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First 'snapshots' of electronic structure of a manganese complex related to water-splitting in photosynthesis
ScienceDaily (Nov. 9, 2012) ? Together with a large international research team, Johannes Messinger of Ume? University in Sweden has taken another step toward an understanding of photosynthesis and developing artificial photosynthesis. With a combination of a x-ray free-electron laser and spectroscopy, the team has managed to see the electronic structure of a manganese complex, a chemical compound related to how photosynthesis splits water.
The experiments used the Linac Coherent Light Source (LCLS), which is a free-electron x-ray laser facility at Stanford University in the US. The wavelength of the laser is roughly the same as the breadth of an atom, and each pulse of light lasts 50 femtoseconds (10-15). This is an extremely short interval of time: there are more femtoseconds in one second than there are seconds in a person's life. Such extremely short wavelengths and short light pulses constitute ideal conditions for imaging chemical reactions with atomic resolution at room temperature while the chemical reactions are ongoing.
The research group has previously used LCLS to perform structural analyses of isolated photosynthesis complexes from plants' photosystem II at room temperature. Now the group has combined the method with spectroscopy and is the first team to succeed in seeing at LCLS the electronic structure of a manganese complex similar to that found in photosystem II. Manganese is a transitional metal that, together with calcium and oxygen, forms the water-splitting catalyst in photosystem II.
A very simple example of a spectrometer is a prism, which separates sunlight into all the colors of the rainbow. The spectrometer used in this study functions in a similar manner, but with a group of 16 specialized crystals that diffract the x-rays emitted from the sample in resonse of being excited by an x-ray pulse onto a detector array.
To the delight of the scientists, the manganese compounds remained intact long enough for them to observe detailed information about the electronic structure before the compounds were destroyed by the very intense X-ray laser beam.
"Having both structural information and spectroscopic information means that we can much better understand how the structural changes of the whole complex and the chemical changes on the active surface of the catalysts work together to enable the enzymes to perform complex chemical reactions at room temperature," says Johannes Messinger, professor at the Department of Chemistry at Ume? University.
The chemical reaction the research group aims to understand is the splitting of water in photosystem II, as this understanding is also key for developing artificial photosynthesis- that is, for building devices for producing hydrogen from sunlight and water. To be able to exploit sunlight for producing fuels that can be stored and the used when needed would help solve the world's ever-more acute energy problems.
The new research findings are being published in the journal Proceedings of the National Academy of Sciences, PNAS.
Two major research projects at Ume? University are focusing on the development of artificial photosynthesis by imitating plants' very successful way of exploiting solar energy. Both projects ("solar fuels" and "artificial leaf") are directed by Johannes Messinger, professor at the Department of Chemistry at Ume? University.
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The above story is reprinted from materials provided by Ume? University.
Note: Materials may be edited for content and length. For further information, please contact the source cited above.
Journal Reference:
- R. Alonso-Mori, J. Kern, R. J. Gildea, D. Sokaras, T.-C. Weng, B. Lassalle-Kaiser, R. Tran, J. Hattne, H. Laksmono, J. Hellmich, C. Glockner, N. Echols, R. G. Sierra, D. W. Schafer, J. Sellberg, C. Kenney, R. Herbst, J. Pines, P. Hart, S. Herrmann, R. W. Grosse-Kunstleve, M. J. Latimer, A. R. Fry, M. M. Messerschmidt, A. Miahnahri, M. M. Seibert, P. H. Zwart, W. E. White, P. D. Adams, M. J. Bogan, S. Boutet, G. J. Williams, A. Zouni, J. Messinger, P. Glatzel, N. K. Sauter, V. K. Yachandra, J. Yano, U. Bergmann. Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode. Proceedings of the National Academy of Sciences, 2012; DOI: 10.1073/pnas.1211384109
Note: If no author is given, the source is cited instead.
Disclaimer: Views expressed in this article do not necessarily reflect those of ScienceDaily or its staff.
