RESUMEN
We are investigated substitution effects of titanium heteroatoms on band gap, charge and local reactivity of C20-nTin heterofullerenes (n = 1-5), at different levels and basis sets. The C18Ti2-2 nanocage is considered as the most kinetically stable species with the widest band gap of 2.86 eV, in which two carbon atoms are substituted by two Ti atoms in equatorial position, individually. The charges on carbon atoms of C20 are roughly zero, while high positive charge (1.256) on the surface of C19Ti1 prompts this heteofullerene for hydrogen storage. The positive atomic charge on Ti atoms and negative atomic charge on their adjacent C atoms implies that these sites can be influenced more readily by nucleophilic and electrophilic regents, respectively. We examined the usefulness of local reactivity descriptors to predict the reactivity of Ti-C atomic sites on the external surface of the heterofullerenes. The properties determined include Fukui function (F.F.); f (k) and local softness s (k) on the surfaces of the investigated hollow cages. Geometry optimization results reveal that titanium atoms can be comfortably incorporated into the CC network of fullerene. It is most likely associated with the triple-coordination characteristic of titanium atoms, which can well match with the sp2-hybridized carbon bonding structure. According to the values of f (k) and s (k) for the C15Ti5 heterofullerene; the carbon atoms in the cap regions exhibit a different reactivity pattern than those in the equatorial portion of the heterofullerene. The titanium impurity can significantly improve the fullerene's surface reactivity and it allows controlling their surface properties. The band gap of C20-nTin ..(H2)n structures is decreased with increasing n. Hence, C15Ti5 is found as the best hydrogen adsorbent.
Asunto(s)
Fulerenos , Titanio , Titanio/química , Modelos Moleculares , Fulerenos/química , Química Computacional , Hidrógeno/química , Carbono/químicaRESUMEN
OBJECTIVE: The authors report a result of application of cervical hollow cage(RABEA(TM)) without bone graft to the patients of one-level cervical spondylosis or acute cervical disc herniation to fill and stabilize a vacant space following anterior decompression. METHODS: Twenty-one patients from May 1999 to April 2001 had been taken procedure with cervical hollow cage system following anterior decompression and there had been no additional bone graft or screw fixation or fusion. Pain relief and clinical outcome were evaluated, and the intervertebral disc height and segmental angle for radiological assessment were examined. All patient were followed up for 12 months at least. RESULTS: The result was excellent in 14 cases(66.7%), good in 6 cases(28.6%) and poor in 1 case(4.8%). In the lateral projection, the mean of preoperative disc height and segmental angle were significantly improved after surgery and maintained during follow-up periods. No abnormal displacement were recorded at dynamic flexion and extension lateral X-ray and no cage rotation or retropulsion was noted in follow-up periods. Three patients(14.3%) was observed to subside of disc height on the postoperative periods and only one of their patients was dissatisfied with surgery. CONCLUSION: Cervical hollow cage is simple to perform and reduces the operation time. Besides clinical improvement, it improves mechanical stability and radiological profile as the physiologic level. The cervical hollow cage might be an alternative to traditional cervical interbody fusion with bone graft.