Conformational complexity of melatonin in water and methanol

Shillady, Donald D.; Castevens, Charles M.; Trindle, Carl; Sulik, Jeffrey; Klonowski, Paula

doi:10.1016/s0301-4622(03)00109-1

Cited by 9 publications

(3 citation statements)

References 47 publications

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“…53 Later work has indicated that a more extended basis set can significantly improve computed energy for S 0 -1 L b transitions (e.g., red shift by 2400 cm À1 of calculated transition energy on going from 6-31G* to 6-311þG** basis set, as reported for indole). 54 On the other hand, the performance of TDDFT method for the lowest electronic transitions (both S 0 -1 L a and S 0 -1 L b states) in donor-acceptor systems such as aminocoumarines, 37,55 ortho-, 56 meta-57 and para-disubstituted 57-59 benzenes, is much better and the TDDFT energies of S 0 -1 L b transitions are in good agreement with experiment. However, the S 0 -1 L b transition in these compounds contains a heavily weighted contribution from charge transfer configuration.…”

Section: Calculated Absorption Transitionsmentioning

confidence: 64%

Photoinduced intramolecular charge transfer to meta position of benzene ring in 6-aminophthalides

Karpiuk

Svartsov

Nowacki

2005

Phys. Chem. Chem. Phys.

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Substitution of non-fluorescent phthalide (Pd) with amino group at meta (6) position in relation to the electron-accepting part of the lactone ring completely changes Pd photophysics: a new long-wavelength absorption band arises and the molecule becomes highly fluorescent. The experimental data and the analysis of vertical electronic transitions with TDDFT method indicate that the first absorption band in 6-aminophthalides (6-APds) comprises a single CT transition to the S1 state. Almost equal absorption and emission transition dipole moments indicate that S0 <--> S1 transition in all 6-APds is not affected by any mixing with other electronic states, the excited-state vibrational relaxation is not accompanied by significant conformational changes and the Stokes shifts reflect mainly solvation energetics of these molecules. Excited state dipole moments obtained from solvatochromic plots and from CASSCF calculations confirm large charge displacement from amino group towards the meta position of the benzene ring upon excitation of 6-APds to S1 state. Long fluorescence lifetimes and high fluorescence quantum yields demonstrate efficient and stable excited state charge separation in 6-APds. Taken together with sensitivity of 6-APds to polarity and proticity of the environment these properties make them good candidates for fluorescent probes of long-time scale molecular dynamics.

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Section: Calculated Absorption Transitionsmentioning

confidence: 64%

Photoinduced intramolecular charge transfer to meta position of benzene ring in 6-aminophthalides

Karpiuk

Svartsov

Nowacki

2005

Phys. Chem. Chem. Phys.

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“…Shillady et al. [29] described different conformations of melatonin dissolved in water and methanol. Degradation of water‐dissolved melatonin and a following transformation of its structure because of the dissolving procedure at 37°C is rather unlikely.…”

Section: Discussionmentioning

confidence: 99%

5‐Hydroxytryptophan is a more potent in vitro hydroxyl radical scavenger than melatonin or vitamin C

Keithahn

Lerchl

2004

Journal of Pineal Research

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Hydroxyl radicals are involved in direct damage of important biomolecules. Potent radical scavengers such as vitamin C and indoles of the tryptophan family can avert the potential damage. Melatonin and its precursor 5-hydroxytryptophan (5-HTP) were compared with water-soluble vitamin C. Different scavenger concentrations were measured in a steady-state luminol chemiluminescence system (SLCL-system) with combined Fe(II) chloride (0.1 mm) and hydrogen peroxide (1.0 mm) as hydroxyl radical generators. 5-HTP showed highest hydroxyl radical scavenging effects with a 50% inhibition concentration (IC50) of 1.8 microm. For vitamin C an IC50 of 12.7 microm was measured, whereas melatonin in pure demineralized water was much less efficient (IC50=724 microm). A comparison between melatonin in aqueous solution and melatonin in ethanol solution revealed that melatonin was significantly more effective in pure demineralized water.

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“…This overestimation is also observed in indole and may owe to the inability of the TDDFT method to provide a good description of L b ‐type states . However, calculation at higher level basis set did not give improvement as reported in indole . The observed negative CE around 283 nm in wax may be associated with negative rotatory strength at 265 nm in the gas phase, which is characterized by a weak magnetic dipole allowed/electric dipole forbidden n→π* type transition.…”

Section: Resultsmentioning

confidence: 81%

Study on the Absolute Configurations of 3‐Alkylphthalides using TDDFT Calculations of Chiroptical Properties

2012

Chirality

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Absolute configurations (ACs) of 3-alkylphthalides including natural products (-)-3-n-butylphthalide ((-)-1) and fuscinarin have been studied using chiroptical properties and quantum chemical calculation. Electronic circular dichroism and optical rotatory dispersion spectra of (S)-1 predicted adopting time-dependent density functional theory and hybrid functionals coincide very well with the experimental and literature data of (-)-1, leading unambiguously to AC assignment as S for levorotatory isomer. The relationship between structures and chiroptical properties of 3-alkylphthalides were also studied using theoretical calculation. It is found that when the alkyl group is adjacent to the single chiral center in the molecule, both the length of the alkyl side chain and the polarity of solvent may exert significant effect on electronic circular dichroism spectra. On the basis of these observations, it is recommended that the long-chain alkyl group may be replaced by at least propyl instead of methyl group in such compounds. The present work shows that combination of chiroptical properties and ab initio calculations can provide a feasible and reliable way to the AC establishment of novel 3-alkylphthalide derivatives with a high degree of confidence.

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Conformational complexity of melatonin in water and methanol

Cited by 9 publications

References 47 publications

Photoinduced intramolecular charge transfer to meta position of benzene ring in 6-aminophthalides

Photoinduced intramolecular charge transfer to meta position of benzene ring in 6-aminophthalides

5‐Hydroxytryptophan is a more potent in vitro hydroxyl radical scavenger than melatonin or vitamin C

Study on the Absolute Configurations of 3‐Alkylphthalides using TDDFT Calculations of Chiroptical Properties

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