Biomedical subjects

D K Kim

Publications and source records attributed to D K Kim.

At least 37 records · Page 2Linked to original sources

PubMed2001

Identification and characterization of a novel member of the heterodimeric amino acid transporter family presumed to be associated with an unknown heavy chain.

We identified a novel amino acid transporter designated Asc-2 (for asc-type amino acid transporter 2). Asc-2 exhibited relatively low but significant sequence similarity to the members of the heterodimeric amino acid transporters. The cysteine residue responsible for the disulfide bond formation between transporters (light chains) and heavy chain subunits in the heterodimeric amino acid transporters is conserved for Asc-2. Asc-2 is, however, not colocalized with the already known heavy chains such as 4F2 heavy chain (4F2hc) or related to b(0,+) amino acid transporter (rBAT) in mouse kidney. Because Asc-2 solely expressed or coexpressed with 4F2hc or rBAT did not induce functional activity, we generated fusion proteins in which Asc-2 is connected with 4F2hc or rBAT. The fusion proteins were sorted to the plasma membrane and expressed the function corresponding to the Na(+)-independent small neutral amino acid transport system asc. Distinct from the already identified system asc transporter Asc-1 which is associated with 4F2hc, Asc-2-mediated transport is less stereoselective and did not accept some of the high affinity substrates of Asc-1 such as alpha-aminoisobutyric acid and beta-alanine. Asc-2 message was detected in kidney, placenta, spleen, lung, and skeletal muscle. In kidney, Asc-2 protein was present in the epithelial cells lining collecting ducts. In the Western blot analysis on mouse erythrocytes and kidney, Asc-2 was detected as multiple bands in the nonreducing condition, whereas the bands shifted to a single band at lower molecular weight, suggesting the association of Asc-2 with other protein(s) via a disulfide bond. The finding of Asc-2 would lead to the establishment of a new subgroup of heterodimeric amino acid transporter family which includes transporters associated not with 4F2hc or rBAT but with other unknown heavy chains.

Amino Acid Sequence↗

PubMed2001

Human L-type amino acid transporter 1 (LAT1): characterization of function and expression in tumor cell lines.

System L is a major nutrient transport system responsible for the transport of large neutral amino acids including several essential amino acids. We previously identified a transporter (L-type amino acid transporter 1: LAT1) subserving system L in C6 rat glioma cells and demonstrated that LAT1 requires 4F2 heavy chain (4F2hc) for its functional expression. Since its oncofetal expression was suggested in the rat liver, it has been proposed that LAT1 plays a critical role in cell growth and proliferation. In the present study, we have examined the function of human LAT1 (hLAT1) and its expression in human tissues and tumor cell lines. When expressed in Xenopus oocytes with human 4F2hc (h4F2hc), hLAT1 transports large neutral amino acids with high affinity (K(m)= approximately 15- approximately 50 microM) and L-glutamine and L-asparagine with low affinity (K(m)= approximately 1.5- approximately 2 mM). hLAT1 also transports D-amino acids such as D-leucine and D-phenylalanine. In addition, we show that hLAT1 accepts an amino acid-related anti-cancer agent melphalan. When loaded intracellularly, L-leucine and L-glutamine but not L-alanine are effluxed by extracellular substrates, confirming that hLAT1 mediates an amino acid exchange. hLAT1 mRNA is highly expressed in the human fetal liver, bone marrow, placenta, testis and brain. We have found that, while all the tumor cell lines examined express hLAT1 messages, the expression of h4F2hc is varied particularly in leukemia cell lines. In Western blot analysis, hLAT1 and h4F2hc have been confirmed to be linked to each other via a disulfide bond in T24 human bladder carcinoma cells. Finally, in in vitro translation, we show that hLAT1 is not a glycosylated protein even though an N-glycosylation site has been predicted in its extracellular loop, consistent with the property of the classical 4F2 light chain. The properties of the hLAT1/h4F2hc complex would support the roles of this transporter in providing cells with essential amino acids for cell growth and cellular responses, and in distributing amino acid-related compounds.

Amino Acid Transport Systems↗

PubMed2001

Characterization of ochratoxin A transport by human organic anion transporters.

