Monodentate Binding Research Articles

Bidentate Substrate Binding Mode in Oxalate Decarboxylase.

Oxalate decarboxylase is an Mn- and O2-dependent enzyme in the bicupin superfamily that catalyzes the redox-neutral disproportionation of the oxalate monoanion to form carbon dioxide and formate. Its best-studied isozyme is from Bacillus subtilis where it is stress-induced under low pH conditions. Current mechanistic schemes assume a monodentate binding mode of the substrate to the N-terminal active site Mn ion to make space for a presumed O2 molecule, despite the fact that oxalate generally prefers to bind bidentate to Mn. We report on X-band 13C-electron nuclear double resonance (ENDOR) experiments on 13C-labeled oxalate bound to the active-site Mn(II) in wild-type oxalate decarboxylase at high pH, the catalytically impaired W96F mutant enzyme at low pH, and Mn(II) in aqueous solution. The ENDOR spectra of these samples are practically identical, which shows that the substrate binds bidentate (κO, κO') to the active site Mn(II) ion. Domain-based local pair natural orbital coupled cluster singles and doubles (DLPNO-CCSD) calculations of the expected 13C hyperfine coupling constants for bidentate bound oxalate predict ENDOR spectra in good agreement with the experiment, supporting bidentate bound substrate. Geometry optimization of a substrate-bound minimal active site model by density functional theory shows two possible substrate coordination geometries, bidentate and monodentate. The bidentate structure is energetically preferred by ~4.7 kcal/mol. Our results revise a long-standing hypothesis regarding substrate binding in the enzyme and suggest that dioxygen does not bind to the active site Mn ion after substrate binds. The results are in agreement with our recent mechanistic hypothesis of substrate activation via a long-range electron transfer process involving the C-terminal Mn ion.

Computational Insights Into Betanin for Dsscs: Unraveling Deprotonation Variations and Identifying Optimal Anchoring Sites on TiO2

AbstractBetanin (Bn), a natural dye in the Betalains family, predominantly takes on a cationic form known as Bn+. However, it exists in a neutral state as Bn_C2, Bn_C15, and Bn_C17 by losing an H+ from one of its carboxylic acids. Density functional theory (DFT) and Time‐dependent density functional theory (TD‐DFT) studies evaluate the efficiency of each betanin form and pinpoint the most probable anchoring point to TiO2. The Bn_C17 variant stands out as a highly promising candidate for DSSC cells, demonstrating a distinctive combination of electron injection efficiency, electrochemical performance, hole transport capabilities, and photovoltaic behavior. Considering factors like adsorption energy, binding mode, structural compatibility, electronic properties, and absorption characteristics, Bn_C17@TiO2 emerges as the most favorable dye@TiO2 complex among the studied betanin forms for DSSC applications. Contrastingly, the C2‐COOH anchoring point presents challenges with monodentate binding, a different orientation, and potential load distribution issues. This behavior, resembling that of a p‐type dye, differs from the n‐type behavior exhibited by the C15‐COOH and C17‐COOH forms, making the latter two more suitable as sensitizers. Consequently, C2‐COOH may not be the optimal anchoring point for TiO2 in the investigated betanin forms, especially when compared to the more favorable C17‐COOH anchoring point.

Study on the Catecholase Activity in the Presence of a Mn(III)-based Catalyst and Base

Background:: This work describes the oxidation of a catechol moiety to the corresponding quinone by using Mn(III)-based catalysts in the presence of an organic base. Two newly reported Mn(III)-Schiff base complexes were utilized for the oxidation of three different substrates, namely, 3,5-di tert-butyl catechol, 1,4-dihydroxy benzene and pyrocatechol, aerobically. Objective:: We intended to understand the role of a base for the above-mentioned oxidation process. Also, we were interested to monitor the progress of reaction using 1H-NMR spectroscopy and to get more insight into the mechanistic path of the reaction. Methods:: The oxidation processes were studied in open air in acetonitrile or methanol solvent. The reaction mixture containing concerned substrate, catalyst, and base were stirred in open air and 1H-NMR spectrum was recorded using the crude reaction mixture in different time intervals. Results:: Interestingly, introduction of a base in the reaction mixture, enhanced the rate to a great extent for the first two substrates. This observation may provide an idea toward the rate determining step of the process. Notably, the third substrate, pyrocatechol, could not be oxidized by any of the two cata-lysts even with a base which might emphasize monodentate binding mode of the substrate. Each of the oxidation was monitored with the help of time dependent 1H-NMR spectroscopy. Conclusion:: A mechanistic pathway has been proposed. The spectra obtained in different cases help to compare the efficiency of the catalysts with or without base. In the absence of the catalysts, triethyl-amine alone cannot complete the conversion in the stipulated time, which may establish the effective-ness of the catalysts via the base-assisted mechanism.

