Synthesis and complexation properties of calix[4]arene glycoconjugates

Pripravljena su tri nova, u vodi topljiva derivata kaliks[4]arena 1–3 s amidnim veznim mjestima za katione. U strukturu kaliksarena ugrađene su glukozne jedinice kao neutralni hidrofilni fragmenti koji omogućuju topljivost u vodi. Sinteza spojeva provedena je nizom reakcija, iz polaznog p-tert-butilkaliks[4]aren. Vezanje glukoznih jedinica je provedeno bakrom kataliziranom cikloadicijom alkina i azida, a amidne skupine uvedene su korištenjem standardnih sintetskih tehnika u kaliksarenskoj kemiji. Spojevi se razlikuju po vrsti amidnog veznog mjesta (sekundarni ili tercijarni) te položaju i broju glukoznih podjedinica. Provedena su istraživanja kompleksiranja alkalijskih kationa u vodi, metanolu i formamidu kako bi se stekao uvid u utjecaj solvatacije te intra- i intermolekulskih vodikovih veza na ravnoteže odgovarajućih reakcija. Konstante stabilnosti kompleksa stehiometrije 1:1 određene su pomoću UV spektrofotometrijskih i mikrokalorimetrijskih titracija, pri čemu su po prvi puta takva istraživanja provedena s neutralnim kaliksarenskim ligandima u vodi. Kalorimetrijskim mjerenjima određene su i pripadne reakcijske entalpije i entropije. Vrijednosti konstanti ravnoteže reakcija kompleksiranja smanjuju se u nizu otapala metanol > formamid > voda, što se može povezati s razlikom u jakosti solvatacije kationa u tim otapalima. Konstante stabilnosti kationskih kompleksa s priređenim spojevima uglavnom padaju u nizu Na+ > K+ > Li+ > Rb+, dok za najveći Cs+ kompleksiranje nije primijećeno. Najveće konstante stabilnosti imaju kompleksi derivata s tercijanim amidnim veznim mjestom i osam glukoznih jedinica na donjem obodu, pri čemu se taj derivat pokazao vrlo efikasnim (logK ≈ 5) i selektivnim receptorom za vezanje Na+ u vodi. Svi dobiveni rezultati detaljno su obrazloženi i raspravljeni, od sintetskih puteva za dobivanje pojedinih receptora do utjecaja njihove strukture i otapala na termodinamičku stabilnost kompleksa tih spojeva s alkalijskim kationima.Three novel water-soluble calix[4]arene derivatives bearing amide binding sites for metal cati-ons were prepared. Glucose units were embedded in their structures as neutral hydrophilic frag-ments which enable solubility in water. Syntheses were performed through a series of reactions starting from p-tert-butylcalix[4]arene. Glycosylation was carried out using copper catalyzed alkyne azide cycloaddition, whereas amide groups were introduced using standard techniques in calixarene chemistry. The compounds differed in the type of cation-binding site (secondary or tertiary amide) as well as position and number of glucose units. Complexation of the prepared ligands with alkali metal cations in water, methanol and formamide was studied in order to get insight into the effect of solvation as well as intra- and intermolecular hydrogen bonds on the equilibria of the corresponding reactions. Stability constants of 1:1 complexes were determined by means of UV spectrophotometric and microcalorimetric titrations. Calorimetric measure-ments provided also reaction enthalpies and entropies. It should be noted that such studies were for the first time undertaken with neutral calixarens in aqueous solutions. The complexation reaction equilibrium constants decreased in the solvent order: methanol > formamide > water, which could be accounted for by considering the differences in solvation of cations in these solvents. In most cases the stability constants of the complexes decreased in the cation order: Na+ > K+ > Li+ > Rb+, whereas no complexation was observed in the case of the largest Cs+. The highest stability constants corresponded to tertiary-amide derivative bearing eight glucose units at the lower rim, and this derivative was proven to be capable of remarkably efficient (log K ≈ 5) and pronouncedly selective binding of sodium cation in water. All the obtained results were thoroughly discussed with respect to the developed synthetic routes, as well as the influ-ence of solvation and ligands structural characteristics on the thermodynamic stability of their complexes with alkali metal cations

