Search

Peptide-like foldamers controlled by normal amide backbone hydrogen bonding have been extensively studied, and their folding patterns largely rely on configurational and conformational constraints induced by the steric properties of backbone substituents at appropriate positions. In contrast, opportunities to influence peptide secondary structure by functional groups forming individual hydrogen bond networks have not received much attention. Here, peptide-like foldamers consisting of alternating α,β,γ-triamino acids 3-amino-4-(aminomethyl)-2-methylpyrrolidine-3-carboxylate (AAMP) and natural amino acids glycine and alanine are reported, which were obtained by solution phase peptide synthesis. They form ordered secondary structures, which are dominated by a three-dimensional bridged triazaspiranoid-like hydrogen bond network involving the non-backbone amino groups, the backbone amide hydrogen bonds, and the relative configuration of the α,β,γ-triamino and α-amino acid building blocks. This additional stabilization leads to folding in both nonpolar organic as well as in aqueous environments. The three-dimensional arrangement of the individual foldamers is supported by X-ray crystallography, NMR spectroscopy, chiroptical methods, and molecular dynamics simulations. Peptide-like foldamers are known to be controlled by amide backbone hydrogen bonding, however, the influence of functional groups forming individual hydrogen-bond networks remains underexplored. Here, the authors report peptide-like α-γ heterofoldamers consisting of alternating α,β,γ-triamino acids, forming ordered secondary structures and folding in both organic and aqueous environments. [ABSTRACT FROM AUTHOR]

Two novel semi-organic salts of tetra- n-propylammonium (1+) and tetra- n-butylammonium (1+) hydrogen selenate have been prepared and characterised. Tetra- n-propylammonium (1+) hydrogen selenate ( a = 15.7949(6) Å, b = 15.3876(6) Å, c = 40.4384(17) Å, V = 9828.4(7) Å, Z = 8 for 8775 observed reflections) and tetra- n-butylammonium (1+) hydrogen selenate ( a = 15.0870(3) Å, b = 15.3380(4) Å, c = 17.4750(4) Å, V = 4043.79(16) Å, Z = 8, R = 0.0432 for 3335 observed reflections) crystallise in the centrosymmetric space groups Pbcn and Pccn of the orthorhombic system, respectively. Both salts were also characterised by the methods of vibrational spectroscopy (IR and Raman). The interpretation of the vibrational spectra is based on ab initio calculations of the isolated cations. The crystal structure of the third analogous compound, tetra- n-ethylammonium(1+) hydrogen selenate was redetermined at 150 K ( a = 8.2109(17) Å, b = 9.072(2) Å, c = 9.431(3) Å, α = 77.13(3)º, β = 74.43(2)º, γ = 63.62(3)º, V = 601.89(3) Å, Z = 2, R = 0.0167 for 2237 observed reflections). This compound crystallises in centrosymmetric space group P-1 of the triclinic system and was previously studied only at room temperature. Graphical Abstract: The preparation and detailed characterisation (using the combination of diffraction and spectroscopic methods) of salts of tetra- n-alkylammonium hydrogen selenates (alkyl = propyl, butyl). [ABSTRACT FROM AUTHOR]

