Publications by authors named "Yatimah Alias"

52 Publications

Polymer-modified mesoporous silica microcubes ([email protected]) for the synergistic oxidative entrapment of Ag(i), Ti(iv), and Zn(ii) from natural river water.

Dalton Trans 2020 Jun;49(24):8265-8273

Department of Geology, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia.

Herein, we demonstrate a hydrothermal route to the one-pot synthesis of polymeric mesoporous silica microcubes ([email protected]) for the adsorption of heavy metal ions. During the synthesis of [email protected] from column silica gel, the roles and combination of the polymer and an etchant were characterized. Moreover, the porosity of [email protected] was tailored by adjusting the reaction temperature between 75 °C and 200 °C. The characterization through UV, FTIR, FESEM, XRD, BET, and EDX techniques exhibited that [email protected] have a well-ordered mesoporous structure with cubic morphology. The [email protected] had a diameter of 2 μm, with an average pore volume and pore size of 0.69 cm3 g-1 and 10.08 nm, respectively. The results indicated that the [email protected] have excellent adsorption capacity for Ag(i), Ti(iv), and Zn(ii) due to the formation of an aggregated complex. These aggregations led to affordable density difference-based separation of these metal ions through centrifugation, filtration or simple decantation. The removal efficiencies for Ag(i), Ti(iv), and Zn(ii) were observed to be 520, 720, and 850 mg g-1, respectively. The kinetic studies demonstrated that the adsorption performance fitted well to the pseudo-second-order kinetic model. The as-synthesized [email protected] were stable in the wide pH range of 4-8. Significantly, the recycling or reuse results displayed effective adsorption performance of these [email protected] for up to 5 cycles. The adsorption results obtained herein will promote the development of similar strategies for the removal of heavy metal ions from natural water.
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http://dx.doi.org/10.1039/d0dt01274bDOI Listing
June 2020

Voltammetric sensing of formaldehyde by using a nanocomposite prepared by reductive deposition of palladium and platinum on polypyrrole-coated nitrogen-doped reduced graphene oxide.

Mikrochim Acta 2019 05 22;186(6):369. Epub 2019 May 22.

Department of Chemistry, University of Malaya, 50603, Kuala Lumpur, Malaysia.

The study presents the synthesis of polypyrrole-coated palladium platinum/nitrogen-doped reduced graphene oxide nanocomposites (PdPt-PPy/N-rGO NC) via direct the reduction of Pd(II) and Pt(II) in the presence of pyrrole monomer, N-rGO and L-cysteine as the reducing agent. X-ray diffraction confirmed the presence of metallic Pd and Pt from the reduction of Pd and Pt cations. Transmission electron microscopy images revealed the presence of Pd, Pt and PPy deposition on N-rGO. Impedance spectroscopy results gave a decreased charge transfer resistance due to the presence of N-rGO. The nanocomposites were synthesized with different Pd/Pt ratios (2:1, 1:1 and 1:2). A glassy carbon electrode (GCE) modified with the nanocomposite showed enhanced electrochemical sensing capability for formaldehyde in 0.1 M sulfuric acid solution. Cyclic voltammetry showed an increase in the formaldehyde oxidation peak current at the GCE modified with PdPt PPy N-rGO. At a typical potential of 0.45 V (vs. SCE), the sensitivity in the linear segment was 345.8 μA.mM . cm. The voltammetric response was linear between 0.01 and 0.9 mM formaldehyde concentration range, with a 27 µM detection limit (at S/N = 3). Graphical abstract Schematic presentation of formaldehyde detection by PdPt-PPy/nitrogen-doped reduced Graphene Oxide Nanocomposite (PdPt-PPy /N-Gr NC). The decrease of charge transfer resistance and the agglomeration of deposited metals in the presence of N-rGO enhance the current response of the electrochemical sensor.
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http://dx.doi.org/10.1007/s00604-019-3481-yDOI Listing
May 2019

L-Glutamine-assisted synthesis of ZnO oatmeal-like/silver composites as an electrochemical sensor for Pb detection.

Anal Bioanal Chem 2019 Jan 29;411(2):517-526. Epub 2018 Nov 29.

Department of Chemistry, University of Malaya, 50603, Kuala Lumpur, Malaysia.

We report a green synthesis of oatmeal ZnO/silver composites in the presence of L-glutamine as an electrochemical sensor for Pb detection. The synthesis was performed via the direct reduction of Ag in the presence of L-glutamine in NaOH. X-ray diffraction indicated that the Ag was completely reduced to metallic Ag. The field emission scanning electron microscopy (FESEM) and energy dispersive X-ray results confirmed an oatmeal-like morphology of the ZnO with the presence of Ag. The FESEM images showed the effect of L-glutamine on the ZnO morphology. The EIS results confirmed a significant decrease in the charge transfer resistance of the modified glassy carbon electrode due to the presence of Ag. From the differential pulse voltammetry results, a linear working range for the concentration of Pb between 5 and 6 nM with LOD of 0.078 nM (S/N = 3) was obtained. The sensitivity of the linear segment is 1.42 μA nM cm. The presence of L-glutamine as the capping agent and stabilizer decreases the size of Ag nanoparticles and prevents the agglomeration of ZnO, respectively. Graphical abstract ᅟ.
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http://dx.doi.org/10.1007/s00216-018-1476-xDOI Listing
January 2019

Transport and retention behavior of carbonaceous colloids in natural aqueous medium: Impact of water chemistry.

