Consequently, iron is assigned an oxidation state of 2+. The iron center has a diamagnetic low-spin d6 electron configuration, although a paramagnetic long-lived metastable state has been observed by EPR spectroscopy.The chemical reactions of sodium nitroprusside are mainly associated with the NO ligand. For example, addition of S2− ion to [Fe(CN)5(NO)]2− produces the violet colour[Fe(CN)5(NOS)]4− ion, which is the basis for a sensitive test for S2− ions. An analogous reaction also exists with OH− ions, giving [Fe(CN)5(NO2)]4−. Roussins red salt (K2[Fe2S2(NO)4]) and Roussins black salt (NaFe4S3(NO)7) are related iron nitrosyl complexes. The former was first prepared by treating nitroprusside with sulfur.
This is because remifentanil will be rapidly eliminated from the blood plasma on termination of the remifentanil infusion, hence the effects of the drug will quickly dissipate even after very long infusions. Owing to synergism between remifentanil and hypnotic drugs (such as propofol) the dose of the hypnotic can be substantially reduced. This leads often to more hemodynamic stability during surgery and a quicker post-operative recovery time. Side-effects
Remifentanil is a specific μ-receptor agonist. Hence, it causes a reduction in sympathetic nervous system tone, respiratory depression and analgesia. The drugs effects include a dose-dependent decrease in heart rate and arterial pressure and respiratory rate and tidal volume. Muscle rigidity is sometimes noted. The most common side effects reported by patients receiving this medication are a sense of extreme "dizziness" (often short lived, a common side effect of other fast-acting synthetic phenylpiperidine narcotics such as fentanyl and alfentanil) and intense itching (pruritus), often around the face. These side effects are often controlled by either altering the administered dose  (decreasing or in some cases, increasing the dose) or by administering other sedatives that allow the patient to tolerate or lose awareness of the side effect. Because pruritus is due to excessive serum histamine levels, antihistamines such as diphenhydramine (Benadryl) are often co-administered. This is done with care, however, as excessive sedation may occur. Nausea can occur as a side effect of remifentanil, however, it is usually transient in nature due to the drugs short half-life which rapidly removes it from the patients circulation once the infusion is terminated.