Improved bone morphogenetic protein-2 retention in an injectable collagen matrix using bifunctional peptides

To promote healing of many orthopedic injuries, tissue engineering approaches are being developed that combine growth factors such as Bone Morphogenetic Proteins (BMP) with biomaterial carriers. Although these technologies have shown great promise, they still face limitations. We describe a generalized approach to create target-specific modular peptides that bind growth factors to implantable biomaterials. These bifunctional peptide coatings provide a novel way to modulate biology on the surface of an implant. Using phage display techniques, we have identified peptides that bind with high affinity to BMP-2. The peptides that bind to BMP-2 fall into two different sequence clusters. The first cluster of peptide sequences contains the motif W-X-X-F-X-X-L (where X can be any amino acid) and the second cluster contains the motif F-P-L-K-G. We have synthesized bifunctional peptide linkers that contain BMP-2 and collagen-binding domains. Using a rat ectopic bone formation model, we have injected rhBMP-2 into a collagen matrix with or without a bifunctional BMP-2: collagen peptide (BC-1). The presence of BC-1 significantly increased osteogenic cellular activity, the area of bone formed, and bone maturity at the site of injection. Our results suggest that bifunctional peptides that can simultaneously bind to a growth factor and an implantable biomaterial can be used to control the delivery and release of growth factors at the site of implantation.

Dynamical splayed ferromagnetic ground state in the quantum spin ice Yb(2)Sn(2)O(7)

From magnetic, specific heat, (170)Yb Mössbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb(2)Sn(2)O(7), we show that below the first order transition at 0.15 K all of the Yb(3+) ions are long-range magnetically ordered and each has a moment of 1.1 μ(B) which lies at ≃ 10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [Phys. Rev. Lett. 108, 037202 (2012)] for a pyrochlore lattice of Kramers 1/2 effective spins.

Magnetic frustration in the disordered pyrochlore Yb(2)GaSbO(7)

In the pyrochlore Yb(2)GaSbO(7), the Yb(3+) sublattice forms a network of corner sharing tetrahedra and the second sublattice is made up of disordered, non-magnetic Ga(3+) and Sb(5+) ions. We have examined this compound using magnetic susceptibility, (170)Yb Mössbauer spectroscopy (down to 0.03 K) and muon spin relaxation (μSR) (down to 0.02 K) measurements. We establish the size of the Yb(3+) magnetic moments and that of the Yb(3+)-Yb(3+) coupling. At low temperatures, the correlated moments fluctuate between directions that are well tilted relative to the local [111] axis. The lattice disorder does not quench the frustration induced low temperature spin fluctuations but it does remove the first order dynamic transition that is present in the crystallographically ordered counterpart Yb(2)Ti(2)O(7). Below 1.0 K, the fluctuation rate of the correlated moments decreases progressively as the temperature is reduced and the moments remain dynamic down to 0.02 K where the rate is 7 × 10(7) s(-1). Magnetic frustration is operative in Yb(2)GaSbO(7) where the Yb(3+)-Yb(3+) interaction is antiferromagnetic as it is in Yb(2)Ti(2)O(7) where the interaction is ferromagnetic.

Energetics of an n --> pi interaction that impacts protein structure

[structure: see text] The trans/cis ratio of the amide bond in N-formylproline phenylesters correlates with electron withdrawal by a para substituent. The slope of the Hammett plot (rho = 0.26) is indicative of a substantial effect. This effect arises from a favorable n --> pi interaction between the amide oxygen and ester carbonyl. In a polypeptide chain, an analogous interaction can stabilize the conformation of trans peptide bonds, alpha-helices, and polyproline type-II helices.

Reciprocity of Steric and Stereoelectronic Effects in the Collagen Triple Helix

In previous work, we demonstrated that 4-fluoroproline residues can contribute greatly to the conformational stability of the collagen triple helix, and that this stability arises from stereoelectronic effects that fix the pucker of the pyrrolidine ring and thereby preorganize the backbone properly for triple-helix formation. Here, we take a reciprocal approach, demonstrating that the steric effect of a 4-methyl group confers stability similar to that from a 4-fluoro group in the opposite configuration. Such fundamental interplay between steric and stereoelectronic effects is heretofore unknown in proteins-natural or synthetic-and provides a new means to modulate conformational stability.

