Zwitterionic Form Research Articles

Electronic structures of zwitterionic and protonated forms of glycine betaine in water: Insights into solvent effects from ab initio simulations

Glycine betaine (GB), a naturally occurring osmolyte, has many biological functions and is used in food supplements, pharmaceuticals, and animal feed. GB usually exists as a zwitterion in aqueous solutions. Due to the hygroscopic property of GB, protonated form of GB, GBH+ (noted as GBH) is often used. In order to understand the hydration structures of GB and GBH at the atomic and electronic-structure level, a combination of ab initio molecular dynamics simulations and electronic structure calculations based on density functional theory (DFT), single-excitation configuration interaction method, and coupled-cluster ansatz was utilized. A hybrid explicit–implicit solvation model was used to elucidate solvent effects. Within the hybrid scheme, microsolvated structures of GB and GBH with up to 100 water molecules were obtained, showing that water molecules bind to GB and GBH in a dramatically different manner. By calculating the molecular electron-density distributions at PBE0-D4/def2-TZVP level, it shows that the variation of electron density for GB is more significant than GBH, suggesting that GB can interact with more water molecules than GBH. The interaction energies of GB–(H2O)n and GBH–(H2O)n systems (n = 1–6) at DLPNO-CCSD(T)/cc-pVQZ level highlight the difference from an energy point of view. Using the microsolvated structures of GB and GBH, the features of experimental K-edge spectra can be reproduced using the efficient PNO-ROCIS/B3LYP method, implying the reliability of the hybrid explicit–implicit solvation approach. The results suggest that complementary insights into the geometries and electronic structures of GB and GBH could be obtained through combined methods, which provides a methodological approach for understanding the hydration structures of zwitterionic and charged molecules.

The First Noncovalent-Bonded Supramolecular Frameworks of (Benzylthio)Acetic Acid with Proline Compounds, Isonicotinamide and Tryptamine

The co-crystallization of (benzylthio)acetic acid (HBTA) with L-proline (L-PRO), D-proline (D-PRO), DL-proline (DL-PRO), isonicotinamide (INA) and tryptamine (TPA) led to the formation of five novel crystalline compounds: L-PRO±·HBTA (1), D-PRO±·HBTA (2), DL-PRO±·HBTA (3), INA·HBTA (4) and TPA+·BTA- (5). The prepared supramolecular assemblies were characterized by single crystal X-ray diffraction, an elemental analysis, FT-IR spectroscopy and a thermal analysis based on thermogravimetry (TG) combined with differential scanning calorimetry (DSC). Additionally, their melting points through TG/DSC measurements were established. All fabricated adducts demonstrated the same stoichiometry, displayed as 1:1. The integration of HBTA with selected N-containing co-formers yielded different forms of multi-component crystalline phases: zwitterionic co-crystals (1-3), true co-crystal (4) or true salt (5). In the asymmetric units of 1-4, the acidic ingredient is protonated, whereas the corresponding N-containing entities take either the zwitterionic form (1-3) or remain in the original neutral figure (4). The molecular structure of complex 5 is occupied by the real ionic forms of both components, namely the (benzylthio)acetate anion (BTA-) and the tryptaminium cation (TPA+). In crystals 1-5, the respective molecular residues are permanently bound to each other via strong H-bonds provided by the following pairs of donor···acceptor: Ocarboxylic···Ocarboxylate and Npyrrolidinium···Ocarboxylate in 1-3, Ocarboxylic···Npyridine and Namine···Ocarboxylic in 4 as well as Nindole···Ocarboxylate and Naminium···Ocarboxylate in 5. The crystal structures of conglomerates 1-5 are also stabilized by numerous weaker intermolecular contacts, including C-H···O (1-3, 5), C-H···S (1, 2, 5), C-H···N (5), C-H···C (5), C-H···π (1-5) as well as π···π (4) interactions. The different courses of registered FT-IR spectral traces and thermal profiles for materials 1-5 in relation to their counterparts, gained for the pure molecular ingredients, also clearly confirm the formation of new crystalline phases.

