Crystal structure of ionic and non-ionic surfactants based on polyoxyethylenated dodecanol: A13C-CP-MAS-NMR and x-ray investigation

Crystal structure of monodisperse non-ionic surfactants having the general formula C₁₂H₂₅O–(CH₂–CH₂–O)_nH (C₁₂E_n),n=7,9, 10, 15, 16 and ionic derivatives, C₁₂H₂₅–O–(CH₂–CH₂–O)_n–CH₂COONa (C₁₂E_nC),n=3,4,5,6,7,9, 12 has been investigated by¹³C-CP-MAS-NMR and x-ray diffraction. A structural model, in which aliphatic and polyether segments are segregated in bilayers stacking parallel to the elongation direction of the molecules, fits the experimental data for both series. The experimental values of the repeat distance along the stacking directiond(001) are linearly dependent onn and the slope is nearly equal to twice the repeat distance of7/2 helix conformation, which is typical for crystalline polyethyleneoxide. The values ofd(001) agree very well with the values expected for the C₁₂ segment in a planar zig-zag conformation, which is tilted with respect to the polyerther segment (7/2 helix conformation) in such a way that both the aliphatic and the polyether regions adopt the mass density of the corresponding crystalline compound. Two additional phases have been detected for C₁₂E_nC. One of them is probably characterized by the planar zig-zag conformation of the polyether chain. The meader model, previously proposed in the literature for surfactants containing polyethylene oxide segments is inconsistent with the obtained experimental data.     

Molecular DFT structure and packing effect of thiodipropionic and dithiodiglycolic acids and salts

Molecular and periodic DFT structure calculations of thiodipropionic and dithiodiglycolic acids, S_n[(CH₂)(COOR)]₂ (n = 1,2, R = H, Na), were performed. Computed structures were analyzed and compared to the experimental data (a C_s conformation is favored in solution than C₂ in solid state). Four close and low-energy optimized conformations were analyzed: C_2v, C₂, C_s and C₁. Small changes in the conformation stability (ΔG) and symmetry group were observed in polar medium. Periodic DFT-GGA approaches have been performed to determine the importance of weak interaction upon the crystal structure of the thiodipropionic acid, e.g., S–H and/or O–H hydrogen bonding. More SH and OH dispersed bands were observed in the optimized structure. Using a full analysis of the DOS of O–H or S–H bonding contributions, a notable interlayer bonding in the parent structure was revealed. Therefore, the presence of such weak interaction ONa⁺ or OH may thus change the point group symmetry of the crystal upon packing effect.     

Tin(IV) complexes ofSchiff bases derived from salicylaldehyde and aminoalcohols

11 and 12 molar reactions of tin(IV) chloride with theSchiff bases, HO–C₆H₄CHNROH [where R=–(CH₂)₂–, –CH₂–, –CH(CH₃)–, –(CH₂)₃–, and –CH(C₂H₅)CH₂–] have been studied in different stoichiometric ratios and derivatives of the type SnCl₄(SBH₂) and SnCl₄(SBH₂)₂ (whereSBH₂ represents theSchiff base molecule) have been isolated. These have been characterised by elemental analysis, conductivity measurements and I.R. spectral studies.     

Disordered Crystal Structure of Bis[(2.2.2-Cryptand)Sodium] Bis[Aqua(Isothiocyanato)(μ-Isothiocyanato)Sodium] 2[Na(2.2.2-Crypt)]+ · [Na2(NCS)2(μ-NCS)2(H2O)2]2–

