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Inorganics, Volume 7, Issue 8 (August 2019)

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Cover Story (view full-size image) In the cover story, the core concept of the coordinating solvent approach (CSA) is described. We [...] Read more.
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Open AccessReview
Nickel Metalloregulators and Chaperones
Inorganics 2019, 7(8), 104; https://doi.org/10.3390/inorganics7080104 - 19 Aug 2019
Viewed by 393
Abstract
Nickel is essential for the survival of many pathogenic bacteria. E. coli and H. pylori require nickel for [NiFe]-hydrogenases. H. pylori also requires nickel for urease. At high concentrations nickel can be toxic to the cell, therefore, nickel concentrations are tightly regulated. Metalloregulators [...] Read more.
Nickel is essential for the survival of many pathogenic bacteria. E. coli and H. pylori require nickel for [NiFe]-hydrogenases. H. pylori also requires nickel for urease. At high concentrations nickel can be toxic to the cell, therefore, nickel concentrations are tightly regulated. Metalloregulators help to maintain nickel concentration in the cell by regulating the expression of the genes associated with nickel import and export. Nickel import into the cell, delivery of nickel to target proteins, and export of nickel from the cell is a very intricate and well-choreographed process. The delivery of nickel to [NiFe]-hydrogenase and urease is complex and involves several chaperones and accessory proteins. A combination of biochemical, crystallographic, and spectroscopic techniques has been utilized to study the structures of these proteins, as well as protein–protein interactions resulting in an expansion of our knowledge regarding how these proteins sense and bind nickel. In this review, recent advances in the field will be discussed, focusing on the metal site structures of nickel bound to metalloregulators and chaperones. Full article
(This article belongs to the Special Issue Bioinorganic Chemistry of Nickel)
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Open AccessArticle
Effect of Coordinating Solvents on the Structure of Cu(II)-4,4′-bipyridine Coordination Polymers
Inorganics 2019, 7(8), 103; https://doi.org/10.3390/inorganics7080103 - 19 Aug 2019
Viewed by 417
Abstract
Solvent can play a crucial role in the synthesis of coordination polymers (CPs). Here, this study reports how the coordinating solvent approach (CSA) can be used as an effective tool to control the nature of the final CP. This study exploited the system [...] Read more.
Solvent can play a crucial role in the synthesis of coordination polymers (CPs). Here, this study reports how the coordinating solvent approach (CSA) can be used as an effective tool to control the nature of the final CP. This study exploited the system Cu(II)-4,4′-bipyridine coupled to different coordinating solvents, such as DMA, DMF and DMSO. This allowed the isolation and structurally characterization of four new CPs: three 2D layered networks and one 1D chain. Moreover, it was evidenced that even adventitious water can play the role of the coordinating solvent in the final CP. Full article
(This article belongs to the Special Issue Functional Coordination Polymers and Metal–Organic Frameworks)
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Open AccessArticle
Local and Average Structure of Yb-Doped Ceria through Synchrotron and Neutron Pair Distribution Function
Inorganics 2019, 7(8), 102; https://doi.org/10.3390/inorganics7080102 - 18 Aug 2019
Viewed by 419
Abstract
As transport properties of doped ceria electrolytes depend significantly on the nature of the dopant and the defectivity, the design of new materials and devices requires proper understanding of the defect structure. Among lanthanide dopants, Yb shows some peculiar characteristics that call for [...] Read more.
