Biomedical subjects

S I Khan

Publications and source records attributed to S I Khan.

At least 19 recordsLinked to original sources

PubMed2006

The emerging strains of Shigella dysenteriae type 2 in Bangladesh are clonal.

A total of 113 strains of Shigella dysenteriae type 2 isolated from patients attending the Dhaka diarrhoea treatment centre of ICDDR,B: Centre for Health and Population Research during the period 1999-2004 were studied. Serotype of the isolates was confirmed using commercially available antisera. Except for arabinose fermentation, all the strains had similar biochemical reactions. More than 60% of the strains were sensitive to commonly used antibiotics; only 6% (n=7) of the strains were resistant to nalidixic acid, and none of the strains were resistant to mecillinam and ciprofloxacin. All strains were invasive as demonstrated by the presence of a 140 MDa plasmid, ial, sen and ipaH genes, Congo Red absorption ability and by the Sereny test performed on representative strains. Plasmid patterns were heterogeneous but more than 50% of strains were confined to a single pattern. All strains possessed a 1.6 MDa plasmid and 87% of the strains contained a 4 MDa plasmid. Middle-range plasmids (90 MDa to 30 MDa) present in 36% of the strains were not associated with antibiotic resistance. All the strains were clustered within a single type with four subtypes by pulsed-field gel electrophoresis while ribotyping patterns of all the strains were identical.

Bangladesh↗

PubMed2005

Dynamic chirality in donor-acceptor pretzelanes.

[Figure: see text]. A series of donor-acceptor pretzelanes has been synthesized, using self-assembly and template-directed protocols, and the dynamic processes that these pretzelanes undergo have been investigated in solution. These compounds exist as libraries of diastereoisomers as a result of their multiple stereoelements, which are dynamically interconverted by several different, in some cases competing, processes. Altering the structure of the pretzelanes changes the rates and mechanisms by which these diastereoisomers equilibrate. Additionally, inserting an element of fixed chirality allows the equilibrium to be biased, while maintaining the barrier to the equilibration processes. These results bode well for the future construction of molecular devices based on switchable diastereoisomerism involving metastable states.

Journal Article↗

PubMed2004

Biological characterization of Aeromonas spp. isolated from the environment.

Cytotoxic enterotoxin (Act) is a key virulence factor in the pathogenesis of infections caused by Aeromonas spp. The cytotoxic enterotoxin gene (act) was detected in 32 out of 69 environmental isolates of Aeromonas spp. by hybridization with the act gene probe. To evaluate the pathogenic potential of the act gene probe-positive isolates, 32 act gene probe-positive and 31 randomly selected act gene probe-negative isolates were tested for enterotoxicity in a suckling mice assay (SMA), for haemolytic activity on sheep blood agar plates, for the presence of CAMP-like factors, and for cytotoxicity in a Vero cell line. The act gene probe-positive isolates significantly differed from the toxin gene probe-negative ones with respect to enterotoxicity in the SMA (P=0.009) and haemolytic activity (P=0.005). The CAMP-haemolysin phenotype was significantly associated with the rabbit ileal loop assay (P= 0.08), Vero cell assay (P= 0.064), and haemolysin production under the microaerophilic conditions (P= 0.056) of the act gene probe-positive isolates of Aeromonas spp. These data indicated the role of Act in the pathogenesis of Aeromonas infections and that the enterotoxic potential of Aeromonas spp. could be assessed by simply performing a CAMP-haemolysin assay.

Aeromonas↗

PubMed2004

Wastewater-grown duckweed may be safely used as fish feed.

Duckweed has been used for the treatment of wastewater and as fish feed. A comparative study was carried out to determine (i) the efficacy of duckweed in treating hospital-based wastewater and (ii) the level of the microbial contamination of fish fed on wastewater-grown duckweed. There were two groups of ponds where fish farming was done. In one group of ponds (control ponds), duckweed that was grown using artificial fertilizer was used as fish feed; in another group (study ponds), wastewater-grown duckweed was used as fish feed. The faecal contamination of water, duckweed, and fish from study and control ponds were monitored by faecal coliform estimation. The presence of enteric pathogens among handlers, water, duckweed, and fish samples was also examined. It was observed that the faecal coliform counts of raw wastewater were 4.7 Log10 CFU/mL, which was reduced to <1 Log10 CFU/mL after treating with duckweed. There was no significant difference (P > 0.05) in faecal coliform counts in water collected from duckweed ponds and fish ponds of study and control areas. The wastewater-grown duckweed did not pose any health hazard to the handlers. These results demonstrated that the wastewater-treated duckweed may be safely used as fish feed.