Crystals of bis[(2.2.2-cryptand)sodium] bis[aqua(isothiocyanato)(-isothiocyanato)sodium]: 2[Na(C₁₈H₃₆N₂O₆)]⁺ · [Na₂(NCS)₂(-NCS)₂(H₂O)₂]^2– (I) were synthesized and studied by X-ray diffraction analysis. The disordered structure of I (a = 12.715 Å, b = 10.458 Å, c = 21.767 Å, = 102.56°, space group P2₁/n) was solved by the direct method and refined by the full-matrix least-squares method in anisotropic approximation to R = 0.058 from 3896 independent reflections (CAD4 automated diffractometer, MoK ). The crystal consists of two complex ions [I¹]⁺ and [I²]^2– (molar ratio 2 : 1). The Na⁺ cation of the host–guest cation I¹ is coordinated by all eight heteroatoms (6O + 2N) of the cryptand ligand. The coordination polyhedron of this Na⁺ cation is a distorted cube. The atoms of two groups (CH₂–CH₂ and CH₂–O–CH₂–CH₂) in the cryptand ligand are disordered over two positions. The independent cation Na⁺ of the centrosymmetric binuclear complex anion I² is coordinated by one bifurcated O atom of the disordered water molecule and by three N atoms of the SCN^– ligands (including two bridging ligands). The coordination polyhedron of this Na⁺ caiotn is a distorted tetrahedron. The complex ions in the crystal structure of I are united by hydrogen bonds.     

Novel Linear Tetrapyrroles: Hydrogen Bonding in Diacetylenic Bilirubins

Summary. Bilirubin congeners with dipyrrinones conjoined to a diaceteylene unit (–CC–CC–) rather than to –CH₂– were synthesized and examined spectroscopically. This new class of rubrified linear tetrapyrroles cannot easily fold or bend in the middle, but the dipyrrinones can rotate independently about the diacetylene unit. Thus, unlike bilirubin, which is bent in the middle and has a ridge-tile shape, the diacetylene unit orients the attached dipyrrinones along a linear path, and intramolecular hydrogen bonding between the dipyrrinones and opposing carboxylic acids preserves a twisted linear molecular shape when the usual propionic acids are replaced by hexanoic. In a bis-hexanoic acid rubin, the extended planes of the dipyrrinones intersect along the –(CC)₂– axis at an angle of 102° for the conformation stabilized by intramolecular hydrogen bonding. With propionic acid chains, however, neither CO₂H can engage an opposing dipyrrinone in intramolecular hydrogen bonding, and the energy-minimum conformation of this linear pigment, shows nearly co-planar dipyrrinones, with an intersection of an angle of 180° of the extended planes of the dipyrrinones. Spectroscopic evidence for such linearized and twisted (bis-hexanoic) and planar (bis-propionic) structures comes from the pigments NMR spectral data and their exciton UV-Vis and induced circular dichroism spectra.     

Crystal structure of the 1 : 4 complex between 18-crown-6 and a polyfunctional guest: 2-hydroxymethyl-4-(1,1,3,3-tetramethylbutyl)phenol

Single crystal X-ray analysis of the 1 : 4 complex between 18-crown-6 and 2-hydroxymethyl-4-(1,1,3,3-tetramethylbutyl)phenol is reported. Crystals of the complex are triclinic witha = 11.929 (2),b = 18.655(2),c = 8.313(1)Å, = 93.14(1), = 94.02(1), = 100.89(1)^o, andD _c = 1.111 g cm^–3 forZ = 1. TheR index is 0.057 for 5935 reflections measured at 293 K. The complex lies on a center of symmetry, the macroring has the Ci symmetry (g ⁺ g ⁺ aag ^– aag ^– ag ^– g ^– aag ⁺ aag ⁺ a). The CH₂-OH group at theortho position to the phenolic OH lies near the benzene ring plane; this conformation differs from the one found for uncomplexed phenol-alcohol molecules. The packing is characterized by layers of hydrogen bonded entities parallel toac; alongb the layers are stabilized by van der Waals interactions.     