Cyrene™ as a tyrosinase inhibitor and anti-browning agent

The tyrosinase pathway takes part in the enzymatic process of food browning and is primarily responsible for food spoilage - manifesting itself from a decrease in its nutritional value to a deterioration of taste, which consequently leads to a gradual loss of shelf life. Finding safe and bio-based tyrosinase inhibitors and anti-browning agents may be of great importance in agriculture and food industries. Herein, we showed that Cyrene™ exhibits tyrosinase inhibitory activity (IC50: 268.2 µM), the 1.44 times higher than ascorbic acid (IC50: 386.5 μM). Binding mode studies demonstrated that the carbonyl oxygen of Cyrene™ coordinates with both copper ions. Surprisingly, both hydroxyl groups of Cyrene gem-diol perform a monodentate binding mode with both copper ions, at similar distances. This fact suggests that both compounds could have a similar binding mode and, as consequence, similar biological activities in tyrosinase inhibition assays and anti-browning activities.

Monodentate binding of zwitterionic ligands for boosting photocatalytic H2 production of perovskite nanocrystals

Perovskite nanocrystals (PNCs) have recently emerged as promising materials for photocatalytic applications. However, weakly bound and long-chain surface ligands on PNCs reduce the colloidal stability, hinder efficient charge transfer, and lower the photocatalytic activity. Herein, we report zwitterionic sulfobetaine (ZSB) ligand-capped CsPbBr3perovskite nanocrystals (PNCs) for visible-light-driven photocatalytic H2 production. In this system, the ZSB ligands passivate PNC surface defects, thus improving the photoluminescence stability and quantum yield. In particular, the positively charged R4N+groups of the ZSB ligands preferentially bind to the Br-rich CsPbBr3PNC surface, leaving unpaired negative SO3− groups in the outermost ligand layer. This unbalanced binding of the ZSB ligands changes the surface potential of the PNCs from positive to negative, inducing a kinetically favorable band alignment at the heterojunction between the PNC and co-catalyst (Pt-deposited TiO2). The heterojunction and electronic structures are stable, even in harsh aqueous environments, resulting in significantly enhanced electron transfer and H2 production rates and greatly improved operational stability. We believe that the use of ZSB ligands for band engineering is highly promising for PNC-based photocatalysis and solar energy conversion systems.

Triangle Cl-Ag1-Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl.

BiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO2 emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl-Ag1-Cl sites on a Cl-terminated, (001) facet-exposed BiOCl can selectively promote one-electron activation of reactant molecular oxygen to intermediate superoxide radicals (•O2-), and also shift the adsorption configuration of product NO3- from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl-Ag1-Cl-landen BiOCl achieved > 90% NO conversion to favorable NO3- of high selectivity (> 97%) in 10 min under visible light, with the undesired NO2 concentration below 20 ppb. Both the activity and the selectivity of Cl-Ag1-Cl sites surpass those of BiOCl surface sites (38% NO conversion, 67% NO3- selectivity) or control O-Ag1-O sites on a benchmark photocatalyst P25 (67% NO conversion and 87% NO3- selectivity). This study develops new single-atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.

Triangle Cl−Ag1−Cl Sites for Superior Photocatalytic Molecular Oxygen Activation and NO Oxidation of BiOCl

