Utilizing Energy Transfer in Mn2+/Ho3+/Yb3+ Tri-doped ZnAl2O4 Nanophosphors for Tunable Luminescence and Highly Sensitive Visual Cryogenic Thermometry

Lanthanide (Ln3+)-doped upconversion (UC) phosphors converting near-infrared (NIR) light to visible light hold very high promise toward biomedical applications. The scientific findings on luminescent thermometers revealed their superiority for noninvasive thermal sensing. However, only few reports showcase their potential for applications in extreme conditions (temperatures below -70 °C) restricted by low thermal sensitivity. Here, we demonstrate the tailoring of luminescence properties via introducing Ho3+-Mn2+ energy transfer (ET) routes with judicious codoping of Mn2+ ions in ZnAl2O4/Ho3+,Yb3+ phosphor. Preferentially, a singular red UC emission is required to improve the bioimaging sensitivity and minimize tissue damage. We could attain UC emission with 94% red component by a two-photon UC process. Higher temperature annealing brings the color coordinates to the green domain, highlighting the potential for color-tunable luminescence switch. Moreover, this work investigates the thermometric properties of ZnAl2O4/Yb3+, Ho3+ in the range of 80-300 K and influence of inducing extra ET pathways by Mn2+ codoping. Interestingly, the luminescence intensities for nonthermally coupled (5F4,5S2) and the 5F5 radiative transitions of Ho3+ ions display opposite behavior at 80 and 300 K, which revealed competition between temperature-sensitive decay pathways. The codoping of Mn2+ ions is fruitful in causing a fourfold increase of absolute sensitivity. Notably, the color tunability from green through yellow to red is helpful in rough temperature estimation by naked eyes. The maximum relative (Sr) and absolute sensitivities (Sa) were estimated to be 1.89% K-1 (140 K) and 0.0734 K-1 (300 K), respectively. Even at 80 K, a Sa of 0.00447 K-1 and Sr of 0.6025% K-1 were achievable in our case, which are higher than most of the other Ln3+-based systems. The above-mentioned results demonstrate the potential of ZnAl2O4/Yb3+,Ho3+ for cryogenic optical thermometry and a strategy to design new Ln3+-based UC thermometers by taking advantage of ET routes.

Magnetite interaction with arsenic during sorptive removal from groundwater: a mechanistic study

A magnetic mixed iron oxide, magnetite (Fe₃O₄), was synthesized in the laboratory and characterized before its use as sorbent for arsenic removal. The characterization techniques used were X-ray diffraction (XRD), specific surface area, zeta potential and particle size measurements. The sorbent was applied for arsenic removal, without any pre or post treatment, from groundwater. The efficiency of sorption can only be improved by understanding the sorbent-sorbate interaction. For onsite monitoring of the sorbent-sorbate interaction, an electrochemical investigation using cyclic voltammetry (CV) measurement was developed. The study confirmed that the sorption of As(III) on Fe₃O₄ is dynamic (reversible) whereas that of As(V) is static (irreversible) in nature. Detailed investigation after the sorption was carried out utilizing X-ray photoelectron spectroscopy (XPS) measurement. The complexation of As(III)-Fe₃O₄ and As(V)-Fe₃O₄ without any redox transformation was evident from the XPS data. By careful examination of the results, a mechanism of arsenic removal by Fe₃O₄ was proposed.

Modulation of Surface Ti-O Species in 2D-Ti3C2TX MXene for Developing a Highly Efficient Electrocatalyst for Hydrogen Evolution and Methanol Oxidation Reactions

Developing cost-effective and earth-abundant noble-metal-free electrocatalysts is imperative for the imminent electrochemical society. Two-dimensional Ti₃C₂T_X (MXene) exhibits tunable properties with high electrical conductivity and a large specific surface area, which improve its electrochemical performance. Herein, the low-temperature annealing method is used to enrich MXene with a maximum number of Ti-O terminals without formation of titanium dioxide (TiO₂) under neutral pH conditions. MXene annealed at 200 °C is found to have a large number of Ti-O termination groups, resulting in a large electrochemically active surface area and increased active sites (-O termination groups) and hence excellent electrocatalytic performance compared to other samples as well as previous reported work. The optimized sample is found to show the lowest overpotential value of 0.07 V at 10 mA cm^-2 and a Tafel slope of 0.15 V dec^-1 toward the hydrogen evolution reaction (HER), whereas for the methanol oxidation reaction (MOR), the current density is 18.08 mA cm^-2, and the onset potential is -0.51 V. In addition, it also shows long-term stability and durability toward HER as well as MOR.

