Marina Šekutor

Cucurbit[7]uril⋅Guest Pair with an Attomolar Dissociation Constant

Host⋅guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by (1) H NMR spectroscopy and X-ray crystallography. (1) H NMR competition experiments revealed that CB[7]⋅6 is among the tightest monovalent non-covalent complexes ever reported in water with Ka =7.2×10(17)  M(-1) in pure D2 O and 1.9×10(15)  M(-1) in D2 O buffered with NaO2 CCD3 (50 mM). The crystal structure of CB[7]⋅6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe3 (+) groups of 6 (7.78 Å), which allows it to establish 14 optimal ion-dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the CO portals within the CB[7]⋅6 complex, and the co-linearity of the C7  axis of CB[7] with the N(+) ⋅⋅⋅N(+) line in 6. This work further blurs the lines of distinction between natural and synthetic receptors.

Unraveling the Structure–Affinity Relationship between Cucurbit[n]urils (n = 7, 8) and Cationic Diamondoids

We report the measurement of the binding constants (Ka) for cucurbit[n]uril (n = 7, 8) toward four series of guests based on 2,6-disubstituted adamantanes, 4,9-disubstituted diamantanes, 1,6-disubstituted diamantanes, and 1-substituted adamantane ammonium ions by direct and competitive 1H NMR spectroscopy. Compared to the affinity of CB[7]·Diam(NMe3)2, the adamantane diammonium ion complexes (e.g., CB[7]·2,6-Ad(NH3)2 and CB[7]·2,6-Ad(NMe3)2) are less effective at realizing the potential 1000-fold enhancement in affinity due to ion-dipole interactions at the second ureidyl C═O portal. Comparative crystallographic investigation of CB[7]·Diam(NMe3)2, CB[7]·DiamNMe3, and CB[7]·1-AdNMe3 revealed that the preferred geometry positions the +NMe3 groups ≈0.32 Å above the C═O portal; the observed 0.80 Å spacing observed for CB[7]·Diam(NMe3)2 reflects the simultaneous geometrical constraints of CH2···O═C close contacts at both portals. Remarkably, the CB[8]·IsoDiam(NHMe2)2 complex displays femtomolar binding affinity, placing it firmly alongside the CB[7]·Diam(NMe3)2 complex. Primary or quaternary ammonium ion looping strategies lead to larger increases in binding affinity for CB[8] than for CB[7], which we attribute to the larger size of the carbonyl portals of CB[8]; this suggests routes to develop CB[8] as the tightest binding host in the CB[n] family. We report that alkyl group fluorination (e.g., CB[7]·1-AdNH2Et versus CB[7]·1-AdNH2CH2CF3) does not result in the expected increase in Ka value. Finally, we discuss the role of solvation in nonempirical quantum mechanical computational methodology, which is used to estimate the relative changes in Gibbs binding free energies.

Adamantane in Drug Delivery Systems and Surface Recognition

The adamantane moiety is widely applied in design and synthesis of new drug delivery systems and in surface recognition studies. This review focuses on liposomes, cyclodextrins, and dendrimers based on or incorporating adamantane derivatives. Our recent concept of adamantane as an anchor in the lipid bilayer of liposomes has promising applications in the field of targeted drug delivery and surface recognition. The results reported here encourage the development of novel adamantane-based structures and self-assembled supramolecular systems for basic chemical investigations as well as for biomedical application.

London Dispersion Directs On-Surface Self-Assembly of [121]Tetramantane Molecules

London dispersion (LD) acts between all atoms and molecules in nature, but the role of LD interactions in the self-assembly of molecular layers is still poorly understood. In this study, direct visualization of single molecules using atomic force microscopy with CO-functionalized tips revealed the exact adsorption structures of bulky and highly polarizable [121]tetramantane molecules on Au(111) and Cu(111) surfaces. We determined the absolute molecular orientations of the completely sp3-hybridized tetramantanes on metal surfaces. Moreover, we demonstrate how LD drives this on-surface self-assembly of [121]tetramantane hydrocarbons, resulting in the formation of a highly ordered 2D lattice. Our experimental findings were underpinned by a systematic computational study, which allowed us to quantify the energies associated with LD interactions and to analyze intermolecular close contacts and attractions in detail.

Neighboring effect in fragmentation pathways of cage guanylhydrazones in the gas phase.

ESI-MS/MS investigation of the mono- and bis(guanylhydrazone) derivatives 1-5 based on adamantane and pentacycloundecane (PCU) skeleton was described. Elimination of neutral guanidine is the most abundant reaction channel in the case of 2,4-adamantyl and PCU derivatives 4 and 5, while the elimination of CH2N2 fragment is preferred for other compounds. This was attributed to the cage opening of adamantane or PCU skeletons in the former case leading to the formation of the cyclohexyl- or cyclopropylcarbinyl carbocation stabilized by the conjugation with the guanylhydrazone subunit. The main fragmentation pathways observed experimentally were analyzed by using DFT calculations. All investigated bis(guanylhydrazone)s formed dications and their abundances were found to be proportional to the interguanidine distance in the considered ions. Calculation of the first and the second proton affinities supported qualitative interpretation of the dication abundance. Close contact of two guanidine subunits is thus confirmed to be crucial in determining preferential fragmentation pathway and to suppress formation of the dication.

