Direct and Indirect Chemiluminescence: Reactions,Mechanisms and Challenges

Emission of light by matter can occur through a variety of mechanisms. When it results from an electronically excited state of a species produced by a chemical reaction, it is called chemiluminescence (CL). The phenomenon can take place both in natural and artificial chemical systems and it has been utilized in a variety of applications. In this review, we aim to revisit some of the latest CL applications based on direct and indirect production modes. The characteristics of the chemical reactions and the underpinning CL mechanisms are thoroughly discussed in view of studies from the very recent bibliography. Different methodologies aiming at higher CL efficiencies are summarized and presented in detail, including CL type and scaffolds used in each study. The CL role in the development of efficient therapeutic platforms is also discussed in relation to the Reactive Oxygen Species (ROS) and singlet oxygen (¹O₂) produced, as final products. Moreover, recent research results from our team are included regarding the behavior of commonly used photosensitizers upon chemical activation under CL conditions. The CL prospects in imaging, biomimetic organic and radical chemistry, and therapeutics are critically presented in respect to the persisting challenges and limitations of the existing strategies to date.     

Factoriality of complete intersections in ℙ<Superscript>5</Superscript>

Let X be a complete intersection of two hypersurfaces F _n and F _k in ℙ⁵ of degree n and k, respectively, with n ≥ k, such that the singularities of X are nodal and F _k is smooth. We prove that if the threefold X has at most (n + k − 2)(n − 1) − 1 singular points, then it is factorial.     

The interaction of diphosphonates with calcitic surfaces: understanding the inhibition activity in marble dissolution

The rates of dissolution of calcitic Carrara marble have been reported to be significantly reduced in alkaline pH (pH 8.25) at 25 degrees C in the presence of (1-hydroxyethylidene)-1,1 diphosphonic acid (HEDP). The adsorption takes place at the calcite/water interface at the double layer through the interaction of charged surface species with the charged solution species of the adsorbate. The present work focused on obtaining a better understanding of the interaction of the calcite surface with HEDP. Calculations were performed according to the triple layer model, assuming the formation of surface complexes between the charged surface species of calcite and the species of HEDP dominant at pH 8.25. According to the model, the adsorbed species are located at the inner Helmholtz plane of the electrical double layer. Strong lateral interactions between the adsorbed species were suggested and were corroborated from the calculation of the respective energy, which was equal to 69 kJ mol(-1). The adsorption isotherm was consistent with the proposed model at low surface coverage values, while discrepancies between the values experimentally measured and the predicted were found at higher adsorbate concentrations. The deviations from the predicted values were attributed to the fact that HEDP adsorption on calcite resulted in the formation of multiple layers. The model explained adequately the changes in the zeta-potential values of calcite in the presence of HEDP in the solution which resulted in charge reversal upon adsorption.     

Phenolic acid contents, essential oil compositions and antioxidant activities of two varieties of Salvia euphratica from Turkey

This study was designed to evaluate the in vitro antioxidant activities of n-hexane (Hex), dichloromethane (DCM), methanol (MeOH) and essential oils (EO) extracts obtained from Salvia euphratica var. euphratica and Salvia euphratica var. leiocalycina and to determine their essential oil and phenolic acid compositions. The samples were screened for their antioxidant activity by using DPPH and β-carotene/linoleic acid assays. Methanol extracts of both varieties exhibited strong antioxidant activities. Our results showed that rosmarinic acid was dominant phenolic acid of MeOH extracts (39.4 and 55.8?μg?mg?1, respectively). The chemical compositions of essential oils of two varieties were analysed and their main components were determined as eucalyptol (18.4%) and trans-pinocarvyl acetate (24.9%), respectively. It can be said that these varieties could be used as natural antioxidant.     

Development and Application of Instrumental Methods for Strain Analysisof Semiconductor Layers and Devices

 Strain effects on semiconductor layers were studied by means of optical spectroscopic techniques with a device developed especially for the study of layered structures and microstructures. Raman, modulated photoreflectance and reflectance anisotropy spectroscopy (RAS) were applied. Measurements were performed on elemental semiconductors (Si), semiconductor alloys (Si–Ge) and III–V semiconductor compounds (GaAs). By application of RAS, strains lower than 10⁻⁴ could be resolved, which is at least one order of magnitude lower than those observable with Raman and modulated reflectance techniques. The RAS spectra of layers strained along either the [010] or [011] direction showed a derivative-like structure at E₁-gap energies, which increased linearly and very quickly with increasing strain. The dependence of this spectral feature on applied strain was used to evaluate strain-dependent effects. This behaviour strongly suggests that RAS can be applied for the optical characterisation of strain in semiconductor microstructures and devices, with a higher efficiency and accuracy than that achieved by previously established optical methods such as Raman and modulation spectroscopy. In addition, the compactness and ease of operation of the instrumentation of RAS provides considerable potential for in situ monitoring/control of semiconductor fabrication conditions.     