The purpose of this study was to investigate the characteristics of ochratoxin A (OTA) transport by multispecific human organic anion transporters (hOAT1 and hOAT3, respectively) using the second segment of proximal tubule (S2) cells from mice stably expressing hOAT1 and hOAT3 (S2 hOAT1 and S2 hOAT3). S2 hOAT1 and S2 hOAT3 exhibited a time- and dose-dependent, and a saturable increase in uptake of [3H]-OTA, with apparent Km values of 0.42 microM (hOAT1) and 0.75 microM (hOAT3). These OTA uptakes were inhibited by several substrates for the OATs. Para-aminohippuric acid (PAH), probenecid, piroxicam, octanoate and citrinin inhibited [3H]-OTA uptake by hOAT1 and hOAT3 in a competitive manner (Ki = 4.29-3080 microM), with the following order of potency: probenecid > octanoate > PAH > piroxicam > citrinin for hOAT1; probenecid > piroxicam > octanoate> citrinin > PAH for hOAT3. These results indicate that hOAT1, as well as hOAT3, mediates a high-affinity transport of OTA on the basolateral side of the proximal tubule, but hOAT1- and hOAT3-mediated OTA transport are differently influenced by the substrates for the OATs. These pharmacological characteristics of hOAT1 and hOAT3 may be significantly related with the events in the development of OTA-induced nephrotoxicity in the human kidney.

Animals↗

PubMed2001

The regulation of elongation by eukaryotic RNA polymerase II: a recent view.

The elongation of mRNA by RNA polymerase II (RNAPII) is controlled by the diverse actions of cis- and trans-acting elements that respond to a variety of biological signals. Elongation regulation, which determines the processivity of RNAPII, occurs during the steps of transcription initiation and elongation through both negative and positive influences. It has been generally accepted that negative elongation factors repress the elongation reaction. It is also generally accepted that positive elongation factors act by allowing the stalled RNAPII to escape from an inactive state, thus facilitating the production of full-length transcripts. However, recent data suggests that these opposing regulatory mechanisms can be achieved through a coupling pattern, rather than through independent activity. In addition, biochemical experiments using 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) have identified several factors involved in DRB-sensitive transcription, and elucidated the mechanism of interplay between the positive and negative elongation factors. Here, we will review the major findings from studies on RNAPII elongation control. We will further discuss the properties of newly identified factors that have resulted from studies on the action of DRB on elongation.

RNA Polymerase III↗

PubMed2001

Human cystine/glutamate transporter: cDNA cloning and upregulation by oxidative stress in glioma cells.

A human cDNA for amino acid transport system x(C)(-) was isolated from diethyl maleate-treated human glioma U87 cells. U87 cells expressed two variants of system x(C)(-) transporters hxCTa and hxCTb with altered C-terminus regions probably generated by the alternative splicing at 3'-ends. Both hxCTa and hxCTb messages were also detected in spinal cord, brain and pancreas, although the level of hxCTb expression appears to be lower than that of hxCTa in these tissues. When expressed in Xenopus oocytes, hxCTb required the heavy chain of 4F2 cell surface antigen (4F2hc) and exhibited the Na(+)-independent transport of L-cystine and L-glutamate, consistent with the properties of system x(C)(-). In agreement with this, 137 kDa band was detected by either anti-xCT or anti-4F2hc antibodies in the non-reducing condition in western blots, whereas it shifted to 50 kDa or 90 kDa bands in the reducing condition, indicating the association of two proteins via disulfide bands. We found that the expression of xCT was rapidly induced in U87 cells upon oxidative stress by diethyl maleate treatment, which was accompanied by the increase in the L-cystine uptake by U87 cells. Because of this highly regulated nature, xCT in glial cells would fulfill the task to protect neurons against oxidative stress by providing suitable amount of cystine to produce glutathione.

Alternative Splicing↗

PubMed2001

Nuclear translocation of cytosolic phospholipase A2 is induced by ATP depletion.

