NMR Techniques Research Articles

Characterization of camphor: thymol or dl-menthol eutectic mixtures; Structure, thermophysical properties, and lidocaine solubility

The low solubility of drugs in aqueous media is a major problem for the pharmaceutical industry. Among the solutions proposed, the use of eutectic mixtures can be highlighted. In them, the components used can also increase the therapeutic advantages of the active principle. In this work, we analyzed the solubility of lidocaine in mixtures of camphor + thymol or dl-menthol. These binary eutectic solvents were also characterized. For all this, several NMR techniques were used and different thermophysical properties (density, speed of sound, refraction index, isobaric molar heat capacity, surface tension, and kinematic viscosity) were measured. The results indicated that the interaction of camphor with thymol was stronger than with dl-menthol, providing a more compact fluid. On the contrary, the steric hindrance was greater in the mixture with dl-menthol, giving rise to a more viscous liquid. Furthermore, the lidocaine was significantly more soluble (up to 540 times) in these mixtures than in water. The lidocaine showed the strongest interactions with thymol molecules, somewhat weaker with dl-menthol, and the weakest were with camphor ones.

Triterpenoids with α-glucosidase inhibitory and cytotoxic activities from the fruits of Schisandra chinensis

An intensive phytochemical investigation into the fruits of Schisandra chinensis afforded 28 triterpenoids incorporating diverse backbones with methyl-migration, ring-expansion and ring-opening features. Among them, ten compounds (1−10) including three likely extracting artefacts (8−10) were described for the first time. Their structures were fully characterized by comprehensive spectroscopic analyses, with the absolute configurations established via electronic circular dichroism and Mosher’s NMR techniques. Preliminary biological evaluations revealed that nine isolates showed inhibitory activity against the hyperglycemic target α-glycosidase and 12 compounds exerted cytotoxicity toward three female tumor cell lines (Hela (cervical), MDA-MB231 and MCF-7 (breast)). Compound 6 exhibited the most promising potency on all the three tested cancer cells, and further assessment demonstrated that it could induce significant cell apoptosis and cycle arrest, as well as suppress cell migration, by regulating relevant proteins in MDA-MB231 cells.

3,6‐Divinyl‐N‐arylcarbazoles‐bridged diruthenium complexes bearing two Ru(CO)Cl(PiPr3)2 moieties: Polyelectrochromism and electronic coupling

A series of five 3,6‐divinyl‐N‐arylcarbazoles‐bridged diruthenium complexes with a general formula of [{Ru(CO)Cl(PiPr3)2}2(μ‐(CH=CH)2‐(N‐arylcarbazole)‐3,6); aryl = 4‐anisyl; [1a], 4‐tolyl; [1b], phenyl; [1c], 4‐(trifluoromethyl)phenyl; [1d], and 4‐nitrophenyl; [1e]] were successfully synthesized. These new square‐pyramidal bis(ruthenium‐vinyl)‐type complexes were characterized in their neutral state via classical NMR, UV/Vis, and IR spectroscopic techniques and in their three various accessible oxidized states via electrochemical techniques and ESR spectroscopy along with UV/Vis/NIR and IR spectroelectrochemistry as well as with DFT calculations. Our obtained results were compared with the closely related bis(ruthenium‐vinyl)‐appended N‐(4‐anisyl)diphenylamine TAARu2 counterpart of [1a]. Electrochemical studies on complexes [1a]–[1e] revealed three consecutive, chemically and electrochemically, well‐separated, reversible one‐electron oxidation processes at low and well‐accessible potentials. Their half‐wave potential separations ΔE½ between the individual redox waves and the derived comproportionation constants Kc1–Kc3 attribute to noteworthy stability of every oxidized intermediate state. The concert electrochemical and UV/Vis/NIR/IR spectro(electro)scopic results on these rotationally restricted N‐arylcarbazoles‐bridged bis(ruthenium‐alkenyl)‐type complexes [1a]–[1e] confirmed the relative weakness influence of altering the para‐substituent on the peripheral aryl ring. This is most probably due to the sizable torsion with nearly 55° between the co‐planarity of the carbazole heterocycle core and the peripheral N‐bound aryl ring. In their mixed‐valent (MV) radical states [1a]+–[1e]+, the observed pattern of two well‐separated Ru(C≡O) bands mirrors the uneven distribution of the uni‐positive charge over the two chemically equivalent bis(ruthenium‐vinyl) moieties as indicated by classical class II of Robin–Day classification of MV states.

