ABSTRACT
In addition to amide hydrogen bonds and the hydrophobic effect, interactions involving π-bonded sp2 atoms of amides, aromatics, and other groups occur in protein self-assembly processes including folding, oligomerization, and condensate formation. These interactions also occur in aqueous solutions of amide and aromatic compounds, where they can be quantified. Previous analysis of thermodynamic coefficients quantifying net-favorable interactions of amide compounds with other amides and aromatics revealed that interactions of amide sp2O with amide sp2N unified atoms (presumably CâO···H-N hydrogen bonds) and amide/aromatic sp2C (lone pair π, n-π*) are particularly favorable. Sp3C-sp3C (hydrophobic), sp3C-sp2C (hydrophobic, CH-π), sp2C-sp2C (hydrophobic, π-π), and sp3C-sp2N interactions are favorable, sp2C-sp2N interactions are neutral, while sp2O-sp2O and sp2N-sp2N self-interactions and sp2O-sp3C interactions are unfavorable. Here, from determinations of favorable effects of 14 amides on naphthalene solubility at 10, 25, and 45 °C, we dissect amide-aromatic interaction free energies into enthalpic and entropic contributions and find these vary systematically with amide composition. Analysis of these results yields enthalpic and entropic contributions to intrinsic strengths of interactions of amide sp2O, sp2N, sp2C, and sp3C unified atoms with aromatic sp2C atoms. For each interaction, enthalpic and entropic contributions have the same sign and are much larger in magnitude than the interaction free energy itself. The amide sp2O-aromatic sp2C interaction is enthalpy-driven and entropically unfavorable, consistent with direct chemical interaction (e.g., lone pair-π), while amide sp3C- and sp2C-aromatic sp2C interactions are entropy-driven and enthalpically unfavorable, consistent with hydrophobic effects. These findings are relevant for interactions involving π-bonded sp2 atoms in protein processes.
Subject(s)
Amides , Water , Amides/chemistry , Entropy , Water/chemistry , Thermodynamics , Proteins/chemistry , Naphthalenes/chemistryABSTRACT
In addition to amide hydrogen bonds and the hydrophobic effect, interactions involving π-bonded sp 2 atoms of amides, aromatics and other groups occur in protein self-assembly processes including folding, oligomerization and condensate formation. These interactions also occur in aqueous solutions of amide and aromatic compounds, where they can be quantified. Previous analysis of thermodynamic coefficients quantifying net-favorable interactions of amide compounds with other amides and aromatics revealed that interactions of amide sp 2 O with amide sp 2 N unified atoms (presumably C=O···H-N hydrogen bonds) and amide/aromatic sp 2 C (lone pair-π, n-π * ) are particularly favorable. Sp 3 C-sp 3 C (hydrophobic), sp 3 C-sp 2 C (hydrophobic, CH-π), sp 2 C-sp 2 C (hydrophobic, π-π) and sp 3 C-sp 2 N interactions are favorable, sp 2 C-sp 2 N interactions are neutral, while sp 2 O-sp 2 O and sp 2 N-sp 2 N self-interactions and sp 2 O-sp 3 C interactions are unfavorable. Here, from determinations of favorable effects of fourteen amides on naphthalene solubility at 10, 25 and 45 °C, we dissect amide-aromatic interaction free energies into enthalpic and entropic contributions and find these vary systematically with amide composition. Analysis of these results yields enthalpic and entropic contributions to intrinsic strengths of interactions of amide sp 2 O, sp 2 N, sp 2 C and sp 3 C unified atoms with aromatic sp 2 C atoms. For each interaction, enthalpic and entropic contributions have the same sign and are much larger in magnitude than the interaction free energy itself. The amide sp 2 O-aromatic sp 2 C interaction is enthalpy-driven and entropically unfavorable, consistent with direct chemical interaction (e.g. lone pair-π) while amide sp 3 C- and sp 2 C-aromatic sp 2 C interactions are entropy-driven and enthalpically unfavorable, consistent with hydrophobic effects. These findings are relevant for interactions involving π-bonded sp 2 atoms in protein processes.
ABSTRACT
SIGNIFICANCE: Clinicians commonly either recommend patients begin contact lens (CL) wear full time or suggest that patients should gradually increase their wear times during the first few days of wear. This study found no differences between these two wear schedules, suggesting that patient preference may be the best schedule. PURPOSE: The purpose of this study was to determine if there are any clinical differences in neophyte, 2-week, reusable soft CL wearers who were randomized to either a full-time or a gradually increasing wear time schedule. METHODS: This was an investigator-masked, three-visit, randomized, clinical trial. Participants were randomized to wear their CLs full time starting on the first day or gradually starting with 2 hours of wear on the first day and increasing wear by 2 hours each day until 8 hours or more of wear per day was achieved. Symptoms (Ocular Surface Disease Index and visual analog scale) and ocular surface signs (tear breakup time, extent of corneal staining, and Schirmer test I) were evaluated at each visit. RESULTS: A total of 25 participants were randomized, with 21 participants completing at least 1 week of follow-up. Completed participants had a mean ± standard deviation age of 23.5 ± 3.0 years, and 48% were female. No significant between-group differences were found when comparing the full-time and gradual wear time schedule groups at 2 weeks (all, P > .32): Ocular Surface Disease Index (10.8 ± 8.5 vs. 16.3 ± 18.8), visual analog scale (89.0 ± 9.7 vs. 81.8 ± 18.7), tear breakup time (11.7 ± 7.0 vs. 9.8 ± 2.7), extent of corneal staining (0.0 ± 0.1 vs. 0.3 ± 0.5), or Schirmer test I (15.9 ± 8.8 vs. 21.2 ± 12.5). CONCLUSIONS: No between-group differences were found for any metric evaluated, which suggests that the best wear schedule may be the one that best suits the neophyte CL wearer's lifestyle.
