Nonpolar Face Research Articles

Janus nanoparticles synthesized from hydrophobic carbon dots and carboxymethyl cellulose: Novel antimicrobial additives for fresh food applications

The aim of this study was to synthesis Janus nanoparticles (JPs) using beeswax-based hydrophobic carbon dots to form the non-polar face and hydrophilic carboxymethyl cellulose to form the hydrophilic face. Size, morphology, composition, and optical properties of the JPs were characterized. Scanning electron microscopy and light scattering analysis showed these nanoparticles were spheroids with average diameters around 4 nm. A cytotoxicity assay (L929 cells) showed that the hydrophobic carbon dots and JPs exhibited significant toxicity (decrease in cell viability) at 1.5 and 5 mg/mL, respectively. For the hydrophobic carbon dots, the minimum inhibitory concentration was 0.02 mg/mL for Escherichia coli and 0.04 mg/mL for Listeria monocytogenes, whereas for the JPs it was 0.04 mg/mL for both bacteria. Both the hydrophobic carbon dots and JPs also exhibited appreciable antioxidant activity. These particles were then incorporated into minced beef as novel preservatives. At 0.05% concentration, both kinds of nanoparticles caused a significant reduction in chemical and microbial degradation of the meat during storage. The JPs had a greater effect on mesophile (3.3 log10 CFU/g reduction) than on psychrophile (2.8 log10 CFU/g reduction) microbial populations within the meat. The preparation of JPs based on carbon dots, reduced cytotoxicity and improved their antimicrobial properties. JPs developed in this study may be used as novel preservatives with antimicrobial and antioxidant properties in foods.

Differences between Polar-Face and Non-Polar Face 4H-SiC/SiO<sub>2 </sub>Interfaces Revealed by Magnetic Resonance Spectroscopy

We performed electron-spin-resonance (ESR) and electrically-detected-magnetic-resonance (EDMR) spectroscopy on 4H-SiC(1120)/SiO2 interface defects to study differences between polar-face and non-polar-face 4H-SiC MOS interfaces. We found that in the non-polar-face MOS system, interface defects prefer to form spin-less states of doubly-occupied states and/or empty states, probably due to charge transfer between Si and C atoms at the interfaces.

Designing a Temporin-1CEa Analog with Improved in Vitro Selectivity towards Prostate Cancerous Cell Line (LNCaP)

Temporins are small antimicrobial peptides which have cytotoxic effects against different cancerous cell lines. However, their cytotoxicity against normal cells has been reported in some studies. Designing new temporin analogs with selective cytotoxicity against cancerous cell lines is considered a goal in drug development. In this regard, four new temporin-1CEa analogs (either C-terminally α-amidated or not) with increased net positive charge, as well as the potential of hydrogen bond formation were designed and their selective cytotoxicity against prostate carcinoma cell line (LNCaP) was evaluated. MTT assay was employed to test the simultaneous effects of the modifications on the cytotoxicity of the analogs against both normal (HFFF2) and cancerous (LNCaP) cell lines. Then, the in vitro selectivity index of each analog was determined using the equation of selectivity index (SI= IC50 of peptide against normal cell line / IC50 of peptide against cancerous cell line). The structural modifications of temporin-1CEa (increasing the net positive charge and removing C-terminally amidated group, as well as the potential of hydrogen bond formation on the non-polar face of α-helical structure) reduced the cytotoxicity of K2K3W15-COOH analog against both cancerous (LNCaP) and normal (HFFF2) cell lines. However, the modifications resulted in improving the in vitro selectivity index of K2K3W15-COOH compared to the temporin-1CEa (1.67 vs. 1.33, respectively). The results of the present study indicated that some structural modifications may lead to a diminution in the cytotoxicity of new analogs against cancerous cells. However, the same modifications can be associated with better selectivity indexes of new analogs due to a further decrease in their cytotoxicity against normal cells.

Unexpected Electronic Features of NiO Quantum Dots Produced by Femtosecond Pulsed Laser Ablation in Water.

