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Biomedical subjects

I Bello

Publications and source records attributed to I Bello.

At least 19 recordsLinked to original sources
PubMed2005

Ab initio and variational transition state approach to beta-C3N4 formation: kinetics for the reaction of CH3NH2 with H.

The CH3NH2 molecule has been considered as either an important intermediate in methane and ammonia mixtures or a precursor in methylamine and hydrogen mixtures in the synthesis of carbon nitride thin films. The fast Hydrogen (H) abstraction from CH3NH2 is an important process involved in the formation of HCN or CNH in the chemical vapor deposition (CVD) of carbon nitride thin films. The energetic and kinetic characteristics of the H abstraction reaction from CH3NH2 by atomic H used in CVD of beta-C3N4 were studied using ab initio direct dynamics methods for the first time. Two primary processes were identified for this reaction: H abstraction from the CH3 group and H abstraction from the NH2 group. On the basis of ab initio data, the rate constants of each channel have been deduced by canonical variational transition state theory with small-curvature tunneling correction over a wide temperature range of 200 to approximately 3000 K. The theoretical results were compared with available experimental data.

Journal Article↗
PubMed2005

Interfacial study of cubic boron nitride films deposited on diamond.

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.

Journal Article↗
PubMed2001

Nanostructure. Epitaxial diamond polytypes on silicon.

Carbon is unique in the variety of configurations it can adopt with itself and other elements. Here we show how ion beams can be used to nanostructure various diamond polytypes, epitaxially aligning them to a silicon substrate. The ready controllability of ion beams, which are already used to manufacture submicrometre-scale devices, means that our findings should enable new carbon and non-carbon materials to be nanostructured for a host of applications.

Journal Article↗
PubMed2001

Antibodies against IFN gamma-binding proteins recognize a member of IFN alpha R complex.

Recombinant human IFN alpha 2b coupled to a silica support was used for the purification of the IFN alpha-binding proteins from placental cell membrane extracts. The 100-kDa (p100) and 64-kDa (p64) proteins, which bind preferentially to an IFN alpha 2b-silica matrix, were identified. Using a monoclonal antibody (A6) against IFN-gammaR1, it was able to isolate p100 and p70, but only if IFN alpha 2b was present during chromatography. Similar interactions were observed using polyclonal antibody anti-IFN gamma binding proteins, as assayed in Western blot. These interactions were identified as conformation dependent. We speculate that IFN alpha 2b receptor complex shares an IFN gamma receptor complex epitope.

Antibodies, Monoclonal↗
PubMed2001

In vitro interferon gamma regulation of CCR-3 mRNA expression in peripheral blood leukocytes from atopic asthmatics.

Interferon gamma (IFN-gamma) exerts major pro-inflammatory, regulatory, and anti-inflammatory actions in immune defense responses. In asthma the infiltration of eosinophils, neutrophils, and lymphocytes is a critical event. Chemokines stimulate the migration of the susceptible subset of inflammatory cells. The chemokine receptors CCR-3 are mainly expressed in eosinophils, basophils, and Th2 cells. More recently it has been demonstrated that the IFN-gamma downregulates the expression of some chemokine receptors. IgE determinations were performed using an ELISA for total IgE Peripheral blood leukocytes from patients and controls were isolated by Ficoll-Hypaque gradient. The cells were incubated in the absence or presence of 500 IU/ml of recombinant human IFN-gamma for different times. After incubation the cells were washed and lyzed for reverse transcription-polymerase chain reaction (RT-PCR) analysis. RT-PCR was performed using a Perkin-Elmer kit. The amplified bands were run in 2% agarose gels and quantified. The basal levels of CCR-3 in asthmatic patients with IgE > 150 IU/ml tend to be higher than in controls. IFN-gamma down-regulates the expression of CCR-3 in peripheral blood leukocytes from asthmatics with IgE >150 IU/ml, when compared with the basal levels of expression. In conclusions, through the modification of the expression of CCR-3 in peripheral blood leukocytes from atopic asthmatics, IFN-gamma could exert a beneficial effect in patients with asthma, regulating the migration of some inflammatory cells involved in the pathogenesis of the disease.

Adolescent↗
PubMed2000

A nucleation site and mechanism leading to epitaxial growth of diamond films

A diamond nucleation site responsible for epitaxial growth of diamond on silicon by chemical vapor deposition (CVD) is identified in high-resolution transmission electron microscopic images. Other sites in the same sample leading to polycrystalline growth, but deleterious to epitaxial CVD growth, are also described. A mechanism for the heteroepitaxial growth of diamond is suggested, in which etching of the nondiamond carbon binder exposes and removes nonadherent nanodiamond nuclei, leaving intact only those directly nucleated on the silicon substrate. This work enhances our understanding of diamond nucleation and heteroepitaxial growth and its potential applications.

Journal Article↗
PubMed1998

High levels of soluble IFN gamma receptor alpha chain in the plasma of rheumatoid arthritis patients.

Soluble receptors for hormones and cytokines have been described. They can serve as natural blockers of their respective ligands. The natural soluble interferon gamma receptor (sIFN gamma R) has been isolated and characterized only in urine. Chromatography of human (hu) plasma from rheumatoid arthritis (RA) patients and controls on immobilized hu IFN gamma or antibodies against IFN gamma R alpha chain permitted us to isolate the sIFN gamma R. The receptor isolated from one control is a protein with a molecular weight between 60-67 kDa depending on the presence of reducing agents. We detected a significantly higher level of plasma sIFN gamma R in patients with rheumatoid arthritis than in apparently healthy subjects.

