Complex Solvent Research Articles

Protein-Ligand Binding Molecular Details Revealed by Terahertz Optical Kerr Spectroscopy: A Simulation Study.

Picosecond fast motions and their involvement in the biochemical processes such as protein–ligand binding has engaged significant attention. Terahertz optical Kerr spectroscopy (OKE) has the superior potential to probe these fast motions directly. Application of OKE in protein–ligand binding study is, however, limited by the difficulty of quantitative atomistic interpretation, and the calculation of Kerr spectrum for entire solvated protein complex was considered not yet feasible, due to the lack of one consistent polarizable model for both configuration sampling and polarizability calculation. Here, we analyzed the biochemical relevance of OKE to the lysozyme–triacetylchitotriose binding based on the first OKE simulation using one consistent Drude polarizable model. An analytical multipole and induced dipole scheme was employed to calculate the off-diagonal Drude polarizability more efficiently and accurately. Further theoretical analysis revealed how the subtle twisting and stiffening of aromatic protein residues’ spatial arrangement as well as the confinement of small water clusters between ligand and protein cavity due to the ligand binding can be examined using Kerr spectroscopy. Comparison between the signals of bound complex and that of uncorrelated protein/ligand demonstrated that binding action alone has reflection in the OKE spectrum. Our study indicated OKE as a powerful terahertz probe for protein–ligand binding chemistry and dynamics.

Prolonged Luminescence Lifetime of a Dual Emissive Ruthenium Dipyridophenazine-Type Complex in Aprotic and Protic Solvents.

A recently reported ruthenium(II) complex bearing an extended dipyridophenazine ligand exhibits unusual long-lived dual emission at room temperature. In this study, the effect of the introduction of a methyl protecting group to the imidazole moiety of this ligand (L1, 11-methyl-11H-imidazo[4,5-i]dipyrido[3,2-a:2',3'-c]phenazine) on the photophysics of the respective ruthenium(II) complex [(tbbpy)2Ru(L1)]2+ (C1) is demonstrated by means of electrochemistry, UV/vis absorption and emission spectroscopy, as well as emission lifetime measurements, and transient absorption spectroscopy on the nanosecond time scale. At room temperature, C1 shows dual emission both in aprotic and in protic solvents with time constants of 1.1/34.2 and 1.2/8.4 μs, respectively. These lifetimes are assigned to the emission from 3MLCT and 3LC states. The introduction of the methyl group increases the lifetime of the 3LC state in C1 almost by a factor of 2 in acetonitrile solution compared to the previously reported compound. Accordingly, the newly introduced methyl group is described as a protecting group for the imidazole moiety of the heterocyclic ligand, which enables prolonged lifetimes of the dual emissive complex in protic solvents. The stabilization of the electronic structure is further underlined by the enhanced stability toward electrochemical reduction as evidenced by cyclic voltammetry.

Structural effect on the formation of hydrogen bonded complexes of benzyl amine and n-propyl amine with aromatic ethers through acoustic and thermodynamic parameters

The present work deals with experimental determination of acoustical parameters to investigate the influence of structure of amines and ethers on thermodynamic properties of four hydrogen bonded complexes in n-hexane solvent at four different temperatures in the range 294.15 K-310.15 K. Benzyl amine (BA) and n-propyl amine (NPA) are used as H-donors while anisole (ANI) and diphenyl ether (DPE) act as H-acceptors. The existence of these H-bonded complexes in solution is also supported by UV spectral data. The formation constants (K) of the complexes determined by ultrasonic and UV-Vis. spectral methods at 303.15 K are comparable. Further, it is observed that the interactions in the aliphatic amine - aromatic ether systems are stronger than aralkyl amine (BA) – ether systems. The thermodynamic parameters confirm that all the four complexes are thermodynamically stable and formation of these complexes is exothermic. The sign of ΔS shows there are strong intermolecular interactions between amines and ethers in n-hexane medium.

