Artur Mardyukov

Interaction and Reaction of the Phenyl Radical with Water: A Source of OH Radicals

Thats radical! A photochemical reaction between the phenyl radical and water results in the abstraction of a hydrogen atom from water and the formation of a hydroxyl radical. The hydroxyl radical forms an OHpi hydrogen bond with benzene (see picture) and does not react with benzene thermally under the conditions of matrix isolation.

Preparation of photoactive polymers and postmodification via nitroxide trapping under UV irradiation.

New types of photoactive homo and block copolymers bearing α-hydroxyalkylphenylketone (2-hydroxy-2-methyl-1-phenylpropan-1-one) moieties as backbone substituents are prepared using nitroxide-mediated radical polymerization (NMP). Such polymers can be readily activated via the Norrish-type I photoreaction to give polymeric acyl radicals. Photolysis in the presence of a persistent nitroxide, which serves as a C- radical trapping reagent, leads to chemically modified polymers conjugated with nitroxide moieties. The number-average molecular weight (M(n)) of the prepolymers and the chemically modified polymers was determined by gel permeation chromatography (GPC). Structures were further confirmed by NMR spectroscopy and by attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy.

Matrix Isolation and Spectroscopic Characterization of the Phenylperoxy Radical and Its Rearranged Products

The phenylperoxy radical 1 has been synthesized by the reaction of the phenyl radical 2 with (3)O(2). Radical 1 could be either generated in the gas phase and subsequently trapped in solid argon at 10 K, or directly synthesized in argon matrices. By reacting 2 as well as its perdeuterated isotopomer [D(5)]-2 with (16)O(2) and with (18)O(2), respectively, the four isotopomers [H(5)]-(16)O(2)-1, [D(5)]-(16)O(2)-1, [H(5)]-(18)O(2)-1, and [D(5)]-(18)O(2)-1 were matrix-isolated and characterized by IR spectroscopy. The experimental IR spectra are in excellent agreement with results from DFT calculations. Irradiation of 1 with visible light produces the 2-oxepinoxy radical 5 in a clean reaction. Subsequent irradiation results in ring-opening and formation of several conformers of ketoketene 6. The radicals 1, 5, and 6 play an important role in the combustion of aromatic hydrocarbons and could now be isolated and spectroscopically characterized for the first time.

Chemical modification of polymer brushes via nitroxide photoclick trapping.

The preparation of polymer brushes (PBs) bearing α-hydroxyalkylphenylketone (2-hydroxy-2-methyl-1-phenylpropan-1-one) moieties as photoreactive polymer backbone substituents is presented. Photoreactive polymer brushes with defined thicknesses (up to 60 nm) and high grafting densities are readily prepared by surface initiated nitroxide mediated radical polymerization (SINMP). The photoactive moieties can be transformed via Norrish-type I photoreaction to surface-bound acyl radicals. Photolysis in the presence of a persistent nitroxide leads to chemically modified PBs bearing acylalkoxyamine moieties as side chains resulting from trapping of the photogenerated acyl radicals with nitroxides. Application of functionalized nitroxides to the photochemical PB postmodification provides functionalized PBs bearing cyano, polyethylene glycol (PEG), perfluoroalkyl, and biotin moieties. As shown for one case, photochemical postfunctionalization of the PB through a mask using a biotin-conjugated nitroxide as the trapping reagent leads to the corresponding site-selective chemically modified PB, which is successfully used for site-specific streptavidin immobilization. Surface analysis of PBs was performed by contact angle (CA) measurements, X-ray photoelectron spectroscopy (XPS), attenuated total reflection (ATR), fourier transform infrared (FTIR) spectroscopy, and fluorescence microscopy.

Photochemistry and Reactivity of the Phenyl Radical-Water System: A Matrix Isolation and Computational Study

The reaction of the phenyl radical 1 with water has been investigated by using matrix isolation spectroscopy and quantum chemical calculations. The primary thermal product of the reaction between 1 and water is a weakly bound complex stabilized by an OH...pi interaction. This complex is photolabile, and visible-light irradiation (lambda>420 nm) results in hydrogen atom transfer from water to radical 1 and the formation of a highly labile complex between benzene and the OH radical. This complex is stable under the conditions of matrix isolation, however, continuous irradiation with lambda>420 nm light results in the complete destruction of the aromatic system and formation of an acylic unsaturated ketene. The mechanisms of all reaction steps are discussed in the light of ab initio and DFT calculations.

Controlled Light-Mediated Preparation of Gold Nanoparticles by a Norrish Type I Reaction of Photoactive Polymers.

