Photoinduced Fragmentation Research Articles

Synthesis of high surface area mesoporous ZnAl2O4 with excellent photocatalytic activity for the photodegradation of Congo Red dye

The large-scale release by the textile and other industries of organic dyes into water courses degrades the aquatic environment and results in serious health problems for wildlife, humans, and domestic animals. The removal of such dyes from wastewater is therefore a pressing and important challenge. The efficient photocatalytic destruction of these dyes using sunlight is an elegant and attractive potential solution. In this work, mesoporous ZnAl2O4 nanomaterials were prepared with high specific surface area, high pore volume and uniform pore size distribution using a modified sol–gel synthetic protocol. BET analysis showed that the highest surface area achieved for ZnAl2O4 reached 344 m2/g. The texture, structure and chemical composition of these materials were further studied using XRD, FTIR, TEM, EDS, CHN and XPS analysis and zeta potential measurements. Band gap energies were obtained from UV/vis spectra and showed a strong decrease as particle size decreased, shifting absorption into the visible range for the finest materials and indicating the potential to improve the efficiency of photocatalysis under solar irradiation. Photocatalytic activity was evaluated by studying the photodegradation of Congo Red dye and, for the best materials, showed that 99 % of the dye was degraded in only 30 mins. These results compared very favourably with those of previously reported studies. The degradation products of the Congo Red were further investigated using mass spectrometry and this detailed study confirmed that true photoinduced fragmentation of the dye molecule occurred rather than simple ‘photobleaching’.

Neutral and Cationic Re(I) Complexes with Pnictogen-Based Coligands and Tunable Functionality: From Phosphorescence to Photoinduced CO Release.

In this work, we have explored Re(I) complexes featuring triphenylpnictogen (PnPh3, Pn = P, As, or Sb)-based coligands and bidentate (neutral or monoanionic) luminophores derived from 1,10-phenantroline (phen), as well as from 2-(3-(tert-butyl)-1H-1,2,4-triazol-5-yl)pyridine (H(N-tBu)). The effect of the increasingly heavy elements on the structural parameters, photoexcited-state properties, and electrochemical behavior as well as the hybridization defects and polarization of the Pn atoms was related to the charges of the main luminophores (i.e., phen vs N-tBu) and explored in terms of photoluminescence spectroscopy, X-ray diffractometry, and quantum-chemical methods. Therefore, an in-depth analysis of the bonding, crystal packing, excited-state energies, and lifetimes was assessed in liquid solutions, frozen glassy matrices, and crystalline phases along with a semiquantitative photoactivation study. Notably, by changing the main ligand from phen to N-tBu, an increase in radiative and radiationless deactivation rates (kr and knr, respectively) at 77 K together with a faster photoinduced CO release and fragmentation at room temperature was detected. In addition, a progressively red-shifted phosphorescence was observed with the growing atomic number of the pnictogen atom, along with a boost in kr and knr at 77 K. Down the Vth main group and upon coordination of the Pn atom to the Re(I) center, an increasingly prominent jump of s-orbital participation on the binding sxp3.00-orbitals of the Pn atoms is evidenced. Based on these findings, the ability of these complexes to act as tunable photoluminescent labels able to perform as light-driven CO-releasing molecules is envisioned.

Addressing electronic and dynamical evolution of molecules and molecular clusters: DFTB simulations of energy relaxation in polycyclic aromatic hydrocarbons.

We present a review of the capabilities of the density functional based Tight Binding (DFTB) scheme to address the electronic relaxation and dynamical evolution of molecules and molecular clusters following energy deposition via either collision or photoabsorption. The basics and extensions of DFTB for addressing these systems and in particular their electronic states and their dynamical evolution are reviewed. Applications to PAH molecules and clusters, carbonaceous systems of major interest in astrochemical/astrophysical context, are reported. A variety of processes are examined and discussed such as collisional hydrogenation, fast collisional processes and induced electronic and charge dynamics, collision-induced fragmentation, photo-induced fragmentation, relaxation in high electronic states, electronic-to-vibrational energy conversion and statistical versus non-statistical fragmentation. This review illustrates how simulations may help to unravel different relaxation mechanisms depending on various factors such as the system size, specific electronic structure or excitation conditions, in close connection with experiments.

