Ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction for the determination of cadmium in water samples: Optimization using response surface methodology

A sensitive, simple, and rapid method is developed for ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction (IPSA-DLLME) and flame atomic absorption spectrometric determination of cadmium in water samples. In this procedure, trace amounts of Cd²⁺ were converted to CdI ₄ ^2– , and after addition of a tetrabutylammonium bromide (TBAB) solution as cationic surfactant the analyte was transformed to the ion-pair state. This cadmium species was extracted by fast injection of a solution containing 200 μL of chloroform and 800 μL of methanol as extraction and disperser solvents, respectively. The pH of the sample solution, concentration of iodide, TBAB amount, and the extractant volume were optimized using a 27-run Box–Behnken design with a triplicate central point. Under the optimized conditions, the calibration curve was linear in the range 1–200 μg L^–1 (R ² = 0.9959); with the detection limit (signal/noise = 3) of 0.28 μg L^–1. The relative standard deviations (RSD) for eight runs (Cd²⁺ = 10 μg L^–1) and enrichment factor were found to be 3.04 % and 50, respectively.     

Hydrophilic alginate based multidentate biopolymers for surface modification of CdS quantum dots

We report that sodium alginate and its graft-copolymers with (2-dimethylaminoethyl) methacrylate may attach to the surface of colloidal CdS-thioglycerol quantum dots (QDs) via a ligand exchange process and result in water-soluble and highly stable QD supramolecules. Optical properties of modified QDs in water showed that the emission intensity of QDs was still high after surface passivation.     

Reinvestigation of intramolecular hydrogen bond in malonaldehyde derivatives: An ab initio,AIM and NBO study

The RAHB systems in malonaldehyde and its derivatives at MP2/ 6‐311++G(d,p) level of theory were studied and their intramolecular hydrogen bond energies by using the related rotamers method was obtained. The topological properties of electron density distribution in O? H···O intramolecular hydrogen bond have been analyzed in term of quantum theory of atoms in molecules (QTAIM). Correlations between the H‐bond strength and topological parameters are probed. The results of QTAIM clearly showed that the linear correlation between the electron density distribution at HB critical point and RAHB ring critical point with the corresponding hydrogen bond energies was obtained. Moreover, it was found a linear correlation between the electronic potential energy density, V(r_cp), and hydrogen bond energy which can be used as a simple equation for evaluation of HB energy in complex RAHB systems. Finally, the similar linear treatment between the geometrical parameters, such as O···O or O? H distance, and Lp(O)→σ*_OH charge transfer energy with the intramolecular hydrogen bond energy is observed. © 2010 Wiley Periodicals, Inc., Int J Quantum Chem, 2011     

N?H···S and S?H···N intramolecular hydrogen bond in β‐thioaminoacrolein: A quantum chemical study

The conformational study of β‐thioaminoacrolein was performed at various theoretical levels, HF, B3LYP, and MP2 with 6‐311++G(d,p) basis set, and the equilibrium conformations were determined. To have more reliable energies, the total energies of all conformers were recomputed at high‐level ab initio methods, G2MP2, G3, and CBS‐QB3. According to these calculations, the intramolecular hydrogen bond is accepted as the origin of conformational preference in thialamine (TAA) and thiolimine groups. The hydrogen bond strength in various resonance‐assisted hydrogen bond systems was evaluated by HB energy, geometrical parameters, topological parameters, and charge transfers corresponding to orbital interactions. Furthermore, our results reveal that the TAA tautomer has extra stability with respect to the other tautomers. The population analyses of the possible conformations by NBO predict that the origin of this preference is mainly due to the π‐electron delocalization in framework of TAA forms, especially usual π_C?C → π*_C?S and Lp (N) → π*_C?C charge transfers. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Reverse nonequilibrium molecular dynamics simulation of thermal conductivity in nanoconfined polyamide-6,6

A new molecular dynamics simulation method, with coupling to external baths, is used to perform equilibrium simulations on polyamide-6,6 trimers nanoconfined between graphene surfaces, in equilibrium with the bulk polymer. The method is coupled with the reverse nonequilibrium molecular dynamics simulation technique to exchange heat in the direction normal to the surfaces. To be able to study the effect of confinement on the heat conductance in nanoconfined pores, in this work a number of simulations on systems with different pore sizes are done. It is concluded that the coefficient of heat conductivity depends on the degree of polymer layering between the surfaces and on the pore width. Our results further indicate a considerable temperature drop at the interface between the surfaces and polymer. The calculated Kapitza lengths depend on the intersurface distance and on the layering of the polymer nanoconfined between the surfaces.     

