Organic Solvents Of Different Polarity Research Articles

Synthesis, Spectral Characteristics, Sensing Properties and Microbiological Activity of New Water-Soluble 4-Sulfo-1,8-naphthalimides

A new water-soluble polyamidoamine (PAMAM) dendrimer modified with 4-sulfo-1,8-naphthalimide (DSNI) and its monomeric structural analogue (MSDI) were synthesized. Their photophysical properties were investigated in organic solvents of different polarities and aqueous solutions. The effect of pH on fluorescence intensity was determined. It was found that the dendrimer emits blue fluorescence in an acidic medium, which is quenched in an alkaline environment. This phenomenon is due to the possibility of suppression of nonradiative photoinduced electron transfer in acidic media. The influence of different metal ions (Cu2+, Pb2+, Sn2+, Sr2+, Mg2+, Ba2+, Co2+, Hg2+, Zn2+, Ni2+, Fe3+, Al3+) and anions (CN−, S2−, S2O52−, HPO42−, H2PO4−, F−, CH3COO−, NO2−, CO32−, SO42−) on the intensity of the emitted fluorescence was studied. Quenching was only found in the presence of Cu2+. This makes the dendrimer suitable for determining copper ions in water solutions in the presence of other metal ions and anions. Additionally, DSNI was used as a ligand to obtain a stable copper complex, the structure of which was investigated by electron paramagnetic resonance (EPR), infrared spectrum, and elemental analysis. Two copper ions were found to form a complex with one dendrimer. The in vitro microbiological activity of the new compounds against bacteria Pseudomonas aeruginosa and two viruses HRSV-2 and HAdV-5 was investigated. With a view to obtaining antibacterial and anti-viral textiles, cotton fabrics were treated with the three compounds, and then their activity against the same microbial strains was investigated. It was found that the microbiological activity was preserved after the application of the new compounds to the cotton fabrics.

Sensing and Microbiological Activity of a New Blue Fluorescence Polyamidoamine Dendrimer Modified with 1,8-Naphthalimide Units.

A novel second-generation blue fluorescent polyamidoamine dendrimer peripherally modified with sixteen 4-N,N-dimethylaninoethyloxy-1,8-naphthalimide units was synthesized. Its basic photophysical characteristics were investigated in organic solvents of different polarity. It was found that in these solvents, the dendrimer is colorless and emitted blue fluorescence with different intensities depending on their polarity. The effect of the pH of the medium on the fluorescence intensity was investigated and it was found that in the acidic medium, the fluorescence is intense and is quenched in the alkaline medium. The ability of the dendrimer to detect metal ions (Pb2+, Zn2+, Mg2+, Sn2+, Ba2+, Ni2+, Sn2+, Mn2+, Co2+, Fe3+, and Al3+) was also investigated, and it was found that in the presence of Fe3+, the fluorescent intensity was amplified more than 66 times. The antimicrobial activity of the new compound has been tested in vitro against Gram-positive B. cereus and Gram-negative P. aeruginosa. The tests were performed in the dark and after irradiation with visible light. The antimicrobial activity of the compound enhanced after light irradiation and B. cereus was found slightly more sensitive than P. aeruginosa. The increase in antimicrobial activity after light irradiation is due to the generation of singlet oxygen particles, which attack bacterial cell membranes.

Optimized extraction of polyphenols with antioxidant and anti-biofilm activities and LC-MS/MS-based characterization of phlorotannins from Sargassum muticum