Chemosphere 2019 Feb 3;217:213-222. Epub 2018 Nov 3.

Department of Geology, Faculty of Science, University of Malaya, Kuala Lumpur, 50603, Malaysia.

Carbon based materials are emerging as a sustainable alternative to their metal-oxide counterparts. However, their transport behavior under natural aqueous environment is poorly understood. This study investigated the transport and retention profiles of carbon nanoparticles (CNPs) and graphene oxide quantum dots (GOQDs) through column experiments in saturated porous media. CNPs and GOQDs (30 mg/L) were dispersed in natural river water (RW) and passed through the column at a flow rate of 1 mL/min, which mimicking the natural water flow rate. After every 10 min, the column effluents were collected and the mass recovery and retention profiles were monitored. Results indicated that the transport of both carbonaceous colloids was predominantly controlled by surface potential and ionic composition of natural water. The CNPs with its high surface potential (-40 mV) exhibited more column transport and was less susceptible to solution pH (5.6-6.8) variation as compared to GOQDs (-24 mV). The results showed that, monovalent salt (NaCl) was one of the dominating factors for the retention and transport of carbonaceous colloids compared to divalent salt (CaCl). Furthermore, the presence of natural organic matter (NOM) increased the transport of both carbonaceous colloids and thereby decreases the tendency for column retention.
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http://dx.doi.org/10.1016/j.chemosphere.2018.11.015DOI Listing
February 2019

Toxicity evaluation of ZnO and TiO nanomaterials in hydroponic red bean (Vigna angularis) plant: Physiology, biochemistry and kinetic transport.

J Environ Sci (China) 2018 Oct 5;72:140-152. Epub 2018 Jan 5.

Department of Geology, Environmental and Earth Sciences, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia.

The toxicity and kinetic uptake potential of zinc oxide (ZnO) and titanium dioxide (TiO) nanomaterials into the red bean (Vigna angularis) plant were investigated. The results obtained revealed that ZnO, due to its high dissolution and strong binding capacity, readily accumulated in the root tissues and significantly inhibited the physiological activity of the plant. However, TiO had a positive effect on plant physiology, resulting in promoted growth. The results of biochemical experiments implied that ZnO, through the generation of oxidative stress, significantly reduced the chlorophyll content, carotenoids and activity of stress-controlling enzymes. On the contrary, no negative biochemical impact was observed in plants treated with TiO. For the kinetic uptake and transport study, we designed two exposure systems in which ZnO and TiO were exposed to red bean seedlings individually or in a mixture approach. The results showed that in single metal oxide treatments, the uptake and transport increased with increasing exposure period from one week to three weeks. However, in the metal oxide co-exposure treatment, due to complexation and competition among the particles, the uptake and transport were remarkably decreased. This suggested that the kinetic transport pattern of the metal oxide mixtures varied compared to those of its individual constituents.
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http://dx.doi.org/10.1016/j.jes.2017.12.022DOI Listing
October 2018

Enhanced amperometric detection of paracetamol by immobilized cobalt ion on functionalized MWCNTs - Chitosan thin film.

Anal Biochem 2018 06 16;551:29-36. Epub 2018 May 16.

Department of Chemistry, Faculty of Science, University Malaya, 50603, Kuala Lumpur, Malaysia.

In the present study, a nanocomposite of f-MWCNTs-chitosan-Co was prepared by the immobilization of Co(II) on f-MWCNTs-chitosan by a self-assembly method and used for the quantitative determination of paracetamol (PR). The composite was characterized by field emission scanning electron microscopy (FESEM) and energy dispersive x-ray analysis (EDX). The electroactivity of cobalt immobilized on f-MWCNTs-chitosan was assessed during the electro-oxidation of paracetamol. The prepared GCE modified f-MWCNTs/CTS-Co showed strong electrocatalytic activity towards the oxidation of PR. The electrochemical performances were investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Under favorable experimental conditions, differential pulse voltammetry showed a linear dynamic range between 0.1 and 400 μmol L with a detection limit of 0.01 μmol L for the PR solution. The fabricated sensor exhibited significant selectivity towards PR detection. The fabricated sensor was successfully applied for the determination of PR in commercial tablets and human serum sample.
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http://dx.doi.org/10.1016/j.ab.2018.05.004DOI Listing
June 2018

Assessment of groundwater salinity and quality in Gaza coastal aquifer, Gaza Strip, Palestine: An integrated statistical, geostatistical and hydrogeochemical approaches study.

Sci Total Environ 2018 Feb 17;615:972-989. Epub 2017 Oct 17.

Faculty of Civil Engineering, University Technology Mara, Malaya, 40450 Shah Alam, Selangor, Malaysia.

