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PubMed1998

Synthesis of Nanoporous Cubic In(CN)(3) and In(1)(-)(x)()Ga(x)()(CN)(3) and Corresponding Inclusion Compounds.

Anhydrous In(CN)(3) and In(1)(-)(x)()Ga(x)()(CN)(3) phases with empty Prussian-blue-type structures have been prepared via low-temperature solution methods utilizing molecular templating agents. Quantitative X-ray powder diffraction was used to refine the In(CN)(3) cubic structure in which In is octahedrally surrounded by an average of three C and three N atoms. The symmetry is Pm&thremacr;m, a = 5.627(1) Å, and the In-(C,N) and C-N bond lengths are 2.251(1) and 1.125(1) Å, respectively. The compound reversibly incorporates krypton atoms into the empty cavities to form In(CN)(3).Kr, which is readily identified by powder diffraction. Similar inclusion systems with n-hexane in the porous framework are also synthesized. In(1)(-)(x)()Ga(x)()(CN)(3) solid solutions are formed by suitable combinations of the binary systems and have lattice constants adjustable between 5.293 Å for Ga(CN)(3) and 5.627(1) Å for In(CN)(3). The variation of the lattice parameters with composition obeys Vegard's Law.

Journal Article↗
PubMed2002

Improper or classical hydrogen bonding? A comparative cryosolutions infrared study of the complexes of HCClF(2), HCCl(2)F, and HCCl(3) with dimethyl ether.

Complexes of haloforms of the type HCCl(n)F(3-)(n) (n = 1-3) with dimethyl ether have been studied in liquid argon and liquid krypton, using infrared spectroscopy. For the haloform C[bond]H stretching mode, the complexation causes blue shifts of 10.6 and 4.8 cm(-1) for HCClF(2) and HCCl(2)F, respectively, while for HCCl(3) a red shift of 8.3 cm(-1) is observed. The ratio of the band areas of the haloform C[bond]H stretching in complex and monomer was determined to be 0.86(4) for HCClF(2), 33(3) for HCCl(2)F, and 56(3) for HCCl(3). These observations, combined with those for the HCF(3) complex with the same ether (J. Am. Chem. Soc. 2001, 123, 12290), have been analyzed using ab initio calculations at the MP2[double bond]FC/6-31G(d) level, and using some recent models for improper hydrogen bonding. Ab initio calculations on the haloforms embedded in a homogeneous electric field to model the influence of the ether suggest that the complexation shift of the haloform C[bond]H stretching is largely explained by the electric field effect induced by the electron donor in the proton donor. The model calculations also show that the electric field effect accounts for the observed intensity changes of the haloform C[bond]H stretches.

Chlorofluorocarbons, Methane↗
PubMed2002

Blue shifting hydrogen bonding in the complexes of chlorofluoro haloforms with acetone-d(6) and oxirane-d(4).

Mixtures of haloforms of the type HCClnF3-n (n = 0-3) with oxirane-d4 and acetone-d6 have been studied in liquid krypton, using infrared spectroscopy. Analysis of the spectra shows that a small fraction of the monomers is transformed into 1:1 complexes in which the haloform C-H bond is hydrogen bonded to the oxygen atom of the base. For all complexes, the haloform CH stretch is blue shifted, with the shift increasing from chloroform to fluoroform, while the ratio of the infrared intensities of the C-H stretching bands of complexed and free C-H bonds changes from a value well over 50 for the chloroform to a value near 0.1 for the fluoroform complexes. These observations have been corroborated by ab initio calculations using CP-corrected gradient techniques.

Journal Article↗
PubMed2003

Noble gas-actinide complexes of the CUO molecule with multiple Ar, Kr, and Xe atoms in noble-gas matrices.

Laser-ablated U atoms react with CO in excess argon to produce CUO, which is trapped in a triplet state in solid argon at 7 K, based on agreement between observed and relativistic density functional theory (DFT) calculated isotopic frequencies ((12)C(16)O, (13)C(16)O, (12)C(18)O). This observation contrasts a recent neon matrix investigation, which trapped CUO in a linear singlet state calculated to be about 1 kcal/mol lower in energy. Experiments with krypton and xenon give results analogous to those with argon. Similar work with dilute Kr and Xe in argon finds small frequency shifts in new four-band progressions for CUO in the same triplet states trapped in solid argon and provides evidence for four distinct CUO(Ar)(4-n)(Ng)(n) (Ng = Kr, Xe, n = 1, 2, 3, 4) complexes for each Ng. DFT calculations show that successively higher Ng complexes are responsible for the observed frequency progressions. This work provides the first evidence for noble gas-actinide complexes, and the first example of neutral complexes with four noble gas atoms bonded to one metal center.

