Preparation,spectral and structural characterization of (2-benzoylpyridine N(4)-methyl-N(4)-phenylthiosemicarbazonato) chloropalladium(II)

The synthesis, as well as spectral and structural characterization, of (2-benzoylpyridine-N(4)-methyl-N(4)-phenylthiosemicarbazonato)chloropalladium(II), [Pd(Bz4MePh)Cl], is described. The unit cell contains two crystallographically independent molecules [Pd(1)(Bz4MePh)Cl], (1), and [Pd(2)(Bz4MePh)Cl], (2), stabilized by intra- and intermolecular hydrogen bonding. The distance between the Pd(1) and Pd(2) centres is 3.5038(11) Å. The spectroscopic techniques used in this study are the following: u.v.-visible, i.r. and ¹H n.m.r. The protonation constants, determined spectrophotometrically, of the uncoordinated HBz4MePh are pK_a1 = 10.82 ± 0.03 and pK_a2 = 4.09 ± 0.02.     

A Review of Wine Authentication Using Spectroscopic Approaches in Combination with Chemometrics

In a global context where trading of wines involves considerable economic value, the requirement to guarantee wine authenticity can never be underestimated. With the ever-increasing advancements in analytical platforms, research into spectroscopic methods is thriving as they offer a powerful tool for rapid wine authentication. In particular, spectroscopic techniques have been identified as a user-friendly and economical alternative to traditional analyses involving more complex instrumentation that may not readily be deployable in an industry setting. Chemometrics plays an indispensable role in the interpretation and modelling of spectral data and is frequently used in conjunction with spectroscopy for sample classification. Considering the variety of available techniques under the banner of spectroscopy, this review aims to provide an update on the most popular spectroscopic approaches and chemometric data analysis procedures that are applicable to wine authentication.     

High‐Energy Long‐Lived Mixed Frenkel–Charge‐Transfer Excitons: From Double Stranded (AT)n to Natural DNA

The electronic excited states populated upon absorption of UV photons by DNA are extensively studied in relation to the UV‐induced damage to the genetic code. Here, we report a new unexpected relaxation pathway in adenine–thymine double‐stranded structures (AT)_n. Fluorescence measurements on (AT)_n hairpins (six and ten base pairs) and duplexes (20 and 2000 base pairs) reveal the existence of an emission band peaking at approximately 320 nm and decaying on the nanosecond time scale. Time‐dependent (TD)‐DFT calculations, performed for two base pairs and exploring various relaxation pathways, allow the assignment of this emission band to excited states resulting from mixing between Frenkel excitons and adenine‐to‐thymine charge‐transfer states. Emission from such high‐energy long‐lived mixed (HELM) states is in agreement with their fluorescence anisotropy (0.03), which is lower than that expected for π–π* states (≥0.1). An increase in the size of the system quenches π–π* fluorescence while enhancing HELM fluorescence. The latter process varies linearly with the hypochromism of the absorption spectra, both depending on the coupling between π–π* and charge‐transfer states. Subsequently, we identify the common features between the HELM states of (AT)_n structures with those reported previously for alternating (GC)_n: high emission energy, low fluorescence anisotropy, nanosecond lifetimes, and sensitivity to conformational disorder. These features are also detected for calf thymus DNA in which HELM states could evolve toward reactive π–π* states, giving rise to delayed fluorescence.     

Organotin‐Drug Interactions. Organotin Adducts of Tenoxicam: Synthesis and Characterization of the First Organotin Complex of Tenoxicam

The synthesis and spectral characterization of the novel organotin complexes [SnBu₂(ten)] ( 1 ) and [SnBu₂(Hten)₂] ( 2 ) of the potent and widely used anti‐inflammatory drug tenoxicam (H₂ten) are reported. A crystal‐structure determination of 1 showed that, in this complex, the ligand is doubly deprotonated at the hydroxy O‐atom and the amide N‐atom and is coordinated to the SnBu₂ fragment via four‐ and six‐membered chelate rings. An extended network of Sn−O−Sn, C−H⋅⋅⋅O and C−H⋅⋅⋅π contacts lead to aggregation and a supramolecular assembly. Potentiometric titrations in nonaqueous solutions support the ionization of the drug by removal of the second H‐atom, the amide H‐atom, in the presence of the diorganotin(IV) fragment. The K_a values of the poorly H₂O‐soluble drug tenoxicam were obtained spectrophotometrically in aqueous solutions of constant ionic strength.     

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.