Synthesis, Characterization and Antimicrobial Activity of Copper(II) Complexes of some Ortho-substituted Aniline Schiff Bases; Crystal Structure of Bis(2-methoxy-6-imino)methylphenol Copper(II) Complex

This study presents the synthesis, characterization and antimicrobial activity of copper(II) complexes of some ortho-substituted aniline Schiff bases (L1–L8). The Schiff bases and their respective copper(II) complexes were characterized by a combination of elemental analysis, infrared and UV/Visible studies. The structures of the ligands were also confirmed from 1H- and 13C-NMR spectral data. The infrared and electronic transition studies showed that the ligands are bidentate coordinating via the imine nitrogen and the phenolic oxygen atoms in a planar configuration. Introduction of aqueous ammonia to the ethanolic solution of L3/L4 and Cu(OAc)2.H2O aliquot yielded an ammonia-based complex due to the hydrolysis of the imine bond. The crystal structure of the resulting complex indicated a square planar geometry. The copper(II) ion crystallizes in the monoclinic system with a space group of P21/c having a = 10.9309, b = 4.85600, c = 17.7030, á = ã = 90 ° and â = 119.658 °. The geometry is slightly distorted from planarity with O1-Cu1-N1 bond angles of 92.19 ° and 87.8 °. The Schiff base ligands and their respective copper(II) complexes were screened for their in vitro antibacterial and antifungal activity against Escherichia  coliATCC® 8739™*, Staphylococcus aureus subsp. aureus ATCC® 6538™*, Bacillus subtilis subsp. spizizeniiATCC® 6633™* and Candida albicansATCC® 2091™*. The o-vanillin-based ligands exhibited higher activity than the salicylaldehyde derivatives which were virtually non-active against the tested organisms.KEYWORDS: o-Vanillin, substituted-aniline, Schiff bases, Cu(II) complexes, antimicrobial activity

Structure, Energetics, and Dynamics of Cs+ and H2O in Hectorite: Molecular Dynamics Simulations with an Unconstrained Substrate Surface

Classical molecular dynamics simulations were performed for the smectite clay hectorite with charge-balancing Cs+ cations using a newly developed structural model with a disordered distribution of Li/Mg substitutions in the octahedral sheet and the fully flexible CLAYFF force field. Calculations for systems with interlayer galleries containing 0–19 H2O/Cs+ suggest that the monolayer hydrate is the only stable state at all relative humidities at ambient pressure and temperature, in agreement with experimental results and previous molecular calculations. The basal spacing of this structure is also in good agreement with experimental values. In contrast to previous molecular modeling results, however, the new simulations show that interlayer Cs+ occurs on 2 different inner sphere adsorption sites: above the center of ditrigonal cavities and above Si tetrahedra. Unlike previous simulations, which employed a rigid clay model and fixed orientations of the structural −OH groups, the present results are obtained for an unconstrained clay substrate structure, where the structural −OH groups are able to assume various orientations, including being nearly parallel to the clay layers. This flexibility allows the Cs+ ions to approach the surface more closely above the centers of the hexagonal rings. In this structural arrangement, Cs+ ions are not hydrated by the H2O molecules which share the same interlayer plane, but rather by the H2O molecules coordinated to the opposite surface. In contrast, on the external basal surface, a significant fraction of H2O molecules are adsorbed above the centers of ditrigonal cavities adjacent to adsorbed Cs+ ions. For these H2O molecules, both HH2O atoms coordinate and H-bond to Ob surface oxygen atoms. The mean residence times for the Cs+–H2O, Cs+–Ob, and H2O–Ob coordination pairs show that Cs+ ions are more strongly coordinated with Ob atoms than H2O molecules. This result is the opposite of the behavior in Ca-hectorite, due to the much smaller hydration energy of Cs+ compared to that of Ca2+

Cation and Water Structure, Dynamics, and Energetics in Smectite Clays: A Molecular Dynamics Study of Ca-Hectorite

The incorporation of Ca2+ into smectite minerals is well-known to have a significant effect on the swelling behavior and mechanical properties of this environmentally and technologically important group of materials. Relative to common alkali cations such as Na+, K+, and Cs+, Ca2+ has a larger charge/ionic radius ratio and thus interacts very differently with interlayer water molecules and the oxygens of the clay basal surface. Recent 2H and 43Ca NMR studies of the smectite mineral, hectorite, show that the molecular scale interlayer dynamics is quite different with Ca2+ than with alkali cations. Classical molecular dynamics (MD) simulations presented here use a newly developed hectorite model with a disordered distribution of Li+/Mg2+ substitutions in the octahedral sheet and provide new insight into the origin of the effects of Ca2+ on the structure, dynamics, and energetics of smectite interlayers. The computed basal spacings and thermodynamic properties suggest the potential for formation of stable monolayer hydrates that have partial and complete water contents, a bilayer hydrate, and possible expansion to higher hydration states. The system hydration energies are comparable to those previously calculated for Ca–montmorillonite and are more negative than for Cs– and Na–hectorite due to the higher hydration energy of Ca2+. The coordination environments of Ca2+ change significantly with increasing interlayer hydration, with the extent of coordination to basal oxygens decreasing as the number of interlayer molecules increases. On external (001) surfaces, the H2O molecules closest to the surface are adsorbed at the centers of ditrigonal cavities and bridge Ca2+ to the surface. The Ca2+ ions on the external surface are all in outer-sphere coordination with the basal oxygens of the surface, and the proximity-restricted region with a significant number of Ca2+ is approximately 6 Å thick. Quantification of these interactions provides a basis for understanding intercalation of Ca2+ by organic species and smectite minerals

