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PubMed2005

On the vibrational spectra and structural parameters of methyl, silyl, and germyl azide from theoretical predictions and experimental data.

The infrared and Raman spectra of methyl, silyl, and germyl azide (XN3 where X=CH3, SiH3 and GeH3) have been predicted from ab initio calculations with full electron correlation by second order perturbation theory (MP2) and hybrid density function theory (DFT) by the B3LYP method with a variety of basis sets. These predicted data are compared to previously reported experimental data and complete vibrational assignments are provided for all three molecules. It is shown that several of the assignments recently proposed [J. Mol. Struct. (Theochem.) 434 (1998) 1] for methyl azide are not correct. Structural parameters for CH3N3 and GeH3N3 have been obtained by combining the previously reported microwave rotational constants with the ab initio MP2/6-311+G(d,p) predicted values. These "adjusted r0" parameters have very small uncertainties of +/-0.003 A for the XH distances and a maximum of +/-0.005 A for the heavy atom distances and +/-0.5 degrees for the angles. The predicted distance for the terminal NN bond which is nearly a triple bond is much better predicted by the B3LYP calculations, whereas the fundamental frequencies are better predicted by the scaled ab initio calculations. The results are discussed and compared to those obtained for some similar molecules.

Azides↗

PubMed2005

Crystal field analysis of energy level structure of LiAlO2:V3+ and LiGaO2:V3+.

A detailed analysis of the energy level structure of tetrahedrally coordinated V(3+) ion in lithium aluminum oxide LiAlO(2) (gamma-phase) and lithium dioxogallate LiGaO(2) is performed using the exchange charge model of the crystal field theory. The parameters of the crystal field acting on the V(3+) optical electrons are calculated from crystal structure data assuming C(1) point symmetry of the [VO(4)](5-) impurity center in LiAlO(2) and LiGaO(2). Crystal field splitting of all five LS terms of the V(3+) ion ((3)F, (3)P, (1)S, (1)D, (1)G) is calculated. The energy levels obtained are compared with experimental absorption spectra and results of application of other crystal field models (the angular overlap model and Racah theory) to the considered crystals; though only one fitting parameter of the exchange charge model was used, a good agreement with experimental data on the ground and excited state absorption is demonstrated.

Aluminum Oxide↗

PubMed2005

Infrared (attenuated total reflection) study of propylene carbonate solutions containing lithium and sodium perchlorate.

Attenuated total reflection infrared spectroscopy was used to examine the concentration dependent solvation of LiClO4 and NaClO4 electrolytes in propylene carbonate (PC). Factor analysis and curve fitting techniques were performed on the measured spectra and the results compared with ab initio computations to provide evidence for ion-solvent solution geometries. Factor analysis of the measured data allowed the identification of the spectrum of ion-associated PC that is uniquely different from the self-associated PC spectrum. The results indicate Li+ and ClO4- ions are contact ion-paired even at relatively low electrolyte concentrations whereas Na+ and ClO4- ions are not, up to approximately 2 mol dm-3.

Cations↗

PubMed2006

Laser Raman and FTIR studies on Li+ interaction in PVAc-LiClO4 polymer electrolytes.

The polymer electrolytes composed of poly(vinyl acetate) (PVAc) with various stoichiometric ratios of lithium perchlorate (LiClO(4)) salt have been prepared by solution casting method. The techniques Fourier transform infra-red (FTIR) and Laser Raman spectroscopy have been used to monitor polymer-salt complex formation, ion-ion and ion-polymer interactions as a function of salt concentration. Significant changes in both Laser Raman and FTIR spectra are observed which reveals an interaction between ester oxygens with lithium cation coordination. These results strongly suggest the interaction of lithium cation and network polymer chains. When the salt content is increased, the intensity of the internal Raman modes of the ClO(4)(-) increases. The ClO(4)(-) stretching mode observed at 934 cm(-1) in Laser Raman shows some additional shoulder peaks with increase in salt concentration. This reveals the presence of free anions, ion contact pairs and higher order ionic clusters. From the FTIR and Laser Raman results the transport mechanism of ions in PVAc:LiClO(4) polymer electrolytes has been discussed.

Electrolytes↗

PubMed2006

Studies of EPR parameters for Mn5+ -doped Li3PO4 and Li3VO4 crystals.