Zwitterionic versus neutral molecules of fluoroquinolones: crystal structure of danofloxacin dihydrate.

The crystal structure of danofloxacin (DFX) as a zwitterionic dihydrate [systematic name: (1S,4S)-5-(3-carboxylato-1-cyclopropyl-6-fluoro-4-oxo-1,4-dihydroquinolin-7-yl)-2-methyl-2,5-diazabicyclo[2.2.1]heptan-2-ium dihydrate], C19H20FN3O3·2H2O, has been determined for the first time. The stability of the crystal structure is ensured by N-H...O and O-H...O hydrogen bonds, some of which are assisted by charge. The zwitterionic molecules of DFX are packed in stacks and this structural motif can be defined as a basic one from a supramolecular and energetic point of view. Hirshfeld surface analysis was used for an additional interpretation of the close contacts. The nature of the intermolecular interactions was evaluated in a pairwise manner. Destabilizing interactions were also discussed. In the context of our study on danofloxacin, we addressed the question: how common is a zwitterionic form for fluoroquinolones (FQ) in the crystalline state? A survey of the Cambridge Structural Database limited to anhydrous/hydrated/solvated forms of the most typical FQs revealed that neutral molecules are preferred, while zwitterions are less common.

Impacts of polarizable continuum models on the SCF convergence and DFT delocalization error of large molecules.

Advances in algorithm developments have enabled density functional theory (DFT) description of large molecules, including whole proteins, but the self-consistent field (SCF) convergence issues often hamper practical applications. The conductor-like polarizable continuum model (CPCM), although initially introduced as an implicit solvent model, was reported to improve SCF convergence in some large molecules. However, the underlying mechanisms and applicable use cases were unclear. We investigated the impacts of CPCM on the SCF convergence of 25 peptides and found that the CPCM only effectively reduced the SCF iterations for molecules with charge separations (e.g., the zwitterionic form of peptides) but had little effect on non-charge-separated molecules. We observed that CPCM increased the HOMO-LUMO gap of both the zwitterionic and non-charge-separated molecules, but only the charge-separated molecules suffered from the vanishing HOMO-LUMO gap problem in the gas phase, which is the origin of the convergence issue. We revealed CPCM's gap-opening mechanism as the selective stabilization/destabilization of molecular orbitals (MOs) based on their local electrostatic environment. Compared to level-shifting, a traditional SCF improvement technique, CPCM has superior performance because the stabilization/destabilization of MOs is consistent through SCF iterations. Finally, we examined CPCM's impacts on DFT density delocalization error (DDE) when used as an SCF accelerator. CPCM can mitigate the DDE and reproduce the density-derived properties (e.g., dipole moments) matching high-level methods when a very low dielectric constant is used but tends to over-localize the electron density at higher dielectric constants.

GO/ionic surfactant inspired photophysical modulation of rhodamine B in Reline with or without additives

Photophysical behaviour of rhodamine B (RB) in deep eutectic solvents (DES, formed by quaternary ammonium salt and hydrogen bond donor (HBD) in a specific eutectic ratio) with or without graphene oxide (GO) or ionic surfactants, is less known. The nature of Reline (choline chloride (ChCl): urea (HBD), 1:2), a well-known DES, has been designed by adding glycerol or water as the second HBD for sustained movement of RB. Effects of GO, surfactant, or GO + surfactant, in controlling RB movement, at various sites (GO surface, surfactant micelle, DES surface, or background solvent), have been fluorometrically reported. The basic nature of Reline (pH = 10.38) causes modification of GO surface (deprotonated site) and nature of RB (cationic → zwitter ionic). Above Reline-inspired changes have been found to modify interactions of RB with GO and/or sodium dodecyl sulphate (SDS, an anionic surfactant) or cetyl trimethyl ammonium bromide (CTAB, a cationic surfactant). SDS (10 mMdm−3, < critical micelle concentration (CMC) in Reline) shows ∼ 2.6, 1.6, and 1.4 fold fluorescence intensity enhancement of RB (in water, pure Reline, and methanol, respectively). However, GO and/or CTAB shows quenching behaviour. Further, the fluorescence of RB shows weak dependence on changing the second HBD (water or glycerol). DES-controlled cationic vs zwitterionic form of RB is responsible for the interaction and sustained movement towards GO surface, micellar surface, or negatively charged ion-pair formation (with SDS monomers). Findings of the work have implications in searching potential fluorescent levels/sensors for photophysics, photobiology, or wider vehicle means for sustained drug delivery.

