Femtosekundenspektroskopie an o-substituierten Nitrobenzolen - von Modellen zu photolabilen Schutzgruppen

In this thesis ultrafast processes occuring in photolabile protecting groups of the ortho-nitrobenzyl type have been studied. These protecting groups enable the spatially and temporarily defined release of chemically or biologically active molecules. Due to these properties they find widespread applications, besides technical ones mainly in biochemical research. Molecules of the o-nitrobenzyl type represent the major part of photolabile protecting groups used today. Therefore, in-depth knowledge of the reaction and release mechanism is desired to improve and adapt the properties of these molecules to their applications. Despite this relevance experiments on the ultrafast behaviour of these molecules are scarce. Here, femtosecond pump probe experiments with UV/VIS, IR and Raman probing have been employed to elucidate the early processes occuring during de-protection. Model systems as well as a "real" protecting group have been investigated. Thereby, a general picture of the ultrafast processes occuring in the photoreaction of these molecules could be obtained. Excitation with uv-light to an upper singlet state leads to ultrafast internal conversion to the S1 state. Three competing processes, internal conversion, inter system crossing and the photoreaction, contribute to the decay of this state on the time scale of 1 ps. For the reaction path the formation of the first intermediate could be traced. It results from a hydrogen transfer from the substituent in o-position to the nitro group and exhibits aci-nitro like structure. In addition to the direct formation from the S1 state this intermediate is also formed via a second channel on the nanosecond time scale. This channel involves a triplet state. The "local" triplet state undergoes a hydrogen transfer reaction resulting in a triplet phased bi-radical. The recombination of this biradical then yields the aci-nitro tautomer. Once formed the aci-nitro tautomer transforms into the final nitroso product and the released functionality in a yield of 100 %. Furtheron, the similarity between the reaction mechanisms of all molecules investigated leads to the conclusion that it is universal for the group of o-nitrobenzenes. Additionally, for oNBA the influence of vibrational excitation on the stability of a ground state intermediate could be traced. The ultrafast formation of the first intermediate is about one order of magnitude faster than typical cooling times for these molecules. Therefore, the dynamics of vibrational excitation and its impact on the subsequent reaction could be studied. The vibrational excitation results in bi-phasic kinetics: a fast phase during vibrational excitation of the molecule and a slower one for the thermalized molecule

A comparative analysis of the UV/Vis absorption spectra of nitrobenzaldehydes.

In a joint experimental and theoretical study, the UV/Vis absorption spectra of the three isomers (ortho, meta, para) of nitrobenzaldehyde (NBA) were analyzed. Absorption spectra are reported for NBA vapors, cyclohexane and acetonitrile solutions. All spectra are poor in vibronic structure and hardly affected in shape by the surroundings (vapor or solution). Moderate solvatochromic shifts of [similar]−0.2 eV are measured. For all isomers vertical transition energies, oscillator strengths, and excited state dipole moments were computed using the MS-CASPT2/CASSCF and CC2 methods. Based on these calculations the experimental transitions were assigned. The spectra of all isomers are characterized by weak (εmax ≈ 100 M−1 cm−1) transitions around 350 nm (3.6 eV), arising from nπ* absorptions starting from the lone pairs of the nitro and aldehyde moieties. The next band of intermediate intensity peaking around 300 nm (4.2 eV, εmax ≈ 1000 M−1 cm−1) is dominated by ππ* excitations within the arene function. Finally, strong absorptions (εmax ≈ 10 000 M−1 cm−1) were observed around 250 nm (5.0 eV) which we ascribe to ππ* excitations involving the nitro and benzene groups

