Unconstrained Homooligomeric γ‑Peptides Show High Propensity for C₁₄ Helix Formation

Monosubstituted γ⁴-residues (γ⁴Leu, γ⁴Ile, and γ⁴Val) form helices even in short homooligomeric sequences. C₁₄ helix formation is established by X-ray diffraction in homooligomeric (γ)_<i>n</i> tetra-, hexa- and decapeptide sequences demonstrating the high propensity of γ residues, with proteinogenic side chains, to adopt locally folded conformations

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds

<i>Syn</i> vs <i>Anti</i> Carboxylic Acids in Hybrid Peptides: Experimental and Theoretical Charge Density and Chemical Bonding Analysis

A comparative study of <i>syn</i> vs <i>anti</i> carboxylic acids in hybrid peptides based on experimental electron density studies and theoretical calculations shows that, in the <i>anti</i> form, all three bond angles surrounding C_carboxyl of the −COOH group are close to ∼120°, as expected for a C-sp² atom, whereas in the <i>syn</i> form, the ∠C_α–C­(O)–O_hydroxyl angle is significantly smaller by 5–10°. The oxygen atom in the carboxyl group is more electronegative in the <i>anti</i> form, so the polarity of the acidic O–H bond is higher in the <i>anti</i> form compared to the <i>syn</i> form, as observed within the limitations of H atom treatment in X-ray diffraction. Consequently, the investigated <i>anti</i> carboxylic acid forms the strongest O–H···O hydrogen bond among all model compounds. Furthermore, according to natural bond orbital analysis, the oxygen lone pairs are clearly nonequivalent, as opposed to the general notion of hybridization of equivalent sp² and sp³ lone pairs on carbonyl or hydroxyl oxygen atoms. The hybridization of the lone pairs is directly related to the directionality and strength of hydrogen bonds