chai

chai

Kết quả (Anh) 1:

bottle

Kết quả (Anh) 2:

bottle.

Kết quả (Anh) 3:

Lignin typically composes 20−30% of lignocellulosic biomassand is the second most natural terrestrial biopolymer aftercellulose and is potentially available as a byproduct of chemicalpulping and biorefining processes.1 Chemically, lignin is abiopolymer that is typically derived from different cinnamylalcohol precursors, including p-coumaryl alcohol (H type),coniferyl alcohol (G type), and sinapyl alcohol (S type) linkedwith different ether and carbon−carbon bonds.2−4The ratio andthe abundance of these three precursors is unique in differentwood species. Lignin in softwood trees contains mainly coniferylalcohol, while hardwood trees most often contain S and G unitsand nonwood plants contain a mixture of all three precursors.4The biosynthesis of lignin in the plant cell wall is an enzymemediated dehydrogenation process. Defining the exact structureof lignin in the plants remains a technical challenge due to itsstructural complexity and the lack of nondegradative methods toextract pure lignin from plants. Chemical models oflignin structures are proposed based on extracted lignin fromplants (Scheme 1),1 but recent advances in whole-cell NMRhave simplified this process. Generally, it is believed that in situlignin has less complexity than extracted lignin and for highsinapyl content lignin it exhibits a high degree of linearity.4,6