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Chemistry, Volume 3, Issue 3 (September 2021) – 32 articles

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Communication
Chirality Transfer in a Calixarene-Based Directional Pseudorotaxane Complex
Chemistry 2021, 3(3), 1089-1100; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030079 (registering DOI) - 18 Sep 2021
Viewed by 162
Abstract
Hexamethoxycalix[6]arene 3 forms a directional pseudorotaxane complex with the chiral axle (S)-(α-methyl-benzyl)benzylammonium 2+. Between the two (endo-chiral)-2+@3 and (exo-chiral)-2+@3 pseudorotaxane stereoisomers, the former is preferentially formed. This [...] Read more.
Hexamethoxycalix[6]arene 3 forms a directional pseudorotaxane complex with the chiral axle (S)-(α-methyl-benzyl)benzylammonium 2+. Between the two (endo-chiral)-2+@3 and (exo-chiral)-2+@3 pseudorotaxane stereoisomers, the former is preferentially formed. This result confirms the validity of the “endo-α-methyl-benzyl rule”, previously reported by us. DFT calculations suggest that C-H···π interactions between the methyl group of 2+ and the calixarene aromatic rings, determine the stereoselectivity of the threading process toward the “endo-α-methyl-benzyl preference”. An amplification of optical rotation is observed upon formation of the pseudorotaxane complex (endo-chiral)-2+@3 with respect to free axle 2+. Thus, the specifical rotation of the 1:1 mixture of chiral 2+∙B(ArF)4 salt and achiral 3 was augmented upon formation of the pseudorotaxane and DFT calculations were used to rationalize this result. Full article
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Article
Absorption and Isomerization of Azobenzene Guest Molecules in Polymeric Nanoporous Crystalline Phases
Chemistry 2021, 3(3), 1074-1088; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030078 (registering DOI) - 16 Sep 2021
Viewed by 240
Abstract
PPO co-crystalline (CC) films including azobenzene guest molecules have been prepared and characterized by WAXD, FTIR and UV-Visible measurements. Isomerization reactions of azobenzene (photo-induced trans to cis and spontaneous cis to trans) included in α and β nanoporous-crystalline (NC) phases leading to CC [...] Read more.
PPO co-crystalline (CC) films including azobenzene guest molecules have been prepared and characterized by WAXD, FTIR and UV-Visible measurements. Isomerization reactions of azobenzene (photo-induced trans to cis and spontaneous cis to trans) included in α and β nanoporous-crystalline (NC) phases leading to CC phases, or simply absorbed in amorphous phase have been studied on thick and thin films. Spectroscopic analysis shows that photo-isomerization of azobenzene occurs without expulsion of azobenzene guest molecules from crystalline phases. Sorption studies of α and β NC films immersed into photo-isomerized azobenzene solution reveal a higher selectivity of the β NC phase toward cis azobenzene isomer than the α NC phase, inducing us to propose the β NC phase as particularly suitable for absorbing spherically bulky guest molecules. Full article
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Article
The B2 Structural Motif as a Tool for Modulating Ring Currents in Monocyclic Li Clusters
Chemistry 2021, 3(3), 1063-1073; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030077 - 14 Sep 2021
Viewed by 225
Abstract
Magnetically induced current densities, calculated at the M06-2X/def2-TZVP level using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method, were employed to study the aromaticity in Li3B2 and Li4B2. It [...] Read more.
Magnetically induced current densities, calculated at the M06-2X/def2-TZVP level using the diamagnetic-zero version of the continuous transformation of origin of current density (CTOCD-DZ) method, were employed to study the aromaticity in Li3B2 and Li4B2. It was found that the Li3/Li4 rings in Li3B2 and Li4B2 remarkably resemble the monocyclic Li3+ and Li42+ clusters. Unlike the parent Li3+ and Li42+ systems that sustain negligibly weak global current density circulation, the Li3B2 and Li4B2 clusters exhibit a strong diatropic current density. The present work demonstrates how structural modifications introduced by the B2 unit can be used for modulating the current density in cyclic Li-based clusters. Full article
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Communication
Spectroscopic Evidence of New Low-Dimensional Planar Carbon Allotropes Based on Biphenylene via On-Surface Ullmann Coupling
Chemistry 2021, 3(3), 1057-1062; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030076 - 13 Sep 2021
Viewed by 259
Abstract
The bottom-up synthesis and preliminary characterizations of a new biphenylene-based 2D framework are presented. This new low-dimensional carbon allotrope potentially completes the many hypothesized carbon networks based on biphenylene. Full article
(This article belongs to the Special Issue On-Surface Synthesis: Methods and Applications)
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Article
The Non-Anhydrous, Minimally Basic Synthesis of the Dopamine D2 Agonist [18F]MCL-524
Chemistry 2021, 3(3), 1047-1056; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030075 - 09 Sep 2021
Viewed by 283
Abstract
The dopamine D2 agonist MCL-524 is selective for the D2 receptor in the high-affinity state (D2high), and, therefore, the PET analogue, [18F]MCL-524, may facilitate the elucidation of the role of D2high in disorders such [...] Read more.
