Spectroscopic Characterization of Soybean Lipoxygenase-1 Mutants:  the Role of Second Coordination Sphere Residues in the Regulation of Enzyme Activity†

The role of substituted anilines as second coordination sphere ligands of cobalt(II) complexes has been investigated. Chemical shifts of the ligand nuclear magnetic resonance (n.m.r.) spectra arising from pseudo-contact interaction with the paramagnetic cobalt complex have been utilized for this purpose. It has been found that in each case the aniline preferentially occupies a position perpendicular to the three fold symmetry axis of the complex and tends to be aligned with the amino group directed towards the cobalt atom. Electron withdrawing substituents para to the amino group enhance the second coordination sphere binding and electron donating substituents diminish it. These results are consistent with the idea that the structure of the second coordination sphere is determined by electrostatic interaction with the negatively charged ligands comprising the first coordination sphere. There is competition between aniline molecules and solvent molecules for a position in the second sphere with the solvent competing with increasing effectiveness in the series carbon tetrachloride, benzene, and methylene chloride.

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Functional Characterization of a Melon Alcohol Acyl-transferase Gene Family Involved in the Biosynthesis of Ester Volatiles. Identification of the Crucial Role of a Threonine Residue for Enzyme Activity*

Plant Molecular Biology ◽

10.1007/s11103-005-8884-y ◽

2005 ◽

Vol 59 (2) ◽

pp. 345-362 ◽

Cited By ~ 118

Author(s):

Islam El-Sharkawy ◽

Daniel Manríquez ◽

Francisco B. Flores ◽

Farid Regad ◽

Mondher Bouzayen ◽

...

Keyword(s):

Enzyme Activity ◽

Gene Family ◽

Crucial Role ◽

Functional Characterization ◽

Acyl Transferase ◽

Threonine Residue ◽

Transferase Gene

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Spectroscopic characterization of free-base hydroxy(arylethynyl)porphyrins in acidic and basic media

Journal of Porphyrins and Phthalocyanines ◽

10.1142/s1088424617500675 ◽

2017 ◽

Vol 21 (10) ◽

pp. 680-691

Author(s):

Kaarin K. Evens ◽

Kathryn E. Splan

Keyword(s):

Spectroscopic Characterization ◽

Spectral Features ◽

Free Base ◽

Enhanced Absorption ◽

Spectral Shifts ◽

Porphyrin Macrocycle ◽

Show Evidence ◽

Acidic Conditions

The addition of arylethynyl groups to the porphyrin macrocycle represents an effective strategy with which to enhance the light-harvesting properties of porphyrins. We now extend this modification to arylethynyl porphyrins with two or four [Formula: see text]-hydroxyphenyl substituents. Arylethynyl porphyrins bearing four, but not two, [Formula: see text]-hydroxyphenyl substituents show evidence of aggregation under acidic conditions. Under basic conditions, deprotonation of the peripheral hydroxyphenyl substituents results in substantially red-shifted spectral features and enhanced absorption in the Q-band region. When the hydroxyphenyl groups are appended to the porphyrin macrocylce via the ethynyl spacers, the spectral shifts observed upon deprotonation are significantly enhanced relative to those observed for hydroxyphenylporphyrins, highlighting the role of expanded conjugation in altering porphyrin photophysics.

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