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Tautomerism is one of the most important phenomena to consider when designing biologically active molecules. In this work, we use NMR spectroscopy, IR, and X-ray analysis as well as quantum-chemical calculations in the gas phase and in a solvent to study tautomerism of 1- (2-, 3- and 4-pyridinecarbonyl)-4-substituted thiosemicarbazide derivatives. The tautomer containing both carbonyl and thione groups turned out to be the most stable. The results of the calculations are consistent with the experimental data obtained from NMR and IR spectroscopy and with the crystalline forms from the X-ray studies. The obtained results broaden the knowledge in the field of structural studies of the thiosemicarbazide scaffold, which will translate into an understanding of the interactions of compounds with a potential molecular target.

The rapidly rising level of carbon dioxide in the atmosphere resulting from human activity is one of the greatest environmental problems facing our civilization today. Most technologies are not yet sufficiently developed to move existing infrastructure to cleaner alternatives. Therefore, techniques for capturing carbon dioxide from emission sources may play a key role at the moment. The structure of the UiO‐66 material not only meets the requirement of high stability in contact with water vapor but through the water pre‐adsorbed in the pores, the selectivity of carbon dioxide adsorption is increased. We successfully applied the recently developed methodology for water adsorption modelling. It allowed to elucidate the influence of water on CO2 adsorption and study the mechanism of this effect. We showed that water is adsorbed in octahedral cage and stands for promotor for CO2 adsorption in less favorable space than tetrahedral cages. Water plays a role of a mediator of adsorption, what is a general idea of improving affinity of adsorbate. On the basis of pre‐adsorption of methanol as another polar solvent, we have shown that the adsorption sites play a key role here, and not, as previously thought, only the interaction between the solvent and quadrupole carbon dioxide. Overall, we explained the mechanism of increased CO2 adsorption in the presence of water and methanol, as polar solvents, in the UiO‐66 pores for a potential post‐combustion carbon dioxide capture application., MOF trap: We successfully applied a recently developed methodology for water adsorption modelling that allows to elucidate the influence of water on CO2 adsorption and study the mechanism of this effect. We show that water is adsorbed in octahedral cage and stands for promotor for CO2 adsorption in less favorable space than tetrahedral cages. We explain the mechanism of increased CO2 adsorption in the presence of water and methanol, as polar solvents, in the UiO‐66 pores for a potential post‐combustion carbon dioxide capture application.

Proton-conducting metal–organic frameworks (MOFs) have been gaining attention for their role as solid-state electrolytes in various devices for energy conversion and storage. Here, we present a convenient strategy for inducing and tuning of superprotonic conductivity in MOFs with open metal sites via postsynthetic incorporation of charge carriers enabled by solvent-free mechanochemistry and anion coordination. This scalable approach is demonstrated using a series of CPO-27/MOF-74 [M2(dobdc); M = Mg2+, Zn2+, Ni2+; dobdc = 2,5-dioxido-1,4-benzenedicarboxylate] materials loaded with various stoichiometric amounts of NH4SCN. The modified materials are not achievable by conventional immersion in solutions. Periodic density functional theory (DFT) calculations, supported by infrared (IR) spectroscopy and powder X-ray diffraction, provide structures of the modified MOFs including positions of inserted ions inside the [001] channels. Despite the same type and concentration of proton carriers, the MOFs can be arranged in the increasing order of conductivity (Ni < Zn < Mg), which strongly correlates with amounts of water vapor adsorbed. We conclude that the proton conductivity of CPO-27 materials can be controlled over a few orders of magnitude by metal selection and mechanochemical dosing of ammonium thiocyanate. The dosing of a solid is shown for the first time as a useful, simple, and ecological method for the control of material conductivity.

The terminal phenoxy group is a moiety of many drugs in use today. Numerous literature reports indicated its crucial importance for biological activity; thus, it is a privileged scaffold in medicinal chemistry. This review focuses on the latest achievements in the field of novel potential agents bearing a terminal phenoxy group in 2013–2022. The article provided information on neurological, anticancer, potential lymphoma agent, anti-HIV, antimicrobial, antiparasitic, analgesic, anti-diabetic as well as larvicidal, cholesterol esterase inhibitors, and antithrombotic or agonistic activities towards the adrenergic receptor. Additionally, for selected agents, the Structure–Activity–Relationship (SAR) is also discussed. Thus, this study may help the readers to better understand the nature of the phenoxy group, which will translate into rational drug design and the development of a more efficient drug. To the best of our knowledge, this is the first review devoted to an in-depth analysis of the various activities of compounds bearing terminal phenoxy moiety.

