Zn Pyropheophorbide a: A β‐Face Selective Nicotine Receptor

Abstract

Nicotine binds to a semisynthetic chlorophyll a derivative, Zn pyropheophorbide a, in a receptor‐like manner to form a 1:1 complex with β‐face diastereomeric configuration. The geometry of the complex structure was evidenced by 1H NMR, ROESY and DOSY spectroscopic experiments combined with molecular modelling DFT B3LYP calculations at the 6‐31G* level. The observed binding between the chlorin and nicotine takes place through a “two‐point binding” mechanism, in which the nicotine N‐pyridyl moiety coordinates to the chlorin zinc atom, whilst the nicotine N‐methyl pyrrolidine unit forms an ion pair with the chlorin acid group. The binding mechanism was further confirmed by association constants (Ka) obtained from titration experiments in CDCl3 with 1H NMR spectroscopic monitoring (8.0 × 105 M–1) and in toluene with UV/Vis (6.1 × 104 M–1) monitoring. The corresponding binding constants obtained for nicotine with one‐point binder, Zn pyropheophorbide a methyl ester, were 4.8 × 105 and 2.3 × 104 M–1, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Biomimetic zinc chlorin–poly(4-vinylpyridine) assemblies: doping level dependent emission–absorption regimes

“…Chlorophyll a was extracted and puried from Spirulina pacica and converted into pyro-pheophorbide a methylester (1), 33 which was used as a starting material for the syntheses. Zn pyropheophorbide a methylester 24,25 and Zn 3 1 -OH-pyro-pheophorbide a methylester (3 1 -epimeric mixture, (3 1 R)/(3 1 S) ¼ 1/1) 34 ( Fig. 2) were synthesized according to literature procedures and their NMR spectra were in agreement with the published data.…”

Coordination‐Driven Dimerization of Zinc Chlorophyll Derivatives Possessing a Dialkylamino Group

“…These peaks coalesced with an increasei nt emperature and relatively sharp peaks wereo btained at 373 K, showing the monomeric specieso fZn-1.T he signals of 5-H and 3 1 -N(CH 3 ) 2 shifted to higher magneticf ields upon cooling to 223 K. These large shifts were ascribable to the shielding effect of the ring current of the chlorin p-system, where their protons were situated above the chlorin moiety via axial coordination of the 3 1 -N atom to the central zinc. [26][27][28][29] Since the shift values of 10-H and 20-H were smaller ( Figure 7, blue square), at low temperature, they were located at relativelyd istant positions from the other chlorin moiety in the resulting supramolecule. When considering the combination of 1 HNMR data with the above optical observations, Zn-1 (1 mm)w as monomeric in CDCl 2 CDCl 2 at 373 K, forminga no pen dimer with af lexible conformationa t room temperature, and transforming to closed dimers which take various conformers through double coordinate bonds with restriction of molecular motion at low temperatures.…”

RM1 Semiempirical Model: Chemistry, Pharmaceutical Research, Molecular Biology and Materials Science

“…Due to the fact that RM1 has not been parameterized for transition metals, only few articles have used RM1 in the context of inorganic chemistry. [155][156][157][158][159] RM1 was mostly restricted to the calculation of properties of the ligands that are interacting with metals 158 and to the calculation of the properties of the inorganic species that participate in organic reactions. 140 Examples of the usage of RM1 in inorganic chemistry include a study of the CO 2 absorption by protic and aprotic ionic liquids, 157 as well as the prediction of HOMO, and LUMO energies of ligands coordinated to trivalent dysprosium and geometry optimization of a set of ligands coordinated to trivalent europium, ytterbium and holmium.…”

“…Inorganic chemistry studies also reported the usage of RM1 as the first step in higher accuracy geometry optimization calculations. 158,159 This strategy can result in a much more adequate starting geometry to more accurate calculations that will employ DFT or ab initio methods. For example, Kavakka et al 158 reported a zinc complex, which is a selective nicotine receptor.…”

“…158,159 This strategy can result in a much more adequate starting geometry to more accurate calculations that will employ DFT or ab initio methods. For example, Kavakka et al 158 reported a zinc complex, which is a selective nicotine receptor. In this study, the geometry of the propionic acid side chain and of the pyrrolidine moiety of the nicotine were calculated by using the RM1 method.…”