The Sargassum genus is rich in glycoglycerolipids, phytosterols, terpenoids, polyphenols, nitrogenous compounds, and other components, and it exhibits various biological activities. Response surface methodology optimization based on Box-Behnken design was applied to extract polyphenols with antioxidant and anti-biofilm activities from Sargassum muticum. Results indicated that the optimal extraction conditions were an ethanol concentration of 56%, a temperature of 58 °C, a time of 5 h, and a liquid/material ratio of 40 mL/g. Under these conditions, the contents of polyphenols and phlorotannins were 10.76 ± 0.42 mg/g and 1.62 ± 0.04 mg/g, respectively. The EtOH extract of S. muticum was further purified with organic solvents of different polarities, and the ethyl acetate fraction (HA-PTs) exhibited the highest purity of polyphenols and phlorotannins, along with the best antioxidant and anti-biofilm activities. In phytochemical analysis, the main substances identified were polysaccharides, phytosterols, polyphenols, flavonoids, and phlorotannins. According to UHPLC-DAD-ESI-MS/MS analysis, four types of phlorotannins were identified from HA-PTs: dibenzodioxine-1,3,6,8-tetraol, tetraphlorethol, pentaphlorethol, and fucopentaphlorethol. These results indicate that the polyphenols of S. muticum have the potential to become new natural antioxidants and antibacterial agents.

Tenability on schiff base Hydrazone derivatives and Frontier molecular orbital

Context hydrazine compounds based on 1,3,5-triazine were synthesised and their molecular structures were characterised by elemental analysis, Electronic, IR and 1H NMR spectra. The spectral behaviour of the newly prepared compounds in organic solvents of different polarities was extensively studied and correlated to the molecular structure. In this study, 1,3,5-Triazine derivatives (L1, L6, L7, L8) have been subjected to theoretical studies using the Semi-empirical PM3 quantum chemical method. The physical-chemical properties of some Hydrazone derivatives are determined theoretically. The molecular geometry, the Highest Occupied Molecular Orbital (HOMO) - Lowest Unoccupied Molecular Orbital (LUMO) energy gap, molecular hardness (η), ionisation energy (IE), Electron affinity and total energy were analysed, and applications as biological effects were done.

Compositing Nanostructured Polyaniline with Single-Walled Carbon Nanotubes for High Thermoelectric Performance

In the face of the growing energy crisis and demand on environmental protection, organic thermoelectric (TE) materials have been coming under the spotlight from global researchers as a potential countermeasure. However, there have been few studies on the relationship between the morphology of conductive polymers (CPs) and their TE performance. In this work, nanostructured polyaniline (PANI) was synthesized by interfacial polymerization with the addition of organic solvents of different polarities, including cyclohexane (CYH), carbon tetrachloride (CCl4), toluene (MB), dichloromethane (DCM), and dimethyl sulfoxide (DMSO). Physical mixing PANI with single-walled carbon nanotubes (SWCNTs) affords PANI/SWCNT composites. The composite of PANI nanobelts and 10 wt% SWCNTs achieves a power factor (PF) of 5.13 ± 0.56 μW m-1 K-2 at room temperature (RT). Spherical PANI doped with 50 wt% SWCNTs followed by pressing affords maximal room temperature PF value of 178.10 ± 3.77 μW m-1 K-2. A prototype TE generator (TEG) constructed with seven pairs of legs of as-prepared PANI/SWCNT composites and their n-type counterparts generates voltage of 10.27 ± 0.15 mV and output power of 36.65 ± 1.18 nW at temperature difference of about 50°C. This work illustrates that well-regulated PANI nanostructure could significantly affect the TE properties of PANI/SWCNT composites, which are promising in future preparation of high-performance polymer-based composites regarding the fabrication of TE devices suitable for harnessing low-grade waste heat.

Yellow-Green and Blue Fluorescent 1,8-Naphthalimide-Based Chemosensors for Metal Cations

Two new 1,8-naphthalimides (NI), emitting yellow-green or blue fluorescence depending on the type of substituents at the C-4 position, have been synthesized and characterized. Their basic photophysical characteristics have been investigated in organic solvents of different polarities. Their ability to detect metal ions (Ag+, Cu2+, Zn2+ Ca2+, Mg2+, Ni2+, and Fe3+) has been studied in DMF solution. The amino (NI1) and alkoxy (NI2) functionalized 1,8-naphthalimides exhibit different optical and metal ion sensing properties attributable to the nature of the C-4 substituents. In addition, theoretical calculations based on the affordable but effective density functional theory (DFT) and time-dependent DFT (TDDFT) methods were performed in order to investigate the geometric and electronic structure of the title NI compounds.

