III. Foldamer Research 3910 A. Overview 3910 B. Motivation 3910 C. Methods 3910 D. General Scope 3912 IV. Peptidomimetic Foldamers 3912 A. The R-Peptide Family 3913 1. Peptoids 3913 2. N,N-Linked Oligoureas 3914 3. Oligopyrrolinones 3915 4. Oxazolidin-2-ones 3916 5. Azatides and Azapeptides 3916 B. The â-Peptide Family 3917 1. â-Peptide Foldamers 3917 2. R-Aminoxy Acids 3937 3. Sulfur-Containing â-Peptide Analogues 3937 4. Hydrazino Peptides 3938 C. The γ-Peptide Family 3938 1. γ-Peptide Foldamers 3938 2. Other Members of the γ-Peptide Family 3941 D. The δ-Peptide Family 3941 1. Alkene-Based δ-Amino Acids 3941 2. Carbopeptoids 3941 V. Single-Stranded Abiotic Foldamers 3944 A. Overview 3944 B. Backbones Utilizing Bipyridine Segments 3944 1. Pyridine−Pyrimidines 3944 2. Pyridine−Pyrimidines with Hydrazal Linkers 3945

A field guide to foldamers.

An electrophotographic photosensitive member that can not easily cause charging lines even where it is an electrophotographic photosensitive member employing as a conductive layer a layer containing metal oxide particles is disclosed. Also disclosed are a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member. The electrophotographic photosensitive member has a conductive layer which contains titanium oxide particles coated with tin oxide doped with phosphorus or tungsten.

Electrophotographic photosensitive member, process cartridge and electrophotographic apparatus

Over the last four decades, intense research has focused on the effects of small organic compounds that noncovalently bind to nucleic acids. These interactions have been shown to disrupt replication and/or transcription culminating in cellular death. Accordingly, DNA binding compounds have potential applications as anti-cancer and anti-viral agents. This report provides an overview of the different DNA-binding modes with an emphasis on DNA groove specificity for the groove-binding and intercalation modes. While most DNA-interacting agents selectively bind to DNA by either groove binding or intercalation, some compounds can exhibit both binding modes. The binding mode with the most favorable free energy for complex formation depends on the DNA sequence and structural features of the bound ligand.

Noncovalent interactions with DNA: an overview.

A novel DNA−lipid complex is prepared by replacing sodium counter cations by cationic amphiphilic lipids (1). The DNA−lipid complex is insoluble in aqueous solutions, but is soluble in most organic media such as benzene, ethanol, and chloroform. The DNA−lipid complex was confirmed to form double helical strands even in organic media, and the internal conformation of DNA strands could be reversibly changed from B-form to C-form in the organic solution (CHCl3/EtOH = 4:1) by changing the water content. A self-standing, water-insoluble DNA−lipid (1) film was prepared by casting from the organic solution and could be stretched to produce oriented DNA strands with their axes aligned along the stretching direction. The film can be impregnated with the drug ethidium bromide in the aqueous solution. The linear dichroism characteristics of the drug−DNA film show that the DNA strands are well oriented and the ethidium molecules are intercalated, as they are in normal aqueous solutions.

A DNA-lipid complex in organic media and formation of an aligned cast film

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1988.tb14425.x

Nucleic acids and nuclear magnetic resonance.

The solution conformations of the dinucleotide d(TT) and the modified duplex d(CGCGAATTCGCG)2 with N3'--> P5' phosphoramidate internucleoside linkages have been studied using circular dichroism (CD) and NMR spectroscopy. The CD spectra indicate that the duplex conformation is similar to that of isosequential phosphodiester RNA, a A-type helix, and is different from that of DNA, a B-type helix, NMR studies of model dimers d(TpT) and N3'--> P5' phosphoramidate d(TnpT) show that the sugar ring conformation changes from predominantly C2'-endo to C3'-endo when the 3'-phosphoester is replaced by a phosphoramidate group. Two-dimensional NMR (NOESY, DQF-COSY and TOCSY spectra) studies of the duplex provide additional details about the A-type duplex conformation of the oligonucleotide phosphoramidate and confirm that all furanose rings of 3'-aminonucleotides adopt predominantly N-type sugar puckering.

An Oligodeoxyribonucleotide N3′→P5′ Phosphoramidate Duplex Forms an A-type Helix in Solution

The 17O chemical shifts for six cyclic ketones which serve as models for quinones, viz. cyclohex-2-enone (1), α-tetralone (2), anthrone (3), 4H-pyran-4-one (4), 1-benzopyran-4(4H)-one (5), xanth-9-enone (6), and for six quinones, viz. benzoquinone, naphthoquinone, anthraquinone, 2,5-dihydroxybenzoquinone 5,8-dihydroxynaphthoquinone and 1,4-dihydroxyanthraquinone, were measured in toluene at 90°C. A shielding effect of approximately 50 ppm per fused benzene ring was noted for the quinones and related carbocyclic ketones; however, the analogous series of heterocyclic fused ring ketones 4–6 showed only a slight fused-ring effect on the carbonyl chemical shift. A single 17O resonance was observed for 2,5-dihydroxybenzoquinone (358 ppm) and 5,8-dihydroxynaphthoquinone (283 ppm), indicating rapid proton exchange between the oxygen atoms of these compounds. However, 1,4-dihydroxyanthraquinone gave two discrete 17O signals at 441 and 87 ppm, indicating that in this case proton exchange between oxygen atoms is slow.

