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Nitric oxide (NO) has many important physiological functions, including its ability to inhibit platelet activation and serve as potent antimicrobial agent. The multiple roles of NO in vivo have led to great interest in the development of biomaterials that can deliver NO for specific biomedical applications. Herein, we report a simple solvent impregnation technique to incorporate a nontoxic NO donor, S-nitroso-N-acetylpenicillamine (SNAP), into a more biocompatible biomedical grade polymer, CarboSil 20 80A. The resulting polymer-crystal composite material yields a very stable, long-term NO release biomaterial. The SNAP impregnation process is carefully characterized and optimized, and it is shown that SNAP crystal formation occurs in the bulk of the polymer after solvent evaporation. LC-MS results demonstrate that more than 70% of NO release from this new composite material originates from the SNAP embedded CarboSil phase, and not from the SNAP species leaching out into the soaking solution. Catheters prepared with CarboSil and then impregnated with 15 wt % SNAP provide a controlled NO release over a 14 d period at physiologically relevant fluxes and are shown to significantly reduce long-term (14 day) bacterial biofilm formation against Staphylococcus epidermidis and Pseudonomas aeruginosa in a CDC bioreactor model. After 7 h of catheter implantation in the jugular veins of rabbit, the SNAP CarboSil catheters exhibit a 96% reduction in thrombus area (0.03 ± 0.01 cm2/catheter) compared to the controls (0.84 ± 0.19 cm2/catheter) (n = 3). These results suggest that SNAP impregnated CarboSil can become an attractive new biomaterial for use in preparing intravascular catheters and other implanted medical devices.

Materials that lack inversion symmetry (noncentrosymmetric) demonstrate a diversity of desirable optical and electronic properties in bulk such as second harmonic generation, chiral emission, and piezo-, pyro-, and ferro-electricity. Unfortunately, it is challenging to reliably access noncentrosymmetric packing motifs because the closest packing of molecules is often achieved through inversion symmetry operators, leading to the relatively low occurrence of noncentrosymmetry in organic crystals. In this study, the occurrence of noncentrosymmetry in materials that adopt planar packing motifs is investigated because molecular species achieve closest packing in two dimensions through rotations and (or) glides, symmetry operators that do not individually lead to centrosymmetry. It is found that of the 18 crystal structures investigated here adopting planar packing motifs, 13 structures (72%) are noncentrosymmetric showing in-plane polarization. The 13 noncentrosymmetric crystal structures differ from the centrosymmetric structures by directional halogen bonding interactions or steric collisions that align the polarization directions of neighboring layers, leading to bulk structural polarity. The results from this investigation will be of use for designing noncentrosymmetric materials for application in optical and electronic devices. Key words: noncentrosymmetry, cocrystal, plane group symmetry, charge transfer. Les structures depourvues de symetrie d'inversion (non centrosymetriques) presentent une diversite de proprietes optiques et electroniques desirables a l'echelle du materiau, notamment la generation de seconde harmonique, des proprietes d'emission chirale ainsi que des proprietes piezo-, pyro- et ferro-electriques. Il est malheureusement difficile d'acceder de maniere fiable a des motifs d'empilement non centrosymetriques, car l'empilement le plus compact de molecules s'obtient souvent par des operations de symetrie d'inversion, ce qui explique que la non-centrosymetrie s'observe dans un nombre relativement faible de cristaux organiques. Dans la presente etude, nous avons etudie la presence de non-centrosymetrie dans des materiaux qui adoptent des configurations d'empilement planaires, car les especes moleculaires s'organisent de la maniere la plus compacte en deux dimensions par des operations de symetrie de rotation et de translation qui ne permettent pas individuellement de donner lieu a la centrosymetrie. Nous avons observe que, parmi les 18 structures cristallines que nous avons etudiees qui adoptent des configurations d'empilement planaires, 13 (72 %) sont non centrosymetriques et presentent une polarisation dans le plan. Ces 13 structures cristallines non centrosymetriques se distinguent des structures centrosymetriques par le caractere directionnel de leurs liaisons halogene ou par les collisions steriques qui alignent les directions de polarisation des couches voisines, ce qui donne lieu a une polarite structurale de l'ensemble. Les resultats de cette recherche pourront servir a la conception de materiaux non centrosymetriques destines a des applications dans des dispositifs optiques et electroniques. [Traduit par la Redaction] Mots-cles: non-centrosymetrie, cocristal, groupe de symetrie planaire, transfert de charge., Introduction Crystallographic noncentrosymmetry is a key property of solid-state materials in numerous optical and electronic applications such as second harmonic generation and piezo-, pyro-, and ferroelectricity. (1-6) Although most current [...]

Emissions from higher excited states are of theoretical and experimental interest but rare. A series of pure organic phosphors, 2,5-dihexyloxy-4-bromobenzaldehyde (Br6A) derivatives, show intriguing dualphosphorescence characteristics. Their phosphorescence emissions are blue-shifted by 20 nm at room temperature compared to those at 78 K. These shifts are accompanied by increasing contributions from a fast-decaying component. The mechanism responsible for the emission shifts observed for Br6A was studied in a 2,5-dihexyloxy-4-bromobenzene (Br6) solid matrix and solvents of various polarities. While the decay curve for Br6A in the Br6 matrix showed a single slow process, pure Br6A exhibited an additional faster decay. We demonstrated that the faster decay of pure Br6A arises from the T2 state, while Br6A in the Br6 matrix emits solely from T1. Compared to the T1 state (π, π*), the n, π* character of the T2 state ensures more efficient spin-orbit coupling with the ground state, which facilitates faster decay. The larger polarity of Br6A compared to that of Br6 leads to a lower T2 level and a smaller T2-T1 energy gap in pure Br6A, but not when in the Br6 solid matrix, which enables a T1 to T2 thermal population shift in pure Br6A at room temperature. Consistently, the emissions from the Br6A solutions gradually red-shifted with increasing solvent polarity at 78 K. Moreover, the decay curves of Br6A in solvents of low polarity were single-exponential unlike the double-exponential ones observed in polar solvents. These results provide insight into the effect of the environment on the dual phosphorescence emissions of pure organic phosphors. [ABSTRACT FROM AUTHOR]