As transport properties of doped ceria electrolytes depend significantly on the nature of the dopant and the defectivity, the design of new materials and devices requires proper understanding of the defect structure. Among lanthanide dopants, Yb shows some peculiar characteristics that call for a possible different defect structure compared to Gd and Sm conventional dopants, which could be linked to its poorer performance. For this purpose, we combine synchrotron and neutron powder diffraction exploiting the Rietveld and Pair distribution Function. By increasing its concentration, Yb produces qualitatively the same structural distortions as other dopants, leading to a domain structure involving the progressive nucleation and growth of nanodomains with a Yb2O3-like (C-type) structure hosted in a fluorite CeO2 matrix. However, when it comes to growing the C-type nanodomains into a long-range phase, the transformation is less pronounced. At the same time, a stronger structural distortion occurs at the local scale, which is consistent with the segregation of a large amount of oxygen vacancies. The strong trapping of VOs by Yb3+ explains the poor performance of Yb-doped ceria with respect to conventional Sm-, Gd-, and Y-doped samples at equal temperature and dopant amount. Full article
(This article belongs to the Special Issue Rare Earth-Doped Ceria Systems and Their Applications)
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Open AccessReview
Human Acireductone Dioxygenase (HsARD), Cancer and Human Health: Black Hat, White Hat or Gray?
Inorganics 2019, 7(8), 101; https://doi.org/10.3390/inorganics7080101 - 18 Aug 2019
Viewed by 380
Abstract
Multiple factors involving the methionine salvage pathway (MSP) and polyamine biosynthesis have been found to be involved in cancer cell proliferation, migration, invasion and metastasis. This review summarizes the relationships of the MSP enzyme acireductone dioxygenase (ARD), the ADI1 gene encoding ARD and [...] Read more.
Multiple factors involving the methionine salvage pathway (MSP) and polyamine biosynthesis have been found to be involved in cancer cell proliferation, migration, invasion and metastasis. This review summarizes the relationships of the MSP enzyme acireductone dioxygenase (ARD), the ADI1 gene encoding ARD and other gene products (ADI1GP) with carcinomas and carcinogenesis. ARD exhibits structural and functional differences depending upon the metal bound in the active site. In the penultimate step of the MSP, the Fe2+ bound form of ARD catalyzes the on-pathway oxidation of acireductone leading to methionine, whereas Ni2+ bound ARD catalyzes an off-pathway reaction producing methylthiopropionate and carbon monoxide, a biological signaling molecule and anti-apoptotic. The relationship between ADI1GP, MSP and polyamine synthesis are discussed, along with possible role(s) of metal in modulating the cellular behavior of ADI1GP and its interactions with other cellular components. Full article
(This article belongs to the Special Issue Bioinorganic Chemistry of Nickel)
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Open AccessArticle
Characterization and Photophysical Properties of a Luminescent Aluminum Hydride Complex Supported by a β-Diketiminate Ligand
Inorganics 2019, 7(8), 100; https://doi.org/10.3390/inorganics7080100 - 17 Aug 2019
Viewed by 408
Abstract
Aluminum hydrides are versatile compounds utilized as reducing agents, precursors of aluminum complexes, and as catalysts for polymerization reactions. However, their photophysical properties have been overlooked, although several luminescent aluminum complexes have been utilized conventionally for emitting layers in modern light-emitting devices. Herein, [...] Read more.
Aluminum hydrides are versatile compounds utilized as reducing agents, precursors of aluminum complexes, and as catalysts for polymerization reactions. However, their photophysical properties have been overlooked, although several luminescent aluminum complexes have been utilized conventionally for emitting layers in modern light-emitting devices. Herein, we report the synthesis and photophysical properties of a luminescent β-diketiminate dihydride complex through the reaction between lithium aluminum hydride and the corresponding ligand. The obtained compound exhibits crystallization-induced emission (CIE) properties at room temperature and long-lifetime phosphorescence at 80 K. Our experimental and theoretical investigations suggest that low-energy molecular vibration could play an important role in the realization of the CIE property. Full article
(This article belongs to the Special Issue Organoaluminum Compounds)
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Open AccessArticle
Preliminary Characterization of a Ni2+-Activated and Mycothiol-Dependent Glyoxalase I Enzyme from Streptomyces coelicolor
Inorganics 2019, 7(8), 99; https://doi.org/10.3390/inorganics7080099 - 14 Aug 2019
Viewed by 398
Abstract
The glyoxalase system consists of two enzymes, glyoxalase I (Glo1) and glyoxalase II (Glo2), and converts a hemithioacetal substrate formed between a cytotoxic alpha-ketoaldehyde, such as methylglyoxal (MG), and an intracellular thiol, such as glutathione, to a non-toxic alpha-hydroxy acid, such as d [...] Read more.
