Biguanides, anion receptors and sensors

Biguanides are strong bases (pK_a > 10), their protonated forms bind anions and may therefore act as receptors for anions. We report on easy-to-make anion receptors and fluorescence-based sensors utilizing the biguanide moieties that respond to the presence of anions with a change in fluorescence. The observed changes in fluorescence are anion-specific and even though the biguanide receptors are cross-reactive, these sensors may be used to identify various anions (halides, carboxylates, phosphates). Paper-based analytical arrays were used to assess the discriminatory ability of the sensors in the qualitative and quantitative analysis of multiple anions.

Toward wearable sensors: optical sensor for detection of ammonium nitrate-based explosives, ANFO and ANNM

An imine-functionalized polymer displays selective fluorimetric response to the component of ANFO and ANNM, ammonium nitrate and nitromethane!

Changes in Conformation of Human Serum Albumin (HSA) and Gamma Globulins (γG) upon Adsorption to Polystyrene and Poly(styrene/acrolein) Latexes: Studies by Fluorescence Spectroscopy

Changes of human serum albumin (HSA) and gamma globulins (γG), labelled with 1-pyrene-carboxaldehyde (PCA) and/or with 1,3-bis(1- pyrene)-propane (BPP), resulting from interactions with polystyrene (PS) and poly(styrene/acrolein) (PSA) latexes, were investigated by fluorescence spectros copy. The proteins in solution readily exchanged with the adsorbed proteins. The fluorescence spectra of the PCA label and BPP probe, incorporated into the protein macromolecules, indicate that the protein macromolecules undergo sig nificant conformational changes on contact with the surface of the latex par ticles, and that these changes are not reversible. The internal fluidity for desorbed protein macromolecules is lower than before the interaction with the latex particles. Moreover, due to the conformational changes the PCA labels, formerly present in the hydrophilic and hydrophobic protein regions, became located predominantly in the latter. The differences in the emission spectra for the labelled proteins before attachment to the latex particles and after desorp tion were used to study the kinetics of the protein conformational changes. The dependence of the overall rate constants for protein conformational rearrange ments on the latex concentration was investigated.

Assessment of the amorphous "solubility" of a group of diverse drugs using new experimental and theoretical approaches

The supersaturation potential of poorly water-soluble compounds is of interest in the context of solubility enhancing formulations for enhanced bioavailability. In this regard, the amorphous "solubility", i.e., the maximum increase in solution concentration that can be obtained relative to the crystalline form, is an important parameter, albeit a very difficult one to evaluate experimentally. The goal of the current study was to develop new approaches to determine the amorphous "solubility" and to compare the experimental values to theoretical predictions. A group of six diverse model compounds was evaluated using the solvent exchange method to generate an amorphous phase in situ, determining the concentration at which the amorphous material was formed. The theoretical estimation of the amorphous "solubility" was based on the thermal properties of the crystalline and amorphous phases, the crystalline solubility, and the estimated concentration of water in the water-saturated amorphous phase. The formation of an amorphous precipitate could be captured transiently for all six compounds and hence the amorphous "solubility" determined experimentally. A comparison of the experimental amorphous "solubility" values to those calculated theoretically showed excellent agreement, in particular when the theoretical estimate method treated the precipitated phase as a supercooled liquid, and took into account heat capacity differences between the two forms. The maximum supersaturation ratio in water was found to be highly compound dependent, varying between 4 for ibuprofen and 54 for sorafenib. This information may be useful to predict improvements in biological exposure for poorly water-soluble compounds formulated as amorphous solid dispersions or other formulations that rely on supersaturation.

Cavitand octa acid forms a nonpolar capsuleplex dependent on the molecular size and hydrophobicity of the guest

We have been exploring the use of a deep cavity cavitand known by the trivial name 'octa acid' as a photochemical reaction cavity for manipulating photochemical and photophysical properties of organic molecules. In the current study, we have monitored the micropolarity of the interior of the cavitand by recording the fluorescence of five different organic probes. They all indicate that the interior of octa acid capsuleplex (2:1, H/G complex) is nonpolar and does not contain water molecules in spite of the complex being present in water. The nature of the octa acid-probe complex in each case has been characterized by 1H NMR data to be a 2:1 capsuleplex. Photophysical and 1H NMR experiments were employed to probe the factors that control the structure of the complex, 2:2, 2:1, and 1:1. The data we have on hand suggest that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule.

Intelligent fluorescent nucleoside in sensing cytosine base: importance of hydrophobic nature of perylene fluorophore

Fluorescence response upon hybridization of perylene labeled oligonucleotide probes depends on the microenvironment experienced by the perylene fluorophore. In mismatched duplex ((Per)U-C), enhanced fluorescence was observed while in matched duplex ((Per)U-A) fluorescence intensity decreased considerably. This observation will be a promising research effort in giving rise to a new powerful tool in detection of SNP.

Pyrene-Labeled Base-Discriminating Fluorescent DNA Probes for Homogeneous SNP Typing

This paper describes the design of novel base-discriminating fluorescent (BDF) nucleobases and their application to single nucleotide polymorphism (SNP) typing. We devised novel BDF nucleosides, (Py)U and (Py)C, which contain a pyrenecarboxamide chromophore connected by a propargyl linker. The fluorescence spectrum of the duplex containing a (Py)U/A base pair showed a strong emission at 397 nm on 327 nm excitation. In contrast, the fluorescence of duplexes containing (Py)U/N base pairs (N = C, G, or T) was considerably weaker. The proposed structure of the duplex containing a matched (Py)U/A base pair suggests that the high polarity near the pyrenecarboxamide group is responsible for the strong A-selective fluorescence emission. Moreover, the fluorescence of the duplex containing a (Py)U/A base pair was not quenched by a flanking C/G base pair. The fluorescence properties are quite different from previous BDF nucleobases, where fluorescence is quenchable by flanking C/G base pairs. The duplex containing the C derivative, (Py)C, selectively emitted fluorescence when the base opposite (Py)C was G. The drastic change of fluorescence intensity by the nature of the complementary base is extremely useful for SNP typing. (Py)U- and (Py)C-containing oligodeoxynucleotides acted as effective reporter probes for homogeneous SNP typing of DNA samples containing c-Ha-ras and BRCA2 SNP sites.