Animal Feed↗

PubMed2001

Synthesis of enantiopure oxorhenium(V) and arylimidorhenium(V) "3 + 2" Schiff base complexes. X-ray diffraction, cyclic voltammetry, UV-vis, and circular dichroism characterizations.

Two new oxorhenium(V) and two new arylimidorhenium(V) complexes of the Schiff base ligands 2-hydroxybenzaldehyde-((1R,2S)-1-amino-2-indanol)imine (1) (H(2)L(1)) and 3-(1-adamantyl)-2-hydroxy-5-methylbenzaldehyde-((1R,2S)-1-amino- 2-indanol)imine (2) (H(2)L(2)) have been prepared from the reaction of the precursor Re(O)(PPh(3))(2)Cl(3), Re(NC(6)H(5))(PPh(3))(2)Cl(3), or Re(NC(6)H(4)OCH(3))(PPh(3))(2)Cl(3) and the free ligands H(2)L(1,2). The complexes Re(O)(HL(1))(L(1)) (3), Re(O)(HL(2))(L(2)) (4), Re(NC(6)H(5))(HL(1))(L(1)) (5), and Re(NC(6)H(4)OCH(3))(HL(1))(L(1)) (6) have been isolated and fully characterized by IR, (1)H NMR, circular dichroism, LRMS-FAB, and elemental analysis. All the complexes have a chiral center at rhenium. A single enantiomer is obtained in all cases. Suitable crystals of 3 and 5 were used in X-ray structural determinations. Crystal data: (3) C(32)H(27)N(2)O(5)Re.CH(2)Cl(2), orthorhombic, P2(1)2(1)2(1), a = 9.5599(16) A, b = 9.9579(16) A, c = 31.712(5) A, V = 3018.9(9) A(3), T = 100(2) K, Z = 4. (5) C(40)H(38)N(3)O(5)Re, monoclinic, P2(1), a = 9.286(3) A, b = 18.759(6) A, c = 9.957(3) A, beta = 102.817(6) degrees, V = 1691.3(10) A(3), T = 100(2) K, Z = 2. The major characteristic of these complexes is the presence of two coordination modes for the Schiff base ligands on rhenium, a tridentate ligand (noted L(1,2)) and another bidentate ligand (noted HL(1,2)). In the latter, the -OH group of the indanol is free and tilts away from the coordination sphere. X-ray structural analyses in conjunction with circular dichroism were used to assign the absolute configuration at rhenium (C). Cyclic voltammetry, UV-vis, and circular dichroism data are presented and discussed. The complexes were found to be highly stable and to resist reduction even when treated with organic phosphanes.

Journal Article↗

PubMed2001

Dodecahydroxy-closo-dodecaborate(2-).

The cesium salt of the icosahedral borane anion dodecahydroxy-closo-dodecaborate(2-), Cs(2)[closo-B(12)(OH)(12)], Cs(2)1, was prepared by heating cesium dodecahydro-closo-dodecaborate(2-), Cs(2)[closo-B(12)H(12)], Cs(2)2, with 30% hydrogen peroxide. The other alkali metal salts A(2)1 (A = Li, Na, K, Rb) precipitated upon addition of ACl to warm aqueous solutions of Cs(2)1. The ammonium salt, [NH(4)](2)1, and the (mu-nitrido)bis(triphenylphosphonium) salt, [PPN](2)1, were obtained similarly. The [H(3)O](2)1 salt precipitated upon acidification of aqueous solutions of Cs(2)1 with hydrochloric acid. The solubility of these salts in water was determined by measuring the boron content of saturated aqueous solutions of A(2)1 (A = Li, Na, K, Rb, Cs), [H(3)O](2)1, and [NH(4)](2)1 using ICP-AES. Although these salts are derived from a dianion with twelve pendant hydroxyl groups, the alkali metal salts surprisingly displayed low water solubilities. Water solubility decreases with a decrease in the radius of A(+), except for the lithium salt, which is slightly more soluble than the potassium salt. The [H(3)O](2)1 and the [NH(4)](2)1 salts provide rare examples of water-insoluble hydronium and ammonium salts. The low water solubility of the A(2)1 salts is attributed to the dianion's pendant hydroxyl groups, which appear to function as cross-linking ligands. Four alkali metal salts, A(2)1 (A = Na, K, Rb, Cs), were characterized in the solid state by single-crystal X-ray crystallography. These data revealed intricate networks in which several anions are complexed through their hydroxyl groups to each alkali metal cation. In addition, the anions are engaged in hydrogen bonding with each other and, if present, with water of hydration. This cross-linking results in the precipitation of aggregated salts. Cation coordination numbers decrease with cation radius. Thus, cesium and rubidium are ten-coordinate, whereas potassium is seven-coordinate and sodium is six-coordinate. The geometry of anion 1(2)(-) is independent of cation identity; the B-B and B-O bond lengths of the various A(2)1 salts (A = Na, K, Rb, Cs) are identical.

