The paper includes two research parts: 1) Structure of the Tunichrome of Tunicates and its Role in Concentrating Vanadium: Tunicates (Urochorda) concentrate vanadium in their blood cells to a million times the concentration in sea water, but the structure of the vanadium compound remains unknown. We developed a simple isolation method with high recovery (80-90%) using methanol extraction and HPLC on polystyrene phases for peptides from Phallusia mammillata. The major component, tunichrome Pm-1, was analyzed by multiple spectroscopies and found to be a dipeptide composed of two L-β-(3,4,5-trihydroxyphenyl)alanine (Topa) molecules and a C-terminally bound trans-3,4,5-trihydroxystyrylamine. Native tunichrome in blood cells exists as a free peptide, not bound to vanadium. Minor components Pm-2 and Pm-3 are sequence isomers with one less hydroxyl group. Tunichromes are suggested to be involved in the vanadium-concentrating process. 2) Mixed Valent Nickel Thiolates with Integral and Nonintegral Metal Oxidation States: Thiolato and sulfidothiolato complexes of divalent nickel are of great interest due to their unusual structures and properties, especially relevant to nickel-containing enzymes (hydrogenases, CO-dehydrogenases) where nickel has planar coordination with up to four cysteine sulfur atoms and participates in redox processes. We previously reported the mixed-valent sulfidothiolatonickel complex [Ni₃S(SC₂H₅)₇] with nickel in an intermediate oxidation state of +1.25, showing that saturated alkanethiolato ligands can reduce nickel under mild conditions and stabilize low oxidation states. Here we report the syntheses and X-ray structural analyses of [Ni₄(SC₂H₅)₈Br] and [Ni₄(SC₃H₇)₈I], obtained from the direct reaction of [Ni₄(SR)₈] with the corresponding halogen.