Sticking of CO to crystalline and amorphous ice surfaces

We present results of classical trajectory calculations on the sticking of hyperthermal CO to the basal plane (0001) face of crystalline ice Ih and to the surface of amorphous ice Ia. The calculations were performed for normal incidence at a surface temperature Ts = 90 K for ice Ia, and at Ts = 90 and 150 K for ice Ih. For both surfaces, the sticking probability can be fitted to a simple exponentially decaying function of the incidence energy, Ei: Ps = 1.0e(-Ei(kJ/mol)/90(kJ/mol)) at Ts = 90 K. The energy transfer from the impinging molecule to the crystalline and the amorphous surface is found to be quite efficient, in agreement with the results of molecular beam experiments on the scattering of the similar molecule, N2, from crystalline and amorphous ice. However, the energy transfer is less efficient for amorphous than for crystalline ice. Our calculations predict that the sticking probability decreases with Ts for CO scattering from crystalline ice, as the energy transfer from the impinging molecule to the warmer surfaces becomes less efficient. At high Ei (up to 193 kJ/mol), no surface penetration occurs in the case of crystalline ice. However, for CO colliding with the amorphous surface, a penetrating trajectory was observed to occur into a large water pore. The molecular dynamics calculations predict that the average potential energy of CO adsorbed to ice Ih is -10.1 +/- 0.2 and -8.4 +/- 0.2 kJ/mol for CO adsorbed to ice Ia. These values are in agreement with previous experimental and theoretical data. The distribution of the potential energy of CO adsorbed to ice Ia was found to be wider (with a standard deviation sigma of 2.4 kJ/mol) than that of CO interacting with ice Ih (sigma = 2.0 kJ/mol). In collisions with ice Ia, the CO molecules scatter at larger angles and over a wider distribution of angles than in collisions with ice Ih.     

Photo ejection of water molecules from amorphous ice films

Water molecules are photo-ejected upon laser irradiation from the surface of ice films grown on graphite (0001) and Pt(111). The films are deposited at temperatures between 40 and 140 K and irradiated with nanosecond laser pulses. The process is investigated in the wavelength range between 275 and 670 nm. The wavelength and photon flux dependence suggest a multi-photon process with energy threshold of around 9 eV. The photo-detachment is less effective or negligible from films annealed at temperatures above the amorphous-crystalline transition temperature of ice films. Coverage dependence of the phenomena relates the photo yield to surface roughness. Electronic excitation mechanism related to the defects in ice is proposed to explain the observations.     

Capture and release of CO2 by polyamidine

By CO₂ bubbling into an aqueous dimethyl sulfoxide solution, the polyamidine ( Poly‐Amd ) prepared from hexamethylenediamine and triethyl orthoacetate was converted to the bicarbonate salt, Poly‐Amd H·HCO₃, which formed aggregates. Conversely, the aggregates disappeared upon Ar bubbling to release the captured CO₂, reverting to Poly‐Amd completely. Polyethyleneimine ( PEI ) also reversibly captured and released CO₂ molecules in solution by bubbling CO₂ and Ar, respectively, in an alternate manner. No appreciable difference was observed between Poly‐Amd and PEI in CO₂ capture in solution. The binary system consisting of Poly‐Amd and polyethylene glycol ( PEG ) captured CO₂ efficiently at ordinary pressure and reached a stationary state within 200 h, at which 66% of the amidine groups bound CO₂ molecules, which was released upon exposure to a N₂ flow. In contrast to the binary system with Poly‐Amd, the binary system of PEI with PEG did not capture CO₂ efficiently, and only 5.7% of the amino groups bound CO₂ molecules after 600 h. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3404–3411     

Organocatalyzed CO2 Trapping Using Alkynyl Indoles

The first organocatalyzed trapping of CO₂ through C? C and C? O bond formation is reported. Alkynyl indoles together with catalytic amounts of an organic base and five equivalents of CO₂ resulted in the formation new heterocyclic structures. These tricyclic indole‐containing products were successfully prepared under mild reaction conditions from aromatic, heteroaromatic, and aliphatic alkynyl indoles with complete regioselectivity. Further investigations suggest that C? C bond formation is the initial intermolecular step, followed by lactone‐forming C? O bond formation.     

