N-Nitroso-β-lactams as β-lactamase inhibitor

AbstractN-Nitroso-β-phenyl-β-lactam has been found to be a specific inhibitor of β-lactamase. N-Nitroso-α-phenyl-β-lactam, by contrast, was virtually ineffective although a transient inhibition of short duration was observed. The acyl enzyme derived from the β-phenyl isomer is presumably involved in a cross-linking reaction, whereas that from the α-phenyl isomer was quenched by spontaneous hydrolysis without formation of a covalent bond. No inhibitory effect of the β-phenyl isomer on chymotrypsin has been observed

Optimization of Network Robustness to Waves of Targeted and Random Attack

We study the robustness of complex networks to multiple waves of simultaneous (i) targeted attacks in which the highest degree nodes are removed and (ii) random attacks (or failures) in which fractions $p_t$ and $p_r$ respectively of the nodes are removed until the network collapses. We find that the network design which optimizes network robustness has a bimodal degree distribution, with a fraction $r$ of the nodes having degree k_2= (\kav - 1 +r)/r and the remainder of the nodes having degree $k_1=1$, where \kav is the average degree of all the nodes. We find that the optimal value of $r$ is of the order of $p_t/p_r$ for $p_t/p_r\ll 1$