• The Journal of the Convergence on Culture Technology
• /
• v.8 no.5
• /
• pp.685-690
• /
• 2022

Recent research on soft adhesives has sought to understand in depth how their chemical or mechanical structures interact strongly with living tissues. The aim is to optimally address the unmet needs of patients with acute or chronic diseases. Synergy adhesion, which includes both electrostatic (hydrogen bonds) and mechanical interactions (capillary stress), appears to be effective in overcoming challenges related to long-term unstable bonds to wet surfaces. Here, we report electrostatic and mechanically synergistic mechanisms of adhesion without chemical residues. To infer the mechanism, a thermodynamic model based on custom combination adhesives has been proposed. The model supported experimental results that thermodynamically controlled swelling of hydrogels embedded in elastomeric structures improves biofluidic insensitive on-site adhesion to wet surfaces and improves detachment without chemical residues in the direction of peeling.

• Korean Journal of Crystallography
• /
• v.6 no.1
• /
• pp.36-42
• /
• 1995

Two types of single crystals of the title compound [6-(2-pyridyl)-3, 5-hexadiyn-ol, PyHxD] were obtained by solution of n-hexane/CH2C12 and n-hexane/Et2O, and their molecular conformations are proved identical in spite of different of space groups; C22H18N2O2 (I), Mr=343.70, Monoclinic, Pa, a=14.595(2), b=5.413(2), c=12.218(2)Å, β=96.86(1)°, V=958.3Å3, Z=2, Dx=1.19 Mgm-3, λ(MoKα)=0.71069Å, μ=0.072mm-1, F(000)=360.0, T=292K, R=0.104 for 756 unique observed reflections. An asymmetric unit contains a dimer connected by two N-H…O intermolecular hydrogen bonds. C11H9NO (II), Mr=171.85, Monoclinic, P21/a, a=14.611(2), b=5.423(6), c=12.191(2)Å, β=96.89(1)°, V=959.0Å3, Z=4, Dx=1.19 Mgm-3, λ(MoKα)=0.71069Å, μ=0.072mm-1, F(000)=360.0, T=293K, R=0.066 for 824 unique observed reflection. The structural asymmetric unit contains a molecule, but two N-H…O hydrogen bonds related by controsymmetry make the molecules form a dimer. In both structure, the dihedral angle between the planar pyridyl ring and the plane defined by C(10)-C(11)-O connected by linear diyne chain is approximately normal, and the molecules are stacked along b-axis with the unit repeat of b-axis.

• Journal of the Korean Chemical Society
• /
• v.21 no.5
• /
• pp.307-319
• /
• 1977

The crystal structure of $N-({\alpha}-dimethyl\;{\beta}-hydroxy)ethyl\;N'-cyclohexyl\;thiourea,\;C_{ll}H_{22}N_2OS)$, has been determined by X-ray diffraction method. The compound crystallizes in the orthorhombic space group Pbca with a = 10.33(3), b = 11.82(3), c = 22.57(4)${\AA}$ and Z = 8. A total of 1414 observed reflections collected by the Weissenberg photographs and was solved by heavy atom method and refined by block diagonal least-squares methods to the R value of 0.13. The cyclohexane ring has a normal chair conformation and the thiourea unit is planar. The primary alcoholic group O-H bonded to C(l) makes an intramolecular hydrogen bond with N(2), which leads to stablize the molecule. There are two independent hydrogen bonds in the structure. One of them is of the type N-H${\cdot}{\cdot}{\cdot}$O intramolecular hydrogen bond with the length 2.71${\AA}$, another is of the type O-H${\cdot}{\cdot}{\cdot}$S intermolecular hydrogen bond with the length 3.21${\AA}$ parallel to the b axis. Apart from the hydrogen bonding system the molecules are held together by van der Waals forces in the crystal.

• Korean Chemical Engineering Research
• /
• v.49 no.1
• /
• pp.1-9
• /
• 2011

Platinum catalysts were prepared by impregnating platinum precursor on titania-, vanadia-, zirconia- and ceria-incorporated silicas followed by hydrogen peroxide treatment. The effects of the oxide incorporation and the hydrogen peroxide treatment in the preparation of the platinum catalysts on their platinum dispersion and catalytic activity in carbon monoxide oxidation were investigated. XRD, TEM, EXAFS, XPS and carbon monoxide chemisorption studies confirmed the high dispersion of platinum even on silica by the oxide incorporation and hydrogen peroxide treatment. However, the type of oxides incorporated on silica caused considerable variances in the adsorption and the catalytic activity in the oxidation of carbon monoxide on them. The incorporation of titania, zirconia and ceria on silica and further hydrogen peroxide treatment enhanced the platinum dispersion, resulting in the improved catalytic activities. Among the catalysts supported on the oxide-incorporated silicas, the platinum catalyst supported on zirconia-incorporated silica exhibited the highest activity because of the highest platinum dispersion due to the formation of Pt-O-Zr bonds.

