Über die Löschung von „Twisted Intramolecular Charge Transfer" (TICT)-Fluoreszenzen durch äußere Schweratom-Störer

The quenching by methyl iodide and ethyl bromide of the TICT fluorescence of N-(p-cyanophenyl)- carbazole (II) and N-(l-naphthyl)-carbazole (III) has been studied in solvents of different polarity. It is found that the heavy atom induced bimolecular fluorescence quenching increases with increasing energy of the TICT fluorescence transition, contrary to the energy-gaprule, and that TICT states are much less readily quenched than locally excited (LE) states. These results are explained by assuming a very small S-T energy gap for TICT states and a solvent polarity dependent distribution function for the intramolecular twist angle.

Organ-specific expression of the colon cancer antigen A33, a cell surface target for antibody-based therapy

Monoclonal antibody mAbA33 recognizes a unique cell surface protein of colorectal cancer, the A33 antigen. Phase I/II studies have shown highly selective targeting of radio-labeled mAbA33 in patients with metastatic colorectal cancer, opening up the possibility of A33-directed therapy. To better understand the basis of selective mAbA33 targeting in patients, the present study was designed to define the A33 distribution in normal organs and examine A33 expression in a broad range of tumor types. Immunohistochemical analysis of normal tissues identified the large and small intestinal mucosa as the principal sites of A33 expression. Tests with over 450 tumor samples showed that only tumors of the gastrointestinal tract are consistently A33-positive. For example, A33 is found in 95% of primary and metastatic colorectal cancers (86 of 90 cases tested), with uniform expression throughout the tumors in most cases. A33 was detected in a subset of gastric cancers (14/24 cases), with uniform expression in 10 cases (including 5 signer ring adenocarcinomas). Among esophageal cancers, squamous cell tumors typed A33-negative (9 cases), whereas one case each of mucinous and intestinal type was A33-positive. A subset of pancreatic carcinomas (6/12 cases) showed A33 expression, although with marked heterogeneity. Other epithelial cancers, sarcomas, neuroectodermal tumors, and lymphoid neoplasms were generally A33-negative. A33 is the first example of a constitutively expressed, organ-specific epithelial membrane antigen permitting highly specific tumor targeting in patients with colorectal cancer.

Photophysical and complexation properties of benzenesulfonamide derivatives with different donor and acceptor moieties

Pyrrolobenzosulfonamide, indolobenzosulfonamide and carbazolobenzosulfonamide derivatives with different acceptor groups were synthesized and their photophysical properties were compared. The electron donor linking sites are found to influence the emission characteristics of these compounds while acceptor linking sites have no noticeable effects on the spectral properties. P2-A5 which is a C-C linked pyrrole derivative exhibited different spectral properties from the C-N linked pyrrole derivatives. The complexation properties of the molecules were also investigated employing Na (I), Ca (II), Li (I), Mg (II), Zn (II) and Cu (II) ions.

Charge-Transfer Transitions in Twisted Stilbenoids: Interchangeable Features and Generic Distinctions of Single- and Double-Bond Twists

The charge-transfer transitions relevant to single- and double-bond photochemical twisting have been studied in the framework of the biradicaloid state theory using the AM1 method for a family of donor-acceptor-substituted stilbenoids and a series of sparkle-simulated model stilbenes. Features in common and mutually interchangeable properties for the two transition types as well as their peculiarities are revealed; they are considered in relation to the varied donor-acceptor strength of the substituents, with particular attention given to the occurrence of S0-S1 state conical intersections. The difference in critical points at which the conical intersections occur for double-bond and single-bond twisted stilbenoids is shown to be related to the splitting of the cyanine limit of their planar counterparts.

Bifunctional Charge Transfer Operated Fluorescent Probes with Acceptor and Donor Receptors. 1. Biphenyl-Type Sensor Molecules with Protonation-Induced Anti-Energy Gap Rule Behavior

On the basis of biphenyl (b) type molecules bpb-R substituted with a 2,2':6',2' '-terpyridine acceptor (bp) and either amino-type donor receptors (R = dimethylamino (DMA), A15C5 = monoaza-15-crown-5) or nonbinding substituents (R = CF(3), H, OMe) of various donor strengths, we developed a family of charge transfer (CT) operated monofunctional and bifunctional fluorescent sensors for protons and metal ions. These molecules are designed to communicate the interaction of an analyte with the acceptor and the donor receptor differing in basicity and cation selectivity by clearly distinguishable spectral shifts and intensity modulations in absorption and in emission as well as in fluorescence lifetime. From the dependence of the fluorescence spectra, fluorescence quantum yields, and fluorescence lifetimes of bpb-R on solvent polarity and proton concentration, the photophysics of bpb-R and their protonated analogues can be shown to be governed by the relaxation to a CT state of forbidden nature and by the switching between anti-energy and energy gap law type behaviors. This provides the basis for analytically favorable red shifted emission spectra in combination with comparatively high fluorescence quantum yields. Accordingly, bpb-H and bpb-OMe are capable of ratiometric emission signaling of protons. bpb-DMA reveals a protonation-induced ON-OFF-ON switching of its emission.