Investigation of Levan-Derived Nanoparticles of Dolutegravir: A Promising Approach for the Delivery of Anti-HIV Drug as Milk Admixture

Nanoparticles composed of Levan and Dolutegravir (DTG) have been successfully synthesized using a spray drying procedure specifically designed for milk/food admixture applications. Levan, obtained from the microorganism Bacillus subtilis, was thoroughly characterized using MALDI-TOF and solid-state NMR technique to confirm its properties. In the present study, this isolated Levan was utilized as a carrier for drug delivery applications. The optimized spray-dried nanoparticles exhibited a smooth surface morphology with particle sizes ranging from 195 to 329 nm. In the in-vitro drug release experiments conducted in water media, the spray-dried nanoparticles showed 100 % release, whereas the unprocessed drug exhibited only 50 % release at the end of 24 h. Notably, the drug release in milk was comparable to that in plain media, indicating the compatibility. The improved dissolution rate observed for the nanoparticles could be attributed to the solid-state conversion (confirmed by XRD analysis) of DTG from its crystalline to amorphous state. The stability of the drug was verified using Fourier Transform Infra-Red Spectroscopy and Thermogravimetry-Differential Scanning Calorimetry analysis. To evaluate the in-vitro cellular toxicity, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was conducted, which revealed the CC50 value of 88.88 ± 5.10 µg/mL for unprocessed DTG and 101.08 ± 37.37 µg/mL for DTG nanoparticles. These results indicated that the toxicity of the nanoparticles was comparable to the unprocessed drug. Furthermore, the anti-HIV activity of the nanoparticles in human cell lines was found to be similar to that of the pure drug, emphasizing the therapeutic efficacy of DTG in combating HIV.

Cyclotriphosphazene‐Based Photocatalysts containing Orthogonal BODIPY Moieties for Chemical Transformations

AbstractMolecular organic photocatalysts developed for use in chemical transformation reactions have gained momentum in recent years. In this study, six new triplet photosensitizers were prepared to determine their photocatalyst capabilities and chemical transformation abilities. The chemical structures of the synthesized orthogonal BODIPYs and their cyclotriphosphazene derivatives were analyzed and then their photophysical characteristics including the UV‐Vis absorption spectra, fluorescence emission spectra, fluorescence quantum yields, were investigated. The quantitative singlet oxygen formation was determined by chemical trapping using DPBF (diphenylisobenzofuran). In particular, cyclotriphosphazene derivative 12 having three BODIPY moieties showed efficient singlet oxygen production with high photostability and good molar extinction coefficient. The photo‐oxidation ratio constant of 1,5‐dihydroxynaphthalene (DHN) was calculated as 28.7×10−3 min−1 for compound 12 and at the end of 22.5 min., DHN converted to juglone with 100 % efficiency. In addition, the ability of the compounds to convert 1,3‐cyclohexadiene into peroxides in the presence of molecular oxygen and light was investigated and the conversion efficiency was determined by NMR technique. All compounds have been presented as photocatalysts for use in different synthetic photochemistry applications.

Disentangling Glycan-Protein Interactions: Nuclear Magnetic Resonance (NMR) to the Rescue.

The interactions of glycans with proteins modulate many events related to health and disease. In fact, the establishment of these recognition events and their biological consequences are intimately related to the three-dimensional structures of both partners, as well as to their dynamic features and their presentation on the corresponding cell compartments. NMR techniques are unique to disentangle these characteristics and, indeed, diverse NMR-based methodologies have been developed and applied to monitor the binding events of glycans with their associate receptors. This protocol outlines the procedures to acquire, process and analyze two of the most powerful NMR methodologies employed in the NMR-glycobiology field, 1H-Saturation transfer difference (STD) and 1H,15N-Heteronuclear single quantum coherence (HSQC) titration experiments, which complementarily offer information from the glycan and protein perspective, respectively. Indeed, when combined they offer a powerful toolkit for elucidating both the structural and dynamic aspects of molecular recognition processes. This comprehensive approach enhances our understanding of glycan-protein interactions and contributes to advancing research in the chemical glycobiology field.