Relativistic frozen density embedding calculations of solvent effects on the nuclear magnetic resonance shielding constants of transition metal nuclei

AbstractNuclear magnetic resonance shielding constants of transition metals in solvated complexes are computed at the relativistic density functional theory (DFT) level. The solvent effects evaluated with subsystem‐DFT approaches are compared with the reference solvent shifts predicted from supermolecular calculations. Two subsystem‐DFT approaches are analyzed—in the standard frozen density embedding (FDE) scheme the transition metal complexes are embedded in an environment of solvent molecules whose density is kept frozen, in the second approach the densities of the complex and of its environment are relaxed in the “freeze‐and‐thaw” procedure. The latter approach improves the description of the solvent effects in most cases, nevertheless the FDE deficiencies are rather large in some cases.

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

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

Complexation of Cyclodextrins with Benzoic Acid in Water-Organic Solvents: A Solvation-Thermodynamic Approach.

The aim of this research is to obtain new data about the complexation between β-cyclodextrin (β-CD) and benzoic acid (BA) as a model reaction of the complex formation of hydrophobic molecules with cyclodextrins (CDs) in various media. This research may help developing cyclodextrin-based pharmaceutical formulations through the choice of the appropriate solvent mixture that may be employed in the industrial application aiming to control the reactions/processes in liquid phase. In this paper, NMR results for the molecular complex formation between BA and β-CD ([BA⊂β-CD]) in D2O-DMSO-d6 and in D2O-EtOH have shown that the stability of the complex in the H2O-DMSO-d6 varies within the experimental error, while decreases in H2O-EtOH. Changes in the Gibbs energy of BA resolvation in water and water–dimethylsulfoxide mixtures have been obtained and have been used in the analysis of the reagent solvation contributions into the Gibbs energy changes of the [BA⊂β-CD] molecular complex formation. Quantum chemical calculations of the interaction energy between β-CD and BA as well as the structure of the [BA⊂β-CD] complex and the energy of β-CD and BA interaction in vacuum and in the medium of water, methanol and dimethylsulfoxide solvents are carried out. The stability of [BA⊂β-CD] complex in H2O-EtOH and H2O-DMSO solvents, obtained by different methods, are compared. The thermodynamic parameters of the [BA⊂β-CD] molecular complexation as well as the reagent solvation contributions in H2O-EtOH and H2O-DMSO mixtures were analyzed by the solvation-thermodynamic approach.

2-Carboxamido-6-(1H-pyrazol-3-yl)-pyridines as ligands for efficient separation of americium(III) from europium(III)

The synthesis, Eu3+ complexation, and selective solvent extraction of Am3+ over Eu3+ in nitric acid solution by 2-carboxamido-6-(1H-pyrazol-3-yl)-pyridines (A-PzPy) ligands were described. Without the aid of any lipophilic anion source, A-PzPy ligands in methyl isobutyl ketone (MIBK) diluent demonstrated a more favorable affinity of Am3+ than Eu3+ at high acidity levels. Slope analysis showed the formation of 1:2 metal/ligand extracted species. The extraction was a spontaneous exothermic process. The analyses of fluorescence titration, Fourier transform infrared (FT-IR), Raman, time-resolved laser fluorescence spectrum (TRLFS), electrospray ionization mass spectrometry (ESI-MS), conductivity and microcalorimetric titration revealed that the composition of complex is [Eu(NO3)2(H2O)∙2(Et-p-Tol-A-PzPy)](NO3). Combining the results of solvent extraction and complexation study, the extraction mechanism was proposed. Furthermore, the stability constants (log β) and thermodynamic parameters (ΔH, ΔS, ΔG) for complexation of Eu3+ with Et-p-Tol-A-PzPy were also presented.

Ion–solvent chemistry in lithium battery electrolytes: From mono-solvent to multi-solvent complexes

The building of safe and high energy-density lithium batteries is strongly dependent on the electrochemical performance of working electrolytes, in which ion–solvent interactions play a vital role. Herein, the ion–solvent chemistry is developed from mono-solvent to multi-solvent complexes to probe the solvation structure and the redox stability of practical electrolytes. The decrease in energies of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of solvents in lithium-ion solvation shells becomes less significant as the number of coordinated solvents increases, but both the HOMO and LUMO energies of the coordinated solvents remain lower than those of free solvents. A positive and approximately linear relationship was found between the decrease in the HOMO/LUMO energy and the average binding energy between Li+ and the coordinated solvents. A binary-solvent complex model further highlight the significant importance of the electrolyte solvation environment in regulating electrolyte stability, and it is essential to consider electrolyte stability from the perspective of ion–solvent complexes. These fresh insights into the energy chemistry of multi-solvent complexes provide critical references for electrolyte design and cell optimization.

