9 research outputs found
<sup>1</sup>H-NMR Karplus Analysis of Molecular Conformations of Glycerol under Different Solvent Conditions: A Consistent Rotational Isomerism in the Backbone Governed by Glycerol/Water Interactions
Glycerol is a symmetrical, small biomolecule with high flexibility in molecular conformations. Using a 1H-NMR spectroscopic Karplus analysis in our way, we analyzed a rotational isomerism in the glycero backbone which generates three kinds of staggered conformers, namely gt (gauche-trans), gg (gauche-gauche), and tg (trans-gauche), at each of sn-1,2 and sn-2,3 positions. The Karplus analysis has disclosed that the three rotamers are consistently equilibrated in water keeping the relation of ‘gt:gg:tg = 50:30:20 (%)’ at a wide range of concentrations (5 mM~540 mM). The observed relation means that glycerol in water favors those symmetric conformers placing 1,2,3-triol groups in a gauche/gauche geometry. We have found also that the rotational isomerism is remarkably changed when the solvent is replaced with DMSO-d6 or dimethylformamide (DMF-d7). In these solvents, glycerol gives a relation of ‘gt:gg:tg = 40:30:30 (%)’, which means that a remarkable shift occurs in the equilibrium between gt and tg conformers. By this shift, glycerol turns to also take non-symmetric conformers orienting one of the two vicinal diols in an antiperiplanar geometry
Soft Nanotubes Derivatized with Short PEG Chains for Thermally Controllable Extraction and Separation of Peptides
By
means of a two-step self-assembly process involving three components,
including short polyÂ(ethylene glycol) (PEG) chains, we produced two
different types of molecular monolayer nanotubes: nanotubes densely
functionalized with PEG chains on the outer surface and nanotubes
densely functionalized with PEG chains in the nanochannel. Turbidity
measurements and fluorescence spectroscopy with an environmentally
responsive probe suggested that the PEG chains underwent dehydration
when the nanotubes were heated above 44–57 °C and rehydration
when they were cooled back to 25 °C. Dehydration of the exterior
or interior PEG chains rendered them hydrophobic and thus able to
effectively extract hydrophobic amino acids from the bulk solution.
Rehydration of the PEG chains restored their hydrophilicity, thus
allowing the extracted amino acids to be squeezed out into the bulk
solutions. The nanotubes with exterior PEG chains exhibited selectivity
for all of the hydrophobic amino acids, whereas the interior PEG chains
were selective for hydrophobic amino acids with an aliphatic side
chain over hydrophobic amino acids with an aromatic side chain. The
higher selectivity of the latter system is attributable that the extraction
and back-extraction processes involve encapsulation and transportation
of the amino acids in the nanotube channel. As the result, the latter
system was useful for separation of peptides that differed by only
a single amino acid, whereas the former system showed no such separation
ability
Preparation and Formation Process of Zn(II)-Coordinated Nanovesicles
Mixing
a glycylglycine lipid and zinc acetate has been reported
to form novel supramolecular ZnÂ(II)-coordinated nanovesicles in ethanol.
In this study, we investigate in detail the formation of nanovesicles
by using three lipids at different temperatures and discuss their
formation process. The original lipids show extremely low solubilities
and appear as plate structures in ethanol. Within a small window of
lipid solubility, the formation of lipid–ZnÂ(II) complexes occurs
mainly on the solid surfaces of plate structures. Controlling of the
lipid solubility by temperature affects the kinetics of complex formation
and the subsequent transformation of the complexes into nanovesicles
and nanotubes. An improved method of two-step control of temperature
is developed for preparing all the three kinds of nanovesicles. We
provide new insights into the formation process of nanovesicles based
on several control experiments. A tetrahedral lipid–cobaltÂ(II)
complex similarly produces nanovesicles, whereas an octahedral complex
gives sheet structures. Mixing of zinc acetate with a β-alanyl-β-alanine
lipid can only give sheet structures, which lack a polyglycine II
hydrogen-bond network and induce no morphological changes. We conclude
that the formation of the lipid–ZnÂ(II) complexes on solid plate
structures, tetrahedral geometry, and polyglycine II hydrogen-bond
network in the complexes shall work cooperatively for the formation
of ZnÂ(II)-coordinated nanovesicles
Spontaneous Nematic Alignment of a Lipid Nanotube in Aqueous Solutions
The dispersibility and liquid crystal
formation of a self-assembled
lipid nanotube (LNT) was investigated in a variety of aqueous solutions.