Control of release properties of guest molecules by the type of benzoheterocyclic ring in supramolecular host complexes

Three types of supramolecular benzoheterocyclic host complexes were successfully prepared using (1R,2S)-2-amino-1,2-diphenylethanol and three types of benzoheterocyclic (benzothiophene, benzofuran, and benzopyrrole) acid derivatives. The host complexes had one-dimensional (1D) channel-like cavities that were formed by the assembly of two-component 2₁-helical columnar network structures, which included guest alcohol molecules. The release behavior of the guest molecules could be tuned by the type of heterocyclic ring in the supramolecular host complex.     

Investigation of vapor-deposited amorphous ice and irradiated ice by molecular dynamics simulation

With the purpose of clarifying a number of points raised in the experimental literature, we investigate by molecular dynamics simulation the thermodynamics, the structure and the vibrational properties of vapor-deposited amorphous ice (ASW) as well as the phase transformations experienced by crystalline and vitreous ice under ion bombardment. Concerning ASW, we have shown that by changing the conditions of the deposition process, it is possible to form either a nonmicroporous amorphous deposit whose density (approximately 1.0 g/cm3) is essentially invariant with the temperature of deposition, or a microporous sample whose density varies drastically upon temperature annealing. We find that ASW is energetically different from glassy water except at the glass transition temperature and above. Moreover, the molecular dynamics simulation shows no evidence for the formation of a high-density phase when depositing water molecules at very low temperature. In order to model the processing of interstellar ices by cosmic ray protons and heavy ions coming from the magnetospheric radiation environment around the giant planets, we bombarded samples of vitreous ice and cubic ice with 35 eV water molecules. After irradiation the recovered samples were found to be densified, the lower the temperature, the higher the density of the recovered sample. The analysis of the structure and vibrational properties of this new high-density phase of amorphous ice shows a close relationship with those of high-density amorphous ice obtained by pressure-induced amorphization.     

Trapping and release of cargo molecules from a micro-stamped mesoporous thin film controlled by poly(NIPAAm-co-AAm)

Materials that utilize the micropatterned structure of a mesoporous silica film to successfully load and release cargo using a thermal sensitive polymer are presented in this paper. Films with pore sizes of ~2 and ~5 nm aligned in the pulling direction were synthesized using evaporation induced self-assembly techniques. The pores are exposed using a new method of stamping micropatterns without the use hydrofluoric acid. A well studied temperature dependent polymer [poly(N-isopropylacrylamide-co-acrylamide)] was grafted onto the surface of these films to act as a temperature activated gatekeeper. Below the lower critical solution temperature (LCST) the polymer is erect and can block the pore openings, trapping cargo inside the pores. When the temperature is above the LCST the polymer collapses and unblocks the pores, allowing cargo to escape. The loading capacities as well as the reusability of these films were studied.     

Enhanced mechanical strength of zeolites by adsorption of guest molecules

We report a molecular simulation study of the mechanical properties of microporous zeolites filled with guest molecules. We show that the adsorption of molecules in the micropores of the material increases its bulk modulus. These results provide a microscopic picture of the deactivation of pressure-induced amorphization by incorporation of molecules.     

Formation of high density amorphous ice by decompression of ice VII and ice VIII at 135 K

Monte Carlo computer simulations of ice VII and ice VIII phases have been undertaken using the four-point transferable intermolecular potential model of water. By following thermodynamic paths similar to those used experimentally, ice is decompressed resulting in an amorphous phase. These phases are compared to the high density amorphous phase formed upon compression of ice Ih and are found to have very similar structures. By cooling liquid water along the water/Ih melting line a high density amorphous phase was also generated.     