Bifunctional Charge Transfer Operated Fluorescent Probes with Acceptor and Donor Receptors. 2. Bifunctional Cation Coordination Behavior of Biphenyl-Type Sensor Molecules Incorporating 2,2‘:6‘,2‘ ‘-Terpyridine Acceptors

Based on donor (D)-acceptor (A) biphenyl (b) type molecules, a family of fluorescent reporters with integrated acceptor receptors and noncoordinating and coordinating donor substituents of varying strength has been designed for ratiometric emission sensing and multimodal signaling of metal ions and protons. In part 2 of this series on such charge transfer (CT) operated mono- and bifunctional fluorescent devices, the cation coordination behavior of the sensor molecules bpb-R equipped with a proton- and cation-responsive 2,2':6',2' '-terpyridine (bp) acceptor and either amino-type donor receptors (R = DMA, A15C5 = monoaza-15-crown-5) or nonbinding substituents (R = CF(3), H, OMe) is investigated employing the representative metal ions Na(I), Ca(II), Zn(II), Hg(II), and Cu(II) and steady-state and time-resolved fluorometry. The bpb-R molecules, the spectroscopic behavior and protonation behavior of which have been detailed in part 1 of this series, present rare examples for CT-operated bifunctional fluorescent probes that can undergo consecutive and/or simultaneous analyte recognition. The analyte-mediated change of the probes' intramolecular CT processes yields complexation site- and analyte-specific outputs, i.e., absorption and fluorescence modulations in energy, intensity, and lifetime. As revealed by the photophysical studies of the cation complexes of these fluoroionophores and the comparison to other neutral and charged D-A biphenyls, the spectroscopic properties of the acceptor chelates of bpb-R and A- and D-coordinated bpb-R are governed by CT control of an excited-state barrier toward formation of a forbidden charge transfer state, by the switching between analytically favorable anti-energy and common energy gap law type behavior, and by the electronic nature of the ligated metal ion. This accounts for the astonishingly high fluorescence quantum yields of the acceptor chelates of bpb-R equipped with weak or medium-sized donors and the red emission of D- and A-coordinated bpb-R observed for nonquenching metal ions.

CT-Operated Bifunctional Fluorescent Probe Based on a Pretwisted Donor–Donor–Biphenyl

Taking into account the structural requirements for TICT-type sensor molecules, a general synthetic route to derive pH and cation-responsive pretwisted donor (D)-donor (D) biphenyls (b) equipped with donor receptors is developed and a first model compound containing a mono aza-15-crown-5 and a DMA receptor is synthesized, see Scheme 1. The spectroscopic properties of this new bifunctional D-D biphenyl are studied in the non-polar and polar solvents cyclohexane, acetonitrile, and methanol. Protonation as well as complexation studies are performed with the representative metal ions Na(I), K(I), Ca(II), Ag(I), Zn(II), Cd(II), Hg(II), and Pb(II) to reveal the potential of this molecule for communication of whether none, only one, or both binding sites are engaged in analyte coordination by spectroscopically distinguishable outputs. The results are compared to those obtained with closely related donor (D)-acceptor (A) substituted biphenyl-type sensor molecules and are discussed within the framework of neutral and ionic D-A biphenyls.

Phase transitions and hydrogen bonding in a bipolar phosphocholine evidenced by calorimetry and vibrational spectroscopy

As a model for natural archaebacterial bolalipids, we have synthesized omega-hydroxybehenylphosphocholine (HBPC, HO-(CH(2))(22)-OP(O(-)(2))O-(CH(2))(2)-N+(CH(3))(3)) and investigated it, by Fourier-transform infrared and Raman spectroscopy and differential scanning calorimetry, both as fully hydrated dispersions (varying temperature) and as aligned films (varying hydration) in terms of particular structural features predestining such bipolar lipids for their occurrence in extremophilic organisms. The phase behavior of HBPC in dispersions depends on sample pretreatment as it comprises metastabilities in annealed samples. However, main transition proceeds consistently near 81 degrees C. Some (extra) deal of headgroup (phosphate) hydration accompanying a gel-gel phase transition near 66 degrees C appears to precede chain melting. Studies with HBPC films revealed lamellar interdigitated-like solid phases with an extraordinarily strong omega-OH--OPO(-) omega-OH--OPO(-) omega-OH hydrogen-bond pattern formed along both sides of the resulting monolayers. The "clamping" effect inherent to such structures provides a clue to explain the relatively high main-transition temperature of HBPC assemblies.

X-ray diffraction and spectroscopic studies of oleic acid-sodium oleate

The sodium oleate-oleic acid (1:1) complex (NaHOl(2)) is characterized using X-ray diffraction, FT-IR photoacoustic spectroscopy, FT-Raman spectroscopy, and DSC. The special arrangement of hydrogen-bonded pairs of carboxylic acid and carboxylate groups into unique "head-group" is supported by frequency shifts and partial or total disappearance of characteristic vibrations of carboxylic acid dimer and of carboxylate groups. The well-ordered state of hydrocarbon chains is demonstrated by the existence of sharp Raman bands in the C-C stretching region (1000-1150 cm-1) and other conformationally sensitive modes. The FT-Raman results suggest that the transition at about 32 degrees C involves the cooperative melting of methyl- and carboxyl/carboxylate-sided hydrocarbon chains. From the X-ray diffraction data it is clear that this transition is associated with the disintegration of the hydrogen-bonded carboxylate-carboxylic acid complex, followed by the separate formation of oleic acid and sodium oleate. The packing of hydrocarbon chain in the acid-soap complex is different from the parent oleic acid or sodium oleate. The hydrocarbon chains in the NaHOl(2) form more stable packing (O subcell) in comparison to that of oleic acid. A temperature composition phase diagram is presented.

