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PubMed2006

Estimating the hydration enthalpies of neutral alkali metal atoms.

Using existing data on the ionization energies of alkali metal atoms in small clusters of water, a thermodynamic cycle is proposed from which the hydration enthalpies of the neutral metal atoms can be estimated. Where comparisons are possible, the results are in reasonable agreement with those obtained using both experimental and ab initio methods. Application of the thermodynamic cycle to neutral alkali metal atoms solvated in ammonia yields solvation enthalpies that are significantly lower than those obtained for water.

Letter↗
PubMed2006

Structural analysis of an alkali-extractable polysaccharide from the seeds of Retama raetamssp. gussonei.

An alkali-extractable polysaccharide (1) was isolated from the seeds of Retama raetam ssp. gussonei. Its composition and linkage determination have been investigated using component analysis, methylation analysis, hydrolysis studies, and NMR spectroscopic analysis. This was shown to contain d-xylose, d-glucose, and 4-O-methyl-d-glucuronic acid in a molar ratio of 7:2:1 and consisted of a backbone of beta-(1-->4)-linked d-xylopyranosyl residues, having branches of alpha-d-glucopyranosyl residues that contain (1-->2)-linkages and 4-O-methyl-alpha-d-glucopyranosyluronic acid at O-2. This is the first report on the isolation of an alkali-extractable polysaccharide from this plant.

Endo-1,4-beta Xylanases↗
PubMed2005

Therapeutic effects of adenoviral gene transfer of bone morphogenic protein-7 on a corneal alkali injury model in mice.

An alkali burn in the cornea is a common serious clinical problem often leading to permanent visual impairment. Since transforming growth factor-beta (TGF-beta) is involved in the response to corneal injury, we evaluated the therapeutic effects of adenoviral gene transfer of mouse bone morphogenic protein-7 (BMP-7), which has antagonistic effects on TGF-beta in tissue fibrosis. Burned cornea did not express endogenous BMP-7 mRNA and protein. Resurfacing of the burned cornea by invading conjunctival epithelium was accelerated by adenoviral introduction of BMP-7. Exogenous BMP-7 expression also suppressed myofibroblast generation, appearance of monocytes/macrophages and expression of MCP-1, TGF-betas, and collagen I alpha2 chain in the affected stroma. Ectopic BMP-7 did not suppress stromal neovascularization throughout the interval studied and also did not reduce VEGF mRNA expression at Day 10. Ectopic BMP-7 in burned corneal tissue resulted in activation of Smad1/5/8 signaling and partial suppression of the phospho-Smad2 signal. These data suggest that overexpression of BMP-7 is an effective strategy for treatment of ocular alkali burns.

Adenoviridae↗
PubMed2001

Evaluation of column temperature as a means to alter selectivity in the cation exchange separation of alkali metals, alkaline earth metals and amines.

The merits of varying column temperature in a cation exchange separation of alkali metals, alkaline earth metals and amines are considered. Increasing the column temperature (up to 60 degrees C) reduced the retention of all cations, but by varying extents. Consequently, selectivity changes were seen, with reversals in elution order in some cases. To ascertain when temperature is most useful as a separation aid, analytes were classed into three groups according to their temperature behaviour: alkali metals; alkaline earth metals; and amines. Adjusting the column temperature caused selectivity changes between analytes in different groups, but no selectivity changes occurred between analytes in the same group. Further, temperature was compared to the addition of modest amounts of acetonitrile as another means to alter selectivity. The benefits of elevated temperature were not just limited to selectivity changes. Improvements in the efficiencies of all analytes were noted at 60 degrees C. This was especially true for the amines which are severely tailed at ambient temperatures.

Journal Article↗
PubMed2004

Iron-catalysed propylene epoxidation by nitrous oxide: dramatic shift of allylic oxidation to epoxidation by the modification with alkali metal salts.

A dramatic shift of allylic oxidation to epoxidation has been observed during the oxidation of propylene by N(2)O when the FeO(x)/SBA-15 catalyst is modified with alkali metal salts, and the roles of alkali metal salts are to suppress the reactivity of lattice oxygen and to induce an iron coordination structure effective for epoxidation with N(2)O.

Journal Article↗
PubMed2004

Heavier alkali metal complexes of 2-phenylamidopyridine: an X-ray crystallographic and theoretical study of a structurally diverse series of crown ether adducts.