The dopamine D2 agonist MCL-524 is selective for the D2 receptor in the high-affinity state (D2high), and, therefore, the PET analogue, [18F]MCL-524, may facilitate the elucidation of the role of D2high in disorders such as schizophrenia. However, the previously reported synthesis of [18F]MCL-524 proved difficult to replicate and was lacking experimental details. We therefore developed a new synthesis of [18F]MCL-524 using a “non-anhydrous, minimally basic” (NAMB) approach. In this method, [18F]F is eluted from a small (10–12 mg) trap-and-release column with tetraethylammonium tosylate (2.37 mg) in 7:3 MeCN:H2O (0.1 mL), rather than the basic carbonate or bicarbonate solution that is most often used for [18F]F recovery. The tosylated precursor (1 mg) in 0.9 mL anhydrous acetonitrile was added directly to the eluate, without azeotropic drying, and the solution was heated (150 °C/15 min). The catechol was then deprotected with the Lewis acid In(OTf)3 (10 equiv.; 150 °C/20 min). In contrast to deprotection with protic acids, Lewis-acid-based deprotection facilitated the efficient removal of byproducts by HPLC and eliminated the need for SPE extraction prior to HPLC purification. Using the NAMB approach, [18F]MCL-524 was obtained in 5–9% RCY (decay-corrected, n = 3), confirming the utility of this improved method for the multistep synthesis of [18F]MCL-524 and suggesting that it may applicable to the synthesis of other 18F-labeled radiotracers. Full article
(This article belongs to the Section Radiochemistry)
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Article
Yb to Tb Cooperative Upconversion in Supramolecularly Assembled Complexes in a Solution
Chemistry 2021, 3(3), 1037-1046; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030074 - 06 Sep 2021
Viewed by 323
Abstract
The podand-type ligand L, based on a tertiary amine substituted by three pyridyl-6-phosphonic acid functions, forms hydrated complexes with Ln3+ cations. The luminescence properties of the YbL complex were studied in D2O as a function of the pD and temperature. [...] Read more.
The podand-type ligand L, based on a tertiary amine substituted by three pyridyl-6-phosphonic acid functions, forms hydrated complexes with Ln3+ cations. The luminescence properties of the YbL complex were studied in D2O as a function of the pD and temperature. In basic conditions, increases in the luminescence quantum yield and the excited state lifetime of the Yb centered emission associated with the 2F5/22F7/2 transition were observed and attributed to a change in the hydration number from two water molecules in the first coordination sphere of Yb at acidic pH to a single one in basic conditions. Upon the addition of TbCl3 salts to a solution containing the YbL complex in D2O, heteropolynuclear Yb/Tb species formed, and excitation of the Yb at 980 nm resulted in the observation of the typical visible emission of Tb as a result of a cooperative upconversion (UC) photosensitization process. The UC was further evidenced by the quadratic dependence of the UC emission as a function of the laser power density. Full article
(This article belongs to the Special Issue Molecular and Supramolecular Upconversion)
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Article
Electronic Currents and Anapolar Response Induced in Molecules by Monochromatic Light
Chemistry 2021, 3(3), 1022-1036; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030073 - 05 Sep 2021
Viewed by 253
Abstract
It is shown that the electric dipole- and electric quadrupole–anapole polarizabilities, denoted respectively by fαβ and gα,βγ, and the anapole magnetizability aαβ, are intrinsic properties of the electron cloud of molecules [...] Read more.
It is shown that the electric dipole- and electric quadrupole–anapole polarizabilities, denoted respectively by fαβ and gα,βγ, and the anapole magnetizability aαβ, are intrinsic properties of the electron cloud of molecules responding to optical fields. fαβ is a nonvanishing property of chiral and achiral compounds, whereas aαβ is suitable for enantiomer discrimination of chiral species. They can conveniently be evaluated by numerical integration, employing a formulation complementary to that provided by perturbation theory and relying on the preliminary computation of electronic current density tensors all over the molecular domain. The origin dependence of the dynamic anapolar response is rationalized via related computational techniques employing numerical integration, as well as definitions of molecular property tensors, for example, electric dipole and electric quadrupole polarizabilties and magnetizability. A preliminary application of the theory is reported for the Ra enantiomer of the hydrogen peroxide molecule, evaluating tensor components of electric dipole-anapole polarizability and anapole magnetizability as functions of the dihedral angle ϕ H-O-O-H in the range 0ϕ180. Full article
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Article
Spatial Contributions to 1H NMR Chemical Shifts of Free-Base Porphyrinoids
Chemistry 2021, 3(3), 1005-1021; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030072 - 05 Sep 2021
Viewed by 297
Abstract
A recently developed methodology for calculating, analyzing, and visualizing nuclear magnetic shielding densities is used for studying spatial contributions including ring-current contributions to 1H nuclear magnetic resonance (NMR) chemical shifts of aromatic and anti-aromatic free-base porphyrinoids. Our approach allows a visual inspection [...] Read more.
