Arindam Ganguly

Grape seed proanthocyanidins increase collagen biodegradation resistance in the dentin/adhesive interface when included in an adhesive

OBJECTIVES Contemporary methods of dentin bonding could create hybrid layers (HLs) containing voids and exposed, demineralised collagen fibres. Proanthocyanidins (PA) have been shown to cross-link and strengthen demineralised dentin collagen, but their effects on collagen degradation within the HL have not been widely studied. The purpose of this study was to compare the morphological differences of HLs created by BisGMA/HEMA model adhesives with and without the addition of grape seed extract PA under conditions of enzymatic collagen degradation. METHODS Model adhesives formulated with and without 5% PA were bonded to the acid etched dentin. 5-μm-thick sections cut from the bonded specimens were stained with Goldners trichrome. The specimens were then exposed to 0.1% collagenase solution for 0, 1, or 6 days. Following collagenase treatment, the specimens were analysed with SEM/TEM. RESULTS Staining did not reveal a difference in the HLs created with the two adhesives. SEM showed the presence of intact collagen fibrils in all collagenase treatment conditions for specimens bonded with adhesive containing PA. These integral collagen fibrils were not observed in the specimens bonded with adhesive without PA after the same collagenase treatment. TEM confirmed that the specimens containing PA still showed normal collagen fibril organisation and dimensions after treatment with collagenase solution. In contrast, disorganised collagen fibrils in the interfacial zone lacked the typical cross-banding of normal collagen after collagenase treatment for specimens without PA. CONCLUSIONS The presence of grape seed extract PA in dental adhesives may inhibit the biodegradation of unprotected collagen fibrils within the HL.

Conformational stability, r0 structural parameters, ab initio calculations, and vibrational assignment for fluorocyclopentane.

The infrared spectra (3200-50 cm(-1)) of the gas and solid and the Raman spectrum (3200-30 cm(-1)) of liquid and solid fluorocyclopentane, c-C5H9F, have been recorded. Additionally the infrared spectra (3200-400 cm(-1)) of liquid xenon solutions have been recorded at -65 and -95 degrees C. In all of the physical states, only the twisted C(1) conformer was detected. Ab initio calculations utilizing various basis sets up to MP2(full)/6-311+G(2df,2pd) with and without diffuse functions have been used to predict the conformational stabilities. These calculations predict only the twisted C1 conformer as the stable form. The two envelope (C(s) symmetry) forms with axial and equatorial structures were predicted to be first order saddle points with average higher energies of 75 +/- 33 and 683 +/- 44 cm(-1), respectively, from the C1 conformer but lower energies of 2442 and 1812 cm(-1), respectively, than the planar form by MP2 calculations. Similar values were obtained from the corresponding density functional theory calculations by the B3LYP method. A complete vibrational assignment is given for the twisted (C1) conformer which is supported by normal coordinate calculations with scaled force constants from MP2(full)/6-31G(d) calculations. The adjusted r0 structural parameters have been obtained by systematically fitting the MP2(full)/6-311+G(d,p) predicted values with the rotational constants obtained from a microwave study. The determined heavy atom r0 distances in A are (C1C2) = 1.531(3), (C1C3) = 1.519(3), (C2C4) = 1.553(3), (C3C5) = 1.533(3), (C4C5) = 1.540(3), and (C1F6) = 1.411(3) and the angles in degrees are angle C3C1C2 = 105.5(5), angle C1C2C4 = 106.2(5), angle C1C3C5 = 102.9(5), angle F6C1C2 = 108.9(5), and angle F6C1C3 = 107.6(5) with a dihedral angle angle C2C4C5C3 = 25.3(3). These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.

Conformational stability of cyclobutanol from temperature dependent infrared spectra of xenon solutions, r0 structural parameters, ab initio calculations and vibrational assignment