Complexes of the anion of the secondary amine 2-phenylaminopyridine (LH) with the heavier alkali metals Na-Cs have been prepared in the presence of various macrocyclic polyether crowns [12-crown-4 (12C4), 15-crown-5 (15C5), and 18-crown-6 (18C6)], which coordinate to the metal ions in all cases. Depending on the combination of alkali metal and crown, the products include separated ion pairs [(crown)(2)M](+)L(-)(12C4/Na, 15C5/K, 15C5/Rb, 15C5/Cs) and contact-ion-pair neutral molecules [(crown)ML](15C5/Na, 18C6/Na, 18C6/K, 18C6/Rb) in which L(-) acts as a bidentate ligand. [((12C4)KL)(2)] is a dimer in which the amido and pyridine N atoms of two ligands bridge the metal ions, while [((18C6)KL(2)K)([infinity])] is a chain polymer with crown O and pyridyl N atoms acting as bridges in corner-sharing KOKN four-membered rings and may be regarded as a potassium potassate complex. [((18C6)Cs(2)L(2))([infinity])] is also polymeric, with a basic arrangement like that of [((12C4)KL)(2)], but with each 18C6 ligand mu-kappa6:kappa6 to two metal centres, generating the polymer. Although most of the [(crown)(2)M](+) sandwich cations have essentially parallel crown ligands, [(12C4)(2)Rb](+) is markedly bent, both in the complex incorporating THF as an additional ligand and in the THF-free complex, where two of these cations form a centrosymmetric dimer through two bridging oxygen atoms; DFT calculations indicate that the bending is inherent, thus enabling the coordination by an extra oxygen atom rather than being a consequence of this coordination. Attempts to isolate the caesium 12C4 derivative were unsuccessful. The compounds have been characterized by NMR spectroscopy, CHN microanalysis and, in most cases, X-ray crystallography.

Journal Article↗
PubMed2004

Reaction of the silylene Si[(NCH2But)2C6H4-1,2] with the alkali metal silylamides M[N(SiMe3)R](M = Li, Na or K; R = SiMe3 or SiMe2Ph).

The thermally stable silylene Si[(NCH(2)Bu(t))(2)C(6)H(4)-1,2] 1 undergoes oxidative addition reactions with the alkali metal silylamides MN(SiMe(3))(2)(M = Li, Na or K) to afford the new alkali metal amides MN(SiMe(3))[(1)SiMe(3)][M = Li (2), Na (3) or K (4)]. Reaction of two equivalents of 1 with LiN(R)(SiMe(3)) leads in a two-step process to the compound LiN[(1)R][(1)SiMe(3)][R = SiMe(2)Ph (5) or SiMe(3) (6)]. Alternatively, 1 reacts with 3 to afford NaN[(1)SiMe(3)](2) (7). The structures of 2-5 and are presented and the formation of 2-7 is discussed.

Journal Article↗
PubMed1969

The action of a bacterial agarase on agarose, porphyran and alkali-treated porphyran.

1. A purified extracellular agarase from a Cytophaga species was used to hydrolyse agarose, porphyran and alkali-treated porphyran. 2. The hydrolysate from agarose was separated by gel filtration into the series of neoagarosaccharides, the predominant member of which was the tetrasaccharide. 3. Enzyme action on alkali-treated porphyran gave neoagarosaccharides and other oligosaccharides containing 6-O-methyl-d-galactose units. From the composition of these oligosaccharides it is deduced that action of the enzyme on a d-galactosidic linkage is four to five times faster than on the 6-O-methyl-d-galactosidic linkage. 4. Enzyme action on native porphyran gives a similar series of oligosaccharides but in smaller yield, much of the polysaccharide being either not degraded or only degraded to a series of large, highly sulphated oligosaccharides. 5. For porphyran, it is concluded that 6-O-methyl ether groups are distributed randomly on half the d-galactose units, but that the 6-sulphate groups on l-galactose units tend to occur in blocks.

Chromatography, Gel↗
PubMed1971

Further studies on the glycerol teichoic acid of walls of Staphylococcus lactis I3. Location of the phosphodiester groups and their susceptibility to hydrolysis with alkali.