AbstractBiOCl photocatalysis shows great promise for molecular oxygen activation and NO oxidation, but its selective transformation of NO to immobilized nitrate without toxic NO2 emission is still a great challenge, because of uncontrollable reaction intermediates and pathways. In this study, we demonstrate that the introduction of triangle Cl−Ag1−Cl sites on a Cl‐terminated, (001) facet‐exposed BiOCl can selectively promote one‐electron activation of reactant molecular oxygen to intermediate superoxide radicals (⋅O2−), and also shift the adsorption configuration of product NO3− from the weak monodentate binding mode to a strong bidentate mode to avoid unfavorable photolysis. By simultaneously tuning intermediates and products, the Cl−Ag1−Cl‐landen BiOCl achieved >90 % NO conversion to favorable NO3− of high selectivity (>97 %) in 10 min under visible light, with the undesired NO2 concentration below 20 ppb. Both the activity and the selectivity of Cl−Ag1−Cl sites surpass those of BiOCl surface sites (38 % NO conversion, 67 % NO3− selectivity) or control O−Ag1−O sites on a benchmark photocatalyst P25 (67 % NO conversion and 87 % NO3− selectivity). This study develops new single‐atom sites for the performance enhancement of semiconductor photocatalysts, and also provides a facile pathway to manipulate the reactive oxygen species production for efficient pollutant removal.

Significance of anchoring group design on light harvesting efficiency of dye-sensitized solar cells and non-linear optical response

Dye-sensitizers designed from coumarin backbone are widely utilized in solar light harvesting due to their versatile performance in dye-sensitized solar cells (DSSC). They are well-known as non-linear optical (NLO) materials. In this case study, we have designed coumarin-based sensitizers containing thiophene as a common spacer with the different acceptor-anchoring groups, ethyl-2-cyanoacrylate (SPDSSC 1) and 2-cyanoacrylic acid (SPDSSC 2). Density functional theory (DFT) and time-dependent- DFT (TD-DFT) computational calculations of these molecules predict superior light harvesting capability and NLO properties. The calculated HOMO–LUMO energy gap of these dyes showed an inverse relation with chemical potential and electrophilicity index and was directly related to hardness and hyperhardness. It was also seen β0 and γ and PCE follow a similar trend. Further, computations of sensitizers@TiO2 indicated sensitizers with ethyl-2-cyanoacrylate bonded with TiO2 cluster via unidentate linkage, whereas 2-cyanoacrylic acid containing sensitizer involved bidentate bonding with TiO2. Apart from this, sensitizers with 2-cyanoacrylic acid anchors showed much planer geometry. Also, the quantitative analysis of the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) and MEP plots showed that more electron clouds shifted to the TiO2 cluster in the sensitizer with 2-cyanoacrylic acid (SPDSSC 2) than ethyl-2-cyanoacrylate (SPDSSC 1). Further, both molecules were taken as sensitizers in the DSSC device. SPDSSC 2 showed higher power conversion efficiency than SPDSSC 1. Overall, results disclosed that sensitizers with ethyl-2-cyanoacrylate having two oxygen atoms in their anchoring part could bind with only carbonyl oxygen. And this monodentate binding of ethyl-2-cyanoacrylate with TiO2 leads to poor charge transfer in the semiconductor's conduction band, resulting in poor DSSC performance.

The impact of anchoring groups on the efficiency of dye-sensitized solar cells: 2-Cyanoacrylic acid vs. ethyl 2-cyanoacrylate

Due to their promising performance, coumarin-based dyes have been widely used in third-generation dye-sensitized solar cells (DSSCs) and as nonlinear optical (NLO) materials. In this study, we have designed and synthesized coumarin-based sensitizers in conjugation with common phenyl as a π-linker and ethyl-2-cyanoacrylate (SPDSSC 7) and 2-cyanoacrylic acid (SPDSSC 8) as an anchor and determined their DSSC performance. Photovoltaic results showed that 2-cyanoacrylic acid-based sensitizer (SPDSSC 8) performed better than ethyl-2-cyanoacrylate-based sensitizer (SPDSSC 7) which improves with a thicker coating of TiO2. Density functional theory (DFT) results showed an inverse relationship between band-gap (BG) and chemical potential and electrophilicity index but a direct relationship between BG and hardness and hyperhardness. Time dependent-DFT (TD-DFT) showed a similar trend as observed in the experiment. It was also found that first-order hyperpolarizability (β0) and second-order hyperpolarizability (γ) and PCE is related directly through CT properties. Furthermore, calculations of sensitizers@TiO2 revealed that sensitizer with ethyl-2-cyanoacrylate was linked as unidentate and 2-cyanoacrylic acid linked bidentatly to TiO2 clusters. Furthermore, quantitative analysis of the HOMO-LUMO and MEP plots revealed that SPDSSC 8 showed more efficient electron transfer from the sensitizer to the TiO2 cluster than SPDSSC 7. These results were consistent with the calculated Eadsorption for both sensitizers. The monodentate binding of SPDSSC 7 to TiO2 results in inferior charge transfer in the semiconductor’s conduction band, ultimately negatively impacting DSSC performance.

