Low-noise rotating sample holder for ultrafast transient spectroscopy at cryogenic temperatures\ud

We present the design and testing of a rotating device that fits within a commercial helium cryostat and is capable of providing at 4 K a fresh sample surface for subsequent shots of a 1–10 kHz amplified pulsed laser. We benchmark this rotator in a transient-absorption experiment on molecular switches. After showing that the device introduces only a small amount of additional noise, we demonstrate how the effect of signal degradation due to high fluence is completely resolve

Femtosecond real-time probing of reactions. XI. The elementary OClO fragmentation

Femtosecond reaction dynamics of OClO in a supersonic molecular beam are reported. The system is excited to the A 2A2 state with a femtosecond pulse, covering a range of excitation in the symmetric stretch between v1=17 to v1=11 (308–352 nm). A time-delayed femtosecond probe pulse ionizes the OClO, and OClO + is detected. This ion has not been observed in previous experiments because of its ultrafast fragmentation. Transients are reported for the mass of the parent OClO as well as the mass of the ClO. Apparent biexponential decays are observed and related to the fragmentation dynamics: OClO+hnu-->(OClO)[double-dagger]*-->ClO+O -->Cl+O2 . Clusters of OClO with water (OClO)n (H2O)m with n from 1 to 3 and m from 0 to 3 are also observed. The dynamics of the fragmentation reveal the nuclear motions and the electronic coupling between surfaces. The time scale for bond breakage is in the range of 300–500 fs, depending on v1; surface crossing to form new intermediates is a pathway for the two channels of fragmentation: ClO+O (primary) and Cl+O2 (minor). Comparisons with results of ab initio calculations are made

Oxidative stress and epigenetic regulation in chronic disease

Oksidacijski stres utječe negativno na procese u stanici, očituje se i kao starenje stanica te utječe na epigenetsku regulaciju. Sve je jasnije da su ovi procesi jako važni u raznim kroničnim bolestima te se pogrešnom kontrolom ekspresije gena omogućuje nastanak i progresija bolesti. Ovaj rad je kratki pregled epigenetskih mehanizama i utjecaja oksidacijskog stresa na određene kronične bolesti. Poseban osvrt stavljen je na histon deacetilaze i njihov utjecaj na procese razvoja tumora te na utjecaj oksidacijskog stresa kod kroničnih bolesti pluća.Oxidative stress negatively affects cellular processes, presents itself as cell ageing, and affects epigenetic regulation. It's becoming more and more clear that these processes are very important in a variety of chronic diseases and that abnormal control of gene expression allows initiation and progression of disease. This paper is a short overview of epigenetic mechanisms and effects of oxidative stress on certain chronic diseases. A special focus is put on histone deacetylases and their effect on development and progression of cancer, and the effect of oxidative stress on chronic lung disease

Background free CARS imaging by phase sensitive heterodyne CARS

In this article we show that heterodyne CARS, based on a controlled and stable phase-preserving chain, can be used to measure amplitude and phase information of molecular vibration modes. The technique is validated by a comparison of the imaginary part of the heterodyne CARS spectrum to the spontaneous Raman spectrum of polyethylene. The detection of the phase allows for rejection of the non-resonant background from the data. The resulting improvement of the signal to noise ratio is shown by measurements on a sample containing lipid

Tailoring a coherent control solution landscape by linear transforms of spectral phase basis

Finding an optimal phase pattern in a multidimensional solution landscape becomes easier and faster if local optima are suppressed and contour lines are tailored towards closed convex patterns. Using wideband second harmonic generation as a coherent control test case, we show that a linear combination of spectral phase basis functions can result in such improvements and also in separable phase terms, each of which can be found independently. The improved shapes are attributed to a suppressed nonlinear shear, changing the relative orientation of contour lines. The first order approximation of the process shows a simple relation between input and output phase profiles, useful for pulse shaping at ultraviolet wavelengths

Femtosecond real-time probing of reactions. IX. Hydrogen-atom transfer

The real-time dynamics of hydrogen-atom-transfer processes under collisionless conditions are studied using femtosecond depletion techniques. The experiments focus on the methyl salicylate system, which exhibits ultrafast hydrogen motion between two oxygen atoms due to molecular tautomerization, loosely referred to as intramolecular ''proton'' transfer. To test for tunneling and mass effects on the excited potential surface, we also studied deuterium and methyl-group substitutions. We observe that the motion of the hydrogen, under collisionless conditions, takes place within 60 fs. At longer times, on the picosecond time scale, the hydrogen-transferred form decays with a threshold of 15.5 kJ/mol; this decay behavior was observed up to a total vibrational energy of approximately 7200 cm-1. The observed dynamics provide the global nature of the motion, which takes into account bonding before and after the motion, and the evolution of the wave packet from the initial nonequilibrium state to the transferred form along the O-H-O reaction coordinate. The vibrational periods (2pi/omega) of the relevant modes range from 13 fs (the OH stretch) to 190 fs (the low-frequency distortion) and the motion involves (in part) these coordinates. The intramolecular vibrational-energy redistribution dynamics at longer times are important to the hydrogen-bond dissociation and to the nonradiative decay of the hydrogen-transferred form

Application of spectral phase shaping to high resolution CARS spectroscopy

By spectral phase shaping of both the pump and probe pulses in coherent anti-Stokes Raman scattering (CARS) spectroscopy we demonstrate the extraction of the frequencies, bandwidths and relative cross sections of vibrational lines. We employ a tunable broadband Ti:Sapphire laser synchronized to a ps-Nd:YVO mode locked laser. A high resolution spectral phase shaper allows for spectroscopy with a precision better than 1 cm-1 in the high frequency region around 3000 cm-1. We also demonstrate how new spectral phase shaping strategies can amplify the resonant features of isolated vibrations to such an extent that spectroscopy and microscopy can be done at high resolution, on the integrated spectral response without the need for a spectrograph

Probing the origin of fluorescence quenching of graphene-porphyrin hybrid material

We report transient absorption spectroscopic studies on the hybrid material composed of porphyrin molecules covalently attached to graphene for investigating the mechanism underlying the reported fluorescence quenching of porphyrin in the hybrid [1]. Excited state dynamics of pure graphene suspension and porphyrin have also been studied as reference samples. A fast excited state decay was observed in the hybrid

Using Murine Models to Understand Tumor-Lymphoid Interactions: Spotlight on CLL and AITL

The role of the tumor microenvironment in leukemias and lymphomas is well-established, yet the intricacies of how the malignant cells regulate and influence their non-malignant counterparts remain elusive. For example, chronic lymphocytic leukemia is an expansion of malignant CD5+CD19+ B cells, yet the non-malignant T cells play just as large of a role in disease presentation and etiology. Herein, we review the dynamic tumor cell to lymphoid repertoire interactions found in two Non-Hodgkin’s lymphoma subtypes: chronic lymphocytic leukemia and angioimmunoblastic T-cell lymphoma. We aim to highlight the pivot work done in the murine models which recapitulate these diseases and explore the insights that can be gained from studying the immuno-oncological regulation of non-malignant lymphoid counterparts