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Biomedical subjects

A S Posner

Publications and source records attributed to A S Posner.

At least 37 records · Page 2Linked to original sources
PubMed1979

The crystal chemistry of submandibular and parotid salivary gland stones.

The mineral composition of 38 human salivary gland stones was described qualitatively on the basis of X-ray diffraction and chemical analysis. In 32 submandibular stones, hydroxyapatite was the most frequently observed phase with a magnesium-substituted whitlockite co-phase (octacalcium phosphate was rarely present). In six parotid gland stones, apatite, magnesium substituted whitlockite and octacalcium phosphate were noted to be the major crystalline phases. Brushite was rarely found in either submandibular or parotid stones. This is the first report of octacalcium phosphate in salivary gland stones. All stones had ash weights ranging from 75--80%, but their Ca/P ratios could not be used to predict the crystalline phases present. Whitlockite was observed more frequently in the central regions of the submandibular stones than in the outer crusts. Possible explanations for the presence of each of these phases are discussed.

Calcium Phosphates↗
PubMed1978

"The chemistry of bone mineral".

In this treatise there has been a general introduction to the nature of bone mineral. Without the studies on the chemistry and structure of hydroxyapatites precipitated under physiological conditions it would have been difficult to interpret the data from bone mineral. Earlier studies on well-crystallized apatite systems helped to delineate the nature of the smaller bone crystals which are so difficult to study by standard crystallographic methods. It was shown that bone mineral is submicroscopic in crystal size and thus, has a high surface area which is highly reactive to specific chemical species. Bone mineral apatite is not an equilibrium phase and is slowly perfecting chemically and in crystal size. It is this lack of perfection resulting from crystalline imperfections due to (a) the presence of carbonate, sodium and other ions, and, (b) the deficiency in Ca and OH, which combine to make bone mineral metabolically active. In closing, it is necessary to point out that this is just a brief introduction to the subject of bone mineral. The interested reader is encouraged to seek more details in the bone text books of Vaughan (1975), Bourne (1972) and Zipkin (1973) and the various review articles noted in the body of this exposition.

Adenosine Triphosphate↗
PubMed1977

The role of synthetic and bone extracted Ca-phospholipid-PO4 complexes in hydroxyapatite formation.

The calcium-phospholipid-phosphate (Ca-PL-PO4) complex isolated from young bone has been shown to initiate hydroxyapatite formation from a metastable calcium phosphate solution. The action of the complex was compared to that of the acidic phospholipids: phosphatidyl serine, phosphatidyl inositol and phosphatidic acid. These phospholipids first remove calcium, and a small amount of phosphate from the metastable solution forming a material similar to the complex isolated from bone, and then form hydroxyapatite. The rate of hydroxyapatite proliferation, once phosphatidyl serine and phosphatidyl inositol are converted to Ca-PL-PO4 complexes, is the same as the rate observed for comparable weights of the complex isolated from bone. It is suggested that the complex isolated from bone was formed in a manner similar to the complexes in our in vitro experiments. Finally, our evidence supports the possibility that a similar complex is responsible for the initial mineralization in matrix vesicles.

Bone Development↗
PubMed1976

Extraction of a calcium-phospholipid-phosphate complex from bone.

A calcium-phospholipid-phosphate complex with a constant 1:1 calcium to total phosphate molar ratio is shown to exist in rabbit and calf bone. This complex, which may be involved in the transport and deposition of bone mineral, appears to constitute a significantly greater proportion of the lipids of younger bone than of more mature bone. The comples was isolated by a modified Folch extraction employing ultrasonic disruption of cellular material. Evidence is presented to show that the complex is a natural constituent of bone rather than one created artifactually during extraction.

Age Factors↗
PubMed1975

Effect of carbonate and biological macromolecules on formation and properties of hydroxyapatite.

Amorphous calcium phosphate (ACP) was transformed at 25 degrees to hydroxyapatite (HA) in horse and bovine serum; solutions of serum-protein fractions in tris-HC1 buffer (pH 7.4), and pH 7.4 buffers containing from 0.1 to 10 times physiological CO3(2-) concentration. The ACP-to-HA transformation was slower in whole serum and serum fractions than in control buffer solution. The observed adsorption of serum proteins on ACP and HA probably inhibits both the dissolution of the ACP particles and the growth of HA crystals. After 72 h all transformations were complete as determined by X-ray diffraction. The HA crystal dimensions decreased with increasing C03(2-) but the shape, as shown by X-ray linewidths, was relatively constant up to about 4% CO3(2-). At 15% CO3(2-) the crystals were more equiaxial and less needle-like in habit. The radial distribution function (RDF) of HA with 3.7% CO3(2-) is less well resolved than the RDF of HA with ambient CO3(2-) (1.1%). The peaks are less sharp and their amplitude falls more rapidly with increasing atomic separation than for low CO3(2-)-HA. These effects show that CO3(2-) decreases the regularity of the atomic arrangement when incorporated in HA. The rapid decrease, with increasing CO3(2-) content, of the IR splitting of the P-O bending mode of CO3(2-)-HA is attributed to reduced crystal size and possibly to a perturbation of the crystal field due to CO3(2-)-induced lattice distortion. Finally, for bone mineral, it is probable that the poor resolution of the X-ray and IR patterns is due, in large part, to small crystal size and internal disorder caused by CO3(2-).

Adsorption↗
PubMed1975

The surface chemistry of bone mineral and related calcium phosphates.

A review of the surface chemistry of bone mineral, hydroxyapatite and amorphous calcium phosphate is presented. Small-angle x-ray scattering and low-temperature nitrogen adsorption measurements show the magnitude of bone mineral surface to range from 100-200 m-2/g; the synthetic hydroxyapatite surface can vary from 25-200 m-2/g, while synthetic amorphous calcium phosphate ranges in surface from 20-60 m-2/g, according to the respective preparation conditions. The magnitude of heats of adsorption of certain small molecules (CO, Ar, N2, H2O, CH3OH) on bone mineral and hydroxyapatite show that these are polarizing surfaces that form strong bonds with polar or polarizable molecules; water is hydrogen-bonded to these surfaces with energies ranging from 23 kcal/mole for low coverage to 11 kcal/mole after two full monolayers; concomitantly, methanol ranges from 24 kcal/mole to 9 kcal/mole after the adsorption of one and a half monolayers. Stearic acid will close-pack perpendicularly on bone apatite surfaces when adsorbed from cyclohexane solution in a way reminiscent of the adsorption of this long, straight-chain molecule on water surface. It is believed that these molecules are hydrogen-bonded to electronegative ions on the apatite surface. Synthetic hydroxyapatite has long been used in chromatographic adsorption columns because of the specific bonding capacity the surfaces have for certain proteins and polynucleotides. The metabolic interrelationship of bone mineral and the body fluids is in great part dependent upon the nature and magnitude of mineral surface. From the surface studies described herein it was suggested that a chemical linkage could exist in bone between the mineral surface and certain free polar groups of collagen.

Adsorption↗
PubMed1975

Atomic structure of intracellular amorphous calcium phosphate deposits.

The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.

Animals↗