Symmetry

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3 pages, 172 KiB

Open AccessEditorial

Chiral Auxiliaries and Chirogenesis II

by Victor Borovkov

Symmetry 2021, 13(7), 1157; https://doi.org/10.3390/sym13071157 - 28 Jun 2021

Cited by 1 | Viewed by 1160

Abstract

Chirality is an inevitable property of our Universe, having an enormous impact in different fields, ranging from nuclear physics and astronomy to living organisms and human beings [...] Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

Research

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33 pages, 45457 KiB

Open AccessArticle

Synchronization in Non-Mirror-Symmetrical Chirogenesis: Non-Helical π–Conjugated Polymers with Helical Polysilane Copolymers in Co-Colloids

by Michiya Fujiki, Shun Okazaki, Nor Azura Abdul Rahim, Takumi Yamada and Kotohiro Nomura

Symmetry 2021, 13(4), 594; https://doi.org/10.3390/sym13040594 - 02 Apr 2021

Cited by 4 | Viewed by 2633

Abstract

A curious question is whether two types of chiroptical amplifications, called sergeants-and-soldiers (Ser-Sol) and majority-rule (Maj) effects, between non-charged helical copolymers and non-charged, non-helical homopolymers occur when copolymer encounter homopolymer in co-colloids. To address these topics, the present study chose (i) two helical [...] Read more.

A curious question is whether two types of chiroptical amplifications, called sergeants-and-soldiers (Ser-Sol) and majority-rule (Maj) effects, between non-charged helical copolymers and non-charged, non-helical homopolymers occur when copolymer encounter homopolymer in co-colloids. To address these topics, the present study chose (i) two helical polysilane copolymers (HCPSs) carrying (S)- or (R)-2-methylbutyl with isobutyl groups as chiral/achiral co-pendants (type I) and (S)- and (R)-2-methylbutyl groups as chiral/chiral co-pendants (type II) and (ii) two blue luminescent π-conjugated polymers, poly[(dioctylfluorene)-alt-(trans-vinylene)] (PFV8) and poly(dioctylfluorene) (PF8). Analyses of circular dichroism (CD) and circularly polarized luminescence (CPL) spectral datasets of the co-colloids indicated noticeable, chiroptical inversion in the Ser-Sol effect of PFV8/PF8 with type I HCPS. PF8 with type IIHCPS showed the anomalous Maj rule with chiroptical inversion though PFV8 with type IIHCPS was the normal Maj effect. The noticeable non-mirror-symmetric CD-and-CPL characteristics and marked differences in hydrodynamic sizes of these colloids were assumed to originate from non-mirror-symmetrical main-chain stiffness of HCPSs in dilute toluene solution. The present chirality/helicity transfer experiments alongside of previous/recent publications reported by other workers and us allowed to raise the fundamental question; is mirror symmetry on macroscopic levels in the ground and photoexcited states rigorously conserved? Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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15 pages, 4291 KiB

Open AccessArticle

“Double-Twist”-Based Dynamic Induction of Optical Activity in Multichromophoric System

by Tomasz Mądry, Agnieszka Czapik and Marcin Kwit

Symmetry 2021, 13(2), 325; https://doi.org/10.3390/sym13020325 - 16 Feb 2021

Cited by 2 | Viewed by 1887

Abstract

The electronic circular dichroism (CD)-silent 2,5-bis(biphen-2-yl)terephthalaldehyde has been used as a sensor (reporter) of chirality for primary amines. The through-space inductor–reporter interactions force a change in the chromophore conformation toward one of the diastereomeric forms. The structure of the reporter, with the terminal [...] Read more.

The electronic circular dichroism (CD)-silent 2,5-bis(biphen-2-yl)terephthalaldehyde has been used as a sensor (reporter) of chirality for primary amines. The through-space inductor–reporter interactions force a change in the chromophore conformation toward one of the diastereomeric forms. The structure of the reporter, with the terminal flipping biphenyl groups, led to generating Cotton effects in both lower- and higher-energy regions of the ECD spectrum. The induction of an optical activity in the chromophore was due to the cascade point-to-axial chirality transmission mechanism. The reporter system turned out to be sensitive to the subtle differences in the inductor structure. Despite the size of the chiral substituent, the molecular structure of the inductor–reporter systems in the solid-state showed many similarities. The most important one was the tendency of the core part of the molecules to adapt pseudocentrosymmetric conformation. Supported by a weak dispersion and Van der Waals interactions, the face-to-face and edge-to-face interactions between the π-electron systems present in the molecule were found to be responsible for the molecular arrangement in the crystal. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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14 pages, 2702 KiB

