There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Tautomeric equilibria in relation to pi-electron delocalization.

A simple and low cost chemosensor is described. This sensor could simultaneously detect three biologically important metal ions through fluorogenic (Zn2+) and chromogenic (Fe2+, Cu2+, and Zn2+) methods in aqueous solution. The sensor could function as a “turn-on” fluorescence receptor only to Zn2+ ions. In addition, the sensor could be successfully applied to the detection of intracellular Zn2+. Meanwhile, the sensor displayed an obvious red color upon selective binding with Fe2+. Therefore, the sensor could serve as a useful tool for the discrimination of Fe2+ from Fe3+ in aqueous media. Moreover, the sensor also showed color changes from yellow to colorless upon selective binding with Zn2+ and Cu2+, respectively. The detection limit of the sensor for Cu2+ (1.5 μM) is far below the guidelines of the World Health Organization (30 μM) as the maximum allowable copper concentration in drinking water, and therefore it is capable of being a practical system for the monitoring of Cu2+ concentrations in aqueous samples. These results provide a new approach for selectively recognizing the most important three trace elements in the human body simultaneously, for Zn2+ by emission spectra and Fe2+, Cu2+, and Zn2+ by the naked eye.

A cap-type Schiff base acting as a fluorescence sensor for zinc(II) and a colorimetric sensor for iron(II), copper(II), and zinc(II) in aqueous media

Intramolecular hydrogen bonding and tautomerism in Schiff bases. Structure of N-(2-pyridil)-2-oxo-1-naphthylidenemethylamine

This review article deals with recent studies on organic photochromic crystals Three basic methods for the selective preparation of photochromic crystals of Schiff bases have been proposed The methodologies are applicable to a wide range of potential photochromic compounds; thus, further development of new types of photochromic solid systems can be expected In this review we introduce structures and photo-properties of recently prepared photochromic organic crystals based on proton transfer as well as other photo-induced bond formation or cleavage, along with discussion on the mechanism of their photo-coloration or photo-isomerization processes

Photochromism of organic compounds in the crystal state

1-[N-(4-chlorophenyl)]aminomethylidene-2(1H)naphthalenone (C17H12NOCl) (1) was synthesized and the crystal structure was determined. Compound 1 crystallizes in the monoclinic space group P21/n with a = 4.761(3) A, b = 20.347(1) A, c = 13.773(2) A, β = 92.89(3)°, V = 1332.4(3) A3, Z = 4, D
c = 1.404 g cm−3, μ(Mo Kα) = 0.28 mm−1, and R = 0.036 for 2680 reflections [I > 2σ(I)]. Molecule 1 is not planar, and the dihedral angle between the naphthaldeyde plane A [C1–C11, 01] and the 4-chloroaniline plane B [C12–C17, C11, N1] is 20.1(3)°. An intramolecular hydrogen bond occurs between the hydroxyl oxygen and imine nitrogen atoms [2.528(3) A]. IR, 1H NMR, and UV measurements and AM1 semiempirical quantum mechanical calculations support the keto form found in the X-ray structure.

Mehmet Kabak

Papers

Keto–enol tautomerism, conformations, and structure of 1-[N-(4-chlorophenyl)]aminomethylidene-2(1H)naphthalenone

Keto–enol tautomerism, conformations and structure of N-(2-hydroxy-5-methylphenyl), 2-hydroxybenzaldehydeimine

Tautomeric properties, conformations and structure of n-(2-hydroxy-5-chlorophenyl) salicylaldimine

Conformational study and structure of bis-N,N′-p-bromo-salicylideneamine-1,2-diaminobenzene

Conformation and structure of 3-methoxyphenyl-salicylaldimine