Photo-induced site-specific oxidative fragmentation of IgG1 mediated by iron(III)-containing histidine buffer: Mechanistic studies and excipient effects

Fragmentation may compromise the clinical efficacy and safety profile of monoclonal antibodies (mAbs). We recently reported that Fe(III)-containing histidine (His) buffer mediates site-specific mAb fragmentation within the Fc domain when exposed to visible light (Y. Zhang and C. Schöneich, Mol. Pharm. 2023, 20, 650–662). Here, we show that this fragmentation proceeds even more efficiently under near-UV light. Several formulation strategies were applied in an attempt to reduce the photo-induced fragmentation. In solution formulations, the fragmentation can be mitigated by reducing the concentration of His buffer, adding Fe(III)-chelating agents, and replacing His with other amino acids. Fragmentation can be almost completely inhibited by formulating the protein in the lyophilized state. Mechanistically, His plays a critical role in the fragmentation process, likely due to its affinity for Fe(II), driving a photo-redox reaction towards product formation.

Fragmentation of the PAH cations of Isoviolanthrene and Dicoronylene: A case made for interstellar cyclo[n]carbons as products of universal fragmentation processes

The photo-induced fragmentation pathways of the cationic forms of isoviolanthrene (C34H18) and dicoronylene (C48H20) are systematically studied with mass spectrometry employing an ion trap coupled with a laser system. The mass spectra of these structurally different species display similar fragmentation products, akin to previous work on three dibenzopyrene isomers, but also display some differences. The products formed in the largest yields are pure carbon clusters, which are likely in the form of ionized cyclo[n]carbons (n = 11–15). These findings are relevant to get a full picture of the molecular makeup of interstellar space, particularly in heavily irradiated regions where polycyclic aromatic hydrocarbon (PAH) molecules are omnipresent and subject to harsh irradiation and are broken down into smaller components. These interstellar species are expected to include the PAH derivatives observed here, but which are not identified in space yet.

SIMS Analysis of Thin EUV Photoresist Films.

This study reports on the application of secondary ion mass spectrometry (SIMS) for examining thin (20-50 nm) chemically amplified resist films on silicon. SIMS depth profiling was carried out using a gas cluster ion beam to ensure minimal sputter-induced damage to the organic constituents of interest. Specific attention concerned the distribution of the photo acid generator (PAG) molecule within these films, along with the photo-induced fragmentation occurring on extreme ultra-violet photo exposure. Positive secondary ion spectra were collected using a traditional time of flight (ToF)-SIMS and the latest generation IONTOF Hybrid SIMS instrumentation equipped with an OrbitrapTM mass analyzer. Tandem mass spectrometry (MS/MS) capability within the OrbitrapTM secondary ion column was utilized to verify that the C19H17S+ secondary ion did indeed have the molecular structure consistent with the PAG structure. The superior mass resolving power of the OrbitrapTM mass analyzer (∼20× of the ToF mass analyzer) along with improved mass accuracy (a few ppm) proved pivotal in the mass spectral and depth profile analysis of these films. This was not the case for the ToF-SIMS experiments, as the mass spectra, as well as the associated depth profiles, exhibited severe molecular (isobaric) interferences.

Non-statistical fragmentation in photo-activated flavin mononucleotide anions.

The spectroscopy and photo-induced dissociation of flavin mononucleotide anions in vacuo are investigated over the 300-500nm wavelength range. Comparison of the dependence of fragment ion yields as a function of deposited photon energy with calculated dissociation energies and collision-induced dissociation measurements performed under single-collision conditions suggests that a substantial fraction of photo-activated ions decompose through non-statistical fragmentation pathways. Among these pathways is the dominant photo-induced fragmentation channel, the loss of a fragment identified as formylmethylflavin. The fragment ion specific action spectra reveal electronic transition energies close to those for flavins in solution and previously published gas-phase measurements, although the photo-fragment yield upon excitation of the S2 ← S0 transition appears to be suppressed.

