Hydrogen-bonded encapsulation complexes in protic solvents

We describe here the behavior of the hydrogen-bonded capsule 1.1 and its complexes in protic solvents. The kinetics and thermodynamics of the encapsulation process were determined through conventional (1)H NMR methods. The enthalpies and entropies of encapsulation are both positive, indicating a process that liberates solvent molecules. The rates of dissociation-association of the capsule were comparable to the rates for the in-out exchange of large guests, which suggests that guest exchange occurs by complete dissociation of the capsule in protic solvents. The stability of the hydrogen-bonded capsule 1.1 toward protic solvents depends strongly on the guests, with the best guest being dimethylstilbene 8. The results establish guidelines for the properties of capsules that could be accessed in water.     

Hydrogen-bonded assemblies of trinuclear metal string complexes

Three kinds of trinuclear metal string complexes, [Ni₃(dpa)₄(L¹)₂]?·?H₂O?·?C₂H₅OH (L¹?=?(E)-3-(2-hydroxyl-phenyl)-acrylic acid) (1), [Ni₃(dpa)₄(L²)₂]?·?2C₂H₅OC₂H₅ (L²?=?(E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2) and [Ni₃(dpa)₄(L³)₂]?·?3CH₂Cl₂?·?1.5CH₃OH (L³?=?(E)-3-(4-hydroxyl-phenyl)-acrylic acid) (3). (dpa^??=?bis(2-pyridyl)amido), have been synthesized. The structures of 1 and 2 have been analyzed by the X-ray single-crystal diffraction showing hydrogen-bonded networks.     

Hydrogen-bonded supramolecular complexes formed between isophthalic acid and pyridine-based derivatives

Two types of supramolecular liquid crystals were prepared through the formation of double hydrogen-bonded complexes between isophthalic acid (A) and two different groups of pyridine-based derivatives ( I n and I _a-e ). The first group of the base, I n (molecular formula 4-C_nH_2n+1OC₆H₄COOC₆H₄-N=N-C₅H₄N) homologues differ from each other by the number of carbon atoms (n) in the alkoxy chain, which varies between 8, 10, 12 and 14 carbons. The second group of the pyridine-based derivatives, I _a-e (molecular formula 4-X-C₆H₄COOC₆H₄-N=N-C₅H₄N) analogues differ from each other by the terminal polar substituent, X, that changes between OCH₃, CH₃, H, NO₂ and Br groups. In this manner two different groups of complexes are formed, one of them is A : 2I n, (Group A ), and the other is A : 2I _a-e , (Group B ). All complexes were investigated for their mesophase behaviour by differential scanning calorimetry and polarised light microscopy. The formation of 1:2 hydrogen-bonded complexes was confirmed by FTIR spectroscopy and binary phase diagrams. Most complexes A and B show nematic and/or SmA phases. X-ray diffraction of the SmA phase of a representative complex of type A indicates a layer distance corresponding to only half of the length of the H-bonded complexes which is interpreted by a phase structure where these complexes adopt a U-shape which intercalate and form non-polar SmA phases.     

Hydrogen-bonded complexes of 1-chloro-2-methylpropan-2-ol with ketones

The interaction of 1-choro-2-methylpropan-2-ol (CMP) with acetone and methyl ethyl ketone was examined in dilute carbon tetrachloride solution. The strengths of the hydrogen-bonded complexes were compared with those of the corresponding complexes of trimethyl carbinol and 1,1,1-trichloro-2-methyl-propan-2-ol with ketones. The aim was to explain the inductive effect of the chlorine atom on the strength of carbinol-ketone hydrogen-bonded complexes. The monomer IR band of CPM appears in solution as a composite of five sub-bands, signifying that many conformers are present; this was confimed by quantum chemical calculations. Chlorine substitution increases the strength of the hydrogen bond.     

Hydrogen-bonded complexes of serotonin with methanol and ethanol: a DFT study

Density functional theoretical studies on hydrogen-bonded complexes of serotonin with methanol/ethanol have been carried out in a systematic way. The conformational analysis led to ten stable conformers that can be either gauche or anti depending on the dihedral angle values taken by ethylamine side chain and the 5-hydroxyl group. Serotonin-molecules strongly bind with ethanol than methanol. Ethylamine side chain is the most reactive site in both methanol/ethanol complexes and it is responsible for the stability order. The topological parameters, electron density, and Laplacian of electron density show excellent correlation with the hydrogen bond length. Natural bond orbital analysis confirms C–H···O hydrogen bond formed between the serotonin–alcohol complexes to be red shift in nature except for Gph(out)anti complex both with methanol and ethanol to be blue shifted. The energy decomposition analysis reveals that strong interactions between serotonin and ethanol/methanol are due to the attractive contributions from the electrostatic component.     

