Zoran Džolić

Intense Optical Activity from Three‐Dimensional Chiral Ordering of Plasmonic Nanoantennas

Twisting nanoparticles: Plasmonic circular dichroism was experimentally obtained in chiral 3D organizations of gold nanorods obtained by self-assembly of the nanoantennas onto a fiber template with a twisted morphology. Numerical simulations based on coupled dipoles confirm the crucial role of gold nanorods in this intense circular dichroism

Neutral Organometallic Halogen Bond Acceptors: Halogen Bonding in Complexes of PCPPdX (X = Cl, Br, I) with Iodine (I(2)), 1,4-Diiodotetrafluorobenzene (F4DIBz), and 1,4-Diiodooctafluorobutane (F8DIBu).

The behavior of a sterically crowded neutral pincer {2,6-bis[(di-t-butylphosphino)methyl]-phenyl}palladium (PCPPd) halides, PCPPdX (X = Cl, Br or I), as XB acceptors with strong halogen bond (XB) donors, iodine (I2), 1,4-diiodotetrafluorobenzene (F4DIBz), and 1,4-diiodooctafluorobutane (F8DIBu) were studied in the solid state. The co-crystallization experiments afforded high-quality single crystals of XB complexes PCPPdCl–I2 (1a), PCPPdBr–I2 (2a), PCPPdI–I2(3a), PCPPdCl–F4DIBz (1b), PCPPdBr–F4DIBz (2b), and PCPPdBr–F8DIBu (2c). The 1:1 iodine complexes (1a, 2a, and 3a) all showed a strong halogen bonding interaction, the reduction of the sum of the van der Waals radii of halogen to iodine being 24.6 (1a), 23.9 (2a), and 19.4% (3a) with X···I–I angles of 177, 176, and 179°, respectively. While the pincer palladium chloride 1 and bromide 2 were crystallographically isomorphous and showed similar XB behavior, the palladium iodide complex, 3, exhibited markedly different properties, and unlike 1 and 2 it does not, under similar conditions, result in XB complexes with the weaker XB donors F4DIBz and F8DIBu. The results indicate that PCPPdI is not nucleophilic enough to have XB interactions with other donors than iodine. However, the weaker XB donors F4DIBz and F8DIBu form XB complexes with the chloride 1 and especially with the bromide 2. The prevalence of the halogen bonding with 2 is probably not only electronic in origin, and it seems to offer the best balance between electron poorness and steric availability. The XB interactions with F4DIBz and F8DIBu are much weaker than with iodine, the reduction of the sum of the van der Waals radii of halogen to iodine being 13.5, 12.3, and 14.6% with C–I···X angles between 163 and 179° for 1b, 2b, and 2c, respectively, and results in polymeric (···1···F4DIBz···1···F4DIBz···)n, (···2···F4DIBz···2···F4DIBz···)n, and (···2···F8DIBu···2···F8DIBu···)n one-dimensional zigzag chains in the solid state.

Synergic effect in gelation by two-component mixture of chiral gelators

Observation of the synergic gelation effect (SGE) in two-component gels is reported. An equimolar mixture of (S,S)-bis(LeuOH) oxalamide [(S,S)-1] and (S,S)-bis(leucinol) oxalamide [(S,S)-2] is able to gel up to 7 times larger a volume of p-xylene than an equal mass of each component and up to 5 times larger a volume than an equal mass of the (S,S)-1 + (R,R)-2 or (S,S)-1 + rac-2 equimolar mixtures. The homochiral (S,S)-1 + (S,S)-2 combination of gelators is capable of hardening a volumes up to 5 times larger of certain solvents than the heterochiral (S,S)-1 + (R,R)-2 combination. Experimental evidence provided by determination of gelation efficiency, by 1H NMR, TEM and XRD studies, by determination of phase transition diagrams and calculations of thermodynamic parameters for gel melting processes shows that synergism depends on the chirality of the components, on the solvent properties and on the gel morphology. It was found that each component tends to form reversed bilayers in lipophilic solvents which then interact and organize into gel unit fibers. The unit fibers formed by interaction of the (S,S)-1 and (S,S)-2 bilayers and of the (S,S)-1 and (R,R)-2 bilayers are distereoisomeric. In certain solvents, such diastereomeric unit fibers give different gel morphologies which in turn results by different thermal stabilities of the gels, and in some cases by dramatically different gelling efficiencies of gelator mixtures. The latter observation is denoted as the synergic gelation effect (SGE).

Fluoride-responsive organogelator based on oxalamide-derived anthraquinone

Anthraquinone derived oxalamide gelator 1 forms with aromatic solvents and alcohols very stable gels which selectively respond to the presence of fluoride anion by colour change and/or gel-to-sol transition.

The Formation of CuCl2‐Specific Metallogels of Pyridyloxalamide Derivatives in Alcohols

Isomeric pyridyloxalamide derivatives 1-3, which differed in the position of the nitrogen atom on the pyridyl ring, showed remarkably different gel-forming aptitudes in the presence of CuCl2 salt in alcohols. Whilst derivatives 1 and 3 formed a soluble complex and a solid precipitate, respectively, ligand 2 generated a remarkably metal- and anion-specific metallogel.

