FACULTY & STAFF

Carlos Enrique Crespo Hernández

Assistant Professor of Chemistry
Office: Millis 219A
Office Tel. 216-368-1911

Physical Chemistry

Email: carlos.crespo [at] case.edu

B.S., University of Puerto Rico, San Juan Campus, 1995
Ph.D., University of Puerto Rico, San Juan Campus, 2002
NIH Postdoctoral Fellow, The Ohio State University (2002-05)
Research Associate of Chemistry, The Ohio State University (2005-06)

Curriculum Vitae (.pdf)


Research Interests: Ultrafast Spectroscopy, Biophysics, Organic Photochemistry and Photophysics, Analytical and Environmental Chemistry, Computational Chemistry, Chemical Dynamics and Kinetics.



Ultrafast Dynamics of Protein-Mediated DNA Damage and Repair Reactions

Ultraviolet (UV) radiation has profound deleterious effects on a vast variety of cellular functions. Ozone and other atmospheric gases absorb high-energy solar photons, significantly diminishing the UV irradiance at the earth's surface. Consequently, the flux of solar wavelengths shorter than 280 nm is very small and electronic excitation is mainly restricted to the nucleic acid bases. This is why much attention has been paid to the study of the excited state dynamics, photophysics, and photochemistry of DNA and its constituents.

Importantly, DNA does not exist in a cell in pure solution but is in intimate contact with proteins, lipids, and other biomolecules. In particular, protein-DNA interactions are ubiquitous in nature and of major biological importance. Recognition and binding of specific sites on DNA by proteins is central to many cellular functions such as transcription, replication, recombination, and repair. Proteins can bind and disrupt the helical structure of DNA by the formation of electrostatic, hydrophobic, stacking, and hydrogen-bonding interactions. In the past, there has been substantial evidence indicating that UV-induced DNA-protein cross-link reactions are important contributors to the deleterious effects of UV irradiation on cells. Yet, protein-DNA interactions could also facilitate repair of oxidative damage to DNA.

Understanding the light-induced mechanisms of protein-mediated DNA damage and repair is stimulating, but also complicated. Knowledge about the mechanistic aspects of UV-induced DNA-protein photophysics has not kept pace with advances in product characterization, synthetic, and structural understanding of these important biomolecular reactions. Despite great progress in the identification of the major mutagenic photoproducts created in DNA-protein complexes by UV light, and in experimental works showing the potential of amino acids to repair oxidative damage in DNA, there are still many gaps in our understanding of the elementary steps that control and govern these reactions. Our group benefits from the ability to directly observe excited state dynamics and reactive intermediate species using state-of-the-art femtosecond techniques and nanosecond laser systems to obtain solutions to these complex problems. Significant progress can be further obtained through the fruitful interplay between experiments and computational chemistry calculations.



Biophysical and Photochemical Studies of Semiconductor Nanocrystal-Biopolymer Conjugates

Research on fluorescent semiconductor nanocrystals or quantum dots (QDs) has evolved from science of electronic materials to biological applications. The new generations of QDs have far reaching potentials for studying intracellular processes, high-resolution cellular imaging, tumor targeting, and diagnostics. They are bright, do not degrade, and can be tuned over the entire visible and near infrared spectrum. These unique optical properties make them appealing as in vivo and in vitro fluorophores in a variety of biological investigations, in which traditional fluorescent labels based on organic molecules fall short of providing long-term stability and simultaneous detection of multiple signals.

Our group focuses on understanding the excited state dynamics and reactive intermediate species formed in QDs-biopolymer conjugates upon selective excitation of the nanocrystal. We also investigate the potential charge and energy transfer processes, and light-induced damage to the biopolymers, in photoexcited QDs-bioconjugates. This information is of fundamental importance for understanding the potential phototoxicity and/or biocompatibility of QDs-bioconjugates to in vivo applications. The long-term goal is to obtain comprehensive, molecular level understanding of the reaction pathways and intermediate reactive species produced in QDs-bioconjugates upon light excitation. Application of these investigations to the use of QDs-bioconjugates as energy donors or photosensitizers to generate damage in a site specific and controlled fashion would be explored, by exploiting the specific molecular recognition properties of biomolecules.



Photophysical and Photochemical Studies of Pharmaceutical and Personal Care Products in Aquatic Environments

Pharmaceutical and personal care products (PPCPs) are an emerging class of aquatic contaminants that have been increasingly detected in field samples in Europe and in the United States of America. There are several indications that photochemical degradation could be a central factor in determining the environmental fate of PPCPs. Most of these compounds contain aromatic, heteroatoms, and other functional groups that can either absorb solar radiation or react with photogenerated transient species produced in natural water. Because much of the pharmaceutical pollutants in surface water have already eluded the rigorous biodegradation environment of wastewater treatment, photochemical degradation may be expected to play a preponderant role than biodegradation in sunlit water. It has yet to be determined whether levels found in drinking water pose a human health risk, but finding these compounds in drinking and surface water has created a major concern due to potential low levels of action and widespread occurrence.

Our group efforts concentrate in unraveling the photophysical properties of selected PPCPs in aqueous environment; identify the reactive intermediate species involved in their photodegradation processes; quantify the transformation rates and identify the major photoproducts. In addition, we are interested in studying the reactivity of PPCPs to reactive oxygen species and natural organic matter.


Selected Publications