Pyrrole-type compounds from the flowers of Calotropis gigantea

Calotropis gigantea, a large shrub, has been used in traditional folk medicines for the treatment of fever, cough, swellings, bronchitis or dyspepsia. Previous studies on C. gigantea reported that its main constituents, specifically cardenolides and pregnanes, had cytotoxic activity against A549 human lung, Hela human cervical cancer cell lines and K562 human chronic myelogenous leukemia. This paper presents the isolation of chemical constituents from the flowers of C. gigantea (Apocynaceae) in order to provide more information about its chemical compounds to the database on medical plants in Vietnam. By using silica gel column chromatography, preparative TLC and eluting with organic solvents of different polarity, results showed that five pyrroles, including pollenopyrroside B (1), epi-acortatarin A (2), shensongine A (3), 5-methoxymethyl-1H-pyrrole-2-carbaldehyde (4), 1-[2-(furan-2-yl)-2-oxoethyl]pyrrolidin-2-one (5), were isolated from the CHCl3 extract of the flowers of C. gigantea (Apocynaceae), collected at Binh Thuan province in March, 2020. Their chemical structures were elucidated by HR-MS and 1D, 2D NMR spectra analysis and comparison with published data. All compounds were the first reported from C. gigantea.

UHPLC-HRMS Method for the Simultaneous Screening of 235 Drugs in Capillary Blood for Doping Control Purpose: Comparative Evaluation of Volumetric and Non-volumetric Dried Blood Spotting Devices.

We present a quick and simple multi-targeted analytical workflow based on ultra-high-performance liquid chromatography coupled to high-resolution mass spectrometry for the screening in dried blood spots and dried plasma spots of a wide variety of drugs with different chemical properties. Seven different microsampling devices were evaluated in view of their application for the detection of the selected target analytes in the framework of doping control analysis. The extraction of the analytes was optimized by assessing the efficacy of protocols based on ultrasonication with aqueous buffers and/or organic solvents of different polarities. Optimal recoveries were obtained by using pure methanol or mixtures of methanol/acetonitrile and methanol/isopropanol, depending on both the device and the target analytes. The method was fully validated according to both ISO17025 and the requirements of the World Anti-Doping Agency: all the analytes were clearly distinguishable from the matrix, with limits of detection in the range of 0.1–3.0 ng mL–1. Stability studies simulating the storage of samples before the analysis and in view of a possible re-analysis showed that most of the analytes were stable for at least 24 h at 50 °C and for at least 3 weeks at 25 and at 4 °C. The real applicability of the method was assessed by analyzing the samples collected after the administration of two model drugs, acetazolamide and deflazacort. The performance of the method was confirmed to be fit for purpose, and data obtained in blood can also be used to complement those available in urine, allowing to refine the knowledge concerning the pharmacokinetic profiles.

A highly selective and sensitive fluorescent sensor based on a 1,8-naphthalimide with a Schiff base function for Hg2+ in aqueous media

Abstract A new fluorescent sensor, N-allyl-4-[(2-(3-methoxysalicylaldimino)ethylamino]-1,8-naphthalimide (HL), for Hg2+ has been developed where the Schiff base substituent acts as a recognition group. This sensor shows a large Stokes shift of 3535–4042 cm−1 and a general fluorescence quantum yield of 0.05, 249–0.11, 866 in organic solvents of different polarity as expected. It also exhibits highly selective and a sensitive response to Hg2+ (Ф Hg+HL/Ф HL = 2.28) over other metal ions (Na+, K+, Ca2+, Mg2+, Al3+, Pb2+, Fe3+, Ni2+, Zn2+, Cu2+, Ag+, Co2+, Cr3+, Mn2+ and Cd2+) in solution (DMF/Tris-HCl buffer, 1:1, v/v, pH = 7.2). The Hg2+-induced fluorescence enhancement at 526 nm is proportional to the concentration of Hg2+ in the range of 0.5–4.0 µm with a detection limit of 0.18 µm. Based on the fluorescence titration and a Job’s plot analysis, the metal-to-ligand ratio of the complex is 2:1 with a binding constant of 1.56 × 1012 m −1.

