Calcium chloride | EPFL Graph Search

Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Calcium chloride is commonly encountered as a hydrated solid with generic formula , where n = 0, 1, 2, 4, and 6. These compounds are mainly used for de-icing and dust control. Because the anhydrous salt is hygroscopic and deliquescent, it is used as a desiccant. By depressing the freezing point of water, calcium chloride is used to prevent ice formation and is used to de-ice. This application consumes the greatest amount of calcium chloride. Calcium chloride is relatively harmless to plants and soil. As a deicing agent, it is much more effective at lower temperatures than sodium chloride. When distributed for this use, it usually takes the form of small, white spheres a few millimeters in diameter, called prills. Solutions of calcium chloride can prevent freezing at temperatures as low as −52 °C (−62 °F), making it ideal for filling agricultural implement tires as a liquid ballast, aiding traction in cold climates. It is also used in domestic and industrial chemical air dehumidifiers. The second largest application of calcium chloride exploits its hygroscopic nature and the tackiness of its hydrates; calcium chloride is highly hygroscopic and its hydration is an exothermic process. A concentrated solution keeps a liquid layer on the surface of dirt roads, which suppresses the formation of dust. It keeps the finer dust particles on the road, providing a cushioning layer. If these are allowed to blow away, the large aggregate begins to shift around and the road breaks down. Using calcium chloride reduces the need for grading by as much as 50% and the need for fill-in materials as much as 80%. The average intake of calcium chloride as food additives has been estimated to be 160–345 mg/day. Calcium chloride is permitted as a food additive in the European Union for use as a sequestrant and firming agent with the E number E509.

Second harmonic scattering of water in a biological context

Tereza Schönfeldová

Water is one of the most abundant molecules in the universe. It forms a hydrogen bond network with unique structure and dynamics. Hydrogen bonding is highly relevant to many biological processes including membrane formation, protein folding, adsorption, and lubrication. However, the underlying molecular interactions within water and between water and membranes are difficult to study and hence not fully understood. In this thesis, we utilize second harmonic scattering (SHS) to investigate inhomogeneities in bulk water, probe structural changes in lipid bilayer membranes, and detect and characterize protein-membrane interactions. Firstly, we explore the structure of bulk water in comparison to a common model liquid, carbon tetrachloride. Combining SHS measurements and molecular dynamics simulations, we report on the nanoscale inhomogeneities in bulk water that occur on femtosecond timescales. We attribute the rise in the coherent second harmonic (SH) intensity to charge density fluctuations with enhanced nanoscale polarizabilities around transient voids. Even though the transient voids also exist in carbon tetrachloride, they do not show polarizability fluctuations and the SH response of carbon tetrachloride thus corresponds to that of a model isotropic liquid. Then, we study the structure of water around large unilamellar vesicles (LUVs), which serve as a model for cell membranes. We focus on the role of water during the lipid melting phase transition. Using SHS, differential scanning calorimetry, and temperature-dependent zeta-potential measurements, we investigate the structural changes of hydration shells around the vesicle membrane. We use lipids with phosphoserine, phosphocholine, and phosphate headgroups and observe different hydration behavior upon the lipid melting transition depending on the membrane composition. Next, we characterize the interface of membranes composed of lipids containing phosphocholine and phosphate headgroups in solutions with different CaCl2 concentrations. We observe that the SH intensity is decreasing with the addition of CaCl2, which we attribute to the formation of a condensed layer of Na+ counterions on the inner leaflet of the LUVs. Additionally, we extract the vesicle surface potential and second-order surface susceptibility from SHS data for membranes with different content of lipids with phosphate headgroups, and observe composition dependent behaviour which suggests structural membrane reorganization. We continue by exploring protein-membrane interactions using water as a contrast agent. We study a pore-forming toxin, perfringolysin O (PFO), known for selective insertion into cholesterol-rich membranes. Combining SHS measurements and cryo-electron microscopy, we compare the interaction between PFO and LUV membranes with a high and low cholesterol content. By obtaining a sub-picomolar insertion constant of PFO, we show that SHS can be used to determine protein-membrane binding constants in concentration ranges not accessible by conventional methods.Finally, we investigate the interaction of protein aerolysin and its mutants with lipid membranes. We observe changes in surface charge in the cap region of membrane-bound aerolysin at different pH of the surrounding solution. By combining SHS with single-channel measurements, we obtain the membrane binding constant of wild-type aerolysin and its mutants, and we dissect their pore-forming mechanism.

EPFL2022

Synthesis of NIR-Absorbing Squaraine Dyes and their Use in Organic Upconversion Devices

Karen Verena Strassel

Squaraines are organic dyes showing the advantages of a simple synthesis, high absorption coefficients and tunable bandgaps from the visible to the near-infrared (NIR) region. Their molecular structure is based on a polymethine chain and a donor-acceptor-donor structure that can be easily matched to the requirements of new application fields. This thesis focuses on the synthesis of squaraine dyes absorbing beyond 1000 nm and their use in organic upconversion devices. Organic dyes are widely studied and applied in optoelectronic devices such as organic solar cells, organic photodetectors (OPDs) and organic light-emitting devices (OLEDs). However, investigations so far were mainly focused on dyes absorbing and emitting in the visible range. With increasing interest in NIR-technology for biomedical and optoelectronic applications, there is a growing demand for organic NIR dyes. Here, a systematic chemical synthesis approach is used to tune the properties of benz[cd]indole substituted squaraine dyes. The donor part of the dye is modified by introducing Ï-conjugated substituents that increase the donor strength and enlarge the Ï-system. Additionally, a stronger acceptor part is introduced. A series of eight dyes is synthesized and characterized. The absorption maxima show bathochromic shifts with increasing conjugation, increasing donor strength and increasing acceptor strength. The beneficial properties of the NIR-absorbing squaraine dyes are demonstrated in organic upconversion devices with sensitivity beyond 1000 nm. The device is composed of a NIR-absorbing OPD possessing an external quantum efficiency of around 80% in the reverse bias and a visible OLED. The upconversion device converts NIR light into visible light without the need of intermediate electronics, allowing for direct NIR imaging. The organic semiconducting layers of the device stack absorb very little in the visible range. Combined with an optimized semitransparent metal top electrode, a device with an average visible transmittance of 65% is achieved. The advantages of visible transparent upconversion devices can be exploited e.g. in window-integrated electronic circuits. Another major benefit of organic electronics is the possibility to fabricate devices from solution, allowing low-cost and large-area production on flexible substrates. Here, the NIR-absorbing squaraine dye is used in upconversion devices consisting of five solution-processed layers. As emitting part, a fluorescent copolymer (super yellow)-based OLED or light-emitting electrochemical cell (LEC) is investigated. The solution-processed upconversion device converts NIR light with a wavelength of 980 nm efficiently to yellow light with a wavelength of around 575 nm, exhibiting a low turn-on voltage of 2.7 V. Replacing the OLED by a LEC allows for eliminating the sensitive calcium layer that acts as electron-injection layer. Due to the presence of ions, the LEC-based device shows a dynamic behavior, which is characterized in detail. A great deal of progress has been made with upconversion devices over the last years, but a number of challenges must be resolved to finally transform present-day prototype NIR imagers into a technology. Here, I address some of the scientific opportunities and challenges, including upconverters with sensitivity beyond 1000 nm, and visibly transparent and solution-processed devices with a narrow spectral response in the NIR.

EPFL2021

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