Displaying publications 61 - 80 of 152 in total

Abstract:
Sort:
  1. Sim YL, Ariffin A, Khan MN
    J Org Chem, 2008 May 16;73(10):3730-7.
    PMID: 18410141 DOI: 10.1021/jo702695k
    The apparent second-order rate constant (k OH) for hydroxide-ion-catalyzed conversion of 1 to N-(2'-methoxyphenyl)phthalamate (4) is approximately 10(3)-fold larger than k OH for alkaline hydrolysis of N-morpholinobenzamide (2). These results are explained in terms of the reaction scheme 1 --> k(1obs) 3 --> k(2obs) 4 where 3 represents N-(2'-methoxyphenyl)phthalimide and the values of k(2obs)/k(1obs) vary from 6.0 x 10(2) to 17 x 10(2) within [NaOH] range of 5.0 x 10(-3) to 2.0 M. Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of 1 decrease from 21.7 x 10(-3) to 15.6 x 10(-3) s(-1) with an increase in ionic strength (by NaCl) from 0.5 to 2.5 M at 0.5 M NaOH and 35 degrees C. The values of k obs, obtained for alkaline hydrolysis of 2 within [NaOH] range 1.0 x 10(-2) to 2.0 M at 35 degrees C, follow the relationship k(obs) = kOH[HO(-)] + kOH'[HO (-)] (2) with least-squares calculated values of kOH and kOH' as (6.38 +/- 0.15) x 10(-5) and (4.59 +/- 0.09) x 10(-5) M (-2) s(-1), respectively. A few kinetic runs for aqueous cleavage of 1, N'-morpholino-N-(2'-methoxyphenyl)-5-nitrophthalamide (5) and N'-morpholino-N-(2'-methoxyphenyl)-4-nitrophthalamide (6) at 35 degrees C and 0.05 M NaOH as well as 0.05 M NaOD reveal the solvent deuterium kinetic isotope effect (= k(obs) (H 2) (O)/ k(obs) (D 2 ) (O)) as 1.6 for 1, 1.9 for 5, and 1.8 for 6. Product characterization study on the cleavage of 5, 6, and N-(2'-methoxyphenyl)-4-nitrophthalimide (7) at 0.5 M NaOD in D2O solvent shows the imide-intermediate mechanism as the exclusive mechanism.
  2. Sim YL, Ariffin A, Khan MN
    Bioorg Chem, 2008 Aug;36(4):178-82.
    PMID: 18440044 DOI: 10.1016/j.bioorg.2008.03.003
    The rate of conversion of 1 to N-(2-methoxyphenyl)phthalimide (2) within [HCl] range 5.0x10(-3)-1.0 M at 1.0M ionic strength (by NaCl) reveals the presence of both uncatalyzed and specific acid-catalyzed kinetic terms in the rate law. Intramolecular carboxamide group-assisted cleavage of amide bond of 1 reveals rate enhancement of much larger than 10(6)-fold compared to the expected rate of analogous intermolecular reaction.
  3. Khan MN, Ariffin A
    Org Biomol Chem, 2003 Apr 21;1(8):1404-8.
    PMID: 12929671
    The rate of formation and disappearance of phthalic anhydride (PAn) intermediate in the aqueous cleavage of N-methoxyphthalamic acid (NMPA) under acidic pH was studied spectrophotometrically in mixed CH3CN-H2O solvents. The rate of formation of PAn from NMPA is almost independent of the change in acetonitrile content from 20 to 70% v/v in mixed aqueous solvents. The rate constants for the formation of PAn from NMPA are approximately 10-fold smaller than the corresponding rate constants for the formation of PAn from o-carboxybenzohydroxamic acid (OCBA). These observations are ascribed to the consequence of the occurrence of slightly different mechanisms in these reactions.
  4. Khan MN, Ismail E
    J Phys Chem A, 2009 Jun 11;113(23):6484-8.