Biopolymeric Ni3S4/Ag2S/TiO2/Calcium Alginate Aerogel for the Decontamination of Pharmaceutical Drug and Microbial Pollutants from Wastewater.

The ubiquitous presence of pharmaceutical drugs and microbes in the water is leading to the development of drug resistant microbes. Therefore, efficient materials that can remove or inactivate the drug and microbe contaminants are required. In this work, nickel sulfide/calcium alginate (Ni3S4/CA), silver sulfide/calcium alginate (Ag2S/CA), modified titanium dioxide/calcium alginate (TiO2/CA), and Ni3S4/Ag2S/TiO2/calcium alginate (Ni3S4/Ag2S/TiO2/CA) aerogels have been synthesized for the removal of the oxytetracycline (OTC) drug and microbial contaminants from real beverage industry wastewater. The results revealed that Ni3S4/Ag2S/TiO2/CA aerogel is highly efficient for OTC adsorption and inactivation of microbes compared to Ni3S4/CA, Ag2S/CA and TiO2/CA aerogels. The OTC adsorption depends greatly on the solution pH, and optimum OTC removal was observed at pH 6 in its zwitterionic (OTC±) form. The formation of H-bonding and n-π electron donor-acceptors is possible to a considerable extent due to the presence of the double bond benzene ring, oxygen and nitrogen, sulfur-containing functional groups on the OTC molecules, and the Ni3S4/Ag2S/TiO2/CA aerogel. Based on the statistical analysis, root-mean-square deviation (RMSD), chi square (χ2) values, and higher correlation coefficient (R2) values, the Redlich–Peterson isotherm model and Elovich kinetic model are most suited to modelling the OTC adsorption onto Ni3S4/Ag2S/TiO2/CA. The prepared aerogels’ excellent antimicrobial activity is observed in the dark and with solar light irradiation. The zone of inhibition analysis revealed that the antimicrobial activity of the aerogels is in the following order: Ni3S4/Ag2S/TiO2/CA > TiO2/CA > Ag2S/CA > Ni3S4/CA, respectively. Moreover, the antimicrobial results demonstrated that reactive oxygen species, electrons, and active radical species are responsible for growth inhibition and killing of the microbes. These results indicated that Ni3S4/Ag2S/TiO2/CA aerogel is highly efficient in decontaminating pollutants from wastewater.