Magnetische Untersuchungen an Komplexen von La(III), Pr(III) und Nd(III) mitSchiffschen Basen

Specific magnetic susceptibilities (_s) of several newly synthesized chelates of some of the lanthanons [La(III), Pr(III) and Nd(III)] are reported. These derivatives are of the general type,Ln(O-i-C₃H₇)_3–n (C₆H₅CHNRO) _n [where,Ln=La(III), Pr(III) or Nd(III);n=1 or 2 and R=CH₂CH₂, CH₂CHCH₃ or C₆H₄] and have been prepared by the reaction of the alkoxides of the lanthanons withSchiff bases such as benzylidene-2-hydroxyethylamine (C₆H₅CHNCH₂CH₂OH), benzylidene-2-hydroxy-n-propylamine (C₆H₅CHNCH₂CHOHCH₃) and benzylidene-o-aminophenol (C₆H₅CHNC₆H₄OH) in different molar relations in dry benzene.The resulting crystalline derivatives are non-volatile, light to deep yellow or blackish in colour. These tend to polymerize on keeping as shown by their insoluble nature and higher melting points, the polymerisation possibly occurring by the intermolecular coordination through oxygen atoms as reported earlier¹.UsingGouy method², the bis-isopropoxy mono-Schiff base and mono-isopropoxy bis-Schiff base complexes of La(III) have been shown to be diamagnetic, with _s values being in the range of –0.32 to –0.45×10^–6 and –0.39 to –0.55×10^–6 c.g.s. units at 305 K respectively.In the remaining derivatives, Pr(O-i-C₃H₇)_3–n (C₆H₅CH NRO) _n and Nd(O-i-C₃H₇)_3–n (C₆H₅CHNRO) _n (where,n=1 or 2 and R=CH₂CH₂, CH₂CHCH₃ or C₆H₄) the magnetic moment values range between 3.25 to 3.32 and 3.30 to 3.33 _B respectively indicating their paramagnetic nature.     

f-Element/crown ether complexes, 11. Preparation and structural characterization of [UO2(OH2)5] [ClO4]2·3(15-crown-5)·CH3CN and [UO2(OH2)5] [ClO4]2·2(18-crown-6)·2 CH3CN·H2O

The reaction of UO₂(ClO₄)·nH₂O with 15-crown-5 and 18-crown-6 in acetonitrile yielded the title complexes. [UO₂(OH₂)₅] [ClO₄]₂·3(15-crown-5)·CH₃CN crystallizes in the triclinic space groupPT with (at–150°C)a=8.288(6),b=12.874(7),c=24.678(7) Å, =82.62(4), =76.06(5), =81.06(5)°, andD _calc=1.67 g cm^–3 forZ=2 formula units. Least-squares refinement using 6248 independent observed reflections [F _o5(F _o)] led toR=0.111. [UO₂(OH₂)₅] [ClO₄]₂·2(18-crown-6)·2CH₃CN·H₂O is orthorhombicP2₁2₁2₁ with (at–150 °C)a=12.280(2),b=17.311(7),c=22.056(3) Å,D _calc=1.68 g cm^–3,Z=4, andR=0.032 (3777 observed reflections). In each complex the crown ether molecules are hydrogen bonded to the water molecules of the pentagonal bipyramidal [UO₂(OH₂)₅]²⁺ ions, each crown ether having exclusive use of two hydrogen atoms from one water molecule and one hydrogen from another water molecule. In the 15-crown-5 complex the remaining hydrogen bonding interaction is between one of the water molecules and one of the perchlorate anions. The solvent molecule has a close contact between the methyl group and a perchlorate anion suggesting a weak interaction. There are a total of three U-OH...OClO₃ hydrogen bonds to the two perchlorate anions in [UO₂(OH₂)₅] [ClO₄]₂·(18-crown-6)·2CH₃CN ·H₂O. The remaining coordinated water hydrogen bond is to the uncoordinated 2H₂O molecule, which in turn is hydrogen bonded to a perchlorate oxygen atom and an acetonitrile nitrogen atom. One solvent methyl group interacts with an anion, the other with one of the 18-crown-6 molecules. Unlike the 15-crown-5 structure, the hydrogen bonding in this complex results in a polymeric network with formula units joined by hydrogen bonds from one of the solvent molecules and the uncoordinated water molecule. Supplementary data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82051 (37 pages).For Part 10, see reference [1].     

