Factors Affecting the Population of Excited Charge Transfer States in Adenine/Guanine Dinucleotides: A Joint Computational and Transient Absorption Study.

There is compelling evidence that the absorption of low-energy UV radiation directly by DNA in solution generates guanine radicals with quantum yields that are strongly dependent on the secondary structure. Key players in this unexpected phenomenon are the photo-induced charge transfer () states, in which an electric charge has been transferred from one nucleobase to another. The present work examines the factors affecting the population of these states during electronic relaxation.

Real-time observation of sub-100-fs charge and energy transfer processes in DNA dinucleotides.

Using as showcase the DNA dinucleotide 5'-dTpdG-3', in which the thymine (T) is located at the 5' end with respect to the guanine (G), we study the photoinduced electronic relaxation of coupled chromophores in solution with an unprecedented refinement. On the one hand, transient absorption spectra are recorded from 20 fs to 45 ps over the 330-650 nm range with a temporal resolution of 30 fs; on the other hand, quantum chemistry calculations determine the ground state geometry of the 4 possible conformers with stacked nucleobases, the associated Franck-Condon states, and map the relaxation pathways leading to excited state minima. Important spectral changes occurring before 100 fs are correlated with concomitant G → T charge transfer and T → G energy transfer processes.

Sub-100-fs energy transfer in coenzyme NADH is a coherent process assisted by a charge-transfer state.

Excitation energy transfer (EET) is a key photoinduced process in biological chromophoric assemblies. Here we investigate the factors which can drive EET into efficient ultrafast sub-ps regimes. We demonstrate how a coherent transport of electronic population could facilitate this in water solvated NADH coenzyme and uncover the role of an intermediate dark charge-transfer state.

Aggregation-Driven Photoinduced α-C(sp)-H Bond Hydroxylation/C(sp)-C(sp) Coupling of Boron Dipyrromethene Dye in Water Reported by Near-Infrared Emission.

Molecular aggregation is a powerful tool for tuning advanced materials' photophysical and electronic properties. Here we present a novel potential for the aqueous-solvated aggregated state of boron dipyrromethene (BODIPY) to facilitate phototransformations otherwise achievable only under harsh chemical conditions. We show that the photoinduced symmetry-breaking charge separation state can itself initiate catalyst-free redox chemistry, leading to selective α-C(sp)-H bond activation/C-C coupling on the BODIPY backbone.

Vibronic Coupling Drives the Ultrafast Internal Conversion in a Functionalized Free-Base Porphyrin.

Internal conversion (IC) is a common radiationless transition in polyatomic molecules. Theory predicts that molecular vibrations assist IC between excited states, and ultrafast experiments can provide insight into their structure-function relationship. Here we elucidate the dynamics of the vibrational modes driving the IC process within the Q band of a functionalized porphyrin molecule.

Sub-50 fs Formation of Charge Transfer States Rules the Fate of Photoexcitations in Eumelanin-Like Materials.

Eumelanins play a crucial role as photoprotective agents for living organisms, yet the nature of the stationary and transient species involved in the light absorption and deactivation processes remains controversial. Moreover, the critical sub-100 fs time scale, which is key to the characterization of the primary excited species, has remained unexplored. Here, we study the eumelanin analogue polydopamine (PDA) and employ a combination of steady-state and transient optical spectroscopies to reveal the presence of spectrally broad coupled electronic transitions with, at least partial, charge-transfer (CT) character.

Engineering Azobenzene Derivatives to Control the Photoisomerization Process.

In this work, we show how the structural features of photoactive azobenzene derivatives can influence the photoexcited state behavior and the yield of the trans/cis photoisomerization process. By combining high-resolution transient absorption experiments in the vis-NIR region and quantum chemistry calculations (TDDFT and RASPT2), we address the origin of the transient signals of three poly-substituted push-pull azobenzenes with an increasing strength of the intramolecular interactions stabilizing the planar trans isomer (absence of intramolecular H-bonds, methyl, and traditional H-bond, respectively, for 4-diethyl-4'-nitroazobenzene, Disperse Blue 366, and Disperse Blue 165) and a commercial red dye showing keto-enol tautomerism involving the azo group (Sudan Red G). Our results indicate that the intramolecular H-bonds can act as a "molecular lock" stabilizing the trans isomer and increasing the energy barrier along the photoreactive CNNC torsion coordinate, thus preventing photoisomerization in the Disperse Blue dyes.