Relationship between Multivalent Cation Charge Carriers and Organic Solvents on Nanoporous Carbons in 4 V‐Window Magnesium Ion Supercapacitors

AbstractMultivalent charge carriers with a smaller ionic radius exhibit strong ionic interactions with solvent molecules. This can lead to unusual characteristics that typically are not observed in conventional monovalent charge carriers. Herein, the capacitive Mg ion storage behavior on nanoporous carbons is investigated within different solvent systems. A larger multivalent charge carrier, Ca ions, and alkali cations with different ionic radii are used as a comparison. In addition, the effects of nanopores on solvated Mg ion physisorption are observed in two types of nanoporous carbon, namely typical microporous carbon and ultramesoporous carbon (MEC). The oxidation stability of dimethoxyethane (DME) solvent is significantly improved by forming a solvation complex with Mg ions, while the destabilization effect of DME induced by anions is suppressed by the Mg ion charge carriers. The use of MEC as an active electrode material in a Mg ion‐DME electrolyte system leads to high electrochemical performance of the Mg ion supercapacitor over a wide range of operating voltages. A high‐performance 4 V Mg ion supercapacitor with charge‐injected symmetric MEC‐based electrodes is evaluated, where excellent specific energy and power densities of ≈106 W h kg−1 and ≈11870 W kg−1, respectively, are achieved.

Mechanism of Ferric Chloride Facilitating Efficient Lithium Extraction from Magnesium-Rich Brine with Tri-n-butyl Phosphate

The synergistic solvent extraction system comprising tri-n-butyl phosphate (TBP) and FeCl3 has been intensively studied for selective extraction of Li(I) from Mg(II)-rich brine. The extraction occurs via the formation of an ion-pair complex [Li(TBP)x][FeCl4] in which the negatively charged [FeCl4]− neutralizes the positively charged [Li(TBP)x]+. Counterintuitively, many other metal chlorides give much lower Li(I) extraction efficiency than FeCl3, although they can also form chlorometallate anions similar to [FeCl4]−. In this study, the capabilities of CuCl2, AlCl3, InCl3, and SnCl4 for Li(I) extraction with TBP were examined and compared with that of FeCl3, accompanied by speciation studies. It was found that (1) AlCl3 does not form [AlCl4]− while other metal chlorides (CuCl2, InCl3, FeCl3, and SnCl4) can form chlorometallate anions that could facilitate Li(I) extraction and (2) CuCl2, InCl3, and SnCl4 form neutral solvation complexes with TBP strongly, which hinders the formation of chlorometallate anions, but FeCl3 does not form neutral complexes with TBP. Concurrently being able to form [FeCl4]− and to avoid forming neutral complexes facilitates the efficient Li(I) extraction by FeCl3 with TBP.

Ultrafast x-ray pump x-ray probe transient absorption spectroscopy: A computational study and proposed experiment probing core-valence electronic correlations in solvated complexes.

Femtosecond x-ray pump-x-ray probe experiments are currently possible at free electron lasers such as the linac coherent light source, which opens new opportunities for studying solvated transition metal complexes. In order to make the most effective use of these kinds of experiments, it is necessary to determine which chemical properties an x-ray probe pulse will measure. We have combined electron cascade calculations and excited-state time-dependent density functional theory calculations to predict the initial state prepared by an x-ray pump and the subsequent x-ray probe spectra at the Fe K-edge in the solvated model transition metal complex, K4FeII(CN)6. We find several key spectral features that report on the ligand-field splitting and the 3p and 3d electron interactions. We then show how these features could be measured in an experiment.

