Three U.S.-based scientists won this year's Nobel Prize in chemistry on Wednesday for developing powerful computer models that any researcher can use to understand complex chemical interactions and create new drugs.

'It was just me being in the right place at the right time and maybe having a few good ideas.'- Michael Levitt

Research in the 1970s by Martin Karplus, Michael Levitt and Arieh Warshel has led to programs that unveil chemical processes such as how exhaust fumes are purified or how photosynthesis takes place in green leaves, the Royal Swedish Academy of Sciences said. That kind of knowledge makes it possible to optimize catalysts for cars or design drugs and solar cells.

The strength of the winning work is that it can be used to study all kinds of chemistry, the academy said.

"This year's prize is about taking the chemical experiment to cyberspace," said Staffan Normark, the academy's secretary.

All three scientists became U.S. citizens.

Levitt, 66, was born in South Africa and is a British, U.S., and Israeli citizen. He is a professor at Stanford University School of Medicine.

Warshel, 72, was born in Israel and is a U.S. and Israeli citizen affiliated with the University of Southern California in Los Angeles.

Work done before age 20

Levitt told The Associated Press the award recognized him for work he had done when he was 20, before he even had his PhD.

"It was just me being in the right place at the right time and maybe having a few good ideas," he said, speaking by telephone from his home in Stanford, California.

"It's sort of nice in more general terms to see that computational science, computational biology is being recognized," he added. "It's become a very large field and it's always in some ways been the poor sister, or the ugly sister, to experimental biology."

Jokingly, he said the biggest immediate impact of the Nobel Prize would be his need for dance lessons before appearing at the Nobel banquet.

"I would say the only real change in my life is I need to learn how to dance because when you go to Stockholm you have to do ballroom dancing," Levitt said. "This is the big problem I have right now."

Karplus told the AP the 5 a.m. call from the Nobel judges had him worried that the caller might be bearing bad news.

"Usually you think when you get a call at 5 o'clock in the morning it's going to be bad news, you know, something's happened. My daughter, you know, who is in Israel, might have been run over by a car or something or other.

"But it turned out to be good news and, after a while, I finally understood it was a call from Sweden and . I had been awarded a Nobel Prize in chemistry with two other people," Karplus said.

Warshel, speaking by telephone to a news conference in Stockholm, said he was "extremely happy" to have been woken up in the middle of the night in Los Angeles to find out he would share the $1.2 million prize, and looks forward to collecting it in the Swedish capital.

"In short, what we developed is a way which requires computers to look, to take the structure of the protein and then to eventually understand how exactly it does what it does," Warshel said.

Blend of quantum and Newtonian physics

When scientists wanted to simulate complex chemical processes on computers, they used to have to choose between software that was based on quantum physics, which applies on the scale of an atom, or classical Newtonian physics, which operates at larger scales. The academy said the three laureates developed computer models that "opened a gate between these two worlds."

While quantum mechanics is more accurate, it's impossible to use on large molecules because the equations are too complex to solve. By using quantum mechanics only for key parts of molecules and classical physics for the rest, the blended approach delivers the accuracy of the quantum approach with manageable computations.

Working together at Harvard in the early 1970s, Karplus and Warshel developed a computer program that brought together classical and quantum physics. Warshel later joined forces with Levitt at the Weizmann institute in Rehovot, Israel, and at the University of Cambridge in Britain, to develop a program that could be used to study enzymes.

Used for drug design, screening

Jeremy Berg, a professor of computational and systems biology at the University of Pittsburgh, said the winning work gives scientists a way to understand complicated reactions that involve thousands to millions of atoms.

"There are thousands of laboratories around the world using these methods, both for basic biochemistry and for things like drug design," said Berg, former director of the National Institute of General Medical Sciences in Bethesda.

Many drug companies use computer simulations to screen substances for their potential as medicines, which lets them focus their chemistry lab work on those that look promising, he said.

Marinda Li Wu, president of the American Chemical Society, was equally enthusiastic about the award.

"I think it's fabulous," she said in a telephone interview. `'They're talking about the partnering of theoreticians with experimentalists, and how this has led to greater understanding."

That is "bringing better understanding to problems that couldn't be solved experimentally," she said. "We're starting as scientists to better understand things like how pharmaceutical drugs interact with proteins in our body to treat diseases. This is very, very exciting."

Earlier this week, three Americans won the Nobel Prize in medicine for discoveries about how key substances are moved around within cells and the physics award went to British and Belgian scientists whose theories help explain how matter formed after the Big Bang.

The Nobel Prize for Literature will be awarded Thursday and the winner of the Nobel Peace Prize will be announced on Friday.

Nobel chemistry facts

This year's prize: Chemical reactions occur at lightning speed; electrons jump between atomic nuclei, hidden from the prying eyes of scientists. The 2013 prize winners in chemistry have made it possible to map the mysterious ways of chemistry by using computers. Detailed knowledge of chemical processes makes it possible to optimize catalysts, drugs and solar cells.
Award history: 104 Nobel Prizes in chemistry have been awarded to 162 individuals from 1901-2012. Frederick Sanger won the prize twice. Linus Pauling is the only person to have been awarded two unshared Nobel Prizes, one of which was chemistry in 1954. He was awarded the Peace prize eight years later.
Famous winners:: The Curies were the most successful "Nobel Prize family." The husband-and-wife partnership of Marie Curie and Pierre Curie were awarded the 1903 Nobel Prize in Physics. Marie Curie herself won the 1911 chemistry prize. Their daughter Irene Joliot-Curie was awarded the 1935 Nobel Prize in Chemistry, together with her husband, Frederic Joliot.
Wartime prizes: Adolf Hitler forbade two German winners from receiving the Chemistry prize
 Richard Kuhn in 1938 and Adolf Butenandt in 1939. -Reuters