Reductive alkylation of lipase

Candida rugosa lipase was modified via reductive alkylation to increase its hydrophobicity to work better in organic solvents. The free amino group of lysines was alkylated using propionaldehyde with different degrees of modification obtained (49 and 86%). Far-ultraviolet circular dichroism (CD) spectroscopy of the lipase in aqueous solvent showed that such chemical modifications at the enzyme surface caused a loss in secondary and tertiary structure that is attributed to the enzyme unfolding. Using molecular modeling, we propose that in an aqueous environment the loss in protein structure of the modified lipase is owing to disruption of stabilizing salt bridges, particularly of surface lysines. Indeed, molecular modeling and simulation of a salt bridge formed by Lys-75 to Asp-79, in a nonpolar environment, suggests the adoption of a more flexible alkylated lysine that may explain higher lipase activity in organic solvents on alkylation.     

Determination of rain attenuation parameters for free space optical link in tropical rain

Free space optics (FSO) is a promising communication technique for various types of services in the optical access network. Single beam FSO system in tropical rainy weather is vulnerable to atmospheric rain attenuation, so it is necessary to have precise power law parameters of rain attenuation in tropical regions. In this study, the power law parameters k, and α are estimated as 2.03 and 0.74, respectively for the FSO applications in tropical South-East Asian weather. These parameters were evaluated by using least square mean equation (LSME) method with Levenberg–Marquardt optimization based on the one year collected heavy rain data. The obtained parameter values for tropical weather are contributed to improve link performance for high-speed networks.     

Phase Behavior and Formulation of Palm Oil Esters o/w Nanoemulsions Stabilized by Hydrocolloid Gums for Cosmeceuticals Application

Palm oil esters (POEs) are wax esters derived from palm oil and cis-9-octadecen-1-ol. The excellent wetting behaviour of the esters without the oily feel make them have great potentials in the manufacture of cosmeceutical and pharmaceutical products. However, little is known about their phase behaviors in ternary systems. The purpose of this investigation was to construct phase diagram of the POEs and mixed surfactants and to consequently select nanoemulsions composition for further studies. The preparation and characterization of oil-in-water nanoemulsions stabilized by hydrocolloid gums were then studied. Two types of nonionic surfactants were selected, namely Tween 80 (T80) and Span 80 (S80). Ternary phase diagram of POEs:Tocotrienol/T80:S80 (80:20)/water system was constructed at 25.0 ± 0.5°C. The emulsification properties of 2 hydrocolloids gum (xanthan gum, carbopol ultrez 20 copolymer) were investigated. Gum dispersions were prepared in water (0.8%) and emulsified with 30% oil using a Polytron homogenizer. The flow curve of the emulsions always exhibited shear thinning behavior and obeys the power law viscosity. The emulsions with carbopol ultrez 20 copolymer was the most stable emulsions which composed of very small oil droplets (50% < 142.43 nm) with a narrow size distribution.     

Utilization of stimulated Raman Scattering as secondary pump on hybrid remotely-pump l-band Raman/erbium-doped fiber amplifier

An L-band remotely-pumped erbium-doped fiber amplifier incorporating a secondary pumping scheme utilizing stimulated Raman Scattering (SRS) was demonstrated. 1423 nm Raman laser was employed to generate SRS which became the secondary pump source. The amplifier displayed excellent gain of up to 27.3 dB at 1570 nm for −30 dBm input. Noise figures were also kept to a minimum, with the highest figure measured at 11 dB which was influenced by imperfection of the C/L coupler utilized in this architecture. Overall transmission performance was measured as well and demonstrated an encouraging outcome with gain as high as 24 dB while the noise figure was maintained at about 11 dB. The L-band signal amplification was also contributed by the stimulated Raman scattering along the transmission fiber. The outcome of this study emphasized the feasibility of secondary pumping scheme using SRS in L-band gain enhancement.     

Multi-wavelength Brillouin-Raman ring-cavity fiber laser with 22-GHz spacing

We experimentally demonstrate a multi-wave length Brillouin-Raman fiber laser configured in a ring-cavity resonator. Interactions between stimulated Brillouin scattering and Raman amplification in a dispersion compensating fiber, attributed to the generation of 16 output channels at injected Raman pump unit power of 650 mW and Brillouin pump power of 2.0 mW. The first output channel has a peak power of 14.8 mW. By discriminating the even-order Brillouin Stokes signals from circulating in the resonator, the generated output channels were found to have wavelength spacing of ∼22 GHz. The output channels were also found to have average optical signal-to-noise ratio value of 11.7 dB.     

