Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature (also obtained by heating on exposure to an electrical current or light illumination). Several papers have described light-induced changes in the shape of polymers and gels, such as contraction, bending or volume changes. Here we report that polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes--such as (but not exclusively) elongated films and tubes, arches or spirals--by ultraviolet light illumination. These new shapes are stable for long time periods, even when heated to 50 degrees C, and they can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength. The ability of polymers to form different pre-determined temporary shapes and subsequently recover their original shape at ambient temperatures by remote light activation could lead to a variety of potential medical and other applications.

Significant advances have recently been made in the development of functional polymers that are able to undergo light‐induced shape changes. The main challenge in the development of such polymer systems is the conversion of photoinduced effects at the molecular level to macroscopic movement of working pieces. This article highlights some selected polymer architectures and their tailored functionalization processes. Examples include the contraction and bending of azobenzene‐containing liquid‐crystal elastomers and volume changes in gels. We focus especially on light‐induced shape‐memory polymers. These materials can be deformed and temporarily fixed in a new shape. They only recover their original, permanent shape when irradiated with light of appropriate wavelengths. Using light as a trigger for the shape‐memory effect will extend the applications of shape‐memory polymers, especially in the field of medical devices where triggers other than heat are highly desirable.

How much translational energy atoms and molecules lose in collisions at surfaces determines whether they adsorb or scatter. The fact that hydrogen (H) atoms stick to metal surfaces poses a basic question. Momentum and energy conservation demands that the light H atom cannot efficiently transfer its energy to the heavier atoms of the solid in a binary collision. How then do H atoms efficiently stick to metal surfaces? We show through experiments that H-atom collisions at an insulating surface (an adsorbed xenon layer on a gold single-crystal surface) are indeed nearly elastic, following the predictions of energy and momentum conservation. In contrast, H-atom collisions with the bare gold surface exhibit a large loss of translational energy that can be reproduced by an atomic-level simulation describing electron-hole pair excitation.

Viewing the atomic-scale motion and energy dissipation pathways involved in forming a covalent bond is a longstanding challenge for chemistry. We performed scattering experiments of H atoms from graphene and observed a bimodal translational energy loss distribution. Using accurate first-principles dynamics simulations, we show that the quasi-elastic channel involves scattering through the physisorption well where collision sites are near the centers of the six-membered C-rings. The second channel results from transient C–H bond formation, where H atoms lose 1 to 2 electron volts of energy within a 10-femtosecond interaction time. This remarkably rapid form of intramolecular vibrational relaxation results from the C atom’s rehybridization during bond formation and is responsible for an unexpectedly high sticking probability of H on graphene.

Inelastic scattering of H and D atoms from the (111) surfaces of six fcc transition metals (Au, Pt, Ag, Pd, Cu, and Ni) was investigated, and in each case, excitation of electron-hole pairs dominates the inelasticity. The results are very similar for all six metals. Differences in the average kinetic energy losses between metals can mainly be attributed to different efficiencies in the coupling to phonons due to the different masses of the metal atoms. The experimental observations can be reproduced by molecular dynamics simulations based on full-dimensional potential energy surfaces and including electronic excitations by using electronic friction in the local density friction approximation. The determining factors for the energy loss are the electron density at the surface, which is similar for all six metals, and the mass ratio between the impinging atoms and the surface atoms. Details of the electronic structure of the metal do not play a significant role. The experimentally validated simulations are used to explore sticking over a wide range of incidence conditions. We find that the sticking probability increases for H and D collisions near normal incidence-consistent with a previously reported penetration-resurfacing mechanism. The sticking probability for H or D on any of these metals may be represented as a simple function of the incidence energy, E, metal atom mass, M, and incidence angle, 𝜗. S=(S+a⋅E+b⋅M)*(1-h(𝜗-c)(1-cos(𝜗-c))), where h is the Heaviside step function and for H, S = 1.081, a = -0.125 eV, b=-8.40⋅10 u, c = 28.88°, d = 1.166 eV, and e = 0.442 eV; whereas for D, S = 1.120, a = -0.124 eV, b=-1.20⋅10 u, c = 28.62°, d = 1.196 eV, and e = 0.474 eV.