Gold nanoparticles (AuNPs) are subjects of broad interest in scientific community due to their promising physicochemical properties. Herein we report the facile and controlled light-mediated preparation of gold nanoparticles through a Norrish type I reaction of photoactive polymers. These carefully designed polymers act as reagents for the photochemical reduction of gold ions, as well as stabilizers for the in situ generated AuNPs. Manipulating the length and composition of the photoactive polymers allows for control of AuNP size. Nanoparticle diameter can be controlled from 1.5 nm to 9.6 nm.

Photochemistry of N-Methylformamide: Matrix Isolation and Nonadiabatic Dynamics

The photochemistry of N-methylformamide (MF) is elucidated by investigating its photodissociation products generated by UV irradiation (248 nm) in an argon matrix (10 K). We find that, starting from trans-MF, prolonged irradiation produces cis-MF, CH3NH2 and CO fragments as major products. Another photoproduct is identified as methylformimidic acid (FIA). Nonadiabatic dynamics simulations starting from both MF conformers revealed that the internal conversion occurs within 1 ps through a C-N dissociation channel. The major product is a weakly bound complex between CH3NH and HCO radicals. This complex owes its existence to the cage effect of the matrix which allows for H-transfer reactions and recombination. By identifying the primary photoisomerization and photodissociation pathways of MF, we gain new insights into the photochemistry of peptide bonds in general, which is a prerequisite for a better understanding of the effect of UV irradiation on living systems.

Matrix Isolation and ab initio study of the noncovalent complexes between formamide and acetylene.

Matrix isolation spectroscopy in combination with ab initio calculations is a powerful technique for the identification of weakly bound intermolecular complexes. Here, weak complexes between formamide and acetylene are studied, and three 1:1 complexes with binding energies of -2.96, -2.46, and -1.79 kcal/mol have been found at the MP2 level of theory (MP2/cc-pVTZ + ZPE + BSSE). The two most stable dimers A and B are identified in argon and nitrogen matrices by comparison between the experimental and calculated infrared frequencies. Both complexes are stabilized by the formamide C=O...HC acetylene and H...pi interactions. Large shifts have been observed experimentally for the C-H stretching vibrations of the acetylene molecule, in very good agreement with the calculated values. Eight 1:2 FMA-acetylene trimers (T-A to T-H) with binding energies between -5.44 and -2.62 kcal/mol (MP2/aug-cc-pVDZ + ZPE + BSSE) were calculated. The two most stable trimers T-A and T-B are very close in energy and have similar infrared spectra. Several weak bands that are in agreement with the calculated frequencies of the trimers T-A and T-B are observed under matrix isolation conditions. However, the differences are too small for a definitive assignment.

Pyridyl- and Pyridylperoxy Radicals – A Matrix Isolation Study

The three isomeric pyridyl radicals 2a–c were synthesised using flash vacuum pyrolysis in combination with matrix isolation and characterised by infrared spectroscopy. The IR spectra are in good agreement with spectra calculated using density functional theory methods. The reaction of the pyridyl radicals 2 with molecular oxygen leads to the formation of the corresponding pyridylperoxy radicals 3a–c. The peroxy radicals 3 are photolabile, and irradiation results in syn–anti isomerisation of 3a and 3b and ring expansion of all three isomers of 3.

Direct synthesis of six-coordinate nitro complexes of cobalt meso-tetraphenylporphyrinate with trans-O-donor ligands

The formation of a series of six-coordinate complexes (B)Co(TPP)(NO2) (B is ketone, aldehyde, ether or epoxide; TPP is meso-tetraphenylporphyrin dianion) on exposure of thin films of five-coordinate Co(TPP)(NO2) to vapors of the O-donor ligands was established by IR and UV/Vis spectroscopy (resorting to the data on isotope-substituted 15NO2). The complex formation is accompanied by shifts of the vibration frequencies of the trans-NO2 ligand and gives rise to new IR bands corresponding to the O-donors in the ν(C=O) or ν(C-O) region shifted with respect to these bands of free ligands. The complexes are rather stable in the solid phase but eliminate the O-donor ligand upon dissolution in an inert solvent (or upon maintenance in a vacuum for some complexes) being converted into the initial five-coordinate nitro complex. Using the IR spectra of CCl4 solutions of the complexes containing a large excess of O-donor molecules, the equilibrium constants and the formation enthalpies of some (B)Co(TPP)(NO2) complexes were determined, indicating weak coordination of these ligands.