Investigation of the mobility of paraffin molecules in channel urea clathrates by nuclear magnetic resonance relaxation spectroscopy

Krieger, Ju. H.; Semenov, A. R.; Chekhova, G. N.

doi:10.1134/1.1417179

Cited by 3 publications

(3 citation statements)

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“…14,18,22 The cylindrical shape of the urea channel accounts for the formation of incommensurate host-guest phases, 80 whose fascinating physical properties continue to attract ever-increasing attention. [81][82][83][84][85][86] However, there is a significant distinction of the channel in the dipeptides studied. Unlike for urea, the center of the channel is displaced from the central axis by up to >1 Å (Table 4).…”

Section: Resultsmentioning

confidence: 99%

“…The channels in all dipeptides studied are very uniform, with the variation of diameter as the channel propagates along c translation being 0.2 Å or less (Table ). Such geometry is very uncommon among inclusion architectures and is reminiscent of the channel in urea. ,, The cylindrical shape of the urea channel accounts for the formation of incommensurate host−guest phases, whose fascinating physical properties continue to attract ever-increasing attention. − …”

Section: Resultsmentioning

confidence: 99%

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Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy

et al. 2006

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Eight crystalline dipeptides were studied: AV (Ala-Val), VA (Val-Ala), AI (Ala-Ile), VV (Val-Val), IA (Ile-Ala), IV (Ile-Val), VI (Val-Ile), and LS (Leu-Ser) (all LL isomers). The first seven form an isostructural series (space group P6(1)), whereas LS has a different structure (P6(5)). All structures display H-bonded tubular assemblies of the dipeptide molecules resulting in open ultramicropores in the form of isolated one-dimensional (1D) channels. The total porosity of the materials ranges from 4 to 12% (micropore volume from 0.04 to 0.12 cm(3)/g). Calculations based on the crystal structures, He pycnometry, and solid-state (129)Xe NMR methods were used to obtain a comprehensive description of the geometry and properties of the micropores. The following order was established for the channel diameter: AV > VA > AI > VV > IA > IV > VI, with >5 A for AV and <4 A for VI; LS is close to AI. The observed sorption behavior cannot be described adequately based on the crystal structure and can only be understood if one takes into account the dynamics of the host matrix. The pores are chiral, with the center of the channel describing a right-handed helix (left-handed for LS). The following order was established for the channel helicity: VA > IA > IV > AV approximately AI approximately VV > VI > LS, with a helix diameter of approximately 2 A for VA, IA, and IV and approximately 1 A or less for the remaining dipeptides. A comparison of the dipeptides studied with other supramolecular materials is given and the potential for applications is discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy

et al. 2006

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“…The dynamics, structure, and phase transitions of n-hexadecane/urea ( Figure 1) have been studied extensively. 11,28,[30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] Although much of the early literature, including the first crystal structure of any UIC, 26 treated this as a commensurate structure with c g = 2c h , it has been known since work by Laves et al 46 and Lenné 24 that the repeat length of the guest along the channel (c g ) is somewhat longer (∼22.6 Å) than that of twice the repeat of the host (22.03 Å). In the mid-1980s, Forst reported a rich sequence of four phases from 380 K to 77 K. 32,33 Above 365 K, a hexagonal structure was reported, whereas between this temperature and ∼150 K, the structure was reported to be approximately trigonal.…”

Section: Introductionmentioning

confidence: 99%

Confined linear molecules inside an aperiodic supramolecular crystal: The sequence of superspace phases in n-hexadecane/urea

Huard

Toudic

Rabiller

et al. 2011

The Journal of Chemical Physics

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High-resolution studies of the host-guest inclusion compound n-hexadecane/urea are reported at atmospheric pressure, using both cold neutrons and x-ray diffraction. This intergrowth crystal presents a misfit parameter, defined by the ratio c(h)/c(g) (c(host)/c(guest)), which is temperature independent and irrational (γ = 0.486 ± 0.002) from 300 to 30 K. Three different structural phases are reported for this aperiodic crystal over this temperature range. The crystallographic superspaces are of rank 4 in phases I and II, whereas phase III is associated with an increase in rank to 5, with a supplementary misfit parameter (δ = 0.058 ± 0.002) that is constant throughout this phase. The superspace group of phase I is hexagonal P6(1)22(00γ) down to T(c1) = 149.5 ± 0.5 K; phase II, which persists down to T(c2) = 127.8 ± 0.5 K is orthorhombic P2(1)2(1)2(1)(00γ), and phase III is orthorhombic P2(1)2(1)2(1)(00γ)(00δ).

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The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds

Mariette

Guérin

Rabiller

et al. 2014

Zeitschrift Für Kristallographie - Crystalline Materials

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n-Dodecane/urea is a member of the prototype series of n-alkane/urea inclusion compounds. At room temperature, it presents a quasi-one dimensional liquid-like state for the confined guest molecules within the rigid, hexagonal framework of the urea host. At lower temperatures, we report the existence of two other phases. Below Tc=248 K there appears a phase with rank four superspace group P6122(00γ), the one typically observed at room temperature in n-alkane/urea compounds with longer guest molecules. A misfit parameter, defined by the ratio γ=ch/cg (chost/cguest), is found to be 0.632±0.005. Below Tc1=123 K, a monoclinic modulated phase is created with a constant shift along c of the guest molecules in adjacent channels. The maximal monoclinic space group for this structure is P1211(α0γ). Analogies and differences with n-heptane/urea, which also presents a monoclinic, modulated low-temperature phase, are discussed.

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Investigation of the mobility of paraffin molecules in channel urea clathrates by nuclear magnetic resonance relaxation spectroscopy

Cited by 3 publications

References 5 publications

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy

Confined linear molecules inside an aperiodic supramolecular crystal: The sequence of superspace phases in n-hexadecane/urea

The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds

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Investigation of the mobility of paraffin molecules in channel urea clathrates by nuclear magnetic resonance relaxation spectroscopy

Cited by 3 publications

References 5 publications

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and129Xe NMR Spectroscopy

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and129Xe NMR Spectroscopy

Confined linear molecules inside an aperiodic supramolecular crystal: The sequence of superspace phases in n-hexadecane/urea

The creation of modulated monoclinic aperiodic composites in n-alkane/urea compounds

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Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy

Micropores in Crystalline Dipeptides as Seen from the Crystal Structure, He Pycnometry, and¹²⁹Xe NMR Spectroscopy