Variable temperature (-55 to -100 degrees C) studies of the infrared spectra (4000-400 cm(-1)) of cyclobutanol, c-C4H7OH dissolved in liquid xenon have been carried out. The infrared spectrum (4000-100 cm(-1)) of the gas has also been recorded. From these data two of the four possible stable conformers have been confidently identified and their order of stabilities has been experimentally determined where the first indicator is for the position of attachment of the hydroxyl group on the bent cyclobutyl ring (Eq=equatorial or Ax=axial) and the second one (t=trans, g=gauche) is the relative position of the hydroxyl rotor, i.e. rotation around the ring C-O bond. The enthalpy difference between the most stable Eq-t conformer and the second most stable rotamer, Eq-g, has been determined to be 200+/-50 cm(-1) (2.39+/-0.60 kJ/mol). This experimentally determined order is consistent with the order of stability predicted by ab initio calculations Eq-t>Eq-g>Ax-g>Ax-t. Evidence was obtained for the third conformer Ax-g which is predicted by ab initio calculations to be less stable by more than 650cm(-1) than the Eq-t form. The percentage of each conformer at ambient temperature is estimated to be Eq-t (50%), Eq-g (47%) and Ax-g (3%). The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for all of the conformers from MP2(full)/6-31G(d) ab initio calculations. The optimized geometries and conformational stabilities have been obtained from ab initio calculations utilizing several different basis sets up to MP2(full)/aug-cc-pVTZ and from density functional theory calculations by the B3LYP method. By utilizing previously reported microwave rotational constants for the Eq-t conformer combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the Eq-t conformer are: the distances C1-C4=1.547(5) angstroms, C4-C6=1.552(5)angstroms, C-O=1.416(5) angstroms and angles angleC6C4C1=86.6(5) degrees , angleC4C1C5=88.9(5) degrees and angleC6C5C1C4=22.8(5) degrees . The results are discussed and compared to the corresponding properties of some similar molecules.

Conformational stability from variable-temperature infrared spectra of xenon solutions, r0 structural parameters, and vibrational assignment of pyrrolidine.

The infrared spectra of gaseous and variable-temperature liquid xenon solutions of pyrrolidine have been recorded. The enthalpy difference has been determined to be 109 ± 11 cm(-1) (1.30 ± 0.13 kJ mol(-1)) with the envelope-equatorial conformer more stable than the twist form with 37 ± 3% present at ambient temperature. Ab initio calculations utilizing various basis sets up to MP2(full)/aug-cc-pVTZ have been used to predict the conformational stabilities, energy at the equatorial-axial saddle point, and barriers to planarity. From previously reported microwave rotational constants along with MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained for both conformers. Heavy atom distances (Å) of equatorial[twist] conformer are as follows: N(1)-C(2) = 1.469(3)[1.476(3)], N(1)-C(3) = 1.469(3)[1.479(3)], C(2)-C(4) = 1.541(3)[1.556(3)], C(3)-C(5) = 1.541(3)[1.544(3)], C(4)-C(5) = 1.556(3)[1.543(3)]; and angles (deg)∠N(1)C(2)C(4) = 102.5(5)[107.6(5)], ∠N(1)C(3)C(5) = 102.5(5)[105.4(5)], ∠C(2)C(4)C(5) = 104.3(5)[104.6(5)], ∠C(3)C(5)C(4) = 104.3(5)[103.7(5)], ∠C(2)N(1)C(3) = 104.1(5)[103.9(5)], τC(2)C(4)C(5)C(3) = 0.0(5)[13.5(5)]. A complete vibrational assignment is proposed for both conformers.

Conformational stability, r0 structural parameters, and vibrational assignments of mono-substituted cyclobutanes: fluorocyclobutane.

Variable temperature (-55 to -100°C) studies of the infrared spectra (3500-400 cm(-1)) of fluorocyclobutane, c-C(4)H(7)F, dissolved in liquid xenon have been carried out as well as the infrared spectra of the gas. By utilizing eight pairs of conformers at 10 different temperatures, the enthalpy difference between the more stable equatorial conformer and the axial form has been determined to be 496±40 cm(-1) (5.93±0.48 kJ/mol). The percentage of the axial conformer present at ambient temperature is estimated to be 8±1%. The ab initio MP2(full) average predicted energy difference from a variety of basis sets is 732±47 cm(-1) (9.04±0.44 kJ/mol) and the average value of 602±20 cm(-1) from density functional theory predictions by the B3LYP method are significantly larger than the experimentally determined enthalpy value. By utilizing previously reported microwave rotational constants for the equatorial and axial conformers combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r(0) parameters have been obtained. The determined heavy atom structural parameters for the equatorial [axial] conformer are: distances (Å) C-F=1.383(3) [1.407(3)], C(α)-C(β)=1.543(3) [1.546(3)], C(β)-C(γ)=1.554(3) [1.554(3)] and angles (°) ∠C(α)C(β)C(γ)=85.0(5) [89.2(5)], ∠C(β)C(α)C(β)=89.3(5) [89.2(5)], ∠F-(C(β)C(α)C(β))=117.4(5) [109.2(5)] and a puckering angle of 37.4(5) [20.7(5)]. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some other monosubstituted cyclobutanes with halogen and pseudo-halogen substituents.