Phospholipase A(2) (PLA(2)) enzymes may play a role in cellular injury due to ATP depletion. Renal Madin-Darby canine kidney cells were subjected to ATP depletion to assess the effects of cellular energy metabolism on cytosolic PLA(2) (cPLA(2)) regulation. ATP depletion results in a decrease in soluble cPLA(2) activity and an increase in membrane-associated activity, which is reversed upon restoration of ATP levels by addition of dextrose. In ATP-depleted cells cPLA(2) mass shifts from cytosol to nuclear fractions. GFP-cPLA(2) is localized at the nuclear membrane of stably transfected ATP-depleted LLC-PK(1) cells under conditions where [Ca(2+)](i) is known to increase. cPLA(2) translocation does not occur if the increase in [Ca(2+)](i) increase is inhibited. If [Ca(2+)](i) is allowed to increase when ATP is depleted and the cells are then lysed, cPLA(2) remains associated with nuclear fractions even if the homogenate [Ca(2+)] is markedly reduced. In contrast, cPLA(2), which becomes associated with the nucleus when [Ca(2+)](i) is increased using ionophore, readily dissociates from the nuclear fractions of ATP-replete cells upon reduction of homogenate [Ca(2+)]. Okadaic acid inhibits the ATP depletion-induced association of cPLA(2) with nuclear fractions. Thus energy deprivation results in [Ca(2+)]-induced nuclear translocation, which is partially prevented by a phosphatase inhibitor.

Active Transport, Cell Nucleus↗

PubMed2001

Intracardiac echocardiographic guidance and monitoring during percutaneous endomyocardial gene injection in porcine heart.

In an effort to develop a guiding and monitoring tool for transmyocardial gene transfer, we have evaluated the feasibility of intracardiac echocardiography (ICE) to guide percutaneous endomyocardial gene transfer (PEGT), and monitor complications, in a pig model. ICE (5.5-10 MHz), complemented by fluoroscopy, was utilized to guide a needle injection into the heart in 19 normal pigs. Using this system, we injected Evans blue dye into eight pigs (group I), a mixture of pCK-CAT plasmid and India ink into seven pigs (group II), and pCK-LacZ plasmid into four pigs (group III). In all pigs, ICE contributed to the injection procedure by guiding the catheter to anatomically distinct sites, and by assisting stabilization of the catheter-endocardial contact. ICE predicted the injection sites correctly in 56 of 64 sites (87.5%) in group I, and in 42 of 42 sites (100%) in group II. Leakage of injectate into the left ventricular cavity could be detected by the microbubbles generated. The sites of injections appeared as foci of bright myocardial echodensity, which persisted until the end of the procedure. The procedures were not associated with significant morbidity or mortality. The expression of the chloramphenicol acetyltransferase (CAT) gene was identified in 40 sites from 42 injections (95.2%) in group II. In group III, histology showed positive beta-galactosidase staining of myocytes limited around the needle track with low transfection efficiency (<1%). These results suggest that real-time ICE monitoring proves safe and useful during PEGT for guiding needle injection, monitoring leakage, ensuring delivery of injectate into the myocardium, and instantly diagnosing cardiac complications, resulting in successful gene transfer.

Animals↗

PubMed2001

Synthesis and biological evaluation of novel A-ring modified hexacyclic camptothecin analogues.

Eleven A-ring modified hexacyclic analogues of camptothecin (CPT) containing a 1,4-oxazine ring were synthesized from 10-hydroxycamptothecin (11a) and 7-ethyl-10-hydroxycamptothecin (3) (SN-38) in four to five steps and were subjected to the biological tests such as cytotoxicity, topoisomerase I (Topo I) inhibitory activity, acetylcholinesterase (AChE) inhibition, and stability in human plasma. Four compounds 15a, 15b, 16a, and 16c were about 2-fold more potent than topotecan and as potent as CPT toward human cancer cell lines A549, H128, WiDr, MKN45, SK-OV-3, and SK-BR-3 in vitro, even though the most active compound 15b was slightly less potent than SN-38. The potency of Topo I inhibition of these compounds showed relatively good correlation with their cytotoxicity. Most of the compounds exhibited AChE inhibitory activity weaker (9 +/- 2 to 20 +/- 3%) than CPT (23 +/- 5%) or topotecan (20 +/- 4%) and similar to SN-38 (13 +/- 2%), indicating that they might have little effect on causing early diarrhea. The stability of lactone forms of these compounds in human plasma seemed to be much higher than that of CPT and similar to that of topotecan but lower than that of SN-38. Among the new hexacyclic CPT analogues, compound 15b showed higher antitumor activity against human tumor xenograft, WiDr, in nude mice compared to that of SN-38. The most promising compound 15b has been selected for further development.

Animals↗

PubMed2001

Preoperative hyperfractionated radiotherapy with concurrent chemotherapy in resectable esophageal cancer.

