Physico-chemical investigation of asymmetrical peptidolipidyl-cyclodextrins

A new class of amphiphilic peptidolipidyl-cyclodextrins is reported. The derivatives are chiral due to the presence of an L-leucine in the spacer arm that links a saccharide moiety and a grafted, saturated hydrocarbon chain. Self-assembly properties of the peptidolipidyl-cyclodextrins are characterized by quasi-elastic light scattering, turbidity and UV-visible absorption measurements. NMR experiments give insight into the intermolecular dipolar interactions as a function of temperature and concentration. N-dodecyl-N alpha-(6 I-amidosuccinyl-6 1-deoxy-cyclomaltoheptaose)-L-leucine (1) is poorly soluble in aqueous media. N-dodecyl-N(alpha)-(6 I-amidosuccinyl-6 I-deoxy-2 I,3 I-di-O-methyl-hexakis-(2 II-VII,3 II-VII,6 II-VII-tri-O-methyl)-cyclomaltoheptaose)-L-leucine (2) is found to be more soluble and self-assembles into stable supramolecular colloidal aggregates with nanometric dimensions above a critical aggregation concentration (CAC). It has a propensity for solubilization of hydrophobic species revealing a micellar-like behavior, which is compared to that of the non-ionic detergent octyl glucoside. On the contrary, compound 1 precipitates in a crystalline phase beyond its water solubility limit, and it does not display any solubilizing capacity. The observed behavior corroborates at the molecular level with the NMR results.     

A rigorous framework to interpret water relaxivity. The case study of a Gd(III) complex with an alpha-cyclodextrin derivative

We present a general theoretical framework suitable for an economical, but rigorous, analysis of the relaxivity and EPR data of paramagnetic metal complexes. This framework is based on the so-called Grenoble method that properly accounts for the fluctuations of the "static" zero-field splitting Hamiltonian and avoids the misinterpretation of experimental data, which occurs with the Solomon, Bloembergen, and Morgan (SBM) formalism and may lead to erroneous conclusions. The applicability of the SBM approximation is discussed. Our approach is implemented in the case of a new Gd(3+) chelate with a cyclodextrin derivative ligand hexakis(2-O-carboxymethyl-3,6-anhydro)-alpha-cyclodextrin (ACX), designed to obtain lanthanide complexes of enhanced stability in comparison to natural cyclodextrins. The introduction of carboxymethyl units on the six residual hydroxyl groups of an alpha-per-3,6-anhydro cyclodextrin leads to mono- and binuclear Ln(3+) complexes with log beta(110) approximately = 7.5. The GdACX complex induces large water proton relaxivity in 0.1 M KCl aqueous solution. The molecular parameters governing the longitudinal (r1) and transverse (r2) relaxivities above 1 T are obtained through simple SBM-like theoretical expressions and complementary experimental techniques. The metal hydration state, the translational diffusion coefficient of the complex, and its rotational correlation time are derived from luminescence lifetime studies, pulse-field gradient NMR, and deuteron quadrupolar relaxation, respectively. The high relaxivity induced by the GdACX complex is attributed to its high hydration state in the presence of potassium ions and to a rotational correlation time lengthened by the hydrophilic character of the ACX scaffold.     

Stochastic estimation and proper orthogonal decomposition: Complementary techniques for identifying structure

The Proper Orthogonal Decomposition (POD) as introduced by Lumley and the Linear Stochastic Estimation (LSE) as introduced by Adrian are used to identify structure in the axisymmetric jet shear layer and the 2-D mixing layer. In this paper we will briefly discuss the application of each method, then focus on a novel technique which employs the strengths of each. This complementary technique consists of projecting the estimated velocity field obtained from application of LSE onto the POD eigenfunctions to obtain estimated random coefficients. These estimated random coefficients are then used in conjunction with the POD eigenfunctions to reconstruct the estimated random velocity field. A qualitative comparison between the first POD mode representation of the estimated random velocity field and that obtained utilizing the original measured field indicates that the two are remarkably similar, in both flows. In order to quantitatively assess the technique, the root mean square (RMS) velocities are computed from the estimated and original velocity fields and comparisons made. In both flows the RMS velocities captured using the first POD mode of the estimated field are very close to those obtained from the first POD mode of the unestimated original field. These results show that the complementary technique, which combines LSE and POD, allows one to obtain time dependent information from the POD while greatly reducing the amount of instantaneous data required. Hence, it may not be necessary to measure the instantaneous velocity field at all points in spacesimultaneously to obtain the phase of the structures, but only at a few select spatial positions. Moreover, this type of an approach can possibly be used to verify or check low dimensional dynamical systems models for the POD coefficients (for the first POD mode) which are currently being developed for both of these flows.The authors wish to thank DRET Grant # 90/171, the French Embassy Chateaubriand Fellowship (CIES) program for L. Ukeiley, NASA/Lewis GSRP for D. Cole, NASA/Ames Dryden, NASA/Langley and NSF/CNRS through the international travel grants program for funding various portions of this work.     