17O NMR studies on polycyclic quinones, hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators

Natural abundance 17O NMR data for fifteen 2- and 4-substituted phenols, ten 3-and 5-substituted 2-hydroxybenzaldehydes and eight 3-substituted benzaldehydes, recorded at 75°C in acetonitrile are reported. The chemical shift change due to intramolecular hydrogen bonding for the phenolic oxygen was found to be 10–14 ppm shielding. In acetonitrile, the 17O NMR chemical shift for phenol signals was insensitive to added water up to water concentrations of 0.5 mole fraction. The 17O NMR chemical shifts of the 4-substituted phenols gave an excellent correlation (r = 0.990) with anisole 17O NMR data; the data also correlated moderately well with σ− (r = 0.974). The chemical shifts of the 3-substituted benzaldehydes were correlated with σ+ values (r = 0.991). A plot of the carbonyl chemical shift data for the substituted 2-hydroxybenzaldehydes versus the carbonyl data for 3-substituted benzaldehydes gave a slope of 0.87 and with r = 0.960. The plot of the 4-substituted phenol data with that for OH of the corresponding 2-hydroxybenzaldehydes gave a slope of 1.04 with r = 0.996. Proton to oxygen coupling for the phenolic group of several of the intramolecular hydrogen bonded systems was observed directly [J(OH) = 58–92 Hz]. MM2 and MOPAC calculations predict that the hydrogen bond distances and angles for the substituted 2-hydroxybenzaldehydes and the partial atomic charges for the carbonyl groups (AMI) were essentially constant. After corrections for electronic effects the chemical shift changes due to hydrogen bonding for the donor (ΔδHBD) and acceptor (ΔδHBA) of the carbonyl–phenol intramolecular bonding system were 5–12 and 30 ± 2 ppm, respectively. The ΔδHBA value was between those for keto and ester acceptors consistent with the relative basicity of the aldehyde group. The ΔδHBD value was substantially larger than those for phenolic donors to keto and ester groups.

17O NMR spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes

At low temperature and low salt concentration, both imino proton and 31p-nmr spectra of DNA complexes with the intercalators ethidium and propidium are in the slow-exchange region. Increasing temperature and/or increasing salt concentration results in an increase in the site exchange rate. Ring-current effects from the intercalated phenanthridinium ring of ethidium and propidium cause upfield shifts of the imino protons of A · T and G · C base pairs, which are quite similar for the two intercalators. The limiting induced chemical shifts for propidium and ethidium at saturation of DNA binding sites are approximately 0.9 ppm for A · T and 1.1 ppm for G · C base pairs. The similarity of the shifts for ethidium and propidium, in both the slow- and fast-exchange regions over the entire titration of DNA, shows that a binding model for propidium with neighbor-exclusion binding and negative ligand cooperativity is correct. The fact that a unique chemical shift is obtained for imino protons at intercalated sites over the entire titration and that no unshifted imino proton peaks remain at saturation binding of ethidium and propidium supports a neighbor-exclusion binding model with intercalators bound at alternating sites rather than in clusters on the double helix. Addition of ethidium and propidium to DNA results in downfield shifts in 31P-nmr spectra. At saturation ratios of intercalator to DNA base pairs in the titration, a downfield shoulder (approximately −2.7 ppm) is apparent, which accounts for approximately 15% of the spectral area. The main peak is at −3.9 to −4.0 ppm relative to −4.35 in uncomplexed DNA. The simplest neighbor-binding model predicts a downfield peak with approximately 50% of the spectral area and an upfield peak, near the chemical shift for uncomplexed DNA, with 50% of the area. This is definitely not the case with these intercalators. The observed chemical shifts and areas for the DNA complexes can be explained by models, for example, that involve spreading the intercalation-induced unwinding of the double helix over several base pairs and/or a DNA sequence- and conformation-dependent heterogeneity in intercalation-induced chemical shifts and resulting exchange rates.

S. Chandrasekaran

Papers

An Oligodeoxyribonucleotide N3′→P5′ Phosphoramidate Duplex Forms an A-type Helix in Solution

17O NMR studies on polycyclic quinones, hydroxyquinones and related cyclic ketones: Models for anthracycline intercalators

17O NMR spectroscopy: Study of intramolecular hydrogen bonding in phenols and salicylaldehydes

Imino 1H- and 31P-NMR analysis of the interaction of propidium and ethidium with DNA.

The effect of intercalator structure on binding strength and base-pair specificity in DNA interactions