ESR study of radical processes in irradiated DNA: The effect of the complexation with cis-dichloro diamino Pt(II)

The room temperature esr spectra of irradiated neat duplex hydrated, dehydrated and thermally denaturated DNA are interpreted in terms of the radicals formed by protonation of the thymine and cytosine anion radicals, by deprotonation of the guanine cation radicals, by addition of OH radicals at C8 of guanine and by loss of a methyl hydrogen from thymine. The complexation of DNA with cis-dichlorodiamino Pt(II) causes a drastic alteration of the radical distribution interpreted in terms of electron scavenging by the Pt(II) complex, a partial inhibition of the radical-cation chemistry of guanine, and enhancement of the reactivity of thymine toward hydrogen abstractions.     

Influence of percentage of guanine molecules, OH radicals, UV irradiation and temperature on electrooxidation of short synthetic oligonucleotides

The electrooxidation of short synthetic 20-nucleotides DNA sequences with various amount of guanine molecules has been studied in a wide temperature range by square wave voltammetry and the results were compared with UV-vis and CD spectra. A twofold increase of dsDNA voltammetric peak, related to an increase in the number of electrons transferred in the guanine electrooxidation process was found to begin at a temperature lower by circa 20 °C compared to the well known increase of the dsDNA absorbance upon denaturation. Since the dsDNA voltammetric peaks are related directly to the electrooxidation of guanine and adenine, early conformational changes in dsDNA are responsible for this effect. An increase in percentage of guanine in the DNA chains caused a delay in the conformational, predenaturation changes. An exception to this behavior was found for polyguanine (100% guanine). Interestingly, two distinct ranges of change in ellipticity in the CD spectra correlate well with the changes obtained by voltammetry. We have also checked the influence of OH radicals and UV irradiation on the dsDNA oxidation.     

Electronic structures and spectra of 6-mercaptopurine and 6-thioguanine

Ultraviolet absorption, steady-state fluorescence and excitation spectra of 6-mercaptopurine (6MP) and 6-(thioguanine) (6TG) have been studied, and excited state life-time measurements on their fluorescence performed. The experimental results have been interpreted with the help of molecular orbital calculations. The study shows that these molecules predominantly exist in thione forms. The properties of the molecules have been compared with those of guanine and the possible significance of the results is discussed.     

Structure and solid-state photochromic properties of two new compounds with pyrazolone-ring

Two new organic photochromic compounds based on pyrazolone were synthesized and further characterized by elemental analysis, MS, IR spectra, and ¹H NMR spectra. The photochromic properties and photochemical kinetics of them have been studied by UV absorption spectra under irradiation of 365 nm light. The photochromism of pyrazolone derivatives in the solid state has been so far explained only in terms of the light-induced change of absorption and their crystal structures, which is caused by the shift of the tautomeric equilibrium between the enol and keto forms. In this work, their IR spectra have been measured before and after irradiation. Based on the IR spectra and crystal structure analysis, a reasonable mechanism was proposed, the photochromic phenomenon may be due to the photoisomerization from enol-form to keto-form through proton transfer.     

Luminescent double-decker type guanine octets with trivalent lanthanide cations: in situ self-assembling and stability evaluation in homogeneous organic media

Silylated guanine formed luminescent double-decker type octet complexes with trivalent lanthanide cations (lanthanide cation : guanine = 1:8) in organic media, while a deaminated guanine derivative gave only 1:2 complexes. The octet formation was evidenced by characteristic UV/Vis absorption changes, CSI-TOF MS and ¹H NMR spectra. The octet with Tb³⁺ showed intense green luminescence with a long lifetime by photo-excitation of the guanine chromophore. The trivalent lanthanie cations stabilized the octets more effectively than common mono- and divalent metal cations.     

Photoemission from matrix-isolated nickel atoms

UV photoelectron spectra from Ni atoms isolated in a xenon matrix at 9 K have been measured for the first time using Hell (40 8 eV). Two peaks have been found at 2.8 and 4.6 eV below E_F, which are interpreted as being due to different d⁸s¹ final states of the Ni ion. including a relaxation shift of 2.0 eV. The existence of atomic Ni species in the matrix has been verified by in situ optical absorption spectra.     

Effect of UV irradiation on stabilized collagen: role of chromium(III)

Research on the effect of UV radiation on stabilized collagen is an area of potential interest owing to the fact that collagen is an important biomaterial finding immense use in various fields. In this present study, effect of UV irradiation on collagen stabilized using chromium(III) has been studied. The physical and optical properties affected by UV irradiation have been detailed. Viscosity measurements have shown that chromium(III) treated collagen has better stability against UV radiation than native collagen. Circular dichroic studies indicate that increase in concentration of chromium(III) does not affect the conformation of collagen however, the duration of irradiation has profound impact on the conformation of collagen. The fluorescence intensity of native collagen has been found to decrease more than that of chromium(III) treated collagen. The difference absorption spectra also shows that chromium(III) treatment brings about more stability to collagen against UV irradiation.     

