Varian Cold Probe

Figure 5.6 Comparative segments from (a) conventional and (b) phase-sensitive 8-Hz optimized HMBC spectra of DP-2 recorded using a 3-mm sample positioned coaxially in a 5-mm gradient inverse triple resonance Varian Cold-probe . ...

Figure 5.7 Phase-sensitive 8-Hz optimized HMBC spectrum of degradant DP-2 recorded overnight using a 500-MHz Varian Cold-probe .

The most important factors in determining the s/n ratio or sensitivity of an NMR experiment in a cryogenic NMR probe, insofar as the hardware itself is concerned, are the temperature of the coil, 7/ the resistance of the coil, Rc the temperature of the sample, Ts and the resistance added to the coil by the presence of the sample or the sample resistance, Rs. The temperature of the rf coil in a cryogenic NMR probe is typically in the range of 15-30K commercial examples of the Varian Cold-probe operate at 25 K. The preamplifier noise temperature is generally in the range of 10-15 K and the coil resistance is small compared to a conventional room temperature NMR probe. The first two terms in the expression below provide the basis for the vast improvement in the performance of a cryogenic relative to a conventional NMR probe. The sample temperature, Ts, and sample resistance, Rs,... 

Fig. 11. Eight transient 500 MHz H-NMR spectra of an 11.9 pg (0.027 pmol) sample of the antibiotic clindamycin (7) prepared in 500 pL of CDC13 in a 5 mm NMR tube (top trace) 292 pL in a 4mm tube (middle trace) and 163 pL in a 3 mm tube (bottom trace). All data were acquired using a 500 MHz 5 mm gradient inverse triple resonance Varian Cold-probe . The s/n ratio was measured for each spectrum using a 200 Hz region of representative noise downfield of the anomeric proton resonating at 5.3 ppm. The s/n ratios were 14.4 1, 20.8 1, and 21.5 1 for the 5, 4, and 3mm tubes, respectively.

Figure 5,20 Portion of a 3D X-filtered NOESY spectrum of uniformly 13C/15N-labeled, stability-enhanced kinaseX in complex with kinaseX inhibitor 2. The protein and inhibitor concentrations used were 300 pM. The F3 (inhibitor1H) plane is at 7.83 ppm. Peaks with protein resonance assignments are labeled. (Note Val-A and Val-B refer to the y-i and y methyl, respectively of the same valine residue.) The spectrum was recorded at 35 °C, 600 MHz 1H frequency using a NOESY mixing time of 100 ms on a Varian Inova spectrometer equipped with a Cold Probe. The spectrum is aliased in the 13C (F2) dimension.

Figure 9.2 Spectra obtained using the Varian 5 mm XSens dual cold probe. (A) 500 MHz H spectrum, 50 pg quinine, 3 mm NMR tube, 1 scan acquisition. (B) 125 MHz 13C spectrum, 50 pg quinine, 3 mm NMR tube, 2.5 hour acquisition (data kindly provided by Varian Inc.).

The cryoprobe is called a CryoProbe or CryoElowProbe by Bruker Biospin Corp. (Billerica, MA) and a Cold Probe by Varian Inc. (Palo Alto, CA). 

Si wafers of n-type and (100) orientation covered by thermally grown 100 nm SiO2 layer fabricated at 1100 °C in dry O2, were used as substrates. The wafers were loaded into an oil free evaporation chamber (Varian VT-460), and the system was evacuated down to lxlO 8 Torr. Ge ingot of 99.999 % purity was supported on a molybdenum plate, and it was evaporated using an electron gun, at an evaporation rate of 0.01-0.03 nm/s, at a pressure of lxlO"7 Torr. During evaporation, and for an additional 1 min after this process, the substrate temperature was kept at 350 °C. The temperatures were monitored by small-heat-capacity Ni-NiCr thermocouples, while the film thicknesses were measured by a vibrating quartz probe. For this study, four different samples have been prepared with different Ge evaporation times of 25, 50, 75, and 100 s for samples No. 1, 2, 3, and 4, respectively. After germanium evaporation, the samples were moved to a cold place inside the vacuum chamber. 

---