A recently developed methodology for calculating, analyzing, and visualizing nuclear magnetic shielding densities is used for studying spatial contributions including ring-current contributions to 1H nuclear magnetic resonance (NMR) chemical shifts of aromatic and anti-aromatic free-base porphyrinoids. Our approach allows a visual inspection of the spatial origin of the positive (shielding) and negative (deshielding) contributions to the nuclear magnetic shielding constants. Diatropic and paratropic current-density fluxes yield both shielding and deshielding contributions implying that not merely the tropicity of the current density determines whether the contribution has a shielding or deshielding character. Instead the shielding or deshielding contribution is determined by the direction of the current-density flux with respect to the studied nucleus. Full article
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Article
Magnetic Aromaticity of Cycloporphyrin Nanorings
Chemistry 2021, 3(3), 991-1004; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030071 - 02 Sep 2021
Viewed by 255
Abstract
The ascertainment of magnetic aromaticity is not necessarily straightforward, especially for large and bent systems, such as the cycloporphyrin nanorings recently synthesized by the group of Anderson. Six of these cycloporphyrin nanorings were studied here computationally. Indirect methods, based on nuclear shielding and [...] Read more.
The ascertainment of magnetic aromaticity is not necessarily straightforward, especially for large and bent systems, such as the cycloporphyrin nanorings recently synthesized by the group of Anderson. Six of these cycloporphyrin nanorings were studied here computationally. Indirect methods, based on nuclear shielding and magnetizabilities, and direct methods, based on standard quantum mechanics, were both used effectively to determine their magnetically induced current strength, which mostly confirmed Anderson’s classification. However, in the case of hexanions, and in particular for cyclohexaporphyrin hexacations, a significant cancellation of delocalized diatropic and paratropic flow occurred, showing that the resultant faint aromatic character was a result of competing aromatic and antiaromatic contributions, as also evidenced by the ipsocentric method. A warning is renewed on the use of isotropic shielding to determine the tropicity of the magnetically induced current. Full article
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Article
Phytochemicals from Rhizophora mucronata Propagules, Its In Vitro Anti-Cancer and In Silico Drug-Likeness Potential
Chemistry 2021, 3(3), 979-990; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030070 - 02 Sep 2021
Viewed by 306
Abstract
This is the first report to identify the presence of 3-O-caffeoyl quinic acid (1), 4-O-caffeoyl quinic acid (2), 5-O-caffeoyl quinic acid (3), epi-catechin (4), and procyanidin B2 (5 [...] Read more.
This is the first report to identify the presence of 3-O-caffeoyl quinic acid (1), 4-O-caffeoyl quinic acid (2), 5-O-caffeoyl quinic acid (3), epi-catechin (4), and procyanidin B2 (5) in the young propagules of Rhizophora mucronata. Compounds 25 were purified and then treated against breast, colorectal, and ovarian cancer cell lines for 72 h and the results of the Sulphorhodomine-B (SRB) assay were evaluated for percent cell viability and IC50 values. Epi-catechin, 4-O-caffeoyl quinic acid, 5-O-caffeoyl quinic acid and procyanidin B2 showed strong to moderate inhibitory effects when treated on breast (T47D), colorectal (HT29), and ovarian (A2780, SKOV3) cancer cell lines with IC50 values ranging from 16.77 ± 0.58 to 28.28 ± 0.89 μg/mL. In silico evaluation was performed to evaluate the drug-likeness and toxicological effects of these compounds using Molinspiration calculation and OSIRIS program. It was found that compounds 2, 3, and 4 have the potential to be orally active and have a low risk in exerting the mutagenic, tumorigenic, irritant, and reproductive effects. Full article
(This article belongs to the Section Biological and Natural Products)
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Review
Questions in the Chemical Enzymology of MAO
Chemistry 2021, 3(3), 959-978; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030069 - 31 Aug 2021
Viewed by 252
Abstract
We have structure, a wealth of kinetic data, thousands of chemical ligands and clinical information for the effects of a range of drugs on monoamine oxidase activity in vivo. We have comparative information from various species and mutations on kinetics and effects of [...] Read more.
We have structure, a wealth of kinetic data, thousands of chemical ligands and clinical information for the effects of a range of drugs on monoamine oxidase activity in vivo. We have comparative information from various species and mutations on kinetics and effects of inhibition. Nevertheless, there are what seem like simple questions still to be answered. This article presents a brief summary of existing experimental evidence the background and poses questions that remain intriguing for chemists and biochemists researching the chemical enzymology of and drug design for monoamine oxidases (FAD-containing EC 4.1.3.4). Full article
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Article
Synthesis and Self-Assembling Properties of Peracetylated β-1-Triazolyl Alkyl D-Glucosides and D-Galactosides
Chemistry 2021, 3(3), 935-958; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030068 - 28 Aug 2021
Viewed by 307
Abstract
Carbohydrate-based low-molecular-weight gelators (LMWGs) are useful classes of compounds due to their numerous applications. Among sugar-based LMWGs, certain peracetylated sugar beta-triazole derivatives were found to be effective organogelators and showed interesting self-assembling properties. To further understand the structural influence towards molecular assemblies and [...] Read more.