We combine experiments and simulations to study the adsorption of water in several UiO-66 frameworks (ideal and defect-containing structures). We propose a new set of charges for the frameworks that accurately provides the water-structure interaction at the molecular level. The new set is suitable for predicting water adsorption in the ideal UiO-66 structure, providing for the first time, good agreement between experimental and calculated isotherms. The proposed procedure for tuning the point charges of the framework to achieve agreement with experiments is universal and can easily be extended to other MOFs. We explore the structural characteristics in terms of adsorption of water and the potential application of these materials to water harvesting from air. Our results show that the number of introduced defects significantly affect water sorption properties, which results in shifting steep water uptake and increasing saturation loading. Additional performed experiments, such as Ar sorption and the use of the QE-TPDA method allow for a broad characterization of structure-containing defects and the impact that these defects exert on the properties of the materials.

Micro- and nanoplatics have been already reported to be potential carcinogenic/mutagenic substances that might cause DNA damage, leading to carcinogenesis. Thus, the effects of micro- and nanoplastics exposure on human health are currently being investigated extensively to establish clear relationships between those substances and health consequences. So far, it has been observed that there exists a definite correlation between exposure to micro- and nanoplastic particles and the onset of several cancers. Therefore, we have conducted research using PubMed, Web of Science, and Scopus databases, searching for all the research papers devoted to cancers that could be potentially related to the subject of exposure to nano- and microplastics. Ultimately, in this paper, we have discussed several cancers, including hepatocellular carcinoma, pancreatic cancer, pancreatic ductal adenocarcinoma, biliary tract cancer, and some endocrine-related cancers.

The present work comprises the characterization of zeolite properties in the view of their usability as catalysts in the isomerization of xylenes and ethanol-to-hydrocarbon (ETH) process. Therefore...

Międzypokoleniowe spotkania chemików to połączenie teraźniejszości (Herbatki - rozmowy z aktualnymi pracownikami Wydziału), przyszłości (wywiady z przyszłymi chemikami - studentami) i przeszłości (wspomnienia byłych pracowników lub o byłych pracownikach Wydziału). Naszą główną motywacją było zachowanie pamięci, która jest nośnikiem tożsamości. Jesteśmy sumą naszych doświadczeń, więc przede wszystkim będzie w tej książce o doświadczeniach chemików (a chemik doświadczenia, choćby myślowe, lubi najbardziej!) jako indywidualnych osób, ale jednocześnie tworzących pewną grupę, można nawet powiedzieć - wspólnotę. Wspólnotę, która w każdej chwili dziejów składa się z adeptów nauk chemicznych, czyli studentów, kadry nauczającej oraz emerytowanych pracowników. W zamyśle główną formą opracowania jest wersja elektroniczna, aktualizowana możliwie na bieżąco. Jednak w dowolnym momencie (na przykład przy okazji jubileuszu czterdziestolecia istnienia Wydziału Chemii) można zrobić ?stop-klatkę" i wydrukować aktualny stan w postaci tradycyjnej, fizycznej książki. Zebrane teksty wydają się dobitnie wskazywać, że nie tylko wynik pokazywany przez Scopusa jest ważny w życiu chemika. Zapewne nie uda się nam dorównać w rzetelności naukowym bazom danych, ale mamy nadzieję, że mimo wszystko zdołamy wykazać, że jest coś istotnego poza nimi. Redakcja

