Novel cotton cellulose by cationisation during the mercerisation process—part 1: chemical and morphological changes

Cationisation is the modification of cotton cellulose by using quaternary ammonium compounds that block negative OH groups, thus resulting in electropositive cotton cellulose. It is an alternative method for achieving better adsorption of chemical compounds and substances, such as dyestuffs, fluorescent whitening agents, and other textile auxiliaries. The cationisation of cotton cellulose changes the surface electrical charge (electrokinetic potential) by significantly increasing its adsorption properties. The presented article investigated the chemical and morphological changes in cotton cellulose when cationised with an epihalohydrin, 2,3-epoxypropyl trimethyl ammonium chloride, after and during the mercerisation process. When comparing mercerised cotton with cationised cotton, it was concluded that cationisation during the mercerisation process using short-chain cationic compounds would result in a novel cotton cellulose that would bring a new dimension to cotton pre-treatment and finishing. The modified cotton would retain all the beneficial properties of mercerised cotton with a change of surface charge that would ensure further improvement in quality.     

The effect of coordinated water on the connectivity of uranium(IV) sulfate x‐hydrate: [U(SO4)2(H2O)5]·H2O and [U(SO4)2(H2O)6]·2H2O,and a comparison with other known structures

Two new solid‐state uranium(IV) sulfate x‐hydrate complexes (where x is the total number of coordinated plus solvent waters), namely catena‐poly[[pentaaquauranium(IV)]‐di‐μ‐sulfato‐κ⁴O:O′] monohydrate], {[U(SO₄)₂(H₂O)₅]·H₂O}_n, and hexaaquabis(sulfato‐κ²O,O′)uranium(IV) dihydrate, [U(SO₄)₂(H₂O)₆]·2H₂O, have been synthesized, structurally characterized by single‐crystal X‐ray diffraction and analyzed by vibrational (IR and Raman) spectroscopy. By comparing these structures with those of four other known uranium(IV) sulfate x‐hydrates, the effect of additional coordinated water molecules on their structures has been elucidated. As the number of coordinated water molecules increases, the sulfate bonds are displaced, thus changing the binding mode of the sulfate ligands to the uranium centre. As a result, uranium(IV) sulfate x‐hydrate changes from being fully crosslinked in three dimensions in the anhydrous compound, through sheet and chain linking in the tetra‐ and hexahydrates, to fully unlinked molecules in the octa‐ and nonahydrates. It can be concluded that coordinated waters play an important role in determining the structure and connectivity of U^IV sulfate complexes.     

An electrochemical peptide-based Ara h 2 antibody sensor fabricated on a nickel(II)-nitriloacetic acid self-assembled monolayer using a His-tagged peptide

We report, for the first time, the use of a Ni(II)-nitriloacetic acid (NTA) self-assembled monolayer (SAM) in the fabrication of an electrochemical peptide-based (E-PB) sensor for detection of anti-Ara h 2 antibodies. We compared the performance of the sensor fabricated on a Ni(II)-NTA SAM using a His-tagged peptide with the sensor fabricated using the conventional approach via direct immobilization of a thiolated peptide. While both sensors responded only to the correct antibody in the presence of random antibodies, we observed differences between the sensors. Specifically, the detection limit of the His-tagged sensor was 1 pM, significantly lower than the 200 pM detection limit of the conventional thiolated sensor. More importantly, unlike our previously developed E-PB sensors, both sensors are regenerable and reusable. The thiolated sensor can be readily regenerated using guanidine hydrochloride; whereas the His-tagged sensor can be regenerated by direct displacement of the His-tagged probes using Ni(II) ions. Overall, our results show that both approaches are well-suited for E-PB sensor fabrication; more importantly, specific sensor properties such as detection limit and dynamic range can be tuned by simply using a different probe immobilization method.     

The length of esterifying alcohol affects the aggregation properties of chlorosomal bacteriochlorophylls

Abstract Chlorosomes, the main light-harvesting complexes of green photosynthetic bacteria, contain bacteriochlorophyll (BChl) molecules in the form of self-assembling aggregates. To study the role of esterifying alcohols in BChl aggregation we have prepared a series of bacteriochlorophyllide c (BChlide c) derivatives differing in the length of the esterifying alcohol (C(1), C(4), C(8) and C(12)). Their aggregation behavior was studied both in polar (aqueous buffer) and nonpolar (hexane) environments and the esterifying alcohols were found to play an essential role. In aqueous buffer, hydrophobic interactions among esterifying alcohols drive BChlide c derivatives with longer chains into the formation of dimers, while this interaction is weak for BChlides with shorter esterifying alcohols and they remain mainly as monomers. All studied BChlide c derivatives form aggregates in hexane, but the process slows down with longer esterifying alcohols due to competing hydrophobic interactions with hexane molecules. In addition, the effect of the length of the solvent molecules (n-alkanes) was explored for BChl c aggregation. With an increasing length of n-alkane molecules, the hydrophobic interaction with the farnesyl chain becomes stronger, leading to a slower aggregation rate. The results show that the hydrophobic interaction is the driving force for the aggregation in an aqueous environment, while in nonpolar solvents it is the hydrophilic interaction.     