(Invited) Optoelectronic and Dielectric Properties of Organic Cation Tin-Based Perovskite Solar Cells

Tin iodide perovskite (ASnI3) is one of the most feasible, less toxic alternatives to lead halide perovskite (APbX3), owing to its readily formed three-dimensional (D) structure and more suited bandgap (1.2–1.4 eV) of the solar cell application than APbX3 (1.5–2.3 eV). Regardless of the skyrocketing boost in Pb perovskite solar cells throughout this decade, Sn-based counterparts have remained constrained because of the intrinsically unstable Sn2+ that is easily oxidized to Sn4+. The resultant p-doping causes electron trapping and a shorting of the diode circuit, which is partly mitigated by SnF2 addition. Nevertheless, the power conversion efficiency (PCE) values of MASnI3 (MA: methylammonium cation) based on a normal cell structure (mesoporous TiO2/active layer/hole transport layer: HTL) have been suppressed due to the p-doping and low film quality. Notably, progress in an inverted cell structure (HTL/active layer/electron transport layer: ETL) has been reported for FASnI3 (FA: formamidinium cation) mixed with either MA, PEA (phenylethylamine cation), EDA (ethylenediammonium dication), or GA (guanidium cation). In addition to this A-site cation mixing strategy associated with 2D/3D perovskites, the use of {en} (ethylenediammonium), SnX2-(pyrazine, trimethylamine, or solvent) complexes, hot anti-solvent treatment (HAT), poly(vinyl alcohol) (PVA) addition, and GeI2 dopingreportedly showed improvement in PCEs. Thus, the updated PCE in the forefront of the Sn perovskite solar cell is ~9–10%, which is enabled by MA/FA mixing, FA/PEA mixing, GA/FA mixing, as well as the addition of 4-fuorobenzohydrazide (FBH), 2-cyano-3-[5-[4-(diphenylamino)phenyl]-2-thienyl]-propenoic acid (CDTA), or passivation with ethylenediamine (edamine). Although the mixing of A-site cations, along with additives, has been found to smooth the film surface, decrease the Sn4+ impurities, and tune the valence band maximum (VBM), their effects on charge carrier dynamics and morphological changes are the subject of ongoing debate.We characterized the solar cells composed of ternary A-site cation-mixed Sn perovskite: ASnI3 [A = (GAxFA1–x)0.9PEA0.1, the ratios are the precursor stoichiometry] by changing the GA content (x = 0–1) and investigated their charge carrier dynamics, surface morphologies, and energetics.[1] The inclusion of 10 mol% PEA was found necessary for performing these evaluations over a wide range of GA:FA ratios. Electrode-less, time-resolved microwave conductivity (TRMC) measurements[2] were applied to a pristine ASnI3 film, double layers of HTL/ASnI3 and ASnI3/ETL, as well as a triple layer of HTL/ASnI3/ETL, where PEDOT:PSS and thermally evaporated fullerene (C60) were used as the HTL and ETL, respectively. These comparative samples with different GA contents discerned the contributions of hole and electron mobilities in the TRMC transients. Notably, the change in electron mobilities corresponded to the PCE dependence on the GA content, highlighting the pivotal role of electron mobility in solar cell performance. We further examined the atomic force microscopy (AFM) surface images, VBM measured by photoelectron spectroscopy (PYS), and crystalline features measured by X-ray diffraction (XRD), which supports the dramatic change of charge carrier mobility and lifetime.On one hand, the dielectric properties of organic-inorganic hybrid perovskite materials have remained poorly understood, despite probably influencing delayed charge recombination and device capacitance. We characterize the unprecedented dielectric behavior of MHPs comprising methylammonium cations, Pb/Sn as metals, and Br/I as halides using TRMC measurements.[3] At specific compositions, the above MHPs exhibit negative real and positive imaginary photoconductivities, the polarities of which are opposite to those observed for conventional photogenerated charge carriers. Comparing the observed TRMC kinetics with that of inorganic perovskites (SrTiO3 and BaTiO3) and characterizing its dependence on temperature, frequency and near-infrared second push pulse, we conclude that the above behavior is due to the trapping of polaronic holes/electrons by oriented dipoles of organic cations, which opens a hitherto unexplored route to the dynamical control of dielectric permittivity by photoirradiation.Reference Nakanishi, R. Nishikubo, A. Wakamiya, A. Saeki, J. Phys. Chem. Lett. 11 (2020) 4043.Saeki, A. Polym. J. 52 (2020) 1307.Yamada, R. Nishikubo, H. Oga, Y. Ogomi, S. Hayase, S. Kanno, Y. Imamura, M. Hada, A. Saeki, ACS Photonics 5 (2018) 3189.

