Trans molecular probes

If the photoequilibrium concentrations of the cis and trans isomers of the photoswitchable ionophore in the membrane bulk and their complexation stability constants for primary cations are known, the photoinduced change in the concentration of the complex cation in the membrane bulk can be estimated. If the same amount of change is assumed to occur for the concentration of the complex cation at the very surface of the membrane, the photoinduced change in the phase boundary potential may be correlated quantitatively to the amount of the primary cation permeated to or released from the membrane side of the interface under otherwise identical conditions. In such a manner, this type of photoswitchable ionophore may serve as a molecular probe to quantitatively correlate between the photoinduced changes in the phase boundary potential and the number of the primary cations permselectively extracted into the membrane side of the interface. Highly lipophilic derivatives of azobis(benzo-15-crown-5), 1 and 2, as well as reference compound 3 were used for this purpose (see Fig. 9 for the structures) [43]. Compared to azobenzene-modified crown ethers reported earlier [39 2], more distinct structural difference between the cis... 

Knozinger, H. and Huber, S. (1998) IR spectroscopy of small and weakly interacting molecular probes for acidic and basic zeolites, J. Chem. Soc., Faraday Trans., 94, 2047. 

The fluorescence spectra of the monomeric cyanine nucleic acid stains family (PO-PRO-1, BO-PRO-1 and YO-PRO-1) introduced by Molecular Probes (http // probes.invitrogen.com) cover the entire visible wavelength range. These dyes may also be used with ultraviolet trans- or epi-illuminator excitation sources. The monomeric cyanine nucleic acid stains exhibit large degrees of fluorescence enhancement upon binding to DNA (or RNA) up to 1,800-fold. Consequently,... 

Kmilarly, Sung et al. recently reported the use of azo chromophoric labels as a molecular probe of physical aging in amorphous polymers . By measuring the kinetics of trans cis photoisomerization of azo duomophores covalently bonded to amorphous polyurethanes, they defined a parameter a which corresponds to the fraction of the free volume above a critical size at a given temperature and time of aging. 

Khodakov A Yu, Kustov L M, Kazansky V B and Williams C (1992), Infrared spectroscopic study of the interaction of cations in zeolites with simple molecular probes. Part 2. Adsorption and polarization of molecular hydrogen on zeolites containing polyvalent cations , J Chem Soc, Faraday Trans, 88, 3251. 

Figure 13.18. The l-t behavior of a Brij 56-templated photoresponsive nanocomposite film under alternate exposure to UV (360 nm) and visible light (435 nm) using various molecular probes, (a) FDM. Inset is the absorbance of the same film at 356 nm attributed to the n n transition of the trans isomer. The time scale of the UV/visible data corresponds to that of the first cycle in l-t response curve, (b) FDMDG. (c) FDMTG.

Muller G (2009) Luminescent chiral lanthanide(III) complexes as potential molecular probes. Dalton Trans 9692-9707... 

Cyanines are a class of conjugate organic dyes. Fluorescence of the trans species is in competition with a photoisomerisation towards the cis species, which represents a technological obstacle to their use as fluorescent molecular probes in imagery [85],... 

Muller G. Luminescent Chiral Lanthanide(III) Complexes as Potential Molecular Probes. Dalton Trans 2009 2009 9692-9707. 

Fig. 1. Capsule permeability as measured by the inverse GPC method. Capsules were made from 1.25% A-carrageenan (Fluka) and 0.02% carboxymethylcellulose (Aqualon) in 0.9% sodium chloride (core polymers) and 2% polydimethylamine-co-epichlorohydrin modified, quater-nized (Scientific Polymer Products) and a quaternary amine (Agefloc B50, CPS) in PBS (receiving bath) using a 3 min reaction time. The capsules were subsequently washed with PBS, coated for 15 min with 0.1% LV alginate (Kelco) and again washed in PBS. Two molecular size dex-trans were used to probe the capsule permeability. 170 kD dextran is almost totally excluded while the lower molar mass polymers permeated the membrane to varying extents...

Reversed-phase liquid chromatography shape-recognition processes are distinctly limited to describe the enhanced separation of geometric isomers or structurally related compounds that result primarily from the differences between molecular shapes rather than from additional interactions within the stationary-phase and/or silica support. For example, residual silanol activity of the base silica on nonend-capped polymeric Cis phases was found to enhance the separation of the polar carotenoids lutein and zeaxanthin [29]. In contrast, the separations of both the nonpolar carotenoid probes (a- and P-carotene and lycopene) and the SRM 869 column test mixture on endcapped and nonendcapped polymeric Cig phases exhibited no appreciable difference in retention. The nonpolar probes are subject to shape-selective interactions with the alkyl component of the stationary-phase (irrespective of endcapping), whereas the polar carotenoids containing hydroxyl moieties are subject to an additional level of retentive interactions via H-bonding with the surface silanols. Therefore, a direct comparison between the retention behavior of nonpolar and polar carotenoid solutes of similar shape and size that vary by the addition of polar substituents (e.g., dl-trans P-carotene vs. dll-trans P-cryptoxanthin) may not always be appropriate in the context of shape selectivity. 

As a last example of a molecular system exhibiting nonadiabatic dynamics caused by a conical intersection, we consider a model that recently has been proposed by Seidner and Domcke to describe ultrafast cis-trans isomerization processes in unsaturated hydrocarbons [172]. Photochemical reactions of this type are known to involve large-amplitode motion on coupled potential-energy surfaces [169], thus representing another stringent test for a mixed quantum-classical description that is complementary to Models 1 and II. A number of theoretical investigations, including quantum wave-packet studies [163, 164, 172], time-resolved pump-probe spectra [164, 181], and various mixed... 

TRPES has been recently reviewed and details of the experimental method and its interpretation can be found elsewhere [5], Trans-azobenzene was introduced via a helium supersonic molecular beam into the interaction region of a magnetic bottle photoelectron spectrometer. The molecules were photoexcited by a tunable femtosecond laser pulse (pump pulse) with a wavelength of 280-350nm. After a variable time delay, the excited molecules were ionized by a second femtosecond laser pulse (probe pulse) with a wavelength of 200 or 207nm. The emitted photoelectrons were collected as a function of pump-probe time delay and electron kinetic energy. 

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