Jaroslav Kříž

Formation and structure of the epoxy-silica hybrids

The organic-inorganic hybrid interpenetrating network (IPN) composed of an epoxide-amine network and silica was prepared and studied. Formation of the inorganic phase from tetraethoxysilane (TEOS) by sol-gel process was characterized by 29Si n.m.r. spectroscopy, gas chromatography, small-angle X-ray scattering and electron microscopy. Kinetics of the silica structure build-up in the organic matrix, its final structure and morphology depend on the method of IPN hybrid preparation. The large compact silica aggregates, 100–300 nm in diameter, are formed during the one-stage polymerization. The two-stage process with the acid prehydrolysis of TEOS leads to an acceleration of gelation and formation of more open and smaller silica structures: 50–100 nm in diameter. The most homogeneous hybrid morphology with the smallest silica domains of size 10–20 nm, appears in the sequential IPN. The development of the silica structure is restricted by a rigid reaction medium of the preformed epoxide network.

A Proton Complex of p-tert-Butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide): NMR Evidence and Probable Structure

Using 1H and 13C NMR together with density functional theoretical (DFT) calculations, it is shown that p-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in nitrobenzene-d 5. Protons were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric but rapidly motionally averaged conformation, which is distinctly more cone-like than ligand 1. The hydroxonium ion H3O+ is bound partly to thiocarbonyl sulphur atoms and partly to phenoxy oxygen atoms of 1 by strong hydrogen bonds and other electrostatic interactions.

Experimental Evidence for Unusual Protonation of Tetraethyl p-tert-Butylcalix[4]arene Tetraacetate and the Most Probable Structure of the Resulting Complex

Using 1H and 13C NMR, FT IR spectroscopy together with quantum mechanical DFT calculations, we show that tetraethyl p-tert-butylcalix[4]arene tetraacetate (1) forms a stable equimolecular complex with proton in the form of hydroxonium ion in acetonitrile-d 3. Protons for this complex were offered by hydrogen bis(1,2-dicarbollyl) cobaltate (HDCC) and converted to hydroxonium ions by traces of water. The complex 1·H3O+ adopts a slightly asymmetric conformation, which is distinctly more cone-like than ligand 1. According to spectral evidence, the hydroxonium ion H3O+ is bound mainly to three of the phenoxy oxygen atoms of 1 by strong hydrogen bonds leaving the ester carbonyl groups, which are the usual coordination site for metal cations, free. Theoretical DFT calculations support the bonding to phenoxy oxygen atoms but slightly prefer a structure with one of the carbonyls being involved in the coordination.

N-(2-Hydroxypropyl)methacrylamide-based polymer conjugates with pH-controlled activation of doxorubicin for cell-specific or passive tumour targeting. Synthesis by RAFT polymerisation and physicochemical characterisation.

Controlled radical reversible addition-fragmentation chain transfer (RAFT) polymerisation was used to prepare water-soluble polymer-drug carriers based on copolymers of N-(2-hydroxypropyl)methacrylamide (HPMA) with a hydrazide group-containing monomer, showing well-defined structure with narrow molecular weight distribution (approx. 1.1-1.2). The anticancer therapeutic doxorubicin was bound to the polymeric carrier by a hydrazone bond, enabling pH-controlled release under mildly acid conditions that mimics the environment in endosomes/lysosomes of tumour cells. RAFT polymerisation facilitated the synthesis of semitelechelic copolymers, which were used in the synthesis of monoclonal anti-CD20 antibody-polymer-drug conjugate designed for cell-specific tumour targeting. They were also used for producing a biodegradable high-molecular-weight graft polymer-drug conjugate that degrade in the presence of glutathione, which is designed for passive targeting to solid tumours. The conjugates exhibited well-defined structures with narrow molecular weight distributions of approx. 1.3 and pH-controlled drug release.

Small-Angle Neutron Scattering Study of Onion-Type Micelles

Onion-type block copolymer micelles were prepared drom polystrene-block-poly(2-vinylpridine) (PS-b-PVP) inner micelles in an acidic solution by basyfyting in the presence of polystrene-block-poly(2-vinylpridine)-block-poly(ethylene oxide) (PVP-b-PEO). This has the effect of depositing the PVP-b-PEO onto the collapsed corona of the PS-b-PVP micelle. These core PS-b-PVP micelle, the small micelles formed by PVP-b-PEO, and the resulting onions micelles were studied by small angle neutron scattering (SANS) techniques . Two recently developed evaluation techniques were employed: 1.Bare-core approximation, which utilizes the data at larger scattering anles provided information about the size and polydispersity of the micelle core. 2. Application of the Pedersen and Gerstenberg micelle model, which utilizes the whole scattering curve. Due to their polyelectrolyte nature, the core micelles had very extentde coronas corresponding to rather large stastistical segment lengths. The SANS data at large scattering angles for the solution of onions-type micelles revealed the presence of a significant number of the small PVP-b-PEO micelles. The contribution of the small micelles to the total scattering was subtracted and the properties and polydispersities of onions cores and stabilizing PEO coronas were obtained.