Enhancing the antibacterial activity of PAMAM dendrimer modified with 1,8‐naphthalimides and its copper complex via light illumination

AbstractThis work describes the synthesis of a new photoactive PAMAM dendrimer of first generation, modified with 4‐dimethylamino‐1,8‐naphthalimide units and its complexation with Cu2+ ions. The photophysical characteristics of the two compounds in organic solvents of different polarity have been determined. The impact of light on reactive oxygen species from the new compounds and on the cotton fabrics dyed with them has been investigated by an iodometric method, consisting of I− transformation into I3−, which absorbs light at 288 and 352 nm. It has been determined that their antibacterial activity towards Gram‐negative and Gram‐positive bacteria enhances upon light illumination, as a resultant synergic effect of the biological activity of the new dendrimers and of the reactive oxygen they generate. The copper complex has been found to be more active than the ligand. Upon their loading onto cotton fabrics both compounds retain their antibacterial activity.

4-(1H-Imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzaldehyde as a probe in pure solvents: Solvatochromism, electric dipole moment and pH influence

The spectral properties of 4-(1H-imidazo[4,5-f][1,10]phenanthrolin-2-yl)benzaldehyde (1) in eleven organic solvents of different polarity have been studied. In order to determine the contributions of specific and non-specific interactions between the considered compound and the solvents, the solvatochromic Lippert-Mataga, McRae, Bakhshiev methods have been applied. The compound demonstrates positive solvatochromism. The dipole moment of the excited state of 1 obtained using the Reichardt method is equal to 10.56/7.08 D for trans- and cis-conformers, respectively, and agrees well with the theoretically calculated value. The influence of the polarizability of 1 on changes in the dipole moments has been analyzed using the Bilot-Kawski method. The multiple linear regression analysis in the framework of the Kamlet-Abboud-Taft and Catalán models has highlighted that the main properties which determine the Stokes shift of 1 are the acidity and dipolarity of the solvent. The variation of pH by additions of acid or base to solution 1 leads to significant changes in absorption and fluorescence spectra, therefore, 1 can be of interest as a solvatochromic probe, being sensitive to acidic/base properties of the environment. It has also been found out that the anion form of 1 is present in the DMSO solution. An addition of N,N-dimethylcyclohexylamine intensifies the dissociation of the considered compound in the DMSO solution and suppresses the fluorescence at a large amine excess.

Inhibiting the growth of Staphylococcus aureus and Staphylococcus epidermis using honeybee extract (Apis mellifera or: Hymenoptera)

An inhibitory action test is conducted in which honeybee body lotion is selected as an inhibitor against Gram-positive bacteria: Staphylococcus aureus and Staphylococcus epidermis. The extraction is done using organic solvents of different polarities to allow the extraction of various active substances against the growth of bacteria, namely methanol alcohol and carbon tetrachloride. The tests are carried out by both methods of discs and drilling using cationic antibiotics ampicillin (AMP) and streptomycin (STRPTO). Results showed less sensitivity to the two types of S. aureus in all extracts, however, the inhibition values appeared to double compared to antibiotics in the event of their positive effect, which are occupied by antibiotics Strep and Amp. The rest of the treatments for the three antibiotics are positive against the two types of bacteria above. For insecticidal solution at concentrations 3.5,4.0, 4.38,3.5 mM mg/ml, it inhibited the growth of all types of bacteria with a range of 3.0-4.5 mm.