Nondirected Pd-Catalyzed C–H Perdeuteration and meta-Selective Alkenylation of Arenes Enabled by Pyrazolopyridone Ligands

The development of ligands and the elucidation of their roles in the catalytic cycle are key to achieving high efficiency and selectivity in nondirected transition-metal-catalyzed C–H functionalization. In particular, careful ligand design can enable the functionalization of previously inaccessible substrate positions, which can lead to regiodivergent transformations of common reactants. In this study, a series of pyrazolopyridone (PzPyOH) ligands that can be easily prepared in a single step was developed for the Pd-catalyzed perdeuteration and meta-selective alkenylation of arenes. In this system, the 2-pyridone moiety was incorporated to function as an internal base, facilitating C–H cleavage and rendering C–H activation reversible, even at challenging sp2 C–H bonds, thus enabling perdeuteration. In addition, the reversible activation of the C–H bonds implies that site selectivity is determined during the migratory insertion step in the alkenylation reaction, thereby preferentially functionalizing the meta-positions rather than the typically more reactive ortho- and para-positions of anisole derivatives. Further, the electronic and structural properties of the pyrazole moiety provide flexibility in the ligand binding to Pd, enabling the facile coordination of an alkene coupling partner during alkenylation. In this process, the hydrogen bonding between pyridone and acetate ligands was crucial to stabilize intermediates, allowing for different types of binding modes, including L,L- and L,X-type bidentate and monodentate binding. Kinetic and computational studies support the proposed mechanisms for perdeuteration and alkenylation, and the findings reveal crucial factors in the design of ligands for Pd-catalyzed C–H functionalization, which will be useful for further development of pyrazole- and pyridone-containing ligands in transition metal catalysis.

Controlling product selectivity in oxidative desulfurization using an electrodeposited iron oxide film.

Sulfur-containing compounds must be removed from raw fuel oils before use and recently, there has been an effort to identify and optimize a more energy efficient method of oil processing. One promising route is electrochemical oxidative desulfurization (ODS), and in this work, we investigate an electrodeposited iron oxide film (FeOx(OH)y) as a working electrode to catalyze the oxidation of dibenzothiophene (DBT). The FeOx(OH)y film displays unexpected selectivity for the DBT sulfoxide (DBTO)-departing from the catalytic behavior of gold, which favors the dimerization of DBT. In addition, we observe a morphological change within our FeOx(OH)y film from γ-FeOOH to γ-Fe2O3. This change provides insight to the activity of each structure for ODS as the rate of oxidation increases after the incorporation of γ-Fe2O3. Our experimental observations are corroborated with DFT calculations, which suggest that the adsorption energy of DBT on Au is significantly greater than on the FeOx(OH)y, favoring the formation of dimeric and oligomeric products. Calculations also demonstrate that DBT binds preferably in a monodentate configuration but that oxidation occurs via DBT bound via a bidentate configuration. Monodentate binding on γ-FeOOH is significantly stronger than binding on γ-Fe2O, resulting in easier conversation to bidentate binding on γ-Fe2O3.

Uranium sorption to organic matter and long-term accumulation in a pristine alpine wetland