Arthritis, Rheumatoid↗
PubMed1989

Hematuria due to hypercalciuria and hyperuricosuria in adult patients.

We have prospectively studied 37 adult patients (15 males, 22 females; age 31 +/- 10.6 years) with previously undiagnosed isolated hematuria in which hypercalciuria or hyperuricosuria was found. Eighteen of them had had episodes of gross hematuria. Isolated hypercalciuria (4.4 to 10.4, X 5.6 +/- 1.9 mg/kg/24 hr) was found in nine patients (Group I), isolated hyperuricosuria (784 to 1500, X 1088 +/- 228 mg/24 hr) in 11 (Group II), and both hypercalciuria (4 to 8, X 4.9 +/- 1 mg/kg/24 hr) and hyperuricosuria (752 to 1476, X 1042 +/- 181 mg/24 hr) in 17 patients (Group III). Thiazide treatment for patients with hypercalciuria and allopurinol for those with hyperuricosuria were administered; calciuria and uricosuria became normal by the first month of therapy in every case. In 22 (59.4%) cases (Responder patients) hematuria resolved completely as soon as calciuria and uricosuria became normal. In the remaining 15 cases (Nonresponder patients) hematuria persisted despite the normal calcium and uric acid excretions. Several disorders that explained hematuria were diagnosed later in most of Nonresponder patients. Responder patients persisted without hematuria on the follow-up; only in three patients a transient relapse of hematuria was seen associated with a sudden increase of calciuria and uricosuria because of treatment withdrawal. There were no differences in age, male/female ratio nor in the basal values of calciuria and uricosuria between Responder and Nonresponder patients. A familial history of urolithiasis was found more frequently in Responder patients (64%) than in Nonresponders (20%) (P less than 0.05). We conclude that hypercalciuria and hyperuricosuria are definable and potentially reversible causes of hematuria in adult patients.

Adolescent↗
PubMed1988

Periglomerular granulomatosis. A limited form of Wegener's granulomatosis with exclusive renal involvement?

Three episodes of acute renal failure, all of them requiring hemodialysis, were observed in two patients. The renal biopsy specimens showed a massive periglomerular granulomatosis with crescentic glomerulonephritis. With cyclophosphamide therapy, a dramatic improvement in renal function was observed in both patients. Although the histologic findings and the response to cyclophosphamide therapy were characteristic of Wegener's granulomatosis, there was no evidence of respiratory involvement or extrarenal manifestations throughout the patients' clinical course. We think that these cases could represent limited forms of Wegener's granulomatosis with exclusive renal involvement.

Acute Kidney Injury↗
PubMed1987

Partial deficit of hypoxanthine guanine phosphoribosyl transferase presenting as acute renal failure.

A 12-year-old boy presented with acute renal failure (ARF) accompanied by a disproportionate increase of serum uric acid level and massive uric acid crystalluria. After alkalinization and allopurinol therapy, serum uric acid and renal function returned to normal values. A further enzymatic study showed the existence of a partial hypoxanthine-guanine phosphoribosyl transferase (HPRT) deficit (less than 1% of HPRT normal activity). Although ARF is an exceptional form of presentation of HPRT deficiency, this possibility should be considered whenever an ARF is accompanied by disproportionate high levels of serum uric acid.

Acute Kidney Injury↗
PubMed1985

Ureolytic Citrobacter freundii infection of the urine as a cause of dissolution of cystine renal calculi.

We report a case of cystinuria with staghorn renal lithiasis in a solitary right kidney and chronic renal failure. Right nephropyelolithotomy was performed and although 29 renal calculi were extracted many stones remained in situ. A permanent nephrostomy was left in the kidney. Several months later the urine was infected chronically with a ureolytic Citrobacter freundii bacteria and urinary pH oscillated between 8.0 and 9.2. Spontaneous dissolution of the cystine calculi was observed and many tiny fragments of cystine were expulsed through the nephrostomy, following which renal function improved. Despite the conditions favoring struvite calculi, formation did not occur.

Citrobacter↗
PubMed1985

Acute worsening of renal function during episodes of macroscopic hematuria in IgA nephropathy.

The appearance of renal failure during episodes of macroscopic hematuria (EMH) in IgA nephropathy (IgAN) has been described as very unusual. The results of a prospective investigation on the effect of EMH on renal function in IgAN are presented. During a 3-year period, 29 episodes of EMH occurring in 21 patients with IgAN have been studied. A derangement of renal function (increase of serum creatinine by more than 0.5 mg/dl) was observed in 11 episodes (37.9%) with peak creatinine values ranging from 1.2 to 6.7 mg/dl. The worsening of renal function was accompanied by a longer duration of EMH (4.8 +/- 1.3 vs. 3.5 +/- 1.5 days; P less than 0.05) but not by arterial hypertension or edema. A complete recovery of renal function was observed in every patient 1 to 2 months after the start of EMH. The histological survey disclosed that the decrease of renal function correlated closely with the presence of red blood cell casts in as much as 50% of the tubular lumen and with findings of tubular necrosis. We conclude that a worsening of renal function can be observed frequently during the EMH. Tubular damage and obstruction by red blood cell casts may play a significant role in the pathogenesis of this complication.

Acute Kidney Injury↗