Molecular,thermodynamic, and kinetic parameters of iodomethanes and iodomethyl radicals: <Emphasis Type="Italic">ab initio</Emphasis> calculations

The wave functions and enthalpies of formation of the ground states of iodomethanes CH_{4– x} I_x and iodomethyl radicals CH_3–x I_x. (x = 1–3) were calculated ab initio with regard to electron correlation. The geometries of the molecules of these compounds were determined, as well as the normal mode frequencies and other parameters, which were used for calculating the thermodynamic functions in the 0–1500 K range. These functions were used for calculating the constants of the CH_4–x I_x CH_4–x I _x–1 + I and CH_4–x I_x + I CH_{4– x} I _x–1 + I₂ equilibria, which, in turn, were used for calculating the corresponding rate constants in the high concentration limit.Translated from Zhurnal Obshchei Khimii, Vol. 74, No. 11, 2004, pp. 1812–1822.Original Russian Text Copyright © 2004 by Dymov, Skorobogatov, Tschuikow-Roux.This revised version was published online in April 2005 with a corrected cover date.     

Synthesis and Crystal Structures of [(Nicotinic Acid)2H]+I-, [(2-Amino-6-methylpyridine)H]+(NO3)-, and the 1:1 Complex Between 1-Isoquinoline Carboxylic Acid (Zwitter Ion) and L-Ascorbic Acid Assembled via Hydrogen Bonds

Summary. Three new complexes, namely [(nicotinic acid)₂H]⁺I^–, [(2-amino-6-methylpyridine)H]⁺ (NO₃)^–, and the 1:1 complex between 1-isoquinoline carboxylic acid (zwitter ion form) and L-ascorbic acid were synthesized. The IR spectra revealed different types of hydrogen bonds in these compounds. The X-ray structure determination has shown the first compound to consist of a packing of [(nicotinic acid)₂H]⁺ cations and I^– anions. In the dimeric cation the two nicotinic acid molecules (zwitter ions) are connected through hydrogen bonds (O–HO). Each dimer is further engaged in other hydrogen bonds with adjacent dimers giving 2D layers. The I^– ion is located at the inversion center. In the second compound the cation and anion are connected via hydrogen bonds formed between oxygen atoms of the NO₃ ^– anion and NH and NH₂ of the cation generating a layer structure. All atoms are coplanar on mirror planes. In the 1:1 complex the two molecules are connected through hydrogen bonds formed between the two oxygen atoms of the carboxylate group of 1-isoquinoline carboxylic acid (zwitter ion) and the oxygen atoms of the two adjacent hydrogen groups of the L-ascorbic acid molecule. These complex molecules are engaged in other hydrogen bonds with each other forming a 2D system normal to the long b-axis of the unit cell.     

Dansyl-Modified γ-Cyclodextrin as a fluorescent sensor for molecular recognition

The crystal structure of thiamine iodide sesquihydrate has been determined by X-ray diffraction methods as a host-guest model for coenzyme-substrate interactions. The asymmetric unit contains two chemical units. Both the thiamine molecules A and B, which are crystallographically independent, assume the usualF conformation and have a disordered hydroxyethyl side chain. An iodide anion (or a water molecule) bridges the pyrimidine and thiazolium rings of molecule A (or B) by forming a hydrogen bond with the amino group and an electrostatic contact with the thiazolium ring to stabilize the molecular conformation. In the crystal the thiamine molecules self-associate to form a pipe-like polymeric structure, in which four thiamine hosts surround an iodide guest and hold it through C(2)-H...I hydrogen bonds and thiazolium...I electrostatic interactions. Crystal data: C₁₂H₁₇N₄OS⁺·I^– · 1.5 H₂O, monoclinic,P2₁/c, a=12.585(2), b=25.303(5), c=12.030(2) Å, =115.15(1)°,V=3468(1) ų,Z=8,D _c=1.606 g cm^–3,R=0.045 for 3328 observed reflections. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP. 82156 (13 pages).     

