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#λmax

3 public questions tagged with this topic.

UV-VIS spectroscopy

Cytochrome-C’s tryptophan emits at what λmax after denaturation?

Cytochrome c model illustrates tryptophan fluorescence quenching by prosthetic group. Native state buries tryptophan 59 adjacent to heme, enabling efficient Förster resonance energy transfer and electron transfer that quenches emission, leaving weak signal near 325 nm if detectable. Chemical denaturation with guanidinium chloride disrupts tertiary fold, distances exceeding Förster radius, abolishes quenching and exposes indole to aqueous solvent. Solvent dipolar relaxation stabilizes excited state, increasing quantum yield and red shifting emission maximum to characteristic water-exposed value

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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UV-VIS spectroscopy

Tryptophan λmax when buried inside protein is:

Tryptophan fluorescence quantum yield and wavelength are exquisitely sensitive to local polarity and hydrogen bonding. Fully solvent-exposed indole in water emits near 350-355 nm because excited state dipole stabilized by reorientation of surrounding water dipoles, lowering emission energy. When buried inside hydrophobic interior of proteins such as azurin, ribonuclease or lysozyme, nonpolar surroundings restrict solvent relaxation, destabilize excited state and reduce dipole stabilization. Consequently emission blue shifts to about 308-335 nm, commonly centered near 325 nm. This shift serves

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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UV-VIS spectroscopy

λmax for nitrogenous bases is typically around:

Purine and pyrimidine nitrogenous bases contain heteroaromatic rings with extensive π electron delocalization and participation of lone pairs, creating strong allowed π→π* and weaker n→π* transitions. Conjugation significantly lowers energy gap, shifting absorption from vacuum UV into middle UV. Maximum absorption occurs near 260 nm with high molar extinction around 10,000 L mol-1 cm-1 per base. This spectral property underpins quantification of nucleic acids by A260, assessment of purity by A260/A280 and A260/A230 ratios, and detection of denaturation via hyperchromic effect as stacked bases

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details