Nickel-Catalyzed Cross-Electrophile Coupling Enabled by Photoinduced Fragmentation of an EDA Complex

Nickel-Catalyzed Cross-Electrophile Coupling Enabled by Photoinduced Fragmentation of an EDA Complex

Photo-induced fragmentation of tyrosine side chains in IgG4-Fc: Effect of protein sequence, conformation and glycan structure

This account summarizes recent work on photo-induced side chain cleavage reactions of Tyr in IgG4-Fc. These processes are initiated via photo-ionization of Trp to a Trp radical cation, followed by one-electron oxidation of Tyr to a Tyr radical cation, where fragmentation of the Cα-Cβ bond leads to an intermediary glycyl radical. The latter converts into Gly via hydrogen atom transfer, or into various backbone cleavage products subsequent to the addition of oxygen. Site-directed mutation of Trp381 to Phe381 significantly reduces the yields of Tyr side chain cleavage products, underlining a critical role of Trp for these reactions. Likewise, conformational changes of IgG4-Fc induced by increasing contents of 1-propanol in the solution diminishes the yields of Tyr side chain cleavage products. Variations of the glycan structure at Asn297 had an effect on Tyr side chain cleavage, where larger glycan structures led to lower yields. This result is in interesting contrast to Trp side chain cleavage in IgG1-Fc, where larger glycan structures led to higher yields. The opposite trends for Trp and Tyr side chain cleavage as a function of glycan structure are consistent with a connection between the precursors for both reactions, radical cations of Trp and Tyr, related by electron transfer. The potential significance of these reactions for protein integrity in formulations of pharmaceutical proteins will be discussed.

New methodologies for the detection, identification, and quantification of microplastics and their environmental degradation by-products

Sampling, separation, detection, and characterization of microplastics (MPs) dispersed in natural water bodies and ecosystems is a challenging and critical issue for a better understanding of the hazards for the environment posed by such nearly ubiquitous and still largely unknown form of pollution. There is still the need for exhaustive, reliable, accurate, reasonably fast, and cost-efficient analytical protocols allowing the quantification not only of MPs but also of nanoplastics (NPs) and of the harmful molecular pollutants that may result from degrading plastics. Here a set of newly developed analytical protocols, integrated with specialized techniques such as pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS), for the accurate and selective determination of the polymers most commonly found as MPs polluting marine and freshwater sediments are presented. In addition, the results of an investigation on the low molecular weight volatile organic compounds (VOCs) released upon photo-oxidative degradation of microplastics highlight the important role of photoinduced fragmentation at a molecular level both as a potential source of hazardous chemicals and as accelerators of the overall degradation of floating or stranded plastic debris.

Continuous flow photo-RAFT and light-PISA

The combinations of microflow technology and photo-induced reversible-addition fragmentation chain transfer polymerization (photo-RAFT) and light-mediated polymerization-induced self-assembly (light-PISA) have enabled distinguished advantages that cannot be done in the traditional batch reactor. Recently, well-defined polymers with precise chemical structures and advanced nano-objects with high-order morphologies have been reported by using microreactor-based photo-RAFT and light-PISA strategies. In this mini-review, continuous flow photoiniferter polymerization, RAFT polymerization with photoinitiator, and photo-induced electron/energy transfer RAFT (PET-RAFT) polymerization are summarized in order. Moreover, the emerging light-PISA in microflow is introduced, and finally, the remained challenges are proposed for the discussion of opportunities. We hope it would provide insights into flow chemistry, polymer precision synthesis, and nanoscience.

Photoinduced Fragmentation Borylation of Cyclic Alcohols and Hemiacetals.

