Patterned Silk Film Scaffolds for Aligned Lamellar Bone Tissue Engineering

The alignment and osteogenic differentiation of MSCs on patterned silk films (PF) is investigated as a bottom‐up approach toward engineering bone lamellae. Screening PF with various groove dimensions shows that cell alignment is mediated by both the pattern width and depth. MSCs are differentiated in osteogenic medium for four weeks on flat films and on the PF that produce the best alignment. The PF support osteogenic differentiation while also inducing lamellar alignment of cells and matrix deposition. A secondary alignment effect is noted on the PF where a new layer of aligned cells grows over the first layer, but rotated obliquely to the underlying pattern. This layering and rotation of the MSCs resembles the cellular organization observed in native lamellar bone.

     

On a transformation and re-transformation technique for constructing an affine equivariant multivariate median

An affine equivariant version of multivariate median is introduced. The proposed median is easy to compute and has some appealing geometric features that are related to the configuration of a multivariate data cloud. The transformation and re-transformation approach used in the construction of the median has some fundamental connection with the data driven co-ordinate system considered by Chaudhuri and Sengupta (1993, Journal of the American Statistical Association). Large sample statistical properties of the median are discussed and finite sample performance is investigated using Monte Carlo simulations.

     

Dynamics of polar solvation: Route to single exponential relaxation via translational diffusion

A microscopic theoretical calculation of time-dependent solvation energy shows that the solvation of an ion or a dipole is dominated by a single relaxation time if the translational contribution to relaxation is significant. Contribution No. 545 from the Solid State and Structural Chemistry Unit     

Orientation-dependent potential of mean force for protein folding

We present a solvent-implicit minimalistic model potential among the amino acid residues of proteins, obtained by using the known native structures [deposited in the Protein Data Bank (PDB)]. In this model, the amino acid side chains are represented by a single ellipsoidal site, defined by the group of atoms about the center of mass of the side chain. These ellipsoidal sites interact with other sites through an orientation-dependent interaction potential which we construct in the following fashion. First, the site-site potential of mean force (PMF) between heavy atoms is calculated [following F. Melo and E. Feytsman, J. Mol. Biol. 267, 207 (1997)] from statistics of their distance separation obtained from crystal structures. These site-site potentials are then used to calculate the distance and the orientation-dependent potential between side chains of all the amino acid residues (AAR). The distance and orientation dependencies show several interesting results. For example, we find that the PMF between two hydrophobic AARs, such as phenylalanine, is strongly attractive at short distances (after the obvious repulsive region at very short separation) and is characterized by a deep minimum, for specific orientations. For the interaction between two hydrophilic AARs, such a deep minimum is absent and in addition, the potential interestingly reveals the combined effect of polar (charge) and hydrophobic interactions among some of these AARs. The effectiveness of our potential has been tested by calculating the Z-scores for a large set of proteins. The calculated Z-scores show high negative values for most of them, signifying the success of the potential to identify the native structure from among a large number of its decoy states.     

Macroscopic solvation of molecules in excited states: An MCSCF model including solvent polarization effects-I

An MCSCF model including the effects of solvent polarization is developed. The model is applied within the limitations of INDO approximations to look into the dominant effects of solvent polarization on the electronic structure in the excited states of a model system (e.g.nπ ^* states of H₂CO). Important features of macroscopic solvation-induced reorganization of electron density and some consequence thereof are noted.     

Hydration layer of a cationic micelle, C(10)TAB: structure, rigidity, slow reorientation, hydrogen bond lifetime, and solvation dynamics