This study examines the effect of quantum confinement and surface orientations on the electronic properties of NiO quantum dots. It compares NiO nanocrystals produced via atmospheric-pressure microplasma and femtosecond laser (fs-laser) ablation in water, finding that both methods yield quantum-confined nanocrystals with a defined face-centered cubic lattice. Notably, fs-laser synthesis generates crystalline nanocrystals from both crystalline and amorphous targets. While the electronic properties, i.e., energy of the highest occupied molecular orbital and lowest unoccupied molecular orbital (LUMO), of microplasma-synthesized NiO nanocrystals are consistent with the literature, the electronic characteristics of NiO nanocrystals produced by a fs-laser, particularly the high-lying LUMO level, are unusual for NiO quantum dots. Supported by density functional theory calculations, we show that the observed level positions are related to the different polar and nonpolar faces of the nanocrystal surface.

Surface cleanliness of hydrothermally grown zinc oxide microparticles compared to commercial nanoparticles

Zinc oxide (ZnO) nanoparticles are attractive candidates for application as antibacterial agents due to their effectiveness against antibiotic-resistant strains of both gram-positive and gram-negative bacteria. Despite this potential, applications are limited by fundamental gaps in current understanding of their underlying antibacterial pathways. ZnO microparticles are less often used in antibacterial research compared to ZnO nanoparticles due to the potential of nanoparticles for internalization into bacterial cells. Microparticles are nevertheless of interest as a research platform as their increased scale allows both the nonpolar and polar faces of the ZnO crystals to be distinguished. This in turn provides a useful platform to study surface interactions with bacteria, allowing for more targeted investigation of antibacterial mechanisms. Previous preliminary studies have indicated that hydrothermally grown ZnO microparticles exhibit comparable antibacterial activity to commercial ZnO nanoparticles further adding to their utility. The purpose of this research was to examine the surface cleanliness of ZnO microparticles in comparison to nanoparticles utilizing both scanning electron microscopy (SEM) as well as Fourier transform infrared spectroscopy (FTIR). The results of our experiments supported our hypothesis that there were no significant differences in the surface contamination of ZnO microparticles compared to nanoparticles. This supports the usage of ZnO microparticles as a viable platform for studying antibacterial mechanisms observed at the nanoscale knowing that in the absence of internalization effects the mechanism of antibacterial action across scales is intrinsic to ZnO and not a result of differing surface cleanliness.

(Invited) Improving Our Understanding of Conducting Polymer Binders

As lithium-ion batteries reach their intrinsic performance limits, next-generation battery technology arises that relies much more strongly on the electrode matrix. Traditional compositions of binders and conductive additives with non-polar surfaces face intrinsic obstacles in these developments. In many next-generation electrode formulations, this incompatibility reveals itself through particle disconnection, increased electrode inhomogeneity1, and conductive additive agglomeration2. Conducting polymers are an apparent solution to such problems. Conducting polymers and their composites can be designed to exhibit increased adhesion, stronger interactions with active material surfaces and electrolytes, and favorable mechanical properties, while providing electronic connectivity at the adhesive contact with the active material3. Many examples have been presented in the literature that demonstrate improved electrode performance using such composites4–6.A common form of conducting polymer composites combines an intrinsically conductive polymer (e.g. polypyrrole, polythiophene, polyaniline) with a polyelectrolyte (e.g. polacrylate, polystyrene sulfonate, carboxymethyl cellulose). This presentation discusses an exploration of some of the fundamental properties of composites of polypyrrole with carboxymethyl cellulose. The work shows intrinsically favorable properties of the composite for application in batteries7. Among those properties are that it can be easily processed in water and N-methyl-2-pyrrolidone, exhibits better adhesion to the current collector, shows competitive conductivity and distributes evenly across active materials. However, it will also be shown that the native structure of this composite is not ideal for long-range conduction and that improvement can be made to the material’s conductivity and capacitance8.Our work is targeting a more complete understanding of the properties of these composites as they are employed in battery environments. It demonstrates enormous promise for the use of conducting polymers as binders, but also gaps in our understanding of their interactions with electrolytes and active materials that need to be addressed to advance their impact on the development of next-generation batteries.