Carbohydrate-based low-molecular-weight gelators (LMWGs) are useful classes of compounds due to their numerous applications. Among sugar-based LMWGs, certain peracetylated sugar beta-triazole derivatives were found to be effective organogelators and showed interesting self-assembling properties. To further understand the structural influence towards molecular assemblies and obtain new functional materials with interesting properties, we designed and synthesized a library of tetraacetyl beta-1-triazolyl alkyl-D-glucosides and D-galactosides, in which a two or three carbon spacer is inserted between the anomeric position and the triazole moiety. A series of 16 glucose derivatives and 14 galactose derivatives were synthesized and analyzed. The self-assembling properties of these new triazole containing glycoconjugates in different solvents were analyzed. Several glucose derivatives were found to be effective LMWGs, with compound 7a forming gels in a variety of organic solvents as well as in the presence of metal ions in aqueous solutions. The organogels formed by several compounds were characterized using optical microscopy, atomic force microscopy (AFM) and UV-vis spectroscopy, etc. The co-gels formed by compound 7a with the Fmoc derivative 7i showed interesting fluorescence enhancement upon gelation. Several gelators were also characterized using powder X-ray diffraction and FT-IR spectroscopy. The potential applications of these sugar-based gelators for drug delivery and dye removal were also studied. Full article
(This article belongs to the Special Issue Supramolecular Materials)
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Article
Topological Analysis of Magnetically Induced Current Densities in Strong Magnetic Fields Using Stagnation Graphs
Chemistry 2021, 3(3), 916-934; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030067 - 26 Aug 2021
Viewed by 189
Abstract
Stagnation graphs provide a useful tool to analyze the main topological features of the often complicated vector field associated with magnetically induced currents. Previously, these graphs have been constructed using response quantities appropriate for modest applied magnetic fields. We present an implementation capable [...] Read more.
Stagnation graphs provide a useful tool to analyze the main topological features of the often complicated vector field associated with magnetically induced currents. Previously, these graphs have been constructed using response quantities appropriate for modest applied magnetic fields. We present an implementation capable of producing these graphs in arbitrarily strong magnetic fields, using current-density-functional theory. This enables us to study how the topology of the current vector field changes with the strength and orientation of the applied magnetic field. Applications to CH4, C2H2 and C2H4 are presented. In each case, we consider molecular geometries optimized in the presence of the magnetic field. The stagnation graphs reveal subtle changes to this vector field where the symmetry of the molecule remains constant. However, when the electronic state and symmetry of the corresponding equilibrium geometry changes with increasing field strength, the changes to the stagnation graph are extensive. We expect that the approach presented here will be helpful in interpreting changes in molecular structure and bonding in the strong-field regime. Full article
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Article
Dispersion of Micro Fibrillated Cellulose (MFC) in Poly(lactic acid) (PLA) from Lab-Scale to Semi-Industrial Processing Using Biobased Plasticizers as Dispersing Aids
Chemistry 2021, 3(3), 896-915; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030066 - 25 Aug 2021
Viewed by 331
Abstract
In the present study, two commercial typologies of microfibrillated cellulose (MFC) (Exilva and Celish) with 2% wt % were firstly melt-compounded at the laboratory scale into polylactic acid (PLA) by a microcompounder. To reach an MFC proper dispersion and avoid the well-known aglomeration [...] Read more.
In the present study, two commercial typologies of microfibrillated cellulose (MFC) (Exilva and Celish) with 2% wt % were firstly melt-compounded at the laboratory scale into polylactic acid (PLA) by a microcompounder. To reach an MFC proper dispersion and avoid the well-known aglomeration problems, the use of two kinds of biobased plasticisers (poly(ethylene glycol) (PEG) and lactic acid oligomer (OLA)) were investigated. The plasticizers had the dual effect of dispersing the MFC, and at the same time, they counterbalanced the excessive stiffness caused by the addition of MFC to the PLA matrix. Several preliminaries dilution tests, with different aqueous cellulose suspension/plasticizer weight ratios were carried out. These tests were accompanied by SEM observations and IR and mechanical tests on compression-molded films in order to select the best plasticizer content. The best formulation was then scaled up in a semi-industrial twin-screw extruder, feeding the solution by a peristaltic pump, to optimize the industrial-scale production of commercial MFC-based composites with a solvent-free method. From this study, it can be seen that the use of plasticisers as dispersing aids is a biobased and green solution that can be easily used in conventional extrusion techniques. Full article
(This article belongs to the Special Issue Multiscale Analysis of Natural Fibre Composites)
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Article
Ultrasonic Dyeing of Polyester Fabric with Azo Disperse Dyes Clubbed with Pyridonones and Its UV Protection Performance
Chemistry 2021, 3(3), 889-895; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030065 - 24 Aug 2021
Viewed by 263
Abstract
The textile sector is closely linked to environmental pollution as a result of the use of toxic chemicals and their disposal in liquid waste, which negatively affects for the environment. Moreover, textile industries, especially wet processing, consume a large amount of energy, water, [...] Read more.