Understanding the controls on uranium (U) mobility in the environment is key to improve the management of sites contaminated by U mining activities. Previous research has shown that natural or engineered wetlands are particularly able to scavenge high amounts of U(VI) and U(IV) under noncrystalline forms. However, questions remain on the respective roles of sorption and reduction processes in the removal of U from running waters in wetlands, as well as on the long-term stability of U storage. Here, we performed a series of geochemical, isotopic (δ238U, (234U/238U)), microscopic (SEM-EDXS, EPMA) and spectroscopic (µ-XRF, µ-XAS, XANES and EXAFS at the U L3 and M4-edges and Fe K-edge) investigations to determine the modes of U accumulation and assess U mobility in a natural exceptionally U-enriched (up to 5000 µg/g) wetland on the shore of Lake Nègre (Mediterranean Alps, France). Uranium (VI) was largely dominant in the two studied soil cores, except a few samples containing as much as ∼50 % U(IV). At the particle scale, U is associated to a variety of organic constituents of the soil matrix with a homogenous oxidation state. Bulk EXAFS spectroscopy at the U L3-edge shows that U is mostly mononuclear, with dominant monodentate binding to organic moieties (C neighbors at ∼3.45 Å). An additional minor fraction of U under polymeric forms is inferred from wavelet (CCWT) analysis of the EXAFS data. These observations are reinforced by 1 M bicarbonate extractions that result in the dissolution of 82–96 % of total U, including putative polymeric species. At the wetland scale, similar or slightly fractionated isotopic ratios (δ238U) between the wetland-feeding creek waters and the wetland soils are observed, supporting the idea that U(VI) sorption on organic matter is the primary U scavenging mechanism. Furthermore, it indicates that partial U(VI) reduction to U(IV) occurs as a second step, after sorption. Analysis of U decay chain disequilibria in the cores as a function of depth suggests that U accumulation in this wetland has lasted for several thousand years. We propose that the wetland acts as an active reactor where U has been massively accumulating for ∼14500 years, especially as U(VI) forms associated to organic matter, and is further partly exported to the lake through soil erosion.

Synthesis, crystal structures and properties of six new mixed ligand cobalt(II) 4-nitrobenzoates

The synthesis, spectral characteristics, thermal properties and single crystal structures of [Co(N-meim)2(4-nba)2] (N-meim = N-methylimidazole; 4-nba = 4-nitrobenzoate) (1), [Co(2-meim)2(4-nba)2] (2-meim = 2-methylimidazole) (2), [Co(pyr)3(4-nba)2] (pyr = pyrazole) (3), [Co(H2O)2(form)2(4-nba)2]·form (form = formamide) (4), [Co(H2O) (aceta)2(4-nba)2] (aceta = acetamide) (5) and [Co(H2O)3(N-mepyr)(4-nba)](4-nba) (N-mepyr = N-methylpyrazole) (6) are reported. The central Co(II) exhibits tetrahedral geometry in 1 and 2, trigonal bipyramidal geometry in 3 and octahedral geometry in 4–6. In the anhydrous compounds 1–3 as well as the diaqua compound 4, the monoaqua compound 5 and the triaqua compound 6, the neutral N-donor co-ligands or the O-donor amides function as terminal ligands. The aromatic 4-nba ligand exhibits monodentate binding mode in 1–4 and monodentate and bidentate binding in 5, while 6 contains an uncoordinated 4-nba in addition to a bidentate 4-nba ligand. A single C-H···O interaction links molecules of 1 into an infinite chain while the N-H···O bonds in 2 result in a two-dimensional network. Compounds 4 and 5 exhibit three varieties of H-bonding. Thermal decomposition of 1–6 results in the formation of a spinel oxide. A comparative study of thirty-one structurally characterized cobalt-4-nitrobenzoates is described.

Biosorption of Pb and Cd onto Polygonum sachalinense

Adsorption of Pb and Cd onto a biosorbent, carbonized Polygonum sachalinense (CPS) was investigated. The carbonization condition was 1 h at 350ºC. The adsorption behaviors of Pb and Cd onto CPS could be explained by a proposed adsorption model based on the monodentate binding of the divalent metal ions with two types of adsorption sites. The adsorption sites were considered as carboxylic and phenolic groups based on the results of Boehm titration and FT-IR analysis. The maximum adsorption capacity of CPS for the divalent metal ions was determined as 1.22 mmol/g, and it was much larger than the values reported in the previous reports. The binding affinities of Pb of the adsorption sites were considered as much higher than those of Cd based of the adsorption constants. The adsorption constants of Pb and Cd with carboxylic group were about 200–2000 times larger than the of the adsorption constants with phenolic group. The kinetics of Pb and Cd onto CPS were also investigated. It was found that the adsorption of the divalent metal ions onto the phenolic group was a rate limiting step.

Genuine Pores in a Stable Zinc Phosphite for High H2 Adsorption and CO2 Capture.

