We examine the borate group intermixing in a series of 25 borosilicate (BS) glasses from the [0.5M₍₂₎O–0.5Na₂O]–B₂O₃–SiO₂ systems with M = {Li, K, Rb, Mg, Ca} along with ternary K₂O–B₂O₃–SiO₂ and Na₂O–B₂O₃–SiO₂ glasses by double-quantum–single-quantum (2Q–1Q) ¹¹B correlation nuclear magnetic resonance (NMR) experiments. The alterations of the fractional populations of B^[3]–O–B^[3], B^[3]–O–B^[4], and B^[4]–O–B^[4] linkages in the glass networks were monitored for variable n_Si/n_B molar ratios, nonbridging O contents of the glass, and the (average) cation field strength (CFS) of the M^z+/Na⁺ network modifiers. A significant B^[4]–O–B^[4] bonding is observed in all glasses, thereby conclusively demonstrating that the normally assumed “BO₄–BO₄ avoidance” is far from strict in BS glasses, regardless of the M^z+ field strength. We show that the degree of B^[4]–O–B^[4] bonding depends foremost on its underlying BO₄ population and to a lesser degree on the NBO content of the glass; we also provide a straightforward prediction of the B^[4]–O–B^[4] population in an arbitrary BS glass from parameters readily obtained by routine ¹¹B NMR. The propensity for forming B^[4]–O–B^[4] linkages increases concurrently with either the CFS or the amount of glass network modifiers, roughly scaling as the square root of the “effective CFS” that encompasses both parameters. Although BO₃–BO₃ and BO₃–BO₄ pairs remain favored throughout all examined BS glass networks, the borate group intermixing randomizes significantly for increasing effective CFS, out of which the amount and charge of the glass-network modifier cations dominate over their size. Our results are discussed in relation to the two prevailing but formally mutually exclusive “random network” and “superstructural unit” models of borate and BS glasses.

We examine the impact of the glass network-modifier cation field strength (CFS) on ion irradiation-induced mechanical property changes in borosilicate (BS) glasses for the ternary M2O-B2O3-SiO2 systems with M = {Na, K, Rb} and the quaternary [0.5M((2))O-0.5Na(2)O]-B2O3-SiO2 systems with M = {Li, Na, K, Rb Mg, Ca, Sr, Ba}. B-11 nuclear magnetic resonance (NMR) experiments on the as-prepared BS glasses yielded the fractional population of four-coordinated B species (B-[4]) out of all {B-[3], B-[4]} groups in the glass network, along with the fraction of B-[4]-O-Si linkages out of all B-[4]-O-Si/B bonds. Both parameters correlated linearly with the (average) CFS of the M+ and/or {M(2)+, Na+} cations. Both the nanoindentation-derived hardness and Young's modulus values of the glasses reduced upon their irradiation by Si2+ ions, with the property deterioration decreasing linearly with increasing Mz+ CFS, that is, for higher Mz+center dot center dot center dot O interaction strength. The irradiation damage of the glass network also increased linearly with the fraction of B-[4]-O-Si linkages, which are the second weakest in the structure after the Mz+center dot center dot center dot O bonds. Our results underscore the advantages of employing BS glasses with high-CFS cations for enhancing the radiation resistance for nuclear waste storage.

The impact of the cation field strength (CFS) of the glass network-modifier cations on the structure and properties of borosilicate glasses (BS) were examined for a large ensemble of mixed-cation (R/2)M₍₂₎O–(R/2)Na₂O–B₂O₃–KSiO₂ glasses with M⁺ ={Li⁺, Na⁺, K⁺, Rb⁺} and M²⁺ ={Mg²⁺, Ca²⁺, Sr²⁺, Ba²⁺} from four series of {K, R} combinations of K = n(SiO₂)/n(B₂O₃) = {2.0, 4.0} and R =[n(M₍₂₎O) ​+ ​n(Na₂O)]/n(B₂O₃) = {0.75, 2.1}. Combined with results from La³⁺ bearing glasses enabled the probing of physical-property variations across a wide CFS range, encompassing the glass transition temperature (T_g), density, molar volume and compactness, as well as the hardness (H) and Young's modulus (E). We discuss the inferred composition–structure/CFS–property relationships. Each of T_g, H, and E revealed a non-linear dependence against the CFS and a strong Tg/H correlation, where each property is maximized for the largest alkaline-earth metal cations, i.e., Sr²⁺ and Ba²⁺, along with the high-CFS La³⁺ species. The ¹¹B MAS NMR-derived fractional BO₄ populations decreased linearly with the average M^z+/Na⁺ CFS within both K–0.75 glass branches, whereas the NBO-rich K–2.1 glasses manifested more complex trends. Comparisons with results from RM₂O–B₂O₃–KSiO₂ glasses suggested no significant “mixed alkali effect”.