The glyoxalase system consists of two enzymes, glyoxalase I (Glo1) and glyoxalase II (Glo2), and converts a hemithioacetal substrate formed between a cytotoxic alpha-ketoaldehyde, such as methylglyoxal (MG), and an intracellular thiol, such as glutathione, to a non-toxic alpha-hydroxy acid, such as d-lactate, and the regenerated thiol. Two classes of Glo1 have been identified. The first is a Zn2+-activated class and is exemplified by the Homo sapiens Glo1. The second class is a Ni2+-activated enzyme and is exemplified by the Escherichia coli Glo1. Glutathione is the intracellular thiol employed by Glo1 from both these sources. However, many organisms employ other intracellular thiols. These include trypanothione, bacillithiol, and mycothiol. The trypanothione-dependent Glo1 from Leishmania major has been shown to be Ni2+-activated. Genetic studies on Bacillus subtilis and Corynebacterium glutamicum focused on MG resistance have indicated the likely existence of Glo1 enzymes employing bacillithiol or mycothiol respectively, although no protein characterizations have been reported. The current investigation provides a preliminary characterization of an isolated mycothiol-dependent Glo1 from Streptomyces coelicolor. The enzyme has been determined to display a Ni2+-activation profile and indicates that Ni2+-activated Glo1 are indeed widespread in nature regardless of the intracellular thiol employed by an organism. Full article
(This article belongs to the Special Issue Bioinorganic Chemistry of Nickel)
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Open AccessReview
Mesoporous Nanocast Electrocatalysts for Oxygen Reduction and Oxygen Evolution Reactions
Inorganics 2019, 7(8), 98; https://doi.org/10.3390/inorganics7080098 - 11 Aug 2019
Viewed by 430
Abstract
Catalyzed oxygen evolution and oxygen reduction reactions (OER and ORR, respectively) are of particular significance in many energy conversion and storage processes. During the last decade, they emerged as potential routes to sustain the ever-growing needs of the future clean energy market. Unfortunately, [...] Read more.
Catalyzed oxygen evolution and oxygen reduction reactions (OER and ORR, respectively) are of particular significance in many energy conversion and storage processes. During the last decade, they emerged as potential routes to sustain the ever-growing needs of the future clean energy market. Unfortunately, the state-of-the-art OER and ORR electrocatalysts, which are based on noble metals, are noticeably limited by a generally high activity towards one type of reaction only, high costs and relatively low abundance. Therefore, the development of (bi)functional low-cost non-noble metal or metal-free electrocatalysts is expected to increase the practical energy density and drastically reduce the production costs. Owing to their pore properties and high surface areas, mesoporous materials show high activity towards electrochemical reactions. Among all synthesis methods available for the synthesis of non-noble mesoporous metal oxides, the hard-templating (or nanocasting) approach is one of the most attractive in terms of achieving variable morphology and porosity of the materials. In this review, we thus focus on the recent advances in the design, synthesis, characterization and efficiency of non-noble metal OER and ORR electrocatalysts obtained via the nanocasting route. Critical aspects of these materials and perspectives for future developments are also discussed. Full article
(This article belongs to the Special Issue Advanced Porous Materials)
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Open AccessCommunication
Iridium Catalyzed Synthesis of Tetrahydro-1H-Indoles by Dehydrogenative Condensation
Inorganics 2019, 7(8), 97; https://doi.org/10.3390/inorganics7080097 - 06 Aug 2019
Viewed by 373
Abstract
Novel synthetic routes to the commonly encountered indole motif are highly sought after. Tetrahydro-1H-indoles were synthesized for the first time from secondary alcohols and 2-aminocyclohexanol in the presence of a well-established iridium catalyst using a modified synthetic procedure recently developed for [...] Read more.
