Patrik R. Callis

Bio: Patrik R. Callis is an academic researcher from Montana State University. The author has contributed to research in topics: Quenching (fluorescence) & Excited state. The author has an hindex of 37, co-authored 115 publications receiving 5113 citations. Previous affiliations of Patrik R. Callis include Washington University in St. Louis & Massachusetts Institute of Technology.

Tryptophan fluorescence shifts in proteins from hybrid simulations: an electrostatic approach

Abstract: We present hybrid quantum chemical−molecular dynamics computations on 15 partially hydrated proteins that support the view that the fluorescence wavelength maximum of a tryptophan (Trp) in a protein is determined almost entirely by the local electric field projection along the long axis of the indole ring, that is to say, an internal Stark effect. The response is 1.3 × 106 V cm-1/nm, with a shift to longer wavelength when the field forces electrons from the pyrrole to the benzene ring. Of 20 Trps simulated, representing a range of exposure to solvent, 15 are predicted within 10 nm of the experimental value. The findings should greatly aid the important task of finding effective methods for computing electrostatic fields and potentials within proteins.

Photophysics of indole derivatives : experimental resolution of La and Lb transitions and comparison with theory

Abstract: Fluorescence excitation and anisotropy spectra are presented for a set of methyl and methoxyindoles at -50 degreesC in propylene glycol glass. These spectra are interpreted in terms of two overlapping (pi)->(pi) * electronic transitions ( 1 L a and 1 L b ). Semiempirical molecular orbital calculations are presented to correlate with the observed spectral changes caused by methyl and methoxy substitution.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

Abstract: 6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

QM/MM Methods for Biomolecular Systems

Abstract: Combined quantum-mechanics/molecular-mechanics (QM/MM) approaches have become the method of choice for modeling reactions in biomolecular systems. Quantum-mechanical (QM) methods are required for describing chemical reactions and other electronic processes, such as charge transfer or electronic excitation. However, QM methods are restricted to systems of up to a few hundred atoms. However, the size and conformational complexity of biopolymers calls for methods capable of treating up to several 100,000 atoms and allowing for simulations over time scales of tens of nanoseconds. This is achieved by highly efficient, force-field-based molecular mechanics (MM) methods. Thus to model large biomolecules the logical approach is to combine the two techniques and to use a QM method for the chemically active region (e.g., substrates and co-factors in an enzymatic reaction) and an MM treatment for the surroundings (e.g., protein and solvent). The resulting schemes are commonly referred to as combined or hybrid QM/MM methods. They enable the modeling of reactive biomolecular systems at a reasonable computational effort while providing the necessary accuracy.

Measurement of two-photon excitation cross sections of molecular fluorophores with data from 690 to 1050 nm

Abstract: Measurements of two-photon fluorescence excitation (TPE) spectra are presented for 11 common molecular fluorophores in the excitation wavelength range 690 nm < λ < 1050 nm. Results of excitation by ∼100-fs pulses of a mode-locked Ti:sapphire laser are corroborated by single-mode cw Ti:sapphire excitation data in the range 710 nm < λ < 840 nm. Absolute values of the TPE cross section for Rhodamine B and Fluorescein are obtained by comparison with one-photon-excited fluorescence, assuming equal emission quantum efficiencies. TPE action cross sections for the other nine fluorophores are also determined. No differences between one-photon- and two-photon-excited fluorescence emission spectra are found. TPE emission spectra are independent of excitation wavelength. With both pulsed and cw excitation the fluorescence emission intensities are strictly proportional to the square of the excitation intensity to within ±4% for excitation intensities sufficiently below excited-state saturation.

Look Back at the U.S. Department of Energy's Aquatic Species Program: Biodiesel from Algae; Close-Out Report

Abstract: The Aquatic Species Program was a relatively small research effort intended to look at the use of aquatic plants as sources of energy. Its history dates back to 1978, but much of the research from 1978 to 1982 focused on using algae to produce hydrogen. The program switched emphasis to other transportation fuels, particularly biodiesel, beginning in the early 1980's. This report summarizes the research activities carried out from 1980 to 1996, with an emphasis on algae for biodiesel production.