Stanley C. Nyburg

Hydroxyapatite Formation in Collagen, Gelatin, and Agarose Gels

Collagen has long been suspected to be a promoter of hydroxyapatite (HA) deposition in bone. This theory was tested by comparison of HA formation in gels composed of collagen, gelatin or agarose. Collagen gels supported substantially more HA precipitation than gelatin gels, but slightly less than agarose gels. Analysis of the relative diffusion rates for calcium in these matrices indicated that, in this system, amount of HA formation is dependent upon the rate of diffusion. Under conditions in which the diffusion rates for collagen and agarose gels were comparable, similar amounts of HA were formed. This suggests that fibrillar collagen is not per se a promoter of HA deposition. Extracellular matrix macromolecules may influence calcification by restricting ionic diffusion through connective tissues.

X-Ray crystallographic determination of the structure of µ-diphenylacetylene-bis-(π-pentaphenylcyclopentadienyl)dipalladium(I)

The structure of µ-diphenylacetylene-bis-(π-pentaphenylcyclopentadienyl)dipalladium(I), which is readily and quantitatively synthesised by the reaction of diphenylacetylene with palladium acetate in methanol, has been determined by X-ray crystallography.

Conformations of the thiathiophthenes and related molecules

A conformational ab initio MO study has been carried out for the thiathiophthene molecule (TTP) and two related model compounds, thiomalonaldehyde (TMA) and its conjugate base (TMA(-)). The conformational energy surfaces for TMA, TMA(-) and TTP were generated using a least squares fit to the calculated data and plotted on a CALCOMP plotter. The results of the calculations showed that the cis-cis planar conformation of TTP is the most stable in agreement with experimental findings. For TMA and TMA(-) the cis-cis planar conformation is not the most stable. Contour plots of the five occupied π-MOs of TTP show great similarity to those of naphthalene.Less detailed calculations were carried out for 3-hydroxy-prop-2-en-1-thione (HPT) and 3-mercapto-prop-2-en-1-thione (MPT). HPT was shown to be most stable in the cis planar hydrogen bonded conformation in agreement with the experimentally obtained results. For MPT the non-hydrogen bonded planar structure was found to be the most stable.

Complexes of a “mono-p-donor crown ether” hybrid ligand with potential for the activation of a coordinated carbon monoxide via selective cation binding

Abstract Derivatives of 1,10-dioxa-4,7-diaza-11-phosphacycloundecane are known to function as mono-P-donor crown ether ligands. When complexed to molybdenum or tungsten in the form of M(CO) 5 P derivatives they provide an additional incentive for nucleophilic attack (RLi reagents) at the C-atom of a coordinated CO via selective Li + ion binding by the benzoylate/acylate product. The structure of one of these products, ci -[ OCH 2 CH 2 N(Me)CH 2 CH 2 N(Me)CH 2 CH 2 O)P (OEt)] — − Mo(CO) 4 (PhCO)→Li + , has been determined by X-ray crystallography.

Crystal structure of two quasi-racemates of (–)-podopetaline and (–)-ormosanine isolated from Podopetalum ormondii; the absolute configuration of (–)-ormosanine

A constant m.p. alkaloid fraction obtained from Podopetalum ormondii has been shown by X-ray analysis to contain two polymorphs, one monoclinic, the other triclinic, both being quasi-racemates of (–)-podopetaline and (–)-ormosanine.

X-Ray crystal structures of 2,2′-bridged biphenyls with heterocyclic bridging rings: contraction in ring size on reduction

X-Ray crystal structure analysis confirms that two of the four tetrabenzo [b,d,h,j][1,6]diazacyclododecines previously investigated have 12-membered rings; there is a strong presumption that the other two have a similar structure. Three of the four compounds undergo (dimethylamino)borane reduction to the tetrahydro derivatives in a process shown by X-Ray analysis and/or n.m.r. spectroscopy to involve C–N bond breaking and ring contraction from 12- to seven-membered rings. The fourth compound is shown by X-ray analysis to retain its (presumed) 12-membered ring structure when the tetrahydro derivative is produced by catalytic hydrogenation.

An unusual bilaterally flanked olefin; X-ray crystal structure of 5,14;7,12-bis-(o-benzeno)-6,13-ethenylidene-5,5a,6,6a,7,12,12a,13,13a,14-decahydropentacene

Spectroscopic and chemical evidence reveals the intramolecular π–π orbital proximity in the novel Diels–Alder adducts (7) and (9); the X-ray crystal structure of (9) is reported.

The crystal structure of penicillopepsin at 6Åresolution

Abstract A 6Aresolution electron density map of crystals of penicillopepsin, an acid protease from Penicillium janthinellum , has been computed from multiple isomorphous replacement phases determined from two heavy metal derivatives, K2PtCl6 and UO2Cl2. The mean figure of merit of the map is 0.939. The boundaries of the molecules, of which there are four per unit cell, are readily discernible. The molecule is highly asymmetric with approximate dimensions 60A× 40A× 30A. The molecule consists of two distinct lobes separated by a deep cleft, which is probably the extended substrate binding site.

E.H.M.O. calculations on the actual conformations of thymine photodimers

Extended Hückel molecular orbital calculations have been carried out on the actual structures of some photodimers of uracil and thymine. The results are compared with those derived for some postulated models by Jordan and Pullman, and the differences between the real structures and the models are examined.

The synthesis and structure of a macrocycle containing a quinone unit by treatment of tetrafluoro-1,4-benzoquinone with 1,11-diamino-3,6,9-trioxaundecane

A one-step synthesis of a novel macrocycle containing a quinone unit by treatment of p-fluoranil with 1,11-diamino-3,6,9-trioxaundecane is described and its structure determined by a combination of X-ray crystallography, multinuclear NMR, IR, and UV-VIS spectroscopy.