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Highly polar M-mol-X (M = alkali metal, mol = molecule, X = halogen) insertion complexes have been predicted to offer potential practical applications, including molecular interactions with light, ion-pair induced isomerization, etc. In the present work, the insertion complexes of the seven-membered, fused bicyclic norcaradiene and its monocyclic isomer trapped in Li-I, Na-I, and K-I counterion pairs were investigated using ab initio methods. The structures, stability, polarities, and simulated infrared spectra are analyzed and the effects of the insertion on the norcaradiene to cycloheptatriene isomerization process are examined. Furthermore, an uncommon bond between iodine and a fully substituted carbon atom is reported upon and hypothesized to be catalyzed by the presence of the cation in the insertion complexes.

Natural product (E)-anethole was isomerized to (Z)-anethole in a photocatalytic reaction. For this purpose, a self-designed cheap photoreactor was constructed. Among 11 photosensitizers (organo and metal complex compounds), Ir(p-tBu-ppy)[sub.3] led to the highest conversion. Triplet energies of (E)- and (Z)-anethole were predicted theoretically by DFT calculations to support the selection of appropriate photosensitizers. A catalyst loading of 0.1 mol% gave up to 90% conversion in gram scale. Further additives were not required and mild irradiation with light of 400 nm overnight was sufficient. As a proof of concept, (E)- and (Z)-anethole were dihydroxylated diastereoselectively to obtain diastereomerically pure like- and unlike-configured diols, respectively.

The photophysical processes and photochemical reactions of 1,4-di(azastyryl)benzene (1) derivative [(E,E)-1](ClO[sub.4])[sub.2] were investigated by absorption, luminescence, and laser kinetic spectroscopy in the water solution. The observed photo processes include dimerization, E-Z isomerization, and intersystem crossing to the triplet state, as well as the complexation [(E,E)-1](ClO[sub.4])[sub.2] with cucurbit[7]uril (CB[7]). The [(E,E)-1](ClO[sub.4])[sub.2] dye dimerization was shown to be energetically more favorable in the excited state than in the ground state. The reversible photoinduced migration of the dye dication in the CB[7] cavity takes place as a result of partial exit of the [(E,E)-1][sup.2+] from the cavity and its subsequent conversion to the (E,Z)-isomer in the excited state, which undergoes conversion to the initial complex of [(E,E)-1]@CB[7][sup.2+] after returning to the ground state. This photoprocess is of interest in relation to the scientific problem of designing photocontrolled supramolecular machines.

The elusiveness of hexazine (a.k.a. hexaazabenzene) and its perhydrogenated derivative, hexazinane, prompted the author of this paper to investigate the possibility of stabilizing the six-membered nitrogen ring by inserting it into [18]-annulene. The resulting compound is made of a central N.sub.6 ring surrounded by an outer ring of 18 carbon atoms that prevents its decomposition into dinitrogen. The N.sub.6 ring is non-planar and with a chair-like conformation that does not undergo conformational isomerization. The designed molecule can be stabilized either by oxidation to a hexa-oxide derivative or by coordination of ZnCl.sup.+. Furthermore, a triangle-shaped macrocyclic isomer made of three pyridazine moieties connected to each other by ethylene bridges represents a possible precursor in the synthesis of the N.sub.6-embedded hydrocarbon. By employing an alkali or alkaline-earth metal cation that coordinates the three pyridazine monomers it becomes possible to bring their nitrogen atoms in close proximity so that a subsequent aromatic fusion reaction could be attempted.

Site-specific modifications of aspartate residues spontaneously occur in crystallin, the major protein in the lens. One of the primary modification sites is Asp151 in [alpha]A-crystallin. Isomerization and racemization alter the crystallin backbone structure, reducing its stability by inducing abnormal crystallin-crystallin interactions and ultimately leading to the insolubilization of crystallin complexes. These changes are considered significant factors in the formation of senile cataracts. However, the mechanisms driving spontaneous isomerization and racemization have not been experimentally demonstrated. In this study, we generated [alpha]A-crystallins with different homo-oligomeric sizes and/or containing an asparagine residue at position 151, which is more prone to isomerization and racemization. We characterized their structure, hydrophobicity, chaperone-like function, and heat stability, and examined their propensity for isomerization and racemization. The results show that the two differently sized [alpha]A-crystallin variants possessed similar secondary structures but exhibited different chaperone-like functions depending on their oligomeric sizes. The rate of isomerization and racemization of Asp151, as assessed by the deamidation of Asn151, was also found to depend on the oligomeric sizes of [alpha]A-crystallin. The predominant isomerization product via deamidation of Asn151 in the different-sized [alpha]A-crystallin variants was L-[beta]-Asp in vitro, while various modifications occurred around Asp151 in vivo. The disparity between the findings of this in vitro study and in vivo studies suggests that the isomerization of Asp151 in vivo may be more complex than what occurs in vitro.

