Dariusz Pogocki

Molecular Sieves in Medicine

During the last few decades microporous and mesoporous materials have been considered for medical use due to biological properties and stability in biological environment. Zeolites have been investigated as drug carriers, and as adjuvants in anticancer therapy, dietetic supplements or antimicrobial agents. This review gives a brief overview of the major aspects of molecular sieves applications in medicine.

Head-to-Tail Interactions in Tyrosine/Benzophenone Dyads in the Ground and the Excited State: NMR and Laser Flash Photolysis Studies

The formation of head-to-tail contacts in de novo synthesized benzophenone/tyrosine dyads, bp logical sum Tyr, was probed in the ground and excited triplet state by NMR techniques and laser flash photolysis, respectively. The high affinity of triplet-excited ketones towards phenols was used to trace the geometric demands for high reactivity in the excited state. A retardation effect on the rates with increasing hydrogen-bond-acceptor ability of the solvent is correlated with ground-state masking of the phenol. In a given solvent the efficiencies of the intramolecular hydrogen-atom-transfer reaction depend strongly on the properties of the linker: rate constants for the intramolecular quenching of the triplet state cover the range of 10(5) to 10(8) s(-1). The observed order of reactivity correlates to a) the probability of close contacts (from molecular-dynamics simulations) and b) the extent of the electronic overlap between the pi systems of the donor and acceptor moieties (from NMR). A broad survey of the NMR spectra in nine different solvents showed that head-to-tail interactions between the aromatic moieties of the bp logical sum Tyr dyads already exist in the ground state. Favourable aromatic-aromatic interactions in the ground state appear to correspond to high excited-state reactivity.

Interaction of silver atoms with ethylene in Ag-SAPO-11 molecular sieve : an EPR and DFT study

The formation of silver–ethylene complexes in dehydrated Ag-SAPO-11 molecular sieve have been observed by electron paramagnetic resonance spectroscopy (EPR) after γ-irradiation at 77 K. Such reactive intermediate can play an important role in catalytic conversion of ethylene on silver loaded molecular sieves. The Ag(C2H4)2 stabilized inside relatively small channels of SAPO-11 molecular sieve it is observed even at 290 K. The ‘gas-phase’ geometries of Ag(C2H4) and Ag(C2H4)2 complexes, and respective hyperfine coupling constants were calculated applying DFT quantum chemical methods. The hyperfine coupling constants calculated for Ag(C2H4)2 complex of D2h symmetry are in very good agreement with those obtained experimentally.

Efficient α-(Alkylthio)alkyl-Type Radical Formation in •OH-Induced Oxidation of α-(Methylthio)acetamide

Pulse radiolysis with UV-vis/ESR detection and steady-state gamma-radiolysis, combined with chromatographic techniques, were used to investigate the detailed mechanism of the (*)OH-induced oxidation of alpha-(methylthio)acetamide (alpha-MTA) in aqueous solution. The main pathway involves the formation of hydroxysulfuranyl radicals alpha-MTA-(>S(*)-OH) and alpha-(alkylthio)alkyl radicals H(3)C-S-(*)CH-C( horizontal lineO)-NH(2) (lambda(max) </= 260 and 340 nm). The latter radicals are highly stabilized through the combined effect of both substituents in terms of the captodative effect. At low pH, alpha-MTA-(>S(*)-OH) radicals undergo efficient conversion to intermolecularly three-electron-bonded dimeric radical cations of alpha-MTA-(>S thereforeS<)(+) (lambda(max) = 480 nm), especially for high alpha-MTA concentrations. In contrast, at low proton concentrations, alpha-MTA-(>S(*)-OH) radicals decompose via the elimination of water, formed through intramolecular hydrogen (attached to the nitrogen atom) transfer to the hydroxysulfuranyl moiety within a six-membered structure. This process leads to the formation of the imine radical H(3)C-S-CH(2)-C( horizontal lineO)(*)NH, which subsequently decays in three independent channels. The first decay channel begins with a beta-scission followed by hydrolysis and a subsequent Hofmann rearrangement. One of the end products of this first decay channel is CO(2), which was detected. The second decay channel involves an intramolecular hydrogen transfer from the deltaC carbon atom to the radical imine site producing the alpha-(alkylthio)alkyl radical H(2)C(*)-S-CH(2)-C( horizontal lineO)-NH(2). In the third decay channel there is a 1,3-hydrogen shift in the imine radical which forms the radical H(3)C-S-(*)CH-C( horizontal lineO)-NH(2). The presence of the amide group induces more complex radical chemistry that leads unexpectedly to the degradation of the CH(3)SCH(2)CONH(2) molecule into gaseous products, CO(2) and NH(3). These features of the mechanism of the (*)OH-induced oxidation of alpha-MTA are quite different from those seen in other organic sulfides in neutral solutions.

