Amino‐functionalised mesoporous silica microspheres for immobilisation of Candida antarctica lipase B – application towards greener production of 2,5‐furandicarboxylic acid

In the present study, amino‐functionalised mesoporous silica microspheres were utilised as support for the covalent immobilisation of Candida antarctica lipase B (CaLB) for the subsequent production of 2,5‐furandicarboxylic acid (FDCA) from 2,5‐diformylfuran (DFF). Under the optimised operating conditions of pH 6.5, particle/enzyme ratio of 1.25:1.0 and glutaraldehyde concentration of 4 mM, a maximum CaLB immobilisation yield of 82.4% on silica microspheres was obtained in 12.25 h. The immobilised CaLB was used for the synthesis of alkyl esters, which were utilised along with hydrogen peroxide for FDCA synthesis. The biocatalytic conversion of 30 mM DFF dictated a 77–79% FDCA in 48 h at 30°C; where the turnover number and turnover frequency of immobilised CaLB were 6220.73 mol mol⁻¹ and 129.59 h⁻¹, respectively, for ethyl acetate, against 6297.65 mol mol⁻¹ and 131.2 h⁻¹, respectively, for ethyl butyrate. Upon examining the operational stability, the immobilised CaLB exhibited high stability till five cycles of FDCA production.Inspec keywords: mesoporous materials, organic compounds, biotechnology, silicon compounds, renewable materials, catalysis, catalysts, enzymes, thermal stability, biofuelOther keywords: FDCA production, amino‐functionalised mesoporous silica microspheres, greener production, 2,5‐furandicarboxylic acid, covalent immobilisation, 2,5‐diformylfuran, CaLB immobilisation, Candida antarctica lipase B immobilisation, ethyl butyrate, time 48.0 hour, temperature 30.0 degC, time 12.25 hour     

Dispersion compensation using only fiber Bragg gratings

Efficient and low cost dispersion compensation is necessary to achieve useful transmission distances in optical communication systems at bit rates above 10 Gb/s. In the paper, we present a novel method for dispersion compensation that uses three fiber gratings in series. This method eliminates the requirement for an optical circulator, commonly used in grating-based dispersion compensators. As a result, our device is inexpensive to fabricate and have a low insertion loss. We present a theoretical model that predicts how the efficiency of the device can be maximized. We also present experimental results showing complete dispersion compensation for 30-ps pulses, broadened to 67 ps by propagating through 10 km of standard, singlemode fiber     

Polymer nanochannels fabricated by thermomechanical deformation for single-molecule analysis

A simple method for fabricating nanoscale channels based on thermomechanical deformation of rigid polymer substrates is demonstrated. Polycarbonate preforms containing microchannels with cross-sectional dimensions on the order of tens of micrometers are controllably deformed to produce submicrometer dimensions. The reduced channel dimensions are achieved by heating the preform while applying a uniaxial tensile force to reduce channel cross sections through the Poisson effect. Nanochannels with circular or elliptical cross sections are defined by varying the channel position and preform geometry prior to deformation. Arrays of parallel nanochannels with critical dimensions down to 400 nm are described. Using the fabrication method, a nanochannel network is fabricated for the detection of single protein molecules via confocal fluorescence microscopy. The chip includes a detection channel with cross-sectional dimensions approaching the confocal volume dimensions of the detection optics and a larger adjacent reference channel used to optimize focusing. Detection of fluorescently labeled bovine serum albumin at 15 and 150 nM concentrations is presented, demonstrating the ability to perform single-molecule fluorescence measurements in polycarbonate chips using visible wavelengths for excitation and detection.     

Equilibrium studies for the adsorption of acid dye onto modified hectorite

The adsorption of Acid dye, C.I. Acid Red 151 from aqueous solution onto modified hectorite at different concentrations and pH has been studied. Hectorite clay has been modified using two cationic surfactants, cetyldimethylbenzylammonium chloride and cetylpyridinium chloride. Present experimental study shows that acidic pH favours enhanced adsorption. The adsorption isotherms are described by means of Langmuir and Freundlich isotherms. The adsorption capacity has been found to be 208.33 and 169.49 mg g(-1) for the modified cetyldimethylbenzylammonium chloride-hectorite (CDBA-hect) and cetylpyridinium chloride (CP-hect), respectively.     

Air quality monitoring in Chennai, India, in the summer of 2005

During the summer of 2005, concentrations of surface ozone (O(3)), oxides of nitrogen (NO(x)), respirrable suspended particulate matter (RSPM) and total suspended particulate matter (TSPM), relative humidity (RH), wind speed (WS) and wind direction (WD) were collected over successive periods of about 24 h at five sites. UV photometric ozone analyzer was used to measure the concentration of surface O(3). The study deals with the characteristics of hourly and daily mean surface O(3) under different climatic conditions, such as temperature, relative humidity, wind speed and wind direction and other pollutant concentrations. The maximum hourly O(3) concentration reached 53 ppb on 17th May. The ground-level O(3) concentration in Chennai varied between 2 and 53 ppb. The concentration of NO(x) and O(3) were below the prescribed limits. The TSPM values were exceeded the National Ambient Air Quality Standards (NAAQS) at Koyambedu, Mandaveli, Taramani and Vallalar Nagar study area.     

