Carbocations are species bearing a formal + charge on carbon. The have sp2 hybridization and trigonal planar geometry, with an empty p orbital on carbon, perpendicular to the plane containing the substituents (see diagrams shown to the right).
Aortic cross-clamp. An aortic cross-clamp is a surgical instrument used in cardiac surgery to clamp the aorta and separate the systemic circulation from the outflow of the heart. An aortic cross-clamping procedure serves, for example, in the repairing of coarctation of the aorta.
Two clamps encircle the two single strands of DNA at the replication fork. A cluster of accessory proteins, called the clamp loader complex, loads the clamps onto DNA strands. The two sliding clamps bind two core enzymes, one for each strand of DNA.