Recent advances of polyoxometalates in multi-functional imaging and photothermal therapy.

Polyoxometalates (POMs) as a kind of molecular metal-oxide cluster with precise chemical composition and architecture have been demonstrated to show potential in multidisciplinary materials. Accompanied by their bioactivities, POM clusters have also been shown to be capable of sensing diseases and allowing synergistic therapy based on their redox and near infrared absorption. In parallel with metal nanoparticles and organic materials, these inorganic clusters have also displayed unique photothermal imaging and therapeutic properties over recent years. In this review, we outlined the main achievements of POMs in the fields of bio-detecting probes and the photothermal effect. Fluorescence detection, magnetic resonance, computed tomography, and photothermal property-supported photoacoustic imaging acting as a multifunction platform that integrates photothermal therapy (PTT) were discussed at the same time. The comparison of nanocomposites to POMs alone in imaging-guided PTT, multi-modal imaging, and the combination of PTT with controlled chemotherapy and gas therapy were described in detail. The advantages and possible drawbacks of POMs as well as perspectives in related areas were analyzed, which ascertained such clusters to be a type of promising agent in biomedical applications.

Electron photodetachment dissociation for structural characterization of synthetic and bio-polymer anions.

Tandem mass spectrometry (MS-MS) is a generic term evoking techniques dedicated to structural analysis, detection or quantification of molecules based on dissociation of a precursor ion into fragments. Searching for the most informative fragmentation patterns has led to the development of a vast array of activation modes that offer complementary ion reactivity and dissociation pathways. Collisional activation of ions using atoms, molecules or surface resulting in unimolecular dissociation of activated ions still plays a key role in tandem mass spectrometry. The discovery of electron capture dissociation (ECD) and then the development of other electron-ion or ion/ion reaction methods, constituted a significant breakthrough, especially for structural analysis of large biomolecules. Similarly, photon activation opened promising new frontiers in ion fragmentation owing to the ability of tightly controlled internal energy deposition and easy implementation on commercial instruments. Ion activation by photons includes slow heating methods such as infrared multiple photon dissociation (IRMPD) and black-body infrared radiative dissociation (BIRD) and higher energy methods like ultra-violet photodissociation (UVPD) and electron photo detachment dissociation (EPD). EPD occurs after UV irradiation of multiply negatively charged ions resulting in the formation of oxidized radical anions. The present paper reviews the hypothesis regarding the mechanisms of electron photo-detachment, radical formation and direct or activated dissociation pathways that support the observation of odd and even electron product ions. Finally, the value of EPD as a complementary structural analysis tool is illustrated through selected examples of synthetic polymers, oligonucleotides, polypeptides, lipids, and polysaccharides.

Multivariate analysis of anionic, cationic and nonionic textile surfactant degradation with the H(2)O(2)/UV-C process by using the capabilities of response surface methodology.

Anionic, cationic and nonionic surfactants being frequently employed in the textile preparation process were subjected to H(2)O(2)/UV-C treatment. As a consequence of the considerable number of parameters affecting the H(2)O(2)/UV-C process, an experimental design methodology was used to mathematically describe and optimize the single and combined influences of the critical process variables treatment time, initial H(2)O(2)concentration and chemical oxygen demand (COD) on parent pollutant (surfactant) as well as organic carbon (COD and total organic carbon (TOC)) removal efficiencies. Multivariate analysis was based on two different photochemical treatment targets; (i) full oxidation/complete treatment of the surfactants or, alternatively, (ii) partial oxidation/pretreatment of the surfactants to comply with the legislative discharge requirements. According to the established polynomial regression models, the process independent variables "treatment time" (exerting a positive effect) and "initial COD content" (exerting a negative effect) played more significant roles in surfactant photodegradation than the process variable "initial H(2)O(2) concentration" under the studied experimental conditions.

Electron capture induced dissociation of nucleotide anions in water nanodroplets.

We have studied the outcome of collisions between the hydrated nucleotide anion adenosine 5'-monophosphate (AMP) and sodium. Electron capture leads to hydrogen loss as well as water evaporation regardless of the initial number m of water molecules attached to the parent ion (m< or =16). The yield of dianions with microsecond lifetimes increases strongly with m, which is explained from dielectric screening of the two charges by the water nanodroplet. For comparison, collision induced dissociation results in water losses with no or very little damage of the AMP molecule itself.

Photoelectron spectroscopy of hydrated adenine anions.