Defect-Induced Adsorption Switching (p- to n- Type) in Conducting Bare Carbon Nanotube Film for the Development of Highly Sensitive and Flexible Chemiresistive-Based Methanol and NO2 Sensor

Lightweight and flexible gas sensors are essentially required for the fast detection of toxic gases to pass on the early warning to deter accident situations caused by gas leakage. In view of this, we have fabricated a thin paper-like free-standing, flexible, and sensitive carbon nanotube (CNT) aerogel gas sensor. The CNT aerogel film synthesized by the floating catalyst chemical vapor deposition method consists of a tiny network of long CNTs and ∼20% amorphous carbon. The pores and defect density of the CNT aerogel film were tuned by heating at 700 °C to obtain a sensor film, which showed excellent sensitivity for toxic NO₂ and methanol gas in the concentration range of 1-100 ppm with a remarkable limit of detection ∼90 ppb. This sensor has consistently responded to toxic gas even after bending and crumpling the film. Moreover, the film heat-treated at 900 °C showed a lower response with opposite sensing characteristics due to switching of the semiconductor nature of the CNT aerogel film to n-type from p-type. The annealing temperature-based adsorption switching can be related to a type of carbon defect in the CNT aerogel film. Therefore, the developed free-standing, highly sensitive, and flexible CNT aerogel sensor paves the way for a reliable, robust, and switchable toxic gas sensor.

Solvated electron-induced synthesis of cyclodextrin-coated Pd nanoparticles: mechanistic, catalytic, and anticancer studies

Herein, using in situ generated solvated electrons in the reaction media, a highly time-efficient, one-pot green approach has been employed to synthesize palladium (Pd) nanoparticles (NPs) coated with a molecular assembly of α-cyclodextrin (α-CD). The appearance of a shoulder peak at 280 nm in the UV-Vis absorption spectra indicated the formation of Pd NPs, which was further confirmed from their cubic phase XRD pattern. The nanomorphology varied considerably as a function of the dose rate, wherein sphere-shaped NPs (average size ∼ 7.6 nm) were formed in the case of high dose rate electron-beam assisted synthesis, while nanoflakes self-assembled to form nanoflower-shaped morphologies in a γ-ray mediated approach involving a low dose rate. The formation kinetics of NPs was investigated by pulse radiolysis which revealed the formation of Pd-based transients by the solvated electron-induced reaction. Importantly, no interference of α-CD was observed in the kinetics of the transient species, rather it played the role of a morphology directing agent in addition to a biocompatible stabilizing agent. The catalytic studies revealed that the morphology of the NPs has a significant effect on the reduction efficiency of 4-nitrophenol to 4-aminophenol. Another important highlight of this work is the demonstration of the morphology-dependent anticancer efficacy of Pd NPs against lung and brain cancer cells. Notably, flower-shaped Pd NPs exhibited significantly higher cancer cell killing as compared to spherical NPs, while being less toxic towards normal lung fibroblasts. Nonetheless, these findings show the promising potential of Pd NPs in anticancer treatment.

3,3'-Diselenodipropionic acid (DSePA) forms 1:1 complex with Hg (II) and prevents oxidative stress in cultured cells and mice model

Mercury is one of the most toxic heavy metal for mammals particularly in inorganic form. In present study, 3,3'-diselenodipropionic acid (DSePA), a well-known pharmacological diselenide was evaluated for its interaction with HgCl₂ and ability to prevent HgCl₂-induced toxicity in experimental cellular and mice models. UV-visible, stopped flow, Fourier-transform infrared spectroscopy and ¹H nuclear magnetic resonance spectroscopy studies confirmed that DSePA sequestered Hg (II) ions with stoichiometry of 1:1 and binding constant of ~10⁴ M^-1. X-ray photoelectron spectroscopy and X-ray powder diffraction analysis suggested that diselenide group of DSePA was involved in the complexation with Hg (II) ions. Further, Hg-DSePA complex degraded within 10 days to form excretable HgSe. The binding constant of DSePA and Hg (II) was comparable with that of dihydrolipoic acid, a standard disulfide compound used in heavy metal detoxification. Corroborating these observations, pre-treatment of DSePA (10 μM) significantly prevented the HgCl₂ (50 μM)-induced glutathione oxidation (GSH/GSSG), decrease of thioredoxin reductase (TrxR) and glutathione peroxidase (GPx) activities and cell death in Chinese Hamster Ovary (CHO) cells. Similarly, intraperitoneal administration of DSePA at a dosage of 2 mg/kg for 5 consecutive days prior to exposure of HgCl₂ (1 mg/kg) significantly suppressed oxidative stress in renal and hepatic tissues of C57BL/6 mice. In conclusion, the protective effect of DSePA against Hg induced oxidative stress is attributed to its ability to rescue the activities of GPx, TrxR and GSH by sequestering Hg (II) ions. DSePA being a relatively safer selenium-compound for in vivo administration can be explored for mercury detoxification.

Evidences on As(III) and As(V) interaction with iron(III) oxides: Hematite and goethite

Arsenic, which is ubiquitous in nature, was found associated with iron oxides in soils and sediments. Our interest was to utilize the same mechanism for the sorptive removal of arsenic from groundwater. The iron(III) oxides: hematite, goethite, were synthesized, characterized and sorption studies of arsenic [As(III) and As(V)] were carried out in batch mode. For studying the evidence of the interaction between arsenic and iron oxide during the process of sorption, a new electrochemical method was developed. Differential pulse voltammetry (DPV) study indicated that the sorbed arsenic species is redox active on the surface of the sorbent. X-ray photoelectron spectroscopy (XPS) measurement was performed for confirmation of the changes occurring to the oxidation states of iron as well as arsenic after the sorption. XPS studies confirmed that the behavior of arsenic species on hematite/goethite was similar and occurs via a partial redox reaction. During sorption of As(III), a partial oxidation occurs resulting in As(V) species, simultaneously the Fe(III) present in the iron oxide gets reduced to Fe(II). However, during the sorption of As(V), there occurs a Fe(II) oxidation followed by As(V) reduction. Based on the results, a mechanistic scheme for sorption of arsenic on iron(III) oxides as sorbents was proposed.