Establishing the Preferential Adsorption of Anion‐Dominated Solvation Structures in the Electrolytes for High‐Energy‐Density Lithium Metal Batteries

AbstractThe practical application of Li metal batteries (LMBs) is severely hindered by the unstable solid electrolyte interface (SEI). In this work, it is revealed that the unstable SEI mainly originates from the kinetic instability of Li+‐solvation structures in the electrolyte which can result in continuous electrolyte decomposition and nonuniform Li deposition. To address this issue, preferential adsorption of anion‐dominated solvation complexes (A‐Coms) are established by integrating preferentially adsorbed anions (NO3− and Li2S8) into the Li+‐solvation structures. In these structures, the locations of the lowest unoccupied molecular orbital energy level shift from solvents to anions, rendering a relieved electrolyte decomposition and an anion‐derived SEI formation. Meanwhile, the anions in the A‐coms preferentially adsorb on the Li metal surfaces due to their stronger chemisorption capability toward lithium metal anodes (LMAs) compared to the solvent molecules, effectively shielding solvent molecules from parasitic reaction with LMAs. Furthermore, the anion‐derived SEI exhibits high Li‐ion conductivity and low Li atom adhesion energy, which can facilitate uniform Li deposition. Consequently, this electrolyte can enable a high Li plating/stripping Coulombic efficiency of 98.5% over 500 cycles and a stable cycling under realistic testing conditions with a high‐energy‐density of 310 W h kg−1 based on a full cell configuration.

OH- and H3O+ Diffusion in Model AEMs and PEMs at Low Hydration: Insights from Ab Initio Molecular Dynamics.

Fuel cell-based anion-exchange membranes (AEMs) and proton exchange membranes (PEMs) are considered to have great potential as cost-effective, clean energy conversion devices. However, a fundamental atomistic understanding of the hydroxide and hydronium diffusion mechanisms in the AEM and PEM environment is an ongoing challenge. In this work, we aim to identify the fundamental atomistic steps governing hydroxide and hydronium transport phenomena. The motivation of this work lies in the fact that elucidating the key design differences between the hydroxide and hydronium diffusion mechanisms will play an important role in the discovery and determination of key design principles for the synthesis of new membrane materials with high ion conductivity for use in emerging fuel cell technologies. To this end, ab initio molecular dynamics simulations are presented to explore hydroxide and hydronium ion solvation complexes and diffusion mechanisms in the model AEM and PEM systems at low hydration in confined environments. We find that hydroxide diffusion in AEMs is mostly vehicular, while hydronium diffusion in model PEMs is structural. Furthermore, we find that the region between each pair of cations in AEMs creates a bottleneck for hydroxide diffusion, leading to a suppression of diffusivity, while the anions in PEMs become active participants in the hydronium diffusion, suggesting that the presence of the anions in model PEMs could potentially promote hydronium diffusion.

Solubility of mono-alkyl magnesium complex in pure and binary solvents: Measurement, correlation, thermodynamics from 268.15 K to 318.15 K