Lignans from the fruits of Pandanus kaida Kurz. (Pandanaceae) and theirs a-Glucosidase inhibitory activities

Pandanus kaida Kurz is a arbsute, which is combined with others medical plants for treatment of kidney stones, epididymitis and eyes diseases in Vietnamese traditional medicines. However, little scientific publication is available for this plant. The aim of this study is to isolate chemical constituents of the fruits of Pandanus kaida K. (Pandaceae) in order to provide more information to add to the database of medical plants in Vietnam. Results showed five compounds including: epi-pinoresinol (1), (+)-pinoresinol (2), (+)-syringaresinol (3), (+)-medioresinol(4), and (+)-isolariciresinol (5), which have been isolated from the fruits of Pandanus kaida K. (Pandanaceae), collected in Duc Hoa District, Long An Province, Vietnam. Extraction was carried out by heating under reflux and liquid-liquid extraction with organic solvents of increasing polarity to yeild corresponding soluble fractions, then, using chromatography methods such as column chromatography on silica gel, preparative TLC and eluting with organic solvents of different polarity for obtaining five compounds. Their chemical structures were elucidated based on the NMR spectroscopic analysis, HR-ESI-MS, the specific optical rotation and comparison with the literature. Three lignans (+)-pinoresinol (2), (+)-syringaresinol (3), and (+)-medioresinol (4) showed potent a-glucosidase inhibitory activity.

SYNTHESIS OF COCRYSTALS OF BETULIN WITH SUBERIC ACID AND STUDY OF THEIR PROPERTIES

Lupane triterpenoids, betulin and its derivatives, are attracting great interest due to their wide range of biological and pharmacological activities. However, the poor solubility of betulin and its derivatives in aqueous media significantly reduces their bioavailability. Obtaining cocrystals, that is, multicomponent crystal systems containing active pharmaceutical ingredients and non-toxic partner molecules in their structure, is used in pharmacy to change the physicochemical properties of drugs, including the rate of dissolution and solubility. In this study, cocrystals of betulin with suberic acid were obtained by liquid-assisted grinding method using organic solvents of different polarity: ethanol, acetone, ethyl acetate, chloroform, toluene, dioxane. The formation of cocrystals was confirmed by X-ray diffraction analysis, IR spectroscopy, and thermal analysis. It has been shown that cocrystals of betulin with suberic acid contain water molecules in their structure; anhydrous cocrystals can be obtained by heating a physical mixture of reagents until the acid melts. The results of experiments on the dissolution of cocrystals of betulin with suberic acid in comparison with the data for cocrystals of betulin with adipic acid showed that an increase in the length of the aliphatic acid chain leads to a decrease in the rate of betulin release into solution.

ANTIMICROBIAL POTENTIALS OF TWO FRESHWATER HETEROCYSTOUS CYANOBACTERIA WESTIELLOPSIS PROLIFICA AND NOSTOCHOPSIS LOBATUS COLLECTED FROM SIMILIPAL BIOSPHERE RESERVE, ODISHA, INDIA

The Similipal Biosphere Reserve, an unique ecosystem in the eastern part of India, occupy the northern boundary of Odisha state, lies between 21°28´ to 22°08´ North latitude and 86°04´ to 86°37´ East longitude, covering a vast area of 5578 sq. km in the district of Mayurbhanj. Westiellopsis prolifica and Nostochopsis lobatus, are a group of heterocystous, true branched, filamentous cyanobacteria belonging to the order Stigonematales, rarely found in the aquatic bodies of this region in the state of Odisha. In the present investigation, an attempt has been made to evaluate the antimicrobial potentials of Westiellopsis prolifica and Nostochopsis lobatus collected from flowing streams of Similipal Biosphere Reserve. The organisms were cultured in nitrogen free BG-11 medium and raised to axenic state. Crude metabolites were extracted from cultured test organisms in late log phase using organic solvents of different polarity viz. methanol and chloroform. The metabolites were tested against some clinically significant microorganisms including bacteria and fungi using agar cup diffusion method and the results of antimicrobial activity of cyanobacteria are summarized. The findings revealed that pattern of inhibition varied with respect to the cyanobacterial strains used, nature of solvent extracts and the pathogenic microorganisms tested. Westiellopsis prolifica was found to be more potent that inhibit all the pathogenic bacteria and fungi both in methanol and chloroform extract. This study illustrates that heterocystous cyanobacteria from freshwater bodies could be a potent source of antimicrobial agents and further characterization of active metabolites and evaluation of their pharmacological potentials are also needed.

