Femtosecond Spectroscopy of Calcium Dipicolinate—A Major Component of Bacterial Spores

Abstract

Bacterial spores are rich in calcium dipicolinate (CaDPA). The role of this compound in the high UV resistance of spore DNA and their unique DNA photochemistry is not yet clarified. Here, the photophysical properties of CaDPA dissolved in water are studied by means of steady-state and time-resolved spectroscopy as well as quantum chemistry. Upon 255 nm excitation, a fluorescence emission with a yield of 1.7 × 10(-5) is detected. This low yield is in line with a measured fluorescence lifetime of 110 fs. Transient absorption experiments point to further transitions with time constants of 92 ps and 6.8 μs. The microsecond time constant is assigned to the decay of a triplet state. The yield of this state is close to unity. With the aid of quantum chemistry (TD-DFT, DFT-MRCI), the following transitions are identified. The primarily excited (1)ππ* state depletes within 110 fs. The depletion results in the population of an energetically close lying (1)nπ* state. An El-Sayed allowed intersystem crossing process with a time constant of 92 ps ensues. Implications of these findings on the interaction between photoexcited CaDPA and spore DNA are discussed.

Impact of Mono‐Fluorination on the Photophysics of the Flavin Chromophore

“…Using the time zero difference spectra Δ A t=0 ( λ ), the triplet yields Φ T are computed following a procedure detailed in ref. . The first step herein is the determination of a scaling factor which converts the spectrum Δ A t=0 ( λ ) into difference absorption coefficients as a function of the wavelength, Δε T ( λ ).…”

Spectroscopic characterization of dipicolinic acid and its photoproducts as thymine photosensitizers

“…[6,7,12] Altogether, the results available until now strongly point toward a triplettriplet energy transfer (TTET) between DPA and thymine residues. [12,14] The involvement of the thymine triplet excited state in SP formation has been further supported by the experiments run on dry film photoreaction of thymidine in the presence of pyridopsoralen derivatives or benzophenone under UVA irradiation. [15,16] However, full characterization of the DPA photophysical properties has not been achieved yet, probably due to its photolability in solution.…”

“…[15,16] However, full characterization of the DPA photophysical properties has not been achieved yet, probably due to its photolability in solution. [14,17] Specifically, a time-resolved study on the kinetics of the interaction between DPA triplet excited state and thymidine would provide highly valuable information on the occurrence of TTET. Moreover, in spite of its efficient photodegradation in solution, the structures and photosensitizing potential of DPA photoproducts have not been elucidated.…”

Placeholder Strategy with Upconversion Nanoparticles−Eriochrome Black T Conjugate for a Colorimetric Assay of an Anthrax Biomarker

“…The spore-forming bacterium Bacillus anthracis ( B. anthracis ) is the etiological agent of the acute disease anthrax. , When B. anthracis is contacted, its spores germinate and release several toxic substances that can cause internal bleeding, swelling, and even tissue death, with strong symptoms occurring only several hours after the exposure. − As delivery vehicles, B. anthracis spores are metabolically dormant and resistant toward harsh environmental conditions (e.g., high temperature, UV radiation, high pressure, and even chemical disinfectants). − Therefore, the rapid, visual, and selective detection of the spores, especially the biomarkers, is of utmost importance …”