The mono-alkyl magnesium complex LMgBu (L = HC(CMeNAr)2, Ar = 2,6-iPr2C6H3) played a significant role in organic synthesis and homogeneous catalysis. However, there were few reports on the solubility of this system. The solubility of the compound between 268.15 K and 318.15 K was determined by gravimetric analysis. Four pure solvents and two binary solvents were selected as experimental solvents. All the operations were carried out by Schlenk line techniques or in a glove box to ensure that the processes were under purified nitrogen atmosphere. The results have shown that the solubility increased with the rising of temperature within the measured temperature range. The difference in solubility can be attributed to the molecular structure, coordination bond, and molecular polarity. Besides, six thermodynamic models were used to correlate experimental solubility data, and Hansen solubility parameters (HSPs) were applied to explain the dissolution behavior. Those results showed that the polynomial model had the most extensive applicability for the pure solvents system. At different temperature, the calculated values of the Apelblat model were in good arrangement with the experimental values, as well as the MRS model was in the best arrangement for different molar ratio of solvent. And all the values of the relative average deviation (RAD and RMSD) of improved Jouyban-Acree models were less than 3%. The apparent thermodynamic properties (ΔsolHo, ΔsolSo, ΔsolGo, %ξH and %ξTS) were also calculated through the Van't Hoff model and Gibbs equation to analyze the heat of the dissolution process and enthalpy-entropy compensation of the compound. In short, the solubility and thermodynamic data of LMgBu obtained from this study will provide theoretical reference and supporting information on synthesis, crystallization, recrystallization, and other processes of the compound.

A Blue Zinc Complex of a Dioxobilin‐Type Pink Chlorophyll Catabolite Exhibiting Bright Chelation‐Enhanced Red Fluorescence

AbstractIn senescent fall leaves and in ripening fruit, colorless phyllobilins (PBs) accumulate from breakdown of chlorophyll, from which yellow PBs (phylloxanthobilins) and pink colored PBs (phylloroseobilins) arise in some leaves. The first described PBs were formyloxobilin‐type PBs, but dioxobilin‐type PBs also occur naturally. Here we report the synthesis and characterization of the blue Zn(II) complex of a dioxobilin‐type pink PB, which chelates a Zn(II) ion fast and tightly in an effectively tridentate manner. The optically active Zn complex featured bright chelation enhanced red fluorescence and exhibited strikingly differing spectral properties in methanol and in acetonitrile. Computational studies based on DFT‐calculations gave detailed insights into low energy structures of the Zn complex in both solvents and provided support for the proposed role of solvent in the coordination sphere of the bound Zn(II) ion.

Host selectivity behaviour of trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine when presented with six-membered heterocyclic guest mixtures

Two compounds, trans-N,N′-bis(9-phenyl-9-xanthenyl)cyclohexane-1,2-diamine (1,2-DAX) and trans-N,N′-bis(9-phenyl-9-thioxanthenyl)cyclohexane-1,2-diamine (1,2-DAT), were assessed for their host ability in the presence of four heterocyclic guest species, namely pyridine (PYR), piperidine (PIP), morpholine (MOR) and dioxane (DIO). Each of these guests formed single solvent complexes with both host compounds. When 1,2-DAX and 1,2-DAT were recrystallized from various guest mixtures, it was shown that their selectivity orders were identical, DIO (46.6%) > MOR (23.0%) > PYR (18.9%) > PIP (11.5%) and DIO (85.9%) > MOR (23.7%) > PYR (8.9%) > PIP (8.5%), respectively, but that the thio host derivative possessed a significantly enhanced preference for DIO compared with its oxygen analogue. Additional experiments in order to investigate the various parameters at play in these complexation experiments involved single crystal diffraction experiments and thermal analyses.

DMSO Deintercalation in Kaolinite–DMSO Intercalate: Influence of Solution Polarity on Removal

This study focused on the deintercalation of dimethyl sulfoxide (DMSO) from a kaolinite–DMSO complex in various solvents. The use of kaolinite as filler in polymer–clay composite generally faced the difficulty of kaolinite dispersion due to its high cohesion. For improved dispersion of kaolinite within a given matrix, previous intercalation of small polar molecules is usually done prior to its displacement during composite-making. The influence of the solvent polarity on the deintercalation in analyzed here to understand its role during the deintercalation process. The intercalation of the DMSO was done by solution-mixing and its displacement was done in distilled water, ethyl acetate, and acetone. The products of deintercalation were analyzed using Fourier transform infra-red (FTIR), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The weakening of the kaolinite cohesion after DMSO intercalation is demonstrated through the broadening of the diffraction peak associated with the kaolinite on XRD patterns. From FTIR spectra, the weakening is associated with the displacement to low wavenumbers of the Si–O or Al–O vibration bands within the kaolinite–DMSO complex. The kaolinite dehydroxylation temperatures from DSC show that the rate of DMSO displacement affects the ordering of the recovered kaolinite. The crystallite size of the kaolinite is reduced from the raw to the recovered kaolinite after DMSO displacement, indicating an exfoliation of the kaolinite. From these results, it is found that the removal of the DMSO from the kaolinite–DMSO complex is influenced by solvent polarity. The higher the polarity, the greater the removal of the DMSO from the complex. Solvent polarity affects the rate of DMSO displacement, which influences the ordering of the recovered kaolinite. It is suggested that solvent polarity can be used to control the removal rate of DMSO, which may be key to the dispersion of the kaolinite platelets.

