Controlling the properties of supramolecular assemblies requires unveiling the specific interactions between their components. In the present work, the catalytic properties and structure of ...co‐assemblies composed of a benzene‐1,3,5‐tricarboxamide (BTA) ligand coordinated to copper (the soldier) and seven enantiopure BTAs (the sergeants) have been determined. Whatever the sergeant, the enantioselectivity of the reaction is directly proportional to the optical purity of the supramolecular helices. More strikingly, the role played by the sergeant in the co‐assembly process differs significantly: from almost pure intercalator (when it is incorporated in the stacks of the soldier and generates long homochiral helices) to pure chain capper (when it leads to the formation of partly helically biased and short assemblies). The former situation leads to optimal enantioselectivity for the catalytic system under study (58 % ee) while the latter situation leads to very low selectivity (8 % ee). The successful rationalization of this high and unexpected difference is crucial for the development of more efficient catalysts and more elaborate supramolecular systems.
Co‐assemblies between a benzene‐1,3,5‐tricarboxamide (BTA) ligand (soldier) and different types of enantiopure BTAs (sergeants) are evaluated as helical catalysts. The selectivity is related to the helicity and structure of the supramolecular helices (length, composition) which strongly depend on the role adopted by the sergeant in the co‐assembly process (from intercalation to pure chain capping).
Aggregation of supramolecular helices, for example through interdigitation of their alkyl side chains or through more directional supramolecular interactions, leads to hierarchical architectures with ...original structural and chiroptical properties. However, when a chiral monomer (the “sergeant”) is introduced as a minor component in these assemblies composed of a majority of achiral monomers (the “soldiers”), it is not clear how the aggregation changes the ability of the sergeant to induce a preferential helicity to the polymer main chain (the so‐called “sergeants‐and‐soldiers” effect). This study reports a detailed investigation of the influence of Cu(OAc)2⋅H2O coordination on the structure and chiroptical properties of helical hydrogen‐bonded co‐assemblies composed of a catalytically‐active benzene‐1,3,5‐tricarboxamide (BTA) monomer, acting as the “soldier”, and an enantiopure BTA monomer derived from cyclohexylalanine, playing the role of the “sergeant”. The copper actually significantly influences the extent of the “sergeants‐and‐soldiers” effect since it acts as a crosslink that induces some chiral defects in the supramolecular helices. These crosslinks appear to be preserved during the catalytic hydrosilylation of 4‐nitroacetophenone. The aggregation of helices through the formation of copper crosslinks is reversible since homochiral single helices are exclusively formed in the case of sergeant‐rich assemblies. The fact that both main chain and side chain aggregation affects the chiroptical properties of supramolecular helices must be considered in the design of elaborated chiral materials.
Lower optical purities of supramolecular helical catalysts embedding a low fraction of “sergeants” is due to the aggregation of single helices through copper crosslinks.MR1
In this work, 6-phosphogluconic trisodium salt (6-PG–Na+) is introduced as a new aqueous and nontoxic cross-linking agent to obtain ionic hydrogels. Here, it is shown the formation of hydrogels based ...on chitosan cross-linked with 6-PG–Na+. This formulation is obtained by ionic interaction of cationic groups of polymer with anionic groups of the cross-linker. These hydrogels are nontoxic, do not cause dermal irritation, are easy to extend, and have an adequate adhesion force to be applied as polymeric film over the skin. This formulation exhibits a first order release kinetic and can be applied as drug vehicle for topical administration or as wound dressing for wound healing. The primary goal of this communication is to report the identification and utility of 6-phosphogluconic trisodium salt (6-PG–Na+) as a nontoxic cross-linker applicable for cationic polymers.