Blue-fluorescent antibodies

The forte of catalytic antibodies has resided in the control of the ground-state reaction coordinate. A principle and method are now described in which antibodies can direct the outcome of photophysical and photochemical events that take place on excited-state potential energy surfaces. The key component is a chemically reactive optical sensor that provides a direct report of the dynamic interplay between protein and ligand at the active site. To illustrate the concept, we used a trans-stilbene hapten to elicit a panel of monoclonal antibodies that displayed a range of fluorescent spectral behavior when bound to a trans-stilbene substrate. Several antibodies yielded a blue fluorescence indicative of an excited-state complex or "exciplex" between trans-stilbene and the antibody. The antibodies controlled the isomerization coordinate of trans-stilbene and dynamically coupled this manifold with an active-site residue. A step was taken toward the use of antibody-based photochemical sensors for diagnostic and clinical applications.

Hydration of DMPC and DPPC at 4 degrees C produces a novel subgel phase with convex-concave bilayer curvatures

Hydration of dimyristoyl- and dipalmitoylphosphatidylcholines at 4 degrees C results in the formation of a characteristic subgel phase designated Pcc. Examination of the phase by freeze-fracture electron microscopy shows convex-concave deformations of the planar bilayer which are of two types. A smaller type with a radius of curvature of about 20 nm predominates in DMPC, and a larger type with about 70 nm radii of curvatures dominates in DPPC. The Pcc phase can also be formed in samples hydrated at temperatures above the main phase transition if the dispersion is frozen slowly and subsequently incubated at 4 degrees C for several days. The subgel Pcc phase was distinguished from the subgel Lc phase by the temperature of transition, packing of the acyl chains on the basis of wide-angle X-ray diffraction, and 2H-NMR spectra characteristic of a 'solid-ordered' phase. Vibrational spectra of the carbonyl and phosphate regions are consistent with a partially reduced hydration state. The origin of the convex-concave bilayer deformation is believed to result from constraints imposed by limiting hydration of the headgroup and a frustration arising from the spontaneous curvature of both monolayers.

Structure of stratum corneum lipids characterized by FT-Raman spectroscopy and DSC. II. Mixtures of ceramides and saturated fatty acids

Fourier transform (FT) Raman spectroscopy and differential scanning calorimetry (DSC) were used to study the thermotropic phase behaviour of mixtures of ceramides type IV (CER) and stearic acid (SA). For comparison the melting behaviour of SA was re-examined. The Raman spectra of all mixtures in the solid state show sharp bands associated with trans sequencies of the alkyl chain residues of both lipids. These features demonstrate that the hydrocarbon chains are highly ordered in the mixtures, too. The temperature dependence of the conformationally sensitive bands is used to estimate the degree of order in terms of the relative population of trans and gauche conformations. The DSC heating curves for the mixtures show two endothermic transitions which are typical for eutectic melting. The factor group splitting of the CH2 scissoring mode, arising from the orthorhombic subcell packing of SA, disappears in the course of the eutectic melting of samples with a SA content lower than 90 mol%. Both DSC and Raman spectroscopic studies reveal that CER and SA are immiscible in the solid state. The phase diagram of the system is a simple eutectic type one. The addition of SA to CER shifts the melting temperature of ceramides to lower values. However, though SA is a major component of stratum corneum (SC) it is not efficient enough to increase the fluidity of ceramides.

Structure of stratum corneum lipids characterized by FT-Raman spectroscopy and DSC. III. Mixtures of ceramides and cholesterol

The thermotropic and lyotropic phase behaviour of mixtures of ceramides type IV and cholesterol was investigated using Fourier transform (FT) Raman spectroscopy and differential scanning calorimetry (DSC). In the dry and in the fully hydrated state of these mixtures the DSC-curves exhibit an eutectic melting followed by the melting of the residual solid component. The Raman spectrum of the mixtures is complex, nevertheless, the appearance of the conformationally dependent bands indicates the ordered structure of the hydrocarbon chains. The temperature dependence of the conformationally sensitive bands in the CH2 stretching region (2800-2975 cm-1) and in the chain C-C stretching region (1050-1150 cm-1) was used to estimate the degree of order in terms of the relative population of trans and gauche conformers. The spectrum of the pure cholesterol shows only a weak temperature dependence in the CH2 stretching region and, therefore, the decrease of the intensity of the asymmetric CH2 stretching mode at 2880 cm-1 can be attributed to the melting of the alkyl chains of ceramides. The temperature and width of the phase transition, derived from Raman data, are similar to those of the DSC study.