A comprehensive study was conducted to identify the salinization origins and the major hydrogeochemical processes controlling the salinization and deterioration of the Gaza coastal aquifer system through a combination approaches of statistical and geostatistical techniques, and detailed hydrogeochemical assessments. These analyses were applied on ten physicochemical variables for 219 wells using STATA/SE12 and Surfer softwares. Geostatistical analysis of the groundwater salinity showed that seawater intrusion along the coastline, and saltwater up-coning inland highly influenced the groundwater salinity of the study area. The hierarchical cluster analysis (HCA) technique yielded seven distinct hydrogeochemical signature clusters; (C1&C2: Eocene brackish water invasion, C3 saltwater up-coning, C4 human inputs, C5 seawater intrusion, C6 & C7 rainfall and mixing inputs). Box plot shows a wide variation of most of the ions while Chadha's plot elucidates the predominance of Na-Cl (71.6%) and Ca/Mg-Cl (25%) water types. It is found that, the highest and the lowest levels of salinization and the highest level of nitrate pollution were recorded in the northern area. This result reflects the sensitivity of this area to the human activities and/or natural actions. Around 90.4% of the wells are nitrate polluted. The main source of nitrate pollution is the sewage inputs while the farming inputs are very limited and restricted mostly in the sensitive northern area. Among the hydrogeochemical processes, ion exchange process was the most effective process all over the study area. Carbonate dissolution was common in the study area with the highest level in clusters 6, 7, 4 and 2 in the north while Gypsum dissolution was significant only in cluster 1 in the south and limited in the other clusters. This integrated multi-techniques research should be of benefit for effective utilization and management of the Gaza coastal aquifer system as well as for future work in other similar aquifers systems.
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http://dx.doi.org/10.1016/j.scitotenv.2017.09.320DOI Listing
February 2018

Immunofluorescence-based biosensor for the determination of dengue virus NS1 in clinical samples.

J Pharm Biomed Anal 2018 Feb 1;149:591-602. Epub 2017 Dec 1.

Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia; University Malaya Centre for Ionic Liquids (UMCiL), University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address:

The sharp increase in incidence of dengue infection has necessitated the development of methods for the rapid diagnosis of this deadly disease. Here we report the design and development of a reliable, sensitive, and specific optical immunosensor for the detection of the dengue nonstructural protein 1 (NS1) biomarker in clinical samples obtained during early stages of infection. The present optical NS1 immunosensor comprises a biosensing surface consisting of specific monoclonal NS1 antibody for immunofluorescence-based NS1 antigen determination using fluorescein isothiocyanate (FITC) conjugated to IgG antibody. The linear range of the optical immunosensor was from 15-500ngmL, with coefficient of determination (R) of 0.92, high reproducibility (the relative standard deviation obtained was 2%), good stability for 21days at 4°C, and low detection limit (LOD) at 15ngmL. Furthermore, the optical immunosensor was capable of detecting NS1 analytes in plasma specimens from patients infected with the dengue virus, with low cross-reaction with plasma specimens containing the Japanese encephalitis virus (JEV) and Zika virus. No studies have been performed on the reproducibility and cross-reactivity regarding NS1 specificity, which is thus a limitation for optical NS1 immunosensors. In contrast, the present study addressed these limitations carefully where these two important experiments were conducted to showcase the robustness of our newly developed optical-based fluorescence immunosensor, which can be practically used for direct NS1 determination in any untreated clinical sample.
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http://dx.doi.org/10.1016/j.jpba.2017.11.064DOI Listing
February 2018

Reviews of the toxicity behavior of five potential engineered nanomaterials (ENMs) into the aquatic ecosystem.

Toxicol Rep 2017 4;4:211-220. Epub 2017 Apr 4.

Department of Geology, Environmental and Earth Sciences, Faculty of Science, University Malaya, Kuala Lumpur, 50603, Malaysia.

Presently, engineered nanomaterials (ENMs) are used in a wide variety of commercial applications, resulting in an uncontrolled introduction into the aquatic environment. The purpose of this review is to summarize the pathways and factors that controlling the transport and toxicity of five extensively used ENMs. These toxicological pathways are of great importance and need to be addressed for sustainable implications of ENMs without environmental liabilities. Here we discuss five potentially utilized ENMs with their possible toxicological risk factors to aquatic plants, vertebrates model and microbes. Moreover, the key effect of ENMs surface transformations by significant reaction with environmental objects such as dissolved natural organic matter (DOM) and the effect of ENMs surface coating and surface charge will also be debated. The transformations of ENMs are subsequently facing a major ecological transition that is expected to create a substantial toxicological effect towards the ecosystem. These transformations largely involve chemical and physical processes, which depend on the properties of both ENMs and the receiving medium. In this review article, the critical issues that controlling the transport and toxicity of ENMs are reviewed by exploiting the latest reports and future directions and targets are keenly discussed to minimize the pessimistic effects of ENMs.
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http://dx.doi.org/10.1016/j.toxrep.2017.04.001DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5615119PMC
April 2017

Geochemical characteristics of rare earth elements in different types of soil: A chemometric approach.

Chemosphere 2017 Oct 9;184:673-678. Epub 2017 Jun 9.

Department of Chemistry, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia; University of Malaya, Centre for Ionic Liquids, Department of Chemistry, Faculty of Science, University of Malaya, 50603, Kuala Lumpur, Malaysia.

Rare earth elements (REEs) are becoming significant due to their huge applications in many industries, large-scale mining and refining activities. Increasing usage of such metals pose negative environmental impacts. In this research ICP-MS has been used to analyze soil samples collected from former ex-mining areas in the depths of 0-20 cm, 21-40 cm, and 41-60 cm of residential, mining, natural, and industrial areas of Perak. Principal component analysis (PCA) revealed that soil samples taken from different mining, industrial, residential, and natural areas are separated into four clusters. It was observed that REEs were abundant in most of the samples from mining areas. Concentration of the rare elements decrease in general as we move from surface soil to deeper soils.
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http://dx.doi.org/10.1016/j.chemosphere.2017.06.032DOI Listing
October 2017

Erratum to: Assessing anthropogenic levels, speciation, and potential mobility of rare earth elements (REEs) in ex-tin mining area.

