Biomedical subjects

Niels H Damrauer

Publications and source records attributed to Niels H Damrauer.

3 recordsLinked to original sources

PubMed2006

Electron transfer driven by proton fluctuations in a hydrogen-bonded donor-acceptor assembly.

The temperature-isotope dependence of proton-coupled electron transfer (PCET) for a noncovalent molecular dyad is reported. The system consists of an excited-state Zn(II) porphyrin that transfers an electron to a naphthalene diimide acceptor through an amidinium-carboxylate interface. Two different isotope effects are observed for variant temperature regimes. A reverse isotope effect (i.e., kH/kD < 1) is observed as T approaches 120 K (kH/kD = 0.9, 120 K), whereas a normal isotope effect (i.e., kH/kD > 1) is recovered as the temperature is increased (kH/kD = 1.2, 300 K). The transition between these limits is smooth, with a crossover temperature of T approximately 160 K. These observations are in accordance with charge-transfer dynamics that are susceptible to bath-induced fluctuations in the proton coordinate.

Electron Transport↗

PubMed2006

General method for the dimension reduction of adaptive control experiments.

Adaptive femtosecond control experiments are expanding the possibilities for using laser pulses as photophysical and photochemical reagents. However, because of the large number of variables necessary to perform these experiments (usually 100-200), it has proven difficult to elucidate the underlying control mechanisms from the optimized pulse shapes. If adaptive control is to become a widespread tool for examining chemical dynamics, methods must be developed that reveal latent control mechanisms. This manuscript presents a generally applicable method for dimension reduction of adaptive control experiments based on partial least squares regression analysis (PLS) of the normalized covariance matrix of the total data set. When applied to experimental results obtained in our laboratory, it shows that only seven fundamental dimensions from an original 208-dimension search space are needed to account for approximately 90% of the variance in the observed fitness of 11,700 laser-pulse shapes explored during the optimization experiment. Furthermore, the seven dimensions have a remarkable regularity in their functional form. It is anticipated that this work will facilitate theoretical treatments directly linking the optimal fields to control mechanisms, allow quantitative comparisons of independent control results, and suggest new experimental methods for rapid adaptive searches.

Letter↗

PubMed2004

Proton-coupled electron transfer: a unifying mechanism for biological charge transport, amino acid radical initiation and propagation, and bond making/breaking reactions of water and oxygen.

Redox-driven proton pumps, radical initiation and propagation in biology, and small-molecule activation processes all involve the coupling of electron transfer to proton transport. A mechanistic framework in which to interpret these processes is being developed by examining proton-coupled electron transfer (PCET) in model and natural systems. Specifically, PCET investigations are underway on the following three fronts: (1) the elucidation of the PCET reaction mechanism by time-resolved laser spectroscopy of electron donors and acceptors juxtaposed by a proton transfer interface; (2) the role of amino acid radicals in biological catalysis with the radical initiation and transport processes of E. coli ribonucleotide reductase (RNR) as a focal point; and (3) the application of PCET towards small-molecule activation with emphasis on biologically relevant bond-breaking and bond-making processes involving oxygen and water. A review of recent developments in each of these areas is discussed.

Amino Acids↗