We report a theoretical study of the structure and dynamics of the water layer (the hydration layer) present at the surface of the cationic micelle decyltrimethylammonium bromide (DeTAB) by using atomistic molecular dynamics simulations. The simulated micelle consisted of 47 surfactant molecules (and an equal number of bromide ions), in good agreement with the pioneering light scattering experiments by Debye which found an aggregation number of 50. In this micelle, three partially positively charged methyl groups of each surfactant headgroup face the surrounding water. The nature of the cationic micellar surface is found to play an important role in determining the arrangement of water which is quite different from that in the bulk or on the surface of an anionic micelle, like cesium perfluorooctanoate. Water molecules present in the hydration layer are found to be preferentially distributed in the region between the three partially charged methyl headgroups. It is found that both the translational and rotational motions of water exhibit appreciably slower dynamics in the layer than those in the bulk. The solvation time correlation function (TCF) of bromide ions exhibits a long time component which is found to originate primarily from the interaction of the probe with the micellar headgroups. Thus, the decay of the solvation TCF is controlled largely by the residence time of the probe in the surface. The residence time distribution of the water molecules also exhibits a slow time component. We also calculate the collective number density fluctuation in the layer and find a prominent slow component compared to the similar quantity in the bulk. This slow component demonstrates that water structure in the hydration layer is more rigid than that in the bulk. These results demonstrate that the slow dynamics of hydration layer water is generic to macromolecular surfaces of either polarity.     

The models of proton assisted and the unassisted formation of CGC base triplets

The triple helix is formed by combining a double and a single strand DNAs in low pH and dissociates in high pH. Under such conditions, protonation of cytosine in the single strand is necessary for triplex formation where cytosine-guanine-cytosine (CGC+) base triplet stabilizes the triple helix. The mechanism of CGC+ triplet formation from guanine-cytosine (GC) and a protonated cytosine (C+) shows the importance of N3 proton. Similarly in the case of CGC (unprotonated) triplet, the donor acceptor H-bond at N3 hydrogen of the cytosine analog (C) initiates the interaction with GC. The correspondence between the two models of triplets, CGC+ and CGC, unambiguously assigned that protonation at N3 cytosine in low pH to be the first step in triplet formation, but a donor acceptor triplet (CGC) can be designed without involving a proton in the Hoogsteen H-bond. Further, the bases of cytosine analogue also show the capability of forming Watson Crick (WC) H-bonds with guanine.     

Influence of oxidative injury and monitoring of blood plasma by DSC on patients with psoriasis

Oxidative stress induced by oxygen free radicals (OFRs) is a casual factor in psoriasis. Our aim was to detect the oxidative stress parameters and blood plasma changes with differential scanning calorimetry (DSC) in psoriatic patients. The study included untreated (n = 39) and treated (retinoids, methotrexate, biologic response modifiers; n = 33) white adult patients from both sex. To monitor oxidative stress concentration of malondialdehyde (MDA), reduced glutathione and sulfhydryl groups, production of OFRs, and activity of myeloperoxidase (MPO), superoxide dismutase, and catalase were measured. Denaturation of plasma components was detected in SETARAM Micro DSC-II calorimeter. Total production of OFRs and MPO activity, and the concentration of MDA were significantly increased both in untreated patients with moderate and severe symptoms and in all drug-treated groups compared with controls (p < 0.001). All of the scavengers and antioxidants were significantly decreased in untreated patients and better preserved after retinoid and biological therapy. DSC scans of blood plasma showed melting temperature a characteristic parameter to follow the severity of disease. The calorimetric enthalpy is exhibiting a moderate decrease with the progression of the inflammation. These findings suggest that an imbalance exists between pro-oxidants and antioxidants in untreated severe psoriatic patients. All drug therapy reduced the changes, mainly the biologic response modifiers. Similarly, DSC showed differences between untreated and conventional systemic drug treatment.     

Universal power law in the orientational relaxation in thermotropic liquid crystals

We observe a surprisingly general power law decay at short to intermediate times in orientational relaxation in a variety of model systems (both calamitic and discotic, and also lattice) for thermotropic liquid crystals. As all these systems transit across the isotropic-nematic phase boundary, two power law relaxation regimes, separated by a plateau, emerge, giving rise to a steplike feature (well known in glassy liquids) in the single-particle second-rank orientational time correlation function. In contrast to its probable dynamical origin in supercooled liquids, we show that the power law here can originate from the thermodynamic fluctuations of the orientational order parameter, driven by the rapid growth in the second-rank orientational correlation length.     

Kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenenthroline)Fe(II) with guar gum–surfactant interactions

The kinetic investigations on the alkaline hydrolysis of tris-(1,10–phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301?K and ionic strength of 0.13?mol?L^?1. Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data.