A study of seed vigour and seedling emergence of maize under field and laboratory conditions : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University

Maximum yield is obtained from an optimum stand of any crop species. However there are many factors influencing the stand which can broadly be grouped as soil and plant factors. Soil moisture, temperature and aeration influence germination. These factors plus soil structure influence emergence and establishment of seedlings. Under field conditions, the factors mentioned are not always at optimum level which in turn influences the growth and final yield. [From Introduction

Vieillardiixanthone B1

The title compound [systematic name: 1,5-dihydr­oxy-3,6-dimeth­oxy-4-(2-methyl­but-3-en-2-yl)-9H-xanthen-9-one], C20H20O6, is a xanthone, which was isolated from the roots of Cratoxylum formosum ssp. pruniflorum. The three rings in the mol­ecule are approximately coplanar, with an r.m.s. deviation of 0.0372 (2) Å for the plane through the 14 non-H atoms. The O atoms of the two hydr­oxy substituents also lie close to this plane with deviations of 0.0669 (2) and 0.1122 (2) Å, respectively. The 1,1-dimethyl-2-propenyl substituent is in a (−)-anti­clinal conformation. Intra­molecular O—H⋯O hydrogen bonds generate S(5) and S(6) ring motifs. In the crystal, mol­ecules are linked into infinite chains along [010] by O—H⋯O hydrogen bonds and weak C—H⋯O inter­actions. π–π inter­actions with centroid–centroid distances of 3.6172 (10) and 3.6815 (10) Å are also observed

Brasilixanthone1

The title xanthone [systematic name: 5,13-dihy­droxy-3,3,10,10-tetra­methyl-3H-dipyrano[3,2-a:2′,3′-i]xanthen-14(10H)-one], C23H20O6, was isolated from the roots of Cratoxylum formosum ssp. pruniflorum. There are two mol­ecules (A and B) in the asymmetric unit, which show chemical but not crystallographic inversion symmetry. The xanthone skeleton in both mol­ecules is approximately planar, with an r.m.s. deviation of 0.0326 (9) Å for mol­ecule A and 0.0355 (9) Å for mol­ecule B from the plane through the 14 non-H atoms. The pyran rings in both mol­ecules adopt sofa conformations. Intra­molecular O—H⋯O hydrogen bonds generate S(5) and S(6) ring motifs. Viewed onto the bc plane, the crystal structure resembles a herringbone pattern. Stacks of mol­ecules are stabilized by π–π inter­actions with centroid–centroid distances of 3.600 (5) Å. The crystal structure is further stabilized by weak C—H⋯O and C—H⋯π inter­actions

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7-Acetoxy­cochinchinone I1

The title compound {systematic name: 12-[(2E)-3,7-dimethyl-2,6-octa­dien­yl]-5,8-dihydr­oxy-2,2-dimethyl-2H,6H-pyrano[3,2-b]xanthen-6-one}, C30H32O6, has four fused rings (A/B/C/D) and the xanthone ring system (A/B/C) is essentially planar, with dihedral angles of 1.85 (13) and 2.47 (13)°, respectively, between rings A and B, and between rings B and C. The chromene ring D is in a sofa form. The geranyl side chain is axially attached to ring C with an (−)-synclinal conformation. The 3-methyl-2-butenyl terminal of the geranyl side chain is disordered with the site-occupancy ratio of 0.513 (5):0.487 (5). The acet­oxy group is attached axially to ring A with an (+)-synclinal conformation. An intra­molecular O—H⋯O hydrogen bond involving the carbonyl and hydroxyl groups generates an S(6) ring motif. In the crystal, weak C—H⋯O and C—H⋯π inter­actions, and π–π inter­actions with centroid–centroid distances of 3.6562 (16) and 3.6565 (16) Å are observed

Polyurethane/poly(ethyl methacrylate) interpenetrating polymer network organoclay nanocomposites

A number of polyurethane (PU) I poly(ethyl methacrylate) (PEMA) interpenetrating polymer network nanocomposites were investigated with regard to morphology and energy absorbing ability. The nanoclays used were umnodified sodium montmorillonite clay and three different types of organically-modified clays: C15A, C20A and C30B. The nanoclays were incorporated into the IPNs by using an in-situ polymerisation method. The clay dispersions were characterised by wide angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM). The morphologies of the IPNs were determined with dynamic mechanical thermal analysis (DMTA), TEM and modulated-temperature differential scanning calorimetry (M-TDSC), while the mechanical properties were investigated using tensile testing and hardness measurements. Firstly, the original synthesis procedure and formulation was adjusted by varying the nanoclay C20A content, IPN composition ratio, nanoclay mixing time and PU catalyst, including a study of the PU and PEMA homopolymer composites. All IPN composites showed only partially intercalated nanocomposites as revealed by WAXD and TEM results. 70PU/30PEMA (70:30 composition ratio) IPN nanocomposites exhibited potential as materials for damping applications as it had a broad loss factor ≥ 0.3 spanning a wide temperature range. Secondly, the synthesis procedure was modified by changing the order of nanoclay mixing with homopolymer components. All lPN composites were based on a composition ratio of 70PU/30PEMA, 5 wt% C20A content, 1.2 wt% of PU catalyst and 30 min mixing time. High intensity ultrasonic waves were also introduced in the nanoclay mixing step for one hour. However, the ultrasonication showed only a marginal change in damping properties. Finally, a number of other nanoclays were incorporated into the 70PU/30PEMA IPN. All IPN composites achieved only a partial intercalation, except for the C30B-filled lPN where no changes were revealed by W AXD. All nanoclays caused a decrease in the glass transition of both homopolymers. IPN nanocomposites tended to reveal a higher extent of phase separation with increased clay content, but only the Na clay-filled lPN still showed a broad loss factor value, even at higher clay content. Improved modulus of elasticity was shown by all nanoclays, with increased clay loading. Whereas a moderate increase in the tensile strength was only shown at 1 wt% clay content.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

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