An uncommon example of stable mixed-ligand zinc phosphite with genuine pores has been synthesized by using zinc metal, inorganic phosphite acid, thio-functionalized O-donor (2,5-thiophenedicarboxylate, TPDC), and tetradentate N-donor [1,2,4,5-tetrakis(imidazol-1-ylmethyl)benzene, TIMB] units assembled into one crystalline structure according to a hydro(solvo)thermal method. This is a very rare case of a metal phosphite incorporating both N- and O-donor ligands. The tetradentate TIMB linker bound to zinc atoms of the isolated zincophosphite hexamers to form a 3D open-framework structure by crosslinking structural components of 1D chains and 2D layers. Here, the TPDC ligand acts as a monodentate binding model to functionalize its porous structure with the uncoordinated S atom and COO- group. Interestingly, this compound demonstrates the highest H2 storage capacity among organic-inorganic hybrid metal phosphates (and phosphites), and a good CO2 capture at 298 K compared with the majority of crystalline materials. The possible adsorption sites and selectivity for CO2 over H2 , N2 , and CO at 298 K were calculated by using density functional theory (DFT), the ideal adsorption solution theory (IAST), and fitting experimental pure-component adsorption data.

Pd-Catalyzed Heteroannulation Using N-Arylureas as a Sterically Undemanding Ligand Platform.

We report the development of ureas as sterically undemanding pro-ligands for Pd catalysis. N-Arylureas outperform phosphine ligands for the Pd-catalyzed heteroannulation of N-tosyl-o-bromoanilines and 1,3-dienes, engaging diverse coupling partners for the preparation of 2-subsituted indolines, including sterically demanding substrates that have not previously been tolerated. Experimental and computational studies on model Pd-urea and Pd-ureate complexes are consistent with monodentate binding through the nonsubstituted nitrogen, which is uncommon for metal-ureate complexes.

Synthesis, spectroscopic characterization, biological screening and POM analysis of potentially bioactive copper(II) carboxylate complexes

ABSTRACT. Here we are reporting the synthesis, characterization of four novel copper(II) complexes with carboxylate ligand and their evaluation for biological applications. The complexes have general formulas C22H18CuN4O12, C32H26CuN6O12, C27H23CuN5O12 and C34H26CuN6O12. The synthesized complexes were characterized by FT-IR and elemental analyses carried out through EDX. The deprotonation of the carboxylate ligand, 4-(2-methoxy-5-nitrophenylamino)-4-oxobut-2-enoic acid, was observed in FT-IR spectrum, indicating that complexation happens via the carboxylate moiety's oxygen. In complexes 1 and 3, the value of Δν value is in between 120-180 cm-1 showing the bridging mode of the carboxylate moiety while in complexes 2 and 4, its value is greater than 180 cm-1 indicating the monodentate binding mode. The findings of antimicrobial activity revealed that the complexes have adequate antibacterial and antifungal properties. The anti-promastigote analysis results showed that the complexes 1 and 4 have significant activity as compared to the standard drug. The binding mode of complexes with DNA was confirmed by UV-Visible spectroscopy and viscosity measurements and the results showed that complexes interact with DNA through intercalative mode. A new and efficient strategy was applied through POM (Petra, Osiris and Molinspiration) analyses for determining the toxicity assessment, bio-availability and drug score of the synthesized complexes. The results showed that the complexes have good bioavailability and drug scores.
 
 KEY WORDS: Copper(II) carboxylate complex, DNA binding, Anti-promastigote analysis, Cytotoxicity, POM analysis, Docking study
 Bull. Chem. Soc. Ethiop. 2022, 36(1), 57-71. 
 DOI: https://dx.doi.org/10.4314/bcse.v36i1.6

Short-range organization and photophysical properties of CdSe quantum dots coupled with aryleneethynylenes

Hybrid organic–inorganic nanomaterials composed of organic semiconductors and inorganic quantum dots (QDs) are promising candidates for opto-electronic devices in a sustainable internet of things. Especially their ability to combine the advantages of both compounds in one material with new functionality, the energy-efficient production possibility and the applicability in thin films with little resource consumption are key benefits of these materials. However, a major challenge one is facing for these hybrid materials is the lack of a detailed understanding of the organic–inorganic interface which hampers the widespread application in devices. We advance the understanding of this interface by studying the short-range organization and binding motif of aryleneethynylenes coupled to CdSe QDs as an example system with various experimental methods. Clear evidence for an incorporation of the organic ligands in between the inorganic QDs is found, and polarization-modulation infrared reflection-absorption spectroscopy is shown to be a powerful technique to directly detect the binding in such hybrid thin-film systems. A monodentate binding and a connection of neighboring QDs by the aryleneethynylene molecules is identified. Using steady-state and time resolved spectroscopy, we further investigated the photophysics of these hybrid systems. Different passivation capabilities resulting in different decay dynamics of the QDs turned out to be the main influence of the ligands on the photophysics.