Modulation of ZnO Nanostructure for Efficient Photocatalytic Performance.

Structure has been considered to play an important role in photocatalytic performance of the semiconductors, but the intrinsic factors were rarely revealed. Herein, ZnO nanomaterials in the structures of thin film, nanowire array and nanosheet array were synthesized, and their structural characteristics, optical properties, photocurrent response and photocatalytic efficiency were compared with each other for illustrating the issue. The photoluminescence intensity decreased in the order of nanosheets, thin film and nanowires for improved lifetime of the photoexcited charges. The absorption of the nanosheets and nanowires improved obviously in the visible range with a redshift of the absorption edge than that of the thin film. The nanowires possessed the highest response current of 82.65μA at a response time of 2.0ms in a sensitivity of 87.93 at the light frequency of 1Hz, and gained the largest catalytic efficiency of 2.45μg/cm2h for the methylene blue degradation in UV light. Nevertheless, the improvement of catalytic efficiency of the nanosheets (up to 42.4%) was much larger than that of nanowires (5.7%) and thin film (2.6%) for the Au coating. The analysis revealed that the photocatalytic efficiency of the ZnO nanomaterials was modulated by the structure as it contained different surface area, roughness, defect and doping states, vacancies, polar and non-polar crystalline faces, which would provide structural design of semiconductor nanomaterials for the photoelectric and photocatalytic applications.

Structural insights on the selective interaction of the histidine-rich piscidin antimicrobial peptide Of-Pis1 with membranes

Of-Pis1 is a potent piscidin antimicrobial peptide (AMP), recently isolated from rock bream (Oplegnathus fasciatus). This rich in histidines and glycines 24-amino acid peptide displays high and broad antimicrobial activity and no significant hemolytic toxicity against human erythrocytes, suggesting low toxicity. To better understand the mechanism of action of Of-Pis1 and its potential selectivity, using NMR and CD spectroscopies, we studied the interaction with eukaryotic and procaryotic membranes and membrane models. Anionic sodium dodecyl sulfate (SDS) and lipopolysaccharide (LPS) micelles were used to mimic procaryotic membranes, while zwitterionic dodecyl phosphocholine (DPC) was used as eukaryotic membrane surrogate. In an aqueous environment, Of-Pis1 adopts a flexible random coil conformation. In DPC and SDS instead, the N-terminal region of Of-Pis1 forms an amphipathic α-helix with the non-polar face in close contact with the micelles. Slower solvent exchange and higher pKas of the histidine residues in SDS than in DPC suggest that Of-Pis1 interacts more tightly with SDS. Of-Pis1 also binds tightly and structurally perturbs LPS micelles. Of-Pis1 interacts with both Escherichia coli and mammalian cell membranes, but only in the presence of Escherichia coli membranes it populates the helical conformation. Furthermore, ligand-based NMR experiments support a tighter and more specific interaction with bacterial than with eukaryotic membranes. Overall, these data clearly show the selective interaction of this broadly active AMP with bacterial over eukaryotic membranes. The conformational information is discussed in terms of Of-Pis1 amino acid sequence and composition to provide insights useful to design more potent and selective AMPs.

In Silico and In Vitro Structure-Activity Relationship of Mastoparan and Its Analogs.

Antimicrobial peptides are an important class of therapeutic agent used against a wide range of pathogens such as Gram-negative and Gram-positive bacteria, fungi, and viruses. Mastoparan (MpVT) is an α-helix and amphipathic tetradecapeptide obtained from Vespa tropica venom. This peptide exhibits antibacterial activity. In this work, we investigate the effect of amino acid substitutions and deletion of the first three C-terminal residues on the structure–activity relationship. In this in silico study, the predicted structure of MpVT and its analog have characteristic features of linear cationic peptides rich in hydrophobic and basic amino acids without disulfide bonds. The secondary structure and the biological activity of six designed analogs are studied. The biological activity assays show that the substitution of phenylalanine (MpVT1) results in a higher antibacterial activity than that of MpVT without increasing toxicity. The analogs with the first three deleted C-terminal residues showed decreased antibacterial and hemolytic activity. The CD (circular dichroism) spectra of these peptides show a high content α-helical conformation in the presence of 40% 2,2,2-trifluoroethanol (TFE). In conclusion, the first three C-terminal deletions reduced the length of the α-helix, explaining the decreased biological activity. MpVTs show that the hemolytic activity of mastoparan is correlated to mean hydrophobicity and mean hydrophobic moment. The position and spatial arrangement of specific hydrophobic residues on the non-polar face of α-helical AMPs may be crucial for the interaction of AMPs with cell membranes.

