and M062X methods, each with a basis set 6–311++G (d, p)to predict the favourable interacting sites of the two molecules and to validate the experimental data with the theoretical calculations. The variation in peak frequencies has been explained for neat l-Threonine and their interactions at different concentrations (0.1 M, 0.3 M, 0.5 M, 0.7 M and 0.9 M). The wavenumbers of all the stretching modes (CO, CH and OH) shows a redshift. The intensity and the topology parameters of the intermolecular hydrogen bond at the bond critical points have been analyzed using the AIM theory of DFT and M062X methods. The intermolecular hydrogen bonding for the mentioned complexes and the study of the surface charge that encompasses the molecular cavity has also been carried out using the IEF-PCM solvation model under the same basis set. Electronic properties such as MEP surface study, frontier orbital analysis, and their corresponding energy gap have also been analyzed using DFT calculation. The frequencies derived from the computational and experimental data are found in good correlation to each other.

Viscosity Blending Approach for 22.42% Efficient Perovskite Solar Cells

We report here the viscosity blending approach toward high efficiency perovskite solar cells. A binary solvent is introduced in the precursor solution, where 2‐methoxyethaol (2ME) is mixed with dimethylformamide (DMF) or dimethylacetamide (DMAc). Viscosity of the binary solvent system is estimated by calculating the viscosity blending number. For the ratio of DMF (DMAc): 2ME = 75:25 leading to the viscosity of 1.0317 (1.1699) cSt, a forward‐scanned power conversion efficiency (PCE) of 22.42% is achieved along with photocurrent density of 25.46 mA/cm2, voltage of 1.122 V and fill factor of 0.785, which is higher than the PCE of 20.59% for the single DMF solvent. The binary solvent with optimal viscosity is found to be beneficial to reducing trap density and improving carrier lifetime even in thicker perovskite film.

The study of the morphology and structural, optical, and J-V characterizations of (CH3NH3PbI3) perovskite photovoltaic cells in ambient atmosphere

In this paper, the synthesis processes of perovskite active films of CH3NH3PbI3 (MAPbI3) have been studied for perovskite hybrid solar cells by spin and dip coating in ambient atmosphere, and without glove box to reduce production cost for technological applications. The morphology and structural, electrical and optical properties of perovskite films have been investigated by X-ray Diffraction (XRD), Field-Emission Scanning Electron Microscopes (FE-SEM), Atomic Force Microscopes (AFM) and Ultraviolet–visible spectroscopy (UV-Vis). A precursor solution of lead Iodide (PbI2) with Dimethylformamide (DMF) solvent by spin coating at two stages (a) R=4500 rpm and (b) R=6000 rpm, and methyl ammonium iodide (CH3NH3I) with isopropanol solvent by dip coating, have been prepared for active perovskite layer (CH3NH3PbI3).

One-step synthesis of metallic Bi deposited Bi2WO6 nanoclusters for enhanced photocatalytic performance: An experimental and DFT study

Non-noble metallic Bi/Bi2WO6 nanocomposites were synthesized by one-step semi-solvothermal method with water - N-N Dimethylformamide (DMF) under mild conditions. The DMF solvent not only prevents the formation of impurities [Bi6O6(OH)3(NO3)3·1.5H2O] from Bi(NO3)3·5H2O hydrolysis, but also in situ reduces Bi3+ ions to metallic Bi. The DMF percentage ranges from 0 to 100%, and the Bi/Bi2WO6 nanocomposites prepared in a 50% DMF precursor (50-BWO) solution were the most effective in the degradation of rhodamine B (RhB) under simulated sunlight irradiation. The RhB degradation efficiency was about 2.98 and 71.8 times higher than those of pristine Bi2WO6 and Bi microspheres, respectively. Then, the photocatalytic mechanisms of Bi/Bi2WO6 were proposed based on DFT calculations and experimental results. The enhanced photocatalytic activity of Bi/Bi2WO6 results mainly from two factors: the surface plasmonic resonance (SPR) of metallic Bi (which enhances light absorption) and the formation of Ohmic junction between Bi microspheres and Bi2WO6 nanosheets. The ohmic junction facilitates the effective separation of photogenerated carriers, enhancing efficiency. Additionally, the ·O2– and h+ radicals are the main active species in the degradation of RhB. Last, the durability and stability of Bi/Bi2WO6 were verified by cyclic experiments.

Antifungal effects of tulsi, garlic, cinnamon and lemongrass in powder and oil form on Candida albicans: An in vitro study.