Synthesis, characterization and theoretical studies of tris-cyclometalated rhodium(III) complexes: applications to asymmetric transfer hydrogenation of ketones

This paper presents the synthesis of {Rh[PyCH=C(O)Rn]3} complexes, where R1 = 4-cyanophenyl (L1), R2 = 3-nitrophenyl (L2), and R3 = 4-fluorophenyl (L3). These complexes were derived from the reactions of potassium hexachlororhodate(III) with related pyridinium ylides: PyCH=C(O)C6H4-p-CN (Y1), PyCH=C(O)C6H4-m-NO2 (Y2), and PyCH=C(O)C6H4-p-F (Y3). The reactions were carried out in methanol-water mixtures under mild conditions. The synthesized complexes were characterized using FT-IR, ESI-MS, multinuclear NMR (1H and 13C), and elemental analysis techniques (CHN). Furthermore, these Rh(III) compounds demonstrated excellent catalytic activity, high turnover number (TON), and turnover frequency (TOF) in the hydrogenation of various ketones, resulting in a series of alcohol products with outstanding yields and efficiencies. To investigate the structures of L1, L2, and L3, density function theory (DFT) calculations were performed at the BP86/def2-SVP level of theory. The study employed natural bond orbital analysis (NBO) and energy-decomposition analysis (EDA) to examine the strength and nature of the donor-acceptor bonds between the pyridinium ylide (Y) and Rh fragments in the complexes. Additionally, variations in natural orbitals for chemical valence (NOCV) were investigated.

Improving the therapeutic window of anticancer agents by β-cyclodextrin encapsulation: Experimental and theoretical insights

3-Nitro-2H-chromene derivatives exhibit promising anticancer activities, but their clinical translation is hindered by poor aqueous solubility. Herein, we report a cyclodextrin complexation strategy to improve the solubility and therapeutic efficacy of 8-methoxy-2-(4-methoxy phenyl)-3-nitro-2H-chromene (MNC), a potent anticancer agent. Solid inclusion complexes of MNC: β-cyclodextrin (β-CD) were synthesized by co-precipitation and kneading methods, and comprehensively characterized using UV–vis, Fluorescence, Fourier Transform Infrared (FT-IR), Differential scanning calorimetry (DSC), X-ray diffraction (XRD), Scanning electron microscope (SEM), 1H NMR, and mass spectrometric techniques. A 1:1 host–guest stoichiometry was verified by phase solubility and UV–Vis spectroscopic studies. β-CD complexation remarkably enhanced the aqueous solubility of hydrophobic MNC. Cytotoxicity evaluation against different human cancer cell lines such as breast cancer (MCF-7, MDA-MB-231), lung cancer (A549), and liver cancer (HepG2) demonstrated superior anticancer activity of the co-precipitated MNC: β-CD complex compared to free MNC and the chemotherapeutic 5-fluorouracil. Although the host–guest interaction energy obtained from molecular docking was modest (−5.1 kcal/mol), it facilitated effective MNC encapsulation and delivery by β-CD. Density functional theory (DFT) calculations provided further insights into the inclusion phenomenon. This cyclodextrin complexation approach paves the way for developing an effective MNC formulation with improved bioavailability and anticancer therapeutic efficacy.

PEG-crosslinked O-carboxymethyl chitosan films with degradability and antibacterial activity for food packaging

This study developed a kind of PEG-crosslinked O-carboxymethyl chitosan (O-CMC–PEG) with various PEG content for food packaging. The crosslinking agent of isocyanate-terminated PEG was firstly synthesized by a simple condensation reaction between PEG and excess diisocyanate, then the crosslink between O-carboxymethyl chitosan (O-CMC) and crosslinking agent occurred under mild conditions to produce O-CMC–PEG with a crosslinked structure linked by urea bonds. FT-IR and 1H NMR techniques were utilized to confirm the chemical structures of the crosslinking agent and O-CMC–PEGs. Extensive research was conducted to investigate the impact of the PEG content (or crosslinking degree) on the physicochemical characteristics of the casted O-CMC–PEG films. The results illuminated that crosslinking and components compatibility could improve their tensile features and water vapor barrier performance, while high PEG content played the inverse effects due to the microphase separation between PEG and O-CMC segments. The in vitro degradation rate and water sensitivity primarily depended on the crosslinking degree in comparison with the PEG content. Furthermore, caused by the remaining –NH2 groups of O-CMC, the films demonstrated antibacterial activity against Escherichia coli and Staphylococcus aureus. When the PEG content was 6% (medium crosslinking degree), the prepared O-CMC–PEG−6% film possessed optimal tensile features, high water resistance, appropriate degradation rate, low water vapor transmission rate and fine broad-spectrum antibacterial capacity, manifesting a great potential for application in food packaging to extend the shelf life.