The EPR parameters (zero-field splitting D and g factors g parallel, g perpendicular) of Mn5+ -doped Li3PO4 and Li3VO4 crystals are calculated from the complete high-order perturbation formulas based on a molecular orbital scheme for a 3d2 ion in tetragonal MX4 clusters. These formulas include not only the contribution coming from crystal-field excitations, but also that arising from charge-transfer excitations (which is discarded in crystal field theory). The calculated results are in reasonable agreement with the observed values. The contributions to EPR parameters coming from the charge-transfer excitations are comparable with those arising from the crystal-field excitations. It appears that for a high valence state 3dn ion in crystals, the reasonable explanations of EPR parameters should take the contributions due to both crystal-field and charge-transfer excitations into account.

Electron Spin Resonance Spectroscopy↗

PubMed2006

FTIR studies of PVC/PMMA blend based polymer electrolytes.

The polymer electrolytes composing of the blend of polyvinyl chloride-polymethyl methacrylate (PVC/PMMA) with lithium triflate (LiCF3SO3) as salt, ethylene carbonate (EC) and dibutyl phthalate (DBP) as plasticizers and silica (SiO2) as the composite filler were prepared. FTIR studies confirm the complexation between PVC/PMMA blends. The CCl stretching mode at 834 cm-1 for pure PVC is shifted to 847 cm-1 in PVC-PMMA-LiCF3SO3 system. This suggests that there is interaction between Cl in PVC with Li+ ion from LiCF3SO3. The band due to OCH3 at 1150 cm-1 for PVC-PMMA blend is shifted to 1168 cm-1 in PVC-PMMA-LiCF3SO3 system. This shift is expected to be due to the interaction between Li+ ion and the oxygen atom in PMMA. The symmetric vibration band and the asymmetric vibration band of LiCF3SO3 at 1033 and 1256 cm-1 shifted to 1075 and 1286 cm-1 in the DBP-EC plasticized PVC-PMMA-LiCF3SO3 complexes. The interaction between Li+ ions and SiO2 will lead to an increase in the number of free plasticizers (which does not interact with Li+ ions). When the silica content increases from 2% to 5%, the intensity of the peak at 896 cm-1 (due to the ring breathing vibration of free EC) increases in PVC-PMMA-LiCF3SO3-DBP-EC system.

Dibutyl Phthalate↗

PubMed2006

Defect models of the three trigonal Ti3+ centers in LiF:Ti3+ and LiF:Ti3+:Mg2+ crystals.

The EPR g factors of the trigonal Ti3+ center A in LiF:Ti3+ and two additional trigonal Ti3+ centers B and C in LiF:Ti3+:Mg2+ crystals are calculated from the third-order perturbation formulas based on the cluster approach. From the calculations and by considering the Ti3+ displacement along 111 axis obtained by ENDOR experiment, the defect models for the three Ti3+ centers are suggested. For center A, there are two possible models: (i) [Ti3+F3-O3(2-)] cluster and (ii) [Ti3+F6-] cluster with the Ti3+ off-center caused by a neighboring Li+ vacancy (VLi+) at <111> axis. The latter seems the more likely. The defect models of centers B and C are the [Ti3+F3-O(3)2-] clusters associated with a neighboring: Mg2+ ion at the Li+ site along 111 axis in the vicinity of three F- ions and three O2- ions, respectively. The reasonableness of these models is discussed.

Crystallization↗

PubMed2006

Synthesis and spectroscopic studies on iron(III) complexes of 1-benzotriazol-1-yl-1-[(p-X-phenyl)hydrazono]propan-2-one.