The textile sector is closely linked to environmental pollution as a result of the use of toxic chemicals and their disposal in liquid waste, which negatively affects for the environment. Moreover, textile industries, especially wet processing, consume a large amount of energy, water, and chemical auxiliaries. Therefore, there is an urgent need to find a solution that takes the problem of environmental pollution into account. Considering ultrasound as an environmentally safe alternative for dyeing polyester fabrics with the disperse dyes that we have prepared before, the comparison between the ultrasonic dyeing method and conventional dyeing at low temperatures was investigated. Dye exhaustion on polyester fabrics and fastness properties such as the washing, rubbing, light, and perspiration of all of the dyed fabrics were performed by two dyeing methods. Additionally, the ultraviolet protection factors (UPF) for dyed polyester fabrics were evaluated. Full article
(This article belongs to the Special Issue Dye Chemistry — In Memory of Prof. Michael R. Detty)
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Review
Chemical Functionalization of Graphene Nanoplatelets with Hydroxyl, Amino, and Carboxylic Terminal Groups
Chemistry 2021, 3(3), 873-888; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030064 - 23 Aug 2021
Viewed by 317
Abstract
As the most studied two-dimensional material, graphene is still attracting a lot of attention from both academia and industry due to its fantastic properties such as lightness, excellent mechanical strength, and high conductivity of heat and electricity. As an important branch of graphene [...] Read more.
As the most studied two-dimensional material, graphene is still attracting a lot of attention from both academia and industry due to its fantastic properties such as lightness, excellent mechanical strength, and high conductivity of heat and electricity. As an important branch of graphene materials, graphene nanoplatelets show numerous applications such as in coating, fillers of polymer composites, energy conversion and storage devices, sensing, etc. Chemical functionalization can introduce different functional groups to graphene nanoplatelets and can potentially endow them with different properties and functions to meet the increasing demand in the fields mentioned above. In this minireview, we present an overview of the research progress of functionalized graphene nanoplatelets bearing hydroxyl, amino, and carboxylic terminal groups, including both covalent and noncovalent approaches. These terminal groups allow subsequent functionalization reactions to attach additional moieties. Relevant characterization techniques, different applications, challenges, and future directions of functionalized graphene nanoplatelets are also critically summarized. Full article
(This article belongs to the Special Issue Chemistry of 2D Materials)
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Article
Magnetic Shielding Study of Bonding and Aromaticity in Corannulene and Coronene
Chemistry 2021, 3(3), 861-872; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030063 - 12 Aug 2021
Cited by 1 | Viewed by 525
Abstract
Bonding and aromaticity in the bowl-shaped C5v and planar D5h geometries of corannulene and the planar D6h geometry of coronene are investigated using 3D isosurfaces and 2D contour plots of the isotropic magnetic shielding σiso(r) and, [...] Read more.
Bonding and aromaticity in the bowl-shaped C5v and planar D5h geometries of corannulene and the planar D6h geometry of coronene are investigated using 3D isosurfaces and 2D contour plots of the isotropic magnetic shielding σiso(r) and, for planar geometries, of the out-of-plane component of the shielding tensor σzz(r). Corannulene and coronene both feature conjoined shielded “doughnuts” around a peripheral six-membered carbon ring, suggesting strong bonding interactions and aromatic stability; a deshielded region inside the hub ring of corannulene indicates that this ring is antiaromatic, more so in planar corannulene. The switch from the planar to the bowl-shaped geometry of corannulene is shown to enhance both bonding and the local aromaticities of the five- and six-membered rings; these factors, in addition to ring strain reduction, favour the bowl-shaped geometry. The most and least shielded bonds in both corannulene and coronene turn out to be the spoke and hub bonds, respectively. The higher π electron activity over spoke bonds in planar corannulene and coronene is supported by σzz(r) contour plots in planes 1 Å above the respective molecular planes; these findings about spoke bonds are somewhat unexpected, given that ring current studies indicate next to no currents over spoke bonds. Full article
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Article
Isolation and Antimalarial Activity of a New Flavonol from Tithonia diversifolia Leaf Extract
Chemistry 2021, 3(3), 854-860; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030062 - 12 Aug 2021
Viewed by 417
Abstract
An antiplasmodial activity-guided isolation was carried out on the dichloromethane extract of Tithonia diversifolia dried leaves. A total of five germacranolide type sesquiterpene lactones and a new flavonol, 3,6-dihydroxy-2-(4′-hydroxyphenyl)-7-methoxy-4H-chromen-4-one, were isolated. The flavonol reported an IC50 above 6.00 µM against [...] Read more.
An antiplasmodial activity-guided isolation was carried out on the dichloromethane extract of Tithonia diversifolia dried leaves. A total of five germacranolide type sesquiterpene lactones and a new flavonol, 3,6-dihydroxy-2-(4′-hydroxyphenyl)-7-methoxy-4H-chromen-4-one, were isolated. The flavonol reported an IC50 above 6.00 µM against the chloroquine sensitive strain, NF54. The antimalarial activity of the Tithonia diversifolia dichloromethane leaf extract was attributed to orizabin and tagitinin C. Full article
(This article belongs to the Special Issue Natural Products: Isolation, Identification and Biological Activity)
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Article
Unveiling the Intramolecular Ionic Diels–Alder Reactions within Molecular Electron Density Theory
Chemistry 2021, 3(3), 834-853; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030061 - 03 Aug 2021
Viewed by 358
Abstract
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the [...] Read more.