Photo-degradation and emission characteristics of benzidine in halomethane solvents

Benzidine is an aromatic base of importance in industry. It represents a serious pollutant in many industrial effluents and its photodegradation is of great interest. The mechanism of photo-chemical decomposition of benzidine in different halomethane solvents in addition to the corresponding UV absorption spectra and fluorescence emission spectra are discussed. The photochemical quantum yields (phiC lambda ex = 254 nm) of benzidine in halomethanes is dependent upon the halogen content in the solvent. This effect may be explained by the assumption that free radicals are formed during photolysis of these solvents followed by the abstraction of electrons from a benzidine molecule forming macroradicals of the latter. Both mono- and di-radical benzidine cations have been detected by different techniques. The well known electron absorption peak at 283 nm is characteristic of neutral benzidine while those observed at ca. 370 and 565 nm are assigned to the blue-monoradical cation and yellow-diradical cation, respectively. The blue-monoradical cation has been isolated after irradiation as a blue precipitate. A comparison between neutral benzidine and the blue monoradical cation are made using both IR and differential thermal analysis (DTA) techniques. The fluorescence quenching of solutions of benzidine in inert solvents using halomethanes have been studied. The results obtained are interpreted in terms of a diffusional quenching mechanism.     

Hydrogen bonding interactions between ethylene glycol and water: density,excess molar volume,and spectral study

Studies of the density and the excess molar volume of ethylene glycol (EG)-water mixtures were carried out to illustrate the hydrogen bonding interactions of EG with water at different temperatures. The re-sults suggest that a likely complex of 3 ethylene glycol molecules bonding with 4 water molecules in an ethylene glycol-water mixture (EGW) is formed at the maximal excess molar volume,which displays stronger absorption capabilities for SO2 when the concentration of SO2 reaches 400×10?6 (volume ratio) in the gas phase. Meanwhile,FTIR and UV spectra of EGWs were recorded at various EG concentra-tions to display the hydrogen bonding interactions of EG with water. The FTIR spectra show that the stretching vibrational band of hydroxyl in the EGWs shifts to a lower frequency and the bending vibra-tional band of water shifts to a higher frequency with increasing the EG concentration,respectively. Furthermore,the UV spectra show that the electron transferring band of the hydroxyl oxygen in EG shows red shift with increasing the EG concentration. The frequency shifts in FTIR spectra and the shifts of absorption bands in UV absorption spectra of EGWs are interpreted as the strong hydrogen bonding interactions of the hydrogen atoms in water with the hydroxyl oxygen atoms of EG.     

Effect of ultraviolet radiation on polyethylene naphthalate films irradiated with high-energy heavy ions

The effect of UV radiation in the spectral range of 280–400 nm on polyethylene naphthalate (PEN) films has been studied. Changes in the optical absorption spectra of PEN after exposure to accelerated ions and UV radiation have been revealed. Changes in the surface properties have been explored, and the depth of the degraded polymer layer after long-term UV irradiation in air has been measured. Depending on the treatment time, the depth has made 0.1–0.9 μm. The photoablation rate and the quantum yield of monomer unit removal due to UV irradiation of the PEN films have been estimated at ~0.7 × 10^?4 molecule/photon. The possibility of the formation of asymmetric pores in PEN films using controlled photooxidative degradation has been shown.     

Facile formation of an intrastrand cross-link lesion between cytosine and guanine upon pyrex-filtered UV light irradiation of d((Br)CG) and duplex DNA containing 5-bromocytosine

Pyrex-filtered UV light irradiation of d(BrCG) and 5-bromocytosine-containing duplex DNA leads to facile formation of a cross-link lesion between the C5 carbon atom of cytosine and the C8 carbon atom of its adjacent guanine. A similar cross-link lesion has been previously found in the X-ray irradiation mixture of d(CGTA).     

UV-irradiation effects on polyester nuclear track detector

The effects of UV irradiation (λ=254 nm) on polyester nuclear track detector have been investigated employing bulk-etch technique, UV–visible spectrophotometry and infra-red spectrometry (FTIR). The activation energy values for bulk-etching were found to decrease with the UV-irradiation time indicating the scission of the polymer. Not much shift in the absorption edge due to UV irradiation was seen in the UV–visible spectra. FTIR studies also indicate the scission of the chemical bonds, thereby further validating the bulk-etch rate results.     

Digital logic circuit based on a single molecular system of salicylidene Schiff base

The salicylidene Schiff base N-3,5-dichloro-salicylidene-(S)-alpha-phenylethylamine (SPEA) has been synthesized and characterized. Stimulated by one optical input (UV light) and two chemical inputs (OH(-) and Zn(2+)), SPEA undergoes reactions of photochemistry, deprotonation, and complexation. Tailing these reactions by means of the UV-vis absorption spectra and fluorescence spectra, two obvious optical outputs, an absorption band at 323 nm and a fluorescent emission peak at 460 nm, have been obtained. On the basis of encoding binary digits in these inputs and outputs applying positive logic conventions, one monomolecular circuit, which integrates one OR, two NOT, and four AND gates, has been achieved.     