A new series of iron(III) complexes are synthesized from the reaction of the polyfunctional ligands 1-benzotriazol-1-yl-1-[p-X-phenyl]hydrazono]propan-2-one (X=H, Cl, NO(2), CH(3) or OCH(3) corresponding to HL(1),HL(2), HL(3), HL(4) or HL(5), respectively, with iron(III) chloride in the presence of LiOH by the conventional and microwave induced energy methods. The conventional method led to the formation of [FeL(3)].nH(2)O but the microwave induced energy gave [FeLCl(2)], n=1-3 and L is the anion of HL(1)-HL(5). The complexes are characterized by the elemental analysis, molar conductivity, magnetic and spectral (FT-IR, UV-vis and ESR) studies. The magnetic and spectral studies showed that [FeLCl(2)] are polymeric octahedral, [Fe(L(1))(3)].H(2)O is a low spin octahedral and (d(xz),d(yz))(4) (d(xy))(1) ground state, [FeL(3)].nH(2)O, L=anion of HL(4) or HL(5) and are octahedral with intermediate spin (S=32) with ground state (d(xy))(2)(d(xz),d(yz))(3) electronic configuration while for the anions of HL(2) and HL(3), they have (t(2g))(3)(e(g))(5) admixed with (d(xy))(2)(d(xz),d(yz))(3) configurations. From the ESR data, the contribution of the high spin (S=52) and low spin (S=32) to the quantum mechanical spin intermediate (QMS), and the crystal field parameters Delta and V are calculated and related to the electronic and steric effects of the ligands. The electronic spectral data confirm that obtained from the ESR, and the different ligand field parameters as well as the pi-->t(2g), t(2g)-->e(g), e(g)-->pi*, pi-->pi* transitions are estimated and compared with that experimentally obtained.

Carbon↗

PubMed2004

MAS-NMR at very high temperatures.

We report MAS-NMR experiments at temperatures of approx. 1200 K using a CO(2) laser as the heating device. An internal NMR thermometer based on the (7)Li T1 data of Li(0.24)La(0.54)TiO(3) is used for temperature calibration. Using this setup, temperatures as high as 1191 K could be reached under MAS conditions as confirmed by the melting of Li(2)B(4)O(7) at 1191 K which could be followed by (7)Li-MAS-NMR.

Hot Temperature↗

PubMed2006

The mechanism investigation in substitution of 21-bromo-3alpha-hydroxyl-3beta-methoxymethyl-5alpha-pregnan-20-one with nucleophiles.

A mechanistic study on the nucleophilic substitution of a strictly geometric 21-bromo-3alpha-hydroxyl-3beta-methoxymethyl-5alpha-pregnan-20-one was described. Reaction of the alpha-bromoketone with excess lithium imidazole followed by the addition of extra bases including n-butyllithium, methyllithium, lithium piperidine, and lithium pyrrolidine provided unexpected alpha-nucleophilic carbonyl adducts that derived from strong base. Data from HPLC and proton NMR suggested an epoxide as the intermediate. Two possible reaction pathways were proposed for the nucleophilic substitution reaction. One pathway is the normal SN2 substitution reaction, directly provided the imidazoly product without the formation of the unexpected alpha-substituted products. The other pathway went through an epoxide intermediate, in which imidazole anion or the strong bases added would attack from the less hindered site of the epoxide to give the substitution product.

Imidazoles↗

PubMed2005

Revisiting lithium-associated hyperparathyroidism in the era of intraoperative parathyroid hormone monitoring.

BACKGROUND: Chronic lithium therapy may cause hyperparathyroidism (HPT). The utility of intraoperative parathyroid hormone monitoring (IOPTH) in these patients is unknown. The authors' hypothesis was that multiglandular disease is more common in these patients, and the ability of IOPTH to predict cure may be limited. METHODS: Twelve patients had HPT during chronic lithium therapy and underwent parathyroidectomy with IOPTH. Criteria for curative resection were a decrease > or =50% from baseline and into the normal range. Calcium and PTH levels were measured during follow-up. RESULTS: Preoperatively, mean calcium was 11.0 +/- 0.1 mg/dL, and PTH was 116 +/- 14 pg/mL. Fifty percent of patients had multiglandular disease confirmed by IOPTH levels. Mean IOPTH decrease from baseline was 74 +/- 4%. Although 10 of 12 patients met criteria for curative resection, only 8 remain normocalcemic. The 2 patients who did not meet criteria remain normocalcemic. Mean postoperative calcium for all patients was 9.5 +/- 0.2 mg/dL. Of the 10 normocalcemic patients, 4 also have hyperparathormonemia (mean PTH, 119 +/- 19 pg/mL). CONCLUSIONS: The incidence of multiglandular disease in HPT after chronic lithium exposure is higher than standard HPT. The ability of IOPTH to predict durable normocalcemia is limited. Bilateral neck exploration should be considered for these patients regardless of whether IOPTH monitoring is used.

