Synthetic and natural polycationic polymer nanoparticles interact selectively with fluid-phase domains of DMPC lipid bilayers

Polycationic polymers are known to disrupt lipid bilayers. In this letter, we report the dependence of this disruption on the lipid structural phase. DMPC bilayers are exposed to two polycationic polymeric nanoparticles, PAMAM dendrimers and MSI-78. We find that regions of the bilayer that are in the gel phase are unaffected by the presence of polymers, whereas the liquid phase is disrupted.     

Recoil studies of fission products formed in the fission of U by protons of energies 25–85 MeV

The recoil properties of ten fission products with masses ranging from 72 to 136 formed in the fission of ²³⁸U with protons of energies 25–85 MeV have been determined radiochemically by the integral-range method. From the recoil properties of the products and the Monte Carlo cascade calculations the average kinetic energy, cascade deposition energy, and anisotropy parameter for each fission product has been calculated. The kinetic energy and the excitation energy of the primary fragments leading to the observed fission product, and the total kinetic energy and the total excitation energy of the primary fragment pair have also been calculated.

The results indicate that up to a bombarding energy of 40 MeV fission takes place predominantly by the compound nucleus mechanism, with an increasing contribution of the direct interaction mechanism as the bombarding energy increases. The kinetic energy deficit was found to decrease with increasing bombarding energy. The fission products formed from the symmetric mode of fission have a larger separation distance between the charge centres of their respective primary fragments than those for the asymmetric mode of fission.     

Determination of the conformation and stability of simple homopolypeptides using solid-state NMR

15N CPMAS, 13C CPMAS and 1H CRAMPS spectra of several polypeptide samples were compared to determine the useful features of each technique. 13C CPMAS is the most well-established technique and is useful for quick determination of secondary structure. The 15N nucleus is more sensitive to exact hydrogen-bonding parameters, which complicates interpretation of the spectra. However, it is better for resolving end effects and structural types in short oligomers. 1H CRAMPS spectra are similar to 13C CPMAS in the information obtained, but the resolution is not as good. Using 13C CPMAS, the conformation of polyglycine was investigated in detail. Precipitation from solvents such as DCA or TFA resulted in the rippled beta-sheet structure (PG I), while 3(1)-helix (PG II) was formed by precipitation from aqueous solutions of LiBr. Grinding the sample resulted in an increase in the amount of PG I, indicating that this form is more stable in the solid state. These results agree with previous work on poly(L-alanine) showing that the beta-sheet form is more stable in the solid state. Homopolypeptides with larger side chains did not change conformation upon grinding due to the greater difficulty in disrupting van der Waals interactions and inertia of the large side chains.     

Structural acoustic silencers--design and experiment

The effectiveness of introducing flexible structural layers into air conveying ducts for controlling noise is investigated through theoretical and experimental means, focusing at low frequencies where conventional passive silencing technology is least effective. Previous theoretical work has shown that using flexible rather than rigid walls has the potential to achieve high transmission losses. The physical mechanisms responsible for structural acoustic silencing, including the relation between transmission loss peaks and structural resonance corresponding to different transverse structural modes, are presented. Sensitivity of the performance to acoustic and structural boundary conditions is discussed. To eliminate radiated noise from these walls (breakout noise), a rigid walled cavity is introduced under the flexible plate. The challenge is to find means to reject plane waves in the two-duct system. Designs that overcome these issues and achieve appreciable transmission loss are investigated. Results based on three-dimensional finite element simulations are compared with experimental results.     

Solid-state NMR spectroscopy of aligned lipid bilayers at low temperatures

This study, for the first time, demonstrates that it is possible to mechanically align lipid bilayers at a very low temperature (as low as the gel-to-liquid crystalline phase transition temperature). Performing NMR experiments on mechanically aligned lipid bilayers at a low temperature increases the signal-to-noise ratio, the resolution, and the span of NMR parameters. The increased lifetime of the alignment and the nature of the bilayer sample would enhance the application of solid-state NMR techniques to study membrane proteins.     

