A review of the flavor profile of metal salts: understanding the complexity of metallic sensation

The oral sensation of metallic is a complex experience. Much of our current understanding of metallic sensation is from the investigation of metal salts, which elicit diverse sensations, including taste, smell, and chemesthetic sensations, and therefore meet the definition of a flavor rather than a taste. Due to the involvement of multiple chemosensory systems, it can be challenging to define and characterize metallic sensation. Here, we provide a comprehensive review of the psychophysical studies quantifying and characterizing metallic sensation, focusing on metal salts. We examine the factors that impact perception, including anion complex, concentration, nasal occlusion, and pH. In addition, we summarize the receptors thought to be involved in the perception of metallic sensation (i.e., TRPV1, T1R3, TRPA1, and T2R7) either as a result of in vitro assays or from studies in knock-out mice. By enhancing our scientific understanding of metallic sensation and its transduction pathways, it has the potential to improve food, pharmaceuticals, help identify suppression or masking strategies, and improve the ability to characterize individual differences in metallic sensation. It also has the potential to translate to clinical populations by addressing the disparities in knowledge and treatment options for individuals suffering from metallic taste disorder (i.e., phantom taste or “metal mouth”). Future psychophysical studies investigating the sensory perception of metal salts should include a range of compounds and diverse food matrices, coupled with modern sensory methods, which will help to provide a more comprehensive understanding of metallic sensation.

Halides as versatile anions in asymmetric anion-binding organocatalysis

This review intends to provide an overview on the role of halide anions in the development of the research area of asymmetric anion-binding organocatalysis. Key early elucidation studies with chloride as counter-anion confirmed this type of alternative activation, which was then exploited in several processes and contributed to the advance and consolidation of anion-binding catalysis as a field. Thus, the use of the halide in the catalyst–anion complex as both a mere counter-anion spectator or an active nucleophile has been depicted, along with the new trends toward additional noncovalent contacts within the HB-donor catalyst and supramolecular interactions to both the anion and the cationic reactive species.

Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

We present the unprecedented <i>η</i>3-coordination of the 2-phosphaethynthiolate anion in the complex (PN)₂La(SCP) (<b>2</b>) [PN = N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate bridged (PN)₂La(<i>μ</i>-1,3-SCN)₂La(PN)₂ (<b>3</b>) and azide bridged (PN)₂La(<i>μ</i>-1,3-N3)₂La(PN)₂ (<b>4</b>) complexes indicates that the [SCP]^– coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π-orbital of the [SCP]^– ligand to the LUMO of complex <b>2</b>, rendering it the ideal precursor for the first functionalization of the [SCP]^– anion. Complex <b>2</b> was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]^– ligand to form the first CAAC stabilized group 15 – group 16 fulminate-type complexes (PN)₂La{SPC(^RCAAC)} (<b>5a,b</b>) (R = Ad, Me). A detailed reaction mechanism for the SCP to SPC isomerization is proposed based on DFT calculations.

Unprecedented η3-Coordination and Functionalization of the 2-Phosphaethynthiolate Anion at Lanthanum(III)

We present the unprecedented <i>η</i>3-coordination of the 2-phosphaethynthiolate anion in the complex (PN)₂La(SCP) (<b>2</b>) [PN = N-(2-(diisopropylphosphanyl)-4-methylphenyl)-2,4,6-trimethylanilide)]. Structural comparison with dinuclear thiocyanate bridged (PN)₂La(<i>μ</i>-1,3-SCN)₂La(PN)₂ (<b>3</b>) and azide bridged (PN)₂La(<i>μ</i>-1,3-N3)₂La(PN)₂ (<b>4</b>) complexes indicates that the [SCP]^– coordination mode is mainly governed by electronic, rather than steric factors. Quantum mechanical investigations reveal large contributions of the antibonding π-orbital of the [SCP]^– ligand to the LUMO of complex <b>2</b>, rendering it the ideal precursor for the first functionalization of the [SCP]^– anion. Complex <b>2</b> was therefore reacted with CAACs which induced a selective rearrangement of the [SCP]^– ligand to form the first CAAC stabilized group 15 – group 16 fulminate-type complexes (PN)₂La{SPC(^RCAAC)} (<b>5a,b</b>) (R = Ad, Me). A detailed reaction mechanism for the SCP to SPC isomerization is proposed based on DFT calculations.