Supramolecular ferroelectric liquid crystals. Hydrogen-bonded complexes between benzoic acids and chiral stilbazoles

Supramolecular ferroelectric liquid crystalline complexes have been obtained from 4-alkoxybenzoic acids and optically active trans-4-substituted-4'-stilbazoles. Chiral smectic C phases are induced by the formation of supramolecular mesogenic structure through the selective intermolecular hydrogen bond between the achiral benzoic acids and the chiral non-mesogenic stilbazoles.     

Hydrogen-bonded dihydrotetraazapentacenes

Three new members of N-heteropentacenes explored herein have adjacent pyrazine and dihydropyrazine rings at one end of the pentacene backbone. Interesting findings from this study include self-complementary N-H···N H-bonds in the solid state, solvent-dependent UV-vis absorption caused by H-bonding, and new p-type organic semiconductors with field effect mobility up to 0.7 cm(2) V(-1) s(-1).     

Hydrogen-bonded complexes involving HF and HCl: the effects of electron correlation and anharmonicity

Calculations on the hydrogen-bonded complexes HCNHF, H₂OHF, ClCNHCl and (CH₃)₂OHCl are reported. SCF harmonic values for the HF and HCl frequency shifts are in considerable disagreement with experiment, by as much as 100 cm^–1. Calculations at the MP2 (harmonic) level yield improved agreement with experiment, reducing discrepancies to the order of 10 cm^–1. We have also calculated all the cubic and quartic force constants for HCNHF at the SCF level, so that the anharmonic constants, x _rs can be evaluated. Although x ₁₁ (v ₁=H-F stretch) is large and negative, it is more than compensated by a positive x ₁₆ (v ₆=NH-F bend), so that the anharmonic correction to v ₁ is small and positive. The validity of these anharmonistudies is examined.     

Hydrogen-bonded mononuclear nickel(II) benzoate complexes: synthesis and structural studies

[Tp^Ph,MeNi(Cl)Pz^Ph,MeH] (1) has been synthesized by the reaction of hydrotris(3-phenyl-5-methyl-pyrazol-1-yl) borate [Tp^Ph,Me], NiCl₂ · 6H₂O and 3-phenyl-5-methyl-pyrazole [Pz^Ph,MeH]. The reaction of 1 with variously substituted sodium p–X–benzoates resulted in the formation of complexes of the type [Tp^Ph,MeNi(p–X–OBz)Pz^Ph,MeH] (X = H for 2, F for 3, Cl for 4, NO₂ for 5, Me for 6, OMe for 7, OH for 8, CHO for 9 and CN for 10). Single crystal X-ray studies suggest that all these complexes have a five-coordinate metal center and the benzoate groups are monodentate in a square pyramidal geometry. The X-ray studies also reveal that the uncoordinated oxygen atom of the benzoate forms intramolecular hydrogen-bonds with the NH group of the coordinated pyrazole. The substituents present on the benzoate ring are involved in different types of intermolecular interactions and the complexes exhibit different crystal packing. Complexes 2–10 were tested for superoxide dismutase activity. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Hydrogen-bonded polycatenar mesogens

The tricatenar, hydrogen-bonded complexes formed between alkoxystilbazoles and an imine were found to be mesomorphic. Subsequently, related tetracatenar complexes were also investigated and found to be non-mesomorphic. We report the transition temperatures of these complexes and discuss structural modifications.     

Hydrogen-bonded complexes of nitrous and nitric acids with ethene Ab initio and DFT studies

The complexes formed by ethene with nitric and nitrous (trans and cis) acids have been investigated by ab initio (SCF and MP2) and B3LYP calculations with 6-311++G(d,p) basis set. Full geometry optimisation has been performed for the complexes studied. The most stable structures of the complexes are established. Bearing in mind the corrected values of the dissociation energy the studied hydrogen-bonded complexes can be ordered as follows: C(2)H(4)...HONO(2)>C(2)H(4)...HONO-trans>C(2)H(4)...HONO-cis. In the complexes the acids act as proton donors forming the pi-type of hydrogen bond with ethene. The predicted changes in the vibrational characteristics (vibrational frequencies and infrared intensities) arising from the hydrogen bonding are in good agreement with the experimentally measured. The predicted frequency shift of the stretching OH vibration in the nitric acid is largest (-210 cm(-1)), followed by the shifts in the trans-HONO (-141 cm(-1)) and cis-HONO (-109 cm(-1)). The calculations predict an increase of the IR intensity of the stretching O-H vibration in the complexes from 6 to 10 times.     

Hydrogen-bonded polycatenar mesogens

The tricatenar, hydrogen-bonded complexes formed between alkoxystilbazoles and an imine were found to be mesomorphic. Subsequently, related tetracatenar complexes were also investigated and found to be non-mesomorphic. We report the transition temperatures of these complexes and discuss structural modifications.     