Reactive Carbon-Chain Molecules: Synthesis of 1-Diazo-2,4-pentadiyne and Spectroscopic Characterization of Triplet Pentadiynylidene (H−C⋮C−C̈−C⋮C−H)

1-Diazo-2,4-pentadiyne (6a), along with both monodeuterio isotopomers 6b and 6c, has been synthesized via a route that proceeds through diacetylene, 2,4-pentadiynal, and 2,4-pentadiynal tosylhydrazone. Photolysis of diazo compounds 6a-c (lambda > 444 nm; Ar or N2, 10 K) generates triplet carbenes HC5H (1) and HC5D (1-d), which have been characterized by IR, EPR, and UV/vis spectroscopy. Although many resonance structures contribute to the resonance hybrid for this highly unsaturated carbon-chain molecule, experiment and theory reveal that the structure is best depicted in terms of the dominant resonance contributor of penta-1,4-diyn-3-ylidene (diethynylcarbene, H-C[triple bond]C-:C-C[triple bond]C-H). Theory predicts an axially symmetric (D(infinity h)) structure and a triplet electronic ground state for 1 (CCSD(T)/ANO). Experimental IR frequencies and isotope shifts are in good agreement with computed values. The triplet EPR spectrum of 1 (absolute value(D/hc) = 0.6157 cm(-1), absolute value(E/hc) = 0.0006 cm(-1)) is consistent with an axially symmetric structure, and the Curie law behavior confirms that the triplet state is the ground state. The electronic absorption spectrum of 1 exhibits a weak transition near 400 nm with extensive vibronic coupling. Chemical trapping of triplet HC5H (1) in an O2-doped matrix affords the carbonyl oxide 16 derived exclusively from attack at the central carbon.

Stereoelectronic and Steric Effects in the Collagen Triple Helix: Toward a Code for Strand Association

Collagen is the most abundant protein in animals. The protein consists of a helix of three strands, each with sequence X-Y-Gly. Natural collagen is most stable when X is (2S)-proline (Pro) and Y is (2S,4R)-4-hydroxyproline (4R-Hyp). We had shown previously that triple helices in which X is (2S,4S)-4-fluoroproline (4S-Flp) or Y is (2S,4R)-4-fluoroproline (4R-Flp) display hyperstability. This hyperstability arises from stereoelectronic effects that preorganize the main-chain dihedral angles in the conformation found in the triple helix. Here, we report the synthesis of strands containing both 4S-Flp in the X-position and 4R-Flp in the Y-position. We find that these strands do not form a stable triple helix, presumably because of an unfavorable steric interaction between fluoro groups on adjacent strands. Density functional theory calculations indicate that (2S,3S)-3-fluoroproline (3S-Flp), like 4S-Flp, should preorganize the main chain properly for triple-helix formation but without a steric conflict. Synthetic strands containing 3S-Flp in the X-position and 4R-Flp in the Y-position do form a triple helix. This helix is, however, less stable than one with Pro in the X-position, presumably because of an unfavorable inductive effect that diminishes the strength of the interstrand 3S-FlpC=O...H-NGly hydrogen bond. Thus, other forces can counter the benefits derived from the proper preorganization. Although (Pro-Pro-Gly)7 and (4S-Flp-4R-Flp-Gly)7 do not form stable homotrimeric helices, mixtures of these two peptides form stable heterotrimeric helices containing one (Pro-Pro-Gly)7 strand and two (4S-Flp-4R-Flp-Gly)7 strands. This stoichiometry can be understood by considering the cross sections of the two possible heterotrimeric helices. This unexpected finding portends the development of a "code" for the self-assembly of determinate triple helices from two or three strands.

Magnetic density of states at low energy in geometrically frustrated systems

Using muon-spin-relaxation measurements we show that the pyrochlore compound Gd(2)Ti(2)O(7), in its magnetically ordered phase below approximately 1 K, displays persistent spin dynamics down to temperatures as low as 20 mK. The characteristics of the induced muon relaxation can be accounted for by a scattering process involving two magnetic excitations, with a density of states characterized by an upturn at low energy and a small gap depending linearly on the temperature. We propose that such a density of states is a generic feature of geometrically frustrated magnetic materials.

Planar spin fluctuations with a quadratic thermal dependence rate in spin liquid Gd3Ga5O12

The spin liquid properties of Gd3Ga5O12 have been examined using 155Gd Mössbauer spectroscopy down to 0.027 K. Information has been obtained concerning both the directional properties of the short range correlated moments and the thermal dependence of their spin fluctuation rates. Each Gd3+ spin (S=7/2) is found to be confined to a plane and its fluctuation rate decreases from approximately 2.8 x 10(9) s(-1) at 0.4 K to approximately 0.03 x 10(9) s(-1) at 0.09 K following a close-to-quadratic thermal dependence.

