Large molecular third-order optical nonlinearities in polarized carotenoids.

Garito and co-workers have suggested a mechanism to dramatically increase the second hyperpolarizability, gamma, in linear pi-electron-conjugated molecules. Polarization is introduced that leads to a difference between the dipole moments of the molecule's ground state and excited state. Here a series of carotenoids was examined that had increasing intramolecular charge transfer (ICT) from the polyenic chain to the acceptor moiety in the ground state, and gamma was measured for these compounds as a function of wavelength by third-harmonic generation. The compound with the greatest ICT exhibited a 35-fold enhancement of gammamax (the gamma measured at the peak of the three-photon resonance) relative to the symmetric molecule beta-carotene, which itself has one of the largest third-order nonlinearities known. Stark spectroscopic measurements revealed the existence of a large difference dipole moment, Delta mu, between the ground and excited state. Quantum-chemical calculations underline the importance of interactions involving states with large Delta mu.

Stark spectroscopy: applications in chemistry, biology, and materials science.

Stark spectroscopy has been applied to a wide range of molecular systems and materials. A generally useful method for obtaining electronic and vibrational Stark spectra that does not require sophisticated equipment is described. By working with frozen glasses it is possible to study nearly any molecular system, including ions and proteins. Quantitative analysis of the spectra provides information on the change in dipole moment and polarizability associated with a transition. The change in dipole moment reflects the degree of charge separation for a transition, a quantity of interest to a variety of fields. The polarizability change describes the sensitivity of a transition to an electrostatic field such as that found in a protein or an ordered synthetic material. Applications to donor-acceptor polyenes, transition metal complexes (metal-to-ligand and metal-to-metal mixed valence transitions), and nonphotosynthetic biological systems are reviewed.

Ultra-fast excited state dynamics in green fluorescent protein: multiple states and proton transfer.

The green fluorescent protein (GFP) of the jellyfish Aequorea Victoria has attracted widespread interest since the discovery that its chromophore is generated by the autocatalytic, posttranslational cyclization and oxidation of a hexapeptide unit. This permits fusion of the DNA sequence of GFP with that of any protein whose expression or transport can then be readily monitored by sensitive fluorescence methods without the need to add exogenous fluorescent dyes. The excited state dynamics of GFP were studied following photo-excitation of each of its two strong absorption bands in the visible using fluorescence upconversion spectroscopy (about 100 fs time resolution). It is shown that excitation of the higher energy feature leads very rapidly to a form of the lower energy species, and that the excited state interconversion rate can be markedly slowed by replacing exchangeable protons with deuterons. This observation and others lead to a model in which the two visible absorption bands correspond to GFP in two ground-state conformations. These conformations can be slowly interconverted in the ground state, but the process is much faster in the excited state. The observed isotope effect suggests that the initial excited state process involves a proton transfer reaction that is followed by additional structural changes. These observations may help to rationalize and motivate mutations that alter the absorption properties and improve the photo stability of GFP.

[Alternative vascular approaches in transluminal angioplasty of infra-inguinal arteries]. / Alternative Gefässzugänge bei der transluminalen Angioplastie infrainguinaler Arterien.

61 procedures using an alternative vascular access for PTA are reported. Puntures of mid and distal femoral arteries and popliteal arteries in antegrade as well as retrograde direction have been proven effective and sufficiently safe, when unfavourable anatomic situations did not allow the performance of a standard procedure. 14 cases necessitated puncture of and access via crural arteries.

[Computerized tomographic study of medieval coffins]. / Computertomographische Untersuchung mittelalterlicher Särge.

Two medieval coffins containing neonates were examined by CT. The advantages of using computed tomography, compared with conventional x-ray techniques, for analysing various objects within a receptacle are demonstrated.

[Isotope phlebography (author's transl)]. / Beitrag zur Isotopen-Phlebographie

Various techniques for showing venous function are recognized. The value of isotope phlebography is shown here on 39 unselected cases in whom contrast filling was also carried out. Rapid injection of 2 m Ci TC 99m into a dorsal vein of the foot produced isotope phlebograms with a Dyna camera 2 C.

[Radiologic diagnosis of secondaries in the liver (author's transl)]. / Röntgendiagnostik der Lebermetastasen

A diagnosis of secondaries in the liver carries considerable weight in prognosis and treatment, particularly pre-operatively, so that a possibly unnecessary operation may be avoided. Among techniques available for screening for metastases of the liver scintigraphy plays an important part. Besides laboratory tests and clinical examination it is relatively efficient and does not burden the patient. But they often are incapable of providing a basis for therapeutic decisions. Radiologic techniques are unsuitable (13). Knowledge and proper interpretation of indirect signs will permit guidance at the right time. In essence they serve the radiologic proof of advanced metastatic growths. Space occupying processes in the liver are the main indication for angiography. This is certainly not a routine method but makes sense when trying to identify the nature of defects shown in scintigrams (10). Where a primary tumor is known, angiography will follow scintigraphy of the liver, the search technique of choice. While the two techniques are correctly positive in 75-90% for avascular secondaries, experience of numerous investigations confirms that vascular metastases can be recognized earlier in angiograms than in scintigrams. Only angiography provides specific information differentiating metastases from a heptoma. The additional proof of primary tumors of the pancreas is important. Angiography is essential for indication and planning of partial hepatectomy. The angiographic picture does not permit conclusions from the metastases as to site and identity of the primary tumor. Critical evaluation of the radiographic techniques for early recognition of secondaries in the liver suggests humility. Only by carefully combining the various techniques will it be possible to demonstrate secondaries in the liver earlier and more frequently.