Synthesis, structural studies, and biological evaluation of some purine substituted 1-aminocyclopropane-1-carboxylic acids and 1-amino-1-hydroxymethylcyclopropanes

Abstract The novel purine derivatives of 1-aminocyclopropane-1-carboxylic acid (8 and 9) and 1-amino-1-hydroxymethylcyclopropane (12 and 13) with methylene spacer between the base and the cyclopropane ring were prepared by multistep synthetic route involving alkylation of adenine and 6-(N-pyrrolyl)purine with 2-hydroxymethyl-1-aminocyclopropane-1-carboxylic acid derivative 3 as a key reaction. All novel compounds were racemic. The N-9 substitution of the purine ring and the Z-configuration of the cyclopropane ring in 4–13 were deduced from their 1H and 13C NMR spectra by analyses of chemical shifts, H-H coupling constants and connectivities in two-dimensional homo- and heteronuclear correlation spectra. An unequivocal proof of the stereostructure of 1, 4 and 5 was obtained by their X-ray structure analysis. The novel compounds were evaluated on cytostatic and antiviral activities in several cell lines. The 6-(N-pyrrolyl)purine derivative of 1,2-aminocyclopropane alcohol 12 exhibited a more pronounced inhibitory activity against the proliferation of cervical carcinoma (HeLa) and human fibroblast (WI-38) cells than other types of tumor cell lines. None of the compounds showed inhibitory activities against cytomegalovirus, varicella-zoster virus or other viruses.

Responsive aggregation-induced emissive supramolecular gels based on bis-cyanostilbene derivatives

In aromatic solvents, V-shaped bis-cyanostilbene derivative 1 forms stable and emissive gels which are capable of responding to light and, selectively, to TFA via a gel-to-sol transformation.

Preparation of potentially porous, chiral organometallic materials through spontaneous resolution of pincer palladium conformers

Understanding the mechanism by which advanced materials assemble is essential for the design of new materials with desired properties. Here, we report a method to form chiral, potentially porous materials through spontaneous resolution of conformers of a PCP pincer palladium complex ({2,6-bis[(di-t-butylphosphino)methyl]phenyl}palladium(II)halide). The crystallisation is controlled by weak hydrogen bonding giving rise to chiral qtz-nets and channel structures, as shown by 16 such crystal structures for X = Cl and Br with various solvents like pentane and bromobutane. The fourth ligand (in addition to the pincer ligand) on palladium plays a crucial role; the chloride and the bromide primarily form hexagonal crystals with large 1D channels, whereas the iodide (presumably due to its inferior hydrogen bonding capacity) forms monoclinic crystals without channels. The hexagonal channels are completely hydrophobic and filled with disordered solvent molecules. Upon heating, loss of the solvent occurs and the hexagonal crystals transform into other non-porous polymorphs. Also by introducing a strong acid, the crystallisation process can be directed to a different course, giving several different non-porous polymorphs. In conclusion, a number of rules can be formulated dictating the formation of hexagonal channel structures based on pincer palladium complexes. Such rules are important for a rational design of future self-assembling materials with applications in storage and molecular recognition.

AIE-active bis-cyanostilbene-based organogels for quantitative fluorescence sensing of CO2 based on molecular recognition principles

Carbon dioxide is a major greenhouse gas, probably responsible for climate change, and a safety concern for workers under specific conditions. Simple and effective means for its detection are thus highly desirable. Herein, the aggregation-induced emissive bis-cyanostilbene derivative 1 was used to develop two sensor systems based on (i) dispersed gel aggregates and (ii) solid supported xerogels for the optical detection of CO2 gas. In the presence of diethylamine, CO2 is transformed into a carbamate ionic liquid (CIL), which binds to 1 acting as an anion receptor. The formation of such a host–guest adduct alters the aggregation state of the system and consequently its fluorescence, which thus responds to CO2 concentration. While the gel aggregate sensing system responds to CO2via fluorescence quenching, the xerogel sensor system works in a dual mode, i.e., by both fluorescence quenching and modulation, reaching very high sensitivity and a low detection limit (4.5 ppm). The sensing behavior of 1 (gel aggregate and xerogel systems) towards CO2 gas was studied in detail by solid state fluorescence and solution 1H-NMR spectroscopies.

Self-Complementary Dimers of Oxalamide-Functionalized Resorcinarene Tetrabenzoxazines

Self-complementarity is a useful concept in supramolecular chemistry, molecular biology and polymeric systems. Two resorcinarene tetrabenzoxazines decorated with four oxalamide groups were synthesized and characterized. The oxalamide groups possessed self-complementary hydrogen bonding sites between the carbonyls and amide groups. The self-complementary nature of the oxalamide groups resulted in self-included dimeric assemblies. The hydrogen bonding interactions within the tetrabenzoxazines gave rise to the formation of dimers, which were confirmed by single-crystal X-ray diffractions analysis and supported by NMR spectroscopy and mass spectrometry. The self-included dimers were connected by numerous and strong intermolecular N-H⋅⋅⋅O and C-H⋅⋅⋅O hydrogen bonds supplemented with C-H⋅⋅⋅π interactions, forming one-dimensional polymers, which were then further linked into three-dimensional networks.