Jhony Orbulescu - Academia.edu (original) (raw)

Papers by Jhony Orbulescu

The Journal of Physical Chemistry, 2012

The human insulin (HI) protein was examined to elucidate its structure at the air−water interface... more The human insulin (HI) protein was examined to elucidate its structure at the air−water interface. Optimal experimental conditions were determined to prepare a homogeneous and stable human insulin (HI) Langmuir monolayer. HI insulin Langmuir monolayer can be used to study interactions of HI with a membrane as Langmuir monolayers are used as an in vitro model of biological membranes. Surface pressure and surface potential-area isotherms were used to characterize the HI Langmuir monolayer. The compression−decompression cycles and stability measurements showed a homogeneous and stable monolayer at the air− water interface. However, higher surface pressures resulted in a higher decrease in area and less stability. In situ UV−vis and fluorescence spectroscopy were used to verify the homogeneity of the HI monolayer and to identify the chromophore residues in the HI. Domain formation was examined through epifluorescence and Brewster angle microscopies. The conformation of HI was examined by circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) in the aqueous phase and at the air− water interface by infrared reflection absorption spectroscopy (IRRAS). HI was found to exist as a monomer in 2-D.

Journal of Physical Chemistry B, Aug 17, 2012

Colloids and Surfaces B: Biointerfaces, Jun 1, 2008

Amyloid peptide (A␤) is found in the brain and blood of both healthy and diseased individuals ali... more Amyloid peptide (A␤) is found in the brain and blood of both healthy and diseased individuals alike. However, upon secondary structure transformation to a ␤-sheet dominated conformation, the protein aggregates. These aggregates accumulate to form neuritic plaques that are implicated in the pathogenesis of Alzheimer's disease. Gold nanoparticles are excellent photon-thermal energy converters. The extinction coefficient of the surface plasmon band of gold nanoparticles is very large when compared to typical organic dyes. In this study, gold nanoparticle-A␤ conjugates were prepared and the photothermal ablation of amyloid peptide aggregates by laser irradiation was studied. Monofunctional gold nanoparticles were prepared using a recently reported solid phase modification method and then coupled to fragments of A␤ peptide, namely A␤(31-35) and A␤(25-35). The conjugates were then mixed with A␤ fragments in solution. The aggregated peptide formation was studied by a series of spectroscopic and microscopic techniques. The peptide aggregates were then irradiated by a continuous laser. With gold nanoparticle-A␤ conjugates present the aggregates were destroyed by photothermal ablation. Gold nanoparticles without A␤ conjugation were not incorporated into the aggregates and when irradiated did not result in photothermal ablation. With gold nanoparticle-A␤ conjugates the ablation was selective to the site of irradiation and minimal damage was observed as a result of thermal diffusion. In addition to the application of photoablation to a protein-based sample the nanoparticles and the chemistry involved provide an easily monofunctionalized photothermal material for the biological conjugation.

Chemical Communications, 2006

Herein, we report the surface modification of quartz with a coumaryl-aza-crown-6 derivative to de... more Herein, we report the surface modification of quartz with a coumaryl-aza-crown-6 derivative to detect Saxitoxin using fluorescence enhancement through Photoinduced Electron Transfer and the sensitivity with this system approaches the limit of the mouse bioassay which is the current benchmark for Saxitoxin detection.