CCDC 1844941: Experimental Crystal Structure Determination

Related Article: Afsaneh Pilevar, Abolfazl Hosseini, Marina Sekutor, Heike Hausmann, Jonathan Becker, Kevin Turke, and Peter R. Schreiner|2018|J.Org.Chem.|||doi:10.1021/acs.joc.8b01392

Synthesis and Anion Binding Assessment of Novel Adamantane Amidopyrroles

Two new adamantane anion receptors with amidopyrrole side arms were prepared and their anion binding ability in DMSO solutions with TBA salts (Cl–, AcO– and H2PO4–) was investigated by UV/Vis spectroscopy. After calculating the corresponding association constants of receptor-anion complexes, it became apparent that only one amidopyrrole side arm was engaged in complexation. These experimental findings were rationalized using computational tools and the binding mode was proposed. In addition to the found 1 : 1 stoichiometry, we showed that the studied receptors bind oxo-anions (H2PO4– and AcO–) more strongly than spherical halogenide (Cl–) anions.

Bioactive Molecules – Polycyclic Guanidine Derivatives

Industrijske otpadne vode predstavljaju posebnu opasnost za okolis buduci da nerijetko sadrže stetne i toksicne tvari organskog i anorganskog podrijetla koje imaju izrazito negativan utjecaj na prijamnike takvih otpadnih voda.1–3 Osim sto prilikom razgradnje trose kisik iz vode, zagađivala organskog podrijetla mogu uzrokovati i akutno trovanje živih organizama, sto ima kao posljedicu narusavanje osjetljive ravnoteže ekosustava. Zbog toga su kvaliteta industrijske otpadne vode i maksimalno dopustene kolicine opasnih i toksicnih spojeva u vodama regulirane zakonskim propisima. Obrada industrijskih otpadnih voda u najvecem broju slucajeva podrazumijeva kombinaciju primarnih, sekundarnih i tercijarnih postupaka obrade koji ukljucuju razlicite fizikalne, kemijske i bioloske metode obrade. U posljednjih nekoliko desetljeca povecao se broj znanstvenih istraživanja vezanih uz iznalaženje novih postupaka s potencijalnom primjenom u procesima obrade industrijskih otpadnih voda. Bioloski nerazgradive ili tesko razgradive organske tvari, kao sto su primjerice policiklicki aromatski spojevi, fenoli, organometalni spojevi i pesticidi, koji se zbog svoje toksicnosti ne mogu ukloniti klasicnim postupcima, najcesce se uklanjanju kemijskim putem. Napredni i termicki kataliticki oksidacijski procesi u kapljevini nove su i obecavajuce tehnologije obrade industrijskih otpadnih voda, cijem je razvoju i unapređenju posveceno mnogo pažnje. Kada se oksidacija organskih oneciscenja provodi pri povisenim temperaturama i tlakovima, tada je rijec o termickim oksidacijskim procesima u kapljevini (eng. Thermal Liquid Oxidation Processes ili Wet Oxidation Processes – WO).4–7 U ovim procesima organska se tvar oksidira uz pomoc hidroksilnih radikala upotrebljavajuci kisik, zrak, ozon, vodikov peroksid ili njihovu kombinaciju kao oksidacijsko sredstvo.8–12 Nastajanje hidroksil radikala, koji su odgovorni za oksidaciju organskih tvari, ostvaruje se provođenjem reakcije pri povisenim temperaturama i tlakovima, uz UV, ultrazvucno i mikrovalno zracenje te uporabom katalizatora. Provođenje reakcije pri ostrijim * Autor za dopisivanje: Dr. sc. Karolina Maduna Valkaj e-posta: kmaduna@fkit.hr Kataliticka oksidacija fenola uz zeolitni katalizator Cu/Y-5. 2. dio: Utjecaj postsintetske termicke i kemijske obrade DOI: 10.15255/KUI.2013.033 KUI-6/2015 Izvorni znanstveni rad Prispjelo 11. listopada 2013. Prihvaceno 4. veljace 2014.Kataliticka oksidacija zagađivala organskog podrijetla vodikovim peroksidom u vodenom mediju, poznata kao CWPO metoda (eng. Catalytic Wet Peroxide Oxidation), jedan je od postupaka kojim je moguce postici smanjenje organskog opterecenja otpadnih voda u praksi. U ovom radu Y-5 zeolit izabran je za nosac u koji je kao kataliticki aktivna tvar ugrađen bakar. U radu je istražen utjecaj reakcijskih parametara te postsintetske kemijske i termicke obrade katalizatora na njegove kataliticke znacajke: aktivnost i stabilnost. Cu/Y-5 katalizator je pripravljen ionskom izmjenom protonskog oblika komercijalnog Y-5 zeolita. U svrhu poboljsanja njegovih katalitickih znacajki provođena je postsintetska kemijska (ispiranje sa H2SO4) i termicka obrada (kalciniranje). Karakterizacija Cu/Y-5 katalizatora obuhvacala je rengensku difrakcijsku analizu na praskastom uzorku (PXRD) i elementarnu analizu na atomskom apsorpcijskom spektrometru (AAS) te određivanje specificne povrsine, volumena pora i raspodjele volumena pora (standardna BET metoda). Aktivnost i stabilnost pripravljenih katalizatora ispitana je u reakciji oksidacije fenola vodikovim peroksidom u vodenoj otopini. Maseni udio bakra na zeolitu bio je 3, 46 % prije postsintetske obrade, odnosno 3, 97 % nakon postsintetske termicke obrade te 0, 94 % nakon postsintetske kemijske obrade.Eksperimentalni podaci dobiveni provođenjem katalitickih testova testirani su slijedecim kinetickim modelima za oksidaciju fenola i raspad vodikovog peroksida . Za procjenu inetickih parametara koristena je Nelder-Meadova metoda nelinearnog optimiranja. Oba postupka postsintetske obrade znacajno su poboljsala stabilnost pripravljenog Cu/Y-5 katalizatora, dok je istovremeno njegova aktivnost ostala nepromijenjena ili je poboljsana.