PURPOSE: To evaluate the local control rates, survival rates, and patterns of failure for esophageal cancer patients receiving preoperative concurrent chemotherapy and hyperfractionated radiotherapy followed by esophagectomy. METHODS AND MATERIALS: From May 1993 through January 1997, 94 patients with resectable esophageal cancers received continuous hyperfractionated radiation (4,800 cGy/40 fx/4 weeks), with concurrent FP chemotherapy (5-FU 1 g/m(2)/day, days 2-6, 30-34, CDDP 60 mg/m(2)/day, days 1, 29) followed by esophagectomy 3-4 weeks later. If there was evidence of disease progression on preoperative re-evaluation work-up, or if the patient refused surgery, definitive chemoradiotherapy was delivered. Minimum follow-up time was 2 years. RESULTS; All patients successfully completed preoperative treatment and were then followed until death. Fifty-three patients received surgical resection, and another 30 were treated with definitive chemoradiotherapy. Eleven patients did not receive further treatment. Among 91 patients who received clinical reevaluation, we observed 35 having clinical complete response (CR) (38.5%). Pathologic CR rate was 49% (26 patients). Overall survival rate was 59.8% at 2 years and 40.3% at 5 years. Median survival time was 32 months. In 83 patients who were treated with surgery or definitive chemoradiotherapy, the esophagectomy group showed significantly higher survival, disease-free survival, and local disease-free survival rates than those in the definitive chemoradiation group. CONCLUSION: Preoperative chemoradiotherapy in this trial showed improved clinical and pathologic tumor response and survival when compared to historical results. Patients who underwent esophagectomy following chemoradiation showed decreased local recurrence and improved survival and disease-free survival rates compared to the definitive chemoradiation group.

Aged↗

PubMed2001

A Phase I study of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-1,3-dioxolane] platinum(II) in patients with advanced malignancies.

BACKGROUND: A Phase I study of cis-malonato[(4R,5R)-4,5-bis(aminomethyl)-1,3-dioxolane] platinum(II) (SKI 2053R), a new platinum derivative, was performed to determine the maximum tolerated dose (MTD), the dose limiting toxicities (DLTs), and the pharmacokinetic profile of SKI 2053R in patients with advanced, refractory malignancies. METHODS: Twenty-one patients were entered into the study. SKI 2053R was administered with an intravenous infusion over 1 hour every 4 weeks. The SKI 2053R dose was escalated from 40 mg/m(2) up to 480 mg/m(2) using a modified Fibonacci scheme. Pharmacokinetic analysis was done in all patients to determine the total and ultrafiltrable platinum concentrations in both the plasma and the urine. RESULTS: All patients were evaluable for toxicity and response. There was no significant toxicity with dosages up to 360 mg/m(2). At 480 mg/m(2), two of three patients developed Grade 4 hepatotoxicity, Grade 3 leukopenia and thrombocytopenia, and Grade 2 azotemia and proteinuria. Other toxicity included nausea and emesis, but it was controlled with antiemetics. SKI 2053R did not cause significant neurotoxicity or mucositis. There were 4 patients with stable disease among the 21 patients. Plasma decay of the total and free platinum concentrations was best fitted by using a two-compartment, open model. The terminal plasma half-life of the total platinum after SKI 2053R administration ranged from 63.4 hours to 114.1 hours in dosages ranging from 40 mg/m(2) to 480 mg/m(2) without significant dose dependency. However, the terminal plasma half-life of the free platinum concentration showed a significant dose dependent, incremental pattern. The renal excretion of SKI 2053R measured as platinum ranged from 49% to 75% of the administered dose. CONCLUSIONS: The MTD of SKI 2053R was 480 mg/m(2). The major DLTs were hepatotoxicity, nephrotoxicity, and myelosuppression. The recommended starting dose for a subsequent Phase II study is 360 mg/m(2) once every 4 weeks.

Adult↗

PubMed2001

Ratio of donor kidney weight to recipient bodyweight as an index of graft function.

Reduced renal mass or mismatching kidney size are risk factors for chronic allograft nephropathy. We assessed the effect of mismatching donor kidney weight and recipient bodyweight on renal graft function in 82 live donor kidney transplant recipients who did not have acute rejection. We calculated the donor kidney weight to recipient bodyweight ratio, and established the relation between this ratio and renal indices with a mixed model regression. We showed that recipients with a high ratio had better graft function.

Adult↗

PubMed2001

Importance of leucine zipper domain of mi transcription factor (MITF) for differentiation of mast cells demonstrated using mi(ce)/mi(ce) mutant mice of which MITF lacks the zipper domain.