Introduction:The use of plants for treating diseases is as old as the human species. Medicinal plants have been a major source of therapeutic agents for alleviation and cure of diseases.Objectives:The objective of the study was to evaluate and compare the antifungal activity of garlic, cinnamon, lemongrass and tulsi in powder and oil form at different concentrations on Candida albicans.Materials and Methods:Powder and oil of garlic, cinnamon, lemongrass and Tulsi dissolved in inert solvent dimethyl formamide to obtain different concentration. Stock solution of different concentration was inoculated on Petri plates containing C. albicans and incubated at 30°C for 48 h. The inhibition zones were measured in millimeters using Vernier caliper. The collected data were analyzed using statistical test like mean value and one-way analysis of variance.Results:Maximum zone of inhibition for the C. albicans was 42 mm at concentrations of 50% for the oil of lemongrass; followed by cinnamon 40 mm, garlic 24 mm and tulsi 20 mm. The P value obtained 0.050, 0.040, 0.036 and 0.031 were found to be statically significant for C. albicans at 20%, 30%, 40% and 50% concentrations of the various oil preparations, respectively. The P value obtained 0.043, 0.033, 0.032 and 0.027 were found to be statically significant for C. albicans at 20%, 30%, 40% and 50% concentrations of various plant powder, respectively.Conclusions:Lemongrass and cinnamon oil shows best antifungal effect against C. albicans as compared to garlic and tulsi. Compared to powder preparations, the oil preparations are better to inhibit the growth and higher the concentrations, greater the zone of inhibition seen in all the plant extracts and in oil.

Preparation and Properties of Benzylsulfonyl-Containing Silicone Copolymers via Ring-opening Copolymerization of Macroheterocyclosiloxane and Cyclosiloxane.

Ring-opening copolymerization (ROCP) of benzylsulfonyl macroheterocyclosiloxane (BSM) and five different cyclosiloxanes was systematically investigated. A general approach for the synthesis of benzylsulfonyl-containing silicone copolymers with various substituents, including methyl, vinyl, ethyl, and phenyl, was developed herein. A series of copolymers with variable incorporation (from 6 % to 82 %) of BSM were obtained by modifying the comonomer feed ratio and using KOH as the catalyst in a mixed solvent of dimethylformamide and toluene. The obtained copolymers exhibited various composition-dependent properties and unique viscoelasticity. Notably, the surface and fluorescent characteristics as well as the glass transition temperatures of the copolymers could be tailored by varying the amount of BSM. Unlike typical sulfone-containing polymers, such as poly(olefin sulfone)s, the prepared copolymers displayed excellent thermal and hydrolytic stability. The universal strategy developed in the present study provides a platform for the design of innovative silicone copolymers with adjustable structures and performance.

Cytotoxicity and Microbicidal Activity of Commonly Used Organic Solvents: A Comparative Study and Application to a Standardized Extract from Vaccinium macrocarpon.

The cytotoxicity and microbicidal capacity of seven organic solvents commonly applied for studying plant extracts and bioactive compounds were systematically investigated based on international standards. Four cell lines of normal (CCL-1, HaCaT) or tumor (A-375, A-431) tissue origin, seven bacterial and one fungal strain were used. The impact of the least toxic solvents in the determination of in vitro cytotoxicity was evaluated using a standardized extract from Vaccinium macrocarpon containing 54.2% v/v proanthocyanidins (CystiCran®). The solvents ethanol, methoxyethanol and polyethylene glycol were the least cytotoxic to all cell lines, with a maximum tolerated concentration (MTC) between 1 and 2% v/v. Ethanol, methanol and polyethylene glycol were mostly suitable for antimicrobial susceptibility testing, with minimum inhibitory concentrations (MICs) ≥ 25% v/v. The MTC values of the solvents dimethyl sulfoxide, dimethoxyethane and dimethylformamide varied from 0.03% to 1.09% v/v. The MICs of dimethyl sulfoxide, methoxyethanol and dimethoxyethane were in the range of 3.125–25% v/v. The cytotoxic effects of CystiCran® on eukaryotic cell lines were directly proportional to the superimposed effect of the solvents used. The results of this study can be useful for selecting the appropriate solvents for in vitro estimation of the cytotoxic and growth inhibitory effects of bioactive molecules in eukaryotic and prokaryotic cells.

Synthesis and characterization of novel tricyanofuran hydrazone probe: solvatochromism, density-functional theory calculation and selective fluorescence, and colorimetric determination of iron (III).