The intramolecular ionic Diels–Alder (IIDA) reactions of two dieniminiums were studied within the Molecular Electron Density Theory (MEDT) at the ωB97XD/6-311G(d,p) computational level. Topological analysis of the electron localization function (ELF) of dieniminiums showed that their electronic structures can been seen as the sum of those of butadiene and ethaniminium. The superelectrophilic character of dieniminiums accounts for the high intramolecular global electron density transfer taking place from the diene framework to the iminium one at the transition state structures (TSs) of these IIDA reactions, which are classified as the forward electro density flux. The activation enthalpy associated with the IIDA reaction of the experimental dieniminium, 8.7 kcal·mol−1, was closer to that of the ionic Diels–Alder (I-DA) reaction between butadiene and ethaniminium, 9.3 kcal·mol−1. However, the activation Gibbs free energy of the IIDA reaction was 12.7 kcal·mol−1 lower than that of the intermolecular I-DA reaction. The strong exergonic character of the IIDA reaction, higher than 20.5 kcal·mol−1, makes the reaction irreversible. These IIDA reactions present a total re/exo and si/endo diastereo selectivity, which is controlled by the most favorable chair conformation of the tetramethylene chain. ELF topological analysis of the single bond formation indicated that these IIDA reactions take place through a non-concerted two-stage one-step mechanism. Finally, ELF and atoms-in-molecules (AIM) topological analyses of the TS associated with the inter and intramolecular processes showed the great similarity between them. Full article
(This article belongs to the Special Issue 2021 Profile Papers by Chemistry' Editorial Board Members)
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Editorial
Coordination Polymers and Metal-Organic Frameworks: Structures and Applications—A Themed Issue in Honor of Professor Christoph Janiak on the Occasion of His 60th Birthday
Chemistry 2021, 3(3), 831-833; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030060 - 28 Jul 2021
Viewed by 374
Abstract
This themed issue of Chemistry is in honor of Professor Christoph Janiak on the occasion of his 60th birthday, and celebrates his innovative contributions to the fields of supramolecular chemistry, coordination polymers, networks and metal-organic frameworks, inorganic/organic hybrid materials and inorganic materials from [...] Read more.
This themed issue of Chemistry is in honor of Professor Christoph Janiak on the occasion of his 60th birthday, and celebrates his innovative contributions to the fields of supramolecular chemistry, coordination polymers, networks and metal-organic frameworks, inorganic/organic hybrid materials and inorganic materials from ionic liquids [...] Full article
Article
Oxidation of Terpenoids to Achieve High-Value Flavor and Fragrances—Questioning Microalgae Oxidative Capabilities in the Biotransformation of the Sesquiterpene Valencene and of Selected Natural Apocarotenoids
Chemistry 2021, 3(3), 821-830; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030059 - 28 Jul 2021
Viewed by 538
Abstract
Natural flavor and fragrance market size is expected to grow steadily due to the rising consumer demand of natural ingredients. This market request is guided by the general opinion that the production of natural compounds leads to a reduction of pollution, with inherent [...] Read more.
Natural flavor and fragrance market size is expected to grow steadily due to the rising consumer demand of natural ingredients. This market request is guided by the general opinion that the production of natural compounds leads to a reduction of pollution, with inherent advantages for the environment and people’s health. The biotransformation reactions have gained high relevance in the production of natural products. In this context, few pieces of research have described the role of microalgae in the oxidation of terpenoids. In this present study, we questioned the role of microalgal based oxidation in the synthesis of high-value flavors and fragrances. This study investigated the role of three different microalgae strains, Chlorella sp. (211.8b and 211.8p) and Chlorococcum sp. (JB3), in the oxidation of different terpenoid substrates: α-ionone, β-ionone, theaspirane and valencene. Unfortunately, the experimental data showed that the microalgal strains used are not responsible for the substrate oxidation. In fact, our experiments demonstrate that the transformation of the four starting compounds is a photochemical reaction that involves the oxygen as oxidant. Even though these findings cast a shadow on the use of these microorganisms for an industrial purpose, they open a new possible strategy to easily obtain nootkatone in a natural way by just using an aqueous medium, oxygen and light. Full article
(This article belongs to the Special Issue Flavors and Fragrances: Biology, Chemistry and Biotechnology)
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Editorial
Memorial Issue Dedicated to Dr. Howard D. Flack: The Man behind the Flack Parameter
Chemistry 2021, 3(3), 818-820; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030058 - 27 Jul 2021
Viewed by 371
Abstract
This Special Issue of Chemistry is dedicated to Dr. Howard D. Flack (1943–2017), a renowned crystallographer who transformed the way in which, by using single crystal X-ray diffraction, we are able to determine the absolute structure of a crystalline material, and thereby determine [...] Read more.