Effect of the DNA Polarity on the Relaxation of Its Electronic Excited States.

The DNA polarity, ., the order in which nucleobases are connected together via the phosphodiester backbone, is crucial for several biological processes. But, so far, there has not been experimental evidence regarding its effect on the relaxation of DNA electronic excited states.

Disclosing Early Excited State Relaxation Events in Prototypical Linear Carbon Chains.

One-dimensional (1D) linear nanostructures comprising -hybridized carbon atoms, as derivatives of the prototypical allotrope known as carbyne, are predicted to possess outstanding mechanical, thermal, and electronic properties. Despite recent advances in their synthesis, their chemical and physical properties are still poorly understood. Here, we investigate the photophysics of a prototypical polyyne (i.

Ultrafast Photophysics of Regioisomeric Triphenylamine Dyes Having Dipolar D-π-A-A and Octupolar D-(π-A-A) Character with a Benzothiazole Unit in Matched or Mismatched Orientation.

Benzothiazole is among prominent electron-withdrawing heteroarene moieties used in a variety of π-conjugated molecules. Its relative orientation with respect to the principal dipole vector(s) of chromophores derived thereof is crucial, affecting photophysical and nonlinear optical properties. Here we compare the photophysics and ultrafast dynamics of dipolar and octupolar molecules comprising a triphenylamine electron-donating core, ethynylene π-conjugated linker(s) and benzothiazole acceptor(s) having the matched or mismatched orientation (with respect to the direction of intramolecular charge transfer), while a carbaldehyde group is attached as an auxiliary acceptor.

Exploring Solvent and Substituent Effects on the Excited State Dynamics and Symmetry Breaking of Quadrupolar Triarylamine End-Capped Benzothiazole Chromophores by Femtosecond Spectroscopy.

We investigate herein the excited state dynamics and symmetry breaking processes in three benzothiazole-derived two-photon absorbing chromophores by femtosecond fluorescence and transient absorption (fs-TA) spectroscopies in solvents of various polarity. The chromophores feature a quasi-quadrupolar D-π-A-π-D architecture comprised of an electron-withdrawing benzothiazole core and lateral triphenylamine donors (), while the acceptor strength of the central unit is enforced by attached cyano groups () and the electron-donating strength of the arylamine moieties by introduction of peripheral methoxy groups (). Steady state spectroscopy reveals positive solvatochromism, which is mostly pronounced for .

Photothermal motion: effect of low-intensity irradiation on the thermal motion of organic nanoparticles.

The effect of local photo-triggered heat release on the motion of organic nanopartcles (NP), a process that is itself thermal, is largely unexplored under low-intensity irradiation. Here, we develop organic NP specifically tailored for this study and demonstrate, comparing three different irradiation intensity regimes, that indeed the NP undergo "acceleration" upon light absorption (Photothermal Motion). These NP have a well-defined chemical composition and extremely high molar absorbance coefficient, and upon excitation, they deactivate mostly non radiatively with localized heat dissipation.

Cyclic stroke mortality variations follow sunspot patterns.

Background: Mapping time-structures is a burgeoning scientific field enriching the (P4) medicine models. Local evidence in Mediterranean populations is underinvestigated.

Methods: The Censused stroke-related death events (D) in the largest East-Mediterranean port (Piraeus), during (1985-1989), when local population had diet (low fat/sugar, proteins and vegetables/fruits daily, and pure olive oil almost exclusively) and genetic homogeneity-later interrupted by the immigration into Greece in 1990; and Sunspot numbers were indexed by Wolf numbers (Rz) (1944-2004), and evaluated using Fast Fourier Analysis and Singular Spectrum Analysis in MATLAB.

Computation of Dolphins' Sound ASPL While Foraging.