Langmuir, Feb 1, 2006

Peptidolipid C 18 H 35 O (stearoyl)-Phe-Trp-Ser-His-Glu (peptidolipid A) was synthesized and spre... more Peptidolipid C 18 H 35 O (stearoyl)-Phe-Trp-Ser-His-Glu (peptidolipid A) was synthesized and spread at the air-water interface to study the interaction with an organophosphorus compound. Paraoxon, sodium dihydrogen phosphate, or 4-nitrophenyl phosphate disodium was added to the subphase, but only paraoxon changed the surface pressure-area (π-A) isotherm of peptidolipid A. This indicated a specific interaction between paraoxon and peptidolipid A. To clarify which amino acid residue of peptidolipid A was responsible for the interaction, peptidolipid B, namely, C 18 H 35 O-Gly-His-Ser-Glu-Glu, was synthesized and studied as a Langmuir film. The difference between the π-A isotherms of peptidolipid B in the absence and presence of paraoxon in the subphase was minimal; consequently, the presence of amino acids phenylalanine (Phe) and tryptophan (Trp) in peptidolipid A may explain the interaction between peptidolipid A and paraoxon. The compression-decompression cycles and kinetic studies of peptidolipid A showed that the Langmuir film was stable. The in situ optical properties of the peptidolipid A Langmuir film such as UV-vis and fluorescence spectroscopies were examined to elucidate the interaction between peptidolipid A and paraoxon. UV-vis absorption of peptidolipid A was investigated in the presence and absence of paraoxon in the subphase. The emission maximum of fluorescence of Trp in peptidolipid A was observed at 351 nm on pure water, and the band intensity decreased when the concentration of paraoxon increased in the subphase. This suggested that the Trp was involved in the molecular recognition process. Epifluorescence micrographs showed domains of peptidolipid A on the pure water subphase. In the presence of paraoxon in the subphase, the Langmuir film of peptidolipid A showed a homogeneity, which was another indication of the recognition between paraoxon and peptidolipid A.

Colloids and Surfaces B: Biointerfaces, Jul 1, 2006

A␤ (31-35) peptide and control peptides as well as full length A␤ (1-40) and A␤ (1-42) peptides w... more A␤ (31-35) peptide and control peptides as well as full length A␤ (1-40) and A␤ (1-42) peptides were labelled with luminescent CdSe/ZnS quantum dots (QDs) to observe the morphology of amyloid fibers. A comparison was made between QDs and an organic dye, namely Dansyl group, which showed that the QDs present a much better contrast for imaging than the organic dye.

Langmuir, Jun 16, 2005

Newly designed poly(amido amine) dendrimers, which have an azacrown core, hexyl spacers, and meth... more Newly designed poly(amido amine) dendrimers, which have an azacrown core, hexyl spacers, and methyl ester terminals (aza-C6-PAMAM dendrimer), were spread at the air-water and air-silver nanoparticle suspension interfaces, and their film structures were examined by surface pressure-area (π-A) and surface potential-area (∆V-A) isotherms and epifluorescence microscopy. It was revealed that generation (G) 1.5 aza-C6-PAMAM dendrimer on a water subphase formed homogeneous film with face-on configuration, and this configuration was maintained during compression. On the other hand, a G2.5 dendrimer film on the air-water interface took initially homogeneous and face-on configuration that was followed by the conformational change during compression. Using a silver nanoparticle suspension as subphase, G1.5 film was significantly reinforced, and the partial collapse (cracks) in the film appeared as network texture. For a G2.5 dendrimer film, the π-A and ∆V-A isotherm properties were similar to that on the water subphase except for the collapsed film; small spots instead of cracks were formed under the film after collapse. These effects of the silver nanoparticle may be due to the formation of a dendrimer/silver nanoparticle composite. The formation process of the nanocomposite film was verified by UV-vis spectroscopy. For the G1.5 dendrimer, silver clusters and nanoparticles adsorbed to the dendrimer film after spreading and formed a small amount of aggregates. During compression, the aggregation proceeded even at low surface pressure. For the G2.5 dendrimer, a dendrimer/nanoparticle composite was also formed after spreading. However, with the initial compression, the absorption bands of clusters, nanoparticles, and aggregate increased together. Upon further compression, while the bands of cluster and nanoparticles decreased, the bands of aggregate still increased. These results suggest that the G2.5 dendrimer covered the cluster and nanoparticles more efficiently than the G1.5 dendrimer did because of the larger molecular size.