In this study, important H1 antihistaminic drugs, i.e., emedastine (EME), epinastine (EPI), and ketotifen (KET), were irradiated with UV/Vis light (300–800 nm) in solutions of different pH values. Next, they were analyzed by new high performance liquid chromatography (HPLC) methods, in order to estimate the percentage of degradation and respective kinetics. Subsequently, ultra-performance liquid chromatography tandem-mass spectrometry (UPLC-MS/MS) was used to identify their photodegradation products and to propose degradation pathways. In addition, the peroxidation of linoleic acid and generation of singlet oxygen (SO) and superoxide anion (SA) were examined, together with the molar extinction coefficient (MEC) evaluation, to estimate their phototoxic risk. The photodegradation of all EME, EPI, and KET followed pseudo first-order kinetics. At pH values of 7.0 and 10.0, EPI was shown to be rather stable. However, its photostability was lower at pH 3.0. EME was shown to be photolabile in the whole range of pH values. In turn, KET was shown to be moderately labile at pH 3.0 and 7.0. However, it degraded completely in the buffer of pH 10.0. As a result, several photodegradation products were separated and identified using the UPLC-MS/MS method. Finally, our ROS assays showed a potent phototoxic risk in the following drug order: EPI < EME < KET. All of these results may be helpful for manufacturing, storing, and applying these substantial drugs, especially in their ocular formulations.

hiosemicarbazide is a useful structural moiety that has the biological potential. Optimization of this structure can result in groundbreaking discovery of a new class of therapeutic agents. In the light of this, 1-(2,4-dichlorophenoxy)acetyl-4-(1-naphthyl)thiosemicarbazide (1) and 1,4-bis[(2,4-dichlorophenoxy)acetylthiosemicarbazide]phenyl (2) were synthesized and characterized by spectroscopic method. Cytotoxicity of obtained compounds was evaluated on MKN74 gastric cancer cell line and human skin fibroblast BJ based on methylthiazolyldiphenyl-tetrazolium bromide (MTT) test. The apoptosis/necrosis and cell cycle analysis were conducted using image cytometry. Additionally, in DNA of treated cells, abasic sites (AP) and double strands breaks (DSB) presence were measured. Intercalating properties of active compounds were evaluated using the UV&ndash, spectroscopic method. Among newly synthesized derivatives, compound 2 showed toxic effects on gastric cancer cells with simultaneous lack of toxicity to normal fibroblasts. Cell cycle analysis revealed that both compounds influence cell division mainly at the stage of replication. Simultaneously with DNA synthesis disorders, DNA damages like AP-sites and DSBs were observed. Spectroscopic studies revealed possible DNA intercalating properties of tested compounds. Obtained results indicate that the newly synthesized thiosemicarbazide derivatives are a promising group of compounds with potential anticancer activity resulted from interactions with DNA and cell cycle interrupt.

We describe a method of determining upper bounds on the variances of linear combinations of the kth records values from i.i.d. sequences, expressed in terms of variances of parent distributions. We...

In this article, the results of computational structural studies on Al-containing zeolites, via periodic DFT + D modelling and FDM (Finite Difference Method) to solve the Schrödinger equation (FDMNES) for XAS simulations, corroborated by EXAFS (Extended X-ray Absorption Fine Structure) spectroscopy and PXRD (powder X-ray diffractometry), are presented. The applicability of Radial Distribution Function (RDF) to screen out the postulated zeolite structure is also discussed. The structural conclusions are further verified by HR-TEM imaging.

Epithelial-mesenchymal transition (EMT) constitutes one of the hallmarks of carcinogenesis consisting in the re-differentiation of the epithelial cells into mesenchymal ones changing the cellular phenotype into a malignant one. EMT has been shown to play a role in the malignant transformation and while occurring in the tumor microenvironment, it significantly affects the aggressiveness of gastric cancer, among others. Importantly, after EMT occurs, gastric cancer patients are more susceptible to the induction of resistance to various therapeutic agents, worsening the clinical outcome of patients. Therefore, there is an urgent need to search for the newest pharmacological agents targeting EMT to prevent further progression of gastric carcinogenesis and potential metastases. Therapies targeted at EMT might be combined with other currently available treatment modalities, which seems to be an effective strategy to treat gastric cancer patients. In this review, we have summarized recent advances in gastric cancer treatment in terms of targeting EMT specifically, such as the administration of polyphenols, resveratrol, tangeretin, luteolin, genistein, proton pump inhibitors, terpenes, other plant extracts, or inorganic compounds.