Journal Article↗
PubMed2005

Stabilities of the C-H...O bonded complexes of the haloforms HCClnF3-n (n = 0-3) with dimethyl ether, oxirane, and acetone: an experimental and theoretical study.

Complexation enthalpies of the complexes of the haloforms HCCl(n)F(3-)(n) (n = 0-3) with dimethyl ether, oxirane, and acetone have been determined in liquid krypton and/or liquid argon using infrared spectroscopy. The same quantities were derived starting from ab initio complexation energies, calculated at the MP2=FULL/aug-cc-VTZ level, and by correcting these energies for thermodynamic and solvent contributions. The two sets of data are compared and discussed.

Acetone↗
PubMed2005

Intermolecular vibrations of the water trimer, a matrix isolation study.

Infrared spectra from 25 to 4000 cm(-1) have been recorded of water (H2O, D2O and H218O) matrix isolated in neon, argon, and krypton matrices. Intermolecular absorption bands of different isotopologues of the water trimer and tetramer have been assigned from concentration dependencies and diffusion behavior, using the well-known mid-infrared trimer and tetramer absorption bands as measures of the trimer and tetramer concentrations. The results are compared to ab initio calculations.

Journal Article↗
PubMed2006

Photodissociation of formyl fluoride in rare gas matrixes.

Photodissociation of formyl fluoride (HCOF) is studied in Ar, Kr, and Xe matrixes at 248 and 193 nm excitation by following spectral changes in the infrared absorption spectra. In all matrixes, the main photodissociation products are CO/HF species, including CO-HF and OC-HF complexes and thermally unstable CO/HF species (a distorted CO/HF complex or a reaction intermediate), which indicate negligible cage exit of atoms produced via the C-F and C-H bond cleavage channels. However, the observation of traces of H, F, CO, CO(2), F(2)CO, FCO, and HRg(2)(+) (Rg = Kr or Xe) in Kr and Xe matrixes would imply some importance of other reaction channels too. The analysis of the decay curves of the precursor shows that dissociation efficiency of HCOF increases as Ar < Kr < Xe, the difference being the factor of 10 between Ar and Xe. Moreover, HCOF dissociates 20-50 times faster at 193 nm compared to 248 nm. Interestingly, whereas the CO/HF species are stable with respect to photolysis in Ar, they photobleach in Kr and Xe matrixes at 248 and 193 nm, even though the first excited states of CO and HF are not energetically accessible with 193 and 248 nm photons. In krypton matrix, the photodissociation of CO/HF species at 248 nm is observed to be a single photon process. Quantum chemical calculations of electronic excitation energies of CO-HF and OC-HF complexes show that the electronic states of HF and CO mostly retain their diatomic nature in the pair. This clearly demonstrates that photodissociation of CO/HF complexes is promoted by the surrounding rare gas lattice.

Journal Article↗
PubMed2006

Structure and matrix isolation infrared spectrum of formyl fluoride dimer: blue-shift of the C-H stretching frequency.

Infrared spectroscopy (IR) of formyl fluoride (HCOF) dimer is studied in low-temperature argon and krypton matrixes. New IR absorptions, ca. 17 cm(-1) blue shifted from the monomer C-H stretching fundamental, are assigned to the HCOF dimer. The MP2/6-311++G calculations were utilized to define structures and harmonic frequencies of various HCOF dimers. Among the four optimized structures, the dimer having two C-H...O hydrogen bonds possesses strongest intermolecular bonding. The calculated harmonic frequencies of this dimer structure are shifted from the monomer similarly as observed in the experiment. Thus, we suggest that the experimentally observed blue shifted C-H bands belong to the dimer with two C-H...O hydrogen bonds. This observation includes the HCOF dimer to the class of hydrogen bonded complexes showing blue shift in their vibrational energies.

Computer Simulation↗
PubMed2006

Infrared spectra of the complexes of trifluoroethene with dimethyl ether, acetone, and oxirane: a cryosolution study.