    PMID: 19449852 DOI: 10.1021/jp902886z
    A kinetic probe, which involves the determination of pseudo-first-order rate constants (k(obs)) for the nucleophilic reaction of piperidine (Pip) with ionized phenyl salicylate (S(-)) at constant [Pip](T) (= 0.1 M), [S(-)](T) (= 2 x 10(-4) M), [CTABr](T), < or = 0.10 M NaOH and varying concentration of MX (= 3-ClC(6)H(4)CO(2)Na and C(6)H(5)CH=CHCO(2)Na), gives the following information. The nonlinear plots of k(obs) versus [MX] reveal indirectly the occurrence of more than one independent ion-exchange processes at the CTABr micellar surface. These observed data fit to a kinetic relationship derived from an empirical equation coupled with pseudophase micellar (PM) model. This relationship gives an empirical constant (K(X/S)) that is used to determine the usual ion-exchange constant (K(X)(Y)). The values of K(X)(Br) (Y = Br) have been calculated for X = 3-ClC(6)H(4)CO(2)(-) and C(6)H(5)CH=CHCO(2)(-). More than 12-fold larger value of K(X)(Br) for X = 3-ClC(6)H(4)CO(2)(-) than that for X = 2-ClC(6)H(4)CO(2)(-) is attributed to the presence and absence of viscoelasticity in the respective presence of 3-ClC(6)H(4)CO(2)(-) and 2-ClC(6)H(4)CO(2)(-).
  5. Sim YL, Ariffin A, Khan MN
    J Org Chem, 2007 Oct 26;72(22):8452-8.
    PMID: 17918997
    A kinetic study on the aqueous cleavage of N-(2-methoxyphenyl)phthalimide (1) and N-(2-hydroxyphenyl)phthalimide (2), under the buffers of N-methylmorpholine, reveals the equilibrium presence of monocationic amide (Ctam) formed due to nucleophilic reactions of N-methylmorpholine with 1 and 2. Pseudo-first-order rate constants for the reactions of water and HO- with Ctam (formed through nucleophilic reaction of N-methylmorpholine with 1) are 4.60 x 10(-5) s-1 and 47.9 M-1 s-1, respectively. But the cleavage of Ctam, formed through nucleophilic reaction of N-methylmorpholine with 2, involves intramolecular general base (2'-O- group of Ctam)-assisted water attack at carbonyl carbon of cationic amide group of Ctam in or before the rate-determining step.
  6. Khan MN, Sim YL, Ariffin A
    ScientificWorldJournal, 2014;2014:592691.
    PMID: 24574900 DOI: 10.1155/2014/592691
    The values of pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of 1, obtained at 1.0 mM NaOH and within [C(m)E(n)]T (total concentration of C(m)E(n)) range of 3.0-5.0 mM for C(12)E(23) and 10-20 mM for C(18)E(20), fail to obey pseudophase micellar (PM) model. The values of the fraction of near irreversible C m E n micellar trapped 1 molecules (F(IT1)) vary in the range ~0-0.75 for C(12)E(23) and ~0-0.83 for C(18)E(20) under such conditions. The values of F(IT1) become 1.0 at ≥ 10 mM C(12)E(23) and 50 mM C(18)E(20). Kinetic analysis of the observed data at ≥ 10 mM C(12)E(23) shows near irreversible micellar entrapment of 1 molecules under such conditions.
  7. Cheong MY, Ariffin A, Khan MN
    J Phys Chem B, 2007 Oct 25;111(42):12185-94.
