PMID- 30973730
OWN - NLM
STAT- MEDLINE
DCOM- 20190521
LR  - 20190521
IS  - 1520-5215 (Electronic)
IS  - 1089-5639 (Linking)
VI  - 123
IP  - 19
DP  - 2019 May 16
TI  - Single-Conformation Spectroscopy of Capped Aminoisobutyric Acid Dipeptides: The 
      Effect of C-Terminal Cap Chromophores on Conformation.
PG  - 4178-4187
LID - 10.1021/acs.jpca.9b01698 [doi]
AB  - Aminoisobutyric acid (Aib) oligomers are known to form racemic mixtures of 
      enantiomeric left- and right-handed structures. The introduction of a chiral cap 
      converts the enantiomeric structures into diastereomers that, in principle, 
      afford spectroscopic differentiation. Here, we screen different C-terminal caps 
      based on a model Aib dipeptide using double resonance laser spectroscopy in the 
      gas phase to record IR and UV spectra of individual conformations present in the 
      supersonic expansion: NH-benzyl (NHBn) as a reference structure because of its 
      common use as a fluorophore in similar studies, NH- p-fluorobenzyl (NHBn-F), and 
      alpha-methylbenzylamine (AMBA). For both the NHBn and NHBn-F caps, a single conformer 
      is observed, with infrared spectra assignable to an enantiomeric pair of type 
      II/II' beta-turns in these molecules lacking a chiral center. The higher oscillator 
      strength of the NHBn-F cap enabled UV-UV hole burning, not readily accomplished 
      with the NHBn cap. The AMBA-capped structure, with its chiral center, produced 
      two unique conformers, one of which was a nearly identical left-handed type II 
      beta-turn, while the minor conformer is assigned to a C7-C7 sequential double ring, 
      which is an emergent form of a 2(7)-ribbon. Although not observed, the type II' 
      beta-turn diastereomer, with opposite handedness, is calculated to be 11 kJ/mol 
      higher in energy, a surprisingly large difference. This destabilization is 
      attributed primarily to steric interference between the C-terminal acyl oxygen of 
      the peptide and the chirality-inducing methyl of the AMBA group. Last, 
      computational evidence indicates that the use of an N-terminal aromatic cap 
      hinders the formation of a 3(10)-helix in Ac-Aib(2) dipeptides.
FAU - Fischer, Joshua L
AU  - Fischer JL
AUID- ORCID: 0000-0001-6183-8606
AD  - Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , 
      United States.
FAU - Elvir, Brayan R
AU  - Elvir BR
AD  - Department of Chemistry and Biochemistry , Fairfield University , Fairfield , 
      Connecticut 06824 , United States.
FAU - DeLucia, Sally-Ann
AU  - DeLucia SA
AD  - Department of Chemistry and Biochemistry , Fairfield University , Fairfield , 
      Connecticut 06824 , United States.
FAU - Blodgett, Karl N
AU  - Blodgett KN
AUID- ORCID: 0000-0002-6827-0328
AD  - Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , 
      United States.
FAU - Zeller, Matthias
AU  - Zeller M
AUID- ORCID: 0000-0002-3305-852X
AD  - Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , 
      United States.
FAU - Kubasik, Matthew A
AU  - Kubasik MA
AD  - Department of Chemistry and Biochemistry , Fairfield University , Fairfield , 
      Connecticut 06824 , United States.
FAU - Zwier, Timothy S
AU  - Zwier TS
AUID- ORCID: 0000-0002-4468-5748
AD  - Department of Chemistry , Purdue University , West Lafayette , Indiana 47907 , 
      United States.
LA  - eng
PT  - Journal Article
DEP - 20190502
PL  - United States
TA  - J Phys Chem A
JT  - The journal of physical chemistry. A
JID - 9890903
RN  - 0 (Aminoisobutyric Acids)
RN  - 0 (Dipeptides)
SB  - IM
MH  - Aminoisobutyric Acids/*chemistry
MH  - Crystallography, X-Ray
MH  - Density Functional Theory
MH  - Dipeptides/*chemistry
MH  - Models, Molecular
MH  - Protein Conformation
MH  - Spectrophotometry, Infrared
MH  - Spectrophotometry, Ultraviolet
EDAT- 2019/04/12 06:00
MHDA- 2019/05/22 06:00
CRDT- 2019/04/12 06:00
PHST- 2019/04/12 06:00 [pubmed]
PHST- 2019/05/22 06:00 [medline]
PHST- 2019/04/12 06:00 [entrez]
AID - 10.1021/acs.jpca.9b01698 [doi]
PST - ppublish
SO  - J Phys Chem A. 2019 May 16;123(19):4178-4187. doi: 10.1021/acs.jpca.9b01698. Epub 
      2019 May 2.