Interfacial chemistry on carboxylate-functionalized monolayer assemblies

Deposition of trichlorosilanes with ester groups at their remote termini provides a convenient entry to carboxylic acid-bearing siloxane-anchored self-assembled monolayers. The de-esterification of these esters has been optimized to minimize monolayer damage, and their quantitative re-esterification provides clear evidence for the stability of these systems. Both the structure of the ester-terminated monolayer and its de-esterification/esterification chemistry can be easily monitored by FTIR-ATR measurements. This spectroscopic tool, together with a liquid cell that enables IR spectra to be measured in an aqueous environment, enables a detailed structural analysis of the carboxylic acid-bearing siloxane-anchored self-assembled monolayers and an assessment of their acid/base behavior (by in situ titration). The use of D₂O instead of H₂O for the in situ titration experiments also improves the available IR window. Both monomeric and dimeric/oligomeric acid groups are seen, and the relative ease of deprotonation of these various species can be directly monitored. Monomers of alkyl carboxylic acids that are hydrogen bonded only to surrounding water molecules have a pK_a = 4.9, while the pK_a for the aggregated molecules is 9.3. Similar behavior is seen for surface-bound benzoic acids, where the two pK_a values are 4.7 and 9.0. The influence of temperature on these structures and their chemistry has been explored to a limited extent as well. When the alkylcarboxylic acid system is cooled to 10 °C, the pK_a value for the acid monomers is reduced from 4.9 to 4.5 and increases from 9.3 to 10.3 for the aggregates.     

Operating experience of the Dhekelia seawater desalination plant using an innovative energy recovery system

Dhekelia Desalination Plant in Cyprus has been in operation for 7 years. It includes eight 5,000 m³/d seawaterreverse osmosis trains operating with Mediterranean seawater with a TDS content of 41,800 ppm, with water temperature ranging from 17°C to 32°C. The energy recovery system originally installed at the plant is the Francis turbine, which, at the time, was considered one of the most efficient and economical devices on the market. Since then, however, market forces to reduce operational costs, by cutting down energy consumption, led to the advent of new energy recovery systems. Today several systems are in operation which reduce the RO energy consumption. Apart from the versions of the Francis turbine and Pelton wheel they include the hydraulic turbocharger, work exchanger and pressure exchanger, all harnessing the pressure energy of the brine. In our effort to be competitive for the years to come we decided to convert our existing energy recovery system from Francis turbines to the pressure exchanger. This paper outlines how it was decided to go ahead with the pressure exchangers, and gives comparisons with other energy recovery methods, and describes our operating experience with the pressure exchangers.     

The Role of Natural Polymorphic Variants of DNA Polymerase β in DNA Repair

DNA polymerase β (Polβ) is considered the main repair DNA polymerase involved in the base excision repair (BER) pathway, which plays an important part in the repair of damaged DNA bases usually resulting from alkylation or oxidation. In general, BER involves consecutive actions of DNA glycosylases, AP endonucleases, DNA polymerases, and DNA ligases. It is known that protein–protein interactions of Polβ with enzymes from the BER pathway increase the efficiency of damaged base repair in DNA. However natural single-nucleotide polymorphisms can lead to a substitution of functionally significant amino acid residues and therefore affect the catalytic activity of the enzyme and the accuracy of Polβ action. Up-to-date databases contain information about more than 8000 SNPs in the gene of Polβ. This review summarizes data on the in silico prediction of the effects of Polβ SNPs on DNA repair efficacy; available data on cancers associated with SNPs of Polβ; and experimentally tested variants of Polβ. Analysis of the literature indicates that amino acid substitutions could be important for the maintenance of the native structure of Polβ and contacts with DNA; others affect the catalytic activity of the enzyme or play a part in the precise and correct attachment of the required nucleotide triphosphate. Moreover, the amino acid substitutions in Polβ can disturb interactions with enzymes involved in BER, while the enzymatic activity of the polymorphic variant may not differ significantly from that of the wild-type enzyme. Therefore, investigation regarding the effect of Polβ natural variants occurring in the human population on enzymatic activity and protein–protein interactions is an urgent scientific task.     