1. The teichoic acid from walls of Staphylococcus lactis I3 is readily degraded in dilute alkali. 2. Degradation proceeds by selective hydrolysis of that phosphodiester group attached to an alcoholic hydroxyl group of the N-acetylglucosamine and gives a repeating unit in high yield. 3. Further studies on a different repeating unit isolated by partial acid hydrolysis have shown that the glycerol diphosphate is attached to the 4-hydroxyl group of the N-acetylglucosamine and not to the 3-hydroxyl group as was proposed earlier. 4. The susceptibility towards hydrolysis by alkali of other structural types of teichoic acid has been examined and found to vary markedly according to their structure.

Biodegradation, Environmental↗
PubMed1985

The borohydride-reducible compounds of human aortic elastin. Demonstration of a new cyclic amino acid in alkali hydrolysate, and changes with age and in patients with annulo-aortic ectasia including one with Marfan syndrome.

Human aortic elastin reduced with [3H]borohydride was analysed by ion-exchange chromatography after alkali or acid hydrolysis. Alkali hydrolysates of elastins contained a radioactive peak that was eluted between proline and leucine. This peak was not present in foetal elastin, but its proportion increased steadily during aging. Aortic samples from patients with annulo-aortic ectasia (aneurysm of the ascending aorta), including one with classical Marfan syndrome, contained less elastin (CNBr-insoluble material) than did the age-matched controls. The proportion of radioactivity in the new peak of all these aortas was low when compared with age-matched controls. Gas-chromatographic/mass-spectrometric analysis suggested that it contained a cyclic derivative of a hydrated aldol-condensation product. The concentration of the cross-link precursors, lysine aldehyde and aldol-condensation product (estimated from the acid-hydrolysis product 6-chloronorleucine and the acid-degradation product of reduced aldol-condensation product) was high in very young aortas but remained quite stable after childhood. No differences were observed in cross-link profiles of acid hydrolysates between pathological and control aortas. A low proportion of radioactivity in the new peak may indicate the presence of young or immature elastin in the pathological aortas.

Adult↗
PubMed2001

The in vitro performance of carbon dioxide absorbents with and without strong alkali apparatus.

We report the in vitro longevity of a conventional soda lime carbon dioxide absorbent and an absorbent free from strong alkali (Amsorb). Although the times taken to breakthrough of carbon dioxide (> 0.5%) within an in vitro low flow breathing system were shorter with the alkali-free absorbent, we found that the size and shape of the absorbent container was the major factor in determining the efficiency of the carbon dioxide absorbents.

Absorption↗
PubMed2005

[Significance of immediate affixation of a hard contact lens in the emergency treatment of severe alkali burns of the cornea (case report)].

BACKGROUND: Severe alkali burns lead to massive limbal stem cell damage resulting in persistent epithelial defects, infiltration and stromal melting early in the disease process. A glued-on hard contact lens may serve as an "artificial epithelium" and protect the cornea from these complications. CASE REPORT: A 39-year-old male presented with severe lime burns in both eyes one week after injury. The right eye showed a totally denuded cornea and conjunctiva with circular paralimbic ischemia. In the left eye "only" two thirds of the cornea and adjacent conjunctiva and limbus were affected with less ischemia. Amniotic membrane transplantation was performed in both eyes but failed after four days already in the right eye. A hard contact lens was therefore glued on the right eye and allowed for visual acuity of 0.4 without correction in this primarily most heavily afflicted eye for 12 months duration. After removal of the contact lens, reepithelisation was quick, and function remained stable with addition of autologous serum eye drops. The primarily far less injured left eye, however, for which the amniotic membrane surgery was primarily judged to be adequate, could not be stabilised. The cornea perforated 4 weeks later necessitating a mini-keratoplasty plus a glued-on contact lens, and correctable vision never became better than 1/35. CONCLUSION: The clinical course confirms former observations that a glued-on hard contact lens is an effective treatment early after alkali burn and prevents the cornea from infiltration and melting. Moreover, two aspects merit consideration: first, with proper technique and timing of the gluing-on a patient may retain useful vision throughout the period of wearing the contact lens; second, for the long period during which the cornea was sealed by the contact lens, improper repopulation by conjunctival epithelium was inhibited, and proper corneal epithelium was given a chance for repopulation after recovery of the limbal area resulting in a stable surface and useful vision without additional keratoplasty measures.

