Direct frequency comb generation from an octave-spanning, prismless Ti:sapphire laser

We describe a self-referenced optical frequency comb generator based on an octave-spanning, prismless Ti:sapphire laser. Dispersion compensation is provided by novel double-chirped mirror pairs and BaF2 wedges. Current versions operate at 80 and 150 MHz. The compact prismless design allows system scaling to a gigahertz repetition rate. Its carrier-envelope beat note is intrinsically stable with a signal-to-noise ratio of 30 dB in a 100-kHz bandwidth. The octave is reached at 25 dB below the average power level. The in-loop accumulated phase error is 1.4 rad (20 mHz to 1 MHz). The technique has the advantages of simplicity and stability compared with previous designs.     

Versatile routes to C-2- and C-6-functionalized glucose derivatives of iminodiacetic acid

A series of novel d-glucose derivatives, functionalized at the C-2 or the C-6 position with an iminodiacetic acid moiety for transition-metal complexation, has been prepared. The sugar and the metal-chelating parts are separated by either propyl or octyl chains and were introduced by the reaction of bromoalkylamine. Either N-1-Boc-3-bromopropylamine (17) or N-(8-bromooctyl)phthalimide (19) reacted with methyl 3,5,6-tri-O-benzyl-alpha-beta-d-glucofuranoside (4) (C-2 position) and 1,2:3,5-(O-methylene)-alpha-d-glucose (11) (C-6 position), respectively, in the presence of sodium hydride in DMF at room temperature, affording the desired intermediates. For aminopropyl derivatives, yields varied between 57% and 65%, and for aminooctyl derivatives, yields varied between 40% and 71%. After deprotection of the amine functionality, the metal chelate was built up by dialkylation (6a-c and 13a,b) with methyl bromoacetate in the presence of triethylamine under reflux in THF. Yields varied between 56% and 69% for the glucose modified at the C-2 position and between 58% and 62% for the one modified at the C-6 position. All compounds were characterized by 1H or 13C NMR or both, IR, and mass spectroscopy. Final products were isolated as a mixture of alpha and beta anomers.     

Comparative studies of substitution reactions of rhenium(I) dicarbonyl-nitrosyl and tricarbonyl complexes in aqueous media

The ligand substitution behavior of [ReBr3(CO)3](NEt4)2 (1) and [ReBr3(CO)2(NO)]NEt4 (2) in aqueous media was compared. Ligand exchange reactions were performed with multidentate chelating systems such as picolylaminediacetic acid (L1; N,N',O,O'), nitrilotriacetic acid (L2; N,O,O',O'), iminodiacetic acid (L3; N,O,O'), and bis(2-pyridyl)methane (L4; N,N'). The products of the substitution reactions were isolated and characterized by means of IR, NMR, MS, and X-ray structure analysis. NMR and crystallographic analyses confirmed the formation of single structural isomers in all cases with a ligand-to-metal ratio of 1:1. With ligands L1 and L2 and precursor 1 the tridentately coordinated complexes [Re(L1)(CO)3] (7) and [Re(L2)(CO)3]2- (8) were formed. With precursor 2 the same ligands unexpectedly coordinated tetradentately after displacing a CO ligand, yielding complexes [Re(L1)(CO)(NO)] (3) and [Re(L2)(CO)(NO)]- (4). In both complexes NO was found to be coordinated trans to the carboxylate group. Time-dependent IR spectra of the reaction of 2 with ligand L1 and L2 confirmed the loss of one CO during the reaction. The product of the reaction of 2 with L3 was identified as the neutral complex [Re(L3)(CO)2(NO)] (5), again, with the nitrosyl coordinated trans to the carboxylate. With 1, ligand L3 formed the anionic complex [Re(L3)(CO)3]- (9). Finally the reactions with L4 yielded the complexes [ReBr(L4)(CO)2(NO)]Br (6) and [ReBr(L4)(CO)3] (10), in which bromide was found to be coordinated trans to the NO and CO, respectively. The X-ray structures of 3, 5-7, and 10 are discussed: 3, monoclinic P2(1)/n, with a = 14.6071(6) A, b = 8.0573(3) A, c = 24.7210(11) A, beta = 107.117(5) degrees, and Z = 4; 5, triclinic P1, with a = 6.9091(5) A, b = 9.8828(7) A, c = 14.2834(10) A, alpha = 89.246(9) degrees, beta = 89.420(9) degrees, gamma = 86.196(9) degrees, and Z = 4; 6, triclinic P1, with a = 9.8236(8) A, b = 10.0949(8) A, c = 12.5346(10) A, alpha = 108.679(9) degrees, beta = 111.992(9) degrees, gamma = 95.426(10) degrees, and Z = 2; 10, monoclinic P2(1)/c, with a = 12.7491(12) A, b = 13.3015(13) A, c = 9.0112(9) A, beta = 107.195(2) degrees, and Z = 7.     