The sound speed in southern deepwater zone of the Caspian Sea,off Anzali Port

Sound velocity determination in seawater is a key component of modern hydrographic surveying; however, little data exists on sound velocity characteristics of the southern Caspian Sea. Hence, a study was undertaken in 2008 to examine the seasonal variability of sound speed in deep-waters of the South Caspian Sea near the Iranian coast. The seasonal cycle of seawater temperature and thermal stratification in the Caspian Sea water created a wide range of spatial and temporal changes of sound speed with relevant differences between shallow water (over the continental shelf) and deep-water area. The collected data showed that seasonal variations of the sound speed were most important in the upper 100 m water depth, while below this level that is in deepwater the changes were small. The maximum values of sound speed were observed at the surface in midsummer around 1517–1519 m s⁻¹ over the continental shelf while the speed of sound was about 1453 m s⁻¹ between 450–470 m depths with no major seasonal variations. Variations in vertical structure of the sound speed were in agreement with temperature changes, while effects of the salinity on the sound speed were little.     

Fabrication and characterization of polymer thermo-optic switch based on mmi coupler

The 2 × 2 polymer thermo-optic switch based on MMI coupler is realized. This device is fabricated using standard fabrication techniques such as coating, photolithography, and dry etching. A crosstalk level of −36.2 dB is achieved at cross and bar states. A power consumption of 1.85 mW is applied to change the state of the switch from the cross to the bar state. A switching time of less than 0.7 ms is traced to change a state of the realized switch.     

Thermal and kinetic studies of epoxidized natural rubber in lithium salts-epoxidized natural rubber polymer electrolytes

The thermal and kinetic studies of epoxidized natural rubber (ENR) and its polymer electrolytes, LiX/ENR PEs, (where X = ClO ₄ ^? , CF₃SO ₃ ^? , COOCF ₃ ^? , I^?, and BF ₄ ^? ) were carried out using thermogravimetric analysis at different heating rates. The thermal behaviors for LiX/ENR PEs are closely related to the morphology and interactions between the LiX and ENR chains. The LiCF₃SO₃, LiCOOCF₃, and LiI form pseudo-crosslinking within the ENR; their thermal behavior resembled purified ENR. The LiClO₄ tends to form aggregates within the ENR. This phenomenon has promoted a much earlier decomposition of epoxide in the ENR. The occurrence of ring-opening and complexation or cross-linking reactions in and between the ENR chains in the LiBF₄/ENR has produced a thermally stable macrostructure. The activation energy for the thermal degradation (E _d) of purified ENR was 239.8 and 239.9 kJ mol^?1 using Kissinger and FWO methods, respectively. According to the Coats–Redfern method, the degradation mechanism of purified ENR follows the F₁ type model, while the Criado method revealed that the degradation starts with F₁ followed by D₃ type models. The E _d for LiX/ENR (X = COOCF ₃ ^? , CF₃SO ₃ ^? , I^?, and BF ₄ ^? ) PE’s obtained via the Kissinger method are 258.5, 257.0, 251.0, and 198.9 kJ mol^?1, respectively, and the corresponding E _d values obtained by FWO are 236.0, 223.6, 349.7, and 206.6 kJ mol^?1, respectively. The degradation of ENR in these PEs followed the D₃ type model. However, for LiClO₄/ENR, the presence of two distinct degradations of ENR gave two E _d values. These are 174.5 and 234.7 kJ mol^?1 using Kissinger and 117.8 and 293.6 kJ mol^?1 using FWO method. The degradation mechanism of ENR in the LiClO₄/ENR PE was similar to purified ENR that is F₁ followed by D₃ type models.     

The properties of Pd/Au bimetallic colloidal catalysts stabilized by chitosan and prepared by simultaneous and stepwise chemical reduction of the precursor ions

Bimetallic Pd/Au nanoparticle catalysts were prepared with chitosan as a stabilizer. The preparation procedure included mixing or stepwise adding palladium and gold ions in various molar ratios followed by simultaneous or stepwise reduction using either methanol or sodium borohydride (nb) as reducing agents. TEM and UV-Vis characterization showed that the particle size of bimetallic Chi-Pd/Au prepared by simultaneous reduction was smaller than that of the samples prepared by stepwise reduction methods. The particle size varied in the 1 to 24 nm range at all Pd/Au molar ratios of bimetallic compositions. Sodium borohydride was the most effective reducing agent for the preparation of bimetallic Chi-Pd_coreA_ushell by the stepwise reduction. The catalytic activities of Chi-Pd/Au prepared by either simultaneous or stepwise reductions were generally higher than those of the respective monometallic systems whereas the most active catalysts were prepared by the simultaneous reduction. Shielding the palladium metal colloid with gold sol led to the decrease in catalytic activity. The turnover frequencies (TOFs) for Chi-Pd/Au-me in catalytic hydrogenation of 1-octene were as high as 20.855 and 89.336 for monometallic and bimetallic catalysts respectively. TOFs for Chi-Pd/Au-nb were in the region between 2.978 and 87.429. The core-shell and alloy formation of the bimetallic Chi-Pd/Au were inferred from the particle size measurements and evaluation of catalytic activity.