AZ Electronic Materials advanced after Merck KGaA agreed to buy the speciality chemicals company for about 1.6bn pounds, a 53 per cent premium to the stock's closing price on Wednesday.Gold miner Centamin rallied as miners rebounded following a sell-off earlier in the week. Sector peer Polymetal however fell after saying that it would not pay a special dividend this year owing to tough market conditions.Packaging firm DS Smith was higher after beating expectations in the first half with a 31% jump in operating profits. Investec raised its target price for the stock, while Numis Securities upgraded its rating from 'hold' to 'add'. Phoenix Group Holdings slumped after private equity firm TDR Capital said it has raised £145.2m from the sale of 22m shares in the firm.FTSE 250 - RisersAZ Electronic Materials SA (DI) (AZEM) 397.90p +51.35%Centamin (DI) (CEY) 42.31p +9.67%Alent (ALNT) 351.90p +5.04%Smith (DS) (SMDS) 312.60p +4.55%Premier Farnell (PFL) 214.60p +4.17%Howden Joinery Group (HWDN) 317.50p +3.56%Ultra Electronics Holdings (ULE) 1,828.00p +3.45%Synthomer (SYNT) 229.90p +3.42%RPS Group (RPS) 320.80p +3.35%Taylor Wimpey (TW.) 106.80p +3.09%FTSE 250 - FallersEssar Energy (ESSR) 71.00p -6.58%Phoenix Group Holdings (DI) (PHNX) 671.00p -4.69%Workspace Group (WKP) 485.60p -3.27%IP Group (IPO) 172.00p -2.82%Ophir Energy (OPHR) 321.00p -2.52%Amlin (AML) 427.70p -2.22%Computacenter (CCC) 645.00p -2.20%Polymetal International (POLY) 489.80p -2.14%Bwin.party Digital Entertainment (BPTY) 120.00p -2.12%Savills (SVS) 627.50p -1.95%RD