Predicted stability, structures, and magnetism of 3d transition metal nitrides: the M4N phases

The 3d transition metal nitrides M4N (Sc4N, Ti4N, V4N, Cr4N, Mn4N, Fe4N, Co4N, Ni4N, and Cu4N) have unique phase relationships, crystal structures, and electronic and magnetic properties. Here we present a systematic density functional theory (DFT) study on these transition metal nitrides, assessing both the I-M4N phase and the II-M4N phase, which differ in ordering of the N atoms within the face-centered cubic (FCC) framework of metal atoms. The calculations showed that for M ¼ Mn, Fe, Co and Cu, the I-M4N phases with perfect metal sub-lattices are favored, while for M ¼ Sc–Cr, and Ni, the II-M4N phases with distorted metal sub-lattices are favored. We predict that several currently not existing II-M4N phases may be synthesized experimentally as metastable phases. From Bader charge analysis the M4N phases are found to be ionic with significant metal–metal bonding. I-M4N with M ¼ Cr to Ni are magnetic, while II-M4N with M ¼ Cr and Ni are non-magnetic. The calculations revealed unusually high local magnetic moments and high spin-polarization ratios of the M1 atoms in I-M4N (M ¼ Cr to Ni). The origin of magnetism and lattice distortion of the M4N phases is addressed with the Stoner criterion. Detailed information about the relative stability, structures, chemical bonding, as well as the electronic and magnetic properties of the phases are of interest to a wide variety of fields, such as chemical synthesis, catalysis, spintronics, coating technology, and steel manufacturing

Predicted stability, structures, and magnetism of 3d transition metal nitrides: the M4N phases

The 3d transition metal nitrides M4N (Sc4N, Ti4N, V4N, Cr4N, Mn4N, Fe4N, Co4N, Ni4N, and Cu4N) have unique phase relationships, crystal structures, and electronic and magnetic properties. Here we present a systematic density functional theory (DFT) study on these transition metal nitrides, assessing both the I-M4N phase and the II-M4N phase, which differ in ordering of the N atoms within the face-centered cubic (FCC) framework of metal atoms. The calculations showed that for M ¼ Mn, Fe, Co and Cu, the I-M4N phases with perfect metal sub-lattices are favored, while for M ¼ Sc–Cr, and Ni, the II-M4N phases with distorted metal sub-lattices are favored. We predict that several currently not existing II-M4N phases may be synthesized experimentally as metastable phases. From Bader charge analysis the M4N phases are found to be ionic with significant metal–metal bonding. I-M4N with M ¼ Cr to Ni are magnetic, while II-M4N with M ¼ Cr and Ni are non-magnetic. The calculations revealed unusually high local magnetic moments and high spin-polarization ratios of the M1 atoms in I-M4N (M ¼ Cr to Ni). The origin of magnetism and lattice distortion of the M4N phases is addressed with the Stoner criterion. Detailed information about the relative stability, structures, chemical bonding, as well as the electronic and magnetic properties of the phases are of interest to a wide variety of fields, such as chemical synthesis, catalysis, spintronics, coating technology, and steel manufacturing

Transglutaminase-Mediated Modification of Glutamine and Lysine Residues in Native Bovine β-Lactoglobulin

Bovine β-lactoglobulin (BLG) is a major component in whey and its physical properties are important for the texture of many dairy-based foods. Modification of proteins with transglutaminase from Streptoverticillium mobaraense (MTGase) can be used to alter their physical properties. MTGase-mediated modification of native BLG was until now, however, not effective. Here we report a method that allows for the enzymatic modification of native BLG with MTGase. Lysines 8, 77, and 141 were modified with α-N-carbobenzyloxy-glutamine-glycine and glutamines 35, 59, 68, and 155 were modified with 6-aminohexanoic acid under nonreducing and nondenaturing conditions. MTGase-mediated BLG crosslinking is hampered by the low reactivity of the lysines and enzymatic deamidation of the glutamines prevails. Modification of BLG with poly-lysine yields a BLG derivative with increased affinity for the water-air interface and stronger surface tension lowering capacities than normal BLG. Hence, this modification method offers the opportunity to change the functional properties of BLG and to prepare novel protein foods. © 2004 Wiley Periodicals, Inc

Modification of Glutamine and Lysine Residues in Holo and Apo α-Lactalbumin with Microbial Transglutaminase

The molecular structures determine the physical properties of milk proteins and are important for the texture of many dairy-based foods. Bovine α-lactalbumin (α-LA) is a globular 123 amino acid Ca2+ binding milk protein. Modification with microbial Ca2+ independent transglutaminase (MTGase) was used to modify lysines and glutamines in holo and apo α-LA. At 30 °C no lysines or glutamines are modified in holo α-LA, whereas in apo α-LA lysines 13, 16, 108, and 114, and glutamines 39 and 43, are modified. At 50 °C lysines 13, 16, 108, and 114, but no glutamines, are modified in holo α-LA, whereas in apo α-LA lysines 5, 13, 16, 108, and 114, and glutamines 39, 43, 54, 65, and 117, are modified. The methods presented here offer the possibility to manipulate the availabilities of residues in α-LA to the MTGase reaction and enable the preparation of α-LA species with different degrees of modification and hence with different physical properties