Electronic factors responsible for the notable decline of NO activation by Cu(II) with respect to Cu(I) sites in zeolites are investigated within spin-resolved analysis of electron transfer channels between the copper center and the substrate. The results of natural orbitals for chemical valence (NOCV) charge transfer analysis for a minimal model of Cu(II) sites in zeolite ZSM-5 ({T1Cu}+ NO) are compared with those for Cu(I)–NO and referenced to an interaction of NO with bare Cu+ cations. The bonding of NO, which is an open-shell and non-innocent ligand, gives rise to a noticeable nondynamical correlation in the adduct with Cu(II) (reflected in a broken-symmetry solution obtained at the density functional theory (DFT) level). Four distinct components of electron transfer between the copper and NO are identified: (i) donation of an unpaired electron from the NO π∥* antibonding orbital to the Cu species, (ii) backdonation from copper d⊥ to the NO antibonding orbital, (iii) “covalent” donation from NO π∥ and Cu d∥ orbitals to the bonding region, and (iv) donation from the nitrogen lone pair to Cus,d. Large variations in channel identity and significance may be noted among studied systems and between spin manifolds: channel i is effective only in the bonding of NO with either a naked Cu+ cation or Cu(II) site. Channel ii comes into prominence only for the model of the Cu(I) site: it strongly activates the NO bond by populating antibonding π*, which weakens the N–O bond, in contrast to channel i depopulating the antibonding orbital and strengthening the N–O bond. Channels iii and iv, however, may contribute to the strength of the bonding between NO and copper, and are of minor importance for the activation of the NO bond. This picture perfectly matches the IR experiment: interaction with either Cu(II) sites or a naked Cu+ cation imposes a comparable blue-shift of NO stretching frequency, while the frequency becomes strongly red-shifted for a Cu(I) site in ZSM-5 due to enhanced π* backdonation.

In this article the interaction between H2 and Ag(+), Cu(+), Mg(2+), Cd(2+), and Zn(2+) cations in cluster models of several sizes has been studied computationally. Depending on the changes imposed by the adsorption process on the H2 molecule the activation can vary in a wide range - from only slight weakening of the H-H bond to complete dissociation of the H2 molecule. The NOCV (Natural Orbitals for Chemical Valence) analysis allowed for decomposition of the electron density distortion into contributions easier for interpretation. Three essential factors have been identified (i-iii). In the case of bare cations the main contribution is a donation from σH2 to the cation (i). When a zeolite framework surrounding the cation is introduced, it hinders σ-donation and enhances π-backdonation from the cation to the antibonding orbital of the molecule (ii). For Cu(i) and Ag(i) sites π-backdonation becomes dominant, while for Mg(ii), Cd(ii), and Zn(ii) cations, the σ-donation, albeit diminished, still remains a dominant contribution. Calculations showed that the localization and coordination of Zn(ii) have crucial influence on its interaction with H2. We identified a Zn(2+) position at which the H2 molecule dissociates - here the interaction between H2 and oxygen framework (iii) plays a crucial role. Based on the calculations the mechanism of H2 transformation has been proposed. Upon heterolytic dissociation of H2 the Zn(0) moiety and two OH groups can be formed. Eventually, in two elementary steps, the H2 molecule can be restored. In this case, the ability of the site to activate/dissociate hydrogen is caused by the low coordination number of the zinc cation and the geometry of the site which allows positively charged H2 to interact with framework oxygen what enhances the formation of OH and Z-O-(ZnH)(+) groups.

Adsorption and activation of formaldehyde molecule by copper and silver sites in ZSM-5 was studied by combined QM/MM methodology. ETS-NOCV analysis was applied to decompose the deformation density (the difference between electron densities of composed systems and non-interacting fragments) into independent density flow channels. The analysis disclosed that the bonding of formaldehyde by the metal site may be described in terms of lone pair donation from carbonyl oxygen to the metal and π*-backdonation from metal d orbitals to antibonding orbital of CO. The former one is responsible for the formation of coordinate bond (“dative covalent”) and the latter one for the activation of carbonyl bond. Cu(I) site is more efficient with respect to both processes than Ag(I) one. Zeolitic environment is shown to weaken the bond between formaldehyde and M(I) with respect to free cations for both metals whereas it enhances π*-backdonation in the case of copper and diminishes π*-backdonation in the case of silver. Calculated red-shifts of CO frequencies agree well with the IR-measured ones and correlate with the degree of π*-backdonation which rationalizes as well very good performance of Cu(I) site compared to Ag(I) as the role of zeolitic framework in modifying exchanged cation properties.