Employing acetoacetamide as a key synthon for synthesizing novel thiophene derivatives and assessing their potential as antioxidants and antimicrobial agents

AbstractThe objective of this study is to synthesize novel heterocyclic scaffolds containing a thiophene moiety using easily accessible acetoacetamide as a key synthon. The reaction of acetoacetamide with diazonium salts resulted in the formation of the corresponding thiophene derivatives 4a–c. Additionally, the reaction of acetoacetamide derivative 3 with malononitrile, ethyl cyanoacetate, or 2‐cyanoacetamide, along with elemental sulfur, under refluxing in dioxane containing triethylamine afforded thiophene‐containing derivatives 5a–c. Furthermore, compound 3 reacted with phenyl isothiocyanate in dry dimethylformamide and K2CO3 to yield compound 7. In situ alkylation of the non‐isolable salt 6 was achieved by the addition of methyl iodide, resulting in the formation of methylthio‐thiophene‐2‐carboxamide 8. Compound 7 was employed with numerous alpha‐halogenated reagents in ethanol, affording thiazole derivative 9 and thiophene derivatives 10a and 10b, respectively. Moreover, compound 8 was reacted with hydrazine to produce the 1H‐pyrazole‐4‐carboxamide derivative 11. Additionally, refluxing acetoacetamide derivative 3 with malononitrile and/or ethyl cyanoacetate in dioxane, in the presence of catalytic amount of triethylamine afforded 4‐imino‐3,7‐dimethyl‐4H‐pyrido[1,2‐a]thieno[3,2‐e]pyrimidin‐9(5H)‐one derivatives 12a and 12b. Furthermore, the reactivity of acetoacetamide derivative 3 with 2‐cyanoacetohydrazide was investigated through refluxing the reactants in dioxane, which subsequently yielded the corresponding cyanoacetamide derivative 13. The chemical identity of the newly synthesized compounds was determined by employing infrared spectroscopy (IR), 1H NMR, and 13C NMR techniques. Newly synthesized heterocycles incorporating thiophenes were evaluated for their antioxidant and antimicrobial potentials. Notably, thiophene scaffolds 5a, 10b, 11, and 13 displayed notable antioxidant and antimicrobial activities.

Phosphorus-Nitrogen compounds part 74. Syntheses of (p-dimethylamino)benzyl-spiro-(N/N)-cyclotriphosphazenes: Structural characterizations, bioactivity studies, DFT calculations and reactivity parameters

Reactions of hexachlorocyclotriphosphazene (HCCP, N3P3Cl6), with equimolar amounts of N-methyl-N'-(p-dimethylaminobenzyl)-1,2-diaminoethane (1), N-ethyl-N'-(p-dimethyl-aminobenzyl)-1,2-diaminoethane (2), and N-methyl-N'-(p-dimethylaminobenzyl)-1,3-diami-nopropane (3) produced the corresponding tetrachloro-(p-dimethylaminobenzyl)spiro-(N/N)-cyclotriphosphazenes (4, 5, and 6), regioselectively. Tetrapyrrolidino (4a-6a), tetrapiperidino (4b-6b), tetramorpholinophosphazenes (4c and 6c), dichlorodimorpholinophosphazene (5c) and tetra-1,4-dioxa-8-azaspiro[4,5]decanophosphazenes (DASD) (4d-6d) were synthesized from Cl-substitution reactions of 4, 5 and 6 with excess pyrrolidine, piperidine, morpholine, and DASD, respectively. Their structures were elucidated by MS, FTIR, NMR and single crystal X-ray diffraction (for 4, 4b and 6a) techniques. Hirshfeld surface (HS) analyzes of 4, 4b, and 6a were performed to visualize intermolecular interactions in the crystals. In addition, according to the antimicrobial activity test results, compound 6b shows a better inhibitory effect on S. aureus ATCC 25923 G(+) (MİC: 78.1 µM) and C. tropicalis Y-12968 (MİC: 19.54 µM) microorganisms. The interactions of cyclotriphosphazenes with 5′-G/GATCC-3′ and 5′-A/AGCTT-3′ sequences of DNA were evaluated by examining BamHI and HindIII restriction enzyme digestion. The quantum chemical calculations of 4, 4b, and 6a were performed using DFT, and their experimental parameters were compared with the theoretical ones. Natural bond orbitals (NBOs) were determined and HOMO-LUMO energy gaps (Eg) were calculated as 3.55, 5.23, and 5.24 eV for 4, 4b, and 6a, respectively.