Chemistry of Materials, Feb 18, 2015

ABSTRACT One prevention and therapeutic strategy for diseases associated with peptide or protein ... more ABSTRACT One prevention and therapeutic strategy for diseases associated with peptide or protein fibrillation is to inhibit or delay the fibrillation process. Carbon dots (C-Dots) have recently emerged as benign nanoparticles to replace toxic quantum dots, and have attracted great attention because of their unique optical properties and potential applications in biological systems. However, the effect of C-Dots on peptide or protein fibrillation has not been explored. In this in vitro study, human insulin was selected as a model to investigate the effect of C-Dots on insulin fibrillation. Water soluble fluorescent C-Dots with sizes less than 6 nm were prepared from carbon powder and characterized by UV-Vis, fluorescence, FTIR, XPS, TEM and AFM. These C-Dots were able to efficiently inhibit insulin fibrillation in a concentration-dependent manner. The inhibiting effect of C-Dots was even observed at 0.2 µg/mL. Importantly, 40 µg/mL of C-Dots prevent 0.2 mg/mL of human insulin from fibrillation for 5 days under 65 oC, whereas insulin denatures in 3 hours under the same condition without C-Dots. The inhibiting effect is likely due to the interaction between C-Dots and insulin species before elongation. Cytotoxicity study shows that these C-Dots have very low cytotoxicity. Therefore, these C-Dots have the potential to inhibit insulin fibrillation in biological system as well as in pharmaceutical industry for the processing and formulation of insulin.

Journal of Materials Chemistry, 2005

... 56 Article CAS ; (e) DJ Doucette, MM Logan, JS Ramsdell and FMV Dolah, Toxicon, 1997, 35, 625... more ... 56 Article CAS ; (e) DJ Doucette, MM Logan, JS Ramsdell and FMV Dolah, Toxicon, 1997, 35, 625–636 Article ; (f) A. Negri and L. Llewellyn, Toxicon, 1998 ... 20, P. Kele, J. Orbulescu, TL Calhoun, RE Gawley and RM Leblanc, Tetrahedron Lett., 2002, 43, 4413–4416 Article CAS . ...

Langmuir, Feb 6, 2012

The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investiga... more The human insulin (HI) Langmuir monolayer at the air-water interface was systematically investigated in the presence and absence of Zn(II) ions in the subphase. HI samples were dissolved in acidic (pH 2) and basic (pH 9) aqueous solutions and then spread at the air-water interface. Spectroscopic data of aqueous solutions of HI show a difference in HI conformation at different pH values. Moreover, the dynamics of the insulin protein showed a dependence on the concentration of Zn(II) ions. In the absence of Zn(II) ions in the subphase, the acidic and basic solutions showed similar behavior at the air-water interface. In the presence of Zn(II) ions in the subphase, the surface pressure-area and surface potential-area isotherms suggest that HI may aggregate at the air-water interface. It was observed that increasing the concentration of Zn(II) ions in the acidic (pH 2) aqueous solution of HI led to an increase of the area at a specific surface pressure. It was also seen that the conformation of HI in the basic (pH 9) medium had a reverse effect (decrease in the surface area) with the increase of the concentration of Zn(II) ions in solution. From the compression-decompression cycles we can conclude that the aggregated HI film at air-water interface is not stable and tends to restore a monolayer of monomers. These results were confirmed from UV-vis and fluorescence spectroscopy analysis. Infrared reflection-absorption and circular dichroism spectroscopy techniques were used to determine the secondary structure and orientation changes of HI by zinc ions. Generally, the aggregation process leads to a conformation change from α-helix to β-strand and β-turn, and at the air-water interface, the aggregation process was likewise seen to induce specific orientations for HI in the acidic and basic media. A proposed surface orientation model is presented here as an explanation to the experimental data, shedding light for further research on the behavior of insulin as a Langmuir monolayer.

Journal of Colloid and Interface Science, Apr 1, 2008

A glycosylphosphatidylinositol (GPI)-anchored enzyme (rat osseous plate alkaline phosphatase-OAP)... more A glycosylphosphatidylinositol (GPI)-anchored enzyme (rat osseous plate alkaline phosphatase-OAP) was studied as monolayer (pure and mixed with lipids) at the air-water interface. Surface pressure and surface potential-area isotherms showed that the enzyme forms a stable monolayer and exhibits a liquid-expanded state even at surface pressure as high as 30 mN m(-1). Isotherms for mixed dimyristoylphosphatidic acid (DMPA)-OAP monolayer showed the absence of a liquid-expanded/liquid-condensed phase transition as observed for pure DMPA monolayer. In both cases, pure or mixed monolayer, the enzyme preserves its native conformation under compression at the air-water interface as observed from in situ p-polarized light Fourier transform-infrared reflection-absorption spectroscopic (FT-IRRAS) measurements. Changes in orientation and conformation of the enzyme due to the presence or absence of DMPA, as well as due to the surface compression, are discussed.