Stability constants of boronic acid diol esters in aqueous solution have been determined potentiometrically for a series of meta-, para-substituted phenylboronic acids and diols of variable acidity. ...The constants β11‑1 for reactions between neutral forms of reactants producing the anionic ester plus proton follow the Hammett equation with ρ depending on pK a of diol and varying from 2.0 for glucose to 1.29 for 4-nitrocatechol. Observed stability constants (K obs) measured by UV–vis and fluorometric titrations at variable pH for esters of 4,5-dihydroxy-1,3-benzenedisulfonate (Tiron) generally agree with those expected on the basis of β11‑1 values, but the direct fitting of K obs vs pH profiles gives shifted pK a values both for boronic acids and diol as a result of significant interdependence of fitting parameters. The subsituent effects on absorption and fluorescence spectra of Tiron arylboronate esters are characterized. The K obs for Tiron determined by 11B NMR titrations are approximately 1 order of magnitude smaller than those determined by UV–vis titrations under identical conditions. A general equation, which makes possible an estimate of β11‑1 for any pair of boronic acid and diol from their pK a values, is proposed on the basis of established Brönsted-type correlation of Hammett parameters for β11‑1 with acidity of diols. The equation allows one to calculate stability constants expected only on basis of acid–base properties of the components, thus permitting more strict evaluation of contributions of additional factors such as steric or charge effects to the ester stability.
Despite recent developments on the design of dynamic catalysts, none of them have been exploited for the in-situ control of multiple stereogenic centers in a single molecular scaffold. We report ...herein that it is possible to obtain in majority any amongst the four possible stereoisomers of an amino alcohol by means of a switchable asymmetric catalyst built on supramolecular helices. Hydrogen-bonded assemblies between a benzene-1,3,5-tricarboxamide (BTA) achiral phosphine ligand coordinated to copper and a chiral BTA comonomer are engaged in a copper-hydride catalyzed hydrosilylation and hydroamination cascade process. The nature of the product stereoisomer is related to the handedness of the helices and can thus be directed in a predictable way by changing the nature of the major enantiomer of the BTA comonomer present in the assemblies. The strategy allows all stereoisomers to be obtained one-pot with similar selectivities by conducting the cascade reaction in a concomitant manner, i.e. without inverting the handedness of the helices, or sequentially, i.e. by switching the handedness of the supramolecular helices between the hydrosilylation and hydroamination steps. Supramolecular helical catalysts appear as a unique and versatile platform to control the configuration of molecules or polymers embedding several stereogenic centers.
Anion Recognition by Benzoxaborole Martínez-Aguirre, Mayte A.; Ortega-Valdovinos, Luis Ramón; Villamil-Ramos, Raúl ...
Journal of organic chemistry,
06/2022, Letnik:
87, Številka:
12
Journal Article
Recenzirano
The binding types (H-bonding or coordinate) and stability constants for complexes of 11 mono- and di-anions with benzoxaborole (1) were determined by 1H and 11B NMR titrations in DMSO or MeCN. ...Compared to phenylboronic acid (PBA), 1 is a stronger Lewis acid and a poorer H-bond donor with only one B-OH group, which is expected therefore to recognize anions mostly through the coordinate bonding. This is the case however only with F–, HPO4 2–, and PhPO3 2– anions, which are coordinately bonded to 1, and partially with SO4 2–, which forms only the H-bonded complex with PBA, but both H-bonded and coordinate complexes with 1. The majority of tested anions (AcO–, PhPO3H–, (PhO)2PO2 –, Cl–, and Br–) form H-bonded complexes with both 1 and PBA, whereas H2PO4 – changes the binding mode from coordinate for PBA to H-bonded for 1. The preferable binding type for each anion is confirmed by calculations of DFT-optimized structures of the anion complexes of 1. The preferable binding type can be rationalized considering the effects of the steric hindrance, more significant for the coordinate bonding, and of increased anion basicity, which is favorable for both binding types, but enhances the strength of coordinate bonding more significantly than the strength of H-bonding.
The relationship between caloric restriction-mediated weight loss and the generation of ROS and its effects on atherosclerotic markers in obesity is not fully understood. Therefore, we set out to ...investigate whether dietary weight loss intervention improves markers of oxidative stress in leukocytes and subclinical parameters of atherosclerosis.