Journal Article↗

PubMed2001

Dodecamethyl-closo-dodecaborate(2-).

Bis(tetraethylammonium) dodecamethyl-closo-dodecaborate(2-), [NEt(4)](2)[closo-B(12)Me(12)], [NEt(4)](2)2, was prepared employing modified Friedel-Crafts reaction conditions from [NEt(4)](2)[closo-B(12)H(12)], [NEt(4)](2)1, trimethylaluminum, and methyl iodide. The [NEt(4)](2)2 salt provides sufficient solubility in water to allow the synthesis of the important alkali metal salts A(2)2 (A = Li, Na, K, Rb, Cs) using cation-exchange procedures. The solid state structure of colorless [AsPh(4)](2)2 reveals a nearly perfect icosahedral B(12) cluster with B-B bonds ranging from 1.785(3) to 1.807(3) A and B-C bonds of 1.597(3)-1.625(3) A. In contrast, the crystal structure of dark-red [Py(2)CH(2)]2 (obtained from [NEt(4)](2)2 and [Py(2)CH(2)]Br(2)) contains a distorted icosahedral dianion [B-B = 1.740(13)-1.811(14) A, B-C = 1.591(13)-1.704(13) A]. In the [Py(2)CH(2)]2 salt, the dianion 2(2-) and its dipositive dipyridiniomethane counterion form a red charge-transfer complex. One-electron oxidation of 2(2)(-) by ceric(IV) ammonium nitrate affords the blue, air-stable radical [hypercloso-B(12)Me(12)](*-), dodecamethyl-hypercloso-dodecaborate(1-), 2(*-), isolated as the PPN salt. X-ray crystallography reveals that the geometries of the B(12) clusters observed in hypercloso-[PPN]2 and closo-[AsPh(4)](2)2 are identical and essentially undistorted icosahedra. The anion in the [PPN]2 structure contains B-B bonds ranging from 1.784(8) to 1.806(7) A and a range of B-C bonds from 1.596(7) to 1.616(7) A.

Journal Article↗

PubMed2001

Survival of Shigella dysenteriae type 1 on fomites.

Studies have shown that various objects, such as utensils, toys, and clothes, can serve as vehicles for transmission of Shigella spp. Shigellae can become viable but non-culturable (VBNC) when exposed to various environmental conditions as shown in earlier studies. The present study was carried out to detect VBNC Shigella dysenteriae type 1 on various fomites by direct viable counting, polymerase chain reaction (PCR), and fluorescent antibody methods. S. dysenteriae type 1 was inoculated onto cloth, wood, plastic, aluminum, and glass objects. Results showed that 1.5-4.0 hours after inoculation, S. dysenteriae type 1 became non-culturable, and after five days, non-culturable but viable S. dysenteriae type 1 could be detected by both PCR and fluorescent antibody techniques. Fomites can be considered an important potential route of transmission of VBNC S. dysenteriae type 1 and a significant factor in the epidemiology of shigellosis.

Bangladesh↗

PubMed2000

Scalar coupling across the hydrogen bond in 1,3- and 1,4-diols.

[reaction: see text] Scalar coupling between hydroxyl groups sharing a 1,4- or 1, 3-intramolecular hydrogen bond can be readily detected using standard 2D NMR techniques. Analyses of isotopically perturbed 2D J-resolved spectra have revealed (h2)J to be on the order of 0.3 Hz in systems such as diols 2 and 3. A standard 2D COSY experiment, modified to detect small coupling constants, is shown to be a convenient method for detecting (h2)J in these systems. Couplings derived from density functional finite perturbation theory (DFT/FPT) are found to be in general agreement with experimental data.

Alcohols↗

PubMed2000

Rationalization of enantioselectivities in dialkylzinc additions to benzaldehyde catalyzed by fenchone derivatives.