Infrared spectra of solutions of trifluoroethene and dimethyl ether, acetone, or oxirane in liquid krypton and liquid argon have been studied. For each Lewis base the formation of a 1:1 complex with the Lewis acid was observed. The C-H stretching of trifluoroethene being perturbed by a strong Fermi resonance, the complexes with trifuloroethene-d were also investigated and showed that in each case the hydrogen bond between the acid and base is of the traditional, red-shifting type. The structures of the complexes were investigated using ab initio calculations. These indicate that with dimethyl ether and acetone two different isomeres can be formed, but with a single one detected in the solution in each case. The Fermi resonance in the complex with unlabeled trifluoroethene is discussed using data derived form ab initio potential and dipole hypersurface calculations. The complexation enthalpies of the complexes were obtained from temperature dependent studies of the solutions and are discussed in relation to the ab initio complexation energies and Monte Carlo free energy perturbation calculations of solvent effects.

Journal Article↗
PubMed1999

When and how to do a grid laser for diabetic macular edema.

Macular edema is a common feature of posterior segment diseases. It is an expression of abnormal permeability in either retinal vessels (inner blood-retinal barrier) or in the retinal pigment epithelium (outer blood-retinal barrier). It occurs in either a diffuse pattern where the macula appears generally thickened or, in more severe cases, as cystoid edema with the typical petaloid appearance. Grid laser treatment may be useful to reduce macular edema. Spots of 100-250 micrometers in diameter are applied to the whole posterior pole, one to two groups apart. The foveal avascular zone remains untouched. In patients treated bilaterally, areas temporal and nasal to the macula must be spared to prevent the development of deep scotomas. The mechanism yielding positive results with the grid technique is still debated. Among the most reliable hypotheses are: Proliferation of pigment epithelial cells, followed by and improved efficiency of the outer blood-retinal barrier; proliferation of endothelial cells in retinal capillaries followed by an improved efficiency of the inner blood-retinal barrier; improvement of the retinochoroidal exchanges, and finally, release by coagulative necrosis of a factor able to improve the efficiency of the blood-retinal barriers. Lasers with long wavelengths, such as krypton red and diode, are the most appropriate ones to perform grid treatment.

Blood-Retinal Barrier↗
PubMed1999

Differences in crystallization behavior between quenched and ground amorphous ursodeoxycholic acid.

PURPOSE: To study the crystallization of ground and quenched ursodeoxycholic acid (UDCA) and to characterize their amorphous states. METHODS: Amorphous UDCA was prepared by grinding and also by rapid cooling of the melt. These samples were characterized by powder X-ray diffraction (XRD), near IR spectra and dynamic water sorption. The heat associated with crystallization was measured in an isothermal microcalorimeter at 25 degrees C at various relative humidities (RH) (50%-100%) and, in the presence of the vapour from a mixed solvent of ethanol and water (ethanol conc. 10%-100%). The specific surface area was calculated from krypton adsorption. Contact angles were measured by using a Wilhelmy plate to calculate the surface energy of the samples. RESULTS: Ground and quenched samples yielded amorphous XRD patterns. Differential scanning calorimetry thermographs of the milled sample revealed that crystallization occurred at around 80 degrees C, whereas the quenched sample did not crystallize. Exposure to humid air did not result in crystallization of either amorphous sample during the microcalorimetric experiments. In the presence of ethanol vapour, the ground sample did, but the quenched sample did not, crystallize. The amount of water sorption into the quenched sample was larger than that of the ground sample at low RH. The surface energy of the quenched material was different to that of the ground. Peak shifts were observed in the NIR spectra at around 1450, 2100 nm, allowing differentiation between the ground and quenched samples. CONCLUSIONS: It can be concluded that different molecular states of amorphous UDCA were obtained depending on the preparation method. The crystallisation of amorphous UDCA was related to the molecular state of disorder.

Crystallization↗
PubMed2003

Microcalorimetric measurement of the interactions between water vapor and amorphous pharmaceutical solids.

PURPOSE: Use a microcalorimetric technique to measure the interactions between water vapor and amorphous pharmaceutical solids and describe the relationship between long-term physical stability and the storage relative humidity (RH) at constant temperature. METHODS: A thermal activity monitor was used to characterize interactions of water vapor with spray-dried amorphous sucrose, lactose, raffinose, and sodium indomethacin. Differential scanning calorimetry was used to measure glass transition temperature, Tg. X-ray powder diffraction was used to confirm that the spray-dried samples were amorphous. Scanning electron microscopy was used to examine particle morphology. Specific surface area was determined by BET analysis of nitrogen and krypton adsorption isotherms. RESULTS: The moisture-induced thermal activity traces (MITATs) of the materials in this study exhibit general behavior that helps explain the effect of moisture content on the physical stability of the glassy phase at a given storage temperature. At some RH threshold, RHm, the MITAT exhibits a dramatic increase in the energy of interaction between water vapor and the glass that cannot be explained by a phase or morphology change. Calorimetric data indicate that water vapor-solid interactions are reversible below RHm; above RHm, energetic hysteresis is observed and water-water interactions predominate. In addition, the MITAT was deconvoluted into sorptive and nonsorptive components, making it possible to assign the observed heat flow to unique thermal events. Samples stored at a RH just below RHm for more than 2 months show no evidence of morphology or phase change. In addition, the MITAT can be deconvoluted into sorptive and nonsorptive components by using a twin-calorimeter arrangement. This analysis provides specificity to the microcalorimetric analysis and helps explain the nature of the physical changes that occur during the hydration glassy phase. CONCLUSIONS: The MITAT is a useful tool to determine the onset of moisture-induced physical instability of glassy pharmaceuticals and may find a broad application to determine appropriate storage conditions to ensure long-term physical stability.

