The magnetic susceptibilities of oxy-and metaquohemerythrin in the range 3-200°K have been determined using an ultrasensitive superconducting quantum magnetometer, and for the first time their antiferromagnetic components have been conclusively resolved. The exchange coupling constants, J , between the two high-spin iron(II1) atoms in each subunit are -77 and -134 cm-l, respectively. The elec-
The magnetic susceptibilities of cobalt(II) and nickel(II) derivatives of carboxypeptidase A (CPA) follow the Curie law over a wide temperature range. The We have been concerned lately with the role of the metal ion in the catalytic activity of carboxypeptidase A. The Zn(II) ligands contributed by the polypeptide chain at the active site have been identified through a combination of x-ray diffraction (1-3) and sequence (4, 5) studies as His 69, Glu 72, and His 196. The x-ray results have shown further that the probable coordination geometry of the Zn(II) site is distorted tetrahedral, with the fourth ligand presumably being a H20 molecule in the resting enzyme. A distorted tetrahedral coordination site assignment also appears to be compatible with the electronic absorption spectrum of Co(II)-CPA (6), which is a fully active derivative (7,8).Our efforts have been channeled into experiments designed to elucidate the electronic ground and excited states of several metallocarboxypeptidase A derivatives, in the hope of establishing some connection between metal-ion structure and activity. We have been particularly interested in the question of whether the metal ion in its role in the multifunctional catalytic apparatus has been endowed with enhanced substrate-attacking properties by virtue of a special (9, 10) ground-state structure. The present paper deals with the ground states of cobalt(II)CPA and nickel(II)CPA, as characterized by measurements of variable-temperature magnetic susceptibility by our ultrasensitive, superconducting, quantum mechanical magnetometer.
MATERIALS AND METHODSPreparation of Sample. Bovine carboxypeptidase A, prepared by the method of Cox (11)
Also isolated were two minor products, methyl 8-( 1 -thionaphthyl)-! -naphthyl sulfide (10%) and methyl 8-[8-(l-thionaphthyl)-1 -thionaphthylj-1 -naphthyl sulfide (7%), resulting from oligomerization of methyl 8-lithio-1 -naphthyl sulfide with 2f (cf ref. 14).(16) Fellow, Cornell University Six-Year Ph.D. Program.
To achieve an areal density approaching 50 Gb/in.2 for the magnetic storage of data in hard disk drives requires reduced mechanical and magnetic spacing. Off-track jitter caused by airflow or contact can cause track misregistration on the order of 20–70 nm which may be excessive for adequate servo performance. The magnetic signal can be used to identify both the vertical spacing modulation due to the air bearing modes and off-track jitter due to suspension modes with nanometer resolution. We find that the off-track jitter in the flying regime is driven by airflow and is a strong function of the disk velocity and the suspension type. In the contact regime, the vertical spacing modulation and off-track jitter increase due to contact. Using a laser Doppler vibrometer we identified the leading contribution to the off-track jitter to be primarily the first torsional mode (T1) and to a lesser extent the first bending mode (B1) of the suspension.
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