A Surface-Enhanced Raman and ab Initio Study of Spectra of Lumazine Molecules

Waziry, Paula A. Faria; Chen, Xingxing; Lombardi, John R.; Birke, Ronald L.

doi:10.1021/la991351y

Cited by 12 publications

(11 citation statements)

References 22 publications

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“…Here, the pH influence on the spheniscin spectrum allows us to confidently assign the 1577 cm 21 band as aromatic C¼C stretching. A similar pH effect has been observed with pterins [49,62,63] and other aromatic compounds such as flavins and imidazoles; [47,64]), all of which contain nitrogen-bearing heterocyclic rings. While this effect is not diagnostic for pterins, it does indicate aromatic functionality and excludes spheniscin from being a completely aliphatic molecule like palmitic acid; note that aliphatic C-H stretching around 2900 cm 21 was not observed in spheniscin.…”

Section: Ph Effectsupporting

confidence: 69%

Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

Thomas

McGoverin

McGraw

et al. 2013

J. R. Soc. Interface.

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Many animals extract, synthesize and refine chemicals for colour display, where a range of compounds and structures can produce a diverse colour palette. Feather colours, for example, span the visible spectrum and mostly result from pigments in five chemical classes (carotenoids, melanins, porphyrins, psittacofulvins and metal oxides). However, the pigment that generates the yellow colour of penguin feathers appears to represent a sixth, poorly characterized class of feather pigments. This pigment class, here termed 'spheniscin', is displayed by half of the living penguin genera; the larger and richer colour displays of the pigment are highly attractive. Using Raman and mid-infrared spectroscopies, we analysed yellow feathers from two penguin species (king penguin, Aptenodytes patagonicus; macaroni penguin, Eudyptes chrysolophus) to further characterize spheniscin pigments. The Raman spectrum of spheniscin is distinct from spectra of other feather pigments and exhibits 17 distinctive spectral bands between 300 and 1700 cm 21 . Spectral bands from the yellow pigment are assigned to aromatically bound carbon atoms, and to skeletal modes in an aromatic, heterocyclic ring. It has been suggested that the penguin pigment is a pterin compound; Raman spectra from yellow penguin feathers are broadly consistent with previously reported pterin spectra, although we have not matched it to any known compound. Raman spectroscopy can provide a rapid and non-destructive method for surveying the distribution of different classes of feather pigments in the avian family tree, and for correlating the chemistry of spheniscin with compounds analysed elsewhere. We suggest that the sixth class of feather pigments may have evolved in a stem-lineage penguin and endowed modern penguins with a costly plumage trait that appears to be chemically unique among birds.

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Section: Ph Effectsupporting

confidence: 69%

Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

Thomas

McGoverin

McGraw

et al. 2013

J. R. Soc. Interface.

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“…Thus, the above calculated value is quite close to all of these experimental values. The experimental setup for these measurements is the same as that we used in our previous measurements 51 except that in the present case we use an in situ oxidation reduction cycle. Table 8 shows several assigned bands from these spectra as a function of electrode potential for 0.1 M KCl.…”

Section: Resultsmentioning

confidence: 99%

Ab Initio Frequency Calculations of Pyridine Adsorbed on an Adatom Model of a SERS Active Site of a Silver Surface

et al. 2003

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Ab initio and Urey−Bradley calculations of normal modes were carried out to analyze the frequency shifts observed on the SERS spectrum of pyridine obtained on a Ag surface. A molecular model with a Ag atom attached to the pyridine nitrogen was used in the Urey−Bradley calculation. The frequency shifts in the SERS spectrum were calculated by adding K(Ag−N) and F(Ag· · ·Cα) force constants and by adjusting the ring stretches according to how their bond lengths changed in an ab initio calculation with a (Ag−Py)+ model. The ab initio calculations were done with the HF, MP2, and B3LYP methods using the 3-21G, 6-31G, 6-31G*, 6-31G**, and LanL2DZ basis sets. The surface active site was modeled in the calculation by means of Ag0, Ag+ atoms, and a Ag4 + pyramidal cluster structure. The calculations were evaluated on how well they matched the observed frequencies, the ν(Ag−N) stretch, and the frequency shifts for the SERS spectrum in an electrochemical environment. The calculation with the Ag4 + model yielded the best results although the (Ag−Py)+ model also gives reasonable results. All calculations were consistent with an edge-on interaction between pyridine and the electrode surface and a Ag+ species as part of the surface active site.

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“…In a previous study, we used UV–vis steady-state and time-resolved fluorescence techniques to study the ESPT process of lumazine in water. Lumazine (see Scheme ) belongs to a class of biologically important compoundsthe pteridines. − Pteridines are heterocyclic compounds containing a bicyclic ring system of pyrimidine and pyrazine. Lumazine exhibits many structural similarities to the alloxazine ring system of the flavins.…”

Section: Introductionmentioning

confidence: 99%

Photoprotolytic Processes of Lumazine

Simkovitch

Huppert

2016

J. Phys. Chem. B

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Steady-state and time-resolved UV-vis spectroscopies were used to study the photoprotolytic properties of lumazine, which belongs to a class of biologically important compounds-the petridines. We found that in water an excited-state proton transfer occurs with a time constant of ∼70 ps and competes with a nonradiative rate of about the same value. The nonradiative rate of the protonated form of lumazine in polar and nonpolar solvents is large k ≥ 1.5 × 10s. The fluorescence properties indicate that in water, the ground-state neutral form of lumazine is already stable in two tautomeric forms. The fluorescence of the deprotonated form is quenched by protons in acidic solutions with a diffusion-controlled reaction rate. We conclude that the neutral form of lumazine is an irreversible mild photoacid.

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A Surface-Enhanced Raman and ab Initio Study of Spectra of Lumazine Molecules

Cited by 12 publications

References 22 publications

Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

Vibrational spectroscopic analyses of unique yellow feather pigments (spheniscins) in penguins

Ab Initio Frequency Calculations of Pyridine Adsorbed on an Adatom Model of a SERS Active Site of a Silver Surface

Photoprotolytic Processes of Lumazine

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