.pi.-Helical conformation of poly(.beta.-phenethyl L-aspartate)

Sasaki, Shintaro; Yasumoto, Yusuke; Uematsu, Ichitaro

doi:10.1021/ma50007a036

Cited by 54 publications

(58 citation statements)

References 1 publication

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The latter diagram is essentially the same as that previously reported by Sasaki et al 5 As shown in the figure, the low-temperature peak (130°C) of PPLA was suppressed when an equal amount of two optical antipodes (PPLA + were indexed with a tetragonal unit cell of a= 13.6 A.…”

Section: Resultssupporting

confidence: 86%

“…These results suggest that the reversible transitions of PPLA and PPDLA observed around 200°C probably arise from two independent causes. As noted by Sasaki et al, 5 formation of the /:I-structure becomes gradually marked at higher temperatures (above 200°C).…”

Section: Discussionsupporting

confidence: 58%

“…Sasaki et al 5 proposed a nL helix for PPLA at higher temperatures on the basis of the X-ray diagram which exhibited a turn layer line at a spacing of 4.95 A. This reflection was observed even at 200°C, indicating that the skeletal conformation was essentially unaffected by the second transition.…”

Section: Discussionmentioning

confidence: 99%

“…4 More recently, Uematsu and his collaborators have investigated the helix-sense inversion characteristic of poly(/J-phenethyl L-aspartate) (PPLA), where R = -CH 2 CH 2 c/>. According to Sasaki et al, 5 PPLA exhibits an irreversible helix-sense inversion from the righthanded ()(-helix to the left-handed n-helix in the solid state at an elevated temperature. Toriumi et al 6 have observed a transition from the right-handed to the lefthanded ()(-helix in chloroform by addition of a small amount of denaturant acid, dichloroacetic acid.…”

Section: +Nh-ch-yo+;-ch2coormentioning

confidence: 99%

See 3 more Smart Citations

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

Okamoto

Furuya

Watanabe

et al. 1996

Polym J

View full text Add to dashboard Cite

ABSTRACT:A racemic mixture (PPDLA) comprising an equal amount of optical antipodes, Poly(/J-phenethyl L-aspartate) (PPLA)+Poly(p-phenethyl o-aspartate) (PPDA), was found to exhibit a moderately sharp and reversible transition at around 200°C. A combined use of X-ray and CP/MAS NMR methods revealed that the transition involves an interconversion of the screw-sense between the right-and left-handed IX-helical molecules. The backbone conformation and the molecular packing (tetragonal) were found to remain nearly identical before and after the transition. The transition mechanism previously deduced in the liquid-crystalline state seems to be consistent with experimental observations in the solid state. On the other hand, PPLA alone is known to transform from the right-handed IX-helix to the left-handed n-helix at around 130°C: the crystallographic form concurrently changes from a tetragonal to a rectangular and eventually to a hexagonal arrangement at about 200°C. The difference between PPDLA and PPLA systems is discussed.KEY WORDS Poly(P-phenethyl aspartate) / Racemic Mixture / Solid-State Phase Transition / HelixSense Inversion/ X-Ray Measurement/ CP/MAS NMR / 13 C NMR Chemical Shifts/ It is well known that poly(L-aspartic acid) esters +NH-CH-yO+,;-CH2COORform an ()(-helix in either the right-handed or left-handed screw sense depending on the chemical structure of the ester group (R). While poly(L-aspartic acid ester) with R = benzyl 1 or methyl 2 forms the left-handed ()(-helix in chloroform, the right-handed arrangement is more popular among polymers having longer alkyl side chains such as R=ethyl 2 or phenethyl 3 group. Reversal of the helical sense in copolymer systems such as those comprising R 1 = nitrobenzyl and R 2 = benzyl residues has been studied by Goodman et al. in l 960's. 4 More recently, Uematsu and his collaborators have investigated the helix-sense inversion characteristic of poly(/J-phenethyl L-aspartate) (PPLA), where R = -CH 2 CH 2 c/>. According to Sasaki et al., 5 PPLA exhibits an irreversible helix-sense inversion from the righthanded ()(-helix to the left-handed n-helix in the solid state at an elevated temperature. Toriumi et al. 6 have observed a transition from the right-handed to the lefthanded ()(-helix in chloroform by addition of a small amount of denaturant acid, dichloroacetic acid. These observations suggest that the energy difference between the two alternative helical forms is relatively small. 7 In our previous studies on PPLA, 8 -10 we have found that the transition between the two ()(-helical forms takes place reversibly in solution as a function of temperature. The transition was observed in the isotropic solution as well as in the anisotropic liquid-crystalline state within certain temperature range (80-90°C). In these measurements, various NMR techniques were employed to follow the transition.In this study, we report a helix-helix transition observed for a racemic mixture comprising an equal amount of PPLA and PPDA (hereafter designated as PPDLA) in the solid state. In ...

show abstract

Section: Resultssupporting

confidence: 86%

Section: Discussionsupporting

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Section: +Nh-ch-yo+;-ch2coormentioning

confidence: 99%

See 2 more Smart Citations

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

Okamoto

Furuya

Watanabe

et al. 1996

Polym J

View full text Add to dashboard Cite

show abstract

“…16 • 17 The aR film of poly(/3-phenethyl L-aspartate) (PPELA) (phenethyl=-CH2CHr C 6 H 5 ) exhibited the transition into the left-handed n-helix with p=0.117nm and t= -84.7°. 18 The sense inversion of PPELA was observed in the chloroform solution by adding a small amount of dichloroacetic acid (DCA) or trifluoroacetic acid (TFA). 19 On the other hand, films of poly(N"-(p-halobenzoyl) L-ornithine)s showed the transition from the aR-helix into the WR-helix withp=0.142nm.…”

mentioning

confidence: 99%

Helix-Sense Inversion in Polyaspartates

Sasaki

Ogawa

Kimura

1991

Polym J

Self Cite

View full text Add to dashboard Cite

ABSTRACT:Solid-state irreversible inversion of helix sense of poly(/J-(p-chlorobenzyl) Laspartate) and poly(/J-(p-methylbenzyl) L-aspartate) was investigated by employing circular dichroism, infrared absorption, and X-ray diffraction techniques. The molecular conformation was the right-handed ()(-helix ((l(R) in the as-cast film prepared from the solution in chloroform. Heat treatment caused the transition from (l(R to the left-handed w-helix (wd. The crystal structure of the wL forms was monoclinic (not tetragonal), i.e., the side chains do not form the fourfold helical structure. The right-to-left helix-sense inversion associated with the 0(-to-w transition was supported by the conformation energy calculation.KEY WORDS Poly(/J-(p-chlorobenzyl) L-aspartate) / Poly(/J-(p-methylbenzyl) L-aspartate) / ()(-Helix/ w-Helix / Helix sense/

show abstract

Crystallographic Data and Melting Points for Various Polymers

Miller

1999

The Wiley Database of Polymer Properties

View full text Add to dashboard Cite

.pi.-Helical conformation of poly(.beta.-phenethyl L-aspartate)

Cited by 54 publications

References 1 publication

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

Reversible Screw-Sense Inversion of α-Helical Poly(β-phenethyl aspartate) in the Solid State

Helix-Sense Inversion in Polyaspartates

Crystallographic Data and Melting Points for Various Polymers

Contact Info

Product

Resources

About