The mi transcription factor (MITF) is a basic helix-loop-helix leucine zipper (bHLH-Zip) transcription factor that is important for the development of mast cells. Mast cells of mi/mi genotype express normal amount of abnormal MITF (mi-MITF), whereas mast cells of tg/tg genotype do not express any MITFs. Mast cells of mi/mi mice show more severe abnormalities than those of tg/tg mice, indicating that the mi-MITF possesses the inhibitory function. The MITF encoded by the mi(ce) mutant allele (ce-MITF) lacks the Zip domain. We examined the importance of the Zip domain using mi(ce)/mi(ce) mice. The amounts of c-kit, granzyme B (Gr B), and tryptophan hydroxylase (TPH) messenger RNAs decreased in mast cells of mi(ce)/mi(ce) mice to levels comparable to those of tg/tg mice, and the amounts were intermediate between those of +/+ mice and those of mi/mi mice. Gr B mediates the cytotoxic activity of mast cells, and TPH is a rate-limiting enzyme for the synthesis of serotonin. The cytotoxic activity and serotonin content of mi(ce)/mi(ce) mast cells were comparable to those of tg/tg mast cells and were significantly higher than those of mi/mi mast cells. The phenotype of mi(ce)/mi(ce) mast cells was similar to that of tg/tg mast cells rather than to that of mi/mi mast cells, suggesting that the ce-MITF had no functions. The Zip domain of MITF appeared to be important for the development of mast cells. (Blood. 2001;97:2038-2044)

Animals↗

PubMed2001

Inhibitory effect on natural killer activity of microphthalmia transcription factor encoded by the mutant mi allele of mice.

The mouse mi locus encodes a basic-helix-loop-helix-leucine zipper-type transcription factor, microphthalmia transcription factor (MITF). Mice of mi/mi genotype express a mutant form of MITF (mi-MITF), whereas mice of tg/tg genotype have a transgene in the 5' flanking region of the mi gene and do not express MITF. Although the mi/mi mouse is deficient in natural killer (NK) activity, it was found that the tg/tg mouse was normal in this respect. To know the cause, spleen cells of both genotypes were compared. Although the proportion of spleen cells expressing an NK cell marker, NK1.1, was comparable in both mice, the proportion of large granular lymphocytes decreased only in mi/mi mice. The difference between mi/mi and tg/tg mice was reproducible in the culture supplemented with interleukin-2. Moreover, the perforin gene expression was reduced in mi/mi-cultured spleen cells. Wild-type (+) MITF transactivated, but mi-MITF suppressed, the perforin gene promoter through the NF-P motif, a strong cis-acting element. However, neither +-MITF nor mi-MITF bound the NF-P motif. Instead, 2 nuclear factors that bound the NF-P motif were retained in the cytoplasm of mi/mi-cultured spleen cells. In addition, overexpression of mi-MITF resulted in cytoplasmic retention of the 2 NF-P motif-binding factors in cytotoxic T lymphocytes. The presence of mi-MITF rather than the absence of +-MITF appeared to lead to poor transactivation of the NF-P motif by intercepting NF-P motif-binding factors. This inhibitory effect of mi-MITF may cause the deficient cytotoxicity of NK cells in mi/mi mice. (Blood. 2001;97:2075-2083)

Alleles↗

PubMed2001

NF-kappa B mediates the adaptation of human U937 cells to hydrogen peroxide.

Low doses of oxidative stress can induce cellular resistance to subsequent higher doses of the same stress. By using human U937 leukemia cells, we previously demonstrated that H(2)O(2) can induce such an adaptive response without elevating the cellular capacity to degrade H(2)O(2), and were able to confer the cells a cross-resistance to an H(2)O(2)-independent lethal stimulus, C(2)-ceramide. In this study, it was found that the adaptation is accompanied by the translocation of cytoplasmic NF-kappa B to the nuclei. This event was promoted or abolished when either IKK alpha or a dominant negative mutant of I kappa B, respectively, was overexpressed. The overexpression of IKK alpha also resulted in the suppression of H(2)O(2)-induced cell death and DNA fragmentation, whereas these events were accelerated by the expression of the I kappa B mutant. The protective effect of IKK alpha was accompanied neither by an elevation of protein levels of various antioxidant enzymes such as catalase, superoxide dismutase, and glutathione peroxidase, nor by an increase in the cellular capacity to consume H(2)O(2). Moreover, the overexpression of IKK alpha resulted in an enhancement of H(2)O(2)-induced resistance to C(2)-ceramide. The overall data suggest that NF-kappa B mediates the H(2)O(2) adaptation induced in a manner independent of H(2)O(2)-degrading activity.