Multi-Stimuli-Responsive Organo-Sulfonated Anil and Its Organic Complex

Sensing by molecules is an intriguing phenomenon that can lead to next-generation intelligent materials. Stimuli-responsive organic molecules or molecular complexes, although less reported, can open up new avenues and opportunities in the area of artificial intelligence and memory. Extending the scope of organo-sulfonated Anils as stimuli-responsive materials, we report hydrated sulfonated Anil 1 and its nonstoichiometric bipyridyl complex 1.BPY. The formation of new materials is well supported and further substantiated through the solid-state structural elucidation of 1. Thermal and crystallographic studies validate the presence of two lattice water molecules each in 1 and 1.BPY. Structural studies also indicate that 1 undergoes intramolecular proton transfer between sulfonate and imine groups and exists in the zwitterionic form. Both 1 and 1.BPY respond to external stimuli: temperature, solvent polarity, and ammonia vapor. The thermochromism in both forms is reversible and interestingly triggered by the breathing of lattice water, a rare phenomenon in organic materials, supported by Fourier-transform infrared (FT-IR), thermal, and diffraction studies. Compared with the transition temperature of 130 °C for 1, 1.BPY undergoes a color change at 65 °C, and their heated forms, 1-Heat and 1.BPY-Heat, in turn, can be used as humidity sensors. Both solid forms exhibit solvatochromism and show emission turn-on in nonprotic polar solvents, dimethyl sulfoxide (DMSO) and dimethylformamide (DMF). The incipience of emission of 1.BPY in highly polar solvents DMSO (φ = 12%) and DMF (φ = 46%), and its absence in the solvents of relatively lower polarity such as H2O and MeOH as well as in solid forms, may be attributed to aggregation-induced quenching, which is supported by the solubility and DLS studies of 1 and 1.BPY in the solvents. Very interestingly and to the best of our knowledge, molecular solids 1 and 1.BPY represent the first examples of organic materials that exhibit emission turn-on on exposure to fumes of a base. When exposed to the fumes of ammonia, 1 and 1.BPY undergo a color change from maroon and orange to yellow, respectively, and the 1.NH3 and 1.BPY-NH3 forms show a striking green emission, which may be attributed to proton transfer within the molecular systems most likely involving the excited-state intermolecular proton-transfer (ESIPT) pathway. The overall analyses of the results indicate that the molecular complex 1.BPY is a better material vis-à-vis its response time (thermochromism), intensity (solvatochromic), and fatigue (vapochromism) and substantiate the scope of the crystal-engineering principles in designing next-generation smart materials.

Active binding sites for ofloxacin resulted from adsorptive fractionation of humic acid on kaolinite

The adsorptive fractionation of humic acid (HA) at the interface between minerals and water can significantly affect the fate of pollutants in water-soil environment. However, the adsorptive fractionation behavior of HA on kaolinite and its effect on the migration of fluoroquinolones (FQs) have not been fully understood. In this study, fluorescence and infrared spectroscopy, combined with two-dimensional correlation analyses, were used to explore the adsorptive fractionation of humic acid (HA) and its effects on ofloxacin adsorption on kaolinite. The results indicated that humic-like, rather than reduced quinone-like and tyrosine-like, was the main adsorptive fractionation component and preferentially bound to the Al–O sites of kaolinite. The adsorption mechanisms of humic-like and tyrosine-like mainly include hydrogen bonds between acidic functional groups and the Si–O or Al–O groups of kaolinite, n-π electron donor-acceptor interaction and electrostatic attraction. At pH 7.0, with addition of 4.0 and 16.0 mg C/L HA in solution, the adsorptive fractionation of HA on kaolinite led to increases in ofloxacin (in zwitterionic form) adsorption capacity by 1.46 and 3.35 mg/g, respectively. The interactions between ofloxacin and the humic-like were mainly hydrogen bonds and electrostatic attraction. Therefore, the influence of adsorptive fractionation of dissolved organic matter on minerals should be considered in estimating FQs environmental behaviors.

Solvent-driven micro/nanostructures of squaraine and croconaine dyes based on quinoxalinone for visual detection of nerve agent simulants

The detection of nerve agents has been the focus of research due to their extreme threat for human health and safety. In this paper, the quinoxalinone-based squaraine (NESQ) and croconaine (NECR) dyes are synthesized and used as chemosensors to investigate the sensing properties with diethyl chlorophosphate (DCP) in solvents. They exhibit a huge absorption spectra red-shift from visible region to near-infrared region due to the transformation of anionic basic form and zwitterionic acidic form, which is verified by experiments and theoretical calculations. The self-assembly micro/nanostructures transformation of NESQ and NECR can be driven by adding different solvents, which is characterized by SEM and AFM technology. Upon adding DCP, the absorption wavelength of NESQ and NECR in DMF respectively exhibits 186 nm and 281 nm red-shifts from visible region to near-infrared region with obvious color change, which is larger than the previously reported. The proposed sensing mechnism was verified by 1H NMR spectra and SEM technology. Compared to NECR, NESQ exhibits a lower limit of detection and a faster responsive time for sensing DCP. The characteristics of these dyes would provide a new design strategy of chromogenic chemsensors with large wavelength shift and self-assembly morphologies transformation for the visual detection of nerve agents.