Environ Sci Pollut Res Int 2017 06;24(17):15207

Department of Chemistry and UMCiL, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia.

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http://dx.doi.org/10.1007/s11356-017-9087-1DOI Listing
June 2017

Assessing anthropogenic levels, speciation, and potential mobility of rare earth elements (REEs) in ex-tin mining area.

Environ Sci Pollut Res Int 2016 Dec 27;23(24):25039-25055. Epub 2016 Sep 27.

Department of Chemistry and UMCiL, Faculty of Science, University of Malaya, Kuala Lumpur, Malaysia.

A study was carried out to determine the level of rare earth elements (REEs) in water and sediment samples from ex-mining lakes and River in Kinta Valley, Perak, Malaysia. Surface water and sediments from an ex-mining lake and Kinta River water samples were analyzed for REEs by inductively coupled plasma mass spectrometry. The total concentration of REEs in the ex-mining lake water samples and sediments were found to be 3685 mg/l and 14159 mg/kg, respectively, while the total concentration of REEs in Kinta River water sample was found to be 1224 mg/l. REEs in mining lake water were found to be within 2.42 mg/l (Tb) to 46.50 mg/l (Ce), while for the Kinta River, it was 1.33 mg/l (Ho) to 29.95 mg/l (Ce). Sediment samples were also found with REEs from 9.81 mg/kg (Ho) to 765.84 mg/kg (Ce). Ce showed the highest average concentrations for mining lake (3.88 to 49.08 mg/l) and Kinta River (4.44 to 33.15 mg/l) water samples, while the concentration of La was the highest (11.59 to 771.61 mg/kg) in the mining lake sediment. Lu was shown to have the highest enrichment of REEs in ex-mining lake sediments (107.3). Multivariate statistical analyses such as factor analysis and principal component analysis indicated that REEs were associated and controlled by mixed origin, with similar contributions from anthropogenic and geogenic sources. The speciation study of REEs in ex-tin mining sediments using a modified five-stage sequential extraction procedure indicated that yttrium (Y), gadolinium (Gd), and lanthanum (La) were obtained at higher percentages from the adsorbed/exchanged/carbonate fraction. The average potential mobility of the REEs was arranged in a descending order: Yb > Gd > Y = Dy > Pr > Er > Tm > Eu > Nd > Tb > Sc > Lu > Ce > La, implying that under favorable conditions, these REEs could be released and subsequently pollute the environment.
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http://dx.doi.org/10.1007/s11356-016-7641-xDOI Listing
December 2016

A lateral flow immunosensor for direct, sensitive, and highly selective detection of hemoglobin A1c in whole blood.

J Chromatogr B Analyt Technol Biomed Life Sci 2016 Mar 23;1015-1016:157-165. Epub 2016 Feb 23.

Chemistry Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address:

An immunosensor that operates based on the principles of lateral flow was developed for direct detection of hemoglobin A1c (HbA1c) in whole blood. We utilized colloidal gold-functionalized antibodies to transduce the specific signal generated when sandwich immuno-complexes were formed on the strip in the presence of HbA1c. The number and intensity of the test lines on the strips indicate normal, under control, and elevated levels of HbA1c. In addition, a linear relationship between HbA1c levels and immunosensor signal intensity was confirmed, with a dynamic range of 4-14% (20-130 mmol mol(-1)) HbA1c. Using this linear relationship, we determined the HbA1c levels in blood as a function of the signal intensity on the strips. Measurements were validated using the Bio-Rad Variant II HPLC and DCA Vantage tests. Moreover, the immunosensor was verified to be highly selective for detection of HbA1c against HbA0, glycated species of HbA0, and HbA2. The limit of detection was found to be 42.5 μg mL(-1) (1.35 mmol mol(-1)) HbA1c, which is reasonably sensitive compared to the values reported for microarray immunoassays. The shelf life of the immunosensor was estimated to be 1.4 months when stored at ambient temperature, indicating that the immunoassay is stable. Thus, the lateral flow immunosensor developed here was shown to be capable of performing selective, accurate, rapid, and stable detection of HbA1c in human blood samples.
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http://dx.doi.org/10.1016/j.jchromb.2016.01.059DOI Listing
March 2016

Quantitative, single-step dual measurement of hemoglobin A1c and total hemoglobin in human whole blood using a gold sandwich immunochromatographic assay for personalized medicine.

Biosens Bioelectron 2016 Apr 21;78:187-193. Epub 2015 Nov 21.

Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address:

We describe a gold nanoparticle-based sandwich immunoassay for the dual detection and measurement of hemoglobin A1c (HbA1c) and total hemoglobin in the whole blood (without pretreatment) in a single step for personalized medicine. The optimized antibody-functionalized gold nanoparticles immunoreact simultaneously with HbA1c and total hemoglobin to form a sandwich at distinctive test lines to transduce visible signals. The applicability of this method as a personal management tool was demonstrated by establishing a calibration curve to relate % HbA1c, a useful value for type 2 diabetes management, to the signal ratio of captured HbA1c to all other forms of hemoglobin. The platform showed excellent selectivity (100%) toward HbA1c at distinctive test lines when challenged with HbA0, glycated HbA0 and HbA2. The reproducibility of the measurement was good (6.02%) owing to the dual measurement of HbA1c and total hemoglobin. A blood sample stability test revealed that the quantitative measurement of % HbA1c was consistent and no false-positive results were detected. Also, this method distinguished the blood sample with elevated HbF from the normal samples and the variants. The findings of this study highlight the potential of a lateral flow immunosensor as a simple, inexpensive, consistent, and convenient strategy for the dual measurement of HbA1c and total Hb to provide useful % HbA1c values for better on-site diabetes care.
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http://dx.doi.org/10.1016/j.bios.2015.11.045DOI Listing
April 2016

Fluoride adsorption by doped and un-doped magnetic ferrites CuCe(x)Fe(2-x)O4: Preparation, characterization, optimization and modeling for effectual remediation technologies.

J Hazard Mater 2015 Dec 23;299:316-24. Epub 2015 Jun 23.

Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia.

A series of doped and un-doped magnetic adsorbents CuCexFe2-xO4 (x=0.0-0.5) for fluoride were prepared with the micro-emulsion method. Fluoride adsorption was optimized for solution pH, temperature, contact time, and initial concentration and was monitored via normal phase ion chromatography (IC). The effect of concomitant anions was also explored to perform and simulate competitive fluoride adsorption in real water samples. Optimal adsorption was discovered by a simple quadratic model based on central composite design (CCD) and the response surface method (RSM). The adsorption, electrochemical and magnetic properties were compared between doped and un-doped ferrites. Doped ferrites (x=0.1-0.5) were found to be superior to un-doped ferrites (x=0) regarding the active sites, functional groups and fluoride adsorption. The characterization, optimization and application results of the doped ferrites indicated enhanced fluoride adsorption and easy separation with a simple magnet.
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http://dx.doi.org/10.1016/j.jhazmat.2015.06.030DOI Listing
December 2015

Scheduling the blended solution as industrial CO2 absorber in separation process by back-propagation artificial neural networks.

Spectrochim Acta A Mol Biomol Spectrosc 2015 Nov 17;150:892-901. Epub 2015 Jun 17.

Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia.

It is believe that 80% industrial of carbon dioxide can be controlled by separation and storage technologies which use the blended ionic liquids absorber. Among the blended absorbers, the mixture of water, N-methyldiethanolamine (MDEA) and guanidinium trifluoromethane sulfonate (gua) has presented the superior stripping qualities. However, the blended solution has illustrated high viscosity that affects the cost of separation process. In this work, the blended fabrication was scheduled with is the process arranging, controlling and optimizing. Therefore, the blend's components and operating temperature were modeled and optimized as input effective variables to minimize its viscosity as the final output by using back-propagation artificial neural network (ANN). The modeling was carried out by four mathematical algorithms with individual experimental design to obtain the optimum topology using root mean squared error (RMSE), R-squared (R(2)) and absolute average deviation (AAD). As a result, the final model (QP-4-8-1) with minimum RMSE and AAD as well as the highest R(2) was selected to navigate the fabrication of the blended solution. Therefore, the model was applied to obtain the optimum initial level of the input variables which were included temperature 303-323 K, x[gua], 0-0.033, x[MDAE], 0.3-0.4, and x[H2O], 0.7-1.0. Moreover, the model has obtained the relative importance ordered of the variables which included x[gua]>temperature>x[MDEA]>x[H2O]. Therefore, none of the variables was negligible in the fabrication. Furthermore, the model predicted the optimum points of the variables to minimize the viscosity which was validated by further experiments. The validated results confirmed the model schedulability. Accordingly, ANN succeeds to model the initial components of the blended solutions as absorber of CO2 capture in separation technologies that is able to industries scale up.
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http://dx.doi.org/10.1016/j.saa.2015.06.036DOI Listing
November 2015

Current aspects in hemoglobin A1c detection: a review.

Clin Chim Acta 2015 Jan 22;439:202-11. Epub 2014 Oct 22.

Department of Chemistry, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia. Electronic address:

Type 2 diabetes mellitus (T2DM) is a pressing health issue that threatens global health and the productivity of populations worldwide. Despite its long-recognized role in diabetes management, glycated hemoglobin (HbA1c) only received WHO endorsement as a T2DM diagnostic tool in 2011. Although conventional plasma-specific tests have long been utilized to diagnose T2DM, the public should be informed that plasma-specific tests are not markedly better than HbA1c tests, particularly in terms of variability and convenience for diagnosing diabetes. In the midst of the debates associated with establishing HbA1c as the preeminent diabetes diagnostic tool, unceasing efforts to standardize HbA1c tests have played an integral part in achieving more efficient communication from laboratory to clinical practice and thus better diabetes care. This review discusses the current status of HbA1c tests in the diagnosis, prevention, treatment and management of T2DM across the globe, focusing on increasing the recognition of glycated hemoglobin variants with effective utilization of different HbA1c methods, updating the current status of HbA1c standardization programs, tapping into the potential of POC analyzers to establish a cost-effective HbA1c test for diabetes care, and inspiring the advancement of HbA1c biosensors for future clinical usage.
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http://dx.doi.org/10.1016/j.cca.2014.10.019DOI Listing
January 2015

Computational evaluation of unsaturated carbonitriles as neutral receptor model for beryllium(II) recognition.