Hydrogen-bonded oxadiazole mesogens

Hydrogen-bonded analogues of recently reported biaxial nematic oxadiazoles have been prepared. These are obtained by having oxadiazole derivatized with either one or two pyridines, leading either to symmetric or unsymmetric materials complexed using several different benzoic acids. The new materials were studied by optical microscopy and DSC and were found to show N and SmA phases, i.e. mesomorphism characteristic of a calamitic rather than a bent-core mesogen. This mesomorphism is discussed in terms of the flexibility of the complexes and the bend angle at the centre of the complexes.     

Hydrogen-bonded charge-transfer complexes of TTF containing a uracil moiety: crystal structures and electronic properties of the hydrogen cyananilate and TCNQ complexes

[structure: see text] A novel TTF-based donor with a uracil moiety, TTF-(1-n-butyluracil-5-yl) (TnbU), was synthesized. Crystal structures of both TnbU and the charge-transfer complex of TnbU-hydrogen cyananilate possess complementary double hydrogen bonds through uracil moieties and pi-stacking dimer structures between TTF skeletons. Furthermore, the TnbU-TCNQ charge-transfer complex shows a high electrical conductivity underlying the partial charge-transfer accompanied by a hydrogen-bonding interaction, which was substantiated in terms of the measurements of the IR, electronic spectra, and conductivity.     

Hydrogen-bonded supramolecular polymer networks

The strong dimerizing, quadruple hydrogen-bonding ureido-pyrimidone unit is used to obtain reversible polymer networks. A new synthetic route from commercially available starting materials is described. The hydrogen-bonding ureido-pyrimidone network is prepared using 3(4)-isocyanatomethyl-1-methylcyclohexyl-isocyanate (IMCI) in the regioselective coupling reaction of multi-hydroxy functionalized polymers with isocytosines. ¹H- and ¹³C-NMR, IR, MS, and ES-MS analysis, performed on a model reaction using butanol, demonstrated the formation of the hydrogen-bonding ureido-pyrimidone unit in a yield of more than 95%. The well-defined, strong hydrogen-bonding ureido-pyrimidone network is compared with a traditional covalently bonded polymer network, a multi-directional hydrogen-bonded polymer network based on urea units, and a reference compound. The advantage of the reversible, hydrogen-bonded polymer networks is the formation of the thermodynamically most favorable products, which show a higher “virtual” molecular weight and shear modulus, compared to the irreversible, covalently bonded polymer network. The properties of the ureido-pyrimidone network are unique; the well-defined and strong dimerization of the ureido-pyrimidone unit does not require any additional stabilization such as crystallization or other kinds of phase separation, and displays a well-defined viscoelastic transition. The ureido-pyrimidone network represents the first example of a truly reversible polymer network showing these features. Furthermore, the ureido-pyrimidone dimerization is strong enough to construct supramolecular materials possessing acceptable mechanical properties. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3657–3670, 1999     

Reaction of lumichrome or 2-thiolumichrome with alkylamines

The reaction of lumichrome ( 2 ) with alkyl (or allyl)amines such as n-butylamine, n-hexylamine and allylamine gave 2,3-disubstituted 6,7-dimethylquinoxalines 4a-d, 5a-d, 6a-d, 7a-d and 8a-d . Similar reaction of 2-thiolumichrome ( 3 ) with alkyl (or allyl)amines gave 2,3-disubstituted 6,7-dimethylquinoxalines 6a-c, 9a-c and 10a-c , 2-alkyl (or allyl)amino-6,7-dimethyl-3,4-dihydrobenzo[g]pteridine-4-ones 11a-c and 2,4-dialkyl (or allyl)amino-6,7-dimethylbenzo[g]pteridines 12a-c .     

Hydrogen-bonded networks of 2,2′-substituted 4,4′-biimidazoles: New ligands for the assembled metal complexes

4,4′-Biimidazole derivatives having alkyl-substituents at 2- and 2′-positions were synthesized as new component molecules of supramolecular assemblies based on hydrogen-bonding interaction. The crystal structure analyses of methyl and ethyl derivatives revealed intriguing three-dimensional structures constructed by hydrogen-bonded networks. Furthermore, the methyl derivative formed a six-membered cyclic motif of hydrogen-bonded network to build up a channel structure. The ethyl derivative gave the two polymorphous, anhydrate and dihydrate, depending on conditions of the crystallization. The anhydrate constructed three-dimensional hydrogen-bonded networks by direct N–H⋯N hydrogen-bondings. In the crystal structure of the dihydrate of ethyl derivative, three-dimensional hydrogen-bonding interaction through water molecules formed a channel structure.