• Clean Technology
• /
• v.29 no.3
• /
• pp.163-171
• /
• 2023

Hydrogen has been gaining a lot of attention as a possible clean energy source that can aid in reaching carbon neutrality. Currently, hydrogen production has relied on the steam reforming of fossil fuels. However, due to the carbon dioxide emissions caused by this process, hydrogen production based on the steam reforming of bio-oil derived from biomass has been proposed as an alternative approach. In order to use this alternative approach efficiently, one of the key issues that must be overcome is that the complexity of bio-oil, which has a large molecular weight and diverse functional groups of hydrocarbons, promotes the catalytic deactivation of nickel-based catalysts. In this review, research efforts to improve nickel-based catalysts for the steam reforming of bio-oil have been discussed in terms of the active phase, support, and promoters. The active phases are involved in activating C-C and C-H bonds of high-molecular-weight hydrocarbons, and noble and transition metals can be utilized. In terms of the support and promoters, the catalytic deactivation of Ni-based catalysts can be inhibited by utilizing reactive lattice oxygen for support or by suppressing the acidity. The development of active and stable Ni-based reforming catalysts plays a critical role in clean hydrogen production based on bio-oils.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.11 no.5
• /
• pp.224-230
• /
• 2001

The characteristics of $NO/N_2O$ annealed reoxidized nitrided oxide being studied as super thin gate oxide and gate dielectric layers of Non-Volatile Semiconductor Memory (NVSM) were investigated by Dynamic Secondary Ion Mass Spectrometry (D-SIMS), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and Auger Electron Spectroscopy (AES). The specimen was annealed by $NO/N_2O$ after initial oxide process and then rcoxidized for nitrogen redistribution in nitrided oxide. Out-diffusion of incorporated nitrogen during the wet oxidation in reoxidation process took place more strongly than that of the dry oxidation. It seems to indicate that hydrogen plays a role in breaking the Si N bonds. As reoxidation proceeds, incorporated nitrogen of $NO/N_2O$ annealed nitrided oxide is obsen-ed to diffuse toward the surface and substrate at the same time. ToF-SIMS results show that SiON species are detected at the initialoxide interface, and Si,NO species near the new $Si_2NO$ interface that formed after reoxidation. These SiON and $Si_2NO$ species most likely to relate to the origin of the state of memory charge traps in reoxidized nitrided oxide, because nitrogen dangling bonds of SiON and silicon dangling bonds of $Si_2NO$ are contained defects associated with memory effect.

• Corrosion Science and Technology
• /
• v.7 no.1
• /
• pp.50-60
• /
• 2008

The majority of the described experimental results deal with relatively pure aluminium. Variations were made in the pretreatment of the aluminum substrates and an investigation was performed on the resulting changes in oxide layer composition and chemistry. Subsequently, the bonding behavior of the surfaces was investigated by using model adhesion molecules. These molecules were chosen to represent the bonding functionality of an organic polymer. They were applied onto the pretreated surfaces as a monolayer and the bonding behavior was studied using infrared reflection absorption spectroscopy. A direct and clear relation was found between the hydroxyl fraction on the oxide surfaces and the amount of molecules that subsequently bonded to the surface. Moreover, it was found that most bonds between the oxide surface and organic functional groups are not stable in the presence of water. The best performance was obtained using molecules, which are capable of chemisorption with the oxide surface. Finally, it was found that freshly prepared relatively pure aluminum substrates, which are left in air, rapidly lose their bonding capacity towards organic functional groups. This can be attributed to the adsorption of contamination and water to the oxide surface. In addition the adhesion of a typical epoxy-coated aluminum system was investigated during exposure to water at different temperatures. The coating was found to quite rapidly lose its adhesion upon exposure to water. This rapid loss of adhesion corresponds well with the data where it was demonstrated that the studied epoxy coating only bonds through physisorptive hydrogen bonding, these bonds not being stable in the presence of water. After the initial loss the adhesion of the coating was however found to recover again and even exceeded the adhesion prior to exposure. The improvement could be ascribed to the growth of a thin oxyhydroxide layer on the aluminum substrate, which forms a new, water-stable and stronger bond with the epoxy coating. Two routes for improvement of adhesion are finally decribed including an interphasial polymeric thin layer and a treatment in boiling water of the substrate before coating takes place. The adhesion properties were finely also studied as a function of the Mg content of the alloys. It was shown that an enrichment of Mg in the oxide could take place when Mg containing alloys are heat-treated. It is expected that for these alloys the (hydr)oxide fraction also depends on the pre-treatment and on the distribution of magnesium as compared to the aluminium hydroxides, with a direct impact on adhesive properties.