J Mol Model 2014 Dec 30;20(12):2533. Epub 2014 Nov 30.

Department of Chemistry, Faculty of Science Building, University of Malaya, Kuala Lumpur, 50603, Malaysia,

Design of neutral receptor molecules (ionophores) for beryllium(II) using unsaturated carbonitrile models has been carried out via density functional theory, G3, and G4 calculations. The first part of this work focuses on gas phase binding energies between beryllium(II) and 2-cyano butadiene (2-CN BD), 3-cyano propene (3-CN P), and simpler models with two separate fragments; acrylonitrile and ethylene. Interactions between beryllium(II) and cyano nitrogen and terminal olefin in the models have been examined in terms of geometrical changes, distribution of charge over the entire π-system, and rehybridization of vinyl carbon orbitals. NMR shieldings and vibrational frequencies probed charge centers and strength of interactions. The six-membered cyclic complexes have planar structures with the rehybridized carbon slightly out of plane (16° in 2-CN BD). G3 results show that in 2-CN BD complex participation of vinyl carbon further stabilizes the cyclic adduct by 16.3 kcal mol(-1), whereas, in simpler models, interaction between beryllium(II) and acetonitrile is favorable by 46.4 kcal mol(-1) compared with that of ethylene. The terminal vinyl carbon in 2-CN BD rehybridizes to sp (3) with an increase of 7 % of s character to allow interaction with beryllium(II). G4 calculations show that the Be(II) and 2-CN BD complex is more strongly bound than those with Mg(II) and Ca(II) by 98.5 and 139.2 kcal mol(-1) (-1), respectively. QST2 method shows that the cyclic and acyclic forms of Be(II)-2-CN BD complexes are separated by 12.3 kcal mol(-1) barrier height. Overlap population analysis reveals that Ca(II) can be discriminated based on its tendency to form ionic interaction with the receptor models.
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http://dx.doi.org/10.1007/s00894-014-2533-9DOI Listing
December 2014

Rational design of carbonitrile-carboxaldehyde cation receptor models: probing the nature of the heteroatom-metal interaction.

J Mol Model 2014 Sep 23;20(9):2428. Epub 2014 Aug 23.

University of Malaya, Kuala Lumpur, Malaysia.

In this work, hybrid functional and G4 methods were employed in the rational design of carbonitrile-carboxaldehyde receptor models for cation recognition. Electron-sharing and ionic interactions between the models and the cations were analyzed utilizing the concepts of overlap population, atomic valence, electrostatic potential, and CHELPG charge in order to elucidate the nature of the heteroatom-metal interaction, the N versus O disparity, and the effect of pH. Receptor fragment models from ionomycin were employed to rationalize the selection of receptor models for discriminating group I cations and enhancing the selectivity for Mg(II) rather than Ca(II), and to examine the effects of keto-enol forms and negatively charged sites. The changes in geometries, overlap population, metal valence, and CHELPG charge upon solvation in heptane medium as compared to the gas phase were negligible. The optimized geometries reveal that the interaction between group II cations and the keto, enol, and enolate forms of 2-cyanoethanal causes 12 % bending of the C-C-N angle from linearity. Overlap populations show that the electron-sharing interaction favors group II cations but that the same mechanism allows Li(I) to compete. The total spin of Li(I) is 17 % greater than that of Ca(II), but the G4 binding energies of the two are separated by more than 50 kcal/mol, favoring group II cations, which may eliminate interference from Li(I). 1,2-Dicyanoethylene, which has only one form, shows similar characteristics. CHELPG analysis shows that Mg(II) transfers 25 and 18 % of its positive charge to 2-cyanoethanal enolate and 1,2-dicyanoethylene, respectively. Hydrogen atoms receive most of the positive charge in both receptors, but the N-termini exhibit strikingly different characteristics. Electrostatic potential contour profiles were found to be in good agreement with the atomic charge distributions. The application of uncharged 1,3-dicarbonyl and 2-cyanocarbonyl receptors and a judicious choice of polymeric membrane that suppresses the Hofmeister effect should lead to high selectivity for magnesium, whereas the utilization of multiple negatively charged ionophores should result in selectivity for calcium.
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http://dx.doi.org/10.1007/s00894-014-2428-9DOI Listing
September 2014

Does cation break the cyano bond? A critical evaluation of nitrile-cation interaction.

J Mol Model 2014 May 27;20(5):2219. Epub 2014 Apr 27.

Department of Chemistry, Faculty of Science Building, University of Malaya, 50603, Kuala Lumpur, Malaysia,

DFT and G4 results reveal that cations display the following trends in imparting its positive charge to acrylonitrile; H⁺ > Li⁺ > Na⁺ > K⁺ for group I and Be²⁺ > Mg²⁺ > Ca²⁺ for group II. Solvation by water molecules and interaction with cation make the cyano bond more polarized and exhibits ketene-imine character. Bond order in nitrile-cation complexes has been predicted based on the s character of the covalent bond orbitals. Mulliken, CHELPG, and NPA charges are in good agreement in predicting positive charge buildup and GIAO nuclear deshileding on C1. G4 enthalpies show that Mg²⁺ is more strongly bound to acrylonitrile than to acetonitrile by 3 kcal mol⁻¹, and the proton affinity of the former is higher by 0.8 kcal mol⁻¹. G4 enthalpies of reductions support prior experimental observation that metalated conjugated nitriles show enhanced reactivity toward weak nucleophiles to afford Michael addition products.
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http://dx.doi.org/10.1007/s00894-014-2219-3DOI Listing
May 2014

Titanium (III) cation selective electrode based on synthesized tris(2pyridyl) methylamine ionophore and its application in water samples.