An Old Story in New Light: X-Ray Powder Diffraction Provides Novel Insights into a Long-Known Organic Solid-State Rearrangement Reaction

The first in situ diffraction study of the long-known solid-state rearrangement of p-bromobenzeneazotribenzoylmethane is reported. This proof-of-principle study demonstrates how modern laboratory X-ray powder diffraction, accompanied by up-to-date processing tools, can be used to monitor and describe mechanisms of organic solid-state reactions while it also underpins its necessity for structural characterisation of in situ formed crystalline phases. (doi: 10.5562/cca2127

Mikroskopski model za računanje početnog broja ekscitona u sudarima atomskih jezgara

A microscopic model for estimating n0, the initial exciton number used in calculating pre-equilibrium emission from heavy-ion reactions, is presented. The model follows the evolution of the geometrical and phase spaces during the process of fusioning of the target and the projectile. A good agreement is found between the calculated values of n0 and the empirical values extracted from fits to nucleon spectra; empirical trends of physical quantities involving n0 are reproduced. An approximate expression for calculating n0 as a function of the mass and energy of the colliding system is given.Prikazan je model pomoću kojeg je moguce odrediti n0, početni broj eksciton a na koji se dijeli energija sudara atomskih jezgara. Taj je parametar potreban za računanje predravnotežne emisije čestica iz teskoionskih reakcija. Prikazani model slijedi evoluciju geometrijskog faznog prostora tijekom procesa fuzije jezgre mete i projektila. Dobro slaganje opaženo je između računatih vrijednosti parametara n0 i onih, dobivenih na empirički način analizom nukleonskih spektara iz teškoionskih reakcija. Model također uspješno reproducira trendove fizikalnih veličina povezanih s n 0 . U članku je dan izraz za računanje približne vrijednosti parametra n 0 u ovisnosti o masi i energiji sudarnog sustava

Soft nanotechnology: the potential of polyelectrolyte multilayers against E. coli adhesion to surfaces

Preprečevanje adhezije bakterij na površine je najbolj učinkovit način obvladovanja rasti biofilmov. Namen te raziskave je bil analizirati anti-adhezivni potencial 5 in 50 mmol/L polielektrolitskih plasti poli(alilamin hidroklorid)/poli(natrijev 4-stirensulfonat), poli(4-vinil-N-etilpiridin bromid/ poli(natrijev 4-stirensulfonat) in poli(4-vinil-N-izobutilpiridin bromid/ poli(natrijev 4-stirensulfonat) na bakterijo E. coli. Pet zaporednih plasti polielektrolitov je bilo sestavljenih na steklenih površinah in izpostavljenih bakterijski suspenziji. Rezultati kažejo, da 50 mmol/L poli(4-vinil-N-etilpiridin bromid/ poli(natrijev 4-stirensulfonat) najbolj učinkovito prepreči adhezijo bakterij 0,4 log bakt./mm2 (60 %), sledi mu poli(4- vinil-N-izobutilpiridin bromid/ poli(natrijev 4-stirensulfonat) 0,3 log bakt. mm-2 (47 %) in poli(alilamin hidroklorid)/ poli(natrijev 4-stirensulfonat) 0,2 log bakt. mm-2 (38 %). Ta raziskava dokazuje, da polieletrolitske plasti z kvartarne amino skupinami igrajo pomembno vlogo pri preprečevanju adhezije bakterij in zato predstavljajo pomembno uporabo v živilski in farmacevtski industriji ter v medicini.Preventing bacterial attachment to surfaces is the most efficient approach to controlling biofilm proliferation. The aim of this study was to compare anti-adhesion potentials of 5 and 50 mmol/L polyelectrolyte multilayers of poly(allylamine hydrochloride)/poly(sodium 4–styrenesulfonate), poly(4-vinyl-N-ethylpyridinium bromide)/ poly(sodium 4–styrenesulfonate), and poly(4-vinyl-N-isobutylpyridinium bromide)/poly(sodium 4–styrenesulfonate) against Escherichia coli. Glass surface was covered with five polyelectrolyte layers and exposed to bacterial suspensions. Poly(4-vinyl-N-ethylpyridinium bromide)/poly(sodium 4–styrenesulfonate) was the most effective against bacterial adhesion, having reduced it by 60 %, followed by poly(4-vinyl-N-isobutylpyridinium bromide)/poly(sodium 4– styrenesulfonate) (47 %), and poly(allylamine hydrochloride)/poly(sodium 4–styrenesulfonate) (38 %). Polyelectrolyte multilayers with quaternary amine groups have a significant anti-adhesion potential and could find their place in coatings for food, pharmaceutical, and medical industry

