The tumor-homing pentapeptide CREKA (Cys-Arg-Glu-Lys-Ala) specifically homes to tumors by binding to fibrin and fibrinassociated clotted plasma proteins in tumor vessels. Previous results show that CREKA-coated superparamagnetic iron oxide particles can cause additional clotting in tumor vessels, which creates more binding sites for the peptide. We have used this self-amplifying homing system to develop theranostic nanoparticles that simultaneously serve as an imaging agent and inhibit tumor growth by obstructing tumor circulation through blood clotting. The CREKA nanoparticles were combined with nanoparticles coated with another tumor-homing peptide, CRKDKC, and nanoparticles with an elongated shape (nanoworms) were used for improved binding efficacy. The efficacy of the CREKA peptide was then increased by replacing some residues with nonproteinogenic counterparts, which increased the stability of the peptide in the circula-

Study on the molecular packing of the R-form of poly(L-lactide) has been attempted taking into account packing energy calculations, refinement against new electron diffraction data, and Monte Carlo simulations. Packing energy has been evaluated for a fixed 107 conformation and an antiparallel arrangement of molecular chains. The energetically allowed space seems to be quite restricted, but with several minima of similar energy. One of them corresponds to a P212121 space group and agrees with the structure refined against diffraction data. Moreover, Monte Carlo simulations show a spontaneous evolution toward the refined model when parameters that define the packing, such as chain axis shift and setting orientation angles, are relaxed. On the other hand, the proposed packing shows asymmetric interactions that may lead to a molecular distortion.

gamma-Butyrolactone, unlike delta-valerolactone, does not polymerize despite a strain energy of approximately 8 kcal mol-1 which could be relieved by opening the s-cis lactone ester bond to an s-trans ester bond in the polymer. To explain this anomaly, we have applied quantum mechanical methods to study the thermochemistry involved in the ring-opening reactions of gamma-butyrolactone and delta-valerolactone, the conformational preferences of model molecules that mimic their corresponding homopolyesters, and the variation of enthalpy associated to the polymerizability of such two cyclic lactones. The overall results indicate that the lack of polymerizability of gamma-butyrolactone should be attributed to the low strain of the ring, which shows much less geometric distortion in the ester group than delta-valerolactone, and the notable stability of the coiled conformations found in model compounds of poly-4-hydroxybutyrate.

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The suitability of the self-consistent reaction field (SCRF) strategy for the study of solutes in chloroform solution has been examined. The SCRF method developed by Miertus, Scrocco and Tomasi (MST) has been parametrized at both ab initio 6-31G* and semiempirical AM1, MNDO, and PM3 levels. The reliability of the MST/SCRF model has been assessed from the comparison with results derived from classical Monte Carlo-free energy perturbation simulations and from mixed Monte Carlo-quantum mechanical/molecular mechanical computations, as well as with experimental data. The parametrized MST/SCRF method estimates the free energy of solvation with a root-mean-square deviation of 0.4 kcal/mol from the experimental value for the molecules studied. Further confidence in the optimized method stems from its ability to reproduce the tautomeric change of 2-and 4-pyridone upon transfer from gas phase to chloroform and the partition coefficient for compounds not considered in the parametrization. The results indicate the suitability of the MST/SCRF model for the study of solvent effects in dilute chloroform solutions.

In this article, the extrapolation procedures of π-π* electronic transition energy on π-conjugated oligomers are reexamined. Different models, including the simplest coupled oscillator, the free electron, the Hückel approach, the molecular exciton model, and some specific fitting-functions, are compared using the transition energies derived from theoretical calculations on three thiophene-based oligomer series. Specifically, oligomers of up to 30 repeating units have been considered to include the saturation effects as a function of chain length. The coupled oscillator model of W. Kuhn and the fitting-function of Hirayama are the models that present the better suit on the transition energy interpolation as a function of chain length. Using only the first four oligomers of the series (n = 2 up to 8) yields an estimation of the transition energy on the polymer limit with an average error of ∼1.5%. The vertical and adiabatic ionization potential present a better fit with the Hückel model approach. Finally, implications of the environmental polarity on the electronic properties, molecular geometry, charge distribution, and aromaticity are shortly discussed.

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