The Proton Center may have finally found both cheap power and a solid foundation in Harlem after a series of other deals went bust.

We’ve learned that the center, which will house energy-sucking tumor-smashing apparatus, is now in discussions to be located somewhere on the six-acre site bounded by E. 125th and E. 127th streets between Second and Third avenues.

The Proton Center participants are led by 21st Century Oncology and include Memorial Sloan Kettering, NYU, Mt. Sinai, Montefiore Medical Center and Continuum Health Partners, which encompasses Beth Israel, St. Luke’s and Roosevelt hospitals.

After being awarded the area by the city in October 2008, a 1.7-million-square-foot East Harlem Media, Entertainment & Cultural Center was to be developed by the Richman Group and others. So far, just a small residential building has risen.

The expected 120,000-square-foot Proton Center would become a heavy anchor so that its other planned uses may eventually be developed.

But finding a spot for the machine — which will reside mostly underground — and numerous treatment rooms has not been easy.

“They need a rectangle of about 40,000 square feet,” explained Mark Weiss of Newmark Grubb Knight Frank, the consortium’s broker, in August of 2012. Weiss did not return requests for comment regarding this location.

The nuclear medicine facility has been bouncing from site to site for many years. Negotiations have stretched from W. 57th, to E. 92nd, to Park Avenue and E. 125th Street, and most recently, as we reported last year, on another East Harlem block at 127th Street, owned by Alan Potemkin. Here, sources said, the eventual sticky wicket was the cost to get rid of the giant contraption if the parties ever split up.

On Tuesday, the state’s Power Authority, through the ReCharge New York program, awarded the Proton project 876 kilowatts of cheap juice in return for creating 82 jobs and making a whopping capital investment of $301,292,228.

The state’s Dept. of Health has already approved the device, designed by VOA Associates.

Most patients will be children — their growing vital organs will be spared by the focused radiation. There is more demand for this therapy than can be accommodated. The counsel for the Florida-based 21st Century Oncology did not return a call for comment.

A new record price-per-foot for a retail condominium is about to be set in Soho this week.

Between the Bricks has learned the 2,750-square-foot ground floor retail space at the otherwise residential 114 Prince will trade for $42 million, or $15,336 per foot. The lower level, with 1,400 square feet, can only be used for storage and offices.

The buyer, Bobby Cayre’s Aurora Capital Associates, should close any nanosecond to spread the green across the pond. Investment brokers Douglas Harmon and Adam Spies of Eastdil Secured have turned these bricks into a pot of gold for the Irish family sellers.

The current tenant, Karen Millen, will vacate by April, sources said, and Aurora will now be seeking its own tenant in an area where asking rents are $1,200 a foot.

The previous record was $15,100 per foot, paid for the 24,800-foot St. Regis Hotel retail, which had in-place leases.

No one returned calls for comment.

This week, another building closed that Harmon and Spies have now marketed three times in the last three years. Opposite Madison Square Park, the deal for 15 E. 26th St. includes eight floors with 150,000 square feet of offices.

The duo sold it in December 2010 from RREEF to Angelo, Gordon for $32,625,00; to Savanna in February 2012 for $57.75 million; and this week to Rockrose for $105 million. There are two vacant floors of more than 19,000 square feet each, and sources said Rockrose may move here, too.

Union Square is getting fitter.

A Reebok Fit Hub and Reebok CrossFit gym have leased 11,600 square feet at 1 Union Square West on the corner of E. 14th Street for a flagship store where Diesel will be burning out.

Jeremy Ezra and Yael Amron of RKF represented Reebok in the lease, while building owners  were represented in-house by Eugene Warren and William Abramson.

Asking rents in the streets around Union Square are $500 a foot.

The Fit Hub brings together sales of clothes and footwear with a CrossFit gym. The store will take up 4,800 square feet on the ground floor, while the workout area will have 6,800 square feet on the lower level.

“This is an area where there are health clubs and fitness-oriented apparel and footwear,” said Ezra. They are in the process of working with the Landmarks Preservation Commission to ensure the design of the windows and signage is in keeping with the historic structure.

There are two other Manhattan locations at 1132 Third Ave. and 420 Fifth Ave., and Fit Hub plans a roll-out to 10 beefy US locations.

As for Diesel, no one answered its office phones.

The residential division of Joseph Sitt’s Thor Equities is in contract to buy two apartment buildings at 120 and 125 Riverside Drive for “upward of $80 million,” our West Side spies tell us.

The historical properties, with curvy facades on the north corner of W. 84th Street, include 37 apartments in a nine-story building and 60 apartments in a 12-story building for a total of 110,000 square feet.

The company did not return calls for comment, and no brokerage information was available.