• Proceedings of the Korean Society of Near Infrared Spectroscopy Conference
• /
• 2001.06a
• /
• pp.1283-1283
• /
• 2001

NIR spectroscopy has been used extensively to investigate the structure of water, alcohol and other self-associate molecules because the frequencies of NIR bands due to OH and NH groups strength of hydrogen bonds. We have studied the structure of water -methanol mixtures by use of NIR spectroscopy. Strong features in the 7200-6300 $cm^{-1}$ / region consist of a number of overlapped bands due to the combination of OH antisymmetric and symmetric stretching modes of water and the first overtone of the OH stretching modes of free and hydrogen bonded methanol, while weak fratures in the 6000-5800 cm-1 region are ascribed to the first overtones of $CH_3$ stretching modes of methanol. We will focus the discussion on the $CH_3$ stretching bands. They seem to show a significant shift is not clear from the spectra shown in figure 1(a). Figure 1(b) depicts the second derivative in the 6000-5700 $cm^{-1}$ / region. Now, it is clear from the second derivative that there are two major bands near 5950 and 5900 $cm^{-1}$ / and that they do show a shift be about 30 $cm^{-1}$ / Why do the $CH_3$ bands show the shift with increasing concentration of methanol\ulcorner Probably, the CH, group interacts directly with OH groups of water. The results in figure 1(b) demonstrate the usefulness of the second derivative in resolution enhancement as well as the potential of NIR spectroscopy in the studies of molecular interactions.(Figure omitted).

• Bulletin of the Korean Chemical Society
• /
• v.35 no.12
• /
• pp.3495-3501
• /
• 2014

A novel crystal, the mono-protonated metformin acetate (1), was obtained and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. It was found that one of the imino group in the metformin cation was protonated along with the proton transfer from the secondary amino group to the other imino group. Its crystal structure was then compared with the previously reported diprotonated metformin oxalate (2). The difference between them is that the mono-protonated metformin cations can be linked by hydrogen bonding to form dimers while the diprotonated metformin cations cannot. Both of them are stabilized by intermolecular hydrogen bonds to assemble a 3-D supermolecular structure. The four potential tautomer of the mono-protonated metformin cation (tautomers 1a, 1b, 1c and 1d) were optimized and their single point energies were calculated by Density Functional Theory (DFT) B3LYP method based on the Polarized Continuum Model (PCM) in water, which shows that the most likely existed tautomer in human cells is the same in the crystal structure. Based on the optimized structure, their Wiberg bond orders, Natural Population Analysis (NPA) atomic charges, molecular electrostatic potential (MEP) maps were calculated to analyze their electronic structures, which were then compared with the corresponding values of the diprotonated metformin cation (cation 2) and the neutral metformin (compound 3). Finally, the possible tautomeric mechanism of the mono-protonated metformin cation was discussed based on the observed phenomena.

• Bulletin of the Korean Chemical Society
• /
• v.35 no.8
• /
• pp.2299-2303
• /
• 2014

Two diastereoisomers of cyclo(Pro-Tyr) have been synthesized simultaneously. The crystal structures and conformations of both cyclo($\small{L}$-Pro-$\small{L}$-Tyr) and a racemic mixture of cyclo($\small{D}$-Pro-$\small{L}$-Tyr) and cyclo($\small{L}$-Pro-$\small{D}$-Tyr), abbreviated as rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr), have been determined by a single-crystal X-ray diffraction study at low temperature. The crystals of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) belong to orthorhombic space group $Pna2_1$ with a = 10.755 (1), b = 12.699 (1), c = 9.600 (1) ${\AA}$ and Z = 4. The tyrosine side chain is folded towards the diketopiperazine (DKP) ring. The DKP ring adopts a twist boat conformation with pseudo symmetry $C_{2v}$. The pyrrolidine ring has an envelope conformation with the N5, C4, C7 and C8 atoms in a plane. The crystal of rac-cyclo($\small{D}$-Pro-$\small{L}$-Tyr/$\small{L}$-Pro-$\small{D}$-Tyr) is stabilized by hydrogen bonds between amide N2-H2 and carbonyl oxygen O2 in the neighbor. The hydroxyl group of tyrosine residue is also hydrogen bonded to the oxygen of the carbonyl group of the DKP ring in the next molecule. The spectroscopic properties of both isomers are also described.