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Pakistan's minority Hindus feel under attack
In this Oct. 4, 2012 photo, Hindu woman Pathani shows that attackers ripped her gold earrings at a local temple in Karachi, Pakistan. An attack on the Hindu temple on the outskirts of Pakistan?s largest city took place in late September on the Day of Love for the Prophet_and residents fear it will not be the last attack. It was the latest in a rising tide of violence and discrimination against Hindus in the 95 percent Muslim country, where Islamic extremism is growing. (AP Photo/Fareed Khan)
In this Oct. 4, 2012 photo, Hindu woman Pathani shows that attackers ripped her gold earrings at a local temple in Karachi, Pakistan. An attack on the Hindu temple on the outskirts of Pakistan?s largest city took place in late September on the Day of Love for the Prophet_and residents fear it will not be the last attack. It was the latest in a rising tide of violence and discrimination against Hindus in the 95 percent Muslim country, where Islamic extremism is growing. (AP Photo/Fareed Khan)
FILE- In this March 26, 2012, file photo, a Hindu mother Sulachhani Bai talks with reporters in Islamabad, Pakistan about her daughter who disappeared from her home in a small village in Pakistan. A few hours later the girl's father got a call telling him his daughter, a Hindu, had converted to Islam in order to marry a Muslim boy. It was the latest in a rising tide of violence and discrimination against Hindus in this 95 percent Muslim country, where Islamic extremism is growing. Pakistan?s Hindu community says it faces forced conversions of Hindu girls to Islam, a lack of legal recognition for their marriages, discrimination in services and physical abuse when they venture into the streets. (AP Photo/B.K. Bangash, File)
In this Oct. 4, 2012 photo, Ragu Lal, member of Pakistani Hindu community shows remains of a worship idol smashed by attackers, at a local temple in Karachi, Pakistan. An attack on the Hindu temple on the outskirts of Pakistan?s largest city took place in late September on the Day of Love for the Prophet_and residents fear it will not be the last attack. It was the latest in a rising tide of violence and discrimination against Hindus in the 95 percent Muslim country, where Islamic extremism is growing. (AP Photo/Fareed Khan)
In this Oct. 4, 2012 photo, Pakistani Hindus gather at Sri Krishna Ram temple in Karachi, Pakistan. They told The Associated Press that attackers came after dusk and chanted into the night sky ?Kill the Hindus, kill the children of the Hindus,? as they smashed religious icons, ripped golden bangles off women?s arms and flashed pistols during an attack on the Hindu temple on the outskirts of Pakistan?s largest city in late September_and residents fear it will not be the last attack. It was the latest in a rising tide of violence and discrimination against Hindus in the 95 percent Muslim country, where Islamic extremism is growing. (AP Photo/Fareed Khan)
KARACHI, Pakistan (AP) ? They came after dusk and chanted into the night sky "Kill the Hindus, kill the children of the Hindus," as they smashed religious icons, ripped golden bangles off women's arms and flashed pistols. It wasn't the first time that the Hindu temple on the outskirts of Pakistan's largest city was attacked, and residents here fear it will not be the last.
"People don't consider us as equal citizens. They beat us whenever they want," said Mol Chand, one of the teenage boys gathered at the temple. "We have no place to worship now."
It was the second time the Sri Krishna Ram temple has been attacked, and this time the mob didn't even bother to disguise their faces. The small temple, surrounded by a stone wall, is a tiny religious outpost in a dusty, hardscrabble neighborhood so far on the outskirts of the city that a sign on the main road wishes people leaving Karachi a good journey.
Local Muslim residents blamed people from a nearby ethnic Pashtun village for the attack, which took place in late September on the Day of Love for the Prophet, a national holiday declared by the government in response to an anti-Islam film made in the U.S. No one was seriously injured in the attack.
It was the latest in a rising tide of violence and discrimination against Hindus in this 95 percent Muslim country, where Islamic extremism is growing. Pakistan's Hindu community says it faces forced conversions of Hindu girls to Islam, a lack of legal recognition for their marriages, discrimination in services and physical abuse when they venture into the streets.
The story of the Hindu population in Pakistan is one of long decline. During partition in 1947, the violent separation of Pakistan and India into separate countries, hundreds of thousands of Hindus opted to migrate to India where Hinduism is the dominant religion. Those that remained and their descendants now make up a tiny fraction of Pakistan's estimated 190 million citizens, and are mostly concentrated in Sindh province in the southern part of the country.
