A theory of micellization of AB diblock copolymer molecules in a selective solvent S is developed here. The micelles are assumed to have a completely segregated core region consisting only of the A block and a shell region consisting of the solvent S and the solvent compatible B block. The theory allows one to predict the critical micelle concentration, the micelle size distribution, the average aggregation number, as well as the core radius and the shell thickness of the micelle. The novel outcome of the present theory, in contrast to the treatments of micellization pioneered by de Gennes, Leibler, Orland, and Wheeler, and Noolandi and Hong, is its prediction that the solvent compatible B block plays an important role in determining the micellization behavior. The influence of the B block becomes relatively more prominent in systems where the solvent S constitutes a very good solvent for the B block. Further, scaling relations that are not system specific have been developed relating explicitly the micellar size parameters to the characteristics of the block copolymer and the solvent.

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Several extrinsic optical probes that have been used to monitor the extent of water penetration in micelles are aromatic in nature. We have studied the ring current-induced alterations in the NMR spectral signals of the various protons of the surfactant chains of micelles brought about by solubilizing some of these probes. The results indicate that such aromatic solubilizates are located near the headgroup region of the micelles. These probes would thus be expected to monitor the polarity and water content of the headgroup region and not the micellar interior.

We develop a theory of solubilization of low molecular weight species in block copolymer micelles, employing the scaling approach and building on the analogy between micelles and star polymers. Specifically, we consider spherical micelles of AB-diblock copolymers formed in selective solvents, in which the core and the shell regions are assumed to have radial concentration variations similar to those occurring in the solution state of a star polymer. Invoking the results for the conformation of a star polymer derived by Daoud and Cotton, expressions are developed for the free energy per molecule of the micelle AG, the core radius R, the shell thickness D, and the overall volume fraction of the polymer within the core #A as functions of the micellar aggregation number g. From the minimization of the free energy of an isolated micelle, the equilibrium values for all the micellar structural parameters and for the extent of solubilization are obtained. The results expressed as scaling relations for g, R, D, and +A are derived for various situations of interest including those of the solvent S being a good or theta solvent for the shell block B, and the solubilizate J being a good or theta solvent for the core block A.

Free volume theories of diffusion developed in the literature successfully treat penetrant transport behavior in rubbery polymers. The potential of such a free volume theory to predict the gas transport behavior in glassy polymers is explored here, duly taking into account the excess hole free volume present in the glassy state. The calculations require values for three model parameters appearing in the theory of diffusion which are obtained by fitting experimental gas permeability data in rubbery polymers. The calculations also require an estimate for the hole free volume in the gas-polymer mixture. This is obtained by fitting experimental gas sorption data in rubbery and glassy polymers to a free volume based theory of gas sorption developed here. Thus, the calculation of gas permeability in glassy polymers is strictly predictive in data in the glassy state.

Introduction of methylene bridges in aegPNA and apgPNA molecules give rise to cyclic five and six membered ring structures. Synthesis of a new six membered cyclic PNA monomer, aminopipecolyl PNA (pipPNA) is reported. Incorporation of pipPNA into PNA oligomers and comparative binding with target DNA sequences is studied.

Two-dimensional nuclear Overhauser enhancement (NOESY) spectra of labile protons were recorded in H 2 0 solutions of a protein and of a DNA duplex, using a modification of the standard NOESY experiment with all three 90" pulses replaced by jump-and-return sequences. For the protein as well as the DNA fragment the strategically important spectral regions could be recorded with good sensitivity and free of artifacts. Using this procedure, sequence-specific assignments were obtained for the imino protons, C2H of adenine, and C4NH2 of cytosine in a 23-base-pair DNA duplex which includes the 17-base-pair OR3 repressor binding site of bacteriophage A. Based on comparison with previously published results on the isolated OR3 binding site, these data were used for a study of chain termination effects on the chemical shifts of imino proton resonances of DNA duplexes.For 'H-NMR studies of nucleic acids in H 2 0 solution, where selective saturation (e.g. [l]) cannot be employed, a variety of different solvent suppression schemes by selective excitation have been applied with one-dimensional (1 D) Fourier transform experiments [2-161. Some of these techniques were recently also adapted for use with two-dimensional (2D) NMR, in particular 2D nuclear Overhauser enhancement spectroscopy (NOESY). Thereby, in all but one [17] of the modifications of the basic NOESY pulse sequence, 90"-t, -9Oo-z,,-90"-Acq. (tz) (1) only the last pulse was replaced by a semiselective excitation scheme [18-231. This leads to a 2D excitation profile which exhibits the spectral amplitude response of the semiselective pulse along wz, but is uniform along the w1 frequency axis. This could be very powerful with a phase program which assures that the combined effects of the first two pulses in the NOESY experiment always lead either to an effective 0-degree or 180-degree rotation at the frequency of the water resonance. The water magnetization would thus be parallel to the z-axis at all times except during t l , but irrespective of the radio-frequency carrier position relative to the water line such phase cycles would invariably also lead to folding of the spectrum along o1 about the water resonance [24]. On the other hand, all experimental schemes which prevent folding of the spectrum along w1 include scans which bring water magnetization into the x,y plane during the mixing time z , , so that after the semiselective observation pulse a huge water signal must be acquired. This situation would be less severe in experiments with a long mixing time, during which most of Correspondence to K. Wuthrich, Institut fur Molekularbiologie und Biophysik, ETH-Honggerberg, CH-8093 Zurich, SwitzerlandAbbreviations. NOESY, two-dimensional nuclear-Overhauser-enhancement spectroscopy; 1 D, one-dimensional; 2D, two-dimensional.the transverse magnetization could relax. Quite generally, it could also be improved with a homospoil pulse applied during the mixing time.Different approaches can be based on the use of three semiselective pulses in the NOESY experiment [17]. The ...