    PMID: 17914797
    Pseudo-first-order rate constants (k(obs)) for alkaline hydrolysis of N-benzylphthalimide (1) show a nonlinear decrease with the increase in [C(m)E(n)]T (total concentration of Brij 58, m = 16, n = 20 and Brij 56, m = 16, n = 10) at constant [CH(3)CN] and [NaOH]. These nonionic micellar effects, within the certain typical reaction conditions, have been explained in terms of the pseudophase micellar (PM) model. The values of micellar binding constants (KS) of 1 are 1.04 x 10(3) M(-1) (at 1.0 x 10(-3) M NaOH) and 1.08 x 10(3) M(-1) (at 2.0 x 10(-3) M NaOH) for C(16)E(20) as well as 600 M(-1) (at 7.6 x 10(-4) M NaOH) and 670 M(-1) (at 1.0 x 10(-3) M NaOH) for C(16)E(10) micelles. The pseudo-first-order rate constants (kM) for hydrolysis of 1 in C(16)E(20) micellar pseudophase are approximately 90-fold smaller than those (kW) in water phase. The values of kM for hydrolysis of 1 in C(16)E(10) micelles are almost zero. Kinetic coupled with UV spectral data reveals significant irreversible nonionic micellar binding of 1 molecules in the micellar environment of nearly zero hydroxide ion concentration at >or=0.14 M C(16)E(20) and 1.0 x 10(-3) M NaOH while such observations could not be detected at M C(16)E(20) and 2.0 x 10(-3) M NaOH. Significantly, such irreversible C(16)E(10) micellar binding of 1 molecules could be detected at 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH as well as at >or=3 x 10(-3) M C(16)E(10) and 7.6 x 10(-4) M NaOH, while the rate of hydrolysis of 1 is completely ceased at >or=0.05 M C(16)E(10) and 7.6 x 10(-4) M NaOH. The rate of hydrolysis of 1 at 5.0 x 10(-2) and 8.8 x 10(-2) M C(16)E(10) and 1.0 x 10(-3) M NaOH reveals the formation of presumably phthalic anhydride, whereas such observation was not observed in the C(16)E(20) micellar system under similar experimental conditions.
  8. Yusof NS, Niyaz Khan M
    J Colloid Interface Sci, 2011 May 1;357(1):121-8.
    PMID: 21333302 DOI: 10.1016/j.jcis.2011.01.061
    The effects of the concentration of inert organic salts, [MX], (MX=2-, 3- and 4-BrBzNa with BrBzNa=BrC(6)H(4)CO(2)Na) on the rate of piperidinolysis of ionized phenyl salicylate (PS(-)) have been rationalized in terms of pseudophase micellar (PM) coupled with an empirical equation. The appearance of induction concentration in the plots of k(obs) versus [MX] (where k(obs) is pseudo-first-order rate constants for the reaction of piperidine (Pip) with PS(-)) is attributed to the occurrence of two or more than two independent ion exchange processes between different counterions at the cationic micellar surface. The derived kinetic equation, in terms of PM model coupled with an empirical equation, gives empirical parameters F(X/S) and K(X/S) whose magnitudes lead to the calculation of usual ion exchange constant K(X)(Br) (=K(X)/K(Br) with K(X) and K(Br) representing cationic micellar binding constants of counterions X(-) and Br(-), respectively). The value of F(X/S) measures the fraction of S(-) (=PS(-)) ions transferred from the cationic micellar pseudophase to the aqueous phase by the optimum value of [MX] due to ion exchange X(-)/S(-). Similarly, the value of K(X/S) measures the ability of X(-) ions to expel S(-) ions from cationic micellar pseudophase to aqueous phase through ion exchange X(-)/S(-). This rather new technique gives the respective values of K(X)(Br) as 8.8±0.3, 71±6 and 62±5 for X(-)=2-, 3- and 4-BrBz(-). Rheological measurements reveal the shear thinning behavior of all the surfactant solutions at 15mM CTABr (cetyltrimethylammonium bromide) indicating indirectly the presence of rodlike micelles. The plots of shear viscosity (η) at a constant shear rate (γ), i.e. η(γ), versus [MX] at 15 mM CTABr exhibit maxima for MX=3-BrBzNa and 4-BrBzNa while for MX=2-BrBzNa, the viscosity maximum appears to be missing. Such viscosity maxima are generally formed in surfactant solutions containing long stiff and flexible rodlike micelles with entangled and branched/multiconnected networks. Thus, 15 mM CTABr solutions at different [MX] contain long stiff and flexible rodlike micelles for MX=3- and 4-BrBzNa and short rodlike micelles for MX=2-BrBzNa.