Diffusion Behavior of Methane in 3D Kerogen Models

As global energy demand increases, natural gas recovery from source rocks is attracting considerable attention since recent development in shale extraction techniques has made the recovery process economically viable. Kerogens are thought to play an important role in gas recovery; however, the interactions between trapped shale gas and kerogens remain poorly understood due to the complex, heterogeneous microporous structure of kerogens. This study examines the diffusive behavior of methane molecules in kerogen matrices of different types (Type I, II, and II) and maturity levels (A to D for Type II kerogens) on a molecular scale. Models of each kerogen type were developed using simulated annealing. We employed grand canonical Monte Carlo simulations to predict the methane loadings of the kerogen models and then used equilibrium molecular dynamics simulations to compute the mean square displacement of methane molecules within the kerogen matrices under reservoir-relevant conditions, that is, 365 K and 275 bar. Our results show that methane self-diffusivity exhibits some degree of anisotropy in all kerogen types examined here except for Type I-A kerogens, where diffusion is the fastest and isotropic diffusion is observed. Self-diffusivity appears to correlate positively with pore volume for Type II kerogens, where an increase in diffusivity is observed with increasing maturity. Swelling of the kerogen matrix up to a 3% volume change is also observed upon methane adsorption. The findings contribute to a better understanding of hydrocarbon transport mechanisms in shale and may lead to further development of extraction techniques, fracturing fluids, and recovery predictions

Role of Cations in the Methane/Carbon Dioxide Partitioning in Nano- and Mesopores of Illite Using Constant Reservoir Composition Molecular Dynamics Simulation

We performed constant reservoir composition molecular dynamics (CRC-MD) simulations at 323 K and 124 bar to quantitatively study the partitioning of fluid species between the nano- and mesopores of clay and a bulk reservoir containing an equimolar mixture of CO2 and CH4. The results show that the basal (001) and protonated edge (010) surfaces of illite both demonstrate a strong preference for CO2 over CH4 adsorption; that the (001) surfaces show a stronger preference for CO2 than the (010) surfaces, especially with K+ as the exchangeable cation; and that the structuring of the near-surface CO2 by K+ is stronger than that by Na+. The protonated (010) surfaces have a somewhat greater preference for CH4, with the concentration near them close to that in the bulk fluid. The effects of the surfaces on the fluid composition extend to approximately 2.0 nm from them, with the fluid composition at the center of the pore becoming essentially the same as the bulk composition at a pore thickness of ∼5.7 nm. The preference of nano- and mesopores bounded by clay minerals for CO2 over CH4 suggests that injection of CO2 into tight reservoirs is likely to displace CH4 into larger pores, thus enhancing its production

Heavy metal profiles in limpets and algae on the Eastern Cape coast of South Africa

Heavy metal pollution is an increasing threat to the marine environment and is a major health concern. Both marine limpets and algae have been employed as biomonitors elsewhere in the world, but there are few or no data for these taxa along the South African coast. We investigated heavy metal concentrations in the tissues of selected limpet and algae species sampled at four sites on the southeast coast of South Africa (Silaka, Hluleka, Mthatha and Mbhashe), and determined whether there was any relationship between heavy metal concentrations in the limpets and their algae food sources as evidenced by the trophic transfer factor (TTF). Samples were collected in July 2019 and the tissues were digested following normal protocols. Heavy metals were detected using inductively coupled plasma optical emission spectrometry (ICP-OES). Significant differences in metal concentrations were observed among the algae species. The soft tissues of limpets from Silaka had the highest heavy metal concentrations, and samples from Mthatha had the lowest, with only mercury (Hg) occurring in high concentrations. Metal concentrations in soft tissues were generally 10-times higher than in shell tissues and differed between lower- and upper-shore species. Cadmium (Cd) biomagnified (TTF > 1) in all limpet species at all sites. Cd, arsenic (As), lead (Pb) and Hg measured in our study were above the maximum limits set by the South African Department of Health. This study suggests that the use of limpet and algae species as bioindicators is feasible since they are widely distributed and can accumulate a wide range of heavy metals

