Absorption and fluorescence spectra are central to the photosciences. The PhotochemCAD initiative, aimed at assembling digital databases of absorption and fluorescence spectra for use across the photosciences, now comprises <1000 absorption spectra and <500 fluorescence spectra for ~1000 compounds along with companion photophysical parameters (molar absorption coefficient, fluorescence quantum yield) and citations to the originating scientific literature. The spectral databases have chiefly been assembled by digitizing spectra from the vast print literature. The conversion of print spectra to digital form presents several technical challenges: (1) print spectra are plagued by line crossing from overlaid spectra, use of discontinuous lines, and interference from grids, tick marks, and the graph baseline; (2) the print spectrum in some cases lacks wavelength markers or is annotated with markers at odds with values in the accompanying text; and (3) the digitized spectra often are composed of data with uneven wavelength (x-axis) intervals. Here, manually assisted digitization – wherein the user steps through a print spectrum with hand-eye assistance to create the corresponding digital dataset – is compared with automated digitization. Graphical features that bear on use of each method are outlined. Two spreadsheet-based tools have been developed for application following digitization: (i) conversion of xy-coordinate data from uneven to uniform x-axis intervals, and (ii) calibration of the digitized spectrum with appropriate wavelength values. The two tools enable more accurate rendition of print spectra into digital form, as required for qualitative comparisons and quantitative calculations, and have been added to the PhotochemCAD website (http://www.photochemcad.com).
PhotochemCAD is a Microsoft Windows-based software program composed of spectral databases and program modules for diverse photochemical calculations and is aimed at addressing fundamental needs of the scientific community. Since initiation in the late 1980’s, ~1000 absorption/fluorescence spectra of ~500 organic compounds of interest across the wide photosciences field have been collected and are now available in PhotochemCAD 3. The spectra are accompanied by quantitative parameters (molar absorption coefficient, fluorescence quantum yield) where available and citations to the original source literature. Many web-based absorption/fluorescence spectra viewers are publicly accessible but are typically aimed at commercial sales by sponsoring companies. Here, a web-browser-based PhotochemCAD spectra viewer is described that enables overlay of spectra for comparative evaluation, can be used on any platform (Windows, Mac, Linux), and does not require downloading or installation of the program. The PhotochemCAD program, databases, and spectra viewer are accessible for free use at http://www.photochemcad.com.
Advances in molecular design and synthetic chemistry enable the development of novel molecular therapeutic treatments of diverse diseases. A strategy proposed nearly 25 years ago for the treatment of metastatic cancer, but never realized, entails the following general processes: (i) Accumulation of an insoluble scaffold in the tumor extracellular space upon native enzyme (Enat) cleavage of a soluble precursor, and (ii) covalent attachment to the scaffold of a non-native (heterologous) enzyme (Ehet), which catalytically converts an abundance of aqueous-soluble radionuclide-bearing prodrug to an aqueous-insoluble drug; the latter precipitates in the tumor extracellular space. Here, the design and chemical synthesis of a molecular entity (1) for formation of the scaffold are described. Compound 1 is an “A2BC”-type lysine-based architecture that contains two chromogenic indoxyl-glucoside units (A), which upon cleavage by a glucosidase (Enat) undergo oxidative dimerization to provide a water-insoluble indigoid polymer; a maleimide (B) for attachment to a cancer-targeting agent; and the binding motif Loracarbef (C), a carbacephem antibiotic that forms a covalent adduct with a mutant β-lactamase (a proposed tether to, and/or possible fusion protein with, Ehet). Studies here also include maleimide–thiol conjugation of I to transferrin (a cell uptake carrier) and the covalent attachment of a mutant b-lactamase to Loracarbef. Together, the work supports an approach for molecular brachytherapy (or endoradiotherapy), where radionuclide seeds are self-assembled directly in the region of therapeutic need.
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