Design of Novel Amphipathic α-Helical Antimicrobial Peptides with No Toxicity as Therapeutics against the Antibiotic-Resistant Gram-Negative Bacterial Pathogen, Acinetobacter Baumannii

We designed de novo and synthesized two series of five 26-residue amphipathic α-helical cationic antimicrobial peptides (AMPs) with five or six positively charged residues (D-Lys, L-Dab (2,4-diaminobutyric acid) or L-Dap (2,3-diaminopropionic acid)) on the polar face where all other residues are in the D-conformation. Hemolytic activity against human red blood cells was determined using the most stringent conditions for the hemolysis assay, 18h at 37°C, 1% human erythrocytes and peptide concentrations up to 1000 μg/mL (~380 μM). Antimicrobial activity was determined against 7 Acinetobacter baumannii strains, resistant to polymyxin B and colistin (antibiotics of last resort) to show the effect of positively charged residues in two different locations on the polar face (positions 3, 7, 11, 18, 22 and 26 versus positions 3, 7, 14, 15, 22 and 26). All 10 peptides had two D-Lys residues in the center of the non-polar face as “specificity determinants” at positions 13 and 16 which provide specificity for prokaryotic cells over eukaryotic cells. Specificity determinants also maintain excellent antimicrobial activity in the presence of human sera. This study shows that the location and type of positively charged residue (Dab and Dap) on the polar face are critical to obtain the best therapeutic indices.

Optical, surface charge state and photocatalysis study of ZnO with different exposure faces

A hydrothermal method was used to synthesize zinc oxide (ZnO) with different exposure faces. Only when the ratio of OH − / Zn2 + is 2/1, ZnO with different morphologies and exposure faces can be obtained by controlling the amount of the polyvinylpyrrolidone as a capping agent. Five samples with representative morphology and wurtzite crystal structure were selected from 28 different synthesis conditions. Their optical, surface charged, and photocatalytical properties are closely related to the exposed faces. The ultraviolet fluorescence emission is related to the nonpolar faces in the low index exposure face. All samples are n-type semiconductors and oxygen element is lacking compared to Zn. There is a great possibility that the oxygen vacancy is the oxygen defect that causes the visible fluorescence emission of the nanosheet. Samples are all positive-charged on the surface. The surface charge is not only related to the particle size but also directly affected by the polarity of exposed face and the missing atoms of the sample. The photocatalytic activity of ZnO with nanocolumn morphology is the best, due to high exposure ratio of the polar faces, maximum positive charge, and moderate particle size.

Class I and II aminoacyl‐tRNA synthetase tRNA groove discrimination created the first synthetase–tRNA cognate pairs and was therefore essential to the origin of genetic coding