Signs of their former stature abound in Karachi, the capital of Sindh. At the 150-year-old Swami Narayan Temple along one of the city's main roads, thousands of Hindus gather during the year to celebrate major religious holidays. Hindus at the 200-year-old Laxmi Narain Temple scatter the ashes of their cremated loved ones in the waters of an inlet from the Arabian Ocean.
But there are also signs of how far the community has fallen. Residents in a city hungry for land have begun to build over Hindu cemeteries, the community's leaders say. Hindus helped build Karachi's port decades ago, but none work there now.
Estimates of the size of the Hindu population in Pakistan are all over the map ? from 2.5 million or 10 million in Sindh province alone to 7 million across the country ? a reflection of the fact that the country hasn't had a census since 1998.
It isn't just Hindus who are facing problems. Other minorities like Christians, the mystical Muslim branch of Sufis and the Ahmadi sect have found themselves under attack in Pakistan, where the rise of Muslim fundamentalists has sometimes unleashed a violent opposition against those who don't follow their strict religious tenets.
The discrimination has prompted some Hindus to leave for India, activists warn, though the extent is not known. Around 3,000 Hindus left this year, part of a migration that began four years ago, sparked by discrimination and a general rise in crime in Sindh, said DM Maharaj, who heads an organization to help Hindus called Pakistan Hindu Sabha.
He said he recently talked to a group of Hindus preparing to move to India from rural Sindh, complaining that they can't eat in Muslim restaurants or that Muslim officials turned them down for farming loans. Even during recent floods, they said Muslims did not want them staying in the same refugee camps.
Other Hindu figures such as provincial assembly member Pitamber Sewami deny there's a migration at all, in a reflection of how sensitive the issue is. Earlier this year, there were a string of reports in Pakistani media about Hindus leaving the country, sparking a flurry of promises by Pakistani officials to investigate.
In India, a Home office official said the Indian government noticed an upward trend of people coming from Pakistan but called reports of Pakistanis fleeing to India "exaggerated." He said he does not have exact figures on how many Pakistani Hindus have stayed in India after entering the country on tourist visas. The official spoke on condition of anonymity due to the sensitivity of the topic.
There's more of a consensus of the seriousness of the problem of forced conversion of Hindus.
Zohra Yusuf, the president of the Human Rights Commission of Pakistan says the pattern goes like this: A Hindu girl goes missing and then resurfaces days or weeks later married to a Muslim boy. During court hearings to determine whether the conversion was voluntary, students from nearby Islamic schools called madrassas often flood the room, trying to intimidate the judges by chanting demands that the conversion be confirmed.
Maharaj says he's tried to intervene in roughly 100 cases of forced conversions but has only succeeded in returning a girl safely back to her family once. If a girl decides to renounce Islam and return to Hinduism, she could be signing a death warrant for herself and her family even if her conversion was forced.
The Hindu community has also been hurt by a lack of unity within its ranks. Hindu society within Pakistan and elsewhere has historically been divided by caste, a system of social stratification in which the lower castes are often seen as inferior. Members of the lower castes in Pakistan say it wasn't until two girls from a high-caste family were forcibly converted this year that high-caste Hindus took the issue seriously, although it's been happening for years.
"We always fight our war ourselves," said Bholoo Devjee, a Hindu activist from Karachi, speaking about the lower castes.
In recent months the government has begun to take the concerns of the Hindu community more seriously. In Sindh province, legislators proposed a law to prevent forced conversions in part by implementing a waiting period before a marriage between a Hindu and a Muslim can go forward, and there's discussion about proposing such a law on the national level as well.
In the case of the Sri Krishna Ram temple, law enforcement authorities opened a blasphemy case against the people who rampaged through the building. But residents here are skeptical that these developments signify any long-term improvement in their plight. Weeks after the incident no arrests have been made, and the Hindus complain that no high-ranking Hindu officials have come to visit them or help them get compensation.
Sunda Maharaj, the spiritual leader at the temple, which was first attacked in January 2011, said he and the other residents do not want to move to India. "We are Pakistani," he said.
But he would like more help from the government, specifically a checkpoint to stop people from getting close to the temple and money for the Hindus to buy weapons.
"Next time anyone comes we can kill them or die defending our temple," he said.
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Follow Rebecca Santana on Twitter (at)ruskygal.
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Associated Press writers Adil Jawad in Karachi and Nirmala George in New Delhi contributed to this report.
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