Stock futures sink as bank concerns swell
* Deutsche Bank's quarterly loss of about $6.4 billion and a brokerage's view that HSBC , Europe's biggest bank, could halve its dividend and may need to raise up to $30 billion of capital soured sentiment.
* Citigroup is another headwind, with its shares sliding on concerns that the bank is in the throes of breaking itself up as losses mount.
* S&P 500 futures slid 14.40 points, while Dow industrials futures shed 108 points. Nasdaq 100 futures lost 16.50 points.
(Reporting by Ellis Mnyandu; Editing by James Dalgleish)