  Far-UV circular dichroism (CD) spectroscopy provides a rapid, sensitive,
nondestructive tool to analyze protein conformation by monitoring secondary
structure composition. Originally intended for educational purposes, a
spreadsheet-based program that implements a rudimentary routine for fitting and
simulating far-UV protein CD spectra became quite used in research papers too,
as it allowed very quick deconvolution of spectra into secondary structure
compositions and easy simulation of spectra expected for defined secondary
structure contents. To make such software more readily available, I present
here an online version that runs directly on web browsers allowing even faster
analyses on any modern device and without the need of any spreadsheet or third
programs. The new version further extends the original capabilities to fit and
simulate alpha, beta and random coil contents now including also beta turns; it
allows to quickly select the effective spectral window used for fitting and
enables interactive exploration of the effects of changes in secondary
structure composition on the resulting spectra. The web app allows ubiquitous
implementation in biophysics courses for example right on student smartphones,
and seamless, rapid tests in research settings before moving to more advanced
analysis programs (a few proposed here too). The web app is freely available
without registration at
http://lucianoabriata.altervista.org/jsinscience/cd/cd3.html