Bone mineral consists of calcium hydroxy-carbonate apatite (HCA) that incorporates other minor cation substituents, primarily Na+ (0.5-0.8 wt %). We examine the carbonate species in various HCA specimens with variable CO32- contents (4-10 wt %), encompassing phases prepared by precipitation and a biomimetic specimen formed from a bioactive glass inside a simulated body fluid as well as bone tissue from beagle dog. Using magic-angle spinning (MAS) nuclear magnetic resonance (NMR) along with infrared spectroscopy experiments, we identified and quantified carbonate anions replacing either hydroxyl (A-type CO32-) or phosphate (B-type CO32-) anions in the HCA lattice, along with the carbonate species present in the amorphous surface layer present at all synthetic and biogenic nanocrystalline HCA particles. Advanced C-13-based NMR experimentation enabled the selective detection of the minor (CO32-)-C-13 population of intact bone monoliths, whose C-13 NMR signals are otherwise swamped by those from collagen, unless chemically invasive deproteination procedures are invoked. The CO32- species present in 4 week- and 8 month-old bone of the alveolar process from beagle dog revealed mainly B-type lattice sites and carbonates present in the amorphous surface layer. No tissue aging effects were observed in the local CO32- environments. Likewise, NMR revealed very similar Na-23(+) parameters in HCA, regardless of its synthetic or biogenic origin or degree of structural order. A combination of interatomic-distance-sensitive MAS NMR experiments allowed the identification of the local environments of the various carbonate, phosphate, hydroxyl, and water species present in both the interior and the surface layer of the synthetic HCA particles. We highlight the similarities/differences in the chemical speciation and the spatial distribution of CO32- anions present in carbonate-bearing amorphous calcium phosphate (ACP) relative to the ACP-like surface layer of HCA and discuss the C-13 NMR peak assignments of the up to four coexisting CO32- populations in the synthetic/biogenic HCA phases.

From a large ensemble of 34 silicate-based glasses from the borosilicate, phosphosilicate, and borophosphosilicate systems that comprise either Na as a sole glass-network modifier or when mixed with Ca, we established a good correlation between the Na-23 average isotropic chemical shift (delta over bar iso) and the average coordination number of Na and the mean Na-O distance. The latter parameters were obtained by atomistic molecular dynamics simulations. We also demonstrated that delta over bar iso is essentially independent on the precise network forming (Si, B, P) species but depends primarily on the net molar fraction of Na and Ca, thereby offering a straightforward Na-23 chemical shift prediction from the glass composition alone.

We provide an extensive experimental and numerical evaluation of MQ-phase (S)M supercycles with M = {3,4} of three groups of symmetry-based homonuclear dipolar recoupling rf-pulse sequences, S = ISR4,SR414,SRNI\NI/21, for establishing proximities among half-integer spin quadrupolar nuclei under moderately fast magic-angle-spinning (MAS) conditions in single-quantum-single-quantum (1Q-1Q) correlation NMR experiments. The relative merits of the (S)M schemes for variations in resonance offsets and rf-amplitude errors were assessed by numerically simulated magnetization transfers in spin-3/2 pairs with variable isotropic chemical shifts and quadrupolar coupling constants. Experimental demonstrations of 23Na (spin-3/2) NMR on Na2Mo04.2H20 and 27A1 (spin-5/2) NMR on AIPO-CJ19 l(NF14)2A14(PO4)4HPO4.H201 are presented at 14.1 T and 24 kHz MAS. We recommend using the (SR2)3 or (SR2)4 supercycles for samples that exhibit small chemical-shift dispersions (<3 kHz), and any (SRNI\N1/2)3 scheme with N 10 for larger spreads of isotropic chemical shifts. However, because the (SRNI\N1/2)3 sequences recouple heteronuclear dipolar interactions, their application to protonbearing samples requires high-power proton decoupling during the mixing period. Alternatively, the (SR214)3 and (SR214)4 schemes may be employed in the absence of proton decoupling, but with poorer compensation to resonance-offsets and rf-amplitude errors.