SUPPORTED PALLADIUM CATALYSTS FOR ALCOHOLS OXIDATION BASEDON CHEMICALLY MODIFIED BOEHMITE

New palladium catalysts based on Pd(II) coordination heterogenization on the surface of synthetic boehmite chemically modified with nitrilotris(methylenephosphonic) acid (NTP) were ob-tained. The catalysts were prepared by impregnating the carrier (boehmite (γ-AlOOH), NTP-boehmite (NTP-γ-AlOOH)) with a PdCl2solution followed by the reduction of Pd(II) to metallic palladium with potassium formate. The resulting samples were characterized by XPA, SEM, XPS, BET, and IR spectroscopy. The carriers have a high specific surface area (100–250 m2/g) and a mesoporous structure. The content of palladium in the obtained metal catalysts is 2–4 wt%, with an average particle size of 10–50 μm. An analysis of the XPS spectra of the catalysts (Pd3d, N1s, P2p) shows that they contain metallic palladium Pd(0) and ionic forms of Pd(II) bonded to the oxygen and nitrogen atoms of the support.The possible composition of Pd(II) surface complexes on boehmite and NTP-boehmite was established by modeling the sorption vs. pH curve according to the theory of surface complexation. The reaction of the selective oxidation of benzyl alcohol to benzaldehyde in an aqueous solution (4 vol.% alcohol, 60°C, 1 h) using atmospheric oxygen was chosen as a model reaction for evaluating the catalytic activity, which corresponds to the principles of "green chemistry": 2C6H5CH2OH+O2= 2C6H5COH+ 2H2O. The oxidation processwas moni-tored by measuring the IR spectra of the chloroform extractof the reaction mixture using the in-tensities of the absorption bands of alcohol (3100–3600 см-1(νO-H)) and aldehyde (1700 см-1(νC=O)). The following series of catalyst activity was established: Pd(II) > Pd(0)/NTP-γ-AlOOH > Pd(0)/ γ-AlOOH > Pd(II)/ γ-AlOOH >> Pd(II)/NTP-γ-AlOOH. The metallic form of palladium is required for the catalytic activity. The coordination fixation of palladium on NTP-boehmite due to chelate binding by an aminophosphonic group increases catalyst activity compared to monodentate binding by hydroxo groups of unmodified boehmite.

Kinetically Controlled Linker Binding in Rare Earth-2,5-Dihydroxyterepthalic Acid Metal-Organic Frameworks and Its Predicted Effects on Acid Gas Adsorption.

In the pursuit of highly stable and selective metal-organic frameworks (MOFs) for the adsorption of caustic acid gas species, an entire series of rare earth MOFs have been explored. Each of the MOFs in this series (RE-DOBDC; RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu; DOBDC = 2,5-dihydroxyterepthalic acid) was synthesized in the tetragonal space group I4/m. Crystallized MOF samples, specifically Eu-DOBDC, were seen to have a combination of monodentate and bidentate binding when synthesized under typical reaction conditions, resulting in a contortion of the structure. However, extended crystallization times determined that this binding is kinetically controlled and that the monodentate binding option was crystallographically eliminated by extended reaction times at higher temperatures. Furthermore, this series allows for the direct study of the effect of the metal center on the structure of the of the MOF; herein, the lanthanide metal ionic radii contraction across the periodic table results in a reduction of the MOF pore size and lattice parameters. Scanning electron microscopy-energy-dispersive spectroscopy was used to investigate the stages of crystal growth for these RE-DOBDC MOFs. All MOFs, except Er-DOBDC had a minimum of two stages of growth. These analogues were demonstrated by analysis of neutron diffraction (PND) to exhibit a cooperative rotational distortion of the secondary building unit, resulting in two crystallographically distinct linker sublattices. Computational modeling efforts were used to show distinct differences on acid gas (NO2 and SO2) binding energies for RE-DOBDC MOFs when comparing the monodentate/bidentate combined linker with the bidentate-only linker crystal structures.