Neutral solvent/crown ether interactions 3. Reorientation of the hydrogen bonds in the low temperature (−150°C) structure of 18-crown-6·2(CH3NO2)

The title complex was crystallized from a saturated solution of 18-crown-6 in nitromethane at 5°C and cooled to –150°C prior to X-ray diffraction data collection. At –150° C 18-crown-6·2(CH₃NO₂) is monoclinic,P2₁/_n witha=9.290(2),b=7.864(6),c=13.627(8) Å, =1000.84(4)° andD _calc=1.31 g cm^–3 for Z=2. Leastsquares refinement using 1521 independent observed reflections [F _o5(F _o)] led to a final conventionalR value of 0.041. The complex at –150°C is isostructural with its room temperature structure with the exception of the orientation of the methyl hydrogen atoms and their crown ether oxygen interactions. The methyl group hydrogen atoms were fully refined isotropically. The crown ether resides around a center of inversion and hasD _3d symmetry. There is one methyl hydrogen...crown interaction at 2.35(3) Å, one apparently bifurcated hydrogen bond utilizing a second methyl hydrogen atom (2.55(3), 2.65(3) Å) and the third hydrogen atom is actually directed away from the crown ring (closest H...O contact=2.67(3) Å). Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82048 (5 pages).For part 2, see reference [24].     

Synthesis and Crystal Structures of [(Nicotinic Acid)2H]+I-, [(2-Amino-6-methylpyridine)H]+(NO3)-, and the 1:1 Complex Between 1-Isoquinoline Carboxylic Acid (Zwitter Ion) and L-Ascorbic Acid Assembled via Hydrogen Bonds

Three new complexes, namely [(nicotinic acid)₂H]⁺I^–, [(2-amino-6-methylpyridine)H]⁺ (NO₃)^–, and the 1:1 complex between 1-isoquinoline carboxylic acid (zwitter ion form) and L-ascorbic acid were synthesized. The IR spectra revealed different types of hydrogen bonds in these compounds. The X-ray structure determination has shown the first compound to consist of a packing of [(nicotinic acid)₂H]⁺ cations and I^– anions. In the dimeric cation the two nicotinic acid molecules (zwitter ions) are connected through hydrogen bonds (O–HO). Each dimer is further engaged in other hydrogen bonds with adjacent dimers giving 2D layers. The I^– ion is located at the inversion center. In the second compound the cation and anion are connected via hydrogen bonds formed between oxygen atoms of the NO₃ ^– anion and NH and NH₂ of the cation generating a layer structure. All atoms are coplanar on mirror planes. In the 1:1 complex the two molecules are connected through hydrogen bonds formed between the two oxygen atoms of the carboxylate group of 1-isoquinoline carboxylic acid (zwitter ion) and the oxygen atoms of the two adjacent hydrogen groups of the L-ascorbic acid molecule. These complex molecules are engaged in other hydrogen bonds with each other forming a 2D system normal to the long b-axis of the unit cell.     