Calorimetry↗
PubMed2001

A pilot study of ICG-guided laser photocoagulation for occult choroidal neovascularization presenting as a focal spot in age-related macular degeneration.

PURPOSE: To evaluate the effect of indocyanine green angiography (ICG)-guided laser photocoagulation in eyes with age-related macular degeneration (AMD) and occult choroidal neovascularization (O-CNV), appearing as a well-defined focal spot on ICG. METHODS: Eyes with extrafoveal or juxtafoveal focal spot on ICG, either without PED (Group A) or with PED (Group B) at baseline, were selected. The hyperfluorescent area was photocoagulated by krypton red laser within 24 hours from diagnosis on ICG guide. At 1, 3, 6, 9 and 12 months from treatment, all eyes underwent clinical examination, FA and ICG. Parameters as best corrected visual acuity (BCVA), CNV closure and recurrence onset were analyzed. RESULTS: 53 eyes were enrolled in Group A and 33 in Group B. After 1 year from treatment, a stabilized (+/-1 Snellen line) or improved (2 or more Snellen lines) visual acuity was measured in 37 eyes (43%), 32 in Group A and 5 in Group B. After 1 year, a complete resolution of exudative signs was achieved with one or more laser sessions in 41 eyes (48%), 34 in Group A and 7 in Group B. After 1 year, 50 eyes (58%) had one or more episodes of recurrent CNV, appearing in 51% of eyes of Group A and in 70% of eyes of Group B. Most of the recurrences (86%) occurred during the first trimester after photocoagulation. CONCLUSIONS: ICG-guided laser photocoagulation for O-CNV appearing as a focal spot produced encouraging anatomical and functional outcome in eyes without PED at presentation. When focal CNV is associated with a PED, our treatment technique produced disappointing results.

Aged↗
PubMed1995

Alteration of volatile inventories by polar clathrate formation on Mars.

Recent models of chaotic variation in the Martian obliquity suggest that CO2 could be released during times of high obliquity and then recaptured in the polar caps as ice or clathrate during times of lower obliquity (Jakosky, et al., 1995). A natural implication of clathrate trapping is that other species in the Martian atmosphere, including noble gases, must incorporate in the water ice structure as well, in varying amounts according to the size and polarizability of the molecules as well as their atmospheric abundances. For nominal estimates of cap volume and amount of incorporated CO2 , we find that the current atmospheric inventory of noble gases is not representative of the bulk inventory in the Martian surface-atmosphere system. In particular, xenon and krypton are underrepresented in the present atmosphere. Models of source regions for Martian volatiles, which are constrained by noble gas abundances, must be modified to take these fractionation effects into account if indeed evidence for large amounts of polar clathrates is found.

Atmosphere↗
PubMed2000

Hyperfluorescence associated with serous retinal pigment epithelial detachment on indocyanine green angiography.