Adaptation, Physiological↗

PubMed2001

XAFS study of copper species stabilized in the interlayer space of layered perovskite oxides.

New intercalation compounds with Cu2+ ions in the interlayer of layered perovskite oxides, OA(1-x)Ca(2-x)La(x)Nb3O10) (OA = n-octylammonium ion, 0 < or = x < 1), have been prepared by ion-exchange reaction, and characterized by means of XRD and XAS. For the detail elucidation of the fine structure of the Cu K-edge XANES spectra, polarized XAS was applied for the [Cu(en)2]2+ and Cu2+ ions intercalated to the single crystal. According to the XANES and EXAFS spectra measured at Cu K-edge, copper ions are four coordinated. In addition, XANES spectra have shown that the charge transfer from host layer to intercalated ions influences on the chemical state of copper ion.

Journal Article↗

PubMed2001

XANES study on Ruddlesden-Popper phase, La(n+1)Ni(n)O(3n+1) (n=1,2 and infinity).

Ruddlesden-Popper phase, La(n+1)Ni(n)O(3n+1 (n=1, 2, and infinity) compounds were prepared by citrate sol-gel method. We revealed the origin of the variation of the electrical conductivities in La(n+1)Ni(n)O(3n+1 (n=1, 2, and infinity) using resistivity measurements, Rietveld analysis, and X-ray absorption spectroscopy. According to the XANES spectra, it is found that the degree of 4p(pi) - 4psigma energy splitting between 8345 eV and 8350 eV is qualitatively proportional to the elongation of the out-of-plane Ni-O bond length. With the decrease of 4p(pi) - 4psigma splitting, the strong hybridization of the sigma-bonding between Ni-3d and O-2p orbitals creates narrow antibonding sigma* bands, which finally results in the lower electrical resistivity.

Journal Article↗

PubMed2001

Ion exchange and fixation of rare-earth cation into expandable tetrasilicic fluorine mica.

Rare-earth cation (Nd3+) are incorporated into the interlayer spaces between the silicate layers of synthetic fluorine mica, Na0.665Mg2.68(Si3.98)Al0.02F1.98, by conventional ion exchange reaction. Subsequent migration of the interlayer cations upon calcination into the vacant octahedra of 2:1 layers is followed by powder X-ray diffraction, diffuse-reflectance UV spectroscopy, and X-ray absorption spectroscopy as a function of calcination temperature. It is found from the spectroscopic analyses that the interlayer cations start to migrate into the octahedral vacant sites from 400 degrees C through the hexagonal siloxane ring of the tetrahedral silicate layers. According to the Nd L(III)-edge XANES spectra, the normalized absorption intensity gradually decreases while the FWHM increases with temperature, suggesting that the bonding character of rare-earth cations and silicate lattices evolves from ionic to covalent as the calcination temperature increases.

Journal Article↗

PubMed2001

Local structure analysis of Ti species stabilized in ion exchangeable layer solids by x-ray absorption spectroscopy.

Nano-sized titanium dioxides are incorporated into the interlayer spaces of ion-exchangeable layered perovskites, H(1-x)Ca2(x)La(x)Nb3O10 (x=0.0-0.75), by replacing the interlayer protons with positively charged TiO2 nano-sol particles or basic titanium glycolate complex (titanatrane). Powder X-ray diffraction analysis. UV-Vis absorption spectroscopy, thermogravimetric analysis, and N2 adsorption-desorption isotherm measurements show that quantum sized TiO2 particles are stabilized in between perovskite lattices to form micropores (S(BET) = 37-110 m2/g). X-ray absorption spectroscopy at the Ti K-edge was used for investigating the local environment around Ti atoms constituting the interlayer pillars. According to the XANES spectra, the 'as-pillared' Ti species have the same local environments with those of precursory species, which subsequently converted into TiO2 clusters with rutile and anatase-like local structures when TiO2 nano-sol particles and titanatrane are used as pillaring species. respectively. It is also found that the local environment of TiO2 remains almost constant irrespective of the layer charge density, while the TiO2 pillar content and the microporosity increase with the latter.

Journal Article↗