Ivo Kuřitka

Preparation and Characterization of Poly (vinyl alcohol)/Lactic Acid Compounded Polymeric Films

Abstract Poly (vinyl alcohol) (PVA) and L-lactic acid (LA) were compounded to get biodegradable polymeric film with useful mechanical, thermal, and bacteriostatic properties for possible medical or packaging applications. Samples with various concentrations of LA were prepared by using the solvent cast technique and characterized by tensile tests, differential scanning calorimetry, Fourier-transform infrared spectroscopy, thermogravimetry, evolved gas analysis, and bacteriostatic tests, and their biodegradability was investigated under aquatic and aerobic conditions. The films show a rapid increase in elasticity and decrease in glass transition temperatures due to the presence of LA. A bacteriostatic effect on Pseudomonas putida, Staphylococcus epidermis, and Micrococcus sp. was proved. The biodegradation of all samples by mixed microflora was completed within 250 hours; however, the course of biodegradation was influenced by both esterification of PVA and the presence of molecules of LA in the polymeric films.

The enhanced magnetorheological performance of carbonyl iron suspensions using magnetic Fe3O4/ZHS hybrid composite sheets

Two-dimensional magnetic Fe3O4/ZHS hybrid composite sheets were prepared via a two-step microwave-assisted solvothermal synthesis. The successful incorporation of Fe3O4 nanoparticles synthesized in the first step into a zinc hydroxysulfate (ZHS) sheet-like structure formed during the second synthesis step was confirmed by X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry. The obtained magnetic Fe3O4/ZHS hybrid composite particles show a hexagonal and sheet-like morphology. The addition of these sheet-like hybrid composite particles into magnetorheological carbonyl iron-based suspensions results in a significant increase in MR performance. Moreover, this addition considerably contributes to the redispersibility enhancement of prepared suspensions in comparison to those consisting only of bare carbonyl iron particles.

Determination of Intrinsic Binding Modes by Mass Spectrometry: Gas-Phase Behavior of Adamantylated Bisimidazolium Guests Complexed to Cucurbiturils

Adamantylated bisimidazolium cations exhibit a distinct fragmentation pathway in contrast to their cucurbit[7]uril (CB7) complexes. The observed alternative fragmentation of the guest molecule in a complex clearly correlates to the supposed sterically hindered or allowed slippage of the macrocycle over the axel molecule.

Novel adamantane-bearing anilines and properties of their supramolecular complexes with β-cyclodextrin

Several novel anilines bearing 1-adamantyl substituents that are useful for drug modification were synthesised from the corresponding 1-adamantyl (nitrophenyl) ketones. The host–guest systems of these prepared ligands with β-cyclodextrin (β-CD) were studied using electrospray ionisation mass spectrometry, NMR spectroscopy, titration calorimetry and semi-empirical calculations. The complexes with 1:1 stoichiometry were found to predominantly exist as pseudorotaxane-like threaded structures with the adamantane cage sitting deep in the cavity of β-CD close to the wider rim. Such geometry was observed for all examined amines and is independent of their structure and/or presence of protic substituents.

Sonochemical synthesis of Gd3+ doped CoFe2O4 spinel ferrite nanoparticles and its physical properties

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe2-xGdxO4; x=0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd3+ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe2-xGdxO4 nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd3+ substitution in CoFe2O4 nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd3+ doped cobalt ferrite (CoFe2-xGdxO4; x=0.20) exhibit enhanced dielectric constant (277 at 100Hz) and ac conductivity (20.2×10-9S/cm at 100Hz). The modulus spectroscopy demonstrated the impact of Gd3+ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd3+ substitution from 234.32Oe (x=0.00) to 12.60Oe (x=0.05) and further increases from 12.60Oe (x=0.05) to 68.62Oe (x=0.20). Moreover, saturation magnetization decreases with Gd3+ substitution from 40.19emu/g (x=0.00) to 21.58emu/g (x=0.20). This work demonstrates that the grain size and cation distribution in Gd3+ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications.

Adamantane-bearing benzylamines and benzylamides: novel building blocks for supramolecular systems with finely tuned binding properties towards β-cyclodextrin

Novel building blocks for the synthesis of supramolecular components based on adamantane-bearing benzylamines were prepared. The binding properties of these amines and the corresponding acetamides towards β-cyclodextrin (β-CD) were studied using mass spectrometry, NMR spectrometry, isothermal titration calorimetry and semi-empirical calculations. It was found that all of the examined guests predominantly formed 1:1 inclusion complexes in an enthalpy-driven manner with association constants of the order of 102–103 M− 1. Stronger binding to the β-CD cavity was observed for guests with a longer spacer between the adamantane and benzene moieties and/or a 1,4-disubstituted benzene ring.