The genetic code likely arose when a bidirectional gene replicating as a quasi-species began to produce ancestral aminoacyl-tRNA synthetases (aaRS) capable of distinguishing between two distinct sets of amino acids. The synthetase class division therefore necessarily implies a mechanism by which the two ancestral synthetases could also discriminate between two different kinds of tRNA substrates. We used regression methods to uncover the possible patterns of base sequences capable of such discrimination and find that they appear to be related to thermodynamic differences in the relative stabilities of a hairpin necessary for recognition of tRNA substrates by Class I aaRS. The thermodynamic differences appear to be exploited by secondary structural differences between models for the ancestral aaRS called synthetase Urzymes and reinforced by packing of aromatic amino acid side chains against the nonpolar face of the ribose of A76 if and only if the tRNA CCA sequence forms a hairpin. The patterns of bases 1, 2, and 73 and stabilization of the hairpin by structural complementarity with Class I, but not Class II, aaRS Urzymes appear to be necessary and sufficient to have enabled the generation of the first two aaRS-tRNA cognate pairs, and the launch of a rudimentary binary genetic coding related recognizably to contemporary cognate pairs. As a consequence, it seems likely that nonrandom aminoacylation of tRNAs preceded the advent of the tRNA anticodon stem-loop. Consistent with this suggestion, coding rules in the acceptor-stem bases also reveal a palimpsest of the codon-anticodon interaction, as previously proposed. © 2019 IUBMB Life, 2019 © 2019 IUBMB Life, 71(8):1088-1098, 2019.

Substitution of lysine for isoleucine at the center of the nonpolar face of the antimicrobial peptide, piscidin-1, leads to an increase in the rapidity of bactericidal activity and a reduction in toxicity.

Purpose: Piscidin-1 is an effective antimicrobial peptide (AMP) against a variety of microbes. However, its toxicity has been reported as a limitation for its potential therapeutic applications. The toxicity of piscidin-1 may be related to the long nonpolar face of this AMP. Here, we investigated different piscidin-1 analogs to reach a peptide with the reduced toxicity.Material and methods: In vitro and in vivo antibacterial activity and toxicity of piscidin-1 analogs generated by replacement of isoleucine at the border (I9) or the center (I16) of the nonpolar face of piscidin-1 by alanine or lysine were investigated.Results: The results indicated that among all peptides, piscidin-1 with the highest HPLC retention time (RT) and I16K-piscidin-1 with the lowest RT had the highest and lowest cytotoxicity, respectively. Although I16K-piscidin-1 possessed the same MIC value as the parent peptide (piscidin-1) and other analogs, I16K-piscidin-1 exhibited a higher rapidity of bactericidal action at 5×MIC. The β-galactosidase leakage and propidium iodide staining assays indicated a higher pore-forming capacity of I16K-piscidin-1 relative to the parent peptide (piscidin-1). Taken together, RT is suggested to have a direct association with the toxicity and an inverse association with the rapidity of bactericidal action and pore-forming capacity. After infection of mice with clinical colistin-resistant Acinetobacter baumannii or clinical methicillin-resistant Staphylococcus aureus strains, treatment with I16K-piscidin-1, but not piscidin-1 and other analogs, resulted in a significantly stronger bactericidal potency. Furthermore, I16K-piscidin-1 exhibited the lowest in vivo toxicity. Conclusion: Overall, in vitro and in vivo comparison of piscidin-1 and its analogs together documented that replacement of isoleucine at the center of the nonpolar face of piscidin-1(I16) by lysine leads to not only a decrease in toxicity potential but also an increase in bactericidal potential.

High-Resolution Structural Studies Elucidate Antiatherogenic and Anti-Inflammatory Properties of Peptides Designed to Mimic Amphipathic α-Helical Domains of Apolipoprotein A-I.

Peptides designed to mimic the antiatherogenic and anti-inflammatory properties of apolipoprotein A-I show that although lipid association is required, not all lipid-associating peptides exhibit these properties. Our studies of a series of peptides showed that peptides with aromatic residues at the center of the nonpolar face were able to interact with inflammatory lipids and inhibited inflammation, which resulted in the amelioration of several lipid-mediated disorders such as lesion development, tumor formation, and Alzheimer’s plaque formation. The pKa values determined using 13C nuclear magnetic resonance (NMR) spectroscopy of K residues located at the polar-nonpolar interface provided the first clue to the relative orientations of the peptide helices with respect to each other and around the edge of the lipid discoidal complexes. High-resolution 1H-NMR studies of peptide-lipid discoidal complex confirmed the amphipathic α-helical structure of the peptide, location of aromatic residues of the peptide closer to the polar-nonpolar interface, and head-to-tail arrangement of the peptide helices around the edge of the disc. Amphipathic α-helical structure and the location of aromatic residues (F, W, Y) closer to the polar-nonpolar interface in a lipid environment allow the peptide to strongly bind oxidized lipids resulting in its anti-inflammatory properties.

