Article

Weakly and strongly associated nonfreezable water bound in bones

Faculty of Chemistry, Maria Curie-Sklodowska University in Lublin, Lyublin, Lublin Voivodeship, Poland
Colloids and surfaces B: Biointerfaces (Impact Factor: 4.15). 04/2006; 48(2):167-75. DOI: 10.1016/j.colsurfb.2006.02.001
Source: PubMed

ABSTRACT Water bound in bone of rat tail vertebrae was investigated by 1H NMR spectroscopy at 210-300 K and by the thermally stimulated depolarization current (TSDC) method at 190-265 K. The 1H NMR spectra of water clusters were calculated by the GIAO method with the B3LYP/6-31G(d,p) basis set, and the solvent effects were analyzed by the HF/SM5.45/6-31G(d) method. The 1H NMR spectra of water in bone tissue include two signals that can be assigned to typical water (chemical shift of proton resonance deltaH=4-5 ppm) and unusual water (deltaH=1.2-1.7 ppm). According to the quantum chemical calculations, the latter can be attributed to water molecules without the hydrogen bonds through the hydrogen atoms, e.g., interacting with hydrophobic environment. An increase in the amount of water in bone leads to an increase in the amount of typical water, which is characterized by higher associativity (i.e., a larger average number of hydrogen bonds per molecule) and fills larger pores, cavities and pockets in bone tissue.

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    • "A fraction of the water in bone exists in the unbound state (also referred to as mobile, bulk, pore or free) within the microscopic pores. The rest of the water is bound to the collagen [8] or mineral [9] phases of bone with various degrees of affinity, reportedly ranging from loosely to tightly bound states [10] [11] [12]. There is evidence that younger bone tissue has higher toughness and higher amount of bound water than aged bone [12]. "
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    ABSTRACT: Matrix bound water is a correlate of bone's fracture resistance and assessment of bound water is emerging as a novel measure of bone's mechanical integrity. Raman spectroscopy is one of the few nondestructive modalities to assess the hydration status in bone; however, it has not been used to study the OH-band in bone. A sequential dehydration protocol was developed to replace unbound (heat drying) and bound (ethanol or deuterium) water in bone. Raman spectra were collected serially to track the OH-band during dehydration. Spectra of synthetic hydroxyapatite, demineralized bone and bulk water were collected to identify mineral and collagen contributions to the OH-band. Band assignments were supported by computational simulations of the molecular vibrations of Gly-Pro-Hyp amino acid sequence. Experimentally and theoretically obtained spectra were interpreted for band-assignments. Water loss was measured gravimetrically and correlated to Raman intensities. Four peaks were identified to be sensitive to dehydration: 3220 cm−1 (water), 3325 cm (N\H and water),3453 cm−1 (hydroxyproline and water), and 3584 cm−1 (mineral and water). These peaks were differentially sensitive to deuterium treatment such that some water peaks were replaced with deuterium oxide faster than the rest. Specifically, the peaks at 3325 and 3584 cm−1 were more tightly bound to the matrix than the remaining bands. Comparison of dehydration in mineralized and demineralized bone revealed a volume of water that may be locked in the matrix by mineral crystals. The OH-range of bone was dominated by collagen and the water since the spectral profile of dehydrated demineralized bone was similar to that of the mineralized bone. Furthermore, water associates to bone mainly by collagen as findings of experimentally and theoretically spectra. The current work is among the first thorough analysis of the Raman OH stretch band in bone and such spectral information may be used to understand the involvement of water in the fragility of aging and in diseased bone.
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    • "In general, water can be an integral part of the mineral phase (LeGeros et al., 1978) and the organic matrix (Nomura et al., 1977; Pineri et al., 1978). It can also be bound to the organic matrix and crystal surfaces (Wilson et al., 2006), and can be present as bulk water that fills the pores, canaliculi and vascular system (Cowin, 1999; Turov et al., 2006). Nomura et al. (1977) identified four types of water: structural water forming hydrogen bonds within the triple helix of collagen molecules (0–0.07 g/g), water bound to the polar side chains and located in the interhelical regions (0.07–0.25 g/g), water in a transition region where both bound and free water are absorbed (0.25–0.45 g/g), and free water (>0.45 g/g). "
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