This Special Issue of Chemistry is dedicated to Dr. Howard D. Flack (1943–2017), a renowned crystallographer who transformed the way in which, by using single crystal X-ray diffraction, we are able to determine the absolute structure of a crystalline material, and thereby determine the absolute configuration of molecular species within the material [...] Full article
Review
Carbon Monoxide Therapy Using Hybrid Carbon Monoxide-Releasing/Nrf2-Inducing Molecules through a Neuroprotective Lens
Chemistry 2021, 3(3), 800-817; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030057 - 23 Jul 2021
Viewed by 583
Abstract
Carbon monoxide (CO) has long been known for its toxicity. However, in recent decades, new applications for CO as a therapeutic compound have been proposed, and multiple forms of CO therapy have since been developed and studied. Previous research has found that CO [...] Read more.
Carbon monoxide (CO) has long been known for its toxicity. However, in recent decades, new applications for CO as a therapeutic compound have been proposed, and multiple forms of CO therapy have since been developed and studied. Previous research has found that CO has a role as a gasotransmitter and promotes anti-inflammatory and antioxidant effects, making it an avenue of interest for medicine. Such effects are possible because of the Nrf2/HO1 pathway, which has become a target for therapy development because its activation also leads to CO release. Currently, different forms of treatment involving CO include inhaled CO (iCO), carbon monoxide-releasing molecules (CORMs), and hybrid carbon monoxide-releasing molecules (HYCOs). In this article, we review the progression of CO studies to develop possible therapies, the possible mechanisms involved in the effects of CO, and the current forms of therapy using CO. Full article
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Article
A New Supported Manganese-Based Coordination Complex as a Nano-Catalyst for the Synthesis of Indazolophthalazinetriones and Investigation of Its Antibacterial Activity
Chemistry 2021, 3(3), 783-799; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030056 - 22 Jul 2021
Viewed by 451
Abstract
A new magnetic supported manganese-based coordination complex (Fe3O4@SiO2@[email protected]@ Mn) was prepared in consecutive stages and characterized via various techniques (VSM, SEM, TEM, XRD, FT-IR, EDX, TG-DTA, and ICP). To evaluate its application, it was used for synthesis [...] Read more.
A new magnetic supported manganese-based coordination complex (Fe3O4@SiO2@[email protected]@ Mn) was prepared in consecutive stages and characterized via various techniques (VSM, SEM, TEM, XRD, FT-IR, EDX, TG-DTA, and ICP). To evaluate its application, it was used for synthesis of divers Indazolophthalazinetriones in a simple procedure via the one-pot three-component condensation reaction of aldehydes, dimedone, and phthalhydrazide in ethanol under reflux conditions. The Mn catalyst can be recycled without any noticeable loss in catalytic activity. Additionally, the antibacterial properties of the nano-catalyst were studied against some bacterial strains. Full article
(This article belongs to the Section Nanoscale Science)
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Article
Singlet/Triplet State Anti/Aromaticity of CyclopentadienylCation: Sensitivity to Substituent Effect
Chemistry 2021, 3(3), 765-782; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030055 - 21 Jul 2021
Viewed by 455
Abstract
It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, [...] Read more.
It is well known that singlet state aromaticity is quite insensitive to substituent effects, in the case of monosubstitution. In this work, we use density functional theory (DFT) calculations to examine the sensitivity of triplet state aromaticity to substituent effects. For this purpose, we chose the singlet state antiaromatic cyclopentadienyl cation, antiaromaticity of which reverses to triplet state aromaticity, conforming to Baird’s rule. The extent of (anti)aromaticity was evaluated by using structural (HOMA), magnetic (NICS), energetic (ISE), and electronic (EDDBp) criteria. We find that the extent of triplet state aromaticity of monosubstituted cyclopentadienyl cations is weaker than the singlet state aromaticity of benzene and is, thus, slightly more sensitive to substituent effects. As an addition to the existing literature data, we also discuss substituent effects on singlet state antiaromaticity of cyclopentadienyl cation. Full article
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Article
Substrate–Solvent Crosstalk—Effects on Reaction Kinetics and Product Selectivity in Olefin Oxidation Catalysis
Chemistry 2021, 3(3), 753-764; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030054 - 19 Jul 2021
Viewed by 407
Abstract
In this work, we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study demonstrated that polar and apolar aprotic solvents modulated the reactions in different [...] Read more.
In this work, we explored how solvents can affect olefin oxidation reactions catalyzed by MCM-bpy-Mo catalysts and whether their control can be made with those players. The results of this study demonstrated that polar and apolar aprotic solvents modulated the reactions in different ways. Experimental data showed that acetonitrile (aprotic polar) could largely hinder the reaction rate, whereas toluene (aprotic apolar) did not. In both cases, product selectivity at isoconversion was not affected. Further insights were obtained by means of neutron diffraction experiments, which confirmed the kinetic data and allowed for the proposal of a model based on substrate–solvent crosstalk by means of hydrogen bonding. In addition, the model was also validated in the ring-opening reaction (overoxidation) of styrene oxide to benzaldehyde, which progressed when toluene was the solvent (reaching 31% styrene oxide conversion) but was strongly hindered when acetonitrile was used instead (reaching only 7% conversion) due to the establishment of H-bonds in the latter. Although this model was confirmed and validated for olefin oxidation reactions, it can be envisaged that it may also be applied to other catalytic reaction systems where reaction control is critical, thereby widening its use. Full article
(This article belongs to the Section Catalysis)
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Article
Light-Induced Charge Accumulation in PTCDI/Pentacene/Ag(111) Heterojunctions
Chemistry 2021, 3(3), 744-752; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030053 - 13 Jul 2021
Viewed by 544
Abstract
The incorporation of singlet fission (SF) chromophores in solar cells is expected to bring significant increases in the power conversion efficiency thanks to multiexciton generation. However, efficient charge generation in the device is determined by the energy level alignment (ELA) between the active [...] Read more.