Novel synthetic routes to the commonly encountered indole motif are highly sought after. Tetrahydro-1H-indoles were synthesized for the first time from secondary alcohols and 2-aminocyclohexanol in the presence of a well-established iridium catalyst using a modified synthetic procedure recently developed for the synthesis of hydrocarbazoles. The catalyst is stabilized by an inexpensive and easy-to-synthesize triazine based PN5P pincer ligand. The reaction proceeds through acceptorless dehydrogenative condensation (ADC) and yields the title compound, dihydrogen, and water and can thus be classified as sustainable synthesis. Overall, five examples, three of which were previously unknown compounds, were prepared. The propitious isolated yields and the mild reaction conditions show the synthetic value of this approach. These tetrahydroindoles can be quantitatively dehydrogenated over a heterogeneous Pd catalyst to yield the corresponding indoles. Full article
(This article belongs to the Special Issue Iridium Complexes)
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Open AccessArticle
The Effect of Storage-Induced Changes in Ammonia Borane on Hydrogen Release during Its Low-Temperature Thermolysis
Inorganics 2019, 7(8), 96; https://doi.org/10.3390/inorganics7080096 - 04 Aug 2019
Viewed by 471
Abstract
In this paper, low-temperature solid-state processes of the dehydrogenation of ammonia borane (NH3BH3, AB) samples of different purity are compared under the conditions of isothermal heating at 100 °C, as well as in the course of thermal analysis which [...] Read more.
In this paper, low-temperature solid-state processes of the dehydrogenation of ammonia borane (NH3BH3, AB) samples of different purity are compared under the conditions of isothermal heating at 100 °C, as well as in the course of thermal analysis which was also carried out at different rates of heating. The composition of boron-containing impurities was studied by attenuated total reflection Fourier transform infrared spectroscopy (ATR FTIR) and 11B magic angle spinning nuclear magnetic resonance (11B MAS NMR). Accumulation in AB of three- and four-coordinated borate anions upon contact of hydride with air moisture is established. The apparent activation energies were calculated from thermal analysis data, and found to decrease from 174 to 163 kJ/mol as the AB purity decreased from 93% to 79%. This showed itself in a shortening of the induction period during the AB thermolysis under isothermal conditions. The prospects of using the thermal analysis for estimating NH3BH3 reactivity are discussed. Full article
(This article belongs to the Section Inorganic Solid-State Chemistry)
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Open AccessReview
Theoretical Studies of Nickel-Dependent Enzymes
Inorganics 2019, 7(8), 95; https://doi.org/10.3390/inorganics7080095 - 29 Jul 2019
Viewed by 479
Abstract
The advancements of quantum chemical methods and computer power allow detailed mechanistic investigations of metalloenzymes. In particular, both quantum chemical cluster and combined QM/MM approaches have been used, which have been proven to successfully complement experimental studies. This review starts with a brief [...] Read more.
The advancements of quantum chemical methods and computer power allow detailed mechanistic investigations of metalloenzymes. In particular, both quantum chemical cluster and combined QM/MM approaches have been used, which have been proven to successfully complement experimental studies. This review starts with a brief introduction of nickel-dependent enzymes and then summarizes theoretical studies on the reaction mechanisms of these enzymes, including NiFe hydrogenase, methyl-coenzyme M reductase, nickel CO dehydrogenase, acetyl CoA synthase, acireductone dioxygenase, quercetin 2,4-dioxygenase, urease, lactate racemase, and superoxide dismutase. Full article
(This article belongs to the Special Issue Bioinorganic Chemistry of Nickel)
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Open AccessArticle
Effect of the (Nd,Dy)-Double Doping on the Structural Properties of Ceria
Inorganics 2019, 7(8), 94; https://doi.org/10.3390/inorganics7080094 - 26 Jul 2019
Viewed by 437
Abstract
The crystallographic properties of the Ce1−x(Nd0.63Dy0.37)xO2−x/2 system (0 ≤ x ≤ 0.6) were studied by means of synchrotron powder X-ray diffraction and compared to the ones of Sm-doped ceria. The aim [...] Read more.