The Born-Oppenheimer approximation (BOA) provides the foundation for virtually all computational studies of chemical binding and reactivity, and it is the justification for the widely used "balls and springs" picture of molecules. The BOA assumes that nuclei effectively stand still on the timescale of electronic motion, due to their large masses relative to electrons. This implies electrons never change their energy quantum state. When molecules react, atoms must move, meaning that electrons may become excited in violation of the BOA. Such electronic excitation is clearly seen for: (i) Schottky diodes where H adsorption at Ag surfaces produces electrical "chemicurrent;" (ii) Au-based metal-insulator-metal (MIM) devices, where chemicurrents arise from H-H surface recombination; and (iii) Inelastic energy transfer, where H collisions with Au surfaces show H-atom translation excites the metal's electrons. As part of this work, we report isotopically selective hydrogen/deuterium (H/D) translational inelasticity measurements in collisions with Ag and Au. Together, these experiments provide an opportunity to test new theories that simultaneously describe both nuclear and electronic motion, a standing challenge to the field. Here, we show results of a recently developed first-principles theory that quantitatively explains both inelastic scattering experiments that probe nuclear motion and chemicurrent experiments that probe electronic excitation. The theory explains the magnitude of chemicurrents on Ag Schottky diodes and resolves an apparent paradox--chemicurrents exhibit a much larger isotope effect than does H/D inelastic scattering. It also explains why, unlike Ag-based Schottky diodes, Au-based MIM devices are insensitive to H adsorption.M ost theoretical studies of atoms and molecules interacting with metal surfaces are based on the Born-Oppenheimer approximation (BOA) (1). However, a growing number of examples have been found where electronic and nuclear degrees of freedom are strongly coupled in violation of the BOA (2-6). H-atom interactions at metals offer a remarkable opportunity to test non-BOA theories against experiment, since H-adsorptioninduced chemicurrent experiments (7-14) offer a direct measure of electronic excitation and H-atom inelastic scattering experiments (15) directly probe nuclear motion. In chemicurrent experiments, exothermic H interactions like adsorption and recombination produce hot electrons that pass over a potential barrier to be collected. Hence, the magnitude of the chemicurrent is dependent on both the reaction-induced production of hot electrons and the likelihood of transmission over the barrier. To reduce uncertainties associated with barrier transmission, the ratio of hydrogen-and deuterium-induced chemicurrent is often measured--H-induced chemicurrents are typically two to five times larger than those from D atoms (7,(11)(12)(13). H-atom surface scattering experiments yield H-atom translational energy loss distributions. The importance of H-atom translation to electronic exc...

DJ-1 is frequently overexpressed in a large variety of solid tumors, but the DJ-1 expression in laryngeal squamous cell cancer and its clinical ⁄ prognostic significance is unclear. We aimed to evaluate DJ-1 protein expression in glottic squamous cell carcinoma (GSCC) and to correlate this with clinicopathological data including patient survival. The expression of DJ-1 in GSCCs (60) and adjacent normal tissue (44) was assessed by immunohistochemistry and western blot analysis. In addition, the role of DJ-1 was investigated in tumorigenesis by transfecting DJ1-specific siRNA into laryngeal squamous cell carcinoma (LSCC) Hep-2 cells. Our data showed that positive expression of DJ-1 was found in 85% of GSCCs. In univariate survival analysis of the GSCC cohorts, a highly significant association between DJ-1 expression with shortened patient overall survival (5-year survival rate 92.9% vs 66.6%; P = 0.001; log rank test) was demonstrated. In multivariate analyses, DJ-1, tumor grading, and pT status were significant prognostic parameters for shortened patient overall survival. Furthermore, siRNA targeting DJ-1 can effectively inhibit DJ-1 expression, resulting in enhanced apoptosis and less proliferation of Hep-2 cells. We concluded that DJ-1 overexpression might be a novel independent molecular marker for poor prognosis (shortened overall survival) of patients with GSCC. (Cancer Sci 2010; 101: 1320-1325 L aryngeal carcinoma accounts for approximately 2.4% of new malignancies worldwide every year, of which over 95% are of the squamous cell carcinoma.(1,2) Glottic squamous cell carcinoma (GSCC) is the most common type of laryngeal cancer. Patients with GSCC often display considerable variability in survival.(3) It is of general importance to predict the biology of the tumor and, thus, the course of the disease in the individual patient to ensure adequate therapy and patient surveillance. Conventional prognostic and predictive markers for GSCC are nodal status, tumor grade, tumor status, and tumor type.(3) Additionally, molecular markers are being sought and established to allow for a refined classification of prognosis, especially in patient subgroups whose outcome can only insufficiently be predicted by conventional parameters. These include, among others, activation of various oncogenes (Ras, (4,5) Myc,epidermal growth factor receptor,and cyclin D1 (8) ), and tumor suppressor gene inactivation (P53 and p16).(9,10) However, accurate and reliable biomarkers that serve for prognosis have yet to be identified.DJ-1 encodes a conserved protein belonging to the ThiJ ⁄ PfpI ⁄ DJ-1 superfamily.(11) The THEMATICS (theoretical microscopic titration curves) predicted eight DJ-1 family members and three different probable functional classes.(12) The exact molecular function of DJ-1 is still unclear although increasing evidence suggests that DJ-1 plays a role in cancer cell lines to protect against stress (13)(14)(15) and affects cell survival by modulating the phosphorylation status of protein kinase B (PKB) ⁄ Akt, (16)(17)(18)...

The novel photosensitizer [Ru( S–S bpy)(bpy) 2 ] 2+ harbors two distinct sets of excited states in the UV/Vis region of the absorption spectrum located on either bpy or S–S bpy ligands. Here, we address the question of whether following excitation into these two types of states could lead to the formation of different long-lived excited states from where energy transfer to a reactive species could occur. Femtosecond transient absorption spectroscopy identifies the formation of the final state within 80 fs for both excitation wavelengths. The recorded spectra hint at very similar dynamics following excitation toward either the parent or sulfur-decorated bpy ligands, indicating ultrafast interconversion into a unique excited-state species regardless of the initial state. Non-adiabatic surface hopping dynamics simulations show that ultrafast spin–orbit-mediated mixing of the states within less than 50 fs strongly increases the localization of the excited electron at the S–S bpy ligand. Extensive structural relaxation within this sulfurated ligand is possible, via S–S bond cleavage that results in triplet state energies that are lower than those in the analogue [Ru(bpy) 3 ] 2+ . This structural relaxation upon localization of the charge on S–S bpy is found to be the reason for the formation of a single long-lived species independent of the excitation wavelength.