Infrared and Raman spectra of 8-azaguanine and 8-azaadenine

The IR and Raman spectra of 8-azaguanine and 8-azaadenine have been studied. The spectra of 8AG have been critically examined and compared with those of guanine and 9-methylguanine. Similarly, the spectra of 8-azaadenine have been examined and compared with those of adenine and 9-methyladenine. It has been possible to refute or accept the assignments for certain frequencies proposed earlier in the parent molecules by other workers, and thus almost unambiguous assignments for several frequencies in guanine and adenine as well as in 8AG and 8AA have been obtained. Several frequencies have been explained as combinations involving a 130 cm⁻¹ vibration which has been assigned to the ring-folding mode. It is found that not as many combination bands involving this mode occur in 8AA as those in 8AG. These observations indicate that guanine and 8AG are geometrically more flexible than adenine and 8AA.     

Singlet oxygen formation in monomeric and aggregated porphyrin c

The absorption and fluorescence spectra of monomeric and aggregated species present in aqueous solutions of porphyrin c have been resolved by steady-state and time-resolved spectroscopy. The dependence of the singlet oxygen formation yield (phi delta) on excitation wavelength has also been determined. In the Q-band spectral region, the aggregate absorption and emission spectra are shifted to longer wavelengths with respect to the monomer spectrum with phi delta (monomer) = 0.59 and phi delta (aggregate) = 0.33. The relevance of these findings to the optimization of irradiation conditions in tumour phototherapy using porphyrin c are discussed.     

Substituent and solvent effects on electronic spectra of some substituted phenoxyacetic acids

The effects of substituents and solvents have been studied through the absorption spectra of nearly 19 para- and ortho-substituted phenoxyacetic acids in the range of 200-400 nm. The effects of substituent on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.     

A Raman spectroscopic study of indolinium steryl dyes

Resonance Raman spectra have been obtained in the region 400–1700 cm⁻¹ for several indolinium steryl dyes under various experimental conditions. The changes in vibrational frequencies have been correlated with changes in the UV—vis absorption maxima observed previously and which are due to solvent polarity variations, the complexation of the dye molecules containing a crown ether ring with Mg²⁺, and the variations in molecular structure. Preliminary assignments of the observed bands to particular vibrations are made.     

Substituent and solvent effects on electronic absorption spectra of some N-(substitutedphenyl)benzene sulphonamides

The effects of substituents and solvents have been studied through the absorption spectra of nearly 23 ortho- and para-N-(substitutedphenyl)benzene sulphonamides in the range of 200-400 nm. The effects of substituents on the absorption spectra of compounds under present investigation are interpreted by correlation of absorption frequencies with simple and extended Hammett equations. Effect of solvent polarity and hydrogen bonding on the absorption spectra are interpreted by means of Kamlet equation and the results are discussed.     

Aqueous solution study of Cu(II) and Ni(II) complexes of macrocyclic oxa- and thia-containing trans-dioxo-tetraamines

Four macrocyclic trans-dioxo-tetraamines containing sulphur or oxygen as additional donors have been prepared: 1-oxa-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-thia-3,14-dioxo-4,7,10,13-tetraazacyclopentadecane, 1-oxa-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane and 1-thia-3,16-dioxo-4,8,11,15-tetraazacycloheptadecane. Their protonation as well as their metal binding properties with Cu²⁺ and Ni²⁺ have been determined at 25°C in 0.10 mol dm⁻³ KNO₃. The complexation process was investigated by potentiometric, calorimetric and UV/VIS-spectroscopic titrations. IR-spectroscopy was used to establish the involvement of the amido groups in the coordination. Oxidation of the complexes to the trivalent state of the metal ion was also investigated by cyclic voltammetry. Metal ion complexation promotes the deprotonation of the amide nitrogens, resulting in a neutral complex with four nitrogen donors and a MLH_-2 stoichiometry at pH 8. Additional complexes with stoichiometry ML and MLH_-1 were needed to describe the complexation in the pH range 2–11. Their stability constants were calculated. The presence of oxygen or sulphur donors as well as ring enlargement influence the complexation properties. The electronic spectra indicate rather distorted tetragonal coordination geometries for the Cu(II)-complexes. The Ni(II)-complexes are all square–planar with the exception of an equilibrium between a square–planar and an octahedral form for NiL¹H₋₂. All complexes are easily but irreversibly oxidized to the trivalent state of the metal ion.     

Multistimuli‐Responsive Supramolecular Assembly of Cucurbituril/Cyclodextrin Pairs with an Azobenzene‐Containing Bispyridinium Guest

A linear supramolecular architecture was successfully constructed by the inclusion complexation of α‐cyclodextrin with azobenzene and the host‐stabilized charge‐transfer interaction of naphthalene and a bispyridinium guest with cucurbit[8]uril in water, which was comprehensively characterized by ¹H NMR spectroscopy, UV/Vis absorption, fluorescence, circular dichroism spectroscopy, dynamic laser scattering, and microscopic observations. Significantly, because it benefits from the photoinduced isomerization of the azophenyl group and the chemical reduction of bispyridinium moiety with noncovalent connections, the assembly/disassembly process of this supramolecular nanostructure can be efficiently modulated by external stimuli, including temperature, UV and visible‐light irradiation, and chemical redox.