Sci Rep 2014 Apr 11;4:4664. Epub 2014 Apr 11.

Chemistry Department, Faculty of Science, University Malaya, 50603 Kuala Lumpur, Malaysia.

The introduction of low detection limit ion selective electrodes (ISEs) may well pave the way for the determination of trace targets of cationic compounds. This research focuses on the detection of titanium (III) cation using a new PVC-membrane sensor based on synthesized tris(2pyridyl) methylamine (tpm) ionophore. The application and validation of the proposed sensor was done using potentiometric titration, inductively coupled plasma atomic emission spectrometry (ICP-AES), and atomic absorption spectrometry (AAS). The membrane sensor exhibited a Nernstian response to the titanium (III) cation over a concentration range of 1.0 × 10(-6)-1.0 × 10(-2) M and pH range from 1-2.5. The Nernstian slope, the lower of detection (LOD), and the response time (t95%) of the proposed sensor were 29.17 ± 0.24 mV/dec, 7.9 × 10-7 M, and 20 s, respectively. The direct determination of 4-39 μg/ml of titanium (III) standard solution showed an average recovery of 94.60 and a mean relative standard deviation of 1.8 at 100.0 μg/ml. Finally, the utilization of the electrodes as end-point indicators for potentiometric titration with EDTA solutions for titanium (III) sensor was successfully carried out.
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http://dx.doi.org/10.1038/srep04664DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3983601PMC
April 2014

G3 assisted rational design of chemical sensor array using carbonitrile neutral receptors.

Sensors (Basel) 2013 Oct 14;13(10):13835-60. Epub 2013 Oct 14.

Department of Chemistry, Faculty of Science Building, University of Malaya, Kuala Lumpur 50603, Malaysia.

Combined computational and experimental strategies for the systematic design of chemical sensor arrays using carbonitrile neutral receptors are presented. Binding energies of acetonitrile, n-pentylcarbonitrile and malononitrile with Ca(II), Mg(II), Be(II) and H⁺ have been investigated with the B3LYP, G3, CBS-QB3, G4 and MQZVP methods, showing a general trend H⁺ > Be(II) > Mg(II) > Ca(II). Hydrogen bonding, donor-acceptor and cation-lone pair electron simple models were employed in evaluating the performance of computational methods. Mg(II) is bound to acetonitrile in water by 12.5 kcal/mol, and in the gas phase the receptor is more strongly bound by 33.3 kcal/mol to Mg(II) compared to Ca(II). Interaction of bound cations with carbonitrile reduces the energies of the MOs involved in the proposed σ-p conjugated network. The planar malononitrile-Be(II) complex possibly involves a π-network with a cationic methylene carbon. Fabricated potentiometric chemical sensors show distinct signal patterns that can be exploited in sensor array applications.
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http://dx.doi.org/10.3390/s131013835DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3859094PMC
October 2013

Conductance studies on complex formation between c-methylcalix[4]resorcinarene and titanium (III) in acetonitrile-H₂O binary solutions.

Molecules 2013 Sep 27;18(10):12041-50. Epub 2013 Sep 27.

Food Quality and Safety Research Department, Food Science and Technology Research Institute, ACECR Mashhad Branch, 91775-1376 Mashhad, Iran.

Calixresorcinarenes have proved to be unique molecules for molecular recognition via hydrogen bonding, hydrophobic and ionic interactions with suitable substrates such as cations. The study of the interactions involved in the complexation of different cations with calixresorcinarenes in solvent mixtures is important for a better understanding of the mechanism of biological transport, molecular recognition, and other analytical applications. This article summarizes different aspects of the complexes of the Ti(3+) metal cation with c-methylcalix[4]resorcinarene (CMCR) as studied by conductometry in acetonitrile (AN)-water (H₂O) binary mixtures at different temperatures. Conductance data show that the metal cation/ligand (ML) stoichiometry of the complexes in solution is 1:1 in all cases. Non-linear behaviour was observed for the variation of logKf of the complexes vs. the composition of the binary solvent mixtures. Selectivity of CMCR for the Ti(3+) cation is sensitive to solvent composition; in some cases and at certain compositions of the mixed solvent systems, the selectivity order is changed. Values of thermodynamic parameters (ΔH(c)(0), ΔS(c)(0)) for formation of the CMCR-Ti(3+) complexes in AN-H₂O binary systems were obtained from the temperature dependence of stability constants, and the results show that the thermodynamics of complexation reactions are affected by the nature and composition of the mixed solvents.
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http://dx.doi.org/10.3390/molecules181012041DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6270418PMC
September 2013

Synthesis and antibacterial evaluation of some novel imidazole and benzimidazole sulfonamides.

Molecules 2013 Sep 26;18(10):11978-95. Epub 2013 Sep 26.

Chemistry Department, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia.

Several new substituted sulfonamide compounds were synthesized and their structures were confirmed by ¹H-NMR, ¹³C-NMR, FT-IR, and mass spectroscopy. The antibacterial activities of the synthesized compounds were screened against standard strains of six Gram positive and four Gram negative bacteria using the microbroth dilution assay. Most of the compounds studied showed promising activities against both types of bacteria.
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http://dx.doi.org/10.3390/molecules181011978DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6270528PMC
September 2013

Study of contaminant transport at an open-tipping waste disposal site.