Cu(I) and Ag(I) sites in ZSM-5 and their interaction with adsorbed benzene are studied by DFT cluster modeling aided with NOCV analysis of charge transfer processes. The interplay between donation and back donation from the cation to the ad-molecule, reinforced by the framework environment correlates with benzene activation shown also by the red shift in calculated and measured IR frequencies. Copper sites have better activation ability due to its stronger interaction with the framework, serving as electron reservoir, and better match between d orbitals and π orbitals of benzene.

Cobalt(II) sites in ferrierites are already well-known from their catalytic activity, their speciation and properties, however, the knowledge are far from completeness. The following paper presents the first in literature combined QM/MM study to elucidate the structure of these sites. With this end force-field parameters describing Co interactions with ionic shells in zeolite have been tested and the cell size for various Al distributions and Co positioning has been determined. Oxide-type Buckingham parameters are shown to perform better than the carbonate ones. Moreover, Co(II) ions stability in α and β sites with various Al distribution indicates at T1T1 Al substitution in β-site as that the preferred Co(II) siting. DFT results show that the quartet spin state of Co(II) is more stable than the doublet one.

In the present work the function of a zeolite framework in modifying the properties of copper sites has been studied. The [Al(OH)4CuNO](0/+) systems were studied by applying the analysis of the electron density flows - contributions to deformation density between two interacting fragments. The systems were divided in the following partition scheme: the first fragment, [Al(OH)4](-) (tagged T1), and the second one, [CuNO](+/2+). The analysis allowed us to elucidate the function of the zeolite fragment in modification of the cation properties towards activating the NO molecule. For both [(T1)CuNO](0/+) systems several channels showing the role of the zeolite framework have been identified. The geometry of the adducts influences either the efficiency of the channels or spin polarization. The two most important channels, zeolites-cations, influence the flow of electrons between the copper site and the antibonding NO orbitals. One channel favors the π-backdonation in the plane perpendicular to the Cu-N-O plane while the other contribution influences the π-backdonation in the C-N-O plane. The first one is found only in the system with copper(I) and it is essential for facilitating the π-backdonation and activating the NO molecule. The second channel is spin sensitive for both copper(I) and copper(II) sites. In the case of the system with copper(i) the second channel favors the π-backdonation while in the system containing copper(ii) the direction of these flows is opposite for α and β electrons.

Cu + ions in zeolites activate organic molecules containing π electrons by π back donation, which results in a distinct weakening of multiple bonds. In this study, we followed the activation of alkenes (ethene and propene) by Cu + ions in CuY and CuX zeolites of various Cu content. We also studied the strength of bonding of alkenes to Cu + ions. IR studies have shown that there are two kinds of Cu + sites of various electron donor properties. We suppose that they could be attributed to the presence of Cu + ions of various number of oxygen atoms surrounding the cation. IR studies have shown that Cu ions introduced into Y and X zeolites in the first-order (at low Cu content) form Cu + ions of stronger electron donor properties (i.e. activate alkenes to larger extend) than Cu ions introduced in the next order (at higher Cu content). IR and TPD studies of alkenes desorption evidenced that Cu + ions of stronger electron donor properties bond alkenes stronger than less electron donor ones. It suggests that π back donation has more important contribution to the strength of bonding alkenes to cation than π donation.

As Cu + ions in zeolites catalyse several reactions of organic molecules, we undertook IR and DFT studies of the interaction of organic molecules with Cu + . Our previous studies had shown that Cu + was able to activate strongly the double and triple bonds in alkenes and acetylene, and less strongly the C O bond in acetone, which resulted in a distinct multiple bond weakening. The DFT calculations provided evidence that this was realized by π back donation of d electrons of Cu + to π * antibonding orbitals of the molecules. The present study concerns the activation of the benzene molecule, which is different from previously studied ones. It is a good electron acceptor, but the LUMO orbital of benzene has only a small antibonding character, therefore the interaction with Cu + was expected to result in a strong adsorption but only slight activation of the C–C bond. Our IR studies have shown, that the C–C bond weakening was indeed very small (Δ ν C–C = 13 cm −1 , a value 10 times less than that for alkenes). DFT calculations showed that the molecule acquired a negative charge (−0.06) indicating that π back-donation prevailed over π donation. Both IR and DFT revealed that benzene adsorption on Cu + ions was relatively strong, which resulted in a withdrawing Cu + from the oxygen ring. DFT provided information on the geometry of the Cu + –benzene adduct and evidenced that the interaction of the benzene molecule with Cu + resulted in non-symmetric adsorption. The distances Cu + –C were in the range: 0.203–0.303 nm. The shorter the Cu + –C distance, the more important the bond activation. The benzene molecule interacting with Cu + was no longer flat, some hydrogens were directed towards Cu + and others in the opposite direction.