Surface-Assisted Selective Air Oxidation of Phosphines Adsorbed on Activated Carbon.

Trialkyl- and triarylphosphines readily adsorb onto the surface of porous activated carbon (AC) even in the absence of solvents through van der Waals interactions between the lone electron pair and the AC surface. This process has been proven by solid-state NMR techniques. Subsequently, it is demonstrated that the AC enables the fast and selective oxidation of adsorbed phosphines to phosphine oxides at ambient temperature in air. In solution, trialkylphosphines are oxidized to a variety of P(V) species when exposed to the atmosphere, while neat or dissolved triarylphosphines cannot be oxidized with air. When the trialkyl- and triarylphosphines PnBu3 (1), PEt3, (2), PnOct3 (3), PMetBu2 (4), PCy3 (5), and PPh3 (6) are adsorbed in a mono- or submonolayer on the surface of AC, in the absence of a solvent and at ambient temperature, they are quantitatively oxidized to the adsorbed phosphine oxides, 1ox-6ox, once air is admitted. No formation of any unwanted P(V) side products or water adducts is observed. The phosphine oxides can then be recovered in good yields by washing them off of the AC. The oxidation is likely facilitated by a radical activation of molecular oxygen due to delocalized electrons on the aromatic surface coating of AC, as proven by ESR. This easy and inexpensive oxidation method renders hydrogen peroxide or other oxidizers unnecessary and is broadly applicable to sterically hindered and even to air-stable triarylphosphines. Phosphines adsorbed at lower surface coverages on AC oxidize at a faster rate. All oxidation reactions were monitored by solution- and solid-state NMR spectroscopy.

Isolation of the Antifungal Compound Alliodorin from the Heartwood of Cordia elaeagnoides A. DC. and the In Silico Analysis of the Laccase.

Cordia elaeagnoides A. DC. is an endemic species of Mexico valued for its timber. Renowned for its durability, resistance, and versatile applications in medicine, this tree holds significant commercial importance. Tetrahydrofuran (THF) extract from the heartwood of C. elaeagnoides was studied. Through chromatographic column purification, the compound 8-(2,5-Dihydroxyphenyl)-2,6-dimethylocta-2,6-dienal, also known as alliodorin, was successfully isolated. Identification of alliodorin was confirmed through comprehensive analysis utilizing NMR, IR, and mass spectrometry techniques. Inhibition tests were conducted using both the THF extract and alliodorin against the rotting fungus Trametes versicolor (L.) Lloyd, employing the agar well diffusion assay. Remarkably, alliodorin exhibited 100% inhibition with a median lethal concentration of 0.079 mg/mL and a total lethal concentration of 0.127 mg/mL, in comparison to the commercial fungicide benomyl, which requires a concentration of 1 mg/mL. In silico analysis through molecular docking on the laccase enzyme was proposed in order to explain the inhibitory activity against the fungus T. versicolor, as this enzyme is one of the main sources of nutrients and development for the fungus. Based on these findings, we deduced that alliodorin holds promise as a potent antifungal agent, potentially applicable in a wide array of technological and environmentally friendly initiatives.

Antimicrobial Activity of Fungal Endophytes Associated with Peperomia argyreia (Piperaceae)

The endophytic fungal biodiversity of unique plants like Peperomia argyreia (Miq.) É. Morren (Piperaceae) has antimicrobial properties and can be employed for infection treatment. Fungal isolates were obtained from appropriately treated plant tissues cultured in solid media, characterized by morphology, and identified by molecular biology using ITS and NL primers. The antimicrobial properties of fungal extracts were analyzed by combining microdilution and bioautographic assays complemented with metabolic profiling by automated thin-layer chromatography and 1H NMR techniques. Thirty-one filamentous fungi were isolated and characterized by ITS and/or D1/D2 region amplification of rDNA, identified as Thermothielavioides, Trichoderma, Cyphellophora, Cladosporium, Arcopilus, Plectosphaerella; Chaetomium, Sporothrix, Alboefibula, and Penicillium. Thermothielavioides spp. inhibited Staphylococcus aureus ATCC 25923; moreover, Penicillium westlingii P4 showed inhibitory activity on Ascochyta rabiei AR2. The bioactivity-guided fractionation of the EtOAc extract (MIC = 62.5 μg/mL) of P. westlingii P4 allowed the purification of citrinin as the main inhibitory compound (MIC = 62.5 μg/mL). Peperomia argyreia harbors a rich and diverse endophytic community able to produce bioactive molecules. Citrinin, with a minor influence of volatile compounds biosynthesized by P. westlingii P4, was responsible for the inhibition of A. rabiei AR2.

