Biomedical subjects

Santanu Bhattacharya

Publications and source records attributed to Santanu Bhattacharya.

23 records · Page 2Linked to original sources

PubMed1998

Synthesis of Some Copper(II)-Chelating (Dialkylamino)pyridine Amphiphiles and Evaluation of Their Esterolytic Capacities in Cationic Micellar Media.

Three new (dialkylamino)pyridine (DAAP)-based ligand amphiphiles 3-5 have been synthesized. All of the compounds possess a metal ion binding subunit in the form of a 2,6-disubstituted DAAP moiety. In addition, at least one ortho-CH(2)OH substituent is present in all the ligands. Complex formation by these ligands with various metal ions were examined under micellar conditions, but only complexes with Cu(II) ions showed kinetically potent esterolytic capacities under micellar conditions. Complexes with Cu(II) were prepared in host comicellar cetyltrimethylammonium bromide (CTABr) media at pH 7.6. Individual complexes were characterized by UV-visible absorption spectroscopy and electron paramagnetic resonance spectroscopy. These metallomicelles speed the cleavage of the substrates p-nitrophenyl hexanoate or p-nitrophenyl diphenyl phosphate. To ascertain the nature of the active esterolytic species, the stoichiometries of the respective Cu(II) complexes were determined from the kinetic version of Job's plot. In all the instances, 2:1 complex ligand/Cu(II) ion are the most kinetically competent species. The apparent pK(a) values of the Cu(II)-coordinated hydroxyl groups of the ligands 3, 4, and 5, in the comicellar aggregate, are 7.8, 8.0, and 8.0, respectively, as estimated from the rate constant vs pH profiles of the ester cleavage reactions. The nucleophilic metallomicellar reagents and the second-order "catalytic" rate constants toward esterolysis of the substrate p-nitrophenyl hexanoate (at 25 degrees C, pH 7.6) are 37.5 for 3, 11.4 for 4, and 13.8 for 5. All catalytic systems comprising the coaggregates of 3, 4, or 5 and CTABr demonstrate turnover behavior in the presence of excess substrate.

Journal Article↗

PubMed1997

Evidence for the Formation of Acylated or Phosphorylated Monoperoxyphthalates in the Catalytic Esterolytic Reactions in Cationic Surfactant Aggregates.

Monoperoxyphthalate (MPP) was solubilized in three different aqueous cationic surfactant aggregates composed of (i) a micellar cetyltrimethylammonium chloride (CTACl) solution; (ii) an oil-in-water (O/W) microemulsion (ME) stabilized by CTACl, and a cosurfactant, tert-butyl alcohol, and (iii) a vesicular medium composed of dispersions of dihexadecyldimethylammonium chloride (DHDAC). At pH approximately 8.5 and 25 degrees C, each of these formulations was used to cleave p-nitrophenyl diphenyl phosphate (PNPDPP). The aggregate and the maximum pseudo-first-order rate constants ([MPP] = 4 x 10(-)(5) M, and [PNPDPP] = 1 x 10(-)(5) M) for the PNPDPP cleavages are the following: buffer alone, 0.00034 s(-)(1); micelle: 0.024 s(-)(1); ME: 0.0048 s(-)(1); and vesicle: 0.025 s(-)(1). Importantly all the catalytic formulations showed "turnover" behavior in the presence of excess substrates. By the combined use of (1)H- and (31)P-NMR spectrometry and synthesis, it was possible to provide evidence for the formation of acylated or phosphorylated monoperoxypthalates in the catalytic hydrolyses in cationic surfactant aggregates.

Journal Article↗

PubMedDate not supplied

Advantage of the ether linkage between the positive charge and the cholesteryl skeleton in cholesterol-based amphiphiles as vectors for gene delivery.