The low temperature adsorption of CO and the room temperature adsorption of propionitrile (PrN), isobutyronitrile (IBN) and pivalonitrile (2,2-dimethyl-propionitrile, PN) have been investigated on NaX (Si/Al atomic ratio = 1.3) and NaY (Si/Al atomic ratio = 2.4) zeolites by FT-IR spectroscopy. The bands of CO adsorbed on NaY have been reassigned. The relevance of Na + ions at S III or S III′ positions also on NaY has been emphasized. Evidence is provided for the formation of complex interactions where nitrile molecules interact with more than one site, likely more than one Na ion, as previously observed on alkali metal containing MOR zeolites. The possible relevance of this interaction is briefly discussed.

The desorption of CO from zeolites CuY and CuX was followed by TPD–IR method. This is a combination of temperature programmed desorption and IR spectroscopy. In this method, the status of activated zeolite (before adsorption), the process of adsorption, and the status of adsorbed molecules can be followed by IR spectroscopy, and the process of desorption (with linear temperature increase) can be followed both by IR spectroscopy and by mass spectrometry. IR spectra have shown two kinds of Cu+ sites in both CuY and CuX. Low frequency (l.f.) band (2140 cm−1 in CuY and 2130 cm−1 in CuX) of adsorbed CO represents Cu+ sites for which π back donation is stronger and σ donation is weaker whereas high frequency h.f. band (2160 cm−1 in CuY and 2155 cm−1 in CuX) represent Cu+ sites for which π back donation is weaker and σ donation is stronger. The TPD–IR experiments evidenced that the Cu+ sites represented by l.f. band bond CO more weakly than those represented by h.f. one, indicating that σ donation has more important impact to the strength of Cu+–CO bonding. On the contrary, π back donation has bigger contribution to the activation of adsorbed molecules.

In this paper, we present quantum chemical calculations for copper sites in the extended model of ZSM-5 framework based on seven T sites in two fused 5T rings cut off the MFI structure. Geometrical and electronic properties of cationic copper centres and their adsorption complexes with NO molecule are analysed from the point of view of the activation mechanism. The calculations show that the NO molecule adsorbed on Cu+ site becomes significantly activated contrary to Cu2+ centre, in full accordance to IR measurements. Our results indicate clearly that the ability of Cu+ site to donate electrons to π-antibonding orbital of NO causes significant bond weakening and makes Cu+ZSM-5 active in decomposition of nitrogen oxides.

The location of Cu cations in CuZSM-5, properties of cationic sites and their interaction with guest molecules have been studied by quantum chemical (DFT) modeling and IR spectroscopy based on the frequency shift of antisymmetric T–O–T vibration of oxygen rings. The shift has been found sensitive both to the framework interaction with cations and to the interaction with adsorbed molecules. It has been measured and estimated theoretically from parameters characterising framework distorsion by Cu+ and Cu2+, with MgZSM-5 and NaZSM-5 used as ‘‘reference samples’’. It was found that the ordering of the cation perturbing effect was: Na+

In this paper we study the properties of Cu ions and their interactions with diatomic molecules in Cu-exchanged ZSM-5. We present DFT quantum chemical calculations for models composed of the Cu site and a diatomic molecule accompanied by IR investigations for various forms of CuZSM-5. Two series of calculations with density functional theory have been undertaken in order to investigate the influence of zeolitic framework on properties of exchanged cations: (i) for small models built of free mono- and divalent copper cation interacting with CO, N2 and NO and (ii) 5- or 6-member ring models of ZSM-5 hosting the cation and a diatomic molecule. Comparison of calculated and experimental IR X–Y frequencies supports our model and brings some insight into the activation mechanism.