In vitro Investigation of the Antimicrobial Activity of a Series of Lipophilic Phenols and Naphthols

Five groups of phenols/naphthols (42 compounds in total) were synthesized and screened against Gram-positive Staphylococcus aureus and Bacillus subtilis, Gram-negative Escherichia coli and Klebsiella pneumoniae, and the fungus Candida albicans. Whereas compounds were found inactive against Gram-negative bacteria, potent activities against Gram-positive bacteria were observed. The activities correlate with the ability of molecules to form quinone methides, suggesting potential new modes of action.KEYWORDS Antimicrobial activity, phenols, naphthols, quinone methides

Complexation of Alkali Metal Cations by a Tertiary Amide Calix[4]Arene Derivative in Strongly Cation Solvating Solvents

The complexation of alkali-metal cations with calix[4]arene tertiary amide derivative (L) was studied in N-methylformamide (NMF), N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) by means of microcalorimetric and UV spectrophotometric titrations. The Gibbs energies, enthalpies, and entropies for transfer of reactants and products from N-methylformamide to other solvents were determined. Favorable enthalpic contribution to overall stability was found to be the most important for all complexation reactions, especially in the case of NaL+ formation, resulting in an affinity peak of L for this cation. The complexation entropy changes were always unfavorable. The ligand dissolution was endothermic in all solvents, accompanied by positive solution entropy. The highest complex stability constants were determined in NMF, whereas in DMSO the affinity of L towards alkali metal cations was the lowest. An interesting interplay between the transfer enthalpies and entropies of the reactants and complexes was revealed and discussed in detail. This work is licensed under a Creative Commons Attribution 4.0 International License

Investigations of Thermally Controlled Mechanochemical Milling Reactions

Mechanochemical milling reactions have received much attention recently as a green and highly efficient path toward various relevant materials. Control over the fundamental reaction parameters in the milling procedure, such as temperature and pressure of the reactor, is still in its infancy, and the vast majority of milling reactions are done by controlling just the basic parameters such as frequency and milling media weight. We demonstrate here how milling under controlled, prolonged, and variable heating programs accomplished in a new milling reactor introduces a new level of mechanochemical reactivity beyond what can be achieved by conventional mechanochemical or solution procedures and also reduces the time and energy costs of the milling process. The methodology is demonstrated on four varied systems: C–C bond-forming Knoevenagel condensation, selective C–N bond formation for amide/urea synthesis, selective double-imine condensation, and solid-state formation of an archetypal open metal-organic framework, MOF-74. The potential of this methodology is best demonstrated on the one-pot selective synthesis of four complex products containing combinations of amide, amine, or urea functionalities from the same and simple acyl azide and diamine reactants. Principal control over this enhanced reactivity and selectivity stemmed from the application of specific heating regimes to mechanochemical processing accomplished by a new, in-house developed mechanochemical reactor. As even a moderate increase in temperature strongly affects the selectivity and the rate of mechanochemical reactions, the results presented are in line with recent challenges of the accepted theories of mechanochemical reactivity