SANS study of multilayer nanoparticles based on block copolymer micelles

A novel type of three-layer nanoparticles was studied using small-angle neutron scattering (SANS). The particles were prepared by adding methyl methacrylate monomer to a polystyrene-block-poly(methacrylic acid) micellar solution in aqueous buffer and subsequent polymerization by γ-irradiation. The contrast-matching SANS experiments revealed that upon polymerization, the PMMA chains form a layer on the surface of the PS cores of the original micelles. This is in agreement with the finding that at room temperature, MMA monomer molecules do not penetrate into the micelle core in detectable amounts. In the presented example, the mean core radius of original micelles and the layer thickness were determined to be 99 and 17 A, respectively. Both characteristics are expected to be controllable by the choice of block copolymer micelles and the parameters of the polymerization process.

Molecular Structure of the Complex of Hexano-6-lactam with Magnesium Bromide

A complex of hexano-6-lactam (e-caprolaclam, CL) with magnesium bromide was synthesized. The complex was characterized by IR and NMR spectroscopy, and thermal analysis (TGA and DSC). Based on interpretations of NMR and vibrational spectra and quantum mechanical calculations, the molecular structure MgBr 2 -CL 6 with almost exactly equivalent positions of all six lactam molecules is proposed.

New soluble polyimides prepared from 4,4'-(alkylenediyldioxy) dianilines

Abstract New soluble aromatic polyimides have been prepared from 4,4′-(hexafluoroisopropylidene)bis(phthalic anhydride) (6FDA) and 4,4′-(alkylenediyldioxy)dianilines. Their structures were determined by i.r., 1 H n.m.r. and 13 C n.m.r. spectroscopic measurements, based on model compounds prepared by reacting 6FDA with p -anisidine. These polymers show low glass transition temperatures and good solubility in various solvents, and are stable up to 440°C in a nitrogen atmosphere.

Interaction of Premicellar States of a PEO-PPO-PEO Triblock Copolymer with Partially Hydrophobic Substances: NMR Study

According to (1)H and (13)C NMR spectra, relaxations, and PFG NMR self-diffusion measurements, partially hydrophobic additives methyl-ethyl ketone (MEK), methyl-isopropyl ketone (MIPK), and methyl-t-butyl ketone (MTBK) facilitate the conformation change and subsequent self-association of the copolymer Pluronic L64. The correlation time (4-9 ms) and activation energy (43-52 kJ/mol) of transition between its conformation states decrease with the increasing hydrophobicity and bulkiness of the additive. The temperature of the first PPO self-association decreases in the same order (by 4 K for MTBK). The interaction of the additives was indirectly proved by the decrease of their rotational and translational mobility in the presence of L64. The rotational correlation time τ(c) is between 3 and 6 × 10(-11) s, whereas that of the same molecules in the absence of L64 is lower than 6 × 10(-12) s. The normalized self-diffusion coefficient decreases to about 0.7 of its original value in the presence of L64. The interaction of the additive with the PPO block is transient but effective enough to facilitate its conformational change and self-association. Its mediation by a water molecule bound to PPO as a possible mechanism is suggested.

Anionic polymerization of acrylates. XI. Effect of composition and ageing of the Li ester enolate/tert‐butoxide initiating complex on the anionic polymerization of methyl methacrylate and 2‐ethylhexyl acrylate

The article presents the results of (meth)acrylate polymerization in THF initiated with various complexes of methyl 2-lithioisobutyrate (MIB-Li) and lithium tert-buioxide (t-BuOLi), prepared from the components in mole ratios 1:3, 1:6 and 1:10 in THF and aged for various time periods and at various temperatures. In dependence on the component ratio, temperature and storage time, the mixtures form cubic cross-aggregates with MIB-Li/t-BuOLi mole ratios 3:1, 2:2 and 1:3 which exhibit different behavior when used as initiators. It was found that the way of synthesis of the complex and its structure not only affect the kinetics of polymerization but also distinctly change the microstructure of the formed polymers.