The values of extinction coefficients of CC and CC IR bands of ethyne and ethene interacting with Cu+ and Ag+ in zeolites were determined in quantitative IR experiments and also by quantumchemical DFT calculations with QM/MM method. Both experimental and calculated values were in very good agreement validating the reliability of calculations. The values of extinction coefficients of ethyne and ethene interacting with bare cations and cations embedded in zeolite-like clusters were calculated. The interaction of organic molecules with Cu+ and Ag+ in zeolites ZSM-5 and especially charge transfers between molecule, cation and zeolite framework was also discussed in relation to the values of extinction coefficients.

Adsorption and activation of ethene, ethyne, and formaldehyde by copper and silver sites in ZSM-5 are reinspected by quantitative assessment of the donation and backdonation processes between the three molecules and either models comprising bare cations (M+) or the cations embedded in zeolite framework (M(I)). ETS-NOCV analysis (decoupling the deformation density upon substrate bonding into independent components) reveals two predominant channels for electron transfer between adsorbed molecule and a cation or a cationic site, namely π*-backdonation from metal d orbitals to π* antibonding orbital of a substrate and σ-donation from π bonding or lone pair orbitals of the substrate to the cation. Alternative fragmentation of a complex modeling the cation embedded in zeolitic framework, treated as a three-part entity, allows for extracting predominant electron transfer channels from framework oxygens to the cation with bound substrate, namely, opposing σ-donation and supporting π*-backdonation. Critical analys...

This paper concerns the activation of ethene and ethyne molecules on two cationic sites (Cu(I) and Ag(I)) in ZSM-5 zeolite. QM/MM calculations were carried out to obtain geometric structure and vibrational frequencies. A novel analysis tool, NOCV (natural orbitals for chemical valence) supported by an ETS energy decomposition scheme, was applied to characterize charge flow between adsorbed molecules and the cationic site in ZSM-5 zeolite. The ETS-NOCV method allows for separating independent components of differential electron density into donation and backdonation channels, responsible for the substrate activation. It also helps to evaluate the importance of particular density transfer channels in the activation process. Two partition schemes into two subsystems are proposed here to extract complete information on the electronic balance between the molecule, the cation, and the zeolite framework. Both cationic sites (Cu(I) and Ag(I)) and both molecules (ethene and ethyne) are compared and the differences...

The present work is focused on the effect of zeolite framework on the activation of benzene by Cu+, Ag+ and Na+ ions. DFT calculations have been carried out to obtain geometric structure and electronic properties of both the cluster models of the cationic sites and bare cations interacting with benzene. NOCV (natural orbitals for chemical valence) has been used to elucidate components of differential electron density: donation and back donation. Zeolite framework is shown to intensify the benzene activation for several reasons, e.g. imposing specific adsorption geometry or modifying cation properties.

In this work charge transfer phenomenon between the admolecule and the active site and its consequences for the bond weakening/strengthening in the adsorbed molecule are discussed on the example of unsaturated hydrocarbons (early alkenes) interacting with Cu + cation embedded in a model of ZSM-5 zeolitic site. Detailed comparison of ethene interaction with various metallic sites based on this work and comparative analysis of other related studies helps to formulate working rules of charge transfer decomposition and interpretation. All studied alkenes form strongly bonded π complexes and become strongly activated on Cu + sites in ZSM-5 by both processes: π donation and π * back-donation, what clarifies the mechanism by which the activation of the C C bond in alkenes adsorbed on Cu + ZSM-5 takes place. Calculated shifts in C C stretching frequencies qualitatively follow the experiment and are a good measure of the activation.

Our previous IR studies as well as quantum chemical DFT calculations evidenced that Cu+ ions in zeolites were able to activate C C double bond in alkenes by π back donation of d electrons of Cu+ to π* antibonding orbitals of alkenes. It resulted in a distinct weakening of C C bond. The present study was undertaken in order to answer the question if Cu+ ions in zeolites were also able to activate another than C C double bond. We studied therefore the interaction of acetone with Cu+ in zeolites CuZSM-5, CuMCM-41, CuX and CuY. IR studies showed a weakening of C O bond and a red shift of IR band by 39–51 cm−1. The experiments in which the small doses of acetone were adsorbed as well as desorption studies evidenced that Cu+ bonded acetone more strongly than other adsorption sites, such as hydroxyl groups. DFT modeling of the adsorption of the acetone molecule on copper site gave the information about the function of the zeolite as a host for transition metal cationic sites and as an electron reservoir. Calculated values of electron affinity and HOMO energy allowed to explain that, on the basis of the charge distribution analysis, electrons flowed from the acetone molecule to the copper site, so that the molecule was positive. It was evidenced by the analysis of the charge distribution. Therefore, the activation upon adsorption has been justified by the electronic structure of the molecule, its electron affinity as well as the ability of the site to π back donation. Moreover, the calculated value of the red shift of the IR band of the activated C O bond was similar as experimental one.

