scholarly journals Guest Inclusion Crystal structures of Macrocyclic Boronic Esters

2014 ◽  
Vol 70 (a1) ◽  
pp. C677-C677
Author(s):  
Ryosuke Toyoshima ◽  
Kotaro Fujii ◽  
Kohei Johmoto ◽  
Hidehiro Uekusa ◽  
Yuji Kikuchi ◽  
...  
Keyword(s):  
Crystal Structures ◽  
Boronic Acid ◽  
Guest Molecule ◽  
Covalent Bond ◽  
Macrocyclic Compound ◽  
Channel Structure ◽  
Monoclinic System ◽  
One Dimensional ◽  
Boronic Ester ◽  
Boronic Esters

Macrocyclic compound has been attracting increasing attention because of their application for guest absorption and storage, guest selectivity, and reaction environment, which would utilize void space in the compound. Recently, such macrocyclic compound, boronic esters, has found to be formed as dynamic self-assembly of organic molecules through solvent dependent dynamic covalent bond formation between racemic polyol and planar 1,4-benzen(boronic acid)[1]. Thus, it is important to determine the crystal structure of the macrocyclic boronic esters with incorporated guest molecule to reveal the features of the compounds. In this study, structures of boronic ester of 1,4- naphthalene(boronic acid) (1) are presented and compared. The boronic ester with toluene guest molecule crystalized in monoclinic system, C2/c, Z=4, V=5099.7(6) Å3. As expected, toluene molecule was accommodated within a ring sandwiched by two naphthalene rings suggesting π-π interaction (ca. 3.6 Å separations). It is interesting that other structures of 1 with 1,4-dicyanobenzene, chloroform, and THF also have isomorphic structures to 1 with toluene. It clearly shows the guest inclusion ability of this boronic ester by weak intermolecular interactions. In the crystal structures, the boronic ester aligned along b-axis forming one-dimensional stacking with channel structure filled with guest molecules. Also, 1 with chloroform has a pseudo-polymorph phase (P21/c, V=5780.8(13) Å3) that has two additional chloroform molecules inside and outside of the ring; however, it also shows similar one-dimensional stacking structure with channel, implying this boronic ester has an easily stacking molecular shape. Although, the molecules have similar [2+2] ring structure, dihedral angle between two facing naphthalene rings is different in 1 with toluene, which is smaller as 14.10than 22 to 240in other structures. It may indicate a flexibility of the macrocyclic ring.

scholarly journals Photochromism change by conformation control in macrocyclic boronic ester cavity

2014 ◽  
Vol 70 (a1) ◽  
pp. C654-C654
Author(s):  
Kohei Johmoto ◽  
Hidehiro Uekusa ◽  
Yuji Kikuchi ◽  
Hiroki Takahagi ◽  
Kosuke Ono ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Molecular Conformation ◽  
Uv Light ◽  
Covalent Bond ◽  
Channel Structure ◽  
Guest Molecules ◽  
Parallel Form ◽  
Boronic Ester ◽  
Residual Electron Density ◽  
Covalent Bond Formation

N-salicylideneaniline derivatives are known to show photochromism by UV light, and it depends on the molecular conformation in the crystal. The twisted molecule is photochromic but the planar one is not[1,2]. N-salicylidene-2-aminopyridine (2SAP) always has a planar conformation due to the chemical structure without steric hindrance, therefore 2SAP is known as non-photochromic. However, by confining the molecule in a cavity of the macrocyclic boronic ester 1[3], the conformation and photochromism can be controlled. The inclusion crystal of 1 (homo-parallel form) has a special feature to have a channel type crystal structure in which the macrocyclic ring aligned one-dimensionally to include guest molecules. Interestingly, the crystals can reversibly absorb/desorb guests maintaining the crystal structure, because the channel structure is robust. To exchange the included guests, the crystal of 1(homo-parallel form) was immersed in the melt of 2SAP at 90°C. The obtained inclusion crystal showed photochromism. In the crystal structure, the shape of residual electron density for 2SAP indicated the conformation of 2SAP was twisted due to the confining in the cavity, which is the reason for photochromism. On the other hand, the recrystallization of 1 and 2SAP from THF / hexane solution unexpectedly gave hetero-antiparallel form of 1 because of the dynamic covalent bond formation in the boronic esters (Fig.). As this hetero-antiparallel form has planar cavity in the molecule, the conformation of the included guest molecule, 2SAP, is also planar as always seen. Therefore the inclusion crystal is non-photochromic. Thus, photochromism change of 2SAP was realized by conformational control through confining in the cavity of macrocyclic boronic ester.