Experimental methods in chemical engineering: X-ray absorption spectroscopy—XAS,XANES, EXAFS

Although X-ray absorption spectroscopy (XAS) was conceived in the early 20th century, it took 60 years after the advent of synchrotrons for researchers to exploit its tremendous potential. Counterintuitively, researchers are now developing bench type polychromatic X-ray sources that are less brilliant to measure catalyst stability and work with toxic substances. XAS measures the absorption spectra of electrons that X-rays eject from the tightly bound core electrons to the continuum. The spectrum from 10 to 150 eV (kinetic energy of the photoelectrons) above the chemical potential—binding energy of core electrons—identifies oxidation state and band occupancy (X-ray absorption near edge structure, XANES), while higher energies in the spectrum relate to local atomic structure like coordination number and distance, Debye-Waller factor, and inner potential correction (extended X-ray absorption fine structure, EXAFS). Combining XAS with complementary spectroscopic techniques like Raman, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) elucidates the nature of the chemical bonds at the catalyst surface to better understand reaction mechanisms and intermediates. Because synchrotrons continue to be the light source of choice for most researchers, the number of articles Web of Science indexes per year has grown from 1000 in 1991 to 1700 in 2020. Material scientists and physical chemists publish an order of magnitude articles more than chemical engineers. Based on a bibliometric analysis, the research comprises five clusters centred around: electronic and optical properties, oxidation and hydrogenation catalysis, complementary analytical techniques like FTIR, nanoparticles and electrocatalysis, and iron, metals, and complexes.     

Transversal thermal patterns in packed‐bed reactors with simple kinetics: Bifurcation criterion and simulations

We derive a new criterion for transversal instability of planar fronts based on the bifurcation condition dV_f/dK|_K=0 = 0, where V_f and K are the front velocity and its curvature, respectively. This refines our previously obtained condition, which was formulated as α = (ΔT_adPe_T)/(ΔT_mPe_C) > 1 to α > 1 + |δ|, where ΔT_ad and ΔT_m are the adiabatic and maximal temperature rise, respectively, Pe_C and Pe_T are the axial mass and the heat Pe numbers, respectively, and δ is a small parameter. The criterion is based on approximate relations for ΔT_m and V_f, which account for the local curvature of a propagating front in a packed bed reactor with a first‐order activated kinetics. The obtained relations are verified by linear stability analysis of planar fronts. Simulations of a simplified 2D model in the form of a thin cylindrical shell are in good agreement with the critical parameters predicted by dispersion relations. Three types of patterns were detected in simulations: “frozen” multiwave patterns, spinning waves, and complex rotating–oscillating patterns. We map bifurcation diagrams showing domains of different modes using the shell radius as the bifurcation parameter. The possible translation of the 2D cylindrical shell model results to the 3D case is discussed. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Evolution of Chemistry,Morphology and Rheology of Various Polymer Systems along a Twin‐Screw Extruder

Intermeshing twin‐screw extruders have been recently identified as useful in special application niches such as the extrusion of PVC dry blends (counter‐rotating machines) and compounding operations (co‐rotating machines). Thus, it is of interest to study the mechanical and/or chemical effects that occur along the screw axis of the extruders, since they will dictate the characteristics and performance of the final material. This work aims at illustrating the usefulness of a simple experimental tool recently developed for the study of the physical, chemical and morphological evolution along the extruder of polymer based systems, data being presented and discussed for a number of composites and blends.     

Reuse of reverse osmosis membranes in advanced wastewater treatment

In areas where tap water has a high salt content, wastewater is not appropriate for reuse in agriculture, particularly for sensitive crops. One alternative is reduction, via desalination, of the brackish character to the secondary effluent. A filtration stage is also required before desalination. On the other hand, used reverse osmosis membranes can be recycled and used as filters in the advanced treatment stage in order to reduce suspended matter contained in the secondary effluent—one advantage being the environmental recovery of solid waste. Used membranes can be treated with strong chemical oxidants to peel off the active separation layer in order to transform them into microfiltration or ultrafiltration elements. Preliminary tests have been carried out with 8″ elements, aimed at comparing membrane performance before and after the peeling process. An index denoted as peeling effectiveness (high flux, high salt passage) is used for comparison. It was soon observed that potassium permanganate was more effective than others, together with sodium hydroxide. Doses around 1000 mg/L KMnO₄ provided the best results. It was also concluded that membrane cleaning, done with sodium bisulphite prior to peeling, was better when recirculating the cleaning solution around the membrane rather than soaking it. Next steps in the research will test the actual filtration capability of the peeled membranes in actual wastewater.