Transformation of cobalt centres in CoZSM-5 of various (Co/AlO 4 ) ratios was investigated as a function of the thermal treatment in the temperature range of 290–830 K, by means of IR, UV-Vis-NIR, TG-QMS, and EPR spectroscopies, supported by DFT calculations. The focus was devoted to elucidation of the speciation of cobalt inside and outside the channels of the ZSM-5 zeolite. A molecular description of the principal phenomena (dehydration, hydrolysis, olation, and oxolation) involved in the thermal activation was provided and rationalised in terms of partial charge model.

It is well-known that Cu+ cations in zeolites, especially in ZSM-5 activate NO molecule resulting in its decomposition. Quantum chemical calculations evidenced that it is due to π-backdonation. The aim of our studies was to answer the question whether Cu+ in zeolites is also able to activate other π-electron systems according to the same mechanism, i.e. by π-backdonation of d electrons of copper to π* antibonding orbitals. We studied the adsorption of alkenes (ethene, propene, cis-but-2-ene, trans-but-2-ene), acetylene, benzene, and acetone with Cu+ sites in CuX, CuY, CuZSM-5. The main experimental method was IR spectroscopy but we also performed DFT calculations. Both evidenced weakening C=C and C≡C bond. IR red shift reaches 78–115 cm–1 for C=C band and 168 cm–1 for acetylene. Moreover, in the case of ethene and acetylene the stretching of the C=C and C≡C bonds which were IR inactive in free molecules became IR active when interacting with Cu+, indicating the loss of symmetry. Contrary, the C=C stretching in trans-but-2-ene was still IR inactive when trans-but-2-ene interacted with Cu+. At high loading some Cu+ ions were able to bond two alkene molecules. Although the activation is small, it occurs also for aromatic C–C bond in benzene adsorbed on Cu+ site; the red band shift was 13 cm–1, i.e. much less than in the case of alkenes and acetylene. Similarly, the activation of C=O bond in acetone interacting with Cu+ results also in the red band shift of 38 cm–1. All the systems have been studied by DFT modeling which reveals the function of zeolite as a host for transition metal cationic centers which act as electron transmitters. Flow of electrons and subsequent activation is determined by the electronic structure of the molecules, their electron affinity and symmetry as well as the ability of the site to π-backdonation. To cite this article: E. Broclawik et al., C. R. Chimie 8 (2005).

The average electron donor properties of Cu + ions in CuZSM-5 were found to be stronger than in CuMCM-41. This was evidenced by IR studies of CO, N 2 and NO adsorption. The stronger electron donor properties of Cu + the stronger it activates adsorbed molecules by π-back donation. This is why Cu + ions in CuZSM-5 are more active in “deNOx” reaction than in CuMCM-41. IR studies of CO and N 2 desorption showed that Cu + ions in both CuZSM-5 and CuMCM-41 were heterogeneous and the Cu + sites of various electron donor properties were present. Quantumchemical DFT calculations showed that the electron donor properties of Cu + (electrical charge and energy of HOMO) depend on the location of Cu + in zeolites. Cu + ions in α sites (of higher number of oxygen atoms surrounding the cation) are stronger electron donor than Cu + ions in β sites. The calculations evidenced also that Cu + in α sites activate stronger NO molecules than in β sites.

A PdCoZSM-5 catalyst was prepared by ion-exchange and impregnation. In such a catalyst besides Co 2+ ions, PdO and Co 3 O 4 are formed while a catalyst is pre-treated in flowing air 770 K. Catalytic runs of deNOx reaction were performed in a flow system. Temperature programmed surface reaction (TPSR) of NO, O 2 , CH 4 show three functions of our PdCoZSM-5 catalyst: oxidation of NO to NO 2 over Co 3 O 4 , methane activation and oxidation by NO 2 to methanol over PdO, and finally the reduction of nitrogen oxides by methanol. The catalyst works efficiently if the temperature windows of each needed function overlap enough