Papers by Shawkat Islam, PhD
Synchrotron Radiation News, 2015
Two very different quantum mechanically based energy decomposition analyses (EDA) schemes are emp... more Two very different quantum mechanically based energy decomposition analyses (EDA) schemes are employed to study the dominant energy differences between the eclipsed and staggered ferrocene conformers. One is the extended transition state (ETS) based on the Amsterdam Density Functional (ADF) package and the other is natural EDA (NEDA) based in the General Atomic and Molecular Electronic Structure System (GAMESS) package. It reveals that in addition to the model (theory and basis set), the fragmentation channels more significantly affect the interaction energy terms (ΔE) between the conformers. It is discovered that such an interaction energy can be absorbed into the pre-partitioned fragment channels so that to affect the interaction energies in a particular conformer of Fc. To avoid this, the present study employs a complete fragment channel—the fragments of ferrocene are individual neutral atoms. It therefore discovers that the major difference between the ferrocene conformers is due to the quantum mechanical Pauli repulsive energy and orbital attractive energy, leading to the eclipsed ferrocene the energy preferred structure. The NEDA scheme further indicates that the sum of attractive (negative) polarization (POL) and charge transfer (CL) energies prefers the eclipsed ferrocene. The repulsive (positive) deformation (DEF) energy, which is dominated by the cyclopentadienyle (Cp) rings, prefers the staggered ferrocene. Again, the cancellation results in a small energy residue in favour of the eclipsed ferrocene, in agreement with the ETS scheme. Further Natural Bond Orbital (NBO) analysis indicates that all NBO energies, total Lewis (no Fe) and lone pair (LP) deletion all prefer the eclipsed Fc conformer. The most significant energy preferring the eclipsed ferrocene without cancellation is the interactions between the donor lone pairs (LP) of the Fe atom and the acceptor antibond (BD*) NBOs of all C–C and C–H bonds in the ligand, LP(Fe)-BD*(C–C & C–H), which strongly stabilizes the eclipsed (D5h) conformation by −457.6 kcal·mol−1.
The aim of the current study was to evaluate the antioxidant, antimicrobial and thrombolytic pote... more The aim of the current study was to evaluate the antioxidant, antimicrobial and thrombolytic potentials of the exocarp of Spondias pinnata fruits. The crude ethanolic extract of the exocarp of S. pinnata fruit was partitioned successively by solvents of different polarity. All fractions were then investigated for qualitative preliminary phytochemical screening by specific standard procedure. The antioxidant potential of all fractions were then evaluated in terms of total phenolic content, total flavonoid content, DPPH free radical scavenging potential, reducing potential and total antioxidant capacity by specific standard procedure. The disc diffusion method was incorporated to evaluate the in vitro antimicrobial activity on nutrient agar medium. The highest total phenolic content was found in aqueous fraction (570.20±0.48 mg GAE/g of dried extract) while the lowest in the n-Hexane fraction (337.51±0.21 mg GAE/g of dried extract). However, ethyl acetate fraction exhibited the highest flavonoid content which amounted to 132.27±0.25 mg quercetin equivalents/g of dried extract. Likewise, ethyl acetate fraction showed the highest antioxidant capacity (21.61±0.11 g of L-ascorbic acid equivalents/g of dried extract) along with the lowest IC 50 (1.72±0.39 µg/ml) & EC 50 (2.25±0.75 µg/ml) value. However, DPPH free radical scavenging activity and reducing power of all fractions were found to be concentration dependent. Nonetheless, comparatively more polar fractions (ethyl acetate and aqueous fraction) were found to be ineffective against all the microbial strains except S. dysentery and P. aeruginosa while nonpolar fractions (n-hexane and dichloromethane fraction) showed variable antimicrobial activity. In addition, all fractions produced statistically significant (P<0.05 for ethyl acetate and aqueous fraction, P<0.001 for others) thrombolytic activity. To conclude, our present study suggested that exocarp of S. pinnata fruit exhibits antimicrobial activity against a wide variety of strains while it produces noteworthy antioxidant and significant thrombolytic activity.
The present study was designed to compare the antioxidant, antimicrobial and thrombolytic effects... more The present study was designed to compare the antioxidant, antimicrobial and thrombolytic effects of the Lannea coromandelica bark and leave extracts. After the initial phytochemical screening, the ethanolic fractions of the L. coromandelica bark and leaves were partitioned by solvents of different polarity. Methods used to evaluate the antioxidant potential of the extracts were total phenolic content, total flavonoid content, free radical scavenging capacity, total antioxidant capacity and reducing power assay. Total phenol and total flavonoid contents were found to be the highest for bark and leaves in the ethyl acetate fraction and lowest in the n-Hexane fraction. In DPPH free radical scavenging test, the lowest IC 50 value was found in the ethyl acetate fraction of the bark and leaf, resulting IC 50 value of 3.8±0.14 μg/ml and 6±0.32 μg/ml respectively. In the same vein, ethyl acetate fraction of both leaf and bark showed the highest antioxidant capacity and reducing power. Reducing power of both bark and leaves were found to be concentration dependent and most prominent was observed with the fractions of higher polarity both in case of bark and in case of leaves. Furthermore, the leaf extracts produced moderate antimicrobial activity whereas the bark extracts showed weak antimicrobial activity. Dichloromethane fraction of leaf showed the most potent antimicrobial activity with zone of inhibition ranging from 8 mm to 21 mm at a dose of 400µg/disc and 10 mm to 23 mm at a dose of 800µg/disc. In addition, extracts from both parts of L. coromandelica produced good thrombolytic activity compared with streptokinase.
Objective: To investigate the antioxidant, antimicrobial, cytotoxic and thrombolytic property of ... more Objective: To investigate the antioxidant, antimicrobial, cytotoxic and thrombolytic property of the fruits and leaves of Spondias dulcis (S. dulcis). Methods: Methanolic extracts of fruits and leaves of S. dulcis were partitioned with chloroform and dichloromethane. The antioxidant potential of the crude extract and partitioned fractions were evaluated in terms of total phenolic content, total flavonoid content, DPPH radical scavenging potential, reducing potential and total antioxidant capacity by specific standard procedures. The antimicrobial activity was evaluated using disc diffusion method. The cytotoxicity was evaluated by using brine shrimp lethality bioassay and compared with vincristine sulfate. The thrombolytic activity was compared with streptokinase. Results: The methanolic fruit extract exhibited the highest phenolic content, flavonoid content and antioxidant capacity, among the other extracts, with the highest DPPH radical scavenging activity at a concentration of 10 µg/mL (IC 50 : 1.91 µg/mL) and maximum reducing power at a concentration of 100 µg/mL (EC 50 : 3.58 µg/mL). Though all extract showed moderate antimicrobial activity against the bacterial strains, weak or no activity against fungus. The range of LC 50 value of all extracts was 1.335-14.057 µg/mL which was far lower than the cut off index for cytotoxicity. All extracts exhibited statistically significant (P<0.001) thrombolytic activity. Conclusions: Our study suggested that S. dulcis exhibits antimicrobial activities against a wide variety of strains while it possesses significant antioxidant, cytotoxic and thrombolytic activity.
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Papers by Shawkat Islam, PhD