Accelerated Solvent Extractions (ASE) of Mitragyna speciosa Korth. (Kratom) Leaves: Evaluation of Its Cytotoxicity and Antinociceptive Activity.

Mitragyna speciosa Korth (kratom) is known for its psychoactive and analgesic properties. Mitragynine is the primary constituent present in kratom leaves. This study highlights the utilisation of the green accelerated solvent extraction technique to produce a better, non-toxic and antinociceptive active botanical extract of kratom. ASE M. speciosa extract had a dry yield (0.53–2.91 g) and showed a constant mitragynine content (6.53–7.19%) when extracted with organic solvents of different polarities. It only requires a shorter extraction time (5 min) and a reduced amount of solvents (less than 100 mL). A substantial amount of total phenolic (407.83 ± 2.50 GAE mg/g and flavonoids (194.00 ± 5.00 QE mg/g) were found in ASE kratom ethanol extract. The MTT test indicated that the ASE kratom ethanolic leaf extract is non-cytotoxic towards HEK-293 and HeLa Chang liver cells. In mice, ASE kratom ethanolic extract (200 mg/kg) demonstrated a better antinociceptive effect compared to methanol and ethyl acetate leaf extracts. The presence of bioactive indole alkaloids and flavonols such as mitragynine, paynantheine, quercetin, and rutin in ASE kratom ethanolic leaf extract was detected using UHPLC-ESI-QTOF-MS/MS analysis supports its antinociceptive properties. ASE ethanolic leaf extract offers a better, safe, and cost-effective choice of test botanical extract for further preclinical studies.

Methanolic Extract of Angelica glauca Edgew Root and Stem: A Possible Component of Herbal Medicines against Respiratory Infections

Plants are identified to produce a variety of compounds to protect themselves against a diversity of pathogens. This study assessed the antibacterial, antioxidant potential and phytochemical screening of medicinal plant Angelica glauca (Choru) root and stem extracts against respiratory tract pathogens i.e., Staphylococcus aureus MTCC 1144, Streptococcus pneumoniae MTCC 655, Streptococcus pyogenes MTCC 442, Pseudomonas aeruginosa MTCC 2474 and Klebsiella pneumoniae MTCC 4030. The plant material was collected from Tungnath 3,800m amsl of Garhwal Himalaya. Root and stem of the plants were washed, shade dried, grinded into fine powder and extracted in the organic solvents of different polarity (petroleum ether, chloroform, methanol and water). Antibacterial activities of prepared extracts were assayed using agar well diffusion and two-fold serial dilution method of MIC determination. Antioxidant potential was determined using DPPH assay and phytochemical analysis was performed using qualitative methods for different phytochemicals. Experimental outcomes revealed maximum antibacterial and antioxidant activity of methanol extract;also the maximum groups of phytochemicals were present in the methanolic extract. The methanol extract produced ZOIs of 11.0±0.54mm to 30.3±1.58mm diameters and MICs ranges were recorded between 3.12 mg/ml to 25 mg/ml against all the tested bacteria. Alkaloids, flavonoids, glycosides, tannins, steroids and saponins were present in the extracts of A. glauca. This study favors a good response towards using A. glauca as natural antioxidant in herbal medicines, either in pure form or as supplement with other herbal formulations already available in the market, to enhance their potential against respiratory tract diseases. In the present COVID-19 pandemic situation, use of A. glauca can be beneficial, as it’s methanolic extract showed promising antibacterial activity against bacterial pathogens of human respiratory tract. © 2021, Association of Pharmaceutical Teachers of India. All rights reserved.