Effect of solutes structure and pH on the n-octanol/water partition coefficient of ionizable organic compounds.

Liquid-liquid partition coefficient is a useful tool to predict biological and environmental fate of organic compounds, for example bioaccumulation or toxicity of lipophilic contaminants. Conversely, the partitioning of ionizable compounds is poorly studied in contrast to that of neutral compounds. Yet, such topic deserves attention, since numerous organic contaminants are ionizable as well as their degradation products. Hence, the contribution of charged species has to be considered in order to model accurately the mass balance or partition of ionizable compounds. In this context, we investigated the liquid-liquid partition of 13 ionizable compounds (oxalic acid, histidine, benzimidazole, etc.), covering various classes of compounds (carboxylic acids, amino-acids, etc.). The n-octanol/water partition coefficient was measured from pH 1 up to 13, in order to fully gather the distribution of both neutral and charged species. Empirical models describing these results are reviewed and partition parameters adjusted for charged species. The study of benzoic acid derivatives (benzoic, salicylic, ortho- and iso-phthalic acids) provides insights on the influence of chemical groups on the partitioning. In the case of tryptophan, the use of acid/base microconstants allowed to estimate the partition of both the zwitterion and its neutral tautomer. Despite a major zwitterionic form (log PZ(tryptophan)=-1.58±0.30), the minor but neutral tautomer (log PN(tryptophan)=+0.03±0.30) drives the partition equilibrium. Overall, the provided data may be useful to assess the retention of contaminants, its dependency on pH and salinity variations, and thus understanding their environmental fate. Such data may also be useful as well for molecular simulation involving solvation of organic ions in aqueous and non-aqueous solvents.

Spiropyran/Merocyanine Amphiphile in Various Solvents: A Joint Experimental-Theoretical Approach to Photophysical Properties and Self-Assembly.

This joint experimental-theoretical work focuses on molecular and photophysical properties of the spiropyran-containing amphiphilic molecule in organic and aqueous solutions. Being dissolved in tested organic solvents, the system demonstrates positive photochromism, i.e., upon UV stimulus the colorless spiropyran form is transformed into colorful merocyanine isomer. However, the aqueous solution of the amphiphile possesses a negative photochromism: the orange-red merocyanine form becomes thermodynamically more stable in water, and both UV and vis stimuli lead to the partial or complete photobleaching of the solution. The explanation of this phenomenon is given on the basis of density functional theory calculations and classical modeling including thermodynamic integration. The simulations reveal that stabilization of merocyanine in water proceeds with the energy of ca. 70 kJ mol, and that the Helmholtz free energy of hydration of merocyanine form is 100 kJ mol lower as compared to the behavior of SP isomer in water. The explanation of such a difference lies in the molecular properties of the merocyanine: after ring-opening reaction this molecule transforms into a zwitterionic form, as evidenced by the electrostatic potential plotted around the opened form. The presence of three charged groups on the periphery of a flat conjugated backbone stimulates the self-assembly of merocyanine molecules in water, ending up with the formation of elongated associates with stack-like building blocks, as shown in molecular dynamics simulations of the aqueous solution with the concentration above critical micelle concentration. Our quantitative evaluation of the hydrophilicity switching in spiropyran/merocyanine containing surfactants may prompt the search for new systems, including colloidal and polymeric ones, aiming at remote tuning of their morphology, which could give new promising shapes and patterns for the needs of modern nanotechnology.

Insight into the Formation of Cocrystal and Salt of Tenoxicam from the Isomer and Conformation.

