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1.  Dynamic Localization of Electronic Excitation in Photosynthetic Complexes Revealed with Chiral Two-Dimensional Spectroscopy 
Nature communications  2014;5:3286.
Time-resolved ultrafast optical probes of chiral dynamics provide a new window allowing us to explore how interactions with such structured environments drive electronic dynamics. Incorporating optical activity into time-resolved spectroscopies has proven challenging due to the small signal and large achiral background. Here, we demonstrate that two-dimensional electronic spectroscopy can be adapted to detect chiral signals and that these signals reveal how excitations delocalize and contract following excitation. We dynamically probe the evolution of chiral electronic structure in the light harvesting complex 2 of purple bacteria following photoexcitation by creating a chiral two-dimensional mapping. The dynamics of the chiral two-dimensional signal directly reports on changes in the degree of delocalization of the excitonic state following photoexcitation. The mechanism of energy transfer in this system may enhance transfer probability due to the coherent coupling among chromophores while suppressing fluorescence that arises from populating delocalized states. This generally applicable spectroscopy will provide an incisive tool to probe ultrafast transient molecular fluctuations that are obscured in non-chiral experiments.
PMCID: PMC3976994  PMID: 24504144
2.  Timescales of Coherent Dynamics in the Light Harvesting Complex 2 (LH2) of Rhodobacter sphaeroides 
The initial dynamics of energy transfer in the light harvesting complex 2 from Rhodobacter sphaeroides were investigated with polarization controlled two-dimensional spectroscopy. This method allows only the coherent electronic motions to be observed revealing the timescale of dephasing among the excited states. We observe persistent coherence among all states and assign ensemble dephasing rates for the various coherences. A simple model is utilized to connect the spectroscopic transitions to the molecular structure, allowing us to distinguish coherences between the two rings of chromophores and coherences within the rings. We also compare dephasing rates between excited states to dephasing rates between the ground and excited states, revealing that the coherences between excited states dephase on a slower timescale than coherences between the ground and excited states.
PMCID: PMC3714110  PMID: 23878622
Spectroscopy; Excited States; Biophysics; Dynamics
4.  Indoor fungal concentration in the homes of allergic/asthmatic children in Delhi, India 
Allergy & Rhinology  2011;2(1):21-32.
Allergy to fungi has been linked to a wide range of illnesses, including rhinitis and asthma. Therefore, exposure to fungi in home environment is an important factor for fungal allergy. The present study was aimed to investigate types of airborne fungi inside and outside the homes of asthmatic children and control subjects (nonasthmatic children). The dominant fungi were evaluated for their quantitative distribution and seasonal variation. The air samples were collected from indoors and immediate outdoors of 77 selected homes of children suffering from bronchial asthma/allergic rhinitis using Andersen volumetric air sampler. The isolated fungal genera/species were identified using reference literature, and statistical analysis of the dominant fungi was performed to study the difference in fungal concentration between indoor and immediate outdoor sites as well as in between different seasons. A total of 4423 air samples were collected from two indoor and immediate outdoor sites in a 1-year survey of 77 homes. This resulted in the isolation of an average of 110,091 and 107,070 fungal colonies per metric cube of air from indoor and outdoor sites, respectively. A total of 68 different molds were identified. Different species of Aspergillus, Alternaria, Cladosporium, and Penicillium were found to be the most prevalent fungi in Delhi homes, which constituted 88.6% of the total colonies indoors. Highest concentration was registered in autumn and winter months. Total as well as dominant fungi displayed statistically significant differences among the four seasons (p < 0.001). The largest number of isolations were the species of Aspergillus (>40% to total colony-forming units in indoors as well as outdoors) followed by Cladosporium spp. Annual concentration of Aspergillus spp. was significantly higher (p < 0.05) inside the homes when compared with outdoors. Most of the fungi also occurred at a significantly higher (p < 0.001) rate inside the homes when compared with immediate outdoors. Asthmatic children in Delhi are exposed to a substantial concentration of mold inside their homes as well as immediate outdoor air. The considerable seasonal distributions of fungi provide valuable data for investigation of the role of fungal exposure as a risk for respiratory disorders among patients suffering from allergy or asthma in Delhi.
PMCID: PMC3390125  PMID: 22852111
Asthma; Delhi; indoor fungi; prevalence; respiratory allergy; seasonal variation

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