Inverse relationship between increased apoptosis and decreased skin cancer in UV-irradiated CD1d-/- mice

We previously demonstrated that CD1d knockout mice were resistant to ultraviolet (UV)-induced immunosuppression. Because immune suppression is a critical factor in the development of UV-induced skin cancers, we investigated the response of wild type (WT) and CD1d-/- mice to UV carcinogenesis. We found that although 100% of WT mice developed skin tumors after 45 weeks of UV irradiation, only 60% of CD1d-/- mice developed skin tumors. To investigate the mechanisms involved in the resistance of CD1d-/- mice to UV-induced carcinogenesis, we determined the time course and kinetics of keratinocyte cell death after UV irradiation. After acute UV exposure, the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL)-positive keratinocytes were eliminated from the skin of WT mice by 72 h post-UV, but they still persisted until 96 h in CD1d-/- mice. The kinetics of p53 protein expression closely followed the kinetics of apoptotic cell death. Chronic UV irradiation resulted in induction of a significantly higher number of apoptotic keratinocytes in CD1d-/- than WT mice. In addition, epidermis and dermis from chronically UV-irradiated CD1d-/- mice harbored significantly fewer p53 mutations than WT mice. These results indicate that the resistance of CD1d-/- mice to UV carcinogenesis may be due to increased cell death and elimination of keratinocytes and fibroblasts containing DNA damage and p53 mutations.     

Modelling a Linker Mix‐and‐Match Approach for Controlling the Optical Excitation Gaps and Band Alignment of Zeolitic Imidazolate Frameworks

Tuning the electronic structure of metal–organic frameworks is the key to extending their functionality to the photocatalytic conversion of absorbed gases. Herein we discuss how the band edge positions in zeolitic imidazolate frameworks (ZIFs) can be tuned by mixing different imidazole‐based linkers within the same structure. We present the band alignment for a number of known and hypothetical Zn‐based ZIFs with respect to the vacuum level. Structures with a single type of linker exhibit relatively wide band gaps; however, by mixing linkers of a low‐lying conduction edge with linkers of a high‐lying valence edge, we can predict materials with ideal band positions for visible‐light water splitting and CO₂ reduction photocatalysis. By introducing copper in the tetrahedral position of the mixed‐linker ZIFs, it would be possible to increase both photo‐absorption and the electron–hole recombination times.     

Hyperpolarization of Nitrogen‐15 Schiff Bases by Reversible Exchange Catalysis with para‐Hydrogen

NMR with thermal polarization requires relatively concentrated samples, particularly for nuclei with low abundance and low gyromagnetic ratios, such as ¹⁵N. We expand the substrate scope of SABRE, a recently introduced hyperpolarization method, to allow access to ¹⁵N‐enriched Schiff bases. These substrates show fractional ¹⁵N polarization levels of up to 2 % while having only minimal ¹H enhancements.     

The dissociation constants of diprotonated chalcogenobispyridines: Transmission of electronic effects across chalcogen bridges

The dissociation constants of the diprotonated chalcogenobispyridines have been determined using potentiometric titrations to establish a method for the measurement of the ability of a bridging ligand to relay electronic effects. The relationship between pK_a and structure of the chalcogenobispyridines results from a balance between inductive, mesomeric, and steric effects. Delocalization of cationic charge onto the bridgehead increases the apparent electronegativity of the bridging atom, thereby relaying a strong base‐weakening effect to the site of first deprotonation. Such delocalization was found to be a function of both the substitution site (4‐X > 2‐X ? 3‐X) and orbital overlap requirements (S > O ≈ Se > Te). J. Heterocyclic Chem., (2011).     

Optical interference coatings-yesterday and today

Although they are common in nature and must certainly have been observed by early man, we have to wait till Newton for the first truly scientific study of what we now understand as interference effects in thin films. Young, Fresnel, and Maxwell all contributed and the theory was well established by the beginning of the 20th century. Coatings depending on interference, at this stage, were in their infancy and antireflection and decorative coatings, and color photography were the primary applications. By the middle of the 20th century, the situation had changed completely. Today almost the entire field of optics depends on interference optical coatings. This paper will start with a rapid account of the history and end with a survey of the range of interference coatings that are employed today with a fleeting glimpse of what might be in the future.     

Dye-sensitized photocathodes: efficient light-stimulated hole injection into p-GaP under depletion conditions

The steady-state photoelectrochemical responses of p-GaP photoelectrodes immersed in aqueous electrolytes and sensitized separately by six triphenylmethane dyes (rose bengal, rhodamine B, crystal violet, ethyl violet, fast green fcf, and brilliant green) have been analyzed. Impedance measurements indicated that these p-GaP(100) photoelectrodes operated under depletion conditions with an electric field of ～8.5 × 10(5) V cm(-1) at the p-GaP/solution interface. The set of collected wavelength-dependent quantum yield responses were consistent with sensitization occurring specifically from adsorbed triphenylmethane dyes. At high concentrations of dissolved dye, the measured steady-state photocurrent-potential responses collected at sub-bandgap wavelengths suggested unexpectedly high (>0.1) net internal quantum yields for sensitized hole injection. Separate measurements performed with rose bengal adsorbed on p-GaP surfaces pretreated with (NH(4))(2)S verified efficient sensitized hole injection. A modified version of wxAMPS, a finite-difference software package, was utilized to assess key operational features of the sensitized p-GaP photocathodes. The net analysis showed that the high internal quantum yield values inferred from the experimental data were most likely afforded by the internal electric field present within p-GaP, effectively sweeping injected holes away from the interface and minimizing their participation in deleterious pathways that could limit the net collection yield. These simulations defined effective threshold values for the charge carrier mobilities (≥10(-6) cm(2) V(-1) s(-1) and ≥10(-1) cm(2) V(-1) s(-1) at dopant densities of 10(18) and 10(13) cm(-3), respectively), hole injection rate constants (≥10(12) s(-1)), and surface trap densities (10(12) cm(-2)) needed to attain efficient hole collection with the quality of p-GaP materials used here. The cumulative experimental and modeling data thus provide insight on design strategies for assembling new types of dye-sensitized photocathodes that operate under depletion conditions.