Elucidating the therapeutic activity of selective curcumin analogues: DFT-based reactivity analysis

Density functional theory (DFT) has been employed to study the structure, stability and reactivity of curcumin and some of its important analogues by computing HOMO-LUMO energy gap (H-L gap), ionization potential (IP), electron affinity (EA), chemical potential (μ), chemical hardness (η), electrophilicity index (ω) and density of states (DOS). In this study, curcumin is found to be more reactive in dimethyl sulfoxide (DMSO) solvent than in the gas phase in both of its enol and keto isomeric forms. Next, reactivities of the keto-based curcumin analogues are found to follow the order of 1,5-bis(3,4-dimethoxyphenyl)penta-1,4-dien-3-one (GO-035) > 1,5-bis(3,4,5-trimethoxyphenyl)penta-1,4-dien-3-one (GO-Y016) > 1,5-bis[3,5-bis(methoxymethoxy)phenyl]penta-1,4-dien-3-one (GO-Y031) > 1,5-bis[3,5-dimethoxy-4-(methoxymethoxy)phenyl]penta-1,4-dien-3-one (GO-Y030) > dibenzalacetone (DBA) in both gas and DMSO solvent phases. However, there is enhancement in reactivities of the complexes in DMSO solvent from those in the gas phase. The reactivity order is observed on the basis of H-L gap, IP, μ, η and DOS analyses. Moreover, GO-Y030, GO-Y031 and DBA possess similar electrophilic behaviours as indicated by their comparable EA and ω values, while GO-Y016 and GO-035 behave as the strongest and the weakest electrophiles. Furthermore, the nature of the reactive sites in the curcumin analogues has been identified via local reactivity descriptors and the molecular electrostatic potential (MEP) maps, results of which are consistent with the molecular orbital analyses.

Synthesis, spectroscopic and thermogravimetric interpretations of UO2(II), ZrO(II), Zr(IV), VO(II) and V(V) ciprofloxacin antibiotic drug complexes

Abstract New five ciprofloxacin (CIP) complexes of dioxouranium(II), oxozirconium(II), zirconium(IV), oxovanadium(II) and vanadium(IV) in the proportion 1:2 have been prepared using CIP as a drug chelate with UO2(NO3)2. 6H2O, ZrOCl2. 8H2O, ZrCl4, VOSO4. xH2O and V2O5 respectively. The CIP complexes have been characterized based on the elemental analysis, molar conductance, magnetic, (FTIR & 1HNMR) spectral and thermal studies. The molar conductance studies of the synthesized complexes in DMSO solvent with concentration of 10–3 M indicate their non-electrolytic properties. At room temperature, the magnetic moment measurements revealed a diamagnetic behavior for all CIP prepared complexes. The different formulas of the new complexes can be represented as [UO2(CIP)2(NO3)2] (I), [VO(CIP)2(SO4)(H2O)] (II), [V2(O)(O2)2(CIP)2] (III), [Zr(O)(CIP)2(Cl)2] (IV), and [Zr(CIP)2(Cl)4] (V). The thermal analysis data of the complexes indicates the absence of coordinated water molecules except for vanadyl(II) complex (II). The CIP chelate is a uni-dentate ligand coordinated to the mentioned metal ion through terminal piperazinyl nitrogen. The transmission electron microscopy (TEM) investigation confirms the nano-structured form of the complexes.