6. Rehybridization of the Acceptor (RICT) 3908 7. Planarization of the Molecule (PICT) 3909 III. Fluorescence Spectroscopy 3909 A. Solvent Effects and the Model Compounds 3909 1. Solvent Effects on the Spectra 3909 2. Steric Effects and Model Compounds 3911 3. Bandwidths 3913 4. Isoemissive Points 3914 B. Dipole Moments 3915 C. Radiative Rates and Transition Moments 3916 1. Quantum Yields and Radiationless Deactivation Processes 3916

Structural Changes Accompanying Intramolecular Electron Transfer: Focus on Twisted Intramolecular Charge-Transfer States and Structures

The review covers the knowledge on photoremovable protecting
groups and includes all relevant chromophores studied in the
time period of 2000–2012; the most relevant earlier works are
also discussed.

/pdf/photoremovable-protecting-groups-in-chemistry-and-biology-2n33qs6p7b.pdf

Photoremovable Protecting Groups in Chemistry and Biology: Reaction Mechanisms and Efficacy

Organic Chemistry By Dr. I. L. Finar. Vol. 2: Stereochemistry and the Chemistry of Natural Products. Pp. xi + 733. (London and New York: Longmans, Green and Co., Ltd., 1956.) 40s. net.

Advanced Organic Chemistry

Fluorescent labeling of biomolecules with organic probes.

Biologically active compounds which are light-responsive offer experimental possibilities which are otherwise very difficult to achieve. Since light can be manipulated very precisely, for example, with lasers and microscopes rapid jumps in concentration of the active form of molecules are possible with exact control of the area, time, and dosage. The development of such strategies started in the 1970s. This review summarizes new developments of the last five years and deals with "small molecules", proteins, and nucleic acids which can either be irreversibly activated with light (these compounds are referred to as "caged compounds") or reversibly switched between an active and an inactive state.

Biologically active molecules with a "light switch".

Synthesis and properties of carbamoyl derivatives of photolabile benzoins

Synthesis and fluorescence properties of substituted 7-aminocoumarin-3-carboxylate derivatives

The synthesis is described of photolabile sulfonamide derivatives of amino acids, most of which incorporate a monophosphate ester to promote water solubility. Points of particular synthetic interets include observations on the reduction of diaryl ketones and diarylmethanols, e.g. compounds 7 and 9, with NaBH4–TFA, and a convenient, effective sequence for conversion of bromoarenes into arenesulfonyl halides, e.g. 10 → 13. Photolysis of the glycine derivative 18a in aqueous solution released free glycine in poor yield, except in the presence of a very large excess of ascorbate as a reducing agent. The likely cause is discussed in terms of a decarboxylation side-reaction occurring during the overall progress of the photocleavage.

Synthesis and evaluation of photolabile sulfonamides as potential reagents for rapid photorelease of neuroactive amines

We have used a new fluorescent ATP analogue, 3'-(7-diethylaminocoumarin-3-carbonylamino)-3'-deoxyadenosine-5'-triphosphate (deac-aminoATP), to study the ATP hydrolysis mechanism of the single headed myosinV-S1. Our study demonstrates that deac-aminoATP is an excellent substrate for these studies. Although the deac-amino nucleotides have a low quantum yield in free solution, there is a very large increase in fluorescence emission ( approximately 20-fold) upon binding to the myosinV active site. The fluorescence emission intensity is independent of the hydrolysis state of the nucleotide bound to myosinV-S1. The very good signal-to-noise ratio that is obtained with deac-amino nucleotides makes them excellent substrates for studying expressed proteins that can only be isolated in small quantities. The combination of the fast rate of binding and the favorable signal-to-noise ratio also allows deac-nucleotides to be used in chase experiments to determine the kinetics of ADP and Pi dissociation from actomyosin-ADP-Pi. Although phosphate dissociation from actomyosinV-ADP-Pi does not itself produce a fluorescence signal, it produces a lag in the signal for deac-aminoADP dissociation. The lag provides direct evidence that the principal pathway of product dissociation from actomyosinV-ADP-Pi is an ordered mechanism in which phosphate precedes ADP. Although the mechanism of hydrolysis of deac-aminoATP by (acto)myosinV-S1 is qualitatively similar to the ATP hydrolysis mechanism, there are significant differences in some of the rate constants. Deac-aminoATP binds 3-fold faster to myosinV-S1, and the rate of deac-aminoADP dissociation from actomyosinV-S1 is 20-fold slower. Deac-aminoATP supports motility by myosinV-HMM on actin at a rate consistent with the slower rate of deac-aminoADP dissociation.

Kinetic mechanism of myosinV-S1 using a new fluorescent ATP analogue.

The synthesis is described of a spin-labeled analog of ATP, 2',3'-0-( 1 -oxy-2,2,6,6-tetramethyl- 4-piperidy1idene)adenosine 5'-triphosphate (SL-ATP). The spin-label moiety is attached by two bonds to the ribose ring as a spiroketal and hence has restricted conformational mobility relative to the ribose moiety of ATP. The synthesis proceeds via an acid-catalyzed addition of adenosine 5'-monophosphate to 1- acetoxy-4-methoxy-2,2,6,6-tetramethyl- lY2,5,6-tetrahydropyridine in acetonitrile. The spiroketal product is pyrophosphorylated, and alkaline hydrolysis with concomitant aerial oxidation gives the required product. The spin-labeled moiety probably takes up two rapidly interconverting conformations with respect to the ribose ring on the basis of the 'H NMR spectra of its precursors and related uridine derivatives (Alessi et al. (1991) J. Chem. Soc., Perkin Trans. 1 , 2243-22471. SL-ATPis a substrate for myosin and actomyosin with similar kinetic parameters to ATP during triphosphatase activity. SL-ATP supports muscle contraction and permits relaxation of permeabilized rabbit skeletal muscle fibers. SL-ADP is a substrate for yeast 3-phosphoglycerate kinase, thus permitting regeneration of SL-ATP from SL-ADP within muscle fibers. Electron paramagnetic resonance (EPR) studies of SL-ADP bound to myosin filaments and to myofibrils show a degree of nanosecond motion independent of that of the protein, which may be due to conformational flexibility of the ribose moiety of ATP bound to myosin's active site. This nanosecond motion is more restricted in myofibrils than in myosin filaments, suggesting that the binding of actin affects the ribose binding site in myosin. EPR studies on SL-ADP bound to rigor cross-bridges in muscle fiber bundles showed the nucleotide to be highly oriented with respect to the fiber axis.

/pdf/synthesis-and-properties-of-a-conformationally-restricted-4bfdlinuie.pdf

John E. T. Corrie

Papers

Synthesis and properties of carbamoyl derivatives of photolabile benzoins

Synthesis and fluorescence properties of substituted 7-aminocoumarin-3-carboxylate derivatives

Synthesis and evaluation of photolabile sulfonamides as potential reagents for rapid photorelease of neuroactive amines

Kinetic mechanism of myosinV-S1 using a new fluorescent ATP analogue.

Synthesis and properties of a conformationally restricted spin-labeled analog of ATP and its interaction with myosin and skeletal muscle.