Scheduled scientific surveys are a valuable asset in beginning to understand the behavior and vocalization of free-ranging cetaceans. The fortuity of a nonscheduled survey has proven to be beneficial as well. In October 2003 a team of biologist oceanographers began a trip aboard a 44.

Ultrafast excited-state dynamics in land plants Photosystem I core and whole supercomplex under oxidised electron donor conditions.

The kinetics of excited-state energy migration were investigated by femtosecond transient absorption in the isolated Photosystem I-Light-Harvesting Complex I (PSI-LHCI) supercomplex and in the isolated PSI core complex of spinach under conditions in which the terminal electron donor P is chemically pre-oxidised. It is shown that, under these conditions, the relaxation of the excited state is characterised by lifetimes of about 0.4 ps, 4.

The effect of inter-implant distance on retention and resistance to dislodging forces for mandibular implant-tissue-supported overdentures.

Objectives: The effect of inter-implant distance on retention and resistance of implant-tissue-supported overdentures is lacking in the literature. An in vitro study was performed to evaluate this effect for mandibular implant-tissue-supported overdentures retained by two ball attachments.

Materials And Methods: An acrylic cast of an edentulous mandible was fabricated.

Adaptations in aquatic organisms for increased sensitivity to light and differences from humans.

The retina of aquatic organisms has been adapted, through evolution, to the specific lighting conditions of water. The purpose of this paper is to present the major morphological and functional differences of photoreceptors between humans and aquatic organisms. Comparison of visual pathways of the nervous system between humans and aquatic organisms is also attempted.

Ectodermal dysplasia: an 11-year follow-up of siblings with 2 implant treatment approaches.

Purpose: To describe 2 different treatment approaches for a 20-year-old Caucasian man and his 22-year-old sister who were affected by ectodermal dysplasia (ED) and compromised maxillary bone.

Materials And Methods: The sister had a history of an iliac crest transplant with 6 implants placed in the maxillary and mandibular arches, 6 years before complications. It was necessary to debride the right sinus, remove the failing infected bone graft and 2 implants.

A retrospective analysis of mandibular bone height changes associated with 81 screw-retained implant-supported prostheses with distal cantilevers: a long-term follow-up analysis.

Purpose: The aims of this study were (1) to evaluate long-term changes in bone height beneath mandibular screw-retained implant-supported prostheses with distal cantilevers and (2) to determine whether the reversal of residual ridge resorption in the posterior mandible is temporary or continues over the long term.

Materials And Methods: Panoramic radiographs, obtained at surgery and at two follow-up visits, of 81 patients rehabilitated with mandibular screw-retained implant-supported prostheses with distal cantilevers supported by four, five, or six implants were followed for 5 to 19 years (overall mean follow-up, 9.00 years.

Predoctoral dental students' perceptions and experiences with prosthodontics.

Purpose: The aims of this study were to: (1) investigate the perceptions and experiences of predoctoral dental students and advanced standing students on mentorship, exposure to prosthodontics, and future need for the specialty, and (2) establish a baseline of students' perceptions of the impact of prosthodontics on salary, personal and patient quality of life, and the profession of dentistry.

Materials And Methods: A survey was distributed to 494 predoctoral and advanced standing students at the University of Pennsylvania School of Dental Medicine. Questions focused on the perceptions and experiences with the specialty of prosthodontics.

Dental students' perceptions of dental specialties and factors influencing specialty and career choices.

The goals of this study were to 1) evaluate dental students' perceptions of dental specialties, 2) identify factors that play an important role in students' decision to pursue specialty training or career choices, and 3) establish a baseline of students' perceptions of the dental fields with the best future in terms of salary, personal and patient quality of life, and overall impact on the dental profession. Surveys were distributed to 494 students at the University of Pennsylvania School of Dental Medicine. Data were collected from 380 traditional four-year students and thirty advanced standing students.

Treatment of a patient with cleidocranial dysplasia using a single-stage implant protocol.

This patient report describes the treatment of a 45-year-old Caucasian woman with cleidocranial dysplasia who had significant dental problems that greatly affected her quality of life. The patient had orthodontic treatment in her earlier years along with surgical removal of supernumerary teeth. Using implants, the maxillary and mandibular arches were restored with fixed screw-retained prostheses.