Synthesis and characterization of a high-temperature polycyanophosphate resin

A phosphorus-containing polymer with very high thermo-oxidative stability was synthesized for the first time by addition of silver nitrate to tricyanophosphine (P(CN)3). By optimizing the reaction time and silver nitrate concentration to a 1:1 molar ratio, a new polycyanophosphate [p(CP)] was formed as the primary phosphorus-containing product over the competing species, P(CN)3. The reactions and products were monitored by FT-IR, ICP-OES, NMR, and XPS spectroscopic techniques, which indicated a complicated oxidation reaction that converted the P(III) precursor species to P(V) polyphosphate species with pendant cyano- and isocyano- moieties. The p(CP) resin was found to contain a high (17.6 at.%) amount of phosphorus by ICP-OES, which contributed to its excellent thermo-oxidative resistance with a high char yield of over 60 wt.% at 1000 °C (1273 K) in air, indicating that the material could be particularly useful for high-temperature applications.

Multi-Step Synthesis, Characterization and Bioevaluation of Novel 2-(3-Methoxy-9H-carbazol-9-yl)-N-phenyl Acetamide Analogues

In this work, the multi-step synthesis and characterization of novel 2-(3-methoxy-9H-carbazol-9-yl)-N-phenyl acetamide analogues is presented. These analogues were synthesized from 2-(3-methoxy-9H-carbzol-9-yl)acetyl chloride with substituted aromatic primary amines in the presence of organic base such as triethylamine and methylene dichloride under reflux conditions. The elemental analysis and structures of these novel compounds were elucidated by analyzing spectral data obtained through 1H NMR, 13C NMR and LCMS techniques. The bioevaluation of these newly synthesized compounds has been studied by evaluating their antibacterial and antifungal activities against various kinds of bacterial and fungal strains, respectively.

Pd(II), Pt(II), Zn(II), Cd(II) and Hg(II) complexes of the newly prepared 1,2-benzo- isothiazol-3(2H)-dithiocarbamate (BIT-DTC) ligand

In the current work, we report the synthesis and characterization of new dithiocarbamate complexes derived from 1,2-benzoisothiazol-3(2H)-one (BitH). The ligand was synthesized by treating the BitH with carbon disulfide in a basic solution. The NMR technique confirmed the preparation of the ligand. The treatment of the Bit-dtcNa with the metal salt’s solution afforded the complexes of the type [M(Bit-dtc)2]; M = Zn, Cd, Hg, Pd, and Pt. The complexes were characterized via FT-IR and 1H-NMR techniques. The Zn, Pd, and Pt complexes were investigated theoretically, and some of their quantum properties were determined. These parameters include HOMO-LUMO energies, electron affinity, ionization potential, chemical hardness, dipole moment and the total energies of the optimized structures. Moreover, the surface structure of Zn and Hg complexes were investigated by SEM and XRD techniques. The SEM pattern showed a cubic structures for the Zn complex while the Hg complex appeared as a nano rods structure. The calculated average particle sizes for Zn and Hg complexes were 23 and 26 nm, respectively. KEY WORDS: Dithiocarbamate, 1,2-Benzoisothiazol-3(2H)-one, DFT, SEM, XRD Bull. Chem. Soc. Ethiop. 2024, 38(3), 889-899. DOI: https://dx.doi.org/10.4314/bcse.v38i4.6

Application of pfg NMR diffusometry to study diffusion and ionization phenomena in plasticized polymeric membranes doped with ionic liquids