Comparison of Ab Initio MP2/6-311+G(d,p) Predicted Carbon–Hydrogen Bond Distances with Experimentally Determined r 0 (C–H) Distances

Fifty different carbon–hydrogen distances have been predicted from ab initio MP2/6-311+G(d,p) calculations, which range from a short value of 1.0611 Å for HCNO to a long value of 1.1044 Å for H₂CO. The values include those predicted for a series of methyl (CH₃) moieties where the two different C–H distances vary by as much as 0.005 Å. These predicted values are compared to r ₀(C–H) distances obtained from the isolated carbon–hydrogen stretching frequencies, as well as to r ₀ or r _s parameters obtained from microwave data. Except for the very short C–H bonds, the ab initio values from the MP2/6–311+G(d,p) calculations can be used for the carbon–hydrogen distances with error limits of ± 0.003 Å. By utilizing the spectral data from CD₃CClO, it is shown that combination bands in the C–H stretching region could cause problems in the identification of the isolated C–H stretching frequency from the CD₂HCClO isotopomer. The value of the ab initio predicted C–H distances for checking unusually long or short r _s (C–H) or r ₀ values is demonstrated.     

Gas Electron Diffraction and Quantum-Mechanical Study of Dimethyloxalate

The geometrical structure and conformation of dimethyloxalate, CH₃OC(O)–C(O)OCH₃, have been studied by gas electron diffraction (GED) and quantum-chemical calculations (MP2 and B3LYP methods with 6-31G* and cc-pVTZ basis sets). The GED analysis with a dynamic model (T = 323 K) results in a mixture of two planar conformers, anti (C_2h symmetry) and syn (C_2v symmetry) orientation of the two C=O bonds. The energy difference between these conformers is 0.02(0.18) kcal/mol and barrier to internal rotation around the C–C bond is 0.44(0.41) kcal/mol. The CH₃ groups occupy synperiplanar positions with respect to the C=O bonds. The following main geometrical parameters for the anti conformer (Å and degrees) have been derived: r_g(C–C) = 1.532(3), r_g(C=O) = 1.203(2), r_g(C_sp3–O) = 1.436(3), r_g(C_sp2–O) = 1.333(3), (C_sp2–C_sp2–O) = 111.9(1.9), (C_sp2–O–C_sp3) = 116.3(1.6), (O–C= O) = 127.0(1.8).This paper is devoted to the 75th anniversary of gas electron diffraction method.     

New water-soluble and film-forming aminocellulose tosylates as enzyme support matrices with Cu<Superscript>2+</Superscript>-chelating properties

Within the framework of our studies on enzyme-compatible support matrix structures, we succeeded in making further derivatives of the new aminocellulose type P–CH₂–NH–(X)–NH₂ (P = cellulose); (X) = –(CH₂)₂– (EDA), –(CH₂)₂–NH–(CH₂)₂– (DETA), –(CH₂)₃–NH–(CH₂)₃– (DPTA), –(CH₂)₂–NH–(CH₂)₂–NH–(CH₂)₂– (TETA) accessible by nucleophilic substitution reaction with ethylenediamine (EDA) and selected oligoamines starting from 6(2)-O-tosylcellulose tosylate (DS_tosylate = 0.8). The ¹³C-NMR data show that the EDA and oligoamine residues are at C6 of the anhydroglucose unit (AGU) and that OH and tosylate are also (partially) present at C6. OH and partially tosylate are at C2/C3. All the synthesized aminocellulose tosylates were soluble in water and formed transparent films from their solutions. The aminocellulose tosylate solutions and the films prepared from them formed blue-coloured chelate complexes with Cu²⁺ ions, whose absorption maxima at wavelengths in the VIS region were located similarly to those of the Cu²⁺ chelate complexes with EDA and with the oligoamines. AFM investigations have shown that the aminocellulose films, depending on structural and environment-induced factors influencing e.g. SiO₂ polymer films, exhibit flat topographies (<1 nm), and on protonated NH₂ polymer films, such as aminopropyl-functionalized polysiloxane films, nanostructured topographies of derivative-dependent shape and nanostructure size as film supports in the form of nanotubes. The aminocellulose films could be covalently coupled with glucose oxidase enzyme by various known and novel bifunctional reactions via NH₂-reactive compounds. In this connection, it was confirmed again that the immobilized enzyme parameters, such as enzyme activity/area and K_M value, can be changed by the interplay of aminocellulose film, coupling structure and enzyme protein in the sense of an application-relevant optimization.     