We report the observation of hydrated adenine anions, A(-)(H(2)O)(n), n=1-7, and their study by anion photoelectron spectroscopy. Values for photoelectron threshold energies, E(T), and vertical detachment energies are tabulated for A(-)(H(2)O)(n) along with those for hydrated uracil anions, U(-)(H(2)O)(n), which are presented for comparison. Analysis of these and previously measured photoelectron spectra of hydrated nucleobase anions leads to the conclusion that threshold energies significantly overstate electron affinity values in these cases, and that extrapolation of hydrated nucleobase anion threshold values to n=0 leads to incorrect electron affinity values for the nucleobases themselves. Sequential shifts between spectra, however, lead to the conclusion that A(-)(H(2)O)(3) is likely to be the smallest adiabatically stable, hydrated adenine anion.

Mechanisms of oxidation of guanine in DNA by carbonate radical anion, a decomposition product of nitrosoperoxycarbonate.

Peroxynitrite is produced during inflammation and combines rapidly with carbon dioxide to yield the unstable nitrosoperoxycarbonate, which decomposes (in part) to CO(3) (.-) and (.)NO(2) radicals. The CO(3) (.-) radicals oxidize guanine bases in DNA through a one-electron transfer reaction process that ultimately results in the formation of stable guanine oxidation products. Here we have explored these mechanisms, starting with a spectroscopic study of the kinetics of electron transfer from 20-22mer double-stranded oligonucleotides to CO(3) (.-) radicals, together with the effects of base sequence on the formation of the end-products in runs of one, two, or three contiguous guanines. The distributions of these alkali-labile lesions were determined by gel electrophoresis methods. The cascade of events was initiated through the use of 308 nm XeCl excimer laser pulses to generate CO(3) (.-) radicals by an established method based on the photodissociation of persulfate to sulfate radicals and the oxidation of bicarbonate. Although the Saito model (Saito et al., J. Am. Chem. Soc. 1995, 117, 6406-6407) predicts relative ease of one-electron oxidations in DNA, following the trend 5'-GGG > 5'-GG > 5'-G, we found that the rate constants for CO(3) (.-)-mediated oxidation of guanines in these sequence contexts (k(5)) showed only small variation within a narrow range [(1.5-3.0)x10(7) M(-1) s(-1)]. In contrast, the distributions of the end-products are dependent on the base sequence context and are higher at the 5'-G in 5'-GG sequences and at the first two 5'-guanines in the 5'-GGG sequences. These effects are attributed to a combination of initial hole distributions among the contiguous guanines and the subsequent differences in chemical reaction yields at each guanine. The lack of dependence of k(5) on sequence context indicates that the one-electron oxidation of guanine in DNA by CO(3) (.-) radicals occurs by an inner-sphere mechanism.

Photodynamic properties of dipeptide-modified hypocrellin B derivatives: the role of tyrosine and tryptophan groups.

Three long-wavelength absorbing dipeptide-modified hypocrellin B (HB) derivatives, Gly-HB, Tyr-HB, and Trp-HB, were prepared for application in photodynamic therapy (PDT). Their abilities to produce free radicals and singlet oxygen were compared in detail with EPR technique, and their binding interactions with calf thymus DNA (CT DNA) were studied by absorption spectra and DNA melting temperature measurements. Tyr-HB and Trp-HB distinguish themselves from Gly-HB and HB remarkably by their significantly improved efficiencies to generate semiquinone anion radicals, superoxide anion radicals, and hydroxyl radicals, as well as their affinity to CT DNA, as the result of the electron-donating properties and intercalating abilities of tyrosine and tryptophan groups. Tyr-HB and Trp-HB show remarkably enhanced photodamage capabilities on CT DNA than their parent HB in aerobic conditions. Moreover, they possess moderate photodamage abilities on CT DNA even in anaerobic conditions, indicating the role of Type I mechanism in their photodynamic behaviors.

Reaction between diiodide anion radicals in ionic liquids.

Photodetachment of electrons from iodide ions produced diiodide anion radicals in ionic liquids containing ammonium, pyrrolidinium, and piperidinium cations. The rates of reaction between diiodide anion radicals in molecular solvents such as H2O, methanol, and ethanol could be estimated by the Debye-Smoluchowski equation, which accounts for electrostatic interactions using dielectric constants for the molecular solvents. In contrast, the rates of reaction between diiodide anion radicals in the ionic liquids were close to the diffusion-limited rates for the neutral molecules, suggesting that electrostatic repulsion between the diiodide anion radicals is weakened by Coulombic shielding in the ionic liquids.

EPR characteristics of chloride-depleted photosystem II membranes in the presence of other anions.

Chloride is an essential cofactor for the oxidation of water to oxygen. Anion substitution (Br(-), I(-), NO(2)(-), F(-)) in Cl(-)-depleted PS II membranes brings out significant changes in the EPR signals arising from the S(2) state and from the iron-quinone complex of PS II. On the basis of the changes observed in the S(2) state multiline signal and the Q(A)Fe(3+) EPR signal in Cl(-)-depleted PS II membranes after substituting with various anions, we report a possible binding site of anions such as chloride and bromide at the PS II donor side as well as at the acceptor side.