Conformational and self-assembly studies of helix forming hexapeptides containing two α-amino isobutyric acids

Single crystal X-ray diffraction studies reveal that three hexapeptides with general formula Boc-Ile-Aib-Xx-Ile-Aib-Yy-OMe, where Xx and Yy are Leu in peptide I, Leu and Phe in peptide II, and Phe and Leu in peptide III, respectively, adopt equivalent conformations that can be described as mixed 3₁₀/α-helice with two 4→1 and two 5→1 intramolecular N-H?OC H-bonds. The peptides do not generate any helix-terminating Schellman motif despite having Aib at the penultimate position from C-terminus. In the crystalline state, the helices are packed in head-to-tail fashion through intermolecular hydrogen bonds to create supramolecular helical structures. The CD studies of the three hexapeptides in acetonitrile indicate that they are folded in well-developed 3₁₀-helical structures. NMR studies of peptide I in CDCl₃ also suggest the formation of a homogeneous 3₁₀-helical structure. The field emission scanning electron microscopic (FE-SEM) images of peptide II in the solid state reveal a non-twisted ribbon-like morphology, which is formed through lateral association of non-twisted filaments.     

Minimizing the passengers’ traveling time in the stop location problem

In this paper we consider the location of stops along the edges of an already existing public transportation network. The positive effect of new stops is given by the better access of the passengers to the public transport network, while the passengers’ traveling time increases due to the additional stopping activities of the trains, which is a negative effect for the passengers. The problem has been treated in the literature where the most common model is to cover all demand points with a minimal number of new stops. In this paper, we follow this line and seek for a set of new stops covering all demand points but instead of minimizing the number of new stops we minimize the additional passengers’ traveling time due to the new stops. For computing this additional traveling time we do not only take the stopping times of the vehicles but also acceleration and deceleration of the vehicles into account. We show that the problem is NP-hard, but we are able to derive a finite candidate set and two tractable IP formulations. For linear networks we show that the problem is polynomially solvable. We also discuss the differences to the common models from literature showing that minimizing the number of new stops does not necessarily lead to a solution with minimal additional traveling times for the passengers. We finally provide a case study showing that our new model decreases the traveling times for the passengers while still achieving the minimal number of new stops.     

Effect of pyrolysis temperature and operating temperature on the performance of nanoporous carbon membranes

Technology designed to capture and store carbon dioxide (CO₂) will play a significant role in the near-term reduction of CO₂ emissions and is considered necessary to slow global warming. Nanoporous carbon (NPC) membranes show promise as a new generation of gas separation membranes suitable for CO₂ capture.We have made supported NPC membranes from polyfurfuryl alcohol (PFA) at various pyrolysis temperatures. Positron annihilation lifetime spectrometry (PALS) and wide angle X-ray diffraction (WAXD) results indicate that the pore size decreases whilst the porosity increases with increasing pyrolysis temperature. The membrane performance results support these findings with a significant increase in permeance being seen with increasing pyrolysis temperature, which relates to the increase in porosity.Mixed gas performance measurements also show an increase in CH₄ permeance as the operating temperature is increased from 35 to 200 °C, which can be related to an increase in the rate of diffusion. However, the selectivity decreases with increasing operating temperature due to the smaller changes in the CO₂ permeance. These smaller changes in CO₂ permeance can be related to the stronger adsorption of this gas on the carbon surface at lower operating temperatures. Interestingly, regardless of the original pyrolysis temperature, the selectivity at higher operating temperatures is similar, whereas the permeance remains related to this pyrolysis temperature.     

Giant micelles of organoplatinum(II) gemini amphiphiles

Organoplatinum(II) gemini amphiphiles with two different chain lengths are synthesized and characterized. Self-assembly at the air-water interface is investigated as a function of chain length and reduction in surface area by using Langmuir-trough techniques. The Langmuir-trough experiments lead to a conjecture that surface aggregates may be the adsorbing units. Atomic force microscopy on the transferred Langmuir-Schaefer films reveals spontaneous formation of wormlike micellar aggregates. A shear-induced transition and alignment are proposed for the observed effects.