We demonstrate that supercycles of previously introduced two-fold symmetry dipolar recoupling schemes may be utilized successfully in homonuclear correlation nuclear magnetic resonance (NMR) spectroscopy for probing proximities among half-integer spin quadrupolar nuclei in network materials undergoing magic-angle-spinning (MAS). These (SR212)M, (SR214) M, and (SR218)M recoupling sequences with M = 3 and M = 4 offer comparably efficient magnetization transfers in single-quantum-single-quantum (1Q-1Q) correlation NMR experiments under moderately fast MAS conditions, as demonstrated at 14.1 T and 24 kHz MAS in the contexts of 11B NMR on a Na2O-CaO-B2O3-SiO2 glass and 27Al NMR on the open framework aluminophosphate AlPO-CJ19 [(NH4)2Al4(PO4)4HPO4 H2O]. Numerically simulated magnetization transfers in spin-3/2 pairs revealed a progressively enhanced tolerance to resonance offsets and rf-amplitude errors of the recoupling pulses along the series (SR212) M < (SR214)M < (SR218)M for increasing differences in chemical shifts between the two nuclei. Nonetheless, for scenarios of a relatively minor chemical-shift dispersions (. 3 kHz), the (SR212) M supercycles perform best both experimentally and in simulations.

We present a comprehensive composition analysis of calcium phosphate cements (CPCs) incorporating increasing amounts of bioactive pyrophosphate species (up to 17 wt% P2O7). These cements comprise primarily poorly ordered monetite (CaHPO4) or brushite (CaHPO4 center dot 2H(2)O) and are investigated for enhanced osteoinductive bone/tooth implants. The specimens were characterized by magic-angle spinning (MAS) P-31 and H-1 nuclear magnetic resonance (NMR) spectroscopy along with powder X-ray diffraction (PXRD). P-31 MAS NMR was employed to quantify the major monetite/brushite constituents, the crystalline and amorphous pyrophosphates, as well as various minor orthophosphate by-products. The NMR-derived contents of the crystalline phases accorded well with those from Rietveld analyses of the corresponding PXRD data. The amounts of crystalline and amorphous pyrophosphate depended on the precise cement precursor mixture and preparation conditions, which together with their distinct structural roles may enable the design of cements with a tunable P2O74 - release into aqueous solutions.

From a multitude of homonuclear and heteronuclear correlation magic-angle-spinning (MAS) NMR experiments, we present thorough structural and phase-quantification analyses of calcium phosphate cements (CPCs) that incorporate either L-serine (Ser) or O-phospho-L-serine (Pser), thereby rendering the cements strongly bone-adhesive and suitable for biomedical implants with capacity to glue both soft and hard tissues together. In the absence of organic additives, the CPCs comprise disordered hydroxyapatite (HA), which forms from the reaction of alpha-Ca-3(PO4)(2) with water. However, the presence of even a few mol % of Pser/Ser drastically changes the cement reactions: the HA formation is quenched, while MAS NMR experiments reveal intimate contacts between the Pser/Ser molecules and amorphous calcium phosphate (ACP) that incorporate HPO42- groups: these organic/inorganic species form a homogeneous amorphous ACP/Pser or ACP/Ser cement component. The amount of ACP/Pser in the cement is shown to correlate qualitatively with its shear strength, also rationalizing why Pser-bearing CPCs exhibit stronger adhesive properties than their Ser-based counterparts, for which the ACP/Ser content does not increase concomitantly with that of Ser (as for the Pser-based CPCs). The Pser-bearing CPCs feature the strongest shear strength for 23-72 mol % Pser, whereas the decline of the adhesive properties for the Pser-richest CPCs (>72 mol %) stems from unreacted Pser and formation of its Ca salt, as well as several minor Ca phosphate phases involving HPO42- and H2PO4- groups. By combining information from various one- and two-dimensional MAS NMR experiments with H-1, C-13, and P-31 as structural probes, we examined the inorganic/organic contacts of the ACP/Pser and ACP/Ser phases, and monitored the alterations of the cement reactions for variable amounts of the organic additives.

From a suite of advanced magic-angle spinning (MAS) NMR spectroscopy and powder X-ray diffraction (PXRD) experiments, we present a comprehensive structural analysis of pyrophosphate-bearing calcium phosphate cements that are investigated for bone-inductive biomedical implants. The cements consist mainly of poorly ordered monetite (CaHPO4), along with minor Ca orthophosphate phases, and two distinct pyrophosphate constituents: crystalline beta-Ca2P2O7 and amorphous calcium pyrophosphate (ACPP), the latter involving one water bearing portion and another anhydrous component. Independent 2D MAS NMR experiments evidenced close contacts between the amorphous pyrophosphates and the monetite phase, where ACPP is proposed to form a thin layer coating the monetite particles. Heteronuclear H-1-P-31 and homonuclear P-31-P-31 correlation NMR experimentation enabled us to detect, identify, and quantify even minor cement constituents (less than or similar to 2 mol%) that could not be ascertained by the Rietveld method. Quantitative phase analyses of the cements, as determined independently by P-31 NMR and PXRD, are contrasted and discussed.