Can anyone tell me about the 3D-QSAR. What is the actual meaning of 3D-QSAR. "Is inclusion of 3D-descriptors/properties or something related to spatial arrangement of the molecules"
3D-QSAR spans a broad range of methodologies, with the common thread being that all 3D-QSAR techniques involve at least one ligand property that can't be quantified without knowing a plausible 3D spatial conformation for the molecule.
Some examples of 3D-QSAR include receptor-based QSAR (one takes into account explicit information about the ligand-receptor contacts), pharmacophore-based QSAR (from the ligand alone, one identifies the spatial relationship between potentially relevant pharmacophore features), shape-based QSAR (conformational information about the molecule can suggest propensity for binding to a given receptor), and finally physicochemical-based QSAR, in which activity is related to physicochemical properties that are best estimated through 3D structural assessment (e.g., amphiphilicity, polarizability, conformational stability).
Because of the tremendous variety of different 3D-QSAR techniques, one can't hope to assemble a single mathematical expression to account for them all.
Does this help?