High-resolution quantitative MRI of multiple sclerosis spinal cord lesions

Purpose: Validation of quantitative MR measuresfor myelin imaging in the postmortem multiple sclerosis spinal cord. Methods: Four fixed spinal cord samples were imaged first with a 3T clinical MR scannerto identify areas of interest forscanning, and then with a 7T small bore scanner using a multicomponent-driven equilibrium single-pulse observation of T1 and T2 protocol to produce apparent proton density, T1, T2, myelin water, intracellular water, and free-water fraction maps. After imaging, the cords were sectioned and stained with histological markers (hematoxylin and eosin, myelin basic protein, and neurofilament protein), which were quantitatively compared with the MR maps. Results: Excellent correspondence was found between high-resolution MR parameter maps and histology, particularly for apparent proton density MRI and myelin basic protein staining. Conclusion: High-resolution quantitative MRI of the spinal cord provides biologically meaningful measures, and could be beneficial to diagnose and track multiple sclerosis lesions in the spinal cord

High-resolution quantitative MRI of multiple sclerosis spinal cord lesions

PURPOSE: Validation of quantitative MR measures for myelin imaging in the postmortem multiple sclerosis spinal cord. METHODS: Four fixed spinal cord samples were imaged first with a 3T clinical MR scanner to identify areas of interest for scanning, and then with a 7T small bore scanner using a multicomponent‐driven equilibrium single‐pulse observation of T(1) and T(2) protocol to produce apparent proton density, T(1), T(2), myelin water, intracellular water, and free‐water fraction maps. After imaging, the cords were sectioned and stained with histological markers (hematoxylin and eosin, myelin basic protein, and neurofilament protein), which were quantitatively compared with the MR maps. RESULTS: Excellent correspondence was found between high‐resolution MR parameter maps and histology, particularly for apparent proton density MRI and myelin basic protein staining. CONCLUSION: High‐resolution quantitative MRI of the spinal cord provides biologically meaningful measures, and could be beneficial to diagnose and track multiple sclerosis lesions in the spinal cord

Complications and short to midterm results in a case series of 52 CUE procedures using a modified caudo-medial approach

Background: Medial coronoid process disease is the most common manifestation of canine developmental elbow disease which can progress to a more severe medial compartment disease (MCompD) characterized by full thickness cartilage loss of the medial coronoid process (MCP) and medial humeral condyle. Among others, the “Canine Unicompartmental Elbow” (CUE) has been reported to be an effective treatment strategy for MCompD, with full in 47.6% and acceptable function in 43.7% at six months or later of follow-up. Aim: To report on our clinical experiences with the CUE system using the caudo-medial approach in terms of both complications and functional outcome. Methods: Medical records of dogs that underwent CUE procedure using a caudo-medial approach over a 3-year period were retrospectively reviewed. This covered epidemiological data, bi-planar radiographs, subjective gait analysis, owner questionnaire, surgical reports as well as second-look arthroscopic findings when available. Results: In total, 52 CUE procedures were performed in 44 dogs with a median age at surgery of 8.0 years (IQ: 5.0-10.0) and a median body weight of 31.9 kg (ranging 20-48 kg). Four cases never return for follow-up, but where included in the analysis to increase the number of cases with pre- and intra-operative data. Mean follow-up time available for the remaining 48 cases was 7.1 (SD: 5.2) months. Radiographic derived implant positioning and alignment proved to be satisfactory in the sagittal plane but parallelism in the frontal plane was only present in three cases. Second-look arthroscopy in 5 cases with delayed or disappointing functional improvement showed evidence of implant related contact lesions and progressive erosion of the medial coronoid area in three elbows. Overall, complications occurred in 11 cases (21%), being major in eight (15%) and minor in three (6%). Major complications included refractory pain and lameness six to twelve months postoperatively in five cases. At last follow-up, twelve cases (25%) were considered to have full function, 35 cases (73%) acceptable function and in one case the function was considered unacceptable. As the only variable related to functional outcome, age had a negative predictive value for full function. Conclusion: The CUE procedure appears to be an effective treatment option for patients with MCompD. Older dogs might be at risk of having an inferior clinical outcome, when compared to young patients. The reason for this is unknown and will have to be evaluated in future studies. Compared to a CUE case series of 103 elbows operated through a medial approach (Cook et al., 2015), using a caudo-medial approach decreased the incidence of approach related complication. Nevertheless, functional outcome in the current case series was less favourable than previously reported. These conflicting findings as well as the occurrence of potentially implant mechanical conflict at the medial joint compartment despite CUE warrants further studies