Formation of a Three-Electron Sulfur–Sulfur Bond as a Probe for Interaction between Side Chains of Methionine Residues

The mechanism of oxidation processes of l-Met-(Pro)n-l-Met peptides that contain two Met residues located on the N- and C-terminal and separated by a defined number (n = 0-4) of proline residues was investigated in aqueous solutions using pulse radiolysis. The use of such peptides allowed for distance control between the sulfur atoms located in the side chains of the Met residues. The formation of a contact between the side chains of the Met residues was probed by the observation of transients with σ*-type 2c-3e S∴S and S∴O bonds as well as of α-(alkylthio)alkyl radicals (αS). This approach enabled the monitoring, in real time, of the efficiency and kinetics of interactions between methionine side chains. Such knowledge is important, inter alia, for long-distance electron transfer processes because methionine side chains can serve as relay stations and also for many aspects of protein folding when the formation of a contact between two amino acid residues in an unfolded polypeptide chain plays a central role in protein-folding mechanisms. The yields of these transients (measured as G-values) were found to be dependent on the number of Pro residues; however, they were not dependent in a simple way on the average distance ⟨rS-S⟩ between the sulfur atoms in Met residues. A decrease in the yield of the (S∴S)(+) species with an increase in the number of Pro residues in the bridge occurred at the expense of an increase in the yields of the intramolecular three-electron-bonded (S∴O)(+) radical cations and αS radicals. A detailed understanding of these trends in the chemical yields was developed by modeling the underlying chemical kinetics with Langevin dynamical simulations of the various oligoproline peptide chains and combining them with a simple statistical mechanical theory on the end-to-end contact rates for polymer chains. This analysis showed that the formation of a contact between terminal Met residues in the peptides with 0-2 Pro residues was controlled by the activated formation of (S∴S)(+) whereas in the peptides with 3 and 4 Pro residues, by the relative diffusion of the sulfur radical cation and unoxidized sulfur atom. In this picture, the dynamics of the other radical products can be seen to be only indirectly dependent on the length of the proline bridges because their formation is in competition with (S∴S)(+) formation.

New Insights into the Reaction Paths of 4-Carboxybenzophenone Triplet with Oligopeptides Containing N- and C-Terminal Methionine Residues

The oxidation processes of l-Met-(Pro)n-l-Met peptides that contain two Met residues located on the N and C termini and separated by a defined number (n = 0-4) of proline residues were investigated in aqueous solutions using laser flash photolysis. The use of such peptides allowed for distance control between the sulfur atoms located in the side chains of the Met residues. Interactions between side chains of the Met residues were probed by the observation of transients with σ*-type 2c-3e (S∴S)+, (S∴N)+, and (S∴O)+ bonds as well as of α-(alkylthio)alkyl radicals (αS). This approach enabled the monitoring, in real time, of the efficiency and kinetics of interactions between amino acid chains. Such knowledge is important, inter alia, for long-distance electron-transfer (ET) processes because amino acid side chains can serve as relay stations. The yields of these transients (measured as quantum yields (Φ)) were found to be dependent on the number of Pro residues, however, not dependent in a simple way on the average distance between sulfur atoms in Met residues. A decrease in the yield of the (S∴S)+ species with the number of Pro residues occurred at the expense of an increase in the yields of intramolecular three electron-bonded (S∴O)+/(S∴N)+ radical cations and αS radicals. These observations were rationalized by the fact that the time required for adequate overlap of the bonding orbitals is a key factor effecting the yield of the (S∴S)+ species. The time, however, can be controlled not only by the average distance but also by the specific geometrical and conformational properties of the peptide molecules.