A visible-light photoinduced fragmentation borylation of O-phthalimido cycloalkanols with bis(catecholato)diboron is described. Structurally diverse keto and formyloxy alkyl boronic esters are shown to be conveniently prepared by radical-mediated ring opening of cyclic alcohols and hemiacetals, respectively. The reactions proceed under mild conditions in the absence of additives or photocatalysts, display excellent functional group tolerance, and are shown to allow cleavage of 4-, 5-, 6-, and 7-membered ring substrates. The mechanism proceeds via sequential homolytic N-O and C-C bond cleavages, the latter of which involves β-scission of an alkoxy radical, generating a carbonyl and an alkyl radical that is trapped by the diboron reagent. Spectroscopic studies suggest direct photoexcitation of either the phthalimide or diboron substrates with blue light can initiate a radical chain mechanism.

Positive/Negative Phototropism: Controllable Molecular Actuators with Different Bending Behavior

Herein, a series of molecular actuators based on the crystals of (E)-2-(4-fluorostyryl)benzo[d]oxazole (BOAF4), (E)-2-(2,4-difluorostyryl)benzo[d]oxazole (BOAF24), (E)-2-(4-fluorostyryl)benzo[d]thi...

Photolysis-induced scrambling of PAHs as a mechanism for deuterium storage

Aims. We investigate the possible role of polycyclic aromatic hydrocarbons (PAHs) as a sink for deuterium in the interstellar medium (ISM) and study UV photolysis as a potential underlying chemical process in the variations of the deuterium fractionation in the ISM. Methods. The UV photo-induced fragmentation of various isotopologs of deuterium-enriched, protonated anthracene and phenanthrene ions (both C14H10 isomers) was recorded in a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer. Infrared multiple photon dissociation spectroscopy using the Free-Electron Laser for Infrared eXperiments was applied to provide IR spectra. Infrared spectra calculated using density functional theory were compared to the experimental data to identify the isomers present in the experiment. Transition-state energies and reaction rates were also calculated and related to the experimentally observed fragmentation product abundances. Results. The photofragmentation mass spectra for both UV and IRMPD photolysis only show the loss of atomic hydrogen from [D − C14H10]+, whereas [H − C14D10]+ shows a strong preference for the elimination of deuterium. Transition state calculations reveal facile 1,2-H and -D shift reactions, with associated energy barriers lower than the energy supplied by the photo-excitation process. Together with confirmation of the ground-state structures via the IR spectra, we determined that the photolytic processes of the two different PAHs are largely governed by scrambling where the H and the D atoms relocate between different peripheral C atoms. The ∼0.1 eV difference in zero-point energy between C–H and C–D bonds ultimately leads to faster H scrambling than D scrambling, and increased H atom loss compared to D atom loss. Conclusions. We conclude that scrambling is common in PAH cations under UV radiation. Upon photoexcitation of deuterium-enriched PAHs, the scrambling results in a higher probability for the aliphatic D atom to migrate to a strongly bound aromatic site, protecting it from elimination. We speculate that this could lead to increased deuteration as a PAH moves towards more exposed interstellar environments. Also, large, compact PAHs with an aliphatic C–HD group on solo sites might be responsible for the majority of aliphatic C–D stretching bands seen in astronomical spectra. An accurate photochemical model of PAHs that considers deuterium scrambling is needed to study this further.

Development of a photoinduced fragmentation ion trap for infrared multiple photon dissociation spectroscopy.

Methods for isomer discrimination by mass spectroscopy are of increasing interest. Here we describe the development of a three-dimensional ion trap for infrared multiple photon dissociation (IRMPD) spectroscopy that enables the acquisition of the infrared spectrum of selected ions in the gas phase. This system is suitable for the study of a myriad of chemical systems, including isomer mixtures. A modified three-dimensional ion trap was coupled to a CO2 laser and an optical parametric oscillator/optical parametric amplifier (OPO/OPA) system operating in the range 2300 to 4000 cm-1 . Density functional theory vibrational frequency calculations were carried out to support spectral assignments. Detailed descriptions of the interface between the laser and the mass spectrometer, the hardware to control the laser systems, the automated system for IRMPD spectrum acquisition and data management are presented. The optimization of the crystal position of the OPO/OPA system to maximize the spectroscopic response under low-power laser radiation is also discussed. OPO/OPA and CO2 laser-assisted dissociation of gas-phase ions was successfully achieved. The system was validated by acquiring the IRMPD spectra of model species and comparing with literature data. Two isomeric alkaloids of high economic importance were characterized to demonstrate the potential of this technique, which is now available as an open IRMPD spectroscopy facility in Brazil.