Quantum calculations of the photoelectron spectra of the OH−·NH3 anion: implications for OH + NH3 → H2O + NH2 reaction dynamics

Quantum dynamics calculations were performed to analyze the experimentally measured photoelectron spectrum of the OH−·NH3 anion complex.

Anion-Dominated Copper Salicyaldimine Complexes—Structures, Coordination Mode of Nitrate and Decolorization Properties toward Acid Orange 7 Dye

A salicyaldimine ligand, 3-tert-butyl-4-hydroxy-5-(((pyridin-2-ylmethyl)imino)methyl)benzoic acid (H2Lsalpyca) and two Cu(II)−salicylaldimine complexes, [Cu(HLsalpyca)Cl] (1) and [Cu(HLsalpyca)(NO3)]n (2), have been synthesized. Complex 1 has a discrete mononuclear structure, in which the Cu(II) center is in a distorted square-planar geometry made up of one HLsalpyca− monoanion in an NNO tris-chelating mode and one Cl− anion. Complex 2 adopts a neutral one-dimensional zigzag chain structure propagating along the crystallographic [010] direction, where the Cu(II) center suits a distorted square pyramidal geometry with a τ value of 0.134, consisted of one HLsalpyca− monoanion as an NNO tris-chelator and two NO3− anions. When the Cu∙∙∙O semi coordination is taken into consideration, the nitrato ligand bridges two Cu(II) centers in an unsymmetrical bridging-tridentate with a μ, κ4O,O′:O′,O″ coordination. Clearly, anion herein plays a critical role in dominating the formation of discrete and polymeric structures of copper salicyaldimine complexes. Noteworthy, complex 2 is insoluble but highly stable in H2O and various organic solvents (CH3OH, CH3CN, acetone, CH2Cl2 and THF). Moreover, complex 2 shows good photocatalytic degradation activity and recyclability to accelerate the decolorization rate and enhance the decolorization performance of acid orange 7 (AO7) dye by hydrogen peroxide (H2O2) under daylight.

Evidence For a Water-Stabilised Ion Radical Complex: Photoelectron Spectroscopy and Ab Initio Calculations

A photoelectron spectrum corresponding to an unknown 174m/z anion complex has been recorded. Initially believed to be I−…CH3CH2OH (173m/z), the spectrum has been assigned as belonging to that of an I−…H2O…CH3CH2 radical anion complex. The major peaks in the photoelectron spectrum occur at 3.54eV and 4.48eV as the 2P3/2 and 2P1/2 spin-orbit states of iodine respectively. Ab initio calculations were performed in order to rationalise the existence of the complex, with all structures converging to a ‘ring-like’ geometry, with the iodide anion bound to both the water molecule as well as a hydrogen of the ethyl radical, with the other hydrogen of water bound to the unpaired electron site of the ethyl. Simulated vertical detachment energies of 3.59eV and 4.53eV were found to be in agreement with the experimental results.

Theoretical Insights on the High Pressure Behavior of Pentazolate Anion Complex [Co(H2O)4(N5)2]·4H2O

Periodic dispersion corrected density functional theory (DFT) calculations were carried out to examine the Hirshfeld surface, two dimensional (2D) fingerprint plots, crystal structure, molecular structure and density of state of all-nitrogen pentazolate anion complex [Co(H2O)4(N5)2]·4H2O under hydrostatic pressure from 0 to 20 GPa. The GGA/PW91-OBS method was applied in the present study. The intercontacts in [Co(H2O)4(N5)2]·4H2O were analyzed by Hirshfeld surfaces and 2D fingerprint plots. With ascending pressure, the lattice constants, compression rates, bond lengths, bond angles, and density of states change irregularly. Under 11.5, 13.0 and 15.8 GPa, covalent interaction competition is obvious between Co−N and Co−O bonds. It is possible to achieve orderly modification and regulation of the internal structure of [Co(H2O)4(N5)2]·4H2O by applied pressure. This is in accordance with the results from density of states analysis. The external compression causes the nonuniformity of electron density and the differential covalent interaction between pentazolate anion, coordinated water and atom Co. It is of great significance to interpret inter/intramolecular interaction and structural stability of [Co(H2O)4(N5)2]·4H2O and provide theoretical guidance for the design of metal complexes of all-nitrogen pentazolate anion.