Adult↗

PubMed1993

Picosecond neodymium:yttrium lithium fluoride laser sclerectomy.

The picosecond neodymium:yttrium lithium fluoride laser, a high-power, short-pulse laser that uses low energy per pulse and has a high repetition rate and a highly coherent energy source of 1,053 nm, was used to perform sclerectomies by an ab externo approach in human cadaver eyes. We evaluated laser settings with regard to full-thickness scleral perforation and thermal damage to surrounding tissue. We studied energy per pulse, depth per burst (a present number of spots), spot and line separation of the pattern (spacing between spots of the laser in length [spot separation] and width [line separation]), and total energy required to perforate the sclera. Efficiency was determined by evaluating which settings required the fewest spots and least total energy to perforate the sclera. We studied histologic sections of the sclerectomy sites to determine thermal damage to the surrounding sclera. The picosecond neodymium:yttrium lithium fluoride laser is effective in performing full-thickness sclerectomy with minimal thermal damage to the surrounding tissue. The anterior chamber could be penetrated with an average total energy of 13.3 +/- 0.4 (SEM) J. The sclerectomy size was 545 +/- 11 microns externally and 163 +/- 4 microns internally. Successful sclerectomies were performed with as little as 3 to 5 microns of thermal damage to the surrounding scleral tissue with 250 microJ per pulse.

Cadaver↗

PubMed1989

Isolation and characterization of the 47 kDa protein and the D1-D2-cytochrome b-559 complex.

The 47 kDa polypeptide and a protein complex consisting of the D1 (32 kDa), D2 (34 kDa) and cytochrome b-559 (9 kDa) species were isolated from a Tris-washed Photosystem II core complex solubilized with dodecylmaltoside in the presence of LiClO4. Although the 43 kDa chlorophyll-binding protein is readily dissociated from the Photosystem II complex under our conditions, two cycles of exposure to high concentrations of detergent and LiClO4 were required for complete removal of the 47 kDa chlorophyll-binding protein from the D1-D2-cytochrome b-559 complex. Spectroscopic characterization of these two species revealed that the 47 kDa protein binds chlorophyll a, whereas the D1-D2-cytochrome b-559 complex shows an enrichment in Pheo a and heme on a chlorophyll basis. A spin-polarized EPR triplet can be observed at liquid helium temperatures in the D1-D2-cytochrome b-559 complex, but no such triplet is observed in the purified 47 kDa species. The zero-field splitting parameters of the P-680+ triplet indicate that the triplet spin is localized onto one chlorophyll molecule. Resonance Raman spectroscopy showed that: (i) beta-carotene is bound to the reaction center in its all-trans conformation; (ii) all chlorophyll a molecules are five-coordinate; and (iii) the C-9 keto group of one of the chlorine pigments is hydrogen-bonded. Our results support the proposal that the D1-D2 complex binds the P-680+ and Pheo a species that are involved in the primary charge separation.

Chlorophyll↗

PubMed1995

Spectroscopic studies of bacteriorhodopsin fragments dissolved in organic solution.

Fourier transform infrared and UV fourth-derivative spectroscopies were used to study the secondary structure of bacteriorhodopsin and its chymotryptic and one of the sodium borohydride fragments dissolved in chloroform-methanol (1:1, v/v), 0.1 M LiClO4. The C1 fragment (helices C, D, E, F, and G) showed an alpha-helical content of about 53%, whereas C2 (helices A and B) had about 60%, and B2 (helices F and G) about 65% alpha-helix. The infrared main band indicated differences in alpha-helical properties between these fragments. These techniques were also used to obtain information on the interactions among helices. According to the results obtained from the hydrogen/deuterium exchange kinetics, about 40% of the amide protons of C2 are particularly protected against exchange, whereas for the C1 fragment this process is unexpectedly fast. UV fourth-derivative spectra of these samples were used to obtain information about the environment of Trp side chains. The results showed that the Trp residues of C2 are more shielded from the solvent than those of C1 or B2. The results of this work indicate that the specific interactions existing between the transmembrane segments induce different types of helical conformations in native bacteriorhodopsin.

Bacteriorhodopsins↗

PubMed1988

Direct measurement of dose at depth in breast cancer using lithium fluoride.