Nano-assembled oligosilane–pyrazoline structures and their optical properties

Specific interactions between low molecular weight poly[diphenylsilane-co-methyl(H)silane] and 1,3-diphenyl-5-{4-[(4-vinylbenzyl)oxy]phenyl}-4,5-dihydropyrazole in solution have been investigated. Thus, a concentrated polysilane solution containing low amounts of pyrazoline was irradiated with UV light using predetermined conditions to produce a photo-induced fragmentation of the polysilane backbone. Spectrophotometric analysis of the bicomponent solution before and after UV irradiation suggested that polysilane and pyrazoline interact, which leads to their aggregation. Quantum chemical calculation indicated that a nano-assembling process between the two components is possible, and proved the Van der Waals (VdW) nature of the main interactions between the two components. The association between polysilane and pyrazoline modifies considerably the internal charge transfer within pyrazoline's chromophore, which results in fluorescence quenching. The electronic effects within the aggregate were studied using quantum computational calculations. Owing to the polysilane influence, polysilane–pyrazoline nanostructures have specific optical properties, which could be used to develop novel materials with fluorescence sensing ability.

Action-spectroscopy studies of positively charge-tagged azobenzene in solution and in the gas-phase.

The absorption of a positively charge-tagged azobenzene molecule is studied in the gas-phase by measuring photoinduced fragmentation of ions as a function of time. This technique provides information on prompt as well as delayed fragmentation, and a single dissociation channel after one-photon absorption is identified. The spectra in solution, as well as in the gas-phase, show a weak S0 → S1, a strong S0 → S2, and a broad absorption band in the UV regime. The bands are assigned through time dependent density functional theory calculations. The ratio of the various absorption bands depends on the trans to cis isomerization fraction and may be tuned by light irradiation. Gas-phase absorption spectra are presented and discussed in terms of trans and cis isomers.

Photoinduced Deaminative Borylation of Alkylamines.

An operationally simple deaminative borylation reaction of primary alkylamines has been developed. The formation of electron-donor-acceptor complexes between N-alkylpyridinium salts and bis(catecholato)diboron enables photoinduced single-electron transfer and fragmentation to carbon-centered radicals, which are subsequently borylated. The mild conditions allow a diverse range of readily available alkylamines to be efficiently converted into synthetically valuable alkylboronic esters under catalyst-free conditions.

Note: An ion imaging spectrometer for studying photo-induced fragmentation in small molecules.

A three-dimensional ion imaging spectrometer has been designed and calibrated by ion trajectories simulations. We present a recipe for the verification of the calibration by obtaining kinetic energy (KE) distribution from the recorded flight times alone and consequently correlating the two KE spectra.

Photo-induced Fragmentation of a Tin-oxo Cage Compound

Tin-oxo cage materials are of interest for use as photoresists for EUV (Extreme­ Ultraviolet) lithography (13.5 run, 92 eV), owing to their large absorption cross section for EUV light. In this work we exposed an n-butyl tin-oxo cage dication in the gas phase to photons in the energy range 4-14 eV to explore its fundamental photoreactivity. At all energies above the onset of electronic absorption at 5 eV (250 run) cleavage of tin-carbon bonds was observed. With photon energies >12 eV (<103 run) photoionization can occur, leading to 3+ ions. Besides the higher charge promotion, butyl chain loss without electron ejection (leading to 2+ fragments) still occurs. Keywords: Tin-oxo cage, Photoresist, Mass spectrometry, Photochemistry