Dynamics of tractor lateral overturn on slopes under the influence of position disturbances (model development)

In order to investigate the effects of forward speed, ground slope and wheel–ground friction coefficient on lateral stability of tractor at the presence of position disturbances, a tractor dynamic model was developed. In this model two types of instability were considered: instability due to overturn and skid and for each case the stability index was determined. Different geometries and mass specifications of tractor MITSUBISHI-2501D were used to examine the model. According to the results of this model forward speed and ground slope had a reverse effect on all stability indexes. Moreover stability of this tractor was more affected by tractor skidding than overturning. Therefore to improve the overall stability of this tractor, preference should be on increasing the tractor stability index derived from skid dynamics of tractor.     

The Effect of Reservoir Wettability on the Production Characteristics of the VAPEX Process: An Experimental Study

The impact of fractional wettability on the production characteristics of a VAPEX process at the macroscale was investigated. Conventional VAPEX experiments were conducted in a 220 Darcy random packing of glass beads in a rectangular physical model and n-pentane was used to recover the Cold Lake bitumen from the oil-saturated model in the absence of connate water. The composition of oil-wet beads in the packed bed was altered from completely water-wet beads to completely oil-wet beads at different proportions of oil-wet beads mixed with water-wet beads. A substantial increase (about 40%) in the production rate of live oil was observed during the VAPEX process when the wettability of the porous packing was entirely oil-wet beads. A critical oil-wet fraction of 0.66 was found for the heterogeneous packing of water-wet and oil-wet beads of similar size distribution. Above this critical composition, the live oil production rate was not affected by further increase in the proportion of the oil-wet beads. It is believed that above this critical composition of the oil-wet beads, the crevice flow process is dominated by the continuity of higher conductivity live oil films between particles through the oil-wet regions. Below this critical composition, the live oil production rate increased linearly with the fraction of the oil-wet beads in the packing. The oil-wet regions favor the live oil drainage compared to that of the water-wet regions as they enhance the rate of imbibition of the live oil from the oil-filled pores to the vacated pores near the nominal VAPEX interface. These two factors enhance the live oil production rate during the VAPEX process. The solvent content of the live oil, the solvent-to-oil ratio (SOR), and the residual oil saturation did not correlate strongly with the proportion of the oil-wet beads in the packing. The average solvent content of the live oil and the residual oil saturation were measured to be 48% by weight and 7% by volume respectively.     

Spectral and thermal studies of divalent transition metal with indole-2-carboxylic acid and 4-substituted hydrazinethiocarbamide

Ternary complexes of Co(II), Ni(II) and Cu(II) with indole-2-carboxylic acid (A) and 4-substituted hydrazinethiocarbamide (L) [4-phenylhydrazinethiocarbamide (L(1)), 4-benzylhydrazinethiocarbamide (L(2)) and 4-(2-propenyl)hydrazinethiocarb-amide (L(3)) were prepared. The structure of the complexes was characterized by microchemical analysis, molar conductance, electronic, IR, (1)H-NMR, mass spectra as well as thermogravimetric studies. An octahedral structure is suggested for Co(II), Ni(II) and Cu(II) ternary complexes.     

Ultrafast MRI of the fetus: an increasingly important tool in prenatal diagnosis of congenital anomalies

Objective

To demonstrate the additional utility of ultrafast magnetic resonance imaging (MRI) of the fetus in the evaluation of sonographically detected or equivocal fetal congenital anomalies.

Material and Methods

Twenty five pregnant women with ultrasound detected fetal congenital anomalies underwent ultrafast fetal MRI.

Results

MRI findings altered the diagnosis of two cases of giant arachnoid cyst and sizable interhemispheric cyst associated with agenesis of the corpus callosum. MRI added additional findings of occult spinal diastematomyelia in two out of four cases of Chiari/meningocele malformation. MRI revealed impaired sulcation and unilateral cleft palate in suspected case of Walker-Warburg syndrome. In the remaining 18 cases MRI confirmed the diagnosis of Meckel–Gruber syndrome in three cases, hydronephrosis in six cases, cerebral ventriculomegaly in five cases, isolated omphalocele in three cases and findings suggestive of aneuploidy in the last case.

Conclusion

Ultrasound is the screening method of choice for evaluation of the fetus. Ultrafast MRI is a complementary adjunctive modality with excellent tissue contrast that can image the fetus in multiple planes and add information in sonographically detected or equivocal congenital anomalies that may be significant to establish definitive accurate diagnosis and hence adequate management and counseling.