Marcetta York Darensbourg is an American inorganic chemist. She is a Distinguished Professor of Chemistry at Texas A&M University. Her current work focuses on iron hydrogenases and iron nitrosyl complexes.

Early life[edit]

Marcetta Bernice (York) Darensbourg was born May 4, 1942, in Artemus, Kentucky. She is daughter to school teachers, Atlas H. York, and Elsie Walton York. She has an older sister named Mary Lucille York, and a younger brother named Larry Hercules York. Darensbourg attended a local high school named Knox Central High School in Barbourville, Kentucky. In high school, she was a studious pupil and was a member of the band, choir, and cheerleading team. This is where Darensbourg met her role model, Mrs. Bolton. Mrs. Bolton taught biology, physics, and chemistry which interested Darensbourg. One of the reasons Darensbourg wanted to go into science and teach was from the great influence that Mrs. Bolton left on her.^[1]

Education[edit]

Darensbourg received a B.S. in Chemistry from Union College in 1963, and a Ph.D. in inorganic chemistry from the University of Illinois under the guidance of Theodore L. Brown in 1967.^[1] Her doctoral work focused on the kinetic studies of organolithium reactions.^[2]

Career[edit]

Darensbourg was an assistant professor at Vassar College from 1967to 1969. From 1971 to 1982, she taught at Tulane University, attaining the rank of professor. In 1982, Marcetta Darensbourg was appointed professor at Texas A&M University together with Donald J. Darensbourg. She was subsequently awarded the title of Distinguished Professor in 2010.^[3] Her research interests include bimetallic hydrogenase enzymes containing CO and CN ligands.

Darensbourg is a member of the board of Inorganic Syntheses,^[4] where she also served as the editor-in-chief of volume 32.^[5] In 2011, she was elected fellow of the American Academy of Arts and Sciences.^[6]

Research projects[edit]

Organolithium chemistry[edit]

Darensbourg investigated certain kinetic aspects of organolithium compounds. During the course of these studies, the kinetics of the rate-determining step of tert-butyllithium dissociation from tetramer to a dimer were analyzed.^[7] Using 7Li nuclear magnetic resonance (NMR), the study delineates the rate-determining step of the equilibrium of the tert-butyllithium mixture, revealing that the dissociation from tetramer to dimer is key. Notably, the dissociation rate was found to be significantly affected by the solvent used, and the dissociation rate of toluene was significantly faster than cyclopentane. The findings also highlight the role of stereoconfiguration in these reactions, where tert-butyllithium exhibits a uniquely slow intermolecular exchange rate compared to other alkyl lithium compounds due to its larger size. It has been observed that the presence of even a small number of bases like triethylamine greatly accelerates the exchange rate.^[7] Using mass spectroscopy, the existence of cross-association with other organolithium species in the vapor phase could also be observed.^[7]

Metal carbonyl chemistry[edit]

Darensbourg's interest in charge distribution molecules that could be probed with reactivity led to her work on mapping nucleophilic attack on metal carbonyls. Infrared, nuclear magnetic resonance and electronic spectroscopy of some carbene pentacarbonyl complexes of chromium(0) and tungsten(0) indicated that carbene ligands are better sigma donors than a carbonyl ligand, while simultaneously behaving as strong pi acceptors.^[8] Substitutions of iron and cobalt sites were made to see how the CO strength force constants affected the nucleophilic attacks. The substitutions illustrated that the nucleophilic attacks always occurred at the CO group with the greater force constant when there is a choice of carbonyl groups present in a molecule.^[9]

Hydrogenase mimics[edit]

Darensbourg has pioneered the development of synthetic mimics of hydrogenase enzymes. These include synthetic complexes featuring Fe-based organometallics species, which serve as precursor for producing iron only Hydrogenase enzyme active site. These enzymes are capable of carry out reaction even in the absence of the protein-based active site organization^[10] or carry out the proton production with high efficiencies. However, these hydrogenase enzymes were found to be highly sensitive with oxygen (O₂), which can over oxidize and inactivate them. Even after the oxygen was removed, they do not regain catalytic activity immediately, requiring multiple steps to do so.^[11]

In 2020, Darensbourg et al. reported a variety of characterizations of Ni-Fe based hydrogenase species, which eventually encounter oxygen damage during their lifetime. Although some hydrogenase catalysts remain tolerant to oxygen damage, a majority of such catalysts typically undergo irreversible damage upon exposure. Darensbourg et al. reported an overview of sustainable water splitting technologies in which the hydrogenase species can be reductively repaired. Modifications of single atoms within hydrogenase active sites allowed for customizable activities, oxygen tolerance, and structures of the catalysts, permitting practical applications of enzymes and fragile biomimetrics of the active sites. Studies of a [NiFeSe]-H₂ase active site presented new applications for selenium in hydrogenase enzymes, as the complex exhibited a high hydrogen-processing catalytic ability and a relatively quick recovery from oxygen damage.^[12]