SPARC promotes pericyte recruitment via inhibition of endoglin-dependent TGF-β1 activity

SPARC prevents endoglin association with αV integrin, which blocks the activation of TGF-β signaling and promotes pericyte migration to nascent blood vessels

Human Tumour Immune Evasion via TGF-β Blocks NK Cell Activation but Not Survival Allowing Therapeutic Restoration of Anti-Tumour Activity

Immune evasion is now recognized as a key feature of cancer progression. In animal models, the activity of cytotoxic lymphocytes is suppressed in the tumour microenvironment by the immunosuppressive cytokine, Transforming Growth Factor (TGF)-β. Release from TGF-β-mediated inhibition restores anti-tumour immunity, suggesting a therapeutic strategy for human cancer. We demonstrate that human natural killer (NK) cells are inhibited in a TGF-β dependent manner following chronic contact-dependent interactions with tumour cells in vitro. In vivo, NK cell inhibition was localised to the human tumour microenvironment and primary ovarian tumours conferred TGF-β dependent inhibition upon autologous NK cells ex vivo. TGF-β antagonized the interleukin (IL)-15 induced proliferation and gene expression associated with NK cell activation, inhibiting the expression of both NK cell activation receptor molecules and components of the cytotoxic apparatus. Interleukin-15 also promotes NK cell survival and IL-15 excluded the pro-apoptotic transcription factor FOXO3 from the nucleus. However, this IL-15 mediated pathway was unaffected by TGF-β treatment, allowing NK cell survival. This suggested that NK cells in the tumour microenvironment might have their activity restored by TGF-β blockade and both anti-TGF-β antibodies and a small molecule inhibitor of TGF-β signalling restored the effector function of NK cells inhibited by autologous tumour cells. Thus, TGF-β blunts NK cell activation within the human tumour microenvironment but this evasion mechanism can be therapeutically targeted, boosting anti-tumour immunity

Combining tractography and cortical measures to test system-specific hypotheses in multiple sclerosis

The objective was to test three motor system-specific hypotheses in multiple sclerosis patients: (i) corticospinal tract and primary motor cortex imaging measures differ between multiple sclerosis patients and controls; (ii) in patients, these measures correlate with disability; (iii) in patients, corticospinal tract measures correlate with measures of the ipsilateral primary motor cortex

Post-mortem assessment in vascular dementia: advances and aspirations.

BACKGROUND: Cerebrovascular lesions are a frequent finding in the elderly population. However, the impact of these lesions on cognitive performance, the prevalence of vascular dementia, and the pathophysiology behind characteristic in vivo imaging findings are subject to controversy. Moreover, there are no standardised criteria for the neuropathological assessment of cerebrovascular disease or its related lesions in human post-mortem brains, and conventional histological techniques may indeed be insufficient to fully reflect the consequences of cerebrovascular disease. DISCUSSION: Here, we review and discuss both the neuropathological and in vivo imaging characteristics of cerebrovascular disease, prevalence rates of vascular dementia, and clinico-pathological correlations. We also discuss the frequent comorbidity of cerebrovascular pathology and Alzheimer's disease pathology, as well as the difficult and controversial issue of clinically differentiating between Alzheimer's disease, vascular dementia and mixed Alzheimer's disease/vascular dementia. Finally, we consider additional novel approaches to complement and enhance current post-mortem assessment of cerebral human tissue. CONCLUSION: Elucidation of the pathophysiology of cerebrovascular disease, clarification of characteristic findings of in vivo imaging and knowledge about the impact of combined pathologies are needed to improve the diagnostic accuracy of clinical diagnoses