Essentials and Perspectives of Computational Modelling Assistance for CNS-oriented Nanoparticle-based Drug Delivery Systems

The blood-brain barrier (BBB) is a complex system controlling two-way substances traffic between circulatory (cardiovascular) system and central nervous system (CNS). It is almost perfectly crafted to regulate brain homeostasis and to permit selective transport of molecules that are essential for brain function. For potential drug candidates, the CNSoriented neuropharmaceuticals as well as for those of primary targets in the periphery, the extent to which a substance in the circulation gains access to the CNS seems crucial. With the advent of nanopharmacology, the problem of the BBB permeability for drug nano-carriers gains new significance. Compared to some other fields of medicinal chemistry, the computational science of nano-delivery is still premature to offer the black-box type solutions, especially for the BBB-case. However, even its enormous complexity can spell out the physical principles, and as such subjected to computation. The basic understanding of various physicochemical parameters describing the brain uptake is required to take advantage of their usage for the BBB-nano delivery. This mini-review provides a sketchy introduction of essential concepts allowing application of computational simulation to the BBB-nano delivery design.

Chapter 1 – Natural Environments for Nanoparticles Synthesis of Metal, Metal Oxides, Core–Shell and Bimetallic Systems

As a result of worldwide problems associated with environmental contamination, the “greener” environmentally friendly processes for material sciences are becoming increasingly popular as required. Therefore, the bionanotechnology and the techniques for obtaining nanoparticles (NPs) applying eco-friendly, naturally occurring reagents seems very promising. NPs can be synthesized by chemical, physical, and biological methods. Recently, biosynthesis with the aid of novel, nontoxic, eco-friendly, and convenient biological material namely; fungi, biomolecules, and plant extracts are under extensive investigation. In the present review we have attempted to systematize recent development in the biosynthesis of metals NPs, metal oxides NPs, and core–shell and bimetallic systems NPs, in the natural environments such as (1) plant extracts, (2) bacteria, and (3) fungi. The NPs are metals (Ag, Au, Cu), metal oxides (ZnO, TiO2, ZrO2, CuO), and core–shell and bimetallic systems (Ti@Ni, Ag-Au, Au@Ag, Cu@Cu2O). Based on the physiochemical characteristics of the natural compounds involved in the processes, we tried to find commonalities in the different pathways of NPs synthesis wherever it was possible.

Organosilver radicals in molecular sieves

Abstract Organometallic radicals are important intermediates in biological and catalytic reactions. The structure and formation mechanism of radicals trapped in γ-irradiated molecular sieves exposed to methanol and ethylene have been studied by EPR spectroscopy. It was found that Ag·CH 2 OH + radical with one-electron bond between Ag and C is formed by the attack of ·CH 2 OH hydroxymethyl radical on Ag + cation. In Ag-SAPO-11/C 2 H 4 zeolite the EPR at 77 K shows the spectra of Ag 0 atoms and ·C 2 H 5 radicals. After annealing at 230 K those species disappeared and then an anisotropic EPR sextet was recorded. Based on DFT calculation the structure of complex was proposed in which two C 2 H 4 ligands adopted eclipsed confirmation on either side of the Ag atom. As a result the overwhelming spin density is localised on ethylene orbitals.