Dynamic Interactions in Synthetic Receptors: A Guest Exchange Saturation Transfer Study

The accumulated knowledge regarding molecular architectures is based on established, reliable, and accessible analytical tools that provide robust structural and functional information on assemblies. However, both the dynamicity and low population of noncovalently interacting moieties within studied molecular systems limit the efficiency and accuracy of traditional methods. Herein, the use of a saturation transfer-based NMR approach to study the dynamic binding characteristics of an anion to a series of synthetic receptors derived from bambusuril macrocycles is demonstrated. The exchange rates of BF₄⁻ are mediated by the side chains on the receptor (100 s⁻¹<k_ex<5000 s⁻¹), which play a critical role in receptor-anion binding dynamics. The signal amplification obtained with this approach allows for the identification of different types of intermolecular interactions between the receptor and the anion, something that could not have been detected by techniques hitherto used to study molecular assemblies. These findings, which are supported by a computational molecular dynamic study, demonstrate the uniqueness and added value of this NMR method.     

Dissipation of chlortetracycline in the aquatic environment: Characterization in terms of a generalized multiphase pseudo–zero-order rate law

The kinetics of the dissipation of chlortetracycline in the aquatic environment was studied over a period of 90 days using microcosm experiments and distilled water controls. The distilled water control experiments, carried out under dark conditions as well as exposed to natural sunlight, exhibited biphasic linear rates of dissipation. The microcosm experiments exhibited triphasic linear rates of degradation both in the water phase (2.7 × 10⁻², 7 × 10⁻³, 1.3 × 10⁻³ μg g⁻¹ day^–1) and the sediment phase (3.4 × 10⁻², 6 × 10⁻³, 1 × 10⁻³ μg g⁻¹ day^–1). The initial slow rate of dissipation in the dark control (3 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation and hydrolysis, whereas the subsequent fast rate (1.8 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation, hydrolysis, and microbial degradation. For the sunlight-exposed control, the initial slow rate of dissipation (1.5 × 10⁻³ μg g⁻¹ day^–1) was attributed to a combination of evaporation, hydrolysis, and photolysis, whereas the subsequent fast rate was attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation (5.1 × 10⁻³ μg g⁻¹ day^–1). The initial fast rate of dissipation in the water phase of the microcosm experiment is attributed to a combination of evaporation, hydrolysis, photolysis, and microbial degradation, whereas all subsequent slow rates in the water phase and all rates of degradation in the sediment phase are attributed to microbial degradation of the colloidal and sediment particle adsorbed antibiotic. A multiphase zero-order kinetic model is presented that takes into account (a) dissipation of the antibiotic via evaporation, hydrolysis, photolysis, microbial degradation, and adsorption by colloidal and sediment particles and (b) the dependence of the dissipation rate on the concentration of the antibiotic, type and count of microorganisms, and type and concentration of colloidal particles and sediment particle adsorption sites within a given aquatic environment.     

Analysing dynamic deep stall recovery using a nonlinear frequency approach

Nonlinear Dynamics - Based on bifurcation theory, nonlinear frequency response analysis is a recent development in the field of flight dynamics studies. Here, we consider how this method can be...     

Design and Synthesis of Imidazole and Triazole Pyrazoles as Mycobacterium Tuberculosis CYP121A1 Inhibitors

The emergence of untreatable drug-resistant strains of Mycobacterium tuberculosis is a major public health problem worldwide, and the identification of new efficient treatments is urgently needed. Mycobacterium tuberculosis cytochrome P450 CYP121A1 is a promising drug target for the treatment of tuberculosis owing to its essential role in mycobacterial growth. Using a rational approach, which includes molecular modelling studies, three series of azole pyrazole derivatives were designed through two synthetic pathways. The synthesized compounds were biologically evaluated for their inhibitory activity towards M. tuberculosis and their protein binding affinity (K_D). Series 3 biarylpyrazole imidazole derivatives were the most effective with the isobutyl ( 10 f ) and tert-butyl ( 10 g ) compounds displaying optimal activity (MIC 1.562 μg/mL, K_D 0.22 μM ( 10 f ) and 4.81 μM ( 10 g )). The spectroscopic data showed that all the synthesised compounds produced a type II red shift of the heme Soret band indicating either direct binding to heme iron or (where less extensive Soret shifts are observed) putative indirect binding via an interstitial water molecule. Evaluation of biological and physicochemical properties identified the following as requirements for activity: LogP >4, H-bond acceptors/H-bond donors 4/0, number of rotatable bonds 5–6, molecular volume >340 ų, topological polar surface area <40 Ų.     

Investigating secondary students beliefs about mathematical problem-solving

Many studies over the past 30 years have highlighted the important role of students’ beliefs for successful problem-solving in mathematics. Given the recent emphasis afforded to problem-solving on the reformed Irish secondary school mathematics curriculum, the main aim of this study was to identify Irish students’ (n = 975) beliefs about the field. A quantitative measure of these beliefs was attained through the use of the Indiana Mathematical Belief Scale, an existing 30-item (five-scale) self-report questionnaire. A statistical analysis of the data revealed that students who were further through their secondary education had a stronger belief that not all problems could be solved by applying routine procedures. In contrast, the same students held less positive beliefs than their younger counterparts that they could solve time-consuming problems and that conceptual understanding was important. The analysis also indicated that gender had a significant impact on three of the five belief scales.     

Melt spinning of propylene carbonate‐plasticized poly(acrylonitrile)‐co‐poly(methyl acrylate)

The primary use of poly(acrylonitrile) (PAN) fibers, commonly referred to as acrylic fibers, is in textile applications like clothing, furniture, carpets, and awnings. All commercially available PAN fibers are processed by solution spinning; however, alternative, more cost‐effective processes like melt spinning are still highly desired. Here, the melt spinning of PAN‐co‐poly(methyl acrylate) (PMA) plasticized with propylene carbonate (PC) at 175°C is reported. The use of methyl acrylate (MA) as comonomer and PC as an external plasticizer renders the approach a combination of internal and external plasticization. Various mixtures of PAN and PC used in this work were examined by rheology, subjected to melt spinning, followed by discontinuous and continuous washing, respectively. The best fibers were derived from a PAN‐co‐PMA copolymer containing 8.1 mol‐% of MA having a number‐average molecular weight M _n of 34 000 g/mol, spun in the presence of 22.5 wt.‐% of PC. The resulting fibers were analyzed by scanning electron microscopy and wide‐angle X‐ray scattering (WAXS), and were subjected to mechanical testing.