Evolution of the structure of amorphous ice: from low-density amorphous through high-density amorphous to very high-density amorphous ice

We report results of molecular dynamics simulations of amorphous ice for pressures up to 22.5 kbar. The high-density amorphous ice (HDA) as prepared by pressure-induced amorphization of I(h) ice at T=80 K is annealed to T=170 K at various pressures to allow for relaxation. Upon increase of pressure, relaxed amorphous ice undergoes a pronounced change of structure, ranging from the low-density amorphous ice at p=0, through a continuum of HDA states to the limiting very high-density amorphous ice (VHDA) regime above 10 kbar. The main part of the overall structural change takes place within the HDA megabasin, which includes a variety of structures with quite different local and medium-range order as well as network topology and spans a broad range of densities. The VHDA represents the limit to densification by adapting the hydrogen-bonded network topology, without creating interpenetrating networks. The connection between structure and metastability of various forms upon decompression and heating is studied and discussed. We also discuss the analogy with amorphous and crystalline silica. Finally, some conclusions concerning the relation between amorphous ice and supercooled water are drawn.     

Analysis of guest molecules in clathrasils

Species included in clathrasils have been analyzed by quantitative IR spectroscopy. In the case of dodecasil 3C, with benzene or piperidine as guest molecules, results showed that only one out of 16 or 8 suitable cavities in the clathrasil structure is occupied. This means that a very low quantity of template molecules is sufficient for the crystal growth.     

Determination of binding energies between cyclodextrins and aromatic guest molecules by microcalorimetry

The inclusion of substituted benzoic acids in -CD or selectively methylated -CDs was investigated by titration microcalorimetry. All thermodynamic functions of the inclusion process G°, H° and S° could be obtained very accurately within one experiment. A very strong influence of the substitution pattern at both the host and the guest on the stability of the inclusion compounds was found.     

Structure transition and swapping pattern of clathrate hydrates driven by external guest molecules

We first report here that under strong surrounding gas of external CH4 guest molecules the sII and sH methane hydrates are structurally transformed to the crystalline framework of sI, leading to a favorable change of the lattice dimension of the host-guest networks. The high power decoupling 13C NMR and Raman spectroscopies were used to identify structure transitions of the mixed CH4 + C2H6 hydrates (sII) and hydrocarbons (methylcyclohexane, isopentane) + CH4 hydrates (sH). The present findings might be expected to provide rational evidences regarding the preponderant occurrence of naturally occurring sI methane hydrates in marine sediments. More importantly, we note that the unique and cage-specific swapping pattern of multiguests is expected to provide a new insight for better understanding the inclusion phenomena of clathrate materials.     

The photodissociative ionization of amorphous ice

Within the energy range 17 hv < 35 eV, the ionic species desorbed and their excitation spectra are reported. The only positive ion desorbed is H⁺. A model for the surface is suggested which explains the absence of OH⁺ desorption. The desorption mechanisms are discussed in terms of an energy analysis.     

Binding of small guest molecules to multivalent receptors

The complexation of phenol derivatives, aromatic carboxylic acids, and n-octylgalactopyranoside by hydrogen-bonded exo-receptors is described. The receptors are formed by self-assembly of differently functionalized calix[4]arene dimelamines with 5,5-diethyl barbiturate or butyl cyanurate. The multivalent complementary recognition site of the receptors is used very efficiently to complex multiple guests. A 1:6 binding mode was observed for phenol derivatives forming single hydrogen bonds with all six recognition sites of an ureido functionalized receptor assembly, while 1:3 complexation was observed for phenol derivatives which form two hydrogen bonds with two different ureido recognition sites of the same receptor. Aromatic carboxylic acids are complexed in a 1:6 ratio by receptors having six amino recognition sites. The complexation of n-octylgalactopyranoside by Gly-L-Ser functionalized receptors is also described, indicating that it is possible to use small peptidic fragments to complex biologically important molecules.