Publications by authors named "Aleksey V Krivandin"

2 Publications

  • Page 1 of 1

Photoinduced Reactions of Benzophenone in Biaxially Oriented Polypropylene.

J Phys Chem A 2018 May 20;122(17):4298-4305. Epub 2018 Apr 20.

Department of Chemistry , Columbia University , New York , New York 10027 , United States.

The photoinduced reactions of benzophenone (B) in biaxially oriented polypropylene (BOPP) were studied with nanosecond laser photolysis (N laser, λ337.1 nm). The first observed transient was a triplet state B*. Decay of B* led to formation of a radical pair (RP) of BH and R, where R is a radical formed by hydrogen abstraction from BOPP (RH) by B*. We studied BOPP after the preheating for a short time in a temperature range 298-423 K, which is essentially lower than its melting point of 453 K. All measurements with not-heated and with preheated (annealed) BOPP were made at 298 K. A radical pair (RP) apparently decays as a contact pair [BH, R] in nonheated BOPP. A critical phenomenon takes place: dissociation of RP with a formation of free radicals in the polymer bulk is observed at preheating temperature T ≈ 403 K and at a higher T. The physical process of heating and cooling of BOPP apparently resulted in the restructuring of crystallites, their agglomeration, shrinking of the distribution of crystallites according to their sizes in BOPP. Overall BOPP becomes softer which manifests itself in the radical kinetics. The decay kinetics of B* and RP in the cage fits well the first-order law. Rate constants were obtained. Radicals BH, which exit into the polymer bulk at temperatures of preheating T ≥ 403 K, decay by cross-termination according to the second-order law. A relatively high rate constant ∼10 M·s for this reaction was obtained due to diffusion of BH enclosed in the soft amorphous phase of BOPP. Properties of BOPP containing B were studied with ESR, DSC, IR, and WAXD.
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http://dx.doi.org/10.1021/acs.jpca.8b01483DOI Listing
May 2018

Structural and thermodynamic properties of rice starches with different genetic background Part 2. Defectiveness of different supramolecular structures in starch granules.

Int J Biol Macromol 2007 Dec 19;41(5):534-47. Epub 2007 Jul 19.

Institute of Biochemical Physics, Russian Academy of Sciences, Kosygina str. 4, 119334 Moscow, Russia.

High-sensitivity differential scanning microcalorimetry (HSDSC), small-angle X-ray scattering (SAXS), light (LM) and scanning electronic (SEM) microscopy techniques were used to study the defectiveness of different supramolecular structures in starches extracted from 11 Thai cultivars of rice differing in level of amylose and amylopectin defects in starch crystalline lamellae. Despite differences in chain-length distribution of amylopectin macromolecules and amylose level in starches, the invariance in the sizes of crystalline lamellae, amylopectin clusters and granules was established. The combined analysis of DSC, SAXS, LM and SEM data for native starches, as well as the comparison of the thermodynamic data for native and annealed starches, allowed to determine the structure of defects and the localization of amylose chains in crystalline and amorphous lamellae, defectiveness of lamellae, clusters and granules. It was shown that amylose "tie chains", amylose-lipid complexes located in crystalline lamellae, defective ends of double helical chains dangling from crystallites inside amorphous lamellae ("dangling" chains), as well as amylopectin chains with DP 6-12 and 25-36 could be considered as defects. Their accumulation can lead to a formation of remnant granules. The changes observed in the structure of amylopectin chains and amylose content in starches are reflected in the interconnected alterations of structural organization on the lamellar, cluster and granule levels.
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http://dx.doi.org/10.1016/j.ijbiomac.2007.07.005DOI Listing
December 2007