  9. Asif M, Khan PA, Irfan F, Salim M, Jan A, Khan M
    Environ Sci Pollut Res Int, 2023 Nov;30(53):114690-114705.
    PMID: 37848790 DOI: 10.1007/s11356-023-30211-6
    In Industry 4.0, sustainability is the heart, and governance is the soul of the business, but diversity washing, greenwashing, and SDG washing are skeptical. This is due to the reactive/normative approach in dealing with sustainability and governance, which has created an amounting number of greenhouse gases, waste generation, and several business washing challenges. This study has explored the Scopus and Web of Science databases and searched for the keywords "Sustainable Development Goals" AND "Director," which provided 76 documents. However, when the authors added the third keyword, "ISO 37001-2021," along with the above two keywords, the database provided no study investigating the moderation role of ISO 37001-2021. Therefore, the study advocates the adoption of newly developed ISO 37000:2021 good governance standards for greenwashing, SDG washing, and diversity washing challenges without failing to contribute to the firm sustainable development goal performance and earning management. Secondly, the independent director attribute's role is vital due to the potential, power, position, and evidence to adopt ISO 37000:2021 standards. Thirdly, the scoping review study has proposed a conceptual model to extend the reporting discloser and transparency. It goes beyond mere compliance, contributes towards societal development, and promotes adopting sustainable development goal performance and reporting as a new non-financial parameter for evaluating the firm's performance. Lastly, this will boost firm sustainability and adopt the circular economic model, creating a unique competitive edge and green governance goodwill among the business's external stakeholders and attracting sustainably responsible investors.
  10. Rafiq W, Bin Napiah M, Hartadi Sutanto M, Salah Alaloul W, Nadia Binti Zabri Z, Imran Khan M, et al.
    Materials (Basel), 2020 Oct 22;13(21).
    PMID: 33105633 DOI: 10.3390/ma13214704
    Moisture damage in hot mix asphalt pavements is a periodic but persistent problem nowadays, even though laboratory testing is performed to identify different moisture-susceptible mixtures. In this study, a Hamburg Wheel Tracking device (HWTD) was used for rutting tests which were conducted on control and a high percentage of recycled asphalt pavement (RAP), i.e., 30%, 50% and 100% of virgin mixtures, under air dry and water-immersed conditions. Similarly, the extracted bitumen from RAP was tested for binder physical properties. Results showed that the asphalt mixtures containing RAP have less rut depth as compared to the control mix both in air dry and immersion conditions and hence showed better anti-rutting properties and moisture stability. Stripping performance of control and RAP containing mixtures was also checked, concluding that the RAP mixture was greatly dependent on the interaction between the binder (virgin plus aged) and aggregates.
  11. Khan M, Khan A, Khan AU, Shakeel M, Khan K, Alabduljabbar H, et al.
    Heliyon, 2024 Jan 15;10(1):e23375.
    PMID: 38169887 DOI: 10.1016/j.heliyon.2023.e23375
    Fiber-reinforced polymers (FRP) are widely utilized to improve the efficiency and durability of concrete structures, either through external bonding or internal reinforcement. However, the response of FRP-strengthened reinforced concrete (RC) members, both in field applications and experimental settings, often deviates from the estimation based on existing code provisions. This discrepancy can be attributed to the limitations of code provisions in fully capturing the nature of FRP-strengthened RC members. Accordingly, machine learning methods, including gene expression programming (GEP) and multi-expression programming (MEP), were utilized in this study to predict the flexural capacity of the FRP-strengthened RC beam. To develop data-driven estimation models, an extensive collection of experimental data on FRP-strengthened RC beams was compiled from the experimental studies. For the assessment of the accuracy of developed models, various statistical indicators were utilized. The machine learning (ML) based models were compared with empirical and conventional linear regression models to substantiate their superiority, providing evidence of enhanced performance. The GEP model demonstrated outstanding predictive performance with a correlation coefficient (R) of 0.98 for both the training and validation phases, accompanied by minimal mean absolute errors (MAE) of 4.08 and 5.39, respectively. In contrast, the MEP model achieved a slightly lower accuracy, with an R of 0.96 in both the training and validation phases. Moreover, the ML-based models exhibited notably superior performances compared to the empirical models. Hence, the ML-based models presented in this study demonstrated promising prospects for practical implementation in engineering applications. Moreover, the SHapley Additive exPlanation (SHAP) method was used to interpret the feature's importance and influence on the flexural capacity. It was observed that beam width, section effective depth, and the tensile longitudinal bars reinforcement ratio significantly contribute to the prediction of the flexural capacity of the FRP-strengthened reinforced concrete beam.