Environ Sci Pollut Res Int 2013 Jul 5;20(7):4689-710. Epub 2013 Jan 5.

Department of Chemistry, University of Malaya, Kuala Lumpur 50603, Malaysia.

Field and laboratory studies were conducted to estimate concentration of potential contaminants from landfill in the underlying groundwater, leachate, and surface water. Samples collected in the vicinity of the landfill were analyzed for physiochemical parameters, organic contaminants, and toxic heavy metals. Water quality results obtained were compared from published data and reports. The results indicate serious groundwater and surface water contamination in and around the waste disposal site. Analysis of the organic samples revealed that the site contains polychlorinated biphenyls and other organo-chlorine chemicals, principally chloro-benzenes. Although the amount of PCB concentration discovered was not extreme, their presence indicates a potentially serious environmental threat. Elevated concentrations of lead, copper, nickel, manganese, cadmium, and cobalt at the downgradient indicate that the contamination plume migrated further from the site, and the distribution of metals and metals containing wastes in the site is nonhomogeneous. These results clearly indicate that materials are poorly contained and are at risk of entering the environment. Therefore, full characterization of the dump contents and the integrity of the site are necessary to evaluate the scope of the problem and to identify suitable remediation options.
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http://dx.doi.org/10.1007/s11356-012-1423-xDOI Listing
July 2013

N,N'-{[Ethane-1,2-diylbis(-oxy)]bis-(ethane-2,1-di-yl)}bis-(4-methyl-benzene-sulfonamide).

Acta Crystallogr Sect E Struct Rep Online 2012 Jul 2;68(Pt 7):o1983. Epub 2012 Jun 2.

Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.

The asymmetric unit of the title compound, C(20)H(28)N(2)O(6)S(2), contains one half-mol-ecule, related to the other half by a twofold rotation axis. The two aromatic rings of the mol-ecule make a dihedral angle of 50.91 (7)°. The O-CH(2)-CH(2)-O and N-CH(2)-CH(2)-O fragments both adopt gauche conformations, with torsion angles of 76.0 (4) and 70.4 (3)°, respectively. In the crystal, adjacent mol-ecules are linked through N-H⋯O hydrogen bonds into chains along the a-axis direction. The chains are further connected via C-H⋯O inter-actions into a two-dimensional supra-molecular network in the ac plane.
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http://dx.doi.org/10.1107/S1600536812024324DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3393259PMC
July 2012

tert-Butyl 2-(1H-benzimidazol-1-yl)acetate.

Acta Crystallogr Sect E Struct Rep Online 2012 Mar 4;68(Pt 3):o571. Epub 2012 Feb 4.

Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.

In the title compound, C(13)H(16)N(2)O(2), the planes of the benzimidazole ring system and the acetate O-C=O fragment make a dihedral angle of 84.5 (3)°. In the crystal, mol-ecules are connected through C-H⋯N hydrogen bonds to form infinite chains in the [-110] direction.
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http://dx.doi.org/10.1107/S1600536812002814DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3297298PMC
March 2012

Inclusion controlled lanthanide-imidazolium functionalised carboxylate complexation.

Dalton Trans 2012 Apr 8;41(16):4884-9. Epub 2012 Mar 8.

Chemistry Department, Faculty of Science, University of Malaya, 50603 Kuala Lumpur, Malaysia.

Imidazolium functionalized carboxylic acid forms a multi-component material with p-sulfonatocalix[4]arene and aquated lanthanide ions, stabilising dinuclear metal complexes for Y(3+) and Gd(3+). These have the simplest binding of two bridging carboxylates between the two metal centres (Y(3+)), or the same arrangement along with the simplest binding of one carboxylate bridging two metal ions for the larger metal ion (Gd(3+)).
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http://dx.doi.org/10.1039/c2dt12410fDOI Listing
April 2012

tert-Butyl 2-(1H-imidazol-1-yl)acetate.

Acta Crystallogr Sect E Struct Rep Online 2012 Feb 18;68(Pt 2):o445. Epub 2012 Jan 18.

Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia.

In the title compound, C(9)H(14)N(2)O(2), the imidazole ring and the acetate O-C=O plane make a dihedral angle of 80.54 (12)°. In the crystal, mol-ecules are connected via pairs of C-H⋯O hydrogen bonds, forming centrosymmetric dimers.
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http://dx.doi.org/10.1107/S1600536812001067DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3275200PMC
February 2012

N,N'-[1,4-Phenyl-enebis(methyl-ene)]bis-(N,N-diethyl-ethanaminium) dibromide.

Acta Crystallogr Sect E Struct Rep Online 2012 Feb 11;68(Pt 2):o369. Epub 2012 Jan 11.

In the crystal structure of the title compound, C(20)H(38)N(2) (2+)·2Br(-), the centroid of the aromatic ring is located on an inversion center, so that the asymmetric unit consists of one-half mol-ecule of the dication and one bromide anion. C-H⋯Br inter-actions connect the two components into a three-dimensional network. An intra-molecular C-H⋯π inter-action is also observed.
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http://dx.doi.org/10.1107/S1600536812000141DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3275048PMC
February 2012