Mössbauer study on photochemistry of ferrocene isolated in low-temperature matrix

Unstable novel species produced by photolysis of ferrocene (Cp₂Fe) isolated in low-temperature matrix were studied by means of the⁵⁷Fe Mössbauer spectroscopy. On the UV-irradiation of⁵⁷Fe-enriched ferrocene co-condensed with CCl₄ in low-temperature N₂ matrix (20 K), unknown high spin ferrous species (I.S.=0.90±0.01 mm/s, Q.S=1.94±0.02 mm/s) were produced as well as ferricinium ion [Cp₂Fe]⁺ (I.S.=0.52±0.01 mm/s, Q.S.=0.0 mm/s). On the annealing, these photoproducts disappeared to reform ferrocene by the reverse reaction in the matrix. The mechanisms of the photochemical reaction were discussed.     

The photochemistry of citral

Citral (I) is cyclized by UV irradiation¹ to 2-isopropenyl-5-methylcyclopentane-carboxaldehyde (II), containing the carbon skeleton of the monoterpenes of ants and catmint. 1,6,6-Trimethylbicyclo[2,1,1]hexane-2-carboxaldehyde (XII, R = H), produced in lesser amount at the same time, was synthesized from camphor. The two photocitrals may, perhaps, come from a common intermediate containing the cyclopentane ring.     

Conformers and photochemistry of propyl nitrites: a matrix isolation study

The infrared spectra of both constitutional isomers (n and i) of propyl nitrite have been recorded in an Ar matrix. Conformational analysis and assignments of the vibrational transitions have been carried out on the basis of quantum chemical calculations. Assignment of spectral lines to different conformers was also aided experimentally, by utilizing the different rate of photodecomposition of the conformers, as well as by employing conformational cooling using a supersonic jet as the inlet source for matrix deposition. The rate of photodecomposition is primarily determined by the steric alignment of the nitrite group, whereas jet cooling affects mainly the conformation of the alkyl tail. On the basis of these experimental observations and computational predictions two to three conformers of isopropyl nitrite and eight conformers of n-propyl nitrite were identified. After broadband ultraviolet-visible (UV-vis) photolysis of isopropyl nitrite in the matrix, HNO, acetone, HNO.acetone complex, acetaldehyde, and nitrosomethane were identified as the main products. Furthermore, in a small amount, NO and possibly the isopropoxy radical were also present in the matrix. Photolysis of n-propyl nitrite yielded HNO, propanal, and their 1:1 complex as the main products together with a small amount of NO and cis-1-nitrosopropanol.     

The photochemistry of 3,4,5-trideuteriopyridine

Irradiation of 3,4,5-trideuteriopyridine at 254 nm in the vapor phase results in the formation of a mixture of 2,3,4-trideuteriopyridine and 2,3,6-trideuteriopyridine. The formation of these products is consistent with a photoisomerization mechanism involving equilibrating azaprefulvene intermediates. This is the first direct evidence that pyridine vapor undergoes photoisomerization resulting in transposition of the pyridine ring atoms.     

The photochemistry of α-acetoxystyrene

Photolysis of α-acetoxystyrene leads to isopropenyl benzoate as a result of reverse photo-Fries rearrangement of the intermediate benzoylacetone.     

The unexpected photochemistry of marbofloxacin

The veterinary antimicrobial Marbofloxacin undergoes none of the general photoreactions of fluoroquinolones. Irradiation rather leads to homolytic cleavage of the N-N bond and loss of a fragment to give a phenoxy radical. The final products result from the dimerization, the reduction, or the disproportionation of the radical.     

The photochemistry of 1,2,2-trimesitylethanone

Irradiation of 1,2,2-trimesitylethanone 1 gives the enol ethers 3 via a 1,3-mesityl shift in a highly efficient process; the postulated intermediacy of 1 in the photoisomerization of enol 2 is confirmed.     

