code: public static final int getChargeOfAminoAcid(char aa) {
  		if (negChargedAAs.contains(String.valueOf(aa))) {
  			return -1;
  		}
  		else if (posChargedAAs.contains(String.valueOf(aa))) {
  			return 1;
  		}
  		return 0;
  	}
docs: Returns the charge of amino acid. At pH=7, two are negative charged: aspartic acid (Asp, D) and glutamic acid (Glu, E) (acidic side chains),
  and three are positive charged: lysine (Lys, K), arginine (Arg, R) and histidine (His, H) (basic side chains).
  
  @param aa The one-letter amino acid code
  @return the charge of amino acid (1 if positively charged, -1 if negatively charged, 0 if not charged)