Andrijana Žekić

Growth rate dispersion of small KDP crystals

The growth rate dispersion of small KDP crystals grown from aqueous solution was studied. These dispersions were described by a mixture of normal distributions with three maxima which were fitted to the frequency distributions of growth data. Dislocation structure of individual crystals and varying degrees of strain in crystal lattice were considered as possible causes of this phenomenon.

Dependence of growth rate on initial crystal size

The connection between growth rate dispersion and the size-dependent crystal growth of potassium dihydrogen phosphate is investigated. A possible resolution of the existing confusion in the size-dependent crystal growth investigations is suggested. It is shown that size-independent growth exists if the crystals belonging to one growth rate distribution maximum are considered separately. On the other hand, a linear dependence exists between the arithmetic mean of growth rates belonging to one maximum and the arithmetic mean of corresponding initial crystal sizes. Possible reasons for the existence of extra growth rate distribution maxima and for their widths are suggested. The high scatter of data on the growth rate versus the crystal size dependence is discussed according to crystal growth theories.

Correlation between the crystal size and crystal growth rate of KDP and Rochelle salt crystals

It is shown that the dependence of the crystal growth rate on the initial crystal size is linear, or probably, more complex, but there is no reason for using some complex functions for describing the mentioned dependence, as many authors do. Correlation between the initial crystal size and the crystal growth rate is positive, i.e. higher growth rate of the crystals corresponds to the larger initial crystal size.

Study of interaction between nitrogen DBD plasma-treated viscose fibers and divalent ions Ca2+ and Cu2+

Viscose fibers were treated with atmospheric pressure dielectric barrier discharge (DBD) plasma obtained in nitrogen in order to activate the fiber surface prior to sorption of the divalent ions Ca2+ and Cu2+. Methylene blue sorption was used for estimation of carboxyl group formation on the surface after DBD plasma treatment, through the degree of fabric staining (K/S). Sorption of divalent ions was performed from solutions of each individual ion and from solutions of calcium and copper in succession onto untreated and plasma-treated viscose samples. The quantity of sorbed metal was determined from the neutralization and iodometric titration method. Scanning electron microscopy coupled with energy dispersive X-ray analysis was used for fiber morphology and surface characterization before and after plasma treatment, and after metal ions sorption. Experiments revealed copper microparticles formation on the fiber surface when sorption of copper was performed on samples with bonded calcium. Further analysis confirmed that for growth of copper particles, both calcium ions and nitrogen DBD plasma pretreatments are necessary.

Electrochemical, theoretical, and morphological studies of antioxidant fullerosteroids

Four fullerosteroidal conjugates, previously confirmed to express two- to threefold better antioxidant activity in vitro than C60, were subjected to additional studies, including electrochemical, theoretical, and morphological examination. All tested compounds underwent reversible, diffusion-controlled reductions. A notable influence of the solvent properties on the reduction potential, the level of aggregation, and the lowest unoccupied molecular orbital (LUMO) energy was observed. Theoretical calculations indicated that the energy gain obtained by an intermediate formation, together with compounds’ polarizability, polarity, and lipophilicity contributed to the radical quenching capacity. Very large supramolecular aggregates of all fullerosteroidal esters with no hierarchical arrangement were observed in precipitated samples, while solvent induced self-assembling led to round nanoplates, which further arranged to flower-shaped hierarchically ordered architectures or uniformly distributed discoid particles. As in electrochemical studies, fine tuning of the aggregation level was achieved by the solvent.Graphical abstract

Fulleropyrrolidine molecular dumbbells act as multi-electron-acceptor triads. Spectroscopic, electrochemical, computational and morphological characterizations

We synthesized three dumbbell-like compounds 2a–c, each containing two C60 groups at the periphery and pyromellitic diimide (PMDI) in the middle, and examined their electronic as well as assembly characteristics with both experimental and computational methods. Cyclic voltammetry (CV) measurements revealed that each of three electron-accepting (AAA) triads could accommodate up to eight electrons. Computational studies (density functional theory, DFT) of 2a–c at PBEPBE/6-311G(d,p) level of theory, with B3LYP/6-31G(d) optimized geometries, revealed that HOMO–LUMO energy gaps are similar to those of the model compound [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Compounds 2a–c were also found to assemble into vesicles and nanoparticles on the copper grid (100–300 nm, TEM), while giving more sizeable aggregates after a deposition on the glass (SEM, >5 μm). Understanding the packing of 2a–c on various solid substrates, as well as the assembly characteristics in general, is important for tuning the properties and fabrication of electronic/optical devices. On the basis of the results of conformational analysis (MM and DFT calculations), we deduced that different alkyl spacers in 2a–c ought to play a role in π–π interactions between the aromatic components of the triad to guide the packing and therefore morphology of the material.

Fulleropyrrolidines derived from dioxa- and trioxaalkyl-tethered diglycines

Two different α,ω-diglicynes linked by linear polyoxaalkyl chains in the presence of formaldehyde underwent Prato reaction to the fullerene C60. The shorter linker templated formation of only cis-bisadducts, while the longer one afforded a mixture of four bisadducts (all cis and the equatorial) and difullerene dumbbell compound. Their structures were confirmed by the extensive analysis of the spectral data and molecular symmetry, as well. All compounds expressed an ability to arrange into hierarchically ordered supramolecular aggregates, the form of which depended both on the addition pattern and the spacer structure. The attenuated electron-accepting affinity, examined by cyclic voltammetry was in agreement with diminished delocalization of the π-electronic system. In addition, all compounds exerted a notable radical scavenging activity.