As the lipid component, we chose a bipolar lipid with glucose and
tetraglycine headgroups, which self-assembled into an LNT with a small
outer diameter of 16 to 17 nm and a high axial ratio of more than
310. The LNT gave a stable colloidal dispersion in its dilute solutions
and showed spontaneous liquid crystal (LC) alignment at relatively
low concentrations and in a pH region including neutral pH. The LNT
samples with shorter length distributions were prepared by sonication,
and the relationship between the LNT axial ratio and the minimum LC
formation concentration was examined. The robustness of the LNT made
the liquid crystal stable in mixed solvents of water/ethanol, water/acetone,
and water/tetrahydrofuran (1:1 by volume) and at a temperature of
up to 90 °C in water. The observed colloidal behavior of the
LNT was compared to those of similar 1D nanostructures such as a phospholipid
tubule
Molecular-Level Understanding of the Encapsulation and Dissolution of Poorly Water-Soluble Ibuprofen by Functionalized Organic Nanotubes Using Solid-State NMR Spectroscopy
A comprehensive study of the encapsulation
and dissolution of the poorly water-soluble drug ibuprofen (IBU) using
two types of organic nanotubes (ONT-1 and ONT-2) was conducted. ONT-1
and ONT-2 had similar inner and outer diameters, but these surfaces
were functionalized with different groups. IBU was encapsulated by
each ONT via solvent evaporation. The amount of IBU in the ONTs was
9.1 and 29.2 wt % for ONT-1 and ONT-2, respectively. Dissolution of
IBU from ONT-1 was very rapid, while from ONT-2 it was slower after
the initial burst release. One-dimensional (1D) <sup>1</sup>H, <sup>13</sup>C, and two-dimensional (2D) <sup>1</sup>H–<sup>13</sup>C solid-state NMR measurements using fast magic-angle spinning (MAS)
at a rate of 40 kHz revealed the molecular state of the encapsulated
IBU in each ONT. Extremely mobile IBU was observed inside the hollow
nanosapce of both ONT-1 and ONT-2 using <sup>13</sup>C MAS NMR with
a single pulse (SP) method. Interestingly, <sup>13</sup>C cross-polarization
(CP) MAS NMR demonstrated that IBU also existed on the outer surface
of both ONTs. The encapsulation ratios of IBU inside the hollow nanospaces
versus on the outer surfaces were calculated by waveform separation
to be approximately 1:1 for ONT-1 and 2:1 for ONT-2. Changes in <sup>13</sup>C chemical shifts showed the intermolecular interactions
between the carboxyl group of IBU and the amino group on the ONT-2
inner surface. The cationic ONT-2 could form the stronger electrostatic
interactions with IBU in the hollow nanosapce than anionic ONT-1.
On the other hand, 2D <sup>1</sup>H–<sup>13</sup>C NMR indicated
that the hydroxyl groups of the glucose unit on the outer surface
of the ONTs interacted with the carboxyl group of IBU in both ONT-1
and ONT-2. The changes in peak shape and chemical shift of the ONT
glucose group after IBU encapsulation were larger in ONT-2 than in
ONT-1, indicating a stronger interaction between IBU and the outer
surface of ONT-2. The smaller amount of IBU encapsulation and rapid
IBU dissolution from ONT-1 could be due to the weak interactions both
at the outer and inner surfaces. Meanwhile, the stronger interaction
between IBU and the inner surface of ONT-2 could suppress IBU dissolution,
although the IBU on the outer surface of ONT-2 was released soon after
dispersal in water. This study demonstrates that the encapsulation
amount and the dissolution rates of poorly water-soluble drugs, a
class which makes up the majority of new drug candidates, can be controlled
using the functional groups on the surfaces of ONTs by considering
the host–guest interactions