The capture of an optical image in the plane of a semiconductor quantum well and the subsequent re-emission of this image in the form of a two-dimensional photon flux is demonstrated. Spatially resolved storage of photonic signals in a two-dimensional lateral potential landscape of the quantum well is employed to imprint optical images in the form of trapped photogenerated charges into the solid. The lateral two-dimensional potential modulation leads to very long storage times by a deliberate spatial separation of photogenerated electron-hole pairs. Once the potential modulation is lifted, the initial optical information is restored and the photographed image is released in a flash of light.
Voltage-controlled lateral potential superlattices are used to dramatically increase the lifetime of photogenerated carriers in a quantum well. These long lifetimes, together with the ability to deliberately trigger radiative recombination, enable us to directly visualize the spreading character of nonlinear Maxwell relaxation of 2D charges along narrow channels. Our system allows for temporal and spatial resolution of Maxwell kinetics, usually a very fast process and difficult to observe. The observed spreading dynamics of a 2D hole plasma is in perfect agreement with our nonlinear model.
Astrocytoma vasculature patterns differ according to histological grade of malignancy with glioblastoma multiforme (WHO grade IV) showing most extensive endothelial proliferation. Here, we determined whether the vascular patterns of medulloblastoma and supratentorial primitive neuroectodermal tumors (PNETs), which can be hardly distinguished histopathologically, differ. We evaluated the spatial organization of vessels in medulloblastomas and PNETs using antibodies to von Willebrand factor (vWF) and CD34. Medulloblastoma capillaries showed slight endothelial cell hyperplasia. Microvessels sprouted from the capillaries and formed glomeruloid clusters. There were areas with chains of unopposed endothelial cells (3-10 cells). Supratentorial PNETs had highly branched capillaries with extensive endothelial cell hyperplasia. Glomeruloid arrays of microvessels extended from the capillaries. Small fragments of endothelial tubes were scattered throughout the tumor. Therefore, medulloblastomas and supratentorial PNETs showed different spatial organization of tumor vessels which can be used for differentiation of each tumor entity. These vascular patterns may reflect different tumor derived angiogenic stimuli.
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Metathesis. -Ring closing metathesis to title compounds (IV) is achieved by using Grubbs' catalyst. The resulting E/Z mixtures are separable by GLC. The lactones (IV) and the ring opening product (VI) show weak cytotoxic activitiy against HL-60 cells.
.2,5-Dialkylfuran and tetrahydrofuran compounds as structural elements of Annonaceae acetogenins like Asitrocin were synthesized starting from furfural by Grignard reactions, lithiation of the furan ring and addition of aliphatic aldehydes. Hydrogenation of the furan rings over Pd-catalyst gave the corresponding tetrahydrofurans. All resulting compounds showed no or rather less antimicrobial activity against grampositive, gram-negative bacteria and fungi compared to tetracycline or clotrimazol but high cytotoxic activity against HL 60 cell line determined in the MTT assay. . So more simple compounds with the same or even higher potency are interesting for the development of new anticancer drugs. One of the discussed mechanisms of action is a complexation of mitochondrial iron by the dihydroxyalkyltetrahydrofuran core of the acetogenins [1]. So this partial structure of the natural compounds was the target of our synthesis. On the other hand some furancarbinols as 4-ipomeanol are well known cytotoxic compounds. 4-Ipomeanol is after bioactivation in lung tissue (clara cells) by cytochrom P 450 an alkylating agent [7]. It is tested in phase II studies against human lung cancer. So bisalkylfuran compounds might be interesting for the development of new anticancer drugs too. In addition, the products should also be tested for their antimicrobial activity (Scheme 1). Keywords Scheme 1. ChemistryCommercially available furan-2-carbaldehyde was reacted in a Grignard reaction with dodecylmagnesium bromide to give the alcohol 1 in good yield [3,4]. The furan ring of 1 was hydrogenated over Pd/C-catalyst under normal pressure to the tetrahydrofuran derivative 2 (mixture of diastereomers). On the other hand the furan ring of 1 was lithiated with n-BuLi, (a second equivalent of n-BuLi was consumed for deprotonation of the hydroxy group) and the resulting dianion was reacted with pent-4-enal to give the dialkylfuran 3 as an inseparable mixture of diastereomers (seperation was impossible by column chromatography). 3 was also hydrogenated with Pd/C in methanol to give the tetrahydrofuran 4 as a diastereomeric mixture. In the course of this hydrogenation the double bond was also reduced (Scheme 2).In the same manner homologues were prepared by reaction of furan-2-carbaldehyde with pent-4-enylmagnesiumbromide to the alcohol 5, followed by lithiation with two equivalents n-BuLi and addition of tridecanal.The diol 6 was obtained only in low yield. Hydrogenation of 6 gave the disubstituted tetrahydrofuran 7 (Scheme 3).It was impossible for us to separate the diastereomeric mixtures by flash column chromatography on silica gel or by preparative high-pressure liquid chromatography. Pharmacological results and discussionThe compounds described above were tested in the agar diffusion assay against E. coli, S. hominis, P. antimicrobia and the yeasts Y. lipolytica, C. glabrata and the filamentou fungi A. niger. All compounds showed only minor or no antimicrobial activity, only 2, 3, 4, 5 and 6 showed a moderate activity (Table 1). The cytot...
Synthesis and Antimicrobial Activity of Hydroxyalkyl-and Hydroxyacyl-phenols and Their Benzyl Ethers.-A variety of phenolic compounds having hydrophilic side chains of the bengazole-type is synthesized and evaluated for their antimicrobial activity. Only the phenol ethers (III) and (V) show poor activity. -(KRAUSS, J.; UNTERREITMEIER, D.; Arch. Pharm. (Weinheim, Ger.) 335 (2002) 2-3, 94-98; Inst. Pharm.,
Furan-2-ylalkenols 2a-d were esterified with undec-10-enoyl chloride and the resulting esters were cyclized to unsaturated 2- and 3-furyl macrolactones by ring closing metathesis using Grubbs catalyst I. Hydrolysis of the macrolactone 4b with NaOH led to the furylalkenoic acid and reaction of 4c with tert-butyllithium gave a tert-butyl ketone. Some of the resulting compounds were tested in the MTT assay for their cytotoxic activities against HL 60 cells and at the National Cancer Institute (NCI) against 60 cancer cell lines. The compounds only showed cytotoxic activities in the muM range.
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