Search results for "ammonium"
showing 10 items of 1070 documents
Effect of the crystallization on the phase transitions IV ⇐ III and IV ⇐ II of ammonium nitrate
1993
Abstract The solid state phase transition path of ammonium nitrate is influenced by the manner of crystallization. Slow crystallization from water gives ideal crystals, which behaved differently from crystals prepared by rapid crystallization from the melt.
A new macrocyclic dipyrazolate salt of diazatetraester structure able to efficiently and selectively interact with psychotropic phenethylammonium sal…
2002
Abstract The equilibrium stability constants (Ks) of a series of ammonium pyrazolate complexes [L22−]2RN(R′)H2+ (7, R′=H and 8, R′=Me) formed from a new macrocyclic disodium dipyrazolate salt of diazatetraester structure 6[L22−] 2Na+ and ammonium salts [RNH3+X− or RN(Me)H2+X−] of psychotropic drugs and neurotransmitter catecholamines has been evaluated by electrochemical methods in DMSO solution. The resulting Ks values demonstrate that in general, the diazatetraester crown-derived dipyrazolate salt 6 exerts a stronger complexing effect over phenethylammonium ions than that of the dioxatetraester crown-derived disodium dipyrazolate salt 2 previously reported. Interestingly, complexes formed…
Complexation Selectivities of Pillar[5]arenes with Primary Ammonium Salts
2013
The complexation of alkyl-substituted pillar[5]arenes with primary ammonium salts is investigated. 1,4-Bis(methoxy)pillar[5]arene (MeP5) can form strong complexes with the primary ammonium salts in CDCl3. However, 1,4-bis(ethoxy)pillar[5]arene (EtP5) shows weak interaction with these guests, and 1,4-bis(butoxy)pillar[5]arene (BuP5) can not form such a complex at all. These results indicate that the modified alkyl chains of pillar[5]arene play an important role in the complexation selectivity.
Radiolabeling of DOTATOC with the long-lived positron emitter 44Sc.
2010
Abstract The positron-emitting radionuclide 44 Sc with a half-life of 3.97 h and a β + branching of 94.3% is of potential interest for clinical PET. As so far it is available from a 44 Ti/ 44 Sc generator in Mainz, where long-lived 44 Ti decays to no-carrier-added (nca) 44 Sc. The 44 Sc is a trivalent metal cation and should be suitable for complexation with many well established bifunctional chelators conjugated to peptides or other molecular targeting vectors. Thus, the aim of this work was to investigate the potential of 44 Sc for labeling of DOTA-conjugated peptides. DOTA-D-Phe 1 -Tyr 3 -octreotide (DOTATOC) was used as a model molecule to study and optimize labeling procedure. Reaction…
O-Alkylation of a lignite humic acid by phase-transfer catalysis
2006
A mild phase-transfer catalytic reaction has been conducted to O-alkylate the acidic functions of a lignite humic acid (HA), using tetrabutylammonium hydroxide as the phase-transfer catalyst. The HA acidic functional groups were made to react, in tetrahydrofuran, by nucleophilic substitution with several alkyl halides-methyl iodide, and ethyl, propyl, and butyl, and benzyl bromide. The occurrence of the O-alkylation reaction was assessed by elemental analysis and 1H NMR, CPMAS 13C NMR, and FTIR spectroscopy. Bonding of alkyl groups increased the carbon and hydrogen content and the H/C ratios of all the humic reaction products. Increased nitrogen in the reaction products suggested incomplete…
Effective complexation of psychotropic phenethylammonium salts from a disodium dipyrazolate salt of macrocyclic structure
2002
The equilibrium stability constants (Ks) of ammonium pyrazolate complexes [L2−]2RN(R′)H2+ (3, R′ = H and 4, R′ = Me) formed from a macrocyclic disodium dipyrazolate salt 2[L2−] 2Na+ and ammonium salts (RNH3+X− or RN(Me)H2+X−) of psychotropic drugs and neurotransmitter catecholamines have been evaluated by electrochemical methods in DMSO solution. The resulting Ks values demonstrate that, except for (±)-amphetamine, the complexes formed by lipophilic primary [mescaline, (+)-amphetamine, (±)-p-methoxyamphetamine (PMA), (±)-3,4-methylenedioxyamphetamine (MDA)] and secondary [(±)-methamphetamine, (+)-methamphetamine and (±)-3,4-methylenedioxymethamphetamine (MDMA ‘ecstasy’)] phenethylamines are…
Cooperative Binding of Divalent Diamides by N-Alkyl Ammonium Resorcinarene Chlorides
2015
N-Alkyl ammonium resorcinarene chlorides, stabilized by an intricate array of hydrogen bonds leading to a cavitand-like structure, bind amides. The molecular recognition occurs through intermolecular hydrogen bonds between the carbonyl oxygen and the amide hydrogen of the guests and the cation-anion circular hydrogen-bonded seam of the hosts, as well as through CH⋅⋅⋅π interactions. The N-alkyl ammonium resorcinarene chlorides cooperatively bind a series of di-acetamides of varying spacer lengths ranging from three to seven carbons. Titration data fit either a 1:1 or 2:1 binding isotherm depending on the spacer lengths. Considering all the guests possess similar binding motifs, the first bin…
Salt effects on the protonation of l-histidine and l-aspartic acid: a complex formation model
1991
Abstract Protonation constants of l -histidine (histidinate: his − ) and l -aspartic acid (aspartate: asp 2− ) were determined potentiometrically, using the (H + ) glass electrode, in aqueous tetraethylammonium iodide (Et 4 NI), calcium chloride and sodium chloride solutions, at 0 −3 and 10 ⩽, T ⩽, 45 ° C. Differences in protonation constants determined in different salt media were explained by a complex formation model and, according to this model, the presence of the following species was hypothesized: Ca(his) + , CaH(his) 2+ , CaH 2 (his) 3+ Na(his) 0 , H 3 (his)X + , H 2 (his)X 0 , Et 4 N(his) 0 , Et 4 NH(his) + , Ca(asp) 0 , CaH(asp) + , CaH 2 (asp) 2+ , Na(asp) − , NaH(asp) 0 , H 3 (a…
Enantioselective self-assembly of antiferromagnetic hexacopper(ii) wheels with chiral amino acid oxamates
2013
The Cu(2+)-mediated self-assembly of oxamato-based ligands derived from either the (S)- or (R)-enantiomers of the amino acid valine leads to the formation of two antiferromagnetically coupled homochiral anionic hexacopper(II) wheels in the presence of templating tetramethylammonium countercations.
ChemInform Abstract: tris-Pentasulfidorhodates(III). X-Ray Structure of (NH4)3(Rh(S5)3)(H2O)2.
1987
Abstract The crystal structure of the racemic dihydrated ammonium salt of the tris -pentasulfidorhodate(III) anion is compared with those of salts of the tris -pentasulfidoplatinate(IV) ion.