Twelve novel cationic cholesterol derivatives with different linkage types between the cationic headgroup and the cholesteryl backbone have been developed. These have been tested for their efficacies as gene transfer agents as mixtures with dioleoyl phosphatidylethanolamine (DOPE). A pronounced improvement in transfection efficiency was observed when the cationic center was linked to the steroid backbone using an ether type bond. Among these, cholest-5-en-3b-oxyethane-N,N,N-trimethylammonium bromide (2a) and cholest-5-en-3b-oxyethane-N,N-dimethyl-N-2-hydroxyethylammonium bromide (3d) showed transfection efficiencies considerably greater than commercially available reagents such as Lipofectin or Lipofectamine. To achieve transfection, 3d did not require DOPE. Increasing hydration at the headgroup level for both ester- and ether-linked amphiphiles resulted in progressive loss of transfection efficiency. Transfection efficiency was also greatly reduced when a 'disorder'-inducing chain like an oleyl (cis-9-octadecenyl) segment was added to these cholesteryl amphiphiles. Importantly, the transfection ability of 2a with DOPE in the presence of serum was significantly greater than for a commercially available reagent, Lipofectamine. This suggests that these novel cholesterol-based amphiphiles might prove promising in applications involving liposome-mediated gene transfection. This investigation demonstrates the importance of structural features at the molecular level for the design of cholesterol-based gene delivery reagents that would aid the development of newer, more efficient formulations based on this class of molecules.

Animals↗

PubMedDate not supplied

Cationic oxyethylene lipids. Synthesis, aggregation, and transfection properties.

Four cationic lipids (1-4) with oligo-oxyethylene units at the linkage region between the pseudoglyceryl backbone and the hydrocarbon chains have been synthesized. Two of these lipids (1 and 2) have an equal number of (CH(2)CH(2)O)(n)() units attached to both C-1 and C-2 positions of the pseudoglyceryl backbone, making their linkage regions similar, while the other two (3 and 4) are unsymmetrical in terms of the number of oxyethylene units in the linkage. Synthesis of lipids 1 and 2 involved the coupling of benzyl glycerol with the corresponding tosylates as a key step. Each of these lipids formed membranous aggregates when dispersed in water and exhibited clear thermotropic phase transitions typical of vesicular assemblies. The lipids 1-4 exhibited enhanced biological activities as gene transfer agents compared to their non-oxyethylene diether analogue, DHTMA. Transfection experiments using aqueous suspensions of these lipids and also their mixtures with cholesterol or dioleoyl phosphatidyl ethanolamine (DOPE) were performed on HeLa cells. The best transfection activity was demonstrated by unsymmetrical lipid 3, which had two oxyethylene units only at the C-1 position of the pseudoglycerylbackbone.

Calorimetry, Differential Scanning↗

PubMedDate not supplied

Efficient conjugation and characterization of distamycin-based peptides with selected oligonucleotide stretches.

Selected sequences of oligodeoxyribonucleotides (ODNs) have been conjugated efficiently with distamycin-based peptides containing reactive cysteine and oxyamine functionalities at the C-terminus. The conjugation was performed easily within 30-60 min, using individual modified oligonucleotide stretches having sequences of 5'-d(GCTTTTTTCG)-3', 5'-d(GCTATATACG)-3', and 5'-AGCGCGCGCA-3'. Two types of linkages were used for making the covalent connection: (i) a five-membered thiazolidine ring and (ii) an oxime. These distamycin-like polyamide-ODN conjugates were then converted to the corresponding DNA duplexes using complementary oligonucleotide sequences. To elucidate the binding specificity of the distamycin-oligonucleotide conjugates, UV-melting temperature measurements were performed. These studies indicated that the distamycin-ODN conjugate favored binding with the duplex with sequence 5'-d(GCTTTTTTCG)-3' rather than 5'-d(GCTATATACG)-3'. On the other hand, no stabilization of the duplex with sequence 5'-d(AGCGCGCGCA)-3' was observed. UV results also suggest that the thiazolidine and oxime linkages do not significantly influence the process of distamycin binding to the minor groove surface of the DNA duplex. The results obtained from duplex UV-melting studies were further corroborated by a temperature-dependent study of the circular dichroism spectra of the conjugates and a fluorescence displacement titration assay using Hoechst 33258 fluorophore as a competitive binder for the minor groove. All these studies reinforce the fact that the specific stabilization of A/T rich DNA-DNA duplexes by distamycin was preserved upon conjugation with oligonucleotide stretches.

Circular Dichroism↗