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1.  Energetics and Dynamics of the Low-Lying Electronic States of Constrained Polyenes: Implications for Infinite Polyenes 
The journal of physical chemistry. A  2013;117(7):1449-1465.
Steady-state and ultrafast transient absorption spectra were obtained for a series of conformationally-constrained, isomerically pure polyenes with 5–23 conjugated double bonds (N). These data and fluorescence spectra of the shorter polyenes reveal the N dependence of the energies of six 1Bu+ and two 1Ag− excited states. The 1Bu+ states converge to a common infinite polyene limit of 15,900 ± 100 cm−1. The two excited 1Ag− states, on the other hand, exhibit a large (~9000 cm−1) energy difference in the infinite polyene limit, in contrast to the common value previously predicted by theory. EOM-CCSD ab-initio and MNDO-PSDCI semi-empirical MO theories account for the experimental transition energies and intensities. The complex, multistep dynamics of the 11Bu+ → 21Ag− → 11Ag− excited state decay pathways as a function of N are compared with kinetic data from several natural and synthetic carotenoids. Distinctive transient absorption signals in the visible region, previously identified with S* states in carotenoids, also are observed for the longer polyenes. Analysis of the lifetimes of the 21Ag− states, using the energy gap law for nonradiative decay, reveals remarkable similarities in the N dependence of the 21Ag− decay kinetics of the carotenoid and polyene systems. These findings are important for understanding the mechanisms by which carotenoids carry out their roles as light-harvesting molecules and photoprotective agents in biological systems.
PMCID: PMC3584643  PMID: 23330819
Linear Polyene Spectroscopy; Forbidden States; Long Polyenes; Cis Polyenes; Molecular Orbital Theory; Energy Gap Law; Excited State Decay
2.  Energies of Low-Lying Excited States of Linear Polyenes 
The journal of physical chemistry. A  2008;112(49):12629-12636.
Room temperature absorption and emission spectra of the all-trans isomers of decatetraene, dodecapentaene, tetradecahexaene, and hexadecaheptaene have been obtained in a series of nonpolar solvents. The resolved vibronic features in the optical spectra of these model systems allow the accurate determination of S0 (11Ag-) → S2 (11Bu+) and S1 (21Ag–) → S0 (11Ag–) electronic origins as a function of solvent polarizability. These data can be extrapolated to predict the transition energies in the absence of solvent perturbations. The effects of the terminal methyl substituents on the transition energies also can be estimated. Franck–Condon maxima in the absorption and emission spectra were used to estimate differences between S0 (11Ag–) → S1 (21Ag–) and S0 (11Ag–) → S2 (11Bu+) electronic origins and “vertical” transition energies. Experimental estimates of the vertical transition energies of unsubstituted, all-trans polyenes in vacuum as a function of conjugation length are compared with long-standing multireference configuration interaction (MRCI) treatments and with more recent ab initio calculations of the energies of the 21Ag– (S2) and 11Bu+ (S2) states.
PMCID: PMC3629814  PMID: 19007144
4.  Does Glycosylation as a modifier of Original Antigenic Sin explain the case age distribution and unusual toxicity in pandemic novel H1N1 influenza? 
A pandemic novel H1N1 swine-origin influenza virus has emerged. Most recently the World Health Organization has announced that in a country-dependent fashion, up to 15% of cases may require hospitalization, often including respiratory support. It is now clear that healthy children and young adults are disproportionately affected, most unusually among those with severe respiratory disease without underlying conditions. One possible explanation for this case age distribution is the doctrine of Original Antigenic Sin, i.e., novel H1N1 may be antigenically similar to H1N1 viruses that circulated at an earlier time. Persons whose first exposure to influenza viruses was to such similar viruses would be relatively immune. However, this principle is not sufficient to explain the graded susceptibility between ages 20 and 60, the reduced susceptibility in children below age 10, and the unusual toxicity observed.
We collected case data from 11 countries, about 60% of all cases reported through mid-July 2009. We compared sequence data for the hemagglutinin of novel H1N1 with sequences of H1N1 viruses from 1918 to the present. We searched for sequence differences that imply loss of antigenicity either directly through amino acid substitution or by the appearance of sites for potential glycosylation proximal to sites known to be antigenic in humans. We also considered T-cell epitopes.