Open AccessEditor’s ChoiceArticle

Supramolecular Chirogenesis in Bis-Porphyrin: Crystallographic Structure and CD Spectra for a Complex with a Chiral Guanidine Derivative

by Irina Osadchuk, Nele Konrad, Khai-Nghi Truong, Kari Rissanen, Eric Clot, Riina Aav, Dzmitry Kananovich and Victor Borovkov

Symmetry 2021, 13(2), 275; https://doi.org/10.3390/sym13020275 - 05 Feb 2021

Cited by 7 | Viewed by 3866

Abstract

The complexation of (3aR,7aR)-N-(3,5-bis(trifluoromethyl)phenyl)octahydro-2H-benzo[d]imidazol-2-imine (BTI), as a guest, to ethane-bridged bis(zinc octaethylporphyrin), bis(ZnOEP), as a host, has been studied by means of ultraviolet-visible (UV-Vis) and circular dichroism (CD) absorption spectroscopies, single crystal X-ray [...] Read more.

The complexation of (3aR,7aR)-N-(3,5-bis(trifluoromethyl)phenyl)octahydro-2H-benzo[d]imidazol-2-imine (BTI), as a guest, to ethane-bridged bis(zinc octaethylporphyrin), bis(ZnOEP), as a host, has been studied by means of ultraviolet-visible (UV-Vis) and circular dichroism (CD) absorption spectroscopies, single crystal X-ray diffraction, and computational simulation. The formation of 1:2 host-guest complex was established by X-ray diffraction and UV-Vis titration studies. Two guest BTI molecules are located at the opposite sides of two porphyrin subunits of bis(ZnOEP) host, which is resting in the anti-conformation. The complexation of BTI molecules proceed via coordination of the imine nitrogens to the zinc ions of each porphyrin subunit of the host. Such supramolecular organization of the complex results in a screw arrangement of the two porphyrin subunits, inducing a strong CD signal in the Soret (B) band region. The corresponding DFT computational studies are in a good agreement with the experimental results and prove the presence of 1:2 host-guest complex as the major component in the solution (97.7%), but its optimized geometry differs from that observed in the solid-state. The UV-Vis and CD spectra simulated by using the solution-state geometry and the TD-DFT/ωB97X-D/cc-pVDZ + SMD (CH2Cl2) level of theory reproduced the experimentally obtained UV-Vis and CD spectra and confirmed the difference between the solid-state and solution structures. Moreover, it was shown that CD spectrum is very sensitive to the spatial arrangement of porphyrin subunits. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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22 pages, 3725 KiB

Open AccessArticle

Synthesis, Structure, and Magnetic Properties of Linear Trinuclear Cu^II and Ni^II Complexes of Porphyrin Analogues Embedded with Binaphthol Units

by Jun-ichiro Setsune, Shintaro Omae, Yukinori Tsujimura, Tomoyuki Mochida, Takahiro Sakurai and Hitoshi Ohta

Symmetry 2020, 12(10), 1610; https://doi.org/10.3390/sym12101610 - 28 Sep 2020

Cited by 2 | Viewed by 2430

Abstract

A porphyrin analogue embedded with (S)-1,1′-bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N₄O₄ coordination environment that enables a linear array of three metal ions. That [...] Read more.

A porphyrin analogue embedded with (S)-1,1′-bi-2-naphthol units was synthesized without reducing optical purity of the original binaphthol unit. This new macrocyclic ligand provides the hexaanionic N₄O₄ coordination environment that enables a linear array of three metal ions. That is, it provides the square planar O₄ donor set for the central metal site and the distorted square planar N₂O₂ donor set for the terminal metal sites. In fact, a Cu^II₃ complex with a Cu(1)–Cu(2) distance of 2.910 Å, a Cu(1)–Cu(2)–Cu(1′) angle of 174.7°, and a very planar Cu₂O₂ diamond core was obtained. The variable-temperature ¹H-NMR study of the Cu^II₃ complex showed increasing paramagnetic shifts for the naphthyl protons as temperature increased, which suggests strong antiferromagnetic coupling of Cu^II ions. The temperature dependence of the magnetic susceptibility indicated antiferromagnetic coupling both for the Cu^II₃ complex (J = −434 cm⁻¹) and for the Ni^II₃ complex (J = −49 cm⁻¹). The linear (L)M(µ-OR)₂M(µ-OR)₂M(L) core in a rigid macrocycle cavity made of aromatic components provides robust metal complexes that undergo reversible ligation at the apical sites of the central metal. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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16 pages, 2092 KiB

Open AccessFeature PaperArticle

Potentially Mistaking Enantiomers for Different Compounds Due to the Self-Induced Diastereomeric Anisochronism (SIDA) Phenomenon

by Andreas Baumann, Alicja Wzorek, Vadim A. Soloshonok, Karel D. Klika and Aubry K. Miller

Symmetry 2020, 12(7), 1106; https://doi.org/10.3390/sym12071106 - 02 Jul 2020

Cited by 11 | Viewed by 2785

Abstract

The NMR phenomenon of self-induced diastereomeric anisochronism (SIDA) was observed with an alcohol and an ester. The alcohol exhibited large concentration-dependent chemical shifts (δ’s), which initially led us to erroneously consider whether two enantiomers were in fact atropisomers. This highlights a [...] Read more.