Three (-)-fenchyl alcohol derivatives, ¿(1R,2R,4S)-exo-(2-Ar)-1,3, 3-trimethylbicyclo[2.2.1] heptan-2-ol, Ar = o-anisyl (2), 2-N-methylimidazolyl (3), 2-N,N-dimethylbenzylamine (4)¿ were synthesized, characterized by X-ray analyses, and employed as precatalysts in diethyl zinc additions to benzaldehyde. Directions and relative degrees of enantioselectivities are rationalized by QM/MM ONIOM computations of mu-O transition structure models. Enantioselectivities arise from repulsive interactions between "transferring" or "passive" alkyl groups at the zinc centers and the substituents at donor groups or the bicyclo[2.2.1]heptane moieties. These results enable predictions for ligand-tuning to improve catalyst efficiency of fenchone-based ligands in dialkylzinc additions to aldehydes.

Benzaldehydes↗

PubMed1997

Endogenous natriuretic factors 6: the stereochemistry of a natriuretic gamma-tocopherol metabolite LLU-alpha.

2,7,8-Trimethyl-(S)-2-(beta-carboxyethyl)-6-hydroxy chroman (S-LLU-alpha) isolated from human uremic urine is apparently an oxidative side-chain degradation product of gamma-tocopherol. This compound exhibits natriuretic activity in vivo and it appears to mediate the inhibition of the 70 pS K+ channel in the apical membrane of the thick ascending limb of the nephron. The stereochemistry at the C-2 of LLU-alpha has been unequivocally established to be S(+) by X-ray crystallographic analysis of a diastereomeric amide derivative. It was also established that the chroman ring oxidation of S-LLU-alpha proceeded without racemization at C-2. This finding can be extended to nonepimerization at C-2 of alpha-delta tocopherols (Vitamin E) during side-chain oxidation and stereospecificity (retention or inversion) of oxidative opening of the chroman ring. The resolution of the enantiomers of the parent compound and derivatives was accomplished by chiral high-performance liquid chromatography. The stereospecific enzymatic hydrolysis by an array of commercially available enzymes of the racemic methyl ester of LLU-alpha was investigated. The lipase from Humicola languinosa appears to be the best enzyme for resolution by selective hydrolysis of the racemic methyl ester.

Chromans↗

PubMed1997

Detection of non-culturable Shigella dysenteriae 1 from artificially contaminated volunteers' fingers using fluorescent antibody and PCR techniques.

Epidemiological studies have demonstrated that hands may be an important vehicle for transmission of shigellosis. The present study was carried out to find out the survival potential of Shigella dysenteriae 1 on fingers of volunteers. Finger surface was inoculated with 10(5) cfu of S. dysenteriae 1 and then the bacteria were detected using conventional culture, PCR and fluorescent antibody (FA) techniques after different time intervals. It was found that S. dysenteriae 1 survived for up to one hour in culturable form but up to four hours in non-culturable form on human fingers. The non-culturable S. dysenteriae was detected by PCR and FA techniques. This study elaborates on the role that fingers have in the transmission of shigellae.

DNA, Bacterial↗

PubMed1996

Two isoxazolidines.

The crystal structures of trans-phenyl-1,6-dioxa-2-azaspiro[4,4]non- 3-yl ketone, C19H19NO3, and (3 alpha,3a alpha,6a alpha)-hexahydro-2-phenylfuro[3,2-d]isoxazol-3-yl phenyl ketone, C18H17NO3, are reported. In both compounds, the isoxazolidine rings adopt envelope conformations in which the O atom is bent out of the approximate plane of the other four ring atoms. Modest to negligible endo selectivities were confirmed in 1,3-dipolar cycloadditions of benzoylmethyleneaniline N-oxide with enol ethers.

Crystallography, X-Ray↗

PubMed1996

Survival of Shigella flexneri in artificial aquatic environment: effects of different physicochemical stress factors.

Survival of bacteria in aquatic environment is influenced by the prevailing physicochemical characteristics of water. A study was carried out to assess the effects of temperature, pH, and salinity of water on the survival of Shigella flexneri in laboratory microcosms. Survival of S. flexneri was assessed by viable counts of Shigella on MacConkey agar plates. At pH 7.0 and temperature of 4 degrees C, S. flexneri survived longer in 0.5% salinity than in salt-free distilled water, while at pH 7.0 and at higher temperatures (25 degrees C and 37 degrees C), the bacteria survived longer in distilled water than in 0.5% salinity. It was also observed that 2.0% NaCl solution was detrimental to bacterial survival at pH 8.0 and temperature of 37 degrees C. Survival times of the viable cells increased with reduction of temperatures and salinity. These findings demonstrated that survival of S. flexneri in the aquatic environment is greatly influenced by physicochemical factors.