Tetrahedron Letters, Jun 1, 2002

Two novel fluorescent chemosensors in which an aza-crown is linked to 4-coumaryl fluorophores by ... more Two novel fluorescent chemosensors in which an aza-crown is linked to 4-coumaryl fluorophores by a methylene spacer have been synthesized for sensing saxitoxin. Fluorescence enhancement was observed upon binding of the dicationic toxin molecule, ...

ChemInform, May 20, 2010

ABSTRACT

Journal of Colloid and Interface Science, Sep 1, 2015

The changes of interfacial properties of b-galactosidase introduced into different pH environment... more The changes of interfacial properties of b-galactosidase introduced into different pH environments are investigated through surface chemistry and in situ spectroscopy. Conditions for an optimal Langmuir monolayer formation were firstly obtained by varying the subphase salt concentration and the surface-pressure area isotherm was used to extrapolate the limiting molecular area of the enzyme monolayer to be around 42,000 Å 2 molecule À1. Surface pressure stability measurements held at 20 mN/m for 90 min along with compression-decompression cycles revealed no aggregate formation at the air-water interface. Consistent with the data obtained from the isotherm, in situ UV-Vis and fluorescence spectroscopy shows a steep rise in absorbance and photoluminescence intensity correlating to with a switch from a liquid-expanded to a liquid-condensed phase. A decrease in subphase pH increased the electrostatic repulsion as the enzyme was protonated, leading to an expanded monolayer. Infrared absorption-reflection spectroscopy demonstrates that the enzyme adopts mainly b-sheet conformation at the air-water interface before and during the compression.

Journal of Physical Chemistry C, Mar 10, 2009

Supporting Information All UV measurements were performed on a Hewlett-Packard 8452A diode array ... more Supporting Information All UV measurements were performed on a Hewlett-Packard 8452A diode array spectrophotometer fitted for air-water interface measurements. A detailed description of the experimental setup was published elsewhere 1 .

Colloids and Surfaces B: Biointerfaces, May 1, 2013

Fluorescent insulin fibrils gold nanoclusters (Au NCs) have been synthesized through the reductio... more Fluorescent insulin fibrils gold nanoclusters (Au NCs) have been synthesized through the reduction of gold by human insulin in fibrillated form. Likewise, nanocluster formation has been regulated by insulin, working as a protein-based template. Environment- and surface-controlled experiments have shown the optimized synthesis conditions is comprised of a pure aqueous alkaline solvent for insulin under constant heat at physiological temperature (37°C) prior to addition of the Au precursor (HAuCl4), followed by subsequent heating (37°C) and vigorous stirring after the addition of HAuCl4 until the completion of the synthetic approach. Microscopy experiments detected the presence of primordial fibril structures in samples of heated human insulin in the alkaline medium prior to addition of HAuCl4, while encountering more developed insulin fibrils in the terminal production of Au NCs. This investigation provides insight to the development of a novel synthesis of Au NCs in the alkaline medium, while providing a graphical description of the environmental and surface-dependent effects that were presented in the synthesis of human insulin nanoclusters. The study provides pertinent information for future synthetic procedures, as the protein state of several protein-nanoparticle systems may reflect on the results that were obtained herein.

Journal of Parkinson's disease and Alzheimer's disease, 2015

Journal of Physical Chemistry C, Feb 24, 2007

The neuritic plaques formed by amyloid-peptide (A) play a seminal role in the pathogenesis of Alz... more The neuritic plaques formed by amyloid-peptide (A) play a seminal role in the pathogenesis of Alzheimer's disease (AD). A sequence 25-35 (GSNKGAIIGLM) is among the most frequently studied A derivatives for the reason that it possesses the structural characteristic of A and remains neurotoxic. A (25-35) was modified with an aliphatic chain (C 18) at the N-terminal of the peptide for the study of the Langmuir monolayer at the air-water interface. The main advantage of the 2D approach is the self-assembly of the peptide moiety in the subphase, and therefore the aggregation process of the peptidolipid A (25-35) was monitored by surface pressure and surface potential-area isotherms. The real-time epifluorescence microscopy was utilized to observe the topography of the domains formed, whereas polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) provided the information on the structural features of the domains at the airwater interface. Langmuir-Blodgett films were prepared to examine by circular dichroism (CD) the conformation of the peptidolipid film in the domains.