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Short-Chain Mono-Alkyl β-D-Glucoside Crystals-Do They Form a Cubic Crystal Structure?

ABSTRACT: Three-dimensional liquid crystal (LC) phases, cubic LC phases, have been extensively studied as fascinating molecular assembled systems formed by amphiphilic compounds. However, similar structures have only been seen in rare instances in lipid crystal states in glycolipid crystal studies. In this study, we prepared short-chain n-alkyl β-D-glucosides (CnG) with an alkyl chain length n ranging from 4 to 6 and investigated their crystal structures. First, differential thermal analysis (DTA) and thermogravimetric analysis (TG) measurements showed the formation of hydrated crystals for C4G and C5G, respectively. Second, the crystal structures of CnG (n = 4, 5, 6) in both anhydrous and hydrated states were examined using a temperature-controlled powder X-ray diffraction (PXRD) measurement. Both hydrate and anhydrous crystals of C4G and C5G with critical packing parameters (CPPs) less than 0.33 formed cubic crystal phases. Bilayer lengths, calculated from the main diffraction peaks in each PXRD profile, depended on crystalline moisture for C5G, but no significant change was confirmed for C4G, indicating that the properties of each hydrophilic layer differ. However, C6G with a CPP of 0.42 formed a crystal structure with a modulated lamellar structure similar to C7G and C8G with similar CPP values. Thus, a glycolipid motif concept with a cubic crystal structure was demonstrated.

SUBMITTER: Ogawa S

PROVIDER: S-EPMC9320782 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The reactions between single crystals of the SHV-1 beta-lactamase enzyme and the carbapenems, meropenem, imipenem, and ertapenem, have been studied by Raman microscopy. Aided by quantum mechanical calculations, major populations of two acyl-enzyme species, a labile Delta (2)-pyrroline and a more tightly bound Delta (1)-pyrroline, have been identified for all three compounds. These isomers differ only in the position of the double bond about the carbapenem nucleus. This discovery is consonant with X-ray crystallographic findings that also identified two populations for meropenem bound in SHV-1: one with the acyl CO group in the oxyanion hole and the second with the acyl group rotated 180 degrees compared to its expected position [Nukaga, M., Bethel, C. R., Thomson, J. M., Hujer, A. M., Distler, A. M., Anderson, V. E., Knox, J. R., and Bonomo, R. A. (2008) J. Am. Chem. Soc. (in press)]. When crystals of the Delta (1)- and Delta (2)-containing acyl-enzymes were exposed to solutions with no carbapenem, rapid deacylation of the Delta (2) species was observed by kinetic Raman experiments. However, no change in the Delta (1) population was observed over 1 h, the effective lifetime of the crystal. These observations lead to the hypothesis that the stable Delta (1) species is due to the form seen by X-ray with the acyl carbonyl outside the oxyanion hole, while the Delta (2) species corresponds to the form with the carbonyl inside the oxyanion hole. Soak-in and soak-out Raman experiments also demonstrated that tautomeric exchange between the Delta (1) and Delta (2) forms does not occur on the crystalline enzyme. When meropenem or ertapenem was reacted with SHV-1 in solution, the Raman difference spectra demonstrated that only a major population corresponding to the Delta (1) acyl-enzyme could be detected. The 1003 cm (-1) mode of the phenyl ring positioned on the C3 side chain of ertapenem acts as an effective internal Raman intensity standard, and the ratio of its intensity to that of the 1600 cm (-1) feature of Delta (1) provides an estimate of the relative populations of Delta (1). In solution, I 1600/ I 1003 equals 2, and in the crystal, I 1600 /I 1003 equals 1. This is strong evidence that the Delta (1) and Delta (2) acyl-enzymes in the crystal are present in approximately equal amounts, in agreement with the X-ray data. However, in solution there are twice as many Delta (1) species per Phe group, and this represents approximately 100% of the active sites, which is consistent with the observed inhibition of the enzyme's activity.

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Short-Chain Mono-Alkyl β-D-Glucoside Crystals-Do They Form a Cubic Crystal Structure?

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