Implicit BEM formulations for usual and sensitivity problems in elasto-plasticity using the consistent tangent operator concept

This paper presents boundary element method (BEM) formulations for usual and sensitivity problems in (small strain) elasto-plasticity using the concept of the local consistent tangent operator (CTO). “Usual” problems here refer to analysis of nonlinear problems in structural and solid continua, for which Simo and Taylor first proposed the use of the CTO within the context of the finite element method (FEM). A new implicit BEM scheme for such problems, using the CTO, is presented first. A formulation for sensitivity analysis follows. It is shown that the sensitivity of the strain increment, associated with an infinitesimal variation of some design parameter, solves a linear problem which is governed by the (converged value of the) same global CTO as the one that appears in the usual problem. Numerical results for both usual and sensitivity problems are shown for a one-dimensional example. They demonstrate the effectiveness of the present approach. In particular, accurate sensitivities with respect to material parameters (e.g., exponent of the power-type hardening law) are obtained even with few integration cells and for large load increments.     

Design,Synthesis and SAR in 2,4,7-Trisubstituted Pyrido[3,2-d]Pyrimidine Series as Novel PI3K/mTOR Inhibitors

This work describes the synthesis, enzymatic activities on PI3K and mTOR, in silico docking and cellular activities of various uncommon 2,4,7 trisubstituted pyrido[3,2-d]pyrimidines. The series synthesized offers a chemical diversity in C-7 whereas C-2 (3-hydroxyphenyl) and C-4 groups (morpholine) remain unchanged, in order to provide a better understanding of the molecular determinants of PI3K selectivity or dual activity on PI3K and mTOR. Some C-7 substituents were shown to improve the efficiency on kinases compared to the 2,4-di-substituted pyrimidopyrimidine derivatives used as references. Six novel derivatives possess IC₅₀ values on PI3Kα between 3 and 10 nM. The compounds with the best efficiencies on PI3K and mTOR induced micromolar cytotoxicity on cancer cell lines possessing an overactivated PI3K pathway.     

Lanthanide-Based Probes for Imaging Detection of Enzyme Activities by NIR Luminescence,T1- and ParaCEST MRI

Applying a single molecular probe to monitor enzymatic activities in multiple, complementary imaging modalities is highly desirable to ascertain detection and to avoid the complexity associated with the use of agents of different chemical entities. We demonstrate here the versatility of lanthanide (Ln³⁺) complexes with respect to their optical and magnetic properties and their potential for enzymatic detection in NIR luminescence, CEST and T1 MR imaging, controlled by the nature of the Ln³⁺ ion, while using a unique chelator. Based on X-ray structural, photophysical, and solution NMR investigations of a family of Ln³⁺ DO3A-pyridine model complexes, we could rationalize the luminescence (Eu³⁺, Yb³⁺), CEST (Yb³⁺) and relaxation (Gd³⁺) properties and their variations between carbamate and amine derivatives. This allowed the design of $$ probes which undergo enzyme-mediated changes detectable in NIR luminescence, CEST and T1-weighted MRI, respectively governed by variations in their absorption energy, in their exchanging proton pool and in their size, thus relaxation efficacy. We demonstrate that these properties can be exploited for the visualization of β-galactosidase activity in phantom samples by different imaging modalities: NIR optical imaging, CEST and T1-weighted MRI.     

Changes of mechanical properties in cold-crystallized syndiotactic polypropylene during aging

Many semicrystalline polymers undergo a process of aging when they are stored at temperatures higher than their glass-transition temperature (T _g). Syndiotactic polypropylene was quenched from the melt to −40 °C, crystallized from the glassy state at 20 or 40 °C and stored at the respective temperature for different aging times up to 7200 h. A significant increase in the tensile modulus and stress at yield and a decrease in strain at yield were observed for both aging temperatures. Differential scanning calorimetry (DSC) scans of aged material showed an endothermic annealing peak 15–30 °C above the previous aging temperature, the maximum temperature and enthalpic content of which increased with aging time. The position and the shape of the melting peak were not affected by aging. Scans of the storage modulus obtained from dynamic mechanical analyser measurements indicated a softening process starting at about 20 °C above the aging temperature and correlating with the annealing peak detected by DSC. Density measurements and wide-angle X-ray scattering investigations revealed that neither the crystallinity increased significantly nor did the crystal structure change. So the observed property changes induced by aging are attributed to microstructural changes within the amorphous phase. Furthermore, it could be shown by annealing experiments carried out at 60 °C, that aging above T _g is, analogous to aging below T _g (physical aging), a thermoreversible process. Received: 18 September 2000 Accepted: 2 January 2001     

One-Pot Synthesis of Asymmetrically Difunctionalized Oligomaltosides by Cyclodextrin Ring Opening

The synthesis of pure difunctionalized hexa-, hepta- and octamaltosides was performed by one-pot chemical reaction from perbenzoylated cyclodextrin. Oligomaltosides with azide, propargyl or allyl on reducing end and an unprotected hydroxyl group on non-reducing end were obtained from perbenzoylated α-, β- and γ-cyclodextrin with 12 to 48 % yields.     

Photochemical synthesis of cyclic peptide models from phthalimido acetamides and phthaloyl dipeptide esters

The photochemistry of several phthalimido acetamides and phthaloyl dipeptide esters has been investigated. Their photocyclization ability strongly depended on the substitution pattern of the amide linker group. While secondary amide-derived starting materials were largely unreactive, the corresponding tertiary amide-linked derivatives furnished the desired cyclic peptide model compounds in acceptable to good yields (41–80%). The structurally related ester-linked model derivatives also remained unreactive upon irradiation. Preferential hydrogen-abstraction from the E-cis-substituent is suggested to explain the observed differences in cyclization ability.