In 23 cases of breast cancer treated conservatively using external beam and interstitial radiotherapy, lithium fluoride thermoluminescent dosimetry has been used to measure the radiation dose received by the breast tissue at depth. Thirty-six investigations were made using a number of lithium fluoride micro-rods for each investigation. Three results could not be analysed because of measurement problems in two and insufficient information in one. Twenty-eight results were obtained at a depth in tissue greater than the build-up zone, 23 of the 28 falling within +/- 5% and 27 of the 28 falling within +/- 10% of the computer-calculated prescribed dose. Of five results obtained within the build-up zone, two fell within +/- 5% and four within +/- 10% of the prescribed dose.

Brachytherapy↗

PubMed2002

Affinity partitioning for membrane purification exploiting the biotin-NeutrAvidin interaction. Model study of mixed liposomes and membranes.

Biotinylated negatively charged liposomes as well as membranes were affinity partitioned in an aqueous poly(ethylene glycol)-dextran two-phase system using NeutrAvidin conjugated to dextran as affinity ligand. Both liposomes and membranes redistributed from top to bottom phase upon addition of NeutrAvidin-dextran. The presence of 35-60 mM Li2SO4 was necessary both to force the components into the top phase without ligand and for ligand-dependent redistribution into the bottom phase. Attaching biotin via a hexanamidohexanoyl spacer and an increased density of biotin or NeutrAvidin enhanced the affinity separation. The separation conditions in these model experiments provide a basis for affinity partitioning of membranes using other affinity ligands.

Avidin↗

PubMed2003

In vitro cytotoxicity of traditional versus contemporary dental ceramics.

STATEMENT OF PROBLEM: The biocompatibility of new dental ceramics has not been assessed with the same scrutiny as has been applied to alloys and composites. Yet, the biocompatibility of ceramics is critical to the long-term success of dental prostheses because ceramics are in close contact with oral tissues for extended periods. MATERIAL AND METHODS: Five dental ceramics (2 traditional feldspathic veneer porcelains [Vita Omega and Duceragold], 2 lithium disilicate pressable materials [Stylepress and Empress-2], and a pressable leucite-based material [Empress-1]) were tested for their ability to alter cellular mitochondrial dehydrogenase activity after fabrication using a tetrazolium assay, after aging for 2 weeks in a biologic solution and after post-aging polishing with either a fine diamond or diamond polishing paste. Cellular responses were compared with polytetrafluoroethylene controls (analysis of variance, Tukey pairwise post-hoc comparison, alpha=.05). RESULTS: The feldspathic porcelains caused only mild (<25% of controls) mitochondrial suppression regardless of aging or polishing. The pressable leucite-based material initially caused a 5% stimulation (not significant) of mitochondrial activity, which decreased significantly (P<.05) by 30% with aging to levels comparable to the feldspathic porcelains, and did not change with polishing. Both lithium disilicate materials caused an initial suppression of mitochondrial activity that decreased significantly with aging, but Empress-2 was severely cytotoxic initially (<20% of controls, P<.01), and became more cytotoxic again after polishing. Stylepress was less cytotoxic initially (85% of controls, not significant) and did not become cytotoxic again after polishing. CONCLUSIONS: Dental ceramics are not equivalent in their in vitro biologic effects, even within the same class of material, and biologic safety should not be assumed. Most ceramics caused only mild in vitro suppression of cell function to levels that would be acceptable on the basis of standards used to evaluate alloys and composites. However, 1 Li-disilicate material (Empress-2) exhibited cytotoxicity that would not be deemed biologically acceptable on the basis of prevailing empirical standards for dental alloys and composites.

Aluminum Silicates↗

PubMed2002

Chemoselective construction of novel steroid derivatives.

Alpha-halo-alpha-heteroarylalkyllithiums, generated by deprotonation of the corresponding halides, when added promptly to steroids with C=O or C=NR groups, lead to epoxides and aziridines. The reactions are regio- and stereoselective; in fact, in the presence of more than one C=O group, the oxido or aziridino functions are formed uniquely at the C=O of C-17 (or C-20 depending on its position in the starting molecule), and the C-20(R) stereoisomer is often the only product isolated. Protection of the hydroxyl group present on several considered steroids was required, and it was accomplished through derivatization in acetyl, ether, or lactone.

Aziridines↗