Observations of the break-up of liquid crystalline polymer threads imbedded in an isotropic fluid

A droplet, a few hundreds of microns, of liquid crystalline hydroxypropylcellulose (HPC) in water is imbedded into a polydimethylsiloxane (PDMS) matrix and subjected to a shear flow. The droplet is deformed into a thread of high aspect ratio. The textures associated with the break-up of the thread once the flow is stopped are observed by optical microscopy. After stopping the flow a banded texture appears. The droplets resulting from the break-up have a bipolar texture with the two opposite poles being along the former thread direction.     

Diastereoselectivity and site dependency in the photochemistry of ketoprofen in the bovine serum albumin matrix

The photodegradation of the S(+)- and R(-)-ketoprofen (KP) enantiomers in the bovine serum albumin matrix was studied by steady-state photolysis with the use of lambda(irr) > 320 nm and transient absorption spectroscopy with lambda(exc) = 355 nm, at 1/1 and 2/1 KP/BSA molar ratios. R(-)-KP was found to be more labile than S(+). Triplet ketoprofen species were evidenced with lifetimes of 400 ns for S(+) and 600 ns for R(-)-KP. Further longer-lived transients with lifetimes of 2.6 and 6.0 mus for S(+) and R(-), respectively, were detected. On the basis of the binding constants of the drug enantiomers to the two main binding sites of the protein, obtained from circular dichroism experiments, the individual disappearance quantum yields of the 1:1 and 2:1 diastereomeric KP:BSA complexes could be estimated. The photoreactivity in the BSA matrix was rationalized on the basis of diastereoselective photodecarboxylation in the two main protein sites.     

Sorption of benzene and N-hexane in polyethylene

Differential sorption data of benzene and n-hexane vapors in polyethylene have been obtained over wider ranges of temperatures and activities than available before. The data are used to develop a better model or help in the choice of the appropriate theory and modeling assumption from the available ones. Whereas the swelling of the walled-in amorphous region, with some modifications, provides the best correlation for the solubilities, in contrast, the integrated giant crosslink model shows remarkable agreement with the experimental values of diffusivities.     

The photochemistry of N-p-toluenesulfonyl peptides: the peptide bond as an electron donor

The scope of photobiological processes that involve absorbers within a protein matrix may be limited by the vulnerability of the peptide group to attack by highly reactive redox centers consequent upon electronic excitation. We have explored the nature of this vulnerability by undertaking comprehensive product analyses of aqueous photolysates of 12 N-p-toluenesulfonyl peptides with systematically selected structures. The results indicate that degradation includes a major pathway that is initiated by intramolecular electron transfer in which the peptide bond serves as electron donor, and the data support the likelihood of a relay process in dipeptide derivatives.     

The solution photochemistry of substituted cycloheptatrienes

The solution photochemistry of several ethoxycarbonyl- and ethoxycarbonyl-methoxy-substituted cycloheptatrienes has been investigated. The results have been used to analyse the directional specificity of ring-closure and 1,7-hydrogen migration reactions. This specificity is interpreted in terms of polarisation within the S₁ state which undergoes either (a) allowed photochemical reactions to give the observed products directly or (b) isomerisation to a trans, cis, cis-cyclohepatriene which then reacts via allowed ground-state processes. In at least two instances the directional specificity of the ring-closure reaction is wavelength dependent and this is attributed to the differing reactivities of the S₁ and S₂ states.     

Physicochemical properties of an electroconductive film based on tetrakis(p-aminophenyl)porphine

A strong, optically transparent electroconductive polyporphyrin film is obtained during the electrooxidation of tetrakis(p-aminophenyl)porphine in dichloromethane on the surface of a platinum electrode. Analysis of electronic absorption and IR spectra indicates that tetrakis(p-aminophenyl)porphine is polymerized during electrooxidation via the formation of dihydrophenazine fragments. It is found that the film deposited on the electrode is insoluble in many organic solvents and mineral acids, is thermally stable when heated up to 200°C, and has a homogeneous surface with an even distribution of oligomer globules. It is found through differential scanning calorimetry that the compound deposited on the electrode is a partially crystalline polymer.