A 2D solid-state NMR experiment to resolve overlapping aromatic resonances of thiophene-based nematogens

In this study, we demonstrate the feasibility of resolving overlapping 13C chemical shift spectral lines of aromatic rings in a thiophene-based nematogen in the mesophase using a 2D PITANSEMA solid-state NMR method. This technique provided the information about chemical shift values as well as dipolar couplings that are used for determining the orientational order parameter. Large C-H dipolar coupling values measured for thiophene in contrast to phenyl rings suggest that the heterocyclic ring is not part of the molecular axis. Using the order parameter, we determined the orientation of C-H vectors of the thiophene ring. We believe that the 2D solid-state NMR can be extended to other types of liquid crystalline materials such as the banana-based mesogens for determining the orientational order and bent angle.     

Preparation and evaluation of99mTc-thiodiglycolic acid (TDGA) for renal function studies

Methods for the preparation and analysis of a new renal radiopharmaceutical,^99mTc-thiodiglycolic acid (TDGA), are reported. The kit for Tc-TDGA contains a lypophilized acidic (pH 2.5) mixture of 5 mg TDGA and 0.05 mg SnCl₂·2H₂O. Acetate buffer has been found to be a suitable solvent for paper chromatography of^99mTc-TDGA. The results of the quantitative organ distribution studies in rats and rabbits indicated the characteristics of^99mTc-TDGA to be intermediate to the renal tubular agent¹³¹I-Hippuran and the GFR agent^99mTc-DTPA.Parts of this work have been presented at the Indo-US Seminar on Radiopharmaceuticals-cum-17th Ann. Conf. of Soc. Nucl. Med. (India) held at Bangalore in Jan. 1986 and at the 18th Ann. Conf. of Soc. Nucl. Med. (India held at Madras in Dec. 1986. Also a part of this work has been included in the dissertation of N. Ramamoorthy submitted to the University of Bombay for the Ph. D. degree in chemistry.     

Synthesis, structure, magnetism and nuclease activity of tetranuclear copper(II) phosphonates containing ancillary 2,2'-bipyridine or 1,10-phenanthroline ligands

The reaction of cyclohexylphosphonic acid (C(6)H(11)PO(3)H(2)), anhydrous CuCl(2) and 2,2'-bipyridine (bpy) in the presence of triethylamine followed by a metathesis reaction with KNO(3) afforded [Cu(4)(mu-Cl)(2)(mu(3)-C(6)H(11)PO(3))(2)(bpy)(4)](NO(3))(2) (1). In an analogous reaction involving Cu(OAc)(2).H(2)O, the complex [Cu(4)(mu-CH(3)COO)(2)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4)](CH(3)COO)(2) (2) has been isolated. The three-component reaction involving Cu(NO(3))(2).3H(2)O, cyclohexylphosphonic acid and 2,2'-bipyridine in the presence of triethylamine afforded the tetranuclear assembly [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(2,2'-bpy)(4) (H(2)O)(2)](NO(3))(3) (3). Replacing 2,2'-bipyridine with 1,10-phenanthroline (phen) in the above reaction resulted in [Cu(4)(mu-OH)(mu(3)-C(6)H(11)PO(3))(2)(phen)(4)(H(2)O)(2)](NO(3))(3) (4). In all the copper(II) phosphonates (1-4) the two phosphonate ions bridge the four copper(II) ions in a capping coordination action. Each phosphonate ion bridges four copper(II) ions in a mu(4), eta(3) coordination mode or 4.211 of the Harris notation. Variable-temperature magnetic studies on reveal that all four complexes exhibit moderately strong intramolecular antiferromagnetic coupling. The DNA cleavage activity of complexes 1-4 is also described. Compounds 1 and 3 were able to completely convert the supercoiled pBR322 DNA form I to nick form II without any co-oxidant. In contrast, 50% conversion occurred with and 40% with 4. In the presence of magnesium monoperoxyphthalate all four compounds achieved rapid conversion of form I to form II.