A tricyanofuran hydrazone (TCFH) spectroscopic probe was produced to visually recognize Fe(III) ions in aqueous environments. The synthesis was started by reacting tricyanofuran with 4-aminophenol diazonium chloride. All the synthesized compounds were characterized by spectroscopic analyses. TCFH showed distinctive solvatochromic behaviour in various organic polar solvents due to intramolecular charge transfer. Its behaviour towards sensing Fe(III) was studied using ultraviolet-visible spectrophotometry. The sensing behaviours of the proposed probe for other metal ions, namely Co(II), Cr(III), Mg(II), Pb(II), Cd(II), Ba(II), Hg(II), Mn(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(III), Na(I) and K(I), were also investigated, but no spectral changes were observed, indicating the probe's potential use as a highly selective and Fe(III)-sensitive colorimetric and fluorescent chemical sensor. The TCFH probe using EtOH/H2 O (5:1; v/v) served as a colorimetric and fluorescent chemosensor for identification of Fe(III) by the naked eye owing to both its high sensitivity and selectivity towards Fe(III) compared with the other examined metal ions. The proposed TCFH probe can therefore be utilized as an effective spectroscopic sensor for Fe(III). Both colorimetric and fluorescence recognition of the analyte depended on the concentration of Fe(III) ions and was accomplished at a pH of 7. A rapid colour change from yellow to red occurred when an aqueous solution of Fe(III) ions was added. The intensity of the colour increased at higher Fe(III) concentrations. Cyclic voltammetry measurements in the dimethylformamide solvent indicated a nonreversible redox potential. This study also explained the possible mechanisms for both solvatochromism and the detection of Fe(III) through TCFH-Fe(III) complex formation. The binding constant of the generated TCFH-Fe(III) complex was explored. Computational modelling was conducted to explain the deprotonation-triggered changes that occur in the photophysical properties of TCFH dyes.

Elucidating and Tuning Catalytic Sites on Zirconium- and Aluminum-Containing Nodes of Stable Metal–Organic Frameworks

ConspectusMetal-organic frameworks (MOFs) are a huge, rapidly growing class of crystalline, porous materials that consist of inorganic nodes linked by organic struts. Offering the advantages of thermal stability combined with high densities of accessible reactive sites, some MOFs are good candidate materials for applications in catalysis and separations. Such MOFs include those with nodes that are metal oxide clusters (e.g., Zr6O8, Hf6O8, and Zr12O22) and long rods (e.g., [Al(OH)]n). These nanostructured metal oxides are often compared with bulk metal oxides, but they are in essence different because their structures are not the same and because the MOFs have a high degree of uniformity, offering the prospect of a deep understanding of reactivity that is barely attainable for most bulk metal oxides because of their surface heterogeneity. This prospect is being realized as it has become evident that adventitious components on MOF node surfaces, besides the linkers, are crucial. These ligands arise from modulators, solvents, or products of solvent decomposition in MOF synthesis solutions, and because they are minor components that are often irregularly placed on defects, they may not show up in X-ray diffraction (XRD) crystal structures. Hydroxyl groups on the nodes (like those on bulk metal oxides) are regarded as native functional groups arising from solvent water, but they may barely be present initially, with common ligands instead being formate and acetate formed from modulators formic acid and acetic acid. (Formate also arises from the decomposition of dimethylformamide (DMF) solvent.) Replacement and control of the node ligands is facilitated by postsynthesis reactions (e.g., with alcohols or aqueous HCl/H2SO4 solutions) or as a result of high-temperature decomposition. In catalysis, adventitious node ligands can be (a) reaction inhibitors that block active sites on the nodes (e.g., formate blocking Zr, Hf, or Al Lewis acid sites); (b) reaction intermediates (e.g., ethoxy in ethanol dehydration); or (c) active sites themselves (e.g., terminal OH groups in tert-butyl alcohol (TBA) dehydration). Surprisingly, in view of the catalytic importance of such ligands on bulk metal oxides, their subtle chemistry on MOF nodes is only recently being determined. We describe (1) methods for identifying and quantifying node ligands (especially by IR spectroscopy and by 1H NMR spectroscopy of MOFs digested in NaOH/D2O solutions); (2) node ligand surface chemistry expressed as reaction networks; (3) catalysis, with mechanisms and energetics determined by density functional theory (DFT) and spectroscopy; and (4) MOF unzipping by reactions of linker carboxylate ligands with reactants such as alcohols that break node-linker bonds, a cause of catalyst deactivation and also an indicator of node-linker bond strength and MOF stability.