Surface ozone measurements at urban coastal site Chennai, in India

The present study was carried out to gain knowledge of current surface ozone concentrations and the effects of meteorological parameters in the highly populated urban area of Chennai, in South India. We have reported measurement results of surface ozone (O(3)) and meteorological parameters from 17th March to 10th October 2005. A photometric ozone analyzer continuously recorded the ozone concentrations at this site. The present study deals with the statistical characteristics of daily and monthly mean ozone levels under different meteorological conditions. The highest ozone concentrations were recorded in ESE-SE sectors. The monthly mean concentrations were higher in May (23+/-14 ppb) and lower in April at this site (10+/-8 ppb). The maximum hourly ozone concentration reached 69 ppb on 21st April.     

Electrocatalytic oxidation of ascorbic acid using a single layer of gold nanoparticles immobilized on 1,6-hexanedithiol modified gold electrode

This paper describes the electrocatalytic oxidation of ascorbic acid (AA) in phosphate buffer solution by the immobilized citrate capped gold nanoparticles (AuNPs) on 1,6-hexanedithiol (HDT) modified Au electrode. X-ray photoelectron spectrum (XPS) of HDT suggests that it forms a monolayer on Au surface through one of the two SH groups and the other SH group is pointing away from the electrode surface. The free SH groups of HDT were used to covalently attach colloidal AuNPs. The covalent attachment of AuNPs on HDT monolayer was confirmed from the observed characteristic carboxylate ion stretching modes of citrate attached with AuNPs in the infra-red reflection absorption spectrum (IRRAS) in addition to a higher reductive desorption charges obtained for AuNPs immobilized on HDT modified Au (Au/HDT/AuNPs) electrode in 0.1 M KOH when compared to HDT modified Au (Au/HDT) electrode. The electron transfer reaction of [Fe(CN)₆]^4−/3− was markedly hindered at the HDT modified Au (Au/HDT) electrode while it was restored with a peak separation of 74 mV after the immobilization of AuNPs on Au/HDT (Au/HDT/AuNPs) electrode indicating a good electronic communication between the immobilized AuNPs and the underlying bulk Au electrode through a HDT monolayer. The Cottrell slope obtained from the potential-step chronoamperometric measurements for the reduction of ferricyanide at Au/HDT/AuNPs was higher than that of bare Au electrode indicating the increased effective surface area of AuNPs modified electrode. The Au/HDT/AuNPs electrode exhibits excellent electrocatalytic activity towards the oxidation of ascorbic acid (AA) by enhancing the oxidation peak current to more than two times with a 210 mV negative shift in the oxidation potential when compared to a bare Au electrode. The standard heterogeneous electron transfer rate constant (k_s) calculated for AA oxidation at Au/HDT/AuNPs electrode was 5.4 × 10⁻³ cm s⁻¹. The oxidation peak of AA at Au/HDT/AuNPs electrode was highly stable upon repeated potential cycling. Linear calibration plot was obtained for AA over the concentration range of 1–110 μM with a correlation coefficient of 0.9950. The detection limit of AA was found to be 1 μM. The common physiological interferents such as glucose, oxalate ions and urea do not show any interference within the detection limit of AA. The selectivity of the AuNPs modified electrode was illustrated by the determination of AA in the presence of uric acid.     

Biological decolourization of C.I. Direct Black 38 by E. gallinarum

In the present study, an Enterococcus gallinarum strain was isolated from effluent treatment plant of a textile industry based on its ability to decolourize C.I. Direct Black 38 (DB38), a benzidine-based azo dye. Effects of dye concentration and medium composition on dye decolourization were studied. The strain was found to decolourize DB38 even under aerobic conditions. Kinetics of DB38 decolourization was also examined, and V(max) and K(s) of decolourization were found to be higher in Luria broth (12.8 mg l(-1)h(-1) and 490.6 mg l(-1)) than in minimal medium (4.09 mg l(-1)h(-1) and 161.84 mg l(-1)). However, decolourization rate/biomass was found to be higher in minimal medium than in Luria broth, indicating greater decolourization efficiency of biomass in the former. The study also revealed biodegradation of DB38 to benzidine and its further deamination to 4-aminobiphenyl (4-ABP) by the culture. Ammonia released during this process was used as nitrogen source for growth of the culture.     

Removal of Acid Violet 17 from aqueous solutions by adsorption onto activated carbon prepared from sunflower seed hull

The adsorption of Acid Violet 17 (AV17) was carried out using various activated carbons prepared from sunflower seed hull (SSH), an agricultural solid waste by-product. The effect of parameters such as agitation time, initial dye concentration, adsorbent dosage, pH and temperature were studied. The Langmuir and Freundlich isotherm models were applied and the Langmuir model was found to best report the equilibrium isotherm data. Langmuir adsorption capacity was found to be 116.27 mg/g. Kinetic data followed pseudo-second-order kinetics. Maximum colour removal was observed at pH 2.0. It was observed that the rate of adsorption improves with increasing temperature and the process is endothermic. The adsorbent surface was analysed with a scanning electron microscope. The results indicate that activated sunflower seed hull could be an attractive option for colour removal from dilute industrial effluents.