Yu Yang, Stevensson Baltzar, Edén Mattias
Physical Chemistry Division, Department of Materials and Environmental Chemistry, Stockholm University , SE-106 91 Stockholm, Sweden.
J Phys Chem B. 2017 Oct 19;121(41):9737-9752. doi: 10.1021/acs.jpcb.7b06654. Epub 2017 Oct 5.
The short and intermediate range structures of a large series of bioactive borophosphosilicate (BPS) glasses were probed by solid-state nuclear magnetic resonance (NMR) spectroscopy and atomistic molecular dynamics (MD) simulations. Two BPS glass series were designed by gradually substituting SiO by BO in the respective phosphosilicate base compositions 24.1NaO-23.3CaO-48.6SiO-4.0PO ("S49") and 24.6NaO-26.7CaO-46.1SiO-2.6PO ("S46"), the latter constituting the "45S5 Bioglass" utilized for bone grafting applications. The BPS glass networks are built by interconnected SiO, BO, and BO moieties, whereas P exists mainly as orthophosphate anions, except for a minor network-associated portion involving P-O-Si and P-O-B motifs, whose populations were estimated by heteronuclear P{B} NMR experimentation. The high Na/Ca contents give fragmented glass networks with large amounts of nonbridging oxygen (NBO) anions. The MD-generated glass models reveal an increasing propensity for NBO accommodation among the network units according to BO < SiO < BO ≪ PO. The BO/BO intermixing was examined by double-quantum-single-quantum correlation B NMR experiments, which evidenced the presence of all three BO-BO, BO-BO, and BO-BO connectivities, with B-O-B bridges dominating. Notwithstanding that B-O-B linkages are disfavored, both NMR spectroscopy and MD simulations established their presence in these modifier-rich BPS glasses, along with non-negligible B-NBO contacts, at odds with the conventional structural view of borosilicate glasses. We discuss the relative propensities for intermixing of the Si/B/P network formers. Despite the absence of pronounced preferences for Si-O-Si bond formation, the glass models manifest subtle subnanometer-sized structural inhomogeneities, where SiO tetrahedra tend to self-associate into small chain/ring motifs embedded in BO/BO-dominated domains.
通过固态核磁共振（NMR）光谱和原子分子动力学（MD）模拟研究了一系列生物活性硼磷硅酸盐（BPS）玻璃的短程和中程结构。在各自的磷硅酸盐基础组成24.1NaO-23.3CaO-48.6SiO-4.0PO（“S49”）和24.6NaO-26.7CaO-46.1SiO-2.6PO（“S46”）中，通过逐渐用BO取代SiO设计了两个BPS玻璃系列，后者构成用于骨移植应用的“45S5生物玻璃”。BPS玻璃网络由相互连接的SiO、BO和BO部分构成，而P主要以正磷酸盐阴离子形式存在，除了涉及P-O-Si和P-O-B基序的少量与网络相关的部分，其含量通过异核P{B}NMR实验估算。高Na/Ca含量产生具有大量非桥氧（NBO）阴离子的碎片化玻璃网络。MD生成的玻璃模型显示，根据BO＜SiO＜BO≪PO，网络单元中NBO容纳的倾向增加。通过双量子-单量子相关B NMR实验研究了BO/BO混合，该实验证明了所有三种BO-BO、BO-BO和BO-BO连接性的存在，其中B-O-B桥占主导。尽管B-O-B键不受青睐，但NMR光谱和MD模拟均证实它们存在于这些富含改性剂的BPS玻璃中，同时存在不可忽略的B-NBO接触，这与硼硅酸盐玻璃的传统结构观点不一致。我们讨论了Si/B/P网络形成体混合的相对倾向。尽管对于Si-O-Si键形成没有明显偏好，但玻璃模型表现出微妙的亚纳米级结构不均匀性，其中SiO四面体倾向于自缔合成嵌入BO/BO主导区域的小链/环基序。