Synthesis and characterization of fluorescent PAMAM dendrimer modified with 1,8-naphthalimide units and its Cu(II) complex designed for specific biomedical application

A new fluorescent dendrimer was obtained by modifying the periphery of a PAMAM dendrimer from zero generation. The modification involves substitution at the C-4 position with 1,8-naphthalimide units containing N-methylpiperazine and the addition of Cu(II) ions forming the metallodendrimer [Cu2(D)(NO3)2]. The dendrimer ligand and metallodendrimer were subjected to UV–vis, fluorescence spectroscopy, FT-IR, NMR, and SEM investigations to define their precise structure. The photophysical characteristics of the yellow-green fluorescent dendrimer were studied in organic solvents of different polarity. Results show that polar solvents favour a photoinduced electron transfer (PET) process. Experiments on the effect of pH in an ethanol - water solution (1:4 v/v) revealed the fluorescence of the dendrimer to be more than seventeen times higher than that in an acidic medium. Electron paramagnetic resonance (EPR) studies were performed to characterize the complexing ability of the dendrimer towards Cu(II) by varying the [Cu(II)/dendrimer external sites] molar ratio in DMSO solution. The EPR results suggest that Cu(II) formed a Cu-N2O2 square-planar coordination with nitrogen sites (N-CH3 sites of 1,8-methylpiperazine, and amine and amide groups) at the dendrimer internal/external interface, and 2 solvent molecules. The Cu(II) complex was characterized by restricted mobility conditions. Copper (II) ions were distributed between the dendrimer interface and the external surface; saturation of the nitrogen sites at the interface occurred at a 1:2 M ratio between Cu(II) and methylpiperazine units. These results are useful in view of the use of this metallodendrimer as anticancer and antimicrobial drugs. The antimicrobial activity of dendrimer ligand and its Cu(II) complex was tested against several model strains bacteria and yeasts in agar, in liquid medium, and after their deposition onto a cotton fabric. The results showed good antibacterial effect of dendrimer ligand, which was enhanced by its Cu(II) complexation.

Fractionation of lignin using organic solvents: A combined experimental and theoretical study

Refining of industrial lignin to produce homogeneous fractions is essential for high-value applications. However, the understanding of key interactions between a variety of solvents with lignin polymer is still uncertain. In this work, single-step fractionation of industrial hardwood kraft lignin (HKL) using organic solvents of different polarities – ethanol, acetone, diethyl ether and hexane – was investigated by combining an experimental and theoretical approach. Experimental results revealed that higher polarity solvents (ethanol and acetone) exhibited higher solubility yield compared to moderate and low polarity solvents. The chemical differences between lignin fractions were proven by pyrolysis gas chromatography mass spectrometry and near infrared spectroscopy. Density functional theory (DFT) results indicated that ethanol presented higher interaction energy followed by acetone, diethyl ether and hexane, which was consistent with experimental findings. Hydrogen bond and non-covalent interaction results from DFT demonstrated that the predominant interaction was found for high polarity of ethanol over other solvents and γ-OH in the lignin model is the key site.

Revisiting the photochemistry 2,5‐dihydroxy benzoic acid (gentisic acid): Solvent and pH effect

AbstractIn the present study, we have reinvestigated photochemistry of 2,5‐dihydroxy benzoic acid (DHBA) in a series of organic solvents of different polarities and the aqueous solution of varying pH from 1 to 14. The investigation was carried out using steady‐state and nanosecond (ns) time‐domain fluorescence measurement techniques at room temperature. Some hitherto not explored spectral features with new insight on different forms of DHBA are reported. It is found that DHBA exists as monoanionic and neutral forms in various polar protic, aprotic, and nonpolar solvents. In aqueous solution (pH 1 to 14), neutral, monoanionic, and dianion forms are found to be responsible for the observed optical spectral profiles. The observed significant Stokes shift in emission is attributed to species undergoing excited‐state intramolecular proton transfer (ESIPT) in different solvents. The analysis presented in this work elucidates and validate the presence of various species and conformers of DHBA.