Texas Red (TR) is a sulfo-analog of ROX dye. It has similar spectral properties, and emits in red region of the spectrum. TR X is a dye with aminohexanoic acid linker, that provides spacing between the fluorophore and the biomolecule, to prevent undesired interactions.
NHS ester is reactive towards amine groups that are ubiquitous in proteins, peptides and other labeling targets.