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In the supramolecular photocyclodimerization of 2-anthracenecarboxylate mediated by 6(A),6(D)-diguanidino-γ-cyclodextrin (CD), the chiral sense and enantiomeric excess of the photoproduct were dynamic functions of temperature and cosolvent to afford the (M)-anti head-to-head cyclodimer in 64% ee in aqueous methanol at -70 °C but the antipodal (P)-isomer in 86% ee in aqueous ammonia at -85 °C, while the corresponding diamino-γ-CD host did not show such unusual photochirogenic behaviors. The ee landscape was very steep against the temperature and sign-inverted against the ammonia content to reveal the opposite temperature dependence at low and high ammonia contents, for which an altered solvent structure and/or guanidinium-carboxylate interaction mode would be responsible.

Wavelength effects on the enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylate (AC) mediated by native and modified γ-cyclodextrins (CDs) were examined in different solvents at varying temperatures to manipulate the photochirogenic outcomes beyond the thermodynamically determined re/si-enantiotopic face selectivity upon 2 : 1 complexation of AC with CD in the ground state. Indeed, the stereochemical outcomes, i.e. syn/anti, head-to-tail/head-to-head (HT/HH) and in particular enantiomer ratios, were critical functions of the irradiation wavelength, irrespective of the CD host employed. Furthermore, the wavelength effects observed strongly depended on the host structure, reaction temperature and solvent employed, for which altered stacking geometry of the complexed AC pair is thought to be responsible. By optimizing the irradiation wavelength, chiral host, temperature and solvent, an enantiomeric excess of up to 54 and -37% were achieved for chiral syn-HT and anti-HH dimers.

Mutant human serum albumins accelerated the photocyclodimerization of 2-anthracenecarboxylate to afford chiral cyclodimers in 75-85% enantiomeric excesses, revealing that the mutations to impair non-productive sites 1 and/or 2 enhanced the substrate binding to site 3 without seriously damaging its inherently high photochirogenic ability.

Competitive cross-/homo-photocyclodimerization of anthracene (AN) and 2-anthracenecarboxylic acid (AC) mediated by a chiral hydrogen-bonding template (TKS) was investigated under various conditions. The cross-photocyclodimerization was favored by a factor of 4-5 at all temperatures and wavelengths examined to afford the AC-AN cross-dimer in 80-84% yield even at AN/AC = 1 and in 98% yield at AN/AC = 10. The enantiomeric excesses (ee's) obtained were 27-47% for the homo-dimers and 21-24% for the cross-dimer. The absolute configuration of the cross-dimer was determined by comparing the experimental and theoretical circular dichroism spectra and further correlated with the re/si enantiotopic-face selectivity upon AC-TKS complexation in the ground state. Detailed analyses of the complexation behavior and the fluorescence lifetime and cyclodimerization rate of excited re/si complexes revealed that the product's ee is critically controlled not only by the relative abundance of the re/si complexes in the ground and excited states but also by their relative photocyclodimerization rate. Crucially, the ground-state thermodynamics and the excited-state kinetics are not synergistic but offsetting in enantiotopic-face selectivity, and the latter overwhelms the former to give the homo- and cross-dimers in modest ee's. Finally, some practical strategies for enhancing the enantioselectivity in chiral template-mediated photochirogenesis have been proposed.

The mechanism for the high enantiomeric excess (ee) (80-90%) observed in the photocyclodimerization of 2-anthracenecarboxylate (AC) in the chiral binding sites of human serum albumin (HSA) was studied using fluorescence anisotropy. A long rotational correlation time of 36 ns was observed for the excited states of the ACs bound to the HSA site responsible for the high ee, suggesting that the ACs have restricted rotational mobility in this site. The ACs in this site have the same prochiral face protected by the protein, and this protection is responsible for the high ee observed. These insights provide a strategy for the rational design of supramolecular photochirogenic systems.

Photocyclodimerization of 2-anthracenecarboxylate tethered to a cyclic nigerosylnigerose scaffold gave a single chiral cyclodimer (out of two achiral and two chiral stereoisomers) in 99% optical and 96% chemical yields, achieving the ultimate stereocontrol of the supramolecular photochirogenesis in aqueous solution at 25 °C.

Circular dichroism (CD) spectral examinations at various host/guest ratios revealed that 2-anthracenecarboxylic acid (AC) forms not only 1:1 but also novel 2:1 hydrogen-bonded/π-stacked complexes with a chiral 4-benzamidoprolinol template (TKS159). The 2:1 complexation is a minor process but causes significant CD spectral changes as a consequence of the exciton coupling interaction of two AC chromophores and greatly accelerates the head-to-head photocyclodimerization to significantly affect the stereochemical outcomes.

Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid (AC-H) and its lithium salt (AC-Li) in chiral ionic liquid (CIL), (R)-1-(2,3-dihydroxypropyl)-3-methylimidazolium acetate {[(R)-GLYMI][AcO]}, gave a mixture of two head-to-tail (HT) and two head-to-head (HH) cyclodimers in HT/HH ratios of 1.3-1.7 (for AC-H) and 2.2-4.3 (for AC-Li) with low enantiomeric excesses (ee) of 0-3% for chiral syn-HT and anti-HH dimers. In contrast, irradiation of AC-H in an aqueous solution, containing cucurbit[8]uril (CB[8]) as a host and [(R)-GLYMI][AcO] or [(R)-GLYMI][Tf(2)N] as a modifier of CB portals, afforded the HH dimers in 91-99% selectivity, although the anti-HH dimer was totally racemic. Interestingly, irradiation of AC-H in a dichloromethane solution, containing [(R)-GLYMI][AcO] as a chiral template, led to the formation of the HH-dimers in 98% selectivity with chiral anti-HH dimer in -14% ee, presumably by the dual ligation of two ACs to a CIL through electrostatic and hydrogen-bonding interactions.