The chloride and l-tartrate salts of the 2,4-diaminoquinazolinium(1+) were prepared and characterized by both X-ray diffraction and infrared spectroscopy. The potential of the 2,4-diaminoquinazolinium(1+) cation as a building block for materials for nonlinear optics was assessed using quantum mechanical computations. Both 2,4-diaminoquinazolinium(1+) chloride dihydrate ( a = 7.2121(1) Å, b = 8.0105(2) Å, c = 18.6157(5) Å, β = 92.493(1)°, V = 1074.46(4) Å, Z = 4, R = 0.0305 for 4605 observed reflections) and 2,4-diaminoquinazolinium(1+) l-tartrate dihydrate ( a = 7.2899(2) Å, b = 11.9508(2) Å, c = 13.4183(3) Å, β = 92.375(2)°, V = 1168.00(5) Å, Z = 2, R = 0.0367 for 4761 observed reflections) belong to the monoclinic space group P2. They are stable, non-hygroscopic, colorless and exhibit non-zero SHG efficiency for powdered samples. Graphical Abstract: Two novel non-centrosymmetric salts of 2,4-diaminoquinazolinium(1+) were prepared and thoroughly characterized during the search for materials for the second harmonic generation. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The crystal structures of the title compounds consist of 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium cation [CHN] and [HPO] or [HSO] anions. Both crystal structures are monoclinic, the structure of the dihydrogen phosphate ( I) is non-centrosymmetric ( P2) with a = 6.4090(2) Å, b = 13.6920(5) Å, c = 7.6140(3) Å, β = 94.620(2)°, V = 665.97(4) Å, Z = 2; whereas the unit cell of the hydrogen sulphate ( II) is centrosymmetric ( P2/ c) with a = 13.8460(2) Å, b = 12.6610(2) Å, c = 8.0360(2) Å, β = 99.5800(12)°, V = 1389.10(5) Å, Z = 4. Both the structures are formed by the different bonding patterns of the anions interlinked by strong and moderate O-H···O hydrogen bonds. While the structure of ( I) consists of a two-dimensional network of the hydrogen bonded dihydrogen phosphates, the infinite chains of the hydrogen bonded hydrogen sulphates are the basic building unit of the structure ( II). In addition to the dominant electrostatic interaction the divalent cations stabilize themselves in the structures by forming several C-H···O hydrogen bonds to the oxygen atoms of the anions. The IR spectra of both the compounds are strongly affected by the hydrogen bonds whose influence on OH stretching vibrations is analysed by means of the DFT calculations in the solid state. Graphical Abstract: The crystal structures of the 1,4-dimethyl-1,4-diazabicyclo[2.2.2]octane-1,4-diium dihydrogen phosphate and hydrogen sulphate comprise strong and moderate O-H···O hydrogen bonds significantly influencing the high energy region of IR spectra.[Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

By employing electrospray ionization mass spectrometry, it was proven experimentally that the [6]helicene-Ag complex (i.e., [Ag(CH)]) exists in the gas phase. Further, applying quantum mechanical DFT calculations, the most probable structure of this cationic complex [Ag(CH)] was derived. Finally, in the solid state, the complex [6]helicene-silver triflate-monohydrate (i.e., CH-AgCFSO-HO), crystallizing in the monoclinic system with the centro-symmetric P2/ c space group, was prepared and analyzed. The characteristic feature of this complex packing in the solid state is the formation of the separated [6]helicene and silver triflate domains. In both of these binding modes, the investigated [6]helicene ligand functions as a molecular tweezer for the univalent silver cation. Graphical abstract: [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The new mineral agricolaite, a potassium uranyl carbonate with ideal formula K(UO)(CO), occurs in vugs of ankerite gangue in gneisses in the abandoned Giftkiesstollen adit at Jáchymov, Czech Republic. The name is after Georgius Agricola (1494-1555), German scholar and scientist. Agricolaite occurs as isolated equant irregular translucent grains to 0.3 mm with yellow color, pale yellow streak, and vitreous luster. It is brittle with uneven fracture and displays neither cleavage nor parting. Agricolaite is non-fluorescent. Mohs hardness is ~4. It is associated with aragonite, brochantite, posnjakite, malachite, rutherfordine, and 'pseudo-voglite'. Experimental density is higher than 3.3 g.cm, Dcalc is 3.531 g. cm. The mineral is monoclinic, space group C2/ c, with a 10.2380(2), b 9.1930(2), c 12.2110(3) Å, β 95.108(2)°, V 1144.71(4) Å, Z = 4. The strongest lines in the powder X-ray diffraction pattern are d( I)( hkl): 6.061(55)(002), 5.087(57)(200), 3.740(100)(202), 3.393(43)(113), 2.281(52)(402). Average composition based on ten electron microprobe analyses corresponds to (in wt.%) UO 48.53, KO 31.49, CO(calc) 22.04 which gives the empirical formula K(UO)(CO). The crystal structure was solved from single-crystal X-ray diffraction data and refined to R = 0.0184 on the basis of the 1,308 unique reflections with F > 4 σF. The structure of agricolaite is identical to that of synthetic K(UO)(CO) and consists of separate UO(CO) groups organized into layers parallel to (100) and two crystallographically non-equivalent sites occupied by K cations. Both the mineral and its name were approved by the IMA-CNMNC. [ABSTRACT FROM AUTHOR]