Low-dimensional compounds containing cyano groups. IX. Preparation,structure and properties of the [Cu(bpy)<Subscript>2</Subscript>(dca)]CF<Subscript>3</Subscript>SO<Subscript>3</Subscript> complex

The ionic [Cu(C₂N₃)(C₁₀H₈N₂)₂](CF₃SO₃) compound, which contains two crystallographic independent formula units, is formed by [Cu(bpy)₂(dca)]⁺ complex cations (bpy=2,2-bipyridine, dca=dicyanamide) and uncoordinated CF₃SO ₃ ^– anions, which are in a staggered conformation. The shapes of coordination polyhedra around both copper atoms, which are fivefold coordinated by two bpy molecules and one dca ligand monodentately coordinated through a cyano N atom in the equatorial plane at a distance of 2.001(3)Å for the first and 1.988(4)Å for the second polyhedron, are distorted trigonal bipyramids. Besides the ionic forces the structure is stabilized by weak C–H...O hydrogen bonds and possible – interactions between pyridine rings of bpy molecules. Along with the structural-spectral correlation we discuss the thermal decomposition of the title complex.     

Iodination of B12H11OC(O)CH2–3, B12H11OH2–, and B12H11SCN2–

Reactions of iodination of monosubstituted derivatives of B₁₂H₁₁X^2–anion (X = OC(O)CH₃, OH, SCN) were studied. The reactions were shown to proceed smoothly to give B₁₂H₁₀(OC(O)CH₃)I^2–((carboxy)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), B₁₂H₁₀(OH)I^2–((hydroxo)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion), and B₁₂H₁₀(SCN)I^2–((thiocyanato)(iodo)[decahydro[I _h1551-²⁰-closo]dodecaborate(2–)] anion) in high yields, irrespective of the solvent used (benzene, H₂O–ROH, where R = C₂H₅, CH₂CH₂CH₃).¹     

Crystal structure of an uncomplexed 25-crown-7 comprising one 2,6-pyridino and two 1,4-benzo condensations

Single crystal X-ray analysis of the uncomplexed crown macroring 1 is reported. Crystals are triclinic, , witha=10.809(1),b=10.945(1),c=10.256(1) Å, =107.85(1), =104.15(1), =87.27(1)°,D _c=1.318 g cm^–3,Z=2. Three torsion angles in the macrocycle take upgauche conformations in contrast to the usualanti conformation. The crystal structure is stabilized by intramolecular van der Waals forces and weak C–H...O and C–H...N hydrogen bond attractions. Stacking of pyridine rings is a noticeable packing feature in the crystal lattice. Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82168 (6 pages).Macroring Uncharged Molecule Complexation. Part 20. For Part 19 of this series see Ref. [1].     

Nuclear magnetic resonance and high-performance liquid chromatographic evaluation of polymer-based stationary phases immobilized on silica

Three poly(ethylene-co-acrylic) acid copolymers (–CH₂CH₂–)_x[CH₂CH(CO₂H)–]_y with different chain lengths and mass fractions of acrylic acid were covalently immobilized as stationary phases on silica via two variants of spacer molecules (3-aminopropyltriethoxysilane and 3-glycidoxypropyltrimethoxysilane). Different mobilities of the alkyl chains in the stationary phases were observed using ¹³C solid-state NMR spectroscopy. The stationary phases with more rigid trans-ordered alkyl chains had better selectivity for geometric -carotene and xanthophyll isomers (provitamin A derivatives). Also, all the separations of the analytes were affected by polar interactions with the chromatographic sorbent. This was further proved by separating more polar cis/trans retinoic acid isomers (vitamin A derivatives). ¹³C high-resolution/magic-angle spinning (HR/MAS) NMR measurements of the chromatographic sorbents suspended in the mobile phase confirmed a dependence of molecular shape recognition ability on alkyl chain conformation.