Adaptation, Physiological↗

PubMed1995

Attenuation of alcohol-induced hypothermia by cyclo (His-Pro) and its analogs.

Acute administration of cyclo (His-Pro) to rats cause a dose-dependent decrease in ethanol-induced hypothermia. Bromination of the imidazole moiety of histidine in cyclo (His-Pro) resulted in a significant increase in its potency to attenuate ethanol hypothermia. In contrast, benzylation of the imidazole moiety of histidine or the substitution of one or both of the amino acids in cyclo(His-Pro) led to a total loss of its thermomodulatory activity. In conclusion, it appears from these preliminary data that it may be possible to design analogs of CHP that may be effective antagonists for ethanol hypothermia.

Animals↗

PubMed1995

Reversal of atherosclerotic obstructions by percutaneous transluminal angioplasty raises high-density lipoprotein cholesterol.

Variation of high-density lipoprotein cholesterol (HDL) levels in man show a strong inverse relationship to the incidence of atherosclerotic vascular disease. Conversely, effects of atherosclerosis and ischemia on lipoprotein metabolism are unclear. We investigated 41 patients, 10 women and 31 men, undergoing percutaneous transluminal angioplasty by measuring fasting lipoprotein cholesterol including high-density lipoprotein subfraction analysis before and one as well as 12 weeks after the procedure. Successful reopening of a haemodynamically significant iliac, femoral or popliteal obstruction was achieved in all patients. A highly significant (p < 0.001) increase of HDL cholesterol from 1.10 +/- 0.05 to 1.31 +/- 0.06 mmol/l was revealed 12 weeks later. This was due to a significant (p < 0.001) increase in HDL3 cholesterol by 26%, whereas HDL2 cholesterol did not change significantly. We conclude that HDL cholesterol levels increase after recanalization of a significant atherosclerotic obstruction which may be a direct effect of reperfusion or an indirect effect due to an increase in exercise tolerance.

Adult↗

PubMed1993

Growth and survival of Shigella flexneri in common Bangladeshi foods under various conditions of time and temperature.

Survival and growth of Shigella flexneri were assessed in various foods, including boiled rice, lentil soup, milk, cooked beef, cooked fish, mashed potato, mashed brinjal, and raw cucumber. Growth at 25 and 37 degrees C and survival at 5 degrees C were observed by viable counts on MacConkey agar. The organism grew well in all tested foods and growth increased from 10(5) to 10(8) to 10(10) cells per ml or g within 6 to 18 h after inoculation at 25 and 37 degrees C.

Bangladesh↗

PubMed1992

Relation of the level of high-density lipoprotein subfractions to the presence and extent of coronary artery disease.

Plasma lipid profiles, including high-density lipoprotein (HDL) subfractions HDL2 and HDL3, were obtained in 115 men undergoing coronary angiography to assess the relation of lipid levels to coronary artery disease (CAD). CAD was present in 87 patients (76%) and absent in 28 (24%). The largest difference between the 2 groups were observed for HDL2 cholesterol, with a mean of 0.13 mmol/liter (5 mg/dl) in patients with CAD compared with 0.25 mmol/liter (10 mg/dl) in those without CAD (p less than 0.005). Smaller differences were found for HDL3 (1.02 mmol/liter [39 mg/dl] vs 1.19 mmol/liter [46 mg/dl]; p less than 0.005) and HDL (1.15 vs 1.42 mmol/liter [45 vs 55 mg/dl]; p less than 0.001) cholesterol, and apolipoprotein A-1 (1.37 vs 1.50 g/liter; p less than 0.01) and plasma triglycerides (1.79 vs 1.38 mmol/liter [159 vs 122 mg/dl]; p less than 0.05). No significant difference was found for plasma and low-density lipoprotein cholesterol, and apolipoprotein B levels. Simple regression analysis revealed that the most powerful independent variable associated with the extent of CAD was HDL2 cholesterol (Spearman rho = 0.311; p less than 0.001). Stepwise multiple regression analysis proved HDL2 cholesterol and age to be the strongest predictors of extent of CAD. The level of HDL2 cholesterol was reasonably well correlated with HDL cholesterol (r2 = 0.6; p less than 0.0001), but less so with plasma apolipoprotein A-1 (r2 = 0.4; p less than 0.0001). The data add to the growing body of information demonstrating an important association of HDL (and more specifically HDL2) with CAD in men.

Age Factors↗