Fabrication of plasmonic dye-sensitized solar cells using ion-implanted photoanodes

Plasmonic dye-sensitized solar cells containing metal nanoparticles suffer from stability issues due to their miscibility with liquid iodine-based electrolytes. To resolve the stability issue, herein, an ion implantation technique was explored to implant metal nanoparticles inside TiO₂, which protected these nanoparticles with a thin coverage of TiO₂ melt and maintained the localized surface plasmon resonance oscillations of the metal nanoparticles to efficiently enhance their light absorption and make them corrosion resistant. Herein, Au nanoparticles were implanted into the TiO₂ matrix up to the penetration depth of 22 nm, and their influence on the structural and optical properties of TiO₂ was studied. Moreover, plasmonic dye-sensitized solar cells were fabricated using N719 dye-loaded Au-implanted TiO₂ photoanodes, and their power conversion efficiency was found to be 44.7% higher than that of the unimplanted TiO₂-based dye-sensitized solar cells due to the enhanced light absorption of the dye molecules in the vicinity of the localized surface plasmon resonance of Au as well as the efficient electron charge transport at the TiO₂@Au@N719/electrolyte interface.

Ion implantation technique can resolve the stability issue of metal nanoparticles with liquid iodine-based electrolyte to improve PCE of plasmonic dye-sensitized solar cells.

Oxygen Reduction Reaction Activity of Microwave Mediated Solvothermal Synthesized CeO2/g-C3N4 Nanocomposite

Electrocatalytic active species like transition metal oxides have been widely combined with carbon-based nanomaterials for enhanced Oxygen Reduction Reaction (ORR) studies because of the synergistic effect arising between different components. The aim of the present study is to synthesize CeO₂/g-C₃N₄ system and compare the ORR activity with bare CeO₂. Ceria (CeO₂) embedded on g-C₃N₄ nanocomposite was synthesized by a single-step microwave-mediated solvothermal method. This cerium oxide-based nanocomposite displays enhanced ORR activity and electrochemical stability as compared to bare ceria.

Carbon nano tubes functionalized with novel functional group- amido-amine for sorption of actinides

The manuscript presents the results on the sorption of U(VI), Am(III) & Eu(III) from pH medium by a novel amido-amine functionalized multiwalled carbon nanotube (MWCNT). The novel functional group was introduced in the MWCNT by two step processes and characterized by various instrumental techniques like Scanning Electron Microscopy (SEM), Raman and X-ray Photoelectron Spectroscopy (XPS). The sorption process was found to be highly dependent on the pH of the solution with maximum sorption for both 233U, 241Am & 152+154Eu at pH 7.0. Kinetics of sorption was found to be fast with equilibrium reached in ∼15min and the sorption was found to be following pseudo 2nd order kinetics for the radionuclides. The sorption for both 233U and 152+154Eu followed Langmuir sorption model with maximum sorption capacity of 20.66mg/g and 16.1mg/g respectively. This has been explained by DFT calculations which shows that more negative solvation energy of U(VI) compared to Am(III) and Eu(III) and stronger U-MWCNT-AA complex is responsible for higher sorption capacity of U(VI) compared to Am(III) and Eu(III).The synthesized amido-amine functionalized MWCNT is a very promising candidate for removal of actinides and lanthanides from waste water solution with high efficiency.

3-Hydroxyphthaloyl-β-Lactoglobulin. II. Anti-Human Immunodeficiency Virus Type 1 Activity in in Vitro Environments Relevant to Prevention of Sexual Transmission of the Virus

It is anticipated that the rate of sexual transmission of viruses could be substantially decreased by the use of topical chemical barrier methods. Chemical modification of bovine (β-lactoglobulin (β-LG), the major protein of whey, led to the generation of a potent inhibitor (designated 3HP-β-LG) of human immunodeficiency virus type 1 (HIV-1) infection which was also active against herpesviruses. Compounds intended for topical application to prevent sexual transmission of viruses need to maintain their antiviral activity at pH <<7, corresponding to an acidic vaginal environment, and in the presence of seminal fluid. Results presented here show that the binding of 3HP-β-LG to the CD4 receptor for HIV, involved in the anti-HIV-1 activity of this compound, decreases with decreasing pH. The presence of seminal fluid also decreased the binding of 3HP-β-LG to CD4 and diminished the inhibitory effect of the compound on CD4-gp120 binding. 3HP-β-LG was shown to bind Zn++, and the inhibitory effect of seminal fluid could be substantially diminished by chelating Zn++ with ethylenediaminetetraacetate. Saliva had no effect on 3HP-β-LG binding to CD4 or on its interference with gp120-CD4 binding. The decreased 3HP-β-LG-CD4 binding and the concomitant reduction of gp120-CD4 binding inhibition by 3HP-β-LG at low pH and in the presence of seminal fluid could be compensated for by an increase of the 3HP-β-LG concentration and by adding Zn++ chelators to 3HP-β-LG. These results provide a background for the design of 3HP-β-LG formulations for topical use.

