Structure and function of propranolol: A β-adrenergic blocking drug

In our earlier studies using quantum chemical methods we had proposed that propranolol has an extended structure. These results were confirmed using proton NMR . We have now carried out extensive magnetic resonance and model building studies to examine the interaction of this drug with model membranes. The effect of propranolol on organization of lipid bilayers has been studied using ESR spin labeling technique. Spin label Tempo and spin labeled stearic acid (5 SASL ) have been used to monitor changes in the fluidity of model membranes. Presence of the drug is found to fluidize the lipids. In case of 0.2M dipalmitoyl phosphatidyl choline (DPPC), presence of drug (0.1M) is found to decrease the gel-liquid crystalline phase transition temperature by about 10°C. The order parameter measured from the spectrum of 5 SASL shows a 4% decrease on incorporation of the drug in membranes. ¹³C spin lattice relaxation time (T₁) measurements have been carried out for different nuclear sites of the drug. The aromatic moiety shows a high degree of molecular rigidity when the drug is bound to the lipid bilayers. The oxypropanolamine group is however relatively flexible. It appears from these studies that the aromatic group binds strongly to the hydrophobic regions of the lipid bilayer, while the oxypropanolamine moiety remains relatively free and lies in the hydrophilic region. The ¹³C chemical shifts indicate the involvement of the β-hydroxyl group in hydrogen bonding with the lipids. The NH group may be involved in electrostatic interactions with the negatively charged phosphate group of the lipid bilayers.     

Mineralized Synthetic Matrices as an Instructive Microenvironment for Osteogenic Differentiation of Human Mesenchymal Stem Cells

The effect of substrate‐mediated signals on osteogenic differentiation of hMSCs is studied using a synthetic bone‐like material comprising both organic and inorganic components that supports adhesion, spreading, and proliferation of hMSCs. hMSCs undergo osteogenic differentiation even in the absence of osteogenesis‐inducing supplements. They exhibit higher expressions of Runx2, BSP, and OCN compared to their matrix‐rigidity‐matched, non‐mineralized hydrogel counterparts. The mineralized‐hydrogel‐assisted osteogenic differentiation of hMSCs could be attributed to their exposure to high local concentrations of calcium and phosphate ions in conjunction with chemical and topological cues arising from the hydrogel‐bound calcium phosphate mineral layer.

     

Disturbance observer based sliding mode control of active suspension systems

In this paper, a novel scheme to reduce the acceleration of the sprung mass, used in combination with sliding mode control, is proposed. The proposed scheme estimates the effects of the uncertain, nonlinear spring and damper, load variation and the unknown road disturbance. The controller needs the states of sprung mass only, obviating the need to measure the states of the unsprung mass. The ultimate boundedness of the overall suspension system is proved. The efficacy of the method is verified through simulations for three different types of road profiles and load variation and the scheme is validated on an experimental setup. The results are compared with passive suspension system.     

Poly(acrylonitrile) ultrafiltration membranes. II. Membrane morphology and permeation characteristics

The rheology and phase‐boundary characteristics of various solutions comprising three polyacrylonitrile (PAN) grades dissolved in solutions of N,N‐dimethylformamide + salt (LiCl, ZnCl₂, or AlCl₃) additives were correlated with the resulting membrane morphology as determined by microscopy and permeability measurements. The phase separation characteristics of the dope solution were not markedly affected by the PAN molecular weight (MW); however, they were affected by the salt additive. For higher MW grades, the effect of salt addition can also be masked by the increased self‐association tendency of the polymer chains. PAN‐B and ‐C membranes were clearly less asymmetric in structure than the lower MW PAN‐A–based membranes. This is attributed to the higher viscosity/lower diffusivity of the PAN‐B and ‐C solutions, which results in slower solvent–nonsolvent exchange during the phase inversion process. Two factors reduce the incidence of surface defects (increased bubble points): (a) higher solution viscosity dampens surface perturbations during phase inversion, and (b) phase inversion pathways resulting in more homogenous morphology lead to membranes with higher bubble points. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2074–2085, 2005     

Minkowskian geometry,convexity conditions and the parallel axiom

The problem of characterising Minkowskian spaces is an important problem of that branch of differential geometry in which spaces more general than the complete Riemann and Finsler spaces are studied axiomatically using synthetic geometric methods. The fundamental theorem in this field is the result that a Desarguesian straightG-space in which the parallel axiom holds and the spheres are convex is Minkowskian. However the question as to whether the hypothesis of the space being Desarguesian is necessary or not has remained unsolved for over forty years. It is therefore natural to investigate conditions stronger than the mere convexity of spheres. In this paper such geometric conditions derived from functions which measure the distance between lines and points on lines are studied. Besides characterising the Minkowskian spaces these investigations also bring out the interplay between the parallel axiom and the convexity and linearity conditions.     

Influence of degeneracy on momentum relaxation times in semiconductors

We have studied the effect of degeneracy on momentum relaxation times under ohmic as well as non-ohmic conditions. We find that a proper momentum relaxation time, within the framework of the Boltzmann transport equation, can no longer be defined for isotropic but inelastic scattering when the carriers are hot whereas under ohmic conditions it can be defined and is appreciably altered by degeneracy. For elastic scattering the momentum relaxation time is found to be unaffected by degeneracy for both ohmic and non-ohmic regimes.     

Generalized inverses and operator equations

In this paper we obtain conditions under which the operator equations of the types AX = C and $\text{AXA}{}^1\text{= C}$ have hermitian and nonnegative definite solutions; here A is assumed to be relatively invertible. In addition we obtain some properties of generalized inverses of operators. Lastly we pose some conjectures; one of them is that the set of all nonzero relatively invertible operators is not connected.