scholarly journals Boronic acid ester with dopamine as a tool for bioconjugation and for visualization of cell apoptosis

2014 ◽  
Vol 50 (48) ◽  
pp. 6390-6393 ◽  
Author(s):  
Wei Scarano ◽  
Hongxu Lu ◽  
Martina H. Stenzel
Keyword(s):  
Cell Apoptosis ◽  
Boronic Acid ◽  
Acid Ester ◽  
Physiological Condition ◽  
Boronic Acids ◽  
Acidic Ph ◽  
Ph Values ◽  
Boronic Ester ◽  
Boronic Esters

Boronic esters between 1,2-benzodiols and boronic acids are an efficient way for bioconjugation. The ester is stable at physiological condition, but it cleaves very slowly at acidic pH values found in the endosomes and lysosomes. During apoptosis, the boronic ester is cleaved, most likely due to the influx of Ca2+ ions and the oxidation of 1,2-benzodiols.

scholarly journals Guest-induced fluorescence property of macrocyclic boronic ester

2014 ◽  
Vol 70 (a1) ◽  
pp. C672-C672
Author(s):  
Haruki Sugiyama ◽  
Kohei Johmoto ◽  
Hidehiro Uekusa ◽  
Yuji Kikuchi ◽  
Hiroki Takahagi ◽  
...  
Keyword(s):  
Crystal Packing ◽  
Uv Light ◽  
Condensation Reaction ◽  
Fluorescence Property ◽  
Channel Structure ◽  
Diffusion Method ◽  
Blue Color ◽  
Guest Molecules ◽  
One Dimensional ◽  
Naphthalene Molecule

Macrocyclic boronic esters (1) are obtained as a self-assembled molecule by condensation reaction between rac-tetrol (2) and 1,4-naphthalenediboronic acid (3) in the presence of toluene molecule [1]. In the crystal, this macrocyclic molecules form a charasteristic one dimensional channel structure that accommodates various small molecules. Interestingly, reversible desorption / absorption phenomena of guest molecules is observed without significant crystal packing change, meaning this crystal may have guest storage, separation, and catalytic abilities. In the course of exploring further functional aspects of the molecule, we give fluorescence property to this crystal by inclusion of acene molecules into this robust one dimensional channel structure. Naphthalene inclusion crystal was obtained by the diffusion method. The crystal structure is isostructural to known crystals, that is, a naphthalene molecule is included in a channel and sandwiched by two naphthalene moieties of the macrocyclic molecule (inter planar distance is about 3.6 angstrom). Under UV light, a blue color fluorescence observed in this crystal, suggesting the guest naphthalene molecule contributes the fluorescence property. After heating by 200 degrees C, the naphthalene was released to leave isostructural apohost crystal without fluorescence property. However, by naphthalene vapor exposure to the apohost crystal, the fluorescence property was recovered, which means naphthalene desorption and absorption are possible in crystalline state. Moreover Anthracene and Tetracene inclusion crystal were obtained, and they also showed light blue and yellow color fluorescence under UV light, respectively. Thus, the fluorescence function was successfully realized by inclusion of acene molecule in the one dimensional channel of the crystals, and furthermore the fluorescent color can be controlled by changing acene molecules.

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