  12. Taqui SN, Syed AA, Mubarak NM, Farade RA, Khan MAM, Kalam MA, et al.
    Sci Rep, 2023 Dec 19;13(1):22665.
    PMID: 38114620 DOI: 10.1038/s41598-023-49471-w
    Research studies have been carried out to accentuate Fennel Seed Spent, a by-product of the Nutraceutical Industry, as an inexpensive, recyclable and operational biosorbent for bioremediation of Acid Blue 113 (AB113) in simulated water-dye samples and textile industrial effluent (TIE). The physical process of adhesion of AB113 on the surface of the biosorbent depends on various parameters, such as the initial amount of the dye, amount and expanse of the biosorbent particles, pH of the solution and temperature of the medium. The data obtained was analyzed using three two-parameter and five three-parameter adsorption isotherm models to glean the adsorbent affinities and interaction mechanism of the adsorbate molecules and adsorbent surface. The adsorption feature study is conducted employing models of Weber-Morris, pseudo 1st and 2nd order, diffusion film model, Dumwald-Wagner and Avrami model. The study through 2nd order pseudo and Avrami models produced complementary results for the authentication of experimental data. The thermodynamic features, ΔG0, ΔH0, and ΔS0 of the adsorption process are acclaimed to be almost spontaneous, physical in nature and endothermic in their manifestation. Surface characterization was carried out using Scanner Electron Microscopy, and identification and determination of chemical species and molecular structure was performed using Infrared Spectroscopy (IR). Maximum adsorption evaluated using statistical optimization with different combinations of five independent variables to study the individual as well as combined effects by Fractional Factorial Experimental Design (FFED) was 236.18 mg g-1 under optimized conditions; pH of 2, adsorbent dosage of 0.500 g L-1, and an initial dye concentration of 209.47 mg L-1 for an adsorption time of 126.62 min with orbital shaking of 165 rpm at temperature 49.95 °C.
  13. Hye Khan MA, Sattar MA, Abdullah NA, Johns EJ
    Br J Pharmacol, 2008 Mar;153(6):1232-41.
    PMID: 18246093 DOI: 10.1038/bjp.2008.13
    This study investigated whether the alpha(1)-adrenoceptor responsiveness of the renal vasculature was altered in the state of hypertension combined with renal failure.
  14. Hammad H, Elbarazi I, Bendak M, Obaideen K, Amanatullah A, Khan BSB, et al.
    J Relig Health, 2022 Sep 04.
    PMID: 36058952 DOI: 10.1007/s10943-022-01646-x
    This cross-sectional survey investigates the influence of youths' religiosity on their attitude towards people with disabilities. The Muslim religiosity questionnaire and multidimensional attitudes scale towards persons with disabilities were used to survey 733 youths from the federal university in the United Arab Emirates. The results indicated that the youths were religious and had positive attitudes towards people with disabilities. An increase in religiosity is associated with a positive attitude towards disability, and both religiosity and total family income positively impacted the attitude towards people with disabilities. Reducing inequalities by including persons with disabilities is one of the UN 2030 Agenda for Sustainable Development objectives. Policies should aim to enhance curriculum, improvise public guidelines and partner with associated faith-based leaders to build an inclusive society for people with disabilities, thus helping to achieve sustainable development goals.