Tenoxicam (TNX) is a new non-steroidal anti-inflammatory drug that shows a superior anti-inflammatory effect and has the advantages of a long half-life period, a fast onset of action, a small dose, complete metabolism, and good tolerance. Some compounds often have tautomerism, and different tautomers exist in different crystalline forms. TNX is such a compound and has three tautomers. TNX always exists as the zwitterionic form in cocrystals. When the salt is formed, TNX exists in the enol form, which exhibits two conformations depending on whether a proton is gained or lost. Currently, the crystal structure of the keto form is not in the Cambridge Structural Database (CSD). Based on the analysis of existing crystal structures, we derived a simple rule for what form of TNX exists according to the pKa value of the cocrystal coformer (CCF) and carried out validation tests using three CCFs with different pKa values, including p-aminosalicylic acid (PAS), 3,5-dinitrobenzoic acid (DNB), and 2,6-dihydroxybenzoic acid (DHB). The molecular surface electrostatic potential (MEPS) was combined with the pKa rule to predict the interaction sites. Finally, two new cocrystals (TNX-PAS and TNX-DNB) and one salt (TNX-DHB) of TNX were obtained as expected. The differences between the cocrystals and salt were distinguished by X-ray diffraction, vibration spectra, thermal analysis, and dissolution measurements. To further understand the intermolecular interactions in these cocrystals and salt, the lattice energy and energy decomposition analysis (EDA) were used to explain them from the perspective of energy. The results suggest that the melting point of the CCF determines that of the cocrystal or salt, the solubility of the CCF itself plays an important role, and the improvement of the solubility after salt formation is not necessarily better than that of API or its cocrystals.

How do alternative amino acids behave in water? A comparative ab initio molecular dynamics study of solvated [formula omitted]-amino acids and [formula omitted]-amino amidines

Among hypothetical alternative biochemistries, ammonia based life is one of the more promising ideas to investigate, due to the many similarities of water and ammonia as well as the existence of various ammonia based equivalents to prominent biomolecules. In this scenario α-amino amidines form the analogues to the α-amino acids, which can also be classified as the building blocks of life. Comparison of basic solvation behaviour between α-amino amidines and α-amino acids can provide insight into general chemical properties. To better understand the solvation of these compounds, we conducted ab initio molecular dynamics simulations for alanine, leucine, 2-aminopropionamidine and 2-amino-4-methylpentanamidine dissolved in 128 water molecules. We started simulations both from the neutral as well as from the zwitterionic form. For the α-amino amidines we observed protonation of the amidine group by water. Amino acids do not change spontaneously between the two states in our simulations. The molecular dipole moment is highly influenced by the state and conformation of the molecule and is a key property to trace in the course of the simulation. Structural analyses demonstrate the interactions of the compound with the surrounding solvent, solvation shells and hydrogen bonding.

Vibrational spectra and molecular structure of sulfanilic acid: IR and low temperature Raman studies and DFT investigation of monomeric and dimeric forms

Room temperature IR and Raman spectra, low temperature Raman spectra and UV–vis spectrum of sulfanilic acid (SA) were measured. Molecular structures of monomeric SA in the OH and zwitter-ion (ZI) forms and dimeric SA were optimized at the b3lyp/6-311++g** level using the Gaussian 09 software. Computations of APT charges, IR, Raman and UV–vis spectra and related quantities were also carried out. MEP, ESP plots and pictorial representations of the HOMO-LUMO were drawn using the optimized structures of the different forms of the SA molecule. Barrier heights were calculated for different tops using one dimensional potential energy scan versus dihedral angle at the same level of theory. The IR, Raman and UV–vis spectra were interpreted in light of the computed quantities. Thermodynamic functions were computed in the temperature range 100–600 K. Bioactivity scores of the SA molecule were also determined. The present investigation suggests that the SA molecule exists in the ZI form as a monomer and in the OH form as a dimer. Appearance of the intense and broad IR band in the range 2200 to 3300 cm−1 could be explained only in terms of the OH stretching mode of the dimeric form of SA.

