Modeling the adsorption of Cd(II) onto goethite in the presence of citric acid

The adsorption of cadmium onto goethite in the presence of citric acid was measured as a function of pH and cadmium concentration at 25 degrees C. Potentiometric titrations were also performed on the system. Cadmium adsorption onto goethite was enhanced above pH 4 in the presence of 50 microM, 100 microM and 1 mM citric acid. While there was little difference between the enhancements caused by 50 and 100 microM citric acid below pH 6, above pH 6 further enhancement is seen in the presence of 100 microM citric acid. When 1 mM citric acid was present, the enhancement of cadmium adsorption was greater below pH 6, with increased Cd(II) adsorption down to pH 3.5. However, above pH 6, 1 mM of citric acid caused slightly less enhancement than the lower citric acid concentrations. ATR-FTIR spectra of soluble and adsorbed citrate-cadmium species were measured as a function of pH. At pH 4.6 there was very little difference between the ternary Cd(II)-citric acid-goethite spectrum and the binary citric acid-goethite spectrum. However, spectra of the ternary system at pH 7.0 and 8.7 indicated the presence of additional surface species. Further analysis of the spectra suggested that these were metal-ligand outer-sphere complexes. Data from the adsorption experiments and potentiometric titrations of the ternary Cd(II)-citric acid-goethite system were fitted by an extended constant-capacitance surface complexation model. The spectroscopic data were used to inform the choice of surface species. Three reactions in addition to those for the binary Cd(II)-goethite and citric acid-goethite systems were required to describe all of the data. They were [formula in text], [formula in text], and [formula in text]. Neither the spectroscopy nor the modeling suggested the formation of a ternary inner-sphere complex or a surface precipitate under the conditions used in this study.     

Twist-bend nematics,liquid crystal dimers,structure–property relations

ABSTRACT

One of the current challenges in liquid crystal science is to understand the molecular factors leading to the formation of the intriguing twist-bend nematic phase (N_TB) and determine its properties. During our earlier hunt for the N_TB phase created on cooling directly from the isotropic phase and not the nematic phase, we had prepared 30 symmetric liquid crystal dimers. These had odd spacers and methylene links to the two mesogenic groups; desirable but clearly not essential features for the formation of the N_TB. Here, we report the phases that the dimers exhibit and their transition temperatures as functions of both the lengths of the spacer and the terminal chains. In addition we describe the transitional entropies, their optical textures, the X-ray scattering patterns and the ²H NMR spectra employed in characterising the phases. All of which may lead to important properties of the twist-bend nematic phase.     

Principles,methodologies, and applications of photon activation analysis: a review

This review describes the basic principles of photon activation analysis (PAA) and gives an extensive overview of its numerous applications. Uses of PAA for environmental, biological, geological, archeological, and forensic samples are reviewed. Both scientific and industrial applications of PAA are covered. Potential future uses of PAA are addressed.     

1-(1-Alkenyl)benzotriazoles: Novel α-Hydroxyacyl Anion Equivalents for the Synthesis of α-Hydroxy Ketones

α-Lithiated 1-(1-alkenyl)benzotriazoles, generated from the reactions of 1-(1-alkenyl)benzotriazoles with n-BuLi, react with a variety of electrophiles to afford α-substituted 1-(1-alkenyl)benzotriazoles which undergo epoxidation with m-CPBA followed by hydrolysis to give α-hydroxy ketones in good yields. Thus, 1-(1-alkenyl)benzotriazoles behave as α-hydroxyacyl anion equivalents.     

A Resin‐Linker‐Vector Approach to Radiopharmaceuticals Containing 18F: Application in the Synthesis of O‐(2‐[18F]‐Fluoroethyl)‐L‐tyrosine

