PH indicator | EPFL Graph Search

A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. Hence, a pH indicator is a chemical detector for hydronium ions (H3O+) or hydrogen ions (H+) in the Arrhenius model. Normally, the indicator causes the color of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their odor. The pH value of a neutral solution is 7.0 at 25°C (standard laboratory conditions). Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic. Since most naturally occurring organic compounds are weak electrolytes, such as carboxylic acids and amines, pH indicators find many applications in biology and analytical chemistry. Moreover, pH indicators form one of the three main types of i

Synthesis of calcium sensors for labelling fusion proteins-synthesis of modified prolines using aza naked sugar methodology

Agostina Ruggiu

Synthesis of Modified Prolines using aza naked sugar methodology R and S-prolines are secondary, cyclic, pyrrolidine-based amino acids. Proline demonstrated excellent catalytic activity to promote enantio- and diatereoselective, intra- and intermolecular cross aldolizations. This efficient organocalyst have been applied to the synthesis of different carbohydrates. In order to enlarge this asymmetric process to aqueous conditions, 4-hydroxyproline derivatives have been developed for the catalysis of cross aldol reaction in water. In this work, with the aim to develop new catalysts based on proline, the reactivity of azanorbornene systems has been explored and the stereoselective transformation of these synthons has been applied to the synthesis of new proline-based aminoacids. The chemistry, previously developed by Vogel and coll. on "naked sugar" has been applied with success on the aza analogues. In summary we have developed a new route for the synthesis of 5-hydroxymethyl-4- hydroxyproline, in particular the synthesis of a new aminoacid, 5-epimer of (-)-Bulgecinine. We have successfully synthesized using an efficient pathway an advanced precursor of 5-hydroxymethyl-3-hydroxyproline. Synthesis of Calcium Sensors for Labelling Fusion Proteins The free cytosolic concentration of calcium plays a central note in signal transduction. The development of indicators of the calcium concentration in living cells can therefore contribute to the understanding of biological systems. Here we describe synthesis and fluorescence properties of a Fura-2FF-O6-Benzylguanine fluorescence sensor that can be used to sense local calcium concentrations in cells. These sensors can be covalently linked to engineered alkyl-guanine-DNA-alkyl-transferase (AGT) fusion proteins. The indicator ΚD is with 4.3 µM optimal to measure locally increased calcium concentrations. This lowered ΚD is achieved by fluorine substitution of the coordinating BAPTA group, while not compromising the calcium to magnesium selectivity. It reacts quickly with mutant alkyl-guanine-DNA-alkyl-transferase (AGT) and can therefore be used to measure calcium near a specific protein. Ultimately this compound can combine advantages of both genetically encoded calcium indicators by being targetable and synthetic calcium indicators of the most popular Fura-2 series. Figure 1. Chemical structure and fluorescence excitation spectra in vitro of non permeable Fura-2FF benzylguanine derivative.

EPFL2008

Genetic targeting of chemical indicators in vivo

Antonino Asaro, Kai Johnsson, Luc Reymond

Fluorescent protein reporters have become the mainstay for tracing cellular circuitry in vivo but are limited in their versatility. Here we generated Cre-dependent reporter mice expressing the Snap-tag to target synthetic indicators to cells. Snap-tag labeling worked efficiently and selectively in vivo, allowing for both the manipulation of behavior and monitoring of cellular fluorescence from the same reporter.

Nature Publishing Group2015

Localizable and highly sensitive calcium indicator based on a BODIPY fluorophore

Kai Johnsson, Mako Kamiya

We introduce here a new class of BODIPY-based Ca2+ indicators which can be derivatized with biological ligands that permit the localization of the indicators in living cells. The underivatized BODIPY-based Ca2+ indicator (BOCA-1) shows a 250-fold increase in fluorescence intensity upon Ca2+ binding. We also prepared its O6-benzylguanine (BG) derivative, BOCA-1-BG, which can be covalently and specifically linked to SNAP-tag fusion proteins in living cells. The indicator retains its properties as a highly sensitive Ca2+ indicator after conjugation to proteins, displaying a 180-fold increase in fluorescence intensity upon Ca2+ binding. We further demonstrated that BOCA-1-BG through reaction with localized SNAP-tag fusion proteins can be used to sense changes in Ca2+ concentrations in the nuclei and in the cytosol of live CHO-K1 cells. The high sensitivity of the indicator together with the possibility to selectively couple it to proteins of interest makes it a powerful tool for measuring local changes in Ca2+ concentrations in living cells.

American Chemical Society2010

Synthesis of calcium sensors for labelling fusion proteins-synthesis of modified prolines using aza naked sugar methodology

Agostina Ruggiu

EPFL2008