Antibody Duration After Infection From SARS-CoV-2 in the Texas Coronavirus Antibody Response Survey.

Understanding the duration of antibodies to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that causes COVID-19 is important to controlling the current pandemic. Participants from the Texas Coronavirus Antibody Response Survey (Texas CARES) with at least 1 nucleocapsid protein antibody test were selected for a longitudinal analysis of antibody duration. A linear mixed model was fit to data from participants (n = 4553) with 1 to 3 antibody tests over 11 months (1 October 2020 to 16 September 2021), and models fit showed that expected antibody response after COVID-19 infection robustly increases for 100 days postinfection, and predicts individuals may remain antibody positive from natural infection beyond 500 days depending on age, body mass index, smoking or vaping use, and disease severity (hospitalized or not; symptomatic or not).

Aesculetin Exhibits Strong Fluorescent Photoacid Character.

Coumarins are bioactive molecules that often serve as defenses in plant and animal systems, and understanding their fundamental behavior is essential for understanding their bioactivity. Aesculetin (6,7-dihydroxycoumarin) has recently attracted attention due to its ability to act as an antioxidant, but little is known about its photophysical properties. The fluorescence lifetimes of its neutral and anion form in water are 19 ± 2 ps and 2.3 ± 0.1 ns, respectively. Assuming the short lifetime of the neutral is determined by ESPT, we estimate kPT ~ 5 × 1010 s-1. Using steady-state and time-resolved fluorescence spectroscopy, we determine its ground and excited-state [Formula: see text] to be 7.3 and -1, respectively, making it one of the strongest photoacids of the natural coumarins. Aesculetin exhibits a strong pH dependence of the relative fluorescence quantum yield becoming much more fluorescent above [Formula: see text]. The aesculetin anion [Formula: see text] slightly photobasic character. We also report that aesculetin forms a fluorescent catechol-like complex with boric acid, and this complex has a [Formula: see text] of 5.6.

Fluorescence of Scopoletin Including its Photoacidity and Large Stokes Shift.

Scopoletin is highly fluorescent in water and acts as a photoacid exhibiting excited-state proton transfer, ESPT, competitive with fluorescence. Its absorbance and emission spectral characteristics yield ground-state and excited-state pKa values of 7.4 ± 0.1 and 1.4 ± 0.1, respectively. The pKa* implies an ESPT rate constant an order of magnitude smaller than that for umbelliferone. This report provides quantum yield measurements in water that are comparable to quinine sulfate, and fluorescence lifetime values that are on a par with other similar coumarins yet provide insight into the ESPT process. The scopoletin anion is observed in tetrahydrofuran by reaction with a strong base. The Stokes shift of aqueous scopoletin is >100 nm in the pH range 3 to 7 due in part to its action as a photoacid. Modeling by density functional theory methods provides reasonable support for the experimental results.