Characterization of supercooling suppression of microencapsulated phase change material by using DSC

Supercooling suppression of microencapsulated n-tetradecane was measured using differential scanning calorimetry. Results indicate that the degree of supercooling is positively affected by the amount and type of nucleating agent present in bulk and microencapsulated n-tetradecane which it is used as a phase change material (MPCM). Results also demonstrate that the melting point of the n-tetradecane is fairly independent of nucleating agent concentration (0 – 4%). Conversely, the latent heat of fusion of n-tetradecane decreases considerably with nucleating agent amount and the initiation of crystallization point is inversely proportional to cooling rate.     

Ru(II) electron transfer systems containing S-donor ligands

The synthesis and properties of 3 new ligand-bridged bimetallic complexes, 1(2+), 2(2+), and 3(2+), containing [RuCl([9]aneS(3))](+) metal centers are reported. Each complex was bridged by a different ditopic ligand. 1(2+) is bridged by 3,6-bis(2-pyridyl)-1,2,4,5-tetrazine (bptz), while 2(2+) and 3(2+) are bridged by 2,3-bis(2-pyridyl)pyrazine (dpp) and 2,2'-bipyrimidine (bpym), respectively. The Ru([II]) isovalent states of these complexes have been investigated using a variety of techniques. In the case of 3(2+), X-ray crystallography studies show preferential crystallization of an anti form with respect to coordinated chloride ligands (crystal data for [3][Cl(2)].4H(2)O: C(20)H(38)Cl(4)N(4)O(4)Ru(2)S(6), monoclinic, space group P2(1)/a, a = 10.929(14), b = 13.514(17), c = 11.299(16) A, beta = 90.52(1), V = 1669 A(3), Z = 2). UV/vis spectroscopy shows that spectra of these complexes are dominated by intraligand (pi-->pi) and metal-to-ligand Ru(d)-->L(pi) charge transfer transitions. Electrochemical studies reveal that metal-metal interactions are sufficiently intense to generate the Ru(III)/Ru(II) mixed valence [[RuCl([9]aneS(3))(2)](L-L)](3+) state, where L-L = individual bridging ligands. Although the 1(3+), 2(3+), and 3(3+) mixed valence states were EPR silent at room temperature and 77 K, isotropic solution spectra were observed for the electrochemically generated radical cations 1(+), 2(+), and 3(+), with 1(+) displaying well-resolved hyperfine coupling to bridging ligand nitrogens. Using UV/vis/NIR spectroelectrochemistry, we investigated optical properties of the mixed valence complexes. All three showed intervalence charge transfer (IVCT) bands that are much more intense than electrochemical data indicate. Indeed, a comparison of IVCT data for 1(3+) with an analogous structure containing [(NH3)(3)Ru](2+) metal centers shows that the IVCT in the new complex is an order of magnitude more intense. It is concluded that although the new complexes show relatively weak electrostatic interactions, they possess large resonance energies.     

Singularities of the solution of a mixed problem for a general second order elliptic equation and boundary stabilizationof the wave equation

We deal here with a second order elliptic mixed problem which is posed in a regular open bounded domain of . We study the regularity of its solution. We apply our results to the boundary stabilization of the wave equation.     

Aqueous phosphoric acid as a mild reagent for deprotection of tert-butyl carbamates, esters, and ethers

Aqueous phosphoric acid (85 wt %) is an effective, environmentally benign reagent for the deprotection of tert-butyl carbamates, tert-butyl esters, and tert-butyl ethers. The reaction conditions are mild and offer good selectivity in the presence of other acid-sensitive groups, including CBZ carbamates, azetidine, benzyl and methyl esters, TBDMS, and methyl phenyl ethers. The mildness of the reaction is further demonstrated in the synthesis of clarithromycin derivative, in which a tert-butyl ester is removed in the presence of cyclic carbamate, lactone, ketal, acetate ester, and epimerizable methyl ketone functionalities. The reaction preserves the stereochemical integrity of the substrates. The reactions are high yielding, and the workup is convenient.     

Searching for cyclin-dependent kinase inhibitors using a new variant of the cope elimination

beta-Piperidinoethylsulfides are oxidized by m-chloroperbenzoic acid to intermediates containing both N-oxide and sulfone functions. These undergo a Cope-type elimination to a vinylsulfone that can be captured by amines to afford beta-aminoethylsulfones. When a beta-aminoethylsulfone group is linked to the 4-position of a phenyl group attached at N-2 of O6-cyclohexylmethylguanine, the resulting derivatives are inhibitors of the cyclin-dependent kinase CDK2. One of the most potent inhibitors (IC50 = 45 nM) contained a N-3-hydroxypropyl group on the aminoethylsulfonyl substituent. The crystal structure of this inhibitor bound to CDK2/cyclin A was determined and shows an unusual network of hydrogen bonds. The synthetic methodology developed can be utilized in multiple-parallel format and has numerous potential applications in medicinal chemistry.     

Aqueous phosphoric acid as a mild reagent for deprotection of the t-butoxycarbonyl group

Aqueous phosphoric acid (85 wt%) is an efficient and mild reagent for the deprotection of N-BOC groups. Acid sensitive functionalities including benzyl and methyl esters, TBDMS ether, CBZ and isopropylidene groups are compatible with the reaction conditions. The reactions are high yielding, and the workup is convenient.