Nonlinear femtosecond pulse reshaping in waveguide arrays

We observe nonlinear pulse reshaping of femtosecond pulses in a waveguide array owing to coupling between waveguides. Amplified pulses from a mode-locked fiber laser are coupled to an AlGaAs core waveguide array structure. The observed power-dependent pulse reshaping agrees with theory, including shortening of the pulse in the central waveguide.     

Frequency comb stabilization with bandwidth beyond the limit of gain lifetime by an intracavity graphene electro-optic modulator

Intracavity loss modulation enables offset-frequency control with bandwidths beyond what is possible by pump power modulation. To demonstrate this new method, we use a subwavelength thick graphene electro-optic modulator to stabilize the offset frequency in a Tm:fiber frequency comb at 1.95?μm wavelength. Record-low residual phase noise of 144?mrads was achieved with this new locking scheme.     

Synthesis, in vitro and in silico assessment of organometallic Rhenium(I) and Technetium(I) thymidine complexes

Thymidine kinases have been identified as suitable targets for non-invasive imaging of gene therapy and cancer. Thus, there is a high interest in new, reliable and inexpensive radiolabeled thymidine analogues for these applications. In this study we present the synthesis and in vitro evaluation of M(CO)₃-complexes of thymidine (M = ^99mTc, Re) for potential use in SPECT tumor imaging. 5′-amino-5′-deoxythymidine was derivatized at position C5′ with spacers of various lengths (∼0-30 Å) carrying tridentate metal chelating entities such as iminodiacetic acid and picolylamine-N-monoacetic acid. The nucleoside derivatives were reacted with the precursors [ReBr₃(CO)₃]²⁻ and [^99mTc(OH₂)₃(CO)₃]⁺, respectively. The organometallic thymidine complexes have been fully characterized by means of IR, NMR and mass spectrometry. Enzyme kinetic studies revealed mixed inhibition of the human cytosolic thymidine kinase with K_i values ranging from 4.4 to 334 μM for all thymidine complexes. Competitive inhibition of herpes simplex virus type 1 thymidine kinase was only achieved when thymidine and the metal core were separated by a spacer of approximately 30 Å length. These findings were supported by in silico molecular docking and molecular dynamic experiments.     

Development of novel water-soluble, organometallic compounds for potential use in nuclear medicine: synthesis, characterization, and (1)H and (31)P NMR investigations of the complexes fac-[ReBr(CO)3L] (L=bis(bis(hydroxymethyl)phosphino)ethane, bis(bis(hydroxymethyl)phosphino)benzene)

The bidentate, water-soluble phosphine ligands, bis(bis(hydroxymethyl)phosphino)benzene (HMPB, 1) and bis(bis(hydroxymethyl)phosphino)ethane (HMPE, 2) were reacted with the organometallic precursor fac-[ReBr(3)(CO)(3)](2-), 3, to produce the complexes fac-[Re(OH(2))(CO)(3)L](+) and fac-[ReBr(CO)(3)L] (L = HMPE, HMPB), respectively, in good yields. The rhenium complexes fac-[ReBr(CO)(3)HMPB], 5, and fac-[ ReBr(CO)(3)HMPE], 8, were characterized using (1)H and (31)P NMR spectroscopy. The structure of fac-[ReBr(CO)(3)HMPB] was confirmed by single-crystal X-ray spectroscopy. The substitution reactions of HMPE/HMPB with the rhenium precursor 3 in aqueous solution were monitored using time-dependent (31)P NMR techniques. A significant discrepancy in the reaction kinetics and the substitution mechanism between the two bidentate ligands could be observed presumably due to the different chemical backbones.     

Nonlinear optics with phase-controlled pulses in the sub-two-cycle regime.

Nonlinear optical effects due to the phase between carrier and envelope are observed with 5 fs pulses from a Kerr-lens mode-locked Ti:sapphire laser. These sub-two-cycle pulses with octave spanning spectra are the shortest pulses ever generated directly from a laser oscillator. Detection of the carrier-envelope phase slip is made possible by simply focusing the short pulses directly from the oscillator into a BBO crystal. As a further example of nonlinear optics with such short pulses, the interference between second- and third-harmonic components is also demonstrated.