3-Hydroxyphthaloyl-β-Lactoglobulin. I. Optimization of Production and Comparison with other Compounds Considered for Chemoprophylaxis of Mucosally Transmitted Human Immunodeficiency Virus Type 1

Modification of the major bovine whey protein, β-lactoglobulin (β-LG) by 3-hydroxyphthalic anhydride (3HP) leads to the generation of a potent inhibitor of infection by human immunodeficiency virus (HIV) types 1 and 2, designated 3HP-β-LG. 3HP-β-LG also has antiviral activity against herpesviruses, albeit at concentrations exceeding those required for inhibition of HIV-1 infection. The topical application of 3HP-β-LG to decrease the rate of sexual transmission of HIV and other sexually transmitted viruses worldwide is being considered. Results presented here: (i) define the conditions for chemical modification of β-LG by 3HP, resulting in 3HP-β-LG with optimum anti-HIV-1 activity; (ii) show that β-LG, prior to chemical modification, or 3HP-β-LG can be exposed to the elevated temperatures used to pasteurize milk without adversely affecting anti-HIV-1 activity; (iii) provide evidence that 3HP-β-LG is a more potent anti-HIV-1 compound than sulphated polysaccharides, other candidate compounds considered as prophylactic agents to prevent sexual transmission of HIV-1; and (iv) confirm that the primary target for 3HP-β-LG is CD4, although binding to the HIV-1 envelope protein gp120 was also observed and contributed to the antiviral activity of 3HP-β-LG.

Change in the Affinity of Ethylene Glycol Methacrylate Phosphate Monomer and Its Polymer Anchored on a Graphene Oxide Platform toward Uranium(VI) and Plutonium(IV) Ions

The complexation behavior of the carbonyl and phosphoryl ligating groups bearing ethylene glycol methacrylate phosphate (EGMP) monomer and its polymer fixed on a graphene oxide (GO) platform was studied to understand the coordination ability of segregated EGMP units and polymer chains toward UO2(2+) and Pu(4+) ions. The cross-linked poly(EGMP) gel and EGMP dissolved in solution have a similar affinity toward these ions. UV-initiator induced polymerization was used to graft poly(EGMP) on the GO platform utilizing a double bond of EGMP covalently fixed on it. X-ray photoelectron spectroscopy (XPS) of the GO and GO-EGMP was done to confirm covalent attachment of the EGMP via a -C-O-P- link between GO and EGMP. The extent of poly(EGMP) grafting on GO by thermal analyses was found to be 5.88 wt %. The EGMP units fixed on the graphene oxide platform exhibited a remarkable selectivity toward Pu(4+) ions at high HNO3 conc. where coordination is a dominant mode involved in the sorption of ions. The ratio of distribution coefficients of Pu(IV) to U(VI) (DPu(IV)/DU(VI)) followed a trend as cross-linked poly(EGMP) (0.95) < EGMP in solvent methyl isobutyl ketone (1.3) < GO-poly(EGMP) (25) < GO-EGMP (181); the DPu(IV)/DU(VI) values are given in parentheses. The density functional theory computations have been performed for the complexation of UO2(2+) and Pu(4+) ions with the EGMP molecule anchored on GO in the presence of nitrate ions. This computational modeling suggested that Pu(4+) ion formed a strong coordination complex with phosphoryl and carbonyl ligating groups of the GO-EGMP as compared to UO2(2+) ions. Thus, the nonselective EGMP becomes highly selective to Pu(IV) ions when it interacts as a single unit fixed on a GO platform.

Enhanced thermoelectric properties of selenium-deficient layered TiSe(2-x): a charge-density-wave material

In the present work, we report on the investigation of low-temperature (300-5 K) thermoelectric properties of hot-pressed TiSe2, a charge-density-wave (CDW) material. We demonstrate that, with increasing hot-pressing temperature, the density of TiSe2 increases and becomes nonstoichiometric owing to the loss of selenium. X-ray diffraction, scanning electron microscopy, and transimission electron microscopy results show that the material consists of a layered microstructure with several defects. Increasing the hot-press temperature in nonstoichiometric TiSe2 leads to a reduction of the resistivity and enhancement of the Seebeck coefficient in concomitent with suppression of CDW. Samples hot-pressed at 850 °C exhibited a minimum thermal conductivity (κ) of 1.5 W/m·K at 300 K that, in turn, resulted in a figure-of-merit (ZT) value of 0.14. This value is higher by 6 orders of magnitude compared to 1.49 × 10(-7) obtained for cold-pressed samples annealed at 850 °C. The enhancement of ZT in hot-pressed samples is attributed to (i) a reduced thermal conductivity owing to enhanced phonon scattering and (ii) improved power factor (α(2)σ).

