A bridged d0 zirconocene dichloride is reported as a first group 4 metal complex possessing rare long-lived ligand-to-metal charge transfer (LMCT) excited states with high emission yields and excited-state lifetimes in fluid solutions (e.g., PhiLUM = 0.41 and tau = 17.6 micros in 1,2-dichlorobenzene at 20 degrees C). The basic emission parameters PhiLUM and tau are shown to be extremely solvent-dependent in fluids at room temperature. The first principle dependences of LMCT emission parameters on solvent properties are revealed with use of the target complex. For fluid solutions, the linear correlation between PhiLUM and tau is reported, thus suggesting that a solvent determines the rate constant for nonradiative decay, knr.

Maduraferrin, a Novel Siderophore from Actinomadura madurae From a strain of Actinomadura madurae, a new siderophore was isolated. Maduraferrin is the Fe complex of an oligopeptide composed of salicylic acid, β‐alanine, glycine, L‐serine, Nδ‐hydroxy‐Nα‐methyl‐L‐ornithine, and L‐hexahydropyridazine‐3‐carboxylic acid. The complexing centers are a salicylamide moiety, a hydroxamic‐acid group and an acid hydrazide group.

Four new dipeptidyl nikkomycins of the Z-and the X-series with a variation in the amino acid moiety of the molecule were isolated from the mutant Streptomyces tendae 901/395 and characterized.Nikkomycins Kz and Kg contain 2-amino-4-hydroxy-4-(2-pyridyl)butyric acid, and nikkomycins Oz and Os 2-amino-4-hydroxy-4-(5-hydroxy-2-pyridyl)butyric acid. In contrast to nikkomycins Z and X, nikkomycins Kx, and 0x are quite stable at alkaline pH and exhibit a lower biological activity against various test organisms. From the mutant S. tendae 901/C37, which is auxotrophic for methionine and threonine, enhanced amounts of two tripeptidyl nikkomycins, Qz and Qx, were produced which are analogues of nikkomycins J and I and contain a homoserine residue instead of glutamic acid. These nikkomycins exhibit a high pH instability.Nikkomycins are nucleoside peptide antibiotics which act as competitive inhibitors of fungal and insecticidal chitin synthetases1.2,3) From the culture filtrate of Streptomyces tendae a spectrum of active nikkomycins has been isolated4-7). The major components are the two dipeptidyl nikkomycins Z and X composed of 2-amino-4-hydroxy-4-(5-hydroxy-2-pyridyl)-3-methylbutyric acid, an unusual amino acid, and a 5-aminohexuronic acid N-glycosidically bound to uracil in nikkomycin Z or to 5-formyl-4-imidazolin-2-one in nikkomycin X. The tripeptidyl nikkomycins J and I, minor components of the culture broth, are analogues of nikkomycins Z and X with a peptidically bound glutamyl residue linked to the carboxy group of the nucleoside moiety. By mutasynthesis and directed fermentation nikkomycin Z and J analogues containing thymine, 5-hydroxymethyluracil or isoorotic acid as base could be obtained8). In the present paper we describe new nikkomycins produced by mutants of Streptomyces tendae. Materialsand Methods MicroorganismsSpores of the wild type strain Streptomyces tendae Tii 901 were mutagenized by UV light at 365 nm in the presence of 8-methoxypsoralen (MOP) according to TOWNSEND et a1.9 . 1010 spores per 10 ml saline plus 1 mg MOP were incubated for 10 minutes at 27°C and subsequently irradiated by UV light. Mutants were selected among 0.1 % survivors.Mutagenesis with ethyl methane sulfonate (EMS) was performed by incubating 109 spores of S. tendae Tii 901 per 10 ml sodium phosphate buffer, pH 7.0 with 5 % (v/v) EMS at 27°C. Mutants were t