Comparison of the Degree of Consolidation of Historic Plaster Layers by Means of Lime Hydrate Nanosuspensions

Historic masonry is usually coated with multiple plaster layers, exposed to long-term extreme loading (climatic effects, elevated moisture levels, salt crystallization and recrystallization, biological effects, etc.). As a consequence of the above negative cyclic effects, degradation processes are triggered off leading to a loss in plaster cohesion with the substrate masonry and successive falling-off of surface layers. The strengthening and rehabilitation of plasters with degraded binder components, impaired structure, insufficient adhesion of individual layers of plaster to the masonry surface, with elevated salt contents in the pore system and surface crusts represent a demanding task in terms of the stabilization of such degraded plasters and coatings. Consolidation (i.e. enhancement of mechanical characteristics) belongs to the basic objectives of the restoration of historic plasters, its principle is to return binder into the material structure, fill in existing hollow spaces, heal cracks, etc. Degraded lime plasters are strengthened with consolidating agents applied in the form of solutions, e.g. lime water, organosilicates or lime nanosuspensions, etc. The lime nanosuspension is composed of lime hydrate nanoparticles, dispersed in an alcoholic medium. Due to the deposition of calcium carbonate in the degraded material, the bonds are re-strengthened and the material consolidated. The article presents partial results of theoretical and experimental research addressing potential consolidation of historic plaster layers with lime nanosuspensions prepared by the synthesis of Ca(OH)2, which were successively modified and enriched with other components.

Dialdehyde cellulose crosslinked poly(vinyl alcohol) hydrogels: Influence of catalyst and crosslinker shelf life

Dialdehyde cellulose (DAC) derived from α-cellulose by periodate oxidation was solubilized and utilized as a suitable crosslinking agent for poly(vinyl alcohol) (PVA). The crosslinking occurs between reactive aldehyde groups of DAC on the C2 and C3 carbons of anhydroglucose unit and hydroxyl groups on PVA backbone in the presence of acidic catalyst. Two catalyst systems based on diluted hydrochloric or sulfuric acid were tested. Their influence on the PVA/DAC network has been investigated by solid-state 13C NMR, XRD analysis and in the terms of network parameters and mechanical properties. Because DAC undergoes structural changes and decays with time, the role of DAC solution age (1, 14 and 28 days old) on material properties of formed PVA/DAC samples was studied as well. Outlined, even after 28 days after solution preparation, DAC exhibited the capability to act as an efficient crosslinker for PVA. The resulting material properties of PVA/DAC hydrogels were found to be dependent on the molecular weight of solubilized DAC closely related to its age and the choice of catalyst system. Furthermore, the DAC potential for PVA crosslinking was investigated in a broad concentration range. Besides, the DAC crosslinking efficiency was also compared to that of common crosslinking agent glutaraldehyde. The results showed different network topology of prepared hydrogels and exceptional crosslinking potential of DAC in comparison to glutaraldehyde, which is most likely related to DAC macromolecular character.

NANOTECHNOLOGY IN THE CULTURAL HERITAGE - INFLUENCE OF NANOSPENSIONS ADOPTED BY NANOPARTICLES OF TiO2 FOR CLEANING THE SURFACE OF HISTORICAL PLASTERS

The continuous development of nanostructure and the study of physico chemical processes in the nanometer range lead to new methods that can slow down the degradation processes of a work of art, or even restore damage caused, for example, by an inappropriate restoration process. The use of nanosuspensions based on calcium hydroxide is probably the most widespread application of nanomaterials in heritage care, especially in the field of hardening of lime building materials (plaster, limestone, etc.). In combination with titanium dioxide, it should be a successful suspension in the fight against biological agents, surface contamination or in the protection of UVresistant building materials.

1-(1-Adamantylmeth­yl)-1H-benzimidazole

The asymmetric unit of the title compound, C18H22N2, contains two independent molecules which differ slightly with respect to the torsion angles involving the atoms joining the adamantyl and benzimidazole groups. The bond angles in the adamantane cage vary within the range 108.27 (9)–110.55 (10)°. The benzimidazole ring system in both molecules is essentially planar, the maximum deviations from the best planes being 0.0134 (15) and 0.0229 (14) Å. In the crystal, weak C—H⋯π interactions link the molecules.