Molecular Dynamics Study of CO2 and H2O Intercalation in Smectite Clays: Effect of Temperature and Pressure on Interlayer Structure and Dynamics in Hectorite

Grand Canonical Molecular Dynamics (GCMD) simulations were performed to investigate the intercalation of CO2 and H2O molecules in the interlayers of the smectite clay, Na-hectorite, at temperatures and pressures relevant to petroleum reservoir and geological carbon sequestration conditions and in equilibrium with H2O-saturated CO2. The computed adsorption isotherms indicate that CO2 molecules enter the interlayer space of Na-hectorite only when it is hydrated with approximately 3 H2O molecules per unit cell. The computed immersion energies show that the bilayer hydrate structure (2WL) contains less CO2 than the monolayer structure (1WL), but that the 2WL hydrate is the most thermodynamically stable state, consistent with experimental results for a similar Na-montmorillonite smectite. At all T and P conditions examined (323-368 K and 90-150 bar), the CO2 molecules are adsorbed at the midplane of clay interlayers for the 1WL structure and closer to one of the basal surfaces for the 2WL structure. Interlayer CO2 molecules are dynamically less restricted in the 2WL structures. The CO2 molecules are preferentially located near basal surface oxygen atoms and H2O molecules rather than in coordination with Na+ ions. Accounting for the orientation and flexibility of the structural -OH groups of the clay layer has a significant effect on the details of the computed structure and dynamics of H2O and CO2 molecules but does not affect the overall trends with changing basal spacing or the principal structural and dynamical conclusions. Temperature and pressure in the ranges examined have little effect on the principal structural and energetic conclusions, but the rates of dynamical processes increase with increasing temperature, as expected

Understanding methane/carbon dioxide partitioning in clay nano- and meso-pores with constant reservoir composition molecular dynamics modeling

The interactions among fluid species such as H2O, CO2, and CH4 confined in nano- and meso-pores in shales and other rocks is of central concern to understanding the chemical behavior and transport properties of these species in the earth's subsurface and is of special concern to geological C-sequestration and enhanced production of oil and natural gas. The behavior of CO2, and CH4 is less well understood than that of H2O. This paper presents the results of a computational modeling study of the partitioning of CO2 and CH4 between bulk fluid and nano- and meso-pores bounded by the common clay mineral montmorillonite. The calculations were done at 323 K and a total fluid pressure of 124 bars using a novel approach (constant reservoir composition molecular dynamics, CRC-MD) that uses bias forces to maintain a constant composition in the fluid external to the pore. This purely MD approach overcomes the difficulties in making stochastic particle insertion-deletion moves in dense fluids encountered in grand canonical Monte Carlo and related hybrid approaches. The results show that both the basal siloxane surfaces and protonated broken edge surfaces of montmorillonite both prefer CO2 relative to CH4 suggesting that methods of enhanced oil and gas production using CO2 will readily displace CH4 from such pores. This preference for CO2 is due to its preferred interaction with the surfaces and extends to approximately 20 Å from them

Influence of depression and interpersonal support on adherence to antiretroviral therapy among people living with HIV

BackgroundPoor adherence and under-utilization of antiretroviral therapy (ART) services have been major setbacks to achieving 95-95-95 policy goals in Sub-Saharan Africa. Social support and mental health challenges may serve as barriers to accessing and adhering to ART but are under-studied in low-income countries. The purpose of this study was to examine the association of interpersonal support and depression scores with adherence to ART among persons living with HIV (PLWH) in the Volta region of Ghana.MethodsWe conducted a cross-sectional survey among 181 PLWH 18 years or older who receive care at an ART clinic between November 2021 and March 2022. The questionnaire included a 6-item simplified ART adherence scale, the 20-item Center for Epidemiologic Studies Depression Scale (CES-D), and the 12-item Interpersonal Support Evaluation List-12 (ISEL-12). We first used a chi-squared or Fisher’s exact test to assess the association between these and additional demographic variables with ART adherence status. We then built a stepwise multivariable logistic regression model to explain ART adherence.ResultsART adherence was 34%. The threshold for depression was met by 23% of participants, but it was not significantly associated with adherence in multivariate analysis(p = 0.25). High social support was reported by 48.1%, and associated with adherence (p = 0.033, aOR = 3.45, 95% CI = 1.09–5.88). Other factors associated with adherence included in the multivariable model included not disclosing HIV status (p = 0.044, aOR = 2.17, 95% CI = 1.03–4.54) and not living in an urban area (p = 0.00037, aOR = 0.24, 95% CI = 0.11–0.52).ConclusionInterpersonal support, rural residence, and not disclosing HIV status were independent predictors of adherence to ART in the study area