The molecules comprising the porphyrin family are the most versatile prosthetic groups in nature. Shuttling electrons in respiration, binding and transporting oxygen, and serving in the active sites of diverse redox enzymes and electron transport chains are only a few of the prominent activities of porphyrinic molecules. Porphyrins work in concert with a diverse array of other molecules, and synthetic model systems of porphyrin- mediated processes enable the molecular interactions to be probed and identified with exacting precision. Our long-term goals are to prepare synthetic porphyrin model systems and to gain deep insight into porphyrin- mediated biological processes. To achieve this goal requires the ability to construct systems having 3-dimensional order incorporating porphyrinic and accessory molecules. Our specific aims are to; 1). Investigate, refine, and broaden the scope of the high concentration aerobic porphyrin synthesis, in order to achieve an eclectic synthetic method with the simplicity and preparative-scale of the Adler method and the milk conditions and scope of the room temperature synthesis. 2) Develop a set of synthetic methods for preparing porphyrins bearing four different meso-substituents (ABCD-porphyrins). This methodology will provide detailed architectural control of the local porphyrin environment and enable study of phenomena mediated by porphyrins in conjunction with collections of other molecules, such as in electron transport chains. 3) Develop simple and rational routes with capabilities for meso- substitution in the spectrum of hydroporphyrins, such as chlorins, bacteriochlorins, isobacteriochlorins, corroles, and ultimately corphins. The methodology will lead to model studies of naturally occurring hydroporphyrins such as green hemes, sirohemss, F430 and ultimately vitamin B12, and enable fundamental studies of hydroporphyrin tautomerization. These routes will make versatile models of reduced porphyrins nearly as accessible as porphyrin model systems are now. 4) Investigate the generality of our new mild synthesis of magnesium porphyrins, extend it to natural and synthetic hydroporphyrins, and determine the thermodynamic stability of magnesium chelates of a spectrum of porphyrins and hydroporphyrins. Taken together these studies will lead to a general advancement in the state of the art of model systems of porphyrinic compounds and deepen our understanding of the fundamental chemistry and functional versatility of the essential and fascinating family of tetrapyrrolic macrocycles.