Metallodithiolates chemistry[edit]

In the beginning of 2017, Darensbourg shifted her focus to studying the metallodithiolates ligands, which act as building blocks for the synthesis of various bimetallic enzyme active sites. The ligands can act as a catalyst to carry out different reactions, depending on which transition metal being at the center.^[13]

Darensbourg et al. reported that metallodithiolates ligands with nickel centers can increase the electron density of bonds such as Fe-S, allowing them to be cleaved easily.^[14] Darensbourg et al. also determined that this nickel center complex associated with a lead atom also plays an important role in the addition of CO and ethylene in the Suzuki-Miyaura reaction, which couples the organic compounds of boron and the halides, along alkyl halides and alkylboranes.^[15] Furthermore, with the cCobalt center, the metallodithiolates ligands can catalyze the transfer of NO and nitrosylate moieties, which allows the glycosidase conjugation of dinitrosyl iron complexes. With this conjugation, other carbohydrates can achieve higher potential in attaching for drug delivery.^[7]

Molecular Magnetism[edit]

In 2023, Darensbourg began exploring metallodithiolates in the field of molecular magnetism. Seeing that few publications had reported analyses of metal-based linkers with sulfur bridge ligands, Darensbourg et al. characterized a paramagnetic nitrosylated iron complex with N₂S₂ ligands.^[16]

In the complex, the [Fe(NO)]²⁺ unit lies centered above the N₂S₂ field, exhibiting strong antiferromagnetic coupling to triplet NO^-. Density Functional Theory (DFT) computations indicate that the Fe spin stabilizes by delocalizing onto the surrounding dithiolate sulfurs.^[17] In expectation of spin delocalization of bimetallic derivatives upon interactions with sulfur, Darensbourg et al. performed syntheses of various sulfur-bridged multimetallic complexes.^[16]

Darensbourg et al. reported that reactions of the paramagnetic (NO)Fe(N₂S₂) with [M(CH₃CN_n][BF₄]₂ salts forms a stairstep bond arrangement with square planar MS₄ conformations. Reactions of the nitrosylated iron complex were conducted with metal salts composed of Ni^II, Pd^II, and Pt^II. Darensbourg et al. reported that each tri-metallic complex demonstrated similar nitrosyl stretching values in IR spectroscopy despite differences in magnetic properties. Magnetic susceptibility and DFT calculations additionally showed that each of the {Fe(NO)}⁷ units exhibited antiferromatic coupling and that each N₂S₂ ligand engaged in a superexchange interaction with the bimetallic derivatives. The interactions presented by each metal ion displayed a trend of increasing covalency in the order of Ni^II << Pd^II << Pt^II. Upon comparisons of the coupling strengths of each Nickel-sulfur-bridged multimetallic complex, Darensbourg et al. concluded that the antiferromatic coupling of each Fe(NO) spin center was facilitated by an intricate d-orbital overlap with the NI₂S₂ plane. ^[16]

Darensbourg et al. explained that the antiferromatic coupling of Fe(NO) presented new strategies for obtaining strong magnetic exchange within metallodithiolate complex through ⁴d and ⁵d orbital interactions. In place of steric effects, differences in the metal ion identity play roles in the electronic effects of each metal-sulfur magnetic interaction. Through combinations of various paramagnetic metallodithiolate donors and metal receivers, a vast collection of thiolate-bridged multimetallic complexes can be prepared with different magnetic communication strengths. ^[16]

The wide variety of possible sulfur-bridged multimetallic complexes presents many opportunities for bioinorganic chemistry. Darensbourg et al. indicated potential for the development of ⁿd-⁴f complexes, of which some can be used as single-molecule magnets. Interactions between orbitals with even higher energies allows for the customization of modern biocatalysts in evolutionary biology.^[16] The improved tunability of such biocatalysts enables the synthesis of catalysts exhbiting long-term sustainability. ^[17]

Awards[edit]

Most recently, Darensbourg has been awarded with the American Chemical Society Willard Gibbs Medal Award, a highly prestigious award recognizing the contributions of a chemist to the field.^[18] In 2018, Darensbourg was recognized as the SEC professor of the year.^[19] Darensbourg was also awarded the American Chemical Society Award in Organometallic Chemistry in 2017 for her application of organometallic chemistry to hydrogenase enzyme active sites and synthetic analogues.^[20] In 2016, Darensbourg received awards for her teaching and mentoring abilities at both Texas A&M University and UCLA.^[21]

External links[edit]

Voices of Inorganic Chemistry Interview - Donald J. Darensbourg and Marcetta Y. Darensbourg (YouTube link)

References[edit]