LIBS using dual- and ultra-short laser pulses

Pre-ablation dual-pulse LIBS enhancement data for copper, brass and steel using ns laser excitation are reported. Although large enhancements are observed for all samples, the magnitude of the enhancement is matrix dependent. Whereas all of the dual-pulse studies used ns laser excitation we see interesting effects when using ps and fs laser excitation for single-pulse LIBS. LIBS spectra of copper using 1.3 ps and 140 fs laser pulses show much lower background signals compared to ns pulse excitation. Also, the atomic emission decays much more rapidly with time. Because of relatively low backgrounds when using ps and fs pulses, non-gated detection of LIBS is shown to be very effective. The plasma dissipates quickly enough using ps and fs laser pulses, that high pulse rates, up to 1000 Hz, are effective for increasing the LIBS signal, for a given measurement time. Finally, a simple near-collinear dual-pulse fiber-optic LIBS probe is shown to be useful for enhanced LIBS measurements. Received: 1 August 2000 / Revised: 2 November 2000 / Accepted: 8 November 2000     

PFAS Degradation in Ultrapure and Groundwater Using Non-Thermal Plasma

Perfluoroalkyl substances (PFAS) represent one of the most recalcitrant class of compounds of emerging concern and their removal from water is a challenging goal. In this study, we investigated the removal efficiency of three selected PFAS from water, namely, perfluorooctanoic acid (PFOA), perfluorohexanoic acid (PFHxA) and pefluorooctanesulfonic acid (PFOS) using a custom-built non-thermal plasma generator. A modified full factorial design (with 2 levels, 3 variables and the central point in which both quadratic terms and interactions between couple of variables were considered) was used to investigate the effect of plasma discharge frequency, distance between the electrodes and water conductivity on treatment efficiency. Then, the plasma treatment running on optimized conditions was used to degrade PFAS at ppb level both individually and in mixture, in ultrapure and groundwater matrices. PFOS 1 ppb exhibited the best degradation reaching complete removal after 30 min of treatment in both water matrices (first order rate constant 0.107 min⁻¹ in ultrapure water and 0.0633 min⁻¹ in groundwater), while the degradation rate of PFOA and PFHxA was slower of around 65% and 83%, respectively. During plasma treatment, the production of reactive species in the liquid phase (hydroxyl radical, hydrogen peroxide) and in the gas phase (ozone, NO_x) was investigated. Particular attention was dedicated to the nitrogen balance in solution where, following to NO_x hydrolysis, total nitrogen (TN) was accumulated at the rate of up to 40 mg^N L⁻¹ h⁻¹.     

Three-stage melting of an annelide-type copper complex. A new type of organized phase: Tegma crystals

The solid—solid phase transition of an annlide type copper complex are described. As the temperature is raised, three different constituents of the complex successively melt. In the temperature range 77–95°C, the polyethylene oxide chains and the paraffinic tail are both in a very mobile state while the copper complex sub-units still form a two-dimensional crystalline array.     

Palladium(II) Complexes of the Thiosemicarbazone and N‐Ethylthiosemicarbazone of 3‐Hydroxypyridine‐2‐carbaldehyde: Synthesis,Properties, and X‐Ray Crystal Structure

Two novel, stable Pd^II complexes, compounds 3 and 4 , of two 3‐hydroxypyridine‐2‐carbaldehyde thiosemicarbazones, 1 and 2 , resp., were prepared from Li₂PdCl₄. The single‐crystal X‐ray structure of complex 3 (= [Pd( 2 )Cl]) shows that the ligand monoanion coordinates in a planar conformation to the metal via the pyridyl N‐, the imine N‐, and the thiolato S‐atoms. Intermolecular H‐bonds, π–π, and CH ? ? ? π interactions lead to a two‐dimensional supramolecular assembly. The electronic, IR, UV/VIS, and NMR spectroscopic data of the two complexes are reported, together with their electrochemical properties. A sophisticated experimental procedure was used to determine the multiple dissociation constants of the ligands 1 and 2 by UV/VIS titration.