A Resin‐linker‐vector (RLV) strategy is described for the radiosynthesis of tracer molecules containing the radionuclide ¹⁸F, which releases the labelled vector into solution upon nucleophilic substitution of a polystyrene‐bound arylsulfonate linker with [¹⁸F]‐fluoride ion. Three model linker‐vector molecules 7 a – c containing different alkyl spacer groups were assembled in solution from (4‐chlorosulfonylphenyl)alkanoate esters, exploiting a lipase‐catalysed chemoselective carboxylic ester hydrolysis in the presence of the sulfonate ester as a key step. The linker‐vector systems were attached to aminomethyl polystyrene resin through amide bond formation to give RLVs 8 a – c with acetate, butyrate and hexanoate spacers, which were characterised by using magic‐angle spinning (MAS) NMR spectroscopy. On fluoridolysis, the RLVs 8 a , b containing the longer spacers were shown to be more effective in the release of the fluorinated model vector (4‐fluorobutyl)phenylcarbamic acid tert‐butyl ester ( 9 ) in NMR kinetic studies and gave superior radiochemical yields (RCY≈60 %) of the ¹⁸F‐labelled vector. The approach was applied to the synthesis of the radiopharmaceutical O‐(2‐[¹⁸F]‐fluoroethyl)‐L ‐tyrosine ([¹⁸F]‐FET), delivering protected [¹⁸F]‐FET in >90 % RCY. Acid deprotection gave [¹⁸F]‐FET in an overall RCY of 41 % from the RLV.     

Compressive Mass Analysis on Quadrupole Ion Trap Systems

Conventionally, quadrupole ion trap mass spectrometers eject ions of different mass-to-charge ratio (m/z) in a sequential fashion by performing a scan of the rf trapping voltage amplitude. Due to the inherent sparsity of most mass spectra, the detector measures no signal for much of the scan time. By exploiting this sparsity property, we propose a new compressive and multiplexed mass analysis approach—multi Resonant Frequency Excitation (mRFE) ejection. This new approach divides the mass spectrum into several mass subranges and detects all the subrange spectra in parallel for increased mass analysis speed. Mathematical estimation of standard mass spectrum is demonstrated while statistical classification on the parallel measurements remains viable because of the sparse nature of the mass spectra. This method can reduce mass analysis time by a factor of 3–6 and increase system duty cycle by 2×. The combination of reduced analysis time and accurate compound classification is demonstrated in a commercial quadrupole ion trap (QIT) system.

The products of the reaction of the hydroxyl radical with 2-ethoxyethyl acetate

The gas-phase reaction products of the OH radical with 2-ethoxyethyl acetate (EEA, CH₃C(O)OCH₂CH₂OCH₂CH₃) have been investigated. 1,2-Ethanediol acetate formate (EAF, CH₃C(O)OCH₂CH₂OC(O)H) and ethyl formate (EF, HC(O)OCH₂CH₃) were identified as the two main products. A third product, ethylene glycol diacetate (EGD, CH₃C(O)OCH₂CH₂OC(O)CH₃), was also observed. EAF, EF, and EGD formation yields were determined to be 0.37 ± 0.03 and 0.328 ± 0.018 and 0.040 ± 0.005, respectively. Proposed reaction mechanisms are discussed and compared with these data. © 1996 John Wiley & Sons, Inc.     

Modal parameter identification using the log decrement method and band-pass filters

This paper presents a time-domain technique for identifying modal parameters of test specimens based on the log-decrement method. For lightly damped multidegree-of-freedom or continuous systems, the conventional method is usually restricted to identification of fundamental-mode parameters only. Implementation of band-pass filters makes it possible for the proposed technique to extract modal information of higher modes. The method has been applied to a polymethyl methacrylate (PMMA) beam for complex modulus identification in the frequency range 10-1100 Hz. Results compare well with those obtained using the Least Squares method, and with those previously published in literature. Then the accuracy of the proposed method has been further verified by experiments performed on a QuietSteel specimen with very low damping. The method is simple and fast. It can be used for a quick estimation of the modal parameters, or as a complementary approach for validation purposes.     

Deuterium dilution technique for body composition assessment: resolving methodological issues in children with moderate acute malnutrition

Childhood malnutrition is highly prevalent and associated with high mortality risk. In observational and interventional studies among malnourished children, body composition is increasingly recognised as a key outcome. The deuterium dilution technique has generated high-quality data on body composition in studies of infants and young children in several settings, but its feasibility and accuracy in children suffering from moderate acute malnutrition requires further study. Prior to a large nutritional intervention trial among children with moderate acute malnutrition, we conducted pilot work to develop and adapt the deuterium dilution technique. We refined procedures for administration of isotope doses and collection of saliva. Furthermore, we established that equilibration time in local context is 3?h. These findings and the resulting standard operating procedures are important to improve data quality when using the deuterium dilution technique in malnutrition studies in field conditions, and may encourage a wider use of isotope techniques.