Sugar compounds are an important part of biomass resources, and their catalytic conversion can prepare a series of platform compounds, such as lactic acid and polyols. One of the key steps is the isomerization of aldoses to ketoses. However, finding a simple method to efficiently convert aldoses to ketoses remains a great challenge. Herein, we report a core-shell structured catalyst, Pt/SiO.sub.2@Mg(OH).sub.2, for the efficient conversion of xylose as well as the further conversion of xylose to xylulose. Xylose, a five-carbon sugar unit with the highest content in biomass, was used as the object of study to determine the optimal reaction conditions in the aqueous system by adjusting the loading amount of Mg(OH).sub.2, catalyst addition, reaction temperature, and reaction time: In the optimum aqueous conditions, the yield of xylulose was 23.61%. We also investigated the effect of solvent effects on the hydrothermal reaction and determined the optimal solvent ratio, the yield of xylulose reached 31.74% at H.sub.2O:MeOH (8:2). We anticipate that this research result can provide a theoretical basis and reference for the industrialized production of subsequent sugar isomerization.

Sugar compounds are an important part of biomass resources, and their catalytic conversion can prepare a series of platform compounds, such as lactic acid and polyols. One of the key steps is the isomerization of aldoses to ketoses. However, finding a simple method to efficiently convert aldoses to ketoses remains a great challenge. Herein, we report a core-shell structured catalyst, Pt/SiO.sub.2@Mg(OH).sub.2, for the efficient conversion of xylose as well as the further conversion of xylose to xylulose. Xylose, a five-carbon sugar unit with the highest content in biomass, was used as the object of study to determine the optimal reaction conditions in the aqueous system by adjusting the loading amount of Mg(OH).sub.2, catalyst addition, reaction temperature, and reaction time: In the optimum aqueous conditions, the yield of xylulose was 23.61%. We also investigated the effect of solvent effects on the hydrothermal reaction and determined the optimal solvent ratio, the yield of xylulose reached 31.74% at H.sub.2O:MeOH (8:2). We anticipate that this research result can provide a theoretical basis and reference for the industrialized production of subsequent sugar isomerization. Graphical

Highly oxygenated organic molecules (HOMs) from α-pinene ozonolysis have been shown to be significant contributors to secondary organic aerosol (SOA), yet our mechanistic understanding of how the peroxy-radical-driven autoxidation leads to their formation in this system is still limited. The involved isomerisation reactions such as H-atom abstractions followed by O.sub.2 additions can take place on sub-second timescales in short-lived intermediates, making the process challenging to study. Similarly, while the end-products and sometimes radical intermediates can be observed using mass spectrometry, their structures remain elusive. Therefore, we propose a method utilising selective deuterations for unveiling the mechanisms of autoxidation, where the HOM products can be used to infer which C atoms have taken part in the isomerisation reactions. This relies on the fact that if a C-D bond is broken due to an abstraction by a peroxy group forming a -OOD hydroperoxide, the D atom will become labile and able to be exchanged with a hydrogen atom in water vapour (H.sub.2 O), effectively leading to loss of the D atom from the molecule.

Photophysical properties of a series of bis(arylydene)cycloalkanone dyes with various donor substituents are studied using quantum chemistry. Their capacity for luminescence and nonradiative relaxation through trans–cis isomerization is related to their structure, in particular, to the donor capacity of the substituents and the degree of conjugation due to the central cycloalkanone moiety. It is shown that cyclohexanone central moiety introduces distortions and disrupts the conjugation, thus leading to a nonmonotonic change in their properties. The increasing donor capacity of the substituents causes increase in the HOMO energy (rise in the oxidation potential) and decrease in the HOMO–LUMO gap, which results in the red shift of the absorption spectra. The ability of the excited dye to relax through fluorescence or through trans–cis isomerization is governed by the height of the barrier between the Franck–Condon and S1–S0 conical intersection regions on the potential energy surface of the lowest π-π* excited state. This barrier also correlates with the donor capacity of the substituents and the degree of conjugation between the central and donor moieties. The calculated fluorescence and trans–cis isomerization rates are in good agreement with the observed fluorescence quantum yields.