Charge transport in ultrathin iron-phthalocyanine thin films under high electric fields

The temperature dependent current-voltage (J-V) characteristics of 20 nm thick iron-phthalocyanine films are investigated in the temperature range of 300-30 K, and in the bias range of ±200 V. In the temperature range of 300-100 K, the charge transport is governed by bulk-limited processes with a bias dependent crossover from Ohmic (J∼V) to exponentially distributed shallow trap mediated space-charge-limited conduction (J∼V(α), α ≥ 2) to space-charge-limited conduction with field enhanced mobility (lnμ∼E(1/2)). However, at temperatures less than 100 K, the charge transport is electrode-limited, and undergoes a bias dependent transition from Schottky (lnJ∼V(1/2)) to multistep tunneling. From shallow trap mediated space-charge-limited conduction data the estimated room temperature mobility was found to be ∼1.9 cm(2) V (-1) s(-1). The high mobility of films is attributed to better structural organization due to the face-on stacking of molecules, which is supported by x-ray diffraction and UV-visible spectroscopy data.

Temperature dependent current-voltage characteristics of iron-phthalocyanine thin films

The current-voltage (I-V) characteristics of the crystalline alpha-phase iron phthalocyanine (FePc) thin films grown by molecular beam epitaxy have been investigated by using a planar geometry in which the metal electrodes are separated by 15 microm. By carrying out the room temperature I-V measurements on vacuum annealed (200 degrees C for 30 min under 10(-6) torr) FePc thin films under vacuum and after exposing them to the air, we demonstrate that the hysteresis in FePc films is intimately related to the filling and de-filling of surface traps created by chemisorbed oxygen. The presence of chemisorbed oxygen has been confirmed by the X-ray photoelectron spectroscopy. Room temperature I-V characteristics of air exposed films showed ohmic conduction in the lower voltage range and space-charge-limited-conductivity (SCLC) in the relatively high voltage. Temperature dependent measurements show that the hysteresis disappears at 250 K and the surface traps are distributed in energy about 0.22 eV deep.

Quantitative structure-activity relationship (QSAR) paradigm--Hansch era to new millennium

The analysis of structure-activity relationships started probably more than hundred years ago but the concept of quantitatively correlating physicochemical properties of molecules with their biological activities, termed as quantitative structure-activity relationship (QSAR), was initiated by Corwin Hansch and his groups in early 1960. Many new methods have emerged since then. The concept evolved from 2D QSAR to 3D QSAR and lately another dimension (4D QSAR) has been added. This evolution is briefly reviewed here.

A salt bridge between an N-terminal coiled coil of gp41 and an antiviral agent targeted to the gp41 core is important for anti-HIV-1 activity

HIV-1 envelope glycoprotein transmembrane subunit gp41 play a critical role in the fusion of viral and target cell membranes. The gp41 C-terminal heptad repeat region interacts with the N-terminal coiled-coil region to form a six-stranded core structure. Peptides derived from gp41 C-terminal heptad repeat region (C-peptides) are potent HIV-1 entry inhibitors by binding to gp41 N-terminal coiled-coil region. Most recently, we have identified two small organic compounds that inhibit HIV-1-mediated membrane fusion by blocking the formation of gp41 core. These two active compounds contain both hydrophobic and acidic groups while the inactive compounds only have hydrophobic groups. Analysis by computer modeling indicate that the acidic groups in the active compounds can form salt bridge with Lys 574 in the N-terminal coiled-coil region of gp41. Asp 632 in a C-peptide can also form a salt bridge with Lys 574. Replacement of Asp 632 with positively charged residues or hydrophobic residues resulted in significant decrease of HIV-1 inhibitory activity. These results suggest that a salt bridge between an N-terminal coiled coil of the gp41 and an antiviral agent targeted to the gp41 core is important for anti-HIV-1 activity.

Development of HIV entry inhibitors targeted to the coiled-coil regions of gp41

The discoveries that synthetic peptides corresponding to the N- and C-terminal heptad repeat (HR) regions of gp41 have potent anti-HIV activity opened a new avenue to identification of small molecule HIV entry inhibitors targeted to the HIV gp41 coiled-coil regions. Based on the structural information of the HIV gp41 core, three distinct approaches to develop small molecule anti-HIV agents have been reported. Each of these approaches has specific advantages, which will have complementary effects on the design of new strategies for identification of more potent HIV entry inhibitors. It is expected that novel antiviral drugs targeted to the HIV gp41 coiled-coil regions will be developed in the near future for the chemotherapy and/or prophylaxis of HIV infection and AIDS.

Structure-based identification of small molecule antiviral compounds targeted to the gp41 core structure of the human immunodeficiency virus type 1

Recent X-ray crystallographic determination of the HIV-1 envelope glycoprotein gp41 core structure opened up a new avenue to discover antiviral agents for chemotherapy of HIV-1 infection and AIDS. We have undertaken a systematic study to search for anti-HIV-1 lead compounds targeted to gp41. Using molecular docking techniques to screen a database of 20 000 organic molecules, we found 16 compounds with the best fit for docking into the hydrophobic cavity within the gp41 core and with maximum possible interactions with the target site. Further testing of these compounds by an enzyme-linked immunosorbent assay and virus inhibition assays discerned two compounds (ADS-J1 and ADS-J2) having inhibitory activity at micromolar concentrations on the formation of the gp41 core structure and on HIV-1 infection. These two compounds will be used as leads to design more effective HIV-1 inhibitors targeted to the HIV-1 gp41 core structure.

A screening assay for antiviral compounds targeted to the HIV-1 gp41 core structure using a conformation-specific monoclonal antibody

The human immunodeficiency virus type 1 (HIV-1) gp41 plays an important role in membrane fusion between viruses and target cells. The gp41 ectodomain contains two heptad repeat regions adjacent to the N and C-termini. Peptides derived from these two regions, designated N and C-peptides, are potent inhibitors of HIV-1 infection and can interact with each other to form a six-stranded coiled-coil, representing the fusogenic core structure of gp41. A monoclonal antibody was generated, designated NC-1, which specifically binds to the complex formed by the N and C-peptides, but not to the individual peptides. An enzyme linked immunosorbent assay (ELISA) was developed using NC-1 for detecting complex formed by N and C-peptides and for screening of organic compounds for antiviral agents that may interfere with complex formation and inhibit HIV-1 infection. Single point mutations in the C-peptides abolish the complex formation also eliminate their anti-HIV-1 activity. A phenylazo-naphthalene sulfonic acid derivative, designated ADS-J1, was found to inhibit both formation of NC-1 detectable complex and HIV-1-mediated membrane fusion, suggesting that the described ELISA is applicable to rapid screening of libraries of organic compounds for HIV-1 inhibitors targeted to the HIV-1 gp41 core structure.

Three-dimensional quantitative structure-activity relationship study on cyclic urea derivatives as HIV-1 protease inhibitors: application of comparative molecular field analysis

Three-dimensional quantitative structure-activity relationship (3D-QSAR) models have been developed using comparative molecular field analysis (CoMFA) on a large data set (118 compounds) of diverse cyclic urea derivatives as protease inhibitors against the human immunodeficiency virus type 1 (HIV-1). X-ray crystal structures of HIV-1 protease bound with this class of inhibitors were used to derive the most probable bioactive conformations of the inhibitors. The enzyme active site was used as a constraint to limit the number of possible conformations that are sterically accessible. The test sets have been created keeping in mind structural diversity as well as the uniform simple statistical criteria (mean, standard deviation, high and low values) of the protease inhibitory activities of the molecules compared to the training sets. Multiple predictive models have been developed with the training sets (93 compounds in each set) and validated with the corresponding test sets (25 compounds in each set). All the models yielded high predictive correlation coefficients (q2 from 0.699 to 0.727), substantially high fitted correlation coefficients (r2 from 0.965 to 0.973), and reasonably low standard errors of estimates (S from 0. 239 to 0.265). The steric and electrostatic effects have approximately equal contributions, 45% and 55% (approximately), respectively, toward explaining protease inhibitory activities. This analysis yielded models with significant information on steric and electrostatic interactions clearly discerned by the respective coefficient contour plots when overlapped on the X-ray structure of the HIV-1 protease. The HINT CoMFA study revealed significant contribution of hydrophobicity toward protease inhibitory activity. The 3D visualization technique utilizing these contour plots as well as the receptor site geometry may significantly improve our understanding of the inhibitor-protease (HIV-1) interactions and help in designing compounds with improved activity.

Comparative molecular field analysis (CoMFA) of a series of symmetrical bis-benzamide cyclic urea derivatives as HIV-1 protease inhibitors

A 3D-QSAR study using CoMFA methodology was conducted on a series of 29 symmetrical bis-benzamide cyclic urea derivatives having anti-HIV-1-protease activities. Active site minimization of the ligands was used to exclude conformations which are not sterically accessible within the active site. A significant cross validated correlation coefficient q2 (0.724) was obtained indicating the predictive potential of the model for untested compounds of this class. A significant non-cross-validated correlation coefficient (r2) of 0.971 with a low standard error estimate (S) of 0.119 was obtained indicating that the model reliably predicted the ant-protease activities of poorly to highly active compounds. The model was used to predict the anti-protease activities of eight test-set compounds, and the predicted values were in good agreement with the experimental values. The CoMFA coefficient contour plots identified several key features which explain the wide range of activities. The already reported 2D-QSAR along with the CoMFA model presented here may help in designing effective HIV-1 protease inhibitors.

Bovine beta-lactoglobulin modified by 3-hydroxyphthalic anhydride blocks the CD4 cell receptor for HIV

Sexual transmission is the most frequent (86%) route of adult HIV-1 transmission worldwide. In the absence of a prophylactic anti-HIV vaccine, other methods of preventing infection should be implemented. Virucidal spermicides have been considered for this purpose, but their application is contraindicated by adverse effects. Anti-HIV drugs or virus-neutralizing monoclonal antibodies are expensive, suggesting that their wide use in topical chemoprophylaxis is unlikely. This emphasizes the importance of developing other methods for preventing HIV transmission. The target cells for sexual and mucosal HIV transmission include T lymphocytes, monocytes/macrophages and dendritic cells. Therefore, compounds blocking HIV-CD4 binding are expected to inhibit virus transmission. In exploring the possibility that chemical modification of food proteins might lead to compounds with anti-HIV-1 activity, we found that bovine beta-lactoglobulin (beta-LG) modified by 3-hydroxyphthalic anhydride (3HP-beta-LG) (1) blocked at nanomolar concentrations the binding to CD4 of human (HIV) and simian (SIV) immunodeficiency virus surface glycoproteins and monoclonal antibodies specific for the HIV binding site on CD4 and (2) inhibited infection by HIV-1, including primary virus isolates, by HIV-2 and by SIV. The inexpensive and widely available source (whey) for production of 3HP-beta-LG suggests its potential application (nonparenteral) for diminishing the frequency of HIV transmission.

Structural requirements for and consequences of an antiviral porphyrin binding to the V3 loop of the human immunodeficiency virus (HIV-1) envelope glycoprotein gp120

Several porphyrin derivatives were reported to have anti-HIV-1 activity. Among them, meso-teta(4-carboxyphenyl)porphine (MTCPP) and other carboxyphenyl derivatives were the most potent inhibitors (EC50 <0.7 mu M). MTCPP bound to the HIV-1 envelope glycoprotein gp120 and to full-length V3 loop peptides corresponding to several HIV-1 isolates but not to other peptides from gp120 + gp41. However, it remained possible that MTCPP bound to regions on gp120 which cannot be mimicked by peptides. Further characterization of the binding domain for MTCPP is important for understanding the antiviral activity of porphyrins and for the design of anti-HIV-1 drugs interfering with functions of the virus envelope. Results presented here show that: (i) deletion of the V3 loop from the gp120 sequence resulted in drastically diminished MTCPP binding, suggesting that the V3 loop is the dominant if not the only target site on gp120; (ii) this site was only partially mimicked by full-length V3 loop peptides; (iii) MTCPP binding to the gp120 V3 loop elicited allosteric effects resulting in decreased accessibility of the CD4 receptor binding site; (iv) the binding site for MTCPP lies within the central portion of the V3 loop (KSIHIGPGRAFY for the HIV-1 subtype B consensus sequence) and does not involve directly the GPG apex of the loop. These results may help in designing antiviral compounds with improved activity.

Blocking of CD4 cell receptors for the human immunodeficiency virus type 1 (HIV-1) by chemically modified bovine milk proteins: potential for AIDS prophylaxis

The chemical transformation of synthetic combinatorial libraries to increase the diversity of compounds of medicinal interest was reported recently. Chemical modification of natural products represents a complementary approach to accomplish this aim. Modification of lysines by aromatic acid anhydrides, preferentially by 3-hydroxyphthalic and trimellitic anhydrides and trimellitic anhydride chloride, converted commonly available proteins (human and bovine serum albumin and casein) into potent inhibitors of (i) binding between the HIV-1 gp 120 envelope glycoprotein and the CD4 cell receptor, probably owing to their binding to CD4, and (ii) infection by HIV-1. Modified bovine milk proteins are also potent HIV-1 inhibitors and may have potential for anti-HIV-1 prophylaxis.

Three-dimensional structure-activity analysis of a series of porphyrin derivatives with anti-HIV-1 activity targeted to the V3 loop of the gp120 envelope glycoprotein of the human immunodeficiency virus type 1

Using comparative molecular field analysis (CoMFA), a 3D-QSAR model was developed for 21 porphyrin derivatives which have anti-HIV-1 activity and bind to the V3 loop of the envelope glycoprotein gp120 of the human immunodeficiency virus type 1. A significant PLS cross-validated r2cv (0.590) was obtained, indicating that the model could be used as a predictive tool for further design of porphyrin analogs. The model revealed at least three important sites for favorable electrostatic interactions and indicated favorable and unfavorable steric interaction sites. It was found that the occurrence of at least three positively charged and several hydrophobic amino acid residues is highly conserved at fixed positions of gp120 V3 loop sequences. This may support the validity of the proposed model and the hypothesis that porphyrins containing anionic and hydrophobic groups may interact with some of the highly conserved positively charged and hydrophobic sites, respectively, of the V3 loop. These interactions may induce conformational changes in the gp120 envelope glycoprotein leading to inhibition of virus entry into cells and of syncytium formation (cell-to-cell fusion) and thus to inhibition of virus replication.

International Commission for Protection Against Environmental Mutagens and Carcinogens. The importance of the hydrophobic interaction in the mutagenicity of organic compounds

The derivation of new QSAR and the review of published QSAR for the mutagenicity of a variety of chemicals acting on a variety of bacterial systems uncovers two classes of equations. 12 examples include a term for hydrophobicity and of these 12, 11 require activation either by S9 or cytosolic enzymes for the reduction of nitro compounds. There are 4 examples of direct-acting mutagens which do not require activation. Of these 4, 3 do not contain a term for hydrophobicity. The odd example is that of the sulfonate esters which do not require activation, but contain a term in log P. The hydrophobicity factor is not correlated with the type of bacteria used for the test.

The importance of hydrophobicity in the mutagenicity of methanesulfonic acid esters with Salmonella typhimurium TA100

The analysis of the mutagenic activity of a series of 15 methanesulfonate esters with Salmonella typhimurium TA100 shows that it can be correlated with the following equation: log TA100 = 1.10 log P + 0.73 log MMI -2.53, where MMI is the relative rate of reaction of the esters with N-methyl-2-mercaptoimidazole and P is the octanol/water partition coefficient. The results are compared with a number of other structure-activity studies on mutagenesis by a variety of types of chemicals.

Mechanistic interpretation of the genotoxicity of nitrofurans (antibacterial agents) using quantitative structure-activity relationships and comparative molecular field analysis

Quantitative structure-activity relationship (QSAR) and comparative molecular field analysis (CoMFA) have been applied to elucidate the mechanisms of genotoxicity (SOSIP) of nitrofuran derivatives on Escherichia coli PQ37. The following equation was developed: log SOSIP = -33.1qc2 + 1.00 log P - 1.50Isat - 1.19MR - 0.76I5,6 - 3.76; n = 40, r = 0.900, s = 0.475. The QSAR model clearly reveals three important factors, namely, electronic (qc2), hydrophobic (log P) and steric (MR, Isat, I5,6) contributing toward the genotoxic activity of this class of compounds. qc2, the charge on the c2 atom attached to the NO2 group, supports a furan ring opening mechanism in explaining the genotoxicity. The finding of the coefficient of 1 with log P conforms to our previous findings with several different classes of mutagens acting on different systems. CoMFA analysis clearly demonstrates its potential in unraveling the steric features of the molecules through contour maps. The CoMFA cross-validated model also supports the importance of the electronic factor. It could not reveal any hydrophobic influence because the interaction energies of the CH3 and H2O probes are collinear. QSAR (classical) and CoMFA, if used judiciously, may complement each other and enhance the applicability of SAR in drug design.

Mutagenicity of quinolines in Salmonella typhimurium TA100. A QSAR study based on hydrophobicity and molecular orbital determinants

The mutagenicity of 33 quinolines in the Salmonella test using TA98 and TA100 cells has been reported. Significant activity was found only with TA100 cells. Quantitative structure-activity relationships (QSAR) could be formulated using molecular orbital parameters or Hammett constants and hydrophobic parameters for those compounds with substituents in the 6, 7 and 8 positions. The QSAR points to the 2-position on the quinoline ring as being the site for activation by S9 oxidation.

Mutagenic activity of a series of synthetic and naturally occurring heterocyclic amines in Salmonella

26 synthetic and naturally occurring heterocyclic amines were tested in the Salmonella/microsome assay (Ames test) using tester strains TA98 and TA100 in the presence of an Aroclor-induced rat-liver S9 fraction. 9 of the compounds were protein-pyrolysis products which had previously been shown to be mutagenic. Mutagenic potencies similar to previously reported values were demonstrated for these compounds with the exception that Trp-P-1 was only mutagenic in strain TA98 in our study, although it had previously been reported to be weakly mutagenic in strain TA100. 17 structurally diverse heterocyclic amines were synthesized and tested for mutagenicity. The structural diversity of these synthetic heterocyclic amines will enhance the sensitivity of future quantitative structure-activity relationship (QSAR) studies by demonstrating the structural characteristics essential for mutagenicity. The results of this study provide a large data base for the mutagenicity of this important class of compounds.

Structure-activity relationship of mutagenic aromatic and heteroaromatic nitro compounds. Correlation with molecular orbital energies and hydrophobicity

A review of the literature yielded data on over 200 aromatic and heteroaromatic nitro compounds tested for mutagenicity in the Ames test using S. typhimurium TA98. From the data, a quantitative structure-activity relationship (QSAR) has been derived for 188 congeners. The main determinants of mutagenicity are the hydrophobicity (modeled by octanol/water partition coefficients) and the energies of the lowest unoccupied molecular orbitals calculated using the AM1 method. It is also shown that chemicals possessing three or more fused rings possess much greater mutagenic potency than compounds with one or two fused rings. Since the QSAR is based on a very wide range in structural variation, aromatic rings from benzene to coronene are included as well as many different types of heterocycles, it is a significant step toward a predictive toxicology of value in the design of less mutagenic bioactive compounds.

Mutagenicity of dimethyl heteroaromatic triazenes in the Ames test: the role of hydrophobicity and electronic effects

The mutagenicities of five heterocyclic 3,3-dimethyltriazenes have been evaluated in the Ames test. The octanol-water partition coefficients (P) for these triazenes have been measured, and their electron distributions and molecular orbital energies were calculated using the MNDO semiempirical molecular orbital method. Molecular structures of three triazenes have been determined using X-ray crystallography. The mutagenicities of these five triazenes, which range from nearly inactive to very highly mutagenic, are well predicted by quantitative structure-activity relationships that had been derived previously for the mutagenicity of aryltriazenes. The form of these equations indicates that more hydrophobic and more electron-rich triazenes are more active in the Ames test. This supports the hypothesis that the ease of initial triazene activation by cytochrome P-450 governs the mutagenicity of these compounds.