Common Acid And Bases

Modern alchemy turns acid boron into a base

ANCIENT alchemists wanted to transform common metals into gold. Now chemists have achieved a more subtle modern-day equivalent - converting the element boron from an acid to a base. The work could lead to safer medicines.

Chemists identify acids and bases by their electronic structure. Each tends to react with different elements. Electron-starved acids gravitate towards electron-rich areas on other atoms, while bases with "free" electrons attack atoms that are electron poor.

Guy Bertrand of the University of California, Riverside, and his colleagues tinkered with the number of electrons surrounding boron. It prefers to remain electron-deficient and often binds to three other atoms. In this state, it has room to borrow electrons from another atom, acting as an acid. The researchers tricked it into feeling as if it had taken on extra electrons, transforming it into its chemical opposite: a base.

The researchers started with borylene, a very reactive form of boron that is bound to only one other atom instead of the normal three, leaving it with two free electrons where the other bonds would be. This gives it a split personality - it has free electrons like a base but could also gain electrons to form stable bonds at those two sites, like an acid.

To force it into behaving like a base, the team added two carbon-containing molecules to the mix. These shared electrons with the borylene in such a way as to resemble stabilising bonds. This removed borylene's need for additional electrons through bonding, shutting down its acid-like side. It still had its own extra electrons, however, making it a base.

This stable, electron-rich state can survive for at least two months at room temperature ( Science , DOI: 10.1126/science.1207573 ). Ordinarily borylene is so reactive that it can only be kept stable at temperatures close to absolute zero.

The boron bases could replace some toxic phosphorus bases used as catalysts to make medicines, says Bertrand. These compounds are difficult to remove from medicines entirely and can affect the central nervous system and respiratory tract if they enter the body.

Bertrand hopes to create a family of molecules that can cling to borylene, stabilising it.

Basically (if I may use that word), what they've done is to bond one hydrogen and two carbenes to the boron. That means the carbons have a formal charge of +1 and the boron a formal charge of -2. (They also made a radical cation in which the boron has a formal charge of just -1.) The boron atom is thus acting more like a nitrogen atom and the molecule is like a secondary amine.

Medicine Science » Complications of Blood Transfusion – Part 2 of ...

Citrate toxicity results when the citrate in the transfused blood begins to bind calcium in the patient’s body. Clinically significant hypocalcemia does not usually occur unless the rate of transfusion exceeds one unit every five minutes or so. Citrate metabolism is primarily hepatic – so hepatic disease or dysfunction can cause this effect to be more pronounced. Treatment is with intravenous calcium administration – but identification of the problem requires a high index of suspicion. Acid-Base balance can be seen after massive transfusion. The most common abnormality is a metabolic alkalosis. Patients may initially be acidotic because the blood load itself is acidic and there may be a prevailing lactic acidosis from hypoperfusion. However, once normal perfusion is restored, any metabolic acidosis resolves and the citrate and lactate are then converted to bicarbonate in the liver.

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