Synthesis and Properties of Electron-Deficient and Electron-Rich Redox-Active Ionic π-Systems.

There is growing interest towards the design and synthesis of organic redox-active systems, which exist in ionic form. Multi- redox systems entail life-sustaining processes like photosynthesis and cellular respiration. The significant challenge for material scientists is to rationally design complex molecular materials that can store and transfer multiple electrons at low operational potentials and are stable under ambient conditions. Also, important are the designed ionic π-systems that combine efficient electron and ion transport. Here, we discuss the synthesis of ionic π-systems which exist in the closed-shell form. Firstly, different classes of ionic arylenediimides and viologens with different π-linkers are discussed from the synthetic, structural and redox perspective. These ionic π-systems are based on the electron deficient π-scaffolds, and are shown to accumulate upto six electrons. We then discuss electron-rich ionic arylenediimides which can exist in anionic form or zwitterionic form. The anionic electron donors have absorption extending to the near Infrared (NIR) region and can be stabilized in aqueous solution. We also discuss the effect of the electron accumulation on the aromaticity and non-aromaticity of the naphthalene and the imide rings of the naphthalenediimides. We finally discuss in brief, the applications related to the organic mixed ionic-electronic conductors.

Ligational aspects of some 4f metal complexes of a mesogenic Schiffbase, N,N’- di-(4-dodecyloxysalicylidene)-1’,3’-diaminopropane: Synthesis and spectral studies

A liquid crystalline (smectic-F and smectic-A phases)Schiff base, N,N′-di-(4-dodecyloxysalicylidene)-1′,3′-diaminopropane(abbreviated as H2L) and a series of lanthanide (III) complexes of the type [Ln2(LH2)3(NO3)4](NO3)2, (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Ho) have been synthesized and characterized by elemental analysis, mass spectrometry, FTIR, and UV-Vis spectral techniques. The IR spectral data imply bidentate chelation of the Schiff base in its zwitterionic form (as LH2) to the LnIII ions through two phenolate oxygens, rendering the overall geometry of the complexes possibly to distorted mono-capped octahedra. The optical and thermal behavior studies (POM &amp; DSC techniques) reveal that despite H2L being mesogenic, none of the LnIII complexes synthesized under this study exhibits mesomorphism. Fluorescence studies show emissions of H2L and SmIII complexx.

Understanding speciation and solvation of glyphosate from first principles simulations

The widespread adoption of the glyphosate (N-phosphonomethylglycine) herbicide has contributed to its increased environmental footprint. Consequently, the sequestration and degradation of excess contaminants are of significant interest, particularly in local aquatic environments. However, this inherently relies on a detailed understanding of glyphosate’s complex speciation and conformational flexibility in the condensed phase. In this work, we investigate the structure and speciation of glyphosate in the vapor and aqueous phases using first-principles simulations. Using the PBE-D3, B3LYP, and ωB97X-D functionals, we found multiple nonzwitterion and five stable zwitterion conformers in the gas phase. Ab initio molecular dynamics (AIMD) simulations in the canonical (NVT) and isothermal-isobaric (NpT) ensembles were employed using the PBE-D3 density functional. Analysis of the equilibrated trajectory allowed an understanding of condensed phase structure through the radial distribution function (RDF), hydrogen bond dynamics, and vibrational spectra. We found evidence that the phosphonate, carboxylic, and amine groups interact strongly with the solvent via hydrogen bonding leading to atypically long O-H bond length (∼ 1.1 Å) on glyphosate’s phosphonate and carboxylic functional groups. Metadynamics simulations using the PBE-D3 and optB88-vdW functionals were performed to estimate the free energy associated with the intramolecular H+ transfer separating the zwitterion and nonzwitterion conformers of glyphosate. Although both functionals confirm the stability of the zwitterion form in the aqueous phase, they differ significantly in the predicted free energy of the reaction.

