A study of the interaction energy between a glycoluril molecular clip and dihydroxybenzenes or diaminobenzenes: a justification for easy separation by affinity chromatography

Theoretical calculations were performed to determine the interaction energy between a glycoluril (GL) molecular clip and hydroxybenzenes (HBs) and aminobenzenes (ABs). The theoretical calculations on the GL and its interactions were carried out using the hybrid functional closed-shell RB3LYP and the 6-31G* basis set, employing gaussian 03. The stability in energy of the guest inside the GL, ΔE_T(1), was in the following order: m-DHB-GL > o-DHB-GL > m-THB-GL > m-DAB-GL > o-THB-GL. The geometric parameters, in particular the bond lengths are discussed for the host molecule GL and guest molecules DHB and DAB and their parameters are compared with the host-guest molecules DHB-GL and DAB-GL, respectively.     

甘脲用作气相色谱固定相的色谱性能研究

甘脲具有双环双脲结构,既是质子给体,又是质子受体,能与溶质产生氢键作用等多种作用力。本文制备了以甘脲作为固定相的填充柱,并对它的色谱性能进行了研究。结果表明:甘脲固定相热稳定性高、柱性能稳定,是一种良好的气相色谱固定相。该固定相对烷烃、卤代烃、芳烃、醇、酯、酮、酸、胺等类物质具有良好的分离能力,尤其是对位置异构体(如二取代苯位置异构体)有较好的分离选择性。本文还初步探讨了甘脲固定相的分离机理。     

Synthesis of glycoluril catalyzed by potassium hydroxide under ultrasound irradiation

Synthesis of the glycolurils catalyzed by potassium hydroxide was carried out in 17–75% yield at 40 °C in EtOH under ultrasound irradiation. Compared to the method using stirring, the main advantage of the present procedure is milder conditions and shorter reaction time.     

Twisted amides: X-ray crystallographic and theoretical study of two acylated glycolurils with aromatic substituents

X-ray crystallography and theoretical analysis were applied to explore the molecular basis for the efficient and selective Claisen-like condensations of diacylglycolurils. The crystal structures of 1-acetyl-6-benzoyl-3,4,7,8-tetramethylglycoluril (4b), and of 1-(3′-oxo-3′-phenylpropionyl)-3,4,7,8-tetramethylglycoluril (5b), the product of base-promoted intramolecular condensation of 4b, were obtained by X-ray diffraction. The acetyl (Ac) group in 4b is essentially coplanar with the attached tetrahydroimidazolone ring of the glycoluril core (τ=7°), while the benzoyl (Bz) group is twisted by τ=45° relative to a plane through the ring to which it is bonded. Product 5b contains a flat amide (τ=7°). Ab initio energy optimizations of the experimental structures for 4b and 5b give optimized geometries which are not dramatically altered, suggesting that crystal packing effects are small. An atoms-in-molecules study of the delocalization of the Fermi hole reveals that electrons in the Bz C=O group of 4b are delocalized into the phenyl ring as well as into the urea moiety of the glycoluril core. This effect stabilizes the Bz over the Ac carbonyl group, and accounts for selective twisting of the Bz group. The Laplacian of the electron density reveals a non-bonded valence shell charge concentration at O of the Ac group, corresponding to a lone-pair region, aligned with a charge depletion in the valence shell of the Bz C=O carbon [(C15–O16C18)=113°]. The angle of approach [(O16C18=O19)] is 100°, equal to the angle for ideal nucleophilic attack on a carbonyl group. Oxygen atom O16 is thus poised to attack C18; only the O16C18 distance (3.248 Å) seems to prevent reaction. These results suggest that the same distance restraint may prevent O-acylation in the enolate intermediate 6b derived from4b. By contrast, the transition state for C-acylation, leading from 6b towards product 5b requires a different geometry, which may explain the observed selectivity for C-acylation in this enolate. The results show that, as 4b is converted to 5b, amide torsional strain is relieved, which may account for the high reactivity of 4b and the efficiency and irreversibility of this condensation process. This study provides a starting point for quantitative correlation of substrate structure in diacylglycolurils with kinetic data for the rearrangement reaction.     

1,6-Dibenzylglycoluril for synthesis of deprotected glycoluril dimer

1,6-Dibenzylglycoluril is not accessible via classical condensation reaction between substituted urea and glyoxal. In this paper 1,6-dibenzylglycoluril was successfully prepared by alkylation of 1,6-diacetylglycoluril with benzylbromide for the first time. 1,6-Dibenzylglycoluril reacted with formaldehyde to give tetrabenzylglycoluril dimer. Deprotection of this dimer and the previously reported o-xylyleneglycoluril dimer was achieved by dissolving metal reduction, whereas propyleneglycoluril dimer was deprotected by action of potassium persulfate.     

Synthesis of 2-imino-5-phenylimidazolidin-4-one and the structure of its trifluoroacetate salt

The trifluoroacetate salt of 2-imino-5-phenylimidazolidin-4-one has been prepared and characterized crystallographically. The complex crystallizes in the monoclinic space group C2, with a = 27.894(3) Å, b = 6.2616(7) Å, c = 7.1989(8) Å, = 93.176(2). The extended structure consists of neutral, one-dimensional, hydrogen-bonded ribbons incorporating both ionic species.     

First immobilization of a glycoluril-derived molecular clip on Merrifield resin: facile separation of dihydroxybenzenes by affinity chromatography

A practical method for the separation and purification of dihydroxybenzenes from phenol-dihydroxybenzene, methoxyphenol-dihydroxybenzene, and isomeric dihydroxybenzene mixtures was developed on the basis of affinity chromatography using a functionalized Merrifield resin. The resin was obtained by immobilization of a glycoluril-derived clip on Merrifield resin. This recyclable resin was repeatedly used for convenient and rapid separation of dihydroxybenzenes from the above-mentioned mixtures.     

Rapid and scalable synthesis of chiral porphyrin cage compounds

An improved and scalable synthetic route to chiral porphyrin cage compounds, which will be used as catalytic machines for the encoding of information into polymers, has been developed. The porphyrin cage was made chiral by introducing one or two nitro groups on its xylylene sidewalls. This nitration was performed with fuming nitric acid at low temperature and occurred in a highly regioselective fashion. The latter was thought to be the result of the binding of a nitronium cation inside the cavity of the cage compound, directing the reaction to the sidewalls. However, ¹H NMR titrations of the porphyrin cage compound with either nitric acid or the nitronium salt [NO₂][BF₄] revealed that the effect of the host-guest binding of the nitronium ion on the selectivity of the reaction is negligible. Instead, protonation of the porphyrin plays an essential role as it prevents the ring from being oxidized, allowing the nitration to be directed to the sidewalls.     

A New Anion Receptor with a Glycoluril Molecular Scaffold

The rational design and synthesis of a new anion receptor containing a glycoluril molecular scaffold are reported. This new receptor utilizes four amide hydrogen bonds arranged at the corner of the glycoluril unit. This new anion receptor binds spherically shaped halide ions in a 1:1 stoichiometry and has a high affinity for fluoride.     

Anion Receptor with Two Imidazolium Rings on the Glycoluril

We have synthesized an anion receptor with two imidazolium groups on the glycoluril. This receptor showed high affinity for Y-shaped anions such as acetate and benzoate. Although the association constants of these anions for the receptor 4 are too large to be estimated from ¹H NMR titration, the receptor 4 has at least 560-fold selectivity for acetate or benzoate over iodide and 360-fold selectivity over nitrate.