A series of anthracenecarboxylate(AC)-appended 2,3-di-O-methylcelluloses (AC-Cells) of varying degrees of substitution (DS) were synthesized to examine their photochirogenic behavior under a variety of conditions. The product distribution and enantiomeric excess of the cyclodimers obtained upon photoirradiation and the subsequent saponification were critical functions of the DS and conversion, for which a conformational change of the flexible polymer backbone is likely to be responsible.

Enantiodifferentiating photocyclodimerization of 2-anthracenecarboxylic acid and its alkali metal salts performed in a chiral ionic liquid gave chiral cyclodimers in good enantiomeric excesses of up to 41%, which is the highest ever reported for a photochirogenic reaction in chiral media.

Photocyclodimerization of 2-anthracenecarboxylate mediated by molecular chaperone protein was performed for the first time to afford chiral syn-head-to-tail and anti-head-to-head dimers (2 and 3) in 10% and 16% enantiomeric excess, respectively, with enhanced yields of sterically and electrostatically less-favored head-to-head dimers (3 and 4).

Here, we evaluate the pressure dependencies of the acid dissociation constants (p K a) of pH indicator dyes and amino acids by spectroscopic methods, including chemometric-assisted direct and indirect absorption spectrometry. These data can be useful for considering molecular properties under extreme conditions, such as in deep sea. We confirmed a positive correlation between the molar volume difference (Δ V °) and the molar compressibility difference (Δ κ) data for the deprotonation of molecules examined here and in literature. This relationship is discussed based on structural changes in the molecules upon deprotonation and associated hydration changes. Deprotonation from a carboxyl or phenolic hydroxyl group results in a negative Δ V °, whereas a molecule has positive Δ V ° when it loses a positive charge by deprotonation. This can be interpreted as a deprotonation-induced change in the size of the hydration sphere around the molecule. The contraction of the hydration sphere by deprotonation leads to negative Δ V ° and Δ κ , particularly for carboxylic acids and phenols. In contrast, when deprotonation causes the hydration sphere to expand, both Δ V ° and Δ κ are positive. Thus, a positive correlation between Δ V ° and Δ κ data is interpreted based on the hydration structural change upon deprotonation. Unlabelled Image • Spectroscopic measurement under hydrostatic pressure. • Change in acid dissociation constant by pressurization. • Elucidation for change in molar volume difference from hydration. • Revealing relationship between difference in molar volume and molar compressibility. [ABSTRACT FROM AUTHOR]

The absolute configuration has been established of the enantiopure anti-head-to-head cyclodimer of anthracene-2-carboxylic acid (AC) cocrystallized with L-propinol and dichloromethane [systematic name: ( S)-2-(hydroxymethyl)pyrrolidin-1-ium (5 R,6 S,11 R,12 S)-8-carboxy-5,6,11,12-tetrahydro-5,12:6,11-bis([1,2]benzeno)dibenzo[ a, e][8]annulene-2-carboxylate dichloromethane monosolvate], C5H12NO+·C30H19O4−·CH2Cl2. In the crystal structure, the AC dimer interacts with L-prolinol through a nine-membered hydrogen-bonded ring [ R22(9)], while the dichloromethane molecule is incorporated to fill the void space. The absolute configuration determined in this study verifies a recent assignment made by comparing theoretical versus experimental circular dichroism spectra. [ABSTRACT FROM AUTHOR]

Stereochemical outcomes were critically tuned by excitation wavelength in the supramolecular photocyclodimerization of 2-anthracenecarboxylic acid mediated by native and diamino-modified γ-cyclodextrins. [ABSTRACT FROM AUTHOR]

A series of secondary-face-substituted and skeleton-modified γ-cyclodextrins (γ-CDs) were prepared as chiral hosts for enantiodifferentiating [4+4] photocyclodimerization reactions of 2-anthracenecarboxylic acid (AC). These γ-CD derivatives form stable ternary complexes with ACs, with altroside-bearing γ-CDs undergoing induced-fit conformational changes upon complexation, and the photocyclodimerization of AC was, thus, dramatically accelerated. The enantiomeric excess (ee) of anti-head-to-head cyclodimer 3 was greatly enhanced in general with altroside-bearing γ-CDs 7–9. Although mono-altro-γ-CD 9 and 3A-azido-3A-deoxy-altro-γ-CD 7 gave 2 in ee's smaller than those obtained with native γ-CD, 3A-amino-3A-deoxy-altro-γ-CD 8 yielded 2 in much higher ee's, which is likely to be ascribed to the combined effects of the less-symmetric cavity and the electrostatic interactions. The influence of temperature and high pressure on the supramolecular photochirogenic reaction has been investigated in depth. An ee as high as 71% was obtained for cyclodimer 2 in the photocyclodimerization of AC mediated by 8 at 210 MPa and -21.5 °C. [ABSTRACT FROM AUTHOR]