The crystallographic properties of the Ce1−x(Nd0.63Dy0.37)xO2−x/2 system (0 ≤ x ≤ 0.6) were studied by means of synchrotron powder X-ray diffraction and compared to the ones of Sm-doped ceria. The aim of this work was to investigate the effect of substituting Sm3+ by a mixture of a smaller and a larger ion that ensures a more pronounced Ce4+/dopant size mismatch while having the same average ionic size as Sm3+. Two main findings came to light: (a) the compositional region of the CeO2-based solid solution widens up to x ranging between 0.4 and 0.5, and (b) the cell parameter is larger than the one of Sm-doped ceria at each composition. Both effects are expected to play a significant role on the ionic conductivity of the material. The results are discussed in terms of disorder and cation-vacancy association. Full article
(This article belongs to the Special Issue Rare Earth-Doped Ceria Systems and Their Applications)
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Open AccessArticle
Adding to the Family of Copper Complexes Featuring Borohydride Ligands Based on 2-Mercaptopyridyl Units
Inorganics 2019, 7(8), 93; https://doi.org/10.3390/inorganics7080093 - 24 Jul 2019
Viewed by 557
Abstract
Borohydride ligands featuring multiple pendant donor functionalities have been prevalent in the chemical literature for many decades now. More recent times has seen their development into new families of so-called soft scorpionates, for example, those featuring sulfur based donors. Despite all of these [...] Read more.
Borohydride ligands featuring multiple pendant donor functionalities have been prevalent in the chemical literature for many decades now. More recent times has seen their development into new families of so-called soft scorpionates, for example, those featuring sulfur based donors. Despite all of these developments, those ligands containing just one pendant group are rare. This article explores one ligand family based on the 2-mercaptopyridine heterocycle. The coordination chemistry of the monosubstituted ligand, [H3B(mp)] (mp = 2-mercaptopyridyl), has been explored. Reaction of Na[BH3(mp)] with one equivalent of Cu(I)Cl in the presence of either triphenylphosphine or tricyclohexylphosphine co-ligands leads to the formation of [Cu{H3B(mp)}(PR3)] (R = Ph, 1; Cy, 2), respectively. Structural characterization confirms a κ3-S,H,H coordination mode for the borohydride-based ligand within 1 and 2, involving a dihydroborate bridging interaction (BH2Cu) with the copper centers. Full article
(This article belongs to the Special Issue Metal Complexes Containing Boron Based Ligands)
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Open AccessCommunication
NHI- and NHC-Supported Al(III) Hydrides for Amine–Borane Dehydrocoupling Catalysis
Inorganics 2019, 7(8), 92; https://doi.org/10.3390/inorganics7080092 - 24 Jul 2019
Viewed by 542
Abstract
The catalytic dehydrocoupling of amine–boranes has recently received a great deal of attention due to its potential in hydrogen storage applications. The use of aluminum catalysts for this transformation would provide an additional cost-effective and sustainable approach towards the hydrogen economy. Herein, we [...] Read more.
The catalytic dehydrocoupling of amine–boranes has recently received a great deal of attention due to its potential in hydrogen storage applications. The use of aluminum catalysts for this transformation would provide an additional cost-effective and sustainable approach towards the hydrogen economy. Herein, we report the use of both N-heterocyclic imine (NHI)- and carbene (NHC)-supported Al(III) hydrides and their role in the catalytic dehydrocoupling of Me2NHBH3. Differences in the σ-donating ability of the ligand class resulted in a more stable catalyst for NHI-Al(III) hydrides, whereas a deactivation pathway was found in the case of NHC-Al(III) hydrides. Full article
(This article belongs to the Special Issue Organoaluminum Compounds)
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