This was an interventional study of 59 obese subjects (BMI > 35 kg/m
) who underwent 6 months of dietary therapy, including a 6-week very-low-calorie diet (VLCD) followed by an 18-week low-calorie diet (LCD). We determined clinical parameters, inflammatory markers-hsCRP, TNFα and NFκB -, oxidative stress parameters-total superoxide, glutathione, catalase activity and protein carbonyl groups-, soluble cellular adhesion molecules-sICAM, sP-selectin, sPSGL-1 -, myeloperoxidase (MPO), leukocyte-endothelium cell interactions-rolling flux, velocity and adhesion-and LDL subfractions, before and after the dietary intervention.
After losing weight, an improvement was observed in the patients' anthropometric, blood pressure and metabolic parameters, and was associated with reduced inflammatory response (hsCRP, TNFα and NFκB). Oxidative stress parameters improved, since superoxide production and protein carbonyl content were reduced and antioxidant systems were enhanced. In addition, a significant reduction of subclinical markers of atherosclerosis-small and dense LDL particles, MPO, sP-selectin and leukocyte adhesion-and an increase in soluble PSGL-1 were reported.
Our findings reveal that the improvement of subclinical atherosclerotic markers after dietary weight loss intervention is associated with a reduction of oxidative stress in leukocytes and inflammatory pathways, suggesting that these are the underlying mechanisms responsible for the reduced risk of cardiovascular disease in obese subjects after losing weight.
Humans are exceptionally flexible in cooperation, partly due to our ability to recognize the roles of cooperative partners. While some non-human animals understand the need for a partner in such ...interactions, it is unclear whether they grasp the consequences of their partner's actions and adjust accordingly. Previous studies utilizing economic games with non-human animals yielded mixed results. We investigated dogs, known for their close cooperation with humans, in a stag hunt game. Dogs could cooperate for better rewards or defect for lower ones, while their human partners would either cooperate, never cooperate, or act randomly. We control for attraction to food, side bias, and local enhancement. Dogs were more likely to coordinate with their partners when it led to better rewards, suggesting that they understood their partner's actions. By highlighting this cognitive skill in dogs, we advance our knowledge of the intricate mechanisms driving cooperative behavior in non-human animals.
The educational tool RADIOGIS for the calculation of radio electric coverage in wireless communication systems is presented and evaluated. Through such software, students can learn about the ...calculation of radio electric coverage while at the same time becoming familiar with the Geographic Information Systems (GIS) philosophy, since it is based on ArcGIS, from ESRI. Specific educational software has been used for years to supplement students’ learning in subjects where the planning of radio communication systems is treated. However, they are not usually based on GIS. On the other hand, most of the professional tools used for radio planning are based on GIS. Even though they incorporate the calculation of radio electric coverage as a key element for the planning and optimization of radio communication systems, they are not usually oriented toward teaching. The educational interest of RADIOGIS consists of the incorporation of five practice exercises with their corresponding instructions, which guide students in carrying them out. Sixty‐four students tested the tool for a total of 320 hr of experimentation. A survey was completed between two different groups of students, who were asked to rate RADIOGIS features, acceptance, and usability. In terms of teaching and learning in the calculation of radio electric coverage for the planning of radio communication systems and GIS, both groups claimed to have greater knowledge after working with the tool, especially students from the last courses.
Human cooperation can be facilitated by the ability to create a mental representation of one's own actions, as well as the actions of a partner, known as action co-representation. Even though other ...species also cooperate extensively, it is still unclear whether they have similar capacities. The Joint Simon task is a two-player task developed to investigate this action co-representation. We tested brown capuchin monkeys (Sapajus Cebus apella), a highly cooperative species, on a computerized Joint Simon task and found that, in line with previous research, the capuchins' performance was compatible with co-representation. However, a deeper exploration of the monkeys' responses showed that they, and potentially monkeys in previous studies, did not understand the control conditions, which precludes the interpretation of the results as a social phenomenon. Indeed, further testing to investigate alternative explanations demonstrated that our results were due to low-level cues, rather than action co-representation. This suggests that the Joint Simon task, at least in its current form, cannot determine whether non-human species co-represent their partner's role in joint tasks.
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