Iron Mountain Incorporated (NYSE:IRM), Concert Pharmaceuticals Inc (NYSE:JMPC) and 58.com Inc (ADR) (NYSE:WUBA) are the day’s top gainers at midday trading. On the flip side are midday losers Community Health Systems (NYSE:CYH),  Merrimack Pharmaceuticals Inc (NASDAQ:MACK) and Turquoise Hill Resources Ltd (NYSE:TRQ).

Iron Mountain

Iron Mountain Climbs

Up +19.85%, Iron Mountain Incorporated (NYSE:IRM) is today’s top midday gainer. The boost is largely the result of after-hours trading yesterday after the company’s board approved its conversion to a real estate investment trust, REIT. Farallon Capital has increased its position in the data and information management firm across three quarters.

Concert Pharmaceuticals Inc (NYSE:JMPC), another Farallon Capital pick, takes the second spot on today’s list of midday gainers. Its price climbed +11.01%. Earlier this week, the clinical stage biopharmaceutical company said it will present at the JMP Securities Healthcare Conference in New York.

Taking the third spot on today’s list of gainers is 58.com Inc (ADR) (NYSE:WUBA), its price up +6.97%. On the 22nd, the Tiger Global pick announced $48.2 million in Q1 2014 revenues, a 103.3% from the same period the year before. Its price is up +27.41% YTD.

Community Health Dips

The share price of Community Health Systems (NYSE:CYH) fell -5.11%. The company is a new first quarter buy for Farallon Capital.

Merrimack Pharmaceuticals Inc (NASDAQ:MACK) slipped -5%. The firm presented study data this week, which has been quite volatile for the company’s stock. On Tuesday, it gained +6%, rebounding from a two-day plunge of nearly -15%. A long-time Farallon Capital holding, Merrimack is having a strong year and is up +34.31% in 2014.

Turquoise Hill Resources Ltd (NYSE:TRQ) holds the final spot on today’s list of midday losers. Its price dipped -3.81%. The possible explanation? A dispute with the Mongolian government over taxes, filed today. Billionaire hedge fund manager George Soros has had a position in the mineral exploration and development company across several quarters, and Ray Dalio has been in the mix since Q1 2013. TRQ’s share price has fallen -41.38% over the past year.