The NMR phenomenon of self-induced diastereomeric anisochronism (SIDA) was observed with an alcohol and an ester. The alcohol exhibited large concentration-dependent chemical shifts (δ’s), which initially led us to erroneously consider whether two enantiomers were in fact atropisomers. This highlights a potential complication for the analysis of chiral compounds due to SIDA, namely the misidentification of enantiomers. A heterochiral association preference for the alcohol in CDCl₃ was determined by the intermolecular nuclear Overhauser effect (NOE) and diffusion measurements, the same preference as found in the solid state. The ester revealed more subtle effects, but concentration-dependent δ’s, observation of intermolecular NOE’s, as well as distinct signals for the two enantiomers in a scalemic sample all indicated the formation of associates. Intermolecular NOE and diffusion measurements indicated that homochiral association is slightly preferred over heterochiral association in CDCl₃, thus masking association for enantiopure and racemic samples of equal concentration. As observed with the alcohol, heterochiral association was preferred for the ester in the solid state. The potential problems that SIDA can cause are highlighted and constitute a warning: Due care should be taken with respect to conditions, particularly the concentration, when measuring NMR spectra of chiral compounds. Scalemic samples of both the alcohol and the ester were found to exhibit the self-disproportionation of enantiomers (SDE) phenomenon by preparative TLC, the first report of SDE by preparative TLC. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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14 pages, 4711 KiB

Open AccessCommunication

Resolution and Racemization of a Planar-Chiral A1/A2-Disubstituted Pillar[5]arene

by Chao Xiao, Wenting Liang, Wanhua Wu, Kuppusamy Kanagaraj, Yafen Yang, Ke Wen and Cheng Yang

Symmetry 2019, 11(6), 773; https://doi.org/10.3390/sym11060773 - 09 Jun 2019

Cited by 15 | Viewed by 4374

Abstract

Butoxycarbonyl (Boc)-protected pillar[4]arene[1]-diaminobenzene (BP) was synthesized by introducing the Boc protection onto the A1/A2 positions of BP. The oxygen-through-annulus rotation was partially inhibited because of the presence of the middle-sized Boc substituents. We succeeded in isolating the enantiopure R_P [...] Read more.

Butoxycarbonyl (Boc)-protected pillar[4]arene[1]-diaminobenzene (BP) was synthesized by introducing the Boc protection onto the A1/A2 positions of BP. The oxygen-through-annulus rotation was partially inhibited because of the presence of the middle-sized Boc substituents. We succeeded in isolating the enantiopure R_P (R_P, R_P, R_P, R_P, and R_P)- and S_P (S_P, S_P, S_P, S_P, and S_P)-BP, and studied their circular dichroism (CD) spectral properties. As the Boc substituent is not large enough to completely prevent the flip of the benzene units, enantiopure BP-f1 underwent racemization in solution. It is found that the racemization kinetics is a function of the solvent and temperature employed. The chirality of the BP-f1 could be maintained in n-hexane and CH₂Cl₂ for a long period at room temperature, whereas increasing the temperature or using solvents that cannot enter into the cavity of BP-f1 accelerated the racemization of BP-f1. The racemization kinetics and the thermodynamic parameters of racemization were studied in several different organic solvents. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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Review

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30 pages, 6900 KiB

Open AccessEditor’s ChoiceReview

Enantioselective Catalytic Synthesis of N-alkylated Indoles

by Dmitri Trubitsõn and Tõnis Kanger

Symmetry 2020, 12(7), 1184; https://doi.org/10.3390/sym12071184 - 17 Jul 2020

Cited by 16 | Viewed by 4784

Abstract

During the past two decades, the interest in new methodologies for the synthesis of chiral N-functionalized indoles has grown rapidly. The review illustrates efficient applications of organocatalytic and organometallic strategies for the construction of chiral α-N-branched indoles. Both the direct [...] Read more.

During the past two decades, the interest in new methodologies for the synthesis of chiral N-functionalized indoles has grown rapidly. The review illustrates efficient applications of organocatalytic and organometallic strategies for the construction of chiral α-N-branched indoles. Both the direct functionalization of the indole core and indirect methods based on asymmetric N-alkylation of indolines, isatins and 4,7-dihydroindoles are discussed. Full article

(This article belongs to the Special Issue Chiral Auxiliaries and Chirogenesis II)

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