PURPOSE: Indocyanine green angiography has been reported to improve detection and delineation of occult choroidal neovascularisation in serous pigment epithelium detachment in age-related macular degeneration. The study aims to evaluate the visual acuity results of eyes affected by serous pigment epithelium detachment in age-related macular degeneration, having had indocyanine green-directed laser photocoagulation, and to correlate them to the pattern of serous pigment epithelium detachment on indocyanine green angiography. METHODS: Thirty-four eyes of 31 patients affected by serous pigment epithelium detachment in age-related macular degeneration were prospectively considered. Each patient underwent an ophthalmological examination including fluorescein and indocyanine green angiography one day before, and 6 weeks, 3 months, 6 months, 9 months, 12 months and 24 months after krypton-laser treatment. The serous pigment epithelium detachment was classified in the late-phases angiograms as either hypofluorescent, isofluorescent or hyperfluorescent comparing the fluorescence of the serous pigment epithelium detachment with the choroidal background fluorescence. RESULTS: The indocyanine green-guided laser treatment was associated with a temporary stabilization and a long-term progressive reduction of visual acuity: after 24 months visual acuity improved in 2.9%, stabilized in 26.5% and worsened in 70.5% of cases. Serous pigment epithelium detachment presenting a pretreatment hyperfluorescence had a final visual acuity of 0.06, with subfoveal choroidal neovascularisation development in 100% of cases, whereas serous pigment epithelium detachment presenting a pretreatment hypofluorescence and isofluorescence showed a final visual acuity of 0.12, with subfoveal choroidal neovascularisation development in 43.5% of eyes, with statistically significant difference. CONCLUSION: Overall visual acuity decreases with time after indocyanine green-guided laser treatment of choroidal neovascularisation in serous pigment epithelium detachment, and serous pigment epithelium detachment becoming hyperfluorescent in the late-phases of indocyanine green angiography has the worst functional outcome.

Aged↗
PubMedDate not supplied

Chernobyl radionuclides in a Black Sea sediment trap.

The Chernobyl nuclear power station accident released large quantities of vaporized radionuclides, and, to a lesser extent, mechanically released small (less than 1-10 micron) aerosol particles. The total release of radioactivity is estimated to be out of the order of 1-2 x 10(18) Bq (3-5 x 10(7) Ci) not allowing for releases of the xenon and krypton gases. The 137Cs releases of 3.8 x 10(16) Bq from Chernobyl can be compared to 1.3 x 10(18) Bq 137Cs released due to atmospheric nuclear weapons testing. Chernobyl-derived radionuclides can be used as transient tracers to study physical and biogeochemical processes. Initial measurements of fallout Chernobyl radionuclides from a time-series sediment trap at 1,071 m during June-September 1986 in the southern Black Sea are presented. The specific activities of 137Cs, 144Ce and 106Ru in the trap samples (0.5-2, 4-12 and 6-13 Bq g-1) are independent of the particle flux while their relative activities reflect their rates of scavenging in the order Ce greater than Ru greater than Cs.

Accidents↗
PubMed1999

A low-temperature origin for the planetesimals that formed Jupiter.

The four giant planets in the Solar System have abundances of 'metals' (elements heavier than helium), relative to hydrogen, that are much higher than observed in the Sun. In order to explain this, all models for the formation of these planets rely on an influx of solid planetesimals. It is generally assumed that these planetesimals were similar, if not identical, to the comets from the Oort cloud that we see today. Comets that formed in the region of the giant planets should not have contained much neon, argon and nitrogen, because the temperatures were too high for these volatile gases to be trapped effectively in ice. This means that the abundances of those elements on the giant planets should be approximately solar. Here we show that argon, krypton and xenon in Jupiter's atmosphere are enriched to the same extent as the other heavy elements, which suggests that the planetesimals carrying these elements must have formed at temperatures lower than predicted by present models of giant-planet formation.

Cold Temperature↗
PubMed1981

CO2 responses of the cerebral circulation during drug-induced hypotension in the cat.

Concern has often been expressed that hypocapnia produced by controlled hyperventilation might further reduce cerebral perfusion during drug-induced hypotension. In the present studies, hypotension was induced in cats with either practolol/trimetaphan (five experiments) or practolol/nitroprusside (five experiments) together with controlled haemorrhage. Arterial PCO2 was altered between 17 and 51 mm Hg by varying inspired CO2 during constant-volume ventilation, first during control conditions of light halothane/nitrous oxide anaesthesia and then during hypotension to mean blood pressure of 36-37 mm Hg. Cerebral cortical perfusion was measured by the krypton clearance technique and pial artery diameter by the image-splitting method. Cerebral cortical blood flow did not alter with PaCO2 changes during trimetaphan hypotension, but some responsiveness to CO2 persisted during nitroprusside hypotension, though at less than half control levels. No changes in pial artery diameter were seen with CO2 during hypotension under either technique. It is postulated that CO2 responsiveness persisted with nitroprusside because cerebral blood flow (CBF) values were higher when hypotension was produced with this drug, as compared with trimetaphan. It would appear that hypocapnia does not further reduce CBF during trimetaphan hypotension but does do so with nitroprusside. However, the combination of hypocapnia and nitroprusside hypotension did not in any instance lower CBF below the values found during trimetaphan hypotension.

Animals↗