In our composite, over 75% of confirmed cases of novel H1N1 occurred in persons ≤ 30 years old, with peak incidence in the age range 10-19 years. Less than 3% of cases occurred in persons over 65, with a gradation in incidence between ages 20 and 60 years.
The sequence data indicates that novel H1N1 is most similar to H1N1 viruses that circulated before 1943. Novel H1N1 lacks glycosylation sites on the globular head of hemagglutinin (HA1) near antigenic regions, a pattern shared with the 1918 pandemic strain and H1N1 viruses that circulated until the early 1940s. Later H1N1 viruses progressively added new glycosylation sites likely to shield antigenic epitopes, while T-cell epitopes were relatively unchanged.
In this evolutionary context, Original Antigenic Sin exposure should produce an immune response increasingly mismatched to novel H1N1 in progressively younger persons. We suggest that it is this mismatch that produces both the gradation in susceptibility and the unusual toxicity. Several murine studies suggest specific cell types as a likely basis of the unusual toxicity. These studies also point to widely available pharmaceutical agents as plausible candidates for mitigating the toxic effects. The principle of Original Antigenic Sin modified by glycosylation appears to explain both the case age distribution and the unusual toxicity pattern of the novel H1N1 pandemic. In addition, it suggests pharmaceutical agents for immediate investigation for mitigation potential, and provides strategic guidance for the distribution of pandemic mitigation resources of all types.
PMCID: PMC3003248  PMID: 20059763
5.  Symmetry control of radiative decay in linear polyenes: Low barriers for isomerization in the S1 state of hexadecaheptaene 
The room temperature absorption and emission spectra of the 4-cis and all-trans isomers of 2,4,6,8,10,12,14-hexadecaheptaene are almost identical, exhibiting the characteristic dual emissions S1→S0 (21Ag− → 11Ag−) and S2→S0 (11Bu+ → 11Ag−) noted in previous studies of intermediate length polyenes and carotenoids. The ratio of the S1→S0 and S2→S0 emission yields for the cis isomer increases by a factor of ~15 upon cooling to 77 K in n-pentadecane. In contrast, for the trans isomer this ratio shows a two-fold decrease with decreasing temperature. These results suggest a low barrier for conversion between the 4-cis and all-trans isomers in the S1 state. At 77 K, the cis isomer cannot convert to the more stable all-trans isomer in the 21Ag− state, resulting in the striking increase in its S1→S0 fluorescence. These experiments imply that the S1 states of longer polyenes have local energy minima, corresponding to a range of conformations and isomers, separated by relatively low (2–4 kcal) barriers. Steady state and time-resolved optical measurements on the S1 states in solution thus may sample a distribution of conformers and geometric isomers, even for samples represented by a single, dominant ground state structure. Complex S1 potential energy surfaces may help explain the complicated S2→S1 relaxation kinetics of many carotenoids. The finding that fluorescence from linear polyenes is so strongly dependent on molecular symmetry requires a reevaluation of the literature on the radiative properties of all-trans polyenes and carotenoids.
PMCID: PMC2518222  PMID: 17284007
6.  Effect of Soybean Casein Digest Agar Lot on Number of Bacillus stearothermophilus Spores Recovered † 
In recent years it has become increasingly apparent that Bacillus stearothermophilus spores are affected by various environmental factors that influence the performance of the spores as biological indicators. One environmental factor is the recovery medium. The effect of different lots of commercial soybean casein digest agar on the number of colony-forming units per plate was examined in two series of experiments: (i) several lots of medium from two manufacturers were compared in single experiments, and (ii) paired media experiments with four lots of medium were carried out and yielded three-point survivor curves. The results demonstrate that commercial soybean casein digest agar is variable on a lot-to-lot basis. The variation was lowest when recovering unheated or minimally heated spores and increased greatly with the severity of heating.
PMCID: PMC243995  PMID: 16345822

Results 1-6 (6)