Ionic liquids (ILs) are increasingly used as promising organic solvents for a variety of applications, including electrochemical processes, novel separation techniques and innovative methods of synthesis, due to their low volatility, excellent solvation properties, high ionic conductivity and electrochemical stability. Moreover, the tunable properties of ILs determined by their composition make them favorable candidates as dopants for composite and/or functional polymeric materials, e.g. in the membranes of chemical sensors. To effectively use ILs in polymeric materials and control the characteristics of the latter, one should develop a complete understanding of the properties of ILs in the polymeric phase, such as their diffusion and ionic behavior.In our previous work, we applied pulsed field gradient (PFG) NMR technique to verify the results of a chronopotentiometric method conventionally used to determine the diffusion coefficients and electrolytic properties of electrolytes in plasticized poly(vinyl chloride) (PVC) membranes of chemical sensors. The results obtained with these two independent methods were in good agreement, confirming that PEG NMR diffusometry is a viable technique for assessing the diffusion properties of species even in highly viscous polymeric media of low polarity.Here we report a comprehensive study of the transport and ionic behavior of IL 1-hexyl-3-methyl-1H-imidazolium bis[(trifluoromethyl)sulfonyl]amide ([C6Meim][NTf2]) in a poly(vinyl chloride) matrix, performed in situ by means of PFG NMR diffusometry. A number of sets of spectra for the 1H and 19F nuclei of the [C6Meim][NTf2] ionic liquid in PVC membranes doped with the plasticizer bis(2-ethylhexyl)sebacate were registered at different amplitudes of the magnetic field gradient. The mobility of both individual ions of the IL and the formed ion associates was investigated over a broad range of IL concentrations in the PVC matrix; in addition, the ionization degree and dissociation constant of [C6Meim][NTf2] were determined and their dependence on the IL content was traced.

Controlled Enzymatic Synthesis of Polyesters Based on a Cellulose-Derived Triol Monomer: A Design of Experiment Approach.

Regioselective enzymatic polycondensation of the bio-based cellulose derived polyol, Triol-citro, and dimethyl adipate using Candida antarctica Lipase B (CaLB) was investigated. A Design of Experiment approach with MODDE® Pro 13 was used to determine important factors in the branching behavior of this polymer, and reactant ratio, temperature, reaction time and enzyme wt % were the studied factors. Multifunctional polyesters with pendant hydroxy groups were synthesized and fully characterized using 2D NMR techniques to determine degree of branching. Branching was minimal, with a maximum of 16 % observed, and monomer ratio, temperature and reaction time were all determined to be significant factors. In this work, Mn of up to 13 kDa were achieved, while maintaining degree of branching below 15 %, resulting in a linear polyester with the potential to be further functionalized.

New silver, rhodium and iridium complexes with anthracene-functionalized N-heterocyclic carbene ligands: Crystal structures, cytotoxicity and fluorescence studies

In the present study, we have synthesized anthracene-functionalized metal complexes to investigate their cytotoxicity and photophysical properties. In this context, firstly, an Ag–NHC (NHC = N-heterocyclic carbene) complex (2a) has been synthesized by the interaction of Ag2O and N-(2-methylbenzyl)-N-((anthracen-9-yl)methyl)benzimidazolium chloride (1a). Corresponding Rh– (3a) and Ir–NHC (4a) complexes have also been synthesized by the transmetalation reaction between 2a and corresponding metal compounds. Additionally, for comparison purposes, an ether-functionalized Ag–NHC complex (2b) with N-(methoxyethyl)-N-((anthracene-9-yl)methyl)benzimidazole-2-ylidene ligand, and [AgL2]NO3 type complex (2c) with a N-coordinated N-((anthracen-9-yl)methyl)benzimidazole ligand have been synthesized. All complexes have been characterized by the combination of NMR and mass spectroscopic techniques, and elemental analyses. Moreover, solid state structures of 2a, 2b and 4a have been determined by the single crystal X-ray diffraction analysis. Cytotoxic potentials of all compounds have been tested against human lung adenocarcinoma alveolar basal epithelial cell line (A549) using the MTT assay, and all complexes performed strong anti-proliferative activity. Stability studies have disclosed that only 1a and 2c are able to retain their structure in the culture medium (DMEM) that biological assays were carried out. Photophysical measurements revealed that all compounds have similar emission bands because of the conjugation of anthracene group. Finally, 1a and 2c have been visualized by fluorescence confocal microscopy to investigate cellular uptake and subcellular distribution of the complexes, and the findings indicated that both compounds dispersed along the cell membranes nuclear regions.