Identification of novel antimicrobial peptide from Asian sea bass (Lates calcarifer) by in silico and activity characterization.

BackgroundThe global crisis of antibiotic resistance increases the demand for the new promising alternative drugs such as antimicrobial peptides (AMPs). Accordingly, we have described a new, previously unrecognized effective AMP, named dicentracin-like, from Asian sea bass and characterized its antimicrobial activity by comparison with moronecidin.Methodology/ ResultsGene expression analysis demonstrated the expression of dicentracin-like peptide in tissues of the immune system such as the skin and the head kidney, which is an important endocrine and lymphoid organ. Moronecidin and dicentracin-like exhibited a higher antibacterial activity against gram-positive bacteria relative to gram-negative ones, while both peptides showed a greater binding ability to gram-negative bacteria compared to gram-positive ones. This contradiction between antibacterial activity and binding affinity may be related to the outer membrane from gram-negative bacteria. Compared with moronecidin, dicentracin-like peptide showed more potent binding ability to all gram-positive and gram-negative bacteria. In addition, dicentracin-like peptide exhibited a high antibacterial activity against the investigated microorganisms, except against Staphylococcus aureus. A direct relationship was found between the binding affinity/cationicity and the antibiofilm activity of the peptides wherein, an elevation in pH corresponded to a decrease in their antibiofilm property. Time-kill kinetics analysis against clinical Acinetobacter baumannii isolate indicated that bactericidal effect of dicentracin-like and moronecidin at inhibitory concentration (1XMIC) was observed after 4 and 6 hours, respectively, while bactericidal effect of both AMPs at concentration of 2XMIC was observed after 2 hours. Dicentracin-like peptide showed higher inhibitory activity at subinhibitory concentration (1/2XMIC), relative to moronecidin. Compared with moronecidin, dicentracin-like peptide possessed greater binding affinity to bacteria at high salt concentration, as well as at alkaline pH; In addition, dicentracin-like exhibited a higher antibiofilm activity in comparison to moronecidin even at alkaline pH. Hemolytic analysis against human RBC revealed that hemolytic activity of moronecidin was more potent than that of dicentracin-like, which is consistent with its greater non-polar face hydrophobicity.ConclusionsIn the present study, In Silico comparative sequence analysis and antimicrobial characterization led to identify a new, previously unrecognized antimicrobial function for named dicentracin-like peptide by comparison with moronecidin, representing a possible template for designing new effective AMPs and improving known ones.

Separation of highly charged (+5 to +10) amphipathic α-helical peptide standards by cation-exchange and reversed-phase high-performance liquid chromatography

We are currently examining the potential of amphipathic cationic α-helical peptides as a new generation of peptide standards for both cation-exchange high-performance liquid chromatography and reversed-phase chromatography. Thus, amphipathic peptides are particularly suitable for high-performance liquid chromatography standards due to the preferred binding of the non-polar face to the hydrophobic stationary phase of reversed-phase packings or the preferred binding of the polar face to the charged/hydrophilic stationary phase of cation-exchange packings. The ability of different reversed-phase or cation-exchange matrices to separate mixtures of peptide standards with only subtle hydrophilicity/hydrophobicity variations in both the non-polar and polar face of the peptides can then be assessed. Currently, we have designed de novo a mixture of six 26-residue all D-conformation amphipathic cationic α-helical peptides with a single, positively charged lysine residue in the center of the non-polar face and an increasing number of lysine residues (4–9 residues) replacing neutral residues in the polar face, resulting in an overall net positive charge of +5 to +10. Thus, the non-polar, preferred reversed-phase chromatography binding face remains constant, with only the polar face varying in hydrophilicity/hydrophobicity. Interestingly, even with the non-polar face remaining constant, reversed-phase columns of varying functional group properties (e.g., C8, C18, phenyl, polar endcapped, polar embedded) and porosity (porous versus superficially porous) were able to separate the six peptides in aq. TFA/acetonitrile gradients, albeit with different selectivities. The value of the standards in cation-exchange chromatography was expressed by monitoring the requirement of acetonitrile (0–40% in the mobile phase) to overcome hydrophobic interactions of the peptides with the cation-exchange matrix matrix when eluting with sodium perchlorate gradients at pH 6.5. Interestingly, the resolution of the higher charged peptides (+8,+9,+10) was particularly sensitive to acetonitrile levels. Our results clearly demonstrate the excellent potential of these novel peptide standards to enable optimal column choice and mobile phase conditions for reversed-phase chromatography and cation-exchange chromatography for peptide separations.