Stereoelectronic effects on collagen stability: the dichotomy of 4-fluoroproline diastereomers

Collagen is the most abundant protein in animals. Natural collagen consists of a triple helix of (Xaa-Yaa-Gly)n chains, in which the Xaa and Yaa residues are often l-proline. Here, a (2S,4S)-4-fluoroproline (flp) residue is shown to be greatly stabilizing in the Xaa position (but destabilizing in the Yaa position). In contrast, a (2S,4R)-4-fluoroproline (Flp) residue is shown to be greatly destabilizing in the Xaa position (but stabilizing in the Yaa position). The dichotomous effect of the diastereomers appears to arise from a gauche effect, which alters pyrrolidine ring pucker and hence properly (or improperly) preorganizes main-chain dihedral angles. Thus, the rational use of stereoelectronic effects can enhance the conformational stability of a protein.

Comparison of the amniotic fluid index with gray-scale and color Doppler ultrasound

OBJECTIVES

This study was undertaken to compare the amniotic fluid index (AFI) obtained with gray-scale ultrasound and color Doppler.

STUDY DESIGN

We examined 77 patients ranging from 22 to 41 weeks' gestation with two of five sonographers obtaining two measures of the AFI utilizing gray-scale and color Doppler.

RESULTS

Of the measurements of AFI, 96% showed the gray scale measurement to be greater than the color measurement (p < 0.0001; mean 9.3 +/- 3.3 cm vs. 8.5 +/- 3.0 cm). At gray-scale AFI < 5 cm, color AFI was essentially the same, but at gray-scale AFI 5-10 cm, color AFI was < 5 cm, 15.2% and 7.8% of the time. At gray-scale AFI > 10 cm, no color AFI was < 5 cm. Individual (n = 5) interobserver reliability was r = 0.79 (p < 0.0001) and intraobserver reliability was r = 0.94 (p < 0.0001).

CONCLUSIONS

AFI by color Doppler was always less than with gray scale. At an AFI of 5-10 cm, color demonstrated an AFI of < 5 cm in up to 16% of patients, and increased the diagnosis of oligohydramnios.

First-order transition in the spin dynamics of geometrically frustrated Yb2Ti2O7

Using neutron diffraction, 170Yb Mössbauer and muon spin relaxation spectroscopies, we have examined the pyrochlore Yb2Ti2O7, where the Yb3+S' = 1/2 ground state has planar anisotropy. Below approximately 0.24 K, the temperature of the known specific-heat lambda transition, there is no long range magnetic order. We show that the transition corresponds to a first-order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate, in the GHz range, follows a thermal excitation law, whereas below, the rate, in the MHz range, is temperature independent, indicative of a quantum fluctuation regime.

The elusive benzocyclobutenylidene: a combined computational and experimental attempt

Ab initio and density functional theory calculations predict that benzocyclobutenylidene (1) has a singlet ground state in contrast to the parent phenylcarbene and many other simply substituted arylcarbenes. Calculations also predict that 1 should lie in a relatively deep potential well, while its triplet state is 14.5 kcal mol(-)(1) higher in energy. However, attempts to observe 1 directly by photolysis of two different nitrogenous precursors were not successful. Irradiation of diazobenzocyclobutene (7) (lambda > 534 nm or lambda > 300 nm) or azibenzocyclobutene (10) (lambda > 328 nm) in Ar matrixes at 10 K leads to the formation of the strained cycloalkyne 7-methylenecyclohepta-3,5-dien-1-yne (3). (13)C-Labeled 3 was also prepared in a similar manner. There is very good agreement between experimental IR spectra and computationally derived harmonic vibrational frequencies for 3 and [(13)C]-3 and excellent agreement between observed and calculated isotopic shifts. Prolonged short-wavelength irradiation converts 3 into benzocyclobutadiene (5). Phenylacetylene (6) and benzocyclobutadiene dimer (11) were identified as products arising from flash vacuum pyrolysis of diazirine 10 at 500 degrees C.

Aerosol extinction contribution to atmospheric attenuation in infrared wavelengths

Atmospheric attenuation in several good transmission windows is estimated for long sea-level paths using relatively unsophisticated techniques. The estimates consist of separate estimates of gas and water vapor absorption, aerosol extinction, and aerosol liquid absorption. The contribution of aerosol extinction and aerosol liquid absorption to total atmospheric attenuation is explored. Estimated spectral aerosol extinction and absorption coefficients between the wavelengths of 2 microm and 14 micron are plotted for a wide variety of relative humidities and aerosol nucleation particle distributions. Total attenuation estimates are compared to accepted field measurement data. The agreement is sufficiently good to provide a base for estimating infrared instrument performance under similar conditions.