  15. Sagadevan S, Vennila S, Suraiya Begum SN, Wahab YA, Hamizi NAB, Marlinda AR, et al.
    J Nanosci Nanotechnol, 2020 09 01;20(9):5452-5457.
    PMID: 32331117 DOI: 10.1166/jnn.2020.17855
    Nanostructure materials are of interest in last few decades due to their unique size-dependent physio-chemical properties. In this paper, zinc oxide (ZnO) and barium doped ZnO nanodisks (NDs) were synthesized using sonochemical method and characterized by various techniques such as X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM), UV-vis absorption and dielectric measurements. The XRD and FTIR studies confirm the crystalline nature of ZnO NDs, and the average crystallite size was found to be ~25 nm for pure ZnO and ~22 nm for Ba doped ZnO NDs. SEM study confirmed the spherical shaped ZnO NDs with average sizes in the range of 20-30 nm. The maximum absorbance was obtained in the 200-500 nm regions with a prominent peak absorbance were observed by UV-vis spectra. The corresponding band gap for ZnO NDs and Ba doped ZnO NDs were calculated using Tauc's plot and was found to be 3.12 and 3.04, respectively. The conductivity and dielectric measurements as a function of frequency have been studied.
  16. Lew MH, Noordin R, Monsur Alam Khan M, Tye GJ
    Pathog Glob Health, 2018 10;112(7):387-394.
    PMID: 30332344 DOI: 10.1080/20477724.2018.1536854
    Toxoplasmosis, a parasitic disease in human and animals, is caused by Toxoplasma gondii. Our previous study has led to the discovery of a novel RAP domain binding protein antigen (TgRA15), an apparent in-vivo induced antigen recognised by antibodies in acutely infected individuals. This study is aimed to evaluate the humoral response and cytokine release elicited by recombinant TgRA15 protein in C57BL/6 mice, demonstrating its potential as a candidate vaccine for Toxoplasma gondii infection. In this study, the recombinant TgRA15 protein was expressed in Escherichia coli, purified and refolded into soluble form. C57BL/6 mice were immunised intradermally with the antigen and CASAC (Combined Adjuvant for Synergistic Activation of Cellular immunity). Antigen-specific humoral and cell-mediated responses were evaluated using Western blot and ELISA. The total IgG, IgG1 and IgG2a antibodies specific to the antigen were significantly increased in treatment group compare to control group. A higher level of interferon gamma (IFN-γ) secretion was demonstrated in the mice group receiving booster doses of rTgRA15 protein, suggesting a potential Th1-mediated response. In conclusion, the rTgRA15 protein has the potential to generate specific antibody response and elicit cellular response, thus potentially serve as a vaccine candidate against T. gondii infection.
  17. Khan FB, Uddin S, Elderdery AY, Goh KW, Ming LC, Ardianto C, et al.
    Cells, 2022 Nov 18;11(22).
    PMID: 36429092 DOI: 10.3390/cells11223664
    Cardiovascular diseases (CVDs) are one of the leading causes of death worldwide. Accumulating evidences have highlighted the importance of exosomes and non-coding RNAs (ncRNAs) in cardiac physiology and pathology. It is in general consensus that exosomes and ncRNAs play a crucial role in the maintenance of normal cellular function; and interestingly it is envisaged that their potential as prospective therapeutic candidates and biomarkers are increasing rapidly. Considering all these aspects, this review provides a comprehensive overview of the recent understanding of exosomes and ncRNAs in CVDs. We provide a great deal of discussion regarding their role in the cardiovascular system, together with providing a glimpse of ideas regarding strategies exploited to harness their potential as a therapeutic intervention and prospective biomarker against CVDs. Thus, it could be envisaged that a thorough understanding of the intricacies related to exosomes and ncRNA would seemingly allow their full exploration and may lead clinical settings to become a reality in near future.
Filters
Contact Us

Please provide feedback to Administrator (afdal@afpm.org.my)

External Links