Calcium atom

The loop region between the two a helices binds the calcium atom. Carboxyl side chains from Asp and Glu, main-chain C =0 and H2O form the ligands to the metal atom (see Figure 2.13b). Thus both the specific main-chain conformation of the loop and specific side chains are required to provide the function of this motif. The helix-loop-helix motif provides a scaffold that holds the calcium ligands in the proper position to bind and release calcium. 

Figure 6.21a) comprising two domains separated by a long straight a helix, similar in shape to troponin-C described in Chapter 2 (see Figure 2.13c). Each domain comprises two EF hands (see Figure 2.13a), each of which binds a calcium atom. The two domains are clearly separated in space at the two ends of the a helix linker. 

Figure 12.7 Ribbon diagram of one subunit of potin from Rhodobacter capsulatus viewed from witbin tbe plane of tbe membrane. Sixteen p strands form an antiparallel p barrel tbat traverses tbe membrane. Tbe loops at tbe top of tbe picture are extracellular whereas tbe short turns at tbe bottom face the periplasm. The long loop between p strands 5 and 6 (red) constricts the channel of the barrel. Two calcium atoms are shown as orange circles. (Adapted from S.W. Cowan, Curr. Opin. Struct. Biol. 3 501-507, 1993.)...

Fi re 12.8 Schematic diagram of the trimerlc porin molecule viewed from the extracellular space. Blue regions illustrate the walls of the three porin barrels, the loop regions that constrict the channel are red and the calcium atoms are orange. 

The insertion of calcium atoms into vinyl and aryl carbon-fluorine bonds has been reported Only the resulting organometallic from the aryl derivatives appears to live long enough to be trapped by water [J]... 

In the preceding equation, the atoms present on both sides are one calcium atom, one carbon atom, and three oxygen atoms. 

Calcium atomic size, 379 atomic volume, 410 chemistry, 382... 

I conceive that when we say the atomic weight of calcium is 40, we really explain the fact, while the majority of calcium atoms have an actual atomic weight of 40, there are not a few which are represented by 39 or 41, a less number by 38 or 42, and so on [15]. 

E.3 In your new nanotechnology lab you have the capability to manipulate individual atoms. The atoms on the left are bromine atoms (molar mass 80 g-mol L), those on the right are atoms of calcium (molar mass 40 g-mol" 1). How many calcium atoms would have to be added to the pan on the right for the masses on the two pans to be equal ... 

C02-0089. When calcium reacts with chlorine, each calcium atom loses two electrons, and each chlorine atom... 

The case of the disalicylate, 1-methyl trimethylene disalicylate, is interesting. Because of steric hindrance it is unlikely that the two salicylate ligands can chelate to one calcium atom. In theory the disalicylate... 

In CaO, the calcium is in the form Ca+2, and the oxygen in the form O-2. That is, two electrons have been transferred from the calcium atom to the oxygen atom. 

HRP C contains two different types of metal center (i.e., iron(III) protoporphyrin IX-heme group and two calcium atoms) that are fundamental for the integrity of the enzyme. The heme group is attached to the enzyme at His 170 by a coordinate bond between the histidine side-chain NE2 atom and the heme iron atom. The second axial coordination site is unoccupied in the resting state of the enzyme but available to hydrogen peroxide during enzyme turnover. Small molecules such as carbon monoxide, cyanide, fluoride, and azide bind to the heme iron atom at this distal site, giving six-coordinated PX complexes. 

A ground-state electron in a calcium atom might have which of the following sets of quantum numbers ... 

Doubly-charged ions exist because the potential of second ionization of many metals is relatively low with respect to the plasma thermal energy. For instance, 11.9 eV are needed to remove two electrons, in contrast with 6.1 eV for one electron, from a calcium atom. At 8000K, a little less than 0.1% of Ca would be in the Ca + form and overlap with Mg+ isotopes. Likewise, Ba is rather easily formed and overlaps with Zn+ isotopes. Isobaric interferences with doubly-charged ions are easily identified as odd-mass atoms will produce peaks at half masses, such as Ca at mass 21.5. 

Fig. 7. The calcium binding sites of HRP C (detail). Ligands to the distal (A) and proximal (B) calcium atoms are shown. The O-donor ligand sets are hsted in Section IV,D.

Anhydrite is a calcium sulfate, CaS04, with an orthorhombic structure (mmm) where sulfur atoms, which are at the centers of tetrahedra of oxygens, and calcium atoms he on the lines of intersection of mirror planes (100) and (010). In nature, REE and Mn can easily substitute for Ca, becoming luminescence... 

In the soft x-ray region, an enhancement by the photoabsorption of phosphorus and of calcium was observed. The condensation of calcium near DNA in spores, as a form of dipicolinic acid, has already been reported [63]. The calcium atom has acted in the same manner as exogenous sensitizers. 

Takakura, K. Double-strand breaks in DNA induced by the K-shell ionization of calcium atoms. Acta Oncol. 1996, 35 (7), 883-888. 

As evidenced by the tremendous power of nuclear bombs, nuclear reactions involve quite a lot of energy. In the laboratory, researchers fabricate nuclides with the aid of special, high-energy equipment such as reactors in which nuclear reactions can take place, or particle accelerators in which particles such as protons are accelerated to high speed and crash into one another, or some other target. For example, in 2006, researchers at the Joint Institute for Nuclear Research in the Russian Federation and the Lawrence Livermore National Laboratory in California synthesized isotopes of element 118 for the first time. To make the new isotope, researchers smashed calcium atoms into a target made of californium (which has an atomic number of 98). These new isotopes decayed quickly. (Element 118 and other recently discovered elements have not yet been named.)... 

In the first reaction, a single calcium atom donates two electrons to two chlorine atoms. This results in the formation of a Ca + ion and two Cl ions. The positive ion and two negative ions are attracted to each other. In the formation of magnesium oxide, magnesium donates two electrons to oxygen resulting in Mg and... 

Excited-state Mg atoms react with methane and other alkanes via H atom abstraction in the gas phase (equation 1). By studying the vibrational states of the MgH product, information on the mechanism has been inferred. It has been found that regardless of the alkane, RH (and thus the C—H bond strength), the vibrational state distributions are essentially identical. This suggests that long-lived vibrationaUy excited [RMgH] complexes are not intermediates for equation 1 in the gas phase. The situation is quite different for excited-state Mg atoms reacting with methane under matrix conditions, where the insertion product (equation 2) is sufficiently stable for analysis via infrared spectroscopy ". Calcium atoms have been shown to insert into the C—H bonds of cycloalkanes. ... 

Me3SiCH2)3Zn] anions, in 13 two additional toluene molecules and in 14 four additional THF molecules have interactions with barium, rendering this atom eight-coordinate. Similarly, in the crystal lattice of 15 and 16 the strontium and calcium atoms interact with two [(Me3SiCH2)3Zn] anions, while a pseudo-octahedral coordination geometry at these atoms is reached by coordination of two THF molecules which are in c -position. 

Klabunde et al. (66) reported that calcium atoms react with unsaturated perfluoroorganic compounds, but there is no reaction with perfluo-roalkanes. Organocalcium compounds were not isolated, but their presence was inferred from reactions of the condensates at low temperatures. The final products on warming to room temperature were calcium fluoride and defluorinated organic compounds, e.g.,... 

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