The incorporation of singlet fission (SF) chromophores in solar cells is expected to bring significant increases in the power conversion efficiency thanks to multiexciton generation. However, efficient charge generation in the device is determined by the energy level alignment (ELA) between the active materials, which should favor exciton transport and separation under illumination. By combining ultraviolet photoemission spectroscopy and optical differential reflectance measurements, we determine the ELA in a prototypical SF heterojunction between pentacene (Pc) and perylene-tetracarboxylic-diimide (PTCDI) grown on Ag(111). Time-resolved X-ray photoelectron spectroscopy on such a system reveals light-induced modifications of the ELA; by measuring the transient shift of the core level photoemission lines we observe an accumulation of long-lived holes in the PTCDI within the first hundred picoseconds after the optical pump. Full article
(This article belongs to the Special Issue A Special Issue in Honor of Professor Josef Michl)
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Article
Novel Ansa-Chain Conformation of a Semi-Synthetic Rifamycin Prepared Employing the Alder-Ene Reaction: Crystal Structure and Absolute Stereochemistry
Chemistry 2021, 3(3), 734-743; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030052 - 11 Jul 2021
Cited by 1 | Viewed by 536
Abstract
Rifamycins are an extremely important class of antibacterial agents whose action results from the inhibition of DNA-dependent RNA synthesis. A special arrangement of unsubstituted hydroxy groups at C21 and C23, with oxygen atoms at C1 and C8 is essential for activity. Moreover, it [...] Read more.
Rifamycins are an extremely important class of antibacterial agents whose action results from the inhibition of DNA-dependent RNA synthesis. A special arrangement of unsubstituted hydroxy groups at C21 and C23, with oxygen atoms at C1 and C8 is essential for activity. Moreover, it is known that the antibacterial action of rifamycin is lost if either of the two former hydroxy groups undergo substitution and are no longer free to act in enzyme inhibition. In the present work, we describe the successful use of an Alder-Ene reaction between Rifamycin O, 1 and diethyl azodicarboxylate, yielding 2, which was a targeted introduction of a relatively bulky group close to C21 to protect its hydroxy group. Many related azo diesters were found to react analogously, giving one predominant product in each case. To determine unambiguously the stereochemistry of the Alder-Ene addition process, a crystalline zwitterionic derivative 3 of the diethyl azodicarboxylate adduct 2 was prepared by reductive amination at its spirocyclic centre C4. The adduct, as a mono chloroform solvate, crystallized in the non-centrosymmetric Sohnke orthorhombic space group, P212121. The unique conformation and absolute stereochemistry of 3 revealed through X-ray crystal structure analysis is described. Full article
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Communication
Electrochemical Switching of First-Generation Donor-Acceptor Stenhouse Adducts (DASAs): An Alternative Stimulus for Triene Cyclisation
Chemistry 2021, 3(3), 728-733; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030051 - 07 Jul 2021
Cited by 1 | Viewed by 419
Abstract
Donor-acceptor Stenhouse adducts (DASAs) are a photo-switch class that undergoes triene cyclisation in response to visible light. Herein, electrochemical oxidation is demonstrated as an effective alternative stimulus for the triene cyclisation commonly associated with photo-switching. Full article
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Article
Microwave-Assisted Synthesis, Optical and Theoretical Characterization of Novel 2-(imidazo[1,5-a]pyridine-1-yl)pyridinium Salts
Chemistry 2021, 3(3), 714-727; https://0-doi-org.brum.beds.ac.uk/10.3390/chemistry3030050 - 06 Jul 2021
Viewed by 919
Abstract
In the last few years, imidazo[1,5-a]pyridine scaffolds and derivatives have attracted growing attention due to their unique chemical structure and optical behaviors. In this work, a series of pyridylimidazo[1,5-a]pyridine derivatives and their corresponding pyridinium salts were synthesized and their [...] Read more.
In the last few years, imidazo[1,5-a]pyridine scaffolds and derivatives have attracted growing attention due to their unique chemical structure and optical behaviors. In this work, a series of pyridylimidazo[1,5-a]pyridine derivatives and their corresponding pyridinium salts were synthesized and their optical properties investigated to evaluate the effect of the quaternization on the optical features both in solution and polymeric matrix. A critical analysis based on the spectroscopic data, chemical structures along with density functional theory calculation is reported to address the best strategies to prevent aggregation and optimize the photophysical properties. The obtained results describe the relationship between chemical structure and optical behaviors, highlighting the role of pendant pyridine. Finally, the presence of a positive charge is fundamental to avoid any possible aggregation process in polymeric films. Full article
(This article belongs to the Section Organic Materials and Polymers)
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