Chemistry informtion about Polymyxin B (CAS NO.1404-26-8) is:
IUPAC Name: 4-Amino-2-[[2-[(4-Amino-2-Formamidobutanoyl)Amino]-4-Hydroxybutanoyl]Amino]-N-[4,13,16-Tris(2-Aminoethyl)-7-Benzyl-19-(2-Hydroxyethyl)-10-(2-Methylpropyl)-2,5,8,11,14,17,20-Heptaoxo-3,6,9,12,15,18,21-Heptazacyclotricos-1-Yl]Butanamide; Sulfuric Acid
Synonyms: Polymyxin B ; Polymyxin-B 2,5-Sulfate ; Polymyxin B Sulfate ; Polymyxin B Sulfate, Bacillus Polymyxa ; Polymyxin B Sulfate Salt ; Polymyxin B Sulphate ; Polymyxin B (Pmb) ; Polymixin B Sulfate 
Product Categories: Interferes with Cell Membrane Permeability (Ionophores)Spectrum of Activity ; PeptidesCell Signaling and Neuroscience ; Protein Kinase InhibitorsMore...Close... ; Antibacterial ; Antibiotics ; Antibiotics A to ; Antibiotics by Application ; Antibiotics N-SAntibiotics ; Antineoplastic and Immunosuppressive AntibioticsAntibiotics ; Chemical Structure Class ; Kinase/Phosphatase Biology ; L - ZAntibiotics ; Mechanism of Action ; Peptides ; beta-Lactam StructureAntibiotics ; PeptidesAlphabetic ; POLB - POLYMore...Close... ; Chemical Structure ; P ; AntibioticsAntibiotics ; Cell Culture ; PeptidesMore...Close... ; Reagents and Supplements 
MF: C₅₆H₁₀₀N₁₆O₁₇S
MW: 1301.56
EINECS: 215-774-7 
Flash Point: 952.3 °C
Boiling Point: 1651 °C at 760 mmHg
Vapour Pressure: 0 mmHg at 25°C 
Enthalpy of Vaporization: 272.45 kJ/mol
Storage temp.: 2-8°C
Merck: 13,7656
Following is the molecular structure of Polymyxin B (CAS NO.1404-26-8) is:

 Polymyxin B (CAS NO.1404-26-8) is an antibiotic primarily used for resistant gram negative infections. It bind to the cell membrane and alter its structure making it more permeable. The resulting water uptake leads to cell death. They are cationic, basic proteins that act like detergents(surfactants}. Side effects include neurotoxicity and acute renal tubular necrosis. It is commonly used in the topical first aid preparation Neosporin. Family of polypeptides with attached fatty acid; cationic detergent at physiological pH, both hydrophilic and hydrophobic properties .Bactericidal for gram-negative; little to no effect on gram-positive since cell wall is too thick to permit access to membrane. In addition to its antibiotic function, it has been used to clear endotoxin contamination in reagents.

Poison by intraperitoneal, subcutaneous, and intravenous routes. Human systemic effects by ingestion: diarrhea, nausea; by intramuscular route: paresthesia, ataxia. When heated to decomposition it emits toxic fumes of NO_x.
Hazard Codes:
Xn
Risk Statements:
R22:Harmful if swallowed. 
Safety Statements:
S22:Do not breathe dust. 
S24/25:Avoid contact with skin and eyes.
RIDADR: 3249
WGK Germany: 3
RTECS: TR1150000
F:
F 3 Hygroscopic.
F 8 Photosensitive.
F 10 Keep under argon.
HazardClass: 6.1(b)
PackingGroup: III

Alters cytoplasmic membrane permeability by binding to a negatively charged site in the lipopolysaccharide layer which has an electrostatic attraction for the positively charged amino groups in the cyclic peptide portion (this site normally is a binding site for calcium);Fatty acid portion dissolves in hydrophobic region of membrane and disrupts membrane integrity;Leakage of cellular molecules, inhibition of cellular respiration;Binds and inactivates endotoxin;Relative absence of selective toxicity: nonspecific for cell membranes of any type, highly toxic.