Adult↗
PubMed2004

Calculations of long-range potential wells for highly excited homonuclear and heteronuclear alkali dimers.

The weakly bound long-range potential curves between a highly excited alkali atom M(*)(n(e)s) and a ground state alkali atom M(n(g)s) are calculated using simple but reasonably accurate models for long-range dispersion and exchange interactions for all homonuclear and heteronuclear combinations. For K(2), where experimental results are available, the agreement is quite good (binding energies of observed vibrational levels within approximately 10%). We find that at least a zero-point vibrational level occurs for n(e)-n(g)</=12.

Journal Article↗
PubMed2004

Relaxation time scales in collective dynamics of liquid alkali metals.

In this paper the investigation of the dynamical processes of liquid alkali metals is executed by analyzing the time scales of relaxation processes in liquids. The obtained theoretical dynamic structure factor S(k,omega) for the case of liquid lithium is found to be in excellent agreement with the recently received inelastic x-ray scattering data. The comparison and interrelation with other theories are given here. Finally, an important part of this paper is the confirmation of the scale uniformity of the dynamic processes in liquid alkali metals predicted by some previous molecular dynamic simulation studies.

Journal Article↗
PubMed2005

Electronic effect on protonated hydrogen-bonded imidazole trimer and corresponding derivatives cationized by alkali metals (Li(+), Na(+), and K(+)).

The electronic effects on the protonated hydrogen-bonded imidazole trimer (Im)(3)H(+) and the derivatives cationized by alkali metals (Li(+), Na(+), and K(+)) are investigated using B3LYP method in conjunction with the 6-311+G( *) basis set. The prominent characteristics of (Im)(3)H(+) on reduction are the backflow of the transferred proton to its original fragment and the remoteness of the H atom from the attached side bare N atom. The proton transfer occurs on both reduction and oxidation for the corresponding hydrogen-bonded imidazole trimer. For the derivatives cationized by Li(+), (Im)(3)Li(+), the backflow of the transferred proton occurs on reduction. The electron detachment from respective highest occupied molecular orbital of (Im)(3)Na(+) and (Im)(3)K(+) causes the proton transferring from the fragment attached by the alkali metal cation to the middle one. The order of the adiabatic ionization potentials of (Im)(3)M(+) is (Im)(3)H(+)>(Im)(3)Li(+)>(Im)(3)Na(+)>(Im)(3)K(+); the order of (Im)(3)M indicates that (Im)(3)H is the easicst complex to be ionized. The polarity of (Im)(3)M(+) (M denotes H, Li, Na, and K) increases on both oxidation and reduction. The (Im)(3)M(+) complexes dissociate into (Im)(3) and M(+) except (Im)(3)H(+), which dissociates preferably into (Im)(3) (+) and H atom, while the neutral complexes [(Im)(3)M] dissociate into (Im)(3) and M. The stabilization energy of (Im)(3)Li(2+), (Im)(3)Na(2+), and (Im)(3)K(2+) indicate that their energies are higher as compared to those of the monomers.

Journal Article↗
PubMed2005

Monte Carlo simulations of hydrogen adsorption in alkali-doped single-walled carbon nanotubes.

Monte Carlo simulations and Widom's test particle insertion method have been used to calculate the solubility coefficients (S) and the adsorption equilibrium constants (K) in single-walled (10,10) armchair carbon nanotubes including single nanotubes, and nanotube bundles with various configurations with and without alkali dopants. The hydrogen adsorption isotherms at room temperature were predicted by following the Langmuir adsorption model using the calculated constants S and K. The simulation results were in good agreement with experimental data as well as the grand canonical Monte Carlo simulation results reported in the literature. The simulations of nanotube bundle configurations suggest that the gravimetric hydrogen adsorption increases with internanotube gap size. It may be attributed to favorable hydrogen-nanotube interactions outside the nanotubes. The effect of alkali doping on hydrogen adsorption was studied by incorporating K+ or Li+ ions into nanotube arrays using a Monte Carlo simulation. The results on hydrogen adsorption isotherms indicate hydrogen adsorption of 3.95 wt% for K-doping, and 4.21 wt% for Li-doping, in reasonable agreement with the experimental results obtained at 100 atm and room temperature.

Journal Article↗