Voltammetric Study of Lomefloxacin Transfer at the Interface between Two Immiscible Electrolyte Solutions: Ionic Partition, Photodegradation, and Sensing Applications

AbstractThe transfer of ionizable lomefloxacin (LOM) across a polarized interface between two immiscible electrolyte solutions (ITIES) was studied using cyclic and differential pulse voltammetry (DPV). The pH values of water (ionic strength=0.02 M) interfacing with the 1,2‐dichloroethane phase were varied to investigate the transfer behavior of differently charged LOM species, including protonated, neutral, and zwitterionic forms of LOM, namely HLOM+, LOM0, and H+LOM−. An ionic partition diagram for LOM was drawn with DPV response at various pH values, and the distinctive features of LOM were compared to those of fluoroquinolone antibiotics, which have similar pKa values. Physical and thermodynamic properties, including the formal transfer potential, lipophilicity, and Gibbs free energy of transfer of LOM were also evaluated. Furthermore, the photodegradation properties of differently charged LOM species and ophthalmic LOM drop samples (pH 5.0) were investigated after exposure to a UV (λ=365 nm) source. Quantitative analysis of HLOM+ concentrations in buffer and diluted commercial eye drop solutions containing LOM was finally demonstrated using differential pulse stripping voltammetric responses at pH 3.0 and 5.0 involving the transfer of HLOM+ at a polarized microhole‐water/polyvinylchloride‐2‐nitropheyloctylether gel interface.

Fully zwitterionic diaminobenzoquinonediimines promoted by cyanoaromatic N-substituents

2,5-Diamino-1,4-benzoquinonediimine (DABQDI) derivatives possessing two electron-withdrawing aromatic N-substituents can potentially exhibit a zwitterionic ground state in lieu of the expected canonical structure. It was previously shown that the use of nitroaromatics electron-withdrawing groups (EWG) could yield the quantitative formation of zwitterionic tautomer of DABQDI in polar solvents, while a mixture of canonical and zwitterionic forms was present in low polarity solvents. In this work, we report that the replacement of nitro-containing EWG by weaker nitrile ones prevents the formation of canonical species in apolar solvents for the benefit of the zwitterionic tautomer. This counterintuitive observation is rationalized with theoretical calculations, which points out that the fully zwitterionic electronic structure of the nitrile-containing DABQDI arises from the absence of possible intramolecular hydrogen bonding between the cyanoaromatic N-substituent and the N–H proton of the bridge in the canonical form.

Antibiotics separation from saline wastewater by nanofiltration membrane based on tannic acid-ferric ions coordination complexes

Excessive discharge of saline antibiotics wastewater into aquatic ecosystem is one crucial environmental issue facing the world today. Herein, an eco-friendly nanofiltration (NF) membrane was fabricated based on coordination complexes of tannic acid and ferric ions (TA-Fe) to selectively separate antibiotic and monovalent salt. Optimal membrane with Fe/TA molar ratio of 3/1 and coordination time of 60 s exhibited Zeta potential of −26.0 mV (pH = 7), water contact angle of 45.5o and pore radius of 0.36 nm. Consequently, TA-Fe@M3-T60 membrane showed high ciprofloxacin/NaCl rejection ratio of ~5.9 and considerable water permeability of 20.6 ± 1.2 LMH. Besides, relatively high rejection rates were obtained for ofloxacin (94.1 ± 2.2 %) and ciprofloxacin (91.9 ± 2.5 %), while rejection rate for trimethoprim was much lower (68.2 ± 4.1 %). Effects of static/dynamic membrane adsorption of antibiotics on subsequent removal performance were investigated for the first time. Rejection rate improvements of 7.4–15.2 % were observed on pristine membrane compared with pre-adsorbed membrane in short-term NF process. Electrostatic shielding experiment and rejection rate prediction further distinguished the contributions of steric hindrance, electrostatic interaction and membrane adsorption on antibiotics removal, especially antibiotics in zwitterionic form at pH = 7. The findings of this work imply that this newly developed NF membrane has great potential for efficient treatment of antibiotics-contaminated wastewater.