Water Dissociation and Further Hydroxylation of Perfect and Defective Polar ZnO Model Surfaces

ZnO is a high-band gap semiconductor material important for microelectronic and catalytic applications, such as water splitting among others. Although the nonpolar face of ZnO has been well-studied, its polar faces (Zn- and O-terminated) are less studied because of intrinsic difficulties to the model. Here, we combine density functional theory calculations and analytical modelling to determine the thermodynamics of the water molecule interaction with perfect ZnO polar model surfaces, (0001) and (0001̅) surfaces (p-Zn and p-O). Defects (oxygen vacancies, pits, and missing oxygen rows) are also investigated. Adsorption, dissociation, surface migration, and agglomeration are considered. We find that H2O preferentially adsorbs and dissociates on Zn atoms on p-Zn and at defects on p-O. At room temperature, water is found to spontaneously dissociate, except for p-O, in which dissociation is endothermic. After dissociation, the resulting protons either bind to surface oxygen atoms or to zinc atoms to form hydrides. Migration of H and OH is limited on p-Zn with moderate barriers and absent on p-O. Interestingly, further agglomeration or islanding of OH species is inhibited by repulsive OH–OH electrostatic forces. Consequently, although polar surfaces are highly reactive with water, they cannot sustain high OH coverages, unless highly defective. This limitation is one obstacle to ZnO catalytic activity, pointing to the need to tune temperature and pressure conditions.

Amphiphile-like self assembly of metal organic polyhedra having both polar and non-polar groups

Mixed linker metal-organic polyhedra (MOPs) with polar and non-polar groups on the same MOP have been synthesized. This yields two types of MOPs, one where the ligands are evenly and symmetrically distributed over each polyhedron, as confirmed crystallographically and the other where respective groups segregate. The segregation is confirmed by the amphiphile-like behavior of the latter MOP in different polarity solvents, as seen through transmission electron microscopy (TEM) even though the anchor points of the functional groups are ∼10 Å apart on the MOP surface.

Enantiomeric Effect of d-Amino Acid Substitution on the Mechanism of Action of α-Helical Membrane-Active Peptides.

V13K, a 26-residue peptide, has been shown to have strong antimicrobial activity, negligible hemolytic activity, and significant anticancer activity. In the present work, V13K was used as the framework to investigate the influence of helicity, as influenced by d-amino acid substitutions in the center of the peptide polar and non-polar faces of the amphipathic helix, on biological activity. The antibacterial and anticancer activities of the peptides were investigated. Atomic force microscopy and other biophysical methods were used to investigate the effect of peptide helicity on biological activity. The results showed the importance of suitable and rational modification of membrane-active peptides, based on helicity, in optimizing potential biological activity.

Identification of polar and nonpolar faces in ZnO nanostructures using conductive atomic force microscopy

ABSTRACTHere we present the local electrical characterization of individual ZnO nanorods (NRs) synthesized by spin coating method using precursor sol. Conductive atomic force microscopy (CAFM) was employed for investigating the local conductivity of these ZnO NRs. I-V curves studies on hexagonal top planes and rectangular side planes have shown nano-Schottky contact between ZnO NRs and tip. The Schottky barrier heights (SBHs) have been calculated to ∼0.63 eV